MEMORANDUM

TO: Docket EPA-HQ-OAR-2006-0790

FROM: Mary Johnson, EPA/OAR/OAQPS/SPPD

DATE: May 2012

SUBJECT: Beyond-the-Floor Technology Analysis for Mercury

Area Source Industrial/Commercial/Institutional Boilers

1.0 BACKGROUND

This memorandum describes the EPA’s beyond-the-floor control 

technology analysis for mercury emissions from new and existing area 

source coal-fired boilers with heat input capacity of 10 million 

British thermal units (MMBtu) per hour or greater. In our final rule 

action on reconsideration, we are amending the maximum achievable 

control technology (MACT)-based mercury emission limit for new and 

existing coal-fired boilers subject to subpart JJJJJJ of 40 CFR part 

63. At the time of the March 2011 promulgation, the mercury limit for 

new and existing coal-fired boilers was 4.8 X 10-6 pounds (lb) of 

mercury per MMBtu. That limit was based on the best performer of 

seven units for which data were available. The best performing boiler 

had a series of controls (dry limestone injection/dry scrubber/fabric 

filter/selective catalytic reduction/selective non-catalytic 

reduction (NH3 Or Urea Injection)) apparently for control of sulfur 

dioxide, particulate matter, and nitrogen oxides in series. All of 

the mercury data for the best-performing boiler were below the method 

detection limit. After promulgation, the EPA determined that the 

boiler on which the mercury limit was based is, in fact, a utility 

boiler and not part of the source categories being regulated under 

this action. Thus, the utility boiler and its emissions data should 

not have been considered in establishing the mercury emission limit 

for new and existing coal-fired boilers.

An examination of the mercury emissions data for the remaining 

six units determined that the top performing boiler is now a unit 

with fabric filter control from Massachusetts that had measured 

emissions of 1.9 X 10-6 lb of mercury per MMBtu. These emissions are 

above the method detection limit. Because the unit is from 

Massachusetts, the fuel variability factor of 10.9 for eastern 

bituminous coal is applicable. Using the data and the fuel 

variability factor of 10.9, the revised mercury emission limit for 
new and existing coal-fired boilers is 2.2 X 10-5 lb of mercury per 

MMBtu.

2.0 BEYOND-THE-FLOOR OPTION

In the beyond-the-floor option for mercury emissions, new and 

existing coal-fired boilers would be required to comply with a 

mercury emission limit more stringent than the MACT floor-based 

emission limit of 2.2 X 10-5 lb of mercury per MMBtu. To comply with a 

limit more stringent than the fabric filter-based MACT floor limit

(e.g., to meet a limit such as the utility boiler-based limit in the 

March 2011 final rule), it is expected that an affected boiler would 

need to employ fabric filter control along with activated carbon 

injection (ACI). Boilers already using a fabric filter would be 

expected to install an ACI system. Boilers without fabric filters 

would be expected to install a fabric filter and ACI system.

The beyond-the-floor analysis for mercury emissions from major 

source boilers assessed the costs of and emission reductions 

associated with installation of ACI. The installation of ACI for 

control of mercury resulted in over $85,000 per additional pound of 

mercury emission reductions. It was determined that the beyond-thefloor option of installing ACI for mercury control is not 

economically feasible.1 Based on the fact that the vast majority of 

area source boilers are small entities and that beyond-the-floor ACI 

control was not appropriate for major source boilers with higher 

levels of mercury and much larger economies of scale, we have also 

determined that the beyond-the-floor option of installing ACI for 

mercury control from area source coal-fired 1boilers is not 

economically feasible. 

 

1

Beyond the Floor Technology Analysis for Major Source Boilers and Process Heaters, January 2011, Docket ID EPA-HQOAR-2002-0058, Document ID EPA-HQ-OAR-2002-0058-3260