Study Of Gas-solid Flow Characteristics Of Parallel Double Cyclones

Multiple parallel separators are universally used to separate solids from flue gas in circulating fluidized bed boilers.However,there are common phenomena that the gas-solid two-phase flow is unevenly distributed during pratical operation.The uniform distribution of gas-solid flow plays an important role in the stable operation of circulating fluidized bed boilers.There are many reasons that affect the uniform distribution of gas-solid flow.Generally,it can be divided into two categories,including the furnace structure arrangement before and after the cyclone and the characterization of cyclone pressure drop.In terms of boiler structure arrangement,the uniform distribution of gas-solid at the outlet of the furnace does not ensure even distribution of gas-solid between the cyclones.The non-monotonic characterization of cyclone pressure drop has an important influence on it.In this thesis,the cyclone of a circulating fluidized bed boiler unit is taken as the research object.The semi-empirical pressure drop calculation correlation and numerical simulation method are used to study the influence of operating parameters and separator structural parameters on the stability of gas-solid uniform distribution.The cyclone pressure drop curve is obtained by using the pressure drop calculation correlation,and the cyclone pressure drop corresponding to different gas-solid distribution ratios under different working conditions is obtained,which is used to analyze the effect of operating parameters and structural parameters on gas-solid distribution.Then use FLUENT to establish a mathematical model,calculate the cyclone pressure drop under different working conditions and its corresponding gas-solid distribution ratio,combine the pressure and velocity distribution to explore the mechanism,and verify the results of the pressure drop correlation.In this thesis,the effects of total inlet particle concentration,total inlet gas velocity,vortex finder diameter and inlet width on the flow characteristics of gas-solid two-phase flow through parallel double cyclone are studied.The results show that the effect of total inlet particle concentration,total inlet gas velocity,vortex finder diameter and inlet width on gas-solid uniformity stability are studied by the cyclone pressure drop correlation and numerical simulation in which the result is consistent.It is reasonable to get the pressure drop trend under different gas-solid distributions based on the Chen-Shi pressure drop correlations.The total inlet gas velocity affects the stability of the uniform distribution and the concentration of the inflection point.The higher the speed,the greater the inflection point concentration,and the higher the stability of the analytical solution with the smallest pressure drop.However,when the finder diameter diameter is large,the change in velocity has little effect on the concentration of the inflection point.The total inlet particle concentration will affect the stability of the gas-solid uniform distribution solution.The smaller the total inlet particle concentration,the more favorable the uniform distribution of gas-solid flow.When a certain particle concentration exists,the pressure drop of the non-uniform distribution is close to the pressure drop of the uniform distribution,and the solid phase fraction is subject to fluctuations due to interference.The inflection point concentration of the cyclone pressure drop curve is an important indicator that affects the uniform distribution.The inflection point concentration can be used to measure the difference between the dynamic energy dissipation loss in the vortex finder and the sum of the inlet expansion loss and the wall friction loss.The greater the concentration of the inflection point,the more favorable the stability of the uniform distribution solution.The structural parameters of the cyclone will affect the uniformity and stability of the gas-solid flow.Reducing the diameter of the vortex finder and increasing the width of the inlet facilitates uniform gas-solid flow through the double cyclones.Reducing the diameter of the vortex finder directly increases the dynamic energy dissipation loss in the core barrel;increasing the inlet width mainly reduces the inlet expansion loss and the wall friction loss.Both of them increase the proportion of the dynamic energy dissipation loss in the total pressure drop,which is beneficial to increase the inflection point concentration and improve the gas-solid uniformity of the parallel double cyclones.