1

MEMORANDUM 

TO: Brian Shrager, US EPA\OAQPS\SPPD 

FROM: Amanda Singleton and Graham Gibson, ERG 

DATE: January 2011 

SUBJECT: Beyond the Floor Technology Analysis for Major Source Boilers and Process 

Heaters 

1.0 INTRODUCTION

This memorandum describes the methods used to analyze the beyond-the-floor control 

technology analysis for each subcategory. EPA considered the new source MACT floor 

emission limits for boilers and process heaters as a beyond the floor option for existing major 

source boilers and process heaters. The new source MACT floor emission limits are based on an 

analysis of emissions data from the best performing single source for each pollutant and are 

detailed in a separate memorandum.1 A discussion of fuel-switching and a facility-wide energy 

assessment as interim beyond-the-floor options are discussed in separate memoranda.2,3 The 

beyond the floor control options are not feasible because the cost of reducing an additional ton 

of pollutant emissions for each subcategory is extraordinarily high, or there are limitations on the 

technology’s pollutant removal efficiency in retrofit applications. This memorandum is divided 

into the following sections: 

1.0 Introduction 

2.0 Summary of Beyond the Floor Option 

3.0 Effectiveness of Beyond the Floor Option 

4.0 Plausibility of Beyond the Floor Option 

5.0 References 

 Appendix A: Unit-Level Emission Reductions and Costs for Beyond the Floor Option 

 Appendix B: Summary of Cost Effectiveness of Beyond the Floor Option 
2

2.0 SUMMARY OF BEYOND THE FLOOR OPTION 

In this beyond the floor option, existing units would comply with more stringent new 

source emission limitations for carbon monoxide (CO), mercury (Hg), filterable particulate 

matter (PM), and hydrogen chloride (HCl). Similar to the MACT floor analysis, this beyond the 

floor option was assessed on a pollutant-by-pollutant basis. Tables 1 and 2 compare the emission 

limits for existing sources to the beyond the floor emission limits. No beyond the floor emission 

limits were considered for dioxins/furans given concerns raised during the public comment 

period about the significant presence of non-detect data used to established the MACT floors, the 

uncertainty surrounding the formation of dioxin/furan in this source category, and the 

demonstrated compatibility of dioxin/furan control devices on units with such low dioxin/furan 

inlet concentrations. 

Table 1 – Comparison of Existing and Beyond the Floor Heat Input-Based Emission Limits 

Fuel Category 

Emission Limits for Existing Sources 

Hg (lb/TBtu) PM (lb/MMBtu) HCl (lb/MMBtu) 

Solid 4.6 0.039 0.035 

Liquid 3.4 0.0075 0.0003 

Non-Continental 

Liquid 0.78 0.0075 0.0003 

Process Gas 13 0.043 0.0017 

Fuel Category 

Beyond the Floor Emission Limits 

Hg (lb/TBtu) PM (lb/MMBtu) HCl (lb/MMBtu) 

Solid 3.5 0.0011 0.0022 

Liquid 0.21 0.0013 0.0031 

Non-Continental 

Liquid 0.781

 0.0013 0.0031 

Process Gas 7.9 0.0067 0.00171

1

 Identical to existing source floor; no beyond the floor cost or emission impacts estimated for this 

pollutant/subcategory. 
3

Table 2 – Comparison of Existing and Beyond the Floor Combustor Design-Based Emission Limits 

Fuel Category Combustor Design 

Existing Source 

Emission Limit 

Beyond the Floor 

Emission Limit 

CO 

(ppm @ 3% O2) 

CO 

(ppm @ 3% O2) 

Biomass/ 

Bio-based solid 

Dutch Oven/ 

Suspension Burner 470 4701

Biomass/ 

Bio-based solid Fluidized Bed 430 260 

Biomass/ 

Bio-based solid Fuel Cell 690 470 

Biomass/ 

Bio-based solid Stoker/Other 490 160 

Biomass/ 

Bio-based solid Suspension/Grate 3,500 1,500 

Coal/Fossil Solid Fluidized Bed 82 18 

Coal/Fossil Solid Pulverized Coal 160 12 

Coal/Fossil Solid Stoker/Other 270 6 

Liquid N/A 10 3 

Non-Continental 

Liquid N/A 160 3 

Process Gas N/A 9 3 1

 Identical to existing source floor; no beyond the floor cost or emission impacts estimated for this 

pollutant/subcategory. 

Existing boilers and process heaters would comply with the beyond the floor emission 

limits via the addition of add-on pollution control devices, similar to compliance with MACT 

standards. A description of each add-on pollution control device is provided in another 

memorandum.2

 This section documents the methods and assumptions used to estimate which 

add-on pollution control devices would be required for beyond the floor compliance. Beyond the 

floor impacts were not estimated for units with a rated heat input capacity of less than 10 

MMBtu per hour or for units burning natural gas, refinery gas, or other gas 1 fuels (including 

metallurgical furnaces). For the same reasons provided in the preamble to the final rule for a 

work practice standard on these units, numerical emission limits, either at the MACT floor level 

or beyond-the-floor level, are unworkable and impractical at these units due to emissions 

measurement difficulties. 
4

2.1 Baseline emissions 

In order to estimate the incremental emission reductions associated with this beyond the 

floor option, baseline emissions were estimated for each unit. The baseline emission levels were 

equal to the MACT floor emission limits with a few exceptions: (1) if the reported baseline 

emission level established in the initial baseline emissions analysis was less than the MACT 

floor emission limit, the initial baseline was maintained; and (2) units subject to work practices 

in lieu of emission limits were assigned to a baseline emission level that applied a 1 percent fuel 

and combustion efficiency factor to the original baseline emission estimates. The methods used 

to estimate emission reductions associated with a 1 percent fuel and combustion efficiency factor 

and for MACT compliance are described in another memorandum.4

2.2 Emission Reductions 

Beyond the floor incremental emission reductions were estimated by subtracting the 

newly calculated baseline from the beyond the floor emission limits shown in Tables 1 and 2. 

However, no beyond the floor control options are proposed for TEQ dioxins/furans and, thus, no 

emission reductions were estimated. Emission reductions of CO, Hg, PM, and HCl were only 

estimated if the unit was not already expected to install the identified beyond the floor control 

technology for MACT compliance discussed in section 2.3 below. Although some air pollution 

control devices can achieve greater efficiencies when multiple controls are employed in series, 

no units were required to install more than one of each specific control technology in this 

analysis due to the economic burden and limited retrofit space available at existing units. 

Beyond the floor percent reductions were estimated for CO, HCl, and PM emissions. 

Emissions of THC and VOC were estimated to be reduced based on the calculated percent 

reduction in CO. Emissions of HF and SO2 were estimated to be reduced based on the percent 

reduction in HCl. Emissions of PM2.5 and total selected metals (TSM) were estimated to be 

reduced based on the percent reduction in PM. No additional emission reductions were 

estimated for limited use units, small units (less than 10 MMBtu/hr), and units firing natural gas, 

refinery gas, or other on-spec gaseous fuels since a beyond the floor analysis was not considered 

for these subcategories. 

Appendix A shows the unit-specific emission reductions associated with the beyond the 

floor option. 
5

2.3 Add-on Pollution Control Devices 

Compliance with the beyond the floor emission limits for CO is expected to be achieved 

via installation of an oxidation catalyst. Boilers and process heaters not meeting the beyond the 

floor CO emission limit would install an oxidation catalyst if one was not already estimated to be 

installed for MACT compliance. Emission and cost impacts for CO were not estimated for 

boilers and process heaters that installed an oxidation catalyst for MACT compliance. The new 

source emission limit for CO is identical to the existing source CO emission limit for boilers and 

process heaters burning process gases or liquid in non-continental states or territories, and thus 

the beyond the floor analysis was not considered for these units for CO control. 

Compliance with the beyond the floor emission limits for Hg and PM is expected to be 

achieved via installation of a fabric filter and activated carbon injection (ACI) system. Boilers 

and process heaters not meeting the beyond the floor limit for either Hg or PM would install a 

fabric filter if the unit did not already have a fabric filter installed or if a fabric filter was not 

installed for MACT compliance. If a boiler or process heater was not meeting the beyond the 

floor emission limit for Hg but already had a fabric filter installed, an activated carbon injection 

(ACI) system was expected to be installed to comply with the beyond the floor Hg emission 

limit. Emission and cost impacts for Hg were not estimated for boilers and process heaters that 

already had ACI installed for MACT compliance because there are no other mercury removal 

technologies demonstrated on industrial/commercial/institutional boilers. 

Compliance with the beyond the floor emission limit for HCl is expected to be achieved 

by installing either a fabric filter and dry injection (DIFF) combination or a wet scrubber. 

Similar to the assumption made in the MACT floor impacts analysis, boilers or process heaters 

located at facilities without wastewater discharge permits could not install a wet scrubber. 

Boilers and process heaters not allowed to discharge wastewater were defined by facilities 

assigned a North American Industry Classification System (NAICS) code of 321 (wood product 

manufacturing) or 322 (paper manufacturing). For boilers and process heaters at facilities with 

allowable wastewater discharge, the cost of DIFF and a wet scrubber were compared and the 

cheaper option was assumed to be installed. If a boiler or process heater already had a wet 

scrubber installed, the rate of caustic injection of the scrubber would be increased to a point 

where compliance is met. Emission and cost impacts for HCl were not estimated for boilers and 
6

process heaters that installed DIFF for MACT compliance. 

Appendix A shows the unit-specific control costs associated with the beyond the floor 

option for each of the target pollutants. 

3.0 EFFECTIVENESS OF BEYOND THE FLOOR OPTION 

The incremental costs and emission reductions above the cost and emission reductions 

achieved from the MACT floor were estimated. Annual costs were estimated for units expected 

to install additional add-on pollution control devices to comply with the beyond the floor 

emission limits. The methods and calculations used to estimate cost impacts are described in 

another memorandum.2

 Since testing and monitoring would be required under both the MACT 

floor and beyond the floor control options, only the costs associated with the installation of 

controls were considered in this analysis. An incremental cost effectiveness was calculated by 

dividing the incremental costs by the incremental emission reductions, to estimate a dollars per 

ton of pollutant reduction for the various types of targeted HAP and HAP surrogates. The cost 

effectiveness estimates for each beyond the floor control option can be found in Appendix B. 

4.0 PLAUSIBILITY OF BEYOND THE FLOOR OPTION 

Oxidation catalysts were estimated to be installed on units in all subcategories in order to 

comply with beyond the floor CO emission limits. For units firing liquid fuels, the cost of 

reducing an additional ton of CO emissions is $86,000 in annual costs. For non-continental 

liquid units and units combusting process gases, that same cost is over $11,000 for each 

subcategory. These costs are unfeasibly high. 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. The installation of fabric filters upstream of the catalyst could reduce the amount of 

dust to which the catalyst bed may be subjected, but this would also impose a significant cost 
7

burden on a facility if the unit is not already required to install a fabric filter for control of other 

pollutants. While dust problems could arise for units required to install an oxidation catalyst for 

MACT compliance, the probability of this problems occurring is estimated to be higher for the 

beyond the floor option considering that a higher efficiency is needed to achieve the more 

stringent beyond the floor limits. For these reasons, the beyond the floor option of installing an 

oxidation catalyst for CO control is technically infeasible. Other methods of reducing CO 

emissions, such as upgrading new burners and overfire air systems, were not a technically 

feasible option available to achieve the beyond the floor emission limits for solid fuel units. In 

many cases the beyond the floor limits were between 30 and 98 percent lower than the MACT 

floor emission levels for existing solid fuel sources and although combustion improvements 

could help achieve the MACT floor emission limits, these combustion controls are not capable of 

constantly achieving these lower emission levels associated with the beyond the floor option. 

Further many existing units may have been designed with specific furnace heat release rates in 

order to be able to fire specific fuel blends, and although the best source in each subcategory is 

demonstrated to meet the emission limit, existing sources may not be able to do so without 

complete overhaul or replacement of major boiler components at an unreasonably high cost. 

All non-continental liquid units subject to emission limits were expected to install a 

fabric filter for MACT compliance. Therefore, compliance with the beyond the floor PM 

emission limit would necessitate an additional fabric filter, doubling the MACT cost for these 

units in exchange for minimal additional PM reductions. Alternatively, these units may require 

additional particular control devices, such as a cartridge filtration system, which would require 

additional capital and operating expenses and additional energy to power the fans for adequate 

draft. For each of the remaining subcategories, where an incremental fabric filter is needed to 

meet the beyond the floor limit, the cost of reducing an additional ton of PM emissions is over 

$100,000 in annual costs. Since PM is the surrogate for non-mercury metallic HAP, the cost 

effectiveness of removing a small incremental amount of non-mercury metallic HAP was 

between $3.4 and $31 million per additional ton removed. The cost of this beyond the floor 

option is not justified given the small incremental reduction in metallic HAP emissions. 

All units combusting process gases were expected to install a fabric filter in order to meet 

the beyond the floor PM emission limit. As a result of the fabric filter’s co-benefit of controlling 

both PM and Hg, no process gas units were estimated to need an ACI system to meet the beyond 
8

the floor Hg limit. For each of the remaining subcategories, the installation of an ACI for 

compliance with beyond the floor Hg limits results in over $85,000 per additional pound of Hg 

emission reductions. For these reasons, the beyond the floor option of installing ACI for Hg 

control is economically infeasible. 

A beyond the floor analysis for HCl was not conducted for the process gas subcategory 

since the beyond the floor HCl emission limit is equal to the HCl MACT floor emission limit. 

All units combusting liquid fuels (including non-continental liquid units) were expected to install 

either a scrubber or DIFF for MACT compliance. Therefore, no other control option exists to 

meet a more stringent beyond the floor option. Only some of the units combusting solid fuels 

were estimated to be required to install a scrubber or DIFF for HCl and acid gas control. The 

cost of reducing an additional ton of HCl from these units firing solid fuels is estimated to be 

over $166,000 in annual costs. When considering reductions in HCl and HF, the costeffectiveness is only reduced to $156,000 in annual costs. For these reasons, the beyond the 

floor option of installing a scrubber or DIFF for HCl control is not economically feasible. 
9

5.0 REFERENCES 

1. Singleton, A., ERG. Revised MACT Floor Analysis for the Industrial, Commercial, 

Institutional Boilers and Process Heaters National Emission Standards for Hazardous Air 

Pollutants – Major Source. January 2011. 

2. Singleton, A. and G. Gibson, ERG. Revised Methodology for Estimating Cost and 

Emissions Impacts for Industrial, Commercial, Institutional Boilers and Process Heaters 

National Emission Standards for Hazardous Air Pollutants – Major Source. January 2011. 

3. Singleton, A. and G. Gibson, ERG. Revised Development of Baseline Emission Factors 

for Boilers and Process Heaters at Commercial, Industrial, and Institutional Facilities. 

January 2011. 

4. Singleton, A. and G. Gibson, ERG. Revised Methodology for Estimating Cost and 

Emissions Impacts for Industrial, Commercial, Institutional Boilers and Process Heaters 

National Emission Standards for Hazardous Air Pollutants – Major Source. January 2011. 
10

Appendix A 

Unit-Level Emission Reductions and Costs for Beyond the Floor Option 

(See Excel spreadsheet) 
11

Appendix B 

Summary of Cost Effectiveness of Beyond the Floor Option

(See Excel spreadsheet)