Page 104 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory
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82 Biomass Gasification, Pyrolysis and Torrefaction
3.6.6 Stoichiometric Calculations for Complete Combustion
Noting that dry air contains 23.16% oxygen, 76.8% nitrogen, and 0.04%
inert gases by weight, the dry air required for complete combustion of a unit
weight of dry hydrocarbon, M da , is given by:
O
M da 5 0:1153C 1 0:3434 H 2 1 0:043S kg=kg of dry fuel (3.32)
8
where C, H, O, and S are the percentages of carbon, hydrogen, oxygen, and
sulfur, respectively, on a dry basis.
The actual air including excess air EAC and moisture, X m , in air is
M wa 5 (1 1 EAC)M da (1 1 X m ).
3.6.6.1 Amount of Product Gas of Complete Combustion
The total weight of the flue gas, W c , produced through combustion of 1 kg
of biomass may be found from stoichiometry as (Basu, 2006, p. 448):
W c 5 M wa 2 0:2315 M da 1 3:66C 1 9H 1 N 1 O 1 2:5S (3.33)
3.6.6.2 Composition of the Product of Combustion
a. Carbon dioxide
Carbon dioxide produced from fixed carbon in coal 5 3.66 C kg/kg fuel.
b. Water vapor
Water in the flue gas comes from the combustion of hydrogen in the
coal and the moisture present in the combustion air, coal, and limestone.
Water vapor in the flue gas 5 ½9H 1 EAC: M da X m 1 M f 1 L q X ml kg=kg fuel
(3.34)
c. Nitrogen
Nitrogen in the flue gas comes from the coal as well as from the
combustion air.
Nitrogen from the air and fuel 5 ½N 1 0:768 EAC: M da kg=kg fuel (3.35)
d. Oxygen
The oxygen in the flue gas comes from oxygen in the coal, excess
oxygen in the combustion air, and the oxygen left in the flue gas for
1
incomplete capture of sulfur. For each mole of unconverted sulfur, /2 mol
of oxygen is saved. Thus:
Oxygen in the flue gas 5 ½O 1 0:2315M da ðEAC 2 1Þ kg=kg fuel (3.36)
e. Sulfur dioxide
The SO 2 present in the flue gas is given below:
Sulfur dioxide in flue gas 5 2S kg=kg fuel (3.37)
