Structure Optimization Design Of Liquid-solid Fluidized Bed Distribution Device

Liquid-solid fluidized bed has a wide range of applications in many fields.The water distribution device is the main component that affects the performance of the fluidized bed.This paper studies the performance and influencing factors of the sieve plate and particle-filled fixed bed as the water distribution device.Through the numerical simulation method,the influence of the structural parameters of the water distribution device on the distribution effect is investigated and optimized,so that the water distribution device with a simple structure and stable performance is constructed as a liquid-solid fluidized bed to provide a uniform and stable flow field environment similar to advection flow,improve the fluidized bed flocculation and sedimentation effect of coal slurry.Firstly,the sieve plate type distribution plate is used as the water distribution device,and a method for optimizing the sieve plate structure(referred to as CFDBernoulli optimization method)is proposed by combining computational fluid dynamics(CFD)simulation,fluid dynamics theory and empirical formula: through literature research,design the initial screen plate,and then obtain the flow velocity distribution of the screen plate inlet and outlet through CFD simulation,and then combine Bernoulli’s equation to calculate the diameter of each sieve hole with the same water outlet speed as the target.thereby reconstructing the screen plate and performing CFD simulation,and so on,until the ideal structural parameters are obtained.The simulation results are evaluated by the velocity unevenness η and the relative standard deviation S of the velocity unevenness.The applicability of the method under the conditions of two-dimensional,three-dimensional single-row and three-dimensional multi-row models is investigated,and the structure of the water distribution device is optimized.The research results show that the CFD-Bernoulli optimization method is very effective for optimizing the water distribution device of the sieve plate.After 2-3 optimizations,the sieve plate structure with good water distribution effect can be obtained.For the exit surface of the two-dimensional model,the range of η decreases from the maximum value of 103% to 11%,and S = 30% to S = 3%;for the exit surface of the three-dimensional single row hole model,the range of η changes from the maximum value of 38% drops to 10%,S = 12% to S = 2%;the exit surface of the threedimensional multi-row hole model,the range of η decreases from the maximum 33% to 12%,and S = 6% to S = 3%.Secondly,the water distribution effect of the fixed bed water distribution method and the optimization of the bed parameters were studied.Starting from the particle accumulation process of the particle bed,the discrete element software EDEM is used to simulate the effect of different particle sizes and different initial velocities on the bed packing density;on this basis,the CFD-DEM coupling method is used to study the particle size and the effect of filling height on the pressure drop and water distribution effect of the bed.The results show that the packing density of the particle bed is related to the particle size.At the same initial falling velocity,the smaller the particles,the greater the packing density of the particle bed;increasing the initial packing velocity and packing density in the range of 1-8 m/s increase,then tend to stabilize;for particles with diameters of 1、2 and 3 mm,the initial velocity tends to be 6、5 and 5 m/s,respectively.The pressure drop of the bed has a linear relationship with the filling height of the particles,which increases with the height.At the same filling height,the smaller the particle size,the lower the porosity,the greater the pressure drop of the fluid flow field,and the better the water distribution effect.At the same filling height,the smaller the particle size of the bed,the more uniform the flow velocity distribution at the outlet surface of the bed;at the same particle size,the higher the filling height is,the more uniform the velocity distribution will be,yet when the filling height reaches a certain level,the velocity distribution no longer fluctuates significantly,and the particle size and filling height parameters of the bed with better water distribution are: d = 3 mm,h = 200 mm;d = 2 mm,h = 80 mm;d = 1 mm,h = 60 mm.When the particle size d and the filling height h are constant,with the increase of the inlet velocity of the fluidized bed,the relative standard deviation S of the velocity unevenness η of the bed outlet surface increase,and the effect of the uniform distribution of the velocity of the outlet surface of the bed decreases.Comparing the η range and S value of the sieve-plate distribution plate and the particle bed: d = 1 mm,h = 60 mm,the water uniformity of the particle bed cloth is higher than that of the sieve-plate distribution plate.Under a specific fluidized bed inlet flow rate,a functional relationship model of ′ = 1)((9,?)was established.Using this model,the suitable particle bed filling height h value under different particle size d conditions can be determined.There are 46 figures,15 tables and 97 references in this paper.