Structural Design And Optimization Of Coal Slurry Water Settling Equipment In Hypergravity/Gravity Composite Field

Coal is a basic energy source in China,coal wet washing will produce a large amount of high ash coal slurry that is difficult to settle and clarify.The efficient settling and clarification of these high ash coal slurry water is an urgent problem to be solved in the coal preparation industry.The commonly used equipment for coal slurry water treatment is mainly gravity settling equipment and centrifugal settling equipment.Among them,gravity settling equipment such as thickeners have problems such as large land area,mixed settling of full particle size,low settling efficiency,and high consumption of reagents.It is difficult to add reagents during the settling process of centrifugal settling equipment.Based on this,the paper proposed a hypergravity/gravity composite field coal slurry water settling equipment(HGCE)under the combined action of gravity and centrifugal force,in order to effectively improve the settling efficiency of coal slurry water and reduce the consumption of flocculants.The paper takes coal slurry water and its main mineral component particles as the research object.The computational fluid dynamics-discrete phase model(CFD-DPM)simulation method and Particle Image Velocimetry(PIV)testing method are used to s study the flow field flow characteristics and particle motion characteristics of coal slurry water settling equipment in a hypergravity/gravity composite field.The classification characteristics of kaolinite,coal,and quartz are compared.We studied the influence of different parameters(classification overflow outlet diameter,classification underflow outlet diameter and feed velocity)on the concentration distribution of classification underflow and classification overflow and classification efficiency of composite sedimentation equipment.The construction scheme of HGCE and the significance of each parameter on classification efficiency were obtained using orthogonal experimental method.The research can provide reference for enriching the theory of coal slurry water composite field and understanding the performance of coal slurry water settling equipment in hypergravity/gravity composite field.The main research and conclusions are as follows:(1)A geometric model of the composite flow field was established using CFD method with a diameter of 200 mm HGCE as the object,and a structured grid was divided.A PIV testing system was also constructed.The combination of CFD method and PIV technology verified the reliability of the model from three aspects: gas volume fraction,velocity distribution,and product split ratio.(2)Based on the validity of the model,the Reynolds Stress(RSM)model and Volume of Fluid(VOF)model were used to explore the velocity distribution characteristics,pressure distribution characteristics,and turbulence distribution characteristics under different parameters.The results show that the axial velocity decreases from the wall to the center,first increasing and then decreasing.When the x-position is around ±35 mm,the axial velocity changes from decreasing to increasing,and when the x-position is around ±22 mm,the increasing axial velocity remains unchanged;The inflection point of increasing axial velocity in the descending direction is located near ±76 mm in the x-direction,while the tangential and radial velocities rapidly decrease from the wall to the center and gradually increase.The inflection point of tangential velocity is located near ±95 mm in the x-direction,and the inflection point of radial velocity is located near ±77 mm in the x-direction.With the increase of feed velocity,the increasing and decreasing axial velocities gradually increase,and the tangential and radial velocity values gradually increase,providing greater centrifugal force for fluid flow in HGCE and promoting sufficient particle classification in the HGCE flow field.As the diameter of the classification overflow outlet increases,the increasing and decreasing axial velocities decrease,while the minimum tangential velocity increases,which is not conducive to the sedimentation of coarse particles and the classification of fine particles.The increasing axial velocity decreases with the increase of the diameter of the classification underflow outlet,which is not conducive to the classification of fine particles.The decreasing axial velocity increases with the increase of the diameter of the classification underflow outlet,which is conducive to the sedimentation of coarse particles.The static pressure in the flow field increases with the increase of feed velocity,decreases with the increase of the diameters of the classification overflow outlet and classification underflow outlet.The higher the feed velocity,the more favorable it is for the sedimentation of coarse particles and the classification of fine particles in the flow field.The smaller the diameter of the classification overflow outlet and classification underflow outlet,the more favorable it is for the classification of particles in the flow field.The turbulent kinetic energy k and turbulent intensity I gradually decrease from the cylinder to the cone,and from the wall to the center.As the feed velocity increase,k,I,and turbulent dissipation rate ε significantly increased.When the diameter of the classification overflow outlet ranges from 120 to 180 mm,the maximum k and I are located near the inlet.When the diameter of the classification overflow outlet is 200 mm,k and I rapidly increase,and the maximum k and I transfer from near the inlet to near the wall of the classification overflow outlet.As the diameter of the classification underflow outlet increases,k,I,and ε first decrease and then increase.(3)Under the combined force field of hypergravity/gravity,particles are mainly affected by gravity,drag force,pressure gradient force,and virtual mass force.Drag force is the dominant force for particle classification and sedimentation,while gravity,pressure gradient force,and virtual mass force hinder particle classification.The classification process of coal slurry particles in HGCE can be divided into initial classification after tangential feeding and centrifugal classification in the cone section.The classification effect is best for kaolinite,followed by quartz,and worst for coal.(4)As the classification overflow outlet diameter increases,the concentration of the classification overflow first increases and then decreases,and the concentration of the classification underflow first decreases and then increases.The highest concentration of the classification underflow is 69.1 g/L,and the classification efficiency gradually decreases,reaching a maximum of 47.6%.As the diameter of the classification underflow outlet increases,the concentration of the classification overflow gradually decreases,while the concentration of the classification underflow first increases and then decreases,and the classification efficiency gradually decreases,reaching a maximum of 49.6%.With the increase of feed velocity,the concentration of classification overflow shows an increasing trend,while the concentration of classification underflow first increases and then decreases,and the classification efficiency gradually increases.The primary and secondary order of factors is feed velocity >classification underflow outlet diameter >classification overflow outlet diameter.The feed velocity is 2.5 m/s,the classification underflow outlet diameter is 20 mm,and the classification overflow outlet diameter is 120 mm,the classification effect is the best and is 54.7%.The feed velocity and classification underflow outlet diameter have a significant impact on the classification efficiency,while the classification overflow outlet diameter has no significant impact on the classification efficiency.(5)0.500 ～ 0.250 mm and 0.250 ～ 0.125 mm coal slurry particles all enter the classification underflow to settle,87.05% of 0.125 ～ 0.075 mm coal slurry particles enter the classification underflow to settle,63.9% of 0.075 ～ 0.045 mm coal slurry particles enter the classification overflow to classify,and more than 90% of-0.045 mm coal slurry particles enter the classification overflow to classify.HGCE can achieve rapid flocculation and sedimentation of coal slurry water under the action of flow field without the need for stirring,rapidly improving turbidity removal rate and saving flocculant dosage.Figure [65];Table [17];References [151]...