重介质旋流器分选过程的离散分析与数值模拟

重介质旋流器广泛应用于煤炭分选,分选过程十分复杂,试验测试研究重介质旋流器内部流场和颗粒运动特性费时费力,成本较高。随着数值计算技术的发展,国内外学者应用数值模拟方法研究旋流器内部的多相流流场。采用计算流体力学(CFD)与离散分析方法(DEM)耦合技术对重介质旋流器的分选过程进行数值模拟研究,为重介质旋流器的结构参数和操作参数的优化提供了一种新途径。用Fluent软件研究了旋流器内部悬浮液速度场、密度场、压力梯度场和黏度场,用EDEM软件研究了旋流分选过程中的煤粒运动行为及分选效果的评价。研究结果表明:悬浮液压力分布和压力梯度分布径向基本对称,溢流口和底流口处压力值最低。器壁沿径向形成了压力梯度,差值逐渐增大,空气柱边界处压力梯度最大;不同尺度的煤粒在旋流器内部的停留时间不同,相同密度的煤粒,粒度越小,停留时间越长。溢流中排出煤粒在旋流器中的停留时间明显长于从底流口排出的煤粒。溢流口排出的煤粒,密度越大,停留时间越长,底流口排出的煤粒,密度越大,停留时间越短。不同的旋流器结构参数对分选的影响程度不尽相同,其中溢流管直径的影响最为显著,溢流管直径超过500 mm时,不能形成完整的空气柱,无法分选。溢流管直径为300 mm时,分选效果较好;溢流管插入深度显著影响分选精度,插入深度为160 mm时,分选密度增大,细小高密度的煤颗粒将错配进入溢流,溢流管插入深度为320～800 mm时,分选密度接近悬浮液密度,分选指标E_p=0. 084～0. 100,分选效果较好。底流口直径对旋流器选精度影响较大,当底流口直径为272和306 mm时,分选密度与悬浮液密度接近,E_p值小于0.1,分选效果较好。圆柱段长度对于分选密度影响不明显。

Discrete analysis and numerical simulation for separation process of dense medium cyclone

The dense medium cyclone is widely used in coal separation process.The experimental study on internal flow field and particle motion characteristics of dense medium cyclone is difficult and time consuming with high cost,due to the complicated separation process.With the development of numerical calculation technology,the numerical simulation method was widely used to study the multiphase flow field inside the cyclone.In this paper,the computational fluid dynamics (CFD) and discrete analysis (DEM) coupling techniques were used to numerically simulate the separation process of dense medium cyclones,which provided a new way to optimize the structural parameters and operating parameters of dense medium cyclones.The Fluent software was used to study the velocity field,density field,pressure gradient field and viscosity field of the internal suspension of the cyclone.The EDEM software was used to study the coal particle movement behavior and the evaluation of separation efficiency during the cyclone separation process.The results showed that the pressure distribution and the pressure gradient of suspension were basically symmetrical,and the pressures at the overflow and underflow outlet were the lowest.The pressure gradient was formed along the radial direction,the difference gradually increased,and the largest pressure gradient was at the boundary of the air column.The coal particles in different sizes had different residence time inside the cyclone.For the coal particles of same density,the smaller the particle size,the longer the residence time.The residence time of the discharged coal particles in the overflow in the cyclone was significantly longer than that from the underflow outlet.For coal particles discharged from the overflow outlet,the higher the density,the longer the residence time.While for coal particles discharged from the underflow outlet,the higher the density,the shorter the residence time.The structural parameters of different cyclones had different effects on separation process,and the influence of the diameter of the overflow pipe was the most significant.When the diameter of the overflow pipe exceeded 500 mm,a complete air column cannot be formed,resulting in failure to separation.When the diameter of the overflow pipe was 300 mm,the separation efficiency was better.In addition,the insertion depth of the over flow pipe significantly affected the separation efficiency.When the insertion depth was 160 mm,the separation density increased,and the fine high density coal particles would misplace into the overflow.When the insertion depth of the overflow was 320-800 mm,the separation density was close to the suspension density,Ep value was 0.084-0.100,and the separation efficiency was better.The diameter of the underflow outlet had a great influence on the separation precision of the cyclone.When the diameter was 272 mm and 306 mm,the separation density was close to the density of the suspension,and the Ep value was less than 0.1,which had a better separation efficiency.The length of the cylindrical section had little effect on the separation density.