Modeling and simulation of combined pyrolysis and reduction zone for a downdraft biomass gasifier

This paper simulates the behavior of a global fixed bed biomass gasification reactor. The pyrolysis zone and reduction zone models are combined to simulate the global process of biomass gasification. The volatiles and gases released from the pyrolysis zone were assumed to crack into equivalent amounts of CO, CH₄ and H₂O. It is considered that the volatiles and gases leave the pyrolysis zone instantaneously and enter the reduction zone as initial gas concentrations. The numerical method applied is a Runge-Kutta fourth order method for solution of the pyrolysis zone model and finite differences for the reduction zone model to solve numerically the coupled ordinary differential equations. Simulations are performed for the varying pyrolysis temperature with a heating rate of 25 K/min and constant temperature of 1400 K as the initial reduction zone temperature at the same time. The simulation results for the temperature and concentrations of the gaseous species are in good agreement with published experimental data.