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EC/R 10 /0 6 /2011 DRAFT: DO NOT CITE OR QUOTE MEMORANDUM

TO: Conrad Chin , USEPA / OAQPS /MMG

FROM: Jeff Harris, EC/R Inc.

DATE: October 6 , 2011

SUBJECT: Methodology for Estimation of Maximum Hourly Emissions for Ferroalloys Sources

Section 112(f)(2) of the Clean Air Act (CAA) directs EPA to assess the risk remaining (residual risk) after the application of maximum achievable control technology (MACT) standards under section 112(d). EPA is to prom ulgate more stringent standards for a category or subcategory of sources subject to MACT standards under section 112(d) if promulgation of such standards is necessary to protect public health with an ample margin of safety or to prevent (taking into consid eration various factors) adverse environmental effects.
In an effort to streamline the process of making residual risk decisions, EPA plans to address residual risk and perform a technology review simultaneously for multiple source categories. For this so urce category, t he first part of this approach is to compile and review facility

- specific data collected by EPA, and to conduct preliminary risk assessments.

The risk assessment will include both chronic and acute inhalation risks. The chronic risks are b ased on long

- term, annual average emissions, while the acute risks are based on short

- term hourly emissions and account for the maximum potential short term emission rates for the industry. Because of differences in control effects for groups of pollutants , we determined that it is necessary to use different methodologies to calculate the estimated maximum hourly emission

rate for emissions of total particulate matter ( PM ) (also representing other HAP metals) , formaldehyde, and a cid g ases ( hydrochloric acid , HC l & hydrofluoric acid , HF) from ferroalloys industry sources. M aximum hourly emission s for PM and formaldehyde are derived from annual emissions rates estimated from available emission test results 1

, while the estimated emissions for

1 For additional detail on calculation of annual emission rates, see Modeling Emission Estimation Methodologies for Ferroalloy Facilities

, October 4, 2011, available in the Ferroalloys source category docket.2

EC/R 10 /0 6 /2011 DRAFT: DO NOT CITE OR QUOTE HC l and HF are calculated assuming an average emission rate due to the consistent chlorine /fluorine content in the co ke burned at the facilities

. Total PM & Formaldehyde
A large portion of the total emissions from ferroalloys facilities are a result of e lectric a rc f urnaces (EAF), which operate continuously and are only shut down for product changes or major maintenance, both of which are uncommon. Other operations, such as tapping of the molten met al product from the furnaces, and casting of the molten metal into ingots, occur on a regular but intermittent basis. ( e.g., Tapping and casting occur about every two hours, and last around 30 minutes each .) Similarly, sizing operations (performed to cru sh the large ingots of product into smaller sized nuggets or powders ) are intermittent, depending on production levels.
Because the furnaces operate continuously, it is reasonable to consider them as steady

- state operations, and then look at the maximum e missions from the remaining processes (tapping, casting, and sizing) as they are the operations that might conceivably result in an emi ssions spike.
Estimated yearly emissions from steady

- state emissions points are divided by 8760 to calculate estimated hourly emissions. Intermittent emission points are assumed to operate 25 percent of the time (30 minutes out of each two hour period.) This is a conservative estimate, because it is very unlikely that all furnaces would ever be tapped simultaneously , and it is impossible for tapping and casting from a given furnace to occur simultaneously since casting of the molten metal must occur after it is tapped. This methodology is also likely to overestimate the operating frequency of product sizing operation s. Following this reasoning, estimated yearly emissions from intermittent emissions points are divided by 2190 (or 8760/4) to calculate estimated hourly emissions. We calculate the maximum hourly emissions as the sum of the hourly steady

- state emissions and the hourly intermittent emissions and have created a separate acute emissions modeling file based on these data (See Tables 1

- 4 at the end of this memo )

. Although we have modeled emissions of formaldehyde and acid gases from some intermittent processes, they may not actually be emitted. Because emissions from tapping and casting
processes were not tested , modeled emissions from tapping and casting were based on the3

EC/R 10 /0 6 /2011 DRAFT: DO NOT CITE OR QUOTE emissions profile of the furnace stack 2 . Removing f orm aldehyde and acid gases from the emissions profiles used for these emissions points might be appropriate for future modeling efforts, but we believe that retaining them is a more conservative approach for this analysis

. Acid Gases ( HC l and HF )

HC l and HF emissions are primarily influenced by the c hlorine and fluorine c ontent of the reducing agent (typically coal or coke) used in the EAF. Because the ferromanganese facilities subject to the rule both use coke as a reducing agent , the variability in impurit y levels ( i.e. , the chlorine and fluorine that result in HCl and HF emissions) is very low . B ecause of this, and because HF and HCl are emitted by processes that operate continuously (as described above), we believe that there should be no difference betw een estimated maximum hourly emissions and average hourly emissions o f acid gases

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EC/R 10 /0 6 /2011 DRAFT: DO NOT CITE OR QUOTE