Mathematical Model for Wood Pyrolysis--Comparison of Experimental Measurements with Model Predictions

摘要

Experimental and modeling work on pyrolysis of wood under regimes controlled by heat and mass transfer are presented. In a single-particle, bell-shaped Pyrex reactor, one face of a uniform and well-characterized cylinder (D = 20 mm, L = 30 mm) prepared from Norwegian spruce has been one-dimensionally heated by using a Xenon-arc lamp as a radiant heat source. The effect of applied heat flux on the product yield distributions (char, tar, and gas varied and converted fraction have been investigated. The experiments show that heat flux alters the pyrolysis products as well as the intraparticle temperatures to a great extent. A comprehensive mathematical model that can simulate pyrolysis of wood is presented. The thermal degradation of wood involves the interaction in a porous media of heat, mass, and momentum transfer with chemical reactions. Heat is transported by conduction, convection, and radiation, and mass transfer is driven by pressure and concentration gradients. The modeling of these processes involves the simultaneous solution of the conservation equations for mass and energy together with Darcy's law for velocity and kinetic expressions describing the rate of reaction. By using three parallel competitive reactions to account for primary production of gas, tar, and char, and a consecutive reaction for the secondary cracking of tar, the predicted intraparticle temperature profiles, ultimate product yield distributions, and converted fraction agreed well with the experimental results.