Equilibrium modeling of global reduction reactions for a downdraft (biomass) gasifier

This article proposed a full equilibrium model of global reduction reactions for a downdraft biomass gasifier in order to predict the accurate distribution of various gas species, unconverted char and reaction temperature. Full equilibrium of the global reduction reactions has been described using thermodynamics principles based on the stoichiometric approach. Model predictions for equilibrium constants for reduction reactions and dry gas composition have been validated by comparing the data collected from various sources. Simulations modeling the influences of moisture content in feedstocks, pressure, equivalence ratio and initial temperature input on dry gas composition, unconverted char, calorific value of gas, gasification efficiency, outlet gas temperature and endothermic heat released in char bed. For optimal energy conversion of Douglas fir bark, the range of moisture content and equivalence ratio should be limited to 10–20% and 0.3–0.45 respectively, while the initial temperature in the reduction reaction zone should not be less than 1200 K. The accuracy of the prediction of the equilibrium model depends on the correctness of the initial conditions of temperature and reactants concentrations.