Page 68 - Wastewater Solids Incineration Systems

Combustion Theory 37

This equation is sometimes known as the modified DuLong equation and was
developed for coals with more than 15% oxygen. Because there is often significant
oxygen content in municipal WWTP residuals, the Mott-Spooner equation may give
slightly better results.
Channiwala (1992) collected data on more than 200 species of biomass and fitted
the following equation to the data:
HHV 0.3491 C 1.1783 H 0.1034 O – 0.0211 A 0.1005 S 0.0151 N

where HHV is expressed in kilojoules per gram.
Of all of the above equations, Channiwala’s equation has the best correlation
with primary and waste activated sludges and digested biosolids.
The U.S. EPA “F-Factor,” used in making emission rate calculations, is another
good tool for verifying that the reported HHV and ultimate analysis are reasonable.
This factor is the ratio of the theoretical volume of dry gases at 0% excess air (0% O )
2
given off by the complete combustion of a known amount of fuel to the gross caloric
value (HHV) of the burned fuel.
The value of the F-Factor (F ) is computed according to the following equation:
d
6
F 10 (3.64 H 1.53 C 0.57 S 0.14 N 0.46 O) / (HHV)
d
Where
6
F dry F-Factor at 0% O , dry standard cu ft (dscf)/10 Btu and
d 2
3
HHV higher heating value, Btu/lb (cu ft/35.315 m ; Btu 1054.8 J).
F-factors are reasonably constant for a given fuel category. Average values for
some typical fuels are presented in Table 4.4.

TABLE 4.4 Average F-factors (F ) for selected fuels.
d
3
6
Fuel F , m /J (dscf/10 Btu)
d
Bituminous coal 2.63 10 –4 (9820)
Oil 2.47 10 –4 (9220)
Gas 2.34 100 –4 (8740)
Wood bark 2.58 100 –4 (9640)
Wood chips 2.49 100 –4 (9280)