| The gas-solid fluidized bed separation technology is the research focus on drycoal preparation. The fluidized bed separation technology for fine coal cleaning hasbeen developed rapidly. Based on the review of the fluidized bed study and relevantliterature, in order to save energy and reduce emission，the gas-solid fluidized bedseparation technology is introduced into the pulverizing process of power plant in thispaper. Therefore, the vibrated fluidized bed applied to separate materials blow0.5mmwas researched basically. The forces in the fluidized bed without external mediumwere analyzed and the difference of drag coefficient among particles with differentReynolds number was studied. Besides, the sine force was exerted on the particles soas to establish dynamic models of motion particles in the different areas of thevibrated fluidized bed. The separation mechanism was explained and the continuousseparation apparatus and experiments were designed, which offered a research basisfor the separation by the fluidized bed without additional dense medium.The numeric simulation of the dynamic models are suitable to calculate anddescribe the velocities and tracks of particles in the vibrated fluidized bed. The resultsof computational fluid mechanics showed that different particles move and gather inthe different areas of the fluidized bed, and finally are stratified by density under thedilute and dense phase.Most particle sizes of the recirculating loads in the pulverizer are fine and theyare mainly between0.125~0.25mm which belong to Geldart B particles. The resultsof fluidization characteristic experiments of the simulated materials showed that thevibration could reduce the bed expansion and minimum fluidization velocitysignificantly. The results of separation characteristic experiments showed that thesimulated materials were separated by size and density. When the fluidization numberwas3and the vibrational frequency was55Hz, the separation efficiency was at itsmaximum level and the particle size and density distribution were uniform. The ash ofthe heavy product of actual material is78.46%. The difference between the heavy andlight product is37.39%. The separation efficiency is51.14%. The recovery ofcombustible matter amounts to94.05%. The backscattered electron imaging andspectrometer element distribution indicate that clay mineral, pyrite and other highdensity components are removed. Besides, fine coal existed in the recirculating loadof the pulverizer render the density and size distribution of fluidized bed more stable.The influence of vibration force field on the separation was studied and the images shooted by a high speed digital camera showed that the induced vibrationpromotes the merge of bubbles and forms the periodic upward air lock in the radialcross section of the fluidized bed. Though the motion of air lock influences thestability of bed, it is beneficial to the separation of particles by density. The separationmechanism of particles in the vibrated fluidized bed showed that the particles wereseparated by different terminal settling velocity in the process of hindered settling bythe synergistic effect between the dilute-phase and dense-phase.The continuous separation to the recirculating load of the pulverizer was carriedout in order to study the relation between ash of heavy and light product, separationefficiency, combustible matter recovery and the air speed, vibration frequency,feeding speed. The results showed that when the air speed was at13.2cm/s, vibrationfrequency was at55Hz and the feeding speed was at1.5kg/min, the comprehensiveseparation effect was the best with the45.37%and75.67%ash content of lightproduct and heavy product respectively. The separation efficiency and combustiblematter recovery reach to the peaks which were58.33%and88.64%respectively. Theresults validate the feasibility to separate the recirculating load of the pulverizer by thevibrated fluidized bed. |
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