**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 fin al 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 (d ry l imestone i njection/ d ry s crubb er / f abric f ilter/ s elective c atalytic r eduction/ s elective n on - c atalytic r eduction (NH 3 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 act ion. 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 emission s 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 forne w 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 st ringent 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 filt er 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 redu ctions 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 - the floor option of installing ACI for mercury contro l 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