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

Table s 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 , 201 3

Purpose of Memo randum :

U nder 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 petit ioners questioned the validity of the N 2 O 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 N 2 O 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 f actors 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 o f the work completed by RTI is presented in this Memorandum.

Conclusion:

RTI found in literature studies of N 2 O emissions fr om fluidized bed combustors (FBCs) that the lower combustion
temperatures in FBCs can substantially increase the fraction of fuel bound nitrogen that is converted to N 2 O as compared to conventional combustion technologies such as pulverized coal combustors. Based on these studies

, RTI is recommending that EPA incorporate separate N 2 O emissions factors for FBC s into Table C

- 2 for coal and

waste coal , as presented in Exhibit 1

. Regarding CH 4 emissions factors f or waste coal combustion in FBCs, RTI recommends using the current CH 4 factor

for coal and coke in Table C

- 2. There is currently no data in the rulemaking record or from re search conducted by RTI during assessment of the petitioners claim to support a new emission factor for CH 4 emissions from burning

waste coal in an FBC

. Data in EPA’s AP

- 42 Chapter 1.1 suggest that CH 4 emissions from burning bituminous coal

in a n FBC are of similar magnitude to CH 4 emissions from conventional combustion types. Typically, variations in

CH 4 emissions are due to unit size, whereby smaller units have higher CH 4 emissions than larger units whose CH 4 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 CO 2 factor of the parent f uel in Table C

- 1 for CO 2 emissions from waste coal

combustion in FBCs . Emissions of CO 2 are directly proportional to the heating value of the fuel. Since w aste 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 CO 2 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 CO 2 emissions from burning waste coal.

Because waste coal is rarely burned in convention al combustion units, RTI recommends using the default CO 2 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 N 2 O and CH 4 emission fact ors for coal and coke in Table C

- 2

.2 Exhibit 1

– Recommended N 2 O Emission Factor s for Fluidized Bed Combustors

Default N 2 O Emission Factor for Fluidized Bed Combustors for Coal and Waste Coal

Fuel Type Current N 2 O emission factor (kg N 2 O/mmbtu) Recommended N 2 O emission factor (kg N 2 O/mmbtu) 1

Anthracite 1.6 E

- 03 1

. 62 E

- 01

Bituminous Coal 1.6 E

- 03 1

. 2 7 E

- 01
Lignite Coal 1.6 E

- 03 1

. 14 E

- 01

Subbituminous Coal 1.6 E

- 03 6

. 5 0 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, 5 00°F

. The typical operating temperature of FBCs is approximately 1100 ° K (1520 ° F). Maximum concentration of N 2 O (250 ppm) occur s in the 1300 to 1400 ° F range for most coal types using the derived equations. A bove 1700 ° F , N 2 O destruction mechanisms overcome N 2 O 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). Author s: Wojtowicz, M.A.; Oude Lohuis, J.A.; Tromp, P.J.J.; and Moul ijn, 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

N 2 

### O Emission Calculations for Different Coal Types from Fluidized Bed Boilers

( T h e calculation i s d e r i v e d f r o m c o p y r i g h t e d m a t e r i a l a n d i s a v a i l a b l e i n h a r d c o p y a t the Air and Radiation Docket, EPA/DC, EPA West, Room B102, 1301 Constitution 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 t elephone number for the Public Reading Room is (202) 566

- 1744, and the telephone number for the Air Docket is (202) 566

- 1742

. )