The Coagulation Acceleration Mechanism And Structure Optimization Of Grid Flocculator

The study of flocculation kinetics shows that the fluid flow state in the flocculation device has an important influence on the flocculation effect.The grid-type flocculation and sedimentation device is a new type of flocculation-sedimentation integrated device.Experiments show that its fluid environment can significantly improve the flocculation effect,but the specific mechanism is not clear,and the structural design lacks scientific basis.To this end,this paper uses computational fluid dynamics and discrete element coupled simulation methods to simulate the movement of fluid and particles in the grid,study the coagulation mechanism of the grid,and optimize the grid structure.Collision between particles is a prerequisite for mutual adhesion.Through the CFD-DEM coupling simulation analysis of the simplified grid device,it is found that the turbulent kinetic energy and turbulent energy dissipation rate around the grid and below the grid are large,and at the same time,the number of collisions between particles will be greatly in these areas.Increase,indicating that turbulent kinetic energy and turbulent energy dissipation rate are the main reasons that promote particle collisions.Therefore,through direct CFD simulation,the structural parameters of the grid device are optimized using the turbulent kinetic energy and turbulent energy dissipation rate.Firstly,a simulation is carried out for a single-row grid with different row-to-diameter ratios(the ratio between the distance between the centers of the two grids l and the grid diameter d).The results show that the corresponding turbulent kinetic energy and turbulent energy dissipation under different grid diameters With the increase of the row-to-diameter ratio,the ratios first increase and then decrease;when the grid diameter is 3,4,5,6,and 7 mm,the best row-to-diameter ratio of the grid is2.3;The smaller the grid diameter,the higher the overall turbulent kinetic energy and turbulent energy dissipation rate of the device.The layer-to-diameter ratio of the two rows of grids with a grid diameter of 3 mm was simulated and studied,and the optimal value of the layer-to-diameter ratio of the multiple rows of grids was determined,l/d=3.5.When the layer-to-diameter ratio reaches 3.5,the energy consumed after the water flow passes through the first row of grids is basically dissipated,and then it encounters the second row of grids for a new dissipation process.At this time,the energy utilization rate is higher.Conducive to promote the flocculation process.Based on the simulation results,the grid in the grid flocculator is optimized and the flocculation process is simulated.The simulation results show that the reasonable distribution of grids can well promote particle collision flocculation.When the particle flow moves from top to bottom,the number of collisions between particles gradually decreases.The flocs grow up gradually,and grow fastest in the grid area.When the flocs flow out of the grid area,they form the average particles of the flocs.The number gradually stabilized.The average number of particles composing flocs increased from19 to 242 initially.Under the condition of 0.1 mol/L flocculant(Al Cl₃)36 mg/L and polyacrylamide(PAM)2 mg/L,the coal slime water flocculation and sedimentation test was carried out in a grid-type flocculation sedimentation device.The results show that the flocs gradually grow up when the slime water is fed from top to bottom,and the average particle size of the flocs can reach 0.906 mm after flowing through the grid area,which is in good agreement with the simulation results.The fractal dimension of the flocs from top to bottom gradually increases,and the flocs become denser and denser,and the turbidity of the overflow supernatant is 11.7 NTU,which is 52.2%lower than the flocculation in the pipeline on average.This paper has 45 map size,9 table,95 references.