A Numerical Study of Entrained Coal Gasification with The Conchas Spray Code

The CONCHAS-SPRAY computer code, which was originally designed to study the coupled fluid dynamics, heat transfer, chemical reactions, and fuel spray dynamics of an engine-cylinder submodel of an internal combustion engine has been modified to study entrained coal gasification. The fuel spray submodel has been replaced by a coal particle submodel, in which parcels of pulverized coal particles are injected into a reactor and subsequently dispersed by a turbulent fluctuating velocity field. A two-step devolatilization submodel is used to determine the transient devolatilization of the particles and the production of char. Two different models of this devolatilization process have been examined, in which the products are acetylene and either ethylene or a combination of carbon monoxide and methane. The coal chemistry submodel in CONCHAS-SPRAY is used to determine the subsequent cracking, reforming and burning of the volatiles and the production of soot. The reaction rate for char oxidation is a function of the local partial pressure of oxygen and the surface area and porosity of the particles. A nonequilibrium radiation submodel is used to determine the radiative energy exchange between the gas field, the particles, and the confining walls. In this submodel the transport equation for the radiation energy density reduces to a diffusion equation in optically thick regions of the reactor and to a freestreaming mode in optically thin regions. We account for the heat transfer within the solid wall, and the exchange of heat with the environment by free convection at the outer wall. This modified version of CONCHAS-SPRAY has been successfully tested by comparison of calculated results with cold flow experimental data. In this paper we present results from the application of the code to a study of entrained coal gasification.