Numerical Study On Separation Performance Of High Temperature Gas-solid Cyclone Separator For Coal Gasification Unit

In the coal gasification device,the gasifier is the equipment for coal gasification,and the crude syngas generated after high temperature gasification contains ash particles.In order to ensure the sensible heat recovery performance of the waste heat boiler,dust removal is necessary.Cyclone separator is widely used in harsh working conditions such as high temperature and high pressure.However,single cyclone separator cannot effectively remove particles below 10μm in diameter.The separation ability of cyclone separator can be improved by using multistage series separator.In this paper,the three-stage series cyclone separator is taken as the research object,and the CFD numerical simulation method is used to study the high temperature gas-solid cyclone separator used in coal gasification plant under different working conditions.RSM model is used to analyze the distribution law of flow field in each stage of cyclone separator,and the unsteady flow law of three-stage series cyclone separator is revealed.The physical properties of coal ash particles are analyzed.The gas-solid two-phase flow of the separator is simulated by DPM model and random trajectory model,and the separation performance of three-stage series cyclone separator under different working conditions is analyzed.Continuous discharge is realized by discharging gas at the bottom of the ash hopper.Numerical simulations are carried out for different discharge rates,and the influence of continuous discharge on the separation performance of the separator is discussed.the results showed:The downward gas flow decreases gradually with the decrease of the height of the separator,and the decrease of the straight section is the largest.The short-circuit flow exist in the lower end of the exhaust pipe of the separator,and the tail swing occurs at the ash hopper.With the increase of the separator stage,the separator gradually becomes stable.The particle size of coal ash below 10μm is standard spherical,and the separation efficiency increases with the increase of particle size.The particle separation efficiency of 1μm,5μm and 9μm is 83.23%,98.53%and 99.98%.The cone pressure drop of the separator is the largest,accounting for more than 50%of the total pressure drop.The pressure drop distribution of each separator is uneven,the pressure drop of the first stage separator is25.87kpa,the pressure drop of the second stage separator is 3.46 times of the first stage,and the third stage separator is 3.63 times of the first stage separator.The separation efficiency increases with the inlet velocity,but the pressure drop increases more.When the inlet particle concentration is less than 0.45kg/m~3,the separation efficiency increases with the increase of inlet particle concentration.When the inlet particle concentration is greater than0.45kg/m~3,the separation efficiency decreases with the increase of inlet particle concentration.Under the same working condition,the efficiency of counter-rotating series separator is higher than that of positive-rotating series separator,and the overall pressure drop of counter-rotating series separator is higher than that of positive-rotating series separator.Continuous discharge reduces the vortex near the ash hopper.With the increase of the bottom discharge rate of the ash hopper,the escape rate of the particles decreases,and the separation performance of the separator is improved obviously.The above research results explore the flow field of three-stage series cyclone separator at high temperature and the separation performance of the separator under different working conditions,and provide the basis for the design of three-stage series cyclone separator with high efficiency,low pressure drop and performance matching between stages.