1

Date: September 2 9 , 201 4

Subject : Development of Background Information on Area Source Emissions Limit

-

Determination of GACT for Wool Fiberglass Furnaces at Area Sources EPA Contract No. EP

- D

- 11

- 084 ; EPA Work Assi gnment No. 2

- 0 9 RTI Project No. 021 3199 .00 2 .0 0 9

From: Cindy Hancy

Dave Reeves

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

I. Introduction

Section 112 (c)(3) and ( k) of the Clean Air Act (CAA) require the U.S. Environmental Protection Agency (EPA) to identify and list the area source categories that represent 90 percent of the emissions of the 33 urban air toxics (urban HAP) associated with areas sources and to subject them to standards under section 112(d). Section 112(k)(3)(B)(ii) also requires EP A to assure that area sources accounting for 90 percent or more of the 3 3 identified urban HAP are subject to standards . The 33 urban HAP are listed in EPA’s Integrated Urban Air Toxics Strategy. 1 EPA may elect to promulgate standards for area sources unde r 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 HAPs . For the development of area source standards, GACT include s methods, practices and te chniques which are commercially available and appropriate for application by the sources in the category considering economic impacts and the technical capabilities of the firms to operate and maintain the emissions control systems.

The purpose of this me morandum is to describe ho w 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. During dev elopment of the residual risk and technology review f o r the major source NESHAP for wool fiberglass manufacturing (Subpart NNN), both the industry trade association (NAIMA) and EPA sent information requests to all major and area source wool fiberglass faci lities in 2010 and 2012

, respectively. S ite visits were conducted and several meetings were held with industry regarding current emissions control practices at wool fiberglass plants. Two information requests were sent to industry: the first, a voluntary I CR, collected source test data and other information on representative processes across industry; the second, a 114 information collection request to conduct source testing at each wool fiberglass furnace in addition to providing information regarding furn ace life, rebuild history, and refractory composition. Th e

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

- air

- toxics

.2

information requests included submission of any previous emissions tests for chromium and PM, in addition to new PM and chromium testing. Because of the large number of emission test reports and ot her documents reviewed, and the fact that most documents were submitted as confidential business information (CBI), the submitted test data is not included in this memorand um. A summary of the test reports and all of the other documents that were used in t he 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

- M elting Furnaces

Glass

- melting furnaces are heat ed by two types of energy sources : natural gas and electricity . Most furnaces ar e heated by only one energy source but a few are heated by a combination of both. The tw o main types of gas

- fired glass

- melting furnaces are air

- gas and oxy

fuel. The main types of electric glass

- melting furnaces currently used in the industry are steel sh ell 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, h eated with natural gas (during startup only), and when the furnace is sufficiently hot, clean cullet is added. When the furnace is full of molten glass, electricity is allowed to flow to the electrodes and a ‘cap’ of raw material is added to the furnace to contain the heat and maintain a molten furnace 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 furnac e 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 furnace. 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 create a flammable mixture that is burned in the furnace. Because a gas/ oxygen mixture fires at a hi gher temperature than an air/gas mixture, oxy

- fuel fired furnaces operate with higher temperatures above the melted glass line (3

, 500 0 F. inside the furnace) than air gas furnaces (2

, 400 0 F), whose temperatures are reduced by the dilution of oxygen in the outside air.

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 , recuperative air gas, or oxy

- fuel). An average gas

- fired furn ace 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 . Oxy

- fue l furnaces are expected to replace all air

gas furnaces a n d many electric furnaces as the number of sources of industrial oxygen increases.

III. Glass

- M elting Furnace Emission s

Glass

- melting furnaces emit particulate matter ( PM ) , a fraction of which occurs as metals entrained in the particulate. In general, the PM emissions from glass

- melting furnaces result from the entrainment of small particles of the feed in the exhaust gas. T he feed materials going into3

the furnace contain trace amounts of chromium and other HAP metals. Therefore, the resulting PM also contains HAP metals (including chromium) in trace amounts. T he gas

- fired furnace refractory materials above the glass melt is a second and more significant source of chromium from these types of f

urnaces . Due to the high temperatures 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 releas es refractory particles into the furnace exhaust as PM. C hromium compounds make up 95

- 100% of the refractory products used to construct gas

- fired furnaces at and above the glass

- metal line. 2
, 3 This results in much higher chromium emissions from gas

- fired furnaces than from electric furnaces. Source tests show chromium constitutes an average of 1 percen t of the PM emissions f rom gas

- fired furnaces , a 1 4 fold increase above the average for electric furnaces , which is 0.0 7 percent.

I V . Glass

- M elting Furnace PM Emission Controls

The type s of control device s used to control PM emissions (which include ch romium)

var y by furnace type. S teel shell electric furnaces are totally enclosed above the melt line and are equipped with a baghouse and/or fabric filter . C old

- top electric 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. A ir

- gas furnaces currently use either electrostatic precipitators (ESP) or baghouses . O x y

- fuel furnaces generally use dry ESP only (with one using a scrubber in series with an ES P ). Figure 1 shows PM emission rates by control device for all reporting furnaces in the wool fiberglass manufacturing source category.

Figure 1. Furnace PM Emission Rate by Control Device

V. Glass

- Melting Furnace Chromium E missions

2 See Information on SEFPRO high chromium oxide products in docket EPA

- HQ

- OAR_2010

- 1042

3 ICR responses on furnace chromium content from wool fiberglass facilities (submitted as CBI).4

T he EPA evaluat ed the chromium emissions data for major and area source glass

- melting furnaces and analyzed the operational differences. The EPA found that e lectric furnaces do not emit chromium at the levels of gas

- fired furnaces, and chromium emissions from electric fu rnaces are multiple orders of magnitude lower than the chromium emissions from gas

- fired furnaces as shown in Figure 2. As noted earlier, s ource tests show chromium constitutes an average of 1 percent of the PM emissions from gas

- fired furnaces and less th an 0.1 percent from electric furnaces.

Figure 2. Chromium Compounds Emission Rate s 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 t o the glass

- melting furnace’s low NOx emissions, low energy demands per volume output of glass, 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 con tains nitrogen) is introduced into the high temperature zone above the glass melt. (US DOE, 2006) T he oxy

- fuel glass

- melting furnace design mixes the natural gas fuel with pure (99 percent industrial

- grade) oxygen for combustion, thus reducing NOx emission s. ( Oxygen

- Enhanced Combustion , Bauk a l 1998)

Although all glass

- melting furnaces are constructed using chromium refractories at and below the glass/metal line, oxy

- fuel and some air gas glass

- melting furnaces have other glass

melting furnace parts or area s constructed using chromium refractories, such as the crown

, forehearth , sidewalls, and appendages

. These differences in design and operation of gas

- fired Oxy Fuel Air Gas ESS Electric Melt5

glass

- melting furnaces cause higher potential chromium emission relative to electric glass

melting f urnaces.

The temperatures above the melt in gas

- fired glass

- melting furnaces range from 2

, 500 0 to 4

, 500 0 F, while the temperatures in electric glass

- melting furnaces are a few hundred degrees. S ince chromium refractories provide the greatest resistance to heat and wear of any refractory in use today

, gas

- fired furnaces are constructed using chromium refractories at various parts or

areas of glass

- melting furnace s

. The presence of chromium above the glass melt line, high temperatures, and corrosive environm ent cause gas

- fired furnace s to have a higher chromium emission potential. Additionall y , studies indicate that under normal industrial temperatures and oxidizing conditions, trivalent chromium present in the refractory oxidize s to hexavalent chromium (Nass aralla 1998)

.

The degradation of the glass

- melting furnace refractory indicates 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 the traditional equations that assume steady

- state deformation ra tes 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 furnace s

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Provided by Owens Corning during Decemb er 2012 site visits.

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 refra ctory loss from degradation of the refractory walls in use is approximately 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 glass (Bro snan 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 signi ficant component of the refractory used above the glass

- metal line
, there is a greater potential increase in chromium emissions w hich 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 campaign of a single oxy

- fuel furnace. The

e missions testing conducted in 2010 for the furnace summarized in Ta ble 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, and may be closely related to specific furnace design and maintenance elements, w e belie v e it is appropriate to set a chromium limit for gas

- fired furnaces. 4

4 Information obtained during site visits in December 2012 indicated that differences in furnace designs, placement7 Table 1 . Summary of Chromium Emissions from 2004

– 2010

Year Chromium Emissions from Highest Emitting Glass

- Melting Furnace at permitted production rate, pounds per year

2004 < 5

2005 30
2008 114

2010 540

V I

. Determination of GACT for Glass

- Melting Furnaces

Wool fiberglass manufacturing was listed as an area source category based on emissions of chromium compounds. In developing area source rules, the CAA allows EPA the fl exibility 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 proposing to set GACT limits on chromium emissions from gas

- fired glass

- melting furnaces at a rea sources

.

In order to determine GACT for chromium emission s the EPA evaluated the met hods, practices and techniques that are commercially available for gas

- fired glass

- melting furnaces. As shown in Figure 1, most gas

- fired furnaces use a n ESP and/or b aghouse to control PM emissions, a fraction of which are chromium compounds

. The EPA then evaluate d the available data on controlled emissions shown in Figure 2 from gas

- fired glass

- melting furnaces and then determine d the control level that appear s to be generally achievable for most sources. The design and operating of a glass

- melting furnace would be exactly the same regardless of whether or not the furnace is located at a major source or an area source. Therefore, t he emission characteristics of a glass

- melting furnace located at an area source versus a major source are identical . In this

case it is appropriate to use the dat a f r om both types of sources to determine GACT. The data in F igure 2 show that generally chromium emissions are well below 0.0001 l b/ton of melt for most facilities , and th e facilities above that level emit above 0.00015 lb/ton

. Therefore EPA initially determined that an emissions level below 0.0001 lb/ton o f melt would represent GACT.

As a second step in determining GACT

, EPA compar ed the emission level above to the chromium emissions level which was proposed for gas

- fired furnaces located at major sources as part of the technology review required b y section 112 (d)(6) of the CAA. In the technology review analysis, which included furn aces located at major sources only, th e EPA had determined that a chromium emissions level of 6.0E

- 5 pounds of chromium compounds per ton of glass pulled reflects a level achievable by most furnaces that are not considered high emitters . The basis for a GA CT determination and a technology review are similar, in that the EPA determines what levels of control are generally achieved by the control technology. A s noted above, furnaces located at major and area sources are identical f r om the standpoint of chromi um

of refractory products, composition and manufacturing specifications of refractory products, differences in installation of refractory produc ts, and composition of refractory patches used in “hot” repairs all may influence chromium emissions from gas

- fired furnaces.8

emissions. Therefore, it is reasonable to set GACT for area sources equal to the emissions limit based on technology review for major sources, namely 6.0E

- 5 pounds of chromium compounds per ton of glass pulled. We note that reducing GACT from 0.0001 to 6.0E

- 5 only results in one additional furnace being above the proposed limit, and that most furnaces are still generally below this level

.

References:

1. Lee, Y., Nassaralla, CL., Minimization of Hexavalent Chromium in Magnesite

- chrome Refractory. M etallurgical and Materials Transactions, 1998.

2. U. S. EPA

, 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

. Au gust 31, 2011.

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

5

. Baukal, Ch arles E., Jr., Oxygen

- Enhanced Combustion, 1998.

6

. Brosnan , D.A., Chromium Emissions from Wool Fiberglass Melting Furnaces . February 2012.9 Appendix101112