Clean Processing and Utilization of Coal Energy

第6卷第3期过程工程学报Vol 6 No. 32006年6月The Chinese Joumal of Process EngineeringJune 2006Clean Processing and Utilization of Coal EnergyCHEN Qing-ru(陈清如, WANG Hai-feng(王海锋)(School of Chemical Engineering and Technology, China University of Mining and Technology, Xuzhou, Jiangsu 221008, China)Abstract: The dominant status of coal on the energy production and consumption structure of China will not be changed inthe middle period of this century. To realize highly efficient utilization of coal, low pollution and low cost are great andimpendent tasks. These difficult problems can be almost resolved through establishing large-scale pithead power stationsusing two-stage highly efficient dry coal-cleaning system before coal buming, which is a highly efficient, clean andeconomical strategy considering the current energy and environmental status of China. All these will be discussed in detail inhis paper.Key words: coal; clean processing; dry beneficiation; separator; energy utilizationCLC No. TD849, TD92Document Code: AArticle ID:1009-606X(20003-0507-051 INTRODUCTIONdominant position of coal will not change within 50years (Table 1). So, if coal can not be realizedChina is abundant in coal resources, with 1000 highly-efficient and clean utilization, it will not onlybillion tons of coal reserves. Coal accounts for 70% in cause the enormous resource wasting and environmentalproduction and consumption of the primary energy and pollution, but also seriously threaten the sustainablewill still be the main energy source for the nation in a development of economic construction of China in themedium or long term. In 2003, Chinas coal output was futurein excess of 1.6 billion tons accounting for 74% in thetal production of primary energy. Because theTable 1 Prediction of energy structure of China inreserving characteristic of fossil energy in China issucceeding 50 years (%)abundant coal, little oil, scarce natural gas", by 2020,Energy20302050the energy structure of China will be developed in5405486pluralism: even if the proportion of coal in primaryPetroleenergy will be decreased down to around 60%, coaloutput will still be up to 2.5 billion tons. AlthoughNuclear enegy7369240.463.31134716,00.12.75biomass energy, solar energy, etc. )is being developedrapidly, it will not account large in the share(except 2 UTILIZATION OF COAL ANDwater and electricity). The share of nuclear energyENVIRONMENTAL POLLUTIONfission) is estimated optimistically to not more than 5%and the dispute is relatively great. Quite a few industrialcoal has caused the serious environmentaland civil liquids, gaseous fuel can be converted from pollution while making enormous contributions tocoal and many chemical raw materials can be stemmed national economic development. China is a typicfrom coal. Because the conversion of energy structure is smoke type air pollution country, national sO2 emissiona very long process, it will take about one hundred years was 21.59 million tons in 2003, ranking first in theto increase the share of a new energy from 1% to 50%. world. The area covered by acid rain has alreadyAccording to the development level of science and exceeded 30% of the total territory. China's co2technology of energy presently, although every country emission is 1/7 of the world, up to 1336 million tons,has paid much attention to the renewable energy sources occupying the second place. China's emission amountsand other new types of energy with rapid development, of中国煤化工 en years are listthey only serve as a supplement to traditional energy Fig.because absolute amount of these energies are veryCNMHsmall. According to national conditions of China, the research and development of processingReceived date: 2005-10-07, Accepted date: 2005-12-18Biography: CHEN Qing-ru(1926-), male, native of Hangzhou City, Zhejiang Province, Ph. D, academician of Chinese Academy of Engineering, research in歐 ogy过程工程学报第6卷transforming in China. Only less than 30% of coal in coal slurry treatment systems which are usually requiredChina is processed annually, at present. Processing in wet coal beneficiationcapacity will be much insufficient compared to the 3.1 Highly-efficient Coal Dry Beneficiationincrease of coal output. In the coal consumptionTechnologystructure of China, the power coal accounts for moreEstablishing large-scale pithead power stationsthan 80%, but only 14% power coal is prepared while with Chinese characteristics should adopt the flow chartmost of coal is burned out directly without beneficiation. including two-stage highly efficient coal diThis will not only cause the serious environmental beneficiation system as followspollution(such as smoke, sulfur dioxide and acid rain),it has also resulted in serious economic lossesHigh-eniciency miningAccording to the 2001 Technological ConsultationResearch Paper of Advanced Energy"edited by theChinese Academy of Engineering, in China, 85% ofGrinding <74 umCO2 and SO2 emission, 70% of the smoke and 60% ofcoal powder power plaNOr come from coal burning (Table 2), and theFig 2 Multistage dry coal separation process of large-scaleonomic losses due to air pollution in the countrypithead power stationaccount for 3%-7% of national GDP. Low percentageof processed coal, outdated coal-fired technology andThe critical technologies in this flow chart arequipment cause that the energy consumption of China's Carse coal dry beneficiation and powder coal drmain industrial products is 20%-60% higher than that triboelectric preparation before burningof the advanced countries, energy efficiency being only(1)Coarse coal dry beneficiation.34%, which is 10% lower than that of the advancedTwo kinds of coarse coal(50-60 mm)countriesbeneficiation are suitable to china. the first one is coaldry beneficiation with air-densified medium fluidized11700bed as shown in Fig 3, which features a wide range of▲-s0. emission4208beneficiation density (1.3-2.2 g/cm), high precision(Ep0.05 g/cm) and adaptability to prepare all kinds of1400coals. This equipment has been commercially used inChinal2-9.The second is a kind of pneumaticbeneficiation with the FGX compound dry separatorwhich is applicable to beneficiate 6~50 mm size ofeasily separated coal for removing gangue. A schematic199419961998200020022004FGX separator is presented in Fig 4. This is aneconomical means to reject high ash rock for upgradinglow rank coals and can significantly reduceFig 1 Emission amounts of So2 and smoke intransportation costs and improve the economics of therecent years in Chinaconventional wet preparation plants, and it has been3 CLEAN COAL STRATEGY OFpopularized in China[8-10]CHINAExhaustImplementing China clean coal strategy, namely,establishing large-scale pithead power stations usingwo-stage high efficiency dry coal-cleaning systembefore coal burning with Chinese characteristics, weCompressed aimust transform and promote the traditional industryadopt advanced technology. Because 90% of the coal中国煤化工 rator with air-densifiedresources are in northwest arid area, as little as possibleCNMHGor even no water should be involved in the coal(2)Coal triboelectric preparation technology forpreparation technology to save the water resources and 1% in some collieries, the circulating fluidized bedcombustion or flow-gas desulphurization device can beBaffleused to the treatment of high-sulphur coal. And thistechnology is extensively addressed elsewhere ,I2)At present, wet coal preparationWind chambetWindoccupy a leading position in coal preparation industryCoal prepared by wet washery is usually used to supplyCleanings Middings Tailingsto power plant, which can also realize clean andhighly-efficient utilization of coal, but needs a largeamount of circulating water as well as groundwater intriboelectric separation, a powder material is charged wet coal processing. The prepared coal products requireeither positive or negative, depending on its surface numerous dewatering and complex slurrywaterelectric properties, as a result of wall friction or treatment systems and equipments, so, wet coalparticle-particle collision in an air flowing at high preparation technologies are unsuitable to be adopted invelocities. When entering a high voltage electrostatic a large-scale pithead power station, especially in aridfield, the particles with opposite charges move to the northwest area that has abundant coal resourcesopposite electrodes, achieving the desired separation. 3.2 Establishing Large-scale Pithead Power StationsThe triboelectric separator is schematically shown inInstalled power-generating capacity was 390Fig. 5. This kind of technology can be used to produce million kilowatts in China by the end of 2003 with 1905low ash and high heat value fuel which is supplied to billion kw.h, and 74% of it relied on coal-fired powerpower plant for the factory boiler and steel mill for the plants with 83% of the total power yield. About 900iron-smelting blast furnace, or produce ultra-low ash million tons of coal was used to generate powermaterials coal to use for yielding such material of accounting for 53.5% of the total consumption of coalcoal-based carbon as high-quality activated carbon, etc. By 2020, the installed power-generating capacity ofChina will exceed 900 million kW. while coal-firedFeedstock Tribochargerpower-generating capacity will account for more than65% and its electricity yield will exceed 75% and powercoal consumption will exceed 1.75 billion tons, beingabout 70% of the total amount of coal consumptionHigh voltageelectrode plateIn the year of 2002, 91.8% of American coals withaverage ash content lower than 9% are used forelectricity generating, but the average ash content ofcoal used for power generating in China was up to 28%Unload brushin 2003. In China most power plants are far away fromcollieries, and usually long distance transportation forpower plant coal supply is needed. High ash content rawcoal causes the environmental pollution and hightransportation cost as wellFig 5 Schematic diagram of separatorEstablishing large-scale pithead power stationsmeans that after being processed into low ash, lowCoal powder produced by triboelectric preparation sulpcan be adjusted according to the quality of raw coal and highrequirement of boilers in power plants. Product ash pitheH中国煤化工 powder by usingn near the collieryCNMHGoilers for generatingcontent of 8% and sulphur content of 0.5% with yield electricity followed by transmitting to consumers viamore than 80% can be obtained by using this technology. high voltage. And this will avoid remote transport,Tailing coal with high ash content can be utilized on the developing co-generating heat/cool and power为丹数霭。 indices can meet China's requirements according to the condition in the mean time. Tailings过程工程学报can be comprehensively utilized in colliery, which the low heat value of steam coal increases about 4.8reduce the environmental pollution of mining area MJ/kg, the coal consumption will save to 96.2 gramsgreatly. This will be optimum, most economic and coal per kw.h for electricity generating. It is 19% lowercleanest energy strategy for the production and than 498 grams per kw.h in 2002, and efficiency ofconsumption of coal resource in Chinaenergy-saving is very remarkable, tailing coal of ashIn summary, as the biggest coal production and content up to 70%-80% can be used to makeconsumption country in the world, China must account construction materials, filling mines, building the road,on advanced technology and implement the strategy of etc.So, the operators of power plants should changehighly-efficient and economic utilization of coal. It also their idea of using the inferior coal to generatehas very important strategic meanings for coal industry electricity fundamentally. The coal power stationsreform, economizing coal resources, promoting should use the high-quality steam coal to generateecological environment protection and realizing electricity, though the coal price rises to some extent,sustainable development.but it improves the thermal efficiency of the boilers and3.3 Economic, Environmental and Energy-saving decreases the amount of coal consumption, decreasingBenefits of Pithead Power Station by Adopting fly ash as well as equipment maintenance andHigh-efficiency Coal Dry Beneficiationenvironmental pollution. The overall economic andAt present, coal-fired power plants in China mostly environmental benefits are very considerable. A coalurn raw coal. As strengthening the control on SO2 mine enterprise produces the low ash, low sulphur andemission of generating electricity with coal constantly, clean coal with high heat value, the price depends on theChina has established and is establishing a large quality, the price is raised rationally, and the colliery hasquantity of desulphurization facilities in coal-fired made very good economic benefits at the end.power plants. Among various kinds of desulphurization 3.4 West-East Electricity Transmission Projectmethods, adding desulphurization additives to boilers ishe great decision-making of energywidely used. However, this will influence the coal heat construction in China to realize "West-East Electricityvalue and increase the coal consumption. It also Transmission Project". To set up large-scale pitheadgenerates SO2 at high temperatures while the capital power stations with Chinese characteristics, it is theexpenditure of flow-gas desulphurization devices after optimum choice to realize " West-East Electricityburning and expenses of operating cost are relatively Transmission Project", the combination of coal andhigh. For example, 600000 kW coal-fired units of electricity, comprehensive development and appropriatepower plant of Huangpu in Guangdong Province will scale of operation, which have complementaryadopt the wet limestone-gypsum flow-gas advantagesdesulphurization (FGD) method with foreignThe western region of China with abundant coalequipments, and the plant will start to run in 2005. It is resources is the base of energy supply of China, butsaid that 16770 t/a of So2 emission can be reduced at an water resource shortage has restricted the developmentestimated investment of *297 million. In the mean time, of this seriously. In light of this when planning rationalthe FGd gypsum generated by wet limestone-gypsum processing and utilizing of coal resources in the westernflow-gas desulphurization process will pollute areas of China, this contradiction must be consideredenvironment again.well“ Three West”( Shannxi, Shannxi and InnerWith two-stage highly-efficient coal dry Mongolia provinces) is the main coal energy base ofbeneficiation technology, desulphurization capital China, transportation of coal by railroad mostly isexpenditure for getting rid of one ton SO2 is only 1/7 restricted in the past due to insufficient transportationcompared to wet limestone-gypsum flow-gas capacity. If the coal-generated electricity on the spot intechnology. Furthermore, its operating costs are much the western areas can be transmitted to the East of Chinalower. After coal being prepared, a large amount of ash itis removed, and generally the ash content or moisture of trathe steam coal is reduced by 1% each time, its low-order andYH中国煤化工 load of railwa-s economic benefitsCNMHnvironmental benefitheat value increases about 0.37 MJ/kg. If supplying to Practice has proved that transmitting electricity is lowerthe power plants with the high-quality steam coal(ash in construction investment and operation costs andcontent is for 15%),now the average ash content of shorter in construction period than those of transporting)毁据 1H be dropped from23015,an第3期CHEN Qing-ru, et al. Clean Processing and Utilization of Coal EnergyFifth China-Japan Symposium[C]. Beijing: Chemical Industry Press,4 CONCLUSIONS[3]Chen QR, Yang Y, Yu Z M, et al. Dry Cleaning of Coarse Coal withBased on the above discussion and the energyAir Dense Medium Fluidized Bed at 10 Tons per Hour [A]. 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China Particuology, 2003, 1(2): 52-56can effectively realize coal conversion and utilization [7] Beeckmans J M, Goransson M. Coal Cleaning by Counter-currentwith high efficiency, low pollution and low cost, andFluidized Cascade [J]. CIM Bull, 1982, 75: 191-194make coal be converted into clean electnc. energy [8]Blagov ES. Hand Book of Coal Preparation [M].Moscow.PetroleumPress, 1974. 331-351(in Russian)because transmitting electricity is superior relatively to [9] Leonard ] w Coal Preparation, 4th Ed (M). New York: AIME, 1979transmitting coal, which is beneficial to the sustainable1110-1132development of energy industry of China[10]Yang Y S. The Development and Application of the FGX Compound(3)Effective desulphurization and deashing of coalDry Coal Separation System []. J. China Coal, 2003, (SuppL): 11-18before burning can increase coal heat value, improve(in Chinese)combustion efficiency, save coal consumption, decrease [ll] Chen Q R, Yang Y. 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