Experimental Research On The Primary Fragmentation Characteristics Of Coal

Circulating fluidized bed combustion technology is a clean coal technology. The development scale and capacity of the circulating fluidized bed boiler is increasing. The two key problems of its design and operation are the material balance and the heat balance. The heat balance is extremely related with the material balance, and the material balance is more basic. The material balance in the circulating fluidized bed is related to the particle size distribution of coal, the primary fragmentation characteristics of coal, the secondary fragmentation characteristics, the performance of the separator and the operation parameters. In the view of different coals, through the experiment, this article makes a further research about the primary fragmentation characteristics of coal, which provides the theory basis for the further analysis and prediction of the material balance and heat balance in the circulating fluidized bed boiler.The primary fragmentation of coal is mainly induced by the compression stress caused by the volatilization of coal and the thermal stress caused by the uneven temperature. And the experiment of the primary fragmentation in the real circulating fluidized bed boiler is complex and the experimental phenomenon is hard to observe. So in this article the primary fragmentation characteristics of different coals are determined in a tube furnace. This article considers the movement of coal particle in the circulating fluidized bed through rotating the self-made metal coal net. The differences of fragmentation form of bituminous coal, lean coal, anthracite coal and gangue are analyzed in the experiment. The effect of coal, particle size of coal, bed temperature, heating atmosphere and taking off moisture and volatile matter of coal on the primary fragmentation characteristics is considered. Finally two kinds of coal gangue are researched in the muffle furnace. The research results show that different kinds of coal have different fragmentation forms. Bituminous coal particles follow the Ring nuclear-Layer fragmentation form; Lean coal and anthracite coal both show the center-fragmentation and the surface-fracture, some particles break into fine particles rapidly due to their heat explosion characteristics; The fragmentation of coal gangue happens parallel to its bedding planes, and the particles break into fragments.The research also shows that the composition of the coal itself has a great influence on the primary fragmentation characteristics. With the volatile matter increasing the average particle size shows a tendency of increasing. With the ash and fixed carbon increasing the average particle size increases first and decreases later. With the volatile matter、the ash and fixed carbon increasing the fragmentation index doesn’t follow a strict change rule. The fragmentation of coal becomes serious with the particle size become larger and the bed temperature become higher. Heating atmosphere has a small impact on the fragmentation of coal gangue, the other coals have larger fragmentation index when the coals are burned then heated in inert atmosphere. Based on lots of experiment results, the relation formula of the mean particle size before fragmentation and after the fragmentation is built in this article. And through the comparison of the experimental results with other coals(coal gangue and five South Korea anthracites) in the relevant literature, the accuracy of the relation formula is further verified, which has a better result, so the relation formula is universal.