Ignition of particles of wet wood biomass with convective diffusion of water vapor in the near-wall area

The results of an experimental and theoretical study of heat and mass transfer occurring during ignition of wet wood particles in a high-temperature gas environment. Experiments were carried out in a facility which provides conditions corresponding to the combustion spaces of boiler units. The main heat transfer parameters (ambient temperature) and integrated ignition characteristics (delay time) were measured. The measurement error of these parameters did not exceed 18%. It is found that the convective transfer of water vapor formed during evaporation of intraporous moisture and pyrolysis products does not have a significant effect on the ignition characteristics and conditions. The results of the experiments were used to develop a mathematical model of the ignition process, which describes the joint flow 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 of 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 one. The numerical model of the diffusion flame adequately (good agreement between experimental and theoretical ignition delays) describes the ignition of a wet wood particle.