IGNITION AND COMBUSTION OF COAL PARTICLE STREAMS

This paper presents a model for group combustion of a cylindrical stre am of coal particles and preliminary experimental data. Results are ob tained for transient ignition and combustion behaviour. It is found th at homogeneous ignition (ignition of volatiles) occurs for a dense clo ud, while heterogeneous ignition (ignition of carbon) occurs for a dil ute cloud. Once ignited, the flame moves towards the cloud, reaches th e cloud surface and then bifurcates into two flames, called the inner and outer flames. The inner flame propagates into an unburnt volatile- air mixture in the cloud, while the outer diffusion flame moves away f rom the cloud. The inner flame propagates at the laminar burning veloc ity and rapidly heats the particles. There is only a diffusion flame o utside the cloud after all the oxygen in the cloud is consumed. The fl ame moves toward the cloud as the volatiles are depleted. The cloud, w ith the volatiles exhausted and starved of oxygen, burns slowly, contr olled by diffusion into the cloud rather than to each particle in the cloud. Qualitative comparisons are given with preliminary experimental data obtained using a digital imaging system.