US2000 12241175.2 

September 8, 2011 

The Honorable Lisa P. Jackson 

Administrator 

U.S. Environmental Protection Agency 

Ariel Rios Building 

1200 Pennsylvania Avenue, N. W. 

Mail Code: 1101A 

Washington, DC 20460 

Re: Supplement to Petition for Reconsideration and Amendment of the Major 

Source Boiler MACT Rule; EPA Docket ID No. EPA-HQ-OAR-2002-0058 

Dear Administrator Jackson: 

 On behalf of the American Home Furnishings Alliance (AHFA), I am submitting 

this written supplement to AHFA’s Petition for Reconsideration and Amendment of the 

Major Source Boiler MACT Rule (the Petition). Our original Petition was filed on May 

20, 2011. In our Petition, we identified several concerns with the Major Source Boiler 

MACT Rule. In particular, we urged EPA to (a) establish a subcategory for boilers 

combusting wood fuel with low moisture content and (b) establish appropriate 

emission limits and work practice standards for such boilers. In this supplement, we 

provide further information to justify the creation of a new subcategory for boilers 

that combust fuel that we describe as Dry Wood Fuel (DWF). 

 Section 112(d)(1) of the Clean Air Act authorizes EPA to distinguish among 

“classes, types, and sizes” of sources that are subject to MACT standards. We believe 

that boilers that combust DWF are distinguishable from other boiler in the various 

subcategories in the Major Source Boiler Rule. For the reasons set forth below, we 

recommend that EPA establish a new subcategory entitled “Nondrying Suspension 

Boilers.” 

Dry Wood Fuel Characteristics 

 For purposes of this analysis, we define DWF as wood with a moisture content 

less than or equal to 20%. The average moisture content of DWF is approximately 

0.5% - 1.5%, based on fuels test results collected for the original Boiler MACT. 

Examples of DWF include (but are not limited to): 

• Dry lumber, wood veneers, and other similar wood products; and 

• Dry wood products (containing resin adhesives) derived from primary 

and secondary wood products manufacturing and comprised of such 

items as board trim, sander dust, and panel trim. 

3 1 7 W . H i g h A v e . , 1 0 t h F l o o r 

P . O . B o x H P - 7 

H i g h P o i n t , N C 2 7 2 6 1 

P h o n e 3 3 6 . 8 8 4 . 5 0 0 0 

F a x 3 3 6 - 8 8 4 - 5 3 0 3 
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September 8, 2011 

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DWF is a clean cellulosic material that is composed principally of carbon, hydrogen, 

and oxygen. It has distinctively low ash content at less than 1 percent mineral ash, and 

is very low in heavy metals. The chlorine and sulfur content of DWF is low compared 

to coal. 

 DWF as produced and combusted has low moisture content. Indeed, DWF is 

much drier than other biomass fuels, which have moisture contents that may range 

from 25% to 70%. Because DWF is produced as dry biomass, driving off moisture in 

the combustion chamber consumes very little energy when compared to other 

biomass fuels. As a result, the heating value for DWF as received is on average higher 

than other biomass fuels. The range of DWF heating values is approximately 7,800 – 

9,000 BTU/lb with an average typically near 8,100 BTU/lb.1 Published heating values 

for other biomass fuels range are in the range of 6,450-8,200 BTU/lb. 

 Unlike many other fuels combusted in boilers, DWF is a renewable fuel. DWF 

produces no net greenhouse gas (GHG) emissions when combusted. Recognizing that 

wood and other forms of biomass may be considered carbon-neutral fuels, EPA has 

instituted a three-year deferral of PSD permitting requirements for biogenic CO2 

emissions, and the IPCC has provided statements supporting the concept of carbon 

neutrality for biogenic fuels. If combustion of DWF became impracticable under the 

Boiler MACT rule, DWF would be disposed of in landfills where it would likely lead to 

methane formation through anaerobic decomposition. Any reduction in DWF 

combustion would likely be replaced by combustion of fossil fuels. 

Characteristics of Dry Wood Fuel Boilers

 DWF boilers are designed to accommodate the unique characteristics of DWF, 

which must be handled and combusted differently than other biomass fuels. Because 

DWF is a unique fuel with its own combustion profile and emissions characteristics, 

boilers must be configured and operated to ensure efficient DWF combustion. In 

addition, DWF boilers are designed to accommodate highly variable conditions and 

swings in operations. 

 In particular, DWF boilers are unique because more of the combustion occurs 

in suspension when compared with other boilers identified the Boiler MACT Rule, such 

as a standard suspension boiler or a hybrid suspension grate boiler. Therefore, we 

believe that an appropriate name for subcategorizing DWF boilers is “nondrying 

suspension boilers.” Based on our survey of our industry boilers and their unique 

characteristics, we define nondrying suspension boilers as: Boilers less than or equal 

to 70 MMBTU/hr (heat input capacity) that combust low moisture fuel while 

suspended in air and complete combustion of the fuel on grates or floors. 

 

1

 Based on fuels testing by AHFA members in 2010. 
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September 8, 2011 

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 As a result of increased combustion of DWF in suspension, nondrying 

suspension boilers have a significantly higher heat release rate than other biomass 

boilers combusting higher moisture fuels. Moreover, nondrying suspension boilers 

require much higher excess air rates than other boilers. The high excess air promotes 

better turbulence, but reduces residence time in the combustion zone. This 

combustion of dry fuel results in relatively high combustion temperatures in the 

boilers and high heat release rates. AHFA is working with a boiler consultant to 

document the time, temperature, and turbulence profile for nondrying suspension 

boilers. We will provide that information to EPA as soon as it is available. 

 The fuel storage and feed systems are integral to nondrying suspension 

boilers. Nondrying suspension boilers include dedicated pneumatic fuel feed systems, 

preceded by dry fuel storage such as silos or covered sheds. Nondrying suspension 

boilers include a continuous DWF supply to the feeders that are specifically designed 

to control the DWF feed rate. Pneumatic injection is used to distribute the DWF 

throughout the width and depth of the boiler. 

 Since both suspension and grate (or floor) combustion occur, the temperature 

profile within the boiler is highly variable. As a consequence, steam production and 

production of carbon monoxide (CO) vary significantly over even short periods of time 

due to changing species and geometry of the DWF and the changing conditions within 

the boiler. Combustion in suspension and a high peak heat combustion temperature 

result in a unique emissions profile, especially with respect to CO, volatile HAP, and 

PM. For other key pollutants related to fuel type, combustion of DWF results in very 

low emissions of heavy metals, mercury, hydrogen chloride (HCl), and sulfur dioxide 

(SO2). 

PM Limits for the Nondrying Suspension Boiler Subcategory

 In the Major Source Boiler Rule, EPA classified non-mercury metallic HAP as a 

fuel-dependent pollutant. EPA then identified PM as a surrogate for non-mercury 

metallic HAP. Finally, EPA established a single PM limit that applies to all existing solid 

fuel boilers. AHFA believes that PM emissions are primarily a function of boiler design 

and operation. Thus, the unique configuration of nondrying suspension boilers 

indicates that PM emissions should be evaluated for this unique subcategory, rather 

than grouping those boilers with the non-discrete subcategory consisting of all solid 

fuel boilers. We urge EPA to establish PM emission standards for the proposed 

nondrying suspension boiler subcategory. 

Conclusion

 Nondrying suspension boilers are unique devices by virtue of their design and 

operation as well as the fuel they combust. Placing nondrying suspension boilers in a 

subcategory with other boilers with different design, operating, and emission 

characteristics would not be appropriate, and would result in unachievable MACT 
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September 8, 2011 

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emission limits. Therefore, AHFA respectfully urges EPA to establish a separate 

subcategory for nondrying suspension boilers in the Major Source Boiler MACT Rule. 

 We welcome the opportunity to continue working with EPA during the 

reconsideration process. Please contact me at 336-884-5000, extension 1017 or 

bperdue@ahfa.us if you have any questions about this supplemental filing. Thank you 

for your consideration of this important issue. 

 

Sincerely, 

Bill Perdue 

Vice President of Regulatory Affairs 

cc (via electronic mail):

Bob Wayland 

Brian Schrager 

Jim Eddinger