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MEMORANDUM

TO: Conrad Chin, U.S. Environmental Protection Agency, OAQPS

FROM: Beth Friedman, Jeff Harris , EC/R

DATE: October 27, 2011

SUBJECT: Draft Selection of Opacity Limits for the Ferroalloys Production Source Category

This memorandum summarizes the results of an analysis to revise the opacity limits included in the 

NESHAP for the Ferroalloys Production industry, as part of EPA’s Risk and Technology Review 

process. This memorandum is organized as follows:

1.0 Background

1.1 Requirements of Section 112(d)(6) of the CAA

1.2 Opacity Standards of the Current NESHAP

2.0 Revisions to Standards for Fugitive Emissions in the Proposed NESHAP

3.0 Recommended Revisions to Opacity Standards in the Proposed NESHAP

1.0 BACKGROUND

1.1 Requirements of Section 112(d)(6) of the CAA

Section 112 of the CAA requires EPA to establish technology-based standards for sources of HAP. 

These technology-based standards are often referred to as maximum achievable control technology, or 

MACT, standards. Section 112 also contains provisions requiring EPA to periodically revisit these 

standards. Specifically, paragraph 112(d)(6) states:

(6) REVIEW AND REVISION. – The Administrator shall review, and revise as necessary 

(taking into account developments in practices, processes, and control technologies), 

emissions standards promulgated under this section no less often than every 8 years.
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1.2 Opacity Standards of the Current NESHAP

The current National Emissions Standards for Hazardous Air Pollutants (NESHAP) for Ferroalloys 

Production: Ferromanganese and Silicomanganese was promulgated on May 20, 1999 (64 FR 27450) 

and codified at 40 CFR part 63, subpart XXX. The 1999 NESHAP (40 CFR 63.1650(a)) applies to all 

new and existing Ferroalloys Production facilities that manufacture ferromanganese or silicomanganese 

and are major sources or are co-located at major sources of HAP emissions. 

HAP generating processes at Ferroalloys Production facilities include electrometallurgical (furnace) 

operations (primary and tapping), other furnace room operations (ladle treatment and casting), building 

fugitives, raw material handling and product handling. HAP are emitted from ferroalloys production as 

process emissions, process fugitive emissions, and outdoor fugitive dust emissions. Most of these 

emissions are discussed elsewhere in greater detail.1 

Process fugitive emissions occur at various points during the smelting process (such as during charging 

and tapping of furnaces and casting) and are assumed to be similar in composition to the process 

emissions. For process sources, and fugitive sources captured and directed to a control device, the 

NESHAP specifies numerical emissions limits for particulate matter (as a surrogate for metal HAP). 

To address process fugitive emissions that escape capture, the 1999 NESHAP established a building 

opacity limit of 20 percent that is measured during the required furnace control device performance test. 

The rule provides an excursion limit of 60 percent opacity for one 6-minute period during the 

performance test. The opacity observation is focused only on emissions exiting the shop due solely to 

operations of any affected submerged arc furnace. 

Blowing taps, poling and oxygen lancing of the taphole; burndowns associated with electrode 

measurements; and maintenance activities associated with submerged arc furnaces and casting 

operations are exempt from the opacity standards. 

 

1 See Draft Technology Review for the Ferroalloys Production Source Category and others, available in the docket for the 

Ferroalloys Production source category.
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2.0 REVISIONS TO STANDARDS FOR FUGITIVE EMISSIONS IN THE PROPOSED 

NESHAP

The pollutants emitted from fugitive emissions sources at Ferroalloys Production sources occur at 

various points during the smelting process (such as during charging and tapping of furnaces and casting) 

and are assumed to be similar in composition to the process emissions. 

We evaluated several options to improve and increase the capture and control of process fugitive 

sources, and selected building ventilation as the preferred option. Additional detail on this selection, and 

discussion of other options considered is included in Draft Technology Review for the Ferroalloys 

Production Source Category, available in the docket for the Ferroalloys Production source category.

We identified a furnace building ventilation system at a ferrosilicon producer with a similar production 

process. This “system” is basically an enclosure of the furnace building at the roof vents with evacuation 

of emission to a control device. We evaluated this option described above.

Based on this evaluation, we conclude that it is feasible to install enclosures and have the fugitive 

emissions at the ridge vents of the shop building collected under negative pressure and ducted to a 

control device. Details of the numeric emission standards associated with this control option, and 

alternative options are included in Draft Technology Review for the Ferroalloys Production Source 

Category, available in the docket for the Ferroalloys Production source category.

3.0 RECOMMENDED OPACITY REVISIONS BASED ON DEVELOPMENTS IN 

PRACTICES, PROCESSES, AND CONTROL TECHNOLOGIES

We conclude that the building ventilation system described above will significantly improve capture and 

control of process fugitives. As a result, we anticipate the observed opacity at the shop building will 

decrease significantly as well. It is reasonable to assume that the building opacity should be close to 

zero after the installation of the ventilation system. However, it is also reasonable to incorporate 

possible short-term process fluctuations as well as other events that may affect the opacity readings.. 

Accordingly, the proposed NESHAP establishes the shop building opacity limit at 10 percent opacity. 

The proposed NESHAP also eliminates the exclusion of several events (blowing taps, poling and 

oxygen lancing of the tap hole; burndowns associated with electrode measurements; and maintenance
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activities) from the opacity observation as they are infrequent, can be avoided in some cases, are better 

controlled under the proposed standard, and can be confusing to enforce. Specifically, these events all 

occur within the furnace shop building, and should now be effectively captured and controlled by the 

building ventilation system described in section 2.

The proposed NESHAP also eliminates the 6-minute excursion level because we believe it does not 

provide any significant flexibility. Review of test data from both facilities shows that during 21 opacity 

tests performed over a 5-year period there were several instances where a facility would have exceeded 

the 10 percent opacity limit, but there was only one instance where a source would have exceeded the

limit for a single 6-minute period. Generally, fugitive emission events last considerably longer than 6

minutes, because the processes they are associated with (tapping, casting, etc.) occur over a longer time 

period. (A typical tapping event, for instance, lasts 20-30 minutes.) Because of this, it is our belief that 

the allowance for excursions for one 6-minute period adds complexity without any meaningful benefit or 

additional flexibility.