Study On The Ultrafine Classification Mechanism Of Fine Coal Based On Hydrocyclone

Hydrocyclone is an effective separation device for multiphase flow separation using centrifugal force field.It has advantages of simple structure,no rotating parts,high separation efficiency,and easy automatic control.It is widely used in industrial field like mineral beneficiation,chemical engineering,biology,etc.As far as mineral beneficiation,hydrocyclone is widely used for classification,concentration,desliming and clarification etc.Although the cyclone has a simple structure,the internal flow field is very complicated.It is the key to the development and application of the cyclone to find the flow field and particle motion laws in the cyclone and to understand the influence of the cyclone structural parameters,operating parameters and material characteristics on the classification efficiency of the cyclone.In order to reduce the low limit of the fine coal in classification,this paper studied the ultrafine classification mechanism by the hydrocyclone.Using the studied technology,and combined with the technologies of enhanced gravity separation and centrifugal dewatering,a new process of the slime enhanced beneficiation can be estabalished.After reading the relevant literature,the flow field motion of the water phase in the hydrocyclone was analyzed firstly.And then,the followability and settlement laws of the particles in the water phase were analyzed.Finally,the motion laws of the particles in radiul and axial directiors was analyzed respectively.The effect of operating parameters and material parameters on the performance of the hydrocyclone was determined by the Krebs hydrocyclone(?100mm)ultrafine classification of fine coal test.The test showed that the optimal operating factors and material factors of the Krebs hydrocyclone were: feed pressure 0.04 MPa,injectionwater pressure 0.015 MPa,and feed concentration 10%.Finally,using the Box-Behnken response surface function in Design-Expert software to design the orthogonal experiment,the steepness index,the Hancock comprehensive efficiency,the cut-size,and the weight of-0.045 mm ultrafines in the underflow were obtained.The Krebs hydrocyclone was modeled by computational fluid dynamics(CFD)technology,and the calculation model,initial conditions and boundary conditions required for the simulation were determined.The selected model was VOF + RSM + DPM.Comparing the CFD calculation results with the Krebs test results,it was found that the experimental research and the CFD simulation results were in good agreement,which indicated that the parameters set by the CFD simulation are reliable,and the reliability of the Fluent software is high.Although the Krebs hydrocyclone used in the test can meet the requirement of ultrafine classification of fine coal,it diameter is small and its capacity is low.It does not match with the thourghput of the current coal preparation plant and the amount of the coal slurry.At the same time,the Krebs hydrocyclone used in the test required flushing water during operation,which not only increase system complexity and energy consumption,but also reduced the the concentration of the hydrocyclone underflow,which was not conducive to slime centrifugal beneficiation.Therefore,based on the initial conditions,boundary conditions and calculation models obtained by the Krebs simulation,taking the large-diameter hydrocyclone which was widely used in coal preparation plants as the research object,the influence of hydrocyclone structural parameters,operational factors,and materal factors on the hydrocyclone classification performance and cut-point size were studied by CFD technology.The found rules are shown hereafter:(1)Increasing the diameter of vortex finder will simultaneously cause a decrease of the classification efficiency and total pressure drop of the hydrocyclone,with the total pressure drop was larger.(2)Increasing the length of vortex finder will lead to a rapid increase in the total pressure drop of the hydrocyclone,but it has little effect on the classification efficiency of the hydrocyclone.(3)Increasing the apex diameter will increase the classification efficiency and reduce the total pressure drop of the hydrocyclone.At the same time,increasing the apex diameter will increase the water-mass ratio,caused low concentration of the hydrocyclone underflow.(4)Increasing the height of the cylindrical section of the hydrocyclone will reduce the total pressure drop,while the classification efficiency of the hydrocyclone will be decreased firstly and then increased.(5)Increasing the cone angle of the hydrocyclone will reduce the classification efficiency and increase the total pressure drop of the hydrocyclone.(6)Increasing the feed rate of the hydrocyclone will increase the classification efficiency and the total pressure drop of the hydrocyclone,and the increase of the total pressure drop was larger.(7)The influence of the feed concentration on the classification efficiency,cutpoint and total pressure drop of the hycyclone is not significant when the feed concentration was low.According to the orbit balance method and the LZVV,the calculating formular for the hydrocyclone cut-size was found,and the influence of the structural parameters and operating factors of the hydrocyclone on its classification performance was also analyzed.By referring to the structural design of the Krebs hydrocyclone,and combining with the research results on the large-diameter hydrocyclone,a new hydrocyclone model was proposed.The new hydrocyclone has features hereafter:(1)For the first time,the concept of annular feeding was proposed.The annular feeding can not only reduce the energy consumption of the hydrocyclone,but also presettling the slime to reduce the adverse effect of the short-circuit flow on the hydrocyclone classification.(2)A smaller cone angle of the hydrocyclone was design to decrease the cut-point.(3)Large cone bottom design,using the small cone angle and big cone bottom to strengthen the positive cleaning effect of turbulence on fine coal in coarse particle cluster,and improve the classification efficiency of the hydrocyclone.(4)There is little difference between the new hydrocyclone and the conventional hydrocyclone,and the new hydrocyclone does not occupy extra effective space,which has little influence on the later replacement of the hydrocyclone.Through the CFD simulation,it was found the the new hydrocyclone is more effective in the ultrafine classification performance and lower cut-point size.There are 91 figures,45 tables,and 183 references in this paper.