| Compared with other common coal slime separation equipment,the spiral separator has the characteristics of low energy consumption,high efficiency,and low operation cost,but its cut-point is high,usually over 1.6 g/cm3.The spiral separator is widely used in power coal preparation plants and coking coal preparation plants with better washability.Restricted by the test conditions,the previous research on the flow field distribution characteristics of a spiral separator is not deep enough,and the flow field distribution and particle moving behavior are lack of theoretical guidance and effective control mean.Based on dynamic analysis,numerical simulation and semi-industrial sorting experiments,this paper expounds the flow field distribution characteristics of the spiral separator,reveals the dynamic conditions of particle stratification-zoning,and emphatically analyses the influence of the trough profile,the transverse angle and the ratio of pitch to diameter on the flow field distribution characteristics and particle movement behavior in a spiral separator.Besides,the controller of the separation density of the spiral separator is also put forward.The main conclusions are as follows:(1)Based on the geometrical characteristics of the groove,the natural coordinate system is established,and the flow field characteristics of the spiral separator are theoretically consistent with the numerical simulation results.The calculated value of flow depth and the simulated value is consistent with the test value.Based on the dynamic analysis and the simulation results,it can be concluded that the flow depth,tangential velocity,and pressure gradient gradually change from inside to outside along the radial direction.The radial velocity is smaller than the tangential velocity,and along the thickness direction of flow depth,the fluid in lower layer move close to the central column,while the fluid in the upper layer is away from the central column,the radial velocity of upper layer fluid is far away from the central axis.Both the radial velocity of the upper and lower layer increase with the increase of radial distance.The radial velocity is strengthened by increasing the tangential velocity difference or pressure gradient along the thickness direction of flow depth.(2)The ratio of radial velocity to tangent velocity(vr/vt)can be used to represent the relative magnitude of radial thrust and the centrifugal force.The larger the ratio,the stronger the effect of radial circulation on particles.The particles near the trough move inward with a stronger radial flow.The greater the vr/vt on elliptic groove surface,the stronger the effect of radial circulation;the smaller the vr/vt on cubic parabolic groove surface,the smaller the radial circulation.The vr/vt is between the elliptic groove surface and the cubic parabolic groove surface at the outer edge of the inner cubic parabola;based on the synthetic profile,the vr/vt value increases with the increase of the transverse angle,and decreases with the increase of the raito of pitch to diameter.(3)Based on Euler-Euler-Lagrange algorithm,the Wen-Yu drag force model is used to calculate the force of the fluid on particles,and the numerical simulation of the particle motion in the spiral groove is realized.The simulation results are consistent with the experimental results;the cubic parabola and the composite groove surface are easier for the high-density particles to gather in the inner edge region;reducing the transverse angle angle and increasing the distance-diameter ratio will make the particles more outward.Marginal movement;(4)Based on the semi-industrial sorting test of spiral separator with six different design parameters,the coarse coal slime sorting process can be divided into the roughing stage and selective stage;roughing stage,about 3 turns,more than 72%of the+1.8 g/cm3 particles enter the inner edge zone,and more than 84%of the-1.4g/cm3 particles accumulate in the outer edge zone for the first time.At this point,the radial distribution of the particles with density of-1,4 g/cm3 is separated from that of partiles with density of 1.8 g/cm3.However,the particles with density of 1.4-1.8 g/cm3 was mixed in the outer zone;Then,after two separation turn,more than 96%of the particles with density of +1.8 g/cm3 were aggregated into the inner zone;More than 90%of the particles with density of-1.4 g/cm3 were accumulate into the outer zone.At this point,the light and heavy particles are initially sorted;For the selection stage,it us about 2 turns.At this stage,the main separation behavior is for the particles with density of 1.4-1.8 g/cm3.The amount of the particles with density of +1.8 g/cm3 and-1.4 g/cm3 has little increasing related to the formor radial possition.(5)NVhen the ratio of pitch to diameter and the transverse angle are constant,the distribution ratios of +1.8 g/cm3 particles at the innermost edges of elliptical,cubic parabolic and composite grooves are 71%,81%,87%,respectively.The grooved surface has better enrichment effect on vermiculite particles;the distribution ratio of-1.4 g/cm3 particles in the outermost edges of elliptical,cubic parabolic and composite grooves is 74%,51%,40%,respectively,indicating that the elliptical groove surface is easy to gather the outer edge of the-1.4 g/cm3 particle;(6)For the synthetic trough profile,appropriately increasing the transverse angle angle or decreasing the ratio of pitch to diameter is beneficial to promote the trend of the middle and high density particles moving toward the inner edge;when the transverse angle angle is increased from 15° to 17°,the ammount of the particles with density of+1.6 g/cm3 in the inner edge region increased by 28%;when the ratio of pitch to diameter decreased from 0.4 to 0.34,the distribution ratio of +1.6 g/cm3 particles in the inner edge region increased by 34%;(7)For the 1-0.25mm coarse coal slurry of the Fangezhuang Coal Preparation Plant,the synthetic trough profile with 0.34 ratio of pitch to diameter and 150 transverse angle is the best optimized structural parameter.With the pre-discharged in the rough selection stage,the cut-point can be reduced to 1.543 g/cm3,where the E value is 0.121 and the I value is 0.223.Compared with the traditional elliptical groove surface and cubic parabolic groove surface,when the clean coal ash requirements are similar,the separation efficiency is increased by 19.41%,13.11%,respectively. |
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