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MEMORANDUM

Date: June 24, 2015

Subject : Development of Background Information on the Final Area Source Emissions Limit - Determination of GACT for Wool Fiberglass Fur naces at Area Sources

From: Susan Fairchild, EPA/OAQPS/SPPD/MMG

To: EPA Air Docket EPA-HQ-OAR-2010-1042

I. Introduction

Section 112(c)(3) and (k) of the Clean Air Act (CAA) requi re the U.S. Environmental Protection Agency (EPA) to identify and list the area s ource categories that represent 90 percent of the emissions of the 33 urban air toxics (urban HAP) a ssociated with areas sources and to subject them to standards under section 112(d). Section 112(k)(3)( B)(ii) also requires EPA to assure that area sources accounting for 90 percent or more of the 33 identified urban HAP are subject to standards. The 33 urban HAP are listed in EPA’s I ntegrated Urban Air Toxics Strategy. 1 EPA may elect to promulgate standards for area sources un der section 112(d)(5) that provide for use of generally achievable control technology ( GACT) or management practices by

affected sources to reduce emissions of these HAP. For th e development of area source standards, GACT includes methods, practices and techniques w hich are commercially available and appropriate for application by the sources in the cate gory considering economic impacts and the technical capabilities of the firms to operate and mai ntain the emissions control systems.

The purpose of this memorandum is to describe how GACT was determined for gas-fired 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. All wool fiberglass furnaces are located at s ources which, prior to development of the MACT standard in 1999, were major sources. Since that time, two-thirds of the facilities have become area sources due to the phaseout of phenol/formalde hyde binders on the bonded lines. No change is made to the furnace when facilities undergo this change, and we therefore considered all furnaces in the source category (regardles s of whether they were located at major or area sources) in the GACT determination.

During development of the residual risk and technology review for the major source NESHAP for wool fiberglass manufacturing (Subpart NNN), both the industry trade association (NAIMA) and EPA sent information requests to all major a nd area source wool fiberglass facilities in 2010 and 2012, respectively. Site visits were co nducted and several meetings were held with industry regarding current emissions control pract ices at wool fiberglass plants. Two information requests were sent to industry: the first, a voluntary ICR, collected source test data and other information on representative processes acros s industry; the second, a CAA section114

1 See Urban Area Toxics information at http://www2.epa.gov/urban-air-toxics

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information collection request to conduct source testing at each wool fiberglass furnace in addition to providing information regarding furnace life, re build history, and refractory composition. The information requests included submission o f any previous emissions tests for chromium and particulate matter (PM), in addition to ne w PM and chromium testing. Because of the large number of emission test reports and other doc uments reviewed, and the fact that most

documents were submitted as confidential business informatio n (CBI), the submitted test data is not included in this memorandum. A summary of the test reports and all of the other documents that were used in the analysis of GACT, other than those that were claimed to be CBI, can be found in docket No. EPA-HQ-OAR-2010-1042.

II. Glass-Melting Furnaces

Glass-melting furnaces are heated by two types of energy sources: natural gas and electricity. Most furnaces are heated by only one energy source but a few are heated by a combination of both. The two general types of gas-fired gla ss-melting furnaces are air-gas and oxy-fuel. The general types of electric glass-melting furn aces currently used in the industry are steel shell and cold-top electric. Furnace diagrams were provided by NAIMA at an industry meeting in December 2012 (see Appendix).

Electric furnaces operate using electrodes embedded beneath the surface of the raw materials. Electric furnaces are started empty, heated with natural gas (during startup only), and when the furnace is sufficiently hot, clean cullet i s added. When the furnace is full of molten glass, electricity is allowed to flow to the electrode s and a ‘cap’ of raw material is added to the

furnace to contain the heat and maintain a molten furna ce interior. 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. Molten glass flows from the electric furnace to the spinning process. The electric steel shell furnace extrudes molten glass from the end of the furnace; the cold-top electric furnace is tapped from the bottom of the furna ce. Temperatures above the raw material

mixture are less than 300 0 F.

Air-gas furnaces use ambient air as the combustion oxygen source, oxy-fuel furnaces mix natural gas with industrial-grade (99 percent pure) oxygen to crea te a flammable mixture that is burned in the furnace. Because a gas/oxygen mixture fires at a higher temperature than an air/gas mixture, oxy-fuel fired furnaces operate with higher temper atures above the melted glass line (5,000 0 F inside the furnace) than air gas furnaces (3,400 0 F), whose temperatures are reduced by the dilution of oxygen in the outside air. According to in dustry data, only one air-gas furnace is still in operation in the US; all others have been re placed with oxyfuel furnaces. This is because permitting of an air-gas furnace involves accounting for emi ssions of PM and nitrogen oxides (NOx), which (because air-gas furnaces use outside air) a re much higher for air-gas furnaces than for oxyfuel furnaces. Oxy-fuel furnaces are expected t o replace all air-gas furnaces and many electric furnaces as the number of sources of indust rial oxygen increases.

About 80 percent of the glass-melting furnaces used in the woo l fiberglass industry are electric (e.g., steel shell or cold-top) and about 20 perc ent are gas-fired (e.g., air gas, recuperative air gas, or oxy-fuel). An average gas-fired furnace produces roughly three to four times the wool fiberglass of an average electric furnace. At least one gas-fired furnace also uses electric boost to provide additional heat at the start of the melt.3

III. Glass-Melting Furnace Emissions

Glass-melting furnaces emit particulate matter (PM), a fraction of which occurs as metals entrained in the particulate. In general, the PM emiss ions 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 resulting PM also contains HAP metals (including chromium) in tr ace amounts. The gas-fired furnace refractory materials above the glass melt is a second and more significant source of chromium from these types of furnaces. Due to the high temperature s and corrosive nature of the gases at and above the melt (i.e., the glass-metal line), the furnace refractory wears with age; the refractory erodes in a process that releases refractor y particles into the furnace exhaust as PM. Depending on the location in the furnace, chromium compo unds make up 50-100 percent of the refractory products used to construct gas-fired furnaces at a nd above the glass-metal line. 2,3 This results in much higher chromium emissions from gas-fi red furnaces than from electric furnaces. Source tests show chromium constitutes an average of1 percent of the PM emissions from gasfired furnaces, a 14 fold increase above the average for electric furnaces, which is 0.07 percent.

IV. Glass-Melting Furnace PM Emission Controls

The types of control devices used to control PM emissions (which include chromium) vary by furnace type. Steel shell electric furnaces are totally enclosed above the melt line and are equipped with a baghouse and/or fabric filter. Cold-top e lectric furnaces, which are not totally enclosed above the melt line, use a water spray to form a crust on the surface of the new material as the method of PM control. Air-gas furnaces currently use either electrostatic precipitators (ESP) or baghouses. Oxy-fuel furnaces generally use dry ES P only (with one using a scrubber in series with an ESP). Figure 1 shows PM emission rates by control device for all reporting furnaces in the wool fiberglass manufacturing source cat egory.

V. Glass-Melting Furnace Chromium Emissions

The EPA evaluated the chromium emissions data for major and area source glass-melting furnaces and analyzed the operational differences. The EPA found that electric furnaces do not emit chromium at the levels of gas-fired furnaces, and chromium emissions from electric furnaces are multiple orders of magnitude lower than the chromium emissions from gas-fired furnaces as shown in Figure 2. As noted earlier, source te sts show chromium constitutes an average of 1 percent of the PM emissions from gas-fired f urnaces and less than 0.1 percent from

electric furnaces.

2 See Information on SEFPRO high chromium oxide products in doc ket EPA-HQ-OAR_2010-1042

3 ICR responses on furnace chromium content from wool fiber glass facilities (submitted as CBI).4 Figure 1. Furnace PM Emission Rate by Control Device

Figure 2. Chromium Compounds Emission Rates by Furnace Type

If a source of reasonably priced oxygen is available, the oxy-fuel glass-melting furnace is the design favored for use by glass manufacturers due to th e glass-melting furnace’s low NOx Oxy Fuel Air Gas ESS Electric Melt5

emissions, low energy demands per volume output of gla ss, increased production rate 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. (US DOE, 2006) The oxy-fuel glass -melting furnace design mixes the natural gas fuel with pure (99 percent industrial-grade) oxygen for combustion, thus reducing NOx emissions. ( Oxygen-Enhanced Combustion , Baukal 1998)

Although all glass-melting furnaces are constructed using c hromium refractories at and below the glass/metal line, oxy-fuel and some air gas gl ass-melting furnaces have other glassmelting furnace parts or areas constructed using chromium re fractories, such as the crown, forehearth, sidewalls, and appendages. These differences in design and operation of gas-fired glass-melting furnaces cause higher potential chromium e mission relative to electric glassmelting furnaces.

The temperatures above the melt in gas-fired glass-melt ing furnaces range from 3,400 to
5,000 0 F, while the temperatures above the melt in electric glass-melting furnaces are a few hundred degrees. Since chromium refractories provide the greatest resista nce to heat and wear of any refractory in use today, gas-fired furnaces are con structed using chromium refractories at various parts or areas of glass-melting furnaces. The pr esence of chromium above the glass melt line, high temperatures, and corrosive environment cause gas- fired furnaces to have a higher chromium emission potential. Additionally, studies indi cate that under normal industrial temperatures and oxidizing conditions, trivalent chromium present in the refractory oxidizes to hexavalent chromium (Nassaralla 1998).

The degradation of the glass-melting furnace refractory i ndicates increasing chromium emissions with furnace age. This process, however, does not necessarily follow a normal 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 highly nonlinear, so t he traditional equations that assume steady-state deformation rates are not appropriate (DOE and Oak Ridge National Laboratory, June 2006 p. 63). The following photographs show examples of the refractory degradation below the melt line at two different Owens Corning furnaces.

For more information on this topic, see “Mechanisms of Chromium Emissions From Wool Fiberglass Glass-Melting Furnaces”, June 2015, in the docket to the rule.6

Provided by Owens Corning during December 2012 site visits.7

Provided by Owens Corning during December 2012 site visits.

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 refractory walls in use is approxim ately 20,000 pounds of refractory annually (EPA/Industry Meeting Minutes 2011), and that much of the loss occurs below the glass-metal line, which is believed to remain in the gla ss (Brosnan 2012). 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 glass-metal line is emitted as particulate to the outside air. Since chromium compounds are a significant component of the re fractory used above the glass-metal line, there is a greater potential increase in chromium emissions which are 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 campai gn of a single oxy-fuel furnace. The emissions testing conducted in 2010 for the furnace summariz ed in Table 1 showed that 93 percent of the chromium was in the hexavalent state ( i.e., Cr 6+ ). Because the increase in chromium emissions may occur as a result of numerous variables, and may be closely related to specific furnace design and maintenance elements, we be lieve it is appropriate to set a chromium limit for gas-fired furnaces. 4

4 Information obtained during site visits in December 2012 i ndicated that differences in furnace designs, placement of refractory products, composition and manufacturing speci fications of refractory products, differences in8 Table 1. Summary of Chromium Emissions from 2004 – 2010

Year Chromium Emissions from Highest Emitting Glass-Melting Fu rnace at permitted production rate, pounds per year

2004 <5

2005 30

2008 114

2010 540

VI. Determination of GACT for Glass-Melting Furnaces

Wool fiberglass manufacturing was listed as an area sour ce category based on emissions of chromium compounds. In developing area source rules, th e CAA allows EPA the flexibility to specifically regulate the pollutants of concern (e.g., c hromium compounds). After analyzing the data provided in Section V of this memorandum, we are fina lizing GACT limits on chromium emissions from gas-fired glass-melting furnaces at area sources.

We initially proposed GACT standards for area sources in t he Wool Fiberglass Manufacturing source category on April 15, 2013 (78 FR 22377). To dev elop the proposed GACT standards, the EPA evaluated the methods, practices and techniques that are commercially available for gas-fired glass-melting furna ces. Because the design, operating, and emissions characteristics of glass-melting furnaces are the same at major and area sources, the EPA used data from both types of sources to determine GACT. As shown in Figure 1, most gasfired furnaces use an ESP and/or baghouse to control PM e missions, a fraction of which are chromium compounds. The EPA also evaluated the available data on controlled emissions shown in Figure 2 from gas-fired glass-melting furnaces and determi ned the control level that appeared to be generally achievable for most sources. Based on th e emissions data in shown Figure 2, the EPA initially determined that an emissions level below 0.0001 lb/ton of melt would represent GACT. The EPA also compared the initial assessment of the GACT emission level to the chromium emissions level (6.0E-5 pounds of chromium compo unds per ton of glass pulled) that was proposed on November 25, 2011 for gas-fired furnaces loca ted at major sources as part of the technology review required by section 112(d)(6) of the CA A. Because the basis for a GACT determination and a technology review under CAA section 112( d)(6) are similar (i.e., the EPA determines what levels of control are generally achieve d by the industry), and because furnaces located at major and area sources are identical from th e standpoint of chromium emissions, the

EPA believed it to be reasonable to set GACT for area sources equal to the emissions limit based on technology review for major sources (6.0E-5 pounds of chr omium compounds per ton of glass pulled).

Based on comments we received in response to the propose d chromium compounds limits for gas-fired glass-melting furnaces the November 2014 notice, we reviewed the cost and control options and found using new cost information that the limit as proposed was not as cost effective

installation of refractory products, and composition of refractory patches used in “hot” repairs all may influe nce chromium emissions from gas-fired furnaces.9

as we initially believed. Consistent with the legislative history on section 112( d)(5), in determining GACT, we may consider costs and economic impa cts, in addition to considering technical capabilities of the facilities and the availa bility of control measures, which is particularly important when developing regulations for sour ce categories that may have few establishments and many small businesses, or when determi ning whether additional control is necessary for sources with emissions that are already well controlled as a result of other existing or applicable standards. (Senate Report Number 101-228, Decem ber 20, 1989).

Here, wW e determined that it was appropriate to modify the propose d limit of 6.0E-5 pounds per ton of glass pulled because the cost effectiveness for t he emission reduction options ($660,000 per pound of chromium reduced for the raw material substitution option, and $620,000 per pound chromium reduced for the furnace rebuild) were not reasonabl e compared to other cases where

the EPA has regulated highly toxic pollutants, such as hexavale nt chromium. We therefore reviewed the data to determine whether a higher limit than previously proposed would be more cost effective while still significantly reducing chromiu m emissions from wool fiberglass gasfired glass-melting furnaces. The EPA found that most woo l fiberglass gas-fired glass-melting furnaces at major sources currently emit chromium compo unds at rates below 2.5E-04 pounds chromium per ton of glass pulled. We compared the chromiu m emission reductions that would have resulted under the previously proposed emission limit of 6.0E-5 pounds chromium per ton of glass pulled to the reductions that result from the fi nal limit of 2.5E-04 pounds chromium per ton of glass pulled. We found that the proposed limit woul d have reduced chromium from major sources by 567 pounds per year, and that the final limit reduces chromium by 524 pounds per year. Because these emissions reductions are comparable , we finalized the emission limit for 2.5E-04 pounds chromium per ton of glass pulled for gas-fire d glass-melting furnaces located at wool fiberglass facilities that are major sources.

Under CAA section 112(d)(5), we may set the GACT emission limit for area sources that provides for the use of control technologies that are gene rally available to reduce HAP, and we are not precluded from setting the limits for area sources equivalent to the limits for major sources. Because there are no differences between gas-fi red glass-melting furnaces in use at area and major sources, we believe that the control measure for reducing chromium emissions (i.e., furnace rebuild) used by major sources is generally availabl e for area sources, and we are finalizing the same emission limit of 2.5E-04 pounds total chromium per ton of glass pulled for gas-fired glass-melting furnaces at area sources, under CA A section 112(d)(5). Although all gasfired glass-melting furnaces located at area sources emi t below the final GACT standards, the final limit sets a backstop so that gas-fired glass-melt ing furnaces that have high chromium emissions cannot be operated at an area source in this i ndustry.10

References:

1. Lee, Y., Nassaralla, CL., Minimization of Hexavalent Chromium in Magnesite-chrome Refractory. Metallurgical and Materials Transactions, 1998.

2. U. S. EPA, Wool Fiberglass Insulation Manufacturing. Ba ckground Information for Proposed

Standards. December 1983.

3. Minutes of EPA Meeting with Representatives of the Woo l Fiberglass Industry and NAIMA. August 31, 2011.

4. U.S. DOE Energy Efficiency and Renewable Energy, Industri al Technologies Program, Final Technical Report. Compressive Creep and Thermophysical Perfo rmance of Refractory Materials”. Oak Ridge National Laboratories. June 2006.

5. Baukal, Charles E., Jr., Oxygen-Enhanced Combustion, 1998.

6. Brosnan, D.A., Chromium Emissions from Wool Fibergl ass Melting Furnaces. February

2012.11 Appendix121314