| Coal plays an important driving role in China's economic development.In recent years,coal has been affected not only by the slowdown of the economic growth around the world but also by the adjustment of the economy structure and the transformation and upgrading of the industries.However,because of its low price,abundant reserves and easy transportation,coal still plays a dominant role in primary energy consumption.Nevertheless,the content of primary coarse coal and secondary coarse coal in the raw coal has remarkably increased because of the deterioration of coalfield geological conditions,the improvement of automation degree for coal mining,the aggravation of mechanical crushing and the argillization in water during the coal separation process.It can not be satisfied in the commonly separation equipment in coal preparation industry at present because the particles are generally too small to be handled in conventional gravity concentration units and too coarse to be efficiently recovered by froth flotation units.At present,there is still a gap in the fundamental and the theoretical research of the combination of the gravity and flotation separation technology,especially in the characteristics of particle fluidization in an aeration liquid-solid fluidized bed.Apart from these,the mechanism between bubble parameters and particle separation behavior is still unclear,which is not conducive to the industrialization of the fluidization flotation separation technology.In view of these problems,this paper has carried out a basic research on the gravity-flotation fluidization separation technology.Based on the analysis of fluidization characteristics,particle motion,force and dynamics in an aeration liquid-solid fluidized bed,the equation of minimum fluidization state of particles in fluidized bed is constructed.From this equation it can be found that the minimum fluidization velocity of bed is not only related to the properties of particles and fluids,but also related to the void fraction of bed,and the effect of density is greater than that of particle size in the fluidized bed separation.Besides,the phenomenon of stratified fluidization in the fluidization test of wide-size particle can be proposed.The experimental value of minimum fluidization velocity is obtained from the void fraction of bed-superficial water flow velocity curve.The relative error between the experimental value and the theoretical value of minimum fluidization velocity is less than 10%.The reasonability of the theoretical deduction process of equation of minimum fluidization stale for particles is proved.Based on the measurement system of bubble parameters in an aeration liquid-solid fluidized bed,we analysis the effects of space location,aeration rate,and concentration of frother on bubble size and gas holdup,and establish a prediction model of bubble size.The prediction equation of bubble Sauter diameter is obtained by dimensional analysis and experimental data.It can be seen from the equation that the bubble diameter is inversely proportional to the concentration of frother and directly proportional to aeration rate.In addition,the accuracy of the prediction equation of bubble Sauter diameter proposed in this paper is verified by the results of bubble size measurements in related literature.The results show that the predicted values are in good agreement with the experimental measurements,and the Pearson correlation coefficient is 0.9907.Based on the basic theoretical analysis of aerated liquid-solid fluidized bed,the calculation model of density spatial distribution of aerated liquid-solid fluidized bed is established.From the calculation correlation,it can be seen that the density of bed is related to particle properties,cross-section area of fluidized bed,gas rate,bubble Sauter diameter and superficial water velocity.The model is verified by using 0.25-1.5 mm coarse coal.The results show that the model can predict the density of aerated liquid-solid fluidized bed.The measured values are in good agreement with the experimental values,and the Pearson correlation coefficient is 0.9098.In addition,the correlation of bed density indicates that the bed density is a statistical mean value based on the time dimension,and can not reflect the fluctuation of bed density.According to the determination of the bed properties of the aerated liquid-solid fluidized bed,it is concluded that it takes about 20 minutes to form the separation bed layer.There are obvious changes in ash content and density of each bed layer in the fluidized bed separator.From top to bottom in the separator,the ash content and density of the bed layer gradually increased,which can reveal that the mechanism between the distribution of bed layer properties and the separation behavior of coarse particles.It should be pointed out that the bed layer density of fluidized bed is not the actual separation density.Using the self-made bed sampler,we take samples of the particle from each bed layer.Through the analysis of the density composition changes of different bed materials,with the introduction of bubbles and the increase of aeration rate,the density of materials in bed layer 4 less than 1.4g/cm3 decreased by 39.39%,the density of materials in bed layer 5 less than 1.4g/cm3 decreased by 26.87%,the density of materials in bed layer 6 less than 1.4g/cm3 decreased by 6.11%.The density of materials in bed layer 4 greater than 1.8g/cm3 unchange,the density of materials in bed layer 5 greater than 1.8g/cin3 increased by 19.81%,the density of materials in bed layer 6 greater than 1.8g/cm3 increased by 11.25%.Therefore,the separation accuracy of equipment was improved.It could provide a technical support for the gravity-flotation fluidization coarse coal separation technology.A new type of aerated liquid-solid fluidized bed separator was designed and manufactured.The separation principle of aerated liquid-solid fluidized bed was expounded.Based on the evaluation index of ash separation degree,the effects of slurry concentration,superficial water velocity,aeration rate,feed rate,feed depth,column height,concentration of frother and collctor on the separation performance of coarse coal were investigated in detail by single factor test method,and the optimum value range of each factor was determined.Compared to the conventional liquid-solid fluidized bed,the aerated liquid-solid fluidized bed improved the recovery of coarse particles.The product of size range 1.5?1 mm increased by 22.55%among all clean coals and reached the highest growth rate,while the product of size range 0.5-0.25 mm reduced by 33.64%among all tailings,which was the largest reduction,and the separation efficiency is improved.The experimental results showed that the Ep value of the aeration liquid-solid fluidized bed separator reached 0.09 g/cm3.Based on the force analysis of feed in aerated liquid-solid fluidized bed and the correlation formula of bed density,the calculation model of separation density of fluidized bed is established.The theoretical value is in good agreement with the experimental value,and Pearson correlation coefficient is 0.9418.A mechanism for regulating separation density is established.The mechanism between fluidization characteristics of bed and particle separation behavior is revealed,which provides an effective way for efficient and reliable control of fluidized bed separation,this paper enriches the theoretical achievements of fluidized flotation technology. |
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