1 

### MEMORANDUM

Date: March 5 , 2013
Subject: Technical Basis for Separate Chromium Emission Limits for Wool Fiberglass Glass

- Melting Furnaces

To: Susan Fairchild, OAQPS

I. BACKGROUND
In the 1999 Wool Fiberglass Manufacturing NESHAP (subpart NNN) , EPA , EPA promulgated emission l imits for PM (0.5 lb PM per ton of glass pulled) as a surrogate for non
- mercury 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 non
- mercury metal HAP with the same efficiency as they remove total PM. Therefore, a limit on PM also creates equivalent control of the non mercury metal HAP. See National Lime v. EPA, 233 F.3d at 639 (use of PM as a surrogate for metal HAP is reasonable under these circumstances).

II. TECHNICAL BASIS FOR SETTING CHROMIUM LIMITS
We continue to believe that PM is an appropriate surrogate for non
- mercury metal HAP for all types of glass

- melti ng 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 non
- mercury metal HAP because HAP because : “(1) HAP metals are invariably 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.” Nation al Lime v. EPA, 233 F.3d at 639 . We have also always 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 be lieve that in the case of gas

- fired furnaces a separate chromium limit is also necessary to provide for additional removal of chromium than provided by PM control alone. This control would be provided by a polishing NaOH scrubber following primary PM cont rol, which scrubber would2 selectively remove chromium (i.e. remove chromium preferentially to removal of other metal HAP)

. . In general, t he PM emissions from glass

- melting furnace s result from the entrainment of small particles of the raw material feed in the exhaust gas. The feed material s going into the furnace contain trace amounts of chromium and other H AP metals. Therefore, the resulting PM also contains HAP metal s (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 , which, for gas

fired furnaces is both chromium

- rich and can become entrained in furnace emissions

. Specifically, d ue 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.
Though all furnaces are lined with chromium ref ractories at and below the glass melt line , g as
fired furnaces may construct the entire furnace (crown, sidewalls, front and back walls, forehearth, etc.) from chromium refractories. This chromium refractory does not contain chromium in merely trace amounts ; rather , chromium compounds make up a significant portion (over 94%) of the refractory composition above the glass melt line 1 . This results in gas
- fired furnaces emitting particulate that contains chromium in larger amounts than that of electric furnaces. Based on PM and chromium emissions test data collected from industry for development of the proposed rule , chromium constitutes an average of 0.96 percent of PM emissions for gas

- fired furnaces, which is 13 times high er than the average for electric furnaces (0.07 percent of PM emissions are chromium ). 2
As an example, if a furnace is emitting 100 pounds per year ( lb /yr) 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 /yr of PM, and controlled chromium emissions would be 0.0001 lb /yr

. However, if the 100 lb /yr of PM came from the chrome refractory located above the glass melt line of a gas

- fired furnace , 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 /yr , but controlled chro mium emissions of 0.05 lb /yr . This is a 500 fold increase in chromium emissions but no increase in total PM emissions.

Because chromium compounds are a significant component of the refractory used above the glass melt line in gas

- fired furnaces , a greater potential for chromium emissions exists , w hich is not associated with a commensurate increase in emissions of other HAP metals

. Emissions test data for glass

- melting furnaces at gas
- fired 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 ca se as high as 5 4 0 lb/year from gas

- fired furnaces, while

1 See the 114 responses from all wool fiberglass manufacturers on furnace design, construction, and refractory composition. Also, see product specification statements from St. Gobain, in references.
2 See the Modeling File in the Docket for this rule.3 emission s from electric furnaces at similar PM emissions levels are below 5 lb/year. Table 2 shows a comparison of the average and maximum total chromium emissions between electric and gas

- fired glass

- melting furnaces . Chromium has been identified by EPA as one of the urban air toxics based on its prevalence and toxicity in urban areas (see EPA’s Urban Air Toxics Strategy, published 64 FR 38705 ( July 19, 1999 ) .)

Table 2 . Average Annual Total Chromium Emissions for Glass

- melting Furnaces 1
Average Chromium Emissions per Furnace (lb/yr) Max imum Chromium Emissions from a

Furnace (lb/yr) Electric Furnaces 0.38 1.7
Gas

- fired Furnaces 42 5 4 0

1. Based on furnaces for which PM and c hromium emissions testing was submitted
Chromium can be controlled preferentially through use of a of a packed bed sodium hydroxide (NaOH) scrubber. However, this type of control is not effective in reducing PM emissions. Thus, a PM limit alone would not adequately control chromium (as just illustrated) and would be a poor match for the control technology o n which the proposed chromium limit is based. Since the control technology would not capture PM indiscriminately with chromium (see 233 F. 3d at 369).
In lieu of setting both a PM and chromium limit, we also considered setting a chromium limit alone. However, the PM limit is the most effective means of assuring control of the other HAP metals, since that control is predicated on performance of a primary control device which controls HAP metals indiscriminately. Moreover, 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

.4 References
1. High Performance Refractories: Chromium Oxide. Saint

- Gobain Product Specification Sheet in Ceramic Materials. Saint

- Gobain.com, 2013.

2. SEFPRO. Saint

- Gobain Product Specification Sheet for Refractories for the Glass Industry. Saint

G obain.com, 2013.
3. Project Database for Development of the Wool Fiberglass Manufacturing RTR and Area Source Rules.