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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 promulgate 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 

consideration 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 source category, the 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 

based 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 acid gases (hydrochloric acid, HCl & hydrofluoric acid, HF) from ferroalloys 

industry sources. Maximum hourly emissions for PM and formaldehyde are derived from annual 

emissions rates estimated from available emission test results1, while the estimated emissions for 

 

1

For additional detail on calculation of annual emission rates, seeModeling Emission Estimation Methodologies for 

Ferroalloy Facilities, October 4, 2011, available in the Ferroalloys source category docket.
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HCl and HF are calculated assuming an average emission rate due to the consistent 

chlorine/fluorine content in the coke burned at the facilities.

Total PM & Formaldehyde

A large portion of the total emissions from ferroalloys facilities are a result of electric arc 

furnaces (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 metal 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 crush 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 emissions from the remaining processes (tapping, 

casting, and sizing) as they are the operations that might conceivably result in an emissions 

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 operations. 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 the 
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emissions profile of the furnace stack2. Removing formaldehyde 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 (HCl and HF) 

HCl and HF emissions are primarily influenced by the chlorine and fluorine content 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 impurity levels (i.e., the 

chlorine and fluorine that result in HCl and HF emissions) is very low. Because 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 between estimated maximum hourly emissions and 

average hourly emissions of acid gases. 

 

2

Ibid.
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Table 1: Calculation of Average & Maximum Hourly PM Metal HAP Emissions Ratio for Eramet

Unit Description Emission Point Type Pollutant Estimated (lb/hr) Maximum (lb/hr) Estimated (lb/hr) Maximum (lb/hr)

Furnace #1 & 12 Building Ventilation Baghouse Steady-State PM Metal HAP n/a n/a 1.39E-01 1.39E-01

Furnace #1 casting Intermittent PM Metal HAP 5.08E+00 2.03E+01 2.23E-01 2.03E-01

Furnace #12 casting Intermittent PM Metal HAP 1.02E+00 4.10E+00 1.02E-02 4.10E-02

MOR casting Intermittent PM Metal HAP 1.53E-01 6.11E-01 2.29E-04 9.17E-04

Electric Arc Furnace #1 Fugitives Steady-State PM Metal HAP 4.96E+00 4.96E+00 1.04E-02 1.04E-02

Electric Arc Furnace #12 Fugitives Steady-State PM Metal HAP 2.50E+00 2.50E+00 2.50E-02 2.50E-02

Electric Arc Furnace #1 Scrubber Outlet Steady-State PM Metal HAP 3.96E+00 3.96E+00 1.98E-01 1.98E-01

Electric Arc Furnace #12 Scrubber Outlet Steady-State PM Metal HAP 2.00E+00 2.00E+00 2.00E+00 2.00E+00

Electric Arc Furnace #1 Tapping Fugitives Intermittent PM Metal HAP n/a n/a 1.03E-02 4.12E-02

Furnace #1 Tapping Baghouse Intermittent PM Metal HAP n/a n/a 5.83E-02 2.33E-01

C2P crushing and sizing fugitives Intermittent PM Metal HAP 3.12E+00 1.25E+01 3.12E-02 1.25E-01

C2P Crushing/Sizing Baghouse #1 Intermittent PM Metal HAP 5.09E-01 2.04E+00 5.09E-01 2.04E+00

C2P Crushing/Sizing Baghouse #2 Intermittent PM Metal HAP 5.09E-01 2.04E+00 5.09E-01 2.04E+00

C2P Crushing/Sizing Baghouse #3 Intermittent PM Metal HAP 5.09E-01 2.04E+00 5.09E-01 2.04E+00

No. 18 Furnace Taphole, MOR Process Fugitives Intermittent PM Metal HAP 2.82E-01 1.13E+00 1.77E-03 7.06E-03

No. 18 Furnace Taphole, MOR Process Baghouse Outlet Intermittent PM Metal HAP 2.26E-01 9.03E-01 1.41E-01 5.64E-01

Total 2.48E+01 5.91E+01 4.17E+00 9.28E+00

Ratio (Max/Average) 2.4 2.2

Table 2: Calculation of Average & Maximum Hourly PM Metal HAP Emissions Ratio for Felman

Unit Description Emission Point Type Pollutant Estimated (lb/hr) Maximum (lb/hr) Estimated (lb/hr) Maximum (lb/hr)

BUILDING VENTILATION BAGHOUSE Steady-State PM Metal HAP n/a n/a 4.57E-02 4.57E-02

ELECTRIC ARC FURNACE NO. 2 CASTING FUGITIVES Intermittent PM Metal HAP 2.63E-01 1.05E+00 5.26E-05 2.10E-04

ELECTRIC ARC FURNACE NO. 5 CASTING FUGITIVES Intermittent PM Metal HAP 1.96E-01 7.83E-01 2.94E-04 1.17E-03

ELECTRIC ARC FURNACE NO. 7 CASTING FUGITIVES Intermittent PM Metal HAP 2.21E-01 8.86E-01 3.32E-04 1.33E-03

ELECTRIC ARC FURNACE NO. 2 Steady-State PM Metal HAP 2.56E-01 2.56E-01 2.56E-01 2.56E-01

ELECTRIC ARC FURNACE NO. 2 FUGITIVES Steady-State PM Metal HAP 1.60E+00 1.60E+00 1.60E-02 1.60E-02

ELECTRIC ARC FURNACE NO. 5 Steady-State PM Metal HAP 1.95E-01 1.95E-01 1.97E-01 1.97E-01

ELECTRIC ARC FURNACE NO. 5 FUGITIVES Steady-State PM Metal HAP 1.22E+00 1.22E+00 1.22E-02 1.22E-02

ELECTRIC ARC FURNACE NO. 7 Steady-State PM Metal HAP 3.07E-01 3.07E-01 3.09E-01 3.09E-01

ELECTRIC ARC FURNACE NO. 7 FUGITIVES Steady-State PM Metal HAP 1.92E+00 1.92E+00 1.63E-02 1.63E-02

CRUSHING AND SCREENING SYSTEM #2 Intermittent PM Metal HAP 4.54E-02 1.81E-01 4.54E-02 1.81E-01

CRUSHING AND SCREENING SYSTEM #2 FUGITIVES Intermittent PM Metal HAP 9.26E-02 3.70E-01 9.26E-04 3.70E-03

Total 6.32E+00 8.78E+00 8.54E-01 9.95E-01

Ratio (Max/Average) 1.4 1.2

Baseline Emissions Controlled Scenario Emissions

Baseline Emissions Controlled Scenario Emissions
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Table 3: Calculation of Average & Maximum Hourly Formaldehyde Emissions Ratio for Eramet

Unit Description Emission Point Type Pollutant Estimated (lb/hr) Maximum (lb/hr) Estimated (lb/hr) Maximum (lb/hr)

Furnace #1 & 12 Building Ventilation Baghouse Steady-State Formaldehyde n/a n/a 1.93E-01 1.93E-01

Furnace #1 casting Intermittent Formaldehyde 5.31E-02 2.12E-01 2.32E-03 2.12E-03

Furnace #12 casting Intermittent Formaldehyde 1.07E-02 4.27E-02 1.07E-04 4.27E-04

MOR casting Intermittent Formaldehyde 5.61E-03 2.24E-02 8.42E-06 3.37E-05

Electric Arc Furnace #1 Fugitives Steady-State Formaldehyde 5.18E-02 5.18E-02 4.36E-04 4.36E-04

Electric Arc Furnace #12 Fugitives Steady-State Formaldehyde 2.61E-02 2.61E-02 2.61E-04 2.61E-04

Electric Arc Furnace #1 Scrubber Outlet Steady-State Formaldehyde 8.28E-02 8.28E-02 8.28E-01 8.28E-01

Electric Arc Furnace #12 Scrubber Outlet Steady-State Formaldehyde 4.17E-02 4.17E-02 4.17E-02 4.17E-02

Electric Arc Furnace #1 Tapping Fugitives Intermittent Formaldehyde n/a n/a 5.05E-04 2.02E-03

Furnace #1 Tapping Baghouse Intermittent Formaldehyde n/a n/a 2.86E-01 1.15E+00

No. 18 Furnace Taphole, MOR Process Fugitives Intermittent Formaldehyde 1.64E-02 6.55E-02 1.02E-04 4.10E-04

No. 18 Furnace Taphole, MOR Process Baghouse Outlet Intermittent Formaldehyde 2.62E-02 1.05E-01 1.64E-02 6.55E-02

Total 3.14E-01 6.50E-01 8.89E-01 9.39E-01

Ratio (Max/Average) 2.1 1.1

Table 4: Calculation of Average & Maximum Hourly Formaldehyde Emissions Ratio for Felman

Unit Description Emission Point Type Pollutant Estimated (lb/hr) Maximum (lb/hr) Estimated (lb/hr) Maximum (lb/hr)

BUILDING VENTILATION BAGHOUSE Steady-State Formaldehyde n/a n/a 9.90E-03 9.90E-03

ELECTRIC ARC FURNACE NO. 2 CASTING FUGITIVES Intermittent Formaldehyde 5.22E-04 2.09E-03 1.04E-05 4.17E-05

ELECTRIC ARC FURNACE NO. 5 CASTING FUGITIVES Intermittent Formaldehyde 3.89E-04 1.55E-03 5.83E-07 2.33E-06

ELECTRIC ARC FURNACE NO. 7 CASTING FUGITIVES Intermittent Formaldehyde 4.39E-04 1.76E-03 6.59E-07 2.64E-06

ELECTRIC ARC FURNACE NO. 2 Steady-State Formaldehyde 5.08E-02 5.08E-02 5.08E-02 5.08E-02

ELECTRIC ARC FURNACE NO. 2 FUGITIVES Steady-State Formaldehyde 3.18E-03 3.18E-03 3.18E-05 3.18E-05

ELECTRIC ARC FURNACE NO. 5 Steady-State Formaldehyde 3.88E-02 3.88E-02 3.91E-02 3.91E-02

ELECTRIC ARC FURNACE NO. 5 FUGITIVES Steady-State Formaldehyde 2.42E-03 2.42E-03 2.42E-05 2.42E-05

ELECTRIC ARC FURNACE NO. 7 Steady-State Formaldehyde 6.10E-02 6.10E-02 6.14E-02 6.14E-02

ELECTRIC ARC FURNACE NO. 7 FUGITIVES Steady-State Formaldehyde 3.82E-03 3.82E-03 3.23E-05 3.23E-05

Total 1.61E-01 1.65E-01 1.51E-01 1.51E-01

Ratio (Max/Average) 1.0 1.0

Baseline Emissions Controlled Scenario Emissions

Baseline Emissions Controlled Scenario Emissions