Modelling of wood chips gasification process in ASPEN Plus with multiple validation approach

Abstract

A thermochemical equilibrium model is formulated for wood chips downdraft gasification. Steady state ASPEN Plus simulator was utilized to evaluate producer gas composition and low heating value. Three cases are considered, due to mathematical model developed issues, and described in details. Experimental work was carried out within commercial small-scale CHP system where twelve beech wood samples were taken. Equivalence ratio is between 0.32 and 0.38 and air-fuel ratio ranges from 1.49 to 1.81, when gasifier capacity is optimal, at 250 kW. Mole fractions of CO2, H2, CO, CH4 and N2, in dry producer gas, are respectively, 16.06-17.64, 17.98-20.33, 13.71-17.26, 1.65-2.89 and 43.21-48.36. Multiple validation approach was applied for model verification. The results are in reasonable agreement with different literature sources (experimental work and modeling) and in a great agreement with the modified equilibrium model developed in Engineering Equation Solver found in the literature. Result deviations are explained by two major facts: wood downdraft gasification experiments are to a certain extent different and the model parameters could not be adjusted enough to fully minimize differences between model results. Predicted low heating value of dry producer gas is between 4.67-5.61 MJ/Nm3.