1

**Date:** March 6 , 2013 **Subject :**  Development of Background Information on Proposed Area Source Emissions

Li mit
- Determination of GACT for Wool Fiberglass Furnaces at Area Sources EPA Contract No. EP - D - 11 - 084 ; EPA Wo rk Assignment No. 1 - 07 RTIProject No. 021 3199 .00 1.07 **From:** Cindy

Hancy Dave Reeves **To:** Susan Fairchild, EPA/OAQPS/SPPD/MMG **I. Introduction** Section 112(k) of the Clean Air Act requires the U.S. Environmental Protection Agency (EPA) to develop standards for area sources which account for 90 percent of the emissions in urban areas of the 33 urban hazardous air pollutants (HAP) listed in EPA’s Integrated Urban Air Toxics Strategy . These area source standards can require emission control levels that are equivalent to generally

achievable control technology (GACT) for affected sources. For the development of area source standards, GACT is meant to include methods, practices and techniques which are commercially available and appropriate for applic ation by the sources in the category

considering economic impacts and the technical capabilities of the firms to operate and maintain the emissions control sy stems. The purpose of this memorandum is to describe ho w GACT was determined for glass
- melting furnaces, which is the affected source for the proposed National Emission Standards for Hazardous Air Pollutants (NESHAP) for Wool Fiberglass Manufacturing Area Sources. In the development of the residual risk and technology review of the major source NESHAP for wool fiberglass manufacturing (Subpart NNN), the industry trade association (NAIMA) and EPA sent information requests to all major and area source wool fiberglass facilities and had several meetings with industry

regarding current practices at wool f iberglass plants. Because of the large number of emission test reports and other documents reviewed, and the fact that most documents included information claimed as confidential business information (CBI), the specific references for the test data are not listed in this memorandum. However, a summary of the test reports and all of the other documents that were used in the analy sis of GACT, other than those that were claimed to be CBI, can be found in the docket. **II. Glass**  **- melting Furnaces**  Glass
- melting furnaces vary according to size, design, fuel source , raw material mixtures, melting times and method s of heat application
. Glass
- melting furnaces can be electric steel shell,2

cold top electric, air
- gas , oxyfuel, or combinations of gas and electric
. There are two ty pes of electric furnaces currently used in the wool fiberglass industry : electric steel shell and cold top electric. There are tw o types of gas
- fired glass
- melting furnaces : air
- gas, and ox y- fuel. There may also be combinations of gas fired and electric furnaces (known as ‘electric boost’) in operation. About 80 percent of the glass
- melting furnaces used in the wool fiberglass industry are electric (e.g., steel shell or cold
- top) and about 20 percent are gas
- fired (e.g., air gas or ox yfuel). E lectric furnaces operate using electrodes embedded beneath the surface of the raw materials. The electrodes melt the raw material mixture while new layers of raw material are constantly added with a water spray on the surface of the molten layer. The elec tric steel shell furnace extrudes molten glass from the end of the furnace; the cold
- top electric furnace is tapped from the bottom of the furnace. Temperatures above the raw material mixture are less than 300 0 F. Gas - fired furnaces (o xy- fuel and air gas) feed raw materials into one end, melt the raw materials using natural gas, and extrude the molten glass from the far end of the furnace. Air gas furnaces use outside ambient air to provide oxygen for combustion of natural gas in the furnace. Ox yf uel furnaces mix natural gas with industrial
- grade (99% pure) ox ygen to create a flammable mixture that is burned in the furnace. Because a gas/ ox yg en mixture fires at a higher temperature than an air/gas mixture, ox yfuel fired furnaces operate with higher temperatures above the melted glass line ( 3500 0 F. inside the furnace) than air gas furnaces (2400 0 F), whose temperatures are reduced b y the dilution of ox ygen in the outside air
. **I I**  **I. Existing**  **Glass -**  **m elting Furnace Emission Controls**  The ty pe of control device used to control particulate matter (PM) emissions varies by furnace ty pe. E lectric steel shell furnaces use a baghouse and/or fabric filter ; cold top electric furnaces use batch wetting as the method of PM control. A ir
- gas furnaces currently use a combination of electrostatic precipitators (ESP) and baghouses ; o x yf uel furnaces use an ESP only (with one oxyfuel furnace using a scrubber along with an ESP ). Figure 1 shows PM emission rates by control device for all furnaces in the wool fiberglass manufacturing source category that submitted PM data. **I V**  **. Glass -**  **M elting Furnace Emission**  **s** Chromium Emissions Wool fiberglass Manufacturing is being l isted as an area source category based on emissions of chromium compounds. In the development of the residual risk and technology review of Subpart NNN (for major sources) , the industry trade association (NAIMA) and EPA received emissions information from the majority of all major and area source wool fiberglass facilities. The EPA evaluated chromium emissions data for major and area source glass
- mel ting furnaces and anal yz ed the operational differences of the different ty pes of glass
- melting furnaces. The EPA found that electric furnaces (electric steel shell and cold
- top electric) do not have the potential to emit chromium at the levels of gas
- fire d furnaces, and that chromium emissions from electric3

furnaces are about 2 orders of magnitude lower than the chromium emissions from gas
- fired furnaces as shown in Figure 2.

**Figure 1. Furnace PM Emission Rate by Control Device** 

**Figure 2. Chromium**  **Compounds Emission Rate**  **s by**  **Furnace Type**4

Th is higher chromium emission potential for gas
- fired glass
- melting furnaces is due to differences in design and operation of gas
- fired glass
- melting furnaces compared to electric glass
- melting furnaces. Altho ugh all glass
- melting furnaces are constructed using chromium refractories at and below the line of contact defined by the refractory

wall and the molten glass within the glass
- melting furnace (the glass/metal line), oxy- fuel and some air gas glass
- melting furnaces have other glass
- melting furnace parts constructed using chromium refractories, such as the crown , sidewalls, front wall, back wall, and forehearth. The use of chromium refractories above the melt line is necessary to obtain the desired furnace l ife and reduce the necessity for hot repairs of the furnace. When the hot, corrosive and reactive gases of a gas
- fired glass
- melting furnace come in contact with the high chromium refractories lining the area above the glass melt in high temperature glass
- melting furnaces, the chromium is available to be oxidized and converted into its hexavalent form. A chromium refractory

product has the greatest resistance to heat and wear of any refractory

in use today . The temperatures above the melt in gas
- fired gl ass - melting furnaces range from 2 , 500 ◦ to 4 , 500 ◦ F, while the temperatures in electric glass
- melting furnaces are less than 300 0 F. Due to their higher operating temperatures, gas
- fired glass
- melting furnaces are constructed using chromium refractories at various parts of the glass
- melting fur nace that are above the molten glass, including the crown. Chromium refractories may contain over 90% chrome bearing compounds, specificall y, chomite ore (as Cr2 O 3 ) and chromic oxide (as Cr3 O 4 ). The use of chromium refractories above the glass melt line an d corrosiv ity due to thermal and chemical degradation of the furnace interior contribute to the greater potential for gas - fired furnace s to chromium compounds
. S tudies indicate that, under normal industrial temperatures and oxidizing conditions, trivalent chromium, which is present in the refractory , oxidize s readily to its hexavalent state. 1 Additionally , while the degradation of the glass
- melting furnace refractory indicates increasing chromium emissions, that process does not necessarily follow a norm al and predictable pattern. The degradation of refractories within the glass
- melting furnace is a function of numerous factors, including temperature, time, stress, and the composite effects of aging and creep response. These processes are highl y nonlinear , so the traditional equations that assume steady
state deformation rates are not appropriate
. 2 We have also found that as the refractories of the gas - fired glass
- melting furnaces degrade, the chromium of those refractories at and above the metal/glass lin e is emitted as particulate to the outside air. Chromium from the refractories below the metal/glass line is absorbed into the molten glass and becomes vitrified with the other raw minerals. Industry

commented that refractory loss from degradation of the r efractory walls in use is approximately

20,000 pounds of refractory annually
. 3 When th at loss occurs below the glass melt line , it i s believed to be incorporated into the molten glass. When that loss occurs above the glass melt line, it is emitted from the furnace. While existing air pollution controls achieve reductions in the total PM, a greater fraction of that PM consists of chromium in the gas fired furnaces than exists in the electric furnaces, and have been measured from gas
- fired furnaces at over 50 0 pounds per ye ar. Therefore, additional chromium reductions for gas
- fired furnaces in this particular industry

are needed.5

EPA has learned that if a source of reasonabl y priced industrial
- grade oxygen is available, the oxyfuel glass
- melting furnace is th e design favored for use by glass manufacturers due to the glass
- melting furnace’s low NOx emissions, low energy demands per volume output of glass , and extended furnace life span . The low NOx emissions of an oxy
- fuel glass
- melting furnace result from the fact that no air (which contains nitrogen) is introduced into the high temperature zone above the glass melt. Instead, the oxy- fuel glass
- melting furnace design mixes the natural gas fuel with pure ox yge n for combustion, thus reducing NOx emissions. In the 1999 Wool Fiberglass Manufacturing NESHAP (subpart NNN) , EPA promulgated emission l imits for PM (0.5 lb PM per ton of glass pulled) as a surrogate for metal HAP emitted from glass
- melting furnaces. The rationale for this surrogacy is that the metal HAP are contained (in trace amounts) in the PM, and that the PM control devices remove metal HAP with the same efficiency as they remove total PM. Therefore, a limit on PM also creates equivalent control of the metal HAP. **I V**  **. Technical Basis For Setting Emi**  **ssions Limits For Both PM And Chromium for Gas Fired Furnaces**  We continue to believe that PM is an appropriate surrogate for metal HAP for electric glass
melting furnaces at wool fiberglass manufacturing facilities. The EPA may use a surrogate to regulate HAP if there is reasonable basis to do so. We have used PM as a surrogate to regulate hazardous pollutants because : “(1) HAP metals are invariabl y present . . . in PM;” (2) “PM Control technology

indiscriminately

captures HAP metals along with other particulates;” and (3) “PM control is the only

means by

which facilities achieve reduction in HAP metal emissions.” National Lime v. EPA, 233 F.3d at 639 . We have also alway s reasoned that “[i]f HAP metals are invariably

present in ...PM, then even if the ratio of metals to PM is small and variable, or simply unknown, PM is a reasonable surrogate for the metals
- assuming ... that PM control technology indiscriminately

captures HAP metals along with other particulates.” Id. Additionally, we believe that PM controls are still effective for chromium emissions at the same efficiency as total PM and other metal HAP. However, we believe that in the case of gas
- fired furnaces a separate chromium limit is necessary in order to insure control of chromium emissions. In general, the PM emissions from glass
- melting furnaces result from the entrainment of small particles of the feed in the exhaust gas. The feed materials going into the furnace contain trace amounts of chromium and other HAP metals. Therefore, the resultin g PM also contains HAP metals (including chromium) in trace amounts. However, there is also a second particulate source which is the refractory above the glass melt line of the furnace. Due to the chemical and thermal properties of the gases, a corrosive environment exists within a gas
- fired furnace. This causes erosion of the refractory lining of the furnace, which releas es chromium
- bearing refractory particles into the furnace exhaust gas as PM. All electric furnaces are lined with chromium refractorie s at and below the glass melt line. The chromium refractory

in an electric furnace extends up to two inches above the melt. Gas
- fired furnaces may

construct the entire furnace (crown, sidewalls, front and back walls, forehearth, etc.) from chromium refract ories. In the case of gas
- fired furnaces, the refractory does not contain chromium in trace amounts, rather chromium compounds make up a significant portion6

of the refractory

composition above the glass melt line. This results in gas - fired furnaces emitti ng particulate that contains chromium in larger amounts than that of electric furnaces. Based on our dataset, chromium constitutes an average of 0.96 percent of PM emissions for gas
fired furnaces, which is 13 times higher than the average for electric fur naces (0.07 percent of PM emissions are chromium). As an example, if a furnace is emitting 100 pounds per year ( lb /y r) of uncontrolled PM and has a 99.9 percent efficient control device ; a ssume that total metal HAP are about 1 percent of the uncontrolled PM, and chromium makes up 10 percent of the metal HAP. Controlled PM emissions would be 0.10 lb /y r of PM, and controlled chromium emissions would be 0.0001 lb /y r . However, if the 100 lb /y

r of PM came from the chrome refractory located above the glass mel t line, the chromium content might be as high as 50 percent of the PM. This would result in the same level of controlled PM emissions, 0.10 lb /y r , but controlled chromium emissions of 0.05 lb /y r . This is a 500 fold increase in chromium emissions but no in crease in total PM emissions. Because chromium compounds are a significant component of the refractory used above the glass melt line , a greater potential for chromium emissions exists , which is not associated with a commensurate increase in emissions of other HAP metals . Historical test data show there can be a delay in the increase of chromium emissions due to the wear of the furnace refractory . Table 1 shows measured total chromium emissions over one campaign of a single oxyfuel furnace. The e missions testing conducted in 2010 for the furnace summarized in Table 1 show ed that 93 percent of the chromium was in the hexavalent state (i.e., Cr+6 )
. B ecause the increase in chromium emissions may occur as a result of numerous variables 1 , and may be closel y re lated to specific furnace design and maintenance elements, we believ e it is appropriate to set a chromium limit in addition to the PM limit.

**Table 1**  **. Summary of Chromium Emissions from 2004**
**– 2010**  **Year Chromium Emissions**  **from Highest Emitting Glass -**  **Meltin g Furnace**  **at permitted production rate, pounds per year** 2004 <5 2005 30 2008 114 2010 540 Additionally , emissions testing conducted at wool fiberglass furnaces raise pollutant
- specific issues. Emissions test data for glass
- melting furnaces at wool fiberglass manufacturing facilities indicated that the phenomena discussed above can result in emissions levels of chromium up to 50 lb/year, and in one case as high as 540 lb/year from gas
- fired furnaces, while emissions from electric furnaces at similar PM emissions levels are below 5 lb/year. Table 2 shows a comparison

1 Information obtained during site visits in December 2012 indicated that differences in furnace designs, placement of refra ctory products, composition and manufacturing specifications of refractory products, differences in installation of refractory products, and composition of refractory patches used in “hot” repairs all may influence chromium emissions from gas
- fired furnace s.7

of the average and maximum total chromium emissions between electric and gas
- fired glass
melting furnaces . Chromium has been identified as one of the urban air toxics based on its prevalen ce and toxicity

in urban areas. **Table 2**  **. Average Annual Total**  **Chromium Emissions for Glass -**  **melting Furnaces 1**  **Average Chromium Emissions per**  **Furnace (lb/yr) Maximum Chromium**  **Emissions from a Furnace (lb/yr)**  Electric Furnaces 0.38 1.7 Gas - fired Furna ces 42 540 1. Based on furnaces for which PM and c hromium emissions testing was submitted In lieu of setting both a PM and chromium limit, we considered setting a chromium limit alone. However, for all the reasons noted above ( i.e. the fact that the PM controls are still effective, but the chromium content of the particulate is increased) we believe it would be difficult to improve the efficiency

of the PM controls to meet a chromium limit based on GACT. We also note that the control technology that would b e required to meet the proposed chromium emissions limit is a packed bed sodium hydroxide (NaOH ) scrubber. However, this ty pe of control is not effective in reducing PM emissions. Therefore, in establishing onl y a chromium limit, PM emissions (and thus emi ssions of other HAP metals) would be left essentially uncontrolled. **V. Determination of GACT for Glass**  **- Melting Furnaces**  In order to set PM and chromium emission control levels that are equivalent to GACT, the EPA evaluated the methods, practices and techniques that are commerciall y available for gas
- fired glass
- melting furnaces. As shown in Figure 1, most gas
- fired furnaces use an ESP and/or baghouse to control PM and chromium emissions. The basic approach to determining GACT was to evaluate the availabl e data on controlled emissions from gas
- fired glass
- melting furnaces and then determine the control levels that appear to be generally available for reducing emissions of chromium and PM from gas
- fired furnaces. Test data from facility emission test repo rts were compiled into a spreadsheet and sorted b y pollutant and furnace type. Figure 2 shows the emission rate test data that were provided b y facilities for chromium compounds. EPA reviewed these data and then used production data for each furnace to e stimate the annual PM and chromium compound emissions. There are no differences between furnaces located at area sources and major sources . The reason is that the differences between major and area sources relate to emissions from the binding process, not to emissions or emissions controls on the furnaces. Therefore we looked to the entire data set to develop options for GACT. In the case of PM we evaluated several options as potential GACT . The first option was 0 .33 pounds PM per ton of glass pulled This are the same PM limit proposed for major source furnaces as a result of technology review performed under 112(d)(6). Given the fact that major and area source furnaces are no different, this was a logical option to evaluate and we believe8

represents the le ast stringent option we should consider. This level would result in no costs or emission reductions because all furnaces currentl y meet this limit. However, this limit would codify the current level of PM emissions and prevent any future PM emissions incre ase. We also looked evaluated potentially lower limits as GACT. These were 0.2, 0.1, and 0.05 lb PM/ton , and at a level of control equal to MACT of 0.0093 lb/ton glass for existing sources and 0.0018 lb/ton glass for new sources. At these levels 5 to 12 f urnaces would have to invest in additional add
- on PM emissions control. We estimate these costs would exceed $50,000 per ton of PM reduction for the first three options. Inthe case of the MACT floor levels of control, the cost of PM reductions would be $4 80,000 per ton PM removal ($200,000 per furnace for a total of $2,400,000 for 12 furnaces that currentl y do not meet the limit to remove five tons of PM annually). These cost effectiveness values are significantly higher than any

the Agency

has accepted as reasonable for PM. For chromium the first GACT option evaluated was 0.00006 lb/ton glass pulled. As was the case with the PM limit, this is the same chromium limit proposed for major source furnaces as a result of technology

review performed under 112(d)(6). There are three area source gas
- fired furnaces that currentl y do not meet the proposed GACT for chromium. However, data are available for industries with similar control requirements that demonstrate that there are effective chromium control technolo gies available. We searched other industries for controls that would remove chromium and found that a sodium hydroxide (NaOH) scrubber is used in both high temperature metallurgical industries and in the chromium electroplating industry for removal of hexavalent chromium. 2 Based on the effectiveness of this technology on to two different ty

pes of exhaust gas streams, we believe this control technology is transferable to wool fiberglass furnaces. Though there are currently no NaOH scrubbers applied in the wo ol fiberglass industry , there is currentl y one gas - fired furnace equipped with a PM control followed by a wet scrubber for SO 2 control. This is directly

analogous to using a NaOH wet scrubber downstream of the PM controls to achieve additional chromium rem oval. Assuming that the facilities not currentl y meeting the proposed chromium emission limit opted to use the NaOH scrubbers to achieve compliance, the cost of the proposed chromium emissions limit is $7,600 per pound of chromium. This is a reasonable c ost given that chromium is an urban air toxic and that a significant portion of the chromium emitted from gas
- fired glass
melting furnaces is hexavalent chromium, which is extremely toxic and carcinogenic even in low amounts. We note that we found $11,000 per pound chromium removed to be a reasonable cost in the final Chromium Electroplating RTR rulemaking, where we regulated chromium compounds (77 FR 59220, September 19, 2012). For chromium we evaluated a MACT floor level emissions limit of 0.000022 poun ds (lb) of chromium compounds per ton of glass pulled (0.022 lb per thousand tons glass pulled) for new and existing sources. In th is case of the MACT floor levels of control, the cost per pound of chromium removed would be $34,400 annuall y ($250,000 for 1 0 furnaces that currently do not meet the limit to remove 75 pounds of chromium compounds annually). Therefore, the cost
effectiveness of achieving the chromium emissions levels would be about five times higher than
2 NaOH Scrubber Information. Telephone discussion and emails between vendors, companies and EPA. Steffan Johnson, Measurement Policy Group. USEPA/OAQPS/SPPD.9

the first option GACT standard which we are proposing. These cost effectiveness values are significantl y higher than any the Agency has accepted as reasonable for chromium. We also considered some level between 0.00006 and 0.000022, but we noted that any level below 0.00006 would incur similar c osts and emissions reductions. In summary , we found the cost effectiveness of the proposed GACT limits to be reasonable. We evaluated more stringent emissions limits that those proposed, but the overall emission levels would not be significantly reduced (because most of the area sources are relativel y low emitters), and the cost and cost
- effectiveness of achieving these emissions would be significantly

higher than the cost of proposed GACT standards without significant added environmental benefit. In addi tion, and more significantly , setting more stringent limit that those being proposed this would result in a situation where area source gas
- fired glass
- melting furnaces would be subject to stricter regulations than the major source gas
- fired glass
- melting furnaces, which would not be appropriate given that there are no discernible differences between area and major source furnaces. **References:** 1. Lee, Y., Nassaralla, CL ., Minimization of Hexavalent Chromium in Magnesite
- chrome Refractory
. Metallurgical and Materials Transactions, 1998
. 2. Wool Fiberglass Insulation Manufacturing. Background Information for Proposed Standards. December 1983. 3. Minutes of EPA Meeting with Representatives of the Wool Fiberglass Industry and NAIMA
. August 31, 2 011. 4. Notes from Steffan Johnson on Caustic Scrubbing of Hexavalent Chromium Emissions from Industrial Sources. October 26, 2011.