Computational Simulation for Local Reactions in a Fluidized Bed Grid Zone

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A cold model experiment and development of a fluidized bed grid zone modelLocal behavior of gas and sohds in a grid zone was investigated by using a fluidized bed cold model. A couple of optical fiber sensors were used to measure a local particle velocity, its concentration, jet diameter and jet height. Local tracer gas concentration was measured by using a gas sampling prove and a gas chromatograph. Circulation of sohds and gas was found to be better when a cone-shaped distributor was employed than that when a flat distributor was used. A numerical model of a fluidized bed grid zone was developed for the description of the cold model data. The numerical results on concentration profiles of gas in the grid zone and particle velocity in jet well coincided with the experimental cold model data when flat distributor was employed. However, when a cone-shaped gas injecter was employed, the numerical results showed lower extent of mixing of gas and solids then those observed experimentally. It was suggest that more complex mixing of gas and solids was occurred in the later case.Applications of the grid zone modelThe grid zone model was applied to chemical vapor deposition of polycrystaflffie silicon by monosilane pyrolysis. The numerical results suggested that the fines mainly tonned in bubbles. The numerical model well expected the experimentally observed effects of gas velocity, bed temperature, silane concentration and grid structure on the likelihood of clogging. A model combining a fluidized bed grid zone model and Kunii-Levenspiel bubbling bed model was proposed and was applied to the analysis of the local progress of coal gasification. From the comparison of the numerical and experimental results, the contribution of the reaction in the grid zone was found to be significant to the overail reactions. Further study on the steam and CO_2 gasification kinetics was found to be necessary.