Numerical Simulation Of Gas-solid Flow And Separation Performance In Coupled Cyclone With Built-in Circulating Granular Bed Filter

As a new type of gas purification device,the coupled cyclone with built-in circulating granular bed filter(C-CGBF)couples the cyclone separator and built-in granular bed.In the cyclone separator part,the larger particles in the gas with dust particles are separated by centrifugation to reduce the filtration load of the subsequent granular bed.In the built-in granular bed,smaller dust particles in the gas are twice filtered by the moving capturing granules to effectively improve the purification effect of the dusty gas.The flow field distribution characteristics and the effect of operation condition on separation performance had been studied in detail by experimental methods.However,it lacks of knowledge on the special phenomenon of gas phase flow field in the separator and the dust deposition law and distribution in the filtration process.Therefore,CFD and CPFD simulation methods were used to simulate the gas,trapped particles and dust particles in the C-CGBF.The numerical models are verified by comparing the simulation and experimental results of pressure drop and velocity.The main conclusions are as follows:(1)CFD method is used to simulate the gas phase flow characteristics in the equipment,and the effect of inlet gas velocity on the static pressure distribution and velocity distribution when there is not dust in the inlet gas.It is found that the static pressure and velocity present non-axisymmetric distribution in the inlet annular space.The static pressure decreases with the angle from 0° to 180 ° and increases with the angle from 180° to 360°.In the axial direction,the static pressure at different angle has a minimum value at the outlet of the annular space,which is due to the short-circuit flow.According to the analysis of gas-phase flow field,it is found that there are non-uniform phenomena,such as secondary flow,top ash ring and back pressure cavity in the C-CGBF.But,there is no oscillating of vortex core,resulting from the steady flow effect of builtin granular bed on the rotating fluid with high velocity.(2)CPFD method is employed to simulate the flow characteristics of gas phase,capturing granular and dust particles,and investigate the influence of physical parameters on the gas-solid separation performance in the equipment.The variation of pressure drop with time is compared when the C-CGBF is operated at fixed bed mode and moving bed mode.The distribution of dust particle content in the C-CGBF is analyzed in detail.By investigating the effects of inlet gas velocity and inlet dust concentration on the distribution of dust particles in the granular bed,three filtration stages of the C-CGBF are identified,i.e.the rapid growth stage,the transition stage and the stable stage of dust content.In the axial direction,the highest content of dust particles is located in the upper part of the granular bed,and the content decreases gradually with drcreasing the axial height.The dust content in the granular bed presents an asymmetric distribution in the circumferential direction,and the largest content is in the angle of 180°.In the radial direction,the dust content on the outer wall of the granular bed is higher and the content on the inner wall is lower.The C-CGBF has high separation performance when operated at appropriate conditions.And its pressure drop changes gently.These results show the C-CGBF can run stably.