Prediction of the gas composition
Introduction of the water-gas equilibrium concept provides the opportunity to calculate the gas composition theoretically from a gasifier which has reached equilibrium at a given temperature, as was shown by Tobler and Schlaepfer (34).
The procedure is to derive from mass balances of the four main ingoing elements (carbon, hydrogen, oxygen and nitrogen), an energy balance over the system and the relation given by the water-gas equilibrium. By further assuming that the amounts of methane in the producer gas per kg of dry fuel are constant (as is more or less the case of gasifiers under normal operating conditions) a set of relations becomes available permitting the calculation of gas compositions for a wide range of input parameters (fuel moisture content) and system characteristics (heat losses through convection, radiation and sensible heat in the gas). Theoretically calculated gas compositions-are given in figures 2.4 to 2.6. Generally a reasonably good agreement with experimental results is found.
Table 2.3 gives typical gas compositions as obtained from commercial wood and charcoal downdraught gasifiers operated on low to medium moisture content fuels (wood 20 percent, charcoal 7 percent).
Table 2.3 Composition of gas from-commercial wood and charcoal gasifiers.
Component |Wood Gas (vol. %) |Charcoal Gas (vol. %)