Research On Energy Function And Separation Echanisms Of Vibrofluidization Of Fine Coal

China’s coal resource and water resource has a reverse distribution. The problemof water shortages restricts the applications of wet coal beneficiation technologies indrought regions. A great amount of coal without deep cleaning enters directly to themarket, leading to serious waste of coal resources. The present situation describedabove highlights the significance and urgency of developing dry beneficiationtechnologies of coal. Thus, for the first time, the density segregation phenomenon inthe field of gas-solid fluidization is introduced into the research on fine coal drybeneficiation. In consideration of the fluidization characteristics of fine coal and theanticipation of separation performance, a vibrated fluidized bed is adopted particularlyto foster the formation of fluidization environment that intensifies density segregationwithin the bed of fine coal, leading to an effective fine coal beneficiation performance.The transfer of vibration energy to gas-solid fluidization systems of GeldartD-type fine coal has two main forms: forcible movement of air distributor and airpressure waves. The optimization mechanism of fluidization behavior due to vibrationis studied by using an advanced high-speed dynamic image analysis system and theresults show that the introduction of vibration energy can effectively destroy theparticulate force chains net, eliminate the disfluidized zones and the short-circuitchannel of air flow and improve the mechanical properties of particles system.Meanwhile, the synergistic functions of vibration and fluidizing air promote the excessfluidizing air to form regular slugging behavior under the excitation of air pressurewaves. The dynamical equation of coalescence due to bubble acceleration in theadjacent region of a slug and the mechanism model of slug growth are established. Theslug-disturbed regions with appropriate feature size provide a hindered settlingenvironment determined by the fluid drag force for the density segregation of particlessystem. Correlations of slug-disturbed region height and slug rising velocity areestablished and the occurence frequency of slugs varies between3.47Hz and3.85Hz,which is independent of fluidizing air velocity.Fluidization environment that intensify density segregation should satisfy thefollowing two conditions: having dilute regions with an appropriate environment ofhydromechanics that ensure the slip of particles with different densities and having astable occurrence mechanism of dilute regions that prevent the back-mixing of the segregated particles layers. The mechanism of fine coal beneficiation usingvibrofluidization based on density segregation is revealed by the comprehensiveanalysis of the hydromechanics environment of vibrated fluidized beds and theelements of fluidization environment that intensify density segregation. The separationprocess is studied from the perspective of the system potential energy changes and theresult of theoretical calculations indicates that the total potential energy of theseparated particles system is reduced by approximately9.3%comparing with that ofthe particles system before separation, which indicates that fine coal beneficiationprocess using vibrofludization based on density segregation has strong spontaneity.The concept of ash content segregation degree is proposed during the factorexperiments to evaluate the effects of factors including superficial air velocity,vibration intensity, bed height and fluidizing time on separation performance. Based onthe determination of optimal range of each factor owing to the single factor experiment,the Box-Behnken response surface method is used to study the interactions betweenfactors and determine the optimal separation conditions of-6+3mm and-3+1mm finecoal respectively. In addition, second-order polynomial predictive models areestablished. The separation results show that the probable error E values of-6+3mmand-3+1mm fine coal separated in an intermittent separation system using a vibratedfluidized bed are0.19~0.225and0.175~0.195, respectively.A continuous separation system using a vibrated fluidized bed is designed andestablished by ourselves based on the results of laboratory study. The bed distributionmodel of a continuous vibrated fluidized bed separator is established by introducingcoefficients that identify the bed transport properties and it is pointed out that thesection having an approximately horizontal bed surface should be prolonged to thegreatest extent in order to ensure a good separation performance. The averagetransmission speed of a continuous vibrated fluidized bed separator is also establishedand the optimal region of vibration angle is63°~67°. The separation results show thatthe probable error E value of-3+1mm fine coal separated in an continuous separationsystem using a vibrated fluidized bed is0.225and the two-stage separation process isrecommend for the purpose of improving separation performance.