DEVELOPMENT OF COAL DRY BENEFICIATION WITH AIR-DENSE MEDIUM FLUIDIZED BED IN CHINA

CHINA PARTICUOLOGY Vol 3. Nos. 1-2. 2005DEVELOPMENT OF COAL DRY BENEFICIATION WITHAIR-DENSE MEDIUM FLUIDIZED BED IN CHINAQingru Chen and Lubin Wei'School of Chemical Engineering and Technology, China University of Mining and Technology, Xuzhou 221008, P.R.ChinaSchool of Chemical and Environmental Engineering, China University of Mining and Technology, Bejing 100083, P R chinaAuthortowhomcorrespondenceshouldbeaddressed.E-mail:cheng@cumt.edu.cnAbstractIn China more than two-thirds of available coal reserves are in arid areas where to beneficiate the run- of-mine coalthere is not enough water resource required by conventional processing. Developing efficient dry beneficiation technologyis of great significance for efficient coal utilization in China, notably the clean coal technology (CCT). the dry coal benefi-ciation technology with air-dense medium fluidized bed utilizes air-solid suspension as beneficiating medium whose density is consistent for beneficiation, similar in principle to the wet dense medium beneficiation using liquid-solid suspensionas separating medium. The heavy portion in feedstock whose density is higher than the density of the fluidized bed willsink, whereas the lighter portion will float, thus stratifying the feed materials according to their densityIn order to obtain efficient dry separation in air-dense medium fluidized bed, stable fluidization with well dispersed micro-bubbles must be achieved to ensure low viscosity and high fluidity. the pure buoyancy of beneficiation materials playsa main role in fluidized bed, and the displaced distribution effect should be restrained. The displaced distribution effectsinclude viscosity displaced distribution effect and movement displaced distribution effect. The former is caused by viscos-ity of the fluidized bed. It decreases with increasing air flow velocity. Movement displaced distribution effect will be largewhen air flow rate is too low or too high. If medium particle size distribution and air flow are well controlled, both displaceddistribution effects could be controlled effectively. A beneficiation displaced distribution model may be used to optimizebeneficiation of feedstock with a wide particle size distribution and multiple components in the fluidized bed. Therheological characteristics of fluidized beds were studied using the falling sphere method. Experimental results indicatedthat the fluidized bed behaves as a bingham fluid the plastic viscosity and yield stress can be obtained by measurementof the terminal settling velocity of spheres and linear regression of the experimental data. Both plastic viscosity and yieldstress increase with increasing size of the fluidized particles. The drag coefficient can be calculated with favorableThe first dry coal beneficiation plant with air-dense medium fluidized bed was established by CUMT with an output320000t a" and a probable error Ep value up to 0.05 was achieved. The plant was accepted by the chinese governmentin June, 1994. Since then, new applications have been found including a 700000 t-a dry coal beneficiation plant put upfor commercial testing. To realize coal dry beneficiation of full size range of 300-0 mm, further research on dry coal ben-eficiation of different size fractions has been under way at the Mineral Processing Research Center of CUMT, leading tothe following resultsDry beneficiation technology with a vibrated air-dense medium fluidized bed for fine coal of size fraction 6--0.5 mmAsh content was reduced from 16. 57%to 8.35%, with yield up to 80. 20% and Ep value up to 0.065Coal dry beneficiation technology with a deep air-dense medium fluidized bed for >50 mm coalAn Ep value up to 0.02 was achieved. This technology is of great value for waste removal from 300-50 mm largefeedstock, especially for big surface mines in ChinaCoal triboelectric cleaning technology for <1 mm pulverized coalCoal is comminuted down to 320 mesh(0.043 mm) to fully liberate the embedded minerals, yielding an ultra-low ashcoal(less than 2%). Currently a pilot system with triboelectric cleaning has successfully passed technical appraisalThree-product beneficiation technology with dual-density fluidized bedThis technology yields three products: clean coal, middling and tailing, with the following typical results: Ep value of0.06-0.09 for the upper layer with a density of 1.5-1.54 g-cm and Ep value of 0.09-0 11 for the lower layer with dersity of 1.84-1 9 g-cm中国煤化工Keywords coal preparation, dry beneficiation, fluidized bedCNMHGAcknowledgementThis work is financially supported by NSFC( Project 50474030, 90210035