Study On The Flow Characteristic And Heat And Mass Transfer Of Oil Shale In Fluidized Bed

Energy is the foundation and pillar of a country and society. With the increase of petroleum usage, petroleum resource will be exhausted in 70 years. It is a major issue all countries are facing to deal with petroleum exhaustion and explore alternative energy sources. Oil shale rich in organic matter, can produce oil and combustible gas by dry distillation, can also be used for combustion power generation. With the decreasing of cost for producing oil shale and greater reserves than petroleum, oil shale resources are becoming a substitute for petroleum. Most of the oil shale with high water content cause increasing energy consumption and oil quality’s decline. High temperature gas is used to dry oil shale particles before drying distillation. Fluidized bed dryer with high efficiency of heat transfer and mass transfer are more appropriate to be applied to oil shale’s drying process. Study on the behavior and mechanism of oil shale in the fluidized bed for drying oil shale more efficiently, provides a good theoretical basis, and the future can make better use of oil shale resources.With limitation of experimental conditions, behavior and mechanism of drying oil shale in a fluidized bed can’t be monitored and measured effectively. Based on two fluid model and particle kinetic theory, for the establishment of a fluidized bed model, using CFD software coupled with the user-defined function (UDF) method, minimum fluidization velocity, bed expansion height, initial bubble size, bed pressure drop, gas-solid heat transfer were studied, and obtained the following conclusion:The difference between full fluidization and the minimum bubbling velocity for small particles is larger than that of large particles. Comparing bed expansion height under different speeds with empirical correlations, bed expansion height is nearly linear increase. With the increase of air velocity, initial bubble size has also increased and vibration can inhibit bubble. With the vibration frequency’s increasing, bubble size reduces and with the vibration amplitude’s increasing, bubble size increases slightly. The bed pressure drop with increasing gas velocity, decreases first and increases later. Adding vibration with vibration intensity’s increasing, variation of pressure drop is small while the standard deviation curve increases gradually. With the increasing of bed height, pressure drop increases gradually and the affection reaches biggest after full fluidization. The gas-solid heat transfer coefficient in the region near the air distribution plate mainly is controlled by difference of gas-solid phase temperature and controlled by particle concentration far away from the air distribution plate region. The particle concentration in two-phase heat exchange coefficient plays an important role in the whole areas. The flue gas temperature affected by wall temperature near the distributor region presents the lower on both sides and higher trend on the middle. The flue gas temperature away from distributor region is uniform. Using CFD software to simulate drying process of oil shale, the result is consistent with the experimental results.The higher is the inlet temperature, fluidized bed drying ability is stronger. Dry in the initial stage is mainly controlled by external flue gas temperature, while it is mainly controlled by internal moisture diffusion in the second stage.The regularity of the flowing characteristic parameters and gas-solid heat transfer of oil shale in the fluidized bed have been studied, it lays the foundation for the design of fluidized bed and oil shale drying mechanism for further study.