Study On Particle Density-size Bivariate Distribution Regularities In Coal Preparation Process

Coal preparation is the basis and premise of its clean utilization.The coal preparation process includes principally different gravity concentration and flotation processes,in which the particle density and size play an important role in deciding the preparation effect.Intensive probe into the influence of the particle density and size on coal preparation process is of great importance for improving the coal preparation effect and coal utilization efficiency.In this paper,a combination method of the particle density and size was proposed based on terminate settling velocity of the particles over a wide Reynolds number range.Taking normal distribution as a fundamental function,a partition surface model made up of 6 parameters including particle density and size was established.In this model,a quartile deviation coefficient was introduced and the relationship among the separation density,the ecart probable moyen,and the particle size can be deduced as a function by it.This established a theoretical and technical foundation for the analyzing the binary effect of the particle density and size.Taking the three-product gravity feed dense medium cyclone(3GDMC),the coal slime dense medium cyclone,and the flotation machine in Tunlan Coal Preparation Plant,as well as the hydro-cyclone and TBS in Dongqu Coal Preparation Plant as a research object,partition data with respect to the particle density and size were obtained by screening and float and sink tests.The partition curves of individual size fraction were plotted for the above separation and classification equipments according to a three-parameter model,and the relationship among the separation density,the ecart probable moyen,and the particle size was quantitatively analyzed.The partition surface as a function of density and size was drawn employing a double-variable model,and a specific function describing the relationship of the separation density,the ecart probable moyen,and the particle size was obtained,which shows that:(1)There is a non-monotone relationship between the separation density and the particle size for 3GDMC,the separation density of the medium size fraction is low,and the separation sharpness monotonously decreases with the decrease of the particle size.(2)For the coal slime dense medium cyclone,the separation density increases while the sharpness decreases with the decrease of the particle size.(3)For the hydro-cyclone,the cutting size and the ecart probable moyen of classification are 0.20 mm and 0.103,respectively.The ash content of each size fraction shows a significant difference between the overflow and the underflow,and the size fractions of-0.5mm all showed significant separation effect based on the density.The separation density increases while the sharpness decreases with the decrease of the particle size.(4)For TBS,the ash content of the clean coal as well as the tailings increases with the decrease of size for all size fractions.TBS can realize effective separation for +0.25 mm materials,and the separation density increases while the sharpness decreases with the decrease of the particle size.(5)In industrial flotation process,coarse losses and fine entrainment both happen.In laboratory,it is difficult to obtain a clean coal of low ash content on the premise of maintaining high yield,employing traditional two-product flotation process,taking kerosene and octanol as a collector and a frother,respectively.By contrast,when the three-product flotation flowsheet involving a scavenger and a cleaner is used,the ash content of the tailings can be as high as more than 65.0% with qualified clean coal ash,and the slime entrainment of the cleaner can reduce 50%.The separation density of the 0.25-0.074 mm fraction in the scavenger is high while that of +0.25 mm and-0.074 mm is low,indicating that the flotation strength of the medium size fraction is high,among which +0.25 mm fraction is the highest.Based on the partition law of the typical separation equipments,aiming at the problems of the current flowsheet in Tunlan Coal Preparation Plant,an optimized scheme was proposed including lump gangue removal by dense medium shallow tank,separation of the coarse slime by a two-stage three-product cyclone designed especially for coal slimes,and three-product flotation.The details are as the followings:To substitute the original moving-sieve jigger with more advanced and reliable dense medium shallow tank to improve the lump gangue removal efficiency as well as capacity before separation and reduce gangue content in the raw coal to be washed,to reduce the amount of coal slime into the dense medium separation system and improve the separation sharpness and the product quality employing 3GDMC with pre-desliming.To separate the coal slime from pre-desliming operation individually employing a two-stage three-product water only cyclone,which has been proved by laboratory tests that three products including clean coal,middlings and reject and an overflow qualified for flotation can be obtained from a single feeding.To apply scavenger-cleaning process in flotation to produce three products,in which,the scavenger firstly minimizes the coarse losses in the clean coal with proper reagent regime,ensuring maximum combustible recovery and obtaining tailings of high ash that can be disposed directly.Then the clean coal of the scavenger is subjected to a cleaning operation,decreasing the slime contaminant of the ultimate clean coal to obtain a low ash clean coal,preventing ash compensation of dense medium separation,and thus increase the yield of the clean coal.The medium coal has an ash content approaching that of steam coal,containing much less slime of high ash,its filter cake easily smashed,and nearly having no influence on the quality of commercial steam coal.The three-product separation process for coarse coal slimes,combined with the three-product dense medium separation,constitutes a three-product coal preparation process for the total size fraction characterized by intensive gangue removal,based on three or four stages of classification of the raw coal.This process can flexibly regulate the separation density among different separation methods,diminishing the negative effect to realize coal preparation based on the same ? principle,improving the economic benefits of the enterprises,and promoting the improvement of coal preparation efficiency and thus utilizing the coal resource sufficiently and properly as well.