Abstract: In the present study, a mathematical model to describe pyrolysis of single biomass particle in flaming pyrolysis zone of downdraft gasifier was developed by heat transfer equation coupled with the chemical kinetics equations.A tridiagonal matrix algorithm(TDMA) method was used for solving the heat transfer equation, and the Runge-Kutta 4th order method for the chemical kinetics equations.The simulated results, which calculated by the present model in oxygen-free atmosphere and flaming pyrolysing zone, were in good agreement with published experimental results.The pyrolysis of biomass particle in the flaming pyrolysing zone was investigated by the model.The results show that in the flaming pyrolysis zone of stratified downdraft gasifier, convective heat transfer coefficient(h_s) and emissivity coefficient(ε) are 80.4 W/(m²·K) and 0.792, respectively. The trend of temperature change inside particls is contrary to that of the particle surface.The average flaming pyrolysis time is 16.52%, which is shorter than that in oxygen-free atmosphere.The heating rate in the particle of the flaming pyrolysis zone was 182.5 K/min, which was close to fast pyrolysis reaction.With the increaseing of flaming temperature, flaming pyrolysis time reduced, residue gradually reduced from 16.92% to 13.97%. With the increasing of particle diameter, pyrolysis time and char yield also increased.The depth of flaming pyrolysis zone was 6.59-44.1 mm, which equals to 1.1-2.2 diameters.

Key words: stratified downdraft gasifier, pyrolysis model, flaming pyrolysis zone, single biomass particle