| At present,coal resource is still the primary energy resource with the largest reserves in China,and its efficient and full utilization will occupy a pivotal position in the process of social and economic development in China.However,low-rank coal is the main coal resource,so the efficient and clean utilization of low-rank coal has become the focus of academic research.In this context,the combustion-pyrolysy-gasification multi-process coupling process proposed by scholars has attracted more and more attention in the process of realizing the cascade efficient utilization of coal,among which the three-tower circulating fluidized bed(TBCFB)technology is one of the typical polygeneration process.However,in this process,the cycle path of particles is long,and it is difficult to realize the high-flux cycle of particles,and the coordination of multiple devices is complex,which increases the cost of system operation.Therefore,the design concept of cyclone pyrolysis reactor is proposed in this paper.The purpose is to reduce the number of equipment in the three-tower circulating fluidized bed,reduce the height of the circulating system,achieve particle concentration under low-flux conditions,strengthen the heat transfer between the circulating heat carrier particles and coal particles,and realize the separation of products and pyrolysis gas in the pyrolysis reaction process,so as to solve the problem of large amount of dust in the pyrolysis products.In this paper,CFD-DEM coupling method is used to simulate the gas-solid flow in a cyclone pyrolysis reactor.The characteristics of the cyclone reactor as a pyrolyzer are explored,and the characteristics of the gas-solid flow in a cyclone pyrolysis reactor are analyzed through the discussion of the simulation results.The results of the main contents of this paper are as follows:(1)Concentration characteristics of particles and quasi-plug flow characteristics:According to the particle distribution diagram under different particle fluxes,with the increase of particle flux,the particle distribution mode changes from the uniform distribution of the side wall and local concentration to the spiral particle belt.When the flux is 90 kg/(m~2·s),an obvious helical particle belt is formed.By statistical analysis of the particle solid holdup in the region,it can be found that the helical particle belt can effectively increase the particle solid holdup(up to more than 0.3)and realize the particle concentration under the condition of low flux.By analyzing the circumferential and axial distribution of the residence time and the total velocity of the particle,it can be seen that the residence time of the particle is narrow and the velocity distribution of the particle zone is uniform,showing the characteristics of quasi-plug flow.(2)the gas-solid separation characteristics:It can be seen from the pressure cloud diagram,the tangential velocity,the axial velocity of the gas,after the formation of particle-belt,there is no obvious lower pressure area.And particles have a greater hindrance to the gas phase,causes a greater reduction in the gas phase tangential velocity,the axial downward speed is also getting smaller and smaller,and the effective separation space of the gas phase is continuously reduced.(3)Mixing characteristics and heat transfer:It can be seen from the binary particle mixing index of the dual-inlet structure at different gas velocities,the increase in inlet gas velocity is conducive to the mixing of binary particles,and the mixing of binary particles in the spiral particle belt is better.According to the heat transfer characteristics of binary particles at different gas velocities,it can be seen that when the gas velocity is higher,good mixing of particles and good heat transfer characteristics near the entrance area.Therefore,although increasing gas velocity cannot improve the separation capacity of the cyclone pyrolysis reactor,increasing gas velocity is beneficial to particle mixing characteristics and heat transfer in the inlet area. |
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