SUBJECT: Emission Factor Updates for Fluidized Bed Boilers and Other Revisions to 

Tables C-1 and C-2 of 40 CFR Part 98 – Summary

FROM: Stephen Boone and Kristine Pelt of RTI International

TO: Mike Hannan, EPA, OAP, CCD

DATE: January 23, 2013

Purpose of Memorandum:

Under a technical directive from the Environmental Protection Agency’s (EPA) Climate Change Division (CCD), 

RTI International (RTI) was asked to review the merits of a petition that was submitted by several environmental 

groups in October 2010 regarding the Greenhouse Gas Reporting Rule codified in 40 CFR Part 98. Specifically, the 

petitioners questioned the validity of the N2O emission factors in Table C-2 for fluidized bed boilers burning coal,

claiming that the low combustion temperatures occurring in fluidized bed boilers inherently produce more N2O than 

conventional boilers. Because many fluidized bed boilers burn waste coal, the petitioners were also concerned about 

properly quantifying GHG emissions from burning waste coal in fluidized bed boilers. The petitioners also asked 

EPA to examine the validity of the GHG emission factors for waste coal from conventional combustion 

technologies. The Climate Change Division requested that RTI review the petition and recommend, if appropriate, 

revised emission factors for fluidized bed boilers burning coal and waste coal. A summary of the work completed 

by RTI is presented in this Memorandum.

Conclusion:

RTI found in literature studies of N2O emissions from fluidized bed combustors (FBCs) that the lower combustion 

temperatures in FBCs can substantially increase the fraction of fuel bound nitrogen that is converted to N2O as 

compared to conventional combustion technologies such as pulverized coal combustors. Based on these studies,

RTI is recommending that EPA incorporate separate N2O emissions factors for FBCs into Table C-2 for coal and 

waste coal, as presented in Exhibit 1.

Regarding CH4 emissions factors for waste coal combustion in FBCs, RTI recommends using the current CH4 factor 

for coal and coke in Table C-2. There is currently no data in the rulemaking record or from research conducted by 

RTI during assessment of the petitioners claim to support a new emission factor for CH4 emissions from burning 

waste coal in an FBC. Data in EPA’s AP-42 Chapter 1.1 suggest that CH4 emissions from burning bituminous coal 

in an FBC are of similar magnitude to CH4 emissions from conventional combustion types. Typically, variations in 

CH4 emissions are due to unit size, whereby smaller units have higher CH4 emissions than larger units whose CH4

emissions are usually at non-detectable levels. The majority of FBCs submitted during the first two years of 

reporting under the GHGRP are large units; all FBCs that reported burning waste coal had a rated capacity of at least 

700 MMBtu/hr. 

RTI recommends the default CO2 factor of the parent fuel in Table C-1 for CO2 emissions from waste coal 

combustion in FBCs. Emissions of CO2 are directly proportional to the heating value of the fuel. Since waste coals 

have highly variable heating values and the heating value is much lower than the parent coal, RTI recommends 

amending 40 CFR 98.33(b) Use of the four tiers, to clarify that Tier 1 may not be used for emission estimates for 

waste coal combustion. The Tier 1 methodology allows the use of default heating values in the CO2 emissions 

calculation. The Tier 2 and Tier 3 methodologies require sampling of the HHV and the carbon content of the fuel, 

respectively, and use of these Tiers or CEMS measurement (Tier 4) should more accurately reflect CO2 emissions 

from burning waste coal.

Because waste coal is rarely burned in conventional combustion units, RTI recommends using the default CO2

emission factors of the parent coal in Table C-1 (i.e., use the anthracite factor for culm and the bituminous factor for 

gob) and the default N2O and CH4 emission factors for coal and coke in Table C-2.
2

Exhibit 1 – Recommended N2O Emission Factors for Fluidized Bed Combustors

Default N2O Emission Factor for Fluidized Bed Combustors for Coal and Waste Coal

Fuel Type Current N2O emission 

factor (kg N2O/mmbtu)

Recommended N2O emission 

factor (kg N2O/mmbtu)1

Anthracite 1.6 E-03 1.62 E-01

Bituminous Coal 1.6 E-03 1.27 E-01

Lignite Coal 1.6 E-03 1.14 E-01

Subbituminous Coal 1.6 E-03 6.50 E-02

Anthracite Culm Waste Coal 1.6 E-03 3.99 E-01

Bituminous Gob Waste Coal 1.6 E-03 2.94 E-01

1 Default factors all assume a fuel with one percent nitrogen content and a combustion temperature of 1,500°F. The typical operating temperature 

of FBCs is approximately 1100°K (1520°F). Maximum concentration of N2O (250 ppm) occurs in the 1300 to 1400°F range for most coal types 

using the derived equations. Above 1700°F, N2O destruction mechanisms overcome N2O formation. Nitrogen contents were derived from data 

in Mark’s Standard Handbook for Mechanical Engineers and The Air Pollution Engineering Manual. Derived from Proceedings of the 11th 

International Conference on Fluidized Bed Combustors, American Society of Mechanical Engineers, E.J. Anthony (Editor). Authors: Wojtowicz, 

M.A.; Oude Lohuis, J.A.; Tromp, P.J.J.; and Moulijn, J.A. N2O Formation in the Fluidized Bed Combustion of Coal pages 1013 to 1020. 

Copyright (1991), with permission from Elsevier and ASME. 
3

Appendix A

N2O Emission Calculations for Different Coal Types from Fluidized Bed Boilers

(The calculation is derived from copyrighted material and is available in hard copy at the Air and Radiation Docket, 

EPA/DC, EPA West, Room B102, 1301Constitution Ave., NW., Washington, DC. The Public Reading Room is 

open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the 

Public Reading Room is (202)566-1744, and the telephone number for the Air Docket is (202) 566-1742.)