Mathematical model for wood pyrolysis - Comparison of experimental measurements with model predictions

Experimental and modeling work on pyrolysis of wood under regimes controlle d by heat and mass transfer are presented. In a single-particle, bell-shape d Pyrex reactor, one face of a uniform and well-characterized cylinder (D = 20 mm, L = 30 mm) prepared from Norwegian spruce has been one-dimensionall y heated by using a Xenon-are lamp as a radiant heat source. The effect of applied heat flux on the product yield distributions (char, tar, and gas yi eld) and converted fraction have been investigated. The experiments show th at heat flux alters the pyrolysis products as well as the intraparticle tem peratures to a great extent. A comprehensive mathematical model that can si mulate pyrolysis of wood is presented. The thermal degradation of wood invo lves the interaction in a porous media of heat, mass, and momentum transfer with chemical reactions. Heat is transported by conduction, convection, an d radiation, and mass transfer is driven by pressure and concentration grad ients. The modeling of these processes involves the simultaneous solution o f the conservation equations for mass and energy together with Darcy's law for velocity and kinetic expressions describing the rate of reaction. By us ing three parallel competitive reactions to account for primary production of gas, tar, and char, and a consecutive reaction for the secondary crackin g of tar, the predicted intraparticle temperature profiles, ultimate produc t yield distributions, and converted fraction agreed well with the experime ntal results.