Study On The Dynamics Of Triboelectrostatic Separation And Enhanced Separation Of Fine Coal

As a potential technology, triboelectrostatic separation has a wide range of application in the field of deash and desulfurization of coal powder, decarburization of fly ash and fine mineral processing. Research on the theory and method of triboelectrostatic separation is one of the frontier topics in the field of mineral processing. On the basis of extensive literature review, this dissertation mainly focused on the fundamental research of triboelectrostatic separation dynamics and enhanced fine coal triboelectrostatic separation by chemical modification. Law of motion of tribocharged particles in the process of triboelectrostatic separation was studied, and conditioning theory and method of enhanced fine coal triboelectrostatic separation by chemical modification was established initially. Mechanism of enhanced tribocharge of coal and mineral particles with opposite charges by chemical modification was discussed. The separation experiment for coal powder which was modified by chemicals was done and studied by using the laboratorial triboelectrostatic separation system. The triboelectrostatic separation system with online chemical modification was designed initially. These provided theoretic basis and technology support for the industrial application of triboelectrostatic separation, and especially for the industrial application of fine coal triboelectrostatic separation.The research on the triboelectrostatic separation dynamics show that the tribocharged particles were affected mainly by the electric field force/ drag force and gravity. The equation of dynamics of the tribocharged particles in electric field was established. The trajectory of the tribocharged particle in high-voltage electrostatic field was simulated using MATLAB software, and the results show that the size of particle,the intensity of electric field, the air speed and the charge-mass ratio have significant effects on the separation processing. The density of particle has a little effect on the separation results. The trajectories of coal and mineral particles were simulated using the charge-mass ratio data of the tribocharge tests by dint of MATLAB software, the simulation results show that the particles in the size fraction of 0.25~0.074 mm are the best ones to be separated easily. The particle trajectory were tested by high speed camera and analyzed by professional analysis software and the results show that the horizontal and vertical acceleration of the particle varies as sine wave, and the smaller the size is, the higher the wave of acceleration.Fundamental study of enhanced tribocharge of the coal and mineral particles by chemical modification were carried out using thirteen kinds of reagents and the results show that the performance of coal and mineral particles were improved after pretreated by chemical modification. The test data of modification by wet and dry process were comprehensive analyzed, and the results indicate that alkanes reagents are better for surface modification and ionic reagents are no conductive to triboelectrostatic separation of coal and mineral for lower selectivity. Ethanol, kerosene, ammonia and lignin are all more effective modification agents for improving fine coal triboelectrostatic separation. The chemical modification experiments of different density fraction coal were conducted and the characteristics of triboelectrification were tested. The results show that the charge performance of each density fraction coal particles pretreated by chemical modification is changed and the difference between the lower and the higher density fraction coal is enhanced. The polarity of tribocharge on high density fraction coal particle is difficult to reverse. The results of FTIR of each density fraction coal particles untreated and pretreated by chemicals show that the tribocharge-mass ratio is observed significant correlation with the absorbance intensity of the main polarity functional group. It is indicated that if the absorbance of the main polarity functional group on the particle surface decrease, the polarity of the tribocharge of the particle would tend to be positive, and if the absorbance of the main polarity functional group on the particle surface increase, the polarity of the tribocharge of the particle would tend to be negative.The results of fine coal triboelectrostatic separation tests show that the efficiency of deash and desulfurization decrease and the combustible recovery enhance with the increase of air flux. The efficiency of deash and the combustible recovery enhance and the efficiency of desulfurization reduce with the increase of the voltage. The interaction of the factors has significant influence on the efficiency of deash. The triboelectrostatic separation results of fine coal which was modified by chemicals show that the efficiency of coal powder triboelectrostatic separation is improved efficiently by chemical modification, and ammonia, kerosene and light diesel oil are the most effective chemical agents with an increase of clean coal yield of about 10%. The optimal amount of reagent is in a range of 500~2000 g per ton of fine coal. The experimental results show that the method of chemical surface modification to enhance fine coal triboelectrostatic separation is practicable with economic feasibility.