Renewable Energy, Vol.145, 1474-1486, 2020
Influence of a wet wood particle form on the characteristics of its ignition in the high-temperature medium
The results of the experimental and theoretical studies of the processes of the single particles ignition of the wood biomass of various forms (a cube, a cylinder and a sphere) have been presented. According to the results of the experimental studies, it has been established that the particles form can have a fairly significant effect on the characteristics and conditions of ignition. It has been shown that the wood particles in the form of a sphere are ignited much faster than cylindrical and cubic ones (ignition delay times are less by 56%). Such a tendency is maintained for particles sizes from 1 . 10(-3) m to 3 . 10(-3) m. According to the results of the experiments, the mathematical model for ignition of a particle of wet wood biomass has been formulated, taking into account the joint occurrence of the main processes of the thermal preparation (radiation-convective particle heating, evaporation of water, thermal decomposition of the organic part of the fuel, output, ignition and combustion of gaseous pyrolysis products, ignition of the char residue). The formulated system of the nonlinear differential equations in the partial derivatives with the corresponding boundary conditions describes the ignition process in a two-dimensional setting, taking into account the substantial nonuniformity of the temperature field of a wood particle in the induction period. We have taken into account that the evaporation process takes place in the front. Up to the present time, the mathematical models of such a degree of detailing of the physical processes occurring together when igniting wet wood have not been formulated. A comparative analysis of the ignition delay times (t(ign)) obtained theoretically and experimentally has showed their satisfactory correspondence. As a result of the numerical simulation, the temperature fields in the system "a fuel particle - high-temperature medium" have been obtained, illustrating the high gradients of the temperatures at the moment of ignition. It has been established that it is possible to ignite the water-saturated wood particles before they dry completely. It has been established that the ignition mode of wood particles is possible before they dry completely. (c) 2019 Elsevier Ltd. All rights reserved.