Cleaning of South African coal using a compound dry cleaning apparatus

Mining Science and Technology( China)21(2011)117-121氵Mining Science and Technology( China)ELSEVIERjournalhomepagewww.elsevier.com/locate/msteCleaning of South African coal using a compound dry cleaning apparatusin, Wu Wanchang, Zhang Cai NingningSchool of Chemical Engineering and Technology, China Universiby of Mining 6 Technology. Xuzhou 221116, ChinaARTICLE INFOA BSTRACTThe compound dry cleaning principle is briefly described. a beneficiation test on South African coal waReceived 10 May 2010onducted using a model compound dry cleaning apparatus. Excellent results were obtained and theReceived in revised formptimum operating parameters were determined. They are: an amplitude of 3.0 mm, a motor frequenc15July2010Accepted 25 July 2010of 47.5 Hz, an air volume of 50%, a transverse angle of 7 and a longitudinal angle of -2'. Theseonditions yield a clean coal containing 11% ash and a coal production of 75%. The organic efficiency, n is5.86%. These results show that the South african coal can be separated effectively by compound dryKeywordscleaning. which will popularize the compound dry cleaning methodCopyright e 2011, China University of Mining Technology All rights reservedSouth African coal1. Introduction2. ExperimentalThe distribution of coal and water resources in China and limi- 2. 1. Apparatustions of coal preparation technology result in a low amount ofcoal being beneficiated [1-3]. Also, the environmental pollutionThe compound dry separator shown in Fig. 1 is provided by theand waste of resources involved with beneficiation are serious. Shenzhou Machinery Co. It consists of coal feed, separation, airsupply,urthermore, the world is troubled by drought or water shortage. dust collection, and electrical control modules. The coal feed section isThus, a dry coal preparation technology, whether for use at home or comprised of skirt-board seals and a vibrational feeder. The separaabroad, is of great significance[4-71.tion section has a concentrator composed of a separation deck, aimpound dry cleaning has the properties of energychamber, back-plate, riffles, discharge baffle plate, and double vibrawater savings, and environmental protection and can meet the tors. also included in the separation module is a discharge machine,needs of different enterprises. It is superior to traditional pneu- frame, and hanging unit. The air supply and dust collection parts arematic separation in many ways such as the cleaning mechanism, a fan, bag type dust collector, and cover for the waste. The electricalthe grain size of coal needed, having larger capacity, and accepting control unit is a step-down starter and an automatic control cabineta wider water content in the coal. this paper presents tests ofAs shown in Fig. 2 the principle of compound dry cleaning isbeneficiation by means of a compound dry separator Compound based on the interaction between vibration, air flow, an autogenoustends to slime such as steam coal, lignite, gangue, or high-sulfur separation effects are the reason separation occur cydry separators are now mainly used in the beneficiation of coal that medium, and the high density material. Buoyancy and bafflecoal. It can be used to discharge gangue in a coking coal preparation The raw coal is fed to the deck through a vibration feeder Stratplant[8-11]. Commercial compound dry separators have achieved ification occurs because of the combined effect of vibration, air flow,great success in economic and social aspects because of the and the autogenous medium. as a result of stratification the highThese products are suitable for the beneficiation of o orry Co Ltd. density particles settle on the deck and lower density material floatsresearch and application done by the shenzhou Machcoal with a size limit of 3 mm and a capacity of 10-480 t/h. More Vibration affects the particles differently in different parts ofmedium.than 1000 sets of compound dry separators have been put into Vibration decreases gradually from the bottom of the bed toward thoperation in China and about 200 million tons of coal have been top Forces from vibration cause the gangue in the bottom of the bedbeneficiated by these separators.to move to the back-plate while the clean coal in the upper layerundergoes a helical motion as it moves toward the discharge baffleplate under the effect of gravitation. The back-plate creates a heightCorresponding author. TeL: +86 516 839952中国煤化工en coal flowsE-mailaddress:fluo@cumt.edu.cn(LZhenCNMHG1674-5264/5-see front matter Copyright e 2011, China University of Mining Technology. Alldoi:101016小mstc201012019L Harbin et aL/ Mining Science and Technology( china)21(2011)117-121Results of a sink-nloat test on 0-25 mm South African coalfraction (%)(3) accumulation(5)accumulation( %)(g/cm)-131792551179255000015-161216-1.8130782440002524where y is the yield of clean coal: A the clean coal ash content: Aythe ash content of the raw coal; and AA is the ash reduction ratioIn this formula smaller ash reduction ratios imply reduced ash inFig 1 Model compound dry coal separator.the cleaned coal Product ash, product yield and the raw coal ashcontent are fully factored into the index, K. As a result, clean coalThe lower density coal on the bed surface is discharged as a lower ash content is lower and the yield of clean coal is higher if the indexash content cleaned product after passing over the discharge baffle K, increases. For a specific separator the value k is useful for eval-plate The gangue particles on the deck move toward the back -plate uating concentration effects under different separation conditions.under the action of vibration and the guiding riffe the gangue And it is a more simple and practical index compared to theparticles then move to the refuse-discharging section and become traditional separation indices probable error E, and uncertainty.the tailings. Other material continues to cycle within the machine.Repeated separations occur after each helical movement and so 3. Results and discussionmultiple products of different ash content may be obtained3. 1. Effect of vibration amplitude on separationVibration plays an important role in compound dry cleaning. TheThe coal used in the separation test was from South Africa. Its vibration amplitude in the separator can be changed by adjustingsize and density composition is shown in Table 1.the angle between the motor eccentric blocks. ExperimentsCoal washability curves can be obtained from the data in Table 1 designed to study the effect of vibration amplitude were performed(Fg3)The motor frequency was 47.5 Hz, the air volume was 50%, thetransverse angle was 7, and the longitudinal angle was.. The2.3. Separation coefficient evaluationamplitude was adjusted to the values of 2.6, 2.8, 3.0, 3. 2, or 3. 4 mm.The data in Table 2 shows that vibration has a significant impactClean coal, middlings, and gangue with different ash contents on separation. The yield of clean coal decreases as the amplitudeare obtained by compound dry cleaning of raw coal. Limitations of increases. The production of refuse is characterized by the oppositethe apparatus cause the yield of tailings to be low. Meanwhile behavior. when the amplitude is in the range from 2.6 to 3.0 mmtailings and middlings are merged into one fraction for easy eval- increasing amplitude loosens material on the bed and the sepa-uation of the separation. Consequently, two kinds of products, rating results become more ideal. That is to say, there is a decreasenamely tailings and clean coal, are obtained. In this paper we adopt in clean coal ash and a concomitant increase in gangue ash Over ana multi-index evaluation system that uses the yield of clean coal, amplitude range of 3. 0-3. 4 mm increasing amplitude causes incr-the clean coal ash content, the yield of tailings, the tailings ash eased back-mixing of the material Back-mixing is characterized bycontent, the absolute ash reduction, and the ash reduction ratio to an increase in clean coal ash and a reduction in tailing ash. Goodcompute a comprehensive evaluation index, Kseparation is obtained for vibration amplitudes between 2.8 and3.2 mm. The maximum K value is obtained when the amplitudeK3.0 mm. In conclusion the optimum amplitude value is 3.0 mm.ack PlateAn amplitude of 3.0 mm, a 50% air flow, and horizontal anCleanvertical inclination angles of 7 and -2 were selected for theCoalfrequency tests. The frequency value was set at frequencies of 47.0Vibration47.5,48.0.48.5,or49.0Hz(Tabe3)DirectionThe separation results show that the clean coal yield decreasesas the frequency increases. Gangue production shows the oppositetrend. When the frequency is either 47.0 or 47.5 Hz the increase”品切A1了improves bed stratification and the ash in the cleaned coal ashChanberthe be中国煤化工 gher frequencies cause-en back-mixing developAir DeckCNMHfromIcu UI ucyucuicy on the product yieldsFig. 2 Apparatus for compound dry coal separationand ash content, absolute ash reduction content and ash reductionL Haibin et aL/ Mining Science and Technology( China)21(2011)117-121Density2.22.121.91.81.71.61.51.41.31.2cUrve10090E Curve20.008 CurveHw5400102030405060708090Ash/%Fig. 3, Washability curves of 0-25 mm South African coaLSeparation of coal at different vibration amplitudes.AmplitudeTailings(%)Absolute ashAsh reductonreduction content(%793720634831214811273134774807235.14ratio changed K values in a way that a frequency of 47. 5 Hz appears increases from 50% to 60% clean coal ash goes up and tailings ashto be the optimum one for separation of this South African coal. decreases. From the optimum k value it is seen that the bestseparation results are obtained with an air volume of 50%.3.3. Effect of air volume on separation3.4. Efect of transverse angle on separationhe air volume used for the separation can be adjusted. It is animportant operating parameter for the complex dry cleaning model An amplitude of 3. 0 mm, a frequency of 47. 5 Hz, an air volume of50% and a longitudinal angle of-2 were used in the bed transverseAir volume has three functions. First, it can loosen the bed layer. angle trials. Transverse angle was set to values of 6, 6.5, 7, 7.5.which makes the material stratify. Second, a steady mixed suspen- and 8(Table 5)sion medium of a certain density forms during concentration becauseAn increase in the horizontal angle causes the lateral force fromof the interaction between the air and the fine coal. Third air flow can gravity to get bigger. This makes the coal discharge earlier and leadsenhance bed liquidity, which can enhance separating capacity.to higher clean coal production and lower yields of tailings. whenAn amplitude of 3.0 mm, a frequency of 47.5 Hz, a transverse the bed horizontal angle is small the low specific gravity coal thenangle of 7 and a longitudinal angle of -2 were used during the air tends to become part of the tailings, which leads to a low ashvolume trials. The air flow was set to the values: 20%, 30%, 40%, 50%. cothe lateral angle increases forces on theand 60%(Table 4)An increase in air flow between 20% and 50% reduces the ash inunderlying coal rsd wme. e pasite t tde notr e en te per cna hethe cleaned coal andes the ash in the tailings. As the air flow cleaned coal ash content increases. the tailings ash contentSeparation of coal at different frequencies.FrequencyYieldYieldash(%reduction content(飞5中国煤化工0533456928ahaCNMHGO5O4906863055L Haibin et aL/Mining Science and Technology(China 21(2011)117-121Table 4at different air flows.Air volumesh reductionYieldash(%)reduction content($)250811.5900000.542427220121870.61Separating coal at different transverse angles.ateralClean coal(%)Raw coalbsolute asAsh reductionash(%)reduction content(寫70.1626432298Separation of coal at different vertical angles.LongitudinalClean coal (%)Absolute ashAsh reductionange(°)ash(‰)eduction content (3-1.56798120632025124.6875.7324.274.10337.58050.7222.50decreases with an increase in lateral angle as more fine coal mixes ash when the absolute value of the longitudinal angle is greater.into the tailings.Then a large amount of low specific gravity gangue and high densityThe comprehensive K value calculated from the absolute ash coal mix into the clean coal discharge Furthermore small coalreduction and ash reduction ratio shows that separation is opt- particles accumulate at the gangue discharge end leading to a lowerimum at a transverse angle of 7.ash content in the tailings. Material moves to the gangue dischargepoint more easily as the longitudinal angle increases. Hence, most3.5. Efect of longitudinal angle on separationgangue is expelled at the gangue discharge end. In addition, theclean coal ash level drops. In contrast, tailings ash levelsThe parameters used during these trials were an amplitude of because there are fewer small coal particles mingled w3.0 mm, a frequency of 47.5 Hz, an air volume of 50% and a trans- tailings. As the vertical angle increases a certain point isverse angle of 7. These are the optimum values found in the work where much more coal mixes into the tailings. the outcome is thatdescribed above. In these trials the longitudinal angle was adj. the tailings ash seems reduced but there is little change in the cleanusted to the following angles:-1.5°,-2.0,-2.5°,-30°,and-3.5° coal ash(Table 6).K values calculated from absolute ash reduction content and ashLarger absolute deck longitudinal angles make it more difficult reduction ratios show that -2 is the optimum longitudinal anglefor the gangue and higher density coal to be pushed out at the for the compound dry cleaning machine.angue discharge end. Also, considerable amounts of lower densityangue are discharged at the clean coal end. This results in a high 3.6. Evaluating separation resultsyield of cleaned coal and a low production of tailings. As theabsolute value of the longitudinal angle decreases the productionThe experiments above show that the best serate of washed coal drops and the yieid of tailings increases. The when beneficiating-25 mm South African colongitudinal angle greatly influences ash content of the products. dry cleaning model apparatus occurs at theFrom the analysis above we see that the cleaned product has more parameters: an amplitude of 3 mm, a motor frequTable 7Partition coefficient of separation at the optimum operating parameters.nsity fractionAverage density(g/cm)of tailings(%)of clean coal(3)13-1431235-1后2.57中国煤化工220CNMHG10000L Haibin et aL/ Mining Science and Technology(china)21(2011)117-121The compound dry cleaning method has a simpler flow sheE=0.23a smaller investment, acycle, andI=0.14lower sorting costs asprovides an economical and practicalcoal utilization and to increase the amount of coal separatedAcknowledgmentsThis research work is financially supporteNatural Science Foundation of China( Nos. 905100and the Fundamental Research Funds for the central UniChina University of Mining and Technology)(No. 2010ZDP01A06References[1 Zhao YM. Comprehensive utilization manual of coal resources. Beijing:Fig. 4 Product partition curve at optimum operating conditions.[2]Luo ZF. Zhu JF. Fan MM. Zhao YM, Tao XXX Low density dry coal beneficiationair volume of 50%, and transverse and longitudinal angles of 7 andum fluidized bed. Journal of China University of-2, respectively (Table 7).Fig. 4 shows that under optimum conditions the separation 13)ole generation and its effects ondensity. op, is 1.70 g/cm and the probable error, E, is 0. 23 with and millimeter scale bubble solutions. Mininguncertainty, I, of 0. 14. The production rate, d+ o1, is 8%, which isless than 10% and which shows that the South African coal is easy to14]Luo ZF. Zhao YM, Fan MM. Tao Xx. chen QR. Wei LB. New progress of coal dprocess. The organic efficiency can be calculated asn=71=79x-×100%=958695Ak、①G的X的SK, Parida A Deof air dense medium fluidized bedwhere Y, is the actual clean coal yield and y1 is the theoretical16) Dwan RK. hanumantha rk Dry beneficiation of coal: a review. Mineral Pro-production rate obtained from washability curves70a如 Extractive Metallurgy820028317-234edium fluidized bed. International Journal of Mineral Processing 2001:4 Co1)Optimum operating parameters for beneficiating-25 mm Southce. Xuzhou: China University of Mining Technologyfrican coal using a model compound dry cleaning apparatusare:an amplitude of 3 mm, a motor frequency of 47.5 Hz, an air t9I u GM Yang Ys. Application of compound dry cleaning technique in chinolume of 50% and transverse and longitudinal angles of 7 and32|n-2, respectively. Under these conditions the clean coal ash and 110) Shen yi Chen RZ Coal cleaning with compound dry coal separator. Inyield are 11.4% and 75.73%, respectively. The E value is 0.23, I isoceedings of international symposium on clean coal technology. Beijing:0. 14 and the organic efficiency is 95. 86%2)Although the separating efficiency during compound d1111 Shen L]. Chen z Analysis of material motion in compound dry separatmal of China University of Mining Technology 2005: 34(4): 447-51 (Incleaning is too low the organic efficiency of the process is high中国煤化工CNMHG