Numerical Simulation Of The Characteristics Of Hydrodynamics And Drying For Oil Shale In Fluidized Bed

Oil shale is recognized as the potential replacement of unconventional hydrocarbon resources,but its high moisture content makes the adverse effect on the large sacle development process.The paper proposes a fluidized bed drying technology with high temperature and low oxygen content flue gas as the drying and fluidized medium for the deep dewatering process of oil shale.Firstly,this paper explored numerical study on the influence of particle-particle restitution coefficient,wall conditions,and operating conditions on the cold fluidization of oil shale particles in the fluidized bed based on the Eulerian modeling incorporating the granular kinetic theory.It is shown that whenswe is 0.2,andsse is 0.9,predicted results of bed pressure drop and expansion height are in good agreement with the experimental data,and the error of predicted initial bubble size and the empirical value of Chiba is small.When the specularity coefficient increases,pressure drop and wall shear stress increases;with the increase of the restitution coefficient,bed expansion height and initial bubble decrease.Increasing fluidized gas velocity is helpful to increase the initial bubble size,accelerate the change of the bubble,and increase bed expansion height.At the same time,the simulated bed pressure drop is compared with the experimental value,and the error is 4.02%,4.32%,5.39%.As the particle size increases,the initial bubble is smaller and the bed expansion height reduces.The heat transfer process of flue gas with high temperature and wet oil shale particles in fluidized bed were numerically studied.It is plotted that the so-called ‘near gas distributor zone' is the most effective heat transfer zone with a significant temperature gradient.The theoretical value(47.48 mm)and the numerical simulation(52 mm)are in good agreement with the relative error of 8.7%,which indicates the Mladen model is sutiable for numerical heat transfer process in fluidized bed.Gas-solid heat transfer coefficient is related to particle distribution,Reynolds number,and temperature difference between gas phase and solid phase.The increasing collision restitution coefficient improves the heat transfer coefficient and effective heat transfer zone in the fluidized bed.The critical moisture content and the wet diffusion coefficient as function of the drying medium temperature and activation energy were determined by comparing the drying characteristics of the oil shale with experimental value at different temperatures.The effects of operating parameters on the drying characteristics of oil shale in the fluidized bed were summarized.Improving the flue gas temperature means the greater impetus of oil shale dehydration process;increasing the gas-solid contact frequency is helpful to improve the gas-solid fluidized quality within the bed by increasing fluidized velocity,it is significantly to improve the heat transfer coefficientd,thus increasing the drying strength of oil shale.Reducing the particle size with larger the heat transfer area;at the same time,the wettest migration path within the particles becomes shorter and the moisture transfer resistance is reduced directly.The height of the initial bed is reduced,which means that the reduced operating load,significantly shorten the drying time.Gas temperature is the most important parameters in the whole drying process;next parameter is fluidized velocity.The particle size has more obvious influence in the falling drying period than the constant drying period.The efficiency f the drying process is higher in the constant drying period than that in the falling drying period.In the constant rate drying period,when the flue gas temperature and fluidization velocity increases,the utilization of flue gas energy directly increases.When the initial bed height increases,the energy efficiency and energy usage remain constant.In the falling rate drying period,decreasing flue gas temperature and fluidized gas velocity and increasing intial bed height is conducive to improving the energy use and energy efficiency.The fluidized gas velocity has the greatest influence on the energy efficiency of the drying process.