Ignition of Particles of Wet Woody Biomass under Convective Diffusion of Water Vapor in the Near-Wall Region

Abstract

This paper presents the results of an experimental and theoretical study of heat and mass transfer during ignition of wet wood particles in a high-temperature gas medium. Experiments were carried out in a setup which provides conditions similar to the combustion spaces of boiler units. The main heat transfer parameters (ambient temperature) and integrated ignition characteristics (ignition delay) were measured. The measurement error of these parameters did not exceed 18%. The convective transfer of water vapor formed during evaporation of pore moisture and pyrolysis products were found to have an insignificant effect on the ignition characteristics and conditions. From the results of the experiments, a mathematical model of the ignition process was developed which describes the simultaneous occurrence of the main processes of thermal preparation under conditions of intense phase (evaporation of water) and thermochemical transformations (thermal decomposition of the organic part of the fuel, thermochemical interaction between water vapor and carbon coke, ignition of volatiles) taking into account the convective diffusion of water vapor and pyrolysis products in the near-wall gas area during the induction period. The theoretical ignition delay is in satisfactory (within the confidence interval) agreement with the experimental value. The numerical model of the diffusion flame adequately (good agreement between experimental and theoretical ignition delays) describes the ignition of a wet wood particle.