Triboelectrostatic Separation-an Efficient Method of Producing Low Ash Clean Coal

Jun.2002Journal of China University of Mining &. TechnologyVol 12 No. 1Triboelectrostatic Separation-anEfficient Method of ProducingLow Ash clean coalZHANG Xin-xi(章新喜), BIAN Bing-xin(边炳鑫)2,DUAN Chao-hong(段超红), XIONG ian-jwn(熊建军)(1. School of Chemical Engineering and Technology, CUMT, Xuzhou Jiangsu, P.R. China2. Heilongjiang Institute of Science and Technology, Jixi, Heilongjiang 158105, P. R. ChinaAbstract: At present, coal is mainly consumed as fuel. In fact, coal is also a kind of precious raw material inchemical industry on the premise that some harmful minerals should be removed from coal. The paper presentthe results of the research on producing low ash (<2%)coal with triboelectrostatic separator used for prodting high-grade active carbon. The test is conducted in bench-scale system, whose capacity is 30-100 kg/h. TIresults indicate that: 1) the ash content of clean coal increases with the increase of solid content of feedstock, onthe contrary, the yield of clean coal is declining: 2)a high velocity may result in a good separation efficiency3)for the same solid content, the reunion caused by intermolecular force makes the separation efficiency dropdown when the ultra-fine coal is separated 4) the separation efficiency is improved with the increase of electricfield intensity, but there is a good optimized match between the electric field intensity and yield of clean coal5) a low rank coal is easy-to-wash in triboelectrostatic separation process 6)the yield of clean coal can be en-hanced and the ash decreased through adapting optimized conditions according to various coalsKey words: triboelectrostatic separation; ultra-fine coal; low ash clean coal bench-scale systeCLC number: TD924 Document code:a Article ID: 1006-1266(2002)01-0035-031 Introductiontrostatic processing hasn't the problems associated with wet methods. Triboelectrostatic separaActive carbon has been used in fields of tion may present unique opportunities to producemedicine, food, environmental protection, mili- low ash coal and link up well with active carbontary,and so on, because it has a developed inner production processspace and a tremendous specific surface area. TheThe purpose of this paper is to study how thepresent active carbon produced from coal is in its factors of solid content in felow-grade because of the high ash content of feed- the average velocity of particle and electric fieldstock coal. To deeply remove ash and produce intensity influence on the triboelectrostatic sepalow-ash (<3% or <2%)clean coal is the key ration efficiencystep to produce high-grade coal-base active car2 Experimental Resultsbon. At present, the wet processing is the mmethod of fine coal treatment, but it requires a 2.中国煤化工temnsiderable investment in bothprocessindCNMH Aspects of bench-scaledesliming treatment. On the contrary, triboelec- system. Coal is fed to tribocharger, in which coalReceived date: 2001-09-11Foundation item National Development Programs of Major Basic Research Project(G1999022205-03)BiograplF #*E Xin-xi(1994-), male, from Jiangsu Province, associate professor, engaged in coal separation and utilization of solidJournal of China University of Mining & TechnologyVol. 12 No. 1and mineral will be electrified with negative and caused by the contact of various mineral may bepositive charge respectively, the charged particles disutility Meanwhile, in the actual separationd to electrostatic separation chamber process the reunion opportunity of negativeand be separated efficientlcharged particle and positive charged particle inTribochargger Separation chambercreases along with the increase of solid contentso the separation efficiency decreases.2.2.2 The influence of average velocityEnter portThe faster the particles move in tribocharger, the larger the value of charge on particles, theeasier the reunion of particles to be destroyed soa high velocity will lead to a good separation reDiagram of bench-scale systemIt. Table 2 shows the test resultThe samples are all comminuted to a size ofTable 2 Influence of average velocity of particles<45um to liberate mineral and exist in a air dryClean coalstate. Test conditions are as following: ash con(ms) Yield/% w(ash)/% Yield/% w(ash)/%tent of feedstock is 4. 19%, volatile is 41. 27%67.8832.12air flow rate is 300 m"/h, electric field intensity is27,500.2 MV/m, average velocity of particle is 20 m/s, and for lkg of air, there is 0. 15kg of solid2.2.3 The influence of coal size distribution2.2 ResultsIt can be seen from Table 3 that the separa2. 2. 1 The influence of solid content in feed- tion effect of coal with the size of <45um is betstockter than that of coal with the size of <100um andThe experiment data are presented in Table 30um. When the size of the coal sample ist been liberatedwith the increase of solid content of feedstockfrom coal, so the separation effect is not good asOn the contrary, the yield of clean coal is declinthat of <45um. But when the size distribution offeed <30solidTable 1 Influence of solid content inthe reunion caused by intermolecular force makesfeedstock on separation efficiencythe separation efficiency dropzo(solid)Clean coalTailingsTable 3 Influence of coal sizeYield/% w(ash)/% Yield/% we(ash)/70,3229,689,64dClean coal70.78um Yield/% w(ash)/% Yield/% w(ash)/%<10063.212.0134.7458,17It is known from the theory of triboelec- 2.2.4 The influence of electric field intensitytrostatic separation that, if only pure coal contactTable 4 gives the electric field intensity testwith one kind of mineral, the polarity of charge result. When the electrode plate length is con-on coal and mineral are determined completely by stant, a lower electric field intensity makes athe difference of their work function. The proper化工 ween negative chargincrease of solid content makes a larger contactCNMHGed particle, with someopportunity for particles, in the ideal conditionTYHeing divided by splitter not by electricparticles is charged enough, so the separation ef- force. The separation efficiency improves alongficiency is high. However, the compositions of with the increase of electric field intensity, butminerals #%9ix1gd in coal is complex in fact, the particles absorbed on electrode will dischargewith the increase of solid content, the charging and be induced with the same polarity of elecZHANG XIn-xi et alTriboelectc sepa-an efficient Method oftrode, and hence be repelled off the electrodecause of the difference in surface electric propermaking the yield of clean coal drop down, Sheties and mineral composition. Table 5 presentsing that there is a good optimized match between the separation effect of different coals. It can bethe value of electric field intensity and yield of seen that a low rank coal is easy-to-wash in triboclean coelectrostatic separation processTable 4 The Influence of Electric Field Intensity2.2.6 Test with optimized conditionsClean coalTailingsBased on the above test results. we have caiMV. m) Yield/% w(ash)/% Yield/% w(ash)/%ried out a further test on optimized conditions64.001.9836.0032.59The conditions are for 1 kg of air, there is 0. lkg30.34of solid; the average velocity of particles is 40 m/69,11.91S, coal size is <45um, electric field intensity is31.272.0 MV/m. The test data are the yield of clean2.2.5 The separation result of various coalscoal is 72. 63%, and the ash of clean coal is 1.Different kinds of coals have different washa91%bility in triboelectrostatic separation process beTable 5 Separation result of different coalsRaw coalCoal rankYield/2Yield/Long flame coa29.889.475.8362.3612.133,68Anthracite33.784) there is a good optimized match between3 Conclusionselectric field intensity and yield of clean coal1) The ash content of clean coal increases a5)A low rank coal is easy-to-wash in tribolong with the increase of solid content of feed- electrostatic separation processstock; On the contrary, the yield of clean coal is6) The yield of clean coaldecliand the ash decreased through adapting optimized2)A high velocity will result in a goodconditions according to the varies coals.ration effectThe research data indicate thafeasible3)In the same solid content state, the re- to produce alow ash(<2%) clean coal using triunion caused by intermolecular force makes the boelectrostatic separator. Yet a lot of researchesseparation efficiency drop down when the ultra- should be done to boost the capacity of separatorfine coal is separatedfor commercial applicationReferences[I] Zhang XX, Duan CH, Qian J C. Study on producing low ash coal with triboelectrostatic separator[A]. X XI Inter-nantional Mineral Processing Congress[C]. Rome, Italy: Elsvier, 2000[2 Zhang XX, Chen QR. The study of the basic theory and the application of removal pyrite and ash from fine coalwith electrostatic separator LJ_. Journal of Coal Science & E(1):77-82[3 Gupta R, Gidaspow D, Wasan D T. Electrostatic separati中国煤化工n the work functions of itsconstituents[J. Powder Technology. 1993,75(1):79-87.CNMHG[4 Dennis F, Terri N, Robert E. Triboelectrostatic beneficiation of fine coalLA]. Parekh B K, GTJ D. Processingand Utilization of High-Sulfur Coals V [C]. 1993 Elsevier Science Publishers B V91-98