INVESTIGATION OF A COAL-WATER SLURRY DROPLET EXPOSED TO HOT GAS-STREAM

In this study a refined theoretical model was devised to estimate the ignition delay of a suspended coal-water slurry (CWS) droplet exposed to hot gas stream. A very detailed temporal temperature variation inside the droplet is taken into account. The effect of the surface radiation was also included in the model. The governing equations are numerically solved and the results are corroborated in comparison with the experimental ones. The outer porous layer could be pyrolyzed as the evaporation front kept going inward to the center of the droplet. Even before the binary mixture in inner region of the droplet was thoroughly evaporated, the volatile gases generated could be ignited in the vicinity of droplet surface. The ignition delay time was primarily comprised of both the heating time and the mixing time. But the heating time, which is required for a droplet to be vaporized and then pyrolyzed, was found to be controlling one. Experimental results were used to validate the numerical results. A reasonable agreement was observed in ignition delays of droplets, only when the surface radiation was incorporated in the model.