The effect of pressure on coal char combustion

Abstract

A two-dimensional, two-phase combustion model of pulverized coal char at elevated pressures is presented in this paper. This is often encountered in furnaces used for power generation, industrial heating and steam production, and for conversion of solids to gas and liquid products. In pressurized circulating fluidized bed boilers, the effect of pressure on char combustion is significant. Of particular importance is to reveal the relative significance of the diffusion and chemical reaction, as controlling mechanisms, and to evaluate the effect of total pressure on the performance of the combustion chamber. The partial differential equations of conservation of mass, momentum and energy are solved taking into consideration turbulent flow, interphase mass- and heat-transfer, radiation and varying operational conditions (e.g. feed of coal and primary and secondary air). The equations are integrated with the finite volume method and are solved for the flow field, temperature field in the gaseous and solid phases and the concentration of reactants and products. The results show that both chemical reaction and diffusion mechanisms control the combustion at elevated pressure. Moreover, the effect of pressure on the reaction kinetics proves to be significant.