Page 327 - Wastewater Solids Incineration Systems

288 Wastewater Solids Incineration Systems

assumed to have an HHV of 1000 Btu/cu ft. Similarly, no. 2 fuel oil exhibits some
variation throughout the United States. In some locations, state and local air environ-
mental regulations govern the maximum quantity of sulfur. Calculations in this
appendix are based on a fuel oil that is free of nitrogen and sulfur, with a composi-
tion of 87% carbon and 13% hydrogen and an HHV of 19 500 Btu/lb. The average
density of no. 2 fuel oil is 7.21 lb/gal (lb/gal 0.119 8 kg/L).

4.0 COMBUSTION OF AUXILIARY FUELS
As with any combustible compound, auxiliary fuels require oxygen to complete their
combustion. In most cases, this oxygen comes from air, which also contains nitrogen
and water vapor. For simplicity these initial illustrative stoichiometric calculations
assume that the combustion air has zero moisture.
The stoichiometric combustion of methane proceeds as follows:
CH 2O CO 2H O
4 2 2 2
Starting with 1 lb-mole of CH :
4
16 lb CH (2 32 lb O ) 44 lb CO (2 18 lb H O)
4 2 2 2
Because the oxygen comes from air, which is a mixture of oxygen and nitrogen,
one must calculate the total mass of nitrogen contained in the combustion air. From
the composition of air (weight fractions), the mass of nitrogen can be calculated and,
hence, the total mass of air, as follows:
64 lb O 0.7685 lb N /0.2315 lb O 212.46 lb N
2 2 2 2
64 lb O 212.46 lb N 276.46 lb air
2 2
Therefore, the equation for the combustion of methane in air is as follows:
16 lb CH 276.46 lb air 44 lb CO 36 lb H O 212.46 lb N
4 2 2 2
The stoichiometric combustion of 1 lb no. 2 fuel oil proceeds as follows:
Reaction inputs (LHS):

1.00 lb oil 0.87 lb C 0.13 lb H
2
Stoichiometric oxygen required
(0.87 lb C/12 (lb/lb-mole C) 1.0 (lb-mole O /lb-mole C)
2
32 (lb/lb-mole O ) 2.32 lb O /lb oil for carbon combustion
2 2
(0.13 lb H /2 (lb/lb-mole H ) 0.5 (lb-mole O /lb-mole H )
2 2 2 2
32 (lb/lb-mole O ) 1.04 lb O /lb oil for hydrogen combustion
2 2
3.36 lb O /lb oil
2