From: Fairchild, Susan <Fairchild.Susan@epa.gov>
Sent: Monday, March 11, 2013 9:16 AM
To: 'Higgins, Cortney'
Cc: Barnett, Keith; Okoye, Winifred; VanLare, Paula Subject: OMB requested documents Attachments: non

- CBI furnace data for OMB request.pptx; Non

- CONFIDENTIALChromeSummarySheet

KCK.xlsx; Industry conversation notes.docx; INDUSTRY CONVERSATION REGARDING THE SOURCE OF HIGH HEX CHROME EMISSIONS.docx; MCCULLOUGH Notes_Redacted.pdf; MW Industry conversation notes.pdf; Wiley Online Library_ hi Cr fused cast ref chap 23 ORDER 35.pdf; 13 August 2012 Telephone conversation with Carlos E. Davisdocx.docx; Hex Chrome in Refractories, Volume 34, Numbers 9

- 10

- SpringerLink.pdf; new high chrome fused cast refractory for use in contact with highly corrosive glasses.pdf; Owens Corning, Delmar Plant oxyfuel replacement of other furnaces.pdf; Re_ Fw_ WF

- PM and Cr Graphs (NEW)

- CWLEE.pdf; Saint

- Gobain SEFPRO.pdf; SG Chromium refractories.pdf; Oak Ridge DOE June 2006 oxyfu el.pdf; DOE refractoriesreportfinal JAN2005.pdf

Cortney,

I am forwarding to you several documents that I think will address your comments to the preamble.

The power point file has is a graph of chrome emissions for each furnace in the source category , grouped by both major and area source status. The other charts in this file were provided by industry during the site visits and provide general (i.e., not specific) designs of different furnace types. Specific furnace information is regarded as CBI, a nd we could not provide that in addressing some of your questions.

Also you requested

The DOE study conducted with Oak Ridge National Laboratories

Information regarding our conversations with the plant manager of the highest chrome emitter

Industry di scussions regarding the use of chromium refractories

I have also attached a few other documents that are in the docket and that we used in development of this proposed rule

Susan Fairchild Senior Environmental Scientist (919) 541

- 5167

USPS Address: OAQPS/SPPD/MMG Mail Code D 243

- 04 Research Triangle Park, NC 2771113 August 2012 Telephone C onversation with Carlos E. Davis, Certainteed, Kansas City, KS

Susan Fairchild, project lead at EPA, contacted Carlos Davis of Certainteed to get clarification of Mr. Davis’ statements in 2011 regarding the chromium content of the K2 furnace refractory versus the information submitted by Certainteed in the 114 information response in 2011

- 12.

Mr Davis reiterated that over 90% of the refractory is chrome bearing, or what EPA may refer to as ‘chromium compounds’, but that only a percentage of the chromium compounds are actually the element chromium. (For instance, Cr2O3 is chromite; the element chromium is 40% of the mineral chromite). Thus, when the statement on the 114 response of the chromium

- content of the refractory was give n by the facility, this should be interpreted as the percentage of the element chromium in the total chromium bearing constituents of the refractory product. This their interpretation of the 114 request questions regarding chromium content of the furnace r efractory.

Regarding the K2 furnace, if each brick of the furnace is examined, over 90% of the refractories would contain chrome. When you look at each piece, however, the chrome content will vary. The varying percentage of chrome in the refractory is bas ed upon it’s purpose. Specifically, at t he metal / glass line

this area has to be very resistive due to the corrosivity and errosivity of the glass melt in the furnace. The metal line is at the top of the ‘cool’ of the glass. The superstructure (entire furnace) will also have chromium containing refractories, but the chromium content above the metal/glass line is generally l ower in chrome content

. Regarding the K2 furnace, that furnace will not re

- start until it is rebuilt. The nature of that

reconstruc tion will be identical to the furnace at Chowchilla, which is a different design than the K2 is now. The Chowchilla furnace can meet the limits; in fact it emits chromium at about 1% of the proposed limit for chromium compounds.

Regarding the K1 furnace, that furnace meets the proposed limits now.

If a furnace is built using chromium refractories, it will last longer. T herefore it will cost less when
amortize d over the life of the furnace; the longer the furnace lasts, the less the total amortized cost.
H igh chromium refractories are needed anywhere that contacts glass to achieve this furnace life. This is a minimum of a 10

- year vs. a 6

- year furnace design.

Regarding the new K2 furnace design, the only way for K2 to meet the proposed limit is to reconstr uct. The new design will still have high chrome refractories in contact with the glass. Look at the emissions of chromium and the Chowchilla furnace : this has an emissions rate at about 1% of the proposed limit.

### The photographs on the cover are an exampl e of an aluminum furnace featured on the Harbison Walk er web page (top), cathodoluminescence of a fusion-cast spinel refractory (center), and cathodol uminescenc e of a fus i on-cast alumina refractory ( bottom).

1

# Refractories for Industrial Processing: Opportunities for Improved Energy Efficiency

Jam e s G. Hem r ick,* H. Wayne Hayden, † 

### Peter Angelini,* Robert E. Moore, § 

### and W illiam L. Headrick §



### *Oak Ridge National Laboratory † 

### Metals Manufacture, Process, and Controls Technology, Inc. § 

### R. E. Moore and Associates

January 2005

Prepared for the DOE-EERE Indus trial Technologies Program

## Table of Contents

List of Figure s and Tables

..................................................................................................... .......... v Executive Summary

.............................................................................................................. ........ vii Abbreviations and Acronyms

..................................................................................................... .... ix

1. Introduction

................................................................................................................... .......... 1 2. Current Refractory Status

...................................................................................................... . 1 2.1 Usage in Industry

......................................................................................................... 4 2.2 Current R&D Status

..................................................................................................... 4 3. Esti m a ted Metrics for Overall Energy Savings Opport unities

............................................... 5 4. Process Technology and Perfor m ance Barriers

...................................................................... 7 4.1 Kilns and Calciners

...................................................................................................... 7 4.2 Reverberator y Furnaces

............................................................................................... 8 4.3 Boilers and Reactor Sy stems

..................................................................................... 10 4.4 Gasifiers

..................................................................................................................... 1 3 5. Overall R&D Barriers and Pathway s for Refractories

.......................................................... 15 6. Specific R&D Areas with Barriers and Pathway s

................................................................ 17 6.1 Im proved Castable and Monolithic Refractory

.......................................................... 17 6.2 Modified Fiber Materials

........................................................................................... 17 6.3 Surface Modification (Coatings, Phy s ical or Therm a l Alteration)

............................ 17 6.4 Synthetic Aggregates and Powders

............................................................................ 18 6.5 High-Tem p erature Properties of Refractories

............................................................ 18 6.6 In Situ and Graded Refractories

................................................................................. 19 6.7 Sensors for Materials Performance

............................................................................ 19 7. Referen ces

..................................................................................................................... ........ 22

Appendix A: Discussion of Refractory Usage by Process Industries

........................................... 26 A.1 Alu m inum

.................................................................................................................. 26 A.2 Cement and Lim e

....................................................................................................... 30 A.3 Chem ical and Petrochem i cal

...................................................................................... 33 A.4 Forest Products

.......................................................................................................... 35 A.5 Glass

.......................................................................................................................... 37 A.6 Heat-Treating and Anneal ing

..................................................................................... 40 A.7 Iron and Stee l

............................................................................................................. 41 A.8 Metal Castin g

............................................................................................................. 44 A.9 Referen ces fo r Appendix A

....................................................................................... 48 Appendix B: Rotary Kiln Analy s is Schem a tic, Conditions, and Re sults

..................................... 50 Appendix C: Reverberator y Furnace Schem a tics

......................................................................... 56 Appendix D: Reverberator y Furnace An aly s is Condit i ons and Results

........................................ 58 Appendix E: Boiler Schematic

................................................................................................... ... 62

iii

## List of Figures and Tables

Figures

ES.1. Tem p erature regim es for industr ial appl ications of refractories

..................................... vii 1. Long-term en ergy benefit opportunities estim ated for the four anal yzed furnace ty pes

................................................................................................................. ..... 6 2. Im proving ref r actory m a terials for im proved energy efficiency

..................................... 16 B.1. Longitudinal section of a typical rotar y kiln

.. ................................................................. 50 C.1. Reverberator y furnace schem ati c

..................................................................................... 56 C.2. Typical reverberatory alum inum

- m elting furnace

........................................................... 57 E.1. Boiler furnace sections

................................................................................................ .... 62



### Tables

1. Types of furnaces utilized i n American industr y

............................................................... 2 2. Refractory barriers for furnaces utilized i n American industr y

.......................................... 3 3. Energ y anal ysis by i ndustr y with estimated short-term and long-te rm energy savings opport unitie s fro m im proved refractories

.................................................. 5 4. Total effect of im proved refractories on rotary kilns

......................................................... 8 5. Total effect of im proved refractories on reverberatory furnaces

...................................... 10 6. Stea m sy ste masse ss ment tool single header analy s is results for i m proved insulation for im proved boiler efficiency

......................................................................... 11 7. Stea m sy ste masse ss ment tool single header analy s is results for i m proved pipework ins u lation for im proved steam transfer sy stems

............................................... 11 8. Potential energy savings fr om i m proved boiler efficiency due to improved refractories and im proved transfer pipe-work insulati on

................................................. 12 9. Renewable energy generation pote ntial (billion kWh/ y ear) from black liquor in the pulp and paper industry in the southeastern Unit ed States

..................................... 15 10. Reco mmended R&D pathway s for advanced refractories

............................................... 20 A.1. Feedstock for energy use in the cem e nt industr y , 1993-2001

.......................................... 32 A.2. Estim a ted en ergy use in melting and ref i ning

.................................................................. 38 A.3. Conversion of North Amer ican glass melters to oxy

- f u el firing as of 1998 and a s of 2004

..................................................................................................... 39 A.4. Process and energy data fo r U.S. metals casting industry

................................................ 45

v

## Executive Summary

Refractory materials with properties suitable fo r high -tem perature applications are used throughout U.S. industr y as insulation and/or cont ainment vessel li nings in high- t em perature and corrosive environm ents. In deed, it woul d be diffi cult to identif y an industrial process that does not use refrac t ory m a teri als in one aspect or anothe r. These material s m u st not only be capable of perform ing these ta sks at el evated te m p e r atures, but may also be called upon to bear mechanic al loads and transfer heat. Re fractories ar e char acte r ized by two aspects that qualify the m as strategic materials in support of American indust r y : (1) their ability to contain he at, chem icals, and m e lt s; an d (2) the cros scutting natur e of their utili ty.
Figure ES.1 s hows the ranges of usage tem p eratur es for num erous industr ial appl ications of refractories. This report and the attached a ppendices describe the current furnace technologie s used b y U.S. industries with specific highlighted anal y s is focused on four furna ce ty pes—kil n s/ calciners, rev e rberatory furnaces, boilers and r eactor sy stem s, and gasifiers

— whi c h are co mmon to m u ltiple industries and are representat i ve of areas where significant energy im provement could be made through future refractory im provem e nt. Anal y ses of these four ty pes of furnaces alone suggest potential energy sa vings of over 400 trilli on B tu/ y ear. In addition t o identify i ng areas of opport unity , th is report describes possible crosscutting resear ch and developm ent (R&D) pathway s for overcom ing refract ory -related performance barriers which could l ead to im proved energy efficiency through both the alterati on of current material s an d practices an d the developm ent of new materi als, furnace designs, or redesigned processes of vary ing sizes.

Fig. ES.1. Te mperatur e r e gimes for in dustrial applications of refractories.

vii

## Abbreviations and Acronyms

BLS black liquor s o lids BOF basic oxy g en furnace Btu British thermal unit DOE U.S. Depart ment of Energy EAF electric arc furnace EERE Energy Efficiency and Renewable Energ y (DOE) FCCU fluidized cataly s t cracking unit ITP Industrial Technolo g ies Pro g ram (DOE) MECS Manufacturing Energ y Co n s u m ption Sur v ey ORNL Oak Ridge National Labor atory R&D resea rch and developm ent TBtu trillion Btu

ixRefractories f o r Industrial Processing



## 1. Introduction

The Industrial Technologie s Program (ITP), part of th e Department of Energ y ’ s Office of Energ y Efficiency and Renewable Energy (DOE-EERE), seek s to im prove the energy intensity of the U.S. industria l sector through a coordi nated program of research and development (R&D), validation, and dissem i nati on of energy effici ency technologies and operating pra c tices. To achieve its m i ssion, ITP partners with industr y , equi p m ent m a nufacturers, and other stakeholders to develop te chnologies th at enable industry to u se le ss energy per unit of out put . Refractories are a class of m a t e rials of critical i m portance to m a nufactu r ing industries with high-te m p erature unit processes. This study describes industrial refr actory applications and identifies refractory performance barriers to energy efficiency fo r processi ng. The report provides rec o mmendations for R&D pathway s leading to im proved refractories fo r energy -effic i ent manufacturing an d processing.



## 2. Current Ref r act o ry Statu s

There are many different types of furna ces used in industries in the United States, each with different refra ctory needs and challenges. A discu ssion of the refractory issues for several ene r gy

intensive processing industries can be f ound in Appe ndix A. Fiftee n classifications of furnaces with several common issues can be identified. T y pical industrial applications of th ese fifteen furnace ty pes are shown in Table 1. Refractory challenges and proble m s relat e d to these furnace types, as reported by industry personnel and discu ssed in detail in Appendix A, are shown in Table 2.

Of these fifte e n furnace types, four are highl ighted in this docum ent: kilns/calciners, reverberatory furnaces, boilers and react ion s y stem s, and gasifiers. These wer e s e lected bec ause they are co mm on to m u ltiple industries and re presentative of areas where significant energy savings [ on the order of tri llions of Btu (TBtu)/y ear] could be realized through f u ture refractory i m provem e nt. Although emphasis was pl aced on bl ast furnaces, basi c oxy g en f u rnaces ( B OFs), and other fur n ace ty pes found i n the steel industr y , w e have chosen not t o focus on these furnaces because of their design practice of intentionall y l eaking energy so a s to induce a steep ther m a l gradient through th e lining. Additionall y, BOF refr actories are known to last thousands of heats, and little im p r ovement is expected in impr oving refractories for these applications.

Analy s is and discussion will address refr actory im provem e nts leadi ng to higher e n ergy efficiency and im proved product yield for each of these four furnace ty pes. Discussion will focus on the energy -i ntensive industries of the United States including alum inum
, cement and lim e, chemicals and petrochemical s, forest products, glass, heat tr eat ment and annealing, iron and steel, and metal casting.

1R e f

ractories f or Industrial Processin g

2Table1.Types of furnacesutilized in American industryFurnace typeIndustrial furnace applicationsAluminumCement &limeChemical/petro­chemicalForestproductsGlassHeat treatIron &steelMetalcastingOtheraBlastfurnaceX1BasicoxygenfurnaceXReverberatoryfurnaceXXXX2Multiplehearth2Ladle/tundishe/troughXXXX3ElectrolyticsmeltingX4KilnsXXXXXX5,6Electricarcfurnace(EAF)X7CupolaXHeattreatXXXXX5,8StillX9Reactor/reformerXBoilerXXXXX10GasifierXXHeatexchangerXXXXXXXXaKey to“Other”:1.Lead6.Mining2.Copper7.Oxidemelting3.Moltenmetalhandling8.Variousmetalproducts4.Magnesium9.Organic and inorganic products5.Ceramics10.VirtuallyallindustriesR e f

ractories f or Industrial Processin gTable 2.Refractorybarriersforfurnacesutilized in American industryFurnace typeRefractorychallengesAbrasionCaking/agglomerationContamination/foulingCorrosion/wearErosionMechanicaldegradationThermalinsulationThermomechanicaldegradation/shockRefractorylife/repairsBlastfurnaceXXXXXBasic oxygen furnaceXXXXXXXReverberatory furnaceXXXXXXMultiplehearthXXXLadle/tundishe/troughXXXXXXElectrolytic smeltingXXXXXKilnsXXXXXXXXXElectricarc furnace (EAF)XXXXCupolaHeattreatStillXXXXXReactor/reformerXXXBoilerXXXXXXXXGasifierXXXXXXXHeatexchangerXXXX

3Refractories f o r Industrial Processing



## 2.1 Usage in Industry

Although refractories are used in m o st, if not all, of U.S. ind u stries, the iron an d steel industry consumes 70% of the refractories produ ced gl oball y , while the cement and lime industr y consumes 7%, the ceram i c s industr y 6%, the glass in dustry 3–4%, and the oi l industry about 4%. 1 In 199 8, a sur v ey was cond ucted b y the U.S. Advanced Ceram i cs Association and Oak Ridge National Laborator y (ORNL) to determ ine oppor tuni t i es for advanced ceramic s to m e et the needs of manufacturing in dustries. 2 These industries included alum inu m , che m ic als an d petrochem i cals, forest product s , glass, m e t a ls casting, and steel. Additionall y , th e supporti ng i n dustry of heat treating and annealing was considered. From this surv ey , a num b er of critical are as wer e identified in e ach of these industries where i m pr ovem e nts could lead to substantial econom ic and energy savings.

Additionall y , the general practice of m o st indus tries is to choose fue l ty pes and sources based primarily on cost and availability

. This, in m a ny cases, leads to variations in fuel quality and purity which will directly i m p act the performance of the refractory materi als used in the respective fur n aces. This must be considered when choosing f u rnace m a terials an d when evaluating energy efficiency.



## 2.2 Current R&D Status

Substantial changes that h a ve occurred in refr actories technolog y o v er the past 25 y ears have resulted in crosscutting impacts on a num b er of m a n u facturing industries, 2 incl uding the use of fibrous and hi gh-strength p o rous insulati on to reduce energy consum ption in heat-treating furnaces. In the steel industry, the use of resin-bonded MgO-C- m e t a l linings in basic oxygen furnaces significantly increases the nu mber of heat s between neede drelinings, and SiC-based refractories have led to inc r eased furnace life fo r steel blast furnaces. In the glass industr y , the advent of o x y -fuel melting has led to renewed inter est in alternative refractory m a terials that wi ll allow for processing at higher te m p eratu r es and greate r corrosion resistance to high alkali and water-ri ch environm ents. Additionally
, many m o re recent ceramic co m positions have received lim it ed evaluation but have not reached maturity or pr oduction status. All of the se events ar e representativ e of industrial process i m pr ovements that can be acco m p lish e d through advances in refractory m a terials, y e t additional im provements could lead to eve n greater ener gy savings throug hout th e various ind u stries.

The choice of refractory materials for a certain a pplication is often dictated by the trade off between cost and perform ance. In the pa st econom ic considerations have led to th e selection of lower cost/poorer perform ing refractories over hi gher performance/higher cost materials. Yet, with rising energy costs, environm ental r e gul ations, and econom ies of scale; higher priced pre m iu m refr actory m a teri als are r eceivi ng renewe d interest and may prove cost effective in many applica tions for whic h the y we re previousl y deemed unsuitable.

4Refractories f o r Industrial Processing



## 3

. Estima ted Me tr ics fo r Overall Energy Savings Opportunities

Energ y usage in several of the industries and estim ates of potential energy savin g s throug h i m prove m e nt s in refractories are shown in Table 3. The values shown in this table are based primarily on DOE Manufa c turing Energy Cons um ption Survey (MECS) data describing manufacturing energ y cons um ption in th e y ear 19 98. 3 The esti m at es of energy us age affect ed by refractorie s ar e based on evaluation of industry roadm a p docum ents and discussions with industry leaders. Ener gy savings goals are bas e d on the n eeds of the industries and esti m ates for the four typical furnace types (Table 1) used throughout m a ny of the industries, which are presented in detail in Appendices B, C, and D. These analy ses are based on heat balance studies where the energy su ppli e d to the s y st em through c o m bustion is equal to the s u m of (1) latent heat in the furnace exhaust gases, (2) heat lost through th e furn a ce wall s and roofs, and (3) heat required for heating reacta n ts to the process t e m p er at ure and phase transfor m a ti ons at that tem p erature. T h e achieve ment of theoretical efficiency would require th at item s 2 and 3 be equal to zero. From a practical point of view, perfect effici enc y is not proba ble, but im provements in furnace refractories could help facilitate i m provements of furnace effi ciency beyond the l e vels of present technology. The projected saving oppor tunities inthe range of 166 TBtu/Yr to 830 TBtu/Yr are equivalent to the y early res i dential electr i cal u sage of New York sta t e and the y early residential air conditioning usage of the US, respec tively

.

Table 3. Ener gy anal ysis b y indus try with es tim a ted sh ort-term and long-term ener gy s avin g s opportunities from impr ove d refr a ctories

E n erg y s avi n g s g oal s f o r

Indus try NAI CS codes To ta l T B t u/ye ar a U s ag e af f e ct ed by refrac t ories

Percent TBtu/Yr improved re fr actories (TBtu/Yr)
Near -ter m 2% Long-term 10%

Al um i num 33 1 3 X X 1 44 1 90 % 39 7 7. 9 39 .7 C h em i c al 32 5 X X X 3, 70 4 50 % 1, 85 2 37 .0 18 5. 2 Fabricated m e tals b 33 2 81 44 5 90 % 40 1 8. 0 40 .1 For e st p r od uct s 32 1 X X X , 3, 24 8 40 % 1, 29 9 26 .0 12 9. 9 3 22X XX Fo un dri e s 33 1 5 X X 23 3 90 % 21 0 4. 2 21 .0 Gl ass 32 7 2 X X 20 3 70 % 14 2 2. 8 14 .2 Ir on& st eel 33 1 11 1, 67 2 85 % 1, 42 1 28 .4 14 2. 1 Petrole u m & coal 32 4 X X X 3, 62 2 50 % 1, 81 1 36 .2 18 1. 1 pr o duct s St one , cl ayp r o duct s c 3 27X XX d 76 6 10 0% 76 6 15 .3 76 .6

All 14 ,3 3 4 — 8, 29 9 16 5. 8 82 9. 9

a TBtu = tr ill ion Btu/ yea r

. Source: U. S. Department of Energy , En erg y Information Administration
, 1998 MECS Consumption, Table N3.2, Fuel Consumption, 1 998. b Includes h eat tr eatm e nt

. c Prim aril y cem e n t and lim e

. d Exclud es categ o r y for glass, 37 27XX.

Additionall y , one m u st con s ider that declines in certain properties may have a di rect influence on other related properties. This is evident for ex a m ple in a furnace wall where lac k of corrosion

5Refractories f o r Industrial Processing

resistanc e ma y result in a reduction in ther m a l efficien cy as decreas es in wall thickness due to corrosion will lead to decreased insulating ability of the furnace wal l . The furnace efficiency will now not onl y be im pacted, but thi nnin g of the re fract ory wall may also lead to shut-down of the furnace for maintenance causing loss of production an d the need for additional energy t o reheat the furnace. Energy conside r ations from a ll these are a s are consider ed in Table 3.

Figure 1 shows the potential energy benefit oppor tunities represe nted by the four furnace types analy zed.

Fig. 1. Long- t erm energy benefit opportunities estimated for th e four analyz ed furnace type s.

6Refractories f o r Industrial Processing



## 4. Process Technology and Performance Barriers

4.1 Kilns and Calciners

Kilns and calciners, or the products pro d u ced b y them, are used in many in dustri es (alu m i nu m, cement, chemical, forest products, glass, iron and steel, and m i ning) and therefore have crosscutting interests. Anal y ses were per f orme d to evaluate cases for both alum ina and lime calcinations, based on use of rotary -ty p e kiln s for various flame te m p eratures, e xhaust tem p eratures, and wall/roof losses (Appendix B). Fo r all the heat supplied by com bustion, the gross available heat is cal c u lated from t h e heat c ontent of the flame less the heat content of the exhaust gases , and a part of the heat supports wall lose s while the re mainder is av ailable for the work of the k iln/calcinations of feed to product.

4.1.1 Industrial Applications of Process Technology
Alu m inum — alu m ina, carbon, lim e Glass - li me Cement and lim e — lime, cement Iron and steel - lime Chem ical and petrochem i cal — lim e Mining — raw m a terials Forest produc ts — lim e

4.1.2 Current Tec hnology
Two ty pes of kilns ty picall y found in the industri es listed were selected for review. In the case of alu m ina calcination, we considered a kiln m e asuring 3.5 m in diameter by 80 m long with an output of app r oxim a tely 2 5 0 ,00 0 tons/ y e a r; for lim e calcinations, we chose a kiln measuring 5 m in diam eter by 50 m long with an outp u t of appro x imately 3 65,0 0 0 tons/ y ear. In the lime calcination process, product is often lost through dust l o ss as loose powder is blown out of the kiln along with the exhaust gases. Theref ore, in the lime analy s is, both the case of no dust and the

m o re realistic condition of up to 20% of the cal cined product being l o st as dust were considered. Calculated heat of reactions (at 77°F) of 634 Btu/l b an d 13 64 Btu/l b were used for the alum ina and lim e calc i nation processes, re specti v ely, leading to a calculate d total heat requirement of 1728 Btu/lb f o r the alum in a calcination process and 2196 Btu/l b for the lime cal cination proc ess.

4.1.3 Energy Im pact Energ y benef its resulting f r om refractories in kilns are related to the following operational im provem e nts:

1. An increase i n the adiabatic flame tem p eratur e of 200°F (as with m odified oxy-fuel firing at about 2 0 % enrich m e nt) can lead to subst a ntia l fuel savings d u e to th erm a l efficiency

. 2. A decrease in the exhaust t e m p erature of 200° F (result ing in greater heat retained for the actual proces s) also leads t o a substantial fuel savings. 3. A decrease in wall/roof losses of 200,000 Btu/to n of product can r esult in subst a ntial energy savings (considering half th e supplied e n erg y go es up the stack, with the remainder available to support work and wall losses). 4. Process y i eld i m provem e nt s will resu lt in substantial energy benefits.

For the energy analy ses, it was assu med that a little over half of the total calcined alum ina produced in th e United States (4.4 m illion m e tric to n s in 2001) was produced us ing a rotar y kiln. Sim i larly
, it was assu med that of the 20 million short tons of lim e produced in th e United States

7Refractories f o r Industrial Processing

in 20 02, ab ou t 80% of the productio n w as perform ed using rotar y k iln calciners. It was also

assu med that 80% of the 103 m illion metric tons of cem e nt produced in the Unit ed States in 2002 was produced using rotar y kilns operatin g in the te m p erature range of 260 0 to 30 00°F. Results of the analy s is are shown in Table 4.

T a bl e 4. T o t a leffec t of i m pr ove d re frac tor i es on ro tar y ki l n s

Energy-intens ive process indus tries Prod uct Fuel decre ase (Btu/t on ) Wa ll lo ss decrease (Btu/t on ) To ns a f fected per ye ar Energy be nefi ts per ye ar (TBtu)

Al um i num Al 2 O 3 41 3, 0 00 20 0, 0 00 2, 50 0, 0 00 1. 5 C e m e nt and l i m e C e m e nt 80 0, 0 00 20 0, 0 00 82 ,4 0 0
, 0 0 0 82 .4 Ce m e nt and lime,

chem ical and petr ochem i cal
, fo rest pr od uct s , gl ass, i r o n an d steel Lim e : N o dust 20 % du st 41 3, 0 00 88 5, 0 00 20 0, 0 00 25 0, 0 00 1 6 ,000 ,0 00 1 6 ,000 ,0 00 9. 8 18 .3

All 11 2 a

a Without carbo n and sulfur con tributions. Source: Portland Cement Association, Economic I ndustry Overview, 2003.

4.1.4 Barrier s Rel a ted to Refr acto ry Materials for Kilns and Calciners
The central c onclusion from the analy ses for c oncerning kilns and c a lciners is tha t as fla m e te m p erature s increase and exhaust te m p eratures appr oach process te m p erature s , greater thermal efficiency is realized. Hence, im provem e nt s in reducin g the therm a l conductivity of the refractories, and im proving the chem ical and m e chan ical properties of the refract ories, will have a significant payoff in overall fuel consumption. Addressing the following barriers associat ed wi th the performa n ce of refract ory m a te rials used in kil n s and calciners would im prove energy efficiencie s

.
1. Unavailability of refractories with sufficien t high-temperature stren g th, erosion/c o rrosion resistance, creep resist ance, r esistance to large tem p erature gr adients, and stability at higher te m p erature s for use with elev ated furnace fla m e te mperatures. 2. Lack of sufficient high-te m p erature durability and c o rrosion/erosi on resistance in current refractorie s for im proved heat transfer t h rough increased levels of sti rring and a g itation of the materi al being processed. 3. Unavailability of refractories with lower th ermal conductivity and greater high-tem p erature stability needed to achieve substantial reductions in wall and roof heat losses. 4. Lack of know ledge concerning o p eration s need ed to in crease refractor y life, redu ce product sticking, and increase l e vel s of product recove ry for the reduction of unschedule doutages, i m prove m e nt of product y i eld, and the increas e of furnace ca mpaig n lives.



## 4.2 Reverberatory Furnaces

Analy ses of reverberatory furnaces were performed to evaluate cas es of alum inu m , copper, and glass- melting furnaces for various assumed values of flam e temperatures, exhaust tem p eratu r es, and wall/roof losses. For all the heat supplied by co m bustion, the gross available heat is the heat

8Refractories f o r Industrial Processing

content of the flam e less the heat content of th e exhaus t gases. Additionally
, part of the gross available heat supports wall losses and the rem a inder supports m e lt ing, the real j ob of th e furnace. Reverberator y furnace sche m ati cs ar e provided in Appendix C.

4.2.1 Industrial Applications of Process Technology
Alu m inum — m e tal melt ing Metal casting — m e tal mel ting Glass — glass m e lting Copper — metal m e lting Iron and steel — m e tal melting

4.2.2 Current T e c hnology Analy ses of reverberatory furnaces we re basedon a nom i nal furnac e having a capacity for melting 20,0 0 0 lb of m a terial per hour. T h is is a typical size used in the alum inu mindustr y an d is used for the other industrial analy ses for co m p arison purposes. For th e fixed m e lti ng capacity of 20,000 lb/ h , th e energy needed for m e lti ng is th e same in all alum i num melting cases, 504 Bt u/lb. In the analy s is, wall and roof losses from 0 (rea lly im possible) to 10 m illion Btu/h, or 0 to 500 Btu/l b of material, hav e been assu med. This range is expected to span the full spectru m of industrial pra c tice. The gross available h eat to do thes e jobs is the d i fference in flam e and exhaust heat contents. It has been assu m e d that natural g as fuel with an adiabatic fla m e t e m p erature of ~3600°F has been used as a base, with increasi ng flame tem p eratu r es that m a y be achieved throug h regen e rators/recup e rators or ox ygen enrichment.

Exhaust tem p eratures rangi ng from 1400 to 2000° F ha ve been assumed. Increasing exhaust te m p erature s at fixed fla m e te m p erature s r esults in tot a l heat consum ptions ranging from 777 Btu/l b (61% ther m a l efficiency ) to 2261 Btu /lb ( 22.3% thermal efficiency ). Furnaces in the alu m inum in dustr y generally fall in this range, as summa rized bel o w:
Furnace type Thermal efficiency Nor m al furnace (poor to good practices) 2500–1350 B tu/lb State-of-the-art new furnace 1350–1200 B tu/lb Furnace builders’ lower limit for reverb. 1200–1000 B tu/lb New/radical technolog y 1000 –50 4 Bt u/lb

Sim i l a r effici encies ar e ex pected in the other two industries studied.

4.2.3 Energy Im pact Energy benefits that could result from i m proved refr actories in re verberatory furnaces are r e lated to the foll owing o p erational im provements:

1. An increase i n the adiabatic flame tem p er ature of 200°F (e.g., oxy-fuel firing w ith 20% oxy g en) leads to substantial fuel savings due to therm a l efficiency

. 2. A decrease in the exhaust t e m p erature of 200° F (result ing in greater heat retained for the actual proces s) also leads t o a substantial fuel savings. 3. A decrease in the wall/roof losses of 2.5 milli on Btu/h also results in substantial energy savings (considering half th e supplied e n erg y go es up the stack, with the remainder available to support m e lting and wall losses).

For the calculations, it was assu med that annuall y in the United States, 9.3 billi on lb of alum inum (half of all the ingot and mill products in the alum inum industry in 1998) are m e lted in reverberatory furnaces, 0.36 billion lb of refined copper fro m scr ap is processed i n reverberatory

9Refractories f o r Industrial Processing

furnaces, and an average of the 40 billion lb of glass is produced us ing reverberator y furnaces (based on 1999 num b er s). In addition, 20% ox y g en e n richment was assu med for the metal melting cases, while 100% oxy g en enric h ment was assu m e d for the glass m e lting case. The details of the calculations a r e presented in Appendi x D. Results of the analy s is are shown in Table 5.

T a bl e 5. T o t a leffec t of i m pr ove d re frac tor i es on rever be rator y furnac es

Energy-intens ive process indus tries Prod uct Fuel decrease (Btu/lb) Wa ll lo ss decrease (Btu/lb) Poun ds

a f

f e c t ed p e r year ( × 10 9 ) Energy be nefi ts per ye ar (TBtu)

Al um i num , coppe r a

Gl ass

All M e t a l m e lt i ng

Gl ass m e l t i ng 45 2

47 6 20 0

10 0 10

40 2 (2 0% e n richm e nt) 76 (1 0 0 % e n ric h m e nt) 78

a Without iron and steel and metal casting con t ributions Sources: Am eric an M e t a l M a rket
, Metal Statistics 1998, 90th ed., 1998; DOE Office of Industrial Techno logies, Energy and En vironmen tal Profile of th e U.S

. Gla ss Industry, 200 2.

4.2.4 Barrier s Rel a ted to Refr actory Materials for Reverberatory F u rnaces The central c onclusion from the se analy ses is that as f l a m e te mpera tures increas e and exhaust te m p erature s approach process t e m p er at ures, greater t h er m a l effi cie n cy is realize d . As shown in Appendices B, D, and E, the im pact of reducing wall losses by 2.5 million Btu/h leads to corresponding savings of 4.5 m illion Btu/h for alum inum (232 Btu/lb), 7. 5 m illion Btu/h for copper (333 Btu/lb), and 11.9 Btu/ h for glass ( 595 Btu/lb). Hence, i m provem e nt s in reducing the therm a l conductivity of th e refractories, and im pr oving the chem ical and m ech anical properties of the refractori es, will have a significant payoff in ove rall fuel consum ption. Addressing the following barriers as sociat ed with the perfor m anc e of refractory materials us ed in reverberatory furnaces would im prove energy efficiencies.

1. Unavailability of refractories with sufficien t high-temperature stren g th, erosion/c o rrosion resistance, creep resist ance, r esistance to large tem p erature gr adients, and stability at higher te m p erature s for use with elev ated furnace fla m e te mperatures. 2. Lack of sufficient high-te m p erature durability and c o rrosion/erosi on resistance in current refractorie s a nd m a teri als f o r im proved heat tran sfer t h rough increased levels of stirring and agitation of the material b e ing processe d. 3. Unavailability of refractories with lower th ermal conductivity and greater high-tem p erature stability

. 4. Lack of know ledge concerning the i n ter actions between refractories and process environm ent/operations which leads to reduced refractory life, pro duct sticking unscheduled outages, low product yield, and lim ited f u rnace cam p aign lives.



## 4.3 Boilers and Reactor Systems

Boilers and reactor sy stems are found in m o st indus trial settings and therefore are of ke y inter est

as a cros scutting unit process. For the following anal y s is, boilers for the production of stea m ar e considered for the alum inu m , cement and lim e, ch emical and petrochem i ca l, forest products, and

10Refractories f o r Industrial Processing

heat treat ment industries. ( S ee Appendix E for a schematic illustrat i on of boiler f u rnace sectio ns.) Additional areas for energ y efficiency im proveme nts also exist in chem ical reactors utilizing cataly s ts and other reactions.

4.3.1 Industrial Applications of Process Technology
Alu m inum — steam production Forest produc ts — steam production Cement and lim e — steam productio n Heat treatment — steam p r oduction Chem ical and petrochem i cal — steam production

4.3.2 Current Tec hnology For the purpose of the performance anal y ses of bo ilers, a standard unit using a single header boiler s y ste m has been ass umed.

4.3.3 Energy Im pact
Im proved refractory practice in boilers will result in energy benefits either fro m im proving the boiler efficiency through i m proved vessel insula tion and/or by reduced heat losses during steam transfer through im proved transfer pipework insulati on.

The DOE Be st Practice s S t ea m Sy ste m Asse ss ment Tool was used to analy ze the effects of im proving bo iler efficiency from 85 to 8 7 % through u se of the follo wing:

• Im proved ins u lation for im proved b o iler efficiency

• Im proved pip e work insulation for im proved steam transfer sy stem s

The effects of increasing boiler efficienc y by 2% and reducing heat losses during stea m tr ansfe r b y 1 0 % are shown in Tabl es 6 and 7.

Table 6. Ste a m sys t em asse ssment toolsingle he ader a n al ysi s resul t s f o r i m pr ove d i n sul a ti on for improved boiler efficiency

85% efficient 87% efficient Vari able boiler case boiler case Improveme nt Fuel c o st , $ 1 0 0 0 /y ear 4, 00 0 3, 90 8 92 (2 .3 0% ) Fuel c o n s um pt i on, st d ft 3 /h 71 ,4 2 1 69 ,7 9 9 1, 62 2 (2 .2 7% ) CO 2 em i ssi ons, 1 0 0 0 l b /y ear 66 ,4 0 3 64 ,8 7 6 1, 52 7 (2 .3 0% ) NO x em i ssi ons , 1 0 0 0 l b /y ear 13 1 12 8 3 (2 .2 9% )

Table 7. Ste a m sys t em asse ssment toolsingle he ader analysis results for impr ove d pipework insulati on for improved s t e a m tr ans f er s y s t ems
Current 10% Vari able oper ati o n improvement Improveme nt Fuel c o st , $ 1 0 0 0 /y ear 4, 00 0 3, 92 4 76 (1 .9 0% ) Fuel c o n s um pt i on, st d ft 3 /h 71 ,4 2 1 70 ,0 6 5 1, 35 6 (1 .9 0% ) CO 2 em i ssi ons, 1 0 0 0 l b /y ear 66 ,4 0 3 65 ,1 4 2 1, 26 1 (1 .9 0% ) NO x em i ssi ons , 1 0 0 0 l b /y ear 13 1 12 9 2 (1 .5 3% )

11Refractories f o r Industrial Processing

As shown in Table 6, a 2% im provement in boi ler efficiency leads to a 2.3% im p r ovement in fuel cost and consum ption, while the 10% improvem e nt in the efficiency of the transfer pipework insulation leads to a 1.9% i m provement in fuel cost and consum ption. As shown i n the tables, there are also decrea ses in e m i ssions as sociated with im prove ments in boiler efficiency and pipework ins u lation. If these fuel savings are then applied to the che m ic al, petroleu m refining, and pul p and paper industri es, estimates can be m a de concerning th e possible energy savin gs resulting from i mple m entation of these im prove ments in each industry . Table 8 shows the res u lts of such an analy s is.

Table 8. P o tential ener gy s a vings fr om improved boiler efficiency due to improved r e frac tories and i m pr ove d tr ansf er pi pe - w ork i n sul a ti o n

Capture Projec ted IOF ind u str y segmen t TBtu % basis fuel s avi n g s (% ) (TBtu) Chemic a l industr y s t eam oppor t uni ties Prese n t u s age of f

u el f o r

ge n e rat i n g st eam 1, 54 0 Op p o rt uni tyf o r i m provi ng b o i l e r effi ci ency 2. 3 fr om 85 t o 8 7 % F u el sa ve d 35 Op p o rt uni tyf o r re d u ced l i n e heat l o sse s by 10 % 1. 9 F u el sa ve d 30 C

h emi c al i n du st ry f u el re duct i on 65 40 26 Pulp and pap er ste a m op portunities Prese n t u s age of f

u el f o r

ge n e rat i n g st eam 2, 59 6 Op p o rt uni tyf o r i m provi ng b o i l e r effi ci ency 2. 3 fr om 85 t o 8 7 % F u el sa ve d 60 Op p o rt unityf o r re d u ced line heat l o sse s by10 % 1. 9 F u el sa ve d 49

Pul p a n d pa pe r i n dust r y

f

u el red u ct i on 10 9 40 44 Petroc hemicalste a m oppor t unities Prese n t u s age of f

u el f o r

ge n e rat i n g st eam 1, 67 5 Op p o rt uni tyf o r i m provi ng b o i l e r effi ci ency 2. 3 fr om 85 t o 8 7 % F u el sa ve d 39 Op p o rt uni tyf o r re d u ced l i n e heat l o sse s by 10 % 1. 9 F u el sa ve d 31

Pet r oche mi cal i n d u st ry f u el re duct i o n 70 40 28 T o t a l ste a m o ppor t uni ty 24 4 40 98

According to the DOE-EE R E Best Pra c tices repor t c oncerning stea m usage in the che m ic al manufacturing, pul p and p a per, and petroleum industries, 4 154 0, 2 5 96, and 167 5 TBtu of fuel, respectively
, is used to generate st ea m p e r y ear by each industry (see Table 8). As can be seen, on a 40% capture basis (i.e., 40% of the existi ng plants w ill use the improved refractor y and insulation s y s t e m s), the lev e ls of projected fuel savings are 26, 44, and 28 TBtu, respectively
, for the chem ical, pulp an d pap e r, and petrol eu m refining industries. Th is results in a total projected fuel savings o f 98 TBtu across the three industries.

12Refractories f o r Industrial Processing

4.3.4 Barrier s Rel a ted to Refr actory and I n sulating Materials for Boilers and Reactors
The central conclusion from th ese analy ses is that decreased fuel co nsum ption resulting from i m proved boiler efficiency can be achieved thro ugh be tter insulation practices. A s shown, the i m pact of increasing boiler efficiency by 2% and reducing heat losses during steam tr ansfer by 10% will result in a total fuel savings of 98 TBtu for th e industries studied. Addr essing the following barriers as sociat ed with the perfor m anc e of refractory and insulatin g materials used in boilers and reactors would reduce energy requirements:
1. Unavailability of insulati ng refractories with su fficiently low thermal conductivit ies to lead to increase s in energy efficiency levels for boiler operations. 2. Unavailability of im proved insulating materi als fo r transfer pipework that could help reduc e heat losses during stea m tra n sfer operations.



## 4.4 Gasifiers

Gasifiers are currently bein g used in th e chem ical and petrochem i cal industr y f o r coal and biom ass gasification and inthe forest pro ducts industr y specifically for black liq uor gasification. This technolo g y has the p o t e ntial for bio m ass solid fuels to be conv erted into fue l gas “sy ngas ” consisting largely of h ydro g en (H 2 ) and carbon m onoxide (CO). This gas can then be burned cleanly and e fficiently in a gas turbine to genera te ele c tricity and/or used to s y nthesize cl ean transportation fuels or chemical s.
Gasification is currently used in the che m ical industry as a m e ans to pro duce clean energy
, h i ghvalue energy products, and various petrochem i ca ls fro m coal (including th e possi bility of producin g h y d rogen fuel, h i gh-grade transportati on f u els, and indus trial-grade methanol). Experimental gasifiers ar e being applied in a few chemical and pulp and paper p l ants for coal or black liquor c onversion, w h ile gasificati on is also bei ng used as a means of using biom ass as an energy so urce rather than a waste product. In th e fut u re, the forest pr oducts ind u stry m a y use gasification to replace Tomlinson boile rs.

A li m itation on the use of these experi mental gasi fiers is the lack of reliable refra ctories for containment. If the refracto ry requirement could be met, coal, black liquor, and biomass gasification could lead to greater reducti ons in purchased energy and evenchange these industries from net energ y im porters to net energ y exporters. 5 G asification holds the prom ise of generating 175% m o re electrical power than do cur r ent technolo g ies, but the gasification technolog y currently in use requires fr equent refract or y re lines of the vessels, hence reducing the econom i c and energy benefits. 5 Addi tionall y , although chem ical or pul p and paper m a nufacturing faciliti es are not currently used to produce transportation fu els from bio m a ss, the y m a y become a valuable asset for est a b lishing an infrastructure f o r su ch technology. Future gasification-based “biorefineries” m i ght prod uce a variety of re newable fuels, electric ity, and chemicals in conjunctionwith pulp an d paper prod ucts.

4.4.1 Industrial Applications of Process Technology
Chem ical and petrochem i cal — coal and biom ass gasification Forest produc ts — black liquor gasification

4.4.2 Current Tec hnology A coal gasifier generally consists of a m e tallic shell protected by a l i ning m a de up of two t o six concentric la y e rs of refractory protecting the interi or of the vessel. Coal gasifers are expected t o

13Refractories f o r Industrial Processing

operate at high tem p er ature s and m odera te pressur es, and with gas and particle flows containing H 2 , CO, H 2 O, C, H 2 S, HCl, hy drocarbons, m e tallic i m purities, and s a lts. These linings have average lifeti m es on the order of 7000 run h ours and generally fail because of ex cessive mechanic al w ear (erosion), che m ic al penetration of slag into the structure of the inner m ost brick (corrosion), or some co m b i n ation of these two m echan is m s . Erosive wear occurs as the feedsto c k itself causes phy s ical decay of refractory hot-f ace surfaces when injected at high velocities. Corrosive attack occurs w h en th e coal slag residues penetrate the r e fractory hot face surfa ce, t hus weakening the refractory by form ing solid-solution phases.

The nom inal scale of an av erage pulp and paper m ill i s 6 m illion lb/d of black liquor solids (BLS)—the equivalent of 1.5 m illion Btu/h or 438 M W fuel—corresponding to 1900 m a chine dry short tons per day of pape r productio n (1 725 m e tric to ns). 5 Pulp m i l l s processing m o r e than 6 m illion lb/day BLS account for about one-third of all U.S. capaci ty today , and this fraction will grow over ti me as m ill co nsolidations c ontinue. A standard sized gasifier for this size mill is considered. This unit was assu m e d to have a BLS concentration of 80% and a stea m pres sure of 1870 psia.

4.4.3 Energy Im pact For the following analy s is, we considered a co m b ined -cy c le gasifier ty pical of those used for coal or black liqu o r gasification with the requi rem e nts above. Co m b ined-cy c le black li quor gasification has the potential of prod ucing m o re th an twice the curr ent output of electricity per ton. 5 In m a ny cases, power in excess of a chem i cal or pulp m ill’ s needs could be produced and exported. Fur t her, if gasified coal or black liq u o r were converted to a high-q u ality sy n t hetic gas sim ilar to sy n g as produced from fossil residual o il, the energy and e c onom ic benefits would be even greater. Conventional processes could then be us ed to convert the gas to liquid fuels or hy d r og en

. According to the econom ic and energ y an aly s is perfor m ed by Larso n et al., 5 f u ll i m pl ementation of the black li quor gasification init iative could achieve the followin g energ y ben e fits by 202 0:

1. Productionof up to 8 GW of electricity from sustainable, renewable raw materials b y 20 20 throug h black liquor gasification alone. 2. Productionof 16 GW or m o re of electric power for th e application of black liqu o r gasification in conju n ctionwith wood re sidual gasification b y 202 0

. 3. Alternatively
, displacem e nt of m o re than 282 m illion barrels of oil per y ear if the se technologies were applied to s y ngas pro duction t o be used for liqui d fuels.

The total of these biomass energy sources consumed at pulp m ills in 2002 was esti m ated at 1.6 q u ads (on e quad is 10 15 Btu). 6 T h e p o tential renewable energy generation p o tential from black liquor i n the pulp and paper industr y in the s outheastern United States is shown in Table 9.

Refractories and insulatio n materials play ke y rol es inmany of the unit o p eration s involved in both of these industries. It i s esti m ated that pr ocesses affected by ref r actories acco unt for about 40% of the industries’ dire ct energy consu m p tion. Based on subsequent analy ses of ty pical furnaces and unit processe s, i m prove m e nt of refractory sy stem s for these two industries could lead to energy savings opport unities up t o 12 9 TBtu/ y ear.

14Refractories f o r Industrial Processing

Ta ble 9

. Renewa ble energ y g e nera ti o n potenti a l (billio n kWh/ y e a r ) fro m bl a c k liquor in the p u lp and paper indus try in th e sou t he as tern United S t ates

Technol o gy Po t e nt i a l by 20 20 (billio n kWh/ y e a r ) Eq u i v a l en t ene r g y (T B t u/ye ar )

C o n v e n t i onal c o al com bust i o n 72 6 (33–35% e ffici ent) (ene rgynee d ed ) Com b ined cycle gasification 66 0 (45–50% e ffici ent) (ene rgynee d ed )
To ta l i m pro v emen t 6 6 Chemic a l 44 0

Fores t pr od uc ts Tom l i n son rec ove ryboi l e r 4. 4 15 Hig h -e fficienc yTom linson 16 .7 57 recovery boiler Com b ined cycle gasi fi cat i o n 36 .2 12 4
To ta l i m pro v emen t 6 7

4.4.4 Barrier s Rel a ted to Refr actory Materials for Gas i fiers Addressing the following barriers as soc i ated with th e performance of refractory materi als use din gasifiers wou l d reduce energy requirements:

1. Unavailability of advanced refractory materi al s wit h im proved corrosion/erosi on resistance, i m proved reliability , and re duced maintenance costs. 2. Lack of refra ctories with resistanc e to high alkali atmospheres and high levels of stress, which lead to gasifier contain m ent issue s

. 3. Lack of alternate refractor y designs which w ould provide refractory surfaces (us i ng coatings, che m ic al alte ration of refractory surfaces, phy s ical alteration of refractory surfaces, etc.) that

are m o re i m p e rvious to wear and corrosive attack. 4. Unavailability of refractory m a t e rials with greater therm a l co m p ati b ility with m e tallic materi als use din gasifiers.



## 5. Overall R&D B a rri ers and Pa thwa ys fo r Re fra c tor i e s

Evaluation of refractory us age, barriers, and needs of these sever al e n ergy -intensive process industries sho w s that several co mm on them es arise in the pursuit of im proving ref r actory materi als for greater energ y efficiency

. These the m e s relate to i m proving energy efficiency by reducing energy loss and i n creasing productivity th r o ugh the development of higher-strength refractories capable of ope rating at high er tem p er atures, the development of refractories with lower ther m a l conductivity to reduce wall losses athigher service tem p eratures, t h e tailoring of ther m a l expa nsion capabilities of current refractor ies, and the devel opm ent of refractories with greater resi sta n ce to che m ic al and mecha n ical w ear ( c orrosion, eros ion, abrasion, etc.). This concept is shown in Fig

. 2

.

15Refractories f o r Industrial Processing

Fig. 2. Improving refractory materials for improved energy eff i ciency.

Through analy s is of current refractory use, current barriers, possible i m prove m e nts in process energy efficiency , and R&D refractory needs fo r several process i ndustries, many issues common to m u ltiple industries become apparent. The r esear ch focus areas and technical R&D topics below have been identified as issues co mm on t o m a ny applications of refractories.

1. Understand t h e degradati o n mechanisms of refractories in different environments Determine the m e chanisms responsible for th e chem ical and m ech anical degradation of refractories in the various envir onm ents in which the y operate.

2. Achieve impr ovements in thermal control Deter m ine the ther m o m e c h anical properties of re fractor y m a terials and develop materials that will allow furnaces to operate with longer cam p ai gns and with higher levels of insulation to reduce heat losses. This may also involve the im ple m entati on of new furnace designs, the form ulation of newly redesigned process es, or the re-e ngineering of existing industrial practices.

3. Evaluate thermomechanical properties at elevated temperature Determine the key properti es of refracto r ies at elevated tem p eratures, includin g h o t m odulus of rupture, hot crushing str e ngth, creep be havior, refractoriness under load, physical and therm a l spall resistance, dimensional chang es (elastic m odulus, therm a l expansion, and growth from chem ical alteration), and th erm a l conductivity

.
4. Form an expert advisory committee Assemble a committee com posed of current a nd retired industr y e xperts to serve in an advisor y role for industr y

- f o cused refractor y R&D projects. Additionall y , i nvent or y and preserve exist i ng industrial equipm ent an d fac ility resources through sy stem ati c surve y s of refractory experts (especi a lly retirees) s o that industrial furnaces an d existing laboratories can be utilized, when possible, to augm ent new experi mental sy stem requirements.

16Refractories f o r Industrial Processing



## 6. Specific R&D Areas with Barriers and Pathways

The following text summa rizes pathway s for overc oming barriers for the six spe c ific R&D ar eas that can y i eld the greatest r e turns in refractories.



## 6.1 Improved Castable and Monolithic Refractory

Barrier Inadequate resistance to co rrosive and mechani cal w e ar, which lim i t s the use of castable and

m onolithic refractories.

Pathways

• Fabricate fusi on-cast refrac t ories (such as alu m ina zir c onia refracto r ies) that do not include silica or other glass for m er s. These refractor ies should possess great er corrosion resistance and therm o el astic properties. The refractories would be of use to i ndustries such as glass, pulp an d pap e r, and many others.

• Fabricate co m ponents for continuous measurementof param e t e rs such as tem p erature, bath chem istry
, etc., that will have long-term stability in hi gh-tem p erature industrial solvents, such as cry o lite for the electroly t i c production of alum inu m . Candidate materials su ch as HfB 2 , HfC, ZrB 2 , ZrC, and TaC should be cons idered.

• Develop oxide/nitride grain boundar y a dditives lead ing to closure of open poros ity in silica,

m

u llite, and magnesiu m alum inates as u sed by the gla ss and other i ndustries.



## 6.2 Modified Fiber Materials

Barrier
Lack of fiber insulation m a terials with lo wer thermal conductiv ity , g r eater chemical resistanc e , and higher te m p erature stabili ty lim its.

Pathways

• Produce froth ed latex/fiber mixes for gun ning t o reduc e airborne fib e rs during ins t allation. Enhance adhesion of m a teri als to steel an d other m e tal s for application in heat treat m e nt furnaces. Dev e lop new inorganic binder sy stems.

• Fabricate fibrous m a t e rials with greater strength and l o wer friability for use in heat treat m e nt and chem ical and petrochemical industries.



## 6.3 Surface Modification (Coatings, Physi c al or Thermal Alteration)

Barrier Lack of techniques and m a t e rials for apply i ng su rface coatings or inducing phy s ic al alteration of refractory surfaces through either m e chanical or therm a l means.

17Refractories f o r Industrial Processing

Pathways

• Modify surfa ces or near-su rfaces of sintered alu m ina and m u llite refractories by apply i ng corrosion/erosion-resistant coatings such as spinel phases (or additi onal corrosion-resistant materi als) for use by industries such as g l ass, pulp, and paper.

• Determine the effect s of “preexisting” refr actory heating conditions that, when applied concurrentl y with high-i n t e nsity i n frared hea ting, m odifies the surface of bonded refractories and results in the residual com p re ssion of a m odified surface at s e rvice te m p er atures. One advantage of this could be an increase in the “strain-free” temperatu r e of refractor ies used in process industries.

• Determine the applicability of radiation-heati ng attenuation/m itigation, and if applicable, si m u late refr a c tory structures that would maxi m i z e its effect to optimize r a diant heat transfer (e.g., im prove ox y -fuel fir e d sy stem s fo r the alum inu m , glass, metal casting, and iron an d steel industries).

• Investigate the effect s of radiative heating and transm i ttance in refra ctories on ther m a l conduction for m i ni mizing ther m a l losses fro m va rious types of fur n aces used throughout th e select ed industrial are as.



## 6.4 Synthetic Aggregates and Pow d ers

Barrier Lack of highe r-perfor m ance aggregates t h at would inc r ease the life and durability of refractory pro ducts used across the various industries and lack of hi gher-quality matrix materi als that would increase the durability of refractories.

Pathways

• Measure and m odel str e ngth as a function of aggr egate size distribution. Tailor m i crostructure so that flexure and com p re ssion strengths are incre ase d.

• Explore candi date aggregate coatings as “add itives” that control or binder grain boundar y effects ( e .g., diffusion, heat transfer, corro sion-resista n ce, etc.) for im proved refr actory processing.



## 6.5 High-Temperature Properties of Refractories

Barrier
Lack of infor m ation on the high-tem p erature therm o mechanical and corrosion properties of current and n e wly develop e d refractory materials.

Pathways

• Develop realistic test methods a nd envir onm ental tests sy stems in order to evalu a te elevated te m p erature p r operties. Evaluate corrosion behavior of refractories for various effects of water/CO/CO 2 /alkali conte n t on th e corrosion and pha se stability of refractories u sed in gasifiers and in the glass, alum inu m , steel, and m e t a l casting industr ies. Develop lab-scale sy stems to evaluate the degradation of re fractories up to 2000°C.

• Sy stem atic all y characteriz e and m odel re heat-generate dpermanent expansion effects in fusion-cast and bonded refractories, a phenom enon known to occur in m a ny refractory sy stems used throughout the various process industries, but not curr ently understood.

18Refractories f o r Industrial Processing

• Perform postm ortem analy s is on failed refract ory components from several industries and identif y servi ce-li m iting flaw ty pes. Use com ponent sam p les for measurement of strength distribution and com p are t o strength dis t ributio n of vi rgin m a teri als. Perform pro b abilistic strength-size-scaling analysis using both distri butio ns as input and p r edict failure time of

co m ponents.

• Measure the corrosion resistance of bonded refractories as a functi on of refractory sintering te m p erature a nd interpret the performance in referenc e to service te m p erature.

• Investigate the effect of sp eci men size i n refractories by m e a s uring strength (m o dulus of rupture) as a function of speci men size i n bonded or fusion-cast ref r actories. D e ter m ine if variations in strength can be represente d by a Weibull distribution and if strength is sizescaled.



## 6.6 In Situ and Graded Refractories

In situ refractories are defi ned as brick or uns haped pr oducts that react internally or with furnace at m o spheres and/or slag co m ponents to enhance their performance. Natural in situ formation of Fe-Mg-O spinels in steel- m aking furnaces per m its i m proved life and durability of these furnaces.

Barrier
Lack of R&D to im prove existing in situ re fractory s y stems and for developm ent of new in situ s y stems for additional industrial applications

Pathways

• Model crack initiation and growth as a function of m a terial, depth, and service properties using m i crost r ucture-based finite ele m en t analy s is (e.g., μ- FEA, OOF). Sim u late and optim ize hy pothetical m i cr ostructures that hinder crack growth.

• Develop high -intensity infr ared heating techni ques to fabricate optimized graded refractory structures, and m e asure therm o m e chanic al stability and corrosion re sistance.

• Model, sim u late, and design refractory micros tructur es that prom o t e m a xi m u m creep and erosion resistances.

• Deter m ine the effect of cry s tallography of base and in situ phases on the development of therm a l stresses and the stability of in sit u lay e rs.

• Deter m ine an d optim ize “ s ubstrate” surf ace geo m etrie s (e.g., dim p les, corrugate d, saw-tooth) that will m i ni mize shear str esses in therm o

- e nvir onmental barrier refractory coatings that are subjected to a thermal gradient.



## 6.7 Sensors for Materials Performance

Barrier
Lack of sensors to m onitor refractory -rela ted issues in cluding wall thickness regression, gas phases, and other environmental conditions.

Pathways

• Develop sens o rs and m e th ods for the m easure ment of spectral e m i ssivity for application in glass tanks and m e t a l m e lti ng furnaces.

• Develop sensors and m e th ods for the m onitorin g of wall regression due to corro sion, erosion, and wear in glass tanks and metal melting furnaces.

19Refractories f o r Industrial Processing

• Develop continuous real-ti m e measur e ment technique s for param e t e rs such as tem p erature, pressure, m e l t analy s is, flue gas an aly s is, and environmental gas phases.

The tasks and the industrie s which will benefit from t h e projects described above are shown in Table 10. As is evident from the t a ble, these s uggested R&D pathway s are crosscutting. Although there is a curr ent trend for many of th ese industries m oving overseas, it is believed that the R & D pathway s proposed will dir ectly benefit U.S. industr y

. Even as processes such as alu m inum

sm elting and glass producti on m ove off shore, ther e will still be a need for remelti ng and other productio n d o m estically

.

Table 10. Rec o mmended R&D pathways for advance d refrac t ories

Tech n i cal R&D pote ntial path w a y s Aluminum Cement & lim e Chem. / pe tr och emica l Ind u str y se gment

Fores t pr oduc ts Glass Heat treat m en t Iron &

s t eel Metal

cas t in g Improved castab l e and m onolith ic refractories X X X X X X X X

Modified f i ber

ma t e ri al s X X X

S u rface m odif i cations (coatings,

a l te ra ti ons) X X X X X X

S y nthetic aggr egates and powders X X X X X X X

Elev ated t e m p erature refractor y properties X X X X X X X

In situ and gr adient refractories X X X X X X X

Sensors for materials performance X X X X X X X X

2021Refractories f o r Industrial Processing



## 7. Ref e ren ces

1. J. Mosser and G. Karhut, “Refractories at the Turn of the Millennium
, ” Paper presented at UNITECR ’99, Berlin, Germany
, p p . x x v–xx x, Sept. 1999

. 2. D. W. Freitag and D. W. Ri cherson, Opportunities for Advanced C eramics to Meet the Needs of the Industries of the Future, DOE/ORO 2076, U.S. Department of Energ y , Of fice of Industrial Technolo g ies, Decem b er 1998.
3. U.S. Department of Energ y , Energ y Inf o rm ation Ad ministration, 1 9 98 M E CS Consumption, Table N3.2, F u el Consum p tion, 1 998

. 4. U.S. Depart ment of Energy, Office of Energy Efficiency and Renewable Energy, Steam System Opportunity Assessment for the Pulp and Paper, Chemical Manufacturing, and Petroleum Refining I ndustr ies: M a in Report, available online at htt p ://www.oit.doe.gov/ bestpractices/technical_publications.s html under “Market Assessments.”

5. E. D. Larson, S. Conson ni, and R. E. Katofsk y , A Cos t -Benefit Assessment of Biomass Gasification Power Generation i n the P u lp and Paper Industry, Princeton University
, October 2003. Available online at http:/ /www.pr incet on.edu/~ener g y / pub lications/pdf/2003/ BLGCC_FINAL_REPORT_8_OCT_2 003. pdf.
6. DOE/EIA Renewable Energy Annu al 20 01, DOE/EIA-0603, 20 01

2223

# APPENDI CES

2425Appendix A — Chemical and Petrochemical



## Appendix A: Discussion of Refractory Usage by Process Industries

A.1 Aluminum

Current Ind u stry Ope r ations and Refractory Use
Alu m inum productionis energ y -intensi ve, consum in g about 0.4 q u ads of electrical energy p e r y ear in the United States. 1 Additionall y , the industr y f aces many of the sam e co mpetitive pressures as t h e steel industry, including global com p etition, energy consum ption issues, and polluti on abat em ent. Therefore, a technology r o ad m a p has been created to address these issu es by targeting ar eas such a s e n ergy consum ption, productivity
, em is sions , recy cling, quality
, alternate tech nologies, and by -products. 2

Many s y stems are used in the producti onof alum inu mand its allo y s , all of which depend onth e proper selecti on and m a na ge m e nt to ensure the cost effectiveness o f the metallur g ical and refractory pra c tices. These sy stems include stea m boil e rs for Bay e r plants, calciners, and carbon baking f u rnaces used for the production of the a nodes which are co nsumed in the Hall-Heroult reduction process. In Hall- Heroult electr o ly tic reduc tion cells, the key refractories are those us ed to support the cathode hearth and to m i n i m i ze the pen e tration of ba th constituent s into the carbon cathode and underl y i ng refractories. Melt ing furnaces for alloy pr oduction by the primary and secondary pr oducers include large fossil-fuel-fire d reverberatory f u rnaces as well as a variety of induction fur n ace designs dom inated by the co reless and the channel induction types. Te m p erature s and corrodant che m istrie s, as well a s furnace at m o spheres, deter m i n e the lining used for each of these processes. The ref r actories used for each will be briefly reviewed.

Primary Alu m inum Prod uction The producti on of prim ary alum inu m metal is based on three m a jo r steps. The first involves th e mining of ba u x ite ore. Ther e are no high-grade deposits in the United States; therefore, refractories play little role in this process.

The second process involves the conversion of b auxit e to metallurgical grade a l umina . The Bay e r process is bas e d on digestion of bauxite in caustic solution heated with superheated stea m to f o rm sodium alu m i n ate. I m purities are r e m ove d from the pregnant caustic by chem i cal reactions wit h dissolved species (pri marily SiO 2 ) and f i ltration of i n soluble im purities (prim a rily iron oxide). The saturated solution is then cooled in precip itator tanks in which alu m inum tri h y d rate is precipitated and then recovered by filtration. The al um inum trihy d ra te is converted to alum ina by calcination. Two methods of calcination are em ploy ed in the i ndus try : use of flu i d bed calciners and use of rot a ry ki lns.

The third pr ocess involves conversion of alum ina to al um inu m by el ectrolytic reduction usin g th e Hall-Heroult process. In the reduction process alu m in a is dissolved in a m o lten bath (cry olite, Na 3 AlF 6 , with additions of AlF 3 , CaF 2 , and som e times LiF and Mg F 2 ). The cell for this process utilizes a contain m ent sy stem consisting of a steel shel l lined with a castable r e fractory
, a porous insulating ref r actory , a less porous sem i- insulati ng ref r actory , and f i nall y firebrick. A carbon cathode acts as the bottom of the cell fo r m o lten alu m inum containment. The side-wall refractorie s ar e generally phospha te-bonded alum ina brick or alumina castable materi als. Be cause the sides of cell have less i n sulation, m o re heat is lost through the w a lls than the floor. The lower

26Appendix A — Chemical and Petrochemical

wall te m p er at ure is actuall y beneficial, causing el ectrol y tes in cont act with the wall to solidif y and form a “f rozen ledge” which protects the walls of the cell fro m penetration by m o lten cry o lite. T h is practice is su ccessful, but i nvolv es a trade-off between energy efficiency and electroly tic cell stability and lifetim es in terms of energy consumption.

Reduction cells currently e m ploy variou s refract ories just below th e carbon cathode which du ring service degrade in various way s , perm itting bath constituents to m ove into th e cathode carbon and refractorie s. The sy stem s i n place today include fireclay bricks, castable refracto r ies, se miinsulating ref r actories, and insulating bri c ks. Sy stem s for prim ary alum inu m production in volv e several different designs d e pending on th e level of am p e rage and the num be rs and array of anode blocks. The current intensity for o p erating reduction c e lls through o u t the world r a nges fro m 60,000 to 500,000 A. Yet, th ey all still invol ve a carbon cathode hearth and consumed carbon anodes in which the bauxite ore charge a nd the s y stems of alkali fluoride fluxes are placed and held while the reduction pr ocess is carri ed out conti nuousl y . T ypic a lly th e reduction pr ocess i s carried out at a tem p erature in the range of 960 to 970 ° C. The refractories are key com ponents in reduction cells. The at m o sphere inside the cavity of a reduction cell is very reactive, containing a mixture of CO 2 , CO, HF, SO 2 , and part iculate fluoride salts.

In all cases it seems that the for m ation of a feld spathic co m position at the interface between the cathode and th e barrier is highl y desirable but that other bath species can still penetrate the barrier and lead to hi ghl y sh ortened cell life. Furthe r, downward m ovem e n t of alkalis and bath constituents through the he arth toward the subhearth insulation eve n tuall y result s in the failur e of the furnace, an event which is still quite unpredic tabl e. Because of this, furnace lives vary fr om hundreds to thousands of d a y s

.
Taberaux 3 ha s reviewed the failure m e c h anis m s of al um inu m redu ction cell sy ste m s. Fire clay brick in one reported case l asted over 3000 day s , showing that the materi al itself can m eet the challenge, all other factors being o p tim al in their selection and control. Castables have disadvantages in cast-in-place sy stems, and current l y the preference is for precast m onolithic sy stems, which have had good success. Two ty pes of dr y barrier refractories ar e currently being used. Their advantages res t on ease and rapidity of installation and lack of joints . The y include alu m inosilicates on the one hand and anorthite fe ldspar on other, chosen because it undergoes beneficial in situ reactions and is, in fact, patented.

Carbon a nod e baking furn aces have historically been constr ucted of alum inosilicate bricks. These bricks have sufficie n t refractoriness that e ffort s to replace the m with alu m ina-reinforce d versions have not been cost-effective. The cha llenge to the brick co mes fro m its coking an d fr om the alkalis present in the electrode feedst ock. Most recently, fireclays with very low alkali content have been used for the production of bricks increasin g ly designed with surface l o cking s y ste m s that reduce the bowing of walls, which is the principal reason for th e replacement of the refractories. Because such large num ber s of br icks are used in carbon baki ng fur n aces, attemp ts have been ma de to recy cle the m , but past effort s have not resulted i n the formulation of a costeffective protocol.

Schubert 4 recently addressed the basic issues of m ove m e nt of the flue walls, and points to the findings i n p o s tm ortems that the insulation m a y be in adequate for the support r o l e that it play s. The many challenges to the flue walls i n clude (1) alkali infiltration and attack from bath carry over, via recy cled anode butts in the recipe ; (2) fluoride salt attack fro m bath carry over, via recy cled anode butts in the recipe; (3) m i nor “squatting” from el evated tem p eratu r es and load; (4) mechanical dam a ge fro m impact of the anode and/ or the crane during l o ading and unl oadin g ; (5) thermal shock, especially duri ng th e cooling c y cle; (6) construction details that aggravate

27Appendix A — Chemical and Petrochemical

norm a l w ear and tear; (7) various proble m s due to im proper expa nsion a llowances; and (8) coke sticking to refractory
, aggravated by alka li content.

Semifabricated and Secondary Aluminum Production Secondary al um inu m production in volv es re cycling of aluminum m e tal scrap . This is carried o u t in a variety of furnace desi gns. When large volum es o f alloy are required, reverberatory furnaces are traditionally used. Thes e furnaces ha ve seen a constantly evolving refractory practice. Monolithics replaced bricks in the distant past, a nd currently m onolithics in the f o rm of precast “big blocks” are receiving renewed interest. A recent paper b y Can o n 5 reports that the real advantage of precast furnace co m ponents rests in th e ti m e savings r a ther than in th e extension of service life.

As in the case of the subhear th refractories usedin pot furnaces, it is essential to develop a freeze zone in the walls of all the furnaces. This is done by s e lection of refractories and appropriate thicknesses. I t is also essen tial to restrict the penetr ation of the alum inum alloy into the refractory
, which is achieved by incor poration of additiv es, some of which are proprietary. As it is im possible to keep ox ygen from reacting with the aluminum met a l, a so-called belly band develops in all ty pes of m e l t ers. Bec ause of the fluctua ting level of th e metal in some furnaces, the belly b and can be quite wide and eventually ex tend into the furnace to such an extent that it

m

u st be re m o ved. In the case of the largest reverberat ory types of furnaces the re m oval is

so m e ti mes carried out using large roboti c devices. In many instanc es the fu rnace has to be shut down to effect adequate rem oval. In the hearth region of the m e lter, linings of sili con nitride– bonded silicon carbide are used for m o lten alum inu m contact areas.

After melting, the m o lten alum inu m flo w s through re fractory

- lined troug hs between the various process steps. These troughs are ty pically lined with oxide ceram i c s such as fused silica or m u llite with 10–15% porosity and special additives to resist wetting. Th ese m a terials ar e installed in board or castable for m and are used due to thei r low ther m a l expan s ion and good therm a l shock resistance. Still, erosion and abrasion issues are of concern. SiC-based material s have been considered for this application but are more expensive than oxi de refractories.

Belly band buildup is th e overriding issu e in melting furnaces. Quesnel et al. 6 have reviewed the problem for a l um inu m holding furnaces and m e lt ers. There is a lac k of understanding concerning the mechanisms of belly band form ation. The two ty pe s of tests ty pically used in the study of candidate refractories are a bellyband cor r osion test (which is a si m p le cup test) and an imm e rsion test (which really looks at the penetr ability of the refractory by th e metal). Long use of these tests has produced inconclusive answers a bout th e mechanism of att ach ment, and it is apparent that new approaches are ne eded.

Barrier s Refractories play ke y role s in m o st of the unit o p erations inv o lved in the pr oduc tion of prim ary and secondary alum inu m

. It is estim ated that about 9 0 % of the dir ect energy us e by the in dus try is in processes a ffected by refractories. Re c o mmended im prove ments for refractories include applications for refining, re duction, carbon anode baking, and m e lti ng operations. Based on subsequent analy ses of typical furnaces and unit proc esse s, i m prove m e nt of refr actory s y stems for the alum inum industry could lead to ener gy savings opport unitie s up to 29.2 T B tu/ y ear. The specific barri ers are as follows:

28Appendix A — Chemical and Petrochemical

• Aluminum Refining Unavailability of im proved refractories fo r superheated steam gen e ration, as well as im proved refractories for calcini ng oper a tions, particularly rotar y kilns for alu m ina and lime, which could l ead to im proved energy efficiency for ref i ning operatio ns.

• Aluminum Reduction
Lack of unde rstanding concerning the mechanisms an d degradation scenarios leading t o the failure of reduction cell refractories and, ultim at el y , th e reduction cell. Further, th ere is a lack of im proved linings and ref r actories with im prove d resistance to bath penetration that would perm it extended lives for reduction cells.

• Carbon Anode Baking Fur naces Unavailability of stronger insulating sh a p es for com p onents of carbon baking f u rnaces.

• Aluminum M e lting Furnac es Lack of unde rstanding reg a rding the m e chanism s of belly ban db u il dup form ation. This is

co m p licated by the inability of current tests to provid e conclusive answers regarding th e mechanism of attach m e nt and to pr ovid e sufficient perform ance projections.

R&D Pathw ays

• Refining

o Develop im proved refractory an d insulat i on s y stems f o r high-tem p e rature ste a m generation.

o Im prove refractory m a terials for calcining ope rations, particularly f o r rotar y kil n s.

• Reduction

o Develop a fuller understanding of cell refr actory failur e throug h chemical and ph y s ical m o d e ling of the re actions and transport m e ch anism s . Develop k nowledg e and control of all aspects o f the che m ica l and phy s ical properties of the refractori es, and optim ize drefractory design approach es for reduction cells carr y ing increasi ng current intensities.

o Develop a sidewall refracto ry design that woul d allow direct contact with the m o l t en cry o lite bath, perm itting elimina tion of th e “frozen ledge.”

o Develop refra ctories with im proved toughness, i m pact resistanc e , a nd abrasion resistance for the hearth region of reduc tion cells.

• Carbon Baki ng

o Develop unde rstanding of th e manner in which insulation com ponents are being affect ed chemically and mechanic ally by the loads f r om the overly i ng charge and wall refra ctories. Perfor m s tudies of the mechanic al properties of such used refractorie s to provide answers to th ese and related questions tied to assuring therm o m e chanical stability.

o Develop im pr oved refractories and furnace d esigns for reducing ene r gy consum ption in carbon m e l ting fur n aces though m odeling of design, process control, quality control, and selection of hot-face refr act ories, not only in the flue walls but in other

co m ponents of the furnaces.

29Appendix A — Chemical and Petrochemical

• Melting Furnaces

o Develop m o r e accurat e si m u l a tions of the melting process.

o Develop a m a terials approach that involv es the development of graded m onolithic linings, cast in place or precast, which have m u ch denser surfac e re gions and m i ght also contain additives to di ssuade penetrants . Determi n e the ke y factors which affect penetration and attachment such as the perm eability of the surface region to the metal or altered m e t a l.

o Develop im proved refractories for alu m inum melting and casting o p erations, including advanced refra ctories for reve rberatory m e l ting furnaces and prefired refractory riser tubes for low-pressure al um inu m die c asting applications that are

econom ical, strong, th ermal-shock-resistan t, and nonwetting to m o lten alum inu m , and that have low gas permeability

.

o Develop efficient, long-life degassing co m ponents for alu m inum alloy production.



## A.2 Cement and Lime

Current Ind u stry Ope r ations and Refractory Use The United States is the third largest cement-pr oducing coun tr y in the world (after China and India). The pr oductionof c e m e nt and its interm edia te product, cement clinker, h as risen steadily over the last decade, with consum ption incr easing 40% while production has only increased 27%. This has led to increased im ports in the short term , mainly from Ca nada and Mexico, but could lead to furthe r expansion o f the dom estic industr y inth e long term . Currently, the r e are 115 cement m a nufacturing plan ts in the Unit ed States, with about 75% of the total pl ants owned b y only 10 large co m p anies: L a farge North A m eri ca, Inc. ; Holci m (US ) , Inc.; CEMEX, SA de CV; Lehigh Cement Com p any ; Ash Grove Cem e nt Co m p an y ; Essroc Cement Corporation; Lo ne St ar Industries, In c.; RC Cement Com p any ; Texas I ndustries, Inc. (TXI); and California Portland Cement Co mpany

.
The 199 7 Econom ic Census report (sam pling 279 e s ta blish m ents) shows that refractories (clay or non-clay ) account f o r 2.5% of the total c o st for the cement industr y, or approximately $61.5 million of the total $2.5 bil lion spent.

A typical m odern cem e nt plant m a y include the following refractory lined units: (1) a preheater equipped with several cy clones as a heat excha nger, (2) a precalciner with a burner for the decarbonization process, (3) a kiln, and (4) a kiln cool er. The preheater, cy clones, and heat exchangers heat the ce men t raw m e al or slurry befo re it is passed to the rota ry kiln. This aids fuel

econom y by decreasing the am ount of heat that the kiln m u st supply. The precalciner uses preheated com bustion air from the clin ker cooler a nd/or kiln exit gases with se parate burners to calcinate up to 95% of the raw material. A precalcine r kiln s y stem c onsisting of a rotary kiln with an external furnace may also be used for heating ce m e nt raw m eal t o calcination te m p erature s

. This sy stem also often has a m u ltistage cy clonic preheater attached to it for f u rther heating efficiency

.
The kiln is w h ere ce ment raw m i x is dried, calci ned, and burned in to clinker at t e m p eratures of 2600 –30 00°F

. Kilns can be rotary (rotati ng at one t o th ree revolutio ns per m i nute) or shaft ty pe and use coal, oil, gas, or other fuel for heating. A rotary kiln will generally be di vided int o zones

30Appendix A — Chemical and Petrochemical

for dr y i n g , pr eheating, calcining, burn i n g , and coo lin g. Kilns havi ng a preheater and/or precalciner d o not usually contain the first thr ee zones. The m o lten batch e m erg es fro m the lower end of the k i l n in the f o rm of ver y h o t, marb le-sized chunks kn own as “clinker.” Once out of the kiln, the clinker goes through a c ooling process in the kiln cooler. When cool, the clinker is ready to pass through a series of grinding and milling processes that result in the gray powder we know

as ce ment.
The kiln is the heart of the plant and is genera lly lined with fired bri c ks. Monolithic refractories are used onl y in tapered parts of the inlet cham be r, the manhole of th e calciner, an d the chargin g inlet of the kiln. These m o nolithics are required to posses high resi stance to reaction with cement

raw material s, high resistance to penetration/in filtration of alkalis, as well as high resistance to mechanic al st ress. G e nerall y, dense low-ce ment , high alu m ina cast a b le with service te m p eratur es of 170 0–1 80 0°C (3092 –3 272°F) is used here.

A typical long kiln will include a dr y i ng zone , a preheating zone, a calcining zone, a burning zone, a transition zone, and a cooling zo ne to cr eate a te m p erature p r ofile in the kiln. Generally, fireclay brick s or high-alu m ina bricks are used in the dr y i n g and c a lcining zone s. Lightweigh t insulating bricks are used t o reduce the heat lo ss from the kiln. In these zones, refractorie s ar e subjected to abrasion and structural spalling caused by reactions wit h alkali from the ce ment raw materi als. The te m p er ature is relatively low inthese zones, but because of the use of various waste s as fuel and constant te m p erature f l uctuations, the refractory wear c a n bec o me sever e. Fuel types vary am ong petroleum coke, tires, solid wastes , etc., resulting in i n creased concentrations of alkalis (Na, K), sulfur (S), and chlorine (Cl) as well as other enviro nmen tally detr i m ental metals (Pb, Zn). As a results, the refractorie s ar e subjected to harsher alkaline sulfate [( K 3 Na(SO 4 ) 2 , K 2 SO 4 ] and alkaline chlori de (KCl, NaCl) condensa tion at cooler zones. Sulfur a dditionall y
co m b ines with the cem e nt co m ponent ( C aO) to form CaSO 4 cotec tic liquid. These liquid and vapor phases infiltrate into bricks, resulting in refractory densification, increased ther m a l conductivity, and thermal expansion whi c h ultim at ely reduces the st ructural flexibility of kiln linings. Add i t i onall y , th e in crease in therma l conductivity often damages the steel shell.

Monolithic refractories ar e also used in sections of cement kilns, typically at the outlet where wear rat es ar e very high. At these zones, de nse silicon carbide–based castables ar e often used. The cy clones in the preheater section of ce ment plan ts are also lined with dense castables, due to the com p lexit y of their sha p es and the wear resi st ance required. Th e shell of the exhaust gas duct is m a de fro m both dense and insulating castable ma teri al. In the cooler section of the plant,

m onolithic refractories are used to line th e ceiling. The upper and middle cy clones of the calciner are generally lined with fireclay castable or equivalent gunning m a terials posse ss ing a service tem p erature o f 1400–1500° C (2552–2732°F). One co mmon problem with this arrangem e nt ari ses when ce ment raw material s reach the inlet cha m be r a nd riser beca use they adhere (stick) to the refractory lini ng and thus c ause clogging . This cl og is either m ech anically rem oved or rem oved with high-pressure wat e r.

In the United States, as in m o st industrialized countries, two types of manufacturing processes have beco m e prevalent in th e cement industr y ; these are known as the “wet process” and the “dr y process.” Alt hough in m a ny respects these processes are the same, or ver y sim ilar, in the ol der wet process, ground raw materi als ar e mixed with wa ter to form a thick liquid s l urry , while in the dry process crushed lim e s t one is used and raw ma teri als are mixed togeth er without the addition of water, lead ing to higher energy efficiency
, since drying is not needed. Currently there is a general trend in the United States to convert wet kiln t echnolog y to dr y kil n techn o log y ; as a result, in 2000 there were 32 wet and 77 dr y kilns.

31Appendix A — Chemical and Petrochemical

The major fuels used in U.S. ce m e nt pla n ts are co al and coke, or coal and petrol eu m , and are used for the clinke ring process. After 1980, however, other fuels—including tires, sol i d and li quid hazardous wastes, and nonhazardous wastes such as o ils and solvents—began to be graduall y used. The use of these alter n ative fuel types h as significantly increased in recent y ears, as shown in Table A.1. Overall, this suggests that there ha ve bee n no m a jor changes in energy -efficient fuel use in cem e nt kilns since 1990, although m o re m ode rn plants have been built. T h e survey , by th e Portland Cement Associati on (PCA), suggests sli ghtly lower avera g e energy uses of 4.73 GJ per million m e tri c ton of clinker and 4.91 GJ per m illion metric ton of Portland cement for 2000. Further, the 1 997 Eco nom ic Census rep o rt (s am pling 279 establish m ents) showed that energ y costs (fuel costs and purchased ele c tricit y costs) acco unt for 40% of the total cost for the ceme n t industr y , with approxim a tely $485 m illion sp ent on fuel and a sim i lar am ount spent on electricity

. 7

Table A.1. Fe edstock for energy use in the cement industry, 1993 -2001 (thous a nd m e tric tons )

1 993 1 994 1 995 1 996 1 997 1 998 1 999 2 000 2 001 % chan ge C o al 10 ,0 3 4 10 ,4 8 4 8, 24 1 8, 76 4 9. 03 5 9, 06 6 9, 20 6 10 ,0 9 5 10 ,2 4 0 2. 05 C oke from coal NA NA 45 5 45 8 35 1 43 2 34 3 44 2 42 0 –7 .6 9

Petrole u m coke NA NA 1, 47 5 1, 29 5 1, 28 8 1, 19 7 1, 62 2 1, 35 1 1, 37 0 –7 .1 1

Fu el o ils a 46 49 42 64 86 73 82 12 4 93 10 2. 2 Natural gas b 66 8 65 0 1, 06 9 71 0 67 2 72 0 65 3 33 8 39 7 –4 0. 5

Ti res 70 12 0 15 8 19 1 27 7 26 9 68 5 37 4 30 0 32 8. 6
So lid wastes 90 74 68 72 68 74 81 6 1, 01 6 32 0 25 5. 6

Li qui d wastes a 74 4 60 0 88 5 91 0 83 5 1, 26 8 90 6 92 9 82 9 11 .4

a Millions of l i t e rs. b Millions of cub i c lit ers.

Barrier s Refractories play ke y role s in calcining operati ons, th e core production m e thod for the cem e nt and lim e industries. It is estim ated that alm o st all of the energy cons um ption is affected by refractories. Reco mmended im provem e nts for refract ories include applications for all of the ther m a l zones of ty pical rotary calciners. Based on subsequent analyses of ty pical furnaces and unit pr ocesses, i m provem e nts to refractory s y stem s fo r the cem e nt and lim e industries could lead to op portu niti es for energy savings of up to 42.3 TBtu/y ear. The specific barrier s are shown below.

• Unavailability of chrom e -free re fractories for use in the trans ition zones of lime kilns, where refractorie s ar e subjected to large te m p er ature fluctuations b y th e repeated detach ment and adhesion of th e cement coating.

• Unavailability of refractories with adequate corrosion resistance an d adhesion (c oating) ability for use in the burning zone of lim e k ilns, where tem p eratures reach to above 1450°C (2642°F).

32Appendix A — Chemical and Petrochemical

• Unavailability of refractory m onolithics with high abr asion resistan ce as well as high resistanc e to mechanic al a nd therm a l sp alling for the inlet cham ber and riser of kilns to replace less adherent silicon carbide cast ables and precast shapes.

• Unavailability of m onolithic refractory materi al s wit h resistance t o alkali reacti on for use as clinkers in the cooling zone of the kiln to replace low-ce ment, high-alu m i na cast ables used in the area.

R&D Pathw ays

• Develop m o n o lithics with better abrasio n resi stance and low or no adherence properties.

• Develop met hods to m odif y the surfaces of c linker zone brick, so a s to encourage the formation of protective coatings by physically altering the refractory surface or through che m ic al alte ration of the s u rface. Devel op and im prove magnesia- spinel brick and dem onstrate t h e effect of zi rconia additions.

• Identify non-chrome-conta i ning refractories wh ich posses s increa se d corrosion re sistance to the environm ent present in ce ment m a n u facturing.

• Develop non destructive techniques for m onitoring wear of refractories.

• Develop and i m prove silicon carbide castables to produce products with im proved thermal properties and even less adherence to ce ment raw mat e rials.



## A.3 Chemical and Petrochemical

Current Ind u stry Ope r ations and Refractory Use
The chem ical industries have processing equipm ent that spans a broad range of types, with associat ed processing temperatures ran g ing from as low as 370–425°C (700–800°F) to as high as 1870°C (3 40 0°F). The refractory

- lined u n its in a ty pic a l full-spectrum refinery can include fluidized cataly s t cracking units (FCCUs ) , cataly tic reformers, fired heaters, boilers, hy drogen refor m er s, et hy lene furnaces, incinerators, a nd carbon furnaces. Some of these units are designed to have substantial insulating capability in their linings, while others are low-temperature-process units, like FCCUs that contain only a single la y e r of re fractory designed to withstand the extre m ely severe abrasion c aused by the cataly s t.

The esti m at e dcost of refractory lining installa tion and m a intenanc e work for the che m i cal an d petroleum industries is relatively low (as low as 1% of the total oper a ting cost) com p ared to oth e r equipm ent co nstruction an d m a intenance costs; y e t, r e fractory lini ng degradatio n and failure are leading factors for frequency and d u ratio n of s hut dow ns. Due to lo wer operating tem p erature, as
co m p ared to other industries, refra ctory is not norm a lly affected by high tem p erat ures, y e t refractory de gradation m a y be caused by erosion, corrosion, and m echanical str e sses caused b y therm a l cy cling, depen d in g on l o cation of the refr actor y within th e unit. Anoth e r problem th at can affect refract or y reliability is the manner in whic h the refractory is installed (i.e., pneum aticall y gunned, shotc r eted, vibration cast, pum p cast, and/or hand packed)

. Additionall y, with operati ng time, m i nor im p e rfections can beco m e l o cations of exacerbated li ning degradation. Lining design (i.e., anchoring, lining thicknesses, and design of construction/expansion joints) can also add to lining degrad ation.

33Appendix A — Chemical and Petrochemical

Also, the total tonnage of refractories in an av erage-sized full-spectrum re finery can be as high as 1000 tons of refractory for a single lining that is in tended to last for at least a decade: a ty pical refinery requi res approximately 2500 t o ns of refract ory

. Som e of the m o re critical units are put on maintenance, with annual t u rnaround, and the re placement and repair of refracto r ies for a single unit can am o unt to 250 to ns, or a fourth of the li nin g

. Virtually all of the refract ories used by chem ic al plants are m onolithics. These include castabl es, cast vibration m i xes, gunni ng m i xes, low- and no-cement cast ables, plastics, an d a variety of insulating refractories. Be c ause many of the te m p eratu r es of refiner y processes a r e too low to prom ote a cer a m i c bond to replace the hydraulic bond of calciu m al um inat e–bonded castables, the refractory practice has been based largel y on phos phate-bonded plastics, which develop the needed prope rties at or below the process te m p er ature s . Refractory practice varie s widely from

one com p any to another. Some co m p ani es have incorporated casta b les, especial ly vibratables, into their practice, and today com p anies are ev aluating shotcretable refractories i n locations where a ceramic bond can be developed at the process tem p er ature.

However, the place where advances in refractories may have the greatest i m p act on efficiency in the chem ical industr y is i n the boilers used to pro duce steam for power generatio n. Im provements in the therm a l efficiency of boilers thems e lves, throug h im proved insulation, an d in the i n sul a tion used on trans f er pipework could lead to reduc tion in h eat loss and lower fuel consu m ption.

In the petroch e m i cal and synthesized gas industr ies in particular, new designs in th e cataly s t support m e dia and the inst allation of refractor y insulation have incr eased operati on life and efficiencies of reactors of various ty pes. New ref r actor y designs for support m e dia have allowed increased flo w rate and longer productive life for expensive catal y s t m a terial s. More attention being paid t o the use of spray a ble refractor y cera m ic f i ber lining materials as we ll as new microporous silica backup materi als. More attention is also being pa id to th e use of precast par t s for com ponent of the various unit pr ocesses, and wider use of precast technology is anticipated. Because it is so im portant to m a intain sh ell te m p eratur es of vessels and reactors above a threshold te m p erature t o avoid condensation onto the shell, designers are try i ng to refine th e m odels for predicting te m p erature gra d ients and cold face te m p er atures. Lack of data on the thermal conductivity of many com m erci al m onolithic refractor ies is holding back progress in this area.

Barrier s Refractories and insulatio n materials play ke y rol es inm o st of the varied unit ope rations invol v e d in the pro duct i on of chem ical and petrochem i cal products; it is estimated that ab out 5 0 % of th e industries’ dir ect energy consum ption is in processes affected by ref r actories. Based on subsequent analy ses of typical furnaces and unit proc esse s, i m prove m e nt of refr actory s y stems for the chem ical and petrochem i cal industries coul d lead to energy savings opportunities of up to 266. 4 TBtu/ y ear. The specific barriers are shown belo w.

• Lack of unde rstanding of h i gh-tem p erature properties such as creep rupture, shor t-time strength, ther mal conductivity , th ermal expans ion, ductility
, and st ability for th e m onolithic refractories used in this industr y

.

• Lack of unde rstanding of th e corrosion properties of refractories used in the chemical and petrochem i cal industries, which subject mate rials to conditions ranging from hot-oxidizi ng environm ents to environm e n ts that contain hot haloge n gases or gases with entrai ned particles.

34Appendix A — Chemical and Petrochemical

• Lack of unde rstanding reg a rding tur n around tim es and m a intenan ce costs, which have beco m e increasingly m o re im portant cost el em ents. Lack of understanding regar d ing th e reduction of e n erg y consu m ption and air polluti on.

• Lack of unde rstanding reg a rding hi gh-t e m p erat ure and corrosive environm ents which lim it refractory life and increase maintenance costs in num e r ous che m ical and petroche mical reactors.

R&D Pathw ays

• Develop im proved refractories for m i nimizing m ech anical dam a g e to refractory

- li ned refining vessels through reduction of th e am ount of m e chanical stresses on the lini ng.

• Perform work to opt im ize the phy s ical properties of refractories (i. e ., thermal insulation, erosion resistance, corrosi on resistance, therma l shock resistance, strength, p o ros ity, and perm eability ) under known required ope rating cond iti ons for specific unit types. Develop realistic and reproducible product development and quality control t esting that can be used to relate st ep i mprovem e nts i n needed physical properties of the current refractory lining materi als in s e rvice.

• Develop im proved m e thods of anal y s is for hi g h -tem p e rature equipment through techniques for online refractory inspe c tion.

• Develop longer-life refract ories that are fi eld-repairable, less brittle, and m o re sh ockresistant.

• Acquire therm ophy sical, kinetic and mechanical data on refractories.

• Develop ceramic- m etal- m atrix com posi t es w ith i m proved stability and explore s u rface

m odification and/or coatin gs for use in corrosive environm ents.

• Develop materials to withstand hig h temper atures (1000–3 000°F) while retaining superior strength, duct ility , corrosion and wear resistan ce to resist dam a ge d u e to corrosion and hi gh tem p eratures present in the chem ical process industry

.

• Develop mate rials with enhanced resist a n ce to organi c acid environments and im proved materi als for chlorine-based processes, t o im prove plant operations and m a intena nce require m e nts and reduce costs.

• Develop refra ctories and refractory coatings for high-te m p erature fu rnaces to red u ce energy and m a intenance costs. Develop hi gh-te m p erat ure nonstick surfaces that do n o t degrade or beco m e volatile at high te m p eratures to help reduce needed m a intenance of chemical process equipm ent.



## A.4 Forest Products

Current Ind u stry Ope r ations and Refractory Use Although the pulp an d pap e r industr y is not a substa nt ial user of refractories, the forest product s industr y is th e third largest consum er of energy i n the United States, at approxim a tely 3. 3 q u ads per y ear. 8 To its credit, the industr y generates 63% of its own energy using rec y c l ed woody w aste products and other renewable sources for fuel (b ark, wood, and pulping li quor)

. Since 1972, th e industr y has reduced its use of fossil fuels and purcha sed energy by about 2% while increasing total production by nearl y 64%. In the f u ture, bl ack li quor and biomass gasification will lead to

35Appendix A — Forest Products

greater reduct i ons in purchased energy and coul d even change the pulp and paper industr y fr om a net energy importer to a net energy expor ter. Gasi fication h o lds the prom ise of generating 17 5 %

m o r e power than do current Tom linson furnaces, but the gasification technology currently in place requires y early refractory relines of the vessels. 9

Lim e recovery kilns are us ed in m o st forest pr oducts industries as an integral co m ponent of the Kraft pulping process, with lime recover y kilns op erating at a level of 7 m illion Btu/ton of lime recovered. Y e t, these kilns have the disadvantag es of cy clic production rates, poor product quality
, dust cy cles, rings, materi al buildups, and bloc kages. Most of these deficiencies c a n be related to premature brickwork failure and buil dups, with loss in productio n of up to 35 days per y ear being attributed to ri nging.

Barrier s It is estim ated that about 4 0 % of direct energyco nsu m ption by the forest produc ts industr y is in processe s aff ected by refractories. Bas e d on su bsequent analy ses of ty pical furnaces and unit processes, i mprovem e nt of refractory s y stems could lead to energy savings opportunities of up to 129 TBtu/ y ear. Specific barriers are shown below.

• Lack of unde rstanding regarding problems associat ed with sticking of reactants and products to the refractor y lini ngs of lime kilns, limiting their operating lives.

• Unavailability of m a teri als with corrosion r esistance t o the harsh, high-alkali bla c k sm elt environm ent (consisting of steam , sulfur, h y dr ogen, and CO) and abrasion/erosion resistance, spall resistan ce, and thermal co m p atibility with m e tall ic m a teri als u sed in the gasifiers.

• Unavailability of im proved m a t e rials fo r containm ent which do not react with the high-alkali at m o sphere p r esent in the gasifier. Such reacti ons res u lt in slabbing, which lim i t s the lining life.

• Lack of a database on the properties of the castable materi als use din this industry
, inform ation which is not provided b y th e refractory producers.

• Unavailability of im proved refractories for Tom linson recovery boilers to replace fireclay
, alu m ina brick, or sim ilar monolithic compositi ons use din the fl oor. Im proved refractories could decrease the am ount of furnace downti m e needed for repairs and woul d decrease energy usage due to shutdown and restar t cy cles.

• Lack of refra ctory s y stem s with sufficient al kali corrosion resistance for storage container linings used for hot pulping chem i cals.

R&D Pathw ays

• Develop im proved refractories for lim e kilns to reduc e downtim e d u e to ringi ng and buil dups, thus leading to increases in energy efficiency due to better ther m a l manage ment and increases in lim e kiln lining lifetim es.

• Develop advanced refractories to provide su itable mate rials for use in black liquor and biom a ss gasif i ers. Advance drefractories could lead to substantial im provements in energy efficiency for the forest pro ducts industr y, which curr ently requires y early refractor y relines of the vessels

.

• Develop mate rials with greater resi stanc e to the corrosion in m o lten salt environments, greater abrasi on/erosion re sistance, and greater sp all r esistanc e . In addition, develop alternate refractory sche m e s to provide refractory surface s whic h are m o re i mpervious to w ear and

36Appendix A — Forest Products

corrosive atta ck through coatings, che m i cal alter a tion of refractory surface s, physical alteration of refractory surfaces, et c.

• Develop refractory m a terial s which are more th erm a lly com p atible with metallic materi als used in gasifiers.



## A.5 Glass

Current Ind u stry Ope r ations and Refractory Use The glass industry produces a wide variety of pr oducts using differe nt process technologies. Perceived differences acro ss the seg ments of the glass industr y remain a barrier to broad-based industr y colla boration. T h ese differences have le d indi vidual segm e nts to select different m e lti ng technologies, prefer different refractories, and operate furnaces that differ in size and scale. Capital and operating costs for the indivi dua l segments reflect these product and process differences. F u rther, differences in glass types and industry segm e nts and the needs of large versus small furnaces li m it the ability to define co mmon interests. There are al so concerns with project defini tion and m a nagem e nt for cooperative e fforts: costs, timing, and shar ing of techni cal and financial risks and the i n tellectual property generated.

Melting of the batch is acc om plished us ing differe nt types and sizes of furnaces, with refining occurring in th e melting cham ber. Furnaces may be di scontinuous ( < 5 ton/day ) or continuous (large operations, esti m ated to last up to 10– 12 y ears today ) . Cont i nuous fur n aces may be directfired (units fi red with natura l gas and producing 20–150 ton/day ) , r ecuperative f u rnaces (directfired furnaces fitted with recuperators to recove r heat f r om exhaust gases), regen e rative furnaces [ t he m o st commonly used furnaces, wit h capac ities o f 100–1000 t on/day , and with the furnace heat collected in a regenerator that is used to preheat com bustion air as high as 12 60°C (230 0°F) and achieve higher energy efficiency ] or all-electric melters.

Co mm only
, a l um ina- zirco n ia-silica refr actories ar e used as sidew a lls, with zirconia content ranging from 33 to 41%. Chrom e

- c ontaining refractories are al so used in the fiber g lass industr y because of their additional corrosion and erosion resi stance, but their use is decreasing because of environm ental concerns about chrom e . Refractories containin g chr o me are not used in the flat, container, or pressed/blown glass industr ies becau se chrom e i m puri ties can disco lor the glass. Silica is co mm only used for the crown of the furn ace, or som e ti mes m u llite if oxy -fuel firing is

em ploy ed. D u e to chem i c al incom p atibilities, a lay e r of alum ina-zi rconia-silica i s often used as a buffer between the crown and sidewall. 1

Significant pr ogress has been made in reducing en ergy intensity i n areas of the glass industry over the last ten y ears. This increase in ef fi ciency has been acco m p li shed m o stly through i m proved process control sy stem s, the development and use of advanced refra ctory m a te rials, and technologies such as oxy -fuel firing and electric boost, which increase production capacity

. Advanced technology has reduced the fuel cons umed per ton of glass m e lt ed by 25% since the early 1980s, and energy use has declined in the fibergl ass sector by 30% since 1978. 10

Still, energy e fficiency depends on the si ze of the operation and the production rate. For exam p l e, a large (120 t on/day ) all-el ectric furnace uses elect ri ci ty at 66% ove rall efficiency , while a sm al l all-electri c furnace (4 ton/day ) has about 34% overall efficiency

. 11 Electric glas s- melting furnaces

are m o re ther mally efficient than oxy-fuel becau se th ere is les s ma ss ( m elt basin only ) and less surface ar ea f o r heat losses. Average oxy -f uel me lters consum e 3–5 MMBtu from fossil fuel per

37Appendix A — Glass

ton of glass melted. This is in com p ari s on with the a v erage electri c consum ptio n of all-electric direct resistan ce glass melt ers of about 2.7 MMBtu/ton.

Yet, m odern glass m e lting still requires a high-tem p er ature device that consum es a significant quantity of energy , with m e lting energy r e presenting about 15% of th e manufactu r ing costs. Although ther e are so me proven energy -r eduction technologies for melting that are not current ly being im plemented and so me con cepts which have been identified to further reduce energy

consum ption (i m p rove m e n t s in corrosion-resistant ref r actories, ins u lation, com bustion, process control), the e c onom ic incentive for adopting th ese proven technol ogies and developing th ese new concepts may not currently be sufficient to justify the cost and the effort. This m a y be because the i ndustr y views m i ni m i zing the energy cost per ton of glass produced as m o re im portant than reducing th e energy con t ent as m e asur e d in therm a l units and bec ause the value of the energy saved at the current cost of energy , w ith an assu m e d low rate of cost escal ation, is not sufficient to justify m a ny energ y -saving technologies. In particular, technologies th at require any significant capital investment are usually di scarded by the glass industry or looked upon unfavorably
, with many glass manufact urers expecti ng a one- to two-y ear pay b ack for capital invest m e nts. 12 Specific energy usage by sector is shown in Table A.2.

Table A.2. Es timated ener gy use in melting and refining Av. speci fic Ann u al Glass s ector energy use energy use (1 0 6 Btu/ton) (10 TBtu) Fl at 8. 6 42 .9 C ont ai ne r 5. 5 53 .1 Presse d/ bl ow n7. 3 18 .1 Fi ber 8. 4 25 .6 Source: DOE, Energy and Environmental Profile of the US Glass Industry, DOE/GO -102002-1590, Office of Indus trial Technologies, April 2002.

Oxy

- f u el firing is also still a viable technology and could im prove efficiency in th e glass industry

. The trend towards using oxy -fuel firing is st eadily increasing beca use an oxy -fuel furnace ca n produce the s a m e am ount of glass as wi th gas and/or air, but at a lower fuel input. 13 Additi ona lly, when regenerative furnaces are conve rted to oxy -fuel firing, the regenerator refractory str u cture is not needed, el im inating the exhaust volu m e by as m u ch as 75%

. 14 As of 199 8, o n l y 20% of the glass furnaces in the United States had been convert ed from air-fu el to oxy-fuel t echnology, with the greatest conversion rat e found i n the fibers sector. 15 To date, it is esti m ated that the num ber of conversions h as increased onl y t o aroun d 25% of the total industr y. 15 A breakdo wn of the nu m b er of conversions to oxy

- f u el t echnology com p l e te d by 1998 i n each sector of the gl ass industry i s shown in Tab l e A.3, along with estim ates of the num ber of conversions m a de to date. Therefore, there is still a great opport unity f o r further im provements in the energy efficiency of the glass industr y th rough further ut ilization of oxy -fuel fi red furnaces. Further im provements in refractory technolog y are needed to full y uti lize the benefits of ox y -fuel tech nolog y.
Boosting with oxygen firi ng will result in increased production but will also increase the melti ng cost per ton of glass. This trade-off is accep ted by the industr y because the additional capacity gained is at a m u ch lower c a pital cost than th at associa t ed with building new furna ces. Sa m p lin g of the industry indicates that to date, 125–15 0 of 500–550 total gla ss furnaces h a ve been

38Appendix A — Glass

Table A.3. Conversi o n of No rth American gl ass m e lter s to oxy-fuel fi ring as

o f

199 8 and a s of 2 004

Glass s ector N o . o f ox y-f u el conversions To ta l no

. of gl ass t a nk s % converted

C ont ai ne rs 23 21 0 10 Fibers 41 11 0 37 Tex tiles In su latio n (3 0) (1 1) (7 0) (4 0) (4 2) (2 7) Fl at 2 45 5 Speci al ty54 23 5 23 Al l sect ors 12 0 60 0 20

C ont ai ne rs 27 18 0 15 Fibers 46 10 0 46 Tex tiles In su latio n (3 5) (1 1) (6 2) (3 8) (5 6) (2 9) Fl at 3 45 7 Speci al ty60 22 5 27 Al l sect ors 13 6 55 0 25 As o f 19 98

As o f 20 04 (est im a t ed )

converted to oxy -fuel firing. This is onl y 25% of all th e furnaces i n the industr y , leaving a large

num ber of furnaces that co uld be converted to th e m o re efficient technology , leading to poll u ti on abate m ent and higher energy efficiency , if im proved alternate refr a c tories with s u fficient corrosion resistance and therm a l efficien cy cou l d be f ound . Of the various segments m a king up the glass industry , the fiber area has mad e the m o st use of oxy

- fuel firing, with nearly 50% of these furnaces having been converted; in second place is the special ty area, with over 25% of th e furnaces converted. Great o pportunities exist in the flat and containe r glass seg ments, which ha ve conversion rates on the ord e r of 5 to 15 %

.
Barrier s Refractories and insulatio n materials play ke y roles inmany of the unit o p eration s involved in the glass producti on; it is estimated that about 70% of th e direct energy consum ption is in processes affect ed by refractories. Ba sed on subsequent analy ses of ty pical furnaces and unit processes, i m prove m e nt of refractory sy stems for the glass industry could lead to energy sa vings opport unities of up t o 13.9 TBtu/ y ear. Specific barriers are shown below.

• Unavailability of durable and inexpensive m a te rials fo r use for refractories in constant contact with m o lten glass, co m bustion gases, and hot glass product s in glass furnaces which operate continuousl y at tem p eratures exceeding 1400°C in the molten bath and 1600°C in th e
co m bustion atm o sphere for operating liv es of 8–10 y e ars.

• Unavailability of parts and installation equipm ent to replace parts and m a teri als t h at fail during prod u c tion cam p aigns, without major furnace shut-downs and loss pro du c tion.

• Li m itations on energy efficiency and degradi ng glass quality
, particularly in oxy-fuel environm ents, due to l i m itations of refractory performance.

• Lack of know ledge that would im prove the pe rformance and quality of existing r e fractories and lead to increas ed production life and lower installa tion costs.

39Appendix A — Glass

• Lack of m odeling of corr osion m echanisms that would help determine solutions for reducing corrosion in r e fractories and for pr ovidi n g ad equate on-line sensors that would opti m i ze operation control, leading t o longer-life, co rrosion-resistant refractor ies, thereby reducing capital costs f o r glass m e lti ng and form i ng applications.

• Lack of know ledge in the f o rm of a materials property database, identification of new m e lting techniques and their associated refractor ies, a nd better methods for th e evaluation and repair of refractorie s in service.

R&D Pathw ays

• Develop integrated furnace m odels for the prediction of methods for im proving th er m a l efficiency , fo r developin g new glassmaking techn o lo gies, and for projecting per f ormance of alternate refr actory m a terial s.

• Develop refra ctories (partic ularly for fu rnace crowns) having sufficient strength and corrosion resistance at higher operating t e m p eratures when using o x y gen enrich ment.

• Develop m o n o lithic and/or coated refractories th at will be m o re resi stant to penetration of corrosive liquid and gaseous specie s

.



## A.6 Heat-Treating and Annealing

Current Ind u stry Ope r ations and Refractory Use Heat-treating is a $20 billi on industr y in the Un ited St ates and represents $75 bill ion or m o re in value-added manufacturing glo b all y

. 16 I t is also crosscutting, enabl i ng technol og y that affects

m o st of the in dustries foun d in the Unite d States, including alum in um , glass, iron and steel, and metal casting. The goal of th e Heat Treating In dustr y Vision 202 0 i s to reduce energy usage in the heat-treating industr y b y 8 0 % . To achieve this goa l, co operation is n eeded between all the related industrial gro ups, includ in g the heat treating co mm u n ity , m e tal producers, foun dr y and f o rgi ng groups, fabric ators, govern ment, and academ i a.

One of the most im portant resea rch needs for th is industry is the development of integrated process m ode ls. Heat tre a ting today is viewed as an experience-bas e d art. However, in the future it m u st functi on in a scienti fic, predictive envi ronm ent, where processes ar e truly understood and capable of being sim u lated

. For exam ple
, it has been de m onstrated t h at the solutionizing tim e for a cast alu m inum alloy could be reduced from 12 to 2 h with no los s of qualit y or properties. This magnitude of heat treat ment cy cle tim e r e duction coul d result in inc r eased productivity and/ or reduced energy consum ption of greater than 50%. Validated databases for m u lticom ponent alloy s and predictive m odels will enable co m p arable resu lts to be achieved for a wide range of allo ys and applications. 17

Barrier s Refractories and insulation materi als play ke y rol es in various furna ce sy ste m s us ed in the heattreating and annealing in du stries; approxim a tely90% of direct energ y consum ption is in processe s aff ected by refractories. Bas e d on su bsequent analy ses of ty pical furnaces and unit processe s, i mprovem e nt of refractory s y ste m s for the heat treat ment and annealing industries could lead to energy savings opport unitie s up to 45 TB tu/ y ear. Specific barriers are shown below.

40Appendix A — Heat Treating a nd An nealing

• Unavailability of hi gh-perf ormance refractories fo r the im provement of therm a l efficiency in furnace sy stems that would lead to reduced cy cle times, lower req u ired energy i nput, and lower process ing costs.

• Unavailability of gradient refractory s y st em s with lower thermal conductivity and hi ghte m p erature s t rength and c o rrosion/erosion resistance for reducing heat losses an d im proving chem ical co mpatibility

.

• Unavailability of refractory m a t e rials with longer lifetimes due to im proved corrosion resistance, extended tem p erature resist ance, and mechanical thermal stability , w h ile also possessing re duced costs.

R&D Pathw ays

• Develop im proved insulati on m a terials to achieve hig h er operating tem p eratures, reduce heat losses, and eliminate rehe ating while also reducing process ti me an d production costs.

• Develop higher-effici ency insulation m a terials to increase the ther mal effi cienc y of current processe s and si m u ltaneously lower heat-treat ment ti mes, leading to significant reduction of energy co nsu m ption levels. This could th en lead to th e developm en t and application of accel erated h eating technologies, which will re quire alternative insulation m a teri als with greater thermal shock resistance and high-tem perature stability

.



## A.7 Iron and Steel

Current Ind u stry Ope r ations and Refractory Use
In the steel industr y , com p etitive pressures such as worldwide over capacity , the high cost of energy , environm ental and safety regula tions, com p et ing m a teri als, customer de mand for high quality , and th e high cost o f capital have led to a need for sweeping changes across the industr y. Therefore, four critical areas for im provem e nt or targets of opport u nity were identified: (1) process ef ficiency thr o ugh im proved throughput
, quality , and energy efficiency, (2) increased recy cling, ( 3 ) new processes to avoid or reduce air and water pollut i on, and (4) product developm ent. 18

As part of the approach to address these areas, r e fract ories currently used throughout th e steel making process wer e analy zed. Oxide-based cer a m i c s of alum inu m , calciu m , zir c onium
, chrom i u m , magnesiu m , and carbon are primarily use din steel cont act in an effort to reduce contam ination and interaction with th e h i ghl y alkaline slags. Nonox ide ceram ics consisting of

co m b inations of silicon, tit anium
, tungsten, and alum inum are used for hot handli ng applications where ther ma l shock resistance, cre e p re sistance, w e a r resistanc e , a nd resistance to acidic spec ies is desired. These materi als may be in the brick or castable for m . In many areas of steel furnac es refractory life is extended by splashing slag agai nst the refractory walls. This slag solidifies on the wall, forming a protective lay e r. T h is process, though highl y s u ccessful, is very i n efficient therm a lly

.
Today , steelmaking from pig iro n commences in the transfer ladle ahead of the basic oxygen furnace (BOF ) and continues after the B O F to the ladle stations and on to the tundish, which distributes the steel into the continuous casting or stationar y m o lds. Refractories for all these unit processes are select ed on the basis of their longevi ty and the cleanliness of the steel that passes throug h them. The cost per pou nd of refr actories for all the various co m ponents, with few

41Appendix A — Iron an d S t eel

exceptions, has increa sed markedly with the awarene ss that adva nced refra ctories can meet t h e goals of greatly extended s e rvice and contribute to th e quality of th e steels.

In steel ladles , maintenance costs are high and h eat efficiency is poor. Currently
, high-alum ina and m a gne sia

- based cast able refractorie s are preferre d for ladle linings at and below the slag line due to the high process te mperatures, ero s ion fro m the stirred bath, and the high c o rrosiveness of the slag. Life is short for these refr actori es; they typically last for only 30 to 50 heats. Highertem p erature-capable oxide/ carbon m i xtures have b een evaluated for use to prov id e a balance between purity, therm a l sh ock resistance, and er osionresistance, along with othe r alternative refractorie s w ith longer life, lower cost, and safer disposal. Yet, no materi al of choice has been identified.

Monolithics (refractory concretes and gunning m i xes) co m p rise at least 60% of all refractories used in iron and steel m a king in the Unite d States today (over 70% in Japan), and there is a stro ng trend to incre ased use of precast ver s ions of m onolithi cs. Installatio n practice has undergone

so m e major a dvances whic h translate to m u ch m o re ra pid original construction, replace ment of working li nin g s, and repair. The adaptation of sh otcreteing methods from constru c tion concrete technolog y h as resulted in significant reductions in d o wntime and in som e cases longer service life as well. I n the ladle lining practice, it has b een possible to succ essively repair the original lining such th at co m p lete r e lining is no l onger necessary

.

Im proved materials for runners (used to flow th e m o lten steel fro m a BOF or an electric arc furnace to the refining ladl es) are needed. Th ese co mponents are generally constr ucted from fireclay brick, alum ina c ast able, or chromia ca stable. They experience corrosion, wear, and therm a l stresses that li m it their lives to one to two weeks. Sim ilar i m prove ments are needed for water- cooled pipes and stirrers enclosed in refr actory

. They also experience corr osion, wear, and ther m a l stre ss es that li m it their life and require weekl y repair.

Energy consum ption in the various unit processes fou nd in th e iron and steel industry has changed substantially due to advances in refractory practice, but it is difficult to identify the role of refractorie s in energy savings because many change s are being made in designs and

co m bustion practic es as we ll as in metall urgical and slag practices. Some unit processe s like blast furnaces and BOF m e lt ers are designed to leak ener gy to induce a steep ther m a l g r adient through the lining. In an extre m e e x a m ple of this pro cess desi gn concept, the walls and roofs of electric arc furnace s a r e water- cooled to cause the steepe s t possible therm a l gradient. Consequently , it i s in the other unit processes where refr act ory practice c ontributes to energy savings in several w a y s (e.g., m o re efficient insulation, extension of the tim e between maintenance shutdowns, reduction in the am ount of refractory scrap and reduction in m e t a l scrap through im proved cleanliness of the final steel products).

As mentioned, blast furnaces and BOF melter s are d esigned to leak energy , and even in the c ase of m o st ladles, insulation i s m i ni m i zed in the wa lls and bott o m s in an effort to induce a thermal gradient in the interest of reducing the r e fr actory wear. Ladle covers, on the other hand, are absolutely necess ary to conserve the te m p eratur e of the contained metals and are m a de fro m increasingly a dvanced materials. There ar e m a ny op portunities for direct ener gy savings in all of the unit pr ocesses and components in ir on and steel plants that are not designed t o incorporate steep thermal gradients. There are also opportun ities to extend refractory l i fe through th e use of lining th ickne ss m onitors and other sensors a nd instru ments which im prove the com bustion efficiency and reduce stack losses as well as releas e of undesirabl e products of the processing of the iron and s t eel.

42Appendix A — Iron an d S t eel

Significant i m provements are needed for m eeting operating challenges for m onolithic refractories. Monolithic linings possess many inhe rent problems. Ideally , steelmakers would like to have m onolithic linings for all of the ladles and even for the basic oxy g en furnace. The socalled basic li ning has recei ved considerable resear ch a ttention, but no reports of succes s in a BOF have been reported to date. Problems exist with the hy dratabi lity of the basic co m ponents of the products, which are based on MgO, ma gnesite, doloma (calcined dol om ite, CaCO 3 ·MgCO 3 ), and spinel. F u rther, m onolithics for BOF linings need to incor por ate substantial am ounts of carbon in the form of graphite, and resear ch is ongoi ng to resolve the problem that derives from the interference of the high volum es of graphite with the binder s y st em s of the monolithics.

Barrier s Refractories and insulation materi als play ke y roles in the sm elting, refining, and melting operations us ed in the iron and steel industries; it is est i m ated that 85% of the industries’ direct energy consum ption is in process es aff e c t ed by refractories. Based on subsequent analy ses of typical furnaces and unit processe s, i m pr ovement of refractory s y stems for the iron and steel industries could lead to ene r gy savings opportun ities up to 148. 5 TB tu/ y ear. Specific barriers are shown below.

• Lack of adequate corrosion resistance f o r refractorie s in contact with m o lten m e tal, which leads to unde sirable equipment lifetimes. This is especially im portant for refractories used in parts of furnaces, ladles, an d tundishes.

• Unavailability of im proved m a terials fo r runners (used to flow th e m o lten steel from a BOF or an electric arc furnace to the refining ladles), wate r- cooled pipes, and stirrers e n closed in refractory

.

• Lack of utilization of advanced m onolithics in ladles due to pr oble m s with their explosive tendencies an d lack of data on som e of the ke y inp u t properties and param e ters for m o st of the m onolithic products that m e et the requirement for steel ladle practice.

• Unavailability of im proved im pact pads at th e bottom of ladles, which experience high wear, ther m a l shoc k, and abrasion.

• Unavailability of thi n -walled alum ina refractory ladle shrouds that are used to reduce oxy g en pick-up during pouring with lifetimes of greater than ten heats in the extreme conditions of this application.

R&D Pathw ays

• Develop met hods for suppressing the hydration of m a gnesites.

• Develop refractory linin gs with im proved life and red u ced maintenance requirements, to reduce the y e arly or even m onthly m a i n tena nce shutdowns generally necessary to repair refractory proble m s . Reduc ing the freque ncy of or eliminating these shutdowns would provide significant cost reduction, not to mention associated energy savings.

• Develop advanced materi als (such as refr actories w ith in situ coatings or externally applied coatings) for resisting corrosion/erosiondamage.

• Develop new materials alo ng with im proved m a te rials databases for mem b ers of the industr y to adapt to new m a terials i n their operat i ons.

• Develop im pr oved refractories for use in various parts of furnaces, heat processi ng equipm ent, la dles, and tundishes.

43Appendix A — Iron an d S t eel

o Develop im provements in runners, water- cooled pipes and stirrers, which all experience co rrosion, wear, and therm a l i ssues that can lim it their lif e and require weekly repair.

o Develop im provements in materials and in stallation methods for ladle bottom s and im pact pads by using ceramic coatings or alternate localized mater i als.

o Develop long-lived, economically feasi ble, prefired refractory crucible linings for inductio n m e lting of stainle ss steel in air-melt operations.

o Develop im pr oved cera m ic /refractory materials for ne t shape steel c asting, eli m inating rolling m ill operations.



## A.8 Metal Casting

Current Ind u stry Ope r ations and Refractory Use Energ y consu m ption for th e m e tals casting in dustr y is on the order of 0.2 quads per y ear. 20 Thi s resulted in an estim ated energy cost f o r th e f oundries i ndustr y i n the United States of $1.2 billi on in 19 97 7 and $1.5 billion i n 1998, 20 or a bout 10% of th e total m a terial cost put in to pro duction and 4–5% of the value of t o tal shipm e nt. 21 Therefore, the industr y wishes to opti m ize melting, holding, and heat-treating furnaces to c onserve energy (i.e., to reduce energy us age by 20%) and mini m i ze pollutant em i ssio n s. Further, th e indus tr y w i shes to increase the life of refractories and other ceram i c com ponents that are exposed to m o lten metal s and/or furnace environm ents and develop in-line sensors that are stable in the m o lten metal environment. 10

The unit pr ocesses utilized in the m e tal casting indus tr y are lined with a wide range of refractory

co m positions (including silica, alu m ino-silicate, high alu m ina, zirc on, m a gnesia, spinel, chrome, and m a gnesia-carbon) and forms ( m onolithics, precastshapes, and bricks). Most metals castin g industr y m e lt ing and holdi ng furnaces are lined with ceramic refr actories which are selected t o mini m i ze r e a c tion with the specific meta l being processed. Major refractory line dunits include reverberatory furnaces, crucible (pot) fur n aces, channel induction furnaces, corel e ss induction furnaces, electric arc furnaces, and pouri ng ladles. These furnaces are lined with wide ranges of refractory co m positions, including silica, alu m ino-s ilicate, high alum ina, zir c on, magnesia, s p inel, chrome, and magnesia-carbon.

Substantial pr oblems do still exist with m o lten mate ri al containment and handli ng. For example, cupola linings for ferrous alloy m e lting usually requir e weekly repairs because of corrosion and mechanic al da m a ge. An alt e rnative to refractor y linings is “skull melting” (in tit anium melting, for exa m ple) where in a mechanis m si milar to th e slag splashing in the steel industry or the formation of a “frozen led g e” in the alu m inum i ndustry
, a protectiv e lay e r of m e tal is solidified on the containment vessel surface, cr eat ing a corro sion-resistant la y e r but lowering the ther mal efficiency of the sy stem

. Iron foundrie s are the major energy consumer fo r this sector, repres enting about 12% of the industr y , f o ll owed by steel foundries at about 10%. Within each process, approxim a t e ly 55% of the total energy cost is used for the m e lt ing of the m e t a l, with other processe s (core m a king, mold making, heat treat ment, and post-casting processes) accounting for th e other 45%. Although the total energ y cost (fuel + electricity ) accounts for o n l y about 1 0 % of the total m a terial cost, it can

44Appendix A – M e tal Casting

be as high as 20% or m o re for many f o u ndries depend ing o n efficiency an d the materials processed. Specific energy usage by the metal s castin g industry is given in Table A.4.

Ta b l e A

. 4

. P r o c e s s a n d e n er g y da ta f o r U. S

. me ta ls ca s t in g in du s t ry

Process Energy c o nsu m ption

Cupo la m e lt in g To tal: 8

. 6 × 10 6 B t u/ t on C oke: 5. 8 × 1 0 6 Electricity: 1

. 1 × 10 6 Natural Gas: 1

. 6 × 10 6 Oxy g en: 0. 1 × 1 0 6 C o re m a ki ng an d m o l dm a ki ng 7 –20 % en erg y , 1– 3 × 1 0 6 B t u/ t on

Electric m e ltin g Induction furnace: 4.3–7.6 × 10 6 B t u/ t on Electric arc furnace: 4.3–5.2 × 10 6 Btu /ton Electric-resistan ce heated re verbe r atory furnace: 5.2–7.9 × 10 6 Btu /ton Gas-fire d m e lting furnace Crucible: 1.8-6.8 × 10 6 Btu /ton R e ver b .: 2. 5- 5. 0 × 1 0 6 Btu /ton Ref i n i ng an d po ur ing p r o cesses Electricity: 0

. 4 × 10 6 Btu /ton Nat u ral gas: 0. 2 × 1 0 6 Btu /ton C l eani n g an d f i ni shi n g pr oces ses 1. 0 × 1 0 6 B t u/ t on In vest m e nt cast i ng Electricity: 3

. 0 × 10 6 Btu /ton Nat u ral gas: 4. 0 × 1 0 6 Btu /ton
Lost foam cast i ng 2. 5 × 1 0 6 B t u/ t on Die casting Electricity: 4

. 0 × 10 6 Btu /ton Nat u ral gas: 5. 0 × 1 0 6 Btu /ton Othe r casting proces ses Perm anent: 2.5 × 10 6 Btu /ton Sh ell m o ld : 2

. 5 × 10 6 Btu /ton Plaster m o ld : 3.0 × 10 6 Btu /ton
So urce : En ergy an d En v i ronmen tal Pr of ile o f th e U.S. Metal Castin g Indu stry.

Although the service life of refractory linings fo r all foundr y practices has been extended greatly in the last decade, m a ny of the problem s identifie d above still persist. For exam ple, m o st channel and coreless i nduction furnaces in iron and steel foundries use spinel-for m ing dry

- vibratable castable, a shift from the w e t ra mming practiced in the past. This extended the s e rvice ca mpai gn of the foundri es, but m e t a l penetration and chem ical corrosion by sl ag still persists. Also, there are few case studies that sh ow good refractory m a intenance m a nag e m e nt, new refractory developm ent, or proper selection methods resulti ng i n great energy savings and reduced melting cost. With the ever-increasi ng dem a nd for qualit y cast metal, alloy com position, and innovative melting technologies, refractories sections have been pushed to m o re challenging positions. Research program s in refractories scien ce and t echnolog y i n the U n ited States have never been as large and as com p rehensiv e as R&D program s for other industr y and technology sectors. Nonetheless, the metal cast ing industr y i s still one of th e largest industry sectors in the United States, and the refractories industr y is essential to it.

For steel casti ng, wear of refractories and reaction of the refractorie s with highly basic (c alciacontaining) sl ag can generate defect-forming in clusions. High-alumina refra ctories are gener a lly used throughout this area of the process, with a pplication of zirconia-based mate rials in areas of high wear and therm a l shock and m a gne sia-based mat e rials in area s of high slag corrosion.

45Appendix A – M e tal Casting

Carbon m a t e r i als cannot be used for this applica tion, as they react with oxi de-based refractories to form CO a nd with alum inum in steel t o form alu m i n a. Sim ilarly
, silica-bas e d refractories cannot be used because of contam ination issues.

There is a serious lack of data on the mechanical, thermal, and chemical propert ies of m onolithic refractories; and m u ch of the data that exists is lacking in detail or is obsolete. There is onl y o n e reference source for such key data as strength, m odulus of elasticity, therm a l conductivity, he at content, permeability , th ermal shock and creep be havior; and this s ource was first available 15 y ears ago. Hundreds of ne w and update d versions of m onolithics are on the m a rket today , but there is very l ittle design and other technical da ta available aside from the product data sheets, which do n o t list m u ch beyond bulk pro p erties and some ty pical values (not to b e used in design but only as guide for selec tion).

Barrier s Refractories are used throughout the vari ous un it proc esses found i n the m e t a l casting industr y ; approxim a tel y 90% of the direct energy consum ption is in processe s affect ed by refractorie s. Based on subsequent analysis of typical furn aces and unit processe s, i m prove m e nt of refractory sy stems for the metal casti ng industr y c ould l ead to energy savings opportunities up to 8.5 TBtu/y ear. Specific barriers are shown below.

• Lack of methods and m a terials to reduce or elim inate refractory failure due to ph y s ical erosion and c h e m ical corro sion by m o lten m e t a l and slags in nearly all stages of metal melting, refining, and pouring processes where refr act ories m a ke co ntact with m o lten metal.

• Lack of methods and m a terials to reduce or el im inate refractory failure related to fusion of refractories and chem ical corrosion b y MnO and FeO in steel foundries where the m o lten steel is generally tap p ed at high tem p erat ures [ up to 2 150°C (39 00° F)]
, and the common practice is to use low-cost silica, zircon, or alum ino-s ilicate ra mmi ng m i xes and plastics, especially in those foundrie s that appl y a c id melting practices in smaller furnaces.

• Lack of methods and m a terials to reduce or elim inate cloggin g or b u ild-up form ation in channels and throats is problem a tic for m o st m e tal casting operatio ns.

• Lack of methods and m a terials to reduce or el i m inate refractory wear in electric arc furnaces for the m e ltin g of steel, where reduced refractory wear and energy savings woul d be especially beneficial.

• Lack of methods and m a terials to reduce or el im inate wear and reaction of refractories with highly basic (calcia- containing) slags for steel ca sting.

• Lack of data on the m echanical, therm a l
, and chem i c al properties of m onolithic r e fractories, with m u ch of the data that exists lacking in detail or bei ng obsolete.

R&D Pathw ays

• Develop im proved refractories that will resist phy sical erosion and c h em ical corro sion by

m o lten metal and slags. Specifically , develop m a teri a l sy stem s for steel containment that are chem ically st able with the m o lten metal and th at provide mechanic a l integrity aga i nst wear and abrasion.

• Develop im proved refractories which are resist ant to corrosion by MnO and FeO to prevent fusion of refractories in ste e l casting.

46Appendix A – M e tal Casting

• Develop refractories which will resist the adhesi on of m o lten metal that results in clogging or build-u p form ation in chan nels and thro ats.

• Develop im pr oved refractories for use in electric ar c f u rnaces for the m e lting of steel that will resist wear an d prov ide energ y savings thoug h im proved insulatio n.

• Determine the m e chanical, therm a l, and chem ic al properties of m onolithic refractories used in the m e tal casting industr y.

• Develop nove l low-cost and hig h -perfor m ance m onolithics (in particular for iron , steel, and alu m inum fo undries), basic gunni ng m i xes, and Mg O-graphite castable for rapid repair of electric arc furnaces.

• Develop and m odel sl ag chem istry com p atible with refractory linings and m a xi mize the sl ag foam ing prop erties, along with efforts to reduce or elim inate repair and patching of electric arc furnaces due to refractory wear.

47Appendix A – Referenc es



## A.9 References for Appendix A

1. D. W. Freitag and D. W. Ri cherson, Opportunities for Advanced Ceramics to Meet the Needs of the Industries of t h e Future, DOE/ORO 2076, U.S. Departm e nt of Energ y , Office of Industrial Technologies, Decem b er 1998.
2. Alu m inum In dustr y Techn o log y Roadmap, The Aluminum Association, Februar y 20 03.
3. A. T. Tabera ux, “Recent Develop m ent in Re fractories for Alu m inum C e lls,” pp. 271–81 in Proceedings of the International Sympos ium: Advances in Refractories for the M

e tallurgical Industries II, ed. M. Rigau dand C. Allaire, Montreal, Quebec, August 4–9, 1996

. 4. D. Schubert, “Refractories for Prim ary Alu m inum Production
, ” pp . 74– 80 i n Proceedings of the Thirty-Seventh Symposium on Refractories, St. Louis, Missour i, March 23, 2001

. 5. J. Canon, “Alum i nu m Furnace Design: Reducti on of Metal into Metal Out Ti m e ,” pp. 237– 53 in 39th Sy mposium on Refractories, STL Section of the ACerS, April 9–10, 2003.
6. S. Quesnel, C. Allaire, and S. Afshar, “C orrosion of Refractories at the Belly band of Alu m inum Holding and M e lting Furnac es,” pp. 321

– 27 in Proceedings of the International Symposium: Advances in Refractories f o r the Metallurgical Industries II, ed. M. Rigaud and C. Allaire, Montreal, Quebec, August 4–9, 19 96

. 7. Econom ic Census 199 7
9. U.S. Enviro n m ental Protection Agenc y , Profile of the Pulp and Paper Industry, 2nd ed., EPA/310-R-9 5 -015, 2002. Available online at http ://w ww.epa.gov/com p liance/resources/ publications/assist ance/s e c t ors/notebooks/pulp.htm l

. 9. E. D. Larson, S. Conson ni, and R. E. Katofsk y , A Cos t -Benefit Assessment of Biomass Gasification Power Generation i n the P u lp and Paper Industry, Princeton University
, October 2003. Available online at http:/ /www.princet on.edu/~ener g y / publications/ pdf/20 03/BL GCC_FINAL_REPORT_8_OCT_2003

. pdf.
10. Glass: A Cle a r Vision for a Bright Future, U.S. Departm e nt of Energ y , Office of Industrial Technologies, 1996. Avail a ble online at http://www.eere.energy .gov/industr y/ glass/pdfs/glass_vision.pdf.
11. All-Electric v s . Oxyfuel Gl ass Melting, EPRI Technical Report TR-11278 8, El ectric Power Research Institute, April 1 999.
12. GMIC Advancing Glass M e lting Technologi es: A Technical and Econom ic Assessment.
13. Energy and E n vironmental Profile of the US Glass Industry, DOE/GO -10200 2-1 590, U.S. Department of Energ y , Off i ce of Industr ial Technolog ies, April 200 2.
14. M. J. Da m s el l, M. L. Joshi, J. R. Latter, and D. B. Wishnick, Glass Technology 37 , 1 14 (1996).
15. Personal correspondence with refr actor y and glass industr y representatives.
16. ASM Heat Tr eating Society, An R& D Plan for t h e Heat Treating C o mmunity , 20 01. Available online at http://w ww.asm-intl.org/ pdf/RD_Plan_Heat_treat_Co m m u n ity.pdf.
17. WPI Integrated Heat Tre a tment Model for Alum inu mCastings, available online at http://www.wpi.edu/Academics/R e s earc h /MPI/News/ twoawards.ht ml.

48Appendix A – Referenc es

18. Steel Technology Roadm a p, Am erican Iron and Steel I n stitute, Decem b er 2001. A v ailable online at http://www.st eel.org/m t/road m a p /roadm ap.htm

. 19. Metal Castin g Industr y Pr ofile, 2004. A v ailable online at http://www.eere. energy.gov/ industr y / m e talcasting/profile.htm l.
20. Metal Castin g: Annual Re port, 2000. Available online at http://www.eere. energy.gov/ industr y / m e talcasting/annualr eport.htm l (2004 report).

49Appendix B



## Appendix B: Rotary Kiln An alysi s Schema tic, Conditions, and Results

Fig. B.1. Longitudinal section of a typical rotary kiln. Reprinted f r om Modern Refractory Practice, 3rd ed., Harbison Walker Re fractories, Pittsburgh, 1950.

Assu mptions for alumina calcination, rotary kiln

Plant prod ucti on 500,00 0 tons Al 2 O 3 /year A ssu me t w o kiln s Output pe r kil n , no downtime 277,77 8 tons Al 2 O 3 /year With 90% upt ime 250,00 0 tons Al 2 O 3 /year Output pe r da y 685 ton s Al 2 O 3 /d Output pe r ho ur 29 tons Al 2 O 3 /h Kiln diameter 3.5 m (11 ft) Kiln length 80 m (26 2 ft) Kiln exterior surface 880 m 2 ( 9 46 8 ft 2 ) Rea c tion 2 Al(OH) 3 → Al 2 O 3 + 3 H 2 O Heat of rea c ti on at 77°F 634 Btu/lb Al 2 O 3 Assu me re act i on tempe r atu r e of 1100 °C 2012 °F
s a y 2000 °F Heatin g pro d u cts to 20 00° F Al 2 O 3 562 Btu/lb Al 2 O 3 3 H 2 O 532 Btu/lb Al 2 O 3 Total heat re quire ment 1728 Btu/lb Al 2 O 3 3,456,82 4 Btu/ton Al 2 O 3 Heat of rea c ti on 35.91 cal/mol Rea c tion 634 64,638 Btu/# m ol Heatin g 562 Al 2 O 3 634 Btu/lb Heatin g 532 H 2 O Total 1,728 Btu/lb Al 2 O 3

50Appendix B

Results of alum ina rotary kiln an alys is (Tem peratures in °F)

Pa ram e t e r B t u /t o n % Usag e F l am e T e m p e r at ur e 36 00 Ex haus t T e m p e r at ur e 20 00 Re ac t i o n Ener g y 3, 456 ,82 4 39. 84 % W a ll L o s s Ener gy 400 ,00 0 4. 61 % Ex haus t Ener gy 4, 821 ,03 0 55. 56 % T o t a l Ener gy 8, 677 ,85 3 100. 00 % P aram et er Bt u / t o n % Us ag e F lam e T e m per at ur e 3800 E x h aus t T e m per at ur e 2000 R ea c t ion En er gy 3

, 4 56, 824 42. 46% W all Lo s s Ener gy 4 00, 000 4. 91% E x h aus t Ener gy 4

, 2 85, 360 52. 63% T ot al Ener g y 8

, 1 42, 183 1 00. 00%

Pa ram e t e r B t u /t o n % Usag e F l am e T e m p e r at ur e 36 00 Ex haus t T e m p e r at ur e 20 00 Re ac t i o n Ener g y 3, 456 ,82 4 37. 87 % W a ll L o s s Ener gy 600 ,00 0 6. 57 % Ex haus t Ener gy 5, 071 ,03 0 55. 56 % T o t a l Ener gy 9, 127 ,85 3 100. 00 % P aram et er Bt u / t o n % Us ag e F lam e T e m per at ur e 3800 E x h aus t T e m per at ur e 2000 R ea c t ion En er gy 3

, 4 56, 824 40. 36% W all Lo s s Ener gy 6 00, 000 7. 01% E x h aus t Ener gy 4

, 5 07, 582 52. 63% T ot al Ener g y 8

, 5 64, 406 1 00. 00%

Pa ram e t e r B t u /t o n % Usag e F l am e T e m p e r at ur e 36 00 Ex haus t T e m p e r at ur e 18 00 Re ac t i o n Ener g y 3, 456 ,82 4 44. 81 % W a ll L o s s Ener gy 400 ,00 0 5. 19 % Ex haus t Ener gy 3, 856 ,82 4 50. 00 % T o t a l Ener gy 7, 713 ,64 7 100. 00 % P aram et er Bt u / t o n % Us ag e F lam e T e m per at ur e 3800 E x h aus t T e m per at ur e 1800 R ea c t ion En er gy 3

, 4 56, 824 47. 17% W all Lo s s Ener gy 4 00, 000 5. 46% E x h aus t Ener gy 3

, 4 71, 141 47. 37% T ot al Ener g y 7

, 3 27, 965 1 00. 00%

Pa ram e t e r B t u /t o n % Usag e F l am e T e m p e r at ur e 36 00 Ex haus t T e m p e r at ur e 18 00 Re ac t i o n Ener g y 3, 456 ,82 4 42. 61 % W a ll L o s s Ener gy 600 ,00 0 7. 39 % Ex haus t Ener gy 4, 056 ,82 4 50. 00 % T o t a l Ener gy 8, 113 ,64 7 100. 00 % P aram et er Bt u / t o n % Us ag e F lam e T e m per at ur e 3800 E x h aus t T e m per at ur e 1800 R ea c t ion En er gy 3

, 4 56, 824 44. 85% W all Lo s s Ener gy 6 00, 000 7. 78% E x h aus t Ener gy 3

, 6 51, 141 47. 37% T ot al Ener g y 7

, 7 07, 965 1 00. 00%

Savings for alumina

Btu/ ton N a tu r e of s avin g sav ed Effec t of 200 ° F increa se in flame temperature 472,62 1
Effec t of 200 ° F decrea s e in exhaust tem peratu r e 912,26 8 Effect of redu cing wall lo ss energy from 600,00 0 to 400,00 0 Btu/ton 413,05 6

51Appendix B

Assu mptions for lime calc ination, rotary kiln

Plant prod ucti on 730,00 0 tons CaO/yea r A ssu me t w o kiln s Output pe r kil n , no downtim e 405,55 6 tons CaO /yea r With 90% upt ime 365,00 0 tons CaO /yea r Output pe r da y 1,000 ton s CaO /d Output pe r ho ur 42 tons CaO /h Kiln diameter 5 m (16 ft) Kiln length 50 m (16 4 ft) Kiln exterior surface 785 m 2 (8,454 ft 2 ) Rea c tion Ca CO 3 → Ca O + CO 2 Heat of rea c ti on at 77°F 1364 Btu/lb CaO Assu me re act i on tempe r atu r e of 1000 °C 1832 °F
s a y 1800 °F Heatin g pro d u cts to 18 00° F CaO 371 Btu/lb Ca O CO 2 391 Total heat re quire ment 2126 Btu/lb CaO 4,252,25 9 Btu/ton CaO Heat of rea c ti on 57.29 cal/mol Rea c tion 1364 103,12 2 Btu/#mol Heatin g 417 CaO 1,839 Btu/lb Heatin g 415 CO 2 Total 2,196 Btu/lb CaO

52Appendix B

Results of li me rotary kiln analysis (neglecting dust loss) (Tem peratures in °F)

Param e t e r B t u / t o n % Us ag e Fla m e T e m p er atu r e 36 00 E x h a u s t T e m p e r ature 20 00 Rea c tio n En er gy 4

, 25 2, 25 9 4 0.6 2 % W a ll Lo s s En er gy 40 0,0 0 0 3 .8 2% Ex ha us t Ene r g y 5
, 81 5, 32 3 5 5.5 6 % T o tal Ene r gy 1 0 ,4 67 ,58 2 10 0.0 0 % P aram e t e r Bt u / t o n % U s a g e F la m e T e m p er atu r e 3 800 E xh au st T e m p e r ature 2 000 R ea c t io n En er gy 4,2 5 2

, 2 5 9 43. 30 % W a ll Lo s s En er gy 40 0, 00 0 4

. 0 7 % E x h a u s t Ene r g y 5,1 6 9

, 1 7 6 52. 63 % T o t al Ene r gy 9,8 2 1

, 4 3 5 1 00. 00 %

Param e t e r B t u / t o n % Us ag e Fla m e T e m p er atu r e 36 00 E x h a u s t T e m p e r ature 20 00 Rea c tio n En er gy 4

, 25 2, 25 9 3 8.9 5 % W a ll Lo s s En er gy 60 0,0 0 0 5 .5 0% Ex ha us t Ene r g y 6

, 06 5, 32 3 5 5.5 6 % T o tal Ene r gy 1 0 ,9 17 ,58 2 10 0.0 0 % P aram e t e r Bt u / t o n % U s a g e F la m e T e m p er atu r e 3 800 E xh au st T e m p e r ature 2 000 R ea c t io n En er gy 4,2 5 2

, 2 5 9 41. 51 % W a ll Lo s s En er gy 60 0, 00 0 5

. 8 6 % E x h a u s t Ene r g y 5,3 9 1

, 3 9 9 52. 63 % T o t al Ene r gy 10, 24 3,6 5 7 1 00. 00 %

Param e t e r B t u / t o n % Us ag e Fla m e T e m p er atu r e 36 00 E x h a u s t T e m p e r ature 18 00 Rea c tio n En er gy 4

, 25 2, 25 9 4 5.7 0 % W a ll Lo s s En er gy 40 0,0 0 0 4 .3 0% Ex ha us t Ene r g y 4

, 65 2, 25 9 5 0.0 0 % T o tal Ene r gy 9

, 30 4, 51 7 1 0 0 .0 0% P aram e t e r Bt u / t o n % U s a g e F la m e T e m p er atu r e 3 800 E xh au st T e m p e r ature 1 800 R ea c t io n En er gy 4,2 5 2

, 2 5 9 48. 11 % W a ll Lo s s En er gy 40 0, 00 0 4

. 5 3 % E x h a u s t Ene r g y 4,1 8 7

, 0 3 3 47. 37 % T o tal Ene r gy 8,8 3 9

, 2 9 1 1 00. 00 %

Param e t e r B t u / t o n % Us ag e Fla m e T e m p er atu r e 36 00 E x h a u s t T e m p e r ature 18 00 Rea c tio n En er gy 4

, 25 2, 25 9 4 3.8 2 % W a ll Lo s s En er gy 60 0,0 0 0 6 .1 8% Ex ha us t Ene r g y 4

, 85 2, 25 9 5 0.0 0 % T o tal Ene r gy 9

, 70 4, 51 7 1 0 0 .0 0% P aram e t e r Bt u / t o n % U s a g e F la m e T e m p er atu r e 3 800 E xh au st T e m p e r ature 1 800 R ea c t io n En er gy 4,2 5 2

, 2 5 9 46. 12 % W a ll Lo s s En er gy 60 0, 00 0 6

. 5 1 % E x h a u s t Ene r g y 4,3 6 7

, 0 3 3 47. 37 % T o tal Ene r gy 9,2 1 9

, 2 9 1 1 00. 00 %

Savings for lime, neglecti n g dust loss

Btu/ ton N a tu r e of s avin g sav ed Effec t of 200 ° F increa se in flame temperature 567,63 1
Effec t of 200 ° F decrea s e in exhaust tem peratu r e 1,095,66 0 Effect of redu cing wall lo ss energy from 600,00 0 to 400,00 0 Btu/ton 413,05 6

53Appendix B

Results of li me rotary kiln analysis (assuming 20% dust loss) (Tem peratures in °F)

P a ra meter Btu/ t on % Usa g e F l am e T e m p er atu r e 36 00 Ex h a u s t T e m p er at ur e 20 00 Re actio n Ene r gy 5
, 1 0 2

, 7 1 0 3 9

. 00% W a ll L o s s En e r gy 40 0, 00 0 3 .0 6 % Exha ust En ergy 7

, 5 8 1

, 7 6 7 5 7

. 94% T o tal Ene r g y 13,08 4,47 8 100 .00% P a r a m ete r B t u/ton % Usa g e F l a m e T e m p er a t u r e 38 00 E x h au s t T e m p er atu r e 2 0 0 0 Reactio n En ergy 5,1 02,7 1 0 4 3.30 % W a l l L o s s En er gy 40 0

, 00 0 3 .3 9% Exha ust E nerg y 6,2 83,0 1 2 5 3.31 % T o tal Ene r gy 1 1 ,78 5 ,72 2 10 0.00 %

P a ra meter Btu/ t on % Usa g e F l am e T e m p er atu r e 36 00 Ex h a u s t T e m p er at ur e 20 00 Re actio n Ene r gy 5
, 1 0 2

, 7 1 0 3 7

. 39% W a ll L o s s En e r gy 60 0, 00 0 4 .4 0 % Exha ust En ergy 7

, 9 4 4

, 2 6 7 5 8

. 21% T o tal Ene r g y 13,64 6,97 8 100 .00% P a r a m ete r B t u/ton % Usa g e F l a m e T e m p er a t u r e 3 8 0 0 E x h au s t T e m p er atu r e 2 0 0 0 Reactio n En ergy 5,1 02,7 1 0 4 1.51 % W a l l L o s s En er gy 60 0

, 00 0 4 .8 8% Exha ust E nerg y 6,5 89,6 7 8 5 3.61 % T o tal Ene r gy 1 2 ,29 2 ,38 9 10 0.00 %

P a ra meter Btu/ t on % Usa g e F l am e T e m p er atu r e 36 00 Ex h a u s t T e m p er at ur e 18 00 Re actio n Ene r gy 5
, 1 0 2

, 7 1 0 4 3

. 87% W a ll L o s s En e r gy 40 0, 00 0 3 .4 4 % Exha ust En ergy 6

, 1 2 7

, 9 3 6 5 2

. 69% T o tal Ene r g y 11,63 0,64 7 100 .00% P a r a m ete r B t u/ton % Usa g e F l a m e T e m p er a t u r e 3 8 0 0 E x h au s t T e m p er atu r e 1 8 0 0 Reactio n En ergy 5,1 02,7 1 0 4 8.11 % W a l l L o s s En er gy 40 0

, 00 0 3 .7 7% Exha ust E nerg y 5,1 04,4 3 9 4 8.12 % T o tal Ene r gy 1 0 ,60 7 ,15 0 10 0.00 %

P a ra meter Btu/ t on % Usa g e F l am e T e m p er atu r e 36 00 Ex h a u s t T e m p er at ur e 18 00 Re actio n Ene r gy 5
, 1 0 2

, 7 1 0 3 7

. 39% W a ll L o s s En e r gy 60 0, 00 0 4 .4 0 % Exha ust En ergy 7

, 9 4 4

, 2 6 7 5 8

. 21% T o tal Ene r g y 13,64 6,97 8 100 .00% P a r a m ete r B t u/ton % Usa g e F l a m e T e m p er a t u r e 3 8 0 0 E x h au s t T e m p er atu r e 1 8 0 0 Reactio n En ergy 5,1 02,7 1 0 4 6.12 % W a l l L o s s En er gy 60 0

, 00 0 5 .4 2% Exha ust E nerg y 5,3 60,4 3 9 4 8.45 % T o tal Ene r gy 1 1 ,06 3 ,15 0 10 0.00 %

Savings for lime, assu min g dust loss

Btu/ ton N a tu r e of s avin g sav ed Effec t of 200 ° F increa se in flame temperature 1,565,16 7
Effec t of 200 ° F decrea s e in exhaust tem peratu r e 965,41 0 Effect of redu cing wall lo ss energy from 600,00 0 to 400,00 0 Btu/ton 885,37 4

5455Appendix C



## Appendix C: Reverberatory Furnace Schematics

Fig. C.1. Reverberatory f u rnace sch e m atic.

56Appendix C

Fig. C.2. Typical reverbe r atory aluminum-melting furnace. Reprinted from Modern Refractory Practice, 3rd ed., Harbison Walker Refractories, Pittsburgh, 1950.

57Appendix D



## Appendix D: Reverb erat ory Furn ace Anal ysis Con d itions and Results

Results of aluminum re verb erator y furnace analysis

Temperature (oF) Wa ll/ro o f L o ss Case Flame Exhaust (Btu/h ) C a se 1 36 0 0 16 0 0 5, 00 0, 0 00 C a se 2 38 0 0 16 0 0 5, 00 0, 0 00 C a se 3 36 0 0 16 0 0 7, 50 0, 0 00 C a se 4 38 0 0 16 0 0 7, 50 0, 0 00 C a se 5 36 0 0 18 0 0 5, 00 0, 0 00 C a se 6 38 0 0 18 0 0 5, 00 0, 0 00 C a se 7 38 0 0 16 0 0 7, 50 0, 0 00 C a se 8 38 0 0 18 0 0 7, 50 0, 0 00

Results of aluminum r e verberatory f u rnace analysis (Tem peratures in °F) Cas e 1 Par a m e t e r Bt u / h % U sag e Fla m e T e m p e r atur e 3600 Ex h aus t T e m p e r atu r e 1600 Me lting Ener gy 10, 095, 271 37. 2% W a ll Los s En er gy 5, 000, 000 18. 4% Ex h aus t Ener g y 12, 076, 217 44. 4% T o t a l Ener g y 27, 171, 489 1 00. 0% Cas e 3 Par a m e t e r Bt u / h % U sag e Fla m e T e m p e r atur e 3600 Ex h aus t T e m p e r atu r e 1600 Me lting Ener g y 10, 095, 271 31. 9% W a ll Los s En er gy 7, 500, 000 23. 7% Ex h aus t Ener g y 14, 076, 217 44. 4% T o t a l Ener g y 31, 671, 489 1 00. 0% Cas e 5 Par a m e t e r Bt u / h % U sag e Fla m e T e m p e r atur e 3600 Ex h aus t T e m p e r atu r e 1800 Me lting Ener gy 10, 095, 271 33. 4% W a ll Los s En er gy 5, 000, 000 16. 6% Ex h aus t Ener g y 15, 095, 271 50. 0% T o t a l Ener g y 30, 190, 543 1 00. 0% Cas e 7 Par a m e t e r Bt u / h % U sag e Fla m e T e m p e r atur e 3600 Ex h aus t T e m p e r atu r e 1800 Me lting Ener gy 10, 095, 271 28. 7% W a ll Los s En er gy 7, 500, 000 21. 3% Ex h aus t Ener g y 17, 595, 271 50. 0% T o t a l Ener g y 35, 190, 543 1 00. 0% C as e 2 P ar a m et e r Btu/ h % Us a g e F lam e T e m per at ur e 380 0 E x hau s t T e m per at ur e 160 0 Melt ing Ener gy 1 0 ,0 95, 271 3 8

. 7 % W a ll Los s Ener g y 5,0 00, 000 1 9

. 2 % Ex hau s t Ener gy 1 0 ,9 78, 379 4 2

. 1 % T o ta l Ener gy 2 6 ,0 73, 651 1 0 0

. 0 % C as e 4 P ar a m et e r Btu/ h % Us a g e F lam e T e m per at ur e 380 0 E x hau s t T e m per at ur e 160 0 Melt ing Ener g y 1 0 ,0 95, 271 33 .2% W a ll Los s Ener g y 7,5 00, 000 2 4

. 7 % Ex hau s t Ener gy 1 2 ,7 96, 561 4 2

. 1 % T o ta l Ener gy 3 0 ,3 91, 833 1 0 0

. 0 % C as e 6 P ar a m et e r Btu/ h % Us a g e F lam e T e m per at ur e 380 0 E x hau s t T e m per at ur e 180 0 Melt ing Ener gy 1 0 ,0 95, 271 3 5

. 2 % W a ll Los s Ener g y 5,0 00, 000 1 7

. 4 % Ex hau s t Ener gy 1 3 ,5 85, 744 4 7

. 4 % T o ta l Ener gy 2 8 ,6 81, 016 1 0 0

. 0 % C as e 8 P ar a m et e r Btu/ h % Us a g e F lam e T e m per at ur e 380 0 E x hau s t T e m per at ur e 180 0 Melt ing Ener gy 1 0 ,0 95, 271 3 0

. 2 % W a ll Los s Ener g y 7,5 00, 000 2 2

. 4 % Ex hau s t Ener gy 1 5 ,8 35, 744 4 7

. 4 % T o ta l Ener gy 3 3 ,4 31, 016 1 0 0

. 0 %

58Appendix D

Savings for aluminum r e verberatory f u rnaces

Furnac e cha nge Btu/h
sav ed Btu/lb Al
sav ed Effec t of 200 ° F increa se in flame temperature 1,411,63 7 70.58

Effec t of 200 ° F decrea s e in exhaust tem peratu r e 3,486,04 6 174.30
Effect of redu cing wall lo ss energy from 7.5 to 5 million 4,642,04 5 232.10

Cas e 1 Par a m e t e r Bt u / h % U sag e Fla m e T e m p e r atur e 3600 Ex h aus t T e m p e r atu r e 2200 Me lting Ener gy 6, 272, 301 21. 6% W a ll Los s En er gy 5, 000, 000 17. 2% Ex h aus t Ener g y 17, 713, 616 61. 1% T o t a l Ener g y 28, 985, 917 1 00. 0% Cas e 3 Par a m e t e r Bt u / h % U sag e Fla m e T e m p e r atur e 3600 Ex h aus t T e m p e r atu r e 2200 Me lting Ener gy 6, 272, 301 17. 7% W a ll Los s En er gy 7, 500, 000 21. 2% Ex h aus t Ener g y 21, 642, 188 61. 1% T o t a l Ener g y 35, 414, 489 1 00. 0% Cas e 5 Par a m e t e r Bt u / h % U sag e Fla m e T e m p e r atur e 3600 Ex h aus t T e m p e r atu r e 2400 Me lting Ener gy 6, 272, 301 18. 5% W a ll Los s En er gy 5, 000, 000 14. 8% Ex h aus t Ener g y 22, 544, 602 66. 7% T o t a l Ener g y 33, 816, 904 1 00. 0% Cas e 7 Par a m e t e r Bt u / h % U sag e Fla m e T e m p e r atur e 3600 Ex h aus t T e m p e r atu r e 2400 Me lting Ener gy 10, 095, 271 24. 4% W a ll Los s En er gy 7, 500, 000 18. 2% Ex h aus t Ener g y 23, 721, 632 57. 4% T o t a l Ener g y 41, 316, 904 1 00. 0% Results of co pper reve r be ratory furnace analysis (Tem peratures in °F)

Savings for c o pper rev erb eratory furnaces C as e 2 P ar a m et e r Btu/ h % Us a g e F lam e T e m per at ur e 380 0 E x hau s t T e m per at ur e 220 0 Melt ing Ener gy 6,2 72, 301 2 3

. 4 % W a ll Los s Ener g y 5,0 00, 000 1 8

. 7 % Ex hau s t Ener gy 1 5 ,4 99, 414 5 7

. 9 % T o ta l Ener gy 2 6 ,7 71, 715 1 0 0

. 0 % C as e 4 P ar a m et e r Btu/ h % Us a g e F lam e T e m per at ur e 380 0 E x hau s t T e m per at ur e 220 0 Melt ing Ener gy 6,2 72, 301 1 9

. 2 % W a ll Los s Ener g y 7,5 00, 000 2 2

. 9 % Ex hau s t Ener gy 1 8 ,9 36, 914 5 7

. 9 % T o ta l Ener gy 3 2 ,7 09, 215 1 0 0

. 0 % C as e 6 P ar a m et e r Btu/ h % Us a g e F lam e T e m per at ur e 380 0 E x hau s t T e m per at ur e 240 0 Melt ing Ener gy 6,2 72, 301 2 0

. 5 % W a ll Los s Ener g y 5,0 00, 000 1 6

. 3 % Ex hau s t Ener gy 1 9 ,3 23, 945 6 3

. 2 % T o ta l Ener gy 3 0 ,5 96, 246 1 0 0

. 0 % C as e 8 P ar a m et e r Btu/ h % Us a g e F lam e T e m per at ur e 380 0 E x hau s t T e m per at ur e 240 0 Melt ing Ener gy 6,2 72, 301 1 6

. 8 % W a ll Los s Ener g y 7,5 00, 000 2 0

. 1 % Ex hau s t Ener gy 2 3 ,6 09, 659 6 3

. 2 % T o ta l Ener gy 3 7 ,3 81, 960 1 0 0

. 0 %

Furnac e cha nge Btu/h
sav ed Btu/lb Al
sav ed Effec t of 200 ° F increa se in flame temperature 3,018,769 150.94

Effec t of 200 ° F decrea s e in exhaust tem peratu r e 5,791,405 289.57
Effect of redu cing wall lo ss energy fr om 7.5 to 5 million 6,662,946 333.15

59Appendix D

Results of glass reverb er atory furnace analysis (Tem peratures in °F)

Cas e 1 Par a m e t e r Bt u / h % U sag e Fla m e T e m p e r atur e 3600 Ex h aus t T e m p e r atu r e 2800 Me lting Ener gy 13, 771, 643 16. 3% W a ll Los s En er gy 5, 000, 000 5. 9% Ex h aus t Ener g y 65, 700, 751 77. 8% T o t a l Ener g y 84, 472, 394 1 00. 0% Cas e 3 Par a m e t e r Bt u / h % U sag e Fla m e T e m p e r atur e 3600 Ex h aus t T e m p e r atu r e 2800 Me lting Ener gy 13, 771, 643 14. 4% W a ll Los s En er gy 7, 500, 000 7. 8% Ex h aus t Ener g y 74, 450, 751 77. 8% T o t a l Ener g y 95, 722, 394 1 00. 0% Cas e 5 Par a m e t e r Bt u / h % U sag e Fla m e T e m p e r atur e 3600 Ex h aus t T e m p e r atu r e 3000 Me lting Ener gy 13, 771, 643 12. 2% W a ll Los s En er gy 5, 000, 000 4. 4% Ex h aus t Ener g y 93, 858, 216 83. 3% T o t a l Ener g y 112, 629, 859 1 00. 0% Cas e 7 Par a m e t e r Bt u / h % U sag e Fla m e T e m p e r atur e 3600 Ex h aus t T e m p e r atu r e 3000 Me lting Ener gy 13, 771, 643 10. 8% W a ll Los s En er gy 7, 500, 000 5. 9% Ex h aus t Ener g y 106, 358, 216 83. 3% T o t a l Ener g y 127, 629, 859 1 00. 0% C as e 2 P ar a m et e r Btu/ h % Us a g e F lam e T e m per at ur e 380 0 E x hau s t T e m per at ur e 280 0 Melt ing Ener gy 1 3 ,7 71, 643 1 9

. 3 % W a ll Los s Ener g y 5,0 00, 000 7. 0 % Ex hau s t Ener gy 5 2 ,5 60, 601 7 3

. 7 % T o ta l Ener gy 7 1 ,3 32, 244 1 0 0

. 0 % C as e 4 P ar a m et e r Btu/ h % Us a g e F lam e T e m per at ur e 380 0 E x hau s t T e m per at ur e 280 0 Melt ing Ener gy 1 3 ,7 71, 643 1 7

. 0 % W a ll Los s Ener g y 7,5 00, 000 9. 3 % Ex hau s t Ener gy 5 9 ,5 60, 601 7 3

. 7 % T o ta l Ener gy 8 0 ,8 32, 244 1 0 0

. 0 % C as e 6 P ar a m et e r Btu/ h % Us a g e F lam e T e m per at ur e 380 0 E x hau s t T e m per at ur e 300 0 Melt ing Ener gy 1 3 ,7 71, 643 1 5

. 4 % W a ll Los s Ener g y 5,0 00, 000 5. 6 % Ex hau s t Ener gy 7 0 ,3 93, 662 7 8

. 9 % T o ta l Ener gy 8 9 ,1 65, 305 1 0 0

. 0 % C as e 8 P ar a m et e r Btu/ h % Us a g e F lam e T e m per at ur e 380 0 E x hau s t T e m per at ur e 300 0 Melt ing Ener gy 1 3 ,7 71, 643 1 3

. 6 % W a ll Los s Ener g y 7,5 00, 000 7. 4 % Ex hau s t Ener gy 7 9 ,7 68, 662 7 8

. 9 % T o ta l Ener gy 10 1,0 40, 305 100 .0%

Savings for glass reverb er atory furnaces

Furnac e cha nge Btu/h
sav ed Btu/lb glass
sav ed Effec t of 200 ° F increa se in flame temperature 19,521,1 02 976.06

Effec t of 200 ° F decrea s e in exhaust tem peratu r e 31,173,9 01 1,558.70
Effect of redu cing wall lo ss energy from 7.5 to 5 million 11,906,2 50 595.31

6061Appendix E



## Appendix E: Boiler Schematic

Fig. E.1. Boiler furnace s e ctions. Reprinted from Mo dern Refractory Practic e, 3rd ed., Harbison Walker Refractori es, Pittsburgh, 1950.

6263

# Copyrighted page(s) removed. Copyrighted material is not available in Regulations.gov since it may not be reproduced without consent of the copyright holder.
Removed pages can be viewed at the USEPA Docket Center, Public Reading Room.

Address: 1301 Constitution Ave, NW Room 3334 Washington, DC 20004
Telephone: 202-566-1744

Email: docket-customerservice@epa.govINDUSTRY CONVERSATION REGARDING THE SOURCE OF HIGH HEX CHROME EMISSIONS
Carlos E. Davis, Certainteed/St. Gobain 14 April 2011

This call was made because I was looking over the test report that BTEC did on KCK furnace...K2 furnace..at Kansas City. I was wondering if there was a problem with the testing, and if the test was done correctly. Mr. Davis confirmed that the test was done correctly ; that the math was check ed on the calculations . I led in that I was interested in w here all this chrome was coming from . By the testing, and the industry’s test agreement that the tested furnace was representative of the K1 furnace, I calculated over 900 pounds a year total chrome from the KCK plant . This was higher than Mr. Davis reme mbered, but confirmed that they had a lot of chrome. He was not aware that 92% of the chrome was hexavalent.

In a glass furnace, you feed the fine sands and by that I mean actual sand with other refined and purified raw materials in a mixture into the fur nace. It’s a continuous furnace. The furnace temperature is about 15600 C. At the surface of the glass, is the metal

- line glass contact.

Now the furnace itself extends above the surface of the glass..the metal line glass contact. We have constructed th e K2 furnace from what is called ‘High Chrome’ or sometimes also called ‘Jade Green’ refractories. They are just that color, a deep beautiful green color. They are that color because they are made of between 98

- 96% chrome. We construct our furnace using noncorrosive materials because you get a much longer life from your furnace

. In older designs, you have to rebuild a glass furnace at least every 7

- 10 years. You can add on to the outside of the furnace (meaning additional refractories) up to a point (2 layers), but after that, you have to shut it down and tear it out.

In the K2 furnace you have glass to a depth of a little more than a meter deep. Then to the top of the straight sides of the furnace, it’s about 2 meters, so there’s this additional strai ght wall up to the beginning of what we call the ‘crown’, this kind of domed curved top of the furnace. That’s the ‘furnace crown’. The surface of the glass is about 70 square meters (70m 2 ).

The molten glass is very corrosive. So there is high corrosivit y and errosivity. And as the molten glass moves through the furnace, it starts to eat away at the refractories, and it doesn’t really eat evenly, it eats little holes in the refractory wall inside the furnace. So these are like little caves, little holes . And so the surface area of the refractory wall is actually increasing with the life of the furnace. Because the molten glass continues to move through these caves or holes, it continues to erode even larger areas inside the refractory wall from the ins ide of the furnace reaching out. So when that outer wall gets hot, you just add some more refractory onto the outside. Otherwise you’d have a real bad situation, a breakthrough and you can’t have that. So your emissions of chromium are actually increasing , not decreasing over the life of the furnace due to this ever

- increasing surface area being exposed to the molten glass. So the degradation accelerates with the age of the furnace. We didn’t realize that this was almost all hexavalent chromium, we’ve only tested total chrome. That’s a big surprise.

K2 furnace at Certainteed in KCK has a p lanned shutdown date of 2013. This furnace is on it’s final end

run.Update 1 from Region 7:

Certainteed is planning to shift all products to the K2 line, but th a t li ne will only hold up for another
year.
Update 2 from Region 7:

We found some 2005 testing in the NEI. We don’t know the test method they used, and the test report is not in our files, but the results of that testing were 0.0166 TPY of total chrome, which is about 300 pounds a year, facility

- wide. We don’t know what fraction of that total chrome is hexavalent chrome;

w e don’t know which furnace was tested, or if one was tested as representative of the other. So there are a lot of unknowns with this test, but this shows that even in 2005, these high levels were being emitted.

## Notes on Differences in Collection Operations in the Mineral Wool Industry

23 June 2011 Steve Edris, Thermafiber

The VERTICAL COLLECTION design.

The collection chamber at Thermafiber is 10

- 15 feet long, about 6 feet wide.

At the end of the chamber is a vertical perforated belt moving belt, running at about 300 feet per minute (this is the fastest in the bonded lines)

The cupola produces at the same steady rate, pouring a thin stream of molten rock onto the spinners. Binder is sprayed onto the fibers through ports on the circumference edge of the spinners. Air flow comes from behind (and under cupola) to blow the fibers away from the spinners as they are formed.

A stronger air flow pulls negative on the screen, sucking the now cooled, binder sprayed fibers against the moving vertical screen, forming a mat that is about 1

- 1.5 inches. This screen moves much faster than any other in the industry because it is vertical. Otherwise, you’ d have the fiber mat slumping along the bottom curve.

This design makes a cleaner product that is low in ‘shot’. Shot is ok for some products, but can’t be present in horticultural applications (tomatoes need a uniform density product without ‘shot’, as do other vegetables). The CHOH is not trapped.

The HORIZONTAL COLLECTION design.

Everything is pretty much the same right up to the collection process. In the horizontal collection, the horizontal mat is much thicker. That belt moves at about 50 feet per minute, and CHOH is trapped in a thicker mat. The belt doesn’t have to move fast because you are not working against gravity as you are in the vertical design. However, there are some products you can’t make on a horizontal design. First, the shot remains in the bonded product. That’s okay for the products they make at that company, because that’s mostly insulation products where some amount of shot does not affect the final application. But you couldn’t sell to the horticultural markets with that product.

The DRUM COLLECTION design.

Again, it’s pretty much the same right up to the collection process. But then this is basically a totally different approach

. Instead of spinners and a moving belt, imagine a piece of equipment that looks like your wa shing machine, except turned. The molten rock is poured from the cupola into this big spinning drum, like the inside of your washer. And the little holes in the inside where the water empties out of the washing machine....that’s where the air flows out of the spinning drum carrying with it the threads of mineral wool. Unlike the other two designs, the air flow is already contained within the drum, and it can be directed as an air stream that lends itself well to controls. Out of the holes flow the forming fibers coming out as a loose long flow of fibers that is pulled from the spinning drum. The air stream from the collection process can then be directed to either the hottest part of the cupola stack or to the RTO on the curing oven. Either way, you achi eve really low emissions of the organics in the binder.

## Notes on the Origins and Cause of COS Emissions in Mineral Wool Industry

Chris Bullock, IIG 28 June 2011

IIG is not ‘afraid’ of adding pollution controls. They do NOT support NAIMA’s approach on the SBAR panel. They said the industry group will look stupid and ineffectual going forward with the proposed limits. They do not think industry should get a pass just because they claim to be small. I IG can meet the li mits EPA will be proposing.

They wouldn’t have to install a new RTO. They route their collection emissions to the hottest part of their cupola stack. This causes the formaldehyde, MeOH and phenol to incinerate in the stack before being emitted to the atmo sphere.

IIG has done research to show the source of sulfur is the SLAG....COKE is the source of CO. Coke is not so much a contributor to formation of COS and SO2. They purchase low

- sulfur slag locally so their costs are still low.

Chris Bullock, IIG 28 June 2011

We mine and melt our own rock so we have better control of our inputs. We can melt at higher temperatures. But we have a 50% cost increase to us on our raw materials.

Low sulfur slag is not an option (?)

Oxyge n injection will increase the COS because it burns hotter (?)

We don’t have a sulfur compounds being emitted from our raw materials, because we don’t put sulfur containing raw materials in to start with. In order to have a problem with SO2 or COS, you hav e to have sulfur in your raw materials. We know exactly what we are melting. All the other companies do too, or they ought to. Everybody keeps records of their raw material inputs because you have to do that to keep a consistent and reliable end product

. Where is the leveling of the playing field? We are good environmental stewards. Again, we don’t think industry should get a pass on regulation just because this industry is full of companies that say they are small.

## Notes on Differences in Collection Operations in the Mineral Wool Industry

23 June 2011 Steve Edris, Thermafiber

The VERTICAL COLLECTION design.

The collection chamber at Thermafiber is 10

- 15 feet long, about 6 feet wide.

At the end of the chamber is a vertical perforated belt moving belt, running at about 300 feet per minute (this is the fastest in the bonded lines)

The cupola produces at the same steady rate, pouring a thin stream of molten rock onto the spinners. Binder is sprayed onto the fibers through ports on the circumference edge of the spinners. Air flow comes from behind (and under cupola) to blow the fibers away from the spinners as they are formed.

A stronger air flow pulls negative on the screen, sucking the now cooled, binder sprayed fibers against the moving vertical screen, forming a mat that is about 1

- 1.5 inches. This screen moves much faster than any other in the industry because it is vertical. Otherwise, you’ d have the fiber mat slumping along the bottom curve.

This design makes a cleaner product that is low in ‘shot’. Shot is ok for some products, but can’t be present in horticultural applications (tomatoes need a uniform density product without ‘shot’, as do other vegetables). The CHOH is not trapped.

The HORIZONTAL COLLECTION design.

Everything is pretty much the same right up to the collection process. In the horizontal collection, the horizontal mat is much thicker. That belt moves at about 50 feet per minute, and CHOH is trapped in a thicker mat. The belt doesn’t have to move fast because you are not working against gravity as you are in the vertical design. However, there are some products you can’t make on a horizontal design. First, the shot remains in the bonded product. That’s okay for the products they make at that company, because that’s mostly insulation products where some amount of shot does not affect the final application. But you couldn’t sell to the horticultural markets with that product.

The DRUM COLLECTION design.

Again, it’s pretty much the same right up to the collection process. But then this is basically a totally different approach

. Instead of spinners and a moving belt, imagine a piece of equipment that looks like your wa shing machine, except turned. The molten rock is poured from the cupola into this big spinning drum, like the inside of your washer. And the little holes in the inside where the water empties out of the washing machine....that’s where the air flows out of the spinning drum carrying with it the threads of mineral wool. Unlike the other two designs, the air flow is already contained within the drum, and it can be directed as an air stream that lends itself well to controls. Out of the holes flow the forming fibers coming out as a loose long flow of fibers that is pulled from the spinning drum. The air stream from the collection process can then be directed to either the hottest part of the cupola stack or to the RTO on the curing oven. Either way, you achi eve really low emissions of the organics in the binder.

## Notes on the Origins and Cause of COS Emissions in Mineral Wool Industry

Chris Bullock, IIG 28 June 2011

IIG is not ‘afraid’ of adding pollution controls. They do NOT support NAIMA’s approach on the SBAR panel. They said the industry group will look stupid and ineffectual going forward with the proposed limits. They do not think industry should get a pass just because they claim to be small. I IG can meet the li mits EPA will be proposing.

They wouldn’t have to install a new RTO. They route their collection emissions to the hottest part of their cupola stack. This causes the formaldehyde, MeOH and phenol to incinerate in the stack before being emitted to the atmo sphere.

IIG has done research to show the source of sulfur is the SLAG....COKE is the source of CO. Coke is not so much a contributor to formation of COS and SO2. They purchase low

- sulfur slag locally so their costs are still low.

Chris Bullock, IIG 28 June 2011

We mine and melt our own rock so we have better control of our inputs. We can melt at higher temperatures. But we have a 50% cost increase to us on our raw materials.

Low sulfur slag is not an option (?)

Oxyge n injection will increase the COS because it burns hotter (?)

We don’t have a sulfur compounds being emitted from our raw materials, because we don’t put sulfur containing raw materials in to start with. In order to have a problem with SO2 or COS, you hav e to have sulfur in your raw materials. We know exactly what we are melting. All the other companies do too, or they ought to. Everybody keeps records of their raw material inputs because you have to do that to keep a consistent and reliable end product

. Where is the leveling of the playing field? We are good environmental stewards. Again, we don’t think industry should get a pass on regulation just because this industry is full of companies that say they are small.

# Chromium Emission Rate (lb/ton) by Furnace Type

1Oxy FuelOxy FuelOxy FuelAir GasAir GasAir GasElectric MeltElectric MeltElectric MeltElectric MeltElectric MeltElectric MeltElectric MeltElectric MeltElectric MeltESSESSESSESSESSESSESSESSESSOxy FuelOxy FuelOxy FuelOxy FuelOxy FuelOxy FuelOxy FuelElectric MeltElectric MeltElectric MeltElectric MeltElectric MeltElectric MeltElectric MeltESSESSESSESSESSESSESSESSESSESSESSESSESSESSESSESSESSESSCr Emission Rate (lb/ton) Major Sources Area Sources Furnaces out of graph range 0.00020

0.00015

0.00010

0.00006 0.00005

0



## Furnace Type

Notes:

- Proposed chromium emission limit is 0.00006 (6x10

- 5 

## ) lb/ton

- Some furnaces were tested in 2010 and 2012. For valid tests, both data points are displayed.

# Air Gas Furnace

2 

## Deliberative Document

– Do Not Cite or Quote

# Oxyfuel Furnace

3 

## Deliberative Document

– Do Not Cite or Quote

# Cold Top Electric Furnace

4 

## Deliberative Document

– Do Not Cite or Quote

# Steel Shell Furnace

5 

## Deliberative Document

– Do Not Cite or QuoteFurnace type Glass Contact -- Side Wall Glass Contact -- Floor Paving Breast Wall Crown Back Wall Portneck/ Stack Throat CrVI Emissions (lb/hr) Detection Limit Reported as lb/hr

Emissions? (Yes/No) CrVI Emissions (lb/year) Tot. Chrome Emissions

(lb/hr) Detection Limit Reported as lb/hr

Emissions? (Yes/No) Tot. Chrome Emissions (lb/year)

1 Oxy-fuel * 30-60% Chrome

- Chrome Chrome Chrome Chrome N/A N/A N/A N/A N/A N/A

2 Oxy-fuel 30-50% 50% 30% 30% 30-50% 50% 50% 0.00023 No 2.0148 0.00026 No 2.2776 KCK ct/SG 5 3 Oxy-fuel 30-50% 50% 30% 30% 30-50% 50% 50% 0.00015 No 1.3140 0.00027 No 2.3652

4 Oxy-fuel 50% Chrome

- - - - Chrome N/A N/A N/A N/A N/A N/A

5 Oxy-fuel 50% Chrome Chrome 50% 50% Chrome Chrome 0.047 No 411.7200 0.051 No 446.76 KCK ct/SG 2 6 Oxy-fuel 49.5% 49.5 - 53.7% 49.5% 49.5% 49.5% 49.5 - 92.0% 50 - 92% 0.00014 No 1.2264 0.00056 No 4.9056

7 Oxy-fuel 30-50% Chrome Chrome

- Chrome Chrome Chrome N/A N/A N/A N/A N/A N/A KCK ct/SG 1

8 Steel shell 30-60% 30% - - - - - 0.000011 Yes 0.0964 0.00011 No 0.9636

9 Steel shell 95% 30% - - - - 95% 0.0000066 No 0.0578 0.000023 No 0.2015

10 Steel shell 30-60% 30% - - - - - N/A N/A N/A N/A N/A N/A

11 Steel shell 95% 30% - - - - 95% 0.000012 No 0.1051 0.00003 Yes 0.2628

12 Steel shell 30-60% 30% - - - - - N/A N/A N/A N/A N/A N/A

13 Steel shell 30-60% 30% - - - - - N/A N/A N/A N/A N/A N/A

14 Steel shell 30-60% 30% - - - - - N/A N/A N/A N/A N/A N/A

15 Steel shell 30-60% 30% - - - - - N/A N/A N/A N/A N/A N/A

16 Steel shell 30-50% 30% - - - - - 0.0000021 Yes 0.0184 0.000045 No 0.3942

17 Steel shell 30-60% 30% - - - - - N/A N/A N/A N/A N/A N/A

18 Steel shell 30-60% 30% - - - - - 0.000012 Yes 0.1051 0.000027 No 0.2365

19 Steel shell 95% 30% - - - - 95% 0.0000056 Yes 0.0491 0.00009 No 0.7884

20 Steel shell 30-60% 30% - - - - - N/A N/A N/A N/A N/A N/A

21 Cold top electric 50% 30% - - - - 50-95% 0.000014 No 0.1226 0.000018 Yes 0.1577

22 Cold top electric 50-60% 50-60% - - 50-60% - 95% 0.00000078 Yes 0.0068 0.00000021 Yes 0.0018

23 Cold top electric 50% Chrome - - - - Chrome N/A N/A N/A N/A N/A N/A

24 Cold top electric 50-60% 50-60% #VALUE! - 50-60% - 95% N/A N/A N/A N/A N/A N/A

25 Cold top electric 50% 30% - - - - 50-95% 0.0000076 No 0.0666 0.000032 No 0.2803

26 Cold top electric 49.5% 49.5 - 53.7% - - - - 50-92 0.0000079 Yes 0.0692 0.000035 No 0.3066

27 Cold top electric 50% 30% - - - - 50-95% 0.000015 No 0.1314 0.000026 Yes 0.2278

28 Cold top electric 50-60% 50-60% - - - - 95% 0.0000022 Yes 0.0193 0.000073 No 0.6395

29 Cold top electric 50% 30% - - - - 50-95% 0.0000055 No 0.0482 0.000039 No 0.3416

30 Cold top electric 50-60% 50-60% - - 50-60% - 95% 0.0000052 No 0.0456 0.00004 Yes 0.3504

31 Air gas 30-50% 30% - - - - 50-95% 0.0000013 Yes 0.0114 0.0000021 Yes 0.0184

32 Air gas 30-50% 30% - - - - 50-95% 0.0000014 No 0.0123 0.000004 No 0.0350

33 Air gas 30-50% 30% - - - - 50-95% 0.0000033 No 0.0289 0.0000046 No 0.0403

34 Air gas 28-95% 28-60% - - 28-95% 95% 75% N/A N/A N/A N/A N/A N/A

35 Air gas 28-95% 28-60% - - 28-95% 95% 75% N/A N/A N/A N/A N/A N/A

36 Air gas 30-50% 30% - - - - 50-95% 0.0000026 No 0.0228 0.0000037 No 0.0324

37 Specialty - - - - - - - 0.00017 No 1.4892 0.000064 Yes 0.5606

38 Specialty 30.0% 30.0% - - 30.0% - - 0.0002 No 1.7520 0.00045 No 3.9420

* BTEC Emisssions Test Data

All oxy

- fuel furnaces use a dry electrostatic precipitator as a control device.Industrial Materials for the Future

Managed by UT-Battelle, LLC 

## Final Technical Report



## Compressive Creep and Thermophysical Performance of Refractory Materials

June 2006



## Principal Investigators:

Dr. M. K. Ferber Dr. A. A. Weresczak Dr. J. G. Hemrick Oak Ridge National Laboratory

ORNL/TM-2005/134DOCUMENT AVAILABILITY
Reports produced after January 1, 1996, ar e generally available free via the U.S. Department of Energy (DOE) Information Bridge.

Web site http://www.osti.gov/bridge
Reports produced before January 1, 1996, may be purchased by members of the public from the following source.

National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone 703-605-6000 (1-800-553-6847) TDD 703-487-4639 Fax 703-605-6900 E-mail info@ntis.fedworld.gov Web site http://www.ntis.gov/support/ordernowabout.htm
Reports are available to DOE employees, DOE contractors, Energy Technology Data Exchange (ETDE) representatives, and International Nuclear Information System (INIS) representatives from the following source.

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Project Title: Compressive Creep and Thermophysical Performance of Refractory Materials

Contract No.: DE-AC05-00OR22725

Project Period: April 1997–June 2000

PI(s): Dr. M. K. Ferber (865) 576-0818 ferbermk@ornl.gov

Dr. A. A. Wereszczak (865) 576-1169 wereszczakaa@ornl.gov

Dr. J. G. Hemrick (865) 574-7601 hemrickjg@ornl.gov

Recipient: Oak Ridge National Laboratory (ORNL) Bethel Valley Road P. O. Box 2008 Oak Ridge, TN 37831

Subcontractor University of Missouri–Rolla Department of Materials Science Engineering 222 McNutt Circle 1870 Miner Circle Rolla, MO 65409ORNL/TM-2005/134



## Compressive Creep and Thermophysical Performance of Refractory Materials

Dr. M. K. Ferber, Dr. A. A. Wereszczak, Dr. J. G. Hemrick Oak Ridge National Laboratory

June 2006

Prepared by OAK RIDGE NATIONAL LABORATORY P.O. Box 2008 Oak Ridge, Tennessee 37831-6283 managed by UT-Battelle, LLC for the U.S. DEPARTMENT OF ENERGY under contract DE-AC05-00OR22725ii 

## Acknowledgments, Disclaimer, and Proprietary Data Notice

Acknowledgments This report is based upon work supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Industrial Technologies Program, Industrial Materials for the Future, under Contract No. DE-AC05-00OR22725. The authors are also indebted to the following individuals for supplying the mullite refractories: Paul Hutchinson (DSF Refractories & Minerals), Michael Nelson (Corhart Refractories), Larry Stove r (Minteq International), D. J. Thomas, (VGTDYKO Industrial Ceramics), Jim Houp (National Refractories & Minerals), and Don McIntyre (NARCO); the guidance provided by the Glass Industry Advisory Committee, which comprises the following individuals: Larry Kotacska (Corning), Al Poolos (Owens-Brockway), Randy Sturtz (Owens-Corning), Warren Curtis (PPG), Jim She ll (Techneglas), Mike Nelson (Corhart), Steve Winder (UKSS/Monofrax), John Tracey/Dilip (Patel VRD-Americas), and Bob Moore (University of Missouri-Rolla); ORNL/HTML machinists L. O’Rour ke, T. Jenkins, and R. Parten for the specimen preparation; and Peter Angelini, ORNL, for project guidance and review.

Oak Ridge National Laboratory is operated by UT-Ba ttelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725.



### Disclaimer This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of an y information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency ther eof. The views and opinions of authors expressed herein do not necessarily state or reflect those of th e United States Government or any agency thereof.



### Proprietary Data Notice If there is any patentable material or protected data inthe report, the recipient, consistent with the data protection provisions of the award, must mark the appropriate block in Section K of the DOE F 241.3, clearly specify it here, and identif y them on appropriate pages of th e report. Other than patentable material or protected data, reports must not c ontain any proprietary data (limited rights data), classified information, information subject to expor t control classification, or other information not subject to release. Protected data are specific tec hnical data, first produced in the performance of the award, which is protected from public release for a period of time by the terms of the award agreement. Reports delivered without such notice may be deemed to have been furnished with unlimited rights, and the Government assumes no liab ility for the disclosure, reproduction, or use of such reports.

## Contents

List of Figures ................................................................................................................ .................... v List of Tables................................................................................................................. ..................... vii Abbreviations and Acronyms..................................................................................................... ........ ix 1. Executive Summary........................................................................................................... .......... 1 1.1 Research and Development................................................................................................ 1 1.2 Technology Transfer .......................................................................................................... 4 1.3 Commerciali zation ............................................................................................................. 4 1.4 Recommendations.............................................................................................................. 4 2. Introduction................................................................................................................ .................. 7 3. Background.................................................................................................................. ................ 9 4. Materials and Experimental Procedures ...................................................................................... 11 4.1 Materials...................................................................................................................... ....... 11 4.2 Creep Testing .................................................................................................................. ... 11 4.3 Specimen Preparation......................................................................................................... 1 4 4.4 Creep Testing and Data Interpretation ............................................................................... 16 4.5 Microstructural Characterization ....................................................................................... 18 4.6 Supplemental Analysis....................................................................................................... 19 5. Results and Discussion ...................................................................................................... .......... 23 5.1 Silica Refractories ............................................................................................................ .. 23 5.2 Mullite Refractories ........................................................................................................... 28 5.3 Fusion-Cast Alumina Refractories..................................................................................... 34 5.4 Fusion-Cast Spinel Refractories......................................................................................... 47 6. Accomplishments............................................................................................................. ............ 53 6.1 Research-Based Accomplishments .................................................................................... 53 6.2 Technology Transfer .......................................................................................................... 5 3 6.3 Publications and Patents..................................................................................................... 5 3 6.4 Commerciali zation ............................................................................................................. 54 7. Summary and Conclusions ..................................................................................................... ..... 55 7.1 Silica......................................................................................................................... .......... 55 7.2 Mullite........................................................................................................................ ........ 56 7.3 Fusion-Cast Alumina ......................................................................................................... 58 7.4 Fused Spinel................................................................................................................... .... 61 8. Recommendations............................................................................................................. ........... 63 9. References.................................................................................................................. .................. 65

Appendix: Publications........................................................................................................ ........ 67

iii

## List of Figures

1 Superstructure refractorie s in glass production furnaces....................................................... 7 3 Primary components of creep frame...................................................................................... 12 2 Schematic of creep frame and supporting instruments.......................................................... 12 4 Schematic of creep frame extensometer................................................................................ 13 5 Dimensions of core-d rilled test specimens............................................................................ 14 6 Schematic of how specimens were core-drilled from as-received bricks.............................. 14 7 Refractory block core-drill locations for physical and chemical analysis............................. 15 8 Schematic representation of the sectioning plan used to fabricate creep specimens from the bulk region of the refractory blocks........................................................................ 16 9 Creep specimen assembly H-shell arrangem ent required for the creep testing of the fusion-cast alumina............................................................................................................ .... 16 10 Example of temperature and stress history used in the creep testing .................................... 18 11 Schematic describing how disk sections we re machined from core-drilled specimens for (a) as-received and (b) post- test RL and CL imaging...................................................... 18 12 Schematic of transient plane source dire ct thermal conductivity method experimental set-up and picture of Kapton sensor ...................................................................................... 19 13 Schematic of dual-rod LVDT system us ed to measure thermal expansion........................... 20 14 Creep behavior of Vega as a function of temperature........................................................... 25 15 Change in volume of “aged” specimens as a function of time and temperature ................... 26 16 Schematic of the change in microstructure from the as-received material state to that after creep or high-temp erature exposure.............................................................................. 27 17 Vega’s microstructural changes as a function of temperature as revealed by reflected-light microscopy..................................................................................................... 28 18 Vega’s microstructural changes as a function of temperature as revealed by cathodoluminescence imaging .............................................................................................. 29 19 Amount of refractory recession when exposed to sodium carbonate at 1400°C for 24 h ..... 30 20 Amount of recession as a function of temperature and sodium carbonate addition for Gen-Sil silica ............................................................................................................. ...... 31 21 Thermal conductivity of mullite refractories as measured by the “hot-disk” method........... 33 22 Creep rate measured at 0.6 MPa as a function of reciprocal temperature ............................. 33 23 Refractory recession when exposed to sodium carbonate at 1400 o C for 24 h (according to ASTM C98)..................................................................................................... 35 24 x 3-, x 7-, and y -core density profiles for the (a) Corhart refractory and (b) Monofrax refractory ..................................................................................................................... .......... 36 25 Optical microscopy of characteristic grain structures for (a) bulk structure, and (b) columnar structure ......................................................................................................... .. 37 26 Optical microscopy of columnar region (micron bar = 200 μm) .......................................... 39 27 Optical microscopy of neph elitic grain boundary phases...................................................... 39 28 Static Young’s modulus values for fu sion-cast alumina sample types ................................. 40 29 Specimen elongation as a function of time for (a) the bulk Corhart and (b) the bulk Monofrax refractories.......................................................................................................... .. 42 30 Monofrax thermal conductivity block section denoting test surfaces ................................... 43 31 Average laser flash thermal conductivity fo r as-cast bulk refractories: (a) Corhart and (b) Monofrax ................................................................................................................... ...... 44 32 Combined plots of expansion and creep effects in Corhart bulk samples............................. 45 33 Combined plots of expansion and creep effects in Monofrax bulk samples ......................... 46 34 Fused spinel accumula ted strain curves ................................................................................ 48

v35 Bonded spinel accumulated strain curve at 1650°C.............................................................. 48 36 Bonded spinel accumulated strain curve at 1550°C.............................................................. 49 37 Bonded spinel accumulated strain curve at 1550°C.............................................................. 49 38 Thermal diffusivity of fused and bonded spinel ................................................................... 50 39 RL (left) and CL (right) images of fused spinel.................................................................... 51

vi

## List of Tables

1 Project and survey participants............................................................................................ .. 10 2 Ranking of refractory categories whose creep data are desired ............................................ 10 3 Silica refractories tested in the present study and their manufacturers ................................. 11 4 Mullite refractories tested in the present study and their manufacturers............................... 11 5 Creep test matrix for the si lica refractories (stress, MPa) ..................................................... 17 6 Creep test matrix for the mu llite refractories (stress, MPa) .................................................. 17 7 Creep-test matrix for the fusion-cast alumina refractories (stress, MPa) .............................. 17 8 Dimensional changes of crept specimens.............................................................................. 23 9 Density changes of crept specimens...................................................................................... 24 10 Summary of microstructural observati on for the mullite refractories before and after creep testing........................................................................................................ .... 31 11 Fusion-cast alumina nanoindentation results......................................................................... 40 12 Calculated strain rates ..................................................................................................... ...... 48

vii

## Abbreviations and Acronyms

AIM Advanced Industrial Materials ASTM American Society for Testing and Materials AZS aluminum-zirconium silicate CL cathodoluminescent imaging DOE U.S. Department of Energy EDS energy-dispersive X-ray spectroscopy LVDT linear variable differential transducer ITP Industrial Technology Program NBA Norton-Bailey Arrhenius OIT Office of Industrial Technologies ORNL Oak Ridge National Laboratory RL reflected light microscopy SEM scanning electron microscopy TPS transient plane source XRD X-ray diffraction XRF X-ray fluorescence

ix

## 1. Executive Summary

1.1 Research and Development Over the last 10 years, the U.S. Department of Energy Office of Industrial Technology, through the Industrial Materials for the Future activity, has f unded a number of projects at industry, university, and national laboratory sites to increase the energy efficiency of energy-consuming industries, including glass, steel, pulp and paper, and chemic al. In the case of the gl ass industry, using valid engineering creep data to optimize furnace superstr ucture design is a means to achieve these goals. The objective of the ORNL project described in th is report was to facilitate that endeavor by conducting creep testing and analysis on refractories of interest to glass manufacturers at representative service temperatures, enabling the av ailability of new and improved refractories by suppliers, and generating creep da ta on “equivalent” refractories that furnace designers can use for optimizing the design of their superstructures or fo r predicting their long-term structural integrity. The choice of refractories evaluated in the project was based on the advice of technical experts from the glass manufacturing industry, refractory suppliers , and academia. Although the results cited in this report are specific to refractories for glass applica tions, the techniques developed in this project are applicable to refractories used in all industrial applications.

The creep and corrosion behaviors of several refractor ies, including six types of conventional silica, ten types of mullite, two types of fusion-cast alum ina, and fused spinel were measured. The data generated for the silica refractories served as a baseline. The mullite refractories were examined because they are used in boros ilicate glass furnace crowns and superstructures and in sidewall applications. Additionally, despite their high cost ( ≈ $500/ft 3 ) they are cheaper than other refractories such as chrome alumina ( ≈ $3000/ft 3 ) or fusion-cast alumina ( ≈ $900/ft 3 ), which are used as replacements for traditional silica refractories in harsh oxy-fuel environments. Fusion-cast alumina refractories, which are a popular choice for crowns and sidewalls in oxy-fueled glass furnaces, were selected for this study because of their homogeneity , low porosity, high refractoriness, low levels of glassy phase, and good spall resistance. Although more expensive, the fused spinel offers improved creep and corrosion resistances.

Compressive creep testing was performed at 1300 to 1650 o C and at static stresses between 0.2 and 0.6 MPa on a pneumatically controlled compressive cr eep frame in an electrica lly heated furnace. The phase content, microstructure, and secondary phase composition of the refractories were characterized before and after their creep testing in an attemp t to correlate the creep responses with any observed changes. Corrosion resistance of each of the refractories was also examined. Lastly, the effect of temperature and time (in the absence of stress) on the dimensional stability of the materials was examined.

In the case of the silica refractories, the compressive creep rates of all six brands could not be represented as a function of temperature and comp ressive stress by using the conventionally used Norton-Bailey Arrhenius (NBA) creep equation. Conc urrently active mechanis ms other than creep resulted in larger or oppositely anticipated dimens ional changes than those produced by creep; this effect limited the ability to identify or interpret th e less-active creep mechan ism in them. The change in dimensions of the compressively crept specimens indicated that their size (both diameter and length) increased (by 0.35 to 1.0%) as a consequen ce of the creep test conditions. The cause of the volume expansion was not identified; however, beca use of the absence of quartz, it can be concluded that the expansion was not due to quartz (a relativ ely high-density phase) conve rting to tridymite or cristobalite (lower-density phases). The secondary phase constituents remained c onstant in all brands

1when they were tested at 1550°C. A fraction of these phases visibly evolved in the specimens at 1600°C. This phenomenon was quite severe at 1650°C. The density changes in the crept specimens (a net effect of the volume expansion and loss in secondary phase mass) ranged from a decrease of 1.6 to 3.9% with a subtle trend of greater density decreases at higher test temperatures. The density decreases among the six brands were statistically e quivalent within the data scatter. The corrosion resistances of the six silicas were statistically equivalent when they were exposed to sodium carbonate at 1400°C (2550°F) for 24 h. The amount of recession increased linearly with temperature between 1250 and 1450°C for the Gen-Sil silica.

Creep rates for three brands of the mullite refractories were on the order of 10 ! 11 s ! 1 at the lower test temperature and 10 ! 10 s ! 1 at the higher test temperature. Creep rates for four of the brands ranged from 10 ! 10 s ! 1 at the lower test temperature and to 10 ! 9 s ! 1 at the higher test temperature. The remaining three brands exhibited creep rates ranging from 10 ! 9 s ! 1 to 10 ! 8 s ! 1 and exhibited low stress exponents (< 0.5) and changes in chemistry or in microstructure due to the creep-testing conditions. Several of the mullite refractories exhibited a cr eep stress exponent approximately equal to unity, suggesting that creep was controlled by diffusion. On e of mullite refractories had a stress exponent of 2.4, indicating that the rate-controlling mech anism may be grain boundary creep. The creep mechanism for the remaining mullite materials, wh ich had stress exponents much less that unity, was attributed to a non-steady-state condition existing duri ng the entire extent of testing. This condition is a consequence of contraction or time-hardening effects occurring during testing and of the samples never reaching a state of equilibrium. Those bra nds possessing high levels of matrix porosity all showed compaction of the microstructure during creep testing, which was ultimately responsible for their poorer creep resistance. One of the mullite refractories was found to be composed of andalusite grains containing free quartz, which was converted to cristobalite during firing. Further, the andalusite grains were fully converted to mullite during creep testing, and the amount of glassy phase increased. These events in combination may lead to the brand’s poor creep resistance.

Activation energies for the various mullite re fractory brands ranged from 50 to 223 kcal/mol. Although no direct correlation between the magnitude of the activation energy and the amount of creep exhibited by a particular brand could be drawn from the data, it is known that materials possessing a high activation energy will have greater sensitivity to temperature than those possessing a lower activation energy. Also, the values for ma ny of the calculated activation energies correspond to the activation energy of vitreous silica. This finding indicates that the glassy phases in these brands affect the overall creep behavior of the material.

The distinction of a brand being fused-grained or non-fused-grained mullite did not appear to have a bearing on the creep resistance of the individual brands.

Eight of the ten mullite refractory brands showed less than a 0.2% change in mass and less than a 0.6% change in volume after thermal aging in th e absence of an applied load. The two exceptions exhibited extraneous amounts of change ( ≈ 8.5%) in both mass and volume due to thermal exposure. All samples showed less than a 0. 5% change in bulk density. The corrosion rates of the ten mullite brands could not be determined through the use of ASTM C987, but it was determined visually that only minimal amounts of recession occurred because of exposure as defined by the ASTM lid test.

Fused-cast alumina refractories from Corhart and Monofrax were examined. Both the density and porosity of the as-cast refractory blocks we re highly consistent. The phase profiles for the α - to β -alumina ratios also showed similar trends to those seen in the density/porosity profiles. X-ray diffraction (XRD) showed that both brands consis ted of only peaks identifiable as corundum (PDF# 10-0173) or sodium aluminum oxide (PDF# 31-12 63). Closer examination of the XRD patterns showed that there were some differences in ratios of α - to β -alumina between the two brands and

2between the bulk and columnar microstructures. The microstructures of the two brands of refractory were also comparable with a columnar region existing in the outer 1 to 1 1⁄2 in. of the blocks and then transitioning to a more equiaxed structure of α -alumina grains embedded in a β -alumina matrix toward the center of the block. Average grain si zes were found to be on the order of 172 μm and 82 μm for the Corhart bulk and columnar regions, r espectively. Average grain sizes were found to be on the order of 231 μm and 79 μm for the Monofrax bulk and columnar regions, respectively.

Both columnar orientations show much less accu mulated strain than the bulk samples under similar stresses because the elongated needle-like grains, whic h are oriented perpendicular to the direction of the applied compressive load, inhibit creep in the transverse columnar sample s. In the longitudinal columnar case, it is expected that the unrecoverable expansion effect plays a role in the reduced strain accumulation. The columnar samples at 1650°C showed less accumulated strain than the bulk sample under similar stress, but the behavior between the bul k and columnar samples was more similar. Both microstructures showed traditional creep behavior under 1.0 MPa of stress and much larger amounts of accumulated strain than the bulk samples at 0.6 and 0.8 MPa.

The three bulk 1650°C/1.0 MPa samples all had simila r creep rates, with the Corhart material on the order of 5 x 10 ! 6 h ! 1 and the Monofrax material on the order of 6 x 10 ! 6 h ! 1 . The columnar structures at 1650°C/1.0 MPa had a lower creep rate , on the order of 4.25 to 4.50 x 10 ! 6 h ! 1 . Creep rates for the other samples were not obtainable because nontrad itional creep behavior occurred. Stress exponents and activation energies could not be calculated from the data because steady-state creep rates were only obtained at one stress and temperature.

Unrecoverable expansion was seen in all mate rials and was thought to be connected to the nontraditional creep behavior seen in the compressiv e creep testing at temperatures and loads up to 1650°C and 0.8 MPa. As the temperature increased, the amount of unrecoverable expansion occurring over a given time interval also increased. The o ccurrence of the unrecoverable expansion was thought to be caused by thermal expansion hysteresis due to microstresses or microcracking. Because of that behavior, the generated creep curves could not be represented by the empirical NBA creep equation. Instead, an empirical fit utilizing an exponential expansion series with multiple time constants was used to represent the behavior exhibited by the fu sion-cast alumina refractories. The same exponential fit used to model the raw creep curves was also utilized to d escribe this composite behavior.

Several samples were analyzed after being crept, and results were compared with those previously obtained from virgin samples. Analysis included thermal conductivity, optical microscopy, and scanning electron microscopy/energy-dispersive X -ray spectroscopy (SEM/EDS) chemical analysis. The thermal conductivity values for the Monofrax post-creep cores were similar to those obtained earlier from the virgin cores, which had thermal conductivities in the range of 5.9 W/mK. The value obtained from the Corhart post-creep core was si gnificantly lower than the average value of 6.61 W/mK found earlier for the Corhart bulk material. Initial optical microscopy and SEM/EDS analyses were performed on Corhart and Monofrax bu lk samples exposed to 1550°C and 1.0 MPa. This work was conducted to determine whether any ch anges in the microstructure or chemistry could be detected at that intermediate condition. No discernible deformation and only slight chemical changes were seen in the samples. Subsequent optical microscopy and SEM/EDS analyses were performed on Corhart and Monofrax bulk samples exposed to the extreme conditions (1650°C and 1.0 MPa). The structure of the Corhart sample w as found to resemble the virgin structure; the Monofrax crept structure displayed a smaller α -alumina grain size and a tighter α -alumina grain structure with more equiaxed angular grains than in the virgin structure. More severe chemical changes were also seen between the virgin and crept samples.

3The fused spinel materials had negligible creep rates up to 1650°C at 8.5MPa of stress. The bonded spinel, surprisingly, crept substantially compared to the fused material. However, this must be compared with other common crown materials; the total creep of the bonded material is less than 0.5% over 100 h at 1550°C and 0.3 MPa which are fairly standard temperature and pressure for testing refractory materials The creep of silica ma terials is approximately 0.4% over 100 h at 1450°C and 0.3 MPa. The spinel materials did not react w ith soda in the exposure tests. There was some limited reaction with silica and calcia from the gasifier atmosphere. Thermal conductivity was determined by laser flash and was found to d ecrease as temperature increases from 14 (100°C) to 8 (700°C) W/mK for the fused spinel and 9.5 (100°C) to 4 (1300°C) for the bonded spinel. A model of the glass tank crown was developed that takes into account nonlinear changes in the refractory material due to time, temperature, and corrosion.



### 1.2 Technology Transfer The results of this project have established hardware and a test methodology that can be used by the refractories community to evaluate the creep and aging behaviors of most refractory materials. Of particular merit is the development of specia lized extensometry, which offers extremely high resolution required for the measurement of small de formations. The project staff made presentations at national meetings and published resu lts in industry technical journals.



### 1.3 Commercialization The data generated in this proj ect were provided to participating refractory manufacturers and are available from those manufacturers to any users of these types of refractories. It has been confirmed with industrial partners involved in this project that creep data and other thermomechanical property information generated as part of this project was u sed in analysis of glass fu rnaces currently in service and for the planning and design of refractory system s for future furnace constructions. The data has not only been used by glass comp anies in their analysis and planning of furnace systems, but by refractory companies and industrial consultants as we ll. The information generated was said to be “invaluable” by one industrial participant and more data of similar scope is felt to be of general interest to the industry as a whole.



### 1.4 Recommendations

Technical efforts should be undertaken to measure and model the composite effects of unrecoverable expansion (aging behavio r) and creep response. Given that th ese processes may be highly nonlinear, the traditional equations, which assume that steady-state deformation rates are dominant, are not appropriate. New models must be derived from b asic theoretical principl es that can describe the nonlinear, transient, nonsteady equilibrium behavior observed in this work. Creep testing needs to include simultaneous measurement of specimen elong ation/contraction occurring in the absence of an applied stress. Such testing could be conducted us ing a system consisting of furnace of sufficient size to accommodate multiple mechanical load trains. Du ring testing one load train would be used to monitor elongation/contraction in the absence of any appreciable stress. The stress range employed with the other load stations must be large enough to promote significant and measurable changes in the deformation response. It is recommended that the stress range cover at least one order of magnitude (e.g., 5 to 50 MPa). Testing times must also be much longer (> 1000 h) to ensure that representative deformation data are generated. A second approach for distinguishing creep from aging effects is to use the stress relaxation technique fo r measuring creep response. Because this method is able to generate an entire creep-rate vs stress cu rve in a matter of a few hours, one could use it to

4measure creep behavior at periodic intervals during a standard aging test. Thus a single sample could be used to assess both aging and creep behavior.

To facilitate technology transfer and commercializat ion, software tools s hould be developed which allow users to readily link the key properties to fi nite element codes used in furnace construction. This software would allow one to quickly assess th e effects of specific materials upon long-term thermal and structural reliability. It should also include a routine that allows the user to optimize performance of a given material by changing the ma terial properties; these altered properties would serve as new targets for those involved in materials development.

Any follow-on effort must also address new materials.

5

## 2. Introduction
Furnace designers and refractory engineers recogni ze that optimized furnace superstructure design and refractory selection are needed as glass production furnaces are continually striving toward greater output and efficiencies. Harsher operating c onditions test refractories to the limit, while changing production technology (such as the convers ion to oxy-fuel from traditional air-fuel firing) can alter the way the materials perform [1–3]. Re fractories for both oxy- and air-fuel fired furnace superstructures (see Fig. 1) are subjected to high temperatures that may cause them to creep excessively or subside during service if the refractory material is not creep resistant, or if it is subjected to high stress, or both. Furnace designers ca n ensure that superstructure structural integrity is maintained if the creep behavior of the refract ory material is well unde rstood and well represented by appropriate engineering creep models.

Fig. 1. Superstructu re refractories in gl ass production furnaces.
Several issues limit the abilities of furnace designers to (1) choose the optimum refractory for their applications, (2) optimize the engineering design, or (3) predict the service mechanical integrity of their furnace superstructures. Published engineeri ng creep data are essentially nonexistent for almost all commercially available refractories used for glass furnace superstructures. The limited data that do exist are supplied by the various refractory supplie rs. Unfortunately, the suppliers generally have different ways of conducting their mechanical tes ting, and they interpret and report their data differently. This inconsistency makes it hard for furnace designers to draw fair comparisons between competing grades of candidate refractories. Furtherm ore, the refractory suppliers’ data are often not available in a form that can be readily used fo r furnace design or for the prediction and design of long-term structural integrity of furnace superstructures.

As a consequence, the U.S. Department of Energy (DOE) Industrial Technology Program (ITP) Glass Industry of the Future sponsored research and development at indu stry, university, and national laboratory sites with the intent to help dom estic glass manufacturers improve their energy and operating efficiencies. The optimization of furnace superstructure design using valid engineering creep data is a means to achieving these ITP goals. The present project at Oak Ridge National Laboratory (ORNL) aided in this endeavor by conduc ting creep testing and analysis on refractories of interest to glass manufacturers at representative service temperatures, enabling the availability of new and improved refractories by refractories suppliers and by generating creep data on equivalent refractories that furnace designers could use for optimizing the design of their superstructures or for predicting their long-term structural integrity. Similar refractory creep-testing projects have been

7conducted at ORNL [4–6], so many of the unique experimental nuances and difficulties associated with the high-temperature creep testing of refr actories have been encountered and overcome.

8

## 3. Background
The ITP program has recognized that a reduction in overall domestic energy consumption will occur if the primary energy-consuming industries improve their own energy efficiencies [7]. Recognizing this need, the glass industry is currently convertin g older, conventional air-fuel-fired furnaces to oxyfuel firing, or in the case of new construction, is building new oxy-fuel-fired furnaces instead. Thishas caused oxy-fuel technology to become one of the fastest growing technologies in the glass industry because it promises pollution abatement, increased glass-pull effectiveness, capital cost savings, and increased energy efficiency. For example, a recent study [8] has shown that approximately $202M in energy savings per year in 2005 and a $445M per year savings by 2020 could be expected with the conversion of air/fuel to oxy-fuel–fir ed glass manufacturing furnaces. These results, which reflect energy savings of 2.8 and 14.2 TBtu/year, respectively, are based on the projection that 61% and 100% furnace conversions will occur by the years 2005 and 2020, respectively.

Unfortunately, the new internal furnace environmen t produced by oxy-fuel firing creates many problems with refractory life not previously encounter ed with conventional firing. These problems include increased potential for corrosion and “rat holing” alon g with deterioration of traditionally used conventional silica crown refractories. Additionally, due to a significant increase in the concentration of volatiles in the furnace, the refractories can experience a more intense alkali attack as water vapor reacts with alkali to form hydroxide vapors. Therefore, alternatives to silica must be considered for refractory superstructure applications, and data must be obtained to predict the performance of the refractories in service. Furthermore, the cost of the alternate refractories must be balanced with their effects on furnace life and glass quality while also considering the comparative performance of the other refractories in the furnace and overall furnace life

. Given the need for data on alternative refractories, the first objective of this project was to identifysuperstructure refractory categories of greatest interest to the glass manufacturing industry via a survey. To achieve this, the advice of project partic ipants and technical experts from the glass manufacturing industry, refractory suppliers, and academia was first sought to organize a list of distinct refractory categories to include in the survey (Table 1).

The mechanical deformation of thirteen different candidate refractory categories was determined to be of possible interest to the flat, fiber, contai ner, and specialty glass manufacturers (Table 2). A list of the categories was then forwarded to nine refr actory suppliers (Table 1), and company representatives were asked to indicate if any of their marketed refractory brands belonged to those categories. From their input, anywhere between four to ten co mpeting or “equivalent” brands were identified per category.
A survey consisting of the thirteen categories (and subcategory brands) was then forwarded to a furnace or refractory specialist at more than thirty domestic glass manufacturers (Table 1). The person taking the survey was asked to rank each refractory category as “high,” “middle,” or “low” priority in terms of their desire to have access to engineering creep data for that particular refractory category. To quantify the results of the survey, a score of te n, five, and zero points was respectively given to a“high,” “middle,” and “low” priority. The total points were summed and then used to rank and compare the interest among the thirteen categories.

Eight categories received relatively high total scoring (> 100 points) while the remaining five received little priority (< 100 points) (Table 2). Creep data for fusion-cast alumina was of greatest interest to the most respondents followed in descending order by creep data for conventional silica,

9Table 1. Project and survey participants Subject matter experts P. Antimarino, Harbison-Walker M. Nelson, Corhart S. Winder, UKSS R. Antram, NARCO J. Petreanu, Owens-Corning J. Wosinski, Corning W. Curtis, PPG P. Ross, Glass Industry Consulting R. Moore, University of Missour i-Rolla J. Shell, Techneglas Refractory suppliers A. P. Green Harbison-Walker NARCO Corhart/SEPR Monofrax VGT-DYKO DSF National Zedmark Survey recipients AFG Industries Glenshaw Philips Lighting Anchor Glass Guardian Industries Pilkington Ball-Foster Glass Holophane Pittsburgh Corning Cardinal FG Ki mble Glass PPG Carr-Lowrey Knauf Fiber Glass PQ Corporation CertainTeed Lancaster Glass Schuller International Corning Leone St. George Crystal Corning Glass - RBMG Libbey Techneglas
Ford Osram Sylvania Thomson Consumer Electronics Gallo Glass Owens-Brockway Vetrotex General Electric Lighting Owens-Corning Wheaton

fusion-cast AZS, fused-grain mullite, bonded AZS, an dalusite, fused silica, and bonded zircon. The relatively high interest in creep data for fusi on-cast alumina and AZS is indicative of the glass industry’s desire to convert to oxy-fuel firing and of the belief that these refractory categories may be attractive alternatives to traditionally used (but pe rhaps unsuitable) conventional silica refractories. The availability of creep data for mullite, spin el, or-containing, and 5–15% chromium-containing refractories received little interest from the respondents.

Creep testing was initiated in 1998. In addition to creep testing, the brand in each category was characterized by analyzing its (1) grain size and grain size distribution, (2) before- and after-testing microstructure using catholuminescence, (3) before- and after-testing phasecontent using X-ray diffraction (XRD), (4) before- and aftertesting density, and (5) corrosi on resistance [9]. The results from efforts (1)–(4) were used to explain any observed differences among the measured creep responses of the refractories, while the results from effort (5) were used to assess their corrosion responses. When the program was completed in 2000, the creep and corrosion behaviors of six types of conventional silica, ten types of mullite, and two types of fusion-cast alumina had been examined. This report summarizes the key findings obtained from the studies and provides recommendations for follow-on research. Detailed results are provided elsewhere [10–13]. Table 2. Ranking of refractory categories whose creep data are desired. The top eight ranked categories were creep tested at ORNL. Ranking Refractory category 1 Fusion-cast alumina 2 Conventional silica 3 Fusion-cast AZS 4 Fused-grain mullite 5 Bonded AZS 6 Andalusite 7 Fused silica 8 Bonded zircon 9 MgO 10 Spinel 11 50–80% Chrome 12 ≈ 30% Chrome 13 5–15% Chrome

10

## 4. Materials and Experimental Procedures

4.1 Materials Six conventional silica refractories were analyzed in the present study (see Table 3). All brands were “Type A” [14] conventional silicas except SI96AU (a Type B silica refractory); namely, their flux factors (alumina content plus twice the alkali conten t) were less than 0.50%. The chosen refractories provided a comparison between similar Type A s ilicas at well as comparison between Type A and Type B silicas. According to the published Teltech Report Crown Refractories for Glass Manufacturing with Oxy-Fuel Combustion [1], Type B conventional silica is not recommended for crowns; however, its mechanical performance at representative furnace crown temperatures and stresses were characterized for the sake of compar ison. The major secondary-phase constituent in all six brands was calcia (CaO), with additional reported constituents cons isting of alumina (Al 2 O 3 ), iron oxide (Fe 2 O 3 ), magnesia (MgO), titania (TiO 2 ), sodium oxide (Na 2 O), and potassium oxide (K 2 O). The amounts of these secondary phase constituents were semiquantitatively measured by the authors using SEM/EDS and are presented a nd described in later sections.

Ten mullite refractories were analyzed in the present study (see Table 4). Seven of the materials were fused-grained and three were not (although one non-fused-grain material did contain a small amount of fine fused mullite grains). Many of the manufacturers listed have merged or changed names since program initiation. Table 3. Silica refractories tested in the present study and their manufacturers Refractory Brand Name Manufacturer Gen-Sil A. P. Green SI96AU VGT-DYKO Stella GGS NARCO Vega Harbison-Walker Vega H Harbison-Walker Unnamed developmental brand Harbison-Walker
Two brands of M-type fusion-cast alumina refractories (Corhart Refractories of Louisville, Kentucky, and Monofrax Inc. of Falconer, New York) were examined. All specimens were fabricated from regular fusion-cast alumina blocks of approximate dimensions 0.60 H 0.50 H 0.30 m (24 H 20 H 12 in.). Key findings are summarized below. Table 4. Mullite refractories test ed in the present study and their manufacturers Brand Name Type Manufacturer BP mullite fused-grained Corhart DURITAL S75 non-fused-grained NARCO Frimul F fused-grained DSF GEM fused-grained NARCO HF 17 fused-grained DSF MU75AF fused-grained VGT-DYKO SL75AD non-fused-grained VGT-DYKO UFALA UCR non-fused-grained Harbison-Walker ZED FMC fused-grained Minteq ZED FM fused-grained Minteq
Two types of spinel were examined: fusion cast and reaction bonded. In the case of the fusion cast material, specimens having both columnar and equiaxed grains were examined. 

### 4.2 Creep Testing The testing frame used for the compressive creep t esting consisted of a large clamshell furnace that used resistance heating, a contacting extensometer that was used to measure axial dimension changes, and silicon carbide push rods that tr ansferred the applied compressive lo ad from an actuator to the test specimen (see Figs. 2 and 3).

11Fig. 2. Schematic of creep frame and supporting instruments. Fig. 3. Primary components of creep frame.

Creep tests were accomplished by using either digitally controlled pneumatic power (by LabVIEW TM software, National Instruments, Austin, Texas) or hydraulic power controlled by an analog controller. The latter feature provides both static (creep) and dynamic loading. The test specimen was heated with a high-temperature furnace capable of 1800 o C. Within ASTM guidelines, temperature fluctuations were approximately ± 2°C and load fluctuations were l ess than 1% of the test load. The specimen was compressed by two long push rods (each 0.3 m long) with the unheated ends connecting to water-cooled anvils. The upper compre ssion anvil was fixed to an upper platen by auniversal joint and was leveled by four turnbuckles. The lower compression anvil rests on a selfaligning coupler that plays an important role in maintaining load-train stability and uniform compression to the specimen. Details of the compressive creep testing system are given elsewhere [10].

The generated creep strain was measured by a scisso rs-type mechanical extensometer, a schematic of which is shown in Fig. 4. The extensomet er employs a capacitance sensor whose gap was conditioned, calibrated, and measure d as a function of time. The lever-arm assembly was made from a continuous rod of silicon carbide. The prob es monitored creep deformation of the specimen continuously in real time with a capacitive transducerattached to the cool end of the extension rod. Concurrently, a laser-based scanner was used to meas ure the movement of two fiducial flags attached to the ends of the extension rods for verifica tion. The extensometer provided an accuracy and resolution of about 5 μm, which is equivalent to th e sensitivity yielded by conventional strain gages. Strain measurements with the transducer and the laser system were in good agreement.

12Fig. 4. Schematic of creep frame extensometer.
Extensometry methods other than the capacitance co ntacting extensometers used in this study are often used for the measurement of refractory creep ; however, the capacitance contacting extensometer circumvents problems that other techniques inherently possess. The deformation of refractories is frequently measured continuously during compressive creep testing using two (sometimes more) linear variable differential transducers (LVDTs) whose mutual displacements coincide with the continuous position of the specimen ends. The creep results generated from this technique are accurate only as long as the accumulated measured defo rmation coincides with the actual specimen heights measured before and after testing. Deformat ion and/or translation of the load train during the creep testing of the specimen, reaction of the speci men ends with the fixturing, and “bedding-down” of the specimen all have been shown to cause a lack of correlation between the measured deformation during testing and the change in pre- and post-test specimen height. If any of these events occurs then the measured contraction during testing is not sole ly due to creep. Consequently, caution must be exercised when interpreting deformation data ge nerated by the LVDT technique because it will only be representative creep data if the experimenter ve rified and correlated pre- and post-test specimen height with the accumulated measured deformation. The advantage of the contacting extensometers used in the present study is that their accurate ope ration is independent of any rigid body motion or deformation of the test hardware, speci men (e.g., “end-crushing”), and push rods.

13

### 4.3 Specimen Preparation
In the case of the silica and mullite refractories, cylindrical creep test specimens having dimensions shown in Fig. 5 were core-drilled from the supplied conventional bricks in the manner illustrated in Fig. 6. The primary axis of the machined cylinder-shaped specimens was oriented parallel to the pressing direction. Although not verified in the present study, the measured creep deformation was assumed to be isotropic, so specimens were not machined from the bricks in different orientations. After core drilling, the specimen ends were ground parallel to within 0.013 mm (0.001 in.). All specimens were dried in an oven at 300°C (570°F) for 4 h after they were core drilled and before they were creep tested.

Using an appropriate aspect ratio of compression test specimens is an important consideration. A specimen aspect ratio of 2.6 or greater is recommended for compressive strength tests so that the friction effects between the specimen ends and loading ram are small compared to the axially applied compressive stresses [15]. However, in the present study (aspect ratio = 2.0), the applied axial compressive stresses during creep testing were already low (i.e

. , much less than the refractories’ compressive strengths). Consequently, the stresses and strains due to such friction were likely negligible, so adherence to the height/diamete r ratio of 2.6 or greater was deemed unnecessary. 3.00 ± 0.02

1.50 Dia. ± 0.01 0.001

Dimensions

in inches

Fig. 5. Dimensions of co re-drilled test specimens.



## 3"

Fig. 6. Schematic of how specimens we re core-drilled from as-received bricks.
In the case of the fusion-cast alumina, large blocks of approximate dimensions 0.60 H 0.50 H 0.30 m (24 H 20 H 12 in.) were prepared by both Corhart Refractories and Monofrax Inc., using their normal processing conditions. These blocks were sectioned in half with one half being shipped to ORNL and one half being retained by the preparing company. Cores of 19 mm (0.75 in.) diameter were drilled from whole regular cast blocks at three locations prior to being sectioned. Location one was in the center of the bottom of the block in the positive y -direction (designated y -core). Locations two and

14Sectioned face

Fig. 7. Refractory block core-drill locations for physical and chemical analysis.

three were in the side of the block at 76 mm (3 in.) and 178 mm (7 in.) from the base in the
y -direction with the cores taken in the x -direction (designated x 3-core and x 7-core, respectively). Core locations and orientations are s hown in Fig. 7. Individual cores were then sectioned into 25-mm (1-in.) pieces for density/porosity and X-ray fluor escence (XRF) analysis. The coordinate system used in Fig. 7, which is a nontraditional left-ha nded coordinate system, was chosen to comply with sample orientations utilized by Monofrax Inc. for its physical and chemical analysis techniques.

The regular cast blocks were further sectioned as shown in Fig. 8 to obtain creep specimens that were representative of the interior bulk region of each cast block. The individual bulk creep specimens were 38 mm (1.5 in.) in diameter and 76 mm (3 in.) in length. A specially cast block of M-type fusion-cast alumina was also prepared at Monofrax Inc. by incorporating an increased cooling rate. The block possessed a columnar zone of ≈ 50 mm (2-in.) thickness (as opposed to a columnar zone of

≈ 25 mm (1 in.) thickness on the regular cast blocks). A 0.30 H 0.20 H 0.05 m (12 H 8 H 2 in.) slab was cut from the exterior of the block and was shi pped to ORNL. Monofrax retained the remainder of the block. The entire 50-mm cross section contained the characteristic columnar zone microstructure. Creep specimens were sectioned such that the orient ation of the columnar structure was oriented in both a longitudinal direction [dimensions: 38 mm (1.5 in.) diameter, 50 mm (2 in.) length] and transverse direction [(38 mm diameter (1.5 in.), 70 mm (2.75 in.) length] with respect to the length of the cylinder.

Cylindrical specimens [dimensions: 13 mm (0.5 in.) diameter, 38 mm (1.5 in.) length] for thermal expansion and elastic modulus determination were also taken from the sectioned regular cast Monofrax and Corhart blocks at locations between the creep specimens. Equivalent specimens were taken from the specially cast Monofrax block possessing th e columnar structure. Similar to that of the creep specimens, the columnar stru cture in the specimens was oriented in both the longitudinal and transverse directions with respect to the length of the cylinders.

The cylindrical specimens were encased in a fine-grained H-type (100% β -alumina) fusion-cast alumina shell (shown in Fig. 9) to inhibit soda evolution from the test specimens into the furnace atmosphere during testing. Attempts were made to ensure that a gap existed between the sample and H-shell during testing, but that was not always the case.

15Fig. 8. Schematic representation of the sectioning pl an used to fabricate creep specimens from the bulk region of the refractory blocks. 

### 4.4 Creep Testing and Data Interpretation Tables 5, 6, and 7 describe the creep test matrices for the silica, mullite, and fusion-cast aluminarefractories, respectively. A typical stresstemperature-time history is provided in Fig. 10. All specimens were preloaded in compression to approximately 0.04 MPa ( ≈ 6 psi) during furnace heat-up to keep all the load train components and the specimen in continuous contact. The specimens were then heated from room temperature up to the test temperature in 4 h. Each of the specimens was soaked at temperature for 25 h prior to the application of the first stress.
Most creep analyses for long-term applications (i.e

. , where steady-state creep accumulation dominates the accumulation of strain, not the amount of primary creep) involve the determination of a steady-state or minimum creep rate and its examination as a function of applied stress and temperature. The steady-state or minimum compressive creep rate ( d ε / d t min ) can be related to the applied compressive stress and temperature by using an empirical Arrhenius power law or the familiar Norton-Bailey creep equation [16]FusionCast Alumina Specimen Dendrytic Alumina Spacer Monofrax M Push Rod

Monofrax M Push Rod Sapphire Extensometer Knife

Sapphire Extensometer Knife High Purity Alumina Disk High Purity Alumina Hemisphere

H Fusion-Cast Alumina Disk H Fusion-Cast Alumina Shell

Fig. 9. Creep specimen assembly H-shell arrangement required for the creep testing of the fusion-cast alumina.

16d ε /dt min = A σ n exp(- Q / RT ), (1)

where A is a constant, σ is the applied stress, n is the stress exponent, Q is the activation energy, R is the universal gas constant, and T is the absolute temperature. Multilinear regression may be performed to determine the constants A
, n , and Q for each material. By performing the analysis in this manner, it is implied that the same dominant (or rate-controlling) creep mechanism is active at all temperatures and stresses. The validity of this assumption is assessed by the goodness-of-fit of this equation to the experimental data and th e reasonableness of the obtained values for n and Q

.

Table 5. Creep test matrix for the silica refractories (stress, MPa) a Refractory 1550°C (2820°F) 1600°C (2910°F) 1650°C (3000°F)
Gen-Sil 0.2, 0.4, 0.6 0.2, 0.4, 0.6 0.2, 0.4, 0.6 SI96AU 0.2, 0.4, 0.6 0.2, 0.4, 0.6 b Stella GGS 0.2, 0.4, 0.6 0. 2, 0.4, 0.6 0. 2, 0.4, 0.6 Vega 0.2, 0.4, 0.6 0.2, 0.4, 0.6 0.2, 0.4, 0.6 Vega H 0.2, 0.4, 0.6 0.2, 0.4, 0.6 0.2, 0.4, 0.6 Unnamed development brand 0.2, 0.4, 0.6 0.2, 0.4, 0.6 0.2, 0.4, 0.6

a 0.2 MPa = 29.0 psi, 0.4 MPa = 58.0 psi, 0.6 MPa = 87 psi.

b Material exhibited excessive creep deformation at 1600°C, so its testing at 1650°C was omitted.

Table 6. Creep test matrix for the mullite refractories (stress, MPa) a Refractory 1300 o C (2370 o F) 1375 o C (2500 o F) 1450 o C (2640 o F)
BP mullite 0.4, 0.6 0.4, 0.6 DURITAL S75 0.2, 0.4, 0.6 0.2, 0.4, 0.6
Frimul F 0.4, 0.6 0.4 & 0.6 GEM 0.2, 0.4, 0.6 0.2, 0.4, 0.6
HF 17 0.4, 0.6 0.4, 0.6
MU75AF 0.4, 0.6 0.4, 0.6 SL75AD 0.4, 0.6 0.4, 0.6 UFALA UCR 0.4, 0.6 0.4, 0.6 ZED FMC 0.4, 0.6 0.4, 0.6
ZED FM 0.4, 0.6 0.4, 0.6

a 0.2 MPa = 29.0 psi, 0.4 MPa = 58.0 psi, 0.6 MPa = 87 psi.

Table 7. Creep-test matrix for the fusi on-cast alumina refractories (stress, MPa) a Refractory 1450°C (2640°F) 1550°C (2820°F) 1650°C (3000°F) Corhart Jargal M cast block, regular bulk 0.6, 0.8, 1.0 0.6, 0.8, 1.0 0.6, 0.8, 1.0

Monofrax M cast block, regular bulk 0.6, 0.8, 1.0 0.6, 0.8, 1.0 0.6, 0.8, 1.0

Monofrax M cast block, special longitudinal columnar 0.6 1.0

Monofrax M cast block, special transverse columnar 0.6 1.0

a 0.6 MPa = 87.0 psi, 0.8 MPa = 116 psi, 1.0 MPa = 145 psi.

170.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

0 500 1000 1500 2000

0 50 100 150 200 250 300Compressive Stress (MPa)Temperature (°C)

Time (h) 100

75

50

25

0 3500

3000

2500

2000

1500

1000

500

0Temperature (°F)

Stress Temperature

4h to temp

Note: shown temperature is 1600°C, but same history was used for 1550 and 1650°C tests

Fig. 10. Example of temperature and stress history used in the creep testing.



### 4.5 Microstructural Characterization The microstructures of the various refractories were examined using reflected light (RL) imaging, cathodoluminescent (CL) imaging, and SEM. In the case of RL and CL, disks for examination were sectioned from both as-received and crept specimens Disks were cut from the top of each as-received specimen as shown in Fig. 11(a); disks were sectione d from crept specimens in their centers as shownin Fig. 11(b). The disk sections were cleaned and dried and were then impregnated with a lowviscosity resin to fill the pores. The impregnated specimens were mounted on Co-Cast mounting media. Cured sections were ground with diamond wheels down to 600 grit and then were finally polished with diamond paste and lapping oil. RL and CL microscopy were utilized for the characterization. A cold-cathode CL microsco py system (Model Mk4, Cambridge Imaging

0.2" Metallographically Polished Surface Core Drilled Specimen

Used for Creep Test
"As-Received" Microstructure 0.2" Metallographically Polished Surface Crept Specimen Sectioning of Specimen

(a) (b) Fig. 11. Schematic describing ho w disk sections were machined fr om core-drilled specimens for (a) as

- received and (b) post-test RL and CL imaging.

18Labophot-Pol with a Nikon UFX-DX photomicrographic system) was used for these microstructural analyses. The CL microscopy characterization techni que has been described in detail by Karakus and Moore [17] and is briefly described here. The CL imaging system utilizes an energetic electron beam that is produced from a cold cathode ray tube. The electron beam is trained on the surface of uncovered polished or unpolished sp ecimens in a low vacuum environment. As a result of the electron beam-solid specimen interaction, minera ls or phases in the specimen produce characteristic colored light known as “cathodoluminescent” emission . The CL technique is unique and provides microstructural information that often cannot be obtained by any other technique. The CL microscopy system can provide an immediate assessment of the phases in refractory materials through the identification of characteristic CL color and crystal habits that minerals exhibit. The CL microscopy system can also be used in conjunction with RL a nd SEM for elemental analysis of individual phases.

Certain minerals produce a characteristic CL color. For example, corundum ( α -Al 2 O 3 ) is characterized by a characteristic bright red CL color while spinel (MgAl 2 O 4 ) produces a characteristic green color. These CL emissions are due to “activator” el ements present in trace amounts in these mineral structures; Cr 3+ in corundum produces a characteristic CL emission at approximately 694 nm, and tetrahedrally coordinated Mn 2+ in spinel produces a CL emission at approximately 520 nm. Activator elements related to CL emission centers in these minerals often require low voltages ( ≈ 8 kV) for excitation.

Important for the materials analyzed in this study are the CL behaviors of mullite, alumina, and silica grains along with that of the glassy matrix phase. Regular mullite grains do not produce bright CL but rather exhibit a dull response. Contrary to this, fused mullite grains produce intense dark blue or violet CL. Secondary mullite bonds between primary fused mullite grains can produce intense violet reddish CL, distinguishing them from primary mullite. Fu sed alumina grains exhibit very bright violet blue CL, while tabular alumina grains appear as an intense violet. Andalusite grains give off dark reddish CL and zirconia, a blue-white CL. 

### 4.6 Supplemental Analysis The bulk densities of various core-drilled specimens were measured prior to creep testing. Masses were measured on a balance that had a resolution of ± 0.0005 g. The masses were then divided by the respective specimens’ volumes (diameters and lengths measured with calipers having a resolution of ± 0.005 mm) to calculate density.

Specimen

Specimen

Specimen Styrofoam Standard Measurement

Single-side Measurement Sensor (side view)

Sensor (side view) Kapton Sensor (for low temps) Fig. 12. Schematic of transient plane source direct thermal conductivity method experimental set-up and picture of Kapton
sensor.Room-temperature thermal conductivity of the “asreceived” bricks was measured by a transient planesource (TPS) technique in the “hot-disk” arrangement [18]. In this arrangement, a Kapton TPS element was used as both a heat source and a temperature sensor to measure the time required to conduct a known amount of heat across a prescribed distanceof sample. Measurements were taken in the “standard method” by sandwiching the Kapton element between two identical cylindrical creep specimens and passing 1 W of power through the sample for 20 s. Five measurements were taken on each specimen type with 15 min. or longer between measurements. The specimen configuration along with the sensor itself is shown in Fig. 12.

19The phase content of the materials in their as-receiv ed state was characterized and was compared with that after creep testing at 1450°C. Specimen preparation involved grinding the refractory to approximately 325 mesh in an agate mortar a nd pestle. XRD was performed with all ten mullite materials in a Scintag 2000 diffractometer. The samples were scanned at a rate of 1°/min with Cu-K a radiation (l = 1.54059 Å), and a step size of 0. 02° over a scan range of 10 to 120° two-theta.

In the case of the fusion-cast alumina, thermal diffu sivity was also measured from room temperature up to 1400°C (2552°F) by the laser flash method [19]. In the laser flash method, a cylinder of the bulk refractory [13-mm (0.5-in.) diam., 32 mm (1.25-in.) length] was sectioned into small disks [2 mm (0.08 in.) thick], and the disks were subjected to a high-intensity, short-duration thermal pulse through their thicknesses. The temperature resulting atthe rear face of each specimen, due to the pulse, was recorded and was used to calculate the time required to raise the rear face temperature a certain percentage of its maximum value. Th ermal conductivity values were then calculated:

λ

= ρ α C p , (2)

where λ is the thermal conductivity, ρ is the density, and C p is the heat capacity. The latter parameter was measured by calorimetery at ORNL and Monofrax, Inc., in New York.

To examine dimensional stability due entirely to only exposure at temperature, specimens from each refractory were subjected to aging at times and temper atures that were equivalent to those applied to the creep specimens. Two methods were used for measuring these aging characteristics. The first involved heating the specimen at temperature for a prescribed number of hours and then cooling the furnace to room temperature. The specimen was then weighed, and its dimensions were measured before it was put back in the furnace for subsequent reheating. The mass, dimensions (volume), and density of the specimens were t hus determined as a function of cumulative time and temperature.

The second method involved measuring the real-time specimen displacement attemperature using a dual-rod LVDT system (Fig. 13). The specimen was supported by a high-purity alumina disk resting on a fixed SiC push rod while the test assembly w as supported by the body of the furnace. The test assembly for monitoring the linear dimensional chan ges consisted of two sa pphire rods in contact with individual LVDTs. One sapphire rod and LVDT pair was used to monitor changes in the test

Fig. 13. Schematic of dual-rod LVDT system used to measure thermal expansion.

20sample (designated LVDT-1) while the other rod and LVDT were placed in contact with the highpurity alumina disk supporting the test specimen (designated LVDT-2). The difference between these readings was used to calculate the di mensional changes of the specimen [13].

The ASTM lid test was used to evaluate the corro sion of the various refractories [9]. A refractory specimen (2.5 H 2.5 H 1 cm) sectioned from the as-received bricks was placed over a small alumina crucible containing 12.5 g of sodium carbonate. The crucible and refractory specimen "lid" were then placed in a secondary alumina container and is othermally exposed at 1400°C for 24 h. After exposure, samples were removed and were examined for recession.

21

## 5. Results and Discussion

5.1 Silica Refractories A major finding from the compressive creep tests of the silica refractories was that concurrently active mechanisms, other than creep, resulted in pos itive dimensional changes. Specifically, as shown in Fig. 14, some specimens exhibited axial expa nsion during creep testing even though an axial compressive load was applied. This peculiarity is a consequence of the bulk expansion that these refractories exhibited. This effect limited the ab ility to identify or interp ret the lesser-active creep mechanism in these silica refractori es. Consequently, the compressive creep rates of all six brands were not able to be represented as a function of temperature and compressive stress using the conventionally used NBA creep equation (i.e ., the Arrhenius power-law creep model).

The change in dimensions of the compressively crept specimens indicated that their size (both diameter and length) had actually increased as a c onsequence of the employed creep test conditions (see Table 8). This expansion phenomenon greatly comp licates creep analysis in which Eq. (1) is used and likely invalidates its use. All six brands showedthis expansion effect. The increases in diameter and length of the creep specimen s were between 0.35 and 1.0%.

Table 8. Dimensional changes of crept specimens . A negative value constitutes contraction and a positive value represents expansion. Length change (%) Gen-Sil SI96AU Stella GGS Vega Vega H H-W Dev. Brand
1550°C
Diameter 1.0 0.65 0.45

! 0.08 0.49 0.38 Length 0.55 0.55 0.36 0.94 0.42 0.41 1600°C
Diameter 1.0 9.12 0.42 0.24 0.46 0.38 Length 0.52

! 24.0 0.70 0.35 0.47 0.49 1650°C
Diameter 0.50 0.71 0.50 0.53 0.50 Length 0.47 0.71 0.59 0.46

Consistent with bulk changes e xhibited by the creep specimens , the unstressed or “aged” silica refractory specimens from all six materials also exhibited loss of mass, dimensional increases, and density decreases between 1550 and 1650°C (see Table 9). The mass losses of the six brands at 1550 and 1600°C were equivalent; however, some silica brands lost more mass than others at 1650°C: Harbison-Walker’s developmental brand lost approximately 0.1% of its mass; SI96AU lost ≈ 0.2%, Vega H lost ≈ 0.3%, Gen-Sil lost ≈ 0.5%, Vega lost ≈ 1.0%; and Stella GGS lost ≈ 1.5%. Most of the mass loss occurred in less than 25 h for all six brands.

The dimensional increases of the silica specimens we re a function of temperature, as illustrated in Fig. 15. Additionally, some brands expanded more than others. Each of the specimens expanded isotropically in each of three directions (within st atistical confidence). The ranges of expansion were

≈ 1

! 2.5% at 1550°C, ≈ 2.25

! 3.75% at 1600°C, and ≈ 3.5

! 6% at 1650°C. Harbison-Walker’s developmental brand expanded the least amount at all three temperatures, followed by Gen-Sil. The ascending order of expansion for the other four brands varied with temperature. Stella GGS expanded

23Table 9. Density changes of crept specimens. A negative value constitutes a decrease in density and a positive value represents an increase.

Gen-Sil SI96AU Stella GGS Vega Vega H H-W Dev. Brand After 1550°C creep testing Density (g/cc) 1.75 1.80 1.81 1.73 1.83 1.90 Change (%)

! 1.8

! 2.6

! 1.9

! 3.2

! 2.8

! 1.6 After 1600°C creep testing Density (g/cc) 1.73 1.79 1.76 1.82 1.90 Change (%)

! 2.7

! 2.0

! 1.8

! 1.9

! 2.2 After 1650°C creep testing Density (g/cc) 1.72 1.79 1.74 1.80 1.88 Change (%)

! 3.0

! 2.2

! 3.1

! 3.9

! 3.0

the most at 1550°C ( ≈ 2.5%), SI96AU expanded the most at 1600°C ( ≈ 3.75%), and Vega expanded the most at 1650°C ( ≈ 6%). Dimensional increases in these aged specimens were greater than axial expansion of the crept silica specimens at the same temperatures, indicating that there may have been a specimen-size effect. The change in the as-receiv ed assemblage of tridymite, amorphous silicate, Ca-silicate, and cristobalite to the crept microstruc ture consisting entirely of cristobalite likely caused the observed volume expansion. The same phenome non appeared to have occurred in the aged specimens. Temperature is the activator of this phenomenon; the application of stress is not a prerequisite for it.

Based upon the data given in Fig. 15 it is reasonable to assume that the deformation rate measured during the application of a compressive stress was composed of two parts: (1) specimen contraction arising from creep-related processes (a function of time, stress, and temperature) and (2) specimen elongation arising from the change in the phase assemblage (a function of time and temperature only). One can therefore estimate the contribution arisi ng from creep alone by subtracting the rate of elongation occurring at zero stress from the rates measured under a fixed stress. To this end, the curves in Fig. 15 were subsequently used to calcula te the linear expansion rates occurring at 250 h for the 1600 and 1650°C aging tests. The calculated rates were then subtracted from the rates measured under an applied stress at comparable times.

For the 1600 and 1650°C aging tests the stress of 0.6 MPa was used because the total time at temperature was comparable to that used to calculate the zero-stress expansion rate:

• Gen-Sil: d ε /dt min (1/s) = 3.6 H 10 20 σ exp[-25 (kcal/mole)/RT]

• SI96AU: d ε /dt min (1/s) = 4.2 H 10 44 σ exp[-44 (kcal/mole)/RT]

• Stella GGS: d ε /dt min (1/s) = 5.5 H 10 14 σ exp[-20 (kcal/mole)/RT]

• Vega: d ε /dt min (1/s) = 1.9 H 10 12 σ exp[-18 (kcal/mole)/RT]

• Vega H: d ε /dt min (1/s) = 1.4 H 10 13 σ exp[-18 (kcal/mole)/RT]

XRD results showed that all six as-received silica refractories consisted of cristobalite (PDF# 39-1425) and tridymite (PDF# 18-1170). Even thoug h a calcium silicate was present in the grain boundaries (as detected by SEM/EDS), its concentration was sufficiently small that XRD did not

24-0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5

-1.0 -0.5 0.0 0.5 1.0 1.5 2.0

0 50 100 150 200 250 300Creep Strain (%)Stress (MPa)

Time (h) Strain

Stress Vega 1600°C

4.5 x 10 -9 s -1 3.5 x 10 -9 s -1 -6.3 x 10-10 s -1

-0.50 -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30 0.40 0.50

-1.0 -0.5 0.0 0.5 1.0 1.5 2.0

0 50 100 150 200 250 300Creep Strain (%)Stress (MPa)

Time (h) Strain

Stress Vega 1550°C

9.9 x 10 -11 s -1 -6.2 x 10-11 s -1 3.6 x 10 -11 s -1

-0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5

-1.0 -0.5 0.0 0.5 1.0 1.5 2.0

0 50 100 150 200 250 300Creep Strain (%)Stress (MPa)

Time (h) Strain

Stress Vega 1650°C

1.9 x 10 -9 s -1 6.1 x 10 -9 s -1 3.8 x 10 -9 s -1

Fig. 14. Creep behavior of Vega as a function of temperature.

25identify it. It was qualitatively determined that Gen-Sil had the highest tridymite content and that SI96AU had the highest cristobalite content. Very small amounts of quartz were detected only in SI96AU and Vega.

0 2 4 6 8 10

0 50 100 150 200 250 300 Vega Vega H Gen-Sil H-W Dev. Brand Stella GGS SI96AUChange in Volume (%)

Time (h) 1550°C (2820°F)

0 2 4 6 8 10

0 50 100 150 200 250 300 Vega Vega H Gen-Sil H-W Dev. Brand Stella GGS SI96AUChange in Volume (%)

Time (h) 1600°C (2910°F) Based on the density differences in the silica minerals (quartz = 2.64 g/cc, tridymite = 2.26 g/cc, cristobalite = 2.32 g/cc), it takes the conversion of approximately 6.5% of residual quartz to tridymite or cristobalite to cause a bulk expansion of 1%. Because no quartz was detected in four of the conventional silicas, and because its concentration was minute inSI96AU and Vega, the phasechange phenomenon could not have caused the volume expansion that these materials exhibited as a consequence of the creep testing. Subsequent creep testing changed the phase content in the six silica refractories in that all the tridymite in the silica refractories was converted to cristobalite. The stable silica phase above 1470°C (2680°F) is cristobalite, so the XRD results are not surprising.

The microstructures of the six silica refractories changed as a consequence of the applied testconditions. The changes in asreceived to crept microstructures in the six materials had commonality and are shown schematically in Fig. 16. The as-received silica microstructures of the six materials typically consisted of cristobalite aggregates or “islands” in a matrix or “sea” or of prismatic tridymite (approximately 10 to 20 μm in size near the cristobalite islands, 20 to 80 μm farther away from them), calcium silicate crystals, and an amorphous silicate. The structure of the cristobalite in the islands often resembled fish scales. The individual cristobalite grains comprising the cristobalite islands had a 0 2 4 6 8 10

0 50 100 150 200 250 300 Vega Vega H Gen-Sil H-W Dev. Brand Stella GGS SI96AUChange in Volume (%)

Time (h) 1650°C (3000°F)

Fig. 15. Change in volume of “aged” specimens as a function of time and temperature.

26rather uniform size distribution, 5 to 10 μm across; the size of the cristobalite islands ranged from approximately 40 μm to more than 1 mm.

During creep testing at 1550, 1600, and 1650°C, the tridymite converted to cristobalite, and a new amorphous silicate (formed between the new and growing cristobalite islands ). Additionally, many of the crept cristobalite microstructures contained pores that resembled tunnels. They appeared to be avenues for vaporization, but their structure was not examined, so their cause is not known.

RL and CL imaging s upplemented one another well to explore these microstructural changes. Examples of the RL images of the as-received and crept microstructures are shown for the Vegarefractory in Fig. 17. Pores, tridymite, and Casilicate were consistently observed in the asreceived microstructures of each refractory. Changes in the microstructure arising from creep testing included the formation of larger pores, larger cristobalite is lands, the new amorphous silicate, and the creation of gaseous pores. The bulk expansion of the crept specimens may be explained by the destruction of original tridymite bonds and the enlargement of pores and of the cristobalite islands.

CL imaging (Fig. 18) provided an interesting anddifferent perspective into how the microstructures changed as a consequence of the creep testing. The CL imaging revealed the tridymite in the as-received state better than the RL imaging, and it provided new insights into how the cristobalite islands changed or grew.

Specifically, the cores of most of the cristobalite aggregates in these specimens exhibited a light blue color while their outer zones or rims were dark blue. The light blue core represents the original fish-scale cristobalite island. The core or center of the islands after creep testing was relatively free of impurity phases, resulting in the light blue CL color. During the creep testing, the tridymite converted to cristobalite or added to the size of existing cris tobalite islands. Additionally, the original calcium and amorphous silicates (containing transition metals and alkalis) formed a liquid phase during creep testing that either diffused into the enlarging cris tobalite islands or was present during their growth.This outer zone or rim was characterized by dark blue CL. The Ca-silicate phase luminesced bluishwhite and locally bright yellow, with some of its crystals being as small as 15 μm, in the as-received microstructures. However, during creep testing, iron impurities in the original amorphous silicate combined with the Ca-silicate phase to form a new amorphous silicate that because of the presence of the iron, did not produce CL color. Boundary Pore Cristobalite Tridymite Ca-silicate crystals + amorphous silicateTypical "As-received" Silica Microstructure

Boundary Pore Cristobalite New amorphous silicateTypical Crept Silica Microstructure

"Gas" or "Tunnel" Pore Fig. 16. Schematic of the change in microstructure from the as-received material state to that after creep or high-temperature exposure.

27In the case of the corrosion testing, a portion of the silica refractory lid was dissolved by the sodium carbonate vapor, forming a liquid phase at temperature. After the test, the maximum amount of recession was measured and summarized (Fig. 19). In general, there was only a slight variation in the amount of attack among the six silicas, and it may be concluded that their corrosion resistances were statistically equivalent. The amount of recession showed an almost linear relationship with temperature, as shown in Fig. 20. Because a vapor attack is expected, this effect seems reasonable. Varying the amount of sodium carbonate by 50% more (18.75 g) and by 50% less (6.25 g) from the standard 12.5 g had very little effect. Apparently, the sodium carbonate is not fully consumed during the test, and the lowest amount does not limit the extent of attack. Fig. 17. Vega’s microstructural changes as a function of temperature as revealed by reflected-light microscopy.



### 5.2 Mullite Refractories The crystalline phases present in each of the ten mullite refractories varied from material to material, but some trends or similarities existed among the brands (see Table 10). The ten brands could be broadly categorized as either fused-grained ornon-fused-grained (see Table 4). The non-fusedgrained materials all contained mullite grains deri ved from andalusite or kyanite while the fusedgrained mullite was made by fusion (melting) of alumina and silica. All the refractories were composed of variously sized mullite grains floating in a matrix of secondary mullite with various levels of glass and porosity present in the matrix . The DURITAL S75, HF 17, and ZED FMC brands all contained very little glassy phase. All the others possessed significant qua ntities of glassy phase. The HF 17, UFALA UCR, and ZED FMC brands were all found to possess high levels of matrix porosity when examined by optical microscopy and SEM; the rest showed little or no matrix porosity.

Room-temperature thermal conductivity testing resu lted in the average values shown in Fig. 21. Frimul F showed the highest thermal conductivity at just under 3.5 W/mK. It was followed by Durital S75, GEM, MU75AF, and ZED FMC, which all had a thermal conductivity of approximately 3.0 W/mK. BP mullite and HF 17 both had similar thermal conductivity values of 2.7 to 2.8 W/mK, followed by ZED FM with a value of just over 2. 5 W/mK. The two brands with the lowest thermal conductivity values were SL75AF and UFALA UCR, wh ich had values of approximately 2.5 W/mK.

28These values were all higher than those given in the manufacturers’ literature, which ranged from 2.0 to 2.4 W/mK.

The results from creep testing at an applied stress of 0.5 MPa are shown in Fig. 22. The amount of compressive creep for th various refractories fell into three levels. BP mullite, HF 17, and Frimul F all showed low amounts of creep at temperatures between 1300 and 1450 e

at

test o C (2370 to 2640 o F). Although the creep rate for the MU75AF at 1450°C was also quite low, it exhibited anomalous behavior in that the creep rate increased as the temperature was lowered to 1375°C. Slightly greater amounts of creep were seen in the GEM, DURITAL S75, and ZED FM brands at temperatures between 1300 and 1450 o C (2370 to 2640 o F). Creep rates for these refractories were found to be on the order of 10 ! 10 s ! 1 the lower test temperature and 10 -9 s ! 1 at the higher temperature. The SL75AD, UFALA UCR, and ZED FMC brands all showed significant amounts of creep at temperatures between 1375 and 1450 o C (2500 to 2640 o F). Their creep rates were on the order of 10 ! 9 s ! 1 at the lower test temperature and 10 ! 8 s ! 1 at the higher test temperature. Because only one specimen per condition was tested, the authors were unable to statistically conclude th at any one of the refractories in each group had superior creep resistance to the others. If differen ces exist within a grouping, they are believed to be insignificant. Fig. 18. Vega’s microstructural changes as a function of temperature as revealed by cathodoluminescence imaging.

The activation energy in the Norton-Bailey creep equation was found for each brand by equating the respective slope in Fig. 22 to the quantity – Q / R . Although the values of the stress exponents could have also been determined from the experimental data, that procedure was not implemented because the uncertainties were high in the r esulting estimates. Specifically, because n is typically very close 1, an increase in stress from 0.2 to 0.6 would only incr ease the creep rate by a factor of 3. Replicate creep tests of other structural ceramics have shown that the minimum creep rate value can vary by an order of magnitude or more. Consequently, the st ress range used in the present investigation was probably not sufficient to generate a significant increase in creep rate with increasing stress. Therefore, the value of A in Eq. (1) was calculated by assuming n = 1. The effect of specimen

29elongation or contraction in the absence of a str ess was ignored in the calculations. The resulting expressions were then derived for the creep rate of the mullite refractories:

• BP mullite d ε /dt min (1/s) = 4.2 H 10 -1 σ exp[

! 73 (kcal/mole)/RT]

• DURITAL S75 d ε /dt min (1/s) = 1.5 H 10 5 σ exp[

! 110 (kcal/mole)/RT]

• Frimul F d ε /dt min (1/s) = 3.3 H 10 7 σ exp[

! 130 (kcal/mole)/RT]

• GEM d ε /dt min (1/s) = 7.4 H 10 1 σ exp[

! 80 (kcal/mole)/RT]

• HF 17 d ε /dt min (1/s) = 6.6 H 10 16 σ exp[

! 200 (kcal/mole)/RT]

• MU75AF [Could not be determined]

• SL75AD d ε /dt min (1/s) = 6.0 H 10 -2 σ exp[

! 50 (kcal/mole)/RT]

• SL75AD d ε /dt min (1/s) = 2.4 H 10 4 σ exp[

! 90 (kcal/mole)/RT]

• ZED FMC d ε /dt min (1/s) = 1.1 H 10 12 σ exp[

! 150 (kcal/mole)/RT]

• ZED FM d ε /dt min (1/s) = 5.1 H 10 8 σ exp[

! 130 (kcal/mole)/RT]

0 1 2 3 4 5Gen-Sil #1Gen-Sil #2Stella GGSVega HH-W Dev. BrandVegaSI96AUMaximum Recession (mm)

Fig. 19. Amount of refractory recession when exposed to sodium carbonate at 1400°C for 24 h.

30

### 1 2 3 4 5 6 7Recession (mm)



### 1200 1250 1300 1350 1400 1450 1500 

## Temperature (°C) 18.75g 6.25 g 12.5 g

Fig. 20. Amount of recession as a function of temperature and sodium carbonate addition for Gen-Sil silica.

Table 10. Summary of microstructural observation for th e mullite refractories before and after creep testing
Brand name Starting microstructure Microstructure after creep
BP mullite RL&CL: large and small fused mullite grains dense matrix of secondary mullite and glass
XRD: mullite and alumina SEM/EDS: mullite is stoichiometric while the glassy phase contains K 2 O, Na 2 O, and CaO No change

DURITAL S75 RL&CL: non-fused mullite grains derived from and alusite along with tabular and fused alumina grains floating in a matrix of secondary mullite, little detectable glass
XRD: mullite and alumina SEM/EDS: mullite is stoichiometric No change

Frimul F RL&CL: fused mullite aggregates floatin g in a very glassy matrix of secondary mullite, small mullite grains present in the glassy matrix
XRD: mullite and traces of alumina SEM/EDS: mullite is stoichiometric while glassy phase contains K 2 O, CaO, and TiO 2 No change

GEM RL&CL: large and medium sized fused mullite grains in a secondary mullite matrix containing amorphous phase XRD: crystalline mullite; SEM/EDS: large mullite crystals and smaller (3–5 μ m) secondary mullite crystals in an amorphous matrix, glassy matrix has a similar composition to the mullite crys tals with small amounts of Na 2 O, CaO, and TiO 2 No change

31Table 10. continued
Brand name Starting microstructure Microstructure after creep
HF 17 RL&CL: large fused mullite grains in a highly porous matrix of fine fused mullite grains plus very tiny alumina crystals
XRD: mullite and alumina SEM/EDS: secondary mullite crystals present as observed as agglomerates devoid of glassy bonding phase Microstructure appeared denser

MU75AF RL&CL: large fused mullite grains or aggregates with round morphology in a fine “granular” mullite and glassy matrix XRD: mullite plus trace alumina SEM/EDS: the glassy phase contains K 2 O and Na 2 O along with trace amounts of TiO 2 and CaO No change

SL75AD RL&CL: andalusite grains partially converted to mullite along with alumina grains and fine fused grain mullite; secondary mullite matrix formed around and between partially mullitized andalusite grains, large fused alumina grains, and fine fused mullite grains; andalusite grains contain free quartz that is converted to cristobalite during firing XRD: andalusite, mullite, alumina, and cristobalite SEM/EDS: glassy matrix contains Na 2 O, MgO, CaO, K 2 O, and TiO 2 Andalusite grains are converted to mullite aggregates and the amount of glassy phase has increased

UFALA UCR RL&CL: finely crystalline mullite aggregates formed through the calcination of andalucite or kyanite in a fine crystalline mullite matrix, which contains a large number of micro-fissures and fine pores along with a large amount of glassy phase
XRD: mullite SEM/EDS: skeletonized mullite containing elliptical and spherical pores characteristic of mullite derived from andalucite; mullite present in the matrix has a prismatic morphology and a variable crystal size with most crystals being small and needle-like but some crystals having a large rectangular shape due to crystal growth, the prismatic mullite crystals contain TiO 2 impurities and the glassy phase contains K 2 O, CaO, and TiO 2 Reduction in porosity,elimination of the microfissures, and appearance of cristobalite

ZED FMC RL&CL: large, medium and fine fu sed mullite grains; the matrix between the large grains contains poorly-sintered fine fused mullite particles as well as large amounts of micro-fissures along with small amounts of alumina and zirconia XRD: mullite plus trace alumina SEM/EDS: very small amounts of silica glass formation (with CaO imourities) along with secondary 1- to 2- μ m mullite crystal No change

ZED FM RL&CL: primarily fused mullite grains similar to the ZED FMC and trace amounts of alumina and zirconia particles; good particle to particle bonding XRD: mullite plus trace alumina SEM/EDS: strong mullite and glassy bonding, glass contains CaO No change

32Fig. 21. Thermal conductivity of mullite refractories as measured by the “hot-disk” method.

1.E-11 1.E-10 1.E-09 1.E-08 1.E-07

5.7E-04 5.8E-04 5.9E-04 6.0E-04 6.1E-04 6.2E-04 6.3E-04 6.4E-04 1/T (1/K) BP Mullite Frimul F MU75AF HF 17 GEM ZED FM DURITAL S75 UFALA UCR ZED FMC SL75AD

Fig. 22. Creep rate measured at 0.6 MPa as a function of reciprocal temperature.

33Activation energies for the various refractory br ands ranged from 50 to 200 kcal/mol. Although no direct correlation between the magnitude of the ac tivation energy and the amount of creep exhibited by a particular brand could be drawn from th e data, it is known that materials possessing a high activation energy have greater sensitivity to te mperature than those possessing a lower activation energy. The values for three of the calculated activ ation energies correspond to the activation energy of vitreous silica, which falls in the range of 120 to 170 kcal/mol [20, 21]. This would indicate that the glassy phases in these brands affect the overall creep behavior of the material.

As indicated in Table 10, all of the refractories except the SL75AD, UFALA UCR, and HF 17 brands exhibited no major changes after creep testing. Th e microstructure of the HF 17 appeared to be slightly denser. In the case of the SL75AD brand, th e andalusite grains were converted to mullite aggregates, and the amount of glassy phase increased in the crept specimens. The crept samples of the UFALA UCR refractory exhibited a reduction in porosity, the elimination of the microfissures, and the appearance of cristobalite. Additional details are provided in Ref. [11].

In subsequent aging tests, eight of the ten refract ory specimens exhibited similar behavior, with the ZED FMC and ZED FM showing extraneous amounts of change ( ≈ 8.5%) in mass and volume due to thermal exposure. The other eight brands showed less than 0.2% change in mass and less than 0.6% change in volume. The changes in volume resulted in less than a 0. 5% change in overall density for all samples, including the ZED FM and FMC brands . The two Minteq brands along with the Frimul F brand all exhibit activation energies associated with vitreous silica. They also exhibit the largest changes in mass, which may indicate that the silica plays some role in the temperature-induced mass changes.

Results from the ASTM lid test showed that only minimal amounts of recession occurred for the mullite refractories under the testing conditions set fo rth by the standard. Also, the mass change data were found to be ambiguous; some of the speci mens had deposits on their surfaces and actually gained weight while others lost a small amount of mass. Therefore, those data are not reported here. Figure 23 shows the small amounts of refractory recession occurring on the various refractory samples. It can be seen that the nonfused graine d refractories (Durital S75, SL75AD, and UFALA UCR) show a minimal amount of recession and some discoloring while the fused grained materials show practically no recession at all.



### 5.3 Fusion-Cast Al umina Refractories The density profiles (Fig. 24) for the Corh art and Monofrax bulk blocks based on the x and y cores (see Fig. 7 for sectioning details) showed a mean bulk density on the order of 3.4 to 3.5 g/cm 3 (212.3 to 218.5 lb/ft 3 ) at their surface. This density is fairly constant for the entire x 3 core and for the y core up to about 5 in. into the block for both cases. At the y core 5-in. mark the densities of both blocks begin to fall off due to porosity encountered in the header zones of the blocks. The x 7 cores for both blocks also showed similar behavior with a fair ly constant density in both cases up to around 3.5 in. and then a decline in density to around 3.3 g/cm 3 (206.0 lb/ft 3 ) for the Corhart block and to around 3.1 g/cm 3 (193.5 lb/ft 3 ) for the Monofrax block. Similar trends were seen in the porosity. If the columnar regions of the blocks are considered to exist in the outer 1 in. of the samples with the remainder of the block exhibiting bulk structure, then average columnar and bulk densities and porosities can be determined for each brand based on the previously described measurements. This determination

34DSF FRIMUL F DSF FRIMUL F

SL75AD GEM

UFALA UCR UFALA UCR DSF HF-17 DSF HF-17

Zed Mullite F Zed Mullite F MU75AF Zed Mullite FC Zed Mullite FC Durital S75 Durital S75 BP Mullite BP Mullite

ASTM Lid Test ASTM Lid Test 12.5g Na 12.5g Na 2 CO 3 for 24h at 1400°C for 24h at 1400°C 2 in.

Fig. 23. Refractory recession when exposed to sodium carbonate at 1400 o C for 24 h (according to ASTM C98).
would result in average columnar density values of 3.45 ± 0.05 g/cm 3 and 3.38 ± 0.02 g/cm 3 and average bulk density values of 3.45 ± 0.08 g/cm 3 and 3.37 ± 0.14 g/cm 3 for the Corhart and Monofrax brands, respectively. Average porosity values were found to be 1.38 ± 0.15% and 1.44 ± 0.19% for the Corhart columnar and bulk regions, respectively, and 2.64 ± 0.55% and 1.78 ± 0.92% for the Monofrax columnar and bulk regions, respectively. These values are close to those published by the manufacturers, although the density and porosity values obtained expe rimentally are a little lower for both brands (Corhart bulk density = 3.54 g/cm 3 and porosity = 2.0%, Monofrax bulk density = 3.40 g/cm 3 and porosity = 1.9%).

Density measurements were ma de on ten bulk Monofrax creep samples, ten bulk Corhart creep samples, two longitudinal columnar Monofrax creep samples, and two transverse columnar Monofrax creep samples. Porosity measurements were only ma de on five of each brand of bulk specimens and on representative samples for each type of columnarspecimens. For the Monofrax bulk material, an average apparent density of 3.44 ± 0.02 g/cm 3 (214.76 ± 1.25 lb/ft 3 ), and bulk density of 3.44 ± 0.01 g/cm 3 (214.60 ± 0.89 lb/ft 3 ) was found with an average porosity value of 1.82 ± 0.31%. An average apparent density of 3.48 ± 0.01 g/cm 3 (217.26 ± 0.69 lb/ft 3 ) and average bulk density of 3.48 ± 0.01 g/cm 3 (217.19 ± 0.75 lb/ft 3 ) with an average porosity of 1.47 ± 0.59% was found for the Corhart bulk material. These values are in line with those supplied by the manufacturers, but the experimental density value is slight ly higher and the experimental porosity value is slightly lower for the Monofrax material while both the experimental de nsity and porosity levels are slightly lower for the Corhart material (Monofrax bulk density = 3.40 g/cm 3 and porosity = 1.9%, Corhart bulk density = 3.54 g/cm 3 and porosity = 2.0%). The longitudinal columnar Monofrax material showed an average apparent density of 3.42 ± 0.01 g/cm 3 (213.51 ± 0.69 lb/ft 3 ), an average bulk density of 3.42 ± 0.01 g/cm 3 (213.35 ± 0.50 lb/ft 3 ), and an average porosity of 1. 06 ± 0.01%. The transverse columnar Monofrax material showed an average apparent density of 3.41 ± 0.01 g/cm 3 (212.89 ± 0.50 lb/ft 3 ), an average bulk density of 3.42 ± 0.01 g/cm 3 (213.29 ± 0.33 lb/ft 3 ), and an average porosity of 1.09 ± 0.21%.

35Corhart AB Regular Cast Block X And Y Core (1in. Segment) Densities

3.0 3.1 3.2 3.3 3.4 3.5 3.6

02468 Mean Depth (in.)Mean Bulk Density (g/cm3)

10 Y Core X 3in Core X 7in Core Beta Zone

PN 1503 Monofrax M Regular Ca st Block X And Y Core (1in. Segment) Densities

3.0 3.1 3.2 3.3 3.4 3.5 3.6

02468 Mean Depth (in.)Mean Bulk Density (g/cm3)

10 Y Core X 3in Core X 7in Core Beta Zone

Fig. 24. x 3-, x 7-, and y -core density profiles for the (a) Corhart refractory and (b) Monofrax refractory.

36The phase profiles of both refractories were measured by X-ray fluorescence (XRF) and XRD. For the x -direction profiles, the Corhart block showed large amounts of β -alumina (much greater than the mean pour stream chemistry of the melt) present in the outer 1 to 2 in. of the block and a lower (below the mean pour stream of the melt), more consistent, β -alumina content through the remainder of the block. In the case of the y core, there was an extremely large amount of β -alumina at the bottom block surface and a fairly consistent level of β -alumina in line with what was seen in the interior x -cores from ≈ 0.5 to 6.5 in. Beyond the 6.5-in. mark, the header of the block was encountered, and the β -alumina content increased to the original high level. The Monofrax block showed levels of β -alumina similar to the mean pour stream chemistry of the melt for all three cores up to ≈ 1.5 in. Beyond that point, the three cores all showed a lower β -alumina content, similar to what was seen in the Corhart block. This low level of β -alumina was sustained for the x 3 core but showed an increase at ≈ 4.5 in. for the x 7 core and at ≈ 6.5 in. for the y core. It is expected that the increase in β -alumina content was due to the cores entering the β -alumina-rich header region of the block, as seen in the Corhart block.

Patterns for bulk and columnar regions of Corh art M and Monofrax M could be matched to known peaks for corundum ( α -alumina) (PDF# 10-0173) and sodium aluminum oxide ( β -alumina) (PDF# 31-1263). Initially, optical microscopy was used to characterize the various co mponents present in the microstructure of the fusion-cast alumina blocks . It was found that both the Corhart and Monofrax ascast blocks displayed a similar variable microstructu re. As shown in Fig. 25, the bulk region of the blocks was composed of blocky α -alumina grains embedded in a continuous matrix of β -alumina while the columnar exterior regions we re composed of longer, more slender α -alumina grains embedded in the continuous β -alumina matrix.

Grain size analysis was performed on characteristic regions (bulk and columnar) of the two regularcast block brands. In-house LabViewTM software that relates the pixels contained in the area of each grain to a calculated average grain diameter in microns was used. For the Corhart columnar regions, 133 grains were analyzed, yielding an average grain size of 82 μm (3.2 mils) ± 43 μm (1.7 mils). The Monofrax columnar region had a similar average grai n size of 79 μm (3.1 mils) ± 46 μm (1.8 mils) based on the analysis of 164 grains. The bulk regi ons of the Corhart and Monofrax as-cast blocks exhibited a larger average grain size and showed more variation between the two brands. Analysis was carried out on 225 grains in various Corhart bulk regions, giving an average grain size of 172 μm

Fig. 25. Optical microscopy of characteristic grain structures for (a) bulk structure, and (b) columnar structure.

37(6.8 mils) ± 20 μm (0.8 mils). For the Monofrax bu lk regions, 179 grains were evaluated, yielding an average grain size of 231μm (9.1 mils) ± 47μm (1.9 mils).

It was originally hypothesized that the c -axes of the hexagonal α -alumina crystals in the columnar microstructural zone would all be aligned along the direction of rapid cooling, as indicated by the long dimension of the columnar crystals. This is in fact not the case, (i.e., Fig. 26). Through analysis of optical micrographs it was found that incomplete α -alumina grains in the microstructure actually have their c -axis aligned perpendicular to the cooling dir ection. The skeletal columnar grains were found to be polycrystalline (not single crystals) and to have their c -axes randomly oriented as additionally seen in the random habit of the α -alumina phase. The shape of these grains was found to therefore be due more to the cooling behavi or than the crystallographic direction.

Other optical images were taken showing the ne phelitic (calcium-aluminosilicate) grain boundary phase present between the α - and β -alumina phases and in isolated areas of the β -alumina phase. These areas appear as grayish, angular feat ures between grains and isolated in the β -alumina phase, as shown in Fig. 27.

Elastic modulus measurements we re generated by cyclic compre ssion. Supplemental values were generated for comparison by using a nanoindentation technique. At room temperature, an average value of 72 ± 4 GPa (10.4 ± 0.6 H 106 psi) was found for the Monofrax bulk material, while the Corhart bulk material showed an average value of 109 ± 7 GPa (15.8 ± 0.9 H 106 psi). The longitudinal columnar Monofrax samples gave an average value of 112 ± 12 GPa (16.2 ± 1.7 H 106 psi), while the transverse columnar yielded a value of 113 GPa (16.4 H 106 psi) based solely on specimen AG18. High-temperature testing was carried out on a sample from each of the above categories. Results from the high-temperature testing are shown in Fig. 28. As expected, in general the modulus decreased with increasing temperature. Unexpectedly, the modulus of the Monofrax bulk at 900°C (1652°F) was higher than that measured atroom temperature. This may suggest that the room-temperature modulus of the Monofrax bulk material should be higher (on the order of 140 GPa, 20.3 H 106 psi).

Nanoindentation measurements were made in each of the three phases ( α -alumina, β -alumina, and nephelitic grain boundary phase) for both the Co rhart and Monofrax bulk materials at room temperature. Three analyses were run in α -alumina grains (one Corhart and two Monofrax) and three in β -alumina grains (one Corhart and two Monofra x). Six analyses were run in nephelitic grain boundary regions (four Corhart and two Monofrax). All results are shown in Table 11. The modulus values obtained through nanoindentation of the alumina phases (214 – 442 GPa, 31.0 H 106 – 64.1 H 106 psi) were higher than those previously found for the bulk material by static and measurements (62 – 117 GPa, 4.6 H 106 – 17.0 H 106 psi). This may partly be due to the fact that in the nanoindentation measurements α - and β -alumina grains are individually sampled where in the other measurements, a composite of the bulk material was sampled. Also, it is documented that values found through nanoindentation are higher than those found through other methods simply due to the technique itself [22]. Regardless, the values are fair ly consistent between the different brands of material for each sample type and provide a me ans of comparison between the different components of the bulk structure. The α -alumina grains were found to have a much higher modulus than the β

alumina grains. The Corhart grain boundary samples also possessed a high modulus on the order of those values measured for the β -alumina grains ( ≈ 260 GPa, 37.7 H 106 psi), but the Monofrax boundary specimens had a modulus value more in line with the values measured previously for bulk materials with the static techniques ( ≈ 95 GPa, 13.8 H 106 psi).

38Fig. 26. Optical microscopy of columnar region (micron bar = 200 μm).

Fig. 27. Optical microscopy of nephelitic grain boundary phases.

39Young’s Modulus Values for Fusion-Cast Alumina Samples

Fig. 28. Static Young’s modulus valu es for fusion-cast al umina sample types.

Initial thermal expansion measurements were made from room temperature up to 900°C on high-purity (99.4%) alumina (theoretical coefficient of thermal expansion and temperature range = 8.2 H 10 ! 6 /°C) using the dual rod dilatometry technique to verify its calibration. Three measurements were made, yielding an average value of 8.7 H 10 ! 6 /°C. This was deemed sufficiently close to the theoretical value for experimental testing to continue. Table 11. Fusion-cast alumina nanoindentation results Young’s modulus (GPa) Grain

Corhart α -alumina 407 ± 15
Monofrax α -alumina 442 ± 13
Monofrax α -alumina 424 ± 14
Corhart β -alumina 237 ± 5
Monofrax β -alumina 214 ± 6
Monofrax β -alumina 231 ± 5 Corhart grain boundary 296 ± 13 Testing on Corhart and Monofrax M bulk material was initially carried out on specimens at 1450°C (2642°F) under the following schedule. Cylindrical samples were heated to temperature in a 4-h period and then held at temperature for 100 h. Following the soak period, the samples were cooled to room temperature through natura l cooling. Three tests were run on each commercial brand with the Corhart material, yielding an average value of 7.8 H 10 ! 6 /°C, and on the Monofrax bulk, yielding an average value of 8.4 H 10 ! 6 /°C. The values published by the manufacturers for Corhart M and Monofrax M are 11.1 x 10 -6 /°C and 7.9 H 10 ! 6 /°C respectively. Theoretically, α

alumina is anisotropic due to its hexagonal crystal structure and possesses thermal expansion values of 8.3 H 10 ! 6 /°C perpendicular to its c-axis and 9.0 H 10 ! 6 /°C parallel to its c -axis. $ -alumina has an isotropic thermal expansion value of 6.4 H 10 ! 6 /C.

Corhart grain boundary 269 ± 11 Corhart grain boundary 249 ± 11 Corhart grain boundary 240 ± 10 Monofrax grain boundary 97 ± 5 Monofrax grain boundary 92 ± 6

40Monitoring of the overall linear sample dimensions during the thermal expansion testing resulted in evidence of unrecoverable expansion of the specimens during exposure to temperature. Exposure for 100 h at 1450°C (2642°F) resulted in a 0.194% ch ange in length for Corhart M specimens and a 0.131% change in length for Monofrax M specime ns. Supplemental testing was performed at 1550°C (2822°F) and 1650°C (3002°F) to evaluate the unrecove rable expansion at those temperatures. Again, cylindrical specimens were heated to temperature in a 4-h-period and then held at temperature for over 100 h before being allowed to return to ro om temperature through natural cooling. Testing revealed that exposure for 100 h at 1550°C (2822°F) resulted in a 0.2151% change in length for Corhart M specimens and a 0.357% change in le ngth for Monofrax M specimens. Exposure for 100 h at 1650°C (3002°F) resulted in a 0.268% change in length for Corhart M specimens and a 0.396% change in length for the Monofrax M specimens. The results for the bulk Corhart and bulk Monofrax refractories are summarized in Figs. 29(a) and 29(b), respectively.

The transient technique was used to make ther mal conductivity measurements on both cylindrical creep specimens and on sectioned pieces of the origin al as-cast blocks. Two bulk creep cylinders and one sectioned piece with both cut surfaces and original surfaces were sampled for each brand. Results from original surfaces are thought to give measurements re presentative of the columnar structure with a parallel orientation to the direction of measurem ent (longitudinal columnar). Results from the center of the cut surfaces are representative of the bulk stru cture, and measurements on the edges of the cut surfaces yield values indicative of the columnar st ructure with a perpendicular orientation to the direction of measurement (transverse columnar). For the creep cylinders, measurements were taken on each sample by the single-sided method and be tween both samples by the standard method.

Sets of three single-sided measurements on the tw o bulk creep cylinders (B1 and B2) yielded average thermal conductivity values of 5.91 ± 0.10 and 5.97 ± 0.04 W/mK, respectively. The three standard measurements taken between the two cylinders ga ve an average value of 6.00 ± 0.11 W/mK. These values agree well with the sectioned block measurements of 6.04 to 6.21 W/mK. Measurements on the longitudinal and transverse columnar microstructures yielded average values of 7.10 and 5.82 W/mK, respectively. The differences in ther mal conductivity values between the two columnar microstructures and the bulk structure are thought to be due to the varying contributions and orientations of the " - and $ -alumina grains in the three different cases.

The piece sectioned from the Corhart block was analyzed along two vertical lines on the cut surface. One was taken along the edge of the surface and the other 3 in. in from the edge. Measurements taken along the edge of the cut surface (line along surface) correspond to the columnar microstructure with a perpendicular orientation to the direction of measurement (transverse columnar). Measurements taken along the 3-in. line are representative of the bul k microstructure except for material in about the first inch. Measurements along that region contain transverse columnar structure due to interaction with surface OS1 (Fig. 30), and the measurements ma de above 7.0 in. are in the header microstructure. The results indicate that the transverse co lumnar microstructure had an average thermal conductivity ranging anywhere from 5.04 to 7.46 W/mK . The lower values occurred at the top of the block, in the vicinity of the header region and were due to the increased porosity in this region and therefore are not considered representative of the actual thermal conductivity of the transverse columnar structure. Thus the average thermal conductivity values are in the range of 6.50 to 7.50 W/mK. If it is hypothesized that the " -alumina columnar structure controls the conductivity in these regions to varying degrees, then these higher values would make sense because the " -alumina grains will possess a higher thermal conductivity than the $ -alumina matrix, thus raising the overall thermal conductivity of the material. The same phenomenon is seen in the sectioned Monofrax block for the longitudinal columnar microstructure. For cut block surfaces, this is considered to be the case because the harder " -alumina grains protrude slightly from the block surface (as seen by the intensity differences in optical microscopy). The slight protrusion would then cause the " -alumina grains to

41Fig. 29. Specimen elongation as a function of time for (a) the bulk Corhart and (b) the bulk Monofrax refractories. The curves represent mathematical fits to the experimental data as described in J. G. Hemrick, “Creep Behavior and Physical Characterization of Fusion-Cast Alumina Refr actories,” Ph.D. dissertation, University of Missouri-Rolla, 2001.

42Fig. 30. Monofrax thermal conductivity block section denoting test surfaces. Parentheses denote hidden surface. Dotted lines designate positions of line scans (os = original surface; cs = cut surface).

dominate the thermal conductivity measuremen ts made on these surfaces and would cause the “composite reading” to be higher than expected.

In the case of the 3-in. line, the bulk microstructure of the Corhart material had an average thermal conductivity on the order of 6.25 to 7.10 W/mK with a mean value of 6.78 W/mK. The higher values in the bulk region may be due to direct measurements of the " -alumina grains as opposed to measurements for areas containing both " - and $ -alumina grains. Therefore, it is thought that the actual bulk thermal conductivity of the bulk Corhart material is on the order of 6.61 W/mK because the continuous $ -alumina phase should dominate the conductivity behavior. Due to the high void content, the thermal conductivity in the header region fell from approximately 5.00 W/mK down to approximately 0.25 W/mK.

The laser flash method yielded thermal diffusivity /conductivity values from room temperature up to 1400°C for both the Corhart and Monofrax bulk as-castmaterials. Two measurements were taken at each temperature value on separate samples with 15 temperatures being measured. Specific heat measurements were also made from room temperature up to 1400°C using a calorimeter method. Plots of the change in thermal conductivity with temperature are shown for the Corhart and Monofrax materials in Fig. 31. The thermal conductivity of th e Corhart material at room temperature was higher than that measured by the transient method (9.0 W/mK as opposed to 6.6 W/mK). This value then decreased to just above 4.0 W/mK at 600°C (1112°F) and then slowly increased to about 7.0 W/mK at 1400°C (2552°F). The thermal conductivity of the Monofrax material was much more consistent. The room-temperature value, measured to be on the order of 6.0 W/mK was similar to that determined from the transient method. The value for the Monofrax sample dropped slightly to around 4.0 W/mK, as it did for the Corhart material, but at a lower temperature, only 100°C (212°F). The thermal conductivity was relatively constant until 900°C (1652°F), at which point the value began to increase to around 6.0 W/mK at 1400°C (2552°F).

The compressive creep curves for the Corhart bulk specimens at 1450°C exhibited a period of rapid strain accumulation followed by a leveling off of th e accumulated strain. The total accumulated strain and the associated length of time over which the rapi d strain accumulation occurs was expected to be related to the applied stress state. This was not always found to be the case. For example, the creep response at 0.8 MPa was significantly lower than th e response at 0.6 MPa. In the case of the curves obtained at 1550°C, the strain accumulation also e xhibited a leveling off with time. However, for a given time, the amount accumulated strain increased with increasing stress, predicted by the creep equation. The creep curves generated at 1650°C were different from those obtained at the lower

43Fig. 31. Average laser flash thermal conductivity for as-cast bulk refractories: (a) Corhart and (b) Monofrax.
temperatures. Both the 0.6-MPa and 0.8-MPa curves exhibited similar behavior, initially showing large amounts of accumulated strain followed by a le veling off at 100 and 150 h, respectively. In both cases a larger amount of total accumulated strain was seen under these stresses than at either 1450°C or 1550°C. The 1.0-MPa curve showed an increase in accumulated strain followed by a region of constant negative slope. This was the first test in which traditional creep behavior was exhibited. Similar trends were observed for the bulk Monofrax specimens.

In the case of the Monofrax refractory, creep curv es were obtained for longitudinal and transverse columnar samples at both the low (1450°C, 6 MPa) and high (1650°C, 1.0 MPa) extreme matrix conditions, with an additional tran sverse columnar sample being tested at 1450°C and 1.096 MPa. For

44the curves at 1450°C, both the transverse and longitu dinal columnar samples showed similar behavior at 0.6 MPa with a small amount of accumulated strain being followed by a leveling off of accumulation after ≈ 150 h. The total amount of accumulated strain was about half as much as that for both the Corhart and Monofrax bulk samples under si milar conditions. The plot of the transverse columnar specimen at 1.0 MPa showed an increase in accumulated strain over that seen at 0.6 MPa and a sharp leveling off of the strain accumulation at an earlier point ( ≈ 50 h). The total accumulated strain in this sample ( ≈ 0.05%) was much lower than that seen in both Corhart and Monofrax bulk samples under similar conditions (0.09 and 0.13% , respectively). At 1650°C both 1.0-MPa curves showed similar behavior to that seen in the Co rhart and Monofrax samples under similar conditions, although the rate of accumulated strain was lower in the columnar cases, resulting in lower total accumulated strains. This behavior included an incr ease in accumulated strain followed by a region of accumulated strain characterized by a cons tant slope and traditional creep behavior.

Based on the above observations, it is clear that nontraditional creep behavior was exhibited by fusion-cast alumina under most test conditions (those below 1650 E C/1.0 MPa). This behavior was thought to be due to the unrec overable expansion phenomenon show n in Fig. 29. Based on those premises, plots were constructed incorporating both the expansion effects and creep effects seen by each material under the various test conditions and the composite effect resulting from the combination of these two concurrent mechanisms. Such plots are shown below for both Corhart (Fig. 32) and Monofrax (Fig. 33) bulk specimens. These plots were constructed by subtracting a similar exponential fit of the measured expansion cu rve as determined by dilatometry at each test temperature from the modeled creep curves at each stress of the representative same temperature.

Fig. 32. Combined plots of expansion and creep effects in Corhart bulk samples

.

45Fig. 33. Combined plots of expansion and creep effects in Monofrax bulk samples.

The new curves predict a greater creep resistance in the Monofrax bulk material at 1450°C (better by

≈ 0.20%), but a greater creep resistance in the Corhart bulk material at 1550°C (better by ≈ 0.15%) and at 1650°C (better by ≈ 0.10%). However, this may not be an accurate portrayal of the creep behavior exhibited by these materials. It must be remembered that the behavior exhibited by these materials in service would still be represented by the measured creep curves. Therefore, by performing the analysis in this fashion, it may be possible to produce creep curves that possess a steady-state, non-zero creep regime from which a model can be conceived by using a traditional method such as the NBA equation. Doing so will not capture the actual behavior exhibited by this material, however, because any model must incorpor ate the effect of the expansion along with the creep. A model is needed that can handle the hi gh degree of nonlinearity seen in the measured creep curves generated for fusion-cast alumina while also being sensitive to the transient nature of the data because no equilibrium state is in effect.

Several samples were analyzed after being crept, and results were compared with those previously obtained from virgin samples. Analysis included thermal conductivity, optical microscopy, and SEM/EDS chemical analysis. The thermal conduc tivity values for the Monofrax post-creep cores were similar to those obtained earlier from the virgin cores, which had thermal conductivities in the range of 5.9 W/mK. The value obtained from the Corh art post-creep core was significantly lower than the average value of 6.61 W/mK found earlier for the Corhart bulk material.

Initial optical microscopy and SEM/EDS analyses were performed on Corhart and Monofrax bulk samples exposed to 1550°C and 1.0 MPa. This work was conducted to determine whether any

46changes in the microstructure or chemistry coul d be detected at that intermediate condition. SEM/EDS analysis was then used to determine wh ether analysis needed to be performed on samples at the lower temperatures and stresses. No discernible deformation and only slight chemical changes were seen in the samples.

Subsequent optical microscopy and SEM/EDS an alyses were performed on Corhart and Monofrax bulk samples exposed to the extreme conditions of 1650°C and 1.0 MPa. The structure of the Corhart sample was found to resemble the virgin structure, while the Monofrax crept structure displayed a smaller

α -alumina grain size and a tighter α -alumina grain structure with more equiaxed angular grains than previously observed in the virgin structure. More severe chemical changes were also seen between the virgin and crept samples.



### 5.4 Fusion-Cast Sp inel Refractories Engineering creep data for selected refractory materials was generated to a temperature of 1650°C in ambient air. Tests for the fusion cast material at 1650 o C and 3.0 MPa. One test was run on bulk material and one was run on columnar (with the st ructure running parallel to the loading direction). There is some initial movement due to the applica tion of the load [the samples were heated to temperature under low load (30–50 lb) and were a llowed to dwell for 24 h before the main load (768.909lb) was applied], then very little creep over the time of testing. The test frame was refitted with a larger air cylinder and load cell to enable testing at higher loads in an attempt to get this material to creep. Also examined was the effect of using smaller samples to obtain higher loads.

The behavior exhibited by the transverse columnar structure was not as expected (Fig. 34). It was expected to be similar to the behavior of the l ongitudinal columnar sample with perhaps even less accumulated strain. Instead, the behavior is more si milar to that of the bulk structure with about the same amount of total accumulated strain but a slower initial rate of strain accumulation. Curves from two separate samples both show the same initial st rain accumulation, showing that the results are repeatable. Rather than analyzing the final 100 h of th e test, all the data available past 100 h of testingwere analyzed (Table 12). This analysis provided a better representation of the apparent “steadystate” creep rates exhibited by these materials. There was a plot of this analysis included as well. The conclusion was that the fusion-cast material does not creep (even at 8.5 MPa). There was more initial strain due to application of the load (~ 3% mo re, which corresponds with the increase from 3 to 8.5 MPa), but there was not a change in steady-state creep rate with the increased load. The creep rate for the longitudinal columnar structure was lower, but the transverse columnar st ructure showed a creep rate similar to that of the bulk structure. The bonded material showed significant creep and was far inferior to the fusion-cast material, as shown in Figs. 35, 36, and 37.

Thermal diffusivity measurements were made by the laser flash method. Density and thermal diffusivity are required as input into the calculation of thermal conductivity. The density of the fused cast spinel was measured as 3.47 g/cc with a porosity of 2.3%. The density of the columnar structure and bulk structure were 3.47 g/cc and 3.5 g/cc with porosities of 2.1% and 2.5%, respectively. The density of the bonded spinel was measured as 3.04 g/cc with a porosity of 14.2%. The calculated thermal conductivity results are shown in Fig. 38.

47Table 12. Calculated strain rates
Material Temperature (°C) Stress (MPa) Strain rate

1.27 × 10 -6 /h Fused spinel longitudinal Columnar 1650 3.0

4.27 × 10 -6 /h Fused spinel transverse columnar 1650 3.0
5.66 × 10 -6 /h Fused spinel bulk 1650 3.0
5.00 × 10 -6 /h Fused spinel bulk 1650 8.5
48.0 × 10 -6 /h Bonded spinel bulk 1650 0.07
8.89 × 10 -6 /h Bonded spinel bulk 1550 0.06
23.8 × 10 -6 /h Bonded spinel bulk 1550 0.3

Fusion Cast Spinel (1650 o C)

-3 -2.5

-2 -1.5

-1 -0.5 0

0 50 100 150 200 250 300 Time (hours)Accumulated Strain (%)

Bulk (3.0 MPa)

Longitudinal Columnar (3.0 MPa)

Transverse Columnar (3.0 MPa)

Bulk (8.5 MPa)

Fig. 34. Fused spinel accumulated strain curves.

Bonded Spinel (1650 o C, 0.07 MPa)

-2.5

-2 -1.5

-1 -0.5

0

0 5 10 15 20 25 Time (hours)Accumulated Strain (%) Application of 3.0 MPa Load

Failur

Fig. 35. Bonded spinel accumulated strain curve at 1650°C.

48Bonded Spinel (1550 o C, 0.06 MPa)

-0.1 -0.09 -0.08 -0.07 -0.06 -0.05 -0.04 -0.03 -0.02 -0.01

0

0 5 10 15 20 25 Time (hours)Accumulated Strain (%)

Fig. 36. Bonded spinel accumulated strain curve at 1550°C.

Bonded Spinel (1550 o C, 0.3 MPa)

-1.2

-1 -0.8 -0.6 -0.4 -0.2

0

0 50 100 150 200 250 300 350 Time (hours)Accumulated Strain (%)

Discontinuity due to gage problem

Fig. 37. Bonded spinel accumulated strain curve at 1550°C.

490 2 4 6 8 10 12 14 16

0 200 400 600 800 1000 1200 1400 Temperature (C)Thermal Conductivity (W/mK) Bonded Fused Columnar Fused Bulk

0 0.005

0.01 0.015

0.02 0.025

0.03 0.035

0.04 0.045

0.05

0 200 400 600 800 1000 1200 1400 Temperature (C)Thermal Diffusivity (cm2/sec) Bonded Fused Columnar Fused Bulk

Fig. 38. Thermal diffusivity of fused and bonded spinel.

The creep specimens were subjected to detailed mi crostructural and phase analysis. One objective of this task was to better understand how creep and co rrosion behavior relates to microstructure and microchemistry. X-ray diffraction data showed little differences in the patterns between the “as supplied” and “exposed” samples. The spinel peaks were slightly shifted due to heat treatment and stress relief. There were no additional phases found after exposure.

The sintered spinel brick was made from high-purity large fused spinel grains. The matrix contained 16% to 18% porosity but was well sintered. No im purity phase (forsterite, monticellite, merwinite or melilite) was identified/recognized at the magnificat ion scale of RL/CL microscope used. This does

50not, however, exclude the presence of small amount s of glassy or ternary phases, which would coat the smaller spinel grains in the matrix. In general, the fused spinel block consisted of spinel and magnesia. The presence of free magnesia or magnesia in clusions suggests that the liquid was rich in MgO. The composition of spinel was also expected to be rich in MgO. Due to the rapid cooling or crystallization columns of spinel skeletons were formed and the magnesia was segregated as tiny inclusions within these skeletal spinel columns. Such rapid crystallization appeared as linear or locally oriented features in the fused block. The orientation of these skeletal spinel columns was, in general, also random. In a single section both tran sversal or longitudinal microstructures were observed. For example, Fig. 39 shows a diagonal (N W to SE) crystallization feature. Although spinel (green CL) crystals still exhibit random orientati on, overall there is a diagonal (in these micrographs) feature developed during crystallization of sp inel liquid. These micrographs illustrate the microstructure of rapidly crystallized spinel colu mns sectioned perpendicularly along the axis of the column.

Fig. 39. RL (left) and CL (right) images of fused spinel.

51

## 6. Accomplishments

6.1 Research-Based Accomplishments This study led to significant improvements in th e resolution of the techniques commonly used to measure thermal expansion and creep of refractori es. For example, the “S tandard Test Method for Load Testing Refractory Brick at High Temperatures” involves loading a refractory brick for a prescribed duration and temperature and then determining the material’s resistance to deformation by comparing its before- and after-test axial dimensions. A shortcoming of this test is the introduction of error in the analysis if the refractory brick’ s ends “bed-down.” The procedures and equipment recommended in the “Standard Test Method of Measuring the Thermal Expansion and Creep of Refractories Under Load” are similar to those used in the present study. A shortcoming of this procedure involves the recommended measurement of dimensional change in the creep specimen. The use of LVDTs to measure the contraction of the sp ecimen ends is advocated but can be problematic for reasons described previously. The extensometry system described in Fig. 2 of ASTM C832 closely matches the extensometry system used in the present study; however, in the present study a capacitance gage is used while in the standard the use of an LVDT for the measurement is shown. The load that activates an LVDT can be enough to affect the intimacy of the extensometer contact with the specimen and thus can yield a misleadi ng creep measurement if there is insufficient horizontal load applied to the specimen. Because of its differing operating principle, the capacitance gage on the extensometry systems used in the present study requires no load for activation and does not introduce uncertainties associated with the horizontal load and the use of an LVDT.

This study also identified new mechanisms respons ible for deformation of fusion-cast alumina and silica refractories in the absence of an applied stress. For both refractories these mechanisms led to expansion of the test specimens in the absence of an applied stress.


### 6.2 Technology Transfer The results of this project have established hardware and a test methodology that can be used by the refractories community to evaluate the creep and aging behaviors of most refractory materials. Of particular merit is the development of specia lized extensometry, which offers extremely high resolution required for the measurement of small de formations. The project staff made presentations at national meetings and published resu lts in industry technical journals.



### 6.3 Publications and Patents
[1] A. A. Wereszczak, T. P. Kirkland, G. A. Pecoraro, and R. A. New, “Compressive Creep Behavior of Fusion-Cast Alumina Refractories,” pp. 401–406 in Ceramic Transactions, Vol. 82, Advances in Fusion and Processing of Glass II, ed. A. G. Clare and L. E. Jones, American Ceramic Society, Westerville, Ohio (1998). [2] A. A. Wereszczak, T. P. Kirkland, and W. F. Curtis, “Compressive Creep Resistance of MgO Refractories at Temperatures ≥ 1400°C (2550°F),”pp. 407–412 in Ceramic Transactions, Vol. 82, Advances in Fusion and Processing of Glass II, ed. A. G. Clare and L. E. Jones, American Ceramic Society, Westerville, Ohio (1998). [3] A. A. Wereszczak, T. P. Kirkland, and W. F. Curtis, “Creep of CaO/SiO 2 - Fluxed MgO Refractories,” J. Mater. Sci (1998) in press.

53[4] A. A. Wereszczak, M. Karakus, K. C. Liu, B. A. Pint, T. P. Kirkland, and R. E. Moore, Compressive Creep Performance and High Temperatu re Dimensional Stability of Conventional Silica Refractories , ORNL/TM-13757, Oak Ridge National Laboratory (1999). [5] J. G. Hemrick, A. A. Wereszczak, M. Karakus, K. C. Liu, H. Wang, B. A. Pint, T. P. Kirkland, and R. E. Moore, Compressive Creep and Thermophysical Performance of mullite Refractories
, ORNL/TM-2002/84, Oak Ridge National Laboratory (2002). [6] J. G. Hemrick and A. A. Wereszczak, “Compressive Creep of Fusion-Cast Alumina as a Function of Microstructure,” Glass Industry (November 1999). [7] J. G. Hemrick, “Creep Behavior And Physical Characterization Of Fusion-Cast Alumina Refractories,” a Dissertation Presented to the Facult y of the Graduate School of the University of Missouri-Rolla in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Ceramic Engineering (2001).



### 6.4 Commercialization The data generated in this proj ect were provided to participating refractory manufacturers and are available from those manufacturers to any users of these types of refractories. It has been confirmed with industrial partners involved in this project that creep data and other thermomechanical property information generated as part of this project was u sed in analysis of glass fu rnaces currently in service and for the planning and design of refractory system s for future furnace constructions. The data has not only been used by glass comp anies in their analysis and planning of furnace systems, but by refractory companies and industrial consultants as we ll. The information generated was said to be “invaluable” by one industrial participant and more data of similar scope is felt to be of general interest to the industry as a whole.

54

## 7. Summary and Conclusions

7.1 Silica The creep and corrosion performances of the six re fractories were examined. The bulk characteristics of the refractories were then characterized before and after their creep testing in an attempt to correlate their changes to the measured creep responses. Bulk density, phase c ontent, microstructure, and secondary phase composition were examined, and th eir changes as a function of test temperature were analyzed. Lastly, the effect of temperature on the dimensional stability of these refractories was examined. Specimens were aged at the same temperatures that the creep tests were performed. The procedures used and the results generated are discussed.

• The amount of compressive creep of Gen-Sil, St ella GGS, Vega, Vega H, and Harbison-Walker’s new developmental brand (flux factors less than 0. 5% or “Type A” for all five of these brands) conventional silica was negligible at temper atures between 1550 and 165 0°C (2820–3000°F) and at compressive stresses from 0.2 to 0.6 MPa (29–57 psi). Only one specimen per condition was tested, so the authors were unable to statistically conclude that any one of the five brands had superior creep resistance to the others; however, if differences do indeed exist, then they are believed to be insignificant. • The compressive creep of SI96AU (flux factor greater than 0.5% or “Type B”) conventional silica was negligible at 1550°C. However, SI96 AU deformed (contracted) by more than 20% at 1600°C at stresses between 0.2 and 0.6 MPa. This beha vior was inferior to that of the other five tested brands. SI96AU was not creep tested at 1650°C; however, its creep deformation was expected to still be inferior to the other five silica brands. • The compressive creep rates of all six brands were not able to be represented as a function of temperature and compressive stress by the conve ntionally used NBA creep equation (i.e., the Arrhenius power-law creep model). Concurrently active mechanisms other than creep, resulted in larger or oppositely anticipated dimensional cha nges than those produced by creep; this effect limited the ability to identify or interpret th e lesser-active creep mechanism in these silica refractories. Models other than NBA (or equivale nt “creep” models that represent creep rate as a function of temperature and stress) should be used to represent or predict the long-term dimensional stability of conventional silica supers tructures that are subjected to compressive stresses less than 0.6 MPa and temperatures between 1550 and 1650°C. • The change in dimensions of the compressively crept specimens indicated that their size (both diameter and length) had actually increased as a consequence of the creep test conditions. The relatively large amount of expansion of the sp ecimen diameters could not have been a sole consequence of “compressive creep barreling” because some specimens did not contract at all, and those that did not contract enough to cause a Poisson effect. All six brands showed this expansion effect. The increases in diameter and length of the creep specimens were between 0.35 and 1.0%. Only a fraction of the expansion was detected during the compressive creep testing. This indicates that most of the permanent expa nsion exhibited by the silica specimens occurred during their heating from ambient to the creep-tes ting temperature or during the cooling from test temperature to ambient. • The secondary phase constituents remained in a ll brands when they were tested at 1550°C (cumulative time at temperature approximately 250 h). A fraction of these phases visibly evolved from the specimens at 1600°C (slight glass bubbling on the specimen and fixturing). This phenomenon was quite severe at 1650°C. The density ch anges in the crept specimens (a net effect of the volume expansion and loss in secondary phase mass) ranged from a decrease of 1.6 to

553.9% with a subtle trend of gr eater density decreases at higher test temperatures. The density decreases among the six brands were statistica lly equivalent within the data scatter. • The cause of the volume expansion was not iden tified; however, because of the absence of quartz it can be concluded that the expansion was not due to quartz (a relatively high-density phase) converting to tridymite or cristobalite (lower-d ensity phases). The authors speculate that the volume expansion is due to the high-temperature process of the conversion of tridymite to cristobalite and the consequential growth of th e residual pores and the original cristobalite aggregates. • Unstressed or “aged” silica refractory specimens from all six materials also exhibited a loss of mass, dimensional increases, and dens ity decreases between 1550 and 1650°C. - The mass losses of the six brands at 1550 and 1600°C were equiva lent; however, some silica brands lost more mass than others at 1650°C: Harbison-Walker’s developmental brand lost approximately 0.1% of its mass; SI96AU lost ≈ 0.2%, Vega H lost ≈ 0.3%, Gen-Sil lost ≈ 0.5%, Vega lost ≈ 1.0%, and Stella GGS lost ≈ 1.5%. Most of the mass loss for all six brands occurred in less than 25 h. - The dimensional increases of the silica specimens were a function of temperature. Additionally, some brands expanded more th an others. The ranges of expansion were

≈ 1–2.5% at 1550°C, ≈ 2.25–3.75% at 1600°C, and ≈ 3.5–6% at 1650°C. Harbison-Walker’s developmental brand e xpanded the least amount at all three temperatures, followed by Gen-Sil. The ascending order of expansion for the other four brands varied with temperature. Stella GGS expanded the most at 1550°C ( ≈ 2.5%), SI96AU expanded the most at 1600°C ( ≈ 3.75%), and Vega expanded the most at 1650°C ( ≈ 6%). Dimensional increases were greater than axial expansion of the crept silica specimens at the same temperatures, i ndicating that the axially applied compressive load during creep testing resulted in some specimen contraction. - The density decreases of the silica specimens were a function of temperature. Additionally, some brands became less den se than others. The changes in density are a consequence of the above-described changes in mass and volume. The ranges of density decreases were

≈ 1–2.75% at 1550°C, ≈ 2.25–4.0% at 1600°C, and ≈ 3.5–7.0% at 1650°C. The density of Harbison-Walker’s developmenta l brand changed the least of the six brands at all three temperatures. The ascending order of density for the other five brands varied with temperature. The density of Stella GGS decreased the most at 1550°C ( ≈ 2.75%), that for SI96AU decreased the most at 1600°C ( ≈ 4%), and that for Vega decreased the most at 1650°C ( ≈ 7%).

• The corrosion resistances of the six silicas were statistically equivalent when they were exposed to sodium carbonate at 1400°C (2550°F) for 24 h. The amount of recession increased linearly with temperature between 1250 and 1450°C for the Gen-Sil silica.



### 7.2 Mullite Compressive creep testing of ten commercially av ailable mullite refractories was performed at 1300 to 1450 o C and at static stresses between 0.2 and 0.6 MPa. The mullite refractories were examined because they are used in borosilicate glass furnace crowns and superstructures as well as in sidewall applications. Additionally, despite their high cost ( ≈ $500/ft 3 ), they are cheaper than other refractories such as chrome alumina ( ≈ $3000/ft 3 ) or fusion-cast alumina ( ≈ $900/ft 3 ), which are used as replacements for traditional silica refractories in harsh oxy-fuel environments. Corrosion resistance was also evaluated. In addition, measurements we re made that tracked their dimensional stability, phase content, microstructure, and composition as a function of temperature and time. The techniques used for these characterizations and th eir respective analyses are described.

56An intent of this study was to provide objective and factual results whose interpretations were left to the reader. The salient observations and conclusions are as follows.

• The amount of compressive creep for the BP mullite, Durital S75, and Frimul F brands was found to be low at temperatures between 1300 and 1450 o C (2370 to 2640 o F) and at compressive stresses between 0.2 and 0.6 MPa (29 to 87 psi) . Creep rates were on the order of 10 ! 11 s ! 1 at the lower test temperature and on the order of 10 ! 10 s ! 1 at the higher test temperature. Only one specimen per condition was tested, so the authors were unable to statistically conclude that any one of the three brands had superior creep resistance to th e others; however, if differences do indeed exist, then they are believed to be insignificant.

• The amount of compressive creep for the GEM, HF 17, MU75AF, and ZED FM brands was found to be slightly higher than that for the thr ee refractories listed above, but still low at 1300 to 1450 o C and 0.2 to 0.6 MPa . Creep rates were on the order of 10 ! 10 s ! 1 at the lower test temperature and on the order of 10 ! 9 s ! 1 at the higher test temperature. The GEM brand specimen showed higher amounts of creep than the other three brands in this group and a low stress exponent (0.4). This places its behavior closer to that described next for the brands exhibiting significant amounts of creep. Again, only one specimen per condition was tested so the authors were unable to statistically conclude that any one of the other three brands had superior creep resistance to the others; however, if differences do indeed exist, then they are believed to be insignificant.

• The amount of compressive creep for the SL75AD, UFALA UCR, and ZED FMC brands was found to be significant at 1375 to 1450 o C and at 0.4 and 0.6 MPa. Creep rates were on the order of 10 ! 9 s ! 1 at the lower test temperature and on the order of 10 ! 8 s ! 1 at the higher test temperature. All three of these brands exhibited low stress e xponents (< 0.5) and changes in chemistry or microstructure due to the creep testing conditi ons. Only one specimen per condition was tested, so the authors were unable to statistically conclude that any one of the three brands had superior or inferior creep resistance to the others; however , if differences do indeed exist, then they are believed to be insignificant.

• Durital S75 was found to have a stress exponent of 2.4, indicating that the rate-controlling mechanism may be grain boundary creep. This is opposed to diffusion-controlled or Coble creep, which is expected to be the rate-controlling m echanism in the brands that exhibited a stress exponent of approximately unity (Frimul F, HF 17, and MU75AF).

• It is believed that the low-stress exponents seen for the BP mullite, GEM, SL75AD, UFALA UCR, ZED FMC, and ZED FM brands are due to a non-steady-state condition existing during the entire extent of testing. This condition is a con sequence of contraction or time-hardening effects occurring during testing and of the samples never reaching a state of equilibrium. The result is measurement of creep due to the applied compr essive stress coupled with contraction of the sample due to time-hardening effects. Therefore, the assumption of a single deformation mechanism being active at all temperatures and stresses is not valid, and multilinear regression falsely yields extremely low stress exponent values.

• The brands that possessed high levels of matr ix porosity (HF 17, UFALA UCR, and ZED FMC) all showed compaction of the microstructure due to creep testing. This is believed to be the reason for the poor creep resistance of the UFAL A UCR and ZED FMC brands. In addition, the UFALA UCR sample was found to possess a fine grain size, which could have contributed to the increased creep rate.

• SL75AD was found to be composed of andalus ite grains containing free quartz, which was converted to cristobalite during firing. Further, th e andalusite grains are fully converted to mullite during creep testing, and the amount of glassy ph ase increased. These events in combination may lead to the brand’s poor creep resistance.

57• Activation energies for the various refractory brands ranged from 50 to 223 kcal/mol. Although no direct correlation between the magnitude of the activation energy and the amount of creep exhibited by a particular bra nd could be drawn from the data, it is known that materials possessing a high activation energy have greater sensitivity to temperatur e than those possessing a lower activation energy. Also, the values fo r many of the calculated activation energies correspond to the activation energy of vitreous silica. This indicates that the glassy phases in these brands affect the overall creep behavior of the material.

• The distinction of a brand being fused-grained or non-fused-grained mullite did not appear to have a bearing on the creep resistance of the individual brands.

• Room-temperature thermal conductiv ity values were similar for all ten brands of mullite with the average being on the order of 3.1 W/mK [21.5 (Btu*in.)/(h*ft 2 * ° F)]. Frimul F was found to have the highest thermal conductivity at just below 3.5 W/mK [24.3 (Btu*in.)/(hr.*ft 2 * ° F)]. SL75AD, UFALA UCR, and ZED FM were found to have the lowest thermal conductivities at around 2.5 W/mK [17.4 (Btu*in.)/(hr.*ft 2 * ° F)].

• Eight of the ten refractory brands showed less than 0.2% change in mass and less than 0.6% change in volume due thermal aging in the absen ce of an applied load. The two exceptions, ZED FM and ZED FMC, exhibited extraneous amounts of change ( ≈ 8.5%) in both mass and volume due to thermal exposure. All samples showed a less than 0.5% change in bulk density.

• The corrosion rates of the ten mullite brands c ould not be determined through the use of ASTM C987, but it was determined visually that only minimal amounts of recession occurred due to exposure as defined by the ASTM lid test.



### 7.3 Fusion-Cast Alumina The creep and corrosion performances of the two br ands of M-type fusion-cast alumina refractories (Corhart Refractories of Louisville, Kentucky, a nd Monofrax, Inc., of Fa lconer, NewYork) were examined. All specimens were fabricated from re gular fusion-cast alumina blocks of approximate dimensions 0.60 H 0.50 H 0.30 m (24 H 20 H 12 in.). Key findings are summarized below.

• As expected, both the density and porosity of th e as-cast refractory blocks were highly consistent. The phase profiles for the α - to β -alumina ratios also showed similar trends to those seen in the density/porosity profiles. XRD showed that both brands consisted of only peaks identifiable as corundum (PDF# 10-0173) or sodium aluminum oxide (PDF# 31-1263). Closer examination of the XRD patterns showed that there were some differences in ratios of α - to β -alumina between the two brands and between the bulk and columnar microstructures. The microstructures of the two brands of refractory were also comparable w ith a columnar region existing in the outer 11⁄2 in. of the blocks and then transitioning to a more equiaxed structure of α -alumina grains floating in a β -alumina matrix as sampling moves into the cente r of the block. Average grain sizes were found to be on the order of 172 μm and 82 μm for th e Corhart bulk and columnar regions, respectively. Average grain sizes were found to be on the order of 231 and 79 μm for the Monofrax bulk and columnar regions, respectively. • With exception of the Monofrax bulk material, all of the elastic modulus values obtained by static testing (cyclic compression) at room temperature were similar, ranging from 109 to 113 GPa. Contrary to this, the Monofrax bulk material showed a significantly lower modulus at room temperature (72 GPa). These values are substantia ted by dynamic values obtained by resonant ultrasound spectroscopy. Although the room-tempera ture value is vastly different and the magnitude of the modulus values at elevated te mperatures for the bulk Monofrax is higher, the general trend of decreasing modulus with increasing temperature holds as it does in the other microstructures. Furthermore, the modulus valu e of the bulk Monofrax at 1400°C is approaching that of the other sample types, indicating that at even higher temperatures (like those experienced

58by these materials in service), the modulus values for the four microstructures may be virtually the same. • Thermal expansion values obtained for the two brands of fusion-cast alumina by the dual-rod dilatometry technique were found to be different from those published in the manufacturers’ literature, but both materials showed similar valu es of expansion. The Corhart material was found to have lower expansion (by ≈ 30%) than published; while the Monofrax material was found to have higher expansion (by ≈ 6%) than published. Based on the published values and the experimental results, it would seem that both mate rials have an experimental thermal expansion of around8.0 H 10 ! 6 /°C over the 500 to 1200°C temperature range. • Room-temperature thermal c onductivity measurements produced by the transient plane source (“hot disk”) technique show the Monofrax bulk material to possess a lower thermal conductivity (on the order of 6.00 to 6.25 W/mK) than the Corhart bulk material (mean value of 6.78 W/mK). The columnar structures in the Corhart block show a range of thermal conductivities between 6.50 and 7.50 W/mK. This is similar to the values obtained for the longitudinal columnar measurements made on the Mono frax block (average = 7.10 W/mK). Values on the transverse columnar structure of the Monofrax block (average = 5.82 W/mK) were lower than those of the two bulk microstructures and lower than those of the Corhart columnar and Monofrax longitudinal columnar microstructures. These results indicate that the columnar structure is not as well oriented in the Corhart blocks as in the Monofrax blocks. • Laser-flash thermal diffusivity/conductivity valu es show a gradual trend moving from the low- to elevated-temperature data. A change in ther mal conductivity from decreasing to increasing slope was seen, as is common in materials where the mechanism controlling thermal conductivity changes with temperature. It is expected that the mechanism controlling the sign of the curves’ slope changes from conduction to radiation. Further, this behavior is characteristic of a material that contains microcracking. The presence of microcracks initially lowers the thermal conductivity of the material, but as the material is exposed to elevated temp eratures, the “healing” of the microcracks will cause therma l conductivity values to increase. • The Monofrax material was found to be slightly more creep-resistant than the Corhart material at 1450°C and 0.6 and 1.0 MPa. The advantage in creep resistance is only slight (0.03% strain at the most extreme) and can be considered negligible in relation to the magnitude of deformation it would cause in a furnace crown. Behavior of the 0. 8-MPa samples is similar with both brands of material, showing an initial period of increas ed strain accumulation followed by a sustained period of decreasing strain accumulation. The final amount of accumulated strain for both brands is also similar, causing the overall trend of the 0.8-MPa curves to show considerably less total accumulated strain than both the 0.6- and 1.0-MPa curves. • Similar behavior occurs at 1550°C, where the Corhart material initially accumulates strain at a more rapid rate but the total accumulated strains for both materials are nearly identical, further negating any advantage the Monofrax material may hold over the Corhart material. • At 1650°C, the behavior of both brands is nearly identical for both 0.6- and 0.8-MPa stresses; all of the curves overlap one another, and neither mate rial shows even a slight advantage. All three of the 1.0-MPa curves display traditional creep be havior, which is not seen in any of the other bulk test conditions. • Both columnar orientations show much l ess accumulated strain than the bulk samples under similar stresses. This is due to the elongated n eedle-like grains, which are oriented perpendicular to the direction of the applied compressive load, acting to inhibit creep in the transverse columnar samples. In the longitudinal columnar case, it is expected that the unrecoverable expansion effect plays a role in the reduced strain accumulati on. The columnar samples at 1650°C show less accumulated strain than the bulk sample under similar stress, but the behavior between the bulk and columnar samples is more similar. Both microstructures show traditional creep behavior under 1.0 MPa of stress and much larger amounts of accumulated strain than the bulk samples at 0.6 and 0.8 MPa.

59• The three bulk 1650°C/1.0-MPa samples all have a similar creep rate; the rate for the Corhart material is on the order of 5 H 10 ! 6 h ! 1 , and that for the Monofrax material is on the order of 6 H 10 ! 6 h ! 1 . The columnar structures at 1650°C/1.0 MPa have a lower creep rate, on the order of 4.25 to 4.50 H 10 ! 6 h ! 1 . Creep rates for the other samples were not obtainable because nontraditional creep behavior occurred. Stress exponents and ac tivation energies could not be calculated from this data because steady-state creep rates were only obtained at one stress and temperature. • The combined expansion/creep plots predict a greater creep resistance in the Monofrax bulk material at 1450°C (better by ≈ 0.20%), but a greater creep resistance in the Corhart bulk material at 1550°C (better by ≈ 0.15%) and at 1650°C (better by ≈ 0.10%). These predictions may not be an accurate portrayal of the creep behavior exhi bited by these materials. Behavior exhibited in service would still be represented by the measured creep curves. • Unrecoverable expansion was seen in all mate rials, and is thought to be connected to the nontraditional creep behavior seen in the compress ive creep testing at temperatures up to 1650°C and loads up to 0.8 MPa. As the temperature increases, the amount of unrecoverable expansion also increases such that when samples are heated and immediately cooled with no hold time at temperature, no unrecoverable expansion occu rs. The mechanism causing the unrecoverable expansion effect occurs during the prolonged e xposure of the sample to high temperatures and therefore would be of great importance during cr eep testing and during service of a brick in a furnace campaign. The occurrence of this unrecoverable expansion is thought to be caused by thermal expansion hysteresis due to microstresses or microcracking. • The data generated in this work for fusion-cast alumina refractories are unique in that very little data of that kind has been generated. The behavior exhibited by this material is highly transient due to the non-steady-state nature of the material (it fails to reach equilibrium). Consequently, the generated creep curves could not be represented by the empirical NBA creep equation. Instead, an empirical fit utilizing an exponential expansion series with multiple time constants was used to represent the behavior exhibited by the fusion-cast alumina refractories. The same exponential fit used to model the raw creep cu rves was also utilized to describe this composite behavior. • Several samples were analyzed after being crept, and results were compared with those previously obtained from virgin samples. An alysis included thermal conductivity, optical microscopy, and SEM/EDS chemical analysis. The thermal conductivity values for the Monofrax post-creep cores were similar to those obtained earlier from the virgin cores, which had thermal conductivities in the range of 5.9 W/mK. The valu e obtained from the Corh art post-creep core was significantly lower than the average value of 6.61 W/mK found earlier for the Corhart bulk material. Initial optical microscopy and SEM/E DS analyses were performed on Corhart and Monofrax bulk samples exposed to 1550°C and 1. 0 MPa. This work was conducted to determine whether any changes in the microstructure or chem istry could be detected at that intermediate condition. This analysis was then used to determine whether analysis needed to be performed on samples at the lower temperatures and stresses. No discernible deformation and only slight chemical changes were seen. Subsequent op tical microscopy and SEM/EDS analyses were performed on Corhart and Monofrax bulk samples exposed to the extreme conditions of 1650°C and 1.0 MPa. The structure of the Corhart sample was found to resemble the virgin structure, but the crept Monofrax structure displayed a smaller α -alumina grain size and a tighter α -alumina grain structure with more equiaxed angular gr ains than previously observed in the virgin structure. More severe chemical changes were also seen between the virgin and crept samples. • Considering that the behavior of fusion-cast alumina in service would be represented by the measured creep curves, any model that is used to capture its true behavior must incorporate both the effect of the expansion and the effect of cr eep. This means that a m odel is needed that can handle the high degree of nonlinearity seen in th e measured creep curves generated for fusioncast alumina while also being sensitive to the transient nature of th e data due to the lack of an equilibrium state.

60

### 7.4 Fused Spinel The fused spinel materials had negligible creep rates up to 1650°C at 8.5MPa of stress. The bonded spinel, surprisingly, crept substantially compared to the fused material. However, these findings must be compared with other common crown materials, the total creep of the bonded material is less than 0.5% over 100 h at 1550°C and 0.3 MPa, which ar e fairly standard temperature and pressure for testing refractory materials The creep of silica ma terials is approximately 0.4% over 100 h at 1450°C and 0.3 MPa. The spinel materials did not react w ith soda in the exposure tests. There was some limited reaction with silica and calcia from the gasifier atmosphere. Thermal conductivity was determined by laser flash and was found to decr ease as temperature increases from 14 (100°C) to 8 (700°C) W/mK for the fused spinel and 9.5 (100°C) to 4 (1300°C) for the bonded spinel. A model of the glass tank crown was developed, which takes into account nonlinear changes in the refractory material due to time, temperature, and corrosion.

61

## 8. Recommendations
• To truly model the deformation behaviors of fusion-cast alumina and silica refractories as a function of temperature, time, and stress, the co mposite effects of unrec overable expansion (aging behavior) and creep response must be known. Given that these processes may be highly nonlinear, the traditional equations, which assume that steady-state deformation rates are dominant, are not appropriate. New models must be derived from basic theoretical principles that can describe the nonlinear, transient, nonsteady e quilibrium behavior observed in this work. • Creep testing needs to include simultaneous measurement of specimen elongation/contraction occurring in the absence of an applied stress. Su ch testing could be conducted using a system consisting of furnace of sufficient size to accommoda te multiple mechanical load trains. During testing one load train would be used to mon itor elongation/contraction in the absence of any appreciable stress. The stress range employed with the other load stations must be large enough to promote significant and measurable changes in the deformation response. It is recommended that the stress range cover at least one order of magnitude (e.g., 5 to 50 MPa). Testing times must also be much longer (>1000 h) to ensure that represen tative deformation data are generated. A second approach for distinguishing creep from aging effects is to use the stress relaxation technique [23] for measuring creep response. Because this method is able to generate an entire creep-rate vs stress curve in a matter of a few hours, one could use it to measure creep behavior at periodic intervals during a standard aging test. Thus a single sample could be used to assess both aging and creep behavior. • To facilitate model development, the microstructural changes responsible for elongation/contraction in the absence of an applied stress must be identified. • Creep testing and physical characterization of salvaged fusion-cast alumina refractory bricks from oxy-fuel furnaces should be carried out. Results fro m such work could be compared with results generated in this work and would be useful in validating any fi nite-element models generated from the data collected in this work. • Work needs to be pursued in the area of nonlinear finite element analysis of furnace crowns. This kind of analysis would provide a better pred iction of furnace life and long-term refractory behavior.

• Technical efforts should be undertaken to measure and model the composite effects of unrecoverable expansion (aging be havior) and creep response. Given that these processes may be highly nonlinear, the traditional e quations, which assume that steady-state deformation rates are dominant, are not appropriate. New models must be derived from basic theoretical principles that can describe the nonlinear, transient, nonsteady e quilibrium behavior observed in this work. Creep testing needs to include simultaneous measurement of specimen elongation/contraction occurring in the absence of an applied stress. Su ch testing could be conducted using a system consisting of a furnace of sufficient size to accomm odate multiple mechanical load trains. During testing one load train would be used to mon itor elongation/contraction in the absence of any appreciable stress. The stress range employed with the other load stations must be large enough to promote significant and measurable changes in the deformation response. It is recommended that the stress range cover at least one order of magnitude (e.g., 5 to 50 MPa). Testing times must also be much longer (> 1000 h) to ensure that repr esentative deformation data are generated. A second approach for distinguishing creep from aging effects is to use the stress relaxation technique for measuring creep response. Because this method is ab le to generate an entire creep-rate vs stress curve in a matter of a few hours, one could use it to measure creep behavior at periodic intervals during a standard aging test. Thus a single sample could be used to assess both aging and creep behavior.

63• To facilitate technology transfer and commercializat ion, software tools should be developed that allow users to readily link the key properties to fi nite element codes used in furnace construction. This software would allow one to quickly assess th e effects of specific materials upon long-term thermal and structural reliability. It should also include a routine that allows the user to optimize performance of a given material by changing th e material properties; these altered properties would serve as new targets for those involved in materials development.

• Any follow-on effort must also address new materials.

64

## 9. References
[1] Crown Refractories for Glass Manufacturing with Oxy-Fuel Combustion, Teltech Research Services, Minneapolis, Minnesota (1996). [2] M. Gridley, “Philosophy, Design, and Perform ance of Oxy-Fuel Furnaces,” Ceram. Eng. Sci. Proc., 18 1–14 (1997). [3] R. W. Schroeder, “Development of Oxy-Fuel Technology in the Glass Industry,” The Glass Researcher 8 (1), 1–4 (1998). [4] A. A. Wereszczak, T. P. Kirkland, G. A. Pecoraro, and R. A. New, “Compressive Creep Behavior of Fusion-Cast Alumina Refractories,” pp. 401–406 in Ceramic Transactions, Vol. 82, Advances in Fusion and Processing of Glass II, ed. A. G. Clare and L. E. Jones, American Ceramic Society, Westerville, Ohio (1998). [5] A. A. Wereszczak, T. P. Kirkland, and W. F. Curtis, “Compressive Creep Resistance of MgO Refractories at Temperatures ≥ 1400°C (2550°F),”pp. 407–412 in Ceramic Transactions, Vol. 82, Advances in Fusion and Processing of Glass II, ed. A. G. Clare and L. E. Jones, American Ceramic Society, Westerville, Ohio (1998). [6] A. A. Wereszczak, T. P. Kirkland, and W. F. Curtis, “Creep of CaO/SiO 2 - Fluxed MgO Refractories,” J. Mater. Sci (1998) in press. [7] Glass: A Clear Vision for a Bright Future, U.S. Dept. of Energy, Office of Industrial Technologies, Advanced Industrial Ma terials Program (January 1996). [8] Refractories for Industrial Processing: Opportunities for Improved Energy Efficiency, U.S. Dept. of Energy, www.eere.energy.gov/industry/ imf/pdfs/ refractories reportfinal.pdf. [9] “Standard Practice for Vapor Attack on Refractories for Furnace Superstructures,” ASTM C987, Vol. 15.01, American Society for Testing and Materials, West Conshohocken, Pa. (1998). [10] A. A. Wereszczak, M. Karakus, K. C. Liu, B. A. Pint, T. P. Kirkland, and R. E. Moore, Compressive Creep Performance and High Temperatu re Dimensional Stability of Conventional Silica Refractories , ORNL/TM-13757, Oak Ridge National Laboratory (1999). [11] J. G. Hemrick, A. A. Wereszczak, M. Karakus, K. C. Liu, H. Wang, B. A. Pint, T. P. Kirkland, and R. E. Moore, Compressive Creep and Thermophysical Performance of Mullite Refractories , ORNL/TM-2002/84, Oak Ridge National Laboratory (2002). [12] J. G. Hemrick and A. A. Wereszczak, “Compressive Creep of Fusion-Cast Alumina as a Function of Microstructure,” Glass Industry (November 1999). [13] J. G. Hemrick, “Creep Behavior And Physical Characterization Of Fusion-Cast Alumina Refractories,” a Dissertation Presented to the Facult y of the Graduate School of the University of Missouri-Rolla in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Ceramic Engineering (2001). [14] “Standard Classification of Silica Refractor y Brick,” ASTM C416, Vol. 15.01, American Society for Testing and Materials, West Conshohocken, Pa. (1998). [15] S. Shin and O. Buyukozturk, Material Property Development for Refractories , US DOE Report ORNL/Sub/79-07862/02 (1990). [16] F. H. Norton, The Creep of Steel at High Temperature , McGraw Hill, New York (1929).

65[17] M. Karakus and R. E. Moore, “CLM—A New Technique for Refractories,” Ceramic Bulletin 77 55–61 (1998). [18] S.E. Gustafsson, “Transient Plane Sour ce Techniques for Thermal Conductivity and Thermal Diffusivity Measurements of Solid Materials,” Review of Scientific Instruments

. 62 (3), 797– 804 (1991). [19] “Standard Test Method for Thermal Diffusivit y of Solids by the Flash Method,” ASTM E1461- 92, Vol. 15.01, American Society for Testing a nd Materials, West Conshohocken, Pa. (2000). [20] G. Hetherington, J. H. Jack, and J .C. Kennedy, “The Viscosity of Vitreous Silica,” Physics and Chemistry of Glasses 5, 130–136 (1964). [21] F. E. Wagstaff, “Crystallization and Melting Kinetics of Cristobalite,” Journal of the American Ceramic Society 52, 650–654 (1969). [22] M. F. Doerner and W. D. Nix, “A Me thod for Interpreting Data from Depth-Sensing Indentation Instruments,” Journal of the Materials Research Society 1 (4) (1986). [23] M. G. Jenkins and M. K. Ferber, “Determination of High-Temperature Creep Parameters in Structural Ceramics From Constant-Displace ment, Stress-Relaxation Tests,” pp. 94–101 in Proceedings of the 1991 SEM Spring Conference on Experimental Mechanics , Milwaukee, Wisconsin, June 9–13, 1991, Society of Experimental Mechanics, Bethel, Connecticut (1991).

6667 

## Appendix: Publications

A. A. Wereszczak, J. Heide, and T. P. Kirkla nd, “High Temperature Deformation of an AZS Refractory,” Advances in Fusion and Processing of Glass II, 379–384.

A. A. Wereszczak, T. P. Kirkland, and W. F. Curtis, “Creep of CaO/SiO 2 –Containing MgO Refractories,” Journal of Materials Science 34 (1999): 215– 227.

A. Wereszczak, H. Wang, M. Karakus, W. Curtis , V. Aume, and D. VerDow, “Postmortem Analyses of Salvaged Conventional Silica Bricks from Glass Production Furnaces,” Glastech. Ber. Glass Sci. Technol. 73 (2000), No. 6: 165–174.



### J. G. Hemrick, C. W. Kistler Jr., A. A. Wereszczak, and M. K. Ferber, “Thermal Conductivity of Alumina Measured with Three Techniques,” 1–13.

# Copyrighted page(s) removed. Copyrighted material is not available in Regulations.gov since it may not be reproduced without consent of the copyright holder.
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Email: docket-customerservice@epa.govFrom: Chun-Wai Lee To: Susan Fairchild Cc: Reeves, David ; Larke Williams ; Bill Linak Subject: Re: Fw: WF - PM and Cr Graphs (NEW) Date: 03/28/2012 05:01 PM Attachments: WF PM and Cr Grpahs 3.22.12 v2.xlsx 

### The first graph shows units which exceed the proposed Cr emission limit (0.00006 lb/ton) are all oxy-fuel furnaces either tested previously (# 16, 17, 38, 39, and 40) or in this year (#23 and 40) with one exception (#26) for a recoup gas fired furnace. Emissions from the other oxy-fuel furnaces below the limit are also high relative to those of other units.
The high Cr emissions shown in the graph support Dr. Brosnan's conclusions that flame temperature is the most important variable in furnace operation influencing the quantity and speciation of chromium emissions from wool fiberglass furnaces employing chromium refractory linings. Refractory linings of a oxy-fuel furnace are well known to be much hotter than those of the conventional air fired furnaces as a result of the exceedingly high temperature produced by oxy-fuel combustion (5,035 o 

### F compared to 3,562 o 

### F produced from conventional air-fired furnaces) greatly enhances radiative heat transfer. He also quotes references which show volatility of Cr2O3 increases rapidly above 2,400 o 

### F , and the high oxygen atmosphere (as it is existed in a oxy-fuel furnace) also promotes the volatilization of Cr2O3 (page 7 in his letter). Furthermore, the high oxygen atmosphere(thermodynamic effect) coupled with the high temperature (kinetic effect) in a oxyfuel furnace provide a favorable conditions to promotes oxidation of Cr2O3 existed in the linings to CrO3 (CrVI). All these factors discussed above provide a strong scientific basis that oxy-fuel furnaces with Cr refractory lining have higher potential for Cr, toxic CrVI in particular, emissions.

CW

************************************ C.W. Lee, Ph.D. U.S. Environmental Protection Agency (E-305-01) Office of Research and Development National Risk Management Research Laboratory 109 T.W. Alexander Drive Research Triangle Park, NC 27711
E-mail: lee.chun-wai@epa.gov Voice: (919) 541-7663 Fax: (919) 541-0554

************************************

▼ Susan Fairchild---03/28/2012 11:29:01 AM---Dear CW and Larke- The contractor has compiled the existing and new chrome test data into a spreadsh

From: Susan Fairchild/RTP/USEPA/US To: Larke Williams/DC/USEPA/US@EPA, Chun-Wai Lee/RTP/USEPA/US@EPA Cc: "Reeves, David" <dwreeves@rti.org> Date: 03/28/2012 11:29 AM Subject: Fw: WF - PM and Cr Graphs (NEW)

### Dear CW and LarkeThe contractor has compiled the existing and new chrome test data into a spreadsheet and has graphed the data. This is attached.
The oxyfuel furnaces are in red.
As you can tell, there are several types of furnaces:

cold top electric Electric Steel Shell (ESS), aka Steel shell electric (we believe these are the same types of furnaces) gas fired electric boost Johns Manville HERM melters other HERM melters (I believe there may be distinct differences, but don't know what they are) Recoup gas fired air gas
We have not answered all the questions about the furnaces that we need to answer, but do these data help in addressing the NAIMA comments and Dr. Brosnan's attached letter supporting those comments?

Thanks,

Susan Fairchild Environmental Scientist U.S. Environmental Protection Agency direct line: 919.541.5167 fax: 919.541-3207 email: fairchild.susan@epa.gov
Overnight mail address: US EPA Mail Code D243-04 109 TW Alexander Drive RTP, NC 27709

----- Forwarded by Susan Fairchild/RTP/USEPA/US on 03/28/2012 11:15 AM -----

From: "Reeves, David" <dwreeves@rti.org> To: Susan Fairchild/RTP/USEPA/US@EPA, Jeff Telander/RTP/USEPA/US@EPA Date: 03/25/2012 10:26 AM Subject: FW: WF - PM and Cr Graphs (NEW)



### Hi Susan and Jeff. I am forwarding the PM and Cr graphs that Cindy finished on

### Friday that include the new 2012 test data for fiberglass furnaces. Note that there

are 8 or 9 furnaces with 2 data points where we had old test data from the facilities and then the new testing was done this year. As you will see, there are no clear data breaks or obvious subcategory differences for major sources. Because of the funding issues, I’ve told Cindy to hold off doing any more analysis

– pending your discussion and decisions.



### Dave Reeves RTI International dwreeves@rti.org (919) 316-3739 From: Hancy, Cindy Wang Sent: Friday, March 23, 2012 5:02 PM To: Reeves, David Subject: WF - PM and Cr Graphs (NEW)

Dave,

Here are new graphs. I based the PM tech review value on K2 since it was the closes
to being ~0.4 lb/ton.

Thanks!

Cindy Wang Hancy RTI International P.O. Box 12194 Research Triangle Park, NC 27709 Phone: (919) 541-6623 Fax: (919) 316-3420

# Copyrighted page(s) removed. Copyrighted material is not available in Regulations.gov since it may not be reproduced without consent of the copyright holder.
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