| Centrifugation has been mainly applied in gold processing and platinum group minerals.The research of centrifugal separation is mainly focus on industrial application,However,little efforts has been directed towards understanding and characterization of the physical analysis,which leads to the theory of particles separation in centrifugal compound field lags behind the engineering practice.In the early years,researcher focused on the explanation of experimental phenomena and tried to describe the essence of separation process with simple models.In addition,the existing centrifugal separators are still unable to achieve a real sense of continuous discharge,hence,its application in the separation of coarse coal slime is limited.In this paper,the coarse coal slime as the research object,a centrifugal compound force field of coarse coal slime separator has been assembled.The mineral processing,fluid mechanics,the theoretical analysis,numerical simulation,experimental research and numerical analysis and other research methods are used to the separation mechanism and migration of particles in centrifugal compound force field.At present work,the film thickness and the influence law of the separation efficiency is determined.The flow field,particle movement rule and the characteristics of turbulent flow are explained.The dynamics equation of particle movement in centrifugal force compound field is also established.The separation mechanism of particles in centrifugal compound force field is revealed.The migration law and separation characteristics of each material property under different operating parameters in the centrifugal complex force field are expounded.The influence of operation parameters on the separation effect of coarse coal slime was investigated.The main contents and conclusions of this paper are listed as follows:(1)The influence of rotation speed and fluidization water pressure on separation behavior of particles in centrifugal compound field was investigated by used 0.25-0.5mm,0.5-0.63 mm,0.63-0.8mm and 0.8-1.0 mm four narrow fraction material: the density partition number is decreased with increasing of each narrow fraction particle group.The density partition number is decreased with increasing of rotation speed,and increased with increasing of fluidization water pressure.The density partition number of fine grain(0.25-0.50mm)and intermediate grain(0.5-0.63 mm and 0.63-0.8mm)in the product can be significantly regulated through the cooperation of rotating speed and fluidization water pressure,while the density partition number of coarse grain(0.8-1.0mm)is not significantly regulated.(2)The spatial distribution of particle size,density and ash content in rotation bowl is investigated.The results show that the step migration rotation bowl,that is,the material migrates according to particle size and density from the bottom to top of rotation bowl.In the separation zone,the lower part of the fluidization water hole is mainly higher density and coarse particles,while the upper part of the fluidization water hole is mainly lower density particles.(3)The separation characteristics of 0.25-0.5 mm,0.5-0.63 mm,0.63-0.8mm and0.8-1.0 mm four narrow fraction material was studied based on the difference of particle.The results show that under a certain speed,as the fluidization water pressure,the separation density increases,Ep value also increase;Under the same fluidization water pressure,the separation density and Ep value decreased with the increase of the rotational speed.The influence of particle size composition on the particle sorting process of 0.25-1.0mm was experimentally studied.The results showed that,under certain separation conditions,the separation density of particle group was determined by the particle size composition of the material: the higher the fine grain content was,the higher the sorting density was,and the higher the fine grain content was,the lower the sorting density was.(4)Based on the characteristics of the flow field in the separation rotation bowl,the force analysis and the order of magnitude compared to particle group.The dynamic differential equation of particles is established on the radial movement.Then,the dynamics of particle movement in centrifugal composite force field is analyzed based on the dynamic differential equation.Finally,the separation mechanism is revealed using the method of numerical calculation.The results show that reveals the centrifugal compound force field particle: centrifugal force accelerates the radial settling of particles,amplifies the settling velocity difference between particles of different densities,and further improves the radial movement difference of heavy and heavy particles under the action of radial fluidizationl water,thus strengthening the separation effect of heavy and heavy particles.(5)Based on theoretical analysis and experimental research,the particle separation process in the centrifugal composite field can be interpreted as follows:?.At the beginning of feeding,there is no bed formed,and only a few low-density particles are separated from the rotation bowl.This process is mainly controlled by centrifugal sedimentation in the flow film.?.The bed is formed quickly.The yield of clean coal is quickly increased with increasing of feed mass until reaches its maximum.In this process,the looseness and stratification of particles is taken place in migration zone due to shear movement produced by flow film tangential velocity,and together with the action of turbulent pulsation diffusion.During this process,separation evolves from a differential settling driven selection to a resuspension driven selection.?.The separation stage,the bed in rotation bowl is completely formed.The particles are separated according to particles density under the interaction of centrifugal force and fluidization water pressure.Due to the high centrifugal force,some of the light density particles are trapped in the bottom layer,Hence,the fluidization water makes the bed loose again,and rearrangement,which enhances the separation of particles in centrifugal compound force field.(6)The average thickness of the flow film in the rotation bowl was measured by the experimental method,and the quantitative relationship between the thickness of the membrane and the rotational speed and the water supply was established.The numerical simulation method is used to study the formation process of the flow film in the rotation bolw,and the results show that the numerical simulation results of the average thickness of the flow film in the rotation bowl are consistent with the experimental results,which indirectly verifies the reliability of the model.(7)The CFD-DEM coupling method is used to simulate the fluid flow and particle movement in centrifugal complex force field.The velocity of liquid flow in the rotary cylinder is: tangential velocity > axial velocity > radial velocity;In the separation zone,the tangential velocity of the liquid flow decreases and the axial velocity and radial velocity both increase due to the radial recoil.(8)Turbulent characteristics in the process of centrifugal composite force field show that compared with the delamination area,the fluid velocity isincreased due to the fluidization water.The turbulent kinetic energy and turbulence dissipation rate was increased,form a significant turbulence velocity gradient,which leads the settlement of particles in the radial is difficult.The pulsation of the fluidization water makes the particle group loose again,and makes the mismatched particles conduct secondary sorting,so as to strengthen the particle sorting process.(9)Design centrifugal compound force field continuous separation system of0.25-1.0 mm and 0.25-2.0 mm two kinds of coarse coal slime separation experiment was carried out,respectively.The quantificationally of cleaned coal yield,ash content,separation density and Ep values between centrifugal force,fluidization water pressure and operation parameters are established.Then,the influence of centrifugal force,fluidization water pressure and feed mass on separation efficiency are examined.The interaction between centrifugal force and fluidization water pressure is the main factor affecting the separation effect of two kinds of coarse coal slime.If the centrifugal force is constant,when the fluidization water pressure increases,the separation density increases,and the probability error may increase.(10)The results of parameter optimization test show that the cleaned coal with yield of 66.16%,ash content of 6.72% and Ep value of 0.13 can be obtained with0.25-1.0mm coarse coal slime under centrifugal force of 40 G and fluidization water pressure of 0.08 mpa.For 0.25-2.0mm coarse coal slime,the yield and ash content of cleaned coal are 58.52% and 5.43%,and the Ep value is 0.15 can be obtained with the centrifugal force is 25 G and the fluidization water pressure is 0.06 mpa,... |
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