The influence of the structure heterogeneity on the characteristics and conditions of the coal–water fuel particles ignition in high temperature environment

Abstract

The results of the experimental and numerical study of the coal–water fuel particles ignition (CWF) have been given, where the thermal properties (thermal conductivity (λ), heat capacity (C), density (ρ)) have been calculated using the different mathematical models. The heterogeneity and porosity of the structure of CWF have been taken into account in calculating λ, C and ρ. The influence of the shape, configuration and size of the pores on the thermal characteristics of coal–water fuel has been analyzed. It has been established that the effective thermal conductivity (λeff) is changed when there are the different ways of describing the thermophysical properties. It has been shown that increasing porosity (mp) of fuel during thermal decomposition affects λeff (or leads to the higher values of the effective coefficient of thermal conductivity, or to its decrease).The set of the core processes of heat and mass transfer (thermal conductivity, filtration of water vapor, ignition) has been taken into account when conducting mathematical modeling. It has been carried out with taking into account the intense physicochemical (thermal decomposition of the organic part of the fuel, thermochemical interaction of water vapor and carbon coke) and phase (evaporation of water) transformations together in the WCF particle in the conditions of high temperature heating.According to the results of the mathematical modeling the delay time of ignition of the coal–water fuel particles has been calculated. The “influence” of the ways of describing the thermal characteristics of CWF has been shown, which can be changed in the process of temperature increase on the delay time of ignition. It has been established that even if the maximum possible change of the coefficient of thermal conductivity (depending on the model λeff) deviation of the ignition delay time from the average values does not exceed 13%.