| Coal is the basic energy in China,and the coal-dominated energy structure will be difficult to change before 2050.In 2020,more than 10 billion m3 of coal sline water will be generated.Coal washing and processing is the source technology of clean and efficient utilization of coal.The high efficient settlement of slime water has always been a difficult technical problem in coal preparation industry,and the traditional mixed concentration settlement technology is difficult to solve this problem effectively.In this paper,three representative fine particles of quartz,kaolinite and coal in coal slime water are taken as research objects.The dynamic characteristics of slime particles settlement are studied by using computational fluid dynamics-discrete element method(CFD-DEM)coupled simulation and experiment.The drag coefficient equation of slime particles settlement is modified based on the shape of slime particles.Based on the sedimentation characteristics of slime particles,the difficulty standards of different mineral particles sedimentation and the difficulty criteria of slime particles classification are put forward.The research can provide a basis for the design of efficient slime water sedimentation and classified sedimentation equipment.SEM statistical analysis shows that 30-500μm coal,quartz and kaolinite particles all belong to block particles within 1-3.Based on the shape of slime particles,the drag coefficient model of fine slime particles is modified and the reliability of the model is verified by experiments.When the new drag coefficient model is used to calculate and simulate the settlement of slime particles,it is found that when the equivalent diameter of particles is larger than 50μm,the length-width ratio has a great effect on the settlement.The particle size of slime is relatively small,especially in the wet state,the microscopic forces between particles such as van der Waals force,electrostatic repulsion force and liquid bridge force are significantly enhanced.The microscopic forces between particles were studied by measuring the Angle of rerest.It was found that when the particle size was between 45 and 500μm,the Angle of rerest decreased with the decrease of particle size.When the particle size decreased,the bite force between particles decreased,and the bite force decreased,the Angle of rerest decreased.When the particle size is 30-45μm,the Angle of rerest increases with the decrease of particle size,and the adsorption between particles is the dominant factor.The smaller the particle size is,the stronger the surface microscopic force is.With the same particle size,the Angle of repose from large to small is coal,kaolinite,quartz.It is found in the study of slime particle group settlement that:(1)As the number of particles increases,the vertical velocity of smaller particles decreases due to the increase of collision probability between particles and the increase of reverse water velocity,and the proportion of particles H50 in the upper part of the settling device gradually increases.In the case of dilute dense phase(particle concentration less than 12%),the difference of settling efficiency of different number of particles of the same mineral is less than 1%,but the difference of settling efficiency of different mineral particles under the same particle size is different due to the difference of density.According to the settling characteristics of slime particles,the difficulty standard of settling of non-mineral particles and the criterion of classification difficulty of slime particles are put forward.(2)The effect of the release velocity of single mineral particles on the sedimentation process decreases with the decrease of particle size.The effect of release velocity on large density particles is stronger than that on small density particles,and the effect increases with the decrease of particle size.(3)30-500μm slime particle H50 decreases with the decrease of coal particle ratio.When the ratio of coal,kaolinite and quartz is 1:1:1,the difference between quartz particle H50 and mixed particle H50 is 8.07%.The difference between kaolinite particle H50 and mixed particle H50 is 7.57%.The difference between coal particle H50 and mixed particle H50 is 15.63%.The main reason for the difference in H50 is the difference in density between different minerals.Surface hydration of mineral particles in coal slime water is one of the important reasons for its difficulty in settling.The existence of hydration film on particle surface leads to the increase of shear viscosity in liquid-solid two-phase flow system.Based on hydration characteristics,a new shear viscosity formula is modified for hydration particle settlement dynamic simulation.At 2s settlement time,the difference of coal slime particles H50 with and without hydration characteristics increases and then decreases with the decrease of particle size.Hydration characteristics have the greatest influence on coal particles 125-250μm,kaolinite particles 75-125μm and quartz particles 45-75μm In the settlement time of 3s,the difference of coal particle H50 with and without hydration characteristics increased and then decreased with the decrease of particle size,while the difference of quartz and kaolinite particle Hso decreased with the decrease of particle size.The hydration characteristics have the greatest influence on 125-250μm coal particles,30-45μm kaolinite particles and 30-45μm quartz particles.The natural settlement classification test of slime particles further verifies the validity of the standard of the difficulty of settling particles and the criterion of slime particles classification.Assuming that the particle size is 125μm as the classification criterion,it is found that when the rising water rate is 0.01m/s,all coal slime particles smaller than 125μm enter the overflow,and the flow velocity can meet the classification criterion of 125μm In the vertical classification device,more slime particles enter the upper position with the increase of rising water velocity.When the rising water rate is 0.04mm/s,the proportion of the three particles in the upper position of the graded sedimentation device is 1:1:1,and D50-coal is 194μm D50-quartz is 148μm,and D50-kaolinite is 150μm.In the horizontal classification device,when the water flow rate is 0.1m/s,the proportion of coal,quartz and kaolinite particles in P3 area is 1:1:1,and the outlet area D50-coal is 170μm,Dso-quartz is 87μm and D50-kaolinite is 88μm;r50-coal is 52%,r50-quartz is 23%and r50-kaolinite is 25%.Figure [108];table [35];reference [66]... |
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