Study On Triboelectric Characteristic And Enrichment Of Fine Coal Particles In Gas-solids Fluidization Bed With Applied Electric Field

Fluidization triboelectric separation,which is a dry separation method for fine particles,has a broad application prospect in fields of coal,minerals,fly ash and waste plastics.Compared with conventional triboelectric separation methods,fluidization triboelectric separator is with simpler configuration.The particles charged by colliding with each other and directly separated by electric force in the fluidized bed with applied electric field,which can achieve multiple charge and multiple separation of particles.The purpose of this paper is to separate coal by fluidization triboelectric separation.the charge characteristics and charge distribution of particles was studied by analyzing particles with different charge level;distribution of quartz mass fraction in the direction of the electric field line was studied by the analysis of particles at different points in the fluidized bed with applied electric field;based on dispersion degree of pulverized coal distribution rate in each product,the enrichment of particles in an fluidized bed with applied electric field was studied.The main conclusions are as follows:Ash determination and mineralogy analysis of the coal shows that the main associated mineral in coal is quartz,calcite,pyrite and kaolin.The triboelectric charge experiment of associated minerals and coal shows that the friction with coal results in all associated minerals being negatively charged.The triboelectric charge characteristics and charge distribution of particles in a fluidized bed were studied using two kinds of mixed particles consisting of coal and quartz and coal and calcite.The results shows that the average charge intensity of the mixed particles gradually increases with the increase of fluidization time,and the charge balance is achieved between 6 and 10 min.The increase of the fluidization gas velocity and the decrease of the bed height can significantly enhance the equilibrium charge strength of the particles.In addition,with the increase of fluidization time,fluidization gas velocity and the decrease of static bed height,the proportion of uncharged particles in the fluidized bed decreased notably,and relatively strong charged particles also increased remarkably.In addition,the difference in charged environment leads to differences in the charging characteristics of quartz,calcite and coal.The quartz and calcite particles,with lower proportion,can charge sufficiently because of the larger collision probability with coal particles,whose charge-to-mass ratio is mainly distributed in the range of-7.21 to-2.40 nC/g and-7.21 nC/g.coal particals,with a higher proportion,are less charged becose most of the triboelectric occurs between particles of the same kind,and it's charge-to-mass ratio is more widely distributed between-2.40 and 2.40 nC/g.Within the equipment parameters,two simulated coal samples,separately composed of 75% coal and 25% quartz and calcite,was used to conduct enrichment tests in the fluidized bed with applied electric field.With the increase of fluidization time,fluidization gas velocity and the decrease of static bed height,the amount of pure minerals in the negative product gradually decreases.It was found that the product enrichment effect was most obvious with 60 kV sorting voltage,16.53 cm/s fluidized gas velocity,and 2.5 mm static bed height.A product with about 10% ash content can be collected in the material collection tank that close to negative electrode plate.Compared with roughly 25% ash content of the input,the mineral mass fraction decreased by about 15%,which confirms the feasibility of fluidization triboelectric separation of fine coal.Three factors and three levels of orthogonal tests were conducted with Fine coal.The result shows that the enrichment effect of fine coal in the fluidized bed will be better with lower bed height,higher fluidization gas velocity and higher separation voltage and there is no interaction between the three factors.The sorting voltage is the most significant factor affecting the enrichment effect among the three.The best sorting conditions are 60 kV sorting voltage,16.53 cm/s fluidization gas velocity,and 2.5 mm static bed height.Under this condition,the lowest ash clean coal can be obtained with 3/7 length on the negative side of the fluidized bed after 30 minutes of enrichment.Its ash was 9.84% and its combustible recovery rate was 21.76%.It is confirmed that the fluidized triboelectric separation is also an effective method to clean the fine coal.