Effect of rapid preheating on the caking properties of coals

In order to obtain fundamental data for rapid preheating process, the swelling and agglomerating behavior of coal particles and the thermoplastic behaviors of coal under various heating conditions were investigated with a fluidized bed apparatus and a rapid heating plastometer. Coal particles undergoing pyrolysis in N-2 or CO2 atmosphere at a heating rate of 300 degrees C/min were filmed using a high-speed camera. The swelling and agglomerating behavior of them were evaluated by image analysis. Coal particle started to increase its size slightly around 350 degrees C and expanded dramatically. Then coal agglomeration occurred around 420 degrees C. Coal swelling and agglomerating behavior was influenced by coal property and atmospheric condition. Especially CO2 atmosphere inhibited dilatation and agglomeration. As the plasticity behavior of coal, minimum apparent viscosity and all characteristic temperatures corresponding to softening, maximum fluidity and resolidification state same as Gieseler method were measured by a rapid-heating plastometer. Coal plasticity was strongly dependent upon the heating conditions. For example, it was clarified that there existed an optimum rapid preheating temperature and that temperature, which had to be less than the softening temperature of Gieseler test, was related to coal rank. Moreover it was suggested that rapid heating effect was improved with the increase of the H/C atomic ratio of raw coal.