MEMORANDUM

TO: Brian Shrager/SPPD

FROM: Eastern Research Group, Inc.

DATE: November 2011

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

Process Heaters

1.0 INTRODUCTION

This memorandum describes the selection of a “beyond‐the‐floor” (BTF) emission limit

for one subcategory of boiler for the boiler MACT reconsideration. The overall approach to the

BTF technology analysis is described in the memo entitled “Beyond the Floor Technology

Analysis for Major Source Boilers and Process Heaters,” January, 2011, that was developed in

support of the final boiler MACT that was published in the Federal Register in March 2011. This

memo describes the selection of one BTF option for one of the alternative emission limits that

is part of the reconsideration proposal.  For existing fuel cells designed to combust biomass

fuels, EPA considered the new source MACT floor emission limit for total selected metals

(TSM8), which include arsenic (As), beryllium (Be), cadmium (Cd), chromium (Cr),lead (Pb),

manganese (Mn), nickel (Ni), and selenium (Se) as a BTF option.  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 another memorandum.1 This analysis estimates

the incremental costs and emission reductions incurred on existing fuel cells designed to burn

biomass if subjected to beyond‐the‐floor numeric emission limitations.  This memorandum is

separated into the following sections:
1.0 Introduction

2.0 Summary of Beyond‐the‐Floor Option

3.0 Cost Effectiveness of Beyond‐the‐Floor Option

4.0 References

Appendix A:  Emission and Cost Impacts for the Beyond‐the‐Floor Option

   
2.0 SUMMARY OF BEYOND‐THE‐FLOOR OPTION

In this BTF option, existing fuel cells designed to combust biomass would comply with

the more stringent new source emission limitations for TSM8.  Table 1 provides a comparison of

the existing source and new source numeric TSM8 emission limitations for fuel cells designed to

combust biomass.

Table 1 – Comparison of Existing and New Source TSM8 MACT Floors for Biomass Fuel Cells 

Subcategory

TSM8 MACT Floor (lb/MMBtu)

Existing Sources New Sources

Fuel cells designed to combust

biomass 0.19 0.000049

Of the units in the boiler and process heater inventory, fuel cells comprise a small

portion of the overall units; only 15 out of over 14,000 units in the inventory are identified as

fuel cells.  Of those 15 units, only two of these units have TSM8 data that could be standardized

and used to compute a MACT floor, as described in another memorandum.1 Because this

subcategory comprises less than 30 units, the MACT floor is computed on all available data, up

to the top five units.  So, both of the fuel cells with TSM8 data available are used to compute

the MACT floor.  There is a large variability between the test results at each of these two units;

the difference in the average emissions of the two units exceeds two orders of magnitude.  As a

result of the small data set, which consists of three total tests, and a large standard deviation

among the test runs from these two units, the 99 percent upper prediction limit (UPL) is

computed to be 0.19 pounds per million British thermal units of heat input (lb/MMBtu).

This computed MACT floor value is two orders of magnitude higher than any of the

other MACT floor for the other biomass subcategories.  The next highest TSM8 MACT floor at

another biomass subcategory is 1.3E‐03 lb/MMBtu for fluidized bed combustors.  Further, the

computed limit is between two and 4 orders of magnitude higher than the emission tests

reported by either of the two fuel cell boilers that comprise the best performers in this

subcategory.  Comparing this alternative TSM8 MACT floor to the filterable particulate matter
(PM) MACT floor emission limit for the same category, the TSM8 limit is an order of magnitude

higher than the PM limit (0.19 lb/MMBtu for TSM8 compared to 0.033 for PM).  Further, the

PM MACT floor was based on data from five units compared to only two units with data for

TSM8.

The current control devices installed on the two fuel cell units with available TSM8 data

shows a large variation.  The top ranked unit, IDPotlatch BP‐1 CE, has an ESP control device

installed while the second ranked unit, ARAnthonyForestProducts SN‐12, has a multiclone.  

There are 13 other units in the fuel cell subcategory that did not report any usable data for

TSM8. The distribution of control devices in this subcategory are summarized in Table 2 below.

Table 2 – Count of Control Types on All Existing Biomass Fuel Cells 

Control Type Number of Fuel Cells

with Control Type

Cyclone or Multiclone 3

Electrified Filter Bed (EFB) 2

Electrostatic Precipitator 7

Fabric Filter 1

Wet Scrubber 2

After considering the qualitative data from this subcategory, we concluded that the

uncontrolled TSM8 data from ARAnthonyForestProducts SN‐12 is not representative of a best

performer in the subcategory given the plethora of PM controls installed at other units in the

subcategory.  Instead, this data point represents the only other data available for the

subcategory.  As such, the MACT floor based on this data point is not considered representative

of the average performance of the best performing units in the subcategory.

The remainder of this section documents the methods and assumptions used to

estimate which add‐on pollution control devices would be required for units in the fuel cell

subcategory to comply with the BTF limit for TSM8, and the resultant incremental emission

reductions achieved as a result of the beyond‐the floor option.
2.1 Baseline Emissions

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

option, baseline emission factors were estimated for each unit.  A description of the methods

used to estimate baseline emissions is discussed in another memorandum.3

  

2.2 Emission Reductions

Under the proposed option, fuel cells designed to combust biomass may demonstrate

compliance with either a PM or an alternative TSM8 numeric emission limit.  To estimate

emission reductions associated with a TSM8 MACT floor value of 0.19 lb/MMBtu, it was

assumed that facilities would elect to demonstrate compliance with the pollutant requiring the

minimum percent reduction compared to its baseline emission levels.  This minimum control

efficiency was applied to emissions of PM, TSM8, and the sum of 10 selected metallic HAP

(TSM10), including cobalt (Co) and antimony (Sb) in addition to the eight metals included in

TSM8.  A description of the methods used to estimate emission reductions for the proposed

regulatory option for existing sources is provided in another memorandum.2,3 In this case, since

the TSM8 MACT floor was so high, all 15 units in the subcategory had estimated baseline

emission factors that were less than the TSM8 MACT floor.  As a result, the minimum control

efficiency to meet the TSM MACT floor limit was zero percent and no emission reductions were

estimated for PM,  TSM8, and TSM10.  Similar to the above discussion, to estimate the emission

reductions associated with a TSM8 BTF option, the minimum control efficiency needed to

achieve either the PM MACT floor or the TSM8 BTF limit was calculated and this control

efficiency was applied to calculate reductions of PM, TSM8, and TSM10.  Under the BTF option,

many of the estimated baseline emissions from fuel cells exceeded the PM MACT floor and

TSM8 BTF limits and emission reductions were estimated for PM, TSM8, and TSM10 at 9 of the

15 fuel cell units.

Details of the estimated emission reductions under both the MACT floor and BTF TSM8

emission limits are presented in Appendix A.
2.3 Add‐on Pollution Control Devices

Based on information available for the 15 units in the fuel cell subcategory, and

estimated baseline emissions at each of these units, five out of seven fuel cell units with an

electrostatic precipitator (ESP) are able to achieve the PM MACT floor emission limit.  One unit

with an ESP and one unit with a fabric filter are also able to meet both the PM MACT floor and

TSM8 BTF emission limits.  As noted above, the top performing unit for TSM8, IDPotlatch BP‐1

CE, has an ESP installed.  Further, some of these fuel cell units are expected to install control

devices in order to demonstrate compliance with the MACT floor emission limits for other

pollutants, which is discussed in another memorandum.1 As a result, compliance with the BTF

numeric emission limitation for TSM8 is expected to be achieved via the installation of an ESP,

unless the unit was already required to install a fabric filter or a combination fabric filter and

dry injection (DIFF) system for MACT compliance.  Fabric filters and DIFF systems are expected

to provide reductions in emissions of PM and metallic HAP emissions in addition to mercury

(Hg) and hydrogen chloride (HCl).

Since most units with an existing ESP met the PM MACT floor or TSM8 BTF limit, if a unit

already had an ESP installed and estimated baseline emissions from the unit were above both

the PM MACT floor and TSM8 BTF limits, it was assumed that the facility would conduct an

engineering assessment of the existing ESP system in order to improve its efficiency and

demonstrate compliance.

Appendix A provides the unit‐specific details of existing controls installed on the unit as

well as other controls that are expected to be installed in order to comply with other pollutant

emission limits.

3.0 COST EFFECTIVENESS OF BEYOND‐THE‐FLOOR OPTION

After evaluating which units might need additional controls installed to meet the TSM8

BTF emission limit, the costs to install these controls were estimated to represent the

incremental costs of the TSM8 BTF emission limit.  The methods and calculations used to

estimate costs for each type of control are provided in other memoranda.2,4 Since testing and
monitoring provisions of the proposed rule would be required regardless of whether the TSM8

MACT floor or the BTF emission limit was selected, only the costs associated with the

installation of controls were included in the incremental cost analysis.

Incremental cost effectiveness was calculated by dividing the incremental costs of ESP

controls by the incremental emission reductions for TSM10 and PM.  Since there are no

reductions in TSM10 and PM estimated when the TSM8 emission limit is equal to the MACT

floor, the incremental emission reductions represent the total amount of reductions in PM and

TSM10 after applying the minimum control efficiency discussed in Section 2.2.  This provided

the cost associated with reducing an additional ton of emissions of each pollutant.  A summary

of the overall cost‐effectiveness associated with selecting a BTF TSM8 emission limit is provided

in Appendix A‐2.

In total, only six of the 15 units in the fuel cell subcategory were expected to install an

ESP for compliance with the BTF option.  For these six units, the incremental cost effectiveness

was $1.4 million per ton of TSM10 and approximately $8,900 per ton of PM.     
4.0 REFERENECS

1. Eastern Research Group, Inc.  Revised MACT Floor Analysis (November 2011) for the

Industrial, Commercial, and Institutional Boilers and Process Heaters National Emission

Standards for Hazardous Air Pollutants – Major Source.  November, 2011.

2. Eastern Research Group, Inc.  Revised (November 2011) Methodology for Estimating

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

Heaters National Emission Standards for Hazardous Air Pollutants – Major Source.  

November, 2011.

3.   Eastern Research Group, Inc.  Revised November 2011 Development of Baseline

Emission Factors for Boilers and Process Heaters at Commercial, Industrial, and

Institutional Facilities.  November, 2011.

4. Eastern Research Group, Inc.  Revised (November 2011) Methodology for Estimating

Control Costs for Industrial, Commercial, Institutional Boilers and Process Heaters

National Emission Standards for Hazardous Air Pollutants – Major Source.  November,

2011.

   
Appendix A

Emission and Cost Impacts for the Beyond‐the‐Floor Option

[see Excel spreadsheet)