ERG No. 0195.00.002 

TECQ Contract No. 582-04-65589 

Work Order No. 05-06 

ASSESSMENT OF NOx EMISSIONS REDUCTION STRATEGIES FOR 

CEMENT KILNS - ELLIS COUNTY 

FINAL REPORT

TCEQ Contract No. 582-04-65589 

Work Order No.05-06 

Prepared by: 

ERG, Inc. 

10200 Alliance Road, Suite 190 

Cincinnati, Ohio 45242-4716 

Prepared for: 

Air Quality Planning Section 

Chief Engineer’s Office 

Texas Commission on Environmental Quality 

Austin, Texas 78711-3087 

July 14, 2006 
i

This study is the work project of a panel of experts assembled at the request of the Texas 

Commission on Environmental Quality. This study was performed under contract to Eastern 

Research Group that provided overall contract management and subcontracted the outside 

experts and laboratory services. While each of the experts brought specific skills to this study 

and was the principal author of individual sections of the report, the overall study represents a 

team effort. The general conclusions of the study have been reviewed and are endorsed by the 

entire expert panel. 

 

 

Walter Koucky, Senior Project Engineer - Contract Manager, Eastern Research Group 

Dr. Ray Merrill, Senior Chemist, Eastern Research Group 

David Gossman, FAIC, President, Gossman Consulting Inc. 

 

Dr. Gabe Miller, Professor of Chemistry, New York University 

Dr. Greg Miller, Principal, Cement Etc., Inc. 
TABLE OF CONTENTS 

1.0 INTRODUCTION ...........................................................................................................1-1 

1.1 Executive Summary.............................................................................................1-2 

1.1.1 Control Alternatives for Holcim Inc........................................................1-4 

1.1.2 Control Alternatives for TXI Cement......................................................1-5 

1.1.3 Control Alternatives for Ash Grove Cement ...........................................1-5 

2.0 DEFINING PARAMETERS FOR CONTROL EVALUATION ....................................2-1 

2.1 Overview of Portland Cement Manufacturing Process and NOx Generation......2-1 

2.1.1 Description of the Cement Industry.........................................................2-4 

2.1.2 Kiln Types and Operation........................................................................2-8 

2.1.3 Thermal Characteristics .........................................................................2-12 

2.1.4 Process Variables...................................................................................2-14 

3.0 NOX FORMATION IN CEMENT KILNS.......................................................................3-1 

3.1 Overview of NOx Formation Mechanisms ..........................................................3-1 

3.1.1 Thermal NOx Formation ..........................................................................3-2 

3.1.2 Fuel NOx Formation.................................................................................3-3 

3.1.3 Feed NOx Formation................................................................................3-5 

3.1.4 Factors Affecting NOx Emissions in Cement Manufacturing..................3-6 

3.1.5 Suspension Preheater (SP) Kilns with Riser Duct Firing. .......................3-9 

3.1.6 Precalcining Kiln Systems. ....................................................................3-10 

3.1.7 Energy Efficiency of the Cement-Making Process................................3-11 

4.0 OVERVIEW OF POTENTIALLY APPLICABLE CONTROL TECHNIQUES AND

TECHNOLOGIES ...........................................................................................................4-1 

4.1 High Temperature Emissions Controls................................................................4-3 

4.1.1 Selective Catalytic Reduction (SCR).......................................................4-3 

4.1.2 Selective Noncatalytic Reduction (SNCR)............................................4-20 

4.2 Combustion Optimization..................................................................................4-33 

4.2.1 Staged Combustion of Air .....................................................................4-34 

4.2.2 Flue Gas Recirculation...........................................................................4-34 

4.2.3 Low-NOx Burners ..................................................................................4-35 

4.2.4 Staged Combustion of Fuel....................................................................4-38 

4.2.5 Preheater/Precalciner and Tire Derived Fuel.........................................4-38 

4.2.6 Low- NOx Precalciners ..........................................................................4-40 

4.2.7 Mid-Kiln Firing......................................................................................4-41 

4.3 Lower Temperature Oxidation Based Technologies .........................................4-43 

4.3.1 Introduction............................................................................................4-44 

4.3.2 LoTOxTM................................................................................................4-44 

4.3.3 Hydrogen Peroxide ................................................................................4-51 

4.3.4 OXONE (Dupont – potassium monopersulfate)....................................4-56 

4.3.5 Sodium Acetate Process.........................................................................4-57 

4.3.6 Potential Applicability of Oxidation Technology to Ash Grove Plant..4-59 

4.3.7 Potential Applicability of Oxidation Technology to Holcim Plant .......4-60 

4.3.8 Potential Applicability of Oxidation Technology to TXI Plant.............4-60 
TABLES OF CONTENTS (Continued) 

Page 

Cement Kiln Report (FINAL – 7/14/2006) iii

4.4 Process Modification .........................................................................................4-63 

4.4.1 Combustion Zone Control of Temperature and Excess Air...................4-64 

4.4.2 Feed Mix Composition ..........................................................................4-64 

4.4.3 CemStar Process ....................................................................................4-65 

4.4.4 Kiln Fuel ................................................................................................4-67 

4.4.5 Increasing Thermal Efficiency...............................................................4-68 

4.5 Performance of Current NOx Control Techniques and Technologies in the 

 Cement Industry.................................................................................................4-74 

4.5.1 Summary of Current Performance of NOx Control Technologies.........4-74 

4.5.2 Summary of Current Regulations ..........................................................4-74 

4.5.3 Summary Of European Experiences......................................................4-79 

5.0 CHEMISTRY OF ELLIS COUNTY MATERIALS AND IMPACTS ON CONTROL

DETERMINATIONS ......................................................................................................5-1 

5.1 Results..................................................................................................................5-1 

5.1.1 Organic Carbon........................................................................................5-2 

5.1.2 Total Kjeldahl Nitrogen ...........................................................................5-3 

5.1.3 Total Sulfur ..............................................................................................5-4 

5.2 Conclusions..........................................................................................................5-5 

6.0 REFERENCES ................................................................................................................6-1

Attachment A ERG Summary of EPA 2000 NOx Controls for Cement Kilns 

Attachment B Sampling Plan 

Attachment C ERG Report on LoTOxTM Application to Refineries 

Attachment D Summary of Current US Cement Regulations for NOx
LIST OF TABLES 

Page 

1-1 Summary of Technologies for Holcim #1 ....................................................................... 1-4

1-2 Summary of Technologies for Holcim #2 ....................................................................... 1-5 

1-3 Summary of Technologies for TXI #1 & #4.................................................................... 1-6

1-4 Summary of Technologies for TXI #2 & #3.................................................................... 1-7

1-5 Summary of Technologies for TXI #5............................................................................. 1-8

1-6 Summary of Technologies for Ash Grove #1.................................................................. 1-9

1-7 Summary of Technologies for Ash Grove #2.................................................................. 1-9

1-8 Summary of Technologies for Ash Grove #3.................................................................. 1-9

1-9 Summary of Technologies – Seasonal for Holcim #1 ................................................... 1-10

1-10 Summary of Technologies – Seasonal for Holcim #2 ................................................... 1-10 

1-11 Summary of Technologies – Seasonal for TXI #1 & #4 ............................................... 1-10

1-12 Summary of Technologies - Seasonal for TXI #2 & #3 ................................................ 1-11

1-13 Summary of Technologies - Seasonal for TXI #5 ......................................................... 1-11

1-14 Summary of Technologies – Seasonal for Ash Grove #1.............................................. 1-11

1-15 Summary of Technologies – Seasonal for Ash Grove #2.............................................. 1-12

1-16 Summary of Technologies – Seasonal for Ash Grove #3.............................................. 1-12

1-17 Environmental and Other Impacts of Control Technologies ......................................... 1-19

2-1 Basic Clinker Compounds (3).......................................................................................... 2-3 

3-1 Calculated Equilibrium Concentrations (In PPM) Of NOx and NOx In Air and Flue 

Gas (15)............................................................................................................................ 3-3 

4-1.1 Summary of Modeling Results for SCR on Ellis County Kilns – Performance 

 Results............................................................................................................................ 4-18 

4-1.2 Summary of Modeling Results for SCR on Ellis County Kilns – Economic Results ... 4-19 

4-1.3 Summary of Test Results for SNCR Test...................................................................... 4-23 

4-1.4 Emissions Reductions From Two Kilns Using NOxOUT®........................................... 4-29 
LIST OF TABLES (Continued) 

Page 

Cement Kiln Report (FINAL – 7/14/2006) v

4-1.5 Summary of Modeling Results for SNCR on Ellis County Kilns – Performance 

 Results............................................................................................................................ 4-32 

4-1.6 Summary of Modeling Results for SNCR on Ellis County Kilns – Economic 

 Results............................................................................................................................ 4-33 

4-2.1 NOx Emissions from a Precalciner Equipped with a Low-NOx Burner........................ 4-36 

4-2.2 NOx Emissions Before and After Installation of Pyro-Jet Low-NOx Burners............... 4-37 

4-2.3 NOx Emissions with 3 Channel and Rotaflam® Low-NOx Burners............................... 4-37 

4-2.4 Emissions Before and After Installation of a Rotaflam® Burner on a Wet Kiln ........... 4-37 

4-2.5 Emissions From Kilns With Mid-Kiln Firing................................................................ 4-43 

4-3.1 Comparison Of Common Post Combustion NOx Abatement Technologies For NOx

Emissions Control.......................................................................................................... 4-47

4-3.2 Oxone Constituents........................................................................................................ 4-56 

4-3.3 Reaction Steps and Pathway Equations for the Sodium Acetate Direct Absorption 

Process For Simultaneous NOx And SOx Removal (OECD, 1983)............................... 4-58 

4-3.4 Summary of Modeling Results for LoTOxTM on Ellis County Kilns – Performance 

 Results............................................................................................................................ 4-62 

4-3.5 Summary of Modeling Results for LoTOxTM on Ellis County Kilns – Economic 

 Results............................................................................................................................ 4-63 

4-4.1 Results of Short-Term Cemstar Tests on a Preheater/Precalciner Kiln......................... 4-66 

4-4.2 Results of Cemstar Tests on a Wet Kiln ........................................................................ 4-67 

4-4.3 Summary of Modeling Results for Wet to Dry Conversion of Ellis County Kilns – 

Performance Results ...................................................................................................... 4-73 

4-4.4 Summary of Modeling Results for Wet to Dry Conversion of Ellis County Kilns – 

Economic Results........................................................................................................... 4-73

4-4.5 Summary of Modeling Results for Calciner Upgrade for Ellis County Kilns – 

Economic Results........................................................................................................... 4-74

4-5.2 National SO2 and NOx Emission Limits for the Production of Cement Within the 

European Union (EU 15), in mg/Nm3

, Around 2000 .................................................... 4-77 

4-5.1 National SO2 and NOx Emission Limits for the Production of Cement Within the 

European Union (EU 15), in mg/Nm3

............................................................................ 4-77 
LIST OF TABLES (Continued) 

Page 

Cement Kiln Report (FINAL – 7/14/2006) vi

4-5.2 National PM Emission Limits for the Production of Cement Within the European Union 

(EU 15), in mg/Nm3....................................................................................................... 4-77 

4-5.3 Midwest RPO – LADCO Study..................................................................................... 4-79 

4-5.4 Fall Line Air Quality Study (Georgia)........................................................................... 4-79 

4-5.5 NOx Control Techniques Summary From European Best Available Techniques 

 Report1 ........................................................................................................................... 4-80

Tables in Attachments 

Table A-1 ERG Summary of EPA 2000 NOx Controls for Cement Kilns 

Table B-1. Feed Chemical Composition 

Table D-1. Summary of US NOx Control Regulations for Cement Kilns – EPA 2004 

NOTE: Table 4-5.1 is a separate spreadsheet that is too large for inclusion in the body of the 

report. It is available as an Excel spreadsheet. 
Cement Kiln Report (FINAL – 7/14/2006) vii

LIST OF FIGURES 

Page 

2-1 Temperature of the Gas and Material in the Rotary Cement Kiln 1.............................. 2-13 

2-2 The Relationship Between Process Temperatures and the Chemistry of Cement 

Clinker Formation.......................................................................................................... 2-13

3-1 Theoretical Equilibrium Concentrations of NOx............................................................. 3-4 

4-1.1 SCR at Solnhofen Zement ............................................................................................. 4-22 

4-1.2 Dependence of NOx Reduction on Temperature for Ammonia and Urea..................... 4-22 

4-1.3 Application of SNCR at Holcim.................................................................................... 4-24 

4-2.1 Schematic of Preheater (58)........................................................................................... 4-39 

4-2.2 Schematic of Precalciner(58)......................................................................................... 4-39

4-3.1 Overall Process Diagram of the LoTOxTM System........................................................ 4-45 

4-3.2 EDV Wet Scrubbing System with LoTOxTM Injection ................................................ 4-46 

4-3.3 Ideal Operating Conditions for NOx Removal from 80% to 95% ................................ 4-49 

4-3.4 Conceptual Design of Hydrogen Peroxide NOx Control System .................................. 4-52 

4-3.5 Effect of Temperature on Peroxide Oxidation of NO.................................................... 4-53 

4-3.6 Effect of Molar Ratio on Peroxide Oxidation of NO..................................................... 4-54 
Cement Kiln Report (FINAL – 7/14/2006) 1-1

1.0 INTRODUCTION 

 This study was conducted to explore potential NOx emissions reduction strategies 

for cement kilns in Ellis County. This project included assessing existing NOx control 

technologies as well as new technologies that have not been previously considered by TCEQ. 

This project evaluated the general performance and cost of applicable NOx control technologies 

for the cement kilns present in Ellis County and further evaluated the application of these control 

technologies to the site-specific requirements of the kilns and raw materials present in Ellis 

County. 

This study was initiated in order to fulfill obligations in the Dallas/Fort Worth Litigation 

Settlement Agreement. TCEQ, in consultation with the Plaintiffs, EPA, and Intervenor the 

Portland Cement Association, developed the scope of work and selected Eastern Research Group 

(ERG) and a panel of experts (the ERG Team) to perform this cement kiln NOx control 

technologies study. This study evaluated the applicability of existing control technologies and 

the potential availability of new air pollution control technologies for cement kilns located in the 

Dallas/Ft. Worth ozone nonattainment area. This report evaluates and establishes the types of 

controls that may be technically applied to the three nonattainment area cement plants with 

specific evaluations of applicability to the 10 cement kilns located at the three plants. This report 

focuses largely on three active types of control technology: SCR, SNCR and NOx Oxidation. 

This focus in based on the need to evaluate technologies that go beyond current requirements of 

30 Texas Administrative Code (TAC) Chapter 117. Economics of these control technologies 

are also investigated and reported. 

 The intent of this study was to establish impartial parameters for the determination of 

applicable controls. Controls were included to the extent that they were technically feasible. 

Control costs and cost effectiveness values, in terms of cost per ton of NOx controlled, were then 

assigned to all technically feasible controls. The ERG Team has not applied value judgments nor 

assessed the economic viability of technically feasible controls. The ERG Team has not 

excluded any control technology on the basis of cost. This study puts forward technically viable 

NOx control technologies and evaluates their cost effectiveness for specific application to Ellis 
Cement Kiln Report (FINAL – 7/14/2006) 1-2

County cement kilns with the intent of allowing TCEQ to have sufficient information to make 

control technology selections. 

 This report uses the USEPA report “NOxControl Technologies for the Cement Industry” 

of September 2000 (EPA 2000) as a baseline for the technical analysis and as boilerplate for 

describing the cement industry and applicable control technologies. The ERG Team has 

reviewed and edited this text to reflect the Team’s understanding of the processes and control 

techniques. As mentioned previously, this report looks at active control technologies beyond the 

combustion and process optimization techniques of 30 TAC Chapter 117. The EPA 2000 report 

evaluates Selective Catalytic Reduction (SCR) and Selective Non-catalytic Reduction (SNCR) 

for the cement industry. This study takes this EPA 2000 information and updates it to the 

present. In addition, this study conducts site-specific evaluations including control cost 

evaluations for the 10 Ellis County cement kilns. This study focuses on application of SCR, 

SNCR and oxidation technologies including LoTOxTM to control oxides of nitrogen. Energy 

improvements are also examined, including replacement of the seven Ellis County wet kilns with 

two large, modern dry process units. 

1.1 Executive Summary

The tables presented below contain summaries of control technology evaluations 

conducted as part of this study. The summaries below generally contain conservative costs and 

scenarios for the selected technologies. For example, performance levels for selective catalytic 

reduction (SCR) and LoTOxTM oxidation are conservatively estimated at 80-85%. These 

technologies typically perform better than these levels in other industrial applications. However, 

using a slightly lower performance value presents a more conservative evaluation of control 

costs, allowing potential difficulties in initial application of these technologies to Ellis County 

cement kilns. 

The tables include a column discussing the status of the control technology for the 

application. This column uses the Top-Down BACT terms, available, transferable and 

innovative, to describe the statuses of the control technologies. However, for the purposes of 

this report, available essentially means that the technology is commercially available and in use 
Cement Kiln Report (FINAL – 7/14/2006) 1-3

on similar types of cement kilns. Transferable means that the technology is commercially 

available and in use on similar process equipment and could reasonably be expected to work on 

that type of cement kiln. Innovative describes technologies that have not been successfully 

applied to a type of cement kiln, but in the judgment of the ERG Team could be expected to 

work on the type of cement kiln if correctly optimized through experimental application. 

Wet kilns use more energy and have higher emissions rates than dry kilns. The only 

available wet kiln control technique fully evaluated in this study is conversion of the wet kilns to 

modern dry preheater/calciner units. This is a high cost alternative with a cost of approximately 

$11 per metric tonne (the metric tonne is the standard unit of measure for cement production and 

is used in this report) of clinker produced, including consideration of substantial fuel savings due 

to increased efficiency. As the cost of alternative controls approaches this value, there is 

reasonably expected to be a point where the cost of control technologies may create a substantial 

incentive to replace the wet kilns. This decision is complex and may require consideration of 

expanded production and use of alternative energy sources to be commercially justified. At the 

time this report was completed, Holcim of France was giving preliminary reports of trials of 

selective non-catalytic reduction (SNCR) on a wet kiln. While these preliminary reports do not 

provide sufficient information for technical evaluation of the results, this may mean that SNCR 

has become an available control technology for wet kilns. 

Burden costs in dollars per tonne clinker produced ($/tonne) are provided to provide 

insight into the impacts of control costs on the cement plant’s cost of product. The emissions 

reductions calculated in Tables 1-1 through 1-8 are based on operation of the control equipment 

for the entire year and not just during the Dallas/Ft. Worth ozone season. Tables 1-9 through 1-

16 are based on operation of the control equipment for just the Dallas/Ft. Worth ozone season. 

The metric tonne is the standard unit both in the US and worldwide for measuring cement 

production. This causes confusion because the metric tonne is often spelled “ton”. This report 

uses the spelling “tonne” to refer to the metric tonne (i.e., 1,000 kilograms or 2,205 pounds). 

Current regulations in Texas are based on pounds of NOx per short ton (i.e., 2,000 pounds). For 

consistency in the technical discussions of controls and regulations in the US and worldwide, this 

report discusses production related information based on the metric tonne of production. To 
Cement Kiln Report (FINAL – 7/14/2006) 1-4

assist in comparison with existing Texas regulations, values in pounds per short ton have been 

added in parentheses to the tables in this Executive Summary. 

 

1.1.1 Control Alternatives for Holcim Inc. 

 Holcim operates two modern dry preheat precalcination kilns, each with an annual 

production capability of slightly over one million tons per year of clinker. Holcim has recently 

completed testing of SNCR on these kilns. SNCR performed reasonably well on Holcim #1, but 

additional optimization may improve performance. 

Holcim #1 

Holcim’s Line #1 began operation in 1987. This unit is a modern design, typical of units 

built in the 1980’s; this kiln may be a candidate for a reconstructed preheater precalcination 

tower to a larger, more energy efficient design (see Section 4.4.5 of the report). This 

reconstruction could also allow for improved staging of combustion, lower NOx generation and 

improved integration with controls such as SNCR or an oxidation control technology. Without 

modification, Holcim #1 will likely achieve somewhat lower control performance than Holcim 

#2 or TXI #5 based on application of similar technologies. However, in spite of its older 

generation of design, Holcim #1 is currently performing nearly as well as Holcim #2. Neither 

Holcim #1 nor Holcim #2 is currently performing as well as TXI #5 in terms of energy efficiency 

or NOx emissions rates even though Holcim #2 is approximately the same age. 

 

Note on the conventions used in the Tables 1-1 through 1-16. 

The metric tonne (1,000 kg. or 2,205 lbs.) is used by the cement industry for 

measuring and reporting production. Emissions are reported in short tons containing 

2,000 lbs./ton. This results in a 10% difference between the metric tonne and the 

short ton. A controlled emissions rate of 1.1 lbs./tonne is equivalent to a controlled 

emissions rate of 1.0 lbs./ton. Emissions reported in tpy are in short tons per year. As 

Texas has used lbs./ton (based on the US ton – or short ton) in the past, these values 

are provided in parentheses in appropriate locations in the tables in this chapter. 
Cement Kiln Report (FINAL – 7/14/2006) 1-5

Table 1-1 Summary of Technologies for Holcim #1 – Full Year Control 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate 

before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Available 2,222 3.76 (3.41) 85% 1,888.7 0.56 (0.51) $1,600 $2.60 

LoTOxTM Transferable 2,222 3.76 (3.41) 85% 1,888.7 0.56 (0.51) $2,200 $3.50 

SNCR Available 2,222 3.76 (3.41) 50% 1,111 1.9 (1.7) $1,400 $1.30 

Calciner 

Upgrade Available 2,222 3.76 (3.41) 40% 888.8 2.2 (2.0) $2,795 $2.70 

40% for new low-NOx calciner based on literature. 

Cost effectiveness for calciner upgrade calculated by ratio of burden costs using SCR data. 

Holcim #2 

Holcim’s Line #2 began operation in 1999. Holcim #2 is a modern design, but emits 

substantially more NOx than TXI #5 that was built only two years later. There may be process or 

combustion optimization options for Holcim #2 that can lower NOx prior to control. Holcim has 

recently completed testing of SNCR on these kilns. SNCR did not perform as well as would be 

expected on Holcim #2 and additional optimization should improve performance. 

 

Table 1-2 Summary of Technologies for Holcim #2 – Full Year Control 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate 

before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Available 1,778 3.01(2.73) 85% 1,511.3 0.45(0.41) $1,900 $2.20 

LoTOxTM Transferable 1,778 3.01(2.73) 85% 1,511.3 0.45(0.41) $2,100 $2.80 

SNCR Available 1,778 3.01(2.73) 50% 889 1.5(1.36) $1,600 $1.20 

1.1.2 Control Alternatives for TXI Cement 

 TXI operates five kilns, one modern dry preheat precalcination kiln and four 

1960’s era wet kilns. Two of the wet kilns are operated full time and two are operated as backup 

units about 15% of the time. 

TXI #1 and #4 

TXI #1 began operation in 1960 and TXI #4 began operation in 1972. These are wet 

kilns that use the old process of making cement from wet slurry. This makes high quality cement 

but uses substantially more energy to make cement. Both energy use and NOx emissions rates 

are substantially higher for wet kilns than for dry process kilns. Because the kilns are of similar 
Cement Kiln Report (FINAL – 7/14/2006) 1-6

size and used in a similar manner, one estimate has been created to represent both TXI #1 and 

TXI #4. Cost and control estimates are based on averaging the operation of these kilns; a similar 

approach has been used for TXI #2 and #3. A control option for replacement of the wet kilns at 

TXI with a new large dry kiln of equal capacity to the old wet kilns is also presented. The model 

for wet to dry conversion contains a calculation for fuel savings that is not entirely accurate for 

TXI because of the use of waste fuels in the wet kilns. However, to the extent that a new, larger 

dry kiln would continue to utilize a similar amount of waste fuels, the savings in fuel expressed 

as coal, would still provide an accurate view of a potential fuel savings. The models for TXI #1 

and #4 presume that mid-kiln firing will be applied as required under the current SIP and that 

this will achieve a 30% reduction in NOx emissions. This 30% assumption is based on 

evaluation of literature and other installations and is not intended to predict the actual ability of 

TXI to reduce emissions through mid-kiln firing. 

 Assuming mid-kiln firing reduces the emissions rate from current actual rates and 

decreases control cost effectiveness. As less NOx is available for control, the cost per ton 

controlled is increased. However, as mid-kiln firing is already required under Texas regulations, 

this was deemed the proper starting place for control analysis. The analyses for TXI #1 and #4 

presented below are based on an average for the two kilns and values presented below, such as 

emissions reductions, should be doubled to account for both kilns. 

Table 1-3 Summary of Technologies for TXI #1 & #4 – Full Year Control 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate 

before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Transferable 838 5.67(5.14) 85% 712.3 0.85(0.77) $4,900 $12.30 

LoTOxTM Transferable 838 5.67(5.14) 85% 712.3 0.85(0.77) $2,800 $6.80 

SNCR Innovative 838 5.67(5.14) 35% 293.3 3.7(3.36) $2,100 $2.10 

Wet to 

Dry Available 1,802 5.67(5.14) 65% 1,171.3 2.0(1.81) $6,700 $11.00 

Large 3 

Kiln SCR Transferable 1,802 5.67(5.14) 85% 1,531.7 0.85(0.77) $5,400 $8.00 

SCR includes the cost of installing and operating RTO’s to reheat gas after ESPs. 

Wet to dry conversion analysis based on one large kiln to replace existing capacity. 

TXI #2 and #3 

TXI #2 began operation in 1963 and TXI #3 began operation in 1967. Similar to TXI #1 

and #4, these are wet kilns that use the old process of making cement from wet slurry. Because 
Cement Kiln Report (FINAL – 7/14/2006) 1-7

the kilns are of similar size and used in a similar manner, one estimate has been created to 

represent both TXI #2 and TXI #3. Cost and control estimates are based on averaging the 

operation of these kilns. Although the kilns are physically similar to TXI #1 and #4, they are 

used as backup units. As backup units, these kilns have a low utilization rate (averaging 15% for 

the two kilns in 2004); the low utilization rate will show poor economics of control, as the fixed 

costs will be averaged over very small NOx reductions. The control option for replacement of 

the wet kilns at TXI with a new large dry kiln of equal capacity to the old wet kilns is an option 

for all four kilns and has identical economics and environmental benefits as described above for 

TXI #1 and #4. Also, as with TXI #1 and #4, mid-kiln firing is assumed as the starting place for 

this analysis as this is already required by Texas regulations. The analyses for TXI #2 and #3 

presented below are based on an average for the two kiln and values presented below, such as 

emissions reductions, should be doubled to account for both kilns. 

Table 1-4 Summary of Technologies for TXI #2 & #3 – Full Year Control 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate 

before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Transferable 85 3.4(3.08) 85% 72.3 0.51(0.46) $66,400 $14.00 

LoTOxTM Transferable 85 3.4(3.08) 85% 72.3 0.51(0.46) $8,000 $11.50 

SNCR Innovative 85 3.4(3.08) 35% 30 2.2(2.00) $11,000 $6.50 

Wet to 

Dry Available 1,802 5.67(5.14) 65% 1,171.3 2.0(1.81) $6,700 $11.00 

Large 3 

Kiln SCR Transferable 1,802 5.67(5.14) 85% 1,531.7 0.85(0.77) $5,400 $8.00 

SCR includes the cost of installing and operating RTO’s to reheat gas after ESPs. 

Wet to dry conversion analysis based on one large kiln to replace existing capacity. 

The higher emissions rate of TXI 1 & 4 is used as representative of operation for combined solutions wet to dry and 

large single SCR. 

TXI #5 

TXI #5 began operation in 2001 and is the largest and most efficient kiln line in the study 

area. It is relatively fuel efficient and intrinsically low in NOx emissions. The low NOx

emissions rate is a function of the design and may also be partly the result of the chemistry of the 

feed materials (see discussion of chemistry in the main report) that may be causing reduction of 

NOx. Because of the relatively low NOx concentrations in the offgas, the expected NOx removal 

efficiencies are lower for TXI #5 than for other kilns. For example, both European and US 

experience with SNCR indicates that removal is less efficient at lower NOx concentration and 

that practical removal is currently understood to be limited to about 200 mg/m3 or 100 ppm. For 
Cement Kiln Report (FINAL – 7/14/2006) 1-8

this reason, TXI #5 is modeled for 35% control for SNCR compared to 50% for the Holcim 

kilns. 

Table 1-5 Summary of Technologies for TXI #5 – Full Year Control 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Available 1,710 1.50(1.36) 80% 1,368 0.30(0.27) $2,000 $1.10 

LoTOxTM Transferable 1,710 1.50(1.36) 80% 1,368 0.30(0.27) $2,400 $1.40 

SNCR Available 1,710 1.50(1.36) 35% 598.5 1.0(0.91) $2,300 $0.60 

1.1.3 Control Alternatives for Ash Grove Cement 

ASH GROVE #1, #2 and #3 

Ash Grove operates three wet kilns that began operation in 1966, 1969 and 1972. Similar 

to the wet kilns at TXI, these are wet kilns that use the older process of making cement from wet 

slurry. This makes high quality cement but uses substantially more energy to make cement. 

Both energy use and NOx emissions rates are substantially higher for wet kilns than for dry 

process kilns. The Ash Grove kilns are currently complying with the SIP requirement for midkiln firing. The NOx emissions rate at Ash Grove from mid-kiln firing of tires appears to be 

substantially lower than at TXI where the mid-kiln firing project has been delayed by permit 

issues. 

Because the Ash Grove kilns are of similar size and used in a similar manner, separate 

discussions are not provided for each kiln. Slight differences in flow rates and emissions rates 

are modeled and presented in the tables below. Similar to the TXI presentation, a control option 

for replacement of the wet kilns at Ash Grove with a new large dry kiln of equal capacity to the 

old wet kilns is presented. A single, large SCR is modeled that combines the emissions and flow 

of the three kilns into one large control unit is modeled to demonstrate the impact on control 

costs. SCR is more cost effective at Ash Grove than at TXI due to higher gas temperatures and 

less required reheat of stack gas. 
Cement Kiln Report (FINAL – 7/14/2006) 1-9

Table 1-6 Summary of Technologies for Ash Grove #1 – Full Year Control 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate 

before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Transferable 702 5.57(5.05) 85% 596.7 0.84(0.76) $5,200 $12.00 

LoTOxTM Transferable 702 5.57(5.05) 85% 596.7 0.84(0.76) $2,900 $7.00 

SNCR Innovative 702 5.57(5.05) 35% 245.7 3.6(3.27) $2,200 $2.20 

Wet to 

Dry Available 2,205 5.68(5.15) 65% 1,433.3 2.0(1.81) $6,500 $11.00 

Large 3 

Kiln SCR Transferable 2,205 5.83(5.29) 85% 1,874.25 0.88(0.80) $4,200 $10.00 

SCR includes the cost of installing and operating RTO’s to reheat gas after ESPs. 

Wet to dry conversion analysis based on one large kiln to replace 3 small emissions are averaged for these scenarios. 

Table 1-7 Summary of Technologies for Ash Grove #2 – Full Year Control 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate 

before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Transferable 750 5.95(5.40) 85% 637.5 0.89(0.81) $5,200 $13.00 

LoTOxTM Transferable 750 5.95(5.40) 85% 637.5 0.89(0.81) $2,900 $7.50 

SNCR Innovative 750 5.95(5.40) 35% 262.5 3.9(3.54) $2,200 $2.30 

Wet to 

Dry Available 2,205 5.68(5.15) 65% 1,433.3 2.0(1.81) $6,500 $11.00 

Large 3 

Kiln SCR Transferable 2,205 5.83(5.29) 85% 1,874.25 0.88(0.80) $4,200 $10.00 

SCR includes the cost of installing and operating RTO’s to reheat gas after ESPs. 

Wet to dry conversion analysis based on one large kiln to replace 3 small. 

Table 1-8 Summary of Technologies for Ash Grove #3 – Full Year Control 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate 

before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Transferable 764 6.06(5.50) 85% 649.4 0.91(0.83) $5,500 $14.00 

LoTOxTM Transferable 764 6.06(5.50) 85% 649.4 0.91(0.83) $3,000 $7.90 

SNCR Innovative 764 6.06(5.50) 35% 267.4 3.9(3.54) $2,200 $2.30 

Wet to 

Dry Available 2,205 5.68(5.15) 65% 1,433.3 2.0(1.81) $6,500 $11.00 

Large 3 

Kiln SCR Transferable 2,205 5.83(5.29) 85% 1,874.3 0.88(0.80) $4,200 $10.00 

SCR includes the cost of installing and operating RTO’s to reheat gas after ESPs. 

Wet to dry conversion analysis based on one large kiln to replace 3 small. 
Cement Kiln Report (FINAL – 7/14/2006) 1-10

1.1.4. Ozone Season Only Control Costs 

The emissions reductions calculated in the tables below are based on operation of the 

control equipment during the Dallas/Ft. Worth ozone season unless otherwise noted. For 

example, SCR is presumed to operate only during the ozone season in the modeling. This results 

in a higher annualized cost effectiveness in dollars per ton of NOx controlled as less NOx is 

controlled on an annual basis. Wet kiln to dry preheat/precalciner unit conversions provide 

benefit for the full year and are not seasonal measures. Tables 1-9 through 1-16 are similar to 

Tables 1-1 through 1-8 except that adjustments have been made to represent seasonal operation. 

Holcim Ozone Season Results 

Table 1-9 Summary of Technologies for Holcim #1 – Ozone Season Control 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate 

before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Available 2,222 3.76 (3.41) 85% 1,267.3 0.56 (0.51) $1,900 $2.00 

LoTOxTM Transferable 2,222 3.76 (3.41) 85% 1,267.3 0.56 (0.51) $2,400 $2.35 

SNCR Available 2,222 3.76 (3.41) 50% 745.4 1.9 (1.7) $1,500 $1.00 

Calciner 

Upgrade Available 2,222 3.76 (3.41) 40% 888.8 2.2 (2.0) $2,795 $2.70 

Emissions reductions are for ozone season unless otherwise noted. 

40% for new low-NOx calciner based on literature. 

Cost effectiveness for calciner upgrade calculated by ratio of burden costs using SCR data. 

Calciner upgrade is not a seasonal ozone measure. 

 

Table 1-10 Summary of Technologies for Holcim #2 – Ozone Season Control 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate 

before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Available 1,778 3.01(2.73) 85% 1,014.0 0.45(0.41) $2,000 $1.70 

LoTOxTM Transferable 1,778 3.01(2.73) 85% 1,014.0 0.45(0.41) $2,300 $1.90 

SNCR Available 1,778 3.01(2.73) 50% 596.5 1.5(1.36) $1,700 $0.90 

Emissions reductions are for ozone season unless otherwise noted. 
Cement Kiln Report (FINAL – 7/14/2006) 1-11

TXI Ozone Season Results 

Table 1-11 Summary of Technologies for TXI #1 & #4 – Ozone Season Only 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Transferable 838 5.67(5.14) 85% 477.9 0.85 (0.77) $5,500 $8.90 

LoTOxTM Transferable 838 5.67(5.14) 85% 477.9 0.85 (0.77) $3,300 $4.70 

SNCR Innovative 838 5.67(5.14) 35% 196.8 3.7 (3.36) $2,400 $1.60 

Wet to Dry Available 1,802 5.67(5.14) 65% 1,171.3 2.0 (1.81) $6,700 $11.00 

Large 3 

Kiln SCR Transferable 1,802 5.67(5.14) 85% 1,027.7 0.85 (0.77) $5,400 $6.00 

Emissions reductions are for ozone season unless otherwise noted. 

SCR includes the cost of installing and operating RTO’s to reheat gas after ESPs. 

Wet to dry conversion analysis based on one large kiln to replace existing capacity, emissions reduction is full year. 

Table 1-12 Summary of Technologies for TXI #2 & #3 – Ozone Season Only 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Transferable 85 3.4 (3.08) 85% 48 0.51(0.46) $96,000 $13.50 

LoTOxTM Transferable 85 3.4 (3.08) 85% 48 0.51(0.46) $11,000 $10.50 

SNCR Innovative 85 3.4 (3.08) 35% 20 2.2 (2.00) $13,000 $5.00 

Wet to Dry Available 1,802 5.67(5.14) 65% 1,171.3 2.0 (1.81) $6,700 $11.00 

Large 3 

Kiln SCR Transferable 1,802 5.67(5.14) 85% 1,027.7 0.85 (0.77) $5,400 $6.00 

Emissions reductions are for ozone season unless otherwise noted. 

SCR includes the cost of installing and operating RTO’s to reheat gas after ESPs. 

Wet to dry conversion analysis based on one large kiln to replace existing capacity, emissions reduction is full year. 

 Table 1-13 Summary of Technologies for TXI #5 – Ozone Season Only 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate 

before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Available 1,710 1.50(1.36) 80% 918.0 0.30(0.27) $2,200 $0.87 

LoTOxTM Transferable 1,710 1.50(1.36) 80% 918.0 0.30(0.27) $2,600 $0.90 

SNCR Available 1,710 1.50(1.36) 35% 401.6 1.0(0.91) $2,500 $0.45 

Emissions reductions are for ozone season unless otherwise noted. 
Cement Kiln Report (FINAL – 7/14/2006) 1-12

Ash Grove Ozone Season Results 

Table 1-14 Summary of Technologies for Ash Grove #1 – Ozone Season Only 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate 

before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Transferable 702 5.57(5.05) 85% 400.4 0.84 (0.76) $5,800 $9.20 

LoTOxTM Transferable 702 5.57(5.05) 85% 400.4 0.84 (0.76) $3,400 $5.00 

SNCR Innovative 702 5.57(5.05) 35% 164.9 3.6 (3.27) $2,500 $1.70 

Wet to 

Dry Available 2,205 5.68 (5.15) 65% 1,433.3 2.0 (1.81) $6,500 $11.00 

Large 3 

Kiln SCR Transferable 2,205 5.83 (5.29) 85% 1,257.6 0.88 (0.80) $4,600 $7.80 

SCR includes the cost of installing and operating RTO’s to reheat gas after ESPs. 

Wet to dry conversion analysis based on one large kiln to replace 3 small, emissions reduction is full year. 

Table 1-15 Summary of Technologies for Ash Grove #2 – Ozone Season Only 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate 

before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Transferable 750 5.95 (5.40) 85% 427.8 0.89 (0.81) $5,800 $9.90 

LoTOxTM Transferable 750 5.95 (5.40) 85% 427.8 0.89 (0.81) $3,500 $5.40 

SNCR Innovative 750 5.95 (5.40) 35% 176.1 3.9 (3.54) $2,400 $1.70 

Wet to Dry Available 2,205 5.68 (5.15) 65% 1,433.3 2.0 (1.81) $6,500 $11.00 

Large 3 

Kiln SCR Transferable 2,205 5.83 (5.29) 85% 1,257.6 0.88 (0.80) $4,600 $7.80 

Emissions reductions are for ozone season unless otherwise noted. 

SCR includes the cost of installing and operating RTO’s to reheat gas after ESPs. 

Wet to dry conversion analysis based on one large kiln to replace 3 small, emissions reduction is full year. 

Table 1-16 Summary of Technologies for Ash Grove #3 – Ozone Season Only 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate 

before 

control tpy 

Emissions Rate 

before control 

lbsNOx/tonne 

(lbsNOx/ton) 

Percent 

Control 

Emissions 

Reduction 

from Control 

tpy 

Controlled 

Emissions 

lbsNOx/tonne 

(lbsNOx/ton) 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

SCR Transferable 764 6.06 (5.50) 85% 435.7 0.91(0.83) $6,100 $10.60 

LoTOxTM Transferable 764 6.06 (5.50) 85% 435.7 0.91(0.83) $3,700 $5.70 

SNCR Innovative 764 6.06 (5.50) 35% 179.4 3.9 (3.54) $2,400 $1.70 

Wet to Dry Available 2,205 5.68 (5.15) 65% 1,433.3 2.0 (1.81) $6,500 $11.00 

Large 3 

Kiln SCR Transferable 2,205 5.83 (5.29) 85% 1,257.6 0.88 (0.80) $4,600 $7.80 

Emissions reductions are for ozone season unless otherwise noted. 

SCR includes the cost of installing and operating RTO’s to reheat gas after ESPs. 

Wet to dry conversion analysis based on one large kiln to replace 3 small, emissions reduction is full year. 
Cement Kiln Report (FINAL – 7/14/2006) 1-13

1.1.5. Summary of Performance and Cost Modeling Assumptions 

 The ERG Team used best engineering judgment in determining modeling parameters 

from the various data available. The ERG Team relied primarily on permit materials and 

emissions statements submitted to the State of Texas as well as material supplied by the 

companies in establishing the modeling parameters used to estimate control performance, cost 

and cost effectiveness. The ERG Team considered long term trends to derive estimated values 

for factors such as annual production capacity of clinker, which was adjusted by an assumed 

capacity factor that may be lower than current high operating levels. Values for airflows and 

temperatures were not always available for the proposed control device locations and values 

were estimated based on temperature and moisture adjustments. 

 Cost effectiveness is calculated for NOx reductions only. A wet to dry kiln conversion, 

calciner upgrade or the addition of a scrubber will result in reduction of other pollutants. As this 

study is performed to assess ozone control measures, these benefits have not been included in the 

cost benefit analyses. A simple spray tower that would not effectively control SO2 is priced as 

part of the LoTOxTM analysis for wet kilns. If a flue gas desulfurization (FGD) scrubber were 

added, the price would increase. However, additional benefits for other pollutants controlled 

would also occur. For example, adding FGD scrubbers to Ash Grove wet kilns could result in 

approximately 1,800 tons per year of SO2 emissions reduction per kiln and a wet kiln conversion 

would result in approximately 1,300 tons per year of SO2 reduction per kiln. Both the oxides of 

nitrogen and sulfur are also precursors of fine particle formation. Control technologies that 

remove these precursors would provide additional, unquantified benefits to regional air quality. 

1.1.5.1. Kiln replacement or upgrading 

 Both kiln replacement and upgrading were considered for modeling of the wet kilns. 

Replacement is the only option actually modeled because none of the wet kilns is large enough to 

be practically upgraded to a semi-wet system. Conversion of wet to semi-wet systems has been 

shown to result in significant production increases and NOx decreases, but fuel savings have 

proven to be limited. Upgrading the preheater/calciner tower on Holcim #1 was also considered 

as an option. This process line is somewhat older than Holcim #2 or TXI #5 and the design 
Cement Kiln Report (FINAL – 7/14/2006) 1-14

somewhat less energy efficient. The assumed performance of Holcim #1 with a modern, 

redesigned low-NOx preheater/calciner tower was based on the survey of the performance of 

recently constructed new facilities and the performance of TXI #5 which is using similar Ellis 

County limestone to make cement. Although Holcim #2 is approximately the same age as TXI 

#5, TXI #5 produces much less NOx per tonne of clinker produced. The expert panel believed 

that a new, intrinsic low- NOx designed tower for Holcim #1 should perform substantially better 

than Holcim #2 and more like TXI #5. The cost values for wet to dry conversions and for 

upgrading the design of Holcim #1, as well as the energy improvements, are taken primarily 

from Department of Energy reports. The emissions rates in tons per year of NOx used in these 

model runs are based on the assumption that a large new modern dry preheater/calciner unit 

would replace several older units. At Ash Grove, where all the kilns are highly utilized, this 

represents a composite of all the kilns. At TXI, where primarily kilns #1 and #4 are used, the 

replacement model looks at the emissions from these units plus a small amount from kilns #2 and 

#3. 

1.1.5.2. SCR 

The SCR cost model is a boiler cost model developed for use on coal-fired utility boilers. 

The SCR model is developed from the OAQPS Cost Manual and has been applied to other 

processes such as refinery FCCUs with reasonable success. 

For the dry kilns, the model assumes that a location for SCR can be found where reheat 

of the process gas is not required. This is a high dust assumption. For the wet kilns, installation 

is assumed to be located after the dust collectors (low dust) and that reheat of the exhaust gas 

will be required. The impact of reheat of the gas on NOx emissions was examined and found to 

be negligible. An increase of 5 to 10 tons per year of NOx was estimated to occur based on 

modeled natural gas fuel use. As the gas reheater emissions could also be controlled by the SCR, 

the increase would reduce to one to two tons per year and was not included in the modeling. 

Based on the installation at Solnhofen (see Figure 4-1.1) of the SCR on the side of the tower, it 

was assumed that this configuration could work at the preheat/calciner kilns in Ellis County. The 

wet kilns, with the SCR located after the particulate controls were also assumed to have adequate 
Cement Kiln Report (FINAL – 7/14/2006) 1-15

space available. The reheat cost model is based on the OAQPS cost model for regenerative 

thermal oxidizers with 70% heat recovery. 

 Although current assumptions for coal-fired power plants would predict 90% or better 

control for SCR, this assumption has been lowered to 85% for these model runs. This was done 

to represent a conservative approach to the cost modeling that included consideration of potential 

problems in applying SCR, such as higher variability of the gas stream comparing a utility boiler 

to a cement plant, and lack of experience in achieving high levels of control using SCR in the 

cement industry. Due to the lower emissions rates at TXI #5, the control efficiency was modeled 

at 80%. This was based on the evaluation of the current relatively low concentrations of NOx in 

the TXI stack and uncertainty about SCR performance in a cement kiln at very low endpoint 

concentrations. These control efficiencies are not intended to define the final performance of 

this technology, but to evaluate costs under conservative assumptions. The actual decrease in 

performance, if any occurs, cannot be determined in advance. In the application of SCR to coalfired boilers, higher levels of performance are typically achieved by increasing the amount of 

catalyst, and, thereby increasing the contact between reagent and catalytic material. Achieving 

higher control efficiencies increases the initial capital cost and maintenance costs for the unit. 

The lower performance rates were selected for the purposes of the cost modeling based on the 

engineering judgment of the expert panel and may not reflect the final capability SCR if installed 

at these locations. 

1.1.5.3. SNCR 

The SNCR cost model is also a boiler cost model developed for use on coal-fired utility 

boilers. The SNCR model is derived from the OAQPS cost manual and EPA’s OTAG cost 

modeling. It has been simplified to obtain capital costs primarily on flow rates. The ERG team 

attempted to verify the reasonableness of these models’ results for the Ellis County dry kilns. 

The estimates for wet kilns are conjecture. No accurate costing can be developed without an 

understanding of the ultimate design of the control system. Limited information on installation 

of SNCR on a wet kiln in France suggests that this is a technically feasible option. Lacking any 

detailed information on the unit in France, controls costs were estimated based on the dry kiln 
Cement Kiln Report (FINAL – 7/14/2006) 1-16

model. Reagent costs are a substantial part of the annualized cost of SNCR, so this rough cost 

estimate for wet kilns was still considered to be a valuable approximation. 

As with the SCR control efficiencies, the cost models were run at conservative control efficiency 

values. A value of 50% was used for the Holcim kilns and 35% was used for TXI #5 and the wet 

kilns. The control efficiency of 35% at TXI was consistent with the reported performance of a 

European application at approximately 100 ppm. The value for wet kilns represented a reduced 

expectation for this experimental approach. The performance rates were selected for the purposes 

of the cost modeling based on the engineering judgment of the expert panel and may not reflect 

the final capability of SNCR if installed at these locations. 

1.1.5.4. Oxidation Technologies 

LoTOxTM

The LoTOxTM model is based on the OAQPS model for thermal oxidation. Specific 

inputs to this model were developed with assistance from the BOC Group, PLC (BOC) and 

should produce results reasonably close to the current costs of their oxidation technology. For 

the dry process kilns, no scrubbers were assumed to be required as the existing scrubbers were 

expected to be sufficient for removal of oxidation products from the process gas. For the wet 

kilns, BOC provided approximate costs for installing LoTOxTM with spray towers. BOC 

provided generalized costs; detailed estimates on scrubber operating costs have not been 

developed. No cost model runs were performed for single LoTOxTM units to control multiple 

kilns as was done for SCR. The LoTOxTM cost model does not have the same benefit of scale for 

larger units as does SCR. Because little or no cost benefit would be predicted from a single, 

large LoTOxTM unit, no cost estimates were done for combined control of multiple kilns. 

The same control efficiencies were used for LoTOxTM as for SCR. Again, this was done 

to make the cost estimates conservative due to lack of application of these technologies to the 

cement industry. BOC asserted that control efficiencies of 95% and 98% could be obtained 

using this technology. However, for this modeling effort, the same performance levels were 

modeled for LoTOxTM as for SCR. As with the SCR modeling, this was not done as a reflection 
Cement Kiln Report (FINAL – 7/14/2006) 1-17

on the final performance capability of the technology, but rather to provide an equivalent and 

conservative basis for evaluating the cost of control. 

The accuracy of OAQPS cost modeling approaches is typically within 30% or so for 

instances where parameters are accurately defined and the process well known. This is a useful 

tool for comparing different technologies. However, closely scrutinized vendor quotes should be 

the basis of any final comparison of technologies. Minor differences in modeling results are 

likely to be the product of assumptions regarding cost of electricity or reagents. For example, for 

Holcim #2, the cost of SCR was predicted to be $1,700 per ton of NOx and LoTOxTM

 was 

modeled at $2,100 per ton. 

A relatively small difference in the cost effectiveness for SCR and LoTOxTM should not 

be viewed as significant without understanding the contributing factors. Reagent cost and 

control efficiency assumptions can account for these differences. Cost for ammonia reagent is 

currently very volatile due to relatively high natural gas costs. A value of $500 per ton was used 

to reflect higher costs experienced in 2005, but not the currently higher short-term prices. If 

current high prices persist, the cost difference between these two technologies would be 

negligible. If LoTOxTM proves better at responding to fluctuations in NOx concentrations and 

achieves a higher level of control than SCR, this would also tend to push cost effectiveness of the 

two technologies closer together. Differences of 20% in the cost effectiveness of two 

technologies should not be a basis for selecting one technology over another. If initial modeling 

results produce similar economic and performance values, both technologies should be 

considered for vendor pricing unless other factors dictate a clear preference for one over the 

other. Other factors, such as a determination that reheat was needed for application of SCR to 

dry kilns, would have a substantial impact and the two technologies would no longer appear 

equivalent in cost effectiveness. 

Other Oxidation Technologies 

There are other oxidation technologies using hydrogen peroxide or other chemical 

reagents. Most of these technologies are new; relatively low temperature end-of-pipe control 

techniques. As mentioned under the discussion for SCR above, the cost for ammonia reagents is 
Cement Kiln Report (FINAL – 7/14/2006) 1-18

currently higher than it has been historically. Other oxidation technologies may allow use of 

lower cost reagents that may improve cost effectiveness for plants with existing wet scrubbers. 

There is one higher temperature hydrogen peroxide technology that may be able to be 

implemented inside an existing precalciner system, although it still requires a wet scrubber. At 

current hydrogen peroxide commodity prices, one of these alternative technologies may be more 

cost effective than ozone or ammonia based reagent alternatives. None of these technologies was 

found to have been used on a cement kiln or comparable system. Therefore, costing of these 

options was not attempted. All of these systems should be considered innovative but should not 

be ruled out of consideration, as a lower cost reagent would have a substantial impact on annual 

control costs. 

1.1.6. Evaluation of Chemistry and Process Variables on NOx Formation 

 As part of the overall evaluation of the potential to control, correlate and predict NOx

formation in the Ellis County Kilns, short-term process and emissions data were evaluated. 

These analyses were performed on data that was considered confidential business information 

and are, therefore, not summarized or reported. The statistical correlations evaluated included 

comparison of NOx emissions rate to: 

 Kiln Feed of SiO2,

 Al2O3, 

 Fe2O3, 

 CaO, 

 MgO, 

 SO3, 

 Na2O, 

 K2O passing 200 mesh, 

Clinker K2O, 

Production rate, 

Coal/Coke passing 200 mesh, 

Chain zone temp, and 

Kiln drive amps. 

In addition, graphs were produced looking at the relationships between gaseous pollutants and 

NOx emissions rate. The conclusion of this investigation was essentially negative. None of the 
Cement Kiln Report (FINAL – 7/14/2006) 1-19

process parameters and relations to formation of gaseous pollutants that were evaluated produced 

any relationships that indicated the potential for further control of NOx beyond the control 

measures already in place (with the exception of the wet kilns at TXI that are not yet permitted 

for mid-kiln injection while burning hazardous waste). Furthermore, these parameters did not 

indicate that changes in feed constituents had an adverse or positive correlation to NOx emissions 

rate. 

 This investigation did not show any correlations between feed and process materials and 

NOx formation rates that would prohibit the use of the control technologies and techniques 

reviewed in this report. This investigation did not show any direct relationships between feed 

materials and NOx formation rates that could potentially be exploited to further reduce NOx

emissions rates through process modifications. However, one interesting aspect of the 

investigation of the chemistry of the feed materials was a strong suspicion that nitrogen bearing 

feed materials present in Ellis County may be producing some limited non-selective noncatalytic reduction of NOx. The exact nature of the material was not identified in this study. 

Similar effects have been noted in other kilns being fed materials such as nitrogen bearing sands. 

This may help to explain the current low NOx emissions rates of TXI #5. This is discussed in 

Section 5.2 of this report. The chemical analyses of the feed materials was requested by the 

three plants to be treated as confidential business information and the site specific information is 

not included in this report for that reason. Generally summaries of the overall characteristics 

based on averages for all three plants are presented in Sections 5.1 and 5.2 of this report. 

1.1.7. Summary of Environmental and Other Impacts 

 Sampling of the materials fed to the kilns was conducted and is summarized in Section 5 

of this report along with characterizations of the kiln feed materials supplied by the cement 

plants. This testing showed that the materials fed to the Ellis County kilns was substantially 

uniform for the purposes of evaluating the impacts of feed materials on control equipment. 

Although there was variation, the variation between different samples, wet and dry kiln feed and 

the different Ellis County plants was not considered by the experts evaluating the individual 

control technologies to be significant enough to impact any of the control determinations. The 

main concerns were levels of sulfur and organics in the feed materials and the resulting 
Cement Kiln Report (FINAL – 7/14/2006) 1-20

concentration of sulfur oxides, hydrocarbons and, additionally, carbon monoxide in the process 

gas streams emitted by the kilns and precalciners. These concerns and potential impacts are 

discussed under Section 4 of this report to the extent that these issues needed to be specifically 

evaluated in considering application of any of the control technologies to Ellis County kilns. For 

example, the concentrations of sulfur dioxide in the gas streams of the Ellis County kilns are 

discussed in Section 4.1.1 in comparison to levels where selective catalytic reduction has been 

applied to electric utility boilers. 

 The potential impacts are summarized and compared in Table 1-17 below for all of the 

major control options considered in this report. To the extent that issues such as reagent release 

to the atmosphere (slip) or clogging and/or corrosion resulting from reagents or reactions in 

process and control equipment were concerns in applying control technologies in Ellis County, 

these issues are also discussed in Section 4 of this report. Table 1-17 summarizes and compares 

potential impacts to allow comparisons between technologies. 
Cement Kiln Report (FINAL – 7/14/2006) 1-21

Table 1-17 Environmental and Other Impacts of Control Technology 

Impact 

Selective Catalytic 

Reduction 

Selective NonCatalytic Reduction Oxidation Technologies Kiln 

Modernizations 

Process Chemistry 

Limits Application 

of Control 

Technology in Ellis 

County 

Ellis County 

chemistry within 

limits a

Ellis County 

chemistry within 

limits a

Ellis County chemistry 

within limits a

 

Chemistry not a 

factor 

Release of 

Additional Criteria 

Pollutants 

Accelerated 

formation of PM2.5 b

Accelerated 

formation of PM2.5 b

Possible decrease in 

VOCs, scrubbers can 

produce co-control of 

SOx and other 

pollutants c

Potential large 

decreases unless 

capacity 

increased d

Reagent Release to 

the Atmosphere 

Possible ammonia 

slip < 5 ppm e

Possible ammonia 

slip < 10 ppm e

Reactive reagents 

unlikely to "slip" 

No 

Clogging and/or 

Corrosion Potential 

Possible depending 

on location f

Possible depending 

on location f

Possible - scrubber & 

ducts design g

No 

Formation of Solid 

or Hazardous 

Pollutants 

Periodic removal of 

ammonia salt 

deposits h

Periodic removal of 

ammonia salt 

deposits h

No, potentially can 

decrease emissions of 

organics. 

No 

Formation of 

Wastewater 

Contaminants 

No No Probably used onsite as 

fertilizer i

No 

Explanation of notes in Table 1-17. 

a The constituents in feed materials and gaseous pollutant concentrations have been evaluated by the experts for 

each control technology and determined to be within acceptable limits for deploying the control technology on Ellis 

County kilns. 

b Presence of "slip" ammonia reagent is expected to form sulfate and nitrate fine particles closer to the stack and 

may cause increased opacity at the stack. However, this is not a “new” pollutant in that the precursor pollutants 

released by cement kilns will tend to form fine particles in the atmosphere using atmospheric ammonia. The excess 

ammonia from SCR and SNCR will cause formation to occur closer to the stack. Excess opacity with the raw mill 

off-line may be exacerbated using SNCR. This occurs in units that do not use SNCR and wet lime injection has 

been suggested as a control measure. 

c Oxidation technologies can also oxidize hydrocarbons, particularly the higher temperature peroxide-based control 

technologies. These technologies have the potential to reduce VOC emissions. Oxidation technologies also require 

the use of a scrubber to remove oxidized pollutants and the scrubber can also be designed to control pollutants such 

as SO2 and acid mists. 

d The major “modernization” projects considered in this report were wet to dry kiln conversion and efficiency 

improvements for the older dry kiln at Holcim. Efficiency improvements result in substantial energy savings and 

emissions reductions. However, these options require large capital investments that may only be economically 

justified by production increases that could negate the efficiency improvements and emissions reductions. 

e In preheater/calciner units, recent German experience suggests that most of the ammonia ends up in the raw meal 

during drying and grinding and is not released to the atmosphere. As discussed above under footnote “b”, this 

recycling of ammonia and ammonia salts may result in increased opacity when the raw mill is off-line. 

f SCR is not likely to produce corrosive byproducts. The potential for clogging is discussed below as sulfate 

deposits. 
Cement Kiln Report (FINAL – 7/14/2006) 1-22

g As the cement kiln exhaust gas steam is typically moist, oxidation products can become hydrated and acidic prior 

to removal in the scrubber. Depending on the reagent and injection location selected, this may require replacement 

of ductwork and components with more corrosion resistant materials. 

h Periodic removal of deposits of ammonia salts (ammonium sulfate/chloride) may be required from equipment 

downstream of SCR and SNCR ammonia injection points. In preheater/calciner units, recent German experience 

suggests that most of the ammonia ends up in the raw meal during drying and grinding and is not released to the 

atmosphere. To the extent that ammonia salts form primarily in the raw mill, this limits potential downstream 

problems except when the raw mill is off-line. 

i Scrubber waters rich in nitrates could be used on-site as fertilizer to promote plantings used to control wind 

erosion in and around quarry areas. 
Cement Kiln Report (FINAL – 7/14/2006) 2-1

2.0 DEFINING PARAMETERS FOR CONTROL EVALUATION 

This section of the report is taken from the EPA 2000 Report and is included, with minor 

editing by the ERG Team. This information is included to provide the Texas environmental 

communities with the comprehensive background information necessary to understand the 

parameters that dictate NOx control options at cement kilns. 

2.1 Overview of Portland Cement Manufacturing Process and NOx Generation

 Portland cement, a fine gray or white powder, is the generic term for the type of cement 

used in virtually all concrete, which is a mixture of aggregates (e.g., crushed stone, gravel, sand), 

water, and cement. The American Society for Testing and Materials (ASTM) defines Portland 

cement as "hydraulic cement (cement that not only hardens by reacting with water but also forms 

a water-resistant product) produced by pulverizing clinkers consisting essentially of hydraulic 

calcium silicates, usually containing one or more of the forms of calcium sulfate as an inter 

ground addition." 

 In 2004, the Portland cement industry in the U.S. consisted of 114 facilities in 37 States 

(and two facilities in Puerto Rico). Approximately 90 million tons of Portland cement were 

produced in 2004, with California, Texas, Pennsylvania, Michigan, Missouri, and Alabama 

accounting for approximately 50 percent of the production (1). 

 Hydraulic Portland cement, the primary product of the cement industry, is made from 

clinker blended with gypsum. Clinker is produced by heating a mixture of limestone, clay, and 

other ingredients to incipient fusion at a high temperature. Limestone is the single largest 

ingredient required in the cement-making process, and most cement plants are located near large 

limestone deposits. Portland cement is used in almost all construction applications including 

homes, public buildings, roads, industrial plants, dams, bridges, and many other structures. 

 In the cement-making process, the solid raw materials are heated to their fusion 

temperature, typically 1400 to 1500 EC (2550 to 2750 EF), by burning various fuels such as 

coal. Portland cement has been defined as Aa hydraulic cement produced by pulverizing Portland 
Cement Kiln Report (FINAL – 7/14/2006) 2-2

cement clinker and usually containing calcium sulfate.”(2) Portland-cement clinker has been 

defined as Aa clinker, partially fused by pyroprocessing, consisting predominantly of crystalline 

hydraulic calcium silicates.”(2) Burning an appropriately proportioned mixture of raw materials 

at a suitable temperature produces hard fused nodules called clinker, which are further ground to 

a desired fineness. 

 Five types of Portland cement are recognized in the United States which contain varying 

amounts of the basic clinker compounds given in Table 3-1. (3) Different types of cements are 

produced by starting with appropriate kiln feed composition, blending the clinker with the 

desired amount of calcium sulfate, and grinding the product mixture to appropriate fineness. 

Manufacture of cements of all of the various types involves the same basic high temperature 

fusion and clinkering process responsible for the NOx emissions from cement kilns. 

 The five basic types of Portland cement recognized and produced in the United States are 

described below. (3,4) In addition, different varieties are prepared by using various blending 

formulations. (5)

 Type I Portland cement is a normal, general-purpose cement suitable for all uses. It is 

used in general construction projects such as buildings, bridges, floors, pavements, and other 

precast concrete products. Type I is also known as regular cement and most commonly known 

as gray cement because of its color. White cement typically contains less ferric oxide and is used 

for special applications. There are other types of cements in general use such as oil-well cement, 

quick-setting cement, and others for special applications. Type IA Portland cement is similar to 

Type I with the addition of air-entraining properties. 
Cement Kiln Report (FINAL – 7/14/2006) 2-3

Table 2-1. Basic Clinker Compounds (3) 

Formula Name 

2CaO SiO2 Dicalcium silicate 

3 CaO Si O2 Tricalcium silicate 

3CaO AL203 Tricalcium aluminate 

4CaO A1203 Fe203 Tetracalcium aluminoferrite 

MgO Magnesium oxide in free state or combined in di- or tricalcium silicate lattice. 

 Type II Portland cement generates less heat at a slower rate and has a moderate resistance 

to sulfate attack. Type II Portland cements are for use where moderate heat of hydration is 

required or for general concrete construction exposed to moderate sulfate action. Type IIA 

Portland cement is identical to Type II, with the exception of inclusion of an air-entraining 

admixture, and produces air-entrained concrete. 

 Type III Portland cement is a high-early-strength cement and causes concrete to set and 

gain strength rapidly. Type III is chemically and physically similar to Type I, except that its 

particles have been ground finer. It is made from raw materials with a lime to silica ratio higher 

than that of Type I cement. It contains a higher proportion of tricalcium silicate (3CaO.SiO2) 

than regular Portland cements. Type IIIA is an air-entraining, high-early-strength cement. 

 Type IV Portland cement has a low heat of hydration and develops strength at a slower 

rate than other cement types, making it ideal for use in dams and other massive concrete 

structures where there is little chance for heat to escape. Type IV Portland cement contains a 

lower percentage of tricalcium silicate (3CaO.SiO2) and tricalcium aluminate (3CaO.

A12O3) than 

type I, thus lowering the heat evolution. Consequently, the percentage of dicalcium silicate is 

increased substantially and the percentage of tetracalcium aluminoferrite (4CaO.A12O3

.Fe2O3) 

may be increased or may stay the same. 

 Type V Portland cement is used only in concrete structure that will be exposed to severe 

sulfate action, principally where concrete is exposed to soil and groundwater with a high sulfate 

content. Type V Portland cements are those which, by their composition or processing, resist 

sulfates better than the other four types. 
Cement Kiln Report (FINAL – 7/14/2006) 2-4

 The use of air-entraining agents increases the resistance of the hardened concrete to 

scaling from alternate freezing and thawing. By adding these materials to the first three types of 

cements, IA, IIA, and IIIA varieties of cements are produced. Additional varieties of cements 

are produced for special applications by blending different ingredients: masonry cement, 

expansive cement, oil-well cement, etc. Masonry cements are commonly finely ground mixtures 

of Portland cement, limestone, and air-entraining agents. Granulated blast furnace slags and 

natural or artificial pozzolans are mixed and interground with Portland cement to prepare still 

other varieties such as blended types IP, IS, S, I(PM), and I(SM). (5) 

2.1.1 Description of the Cement Industry 

 About 77.6 million metric tons of gray Portland and 274,000 metric tons of white cement 

were produced in a total of 198 cement kilns at 118 plants in the United States in 1998. (6) This 

was a 6.0 percent increase from the 1990 reported total production of 73.5 million metric tons. 

As shown in Figure 3-1, cement industry annual clinker capacity steadily declined from the 1975 

peak through 1990 and has steadily increased since the 1990 low. While the number of kilns has 

dropped sharply, average kiln size has increased. Since 1973 when average kiln size was 

173,000 metric tons, average kiln size has now reached 393,000 metric tons. Although 42 

cement companies produced clinker in 1998, the top 5 companies provided about 44.2 percent of 

the total finish grinding capacity. This is evidence of a high concentration of the U.S. production 

among a limited number of top producers. Table 2-2 provides a list of all companies along with 

their share of the total clinker production. Table 2-3 lists the clinker producing capacity in the 

United States by States. The locations of the operating kilns are shown in Figure 2-2. California 

and Texas are the two largest states in terms of clinker capacity with Pennsylvania, Missouri, and 

Alabama rounding out the top five. Fourteen states and the District of Columbia had no cement 

clinker-producing plants in 1998. (6) 

 The large majority of the cement plants (about 82.4 percent) in the United States are coal 

fired with about 2.8 percent using natural gas, and 0.9 percent using oil as the primary fuel. (6) 

The remaining 13.9 percent of the plants used other combinations, e.g. coal/waste as primary 
Cement Kiln Report (FINAL – 7/14/2006) 2-5

fuel. In 1998, 11 plants used waste as a primary fuel with 49 plants reporting waste as an 

alternate fuel. 

Overview of Cement Manufacturing Process 

 The process of Portland cement manufacture consists of: (7) 

y Quarrying and crushing the rock; 

y Grinding the carefully proportioned materials to high fineness; 

y Subjecting the raw mix to pyroprocessing in a rotary kiln; and 

y Grinding the resulting clinker to a fine powder. 

 A layout of a typical plant is shown in Figure 3-3, which also illustrates differences 

between the two primary types of cement processes: wet process and dry process. (7) Newer 

designs of dry process plants are equipped with innovations such as precalciners and/or 

suspension preheaters to increase the overall energy efficiency of the cement plant. (7) Figure 34 

is an illustration of a preheater/precalciner type of dry process system. (8) 

 The choice between the wet or dry process for cement manufacturing often depends upon 

the moisture content in the raw feed materials mined from quarries. If the moisture content of 

the feed materials is already very high (15 to 20 percent), a wet process may be attractive. The 

recent trend, however, has been toward the dry process with preheater/precalciner systems. In 

1998, about 20.6 million metric tons of clinker were produced by the wet process with 57.4 

million metric tons produced by a dry process. Within the dry process category, 14.2 million 

metric tons were produced by facilities equipped with a preheater system and 26.1 million metric 

tons were produced by facilities equipped with a precalciner system. (6) 

 The different steps involved in the cement manufacturing process are described in the 

following subsections. 

Raw Materials and Kiln Feed Preparation 

 Calcium carbonate and the oxides of silicon, aluminum, and iron comprise the basic 

ingredients of cement raw mix. Because of the large requirement for calcium, the plants are 
Cement Kiln Report (FINAL – 7/14/2006) 2-6

generally located near the source of the calcareous material. The requisite silica and alumina 

may be derived from a clay, shale, or overburden from a limestone quarry. Such materials 

usually contain some of the required iron oxide, but many plants need to supplement the iron 

with mill scale, pyrite cinders, or iron ore. Silica may be supplemented by adding sand to the 

raw mix, whereas alumina can be furnished by bauxites and alumina-rich flint clays. (7) 

Industrial byproducts are becoming more widely used as raw materials for cement, e.g., slags 

contain carbonate-free lime, as well as substantial levels of silica and alumina. Fly ash from 

utility boilers can often be a suitable feed component, since it is already finely divided and 

provides silica and alumina. 

 The bulk of raw materials originates in the plant quarry. A primary jaw or roll crusher is 

frequently located within the quarry and reduces the quarried limestone or shale to about 100 

mm top size. A secondary crusher, usually roll or hammer mills, typically gives a product of 

about 10 to 25 mm top size. Combination crusher-dryers can utilize exit gases from the kiln or 

clinker cooler to dry wet material during crushing. Each of the raw materials is stored separately 

and proportioned into the grinding mills separately using weigh feeders or volumetric 

measurements. Ball mills are used for both wet and dry processes to grind the material to a 

fineness such that only 15 to 30 wt% is retained on a 74-μm (200 mesh) sieve. 

 In the wet process the raw materials are ground with about 30 to 40 percent water, 

producing a well-homogenized mixture called slurry. Raw material for dry process plants is 

ground in closed-circuit ball mills with air separators, which may be adjusted for the desired 

fineness. Drying may be carried out in separate units, but most often is accomplished in the raw 

mill simultaneously with grinding. Waste heat can be utilized directly in the mill by coupling the 

raw mill to the kiln- and/or clinker cooler exhaust. For suspension preheater-type kilns, a roller 

mill utilizes the exit gas from the preheater to dry the material in suspension in the mill. A 

blending system provides the kiln with a homogeneous raw feed. In the wet process the mill 

slurry is blended in a series of continuously agitated tanks in which the composition, usually the 

calcium oxide content, is adjusted as required. These tanks may also serve as kiln feed tanks or 

the slurry may be pumped to large kiln feed basins. Dry process blending is usually 

accomplished in a silo with compressed air. (7) 
Cement Kiln Report (FINAL – 7/14/2006) 2-7

Pyroprocessing 

 All cement clinker is produced in large rotary kiln systems. The rotary kiln is a 

refractory brick-lined cylindrical steel shell [3 to 8 m (10 to 25 ft) diameter, 50 to 230 m (150 to 

750 ft) long] equipped with an electrical drive to rotate the kiln on its longitudinal axis at one to 

three rpm. It is a countercurrent heating device slightly inclined to the horizontal, so that 

material fed into the upper end travels slowly by gravity to be discharged into the clinker cooler 

at the lower, discharge end. The burners at the firing end, i.e., the lower or discharge end, 

produce a current of hot gases that heats the clinker, and the calcined and raw materials in 

succession, as it passes upward toward the feed end. Refractory bricks of magnesia or alumina 

combinations line the firing end. In the less heat-intensive midsection of the kiln, bricks of lower 

thermal conductivity are often used. Abrasion-resistant bricks or monolithic castable linings are 

used at the feed end. (7) 

 Pyroprocessing may be conveniently divided into four stages, as a function of location 

and temperature of the materials in the rotary kiln. (9) 

1. Evaporation of uncombined water from raw materials, as material temperature 

increases to 100°C (212°F); 

2. Dehydration, as the material temperature increases from 100oC to approximately 

430°C (800°F) to form dehydrated clay minerals composed of oxides of silicon, 

aluminum, and iron; 

3. Calcination, during which carbon dioxide (CO2) and CaO are formed from 

calcium carbonates, primarily between 900°C (1,650°F) and 982°C (1,800°F); 

and 

4. Reaction, of the oxides in the burning zone of the rotary kiln, to form cement 

clinker at temperatures of approximately 1,510°C (2,750°F). 

 The duration and location of these stages in an actual kiln depend upon the type of 

process used, e.g., wet or dry, and the use of preheaters and precalciners as discussed in the 

following section. 

 It is desirable to cool the clinker rapidly as it leaves the burning zone. Heat recovery, 

preheating of combustion air, and fast clinker cooling are achieved by clinker coolers of the 
Cement Kiln Report (FINAL – 7/14/2006) 2-8

reciprocating-grate, planetary, rotary, or shaft type. Most commonly used are grate coolers 

where the clinker is conveyed along the grate and subjected to cooling by ambient air, which 

passes through the clinker bed in cross-current heat exchange. The air is moved by a series of 

undergrate fans and becomes preheated to 370 to 1,000°C (700 to 1,830°F) at the hot end of 

cooler. A portion of the heated air serves as secondary combustion air in the kiln. Primary air is 

that portion of the combustion air needed to carry the fuel into the kiln and disperse the fuel. (7) 

2.1.2 Kiln Types and Operation 

 There are four main types of kilns used in Portland cement manufacture: 

y Long wet kilns; 

y Long dry kilns; 

y Dry kilns with preheaters; and 

y Dry kilns with precalciners. 

Wet kilns tend to be older units and are often located where the moisture content of feed 

materials from local sources (quarries) tends to be high. (10) 

Long Wet Kilns 

 In a long wet-process kiln, the slurry introduced into the feed end first undergoes 

simultaneous heating and drying. The refractory lining is alternately heated by the gases when 

exposed and cooled by the slurry when immersed; thus, the lining serves to transfer heat as do 

the gases themselves. Large quantities of water must be evaporated; thus most wet kilns are 

equipped with chains suspended across the cross section of the kiln to maximize heat transfer 

from the gases to the slurry, or chain garlands that serve to recuperate heat and simultaneously 

convey the slurry. After most of the moisture has been evaporated, the nodules, which still 

contain combined water, move down the kiln and are gradually heated to about 550°C (1,022°F) 

where the calcination reactions commence. The calcined material further undergoes clinkering 

reactions. As the charge leaves the burning zone and begins to cool, clinker minerals crystallize 

from the melt, and the liquid phase solidifies. The granular clinker material drops into the 

clinker cooler for further cooling by air. (7) 
Cement Kiln Report (FINAL – 7/14/2006) 2-9

 Wet kilns typically represent an older cement technology with smaller capacity kilns. In 

the United States wet cement kiln capacities range from 77,000 to 1,179,000 metric tons/year 

with an average of 307,000 metric tons/year. (6) 

Dry Process Kilns 

 The dry process utilizes a dry kiln feed rather than a slurry. Early dry process kilns were 

short, and the substantial quantities of waste heat in the exit gases from such kilns were 

frequently used in boilers to generate electric power, which often satisfied all electrical needs of 

the plant. In one modification, the kiln has been lengthened to nearly the length of wet-process 

kilns and chains were added. The chains serve almost exclusively a heat exchange function. 

Refractory heat-recuperative devices, such as crosses, lifters, and trefoils, have also been 

installed. So equipped, the long dry kiln is capable of better energy efficiency than wet kilns. 

Other than the need for evaporation of water, its operation is similar to that of a wet kiln. To 

improve the energy efficiency of the dry process, variations such as suspension preheaters and 

precalciners have been introduced as discussed in the next sections. (7) 

 Long dry process kilns are generally of a smaller capacity compared to long wet kilns. In 

the United States dry cement kiln capacities range from 50,000 to 590,000 metric tons/year with 

an average capacity of 265,000 metric tons/year. (6) 

Dry Kilns With Preheaters 

 In dry kilns with suspension preheaters, the pulverized feed passes by gravity through a 

series of cyclones and riser ducts in a vertical arrangement, where it is separated and preheated 

several times, typically in a four-stage cyclone system. The partially (40 to 50 percent) calcined 

feed exits the preheater tower into the kiln at about 800 to 900°C (1,500 to 1,650°F). The kiln 

length required for completion of the cement formation is considerably shorter than that of 

conventional kilns, and heat exchange is very good. Suspension preheater kilns are very energy 

efficient compared to wet or long dry kilns. The intimate mixing of the hot gases and feed in the 

preheater riser ducts promotes condensation of alkalies and sulfur on the feed, which sometimes 

results in objectionable high alkali and sulfur contents in the clinker, or occasions buildups in the 
Cement Kiln Report (FINAL – 7/14/2006) 2-10

preheater tower. To alleviate this problem, some of the kiln exit gases can bypass the preheater 

through a slipstream, or fewer cyclone stages can be used in the preheater with some sacrifice of 

efficiency. 

 Suspension preheater kilns represent a newer cement technology compared to the long 

dry kilns. They are also somewhat larger in production capacity than the conventional long 

rotary kilns. In the United States the preheater type kiln capacities range from 223,000 to 

1,237,000 metric tons/year with an average capacity of 406,000 metric tons/year. 

Dry Kilns With Precalciners 

 The success of preheater kiln systems, led to precalciner kiln systems. These units utilize 

a second burner to carry out calcination in a separate vessel attached to the preheater. The 

calciner utilizes preheated combustion air drawn from the clinker cooler or kiln exit gases and is 

equipped with a burner that typically burns about 60 percent of the total kiln fuel. Most often 

coal is used as a fuel in a calciner furnace; however, almost any fuel may be used including 

chipped tires. The raw material is calcined almost 95 percent, and the gases continue their 

upward movement through successive cyclone/riser duct preheater stages in the same manner as 

in an ordinary preheater. The precalciner system permits the use of smaller dimension kilns, 

since only actual clinkering is carried out in the rotary kiln. Energy efficiency is often even 

better than that of a preheater kiln, and the energy penalty for bypass of kiln exit gases is reduced 

since only about 40 percent of the fuel is being burned in the kiln. The burning process and the 

clinker cooling operations for the modern dry-process kilns are the same as for long wet kilns. 

 The precalciner technology is the most modern cement manufacturing technology and 

almost all of the newer cement plants are based on these designs. Precalciner kilns are also much 

larger in capacity than the conventional rotary kilns. The precalciner type kilns in the United 

States range from 449,000 to 1,580,000 metric tons/year with an average of 869,000 metric 

tons/year. Because of the new large precalciner plants replacing older and smaller plants, the 

overall average kiln capacity has been steadily increasing in the United States. It has increased 

from an average of 239,000 metric tons/year in 1980 to an average capacity of 393,000 metric 

tons/year in 1989. 
Cement Kiln Report (FINAL – 7/14/2006) 2-11

Finish Grinding 

 The cooled clinker is conveyed to clinker storage. It is subsequently mixed with 4 to 6 

percent gypsum and introduced directly into the finish mills. These are large, steel cylinders [2 

to 5 m (7 to 16 ft) in diameter] containing a charge of steel balls, which rotate at about 15 to 20 

rpm. Rarely, the desired size reduction may be accomplished in a roller mill, rather than in ball 

mills. Recently, the industry has also adopted the use of roller presses to precrush the clinker to 

smaller size prior to introduction to the finish mills. The roller press is more efficient than the 

crushing stage of the ball mill, and production capacities of finish grinding systems have been 

substantially increased and electrical energy requirements reduced by the incorporation of roller 

presses into finish circuits. The clinker and gypsum are ultimately ground to a fine, 

homogeneous powder. About 85 to 96 percent of the product is in particles less than 44 μm in 

diameter. This grinding may be accomplished by two different mill systems. In open-circuit 

milling, the material passes directly through the mill without any separation. A wide particle 

size distribution range is usually obtained with substantial amounts of very fine and rather coarse 

particles. Open circuit grinding is, however, rarely practiced in U.S. cement plants. In closedcircuit grinding, the mill product is carried to a cyclonic air separator in which the coarse 

particles are rejected from the product and returned to the mill for further grinding. (7) 

Quality Control 

Beginning at the quarry operation, quality of the end product is maintained by 

adjustments of composition, burning conditions, and finish grinding. Control checks are made 

for fineness of materials, chemical composition, and uniformity. Clinker burning is often 

monitored by the liter weight test (which involves weighing a portion of sized clinker), a free 

lime test, or may be checked by microscopic evaluation of the crystalline structure of the clinker 

compounds. Samples may be analyzed by wet chemistry, X-ray fluorescence, atomic absorption, 

or flame photometry. Standard cement samples are available from the National Institute of 

Standards and Technology. Fineness of the cement is most commonly measured by the air 

permeability method. Finally, standardized performance tests are conducted on the finished 

cement. (7)
Cement Kiln Report (FINAL – 7/14/2006) 2-12

2.1.3 Thermal Characteristics 

 Figure 2-1 provides a detailed look at the material and gas temperatures inside cement 

kilns. The concepts of high-grade heat and low-grade heat are well discussed by Weber. (11) 

Weber states, “The boundary between the main and the subsidiary thermal system is assumed 

always to correspond to a material temperature of 550°C, since decarbonation in the rotary kiln 

in general already begins at this temperature. A certain amount of heat whose temperature is 

below the gas temperature at the commencement of decarbonation will always be left over from 

the calcining zone. This heat is ‘lower-grade’ in the sense that, because of the low temperature, 

it cannot be further used for decarbonation or sintering, but only for preheating and drying.” 

 In turn, Figure 2-2 provides a graphical look at the relationship between temperatures in 

the cement manufacturing process and the chemistry of cement clinker formation. Except for the 

process of drying the raw material slurry in wet kilns these profiles are essentially the same for 

both wet and dry process cement kilns. The only substantive difference is that the difference 

between the gas and material temperature in a preheater tower is less than in the back end of a 

wet kiln because of the more efficient heat transfer in the cyclones. 
Cement Kiln Report (FINAL – 7/14/2006) 2-13

Figure 2-1. Temperature of the Gas and Material in the Rotary Cement Kiln 1 

Figure 2-2. The Relationship Between Process Temperatures and the Chemistry of Cement 

Clinker Formation 
Cement Kiln Report (FINAL – 7/14/2006) 2-14

2.1.4 Process Variables 

 The formation of clinker of suitable quality for manufacture of Portland cement depends 

on the characteristics of feed materials and the temperature profile of the pyroprocessing step. 

The most critical process variables are: 

y Feed composition; 

y Feed particle size; 

y Feed moisture concentration; 

y Feed mass flow rate; 

y System heat losses; and 

y Ambient air infiltration. 

More than 30 raw materials (primarily calcium carbonate, aluminosilicates, silica and iron oxide) 

are known to be used in Portland cement manufacturing. (12) These materials are ground and 

mixed to create a feed that has the appropriate chemical and physical properties to produce 

clinker with the desired properties. Uniform feed composition and size ensure consistent quality 

and characteristics of the clinker produced. 

 Higher moisture contents require more heat input to maintain proper temperature profile 

in the kiln. Cement raw materials are received with an initial moisture content varying from one 

to more than 50 percent. In dry kilns, the moisture content is usually reduced to less than one 

percent before or during the grinding process (e.g., using drum dryers, air separators, or 

supplying supplemental heat to the raw mill). In the wet process, water is added to the raw mill 

during the grinding of the raw materials, thereby producing a slurry of approximately 65 percent 

solids. (12) 
Cement Kiln Report (FINAL – 7/14/2006) 3-1

3.0 NOX FORMATION IN CEMENT KILNS 

 This section of the report is taken from the EPA 2000 Report and is included, with minor 

editing by the ERG Team. This information is included to provide the Texas environmental 

communities with the comprehensive background information necessary to understand the 

parameters that dictate NOx control options at cement kilns. 

3.1 Overview of NOx Formation Mechanisms

In cement manufacturing, conditions favorable for formation of nitrogen oxides (NOx) 

are reached routinely because of the high process temperatures involved. Essentially, all of the 

NOx emissions associated with cement manufacturing are generated in the cement kilns. 

Although, there are other heating operations in a cement plant, such as drying of raw feed or 

coal, often the heat from the kiln exhaust gases is used for these operations making their 

contribution to NOx emissions negligible. In cement kilns, NOx emissions are formed during 

fuel combustion by two primary mechanisms: 

y Oxidation of the molecular nitrogen present in the combustion air which is termed 

thermal NOx formation; and 

y Oxidation of the nitrogen compounds present in the fuel, which is termed fuel 

NOx formation. 

Sometimes the raw material feed to the kiln may also contain nitrogen compounds, which may 

lead to feed NOx formation similar to fuel NOx formation. Because of the high temperatures 

involved in the burning or clinker formation step, the thermal NOx formation provides the 

dominant mechanism for NOx formation in cement manufacturing. The term NOx includes both 

NO and NO2 species, although NO2 normally accounts for less than 10 percent of the NOx

emissions from a cement kiln exhaust stack. (13) The concentration and emission of NOx are, 

however, typically expressed in equivalent NO2 form. 
Cement Kiln Report (FINAL – 7/14/2006) 3-2

3.1.1 Thermal NOx Formation 

 Thermal NOx is formed by the homogeneous reaction of oxygen and nitrogen in the gas 

phase at high temperatures. In the overall reaction mechanism proposed by Zeldovich, (14) the 

two important steps in NOx formation are given as: 

N2 + O x NOx + N kf = 2 x 1014 exp(-76500/RT) 

N + O2 x NOx + O kf = 6.3 x 109 exp(-6300/RT) 

where kf are the rate constants for the reactions shown. The high activation energy of reaction 

(4-1), 76.5 kcal/mol, means that this reaction is the most temperature sensitive. An equilibrium 

reaction of NOx with O2 further results in NO2 formation. 

 The equilibrium concentrations of NOx and NO2 formed thus depend strongly upon the 

gas-phase temperature as well as the concentration of O2 and N2 in the gas phase. Table 3-1 

shows the equilibrium concentrations of NO and NO2 for two conditions. (15) First, the 

equilibrium concentrations of NOx and NO2 for N2 and O2 concentrations found in ambient air 

are shown. Secondly, Table 3-1 also shows the NOx and NO2 concentrations at flue gas 

conditions where the O2 and N2 concentrations are defined for this table as 3.3 percent O2 and 76 

percent N2. The equilibrium NOx concentrations for the flue gas conditions are lower than those 

for ambient conditions due to the lower O2 concentration. The excess air used during fuel 

combustion can substantially affect NOx formation by determining the amount of oxygen 

available for NOx reaction. The cement kiln burning zones usually have about 5 to 10 percent 

excess air while higher excess air levels are not uncommon. Figure 3-1 shows the theoretical 

equilibrium concentrations of NO in the flue gas for different excess air levels. (13) As can be 

seen from this figure, over 1000 ppm of NO may possibly be formed at the typical kiln solids 

temperatures of 1430 to 1480°C (2600 to 2700°F) as the corresponding gas-phase temperatures 

are on the order of 1650°C (3000°F). 
Cement Kiln Report (FINAL – 7/14/2006) 3-3

Table 3-1. Calculated Equilibrium Concentrations (In PPM) Of NOx and NOx In Air and 

Flue Gas (15) 

Temperature Air Flue Gas 

K °F NO NO2 NO NO2

300 80 3.4 (10)-10 2.1 (10)-4 1.1 (10)-10 3.3(10)-3

800 980 2.3 0.7 0.8 0.1 

1440 2060 800 5.6 250 0.9 

Fuel combustion in the kiln burning zone is the primary source of thermal NOx, formation in 

cement kilns due to temperatures well above 1,400°C (2,550°F). In contrast, the fuel combustion 

temperature in a precalciner or in a kiln riser duct is well below 1,200°C (2,200°F), suppressing 

thermal NOx formation. (16) Mainly fuel and feed NOx may be formed in the secondary firing 

zone of preheater and precalciner kiln systems. Along with the combustion temperature, the gasphase residence time and the available oxygen concentration in the high temperature kiln burning 

zone are important parameters. Longer residence times at the high temperatures will allow the 

NO to be formed in the equilibrium quantities. Greater amounts of oxygen in the combustion 

zone will of course lead to greater amounts of NO formation. Once formed, the decomposition 

of NO at lower temperatures, although thermodynamically favorable, is kinetically limited. Thus, 

strategies to reduce NOx emissions need to be based upon reducing formation of NOx, which may 

be achieved by reducing combustion temperature, oxygen concentration in the high temperature 

combustion zone, and the gas residence time at high temperatures. 

3.1.2 Fuel NOx Formation 

 Fuel NOx is formed by the conversion of nitrogen present in the fuel used. A recent 

survey of the cement industry by Portland Cement Association (PCA) indicates that almost 82 

percent of the energy requirement of the cement industry is provided by coal. (17) Natural gas 

contributed about 3 percent of the energy demand, oil about one percent, and other fuels such as 

waste solvents provided about 14 percent of the energy. Both oil and natural gas have relatively 

low fuel bound nitrogen content, whereas coal may contain one to three percent of nitrogen by 

weight depending upon the source of coal. Waste-derived fuels (WDF) such as scrap tires, used 

motor oils, surplus printing inks, dry-cleaning solvents, paint thinners, sludge from the petroleum 

industry, agricultural wastes such as almond shells, and even municipal biosolids (dewatered 
Cement Kiln Report (FINAL – 7/14/2006) 3-4

sewage sludge) are finding an increasing application in the cement kilns. (18) The nitrogen 

content in these fuels may be significant depending on the chemicals included in the waste mix 

being burned. 

Figure 3-1. Theoretical Equilibrium Concentrations of NOx

 The maximum possible fuel NOx formation may be estimated from the fuel nitrogen 

content by assuming 100 percent nitrogen conversion. The typical heat requirement for a wet 

process is estimated to be about 6 million Btu for a ton of clinker and the corresponding 

requirement for a dry process is estimated to be about 4.5 million Btu for a ton of clinker. 

Assuming an average heat requirement of 5.3 million Btu for a ton of clinker, and a coal heating 

value of 12,000 Btu/lb, about 442 lb. of coal will be required per ton of clinker produced. With a 

nitrogen content of one percent by weight, approximately 9.5 lb. of NO (14.5 lb. expressed as 

NO2) would be produced per ton of clinker with 100 percent nitrogen conversion. Thus, even 

with only 10 percent conversion of coal nitrogen to NOx, 1.5 lb. of fuel NOx (expressed as NO2) 

may be formed per ton of clinker when coal is used as a primary fuel. 

 The amount of fuel NOx formed is difficult to identify separately from thermal NOx as 

measurements indicate the overall NOx formed. In general, however, thermal NOx is assumed to 

be the dominant mechanism in cement kilns. (19) Typically, gas burners produce more intense 

and hot flames compared to the less intense "lazy" flames produced by coal burners. Thus, gasfired kilns may be expected to produce greater thermal NOx as compared to coal-fired kilns. 
Cement Kiln Report (FINAL – 7/14/2006) 3-5

Coal, on the other hand, contains much greater amounts of fuel-bound nitrogen than natural gas, 

which has almost no fuel-bound nitrogen. The coal-fired kilns may thus be expected to produce 

more fuel NOx than gas-fired kilns. A study of gas- and coal-fired kilns, however, clearly 

indicated that gas-fired, dry-process kilns typically produce almost three times more NOx than 

the coal-fired, dry-process kilns. (19) This fact indicates the dominance of thermal NO in overall 

NO formation. 

3.1.3 Feed NOx Formation 

 Similar to coal, the raw materials used in cement production may contain a significant 

amount of nitrogen. In most cases, limestone is the major raw material, with the remainder of 

the raw mix being composed of clays, shales, sandstones, sands, and iron ores. Fly ash from 

coal-fired power plants is used as a raw material and may contain substantial amounts of 

nitrogen compounds, since it is usually derived from coal. Most of these raw material 

components are sedimentary minerals and they may contain small amounts of chemically bound 

nitrogen, presumably of organic origin. Various kiln feeds contain appreciable amounts of 

nitrogen, ranging from about 20 ppm up to as much as 1,000 ppm (as N). (20) The higher values 

(>100 ppm) are generally associated with minerals displaying noticeable kerogen contents. 

Since 100 ppm N in a kiln feed is equivalent to about one lb. NOx per ton of clinker (if it all 

converted), NOx emissions from the kiln feed may represent a major source of NOx from cement 

kilns. Nevertheless, it is probably less important than thermal NOx and fuel NOx in most cases. 

 The same study indicated that conversion of feed nitrogen to NOx occurs mainly in the 

300 to 800°C (570 to 1,470°F) temperature range and depends upon the feed heating rate. (20) 

Rapid heating rates (~1,000°C flash heating) of the kiln feed mixtures were found to give much 

lower conversion efficiencies, whereas slow heating rates of kiln feed mixtures (~60°C/min) 

gave fairly high conversion of about 50 percent of bound nitrogen to NOx. These results were 

explained by assuming that the organic nitrogen must vaporize from the sample prior to 

oxidation if high conversion efficiencies to NOx are to be achieved. If heating rates are rapid, 

"cracking" of these volatile compounds may occur in situ, and this may result in conversion of 

the bound nitrogen directly to N2 before it comes into contact with gaseous oxygen, thus 

reducing the fraction converted to NOx. Such a hypothesis is also consistent with the observation 
Cement Kiln Report (FINAL – 7/14/2006) 3-6

that, during coal combustion, the involatile or "char" nitrogen is converted to NOx much less 

efficiently than the volatile nitrogen. (21) 

3.1.4 Factors Affecting NOx Emissions in Cement Manufacturing 

 There are four primary types of cement kilns used in the industry: wet kilns, long dry 

kilns, kilns with a preheater, and kilns with a preheater/precalciner. The wet and long dry kilns 

and some preheater kilns will have only one fuel combustion zone, whereas the newer preheater 

and precalciner kiln designs have two or three fuel combustion zones: kiln burning zone, riser 

duct and precalciner. Because the typical temperatures present in the combustion zones are 

different, the factors affecting NOx formation are also somewhat different in different kiln types 

and are discussed in the following sections. In addition to the specific NOx formation 

mechanisms, the energy efficiency of the cement-making process is also important as it 

determines the amount of heat input needed to produce a unit quantity of cement. A high 

thermal efficiency would lead to less consumption of heat and fuel, and would generally produce 

lower NOx emissions. 

NOx Formation in the Kiln Burning Zone 

 In the kiln burning zone, thermal NOx provides the primary mechanism for NOx

formation. Thermal NOx formation depends upon the combustion zone temperature, the 

gasphase residence time and the oxygen concentration in the high temperature combustion zone. 

The flame temperature strongly depends upon the type of fuel burned. The temperature and 

intensity are generally greater for gas burners than coal burners. The oxygen concentration in the 

combustion zone depends upon the overall excess air used and on the source and proportion of 

primary and secondary combustion air. Less primary air may produce an initial hightemperature, fuel-rich combustion zone followed by a low-temperature fuel-lean combustion 

zone. Such a combination is likely to reduce NOx formation. 

 The firing system used in the kiln affects the proportion of primary and secondary 

combustion air. Direct firing systems introduce a large proportion of combustion air with the 

fuel being burned. This produces two conflicting effects for NOx emissions: higher oxygen 
Cement Kiln Report (FINAL – 7/14/2006) 3-7

concentration or fuel lean combustion and lower gas temperature. Indirect firing systems on the 

other hand use only a small portion of combustion air to convey fuel and thus use less primary 

air. In general, direct fired systems may be expected to produce greater NOx emissions 

compared to indirect fired systems. The flame shape and the theoretical flame temperature are 

important factors in thermal NOx formation as these factors determine the hottest points in the 

flame. A long "lazy" flame will produce less NO than a short intense flame. 

 The flame shape depends on the fuel being burned as well as the proportion of air. For 

the same amount of primary air, gas burning may be expected to produce a shorter and more 

intense flame than coal burning. The lower the secondary air temperature and the greater the 

dust content in the secondary air, the lower the NOx formation in the kiln burning zone. A large 

amount of water in the primary air (from a direct firing coal mill) and injection of cement kiln 

dust (CKD) in the burning zone (insufflation) may also reduce NOx formation. With increasing 

excess air percentage, the NOx formation in the kiln will increase, but only up to a certain point 

as an increasing excess air rate will reduce the secondary air temperature and, consequently, the 

flame temperature. 

 Process conditions that can affect NOx emissions substantially are: temperature stability, 

stability of raw mix feed rate, burnability of raw mix, and alkali and sulfur control. Temperature 

stability is important to maintain the quality of clinker and is achieved by stable-flame conditions 

and energy efficiency. Clinker formation reactions require temperatures of 2,650 to 2,800°F 

(1,450 to 1,540°C) and an oxidizing environment. Sometimes natural gas or liquid waste derived 

fuel is used to control flame conditions and improve clinker quality. The excess air used during 

combustion has a substantial influence on NOx emissions. Oxygen levels of 4 to 5 percent in 

kiln exhaust gases would correspond to high NOx emissions, whereas oxygen levels of only 0.5 

to 1.5 percent would mean lower NOx emissions. Thus, NOx emissions in a kiln may depend 

upon the care exercised by the operator in minimizing excess oxygen needed to maintain the 

quality of the clinker produced. All but one of the clinker formation reactions are exothermic 

and represent a dynamic process that requires constant operator adjustments which can vary NOx

formation. 
Cement Kiln Report (FINAL – 7/14/2006) 3-8

 The heating value of the fuel burned may also affect NOx emissions. High heating value 

fuels, such as petroleum coke may require less combustion air and produce less NOx per ton of 

clinker. 

 Different raw material compositions require different burning conditions to maintain the 

quality of clinker produced. Thus, similar types of kilns with different feed materials may 

produce different levels of NOx emissions. The alkali content of finished cement needs to be 

below a certain acceptable level. Low alkali requirements may require higher kiln temperatures 

and longer residence times at high temperatures to volatilize the alkali present in the molten 

clinker. Raw materials with greater alkali content may need to be burned longer at higher 

temperatures to meet alkali requirements and thus may produce greater NOx emissions. 

Increased volatilization of alkali results in increased alkali emissions in kiln exhaust gases. To 

control alkali emissions, a part of the kiln exhaust gases may be bypassed around a downstream 

unit, e.g., a precalciner. The bypassed gases are quenched to remove alkali and sent through a 

particulate matter collector. This alkali-rich particulate matter is removed from the process and 

disposed. The bypass of kiln exhaust gases typically involves a fuel penalty, e.g., about 20,000 

Btu/tonne clinker for every one percent gas bypass. The additional heat requirement will 

contribute to increased NOx emissions. 

 Wet kilns require about 33 percent more thermal energy than a dry kiln. This means a 

greater volume of exhaust gas from a wet kiln for the same production. On the other hand, the 

greater amount of combustion air will also mean a somewhat lower secondary air temperature. 

Based on these contradicting factors, one might expect the NOx emissions from a wet process 

kiln to be similar to the dry and preheater kilns without riser duct firing. 

NOx Formation in Secondary Firing 

 In the secondary firing region of precalcining kilns, where temperatures range from 820 

to 1100°C (1500 to 2000°F), the following reactions may take place: 

"N" + O → NO (4-3) 

"N" + NO → N2 + O (4-4) 
Cement Kiln Report (FINAL – 7/14/2006) 3-9

where "N" means nitrogen originating from nitrogen compounds in the fuel. (13) Reaction (4-3) 

shows that NO formation in the secondary firing zone will depend upon the nitrogen content in 

the fuel and the oxygen level in the firing zone. Reaction (4-4) indicates that, if there is already 

NO present in the gas introduced into the secondary firing zone, a reduction of this NO may 

occur with the fuel nitrogen compounds acting as reducing agents. Accordingly, the net 

formation of NO in the secondary firing zone will also depend upon the initial NO concentration 

in the combustion gas. Finally, measurements have shown that the volatile content in the solid 

fuel and the temperature in the secondary firing zone also influence the NO formation in the 

secondary firing zone. (22) With increased volatile content in the fuel, the ratio of fuel nitrogen 

conversion into NO seems to decrease and, as the reaction rate of reaction (4-4) increases more 

rapidly with the temperature than that of reaction (4-3), an increase in the temperature of the 

secondary firing region may reduce-the net NO formation. (13) 

3.1.5 Suspension Preheater (SP) Kilns with Riser Duct Firing. 

In many SP kiln systems 10 to 20 percent of the fuel is fired into the riser duct. The 

preheater systems are more energy efficient compared to long dry kilns. The increased energy 

efficiency and the reduction in the amount of fuel burned at the higher clinker burning 

temperature may be expected to reduce the NOx emissions from preheater kilns when compared 

with the long dry and wet kilns. Measurements at several riser-duct fired kiln systems indicate 

that firing coarse fuel (e.g., tires) into the kiln riser duct will reduce NOx emissions from the kiln 

systems. (23) This may be explained by the fact that a large part of the fuel falls directly down 

into the kiln charge, creating a reducing atmosphere in the kiln back-end where NOx from the 

burning zone is reduced. 

 Conversely, when firing finely ground fuel into the kiln riser duct, the NOx content in the 

exhaust gas may increase on passing through the riser duct. As the NOx emissions from the kiln 

may also increase slightly due to an increased excess air rate, the total NOx emissions from the 

kiln system may increase when starting up riser duct firing with finely ground fuel. (13)
Cement Kiln Report (FINAL – 7/14/2006) 3-10

3.1.6 Precalcining Kiln Systems. 

 In precalcining kiln systems with a tertiary air duct, firing into the rotary kiln typically 

accounts for only 40 to 50 percent of the total heat consumption and the specific amount of 

combustion gases from the kiln burning zone is reduced proportionally. Precalciner kilns also 

typically require the least amount of energy per unit amount of clinker produced. The lower 

energy requirement and the substantial reduction in the proportion of the fuel burned at clinker 

burning temperatures may be expected to reduce the NOx emissions from the precalciner kilns as 

compared to the preheater kilns. On the other hand, the NOx concentration (in ppm) in the kiln 

gas may be considerably higher than in preheater kilns. This is probably due to the shorter 

material and longer gas retention times in the precalciner kiln burning zone combined with a 

very high secondary air temperature. (13)

 When examining the contribution from the calciner firing to the emission of NOx, two 

basically different types of precalcining kiln systems need to be considered: 

y The in-line (ILC) type in which the kiln gas passes through the firing region of the 

precalciner; and 

y The separate line (SLC) type in which the kiln exhaust gas bypasses the firing 

region of the precalciner. 

 ILC systems: In these systems, the fuel combustion in the calciner takes place in a 

mixture of the kiln exhaust gas and hot air from the cooler (tertiary air). Some of the nitrogen in 

the fuel reacts with NO from the kiln exhaust gas while another part reacts with oxygen to form 

NO. The result may be a net increase or a net reduction of NO in the calciner. 

 SLC systems: In these systems, the fuel combustion in the calciner takes place in pure hot 

air. In the case of oil firing, NO production in the calciner is negligible; but when using fuels 

containing fuel-bound nitrogen, up to 50 percent of the nitrogen compounds in the fuel may be 

converted into NOx. The specific NOx, production in an SLC calciner may be as high as 4 lb. 

NOx per ton of clinker as measured in a calciner fired with petroleum coke which has a high 

nitrogen content and low volatile content. (13) The NOx in the calciner exhaust gas is added to 

the NOx in the gas from the rotary kiln which leaves this type of kiln system without being 
Cement Kiln Report (FINAL – 7/14/2006) 3-11

reduced. When fired with solid fuels, SLC systems may therefore be expected to generate 

somewhat higher NOx emissions than the ILC systems. (13) We should note, however, that 

some of the oxygen for combustion of the fuel in ILC systems passes through the burning zone, 

so the NO generated there may be higher (or lower due to lower temperatures) than for SLC 

systems.

3.1.7 Energy Efficiency of the Cement-Making Process 

 Since NOx formation is directly related to fuel combustion, any reduction in the amount 

of fuel burned per unit amount of clinker produced should reduce NOx emissions per unit clinker. 

Attempts to improve energy efficiency of the process by avoiding excessive clinker burning and 

utilizing waste heat effectively for preheating combustion air, coal, and raw mix is likely to 

reduce NOx emissions. Improving heat transfer between hot gases and solid materials, e.g., by 

chain systems, will improve energy efficiency. The newer preheater and precalciner kiln designs 

provide very efficient preheating and precalcining of the raw mix with intimate gas-solids 

contact in cyclone towers. New cement kiln installations or renovations of older kilns thus 

predominantly involve precalciner designs for their energy efficiency. The inherent energy 

efficiency of these kiln designs is likely to produce lower NOx emissions per unit amount of 

clinker as compared to the wet or long dry kilns. 
Cement Kiln Report (FINAL – 7/14/2006) 4-1

4.0 OVERVIEW OF POTENTIALLY APPLICABLE CONTROL TECHNIQUES AND

TECHNOLOGIES 

 Nitrogen oxides are formed by the oxidation of nitrogen during the fuel combustion 

process. The formation of thermal NOx is a function of the flame temperature, flame turbulence, 

the amount of nitrogen and oxygen available for the thermal reaction, and the gas phase 

residence time at high temperature. To reduce the amount of thermal NOx formed, one or more 

of these variables needs to be minimized. The formation of fuel and feed NOx is not as well 

understood as the thermal NOx formation. In general, however, the greater the concentration of 

nitrogen in the fuel and feed, the greater the fuel NOx emissions. Therefore, reducing the amount 

of fuel and feed-bound nitrogen should reduce the contribution of the fuel and feed NOx. 

 The typical NOx emissions from a cement plant depend upon the type of the cement kiln 

as shown in Table 4-1. For any given type of kiln, the amount of NOx formed is directly related 

to the amount of energy consumed in the cement-making process. Thus, measures that improve 

the energy efficiency of this process should reduce NOx emissions in terms of lb. of NOx/tonne 

clinker. With the rising costs of energy and the very competitive cement market, greater 

attention is being paid to increasing overall energy efficiency, such as through reduction of 

overburning of clinker and improvement in gas-solids heat transfer. Continuous emissions 

monitoring of CO, NOx, and O2 provide an indication of kiln conditions and also provide inputs 

for process control. Newer cement kiln designs are generally based on preheater/precalciner 

systems which provide very efficient gas-solids contact and greater energy efficiency. NOx

control approaches are evaluated below under four categories: 

y High Temperature Emissions Controls; 

y Combustion Optimization; 

y Low Temperature Oxidation Emissions Controls; and 

y Process Modifications. 

 This section of the report uses the EPA 2000 Report as the baseline for evaluating current 

control options for Ellis County kilns. The combustion and process optimization sections are 

included, with editing, from this report and describe the essential controls that have been 

considered and largely installed under the requirements of 30 TAC Chapter 117. Additions to 

sections for process modifications to improve energy efficiency through calciner modifications 
Cement Kiln Report (FINAL – 7/14/2006) 4-2

and wet to dry conversions is discussed as site-specific options where applicable for Ellis County 

kilns. The section on oxidation controls is entirely new and was not considered in EPA 2000. 

The sections on SCR and SNCR consider EPA 2000 background information, but are written to 

reflect current status of these technologies and site-specific application to the Ellis County kilns. 

For the purposes of this report, available essentially means that the technology is commercially 

available and in use on similar types of cement kilns. Transferable means that the technology is 

commercially available and in use on similar process equipment and could reasonably be 

expected to work on the specified type of cement kiln. Innovative describes technologies that 

have not been successfully applied to a type of cement kiln, but in the judgment of the ERG 

Team could be expected to work on the type of cement kiln if correctly optimized through 

experimental application. 

 When discussing the transfer of technologies, comparisons are made between cement 

kilns, coal-fired utility boilers and refinery fluidized catalytic cracking units (FCCUs). While the 

emissions from these units vary widely, they are all capable of emitting thousands of tons of NOx

and SO2 and typically use electrostatic precipitators (ESPs) to control particulate emissions that 

would also be thousands of tons per year prior to control. For the purposes of this discussion, a 

modern cement kiln producing one million tons per year of clinker would be roughly comparable 

to a coal-fired utility boiler of approximately 200 megawatts generating capacity and an FCCU 

of approximately 80,000 barrels per day. All of these units would have a typical air flow of 

approximately 300,000 cubic feet per minute. For comparison with the Ellis County kilns, a 

typical refinery of comparable air flow rate would tend to produce less NOx and a utility boiler 

would typically produce more NOx. The amount of SO2 from these units would vary widely due 

to site specific operating conditions including fuels and feeds materials. The impact of SO2 and 

particulate matter concentrations on the operation of SCR is discussed in depth below under 

Section 4.1.2. Other constituent pollutants in the gas stream are not considered to interfere with 

LoToxTM operation. Both SCR and LoToxTM have been demonstrated in units of comparable air 

flow to the Ellis County kilns. 

 
Cement Kiln Report (FINAL – 7/14/2006) 4-3

4.1 High Temperature Emissions Controls

4.1.1 Selective Catalytic Reduction (SCR) 

 SCR is a process that uses ammonia in the presence of a catalyst to selectively reduce 

NOx emissions from exhaust gases. This technology is widely used for NOx abatement in other 

industries, such as coal-fired power stations and waste incinerators. The SCR process has been 

used extensively throughout the world to achieve a 90 percent reduction in NOx emissions from 

fossil fuel fired boilers. In the United States SCR technology has successfully been used for gas 

turbines, internal combustion engines, and utility boilers. 

 In SCR, anhydrous ammonia, usually diluted with air or steam, or urea, is injected 

through a grid system into hot flue gases that are then passed through a catalyst bed to carry out 

NOx reduction reactions. The two principal reactions are: 

4 NH3 + 4 NO + O2 --- 4 N2 + 6 H2O and 

4 NH3 + 2 NO2 + O2--- 3 N2 + 6 H2O 

 The first reaction represents the predominant reaction since 90 to 95 percent of NOx

emissions in the flue gas are in the form of NO. A number of materials have been used for 

catalysts. Titanium dioxide (TiO2) and vanadium pentoxide (V2O5) mixtures are most 

commonly used as catalysts due to their resistance to SOx poisoning. Zeolite-based catalyst 

materials have also been developed capable of operating at higher temperatures than 

conventional metal-based catalysts. The catalyst is typically supported on ceramic materials, 

e.g., alumina in a honeycomb monolithic form. The active ingredients of the base metal (titaniavanadia) and zeolite catalysts often make up the bulk of the substrate material. The catalyst 

shape and reactor design vary depending upon the manufacturer. 

 The optimum temperature for the catalytic reactions depends upon the specific catalyst 

used and is usually in the range between 300 to 450oC (570 to 840oF). Without pre-heater and/or 

pre-calciner systems this temperature range may be higher than typical cement kiln flue gas 

temperatures, especially in plants using heat recovery systems or baghouses for particulate 
Cement Kiln Report (FINAL – 7/14/2006) 4-4

collection. But it may be possible to reheat the exhaust using heat recovery systems. Of 

particular relevance, then, is the ability to use SCR at wet kilns. 

 Ammonia is typically injected to produce a NH3: NOx molar ratio of 1.05-1.1:1 to 

achieve NOx conversion of 80 to 90 percent with an ammonia "slip" of about 10 ppm of unreacted ammonia in the gases leaving the reactor. The NOx destruction efficiency depends upon 

the temperature, NH3: NOx molar ratio, and the flue gas residence time (or the space velocity) 

used in the catalyst bed. The SCR reactor system can be designed for a desired NOx reduction 

using appropriate reagent ratio, catalyst bed volume, and operating conditions. In general, the 

catalysts may be fouled or deactivated by the particulates present in the flue gas. In the case of 

cement plants, the presence of alkalis and lime, as well as sulfur dioxide, in the exhaust gases is 

also of concern. Recent developments, however, have led to sulfur tolerant SCR catalysts. In 

addition, soot blowers may be used to prevent dust accumulation on SCR catalysts. 

 In the cement industry, basically two SCR systems are being considered: low dust 

exhaust gas and high dust exhaust gas treatment. Low dust exhaust gas systems require 

reheating of the exhaust gases after de-dusting, resulting in additional cost. High dust systems 

are considered preferable for technical and economical reasons. 

 SCR may only be available as an applicable technology for dry kilns with preheat, as is 

described later herein. There are currently no installations of SCR units in any United States 

cement plants, however, a full-scale unit has been operating in Germany for over three years 

with SCR. As set forth in greater detail below, selective catalytic reduction has been installed 

and successfully operated at this one cement plant in Germany and SCR is now commonly used 

to control NOx emissions from coal-fired power plants. This technology achieves NOx emission 

reductions in the range of 80 to 90 percent or higher. 

 The experience of the German cement plant may be sufficient to demonstrate that the 

concerns regarding catalyst poisoning and fouling have been addressed with the development of 

a special catalyst specifically designed for the cement industry. In a typical design of a dry kiln 

with preheat, the SCR system could be located downstream of the pre-heater cyclones, prior to 
Cement Kiln Report (FINAL – 7/14/2006) 4-5

the roller mill. The process exhaust temperature at the outlet of the pre-heater cyclones would be 

approximately 320°C (608°F), which is ideal for a SCR system. 

Potential Advantages of SCR 

 The potential advantages of SCR are as follows: 

y SCR can potentially provide a high degree of NOx removal. Presently, 

guarantee levels on SCR systems being provided in the power industry are in the 

90% to 94% range. Even on difficult applications such as coal-fired power plants, 

which have very dusty flue gases, NOx control efficiencies of 90%+ are being 

guaranteed by vendors and being achieved. 

y SCR is an add-on or end-of-pipe control technology. For dry kilns with 

preheat, the SCR system would be located downstream of the cement kiln and 

pre-heater furnace and cyclones and hence it would not interfere with or affect the 

cement manufacturing process. This would be a big advantage over the Selective 

Non-Catalytic Reduction (SNCR) process, which must be carried out in process 

conditions. 

y SCR can use urea (CO(NH2)2) rather than ammonia as the reducing agent. 

To use urea, a conversion system is required. In a typical conversion system, urea 

is mixed with water and then heated. The process converts the urea to gaseous 

ammonia, which is then injected into the flue gas. This system is commonly used 

where there are safety concerns arising from the transport and storage of 

ammonia. 

SCR at Coal-Fired Power Plants 

 Prior to 2001, there were approximately 12 coal-fired power plants in the United States 

utilizing SCR for NOx control. According to the Electric Power Research Institute, there are 

now about 200 coal-fired power plants (totaling 100,000 megawatts of generating capacity) online utilizing SCR control. Most of the plants on which SCR has been installed are designed for, 

and have been achieving, 80% to 90% control of NOx. 

 One possible problem mentioned with respect to utilizing SCR in cement plants is the 

technical feasibility of installing SCR in an environment where dust from the kiln could poison 

the catalyst, making SCR technically infeasible. On coal-fired power plants, the SCR catalyst is 

usually installed downstream of the boiler (between the economizer and the air pre-heater) prior 
Cement Kiln Report (FINAL – 7/14/2006) 4-6

to the particulate control device. As a result, the catalyst is subject to the full dust loading from 

coal combustion, just as it would be at a cement plant. Typically, coal contains 6% to 20% ash 

on a dry basis. The high dust, high temperature characteristics of coal plant emissions thus are 

similar to those of cement kiln exhaust gases. The experience of the power industry with SCR 

on coal-fired power plants suggests that the catalyst poisoning and fouling concerns may be 

manageable. 

SCR Experience in Cement Kilns 

 Differences in the nature of the cement kiln and coal fired power plant processes, the 

chemical composition of the ash and other factors mean that the success of SCR in controlling 

NOx emissions from coal-fired power plants is not definitive evidence that the technology can be 

successfully applied at a cement plant. Among other things, dust from cement kilns is high in 

calcium, relative to coal dust, and calcium deactivates most conventional SCR catalysts. Also, 

the grain loading of cement kilns is likely to be different from that of coal-fired power plants, 

placing different stresses on the control device. As discussed in greater detail below, however, 

the recent successful use of SCR at a German cement plant demonstrates that these and other 

issues may have been resolved and that SCR is, under certain conditions, a technically feasible 

alternative for significantly reducing NOx emissions from cement kilns. 

 The Solnhofen Portland-Zementwerke AG cement plant in southern Germany located 

between Munich and Nuremburg has been in successful operation with SCR since 2001. Lurgi, 

the engineering company who supplied the SCR system, addressed the problem of catalyst 

deactivation discussed above (caused by the high calcium content of cement plant ash) by 

developing a catalyst specifically for the cement industry. The catalyst can use ammonia or urea 

as a reagent. If urea is used, a conversion unit is used to convert the urea to ammonia prior to 

injection in the SCR system. These units, which are quite common, avoid the need to store 

ammonia on-site for use as a reagent. 

 As of the beginning of 2005, there was no evidence of catalyst poisoning or deactivation. 

The problem of fouling from the heavy dust loading has proven to be quite manageable with 

regular maintenance (i.e., cleaning of the catalyst with a vacuum cleaning system). 
Cement Kiln Report (FINAL – 7/14/2006) 4-7

 The SCR system is achieving NOx emission reductions far in excess of those achievable 

using SNCR. Prior to installation of SCR, the Solnhofen plant, with SNCR, was achieving NOx

emissions of 700 to 800 mg/ Nm3

 (equivalent to 2.8 to 3.2 lb./tonne clinker). With SCR, the 

plant has been achieving approximately 200 mg of NOx/Nm3

 (0.8 lb./tonne clinker). Based on an 

uncontrolled NOx emission rate of 1050 mg/Nm3 (4.2 lb./tonne clinker), the emission rate 

corresponds to a NOx control efficiency of 80% for SCR compared with approximately 25-35% 

control efficiency for SNCR. It has been indicated, however, that the SCR system was capable 

of achieving a lower NOx emission rate (they are not using all of their beds), but that they were 

operating at 200 mg/Nm3

 since German law only required a NOx emission limit of 500 

mg/Nm3.(23a, 23b, 23c, 23d) 

Figure 4-1.1 SCR on Preheater Tower at Solnhofen Zement, Germany 

 
Cement Kiln Report (FINAL – 7/14/2006) 4-8

 At approximately 500,000 tonnes per year of clinker, Solnhofen is smaller in capacity 

than the preheater/calciner units in Ellis County and larger than the wet kilns. With an 

uncontrolled NOx emission rate of approximately 4.2 lb./ton, Solnhofen has a slightly higher 

emissions rate than the Holcim units and slightly lower than the Ash Grove kilns. The emissions 

rate is much higher than TXI #5 and much lower than the TXI wet kilns. 

Site Specific Application of SCR to Ellis County Cement Kilns 

 SCR offers the possibility of significant NOx reduction at the plants in Ellis County. As 

an “add on” technology, which can achieve 90% or greater NOx reduction, with demonstrated 

performance at hundreds of coal fired power plants, SCR is a viable technology that is available 

for both dry and wet kilns. The economics of SCR are greatly influenced by the temperature of 

the flue gas at the point of installation. For the three dry precalciner kilns in Ellis County, a 

location in process with suitable temperatures is assumed and this leads to lower overall costs 

and cost effectiveness. For the wet kilns, a location downstream from the electrostatic 

precipitators (ESPs) is selected for installation, and reheat of the process gas is required. This 

substantially increases the overall cost and decreases the cost effectiveness of SCR in 

comparison to the dry kiln applications. 

 The technology has been available at only one cement plant, the Solnhofen Portland – 

Zementwerke AG dry kiln plant in Southern Germany, now in its fourth year of operation with 

SCR. While there are, at this time, no operating units in the U.S., the German experience leads 

one to assess the possibility that SCR can make a significant impact on NOx reduction in Ellis 

County. In fact, the Midwest Regional Planning Organization has recently concluded that SCR 

is a reasonably available technology for controlling NOx at cement plants (23e), and the 

possibility exists, with reheat, to utilize SCR at wet, as well as dry, kilns. 

Applicability of SCR to Cement Kilns and Areas of Concern 

 Before examining site-specific data, it is important to first examine the areas of concern 

with respect to SCR, many of which have been raised in the literature (23f, 23g, 23h, 23i). This 

is necessary to see whether the data from the coal fired plants and from the one cement plant, is 
Cement Kiln Report (FINAL – 7/14/2006) 4-9

sufficient to attempt to make even qualified statements with respect to existing facilities, even 

though some analyses now suggest that the German data indicates that these problems will not 

exist for the cement industry in the U.S. (23g). These concerns are delineated and discussed 

here. They include: catalyst deactivation due to catalyst poisoning; catalyst plugging and fouling 

due to high dust loading and deposits; reduction in NOx control efficiency due to high sulfur 

levels; temperature related factors leading to lower NOx removal efficiencies; NOx concentration 

variability and ammonia slip; and undesirable by-product formation in the SCR causing adverse 

affects on downstream equipment. 

Catalytic Deactivation Due to Catalyst Poisoning

 Poisoning occurs when the contaminants in the gas being treated react with the catalyst, 

resulting in catalyst deactivation. It has been argued that the SCR catalyst in a cement plant will 

be subject to poisoning, principally from sodium (Na), potassium (K), and arsenic trioxide 

(As2O3). Phosphorus, chromium and lead compounds can also poison an SCR catalyst, but since 

these are expected to be present in lower concentrations at cement kilns, they are of lesser 

concern. However, the typical concentration of sodium oxide (Na2O) in the particulate matter 

(PM) of certain coal-fired plants is greater than double the concentrations of Na2O in the PM of 

the average cement plant, and the maximum concentration of Na2O can be significantly greater 

than the maximum expected concentration of Na2O in the PM of the average cement plant. 

Similarly, the concentration of As2O3 in the flue gas of the typical coal fired plant is well above 

the concentration of As2O3 in the expected flue gas from the average cement plant. Regarding 

the availability of catalyst poisons, an additional argument deals with the solubility of Na and K 

in the fly ash and the form of the fly-ash particles. 

 It is argued that in cement pre-heater pre-calciner kilns, materials such as sodium and 

potassium compounds may be present in relatively elevated concentrations on the surfaces of 

particles in “water soluble” form that can contact the surface of the SCR catalyst bed and thereby 

provide an opportunity to poison the V2O5 “active ingredient” in the SCR bed. Conversely, it is 

argued, in coal-fired boilers, the sodium and potassium are, to a major extent, trapped within a 

glass-like fly-ash particle. It is widely known however that fly-ash particles from coal-fired 

boilers are in the form of tiny spheres (cenospheres) and that during the combustion of the coal, 
Cement Kiln Report (FINAL – 7/14/2006) 4-10

the particles are actually liquid and the spheres are formed as tiny bubbles by evolved gases 

trying to escape. Boilers are designed to cool the molten particles to a solid state such that they 

can be easily removed from boiler tubes. However, depending on the temperature of the fly ash 

and its chemical composition, some of the fly ash will deposit in various sections of the boiler. 

The deposits that form at the back-end of the boiler (on the economizer and air heater) are called 

“low-temperature deposits”. Low temperature deposits are usually characterized by low pH 

(highly acidic); many contain hydrated salts, and for most bituminous coals are water-soluble. 

Therefore, coal-fired boilers have fly-ash deposits in the economizer section of the boiler that are 

water-soluble. However, deactivation has not been found to occur. In addition, SCR systems 

have been installed on oil-fired boilers despite the relatively higher levels of water-soluble 

alkaline metals found in the fly ash from such boilers. 

Catalyst Plugging and Fouling Due To High Dust Loading and Depositing of “Sticky” 

Materials

 Catalyst plugging and fouling involves the accumulation of dust that blocks access to the 

pores of the catalyst. It is argued that high dust loadings could plug or foul the SCR catalyst 

beds. However, the Solnhofen SCR system has operated at a dust loading of 80 g/Nm3, a 

relatively high dust loading. The level of NOx removal shows that high dust loading can be 

managed to avoid catalyst plugging and fouling while maintaining high levels of control. 

Related to the plugging and fouling issues, it is argued that “sticky deposits” in the pre-heater 

exhaust gas could foul and plug the SCR catalyst. Specifically, certain cement kiln operations 

could be prone to producing sticky deposits at exactly the temperature ranges in which SCR 

systems operate. Sticky deposits are a widespread problem occurring throughout the world on 

cement kiln induced draft (I.D.) fans. In many plants it is an extremely hard, layered, brick-like 

build-up that is associated with impingement of particulate at high velocity against the rotating 

parts of the fan impeller. 

 While the presence of alkali in the cement kiln system is a factor in the build-up, the 

mechanical aspect (namely, impact velocity) is more critical to the formation of build-up. The 

recommendation for avoiding build-up is to select a fan that minimizes the gas/dust velocity at 

the inlet of the fan rotor. Alternatives include using double inlet fans or using larger diameter, 

lower RPM (revolutions per minute) fans. Sticky deposits or build-up developing on other parts 
Cement Kiln Report (FINAL – 7/14/2006) 4-11

of the cement kiln system are not common. Thus, the sticky deposit problem appears to be 

related solely to the I.D. fan and is due to the high impact velocity of the dust particles mostly on 

the fan. This problem should not affect an SCR catalyst that is subject to comparatively low gas 

velocities in comparison to an I.D. fan. 

 For instance, gas velocities through an SCR system are typically less than 6.2 meters per 

second (1220 ft./min.), whereas peripheral gas speed at the kiln I.D. fan rotor inlet is 

approximately 15,000 ft./min. Possible problems relating to thermal sintering and catalyst 

erosion have been addressed by advances in catalyst technology and proper system design. The 

problem of thermal sintering has been avoided by the incorporation of tungsten in the catalyst 

formulation and also by providing a bypass around the SCR system so that the catalyst is not 

exposed to high temperature excursions. Hardening the leading edge of the catalyst and also 

arranging the catalyst bed so that the airflow is parallel to the catalyst channels have addressed 

catalyst erosion. 

Reduction in NOx Control Efficiency Due to High Sulfur Levels

 In general, operational histories of SCR installations at coal fired plants and the one 

cement plant indicate that NOx reductions are being achieved in a reliable manner. The reason 

that many of the older units are not achieving NOx removals greater than 80% is that the plants 

were not designed to achieve such high removal efficiencies. Great advances in the application 

of SCR technology have taken place. Present day SCR systems are typically achieving NOx

reduction efficiencies of 90% or greater. It is argued that when only a low NOx reduction is 

required, the catalyst manufacturer can use a catalyst with a lower vanadium oxide content which 

will reduce the oxidation of SO2 to SO3 and thereby avoid the potential for CaSO4 masking. 

However, the Solnhofen SCR system is achieving a high degree of NOx control. 

 It is argued that high SO3 concentrations could lead to catalyst deactivation and other 

serious problems relating to SO2 oxidation. A high SO3 concentration (10 -20 ppmv) when 

coupled with the high calcium level in the cement kiln flue gas could purportedly cause 

deactivation of the SCR catalyst due to the masking effect of calcium sulfate (CaSO4). In 

addition, any SO3 that does not react with the calcium could react with any unused NH3 to form 
Cement Kiln Report (FINAL – 7/14/2006) 4-12

ammonium sulfate (AS) or ammonium bisulfate (ABS) that could cause fouling of downstream 

equipment. Sulfur in the raw mix can be in several forms, namely: calcium sulfate, magnesium 

sulfate, and sulfides such as pyrites or organically bound sulfur. Only the volatile sulfur 

compounds (namely: the sulfides and organically bound sulfur) are oxidized and released in the 

pre-heater as SO2. With respect to these concerns, the success of SCR systems at a number of 

coal-fired boilers show that SCR systems can be designed for high calcium and high sulfur flue 

gases and the SCR catalyst suppliers have indicated that CaSO4 formation does not pose a major 

concern, as they assert that the SO3 generated in the process is captured by the large amount of 

free lime in the gas stream. SO2 oxidation by the catalyst will then have no negative impact on 

the amount of SO3 formed and subsequently captured. There is also concern regarding the 

possible formation of ammonium salts, which can form in SCR systems at temperatures below 

580 to 590°F. However, this problem can be avoided by ensuring that the SCR inlet temperature 

is always 600F or greater. 

Temperature Related Factors Leading to Lower NOx Removal Efficiencies

 Several temperature-related factors have been identified as important to successful 

operation of an SCR system. These are: (1) an acceptable normal operating temperature; (2) an 

even temperature distribution; and (3) avoiding temperature extremes (which may lead to 

catalyst deactivation or sintering). Low temperatures can lead to lower NOx reduction 

efficiencies and/or higher catalyst activity (leading to possible SO2 oxidation) and to possible 

ABS/AS formation in the catalyst pores. Concerns regarding a slightly lower than desirable inlet 

temperature, however, can be resolved by installing equipment to ensure a desired temperature of 

600°F or greater going into the SCR system. Such control systems are commonly used on boiler 

air supply systems and economizer bypass ducts. Note that the SCR reactor should also have an 

automatically activated bypass duct around the SCR reactor, so that in the event of high 

temperature fluctuations (greater than approximately 800°F), automatically controlled dampers 

would send the hot flue gas to a reactor bypass duct, thus preventing any damage to the SCR 

catalyst. Therefore, temperature issues, whether involving normal operating temperatures or 

temperature fluctuations, should be correctable with simple process reconfigurations. 
Cement Kiln Report (FINAL – 7/14/2006) 4-13

NOx Concentration Variability and NH3 Slip

 It has been argued that unlike a coal-boiler SCR application, an SCR system applied to a 

cement kiln will be faced with highly variable inlet NOx loadings and that elevated NH3 slip 

levels are possible, which, coupled with possibly higher sulfur oxide levels, represent a serious 

risk. However, in an SCR system, the injected NH3 is adsorbed onto the surface of the catalyst. 

Thus, there is a reservoir of unused NH3 on the surface of the catalyst that is available to handle 

sudden peaks in inlet NOx concentrations and thereby enable SCR systems to control fluctuating 

levels of NOx. SCR systems do not have to overfeed ammonia to handle surges in inlet NOx

concentration and so tend to have very low NH3 slip levels. 

 Coal-fired boilers have been operating SCR systems successfully for years despite 

considerable NOx fluctuations in their flue gases. SCR suppliers typically guarantee a NH3 slip 

of no more than 2 ppmv for any coal-fired boiler SCR application. In addition, the Solnhofen 

plant is a cement kiln with all of the inherent variability and has nevertheless been achieving a 

high degree of NOx control with a low ammonia slip level. Data at Solnhofen indicates that the 

SCR inlet NOx concentration varies considerably, from less than 1000 mg/Nm3 to 2030 mg/Nm3

while the outlet NOx concentration varies from approximately 300 to 726 mg/Nm3

, but maintains 

an average outlet NOx concentration of less than 500 mg/Nm3. At these variable conditions, 

however, NH3 slip has been maintained in the 1-2 ppmv range. 

Undesirable Byproduct Formation in the SCR Causing Adverse Effects on Downstream 

Equipment

 Concerns have been raised regarding the generation and release of SO3 that could cause 

corrosion of downstream equipment, or that the SO3 may react with unused NH3 to form 

ammonium salts (ABS and AS), which could plug or corrode downstream equipment. In 

addition it is argued that ammonium salts could increase condensable particulate matter levels, 

making it difficult for a facility to meet its particulate matter emission limit. In SCR systems 

with SO3, NH3 and moisture present, ammonium salts will form at temperatures below 580-

590°F. The best way to prevent their formation is to continuously control the SCR inlet 

temperature such that it is always 600°F or greater. Regarding the possible release of SO3, 

catalyst manufacturers report that the SO3 gas is totally captured by conversion to particulate 
Cement Kiln Report (FINAL – 7/14/2006) 4-14

calcium sulfates and sulfites as it is contacted by free lime upstream, within, and downstream of 

the SCR catalyst. Thus, the formation of undesirable byproducts should be inherently controlled 

by the free lime in the system and can be further controlled by controlling the SCR inlet 

temperature. 

General Conclusions 

 The experience of coal-fired power plants and the one cement plant with SCR offers the 

following lessons. First, the success of coal-fired power plants shows that catalyst deactivation 

from alkali poisoning is not expected to be a significant problem for cement kiln applications. 

Second, the success of SCR systems on a number of coal-fired boilers reveals that even when 

flue gases have significant levels of both calcium oxide (CaO) and sulfur dioxide (SO2), the 

condition can be handled in SCR systems without the occurrence of pore masking from calcium 

sulfate (CaSO4) formation. Third, the power plant experience shows that SCR systems can be 

designed to achieve at least 85% NOx reduction despite extremely large gas flow rates with 

significant NOx variability and relatively high particulate loadings. Last, the power plant 

experience shows that equipment can be designed and operated such that the flue gas entering 

the SCR catalyst will always be in the proper temperature range. For wet kiln applications, this 

can lead to a requirement for significant gas re-heat. 

Site-Specific Analyses 

 The follow sub-sections are specific to TXI, Holcim, and Ash Grove. In what follows, the 

additional NOx associated with gas re-heat, if required, has not been added, as the level of 

additional NOx would be below 10 tons per year and 85% of that would be removed. 

SCR at the TXI Kilns

 To consider SCR at the TXI facilities, one must perform separate analyses for Kiln 5 (the 

dry kiln with pre-heater/pre-calciner, as found at the Solnhofen plant) and Kilns 1-4 (the long 

wet kilns, which usually operate as kilns 1 and 4 in tandem, or 2 and 3 in tandem). Neither the 

alkali percentages, the sulfur fuel percentages nor the stack concentrations (extrapolated to 
Cement Kiln Report (FINAL – 7/14/2006) 4-15

uncontrolled for TXI #5) would be considered high for SCR utilization in coal-fired power plants 

(see Confidential Attachment – TXI). 

 With respect to the dry kiln (TXI 5), it would be expected that an SCR system would be 

installed downstream of the pre-heater, where the temperature would be in the range required. 

With respect to process economics, this temperature is assumed to be 700°F (the temperature 

utilized in all the cases at all the plants studied). With respect to this particular kiln, the present 

data indicates a low NOx level in the 150-ppm range. For conservatism, it is therefore assumed 

that an SCR system for this kiln would operate at an 80% reduction efficiency, as opposed to a 

significantly higher level (85%) to be expected at the other kilns at TXI and at the other facilities 

in Ellis County. 

 The economic analysis for this case is found in the confidential attachments. It is found 

that the cost effectiveness, based on NOx removed ($/ton NOx removed) is approximately 

$2,200/ton. With respect to cost effectiveness based on metric tonnes of clinker produced 

($/tonne clinker), the cost is approximately $0.87/tonne. 

 The wet kilns have been economically modeled based on a number of possible scenarios. 

The reported stack gas temperature 160°C (320°F) was utilized in the reheat calculations (to 700 

oF at the SCR inlet) in all cases, and natural gas, at $12.00/therm is utilized. Three different 

scenarios were studied. In the first scenario, one SCR system serves kilns 1 and 4 consistent 

with TXI’s operation (85% of the time). In the second scenario, one SCR system serves kilns 2 

and 3 again consistent with TXI’s operation (15% of the time). In the third scenario, one SCR 

system serves all four wet kilns with piping and controls to match the normal operating 

scenarios. These three scenarios were again modeled based on the possibility that TXI might 

introduce mid-kiln firing as a method of NOx control in its four wet kilns. Therefore, a total of 

six economic analyses for the TXI wet kilns are found in the confidential attachment. 

 For the scenario without mid-kiln firing in kilns 1 and 4, the cost effectiveness based on 

NOx removal ($/ton NOx removed) is approximately $5,500/ton. The cost effectiveness based on 

metric tonnes of clinker produced ($/tonne clinker) is approximately $8.90/tonne. These 

estimates are based on the assumption that mid-kiln firing is in place as required under the 
Cement Kiln Report (FINAL – 7/14/2006) 4-16

existing Texas regulations. Mid-kiln firing is currently required at Ash Grove, but has not been 

installed due to permit issues. Assuming mid-kiln firing avoids possible double counting of the 

emissions reductions achieved by mid-kiln firing. 

 The scenarios involved with kilns 2 and 3 with SCR lead to what must be considered 

unacceptable economics, since capital cost is essentially equal to that for kilns 1 and 4, but 

operation (both from the standpoints of NOx removed and clinker produced) is only 15% of the 

total. Therefore, without mid-kiln firing, the economics yields a cost effectiveness based on NOx

removal of approximately $96,000/ton, while the cost effectiveness based on clinker produced is 

in the $13.50/tonne range. Mid-kiln firing is also assumed for kilns 2 and 3. 

 Based on economies of scale, utilizing one large SCR unit to service all four kilns (the 

model assumes a capacity equivalent to approximately 3 kilns in operation at any time) should 

lead to the most cost effective manner of control. With mid-kiln firing, the cost effectiveness 

based on NOx removal is approximately $5,300/ton, while the cost effectiveness based on clinker 

produced is about $5.90/tonne. 

 It is clear that while the reheat required in the wet kilns significantly increases the costs 

associated with NOx control with the utilization of SCR, the cost effectiveness is best when one 

SCR unit is installed for all four wet kilns. For the dry kiln, the economics is, of course, 

significantly better and assuming space for the catalyst beds and ancillary equipment is available, 

SCR must be seriously considered. 

SCR at the Holcim Kilns

 To consider SCR at the Holcim facilities, separate analyses are performed for each of the 

two dry units. Each is equipped with precalciners and preheaters, but Holcim 2 is a newer, more 

efficient unit, emitting 26% less NOx (in mg/m3

). The temperature after the preheater for both 

Holcim 1 and 2 is expected to be adequate (i.e. 700°F), so no reheat would be required, and 85% 

NOx removal is assumed. Neither the alkali percentages, the sulfur fuel percentages, nor the 

stack concentrations extrapolated to uncontrolled would be considered high for SCR utilization 
Cement Kiln Report (FINAL – 7/14/2006) 4-17

in coal-fired power plants (see Confidential Attachment – Holcim). The utilization of SCR is, 

therefore, not precluded. 

 The annual cost spreadsheets are found in the confidential attachments for each cement 

plant. The cost effectiveness based on NOx removal ($/ton NOx removed) for Holcim 1 is 

approximately $1,950/ton. The cost effectiveness based on metric tonnes of clinker produced 

($/tonne clinker) is about $2.00/tonne. 

 For Holcim 2, which is more efficient, the NOx removed is less (since less NOx is 

produced) and the clinker production is greater. Therefore, the cost efficiency based on NOx

removal is slightly greater for Holcim 2, at approximately $2,000/ton, and the cost effectiveness 

based on tonnes of clinker produced is approximately $1.70/tonne. 

SCR at the Ash Grove Kilns

 Ash Grove has three wet kilns with mid-kiln firing: Ash Grove 1, Ash Grove 2 and Ash 

Grove 3. Data indicate nearly identical operating conditions and NOx emission levels (in the 350 

ppm to 400 ppm range). Neither the alkali percentages, the sulfur fuel percentages nor the stack 

concentrations would be considered high for SCR utilization in coal-fired power plants (see 

Confidential Attachment – Ash Grove). In addition, Ash Grove reports temperatures at the air 

pollution control device (APCD) inlets of 330°F to 370°F. Assuming the installations of SCR 

between the APCDs and the stacks, these temperatures indicate that Ash Grove can install SCR 

at each of their kilns with reheat required, and 85% NOx removal can be expected. 

 Four scenarios are presented, that of the installation of an SCR at each of the three wet 

kilns, the fourth being the installation of one SCR for all three units. For Ash Grove 1, the cost 

effectiveness based on NOx removal ($/ton NOx removed) is about $5,800/ton (all reheat at 

$12.00/therm). The cost effectiveness based on clinker produced ($/tonne clinker) is 

approximately $9.20/tonne. 

 For Ash Grove 2, the cost effectiveness based on NOx removal is approximately 

$5,800/ton. The cost effectiveness based on clinker produced is about $9.90/tonne. 
Cement Kiln Report (FINAL – 7/14/2006) 4-18

 For Ash Grove 3, the cost effectiveness based on NOx removal is approximately 

$6,100/ton. The cost effectiveness based on clinker produced is approximately $10.60/tonne 

clinker. 

 If space is available and operation is not impeded, one SCR unit can be installed to 

service all three kilns. In this case, the cost effectiveness based on NOx removal improves to 

about $4,600/ton. The cost effectiveness based on clinker production improves to approximately 

$7.70/tonne. 

 It is clear that if space is available for one SCR unit and its ancillary equipment, in order 

to serve all three kilns, the economics is far more favorable than if three SCRs are installed. 

SCR, therefore, for these wet kilns is an available technology at 85% NOx control, albeit at a 

high cost/tonne of clinker removed. 

Table 4-1.1. Summary of Modeling Results for SCR on Ellis County Kilns – Performance 

Results 

Existing Unit 

Control 

Technology 

Emissions 

Rate 

tpy before 

Emissions 

Rate 

tpy after (a) 

Controlled 

Emissions 

Rate ppm 

Controlled 

Emission Rate 

lb./tonne clinker 

Control 

Efficiency % 

Reduction 

tpy 

Ash Grove #1- wet SCR 702 301.6 60 0.84 85% 400.4 

Ash Grove #2- wet SCR 750 322.2 58 0.89 85% 427.8 

Ash Grove #3- wet SCR 764 328.3 53 0.91 85% 435.7 

Ash Grove #1,2,&3 (c) SCR 2205 947.4 57 0.88 85% 1,257.6 

TXI #1 and #4–wet (b) SCR 838 155.3 109 0.85 85% 478.0 

TXI #2 and #3–wet (b) SCR 121 52 109 0.51 85% 69.0 

TXI #1,2,3,4 –wet (c) SCR 1802 774.2 109 0.85 85% 1,027.8 

TXI#5 – dry SCR 1710 734.7 29 0.30 80% 975.3 

Holcim #1 – dry SCR 2222 954.7 108 0.56 85% 1,267.3 

Holcim #2 – dry SCR 1778 763.9 80 0.45 85% 1,014.1 

(a) NOx emission rate after SCR does not reflect SCR efficiency reduction due to adjustment by the ozone season factor of 0.671 

(NOx reduction is modeled to occur only during the ozone season). 

(b) The results for TXI 1 & 4 and #2 & #3 are average per kiln – for example, total emissions reductions for controlling both TXI 

#1 & #4 are double the value listed in the table. 

(c) A large single SCR was modeled for the Ash Grove and TXI wet kilns with the capacity of 3 wet kilns. 

(d) Models assume mid-kiln firing installed at TXI as required under current SIP. 
Cement Kiln Report (FINAL – 7/14/2006) 4-19

Table 4-1.2. Summary of Modeling Results for SCR on Ellis County Kilns – Economic 

Results 

Existing Unit 

Control 

Technology 

Capital 

Cost 

Annual 

Cost 

Cost 

Effectiveness 

$/ton NOx

Energy 

Penalty or 

Benefit 

Emissions 

Penalty or 

Benefit 

Burden Cost 

$/tonne clinker 

Ash Grove #1- wet (e) SCR $5.0MM $2.3 MM $5,800 (a) (b) $9.20 

Ash Grove #2- wet (e) SCR $5.2MM $2.5MM $5,800 (a) (b) $9.90 

Ash Grove #3- wet (e) SCR $5.3MM $2.7MM $6,100 (a) (b) $10.60 

Ash Grove #1,2,&3(d) SCR $11.8MM $5.7 MM $4,600 (a) (b) $7.70 

TXI #1 & #4–wet (c,e) SCR $5.7MM $2.6MM $5,500 (a) (b) $8.90 

TXI #2 & #3–wet (c,e) SCR $5.7MM $0.6MM $96,000 (a) (b) $13.50 

TXI #1,2,3,4 –wet (d,e) SCR $11.2MM $5.4MM $5,300 (a) (b) $5.90 

TXI#5 – dry SCR $8.4MM $2.2MM $2,200 (a) $0.87 

Holcim #1 – dry SCR $7.5MM $2.4MM $1,900 (a) $2.00 

Holcim #2 – dry SCR $6.7MM $2.0MM $2,000 (a) $1.70 

(a) Increased fan power due to pressure drop across catalyst bed included in the models 

(b) Increase in NOx from gas reheat occurs, but is controlled by the SCR 

(c) The results for TXI #1 & #4 and #2 & #3 are average per kiln – for example, total capital costs for controlling both TXI #1 & 

#4 are double the value listed in the table. 

(d) A large single SCR was modeled for the Ash Grove and TXI wet kilns with the capacity of 3 wet kilns. 

(e) Costs for wet kilns include cost of RTO to reheat flue gas. 
Cement Kiln Report (FINAL – 7/14/2006) 4-20

4.1.2 Selective Noncatalytic Reduction (SNCR) 

 This control technique relies on the reduction of NOx in exhaust gases by ammonia or 

urea, without using any catalyst, with the same reactions as in the case of the SCR process. 

Because of low capital and maintenance costs associated with this technology vis-à-vis other 

end-of-pipe technologies like SCR and oxidative methods, it is likely to command attention in 

the near future within the industry. This approach combines a low initial capital cost and avoids 

the problem related to catalyst fouling and replacement associated with SCR technology. SNCR 

requires injection of the reagents in the kiln at a temperature between 870 to 1,090°C (1,600 to 

2,000°F). In principle, any of a number of nitrogen compounds may be used as SNCR reagents 

(e.g., cyanuric acid, pyridine, and ammonium acetate). However, for reasons of cost, safety, 

simplicity, and by-product formation, ammonia and urea have been used in most of the SNCR 

applications. The selection of reagents is process and temperature specific. At higher 

temperatures, urea decomposes to produce ammonia, which is responsible for NOx reduction. In 

cement kiln applications, ammonia typically has performed best as the reducing reagent. 

 Because no catalyst is used to increase the reaction rate, the temperature window is 

critical for conducting this reaction. At higher temperatures, the rate of a competing reaction for 

the direct oxidation of ammonia, which actually forms additional NOx, becomes significant. At 

lower temperatures, the rates of NOx reduction reactions become too slow resulting in too much 

unreacted ammonia being released to the atmosphere (i.e., ammonia slip). The effective 

temperature window range can be lowered to about 700°C (1,300°F) by the addition of hydrogen 

along with the reducing agent. (24) Addition of hydrogen can promote SNCR reactions 

(enhanced SNCR), but high levels of sulfur oxides may interfere with this reaction (Recent 

evidence tends to call into question this tentative conclusion). Nalco Fuel Tech, the producer of 

the SNCR technology NOxOUT®, has also introduced NOxOUT® PLUS which is said to 

broaden the operating temperature window and to reduce ammonia slip and CO and NO2

formation. 

 In a conventional long kiln, the appropriate temperature window is in the middle of a 

kiln. Until quite recently, because of the rotating nature of a long kiln, continuous injection of 

ammonia- or urea-based reagents had not been considered possible. The technology developed 
Cement Kiln Report (FINAL – 7/14/2006) 4-21

for mid-kiln firing of containerized solid fuels allows injection of a certain amount of material 

once during the kiln revolution. Injection of solid ammonium or urea salts in this manner had 

not been used because of the assumption of rapid decomposition of such salts. Therefore, SNCR 

technology had not been thought applicable to date for long dry or wet kilns. There is some 

limited evidence from Europe, suggesting that injection of urea into long wet kilns may have 

promise(25). Urea injection was reportedly continued over a four month period with satisfactory 

results at a wet kiln in France. The publicized information does not, however, give detailed data 

needed to evaluate this test. The test does not stipulate: 

• Location of reagent injection, 

• Titration rate for reagent, 

• Reagents tried and their performance (only urea is mentioned), 

• NOx reduction rate vs. titration rate, 

• NOx reduction rate vs. temperature, 

• Average NOx emissions rates for controlled and uncontrolled operation, 

• Operating costs, 

• Other NOx control measures employed at the kiln, and 

• A physical description of the kiln and information on feed and production materials. (25) 

Without this type of detailed information, it is difficult to draw any definitive conclusions about 

the potential for application to wet kilns in Ellis County. 

 

 In addition, Fuel Tech Inc. is currently evaluating dry dust or pellet injection methods for 

direct injection into kilns. (26) The possibility of injection of ammonia or solid urea inside 

automobile tires that are injected into the kiln has still to be evaluated. With the known ability of 

mixing air fans to induce turbulence in the system, mixing combustion gases containing NOx

with ammonia, either generated from urea or from ammonium salts, may also offer possibilities. 

Chain gas temperatures generally are in the range of 1500-1600oF (815-871oC). The mid-kiln 

injection systems are usually down kiln somewhat from this point, which means that they will be 

higher than this in gas temperature. There is a good possibility that the correct temperature range 

can be achieved if mixing is induced and volatilization or decomposition of the urea can be 

delayed by inserting it in a solid form in a carrier such as a tire. This option needs to be 

explored. It will clearly be necessary to mix the NOx with the reagent before the latter has an 

opportunity for decomposition. Inducing turbulence is presently conceived as a key element in 

this strategy. 
Cement Kiln Report (FINAL – 7/14/2006) 4-22

 In preheater/precalciner type cement kilns, the temperatures at the cooler end of the 

rotating kiln, in the riser duct, and in the lower section of the cyclone preheater tower are likely 

to be in the temperature window appropriate for SNCR. Such kilns are therefore good candidates 

for application of SNCR technology. 

 The NOx reduction efficiency of SNCR depends upon the temperature, oxygen, carbon 

monoxide, and residence time, as well as the ammonia and NOx concentrations in the flue gas. 

Injection of ammonia at a NH3:3 NOx proportion of 1 to 1.5 will reduce NOx emissions between 

60 to 80 percent. Using a molar ratio of 0.5 will give NOx reductions of approximately 40 

percent. (27) Work done by the German equipment supplier Polysius (28) has shown that the 

optimum temperature for reduction of NOx by ammonia is about 950oC (1,740oF), while for urea, 

the temperature increases to about 1,000oC (1,830oF). Ammonia is also somewhat more 

efficient, as shown in Figure 4-1.2. below. 

Figure 4-1.2. Dependence of NOx Reduction on Temperature for Ammonia and Urea 

 Actual SNCR results with ammonia (19% aqueous solution) at one US plant employing a 

calciner are given in Table 4-1.3. It can be seen that the reduction was remarkably good, 

considering that ammonia was never added at greater than a stoichiometric equivalent to NOx
Cement Kiln Report (FINAL – 7/14/2006) 4-23

Due in part to the fact that no excess ammonia was introduced into the system, no ammonia slip 

was demonstrated. The ammonia emissions were undetectable. 

Table 4-1.3. Summary of Test Results for SNCR Test 

Run # 

Molar Ratio 

NH3:NO 

NOx

Reduction 

% 

Average NOx

Before 

lb./hr 

Average NOx

During SNCR 

lb./hr 

1 0.918 65.49% 325.47 112.31 

2 0.533 36.71% 322.90 204.35 

3 0.425 44.93% 345.52 190.27 

4 0.331 16.90% 282.70 234.91 

5 0.465 15.49% 290.18 245.25 

6 0.286 12.95% 269.35 234.47 

7 0.534 45.06% 269.35 147.97 

8 0.552 31.91% 281.71 191.81 

Long term 0.368 47.78% 329.83 172.24 

 These results were very good. The temperature and oxygen concentrations were nearly 

optimum for the SNCR system. The carbon monoxide levels were somewhat higher than has 

been considered optimum, but according to Brouwer et al. (29), CO may promote the reaction at 

the lower end of the temperature range, because of the temperature increase due to the heat given 

off by the reaction of CO with OH radicals. Among other SNCR tests recently performed, tests 

have been carried out at a preheater plant and four calciner plants. Some of these tests were 

carried out using ammonia, and others using urea. At the preheater plant, both ammonia and 

urea were tested, injecting the reagents into the kiln riser duct. Ammonia proved to be 

considerably more effective than urea, in keeping with the Polysius plot given above. 

 Despite these successes, reagent consumption can be significantly higher with greater 

ammonia slip in SNCR systems as compared to SCR systems. Operating experience has 

identified several concerns with both ammonia and urea-based SNCR processes. The most 

frequently reported is the buildup of ammonium bisulfite or bisulfate scale, which is significant 

for sulfur-containing fuels. SNCR processes also appear to convert some NOx to N2O. (30) The 

rate of N2O formation is a weak function of both the reactant and the NO concentration. 

However, N2O formation seems to be inherently more prevalent in systems using urea than those 

using ammonia. (31) 
Cement Kiln Report (FINAL – 7/14/2006) 4-24

 The NOx destruction efficiency also depends upon the flue gas residence time in the 

appropriate temperature window. Unlike an SCR system where the reaction temperature is 

controlled in a dedicated reactor, an SNCR system relies on the existing gas temperature profile 

to provide an adequate residence time for a desired NOx destruction. Maximum achievable NOx

reduction in a cement kiln may thus depend upon the gas temperature profile. 

 The SNCR process was demonstrated in Europe in a preheater type kiln. Both ammoniaand urea-based reagents were investigated. The reagents were injected in the gas duct as shown 

in Figure 4-1.3. (32) With a molar ratio of reagent to NO2 of 1:1, about 70 percent reduction in 

NOx emissions was observed with ammonia-based reagent and about 35 percent NOx reduction 

was obtained with urea. (32) With this reagent ratio, there was no major increase in ammonia 

emissions in exhaust gases over the background level of ammonia emissions generated by kiln 

feed material. Greater NOx reductions were observed with more than stoichiometric amount of 

reagent, although there was increasing ammonia 'slip' in the exhaust gases. 

Figure 4-1.3. Application of SNCR at Holcim 

 Albert Scheuer, of the Research Institute of the Cement Industry in Düsseldorf, Germany, 

reported on 148 SNCR trials carried out on five different kilns. Three kiln systems had cyclone 

preheaters and two had grate preheaters. A 25% molar concentration of NH3 in water was the 

main reagent tested, with some additional testing done with ammonium sulfate solutions and 
Cement Kiln Report (FINAL – 7/14/2006) 4-25

with urea solutions. Scheuer reported that NO reductions with the NH3/water solution ranged 

from 15% to 75% and that temperature appeared to be one of the main determinants of the 

effectiveness of the reagent. Maximum NO reduction occurred at 980°C (1796°F). NH3 escape 

occurred when temperatures were less than 900°C (1652°F) and when the NO concentration 

fluctuated. NH3 utilization decreased significantly with increasing NH3:NO molar ratio and with 

decreasing NO concentration in the exhaust gases, indicating that SNCR appears to be a less 

promising methodology at low NO emissions rates. (33,34) 

 SNCR is presently being used in 18 cement kilns in Europe. Fifteen kilns are in 

Germany, two are in Sweden, and one is in Switzerland. These kilns are either suspension 

preheater kilns or precalciner kilns. The names and locations of these installations have not been 

found in any of the European references that discuss these installations. The most common 

reagent used is 25% ammonia water. (35) NOx reduction rates vary from 10 to 50 percent with 

NH3/NO2 molar ratio of 0.5 to 0.9, NOx emissions at these reductions are 2.4 to 3.8 lb./tonne 

clinker. Two dry process cyclone preheater/precalciner kilns in Sweden achieve 80 to 85 percent 

reduction (1.0 lb./tonne clinker) at a NH3/NO2 molar ratio of 1.0 to 1.1. (35) One reason for the 

remarkable results in these kilns is the use of multiple injection points (12 in all) that ensure long 

enough retention time for the reaction to take place. The optimum temperature is said to be 900-

1,100oC (1,650-2,010oF) in good agreement with other authors. These results suggest that some 

SNCR tests may have been carried out under lower-than-optimum temperatures. 

 F. L. Smidth and Company tested SNCR on a preheater/precalciner kiln. (36) Ammonia 

was injected into the lower cyclone of the preheater tower where temperatures are favorable for 

the reduction reactions to occur. NOx emissions reductions during this experiment averaged 40 

percent, but NOx reductions of over 90 percent were obtained when the ammonia injection rate 

was 10 to 20 percent in excess of stoichiometric. 

 In North America, SNCR has been tested on at least nine kilns. In some of the earlier 

work, NOxOUT® technology was tested under ten different operating conditions at a 

preheater/precalciner kiln in Seattle, Washington during October 1993. NOx emissions were 

effectively reduced from 3.5 to 6.0 lb. NOx/tonne clinker to less than one lb. NOx/tonne clinker. 

(37,38) Another test of NOxOUT® technology was conducted during October 1998 in 
Cement Kiln Report (FINAL – 7/14/2006) 4-26

Davenport, Iowa. This test found NOx reductions of 10 to 20 percent from a baseline of 

approximately 350 pounds NOx/hour, although higher levels of reduction are thought to be 

achievable when the baseline is higher. (39) An evaluation of NOxOUT® technology was 

conducted in 1994 for a long dry kiln in Southern California, but the study concluded that 

application of the NOxOUT® technology at the subject kiln was technically infeasible. (40) The 

details of this testing are not known. 

Biosolids Injection (BSI). The Mitsubishi Cement Corporation’s Cushenbury plant in 

Lucerne Valley, CA, uses biosolids injection technology (BSI) to achieve SNCR of NOx. The 

BSI process was developed by the Cement Industry Environmental Consortium (CIEC). The 

founding participants in the CIEC are Southdown, Inc., Riverside Cement Company, Mitsubishi 

Cement Corporation, California Department of Commerce (now Trade & Commerce Agency), 

and the San Bernardino County Air Pollution Control District (now Mojave Desert Air Quality 

Management District). This technology is covered under U.S. Patent No. 5,586,510 issued 

December 24, 1996. (33) 

 The basic principle is to utilize the naturally occurring ammonia content of dewatered 

biosolids as the reagent. The dewatered biosolids are obtained from wastewater treatment plants. 

Since the biosolids are mechanically dewatered without heat input, the solids content varies 

between 16 and 30 percent (moisture content of 84 to 70%). Depending on the moisture content, 

the net Btu content (after evaporating the moisture) of the biosolids varies between -750 and 

+2200 Btu/lb. Since the biosolids heating value is relatively small, the net effect on kiln fuel 

combustion is expected to be small. (41) 

 The same conditions that affect NOx reduction performance in SNCR affect BSI 

performance: temperature (927°C / 1,700°F is optimal), residence time (> 0.5 seconds is 

desirable), inlet NOx concentration, inlet CO concentration, and NH3/ NOx molar ratio. Another 

key issue is mixing effectiveness, which affects the extent of contact and, hence, reaction 

between NH3 and NOx. The BSI technology is applicable to preheater/precalciner kilns because 

the temperature window for BSI (927°C / 1700°F) occurs in a location where it is feasible to 

inject biosolids. (41) 
Cement Kiln Report (FINAL – 7/14/2006) 4-27

 The biosolids are injected into the mixing chamber where the flue gas stream leaves the 

kiln and precalciner mix. The mixing chamber offers the benefits of good residence time in the 

appropriate temperature window (927°C / 1700°F) and high mixing effectiveness. (41) 

 At the Cushenbury plant, BSI underwent long-term testing and eventual adoption in 1994 

and 1995. The kiln is fueled with coal (85 percent) and tires (15 percent). The plant began using 

tire-derived fuel (TDF) in mid-1993, so it is difficult to isolate the effects of TDF or BSI on NOx

emissions. The company estimates that the use of TDF reduces NOx emissions from the kiln by 

30 to 40 percent. (42) Before the SNCR technology was adopted, the company estimated NOx

emissions averaged 2.4 lb./tonne clinker; afterwards, the average fell to 1.2 lb./tonne clinker, a 

50 percent reduction. The effects of BSI on CO emissions varies between a large increase and 

no change at all, but in all cases it has remained below 500 ppm. BSI has not caused any 

significant changes in either metal HAP or organic HAP emissions. Using the SNCR biosolids 

technology, the kiln also reduced its fuel consumption by 5 percent. (41) 

NOxOUT®. An SNCR process using aqueous urea was developed by Electric Power 

Research Institute (EPRI) and is now marketed by Nalco Fuel Tech, Inc., under the trade name 

NOxOUT®. In the urea reaction with NO, one mole of urea reacts with two moles of NO to 

complete the reaction to nitrogen, carbon dioxide and water. Normalized Stoichiometric Ratio 

(NSR) is used to express the reagent feed rate relative to the reaction stoichiometry. The NSR 

takes into account the 2:1 mole ratio of the NO:urea reaction as the “normalized” ratio. If 50% 

of the urea reacts to reduce NO to nitrogen, reduction of 100% NOx occurs at NSR=2; 80% 

reduction at NSR=1.6; 50% reduction at NSR=1.0, etc. Performance improves with increased 

turbulence or mixing, residence time, and more favorable temperature conditions. A higher NOx

baseline generally leads to a higher percentage of NOx reduction. (26) 

 Urea is safer to handle than anhydrous ammonia. Both ammonia and urea need to be 

injected in a similar temperature window, which is 870 to 1090°C (1600 to 2000°F). The 

Polysius results earlier noted, however, appear to suggest that the ammonia optimum may be 

lower than the urea optimum. Proprietary additives have been developed by Nalco to widen the 

temperature window. (43) One modification of the urea-based SNCR system is the addition of 

methanol injection downstream of the urea injection point to improve overall NOx removal. 
Cement Kiln Report (FINAL – 7/14/2006) 4-28

Nalco also introduced an improved NOxOUT® PLUS, which is said to further broaden the 

operating temperature window and to reduce ammonia slip and CO and NO2 formation. 

 The Ash Grove plant in Seattle is a preheater/precalciner kiln with average processing 

rates of 160 tons dry feed/hour producing approximately 100 tonnes clinker/hour. NOxOUT®

was tested on this kiln under varying conditions, including the use of different fuel types (natural 

gas and coal), heat input to the calciner (5 to 9 percent), and preheater O2 (1.8 to 2.9 percent). (It 

is probably necessary to point out that this calciner is an example of the so-called “air through” 

unit which employs no tertiary air duct; all air for combustion in the calciner must be furnished 

through the kiln. As of the present time, this heat input is in the range of 20-30% of the total. 

The baseline NOx levels varied from 350 to 550 lbs. NOx/hour. When NOxOUT® was used, 

NOx emission reductions varied significantly depending on the conditions, with a maximum 

reduction of 90 percent (less than 100 lbs. NOx/hour). Typical reductions were greater than 50%. 

(38) 

 NOxOUT® was tested for one week in October of 1998 on the preheater/precalciner kiln 

at the Lafarge-Davenport Plant. Operating conditions were unstable most of that week and only 

five hours of testing produced results that could provide a reasonable indication of what may be 

achievable with NOxOUT®. The baseline NOx rate was approximately 350 lbs. NOx/hour. 

Using NOxOUT®, emission reductions of 10 to 20 percent were achieved. (39) Operating 

conditions such as residence time, temperature, and the use of coal at this kiln were contrasted to 

conditions at the Ash Grove kiln that achieved greater reductions to explain why NOxOUT® may 

achieve better results on some kilns than others. 

 Nalco also has conducted a number of demonstrations and commercial projects in 

preheater/precalciner cement kilns. The fuels have included coal, and coal in combination with 

No. 6 heavy fuel oil, waste oil, and/or tire chips. The clinker capacity on these kilns ranged from 

approximately 1,000 metric tons to 3,200 metric tons per day. The results of two tests with 

average NOx reductions of approximately 50%, were featured in a recent report (see Table 

4-1.4). (26) 
Cement Kiln Report (FINAL – 7/14/2006) 4-29

Table 4-1.4. Emissions Reductions From Two Kilns Using NOxOUT® 

Baseline NOx

Emissions (ppm) 

NOx Emissions with 

NOxOUT® (ppm) 

Percent 

Reduction (%) 

Kiln A, Test 1 412 203 51 

Kiln A, Test 2 389 185 53 

Kiln B 525 284 46 

Site-Specific Analyses 

SNCR at Holcim

Holcim Kiln #1 

 Holcim carried out trial SNCR tests on both of their precalciner kilns in Midlothian, TX. 

For the injection in line 1, (the older unit) the optimum location was identified to be on the riser 

duct, after the precalciner and before the bottom stage cyclone. This location would address NOx

formed both in the kiln (principally presumably thermal NOx) and in the calciner (principally 

presumably fuel NOx). The reports do not indicate the temperature, oxygen, or carbon monoxide 

concentrations of the flue gas, considered very important for optimum efficiency. There is 

therefore no basis for concluding that conditions had been optimized. With this condition, it 

proved possible to obtain about 50% removal of NOx at a molar ratio of ammonia to NOx of 

0.75. This is not considered to be as good as obtained in the Florida kiln indicated earlier, nor 

for some of the Northern European kilns. However, the removal efficiency appears to be in good 

agreement with the data cited earlier, where a molar ratio of 0.5 is cited as achieving 40% 

removal, while a molar ratio of 1.0 is said to achieve 60% removal. While the conditions may 

not have been optimized, the results are considered acceptable compared to performance at other 

similar kilns. Experience at other kilns indicates further optimization may result in better 

performance at Holcim #1 than was achieved during the initial trial period. 

Holcim Kiln #2 

 For the Kiln #2 system, the injection point was on the riser duct after tertiary air input and 

before the Pyroclon (calciner). This differs from the location for the Kiln #1 system, where the 
Cement Kiln Report (FINAL – 7/14/2006) 4-30

injection point is post-calciner. This difference implies that the gases from the calciner were 

treated in the Kiln #1 system, but no SNCR was applied to calciner exhaust gases in the Kiln #2 

system. Experience to date suggests that with normal bituminous coal fuel, roughly 70% of the 

system NOx may be generated in the kiln, and 30% in the calciner as a general rule of thumb. To 

the extent that this supposition is justified, it appears as though an SNCR injection location that 

does not treat gases from the calciner may be omitting treatment of about 30% of the NOx. In 

addition, the injection location for this kiln system may be experiencing a temperature decrease 

from the cooler tertiary air. Any residual carbon monoxide from the kiln exit gases was probably 

oxidized by the high O2 content at this location, further compromising the results. If this is the 

case, further erosion of the efficiency of the SNCR system may be occurring. 

 As a result, with a molar ratio of 0.75, the efficiency of removal of NOx was only 35%. 

This cannot be considered satisfactory. It proved possible to increase the NOx removal to as high 

as 80%, but this was with a molar ratio of about 2.0. At this molar ratio, ammonia slip and 

detached plumes were severe. In addition, the plant reported a buildup of ammonium 

sulfate/ammonium bisulfate in the top preheater stage forming under conditions of high ammonia 

injection. They claim that this buildup had the potential to assume catastrophic dimensions, but 

was removed before this occurred. 

 It does not appear likely that the location for NOx removal on Kiln #2 was optimized. 

The lack of any data on temperature, oxygen, and/or carbon monoxide suggests that these data 

were not collected. It was discovered during the Florida test that optimization of these 

parameters was important to the success of the experiment. We believe that if the conditions are 

properly optimized using the necessary temperature, oxygen, and CO data, that better results are 

achievable at Holcim#2. 

SNCR at TXI

TXI Kiln #5 

 This kiln is already achieving very good NOx control without employing any end of pipe 

technologies. It appears that the kiln is running at about 1.9 lb. NO2/tonne clinker at present – 
Cement Kiln Report (FINAL – 7/14/2006) 4-31

this may be the lowest value for any Portland cement kiln in the country. The application of 

SNCR may be worth consideration for further reduction of NOx. It should be recognized, 

however, that 35% removal may be the best achievable, and even this level may not be 

achievable without optimization of the location in the preheater tower for temperature, oxygen, 

and CO. SNCR becomes less effective at lower NOx concentration and European experience 

indicates that 200 mg/m3

 or approximately 100 ppm may be a lower limit for efficient 

application of SNCR at cement kilns. As earlier indicated, TXI has a high level of relatively 

nonvolatile organic carbon, a high level of total Kjeldahl nitrogen (unfortunately, the temperature 

profile of nitrogen release from the feed at TXI is not known), and an apparently relatively easy 

burning mix. All these factors mitigate in the direction of lower uncontrolled NOx numbers.

TXI Wet Kilns 

 The ERG Team has estimated that the TXI wet kilns are currently operating at over 8 lb. 

NO2/tonne clinker. The Texas Code (Chapter 117) requires mid-kiln injection or meeting an 

emissions limitation of 4.0 lbs./tonne clinker. For the purposes of modeling SNCR and other 

control techniques on the TXI wet kilns, a 30% reduction in NOx emissions is assumed to result 

in emissions similar to the Ash Grove wet kilns when the mid-kiln firing is installed. The ERG 

Team understands that TXI is waiting for permit approval to convert the wet kilns to mid-kiln 

firing with tire injection. As discussed above, the lack of available alternative NOx controls for 

wet kilns leads the ERG Team to a recommendation of trying innovative or experimental 

techniques involving some SNCR injection involving urea or another reagent in tires. This 

experimentation would determine if mixing and the proper form of ammonia might travel into 

the proper temperature range of the kiln to be effective. These ideas will have to be verified or 

disproved with experimentation. For the purposes of cost modeling, a 35% efficiency is assumed 

to be achievable through a mid-kiln injection of a SNCR reagent. 

SNCR at Ash Grove

Ash Grove Wet Kilns 

 The Ash Grove wet kilns are already using mid-kiln firing and are emitting 

approximately 5.0 lbs./tonne clinker. Mid-kiln firing is traditionally regarded as the most 
Cement Kiln Report (FINAL – 7/14/2006) 4-32

effective wet kiln method for controlling NOx. As discussed above, it may be worthwhile 

considering a modification of traditional SNCR here, in which the urea is introduced inside 

whole tires, and mixing air is used to promote reaction with NOx before the urea is decomposed. 

This is innovative and speculative, and requires testing to verify, but it should be quite 

inexpensive and cost effective for a plant already employing mid-kiln firing. Attempting an 

innovative control method for wet kilns based on SNCR seems to be a worthwhile option since 

other control options have not been applied to wet kilns. SCR and LoTOxTM appear to be 

transferable from other applications but have high costs associated with reheating the flue gas in 

the case of SCR and installing a spray tower in the case of LoTOxTM. As mentioned in 

evaluating TXI #5, there appears to be the potential for some NOx reduction to be occurring from 

the materials already being fed to this kiln. With other mid-kiln injection in long kilns, NOx

reduction has occurred through feeding nitrogen containing sands at mid-kiln. It might be 

possible to introduce another material high in non-volatile carbon and/or TKN nitrogen at midkiln to see whether the foregoing explanation for the low NOx from the TXI kilns is valid. 

Again, this would not be expensive as an experimental investigation. Similar to the TXI wet 

kilns, for the cost models, it was assumed that one of these experimental techniques could result 

in 35% NOx reduction and that the costs would be similar to the costs of installing SNCR on a 

utility boiler. 

Table 4-1.5. Summary of Modeling Results for SNCR on Ellis County Kilns – 

Performance Results 

Existing Unit 

Control 

Technology 

Emissions 

Rate 

tpy before 

Emissions 

Rate 

tpy after (a) 

Controlled 

Emissions 

Rate ppm 

Controlled 

Emission Rate 

lb./tonne clinker 

Control 

Efficiency % 

Reduction 

tpy 

Ash Grove #1- wet SNCR 702 537.1 200 3.6 35% 164.9 

Ash Grove #2- wet SNCR 750 573.9 200 3.9 35% 176.1 

Ash Grove #3- wet SNCR 764 584.6 200 3.9 35% 179.4 

TXI #1 and #4–wet (b) SNCR 838 641.2 250 3.7 35% 196.8 

TXI #2 and #3–wet (b) SNCR 121 92.6 250 3.7 35% 28.4 

TXI#5 – dry SNCR 1710 1,308.4 100 1.0 35% 401.6 

Holcim #1 – dry SNCR 2222 1,476.5 190 1.9 50% 745.5 

Holcim #2 – dry SNCR 1778 1,181.5 150 1.5 50% 596.5 

(a) NOx emission rate after SNCR does not reflect SNCR efficiency reduction due to adjustment by the ozone season factor of 

0.671 (NOx reduction is modeled to occur only during the ozone season). 

(b) The results for TXI 1 & 4 and #2 & #3 are average per kiln – for example, total emissions reductions for controlling both TXI 

#1 & #4 are double the value listed in the table. 

Models assume mid-kiln firing installed at TXI as required under current SIP. 
Cement Kiln Report (FINAL – 7/14/2006) 4-33

Table 4-1.6. Summary of Modeling Results for SNCR on Ellis County Kilns – Economic 

Results 

Existing Unit 

Control 

Technology 

Capital 

Cost 

Annual 

Cost 

Cost 

Effectiveness 

$/ton NOx

Energy 

Penalty or 

Benefit 

Emissions 

Penalty or 

Benefit 

Burden Cost 

$/tonne clinker 

Ash Grove #1- wet SNCR $1.2 MM $0.4MM $2,500 (a) (b) $1.70 

Ash Grove #2- wet SNCR $1.3MM $0.4MM $2,400 (a) (b) $1.70 

Ash Grove #3- wet SNCR $1.4MM $0.4MM $2,400 (a) (b) $1.70 

TXI #1 and #4–wet (c) SNCR $1.4MM $0.5MM $2,400 (a) (b) $1.60 

TXI #2 and #3–wet (c) SNCR $1.4MM $0.3MM $13,000 (a) (b) $5.00 

TXI#5 – dry SNCR $2.3MM $1.0MM $2,900 (a) $0.45 

Holcim #1 – dry SNCR $2.3MM $1.1MM $1,500 (a) $1.00 

Holcim #2 – dry SNCR $2.3MM $1.0MM $1,700 (a) $0.90 

(a) SNCR should not have energy impacts. 

(b) Ammonia slip can be significant for SNCR when not properly optimized. 

(c) The results for TXI 1 & 4 and #2 & #3 are average per kiln – for example, total capital costs for controlling both TXI #1 & #4 

are double the value listed in the table.

4.2 Combustion Optimization

 This section of the report is taken from the EPA 2000 Report and is included, with minor 

editing by the ERG Team. This information is included to provide the Texas environmental 

communities with the comprehensive background information necessary to understand the 

parameters that dictate NOx control options at cement kilns. Combustion optimization is largely 

in place in the Ellis County kilns, with the exception of the TXI wet kilns that are awaiting 

permits for mid-kiln firing to comply with the requirements of 30 TAC Chapter 117. 

 Combustion optimization is generally applicable to all types of kilns and is an efficient 

way to reduce the formation of thermal NOx. The combustion modifications discussed in this 

section focus on staging the combustion to minimize combustion at the maximum temperatures. 

This can be accomplished by modifying the way oxygen or fuel is provided for combustion. For 

the purposes of this report, the level of emissions reduction contained in 30 TAC Chapter 117 is 

the level associated with combustion and process optimization. As such, the techniques below 

have largely been already required and implemented at the Ellis County cement plants. 

However, the differing performance of the kilns may indicate that more combustion and process 

optimization could be implemented as part of the effort to reach higher NOx emissions reductions 

levels. 
Cement Kiln Report (FINAL – 7/14/2006) 4-34

4.2.1 Staged Combustion of Air 

 Staging of combustion air allows combustion of fuel to proceed in two distinct zones. In 

the first zone, the initial combustion is conducted in a fuel-rich, oxygen-poor flame zone. This 

zone provides the high temperatures necessary for completion of the clinkering reactions, but the 

lack of available oxygen minimizes the formation of thermal and fuel NOx. The lack of 

sufficient oxygen leads to only partial combustion of the fuel. 

 In the second, fuel-lean zone, additional (secondary) combustion air is added to complete 

the combustion process. However, the temperature in this second zone is much lower than the 

first zone because of mixing with the cooler secondary air, so the formation of NOx is minimized 

in spite of the excess available oxygen. This staged approach can be used for combustion of all 

fossil fuels. Staged combustion is typically achieved by using only a part of the combustion air 

(primary air) for fuel injection in the flame zone, with remaining secondary air being injected in 

the subsequent cooler zone. 

 For effective staging of combustion air to reduce NOx emissions, cement plants must 

have indirect-fired kilns. In a direct-fired cement kiln, air used for conveying pulverized coal 

from a coal mill, i.e., primary air, is typically 17 to 20 percent of the total combustion air. The 

amount of primary air may be reduced by separating the coal mill air from coal. A cement kiln 

using less than 10 percent of primary air is an indirect-fired kiln. Conversion of a direct-fired 

kiln to an indirect-fired kiln involves adding particle separation equipment such as a cyclone or a 

baghouse and a fan to provide the primary air used to transport the powdered coal from storage 

to the kiln. An indirect-firing system increases overall energy efficiency by allowing a greater 

proportion of hot clinker cooler air to be used as secondary combustion air. 

4.2.2 Flue Gas Recirculation 

 In addition to changing the combustion air distribution, the oxygen content of the primary 

air may be reduced to produce a fuel-rich combustion zone by recycling a portion of the flue gas 

into the primary combustion zone. (44) The recycled flue gas may be premixed with the primary 
Cement Kiln Report (FINAL – 7/14/2006) 4-35

combustion air or may be injected directly into the flame zone. Direct injection allows more 

precise control of the amount and location of the flue gas recirculation (FGR). In order for FGR 

to reduce NOx formation, recycled flue gas must enter the flame zone. The FGR also reduces the 

peak flame temperature by heating the inert combustion products contained in the recycled flue 

gas. 

 The use of FGR may not be a viable method of reducing NOx in a full-size cement kiln 

burning zone. FGR’s effectiveness relies on cooling the flame and generating an oxygendeficient (reducing) atmosphere for combustion to reduce NOx formation, conditions that may 

not be compatible with cement kiln operation. High flame temperature and an oxidizing 

atmosphere are process requirements to produce a quality clinker product. A cement kiln differs 

from a utility boiler and other combustion devices because minimum temperatures and an 

oxidizing atmosphere are required to initiate chemical reactions in a cement kiln in addition to 

providing the required heat (Btu/tonne clinker). Reduced flame temperatures and reducing 

conditions in the burning zone of a cement kiln may not be compatible with the production of 

cement clinker. (33) 

 Coupling a low-NOx step burner with flue gas recirculation has been shown to reduce 

NOx emissions further in a cement kiln. (45) The additional NOx reduction attributable to FGR 

was estimated to be about 15 to 38 percent depending upon the proportion of FGR used. (45) 

Incorporation of FGR in a cement kiln also results in somewhat increased power consumption 

and reduced kiln output. 

4.2.3 Low-NOx Burners 

 Some cement kiln burners, specifically marketed as low- NOx, burners, typically use 5 to 

7 percent primary air (46,47) and thus can be used only on indirect-fired kiln systems. Low-NOx

burners can be installed on any type of kiln. Low-NOx burners are designed to reduce flame 

turbulence, delay fuel/air mixing, and establish fuel-rich zones for initial combustion. The 

longer, less intense flames resulting from the staged combustion lower flame temperatures and 

reduce thermal NOx formation. Some of the burner designs produce a low pressure zone at the 

burner center by injecting fuel at high velocities along the burner edges. Such a low pressure 
Cement Kiln Report (FINAL – 7/14/2006) 4-36

zone, as shown in Figure 4-2, (46) tends to recirculate hot combustion gas which is retrieved 

through an internal reverse flow zone around the extension of the burner centerline. The 

recirculated combustion gas is deficient in oxygen, thus producing a similar effect as FGR. 

Combustion of the fuel in the first stage thus takes place in an oxygen-deficient zone before the 

fuel is diluted in the secondary air. Installing such a burner reduces NOx emissions from the 

kiln-burning zone by up to 30 percent. (46,48,49) 

 Low- NOx burners have been used by the cement industry for twenty years. (50) Many 

suppliers offer low-NOx burners and most of these systems focus on lowering the NOx formation 

in the calciner by air or fuel staging, by reburning, or by high temperature combustion. (51) Test 

data from several different low-NOx burners are now available. Thomsen, Jensen, and 

Schomburg reported on tests of a F.L. Smidth in-line calciner low-NOx system in a 

preheater/precalciner kiln where different percentages of coal were added to the reduction zone 

of the precalciner (the remaining coal was added to the oxidizing zone). (51) When 100 percent 

of the coal was added to the reduction zone of the precalciner, the NOx content at the preheater 

exit was reduced by 44 percent relative to when zero coal was added (see Table 4-2.1). 

Table 4-2.1. NOx Emissions from a Precalciner Equipped with a Low-NOx Burner 

Percent Coal Added to Reduction 

Zonea (lb. NOx/tonne clinker) 

Nox Emissionsb 

(lb. NOx/tonne clinker) 

Percent 

Reductionc (%) 

0 2.8 - 

50 1.9 31 

100 1.6 44 

a

The remaining percentage of the coal was added to the oxidizing zone. 

b

Emission measurements were taken at the preheater exit. 

c

Percent reductions are relative to emissions when zero percent of the coal was added; the 

original measurements were in kg NOx/tonne clinker to the hundredth place - the percent 

reductions were calculated using the original measurements, which results in slightly 

different values than when lb. NOx/tonne clinker are used. 

 Steinbiß, Bauer, and Breidenstein reported emissions changes for five kilns before and 

after the installation of Pyro-Jet low-NOx burners (see Table 4-2.2). (50) The emission 

reductions ranged from 15 to 33 percent. Information on kiln-type was not provided. 
Cement Kiln Report (FINAL – 7/14/2006) 4-37

Table 4-2.2. NOx Emissions Before and After Installation of Pyro-Jet Low-NOx Burners 

Kiln 

Before Installation 

(ppm) 

After Installation 

(ppm) 

Percent 

Reduction (%)

A 970 650 33 

B not given not given 30 

C 650 460 29 

D 900 730 19 

E not given not given 15 

 There are two new data sources on emissions reductions from the use of Rotaflam® lowNOx burners. The Pillard Combustion Equipment and Control Systems published data on four 

kilns, comparing NOx emissions with a 3 channel burner to emissions when a Rotaflam® burner 

was used (see Table 4-2.3). (52) The emission reductions ranged from 23 to 47 percent. 

Information on kiln-type was not provided. 

Table 4-2.3. NOx Emissions with 3 Channel and Rotaflam® Low-NOx Burners 

Kiln 

With 3 Channel 

Burner (ppm) 

With Rotaflam®

Burner (ppm) 

Percent 

Reduction (%) 

A 774 409 47 

B 865 664 23 

C 484 350 28 

D 487 336 31 

 Emissions data are also available before and after a Rotaflam® low-NOx burner was 

installed on a long-wet kiln (see Table 4-2.4). (53) The average emissions decreased 14 percent. 

Table 4-2.4. Emissions Before and After Installation of a Rotaflam® Burner on a Wet Kiln 

Year 

Average Emissions (lb. 

NOx/tonne clinker) Percent Reductiona (%) 

1990 277 - 

1992b 288 - 

1993 269 - 

1994 275 - 

1995 (Rotaflam® installed) 239 14 

a

 Percent reduction is relative to the 1990, 1992-1994 average NOx emissions, 277.25 lb. NOx/hr. 

b

 1991 data were not provided. 
Cement Kiln Report (FINAL – 7/14/2006) 4-38

 The Fuller Company low NOx In-Line Calciner was installed in an RMC Lonestar kiln, 

which reported 30-40 percent reductions in the amount of thermally formed NOx after 

installation. (54) 

 In January 2000, the PCA provided results of a survey of cement facilities where the 

respondents indicated 14% of the operating U.S. kilns (22 kilns) have already installed a lowNOx burner (81% of the facilities representing 81% of the operating U.S. kilns responded to the 

survey). The remaining 139 kilns that are represented by the survey have not installed low- NOx

burners. (55,56) 

4.2.4 Staged Combustion of Fuel 

 In conventional long (wet or dry) rotary kilns, all heat required for the cement-making 

process is supplied in the primary kiln burning zone, where the combustion occurs at the hottest 

temperature in the kiln. In the cement-making process, the preheating and calcination of the raw 

materials requires a large amount of heat but are typically at a temperature of 600 to 900°C 

(1,100 to 1,650 °F) which is much lower than the kiln’s clinker-burning temperature of 1,200 to 

1480 °C (2,200 to 2,700 °F). (57) In the secondary combustion method, part of the fuel is 

burned at a much lower temperature in a secondary firing zone to complete the preheating and 

calcination of the raw materials. 

4.2.5 Preheater/Precalciner and Tire Derived Fuel 

 This concept of a secondary firing zone is the basis of the preheater/precalciner cement 

kiln design. Almost all new cement kilns have a preheater/precalciner-type design. In the 

preheater kilns, the primary emphasis is on efficient heat recovery from kiln exhaust gases (see 

Figure 4-4.1). (58) However, up to 15 to 20 percent of the fuel may be fired in the riser duct in 

preheater designs. (58) 

 Precalciner systems typically employ a tower of four-stage cyclones for efficient gassolids contact, which improves the energy efficiency of the overall process (see Figure 4-4.2). 
Cement Kiln Report (FINAL – 7/14/2006) 4-39

(58) In a typical precalciner kiln almost 40 to 50 percent of the fuel is burned at a lower 

(calcination) temperature which reduces the thermal NOx formation considerably. 

Figure 4-2.1. Schematic of Preheater (58) Figure 4-2.2. Schematic of Precalciner(58) 

 Tire-derived fuel can also be added to the feed end of a preheater or precalciner kiln. The 

Mitsubishi Cement Company’s Cushenbury Plant in Lucerne Valley, CA began using whole 

waste tires as a fuel supplement in 1993. The waste tires are delivered in enclosed container 

trucks and dumped into the plant’s automated handling system. A live bottom hopper and 

singulator place the waste tires on a conveyor system. This conveyor system transports the tires 

to the feed end of the kiln and drops the tire into an airlock system that allows the waste tire to 

fall onto the feed plate inside the kiln at a rate of five to six tires per minute. 

 Currently, 8,000 to 9,000 tires are burned per day, totaling about 13 percent of the fuel. 

Tires have a fuel content of approximately 14,000 Btu/lb. and a sulfur content that is roughly the 

same as the coal that would be used. The steel belting in the waste tires supplements the iron 

requirements and approximately two percent of the iron in the final product comes from the tires. 

The addition of waste tires reduces NOx emissions from the kiln by 30 to 40 percent, and there is 

no significant change in toxic, hydrocarbon, or metal emissions. (59,60,61) 
Cement Kiln Report (FINAL – 7/14/2006) 4-40

4.2.6 Low- NOx Precalciners 

 Most of the major cement kiln suppliers are now offering “low NOx” precalciner designs 

for new kilns. These designs typically inject a portion of the fuel into the feed end of the kiln, 

countercurrent to the exhaust gas flow.(62) This fuel is burned in a substoichiometric O2

environment to create a strongly reducing atmosphere (relatively high concentrations of CO) by 

following the simplified reactions: 

NO + C → N + CO 

and 

NO + CO → N + CO2

 This reducing atmosphere inhibits the formation of fuel NOx and destroys a portion of the 

NOx formed in the kiln burning zone. In some designs, additional fuel is then added, again with 

insufficient O2 for complete combustion, to create another reducing zone. Several precalciner 

kilns in the US have recently been retrofitted with these “low NOx” precalciners and preliminary 

information indicates a noticeable reduction in NOx per ton of clinker. (33) Up to 46 percent 

reduction of NOx emissions has been reported without causing excessive coating difficulties in 

the kiln. (62) 

 Nitrogen present in the fuel may also participate in the reduction of NOx. The primary 

NOx formation mechanism in the secondary firing is the fuel NOx formation that depends upon 

the nitrogen content of the fuel used. In order for the above reactions to proceed at reasonable 

rates the temperature in the reduction zone should be maintained between 1000 and 1200°C 

(1830 to 2190°F). These temperatures may lead to coating difficulties, particularly if the fuel 

used is coal with high ash content. (63) 

 It is not possible to use “staged combustion” on preheater kilns that are firing fuel in the 

riser since in staged combustion it is necessary to add the fuel in an oxygen deficient atmosphere 

and then supply additional combustion air to fully combust the fuel. Preheater kilns do not have 

tertiary air ducts to supply the additional combustion air. The air for combustion of the 
Cement Kiln Report (FINAL – 7/14/2006) 4-41

secondary fuel must come through the kiln, which precludes introducing the secondary fuel into 

an atmosphere with insufficient oxygen for complete combustion. (33) 

 Emissions reductions have also been found when tire derived fuel was burned in a 

precalciner. In one case, when 47 percent of the coal fired in the calciner was substituted with 

tire-derived-fuel, a reduction in NOx emissions of about 29 percent was observed. (64) 

4.2.7 Mid-Kiln Firing 

 The concept of staged combustion of fuels may also be used in conventional wet and 

long-dry kilns by injecting solid fuel into the calcining zone of a rotating long kiln using a 

specially designed feed injection mechanism. (65) This system is known as mid-kiln firing 

(MKF) and allows part of the fuel to be burned at a material calcination temperature of 600 to 

900°C (1100 to 1650°F) which is much lower than the clinker burning temperature of 1200 to 

1480°C (2200 to 2700°F). (57) 

 To maintain continuity in the heat input, solid and slow burning fuels (such as tires) are 

most amenable for MKF. The Cadence feed fork MKF technology was first introduced in 1989. 

It can be installed during an annual maintenance shutdown. It is comprised of three primary 

components: (1) a staging arm or ‘feed fork’ that picks up the fuel modules and positions them 

for entry into the kiln, (2) two pivoting doors that open to allow the fuel modules to drop into the 

kiln, and (3) a drop tube that extends through the side wall of the kiln. In addition to these basic 

components, feed fork technology also requires a delivery system, which positions the fuel 

modules so they can be picked up by the feed fork and a mechanism for opening the doors so the 

fuel modules can enter the kiln. (66) Due to the rotation of the kiln, fuel can be conveniently 

injected only once per revolution from the top. 

 Although most feed forks today are dedicated to whole tires, one facility uses baled 

industrial waste as a fuel, and many others are investigating a variety of energy containing waste 

materials from carpet scrap to pharmaceutical waste. These energy-bearing waste materials can 

be containerized or dimensionalized into discrete fuel modules to be fed to the kiln using the feed 

fork. (66) 
Cement Kiln Report (FINAL – 7/14/2006) 4-42

 Inserting whole tires into mid-kiln locations can give precalciner stability to the kiln. The 

operators have two points of control to assist in stabilizing kiln operation. Tires burn for 15 to 

20 minutes within the kiln after entry. This is deduced from observations of the rate of change in 

kiln exit oxygen levels after entry of tires begins. With proper instrumentation, control of the kiln 

can be improved by adding solid fuels midkiln. (67) 

 Mid-kiln firing of tires or other waste-derived fuels does not reduce the final product 

quality; in fact, many of Cadence’s cement kiln partners have reported an improvement in the 

clinker burnability and mineralogy. The enhanced control has shown to impart better formation 

of clinker. Reductions in cement fineness have been shown while maintaining similar seven-day 

strengths. Several facilities also have reported an extended life of the refractory in the burn zone. 

(66,67) 

 By adding fuel in the main flame at mid-kiln, MKF changes both the flame temperature 

and flame length. These changes may reduce thermal NOx formation by burning part of the fuel 

at a lower temperature and by creating reducing conditions at the solid waste injection point, 

which may destroy some of the NOx, formed upstream in the kiln burning zone. MKF may also 

produce additional fuel NOx depending upon the nitrogen content of the fuel. (68) However, as 

discussed in section 5.1.3, fuel NOx is unimportant relative to thermal NOx formation. 

Additionally the discontinuous fuel feed from MFK can result in increased CO emissions 

especially if hazardous wastes are used. To control CO emissions, the kiln may have to have 

increased combustion air, which can decrease production capacity. (69) 

 According to literature from Cadence, in tests of its feed fork technology, one kiln 

reduced NOx emissions by 38%, overall particulate emissions by 14%, metal emissions by 30%, 

SO2 emissions by 36%, and net emissions of all hydrocarbons by 29%. (66,67) In the research 

conducted for this report, test data were compiled for seven dry kilns and three wet kilns with 

MKF technology. In nine tests on the dry kilns, the average reduction in NOx emissions was 

33%, with a range from 11% to 55%. In three tests on the wet kilns, the average reduction in 

NOx emissions was 40%, with a range from 28% to 59% (see Table 4-8). (69,70,71,72,73) It 
Cement Kiln Report (FINAL – 7/14/2006) 4-43

should be noted that the three kilns that are known to have CEMS all reported emissions 

reductions of 45 percent or more. 

Table 4-2.5. Emissions From Kilns With Mid-Kiln Firing 

Emissions 

(lb. NOx/tonne clinker) 

Percent Reduction 

(%) 

Emissions Based on 

CEMS Data 

Dry Kilnsa

A40 not given 13.6 unknown 

B40 not given 11.1 unknown 

C24,44 not given 45.1 yes 

C40 not given 55.3 yes 

D21,41 2.7 not given unknown 

E22,42 10.2 13.9 unknown 

F40 not given 46.6 unknown 

F40 not given 50.4 unknown 

F40 not given 28.3 unknown 

Average (Dry Kilns) 6.4 33.3 

Wet Kilns 

G23,43 not given 59.0 yes 

H40 not given 35.0 unknown 

I

40 not given 27.6 unknown 

Average (Wet Kilns) n/a 40.5 

Average (Dry & Wet 

Kilns) 

6.4 35.1 

a

 There was more than one test at some kilns.

 Waste-derived fuels with high heating values represent an economical source of energy 

for the cement industry and its consumption has been increasing during the past decade.12 

Midkiln firing is a proven technology and so far at least 21 long kilns in the U.S. and nearly 40 

kilns worldwide have been modified to allow mid-kiln firing of solid and hazardous waste. 

(66,74) 

4.3 Lower Temperature Oxidation Based Technologies 

 Oxidation technologies were not evaluated in the EPA 2000 Report. One of these 

technologies, LoTOxTM, is currently being installed in refineries at fluidized catalytic cracking 

units (FCCUs). The temperatures, gas flow rates and other characteristics of FCCUs are similar 
Cement Kiln Report (FINAL – 7/14/2006) 4-44

enough to cement plants that these technologies should be considered as candidates for 

evaluation as transferable technologies to application at cement kilns. 

4.3.1 Introduction 

 Oxidation technologies for flue gas NOx control developed in recent years have become 

commercially successful and economically viable as an alternative to ammonia and urea based 

technologies using reduction chemistry to remove NOx. Commercially available technologies 

such as Selective Catalytic Reduction (SCR) and Selective Non-Catalytic Reduction (SNCR), 

which reduce NOx to nitrogen using ammonia or urea as an active chemical are optimized to 

specific temperature windows and have similar reagent costs for the varying ammonia based 

reagents. Oxidation technologies can work in other temperature regimes and use different 

reagents that are not linked to ammonia costs and, thereby, provide important control options to 

ammonia-based NOx reduction technologies. 

 Oxidation technologies convert lower nitrogen oxides such as nitric oxide (NO) and 

nitrogen dioxide (NO2) to higher nitrogen oxides such as nitrogen sesquioxide (N2O3) and 

nitrogen pentoxide (N2O5). These higher nitrogen oxides are highly water soluble and are 

efficiently scrubbed out with water as nitric and nitrous acids or with caustic solution as nitrite or 

nitrate salts. NOx removal in excess of 90% has been achieved using oxidation technology on 

NOx sources with high sulfur content, acid gases, high particulates and processes with highly 

variable load conditions. Generally these technologies work at relatively low temperatures (100-

950oF) and some of these technologies are likely most cost effective for use on plants with 

existing scrubbers. But may also prove to be cost effective options due to their potential 

application in lower temperature windows which can avoid expensive options like gas reheat. 

These technologies are used for NOx control for a variety of NOx emission sources but are not 

known to have been used to date on a cement kiln. 

4.3.2 LoTOxTM

 General description. The LoTOxTM System uses ozone as the oxidizing agent, which 

selectively oxidizes relatively insoluble NOx to higher oxides of nitrogen. These higher oxides 
Cement Kiln Report (FINAL – 7/14/2006) 4-45

are readily soluble and easily removed in a wet scrubber. The patented system, which can be 

installed as a stand-alone or retrofit design, provides sufficient residence time under maximum 

load conditions to allow complete reaction of the ozone. The system's small and adaptable 

footprint, as well as its ability to produce ozone on demand, provides control of the installation to 

maximize NOx control and minimize capital and operating costs. The LoTOxTM System is very 

selective for NOx removal, oxidizing only the NOx and therefore efficiently using the treatment 

chemical, ozone, without causing any significant SOx oxidation and without affecting the 

performance of the downstream SOx scrubber. 

 Figure 4-3.1. is an overall process diagram of the LoTOxTM System. 

Figure 4-3.1. Overall Process Diagram of the LoTOxTM System 

 Figure 4-3.2. provides another example of a LoTOxTM system where the ozone injection 

is included in the scrubber. 
Cement Kiln Report (FINAL – 7/14/2006) 4-46

Figure 4-3.2. EDV Wet Scrubbing System with LoTOxTM Injection 

Potential applicability. The large gas volumes, high moisture levels and large quantities 

of dilution air needed to reach the operating temperature range in some systems may limit the 

applicability of the LoTOxTM system. 

Advantages. Table 4-3.1 provides an overview comparing the LoTOxTM process with 

SNCR and SCR technologies. 
Cement Kiln Report (FINAL – 7/14/2006) 4-47

Table 4-3.1. Comparison Of Common Post Combustion NOx Abatement 

Technologies For NOx Emissions Control 

SNCR SCR LoTOxTM

Mode of Treatment Reduction Reduction Oxidation 

Active Chemical NH3 / Urea NH3 / Urea Ozone 

Gas Temperature 

Required °F 

1650 - 2000 500 - 900 150 – 250 

Pressure Required, psig 0+ 0++ 0+ 

Placement in 

Exhaust System 

Near Combustion Chamber Between Air Pre-Heater 

and Economizer (boiler) 

Tail End 

Catalyst Bed No Yes No 

Gas Phase Reaction Duct Yes No Yes 

Scrubber Optional Optional Yes 

NOx Reduction Achieved 40 - 70 Percent 60 - 95 Percent 90 - 95 Percent 

Slip of Active Agent NH3 – Yes NH3- Yes Ozone - No 

CO Emissions 

After Treatment 

May Increase May Increase No Effect 

SOx Emissions 

After Treatment 

Little Effect – Maybe H2S Little Effect - Maybe H2S No Effect or 

Significantly Reduced 

Gas Temperature 

Outside Operating Range 

- Overshoot 

More NOx Emissions 

Through NH3 Oxidation 

More NOx Emissions 

Through NH3 Oxidation, 

Ammonia Slip 

Increased O3 

Consumption for the 

Time Period of Overshoot 

Gas Temperature 

Outside Operating Range 

- Undershoot 

More NOx Emissions 

Through Reduced 

Reduction by NH3 

More NOx Emissions 

Through Reduced 

Reduction 

by NH3, Ammonia Slip 

No Effect 

 An additional advantage is the control of SOx emissions that would likely be achieved if 

the LoTOxTM system were added to any system that currently does not have a wet scrubber if 

joint control of SOx and NOx is required. Lower cost spray towers that do not appreciably control 

SOx can be installed at lower cost than flue gas desulfurization scrubbers. The cost models for 

application of LoTOxTM at wet kilns are based on installing simple spray towers that do not 

control SOx. 

Disadvantages. It is likely that for most applications, the LoTOxTM option would be an 

add-on to existing APCD systems. Because of high electrical power usage, costs are reported to 

be high. Electricity and oxygen costs alone are estimated to be greater than $1,600/ton of NOx

controlled. 
Cement Kiln Report (FINAL – 7/14/2006) 4-48

 Additional nitrate captured in the existing sulfate scrubber could impact the quality of the 

plant’s artificial gypsum although, with a typical dewatering system, this should not be a 

problem because of the much higher solubility of the nitrates relative to sulfates. High nitrate 

wastewater could be used by local farmers as fertilizer or could be used at the plant to fertilize 

grass areas as well as water/fertilize in quarry reclamation areas. Lowering the exit gas 

temperature and adding moisture may result in problems with condensation in the stack. 

Emissions performance. There are three primary process variables which impact the 

NOx control capabilities of the LoTOxTM process: temperature of the flue gas (T), residence time 

of the flue gas in the reactor duct (RT) and amount of ozone (O3 Factor) injected into the reactor 

duct. Based on the results of LoTOxTM demonstration testing, the most efficient control 

parameters for a full scale system on the Quemetco, Inc., furnace are a temperature of 175 °F or 

less, a residence time of four seconds, and an ozone injection factor of 80 to 90. The O3 Factor 

represents the O3 to NOx ratio at the inlet to the reaction duct. The presented data uses O3 Factor 

for the sake of clarity and to provide meaningful data while maintaining confidentiality 

of proprietary intellectual information. Figure 4-3.3. depicts the performance conditions of the 

LoTOxTM process for the design conditions of RT = 4 seconds, T = 175 °F and O3 Factor = 70 to 

90. Under these design conditions the NOx removal achieved ranges from 80 percent at an O3

Factor of 70 to 95 percent at an O3 Factor of 90. 

 This technology should be considered transferable in nature. It has not been used on a 

cement kiln but it has been used on similar large sources. Discussions with this technology’s 

vendors reveals that existing SOx and CO levels at the cement plants in Midlothian should not be 

a factor in the use of this technology. Applications or tests have already been performed at CO 

and SOx levels well above those seen in any of these cement plants. 
Cement Kiln Report (FINAL – 7/14/2006) 4-49

Figure 4-3.3. Ideal Operating Conditions for NOx Removal from 80% to 95% 

Cost. Ohio Coal Development Office (OCDO) provided 65 percent of the capital to 

install a $6.3 million LoTOxTM unit at the Medical College of Ohio. The project includes two 

processes: LoTOxTM for NOx and particulate material control and Rapid Absorption Process 

(RAP, another BOC licensed process) for sulfur dioxide control. The controls are for 25 

megawatt capacity boilers burning Ohio coal containing 3 percent sulfur. According to the BOC 

Company literature, the unit is designed to remove about 90 percent of the NOx in emission 

gases. The RAP process uses a slurry of lime injected into the flue gas to capture SO2 and a 

fabric filter (baghouse) to remove the calcium sulfate particles. Cost effectiveness has been 

estimated to be in the range of $1,700 to $1,950 per ton NOx removed. (54) 

 In June 2001, BOC announced that they had installed, started up and commissioned a 

LoTOxTM unit at J & L Specialty Steel’s Midland, PA plant. Details of the installation are not 
Cement Kiln Report (FINAL – 7/14/2006) 4-50

published in any detail. However, Robert Ferrell, BOC Vice President of Business 

Development, said, “We were able to modify the system to achieve a higher level of control than 

was originally anticipated. We have been able to reduce NOx emissions by more than 95 

percent.” No costs or capacity numbers were available. 

 A subsequent search of EPA’s RBLC27 Database indicates that at least two other plants 

in the U.S. are using (or are planning to use) BOC’s LoTOxTM process in their facilities. These 

plants are Lion Oil Company in El Dorado, AR and Marathon-Ashland Oil in Texas City, TX. 

Both plants use (or will use) the LoTOxTM on their Fluidized-Bed Catalytic Cracking Units 

(FCCU) for NOx control. Operating conditions and performance results are not available. 

 Another article, written by a BOC employee, stated, “The capital (recovery) and 

operating costs for the (LoTOxTM) system have been evaluated for various system sizes and 

(they) fall well within the costs per ton of NOx removed typical for post-combustion treatment 

technologies in non-utility applications.” Unfortunately, this information is not very helpful for 

determining cost for the cement industry since a paper published by NESCAUM gives the cost 

effectiveness range for NOx removal from $390 to $5,450 per ton NOx. Cost effectiveness is 

heavily dependent on each individual facility’s situation. This includes their existing control 

equipment, extent of modifications necessary to install new control equipment, and the degree of 

DRE required to achieve the desired results. 

 Based on the data available, capital costs for adding LoTOxTM to a system that does not 

have a wet scrubber such as the wet kilns in Midlothian are likely to be much more costly than 

the kilns that already have wet scrubbers. Vendor information was used to calculate costs 

associated with the application of LoTOxTM to the cement plants in Midlothian. Estimated costs 

associated with the precalciner kilns which already have scrubber systems in place are $2,300-

$2,600/ton of NOx controlled. Estimated costs associated with the wet kilns which do not have 

scrubber systems in place are $3,000-$3,700/ton of NOx controlled. The costs for the wet kilns 

include installation of a spray tower to remove the soluble NOx oxidation products produced by 

the LoTOxTM system. (74a, 74b, 74c, 74d, 74e, 74f, 74g, 74h, 74i, 74j, 74k, 74l, 74m, 74n) 
Cement Kiln Report (FINAL – 7/14/2006) 4-51

4.3.3 Hydrogen Peroxide 

General description. There are several methods for controlling NOx emissions. Gas 

scrubbing is one of the most common forms of NOx treatment, with sodium hydroxide being the 

conventional scrubbing medium. However, the absorbed NOx is converted to nitrite and nitrate, 

which may present wastewater disposal problems. Scrubbing solutions containing hydrogen 

peroxide are also effective at removing NOx, and can afford benefits not available with NaOH. 

For example, H2O2 adds no contaminants to the scrubbing solution and so allows commercial 

products to be recovered from the process, e.g., nitric acid or nitrate salts (for use as fertilizer). 

In its simplest application, H2O2 (0.5-1 wt.%) and nitric acid (35-45 wt.%) are used to scrub both 

nitric oxide (NO) and nitrogen dioxide (NO2) -- the chief components of NOx from many 

industrial sources. The reactions are rapid at moderate temperatures (30-80 °C), with about 1.7 

and 0.37 lb. H2O2 required per lb. NO and NO2, respectively. The chemistry controlling the 

process is outlined below: 

3NO2 + H2O < == > 2HNO3 + NO 

NO + HNO3 + H2O ----> 3HNO2 

HNO2 + H2O2 ----> HNO3 + H2O 

 There are several other processes that also use hydrogen peroxide to remove NOx. The 

Kanto Denka process employs a scrubbing solution containing 0.2% hydrogen peroxide and 10% 

nitric acid while the Nikon process uses a 10% sodium hydroxide solution containing 3.5% 

hydrogen peroxide. A fourth process, the Ozawa process, scrubs NOx by spraying a hydrogen 

peroxide solution into the exhaust gas stream. The liquid is then separated from the gas stream, 

and the nitric acid formed is neutralized with potassium hydroxide. The excess potassium nitrate 

is crystallized out, and the solution reused after recharging with hydrogen. In addition to the 

methods cited above in which NOx is oxidized to nitric acid or nitrate salts, a series of Japanese 

patents describe processes and equipment for reducing NOx to nitrogen using hydrogen peroxide 

and ammonia. The processes are efficient but must be carried out at higher temperatures than the 

processes cited earlier. 
Cement Kiln Report (FINAL – 7/14/2006) 4-52

 The injection of hydrogen peroxide (H2O2) into hot flue gases to prevent emissions of 

nitrogen oxides (NOx) has been demonstrated at the pilot scale at a boiler at Kennedy Space 

Center (KSC). That project was an outgrowth of research funded by the Gulf Coast Hazardous 

Substance Research Center from the years 1993-1996. The H2O2 is injected into hot boiler flue 

gases to oxidize the NO into NO2, HNO2 and HNO3, which can then be removed in a wet or dry 

scrubber (see Figure 4-3.4). (74o) 

Figure 4-3.4. Conceptual Design of Hydrogen Peroxide NOx Control System 

 In one of several sets of experiments to demonstrate the feasibility of the method, the 

optimum temperature for conversion of NO to HNO2, HNO3, and NO2 by use of injected H2O2

was found to be about 500 °C (see Figure 4-3.5). 
Cement Kiln Report (FINAL – 7/14/2006) 4-53

The conversion of NO by oxidation to other species was measured as a function of reactor 

temperature. The reactor inlet conditions for the points shown here were 400 ppm NO and 400 ppm 

H2O2 for a molar ratio of 1:1. 

Figure 4-3.5. Effect of Temperature on Peroxide Oxidation of NO 

 In a study performed under guidelines of the EPA, EPRI compared the economics of 

SCR and the experimental H2O2-injection/scrubbing method for a design base case and a variety 

of alternative cases. This study illustrated the tradeoff between capital and operating costs for 

the two methods. The single largest factor in determining the total cost of one method relative to 

the other method was found to be the H2O2:NO molar ratio. At the H2O2:NO molar ratio of 1.92, 

which was previously demonstrated in the laboratory, the H2O2-injection/scrubbing method was 

shown to be uneconomical. However, it was also concluded that the molar ratio in a full-size 

coal-fired power plant could be lower than that found in the laboratory, and that on the basis of 

all the assumptions of the study, at an H2O2:NO molar ratio of 1.37, the H2O2 injection/scrubbing 

method could be an economically feasible alternative to SCR. 

 Pilot-scale tests run at Kennedy Space Center demonstrated the feasibility and 

competitiveness of this new technology. The H2O2 to NO molar ratio, at 500 °C shown to 

achieve a NO conversion efficiency of greater than 90 percent was 1:1, which is significantly 

lower than the required 1.37:1 (See Figure 4-3.6). (74l) 
Cement Kiln Report (FINAL – 7/14/2006) 4-54

The outlet concentration of the O was significantly reduced when the H2O2 was injected. At 500 °C, 

400 ppm NO, and various inlet concentrations of H2O2 (represented as the molar ratios), 90 percent 

conversion of NO was achieved at the reactor outlet for a molar ration of 1:1. 

Figure 4-3.6. Effect of Molar Ratio on Peroxide Oxidation of NO 

Potential applicability. This option is a solution that may have particular applicability 

to kilns with existing scrubber systems. Data suggests it may work over a wide range of 

temperatures depending on the specific version of this technology that is implemented. For the 

high temperature version of this process, injection of the hydrogen peroxide into the upper 

portion of the preheater tower of a precalciner kiln at the appropriate temperature may be 

possible. 

Advantages. The biggest advantage of this technology may be a relatively low capital 

investment for plants with existing scrubbers. An additional advantage is that there are 

indications that hydrogen peroxide based scrubbers may also enhance SOx scrubbing and may 

lower hydrocarbon emission depending on the operating temperature, reagent system and 

retention time of the system. 

 An additional advantage of this technology is that it operates in a unique temperature 

window that is slightly below the temperatures commonly used for SCR. The optimal 

technology for any specific cement kiln process may be the technology that installs best in the 
Cement Kiln Report (FINAL – 7/14/2006) 4-55

existing temperature windows of the process with the least potential adverse impact on 

downstream processes and equipment. Prices of ammonia-based reagents fluctuate with natural 

gas prices and are currently relatively high. Cement plants may elect to use more than one NOx 

control technology to take advantage of changes in the market for reagents. Hydrogen peroxide 

currently appears to be a more cost effective reagent than ammonia-based reagents. 

Disadvantages. For plants without scrubbers, add on systems are required. An additional 

factor is that the cost of hydrogen peroxide has risen significantly in recent years with increased 

natural gas prices and fluctuating supplies. Hydrogen peroxide has become a major commodity 

chemical as a bleaching agent for paper production free of chlorine. Recent production capacity 

increases appear to be stabilizing prices. 

 Additional nitrate captured in the existing sulfate scrubber could impact the quality of the 

plant’s artificial gypsum although, with a typical dewatering system, this should not be a 

problem because of the much higher solubility of the nitrates relative to sulfates. High nitrate 

wastewater could be used by local farmers as fertilizer or could be used at the plant to fertilize 

grass areas as well as water/fertilize in quarry reclamation areas. 

Emissions performance. At 500 °C and with a molar ratio of 1:1 H2O2/NOx removal 

efficiencies of greater than 80% appear to be achievable. Scrubber efficiency data for the wet 

low temperature process was not available. Either of these technologies should be considered 

investigative in nature. Application of this technology would clearly be an innovative approach 

that does not have a history of commercial application compared to SCR, SNCR or LoTOxTM. 

Testing in a cement plant application would clearly be required to determine performance and 

process impacts. 

Cost. Assuming a cost of $0.50/lb. of hydrogen peroxide the reagent cost would be 

approximately $739/ton of NO2 removed (depending on the existing oxidation state of the NO in 

the system). This might be offset to some extent by the sale of solutions of nitrate salts as 

fertilizer. This cost appears to be favorable relative to the electrical and oxygen costs of the 

LoTOxTM that exceed $1,600/ton of NOx controlled. It is also favorable to the current ammonia 

cost of about $1,200/ton of NOx controlled using SNCR. 
Cement Kiln Report (FINAL – 7/14/2006) 4-56

4.3.4 OXONE (Dupont – potassium monopersulfate) 

General description. Scrubbing with strong aqueous oxidants promises to be less 

expensive than competing post-combustion methods for NOx removal such as selective catalytic 

reduction (SCR) and thermal NOx removal. The goal of a project by Yusuf G. Adewuyi at North 

Carolina A&T State University is to develop an innovative and cost-effective aqueous scrubber 

for the simultaneous removal and destruction of oxides using strong oxidizing agents such as 

oxone. Oxone (2KHSO5.KHSO4.K2SO4) is a triple salt of potassium and may be regarded as a 

mono-substituted derivative of hydrogen peroxide. However, it has an oxidation potential greater 

than that of hydrogen peroxide (E HSO5

-

/HSO4

-

 = 1.82 eV compared to E H2O2/H2O = 1.77 eV). 

The aqueous absorption and kinetics of oxidation of nitrogen oxides (NOx) and SO2 by OXONE 

in a bubble column operated as batch or continuous OXONE was presented at an AIChE meeting 

in October of 2005. Table 4-3.2 provides a breakdown of the chemical constituents of the Oxone 

reagent. (74p) 

Table 4-3.2. Oxone Constituents 

Material CAS Number % 

"Oxone" Monopersulfate Compound 70693-62-8 

Potassium Peroxymonosulphate 10058-23-8 34-43 

Potassium Bisulfate 7646-93-7 18-23 

Potassium Sulfate 7778-80-5 23-29 

Potassium Peroxydisulfate 7727-21-1 2-3 

Sodium Carbonate 497-19-8 0-20 

Magnesium Carbonate 546-93-0 1-2 
Cement Kiln Report (FINAL – 7/14/2006) 4-57

Potential applicability. Applicability is similar to the wet low temperature hydrogen 

peroxide option. 

Advantages. Advantages are similar to the hydrogen peroxide option. Costs may be 

lower. 

Disadvantages. This is an experimental technology. Additional nitrate captured in the 

existing sulfate scrubber could impact the quality of the plant’s artificial gypsum although with a 

typical dewatering system this should not be a problem because of the much higher solubility of 

the nitrates relative to sulfates. High nitrate wastewater could be used by local farmers as 

fertilizer or could be used at the plant to fertilize grass areas as well as water/fertilize in quarry 

reclamation areas. 

Emissions performance. As an experimental technology performance is not clear but is 

likely to be similar to the hydrogen peroxide technology. This technology should be considered 

investigative in nature. 

Cost. Oxone is a commercial product manufactured by Dupont. Inquiries to Dupont 

about cost have not been responded to at this time. 

4.3.5 Sodium Acetate Process 

 General description. This process involves absorption and subsequent reaction of NOx

in the aqueous phase. Direct absorption involves a reaction chain that achieves both SOx and 

NOx removal. One form involves an SO2 reaction step, a subsequent NO reaction, and a 

termination step that produces gypsum. Table 4-3.3 shows the different steps involved in the 

process. 
Cement Kiln Report (FINAL – 7/14/2006) 4-58

Table 4-3.3. Reaction Steps and Pathway Equations for the Sodium Acetate Direct 

Absorption Process For Simultaneous NOx And SOx Removal (OECD, 1983). 

Absorption and Gypsum Formation 

Absorption 

SO2 + 2CH3COONa + H2O →Na2SO3 + 2CH3COOH 

2NO + 5Na2SO3 + 4CH3COOH →2NH(NaSO3) 2 + Na2SO4 + 4CH3COONa + H2O 

Gypsum formation 

Na2SO4 + Ca(OH) 2 +2CH3COOH →CaSO4

.2H2O + 2CH3COONa 

Imide Treatment Step 

Hydrolysis 

NH(NaSO3) 2 + 2H2O →NH4HSO4 + Na2SO4

Release of NH3

NH4HSO4 + Ca(OH) 2 →NH3 + CaSO4_2H2O 

Nitrogen gas formation 

4NH3 + 3O2 →2N2 + 6H2O 

Potential applicability. Applicability is likely to be similar to the wet low temperature 

hydrogen peroxide process. 

Advantages. The advantage of this process is its ability to eliminate gaseous NOx and 

SOx simultaneously. For plants with existing SOx scrubbers the application may be as simple as 

adding selected reagents to the recirculating scrubber solution and subsequent scrubber treatment 

tanks. For plants with cooling towers the option of adding the reagents to the cooling tower 

water feed may be functional. 

Disadvantages. SOx is required in adequate quantities to maintain the chain-reaction 

mechanism. Also, this process turns an air-pollution problem into a wastewater problem. 

Additional nitrate captured in the existing sulfate scrubber could impact the quality of the plant’s 

artificial gypsum although with a typical dewatering system this should not be a problem because 

of the much higher solubility of the nitrates relative to sulfates. High nitrate wastewater could be 

used by local farmers as fertilizer or could be used at the plant to fertilize grass areas as well as 

water/fertilize in quarry reclamation areas. 
Cement Kiln Report (FINAL – 7/14/2006) 4-59

Emissions performance. Unknown. Data for application of this technology to cement 

kilns and similar emission sources was not found in the literature. This technology should be 

considered investigative in nature. 

Cost. Costs are not clear at this time but may be lower than the hydrogen peroxide 

option. 

4.3.6 Potential Applicability of Oxidation Technology to Ash Grove Plant 

General Discussion. The Ash Grove plant has three wet process kilns without any 

existing wet scrubber system. That would require them to place a complete oxidation system in 

place as an add-on technology including the scrubber or alternatively just a spray tower after the 

existing ESPs. Assuming that all of the available options would have a similar capital cost for a 

spray tower/scrubber system careful evaluation of the alternative reagent systems is warranted. 

 A trial system for evaluating the reagent systems may be warranted. As an example, 

three one-month trials using alternative reagents in a skid-mounted scrubber could be performed 

prior to scaling up to a full system. It may be possible to combine the gas flows from the three 

kiln systems into a single flow to minimize the cost of the scrubber system. 

 Because of the high moisture levels in the gasses from wet kilns it may be necessary to 

bypass a portion of the stack gasses around the spray tower/scrubber for use as reheat gas after 

the spray tower/scrubber to prevent condensation problems in the stack. To the extent that such 

a strategy is required the efficiency of the NOx removal would be proportionately impacted. 

 Conclusions. SCR at the Ellis County wet kilns would require reheat of the exhaust gas. 

This suggests that further investigation of the oxidation technologies is likely to be a cost 

effective option. As these technologies would require a scrubber, consideration of the benefits of 

control of sulfur oxides should also be considered in evaluating scrubber options. The cost 

modeling for oxidation technologies is based on a simple spray tower that does not control sulfur 

oxides. However, additional air quality benefits, including reduction in fine PM precursors 

would occur should a source choose to install flue gas desulfurization. A combination of midkiln 
Cement Kiln Report (FINAL – 7/14/2006) 4-60

combustion, midkiln SNCR and a low temperature oxidation technology may provide 

exceptional NOx control at the most effective aggregate cost per ton of NOx controlled for wet 

kilns. 

4.3.7 Potential Applicability of Oxidation Technology to Holcim Plant 

General Discussion. The Holcim Plant has two large precalciner kiln systems with 

existing scrubbers. An oxidative control technology for these kiln lines has significant potential 

to provide NOx control using the existing scrubber system. 

 A variety of low temperature oxidation reagent systems could be tested for efficiency in 

the existing wet scrubber system. It should also be relatively simple to set up a temporary 

system to test the high temperature hydrogen peroxide control option in a manner similar to the 

set up that was used to test SNCR. The critical factor in the successful use of the high 

temperature hydrogen peroxide control technology will be determining the best location for 

injection. Careful gas phase temperature measurements and modeling should help determine the 

optimum location. 

Conclusions. It may be possible to add a hydrogen peroxide injection system to the 

preheater tower at the correct location with a relatively low capital expenditure. By combining 

SNCR and the high temperature hydrogen peroxide system, an effective control system could be 

put in place at a minimal capital expenditure that would then allow the plant to use more or less 

of the hydrogen peroxide and ammonia reagents based on their current costs – thus optimizing 

the long term cost per ton of NOx control. 

4.3.8 Potential Applicability of Oxidation Technology to TXI Plant 

General Discussion. The TXI plant has 4 wet process kilns without any existing wet 

scrubber system. That would require them to place a complete oxidation system in place as an 

add-on technology including the scrubber for these systems. Assuming that all of the control 

options would have a similar capital cost for a spray tower/scrubber system careful evaluation of 

the alternative reagent systems is warranted. 
Cement Kiln Report (FINAL – 7/14/2006) 4-61

 A trial system for evaluating the reagent systems may be warranted. As an example, 

three one-month trials using alternative reagents in a skid-mounted scrubber could be performed 

prior to scaling up to a full system. It may be possible to combine the gas flows from the kiln 

systems into a single flow to minimize the cost of the scrubber system. 

 Because of the high moisture levels in the gasses from wet kilns it may be necessary to 

bypass a portion of the stack gasses around the spray tower/scrubber for use as reheat gas after 

the spray tower/scrubber to prevent condensation problems in the stack. To the extent that such 

a strategy is required the efficiency of the NOx removal would be proportionately impacted. 

 TXI also has a large modern precalciner kiln with a scrubber system on-site. An oxidative 

control technology for the precalciner kiln has significant potential to provide NOx control using 

the existing scrubber system. A variety of low temperature oxidation reagent systems could be 

tested for efficiency in the existing wet scrubber system. It should also be relatively simple to set 

up a temporary system to test the high temperature hydrogen peroxide control option. The 

critical factor in the successful use of the high temperature hydrogen peroxide control technology 

will be determining the best location for injection. Careful gas phase temperature measurements 

and modeling should help determine the optimum location. 

 For TXI the added benefit of the high temperature hydrogen peroxide control technology 

might be the added control of hydrocarbons. There is the real potential that at the temperatures, 

which the hydrogen peroxide system operates at, those hydrocarbons will also be oxidized. 

Because these hydrocarbons may be evolved from the raw feed at a lower temperature this is not 

a certainty but, if it were to occur, the potential does exist for such a system to replace the 

existing catalytic control system. In that event, the savings on natural gas costs would be 

substantial. 

Conclusions. For the precalciner the addition of the high temperature hydrogen peroxide 

oxidation control technology to the preheater tower has significant potential. In addition to 

controlling NOx emissions this oxidation technology has the potential to control hydrocarbon 

emissions and eliminate the need for the existing catalytic control system and the associated 
Cement Kiln Report (FINAL – 7/14/2006) 4-62

operating costs. These potential cost savings could more than offset the cost of the hydrogen 

peroxide and capital investment for this kiln line to achieve even greater NOx control than its 

already relatively low levels. Tests of this technology should be able to be conducted with 

minimal investment. Alternatively tests of various wet scrubber reagent systems could also be 

conducted in the existing SOx scrubber system. 

 In the wet kilns, because of the reheat costs, further investigation of the low temperature 

oxidation technologies is likely to be the most cost effective and is therefore recommended for 

further investigation. Combination of midkiln combustion, midkiln SNCR and a low 

temperature oxidation technology may provide exceptional NOx control at the most effective 

aggregate cost per ton of NOx controlled for these kilns.

Table 4-3.4. Summary of Modeling Results for LoTOxTM on Ellis County Kilns – 

Performance Results 

Existing Unit 

Control 

Technology 

Emissions 

Rate 

tpy before 

Emissions 

Rate 

tpy after (a) 

Controlled 

Emissions 

Rate ppm 

Controlled 

Emission Rate 

lb./tonne clinker 

Control 

Efficiency % 

Reduction 

tpy 

Ash Grove #1- wet LoTOx

TM 702 301.6 60 0.84 85% 400.4 

Ash Grove #2- wet LoTOx

TM 750 322.2 58 0.89 85% 427.8 

Ash Grove #3- wet LoTOx

TM 764 328.3 53 0.91 85% 435.7 

TXI #1 and #4–wet (b) LoTOx

TM 1197 514.3 109 1.21 85% 682.7 

TXI #2 and #3–wet (b) LoTOx

TM 121 52 109 0.49 85% 69.0 

TXI#5 – dry LoTOx

TM 1710 734.7 29 0.30 80% 975.3 

Holcim #1 – dry LoTOx

TM 2222 954.7 73 0.38 85% 1,267.3 

Holcim #2 – dry LoTOx

TM 1778 763.9 53 0.30 85% 1,014.1 

(a) NOx emission rate after SCR does not reflect SCR efficiency reduction due to adjustment by the ozone season factor of 0.671 

(NOx reduction is modeled to occur only during the ozone season). 

(b) The results for TXI #1 & #4 and #2 & #3 are average per kiln – for example, total emissions reductions for controlling both

TXI #1 & #4 are double the value listed in the table. 

(c) Models assume mid-kiln firing installed at TXI as required under current SIP. 
Cement Kiln Report (FINAL – 7/14/2006) 4-63

Table 4-3.5. Summary of Modeling Results for LoTOxTM on Ellis County Kilns – 

Economic Results 

Existing Unit 

Control 

Technology 

Capital 

Cost 

Annual 

Cost 

Cost 

Effectiveness 

$/ton NOx

Energy 

Penalty or 

Benefit 

Burden Cost 

$/tonne clinker 

Ash Grove #1- wet (c} LoTOx

TM $4.8 MM $1.4 MM $3,400 (a) $5.00 

Ash Grove #2- wet (c} LoTOx

TM $5.2MM $1.5MM $3,500 (a) $5.40 

Ash Grove #3- wet (c} LoTOx

TM $5.8MM $1.6MM $3,700 (a) $5.70 

TXI #1 & #4–wet (b,c) LoTOx

TM $5.4MM $1.6MM $3,300 (a) $4.70 

TXI #2 & #3–wet (b,c) LoTOx

TM $2.8MM $0.5MM $11,000 (a) $10.50 

TXI#5 – dry LoTOx

TM $5.2MM $2.4MM $2,600 (a) $0.90 

Holcim #1 – dry LoTOx

TM $6.7MM $3.1MM $2,400 (a) $2.35 

Holcim #2 – dry LoTOx

TM $5.4MM $2.5MM $2,300 (a) $1.90 

(a) Increased fan power due to pressure drop across scrubber included in the models 

(b) The results for TXI 1 & 4 and #2 & #3 are average per kiln – for example, total capital costs for controlling both TXI #1 & #4 

are double the value listed in the table. 

(c) Costs for wet kilns include addition of spray tower to scrub oxidation products. 

4.4 Process Modification

 Process modifications are applicable to any type of kiln and are usually done to reduce 

heat consumption, to improve clinker quality, and to increase the lifetime of the equipment (such 

as the refractory lining) by stabilizing process parameters. Reduction of emissions, such as NOx, 

SOx, and dust, are secondary effects of these modifications. Smooth and stable kiln operation 

close to design values for process parameters is beneficial for all kiln emissions. Process 

modifications can include many elements, such as instruction and training of the kiln operators, 

homogenizing raw material, ensuring uniform coal dosing, improving the cooler’s operation, and 

installing new equipment. Process modifications are primarily done to reduce operating costs, 

increase capacity, and improve product quality. Adopting process modifications usually results 

in a reduction of operating costs for a kiln. The savings result from reduced fuel and refractory 

consumption, lower maintenance costs, and higher productivity, among other factors. (35) 

 This section describes process modifications that improve fuel efficiency and kiln 

operational stability with an emphasis on reducing NOx formation. Since NOx formation is 

directly related to the amount of energy consumed in cement-making, improving fuel efficiency 

and productivity will reduce NOx emissions. 
Cement Kiln Report (FINAL – 7/14/2006) 4-64

4.4.1 Combustion Zone Control of Temperature and Excess Air 

 Continuous monitoring of O2 and CO emissions in the cement kiln exhaust gases 

indicates the amount of excess air. At a given excess air level, NOx emissions increase as the 

temperature of the combustion zone increases. A typical kiln combustion zone solids 

temperature range is about 1,430 to 1,540 °C (2,600 to 2,800 °F) for completion of clinkering 

reactions and to maintain the quality of the cement produced. (75) The corresponding gas-phase 

temperature is usually greater than 1,700 °C (3,100 °F). (76) Maintaining the combustion zone 

temperature at a necessary minimum value would minimize both the process energy requirement 

and the NOx emissions. 

 Along with the appropriate temperature, it is also necessary to maintain an oxidizing 

atmosphere in the clinker burning zone to ensure the quality of the clinker produced. Although a 

kiln could be operated with as little as 0.5 percent kiln exhaust oxygen level, typically the kiln 

operators strive for an oxygen level of one to two percent to guarantee the desired oxidizing 

conditions in the kiln burning zone. An experimental test on a cement kiln showed that by 

reducing excess air from 10 to 5 percent (i.e., reducing exhaust oxygen levels from two to one 

percent) NOx emissions per unit time can be reduced by approximately 15 percent. (77,78) 

 With state-of-the-art continuous emissions monitoring systems (CEMS) and feedback 

control, excess air can be accurately controlled to maintain a level that promotes optimum 

combustion and burning conditions in addition to lowering NOx emissions. Reducing excess air 

level also results in increased productivity per unit amount of energy consumed and thus results 

in an indirect reduction of NOx emissions per unit amount of clinker product. 

4.4.2 Feed Mix Composition 

 Heat requirements for producing clinker are dependent on the composition of the raw 

feed which varies among cement plants. Experiments have demonstrated that by improving the 

burnability of the raw feed, the heat requirement of clinker can be reduced by 15 percent.

 (79) If 

the raw feed composition can be formulated to require less heat input per ton of clinker, less fuel 
Cement Kiln Report (FINAL – 7/14/2006) 4-65

is burned and less NOx per unit product is produced. This approach of changing the feed 

composition may, however, be highly site specific and may not be applicable at all locations. 

 Reduction of Alkali Content of Raw Feed. The alkali content of finished cement 

generally needs to be below a certain acceptable level. Low alkali requirements need higher kiln 

temperatures and longer residence times at high temperatures to volatilize the alkali present in 

the semi-molten clinker. Raw materials with greater alkali content need to be burned longer at 

higher temperatures to meet alkali requirements and thus may produce greater NOx emissions. 

Increased volatilization of alkali also results in increased alkali emissions in kiln exhaust gases. 

To control alkali emissions, a part of the kiln exhaust gases may be bypassed around a 

downstream unit, e.g., a precalciner. The bypassed gases are quenched to remove alkali and sent 

through a particulate collector. The bypass of kiln exhaust gases typically involves a fuel 

penalty, e.g., about 20,000 Btu/tonne clinker for every one percent gas bypass. The additional 

heat requirement may also contribute to increased NOx emissions; thus, reducing the alkali 

content of the raw feed mix may contribute to a reduction in the NOx emissions. 

4.4.3 CemStar Process 

 Another feed modification that can reduce NOx emissions is the addition of a small 

amount of steel slag to the raw kiln feed. This patented technique is known as the CemStar 

Process and was developed by TXI Industries. Steel slag has a low melting temperature and is 

chemically very similar to clinker. Since many of the chemical reactions required to convert 

steel slag to clinker have already taken place in a steel furnace, the fuel needed to convert steel 

slag into clinker is low. The decreased need for limestone calcination per unit product and 

improved thermal efficiency of the process both contribute to reduced thermal NOx and CO2

emissions. (80)

 Eleven facilities are using or in the process of incorporating CemStar. (81) CemStar 

requires little extra equipment and the addition of steel slag to the feed mix can result in a 

reduction or elimination of the need for some mineral sources, such as shale or clay. This process 

can also increase production by 15 percent. (80) 
Cement Kiln Report (FINAL – 7/14/2006) 4-66

 According to the Entellect Environmental Services “Evaluation of the Effects of the 

CemStar Process on a Wet Process Cement Kiln” report, the CemStar process reduces the kiln 

material temperature in the region of the flame by an average of 200°F (from 2,610°F to 

2,405°F); the lower gas temperature of the flame results in lower NOx emissions. (82) Another 

test of CemStar technology found an average reduction in burn zone temperature of 160°F, a six 

percent reduction. (82) The amount of NOx emissions reductions achievable with CemStar 

varies by kiln type but ranges from over 20 to 60 percent. (80) Short- and long-term tests of 

CemStar were conducted at two different types of TXI cement kilns in 1999. Short-term tests 

(two days) on a preheater/precalciner kiln found NOx emissions reductions in lbs. NOx/tonne 

clinker of 44 percent when operated at maximum capacity, and between 9 and 30 percent when 

operated at normal capacity, depending on the quality of the raw feed mix (see Table 4-4.1). 

Table 4-4.1. Results of Short-Term Cemstar Tests on a Preheater/Precalciner Kiln 

Poor Quality Feed 

Mix (lb. NOx/tonne 

clinker) 

Percent 

Reductiona

(%) 

Ideal Quality Feed 

Mix (lb. NOx/tonne 

clinker) 

Percent 

Reductiona

(%) 

Without CemStar 4.98 - 5.59 

With CemStar at normal 

feed rateb

4.51 9 3.89 30 

With CemStar at maximum 

feed ratec

(no test) - 3.15 44 

a

 Percent reductions are relative to the emission rate without CemStar. 

b

 The normal feed rate is 170 - 180 tons per hour of dry feed. 

c

 The maximum feed rate is 195 tons per hour of dry feed. 

 Andover Technologies also reported on short-term and long-term tests of a wet kiln using 

CemStar Technology. The short-term tests (one day) found emission reductions of 36 to 55 

percent in lbs. NOx/tonne clinker, and the long-term tests (approximately two and a half months) 

found reductions of 24 percent (see Table 4-4.2). (80) 

 Kilns with lower initial baseline NOx emissions would have less NOx reduction with 

CemStar than those with higher baseline emissions. Wet and long-dry kilns would have greater 

NOx reductions with CemStar because more energy is used per ton of clinker produced than 

preheater/precalciner kilns. Wet kilns may achieve the greatest NOx reductions with CemStar 

because the addition of steel slag would reduce the amount of water needed to create the slurry 

and consequently decrease the amount of heat needed to dry it. (80) 
Cement Kiln Report (FINAL – 7/14/2006) 4-67

Table 4-4.2. Results of Cemstar Tests on a Wet Kiln 

Test 1 (lb. NOx/tonne 

clinker) 

Test 2 (lb. 

NOx/tonne clinker) 

Percent Reductiona

(%) 

Short-Term Test 

Without CemStar 17.53 24.7 - 

With CemStar 11.24 no 2nd test Test 1 = 36 

Test 2 = 55 

Long-Term Test 

Without CemStar 5.23 no 2nd test - 

With CemStar no 2nd test 24 

a

 Percent reductions are relative to the emission rate without CemStar. 

4.4.4 Kiln Fuel 

 Changing the primary kiln fuel from natural gas to coal can reduce the flame 

temperatures significantly, resulting in lower thermal NOx emissions. (83,84) Although nitrogen 

present in coal may provide greater fuel NOx contribution, switching the fuel burned in kilns 

from natural gas to coal has been shown to provide substantial reduction in the total NOx

emissions in one experimental study. (83) In the dry process kilns tested in this study the 

average NOx emissions decreased from 20.4 lb./tonne clinker to 6.2 lb./tonne clinker when the 

fuel was changed from natural gas to coal. A number of cement kilns have already made the 

switch from natural gas to coal and currently 87 percent of cement kilns in the United States use 

coal as the primary fuel. (85)

 When natural gas (with no nitrogen in the fuel) is used in the burning zone of a cement 

kiln, the NOx emissions are significantly higher than when coal is used. There may be additional 

environmental impacts when coal is burned as opposed to natural gas (e.g., sulfur dioxide and 

sulfate emissions may increase). Although switching to a lower nitrogen fuel in a precalciner 

may reduce NOx, the fuel nitrogen content in the burning zone has little or no effect on NOx

generation. Some researchers have found no relationship between fuel nitrogen content and the 

NOx emissions from a cement kiln. (86) 
Cement Kiln Report (FINAL – 7/14/2006) 4-68

 Switching to a fuel with a higher heating value and lower nitrogen content may reduce 

NOx emissions in a cement kiln, e.g., petroleum coke has a lower nitrogen content per million 

Btu than coal. Petroleum coke is also more uniform in terms of heat value, lower in volatile 

matter content and burns with a lower flame temperature. However, some claim that petroleum 

coke cannot be burned alone because it does not provide enough volatile matter. (87) 

4.4.5 Increasing Thermal Efficiency 

 The thermal efficiency of the cement-making process has improved substantially as 

energy costs have increased and new technology has been developed. Although there are a 

variety of cement process technologies used in the US, the kilns in this study are all either 1960’s 

wet kiln technologies that are not energy efficient or modern dry process kilns with preheat and 

precalcination that represent the most energy efficient process for making Portland cement. Both 

Holcim #2 and TXI #5 are new and energy efficient units. Holcim #1 began operation in 1987 

and is slightly less efficient and could potentially be upgraded by options such as calciner 

modification discussed below. In addition, there are interim steps that improve the efficiency of 

wet process to semi-wet or semi-dry process. However, the main opportunity for substantial 

reductions in NOx emissions in Ellis County from energy improvements comes from closing the 

wet process units and replacing them with modern, dry-process production. 

Calciner Modifications 

 A study for the Department of Energy (88) evaluates use of low pressure drop cyclones 

for suspension preheaters. Worrell reports, “Cyclones are a basic component of plants with preheating systems. The installation of newer cyclones in a plant with lower pressure losses will 

reduce the power consumption of the kiln exhaust gas fan system. Depending on the efficiency 

of the fan, 0.6-0.7 kWh/ton clinker can be saved for each 50 mm W.C. (water column) the 

pressure loss is reduced. For most older kilns this amounts to savings of 0.6-1.0 kWh/ton (89). 

Fujimoto (1994) discussed a Lehigh Cement plant retrofit in which low-pressure drop cyclones 

were installed in their Mason City, Iowa plant and saved 4 kWh/ton clinker (90). Installation of 

the cyclones can be expensive, however, since it may often entail the rebuilding or modification 

of the preheater tower, and the costs are very site specific. Also, new cyclone systems may 
Cement Kiln Report (FINAL – 7/14/2006) 4-69

increase overall dust loading and increase dust carryover from the preheater tower. However, if 

an inline raw mill follows it, the dust carryover problem becomes less of an issue. A cost of 

$2.7/annual ton clinker is assumed for a low pressure drop cyclone system.” 

 The only candidate for a calciner upgrade among the Ellis County kilns is Holcim #1. 

This process line represents a slightly older version of the technology than Holcim #2 or TXI #5. 

Low-NOx and low energy consumption performance is largely inherent in the design and Holcim 

#1 would appear to be the unit that could best benefit from this upgrade. Cost modeling has been 

provided based on the assumption that this unit could move to a level of performance similar to 

TXI #5 after the upgrade. The expert panel reviewed the current performance of the Holcim 

kilns in comparison to TXI #5. Although Holcim #2 and TXI #5 were both built near the year 

2000, TXI #5 has typical NOx emissions that are substantially lower than Holcim #2. It was the 

judgment of the expert panel that an intrinsic low- NOx redesign of Holcim #1 should produce 

performance more similar to that of TXI #5 than Holcim #2. These results are provided in Table 

4-4.5. 

Semi-Wet Upgrades to Wet Kilns 

 Hendriks and Worrell (91) report that conversion from a wet to a semi-wet process can 

save between 0.8 and 1.6 GJ/tonne clinker. There is a penalty of increased electrical energy use 

of approximately 3 to 5 kWh associated with this conversion. 

 Worrell (88) also reviews this option and describes it as a filter press system. “In the wet 

process the slurry typically contains 36% water (range of 24-48%). A filter press can be 

installed in a wet process kiln in order to reduce the moisture content to about 20% of the slurry 

and obtain a paste ready for extrusion into pellets (92). In the U.S. several plants have tried 

slurry filters, but have not been very successful. Currently, there seem to be no plants in the U.S. 

using this technology (93). Additional electricity consumption is 3-5 kWh/ton clinker (94). In 

this analysis it is assumed that energy use increases by 4 kWh/ton clinker to reduce the moisture 

content to 20%. The corresponding fuel savings are 1.0 MBtu/ton (94). Jaccard and Willis 

(1996) estimate the conversion cost to run $1.6/annual ton clinker capacity with increased 

operation costs of $0.1/ton clinker (95).” 
Cement Kiln Report (FINAL – 7/14/2006) 4-70

Semi-Dry/Semi-Wet Upgrades to Wet Kilns 

 Hendriks and Worrell (91) report that conversion from a wet to a semi-dry process can 

save approximately 2.0 GJ/tonne clinker. They report a “small” increase in electrical energy use 

associated with this conversion of approximately 3 to 5 kWh. 

Buzzi-Unicem operates a semi-dry/semi-wet system in Greencastle, IN, which had been 

converted from a large wet kiln system. While anticipated increases in production capacity were 

achieved, predicted improvements in thermal efficiency were not fully realized. Actual thermal 

efficiency improvement was only about 15%. Capital cost for this type of conversion are likely 

to be in the range of $75-85/tonne. Significant NOx improvements have been observed in this 

conversion although not to the levels predicted by the vendor. Even with a 50% increase in 

production total NOx emissions have been significantly reduced. 

 Because kiln conversion economics are significantly impacted by the size of the existing 

kiln the conversion of any of the wet kilns at TXI or Ash Grove is not considered a feasible 

alternative for further analysis. 

Replacement of Wet Kilns with Dry 

 Worrell evaluates conversion of a wet kiln to a dry preheat/precalciner process (88). This 

conversion is essentially a reconstruction of the main kiln and processing areas with a new, 

modern dry plant. Worrell reports “If economically feasible a wet process kiln can be converted 

to a state-of-the art dry process production facility that includes either a multi-stage preheater, or 

a pre-heater/pre-calciner. Average specific fuel consumption in U.S. wet kilns is estimated at 6.0 

MBtu/ton clinker. Studies of several kiln conversions in the U.S. in the 1980s found fuel savings 

of 2.9 MBtu/ton or less (96). In Hranice (Czech Republic) a 1,050 tonne per day wet process 

plant was converted to a dry kiln plant with a new kiln specific fuel consumption of 2.7 

MBtu/ton clinker (97). Fuel savings of 2.7 MBtu/ton clinker and an increase in power use of 

about 9 kWh/ton clinker (98) are assumed. The cost of converting a wet plant to a dry process 
Cement Kiln Report (FINAL – 7/14/2006) 4-71

plant may be high, as it involves the full reconstruction of an existing facility. Costs may vary 

between $50/annual ton clinker capacity and $100/annual ton clinker capacity (99,100).” 

 This option is also discussed by Hendriks (91). Hendriks gives a cost of approximately 

$133/tonne of annual capacity as the cost of building the new dry process plant. Hendriks 

estimates that about 2.2 GJ/tonne of energy can be saved. Increased energy use of about 

10kWh/tonne is required for operation of the preheat/precalcination tower. These models do not 

consider any lost revenues that may be associated with wet to dry conversion. Certain types of 

cement, such as oilfield cement, are typically produced by wet kilns. This means that a plant that 

converts from a wet to dry process may lose some revenues. Companies that operate wet kilns 

and companies that operate preheat/calciner kilns are likely to have differences of opinion about 

the magnitude of difference in cement quality. This cost impact depends on the amount of 

materials sold by a particular plant and may include subjective criteria regarding cement qualities 

that cannot be quantified as part of this project. 

Wet to Dry Conversion of Ellis County Kilns 

 On average, dry preheat/precalciner kilns emit substantially less NOx per tonne of cement 

produced and require less energy per tonne of cement produced. Both in terms of energy use and 

NOx emissions rates, the wet process units are often nearly double the modern dry process units. 

The cost modeling presumed that the wet kilns could obtain a value approximately that of high 

performing modern kilns and that would result in an approximate 65% decrease in NOx

emissions. A substantial energy savings was predicted to result in fuel savings in the cost 

models (see Confidential Attachment Wet to Dry Conversions). 

 The economics of wet kilns compared to dry kilns are very complex and involve issues 

such as lower production capacity of wet kilns, use of waste fuels and quality of cement 

products. However, as the energy costs of wet production are higher than for modern dry 

process units, there is a point at which the higher costs of pollution controls that may result from 

the final determinations of this study would trigger a decision to close the wet kilns and replace 

them with dry. Stating this another way, it is likely that at a certain cost of pollution controls in 

terms of dollars per tonne of clinker produced, the economics of the wet process including higher 
Cement Kiln Report (FINAL – 7/14/2006) 4-72

fuel costs and higher pollution control costs would reach a point where replacement of the wet 

units with larger dry process units would be the reasonable alternative for a cement plant to 

continue operations at that site. 

 It is likely that any new kilns built to replace the wet kilns in Ellis County would include 

increased production capacity in the economic justification. However, for purposes of control 

cost modeling, the units need to replace the existing capacity for the evaluations to make sense in 

the context of our control option evaluations. For this reason, two dry process kiln replacement 

scenarios were modeled. One involved replacing the three wet kilns at Ash Grove with one new 

dry process unit and the second involved replacing the four wet kilns at TXI with one new dry 

process unit. The capacity of the new units was modeled as essentially equal to the capacity of 

the existing wet units combined. It is likely that Ash Grove and perhaps TXI would replace the 

existing kilns with a new dry preheat/precalcination process typical of current generation dry 

process plants with approximately twice (over two million tons per year of clinker) the capacity 

of the existing wet kilns (under one million tons per year of clinker) and the added production 

capacity would be an important part in cost justification of the expense of the new dry process 

unit. 

 The modeling, summarized in Table 4-15, shows an annualized cost of approximately 

$11 per tonne clinker for the replacement dry process units. This cost includes an annual benefit 

of approximately $4.0 to $4.5 million in reduced fuel costs. An increased annual cost of 

electricity of approximately $0.5 million results from the additional fan power required to move 

air through the preheat and precalcination tower. This information indicates that energy savings 

are very significant, but are not sufficient for a company to justify replacement of the wet kilns. 

Annual operating costs (capitalization of the new equipment) are reduced by nearly one third to 

approximately $9 million dollars by energy savings; however, even with the current high costs of 

energy this would not by itself justify replacement of the wet kilns. 

 The current use of alternative fuels complicates this analysis. The fuel savings are based 

on an assumption that the energy for the current wet kilns is all based on coal. Lower cost 

alternative fuels lessen the economic benefit of the increased energy efficiency. Preserving these 

alternative fuel programs may be important economic considerations in company analyses of wet 
Cement Kiln Report (FINAL – 7/14/2006) 4-73

to dry conversions and the overall economics of cement production on a dollars per tonne clinker 

basis. The realistic assumption that larger modern units of a size similar to TXI #5 are needed to 

achieve the energy efficiency desired and using increased production to offset the high cost of 

these projects both impact fuel economics. If it is assumed that the current amounts of 

alternative fuels are permitted to be used in a new larger kiln, the amount of coal predicted to be 

reduced would still be reflected in the overall reduction in fuel use. 

 Conversion of the Ellis County wet kilns to dry process would result in year-round 

emissions reductions for NOx, SO2, particulate matter and hazardous air pollutants. The modern 

dry process unit would have updated controls that would result in potentially large emissions 

reductions for SO2 and other air quality benefits for the region including reduction in fine PM 

precursors. 

Table 4-4.3. Summary of Modeling Results for Wet to Dry Conversion of Ellis County 

Kilns – Performance Results 

Existing Unit Replacement Unit 

Emissions 

Rate 

tpy before 

Emissions 

Rate 

tpy after (a)

Controlled 

Emissions 

Rate ppm 

Controlled 

Emission Rate 

lb./tonne clinker 

Control 

Efficiency 

% 

Reduction 

tpy 

Ash Grove #1- wet Ash Grove #4 - dry 2,200 772 180 1.99 65% 1,428 

Ash Grove #2- wet 

Ash Grove #3- wet 

TXI #1 –wet TXI #6 – dry 1,800 630 180 1.94 65% 1170 

TXI #2 –wet 

TXI #3 –wet 

TXI #4 –wet 

Table 4-4.4. Summary of Modeling Results for Wet to Dry Conversion of Ellis County 

Kilns – Economic Results 

Existing Unit Replacement Unit 

Capital 

Cost 

Annual 

Cost 

Cost 

Effectiveness 

$/ton NOx

Energy 

Penalty or 

Benefit* 

Emissions 

Penalty or 

Benefit** 

Burden Cost 

$/tonne clinker 

Ash Grove #1- wet Ash Grove #4 - dry $169 M $9.3 M $6,500 -$4.4 M -1,428 tpy $10.94 

Ash Grove #2- wet 

Ash Grove #3- wet 

TXI #1 -wet TXI #6 - dry $143 M $7.9 M $6,700 -$3.7 M -1,170 tpy $10.94 

TXI #2 -wet 

TXI #3 -wet 

TXI #4 -wet 
Cement Kiln Report (FINAL – 7/14/2006) 4-74

* Large benefit in fuel efficiency partly offset by increased electrical use in tower 

** Large benefit in reduced fuel – does not account for increased emissions at power plant for power used in tower. 

Table 4-4.5. Summary of Modeling Results for Calciner Upgrade for Ellis County Kilns – 

Economic Results 

Control 

Technology 

Control 

Technology 

Status 

Emissions 

Rate Before 

Control tpy 

Emissions 

Rate Before 

Control 

lbsNOx//tonne 

Percent 

Control 

Emissions 

Reduction 

from Control

tpy 

Controlled 

Emission 

Rate 

lbNOx/tonne 

Cost 

Effectiveness 

$/ton NOx

Burden 

Cost 

$/tonne 

clinker 

Holcim #1 Available 2,222 3.76 40% 888.8 2.2 $2,795 $2.70 

40% for new low-NOx calciner based on TXI #5 performance. 

Cost effectiveness for calciner upgrade calculated by ratio of burden costs using SCR data. 

Calciner upgrade is not a seasonal ozone measure – emissions benefit is for full year. 

4.5 Performance of Current NOx Control Techniques and Technologies in the Cement

Industry 

4.5.1 Comparison of Current Performance of NOx Control Technologies 

 Table 4-5.1 is a spreadsheet that is too large for inclusion as a table in the body of this 

report. This table compares the performance of different technologies against a standard 

performance criterion of pounds of NOx per tonne (lbs./tonne) of clinker produced. Only 

information on complete references is included in this table. When sufficient information could 

be located to identify the plant and calculate performance of the control technology in lbs./tonne 

clinker, the information was included in this table. There are additional, less complete references 

to performance in this report that could not be included in this table because insufficient 

information was available to compare performance. 

4.5.2 Summary of Current Regulations 

 This report focuses on evaluating the NOx control measures for Portland cement 

manufacturing that go beyond current 30 TAC Chapter 117 requirements. In the US, it appears 

that several areas of the country are in a similar position to Texas in that they are currently 

evaluating more stringent active controls of NOx for ozone attainment under the 8-hour standard. 

While active NOx controls may be required under New Source Review requirements, current 

State SIP requirements are less stringent. ERG reviewed and summarized current US NOx 

control requirements for cement kilns and this summary is presented in Attachment D as Table 

D-1. This review showed that four states had performance standards that were similar in 

stringency to Texas (Maryland, Illinois, Indiana and Michigan). Five states (Pennsylvania, South 
Cement Kiln Report (FINAL – 7/14/2006) 4-75

Carolina, Tennessee, Ohio and Alabama) had technology based standards that were similar in 

stringency to the option under Texas regulations to comply by installing a technology such as 

mid-kiln injection instead of meeting a specific performance standard. Kentucky and 

California’s South Coast Air Quality Management District has standards that appear to be less 

stringent than Texas. New York uses a case-by-case approach so that the stringency of the 

regulation is not clear. States are currently considering more stringent measures to comply with 

the NOx SIP Call and with projected noncompliance with the 8-hour ozone standard. Both the 

State of Georgia and the Great Lakes States are considering more stringent control requirements 

of cement kilns; these measures are discussed below. 

 Control requirements in Europe are generally moderately stringent emissions limitations 

based on a performance requirement such as 500 mg/m3. These requirements have prompted use 

of SNCR (recent documents report as many as 50 installations), but generally are not stringent 

enough to require higher performing technologies. One exception is Sweden, that has a very 

stringent performance requirement of 200 mg/m3 (approximately 98 ppm). There are currently 

two cement plants in Europe capable of meeting this 200 mg/m3 limit. The Solnhofen 

Portlandzementwerke in Germany (using SCR) and Scancem Slite in Sweden (using SNCR with 

multi-point injection). European control requirements are presented in Tables 4-5.2 and 4-5.3 

 Japan has a national standard for NOx from cement plants and divides the emissions 

limits into those that apply to plants built before 1975 and those built after 1975. For pre-1975 

plants the NOx standard is 480 ppmv and for those built after, the standard is 250 ppmv. The 250 

ppmv standard is very similar to the German standard of 500 mg/m3

. For the purposes of 

evaluating the particulate matter standards table, a US standard of 0.02 grains per dry standard 

cubic foot would be equivalent to a European standard of 50 mg/Nm3

. 

 As noted above, the US is somewhat behind Europe in requiring active controls on 

Portland cement manufacturing plants. Communications between TCEQ and EPA Region 6 

indicate that recent BACT determinations typically require 1.95 lbs./tonne clinker (2.15 

lbs./tonne) and SNCR. Other recent US studies include planning studies for compliance with the 

8-hour ozone standard. 
Cement Kiln Report (FINAL – 7/14/2006) 4-76

 Two recent documents that recommend measures beyond current 30 TAC Chapter 117 

requirements are the Midwest Regional Planning Organization’s “Identification and Evaluation 

of Candidate Control Measures, April, 2005” and the “Fall Line Air Quality Study. November, 

2004”. Both of these studies are evaluations of potential measures to reduce ozone and 

recommend consideration of SCR for control of cement kilns. The Fall Line Study was 

conducted for the State of Georgia and recommends SCR for wet kilns as well as dry process 

kilns and provides estimates of cost effectiveness per ton of NOx controlled. The Midwest RPO 

Study also discusses the potential for control of wet kilns with SCR, particularly for low-dust 

applications (after pollution controls) and mentions the high cost of gas reheat as a limitation in 

application of this technology. SCR costs are only estimated for long dry and dry 

preheat/precalcination process kilns. The cost information from these two studies is 

summarized in Tables 4-5.4 and 4-5.5. 
Cement Kiln Report (FINAL – 7/14/2006) 4-77

Table 4-5.2. National SO2 and NOx Emission Limits for the Production of Cement Within 

the European Union (EU 15), in mg/Nm3, Around 2000 

Country 

Data 

Based 

on 

New/Modified or 

Existing Plant 

SO2 Normal 

Situation 

SO2 S-rich Raw 

Materials NOx

PCDD/Fs* 

ng TEQ/Nm3

Austria Na (a) New/modified 

Existing 

200 

200 

400 

400 

500 

1000 

Belgium P New/modified 

Existing 

1000 

1000 

 1800 

1800 

Denmark P (a) Existing 5/250/450 (b) No limit 1200/2500/850 (c) no limit 

Finland P (d) Existing 150–400 1200–1800 

France Na New/modified 

Existing 

500 

500 (e) 

1200/1800 (f) 

1200/1800 (e)(f) 

1200/1500/1800 (g) 

1200/1500/1800 (g) 

Germany Na New/modified 

Existing 

400 

400 

400 

400 

500 

800 

Greece 

Ireland Na New/modified 

Existing 

400 

400 

700 

700 

1300 

1300 

n.a. 

n.a. 

Italy Na/P New/modified 

Existing 

600 1800 10000 (h) 

10000 (h) 

Luxembourg P Existing 100 (i) 80(j) 0.1 (k) 

Netherlands P Existing (l) 1300(j) 0.1 

Portugal Na New/modified 

Existing 

400 1300 0.1 

0.1 

Spain Na New/modified 

Existing 

2400/6000 (m) 

600 (n) 

2400/6000 (m) 

600 (n) 

2400/6000 (m) 

1800 (n) 

2400/6000 (m) 

1800 (n) 

1300-1800 (n) 

Sweden P Existing - <200 <200 0.1 

UK Na (o) New/modified 

Existing 

200 (p)(q) 600-2500 (r) 900 (p) 

500-1200 (q)(s) 

Source: EIPPC Cement BREF (2000). Based on Cembureau report (1997) and information provided by experts of the Technical Working Group 

set up in order to support the production of the BREF 

* Polychlorinated dibenzo dioxins and furans (total emitted quantity in nano g/ Norm m3

). 

Na = National law; R=Regional law; P=Typical permit; in mg/ Norm m3

. 

a) Daily averages and reference condition of 273 K, 101.3 kPa, dry gas and 10% O2. 

b) 5 for semi-dry process, 250 for wet process and 450 for wet process with wet scrubber and heat recovery. Limits under discussion. 

c) 1200 for semi-dry process, 2500 for wet process and 850 for wet process with wet scrubber and heat recovery. Limits under discussion. 

d) Monthly averages, reference condition of 10% O2 and dry gas. 

e) Existing plant must meet limit for new plant by 2001. 

f) 1200 mg/Nm3

 if ≥ 200 kg/h; 1800 mg/Nm3 if < 200 kg/h. 

g) 1200 mg/Nm3

 for dry process with heat recuperation, 1500 mg/Nm3 for semi dry and semi wet processes, and 1800 mg/Nm3 for wet and dry 

processes without heat recuperation. 

h) General rule for any kind of industrial emission. 

i) Half hour average. 

j) Daily average value. 

k) 6 hour average. 

l) 90 kg/h as daily average, maximum 375 tonne/year. 

m) Current limits. 

n) Limits under discussion. 

o) IPC Guidance Note S2 3.01. 

p) ‘Benchmark releases’. 

q) Benchmark releases are, in particular, not applicable to existing plant but are a factor in considering appropriate limits. 

r) Limit values reflect the actual levels of releases. Daily averages and reference condition of dry gas and actual O2 content. 

s) Actual releases, daily averages, not all plants currently have limits. 
Cement Kiln Report (FINAL – 7/14/2006) 4-78

Table 4-5.3. National Emissions Standards for PM of the European Union Countries 

for Cement Manufacturing in mg/Nm3 

Country 

Data 

Based 

on 

New/Modified or 

Existing Plant Kiln Stack Clinker Cooling Cement Grinding 

Other Point 

Sources 

Austria Na (a) New/modified 

Existing 

50 

50 

50 

50 

50 

50 

50 

50 

Belgium P New/modified 

Existing 

50 

50 - 150 

50 

50 - 400 

50 

50 - 150 50 – 300 

Denmark P Existing 50 (b) 50 (b) 50 (b) 50 (b) 

Finland P New/modified 

Existing 

50 

50 (c) 

50 

50 

30 – 50 

30 - 50 

30 – 50 

30 – 50 

France Na New/modified 

Existing 

50 

50 (d) 

100 

100 (d) 

50 

50 (e) 

30 

30 

Germany Na New/modified 

Existing 

50 

50 

50 

50 

50 

50 

50 

50 

Greece Na/R New/modified 

Existing 

100 

150 

100 

150 

100 

150 

Ireland Na New/modified 

Existing 

50 

50 

100 

100 

75 

75 

50 

50 

Italy Na/P Existing 50 50 50 50 

Luxembourg P Existing 30 (f) 

Netherlands P Existing 15 (f) 10 (f) 10 (f) 10(f) 

Portugal Na New/modified 

Existing 

50 

100 

100 

100 

75 

75 

50 

50 

Spain Na New/modified 

Existing 400/250 (g) 

100 (h) 

170/100 (g) 

100 (h) 

170/100 (g) 

100 (h) 

300/250 (g) 

75 (h) 

300/250 (g) 

75 (h) 

300/250 (g) 

50 (h) 

300/250 (g) 

50 (h) 

Sweden P Existing 50 (i) 50 50 20 

UK Na (j) New/modified 

Existing 

40 (k) 

(l) 

50 (k) 

(l) 

40 (k) 

(l) 

50 (k) 

(l) 

Na= National law; R= Regional law; P= Typical permit 

a) Daily averages and reference condition of 273 K, 101.3 kPa, dry gas and 10% O2. 

b) Limits under discussion. Reference condition of 273 K, 101.3 kPa, dry gas and 10% O2. 

c) Existing plant must meet 50 mg/Nm3 by January 1, 2001. Monthly averages and reference condition of 10% and dry gas. 

d) Existing plant with emission < 150 mg/Nm3 must meet limit for new plant by 2001. 

e) Existing plant must meet limit for new plant by 2001. 

f) Daily average values. 

g) Current limits. 

h) Limits under discussion. 

i) Daily average value. A limit value of 90 mg/Nm3, including start/stop and CO-trips, applies for monthly averages. 

j) IPC Guidance Note S2 3.01. 

k) “Benchmark releases.” 

l) Benchmark releases are, in particular, not applicable to existing plant but are a factor in considering appropriate limits. 

[Based on [Cembureau report, 1997] and information provided by the Technical Working Group of the European Commission BREF 

Report (2000)].
Cement Kiln Report (FINAL – 7/14/2006) 4-79

 

Table 4-5.4. Midwest RPO – LADCO Study 

(Large Preheater Kiln SCR 1,200,000 tpy clinker 2,880 tpy uncontrolled emissions) 

70% Removal Efficiency 90% Removal Efficiency 

Low Capital 

Cost 

High Capital 

Cost 

Low Capital 

Cost 

High Capital 

Cost 

Total Capital Investment – TCI $1,760,296 $14,668,188 $1,760,296 $14,668,188 

Total Annual Cost $1,305,377 $3,040,107 $1,305,377 $3,040,107 

Pollutant Removal - tpy 2,016 2,016 2,592 2,592 

Cost Per Ton of NOx Removed $648 $1,508 $504 $1,173 

Table 4-5.5. Fall Line Air Quality Study (Georgia) 

In-process fuel use – coal SNCR $1,726 

Cement manufacturing dry Mid-kiln firing $62 

Mid-kiln firing $62 

Medusa 

Cement 

(Houston) Cement manufacturing wet 

SCR $3,947 Mid-kiln 

 In summary, current US emissions limitations indicate that 1.95 lbs./tonne clinker using 

SNCR is currently considered BACT for dry kilns. In order to meet 8-hour ozone standards, 

several areas of the country are looking at requiring more stringent NOx controls on Portland 

cement plants and at least two areas are looking at requiring SCR. Experience in Europe 

indicates that emissions levels of approximately 200 mg/m3

 (98 ppm) and less than 1.0 lb./tonne 

clinker are being achieved at two dry precalciner kilns, one using SNCR and one using SCR. 

4.5.3 Summary of European Experiences 

In Europe, many cement plants have adopted general primary measures, such as process 

control optimization, use of modern, gravimetric solid fuel feed systems, optimized cooler 

connections and use of power management systems. These measures are usually taken to 

improve clinker quality and lower production costs but they also reduce energy use and air 

emissions.1

 In March 2000, the European Integrated Pollution Prevention and Control (IPPC) Bureau 

issued a report on Best Available Techniques for European cement kilns. (35) The report 

collected emissions data from several sources. Emission rates for European kilns included in this 
Cement Kiln Report (FINAL – 7/14/2006) 4-80

study range from less than 0.8 to 12 lb. NOx/tonne clinker. A set of German kiln emission 

measurements presented in the European report found NOx emissions for a cyclone preheater 

with heat recovery of 1.2 to 6.2 lb./tonne clinker, for a cyclone preheater without heat recovery 

of 1.6 to 7.0 lb./tonne clinker, and for a grate preheater of 1.6 to 8.2 lb./tonne clinker. These rates 

are similar to the averages for preheater and precalciner kilns found by EC/R in the new data 

presented in Chapter 4 (1.7 and 2.7 lb./tonne clinker respectively), but are less than those 

reported in the ACT document (5.9 and 3.8 lb./tonne clinker respectively). (35) 

 Table 4-5.5 presents a summary of NOx control device applicability, reduction efficiency, 

and reported average emissions from the IPPC Bureau report on BAT for European cement kilns. 

(35) There are no emissions data in the IPPC report for kilns with CemStar technology or 

midkiln firing. For low-NOx burners, the IPPC report found a lower average NOx emissions rate 

(1.6 lb./tonne clinker) than EC/R found in the new State data (8.98 lb./tonne clinker). Both the 

IPPC report and the 1994 ACT document had estimated reduction efficiencies for low- NOx

burners of up to 30 percent. The reduction efficiencies in the IPPC report for SNCR (10 to 85 

percent) and SCR (85 to 95 percent) are close to but slightly greater than those reported in the 

1994 ACT document (30 to 70 percent and 80 to 90 percent respectively). (35) 

Table 4-5.5. NOx Control Techniques Summary From European Best Available 

Techniques Report (35) 

Reported Emissions 

Technique 

Kiln Systems 

Applicability 

Reduction 

Efficiency mg/Nm3 a

kg/tonne b

(lb./ton) 

Flame cooling All 0 to 50% 

Low-NOx burner All 0 to 30% 

400 0.8 

(1.6) 

Staged combustion Preheater and Precalciner 10 to 50% <500 to 1000 < 1.0 to 2.0 

(2.0 to 4.0) 

Mid-kiln firing Wet and long dry 20 to 40% no info no info 

SNCR Preheater and Precalciner 10 to 85% 200 to 800 0.4 to 1.6 

(0.8 to 3.2) 

SCR - data from pilot 

plants only 

Possibly all 85 to 95% 100 to 200 0.2 to 0.4 

(0.4 to 0.8) a

 Normally referring to daily averages, dry gas, 273 K, 101.3 kPa and 10% O2. b kg/tonne clinker is based on 2000 m3

/tonne clinker. 
Cement Kiln Report (FINAL – 7/14/2006) 4-81

 The IPPC report concludes that BAT for reducing NOx emissions are a combination of 

general primary measures, primary measures to control NOx emissions, staged combustion and 

SNCR. The BAT emission level associated with the use of these techniques is 0.4 to 1.0 lb./tonne 

clinker (200-500 mg NOx/m3 (as NO2)). This emission level could be seen in context of the 

current reported emission range of 0.4 to 6.0 lb./tonne clinker (<200-3000 mg NOx/m3), and that 

the majority of kilns in the European Union is said to be able to achieve less than 2.4 lb./tonne 

clinker (1200 mg/m3

) with primary measures. (35) 

 While there was support for the above concluded BAT to control NOx emissions, there 

was an opposing view that the BAT emission level associated with the use of these techniques is 

1.0 to 1.6 lb./tonne clinker (500-800 mg NOx/m3 (as NO2)). There was also a view that selective 

catalytic reduction is BAT with an associated emission level of 0.2 to 0.4 lb./tonne clinker (100- 

200 mg NOx/m3 (as NO2)). (35) 
Cement Kiln Report (FINAL – 7/14/2006) 5-1

5.0 CHEMISTRY OF ELLIS COUNTY MATERIALS AND IMPACTS ON CONTROL

DETERMINATIONS 

 In order to evaluate the characteristics of feed material and their potential impacts on 

controls, the expert panel worked together to select the parameters they determined necessary for 

their evaluations. During the team’s site visits, it was determined which of these parameters 

could be supplied by the companies, and which would need to be obtained through chemical 

analyses. The expert panel assisted TCEQ in preparing an information request for the 

parameters that could be obtained from the plants and a sampling protocol for the additional 

chemical analyses that would be required. The additional testing that was required is discussed 

below under analytical results. 

5.1 Analytical Results

 Analysis was conducted to determine the chemical, mineral and elemental composition of 

limestone and other raw materials used in clinker production in Ellis County. Total organic 

carbon, total sulfur, various forms of sulfur including sulfite and sulfate, chloride, and total 

Kjeldahl nitrogen content were determined. Three samples of each type (dry powder, wet slurry, 

slag) were collected from representative operating kiln sites using Ellis County limestone feed 

material. Analyses were chosen based on the need to identify composition that was expected to 

affect NOx emissions or control option performance. 

 Total organic carbon results are determined using a technique known as differential 

scanning calorimetry (DSC). Analyses are carried out in gas with a composition of 20% carbon 

dioxide, 3% oxygen, and 77% nitrogen similar to the basic constituents of kiln flue gas. This 

causes an oxidative pyrolysis, which closely parallels actual kiln conditions. The formation of 

char residues is very unlikely for this testing method. Several samples were also analyzed by an 

alternative technique that gradually heats the material electrically from an external source using 

nitrogen as the carrier gas. The results reflect a pyrolysis regimen and provide additional 

supplemental data on the temperature profile at which carbon is released. 

 Total Kjeldahl Nitrogen (TKN) is a measure of organic nitrogen and ammonia in any 

form found in the samples. Total nitrogen results are determined by a heated digestion of the 
Cement Kiln Report (FINAL – 7/14/2006) 5-2

samples. The ammoniacal nitrogen is the most volatile form of nitrogen. The TKN test does not 

measure nitrite or nitrate. Since nitrate and nitrite nitrogen would not react with NOx they are of 

little interest for the feed evaluation. 

 There are some distinct differences among the feed types that are independent of the 

incinerator site or treatment. Slag is a manufactured feed material that aids burnability and so 

would be expected to reduce thermal NOx generation. It also has lower content of some of the 

key chemicals of concern for emissions control or new control technology application. For 

instance, nitrogen and total sulfur in slag is less than the amount found in wet slurry or dry 

powder, sulfate in slag and slurry less than sulfate in dry powder, and pyritic sulfur in slag is 

present at lower concentrations than pyritic sulfur in all other feed types. As a percent of total 

mass, organic sulfur tends to be higher in slag than other feed materials. There is a caveat: The 

methodology used by the laboratory lumps organic sulfur with simple sulfide (non pyrite). The 

sulfate in feed tends to be relatively constant compared to other compounds tested in the feed 

material. Site specific results of kiln feed sample chemical analysis are summarized in 

confidential attachments for each kiln site (Appendix A, B, and C, and Tables 1 through 5). 

Results are summarized in the remainder of this section. 

5.1.1 Organic Carbon 

 One set of kiln feed materials had higher organic content than all others. Organic carbon 

in these dry feed materials is much greater than in all other feed material. Organic carbon in wet 

slurry from the same site is also higher than the organic carbon in other slurry feed materials. 

One kiln dry feed material had higher total organic carbon than the others in this sample set. The 

highest carbon containing feed material also contained higher organic nitrogen. This site also 

demonstrated lower NOx emissions than other sites. Results for feed sample carbon analysis 

from this site are provided in confidential data Appendix A. 

 The lowest organic carbon content was found in dry powder limestone feed from a 

different site and supplier. The organic content in these feed materials is quite variable, Total 

nitrogen was also lower in samples from the same site. This site demonstrates higher NOx
Cement Kiln Report (FINAL – 7/14/2006) 5-3

emission than other comparable sites. Results of percent carbon analysis in feed are shown in 

confidential data Appendix B. 

 Most of the organic material in the dry feed is released between 350 and 500 oC 

indicating high molecular weight organic or pure carbon material. It was noted in the DSC data 

that some of the samples began generating heat at temperatures below 150 oC, while others only 

began above 200 oC. The higher temperatures required to liberate the carbon are a function of 

the volatility (molecular weight) of the carbonaceous material. It is not known whether this has 

any effect on NOx emissions, but could influence VOC emissions. However, NOx emissions 

were lower from the site supplying samples containing higher molecular weight carbon 

compounds. Efforts to control VOC emission should take into account the resulting oxidative 

conditions that do not favor reduction of NOx. 

 The pattern of organic combustion determined by DSC appears to be fairly similar for all 

samples, except of course the slags. Much of the exothermic activity at 400-450 oC for all kiln 

feeds is probably attributable to pyrite oxidation. In preheater or calciner kilns, this may be 

occurring in Stage 2 of the preheater. Whether this has any impact on NOx emissions is 

questionable. It is possible, of course, that nascent, freshly formed SO2 may reduce NO2. 

 The results for total heat generated during carbon analysis by the alternative nitrogen 

purged technique appear to be higher for samples containing higher molecular weight carbon. 

The heat release results for these higher carbon containing samples show characteristics 

indicating considerable amounts of char, as evidenced by the lower heating results vis-à-vis the 

DSC results on samples analyzed using both approaches. If this char is produced in the kiln, it 

may serve as a reducing agent for NOx assuming it was available in the hot zone of the process, 

or it may be oxidized to CO which itself may be acting as a reducing agent. The additional 

carbon could be a partial explanation for the very low NOx emissions at this site. 

5.1.2 Total Kjeldahl Nitrogen 

 The high carbon content feed also has the highest Total Kjeldahl Nitrogen (TKN) 

content. Dry powder feed from this site contains slightly more Total Kjeldahl Nitrogen (TKN) 
Cement Kiln Report (FINAL – 7/14/2006) 5-4

than similar dry feed materials from other sites. While the ratio of %carbon to TKN feed 

materials is approximately the same for all samples, the total carbon and TKN in wet slurry from 

sites generating higher NOx is less than that found in sites using dry powder limestone feed that 

generate lower NOx emissions. Results sorted by TKN values are shown in separate tables in 

confidential Appendices A-4, B-4, and C-4. Assuming the TKN nitrogen is the nonvolatile 

nitrogen component of the feed, it is likely to be organic based and that nitrogen and carbon are 

released in the process from the feed at approximately the same time. Such nitrogen release 

could act as a source of ammoniacal nitrogen at high temperatures, which could establish a 

quasi-”SNCR/SCR” reductive path for NO, particularly in the presence of iron based catalysts, 

which at that point in the process have not yet been converted to the ferrite phase of cement 

clinker, and so may exert a catalytic action. This is admittedly unproven. 

5.1.3 Total Sulfur 

 Total Sulfur and speciated sulfur results are shown in Appendices A, B, and C, and 

confidential Tables A-4 through C-4. Total sulfur in samples with higher carbon and nitrogen is 

generally higher than total sulfur from other kiln sites. Total sulfite in dry feed material follows 

the same trend with the highest carbon containing material also showing the highest sulfur as 

sulfite. Pyritic sulfur content in high organic samples trends higher than other kiln sites. 

5.1.4 Summary of Analytical Results 

As discussed above, the results of the testing conducted at the three Ellis County plants to 

characterize feed materials are considered confidential business information and are, therefore, 

reported in confidential attachments to this report. The table below summarizes testing results. 

All feed material is averaged together for the results below and the slag samples are omitted. 

Averaging the results from the three plants provides protection of confidentiality. As the slag 

material was understood to be obtained from only one source, this information could not be 

presented in a manner that protected confidentiality. Table 5-1.1 presents the results for both wet 

and dry feed materials averaged together, as there are only two plants running wet and two 

running dry, reporting the results of the averages of two plants’ data does not protect 

confidentiality. 
Cement Kiln Report (FINAL – 7/14/2006) 5-5

Table 5-1.1. Summary of Analytical Results on Feed Materials 

 

Carbon 

Evolution 

Temp. 

range, oC 

Total 

DH, J/g 

Organic 

% 

Organic 

Sulfur 

% 

Pyritic 

Sulfur 

% 

Sulfate 

% 

Sulfite 

% 

Sulfur 

% 

Chloride 

(Water 

Soluble) 

% 

Kjeldahl 

Nitrogen 

mg/kg 

mean NA 161.01 0.320 0.110 0.295 0.099 0.035 0.539 0.003 236.27 

std. deviation NA 51.73 0.1028 0.0346 0.0696 0.0296 0.0207 0.0782 0.0012 93.73 

range 115-630 NA NA NA NA NA NA NA NA NA 

5.2 Data from Plant Surveys

The other source of data on the composition of feed materials was an information request 

that the expert panel assisted TCEQ in preparing and forwarding to the plants. This information 

was also requested to be treated as confidential by the plants. As discussed above, data from all 

three plants was averaged to protect confidentiality. Although other data were requested and 

obtained, when less than all three plants reported a parameter, that parameter was not included in 

Table 5.2.1 to protect confidentiality. 

Table 5-2.1. Summary of Plant Reports on Feed Materials 

 Feed Composition (% wt typical) Kiln Feed Size Sulfur 

 Limestone Shale Silica Other 

Lime 

Saturation 

Factor 

Silica 

Ratio Alkali 

% + 200 

mesh weight % 

mean 88.1% 3.8% 5.8% 2.4% 100.9% 2.985 0.4927 29.5% 1.3% 

std. deviation 0.0078 0.0359 0.0238 0.0076 0.0494 0.3066 0.1153 0.2948 0.0023 

5.3 Conclusions

 Total carbon nitrogen and sulfur content seem to be major factors in the difference 

between kiln feed materials. TKN can impact NOx emissions by oxidation to NO, but also as a 

component that may reduce NO formed in the burning zone, by a reaction similar to SNCR or 

SCR. We do not know the temperature profile of organic nitrogen generation from these feeds, 

only that nitrate or nitrite nitrogen is not reflected in the values. However, process emissions 

tests from the site providing highest carbon organic nitrogen and sulfur also show the lowest 
Cement Kiln Report (FINAL – 7/14/2006) 5-6

uncontrolled NOx release. Other sites use dry powder feed material contains slightly lower levels 

of TKN but do not show the organic carbon or nitrogen content found in the lower NOx emitting 

site. 

 Feed nitrogen under high carbon loading may be released into a reducing environment 

and need not generate NO. The temperatures required for organic carbon and nitrogen release 

are too cold for authentic SNCR, and the process doesn't have the right catalysts for SCR. 

However, the low NO emissions at the site with the higher carbon in feed limestone suggest that 

these latter reactions may be occurring. One possible conclusion from the feed analysis 

information is a reaction under reducing conditions, similar to SNCR or SCR, as follows: 

CO + NO ==> CO2 + N 

12NH3 (from TKN in feed) + 8NO + 5 O2 ==> 10N2 + 18H2O 

 While this site may not have the right temperature/oxygen/CO conditions in the tower for 

SNCR to be maximally effective, there seems to be some combination of chemistry and process 

conditions occurring that reduces the NOx emissions. Further evidence of this possibility can be 

found in a paper from Zement-Kalk-Gips (German cement journal) written by M. Ono and coworkers, Japan, the authors show the effects of certain iron compounds in catalyzing the reaction 

of carbon monoxide with NO at temperatures below those usual in SNCR (the reference for this 

report has not been located). 

 It is possible that the calciner design and process conditions at the site with the lowest 

NOx emissions may be better in general or that its design may produce the right conditions for 

reduced NOx emissions with the higher carbon/higher organic nitrogen containing feed. Several 

additional feed analyses (e.g. temperature related nitrogen release, speciated metals analysis) 

coupled with measurement of gases in kiln emissions are necessary to validate this conclusion. 

 SO2 is a high-temperature scavenger for high oxygen radicals like OH and O, and may 

thereby help reduce NOx. Feed material containing higher carbon and a higher level of sulfur 

than other kiln feed materials may contribute to the reducing environment and lower NOx
Cement Kiln Report (FINAL – 7/14/2006) 5-7

emissions. The “organic sulfur” found in samples also includes sulfide (nonpyritic) sulfur. 

Sulfite is not usually present in materials taken directly from ore deposits. There is more sulfite 

in the feed at the lower NOx emission site than in the other feed from the other sites. This may 

reflect the return kiln dust and its sulfite content, which in turn may reflect the effect of oxygen 

upstream of the dust collector. If the available O2 is lower in the kiln process gas this may also 

reduce low temperature formation of NO. 
Cement Kiln Report (FINAL – 7/14/2006) 6-1

6.0 REFERENCES 

(1) US Geological Survey, Mineral Industry Survey – Cement, 2004 

http://minerals.usgs.gov/minerals/pubs/commodity/cement/ 

(2) American Society for Testing and Materials. 1998 Annual Book of ASTM Standards. 

ASTM Volume 04.01 Cement; Lime; Gypsum. West Conshohocken, PA. 1998. 

(3) Shreve, R.N., and J.A. Brink. Chemical Process Industries. Fourth Edition. New York, 

NY. McGraw Hill, Inc. 1977. pp. 156-162. 

(4) Dorris, V.K., A. Gerson, and M.McIntyre. Portland Cement Association. Cement and 

Concrete Reference Guide. Skokie IL. 1997. 

(5) U.S. Environmental Protection Agency. Alternative Control Techniques Document – NOX 

Emissions from Cement Manufacturing. EPA-453/R-94-004. Research Triangle Park, 

NC. March 1994. 

(6) Portland Cement Association. U.S. and Canadian Portland Cement Industry: Plant 

Information Summary, December 31, 1998. Skokie, IL. 214 pp. 

(7) Helmuth, R.A., F.M. Miller, T.R. O'Connor, and N.R. Greening. Kirk-Othmer 

Encyclopedia of Chemical Technology. Vol. 5. Fourth Edition. New York, NY. John 

Wiley & Sons, Inc. 1992. pp. 564-598. 

(8) Kosmatka, S.H. and W.C. Panarese. Design and Control of Concrete Mixtures, 

Thirteenth Edition. Portland Cement Association. Skokie, IL. 1994. 

(9) U.S. Environmental Protection Agency. Compilation of Air Pollutant Emission Factors. 

AP-42. Fifth Edition. Volume I - Stationary Point and Area Sources. Research Triangle 

Park, NC. January 1995. pp. 11.6-1 - 11.6-26. 

(10) Midwest Regional Planning Organization: Identification and Evaluation of Candidate 

Control Measures, prepared for The Lake Michigan Air Directors Consortium, April 

2005 

(11) Weber, Dr. Paul, Heat Transfer in Rotary Kiln with due Regard to Cyclic Processes and 

Phase Formation, Bauverlag GmbH Wiesbaden, 1963 

(12) US Environmental Protection Agency, AP-42 – Compilation of Air Pollution Emissions 

Factors, Chapter 11.6 Portland Cement Manufacturing. 

(13) Nielsen, P.B., and O.L. Jepsen. An Overview of the Formation of SOX and NOX in Various 

Pyroprocessing Systems. Presented at the IEEE Cement Industry Technical Conference 

XXXII. Tarpon Springs, FL. May 22-24, 1990. 

(14) Zeldovich, J. The Oxidation of Nitrogen in Combustion and Explosions: Acta. 

Physiochem. 21(4). 1946. 
Cement Kiln Report (FINAL – 7/14/2006) 6-2

(15) U.S. Environmental Protection Agency. Control Techniques for Nitrogen Oxide 

Emissions From Stationary Sources. Publication AP-47. National Air Pollution Control 

Administration. Washington D.C. 1970. 

(16) Shreve, R.N., and J.A. Brink, Jr. Chemical Process Industries. New York, NY. Fourth 

Edition. McGraw Hill, Inc. 1977. 

(17) Portland Cement Association. U.S. and Canadian Portland Cement Industry: Plant 

Information Summary. December 31, 1998. 1999. 

(18) Portland Cement Association. Website: 

(http://www.Portlandcement.org/env/enviro2.asp). Accessed on July 11, 2000. 

(19) Hilovsky, R.J. NOX Reductions in the Portland Cement Industry With Conversion to 

Coal-Firing. Presented at the 1977 U.S. EPA Emission Inventory/Factor Workshop. 

Raleigh, NC. September 13-15, 1977. 

(20) Gartner, E.M. Nitrogenous Emissions From Cement Kiln Feeds: Portland Cement 

Association Interim Report on Project HM7140-4330. Skokie, IL. June 1983. 

(21) Payne, R., T. Akiyama, and J.G. Witkamp. Aspects of NOX Formation and Reduction in 

Coal Fired Combustion Systems. International Flame Research Foundation. Report NOX 

F37/a/10. Ijmuiden, Netherlands. 1981. 

(22) Johansen, V., A. Egelov, and A. Eirikson. Emission of NOX and SO2, From Cement 

Clinker Burning Installations. Zement-KalkGips NOX 10. 1986. 

(23) Scheuer, A. Theoretische und betriebliche untersuchungen zur bildung und zum abbau 

von stickstoffmonoxid in zementdrehofenanlagen. Schriftenreihe der Zementindustrie, 

Heft 49. 1987. 

23(a) Huag N., Sauter G., Samant G., Einsatz der High-Dust-SCR –Technologie in der 

 Zementindustrie, VDI-Vortag, 2002.

23(b) Fischer K., Samant G., Der Kat furs Zementwerk, UmwltMagazin, Dezember, 2002. 

23(c) Anon, Erste Anlage Zur Katalytischen Entstickung in Einem Zementwerk, 

 Umweltbudesamt, July, 2003. 

(23d) Midwest Regional Planning Organization: Identification and Evaluation of Candidate 

 Control Measures, prepared for The Lake Michigan Air Directors Consortium, April 

 2005. 

(23e) C. Senior, et. al., SCR Deactivation Mechanisms Related to Alkali and Earth Elements, 

 2003 Conference on SCR and SNCR, NETL Publications, October 2003. 

(23f) Jens, B., et. al., Deactivation Mechanisms of SCR Catalysts During the Co-Combustion 
Cement Kiln Report (FINAL – 7/14/2006) 6-3

 of Bio-Residues, 2003 Conference on SCR and SNCR, NETL Publications, October 

 2003. 

(23g) Vredenbregt, L.H.J., et. al., The Effect of Co-Firing Large Amounts of Secondary Fuels 

 on SCR Deactivation, 2003 Conference on SCR and SNCR, NETL Publications, October 

 2003. 

(23h) Nielson, M. T., On the Relative Importance of SO2 Oxidation to High Dust SCR DeNOx 

 Units, 2003 Conference on SCR and SNCR, NETL Publications, October 2003. 

(23i) Linero, A. A., Letter to Sumter Cement Company, LLC, From Program Administrator, 

 Bureau of Air Regulation, Florida Department of Environmental Protection, October 7, 

 2005. 

(24) Haas, G.A. Selective Noncatalytic Reduction (SNCR): Experience with the Exxon 

Thermal DeNOX Process. Presented at the NOX Control V Conference. Council of 

Industrial Boiler Owners. Long Beach, CA. February 10-11, 1992. 

(25) Bilan Lumbres, Holcim France; “Bilan environnement et sécurité 2004“. 

(26) Lin, M.L., M.J. Knenlein, Fuel Tech Inc. “Cement Kiln NOX Reduction Experience Using 

the NOXOUT® Process,” proceedings of the 2000 International Joint Power Generation 

Conference, Miami Beach, FL, July 23-26, 2000. 

(27) Joseph, G.E., and D.S. Beachler. Student Manual, APTI Course 415 Control of Gaseous 

Emissions. U.S. EPA, Air Pollution Training Institute. EPA 450/2-81-006. December 

1981. 

(28) Campbell, L.M., D.K. Stone, and G.S. Shareef. Sourcebook: NOX Control Technology 

Data. U.S. EPA, Air and Energy Engineering Research Laboratory. EPA-600/2-91-029. 

July 1991. 

(29) Siddiqi, A.A., and J.W. Tenini. Hydrocarbon Processing. 115-124. October 1981. 

(30) Kokkinos, A., J.E. Cichanowicz, R.E. Hall, and C.B. Sedman. Stationary Combustion 

NOX Control: A Summary of the 1991 Symposium. J. Air Waste Manage. Assoc. 1252. 

1991. 

(31) Teixeira, D. Widening the Urea Temperature Window. In Proceedings of 1991 Joint 

Symposium on Stationary Combustion NOX Control. NTIS. 1991. 

(32) Kupper, D., and Brentrup, L. SNCR Technology for NOX Reduction in the Cement 

Industry. World Cement 23(3):4-9. March 1992. 

(33) Penta Engineering Corporation Report on NOX Formation and Variability in Portland 

Cement Kiln Systems Potential Control Techniques and Their Feasibility and Cost 

Effectiveness. Penta Project No. 971212. Prepared for the Portland Cement Association. 

PCA R&D Serial No. 2227. Skokie, IL. 1999. 
Cement Kiln Report (FINAL – 7/14/2006) 6-4

(34) Scheuer, A., Non-catalytic reduction of NO with NH3 in the cement burning process. 

Zement-Kalk-Gips, No. 3/1990, Wiesbaden, Germany. 

(35) European Integrated Pollution Prevention and Control Bureau (EIPPCB). Reference 

Document on Best Available Techniques in the Cement and Lime Manufacturing 

Industries. World Trade Center, Seville, Spain. March 2000. 

(36) Yee, G.M. Suggested Control Measure for the Control of Emissions of Oxides of 

Nitrogen from Cement Kilns. Presented to the State of California, Air Resources Board 

for Discussion on October 21, 1981. 

(37) Sun, William H., Nalco Fuel Tech. NOXOUT® Process Demonstration on a Cement 

Kiln/Calciner, Ash Grove Cement, Seattle Plant, Seattle, Washington. October 28, 1993. 

(38) Sun, et. al. Reduction of NOx Emissions from Cement Kiln/ Calciner through the Use of 

the NOXOUT® Process. Presented at the International Specialty Conference on Waste 

Combustion in Boilers and Industrial Furnaces. Kansas City, MO. April 1994. 

(39) Interoffice Correspondence from McAnany, L. to H. Knopfel, H, LaFarge Corporation. 

October 26, 1998. re: Fuel Tech NOXOUT® Testing. 

(40) PSM International Inc. and Penta Engineering Corp. Review of Nalco Fuel Tech 

NOXOUT® Program for Mid-Kiln Injection Urea to Reduce NOX at the Colton California 

Plant of California Portland Cement Company. October 26, 1994. 

(41) Biggs, H.O., Plant Manager, Mitsubishi Cement Corporation. Biosolids Injection 

Technology: An Innovation in Cement Kiln NOx Control. (no date). Received during 

December 1999 trip report. 

(42) Shumway, D.C. Tire Derived Fuel at Mitsubishi Cement Corporation. (no date) Received 

during December 1999 site report. 

(43) McInnes, R., and M.B. von Wormer. Cleaning Up NOX Emissions. Chem. Eng. 130-135. 

September 1990. 

(44) U.S. Environmental Protection Agency. Summary of NOX Control Technologies and Their 

Availability and Extent of Application. EPA450/3-92-004. Research Triangle Park, NC 

27711. February 1992. 

(45) Xeller, H. Reducing NOX Formation Using a Step Burner with Exit Gas Recycling from 

Preheater. World Cement. 19(3):8492. March 1988.

(46) Bauer, C. PYRO-JET Burners to Reduce NOX Emissions Current Developments and 

Practical Experience. World Cement. 21(4). April 1990.

(47) The ROTAFLAM Kiln Burner. Product Information Brochure. Procedair Industries, 

Combustion Division, Pillard Products, Louisville, KY. 1992

(48) Vollan, P., and L. Klingbeil. Modernization and Capacity Increase of Kiln Line No. 6 at 

the Dalen Plant, Norway. World Cement. January 1988.
Cement Kiln Report (FINAL – 7/14/2006) 6-5

(49) Wolter, A. Fast Gas Trace Analysis Optimizes and Reduces the Emission of Pollutants in 

Cement Plants. Zement-KalkGips No. 12, 1987.

(50) Steinbiß, V.E., C. Bauer, and W. Breidenstein. Current state of development of the 

PYRO-JET® burner. VDZ Kongress. 1993.

(51) Thomsen, K., L.S. Jensen, and F. Schomburg. FLS-Fuller ILC-lowNOx calciner 

commissioning and operation at Lone Star St. Cruz in California. ZKG International. 

October 1998. pp. 542 - 550.

(52) Letter and attachments from M.H. Vaccaro, Pillard Combustion Equipment and Control 

Systems, to G.J. Hawkins, Portland Cement Association, re: Low NOX Rotaflam® burner, 

dated January 20, 1999.

(53) PSM International, “Response to USEPA Comments, 13 September 1995, on the 

proposed alternative NOX RACT for a Portland cement manufacturing plant located in 

Thomaston, Maine and owned by Dragon Products Company,” Jan 31, 1996.

(54) Renfrew, S, Process Engineer, RMC Lonestar. Calciner modification highly effective in 

meeting Northern California Plant’s alkali reduction and emission control requirements. 

no date.

(55) Portland Cement Association and American Portland Cement Alliance. Results of the 

NOX Control Presurvey Results. January 2000. 

(56) Memorandum from Battye, R.E., and S. Edgerton, EC/R Incorporated, Chapel Hill, NC, 

to B. Neuffer, U.S. EPA, RTP, NC. Summary of February 4, 2000 teleconference to 

discuss results of NOX Control Presurvey Results. February 11, 2000.

(57) Portland Cement Association. A New Stone Age: The Making of Portland Cement. 

Skokie, IL. 1992. pg. 4.

(58) Cadence Environmental Energy, Inc. www.cadencerecycling.com.

(59) Battye, R., and S. Edgerton, EC/R Incorporated. “December 2, 1999 Trip Report to 

Mitsubishi Cement Corporation, Cushenbury Plant.” Lucerne Valley, CA. Submitted to 

Dave Sanders, US EPA, under contract No. 68-D-98-026, work assignment No. 2-28. 

August 31, 2000.

(60) Shumway, D.C. “Tire Derived Fuel at Mitsubishi Cement Corporation.” Received during 

December 2, 1999 visit to Mitsubishi.

(61) Shumway, D.C. Mitsubishi Cement Corporation’s Cushenbury Plant presented at the 

IEEE West Coast Cement Industry Conference. Victorville, CA. Oct 1995.

(62) Rother, R. and D. Kupper. Staged Fuel Supply - An Effective Way of Reducing NOX 

Emissions. Zement-Kalk-Gips. No. 9. 1989.
Cement Kiln Report (FINAL – 7/14/2006) 6-6

(63) Nielsen, P.B., and O.L. Jepsen. An Overview of the Formation of SOX and NOX In Various 

Pyroprocessing Systems. Presented at the IEEE Cement Industry Technical Conference 

XXXII. Tarpon Springs, FL. May 22-24, 1990.

(64) Facsimile from Bennett, J., California Portland Cement Company, to Damle, A.S., 

Research Triangle Institute. August 4, 1993. Process modifications in cement kilns.

(65) Benoit, M.R., E.R. Hansen, and T.J. Reese. Method for Energy Recovery from 

Containerized Hazardous Waste. U.S. Patent No. 4974529. December 1990.

(66) Walquist, C., Cadence Environmental Energy. “Cadence system leads to fall in NOX 

emissions,” World Cement, Dec 1997, pp. 26, 27.

(67) Cadence Environmental Energy and Ash Grove Cement. “Mid-Kiln Fuel Entry Benefits,” 

section 3 of the report, Emission, Reduction, Technology: Resource Conservation & 

Recovery. (no date).

(68) Hansen, E.R. New Way to Burn Hazardous Waste. Rock Products. April 1990.

(69) Letter from Edgerton, S. and T. Stobert, EC/R Inc., to Bill Neuffer, EPA, Feb 8, 2000. 

Minutes from Dec 16, 1999 meeting with representatives from EPA and Cadence.

(70) Texas Natural Resources Conservation Commission. A list of permitted NOX levels for 

cement plants in the state, CEMS data as reported by the facilities for 1994 - 1999, and 

information on the control technology in use at each facility. 

(71) May, M. and L. Walters, Jr. "Low NOX & Tire-derived Fuel for the Reduction of NOX 

from the Portland Cement Manufacturing Process." Cement Americas, August 1999, pp. 

10-1. 

(72) Letter and attachments from Bramble, Kim, Cadence, to Bill Neuffer, USEPA, re: NOX 

Emission Reducing Technology, dated Feb 14, 2000. 

(73) Radian Corporation, "MDE Air Permit Test Report for Lehigh Portland Cement 

Company, Union Bridge, Maryland Facility," January 1996.

(74) Email transmission from Hawkins, G., PCA, Skokie, IL to B. Neuffer, U.S. EPA. Results 

of PCA Survey - Preliminary NOX Control Technology Questionnaire. January 2000.

(74a) The BOC Group-LoTOxTM. 

http://www.boc.com/markets/environment/bulk_gasses/lotox.asp. 

(74b) “Pilot Demonstration Testing of LoTOxTM Report” EPRI: Pilot Demonstration Testing of 

 LoTOxTM. http://www.epri.com//OrderableitemDesc.asp?product_id=0000000. 

(74c) “Innovative Clean Air Technology Grant Report Low Temperature Oxidation System 

 Demonstration.” RSR Quementco, Inc., City of Industry, California. BOC Process Gas 

 Solutions, 575 Mountain Avenue Murray Hill, NJ 07974. Event: 2000-12-08 
Cement Kiln Report (FINAL – 7/14/2006) 6-7

 Demonstration for Low Temperature Oxidation. 

http://www.arb.ca.gov/research/icat/projects/boc.htm. 

(74d) “Status of Multi-Pollutant Process Development: LoTOx/BOC, GSA/FLS, Pahlmanite 

 Cost Projections Report”. EPRI: Status of Multi-Pollutant Process Development: 

 LoTOx/BO... http://www.epri.com/OrderableitemDesc.aps?product_id=0000000. 

(74e) “Multi-Pollutant Control Technologies: cost Projections of LoTOx/BOC, GSA/FLS, and 

 Pahlmanite.” EPRI: Fossil Steam Plants & Combustion Turbines>Integrated En... 

 http://www.epri.com/targetHigh.asp?program=262194&value=03... 

(74f) “Status and Performance of Best Available Control Technologies Report” EPRI: Status 

 and Performance of Best Available Control Technologies. 

http://www.epri.com//OrderableitemDesc.asp?product_id=0000000/. 

(74g) “A Report on the Application of Low Temperature Oxidation for Control of NOx 

 Emissions.” R. Ferrell, N. Suchak, S.C. Hwang, J. Tsens, R. Kelton. The BOC Group, 

 Inc., Process Gas Solutions 575 Mountain Ave., Murray Hill, NH 07974. W. Goss, 

 Beaumont Environmental Systems 108 Lintel Drive, McMurray, PA 15317. R. Lutwen, 

 SFT, Inc. 6629 W. Central Ave., Toledo, OH 43617 

(74h) “Low Temperature Oxidation System Demonstration at RSR/Quemetco, Inc. City of 

 Industry, California. http://www.arb.ca.gov/research/icat/projects/boc.htm. 

(74i) “LoTOXTM Technology Demonstration at Marathon Ashland Petroleum LLC’s Refinery 

 in Texas City, TX.”Marathon Ashland Petroluem LLC, Jeffrey Sexton, 539 South Main 

 St., Findlay, OH 45840. Belco Technologies Corporation, Nicholas Confuorto, 7 Entin 

 Rd., Parsippany, NJ 07054. BOC Process Gas Solutions, Michael Barrasso/Naresh 

 Suchak, 575 Mountain Avenue, Murray Hill, NJ 07974. 

(74j) “Applications and Economics of Low Temperature Oxidation NOx Control.” BOC Gases 

 575 Mountain Avenue Murray Hill, NJ 07974. M.H. Anderson, R.J. Ferrell, Dr. S.C. 

 Hwang, Dr. N. Suchak, Dr. James Tseng, R. Kelton 

(74k) “Application of Low Temperature Oxidation for NOx Emissions Control on a Lead 

 Recovery Furnace.” R. Ferrell RJF Consultants 196 Hollister Avenue, Rutherford, NJ 

 07070. Dr. N. Suchak, R. Kelton The BOC Group, Inc., Process Gas Solutions 575 

 Mountain Ave., Murray Hill, NJ 07974. H. Hine, RSR Corporation, Dallas, TX M. 

 Vondersaar, Quemetco, Inc., City of Industry CA. Shyam Nadkarni, 144 Woodmere 

 Blvd., Woodmere, NY 11598. 

(74l) “New Process and Equipment for Waste Minimization: Conversion of Nitrogen Oxide 

 (NOx) Scrubber Liquor to Fertilizer.” Conversion of Nitrogen Oxide (NOx) Scrubber 

 Liquor to Fertilizer. http://rtreport.ksc.nasa.gov/techreports /95 report/environf/environ0. 

(74m) “Using Non-Thermal Plasma to Control Air Pollutants.” EPA-456/R-05-001. The Clean 

 Air Technology Center (CATC). U.S. Environmental Protection Agency (E143-03). 

 Research Triangle Park, North Carolina 27711. 
Cement Kiln Report (FINAL – 7/14/2006) 6-8

(74n) “ETV for Add-On NOx APT Update.” Douglas VanOsdell. 

(74o) “Nitrogen Oxides (NOx) Abatement With Hydrogen Peroxide.” Reference 

 Library/Applications: Industrial Wastewater 

http://www.h2o2.com/applications/industrialwastewater/nox.html

(74p) “Kinetics of NOx Absorption into Aqueous Solutions of Oxone.” Kinetics of NOx 

 Absorption into Aqueous Solutions of Oxone. 

http://aiche.confex.com/aiche/2005/techprogram/P15564.HTM

(75) Helmuth, R.A., F.M. Miller, T.R. O'Connor, and N.R. Greening. Kirk-Othmer 

Encyclopedia of Chemical Technology. Vol. 5. Third Edition. New York, NY. John Wiley 

& Sons, Inc. 1979. pp. 163-193.

(76) Yee, G.M. Suggested Control Measure for the Control of Emissions of Oxides of 

Nitrogen from Cement Kilns. Presented to the State of California, Air Resources Board 

for Discussion on October 21, 1981.

(77) Miller, F.M. Oxides of Nitrogen. GTC Presentation, Kansas City, MO, September 20, 

1977.

(78) Hansen, E.R., “The Use of Carbon Monoxide and Other Gases for Process Control,” 27th 

IEEE Cement Industry Technical Conference Proceedings, May 1985.

(79) Mehta, P.K. Energy, Resources and the Environment - A Review of the U.S. Cement 

Industry. World Cement Technology. July/August 1978.

(80) Andover Technology Partners. NOx Reduction from Cement Kilns Using the CemStar 

Process, Evaluation of CemStar Technology - Final Report to Texas Industries. Dallas, 

Texas. April 18, 2000.

(81) Battye, R., and S. Edgerton, EC/R Incorporated. “December 2, 1999 Trip Report to Texas 

Industries (TXI) Riverside Cement, Oro Grande facility.” Oro Grande, CA. Submitted to 

Dave Sanders, US EPA, under contract No. 68-D-98-026, work assignment No. 2-28. 

August 31, 2000.

(82) En-tellect Environmental Services, Inc., “Evaluation of the Effects of the CemStar 

Process on a Wet Process Cement Kiln,” (no date, but includes data for July-Sept 1999).

(83) Hilovsky, R.J. NOX Reductions in the Portland Cement Industry With Conversion To 

Coal-Firing: Presented at the 1977 U.S. EPA Emission Inventory/Factor Workshop. 

Raleigh, NC. September 13-15, 1977. 

(84) Radian Canada, Inc. Assessment of NOX Emission Control Technologies for Cement and 

Lime Kilns. Radian Report No. 714-061-01. Prepared for Environment Canada, Contract 

No. K2035-3-7044. October 1994. Pg.iv.
Cement Kiln Report (FINAL – 7/14/2006) 6-9

(85) Portland Cement Association. U.S. and Canadian Portland Cement Industry Plant 

Information Summary. Skokie, IL. December 31, 1998.

(86) Penta Engineering Corporation Report on NOX Formation and Variability in Portland 

Cement Kiln Systems Potential Control Techniques and Their Feasibility and Cost 

Effectiveness. Penta Project No. 971212. Prepared for the Portland Cement Association. 

PCA R&D Serial No. 2227. Skokie, IL. 1999.

(87) Comments on Alternative Control Techniques Document - NOX Emissions from Cement 

Manufacturing submitted by Greer, W.L. to William Neuffer, U.S. EPA through T.B. 

Carter, APCA. October 27, 1999.

(88) Worrell, Ernst and Galitsky, Christina, “Energy Efficiency Improvement Opportunities 

for Cement Making An ENERGY STAR Guide for Energy and Plant Managers”, Energy 

Analysis Department, Environmental Energy Technologies Division., Ernest Orlando 

Lawrence Berkeley National Laboratory, University of California, January 2004. 

(89) Birch, E., “Energy Savings in Cement Kiln Systems” Energy Efficiency in the Cement 

Industry, London, England, 1990. 

(90) Fujimoto, S., “Modern Technology Impact on Power Usage in Cement Plants, 1994. 

(91) Hendriks, C.A., E. Worrell, D. de Jager, K. Blok, and P. Riemer. 1998. Emission 

Reduction of Greenhouse Gases from the Cement Industry Lawrence Berkeley National 

Laboratory, Berkeley, California. IEA. 

(92) COWIconsult, Internahsauon and the External Cost of Transport Lyngby, Denmark 

Danish Ministry of Energy, EFP-91, 1993. 

(93) Young, Gerald L. “Review of NOx Control Technologies for Cement Kilns, Associated 

Costs and NOx Reduction Efficiencies, 2002. 

(94) COWIconsult, Internahsauon and the External Cost of Transport Lyngby, Denmark 

Danish Ministry of Energy, EFP-91, 1993. 

(95) Jaccard and Willis Energy Services, “Industrial Energy End-Use Analysis and. 

Conservation Potential in Six Major Industries in Canada, 1996. 

(96) Venkateswaran, SR and HE Lowitt, “The US Cement Industry: an Energy Perspective, 

DOE, Washington, DC, USA, 1988. 

(97) Anonymous, “Cement Plant Modernization in Central Europe,” World Cement, 

November 1994. 

(98) Vleuten, Cement in Development: Energy and Environment. Petten, Netherlands: 

Netherlands Energy, 1994. 

(99) van Oss, US Geological Survey, Communication with authors (see reference 88) , 1999. 
Cement Kiln Report (FINAL – 7/14/2006) 6-10

(100) Nisbet, M., 1996. “The Effects of New Climate change Commitments on Energy 

Intensive Industries, The Cement Industry”, 1996. 
Cement Kiln Report (FINAL – 7/14/2006) 

Attachment A 

ERG SUMMARY OF EPA 2000 NOx CONTROLS FOR CEMENT KILNS 
Attachment A – Table A-2 

Table A-1. Summary of EPA Reported NOx Control Technologies for Cement Kilns – EPA 

NOx Control Strategies Applicability 

NOx Reduction 

Efficiency (%) Estimated Costs 

Excess air and temperature optimization (using CO and O2 CEMS and feedback 

control) 

All kiln types 15a Capital cost = ~$750,000s 

Reduce alkali content of feed where feasible 

All kiln types Not available Not available 

CemStar (addition of steel slag) 

All kiln types although higher NOx

reductions expected from wet and long-dry kilns due to greater heat input offsets 

9 - 60b Capital cost = $200,000 - 

$500,000tAnnual costs are highly site-specific (e.g., slag injection rate, potential cossavings due to increased production) 

Fuel switching (natural gas to coal) 

All kiln types 70c Not available 

Process modifications 

Improving thermal efficiency 

All kiln types Not available Not available 

Staged air combustion - staged fuel combustion 

All kiln types (most effective with indirect fired kilns) 

Not available Not available 

Staged air combustion - flue gas recirculation 

May not be suitable for cement kilns. 

Incorporation of FGR in a cement kiln also results in somewhat increased power consumption and reduced kiln output. 

Not available Not available 

Staged air combustion - flue gas recirculation w/low-NOx burner 

 15 - 38d Not available 

Combustion modification 

Staged air combustion - Low-NOx burner 

All kiln types (burners that use 5-7% excess air are only for indirect-fired kilns) 

44e

15 - 33f 

23 - 47g

14h

Capital cost = $511,000 - $966,000u

Annual cost = $136,000 - $204,000u
Attachment A – Tables A-1 (continued) 

Cement Kiln Report (FINAL – 7/14/2006) 

NOx Control Strategies Applicability 

NOx Reduction 

Efficiency (%) Estimated Costs 

Staged fuel combustion - Tire-derived fuel (TDF) 

All kiln types 30 - 40i 

Staged fuel combustion - Low-NOx precalciner 

Not applicable to preheater kilns that f ire fuel in the riser 

<46j Not available 

Combustion modification (cont.) 

Staged fuel combustion - Mid-kiln firing 

Wet and long-dry kilns 38k

11 - 55l

28 - 59m

Capital cost = ~ $3,000,000vAnnual cost = ($370,000) - $189,000v

Selective catalytic reduction (SCR) 

No cement kilns had SCR at the time of the EPA Study prior to 2000. 

 Not available in 2000. 

Selective non-catalytic reduction (SNCR) 

Best application is for preheater/ precalciner kilns. Generally not applicable to long-dry or wet kilns 

71 -98n

10-20o

Not available 

Biosolids (SNCR) Preheater/precalciner kilns Not available Capital cost = $240,000w

Annual cost = ($322,000)w

NOxOUT (SNCR) Preheater/precalciner kilns > 50 - 90p

10 - 20q

46 - 53r

Capital cost = ~$1,200,000x

Annual cost = $560,000 - $2,000,000x

Postformation removal 

Low Temperature Oxidation (LoTOxTM, Hydrogen Peroxide, OXONE (Dupont) & Sodium Acetate) 

Oxidation technologies were not discussed or considered in the EPA 2000 report. 

Not considered Not considered 

aResults based on experimental test on one kiln. bResults derived from short- and long-term tests on two different kiln types. cResults based on emission tests of dry kilns. dResults based on a single 1988 study. The percent reduction depends on degree of flue gas recirculation. eResults based on emission tests of a preheater/precalciner kiln. fResults based on emission tests of five kilns. gResults based on emission tests of four kilns. 
Attachment A – Tables A-1 (continued) 

Cement Kiln Report (FINAL – 7/14/2006) hEmission test of one kiln. iResults based on tests conducted at one California facility. jResults based on a test conducted by the Portland Cement Association. kResults based on one study. lResults based on testing of seven dry kilns. mResults based on testing of three wet kilns. nBased on emission tests of a preheater/precalciner kiln at one facility. oResults based on emission test at one facility pResults based on emission tests of a single kiln. qResults based on a emission tests of a single kiln (operating conditions during most of the test were unstable). rResults based on emission test of two kilns. sEstimate for a commercially available process control system. tCost estimates obtained from Texas Industries (TXI). uCosts derived for retrofitting low-NOx burners to eight model kilns with clinker production capacities ranging from 25 to 150 tons of clinker per hourvCosts derived for retrofitting low-NOx burners to four model kilns with clinker production capacities ranging from 25 to 50 tons of clinker per hour. 

credit associated with using tire-derived fuel. 

wCosts based on a clinker production rate of 215 tons per hour. xCosts based on two preheater/precalciner kilns with a clinker production rates of 92 tons per hour and 133 tons per hour. 
Cement Kiln Report (FINAL – 7/14/2006) 

ATTACHMENT B 

SAMPLING PLAN
Cement Kiln Report (FINAL – 7/14/2006) B-1

Sample Acquisition and Handling

Clean, clear, pre-labeled, one (1) liter sample bottles were shipped to each Kiln site on August 

23, 2005 via Federal Express. The nine (9) samples returned on August 25 in good condition 

from Texas Industries Inc. included three wet slurry, three dry powder and three slag samples. 

The six (6) samples returned from Ash Grove Cement on August 26 included three (3) wet slurry 

and (3) slag samples. The 6 samples returned from Holcium on August 31 included three (3) 

samples from line 1 and 3 samples from line 2. 

All were samples returned to ERG’s analytical laboratory with chain of custody and security 

seals. ERG consulted with three cement kiln experts, F. MacGregor Miller, Gabriel Miller, and 

David Gossman on the analyses required to determine key features of the kiln feed chemistry 

important to NOx emissions and control. Recommendations were sought from the experts on 

laboratories experienced in each analysis. Three laboratories were ultimately selected on the 

basis of expertise and price. Table 1 summarizes the analyses requested for each sample. 

ERG repackaged samples for distribution to the specialty analysis laboratories scheduled to 

perform feed material composition analysis. Repackaged samples were give unique 

identification numbers to keep Kiln identity anonymous to the analysis laboratories.
Cement Kiln Report (FINAL – 7/14/2006) B-2

Table B-1. Feed Chemical Composition

Plant Name 

Samples 

Received Sample Type 

Total 

Sulfur Sulfate Sulfite 

Pyritic 

Sulfur 

Organic 

Sulfur Chloride 

Texas Industries Inc (TXI) 

3 Wet Slurry X X X X X X 

Texas Industries Inc (TXI) 

3 Dry Powder X X X X X X 

Texas Industries Inc (TXI) 

3 Slag X X X X X X 

Holcim US Inc 0 Dry Power Line 1 X X X X X X Holcim US Inc 0 Dry Power Line 2 X X X X X X Ash Grove Cement Inc 

3 Wet Slurry X X X X X X 

Ash Grove Cement Inc 

3 Slag X X X X X X 
Cement Kiln Report (FINAL – 7/14/2006) 

ATTACHMENT C 

ERG Report on LoTOxTM Application to Refineries 
Cement Kiln Report (FINAL – 7/14/2006) 

1 

ERG Report - Refinery Application of Low Temperature Oxidation Emissions 

Controls 

LoTOxTM

LoTOxTM is a trademark of the BOC Group Inc. for an end-of-pipe process that uses ozone to 

oxidize insoluble species of NOx, such as NO and NO2, to highly soluble species, primarily 

N2O5. N2O5 then reacts with moisture in the flue gas to form nitric acid (HNO3) and is removed 

from the gas in a wet gas scrubber. LoTOxTM is a developing technology for NOx control, and 

there are currently only about three commercial applications of LoTOxTM. Another three 

installations are planned in the next two years. LoTOxTM has been demonstrated using 

slipstream testing at ten types of facilities, including a smelting plant, a glass furnace, a lead 

furnace, a petroleum coke and high sulfur coal fired boiler, a chemical plant, a steel pickling bath 

process, a gas-fired boiler, a composite fuel fired boiler, a petroleum refinery fluid catalytic 

cracking unit (FCCU), and a lignite-fired boiler. No cement plants have tested LoTOxTM. 

In the LoTOxTM process, ozone is formed from oxygen using a corona-discharge ozone 

generator. The resulting concentration of ozone is between 7 and 15 weight percent (1). The 

ozone/oxygen mixture is injected into the flue gas stream as it enters either a wet gas scrubber or 

a reaction vessel adjacent to a wet gas scrubber. The ratio of ozone to NOx is 0.2-2.8:1, and 

varies with factors such as flue gas temperature and residence time. The principal reactions for 

NOx oxidation are: 

NO + O3 → NO2 + O2

2 NO2 + O3 → N2O5 + O2

N2O5 + H2O → 2 HNO3

The maximum temperature for the oxidation reactions is 325 °F (163 °C), while the optimal 

temperature is generally less than 300 °F (149 °C). The NOx oxidation reactions become 

unstable over 325 °F. Trials at a coal-fired power plant and a steel pickling process found the 

optimal temperature was in the range of 160 to 250 °F (1). A trial at a battery lead recovery 

furnace found the optimal temperature was 175 °F or less, although the temperature could be 

increased up to 225 °F without sacrificing NOx removal, but at the cost of increased ozone 

demand (2). A trial at Marathon Ashland Petroleum’s (MAP) Texas City refinery FCCU found 

the optimal temperature was 140 to 150 °F (3). These temperatures are lower than typical 

cement kiln flue gas temperatures. In addition to cooling using heat recovery systems, 

quenching with water is typically used to lower the gas temperature to the adiabatic saturation 

temperature. 

After NOx is oxidized to N2O5, it is absorbed from the flue gas by water spray in a wet gas 

scrubber. The relative solubility of N2O5 compared to other flue gas species is presented below. 
Cement Kiln Report (FINAL – 7/14/2006) 

2 

Relative Solubility of Flue Gas Components 

Species Relative Solubility at 25 °C 

NO 1 

NO2 20 

SO2 2000 

N2O5 >>2000 

HNO3 Mixes with water in all proportions 

Ferrell 2003, p. 4 

N2O5 reacts immediately and irreversibly with water to form nitric acid. The nitric acid then is 

neutralized with caustic or lime in the scrubber liquor to form sodium or calcium nitrates. 

Potential Advantages of LoTOxTM

The potential advantages of LoTOxTM are as follows. 

LoTOxTM can provide a high degree of NOx removal. Based on slipstream testing, 70 

to 90 percent NOx removal is typical, with greater than 95 percent NOx removal 

achievable.

LoTOxTM can respond quickly to variable NOx emissions. Since ozone is produced on 

demand, changes in NOx load can be met without loss of NOx removal efficiency. 

Swings in NOx concentration by 100 percent or more over the course of minutes have 

been accommodated using combined feed-forward/feed-back control schemes (Ferrell 

2000, pp. 8-9; Ferrell 2003, pp. 13-14). Although most LoTOxTM trials have been for 

combustion processes (90:10 NO to NO2 ratio), the steel pickling process had variable 

NO to NO2 ratios, with NO2 sometimes higher than NO. Ozone production was 

decreased since less ozone was required to oxidize NOx to N2O5, while NOx removal was 

maintained above 95 percent (1). 

LoTOxTM does not emit excess reactant. Unlike SCR and SNCR, which can emit 

excess ammonia, the ozone that does not react with NOx in the LoTOxTM process is 

scavenged by sulfite in the scrubber solution. A trial at a lead furnace examined the 

potential for unreacted ozone to be emitted from the process. It was found that the ozone 

addition had to be increased by a factor of eight over what was required for NOx removal 

to cause 0.6 ppm of ozone to be measured in the stack gas (2). 

LoTOxTM is highly selective for NOx. Although ozone can oxidize SO2 and CO, the 

presence of SO2 and CO does not impact NOx removal. This is due to the faster reaction 

rates for NOx oxidation compared to oxidation of other gas species. 
Cement Kiln Report (FINAL – 7/14/2006) 

3 

Relative Reaction Rates of Flue Gas Components with Ozone

Species Relative Reaction Rates 

NO + O3 → NO2 + O2 62,500 

2 NO2 + O3 → N2O5 + O2 125 

SO2 + O3 → SO3 + O2 5 

CO + O3 → CO2 + O2 1 

Ferrell 2003, p. 3 

LoTOxTM does not interfere with other pollution control technologies. The trial at 

MAP’s Texas City refinery FCCU indicated LoTOxTM does not have a negative impact 

on SO2 scrubbing efficiency. The scrubber maintained SO2 removal in excess of 99 

percent during the LoTOxTM trial (3).

Areas of Concern 

Wet Gas Scrubber Required 

A wet gas scrubber is necessary to take advantage of the increased solubility of N2O5

over NO and NO2. For cement plants with an existing wet gas scrubber for SO2 and 

particulate matter removal, LoTOxTM can be installed as an upstream retrofit. For plants 

that do not require a scrubber for SO2 or particulate matter removal, installing a scrubber 

for NOx removal only may not be cost effective. 

Gas Temperature 

Cement kiln flue gases typically have temperatures greater than the LoTOxTM maximum 

temperature of 325 °F. If the flue gas temperature is greater than 325 °F after useful heat 

has been recovered, quenching with water is required prior to ozone injection. BOC 

indicates that water quenching can be used on gas streams with temperatures up to 650 °F 

and moisture contents of 30 to 35 percent. 

Nitrates in Wastewater 

Sodium nitrate is typically the primary byproduct of the LoTOxTM process. This may be 

a concern for treatment and/or discharge of the wastewater. MAP examined the possible 

problems of increased nitrates in the study at the Texas City refinery (3). Regarding 

sodium toxicity, MAP found that the contribution of sodium nitrate from LoTOxTM was 

small compared to sodium sulfate from SO2 scrubbing. Regarding wastewater treatment 

impacts, monovalent cations, such as sodium, can have a destabilizing effect on 

bioflocculation by displacing divalent cations, such as calcium or magnesium. This can 

lead to decreased biofloc settling and increased suspended solids. This problem does not 

occur if the monovalent to divalent cation ratio is maintained at 2:1 or less (by addition of 

divalent cations if necessary). In addition, nitrogen gas produced by denitrification in the 

secondary clarifier sludge bed can cause the bed to rise, increasing suspended solids. In 

this case, a holding tank can be installed to shift the denitrification reactions out of the 

secondary clarifier.
Cement Kiln Report (FINAL – 7/14/2006) 

4 

Cost 

BOC indicates NOx removal of 70 percent or greater must be required for LoTOxTM to be cost 

effective. In ERG’s experience, the estimated cost effectiveness for LoTOxTM installations at 

refineries has ranged from approximately 2,500 to 10,000 dollars per ton of NOx (as NO2) 

removed. In general, the cost per ton of NOx removed was lower for units with high NOx

removal (greater than 85 percent), due to economy of scale. Similarly, the annual operating cost 

was at least 50 percent of the total annualized cost for those units with the lowest cost per ton of 

NOx removed. The costs of oxygen and electricity for the ozone generator accounted for 80 to 

90 percent of the annual operating costs. 

For a 200 MW coal-fired power plant, BOC estimated the cost to be only 1,696 dollars per ton of 

NOx removed (1). This application was designed for 95 percent NOx removal, and the annual 

mass of NOx removed was 4 to 46 times larger than the refinery applications. 

References Cited 

(1) (Ferrell 2000). Ferrell, R., M.H. Anderson, S.C. Hwang, N.J. Suchak, R. Kelton, J.T. 

Tseng. “Applications and Economics of Low Temperature Oxidation NOx Control.” 

Paper presented at Power-Gen 2000, November 14, 2000, Orlando, FL. 

(2) (Ferrell 2003). Ferrell, R., N. Suchak, R. Kelton, H. Hine, Shyam Nadkarni. 

“Application of Low Temperature Oxidation for NOx Emissions Control on a Lead 

Recovery Furnace.” Paper presented at ACE 2003, June 22-26, 2003, San Diego, CA. 

(3) (Sexton 2004). Sexton, J., N. Confuorto, M. Barrasso, N. Suchak. “LoTOxTM 

Technology Demonstration at Marathon Ashland Petroleum LLC’s Refinery in Texas 

City, Texas.” Paper presented at NPRA Annual Meeting, March 21-23, 2004, San 

Antonio, TX.
Cement Kiln Report (FINAL – 7/14/2006) 

5 

ATTACHMENT D 

SUMMARY OF CURRENT US REGULATIONS FOR NOx 
Cement Kiln Report (FINAL – 7/14/2006) 

1 

Table D-1. Summary of US NOx Control Regulations for Cement Kilns – EPA 2004 

State 

Effective Date 

Source Type Description Emission Limit Applicability Avg. Time Test/CEM 

NY 5/1/03 

NOx Budget Trading Program 

EGUs ≥ 15 MW; non EGUs ≥250mmBtu/hr; Portland Cement Plants ≥250mmBTU/hr 

Allowances & Trading Program 

All statewide 

Ozone season CEM 

05/31/95 

Portland cement kilns 

Sources with PTE 25 TPY in NYC and lower Orange county metro areas; PTE 100 TPY elsewhere in State 

Analysis of RACT controls; select control; NY approves RACT emission limit & submits to EPA as a SIP revision 

MD 11/24/03 

Cement kilns 

Capacity no more than 600,000 TPY 0.5 tons per hour 

30 day rolling avg CEM 

11/24/03 

Capacity greater than 600,000 TPY 0.9 tons per hour 

30 day rolling avg CEM 

 05/1/03 

Nontrading source Cement Kilns 

Long wet-6.0 lb./T of clinker;long dry5.1;preheater/precalciner or pre-calciner-2.8 CEM 

PA Proposed Cement Kilns 

LNB or mid-kiln firing or alt. that achieves 30% reduction Statewide Season CEM 

AL 04/06/01 

Cement kilns 

Long dry -12 TPH; Long wet - 10TPH;Preheater16TPH ; Precalciner & PH/PC-22 TPH 

LNB or mid-kiln firing or equivalent controls 

Various counties 

Ozone season 

KY 08/15/01 

Cement kilns 

Process rates at least(TPH)-long dry12;long wet10;preheater16;PH/PC-22 6.6 lbs./T of clinker Statewide 30 day rolling avg- ozone season CEM 
Cement Kiln Report (FINAL – 7/14/2006) 

2 

Table D-1. Summary of US NOx Control Regulations for Cement Kilns – EPA 2004 

SC 05/31/04 

Cement kilns 

Process rates at least(TPH)-long dry12;long wet10;preheater16;PH/PC-22 or NOx>1 TPD 

LNB or mid-kiln firing or similar controls 

All Statewide 

ozone season 

CEM or annual source test 

Early Action Compact (EAC) Cement kilns 

LNB or equivalent capable of achieving 30% reduction 

TN 05/31/04 

Cement kilns 

Process rates(TPH) at least-long dry12;long wet10;preheater16;PH/PC-22 LNB or mid-kiln firing or similar controls or RACT Statewide ozone season 

IL 05/30/04 

Cement kilns 

Long dry kilns at least 12 TPH 

5.1 lb./T or 30% reduction or LNB or mid kiln firing Statewide 

Ozone season 

Annual stack test 

05/30/04 

Cement kilns 

Long wet kilns at least 10 TPH 

6.0 lb./T or same as above Statewide 

Ozone season 

Annual stack test 

05/30/04 

Cement kilns 

Preheater kilns at least 16 TPH 

3.8 lb./T or same as above Statewide 

Ozone season 

Annual stack test 

05/30/04 

Cement kilns 

Preheater/precalciner kilns at least 22 TPH 

2.8 lb./T or same as above Statewide 

Ozone season 

Annual stack test 

IN 08/04/97 

Emission limits 

Cement kilns - long dry-at least 20 TPH 

Daily – 10.8 lb./T; Rolling 30 day - 6.0 lb./T 

Clark, Floyd Cos;may avg among plants statewide under same owner 

ozone season CEM 

08/04/97 

Preheater kilns at least 20 TPH 

Daily - 5.9 lb./T; Rolling 30 day – 4.4 lb./T 

Same as above 

ozone season CEM 
Cement Kiln Report (FINAL – 7/14/2006) 

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Table D-1. Summary of US NOx Control Regulations for Cement Kilns – EPA 2004 

03/01/04 

Reduction - certain categories 

Cement kilns - long dry at least 12 TPH;long wet- 10 TPH 

5.1, 6.0 lb./T or LNB or mid kiln firing or 30%control Statewide 

ozone season 

CEM unless LNB or mid-kiln 

03/01/04 

Preheater kilns at least 16 TPH;precalciner and PH/PC - 22 TPH 

3.8, 2.8 lb./T; same as above Statewide 

ozone season 

same as above 

MI 12/04/02 

Non SIP Call Cement kilns 

LNB or mid-kiln or 25% red from 1995 Statewide 

ozone season 

12/04/02 

Cement kilns 

Long dry -12 TPH; Long wet - 10TPH;Preheater16TPH 

LNB or mid-kiln or long wet - 6.0 lbs./T; long dry - 5.1 lbs./T Fine grid 

ozone season 

Annual stack test or CEM 

12/04/02 

Cement kilns 

Precalciner & PH/PC-22 TPH 

Preheater - 3.8 Lb/T; PH/PC-2.8 lb./T or 30%red Fine grid 

ozone season 

OH 04/30/04 

Cement kilns 

Long dry -12 TPH; Long wet - 10TPH;Preheater16TPH LNB or mid-kiln firing or similar controls Statewide ozone season 

Annual stack test or CEM 

04/30/04 

Cement kilns 

Precalciner & PH/PC-22 TPH 

LNB or mid-kiln firing or similar controls Statewide 

ozone 

season 

Annual stack test or CEM 

TX * 03/27/03 

Cement kilns Wet kilns 6.0 lb./T of clinker 

Bexar, Hays, Comal and McLennan Cos 

30 day rolling avg 

CEM or PEMS 

03/27/03 

Cement kilns Wet kilns 4.0 lb./T Ellis Co. 

30 day rolling avg 

CEM or PEMS 

03/27/03 

Cement kilns Long dry kilns 5.1 lb./T 

Bexar, Hays, Comal and McLennan Counties 

30 day rolling avg 

CEM or PEMS 
Cement Kiln Report (FINAL – 7/14/2006) 

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Table D-1. Summary of US NOx Control Regulations for Cement Kilns – EPA 2004 

03/27/03 

Cement kilns Preheater kilns 3.8 lb./T 

Above counties 

30 day rolling avg 

CEM or PEMS 

03/27/03 

Cement kilns 

Preheater/precalciner or precalciner kilns 2.8 lb./T 

Above counties 

30 day rolling avg 

CEM or PEMS 

SCAQMD 07/01/86 

Cement kilns Any gray cement kiln 11.6 lbs./T; 6.4 lbs./T Districtwide 

24 cons. Hrs/30 consecutive days 

TPH refers to tons of clinker per hour of cement production. * Texas has the option of complying with the following technical standard: Each long wet or long dry kiln for which the following controls are installed and operated during kiln operation is not required to meet the NOx emission limits of subsection (a) of this section, provided that each owner or operator choosing this option submits written notification of this choice to the executive director, the appropriate regional office, and any local air pollution control program with jurisdiction before the appropriate compliance date in §117.524 of this title: (1) a low-NOx burner and either: (A) mid-kiln firing; or (B) some other form of secondary combustion achieving equivalent levels of NOx reductions; or alternatively; (2) other additions or changes to the kiln system achieving at least a 30% reduction in NOx emissions, provided the additions or changes are approved by the executive director with concurrence from EPA. (d) Each preheater or precalciner kiln for which either a low-NOx burner or a low-NOx precalciner is installed and operated during kiln operation is not required to meet the NOx emission limits of subsection (a) of this section. Each owner or operator choosing this option shall submit written notification of this choice to the executive director, the appropriate regional office, and any local air pollution control program with jurisdiction before the appropriate compliance date in §117.524 of this title. ERG reviewed US EPA’s Summary of State / Local NOx Regulations for Stationary Sources and selected and reviewed those control m

kilns to create this table. This file is locate at : www.epa.gov/ttn/naaqs/ozone/ozonetech/statenoxregs518.pdf