MEMORANDUM

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

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

DATE: December 2012

SUBJECT: Beyond-the-Floor Analysis for Mercury

and Carbon Monoxide

Area Source Industrial/Commercial/Institutional Boilers

1.0 BACKGROUND

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

for mercury emissions and carbon monoxide (CO) 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 bestperforming 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 coalfired 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 
2

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.

As discussed in the final reconsideration rule, we are amending 

the CO emission limit for new and existing coal-fired boilers from 

400 parts per million (ppm) by volume on a dry basis, corrected to 3 

percent oxygen, to 420 ppm by volume on a dry basis, corrected to 3 

percent oxygen. It is anticipated that combustion controls, either a 

basic tune-up or a more advanced burner replacement or installation 

of a linkageless boiler management system, can achieve the MACT floor 

emission limit.

2.0 BEYOND-THE-FLOOR ANALYSIS

As discussed in the preamble to the June 2010 proposed rule (75 

FR 31896) and the preamble to the March 2011 final rule (76 FR 

15554), the EPA determined that fuel switching was not an appropriate 

control technology for purposes of determining either the MACT floor 

level or beyond-the-floor level of control. As also discussed in the 

June 2010 and March 2011 preambles, we determined that an energy 

assessment requirement was an appropriate beyond-the-floor option for 

existing large boilers. These previous analyses continue to be 

applicable for mercury as well as the pollutants for which CO is a 

surrogate.

In this beyond-the-floor analysis for mercury emissions, new and 

existing large 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,

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 
3

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.

In this beyond-the-floor analysis for CO emissions, new and 

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

CO emission limit more stringent than the MACT floor-based emission 

limit of 420 ppm by volume on a dry basis, corrected to 3 percent 

oxygen. To comply with a limit more stringent than the MACT floor 

based limit, it is expected that an affected boiler may need to 

install an oxidation catalyst.

The beyond-the-floor analysis for CO emissions from major source 

boilers assessed the costs of and emission reductions associated with 

installation of an oxidation catalyst. For units combusting solid 

fuel, the cost for reducing an additional ton of CO emissions is only 

$2,000 in annual costs. However, combustion of solid fuels results in 

significant amounts of dust and fly ash, which can plug or blind 

catalyst reactive sites necessary to oxidize CO. This reduces the 

efficiency of the oxidation catalyst. To maintain the effectiveness 

of the oxidation catalyst, the unit may require shutting down more 

frequently for cleaning or replacement of the catalyst, incurring 

additional costs on the facility. For these reasons, the beyond-thefloor option of installing an oxidation catalyst for CO control was 

determined to be technically infeasible.2 Other methods of reducing CO

emissions, such as upgrading new burners and overfire air systems, 

were also determined to be technically infeasible options available 

for solid fuel units.3 These combustion controls are not capable of

constantly achieving lower beyond-the-floor emission levels. Many 

existing units may have been designed with specific furnace heat 

release rates in order to be able to fire specific fuel blends, and 

may not be able to meet lower emission levels without complete 

overhaul or replacement of major boiler components at an unreasonably 

high cost.

 

 

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

2

Ibid.

3

Ibid.