11/4/2011

Revised draft mercury section of the Ferroalloys preamble

1. Mercury Emissions

The raw materials used to produce ferroalloys contain 

various amounts of mercury, which is emitted during the smelting 

process. These mercury emissions are derived primarily from the 

manganese ore although there may be trace amounts in the coke or 

coal used in the smelting process. While some of the mercury 

that is in particulate or oxidized forms is captured by the 

particulate control devices, the more volatile elemental mercury 

is largely emitted to the atmosphere. We found that mercury 

emissions are emitted from the furnaces as measured during the 

ICR test program (estimated to be 540 pounds per year (lb/yr) at 

one plant and 140 lb/yr at the other plant). Pursuant to CAA 

section 112(d)(2) and 112(d)(3), we are proposing to revise the 

1999 NESHAP to include emission limits for mercury.

As discussed above, the MACT floor limit is calculated 

based on the average performance of the units in each category 

plus an amount to account for these units’ variability. To 

account for variability in the operation and emissions, the 

stack test data were used to calculate the average emissions and 

the 99 percent upper predictive limit (UPL) to derive the MACT 

floor limit. For more information on how we calculated the MACT 
floors and other emission limits, see the Ferroalloys Production 

MACT Floor Analysis document, which is available in the docket.

Using this method, the MACT floor (or 99 percent UPL) for 

exhaust mercury concentrations from existing furnaces is 80 

μg/dscm at 2 percent carbon dioxide (CO2). This MACT floor limit 

is higher than the actual emissions measured during the ICR 

performance tests at each plant. Therefore, we anticipate that 

both of the existing sources would be able to meet this limit 

without installing additional controls. 

With regard to new sources, as described above, the MACT 

floor for new sources cannot be less stringent than the 

emissions performance that is achieved in practice by the bestcontrolled similar source. A variability analysis similar to 

that used for existing sources was then performed to calculate a 

99 percent UPL using the three run test data from the top 

source. For this source category, we calculate that the UPL MACT 

floor limit for new sources is 16 μg/dscm at 2 percent CO2. This 

limit is based on the performance of the best performing source.

The next step in establishing MACT standards is the beyond 

the floor analysis. In this step, we investigate other 

mechanisms for further reducing HAP emissions that are more 

stringent than the MACT floor level of control in order to 

“require the maximum degree of reduction in emissions” of HAP. 

In setting such standards, section 112(d)(2) requires the 
Agency to consider the cost of achieving the additional emission 

reductions, any non-air quality health and environmental 

impacts, and energy requirements. Historically, these factors 

have included factors such as solid waste impacts of a control, 

effects of emissions on bodies of water, as well as the energy

impacts.

As described below, we considered beyond-the-floor control 

options to further reduce emissions of mercury. Because of our 

limited data set, we considered setting a MACT limit for 

existing sources based on the performance of the best performing 

source (i.e., based upon the test data used to calculate the 

MACT floor for new sources) such that the MACT limit for 

existing sources would be the same as the UPL MACT limit for new 

sources (i.e., 16 μg/dscm). Under this option, the best 

performing source would need no additional controls to meet the 

limit, since their current performance defines the new source 

limit. With regard to the other facility in the source category, 

as described below, we believe this limit could be achieved by 

the addition of an activated carbon injection system, which is a 

proven technology for mercury control. Compliance would be 

demonstrated by periodic performance testing and continuous 

parameter monitoring. 

In evaluating a beyond the floor option, we evaluate, among 

other things, the costs of achieving additional emission 
reductions beyond the floor level of control. No facilities in 

the source category use add-on control devices or work practices 

to limit mercury emissions beyond what is achieved as co-control 

of the emissions with the particulate matter control device. 

However, we identified both carbon bed technology and activated 

carbon injection as commercially available mercury emission 

reduction techniques. Carbon bed technology (which is one of the 

primary control devices used at Industrial Gold Production 

facilities in the U.S. to minimize mercury emissions, as 

described in the proposed rule for that category1) does not 

appear to be a viable technology to control the large volumes of 

airflow generated by the electric arc furnaces in the 

Ferroalloys Production source category. The carbon bed 

technology is applicable to gas streams with low volumes of 

airflow, and is characterized with relatively high pressure 

drops. Accordingly this technology is not used in industries 

with high volumes of airflow, such as industrial boilers and 

power plants.

In contrast, activated carbon injection has been used to 

control mercury emissions at various types of facilities that 

have large volumes of airflow including some coal-fired power 

plants, waste incinerators and cement kilns. Based on available 

information, activated carbon injection appears to be a 

 

1 National Emission Standards for Hazardous Air Pollutants: Gold Mine Ore 

Processing and Production Area Source Category. Proposed Rule (75 FR 22470);
technologically feasible control for mercury for these larger 

volume combustion sources. Mercury reductions of up to 90 or 95

percent have been reported at these other sources and should 

also be achievable at ferroalloys production facilities. Based 

on data and information on these mercury controls for other 

combustion sources (such as utility boilers, incinerators and 

cement kilns), and based on our experience with these controls, 

we conclude that activated carbon injection is a viable control 

technology for the Ferroalloys Production source category. 

Activated carbon injection can be installed upstream or 

downstream of an existing particulate matter control device. In 

cases where a source is concerned about potential impacts of 

waste carbon on the source’s waste stream and resulting disposal 

options or the ability to sell or reuse baghouse dust, the 

source can install the activated carbon injection downstream of 

the particulate matter control device with a separate polishing 

baghouse to collect the carbon. In other cases, the source can 

install the activated carbon injection upstream of the 

particulate matter control device and use the existing 

particulate control device to remove the carbon from the 

airstream.

We reviewed facility specific control options that included 

putting the mercury controls downstream of the existing furnace 

baghouse to avoid the potential issues with sale or reuse of 
baghouse dust associated with upstream controls. Under this 

scenario, the activated carbon injection system would be 

followed by a “polishing” baghouse to capture the activated 

carbon for disposal. In the case of the existing furnace 

scrubber, we assumed the source could put the activated carbon 

injection system upstream of the scrubber, the carbon would be 

captured by the scrubber and the resulting sludge treated 

according to the existing treatment process at the plant. Based 

on discussion2 with a vendor and other control technology 

experts, we do not believe that the resulting carbon waste in 

either scenario would trigger waste disposal concerns. We 

request comment on these assumptions. 

We estimate that under this beyond the floor option 

described above (i.e., a proposed limit of 16 μg/dscm), that one 

facility would need to install additional controls such as 

activated carbon injection to meet this limit, and that this 

would achieve about 420 pounds of reduction per year in mercury 

emissions. The capital costs are estimated to be $1.7 million, 

annualized capital and operating costs to be $1.4 million, with 

an overall cost-effectiveness of $3,300 per pound. The general 

range of costs for mercury controls from other MACT rules has 

been about $1,250 to $55,200 per pound of mercury removed (76 FR 

25075, May 3, 2011). The EPA requests information on other 

 

2 Conversation with D. Lipscomb, Albemarle. August 22, 2011.
control technologies available to Ferroalloys Production 

manufacturers to reduce mercury emissions. Other controls might 

include process changes, substitution of materials, collection 

or enclosure systems, work practices, or combinations of such 

methods; which reduce the volume of mercury emissions from 

existing sources.

It is important to note that there is no bright line for 

determining cost-effectiveness. Each rulemaking is different and 

various factors must be considered. Nevertheless, the costeffectiveness of mercury controls in this proposed rule for 

Ferroalloys Production is near the lower end of the range. Some 

of the factors we consider in determining the costs of control 

technologies under section 112(d)(2) include, but are not 

limited to the following: total capital costs; annual costs; and 

costs compared to total revenues (e.g., costs to revenue 

ratios). Other factors besides cost are considered into our 

decision. For example, whether the standards significantly 

impact one or more small businesses, whether the controls would 

significantly impact production, and whether, and to what 

extent, the controls result in adverse impacts to other media 

(e.g., hazardous waste issues). We propose that these mercury 

controls are feasible for the Ferroalloys Production source 

category from a technical standpoint and are cost effective. We 

are proposing a MACT standard for mercury emissions of 16 
μg/dscm for both existing and new sources under the authority of 

sections 112(d)(2) and (d)(3). To meet this proposed limit, we 

have preliminarily determined that activated carbon injection is 

feasible to implement for the Ferroalloys Production source 

category from a technical standpoint and that control costs fall 

within the range of other mercury controls in other MACT rules. 

More information regarding how the MACT standards were 

calculated and the costs is provided in Ferroalloys Production 

MACT Floor and Cost Memos, which are available in the docket for 

this rulemaking.

We are requesting comment on the proposed standard of 16

μg/dscm for mercury. We also seek comments and information on 

our conclusion that activated carbon injection technology to 

meet the mercury emissions limit for this source category is

technically and economically feasible. Moreover, we seek 

comments on the factors related to costs and economics (such as 

those described in the paragraph above) regarding the 

feasibility and costs of activated carbon injection for this 

industry. We also seek comments on other possible controls that 

could be effective to reduce mercury emissions beyond the floor, 

including the amount and cost of the resulting emissions

reductions. Furthermore, we seek comment on whether work 

practices to minimize mercury emissions, such as switching to 
manganese ores with low mercury content, could be technically 

and economically feasible.

Moreover, we request comment on whether there is a basis to 

subcategorize manganese production operations for mercury. For 

example, is there a basis on which to subcategorize

ferromanganese production and silicomanganese production 

processes? Although we are requesting comment on 

subcategorization, we do not believe that subcategorization 

would have any substantive effect on the resulting standards or 

the costs of controls since there would be no change in the 

costs and feasibility of mercury controls evaluated for these 

sources. 

We are proposing that any source installing activated 

carbon injection would be required to continuously monitor the 

carbon injection rate into the airstream being controlled. We 

request comment on the level of variability in the carbon 

injection rate that should be allowed, and what percent decrease 

in the rate should be considered significant.

We also propose that sources monitor the mercury content in 

the manganese ore. Specifically, we propose that the 

determination of a significant increase in mercury content would 

be that the 12-month rolling weighted average mercury 

concentration based on monthly sampling in the manganese ore 

increases by 10 percent or more compared to the baseline 
weighted average mercury concentration. If that limit is 

exceeded, the source would be required to readjust the carbon 

injection rate as specified in the source’s monitoring plan or 

retest within 30 days if there is not a dedicated mercury 

control device. If a new ore is added, sampling would be 

required as well.

We request comment on this ore monitoring provision. We are 

especially interested in any data that would show the 

variability in mercury concentration between different ore 

samples from the same location and the variability of the types 

of ores used in manganese production. If ore type and mercury 

content are demonstrated to be stable, we might consider 

reducing the frequency of sampling/calculations to quarterly or 

less.