Conversion Excess Coal Gas to Dimethyl Ether in Steel Works

Vol 9 No. 1J. Iron Steel Res., IntMay 2002Conversion Excess Coal Gas to Dimethyl Ether in Steel WorksLI Jun-ling, WEN Hao, GUO Zhan-cheng, XU Zhi-hongInstitute of Chemical Metallurgy, CAS, Beijing 100080 ChinaAbstract: With the technical progress of metallurgical industry more excess gas will be pro-duced in steel works. The feasibility of producing dimethyl ether by gas synthesis was discussed, which focused on marketing energy balance process design economic evaluationand environmental protection etc. DME was considered to be a new way to utilize excess coalgas in steel worksKey words: steel works excess coal gas dimethyl ether chemical technologyWith the technical progress of metallurgical in- the emission of carbon dioxide it is necessary todustry more excess gas will be produced in steel find out another way to utilize excess coal gasworks. Table 1 listed the typical composition of eThe conversion of excess gas to higher-valuecess gas in an steel works. It can be seen that coke- chemicals is a new way for energy saving in ironoven gas mainly consists of hydrogen and methane, steel plants. The production of chemicals from exwhile converter gas contains much more carbon cess gas will not only increase the profit of themoIoxideplant but also reduce the emission of carbon dioxide. It is essential to determine which products canTable 1t an steel works Vol, %ube made from the excess gas. The product to be seCoke-oven gas Blast-furnace gas Converter gaslected should have a large market be produced withCarbon monoxidereliable process appropriate profit margins and enCarbon dioxide20.05,0vironment-friendliness and so on. Taking these fac-Hydrogetors into account dimethyl ether is considered to bea right product to utilize excess gas in steel workIntroduction to dimethyl etherIn China excess gas is used mainly as low valuefuel gas in this way not only the valuable resource 1. I Physical property of dimethyl etherincreased. As stern restrictions have been placed on dimethyl ether( DME )and certain other fuels/,oris wasted, but also the emission of carbon dioxide isTable 2 showed the physical propertiesTable 2 Physical property of DME and certain other fuelsPropaneMethanolDiesel fuelBoiling point!℃l61.56180-370Liquid density( 20C ykg mGas specific gravity relative to air0.55Saturated vapor pressur(25℃y×10Pa9.42249.26Ignition temperature/C235450Explosion limit/%2.1-9.45.5-36Cetane numberNet heating value/k) m-35941391211359822887046442502082083418401.2 Advantage of DMEetc. They were described as follows:There are many advantages of selecting dME as中国煤化工 ventional diesel fuellarge potential of market, large margin of proli, DMEproduct such as environment-friendly properties-umber(>55)and inCNMHGerenons. Moreover, DMEFoundation item: Item Sponsored by National Natural Science Foundation(59874024)Biography LI Jun-ling( 1972-), Male, Doctor candidate Received date: April 3, 2001No. IConversion Excess Coal Gas to Dimethyl Ether in Steel WorksMcontains little impurities such as sulfur nitrogen and two steps i namely methanol synthesis and dehymetals. All these characteristics make dme an ideal dration of methanol. These two steps are performedclean diesel fuel in the 21st centuryn two separate reactors. As this process is a reliable2) Ideal substitute for freons. The physical one and has been applied in chemical industries atproperties of dme are similar to those of freons but home and abroad for many years it was adopted inDME has low toxicity and is considered not to cause this paperthe green house effect and ozone layer depletionRecently a new process which directly conHence dme is an ideal substitute for freons21verts synthesis gas( mixture of CO and H2 )to DME(3)Large market potential. Presently DMEn a single reactor has been developed and tested forused mainly as aerosol propellants in China. The do- large-scale DME production. Air Products andmestic demand for DME amounted to 30 000 t in Chemical of the United States, Haldor Topsoe of2000, while its own production capacity was only Denmark, and NKK Corporation of Japan have de7 000 t or so. Production of dme as a clean fuelveloped such techniques but they are still in experiture, there will be a large market for DME of the mental stage. For example, a 5 t day of DMEstill in the initial stage in China. Becausegreat consumption of clean diesel fuel in the near fu- demonstration unit has been set up and operated byNKK Corporation. More work has to be done to(4)Large margin of profit. Recently the average make this new process commercialle price of dme(>99 % free of water )in Chinese market is 5 200 yuan/t, much higher than thatProcess design for Conversion of excessof methanol( 1 900-2 200 yuan/t)and urea(1 100Gas to dme1 600 yuan/t )3]. When DMEd as clean fuThe flow diagram of the process was shownel its price is estimated to be 3 000 yuan/t due to Fig. 1. After mixing with an appropriatelower purification requirementIt was reported that a dme plant with a capand then fed to the combustion reactor to convertty of 20 000 t per year will be set up in Shanxi most of the methane into hydrogen and carbontal investmentde, Thethe combustion reactewas estimated to be 180 million yuan with 63 million was cooled, purified mixed with the unreacted re-yuan of net profit per year. The internal rate of recycled gas and then enters the methanol reactorturn of the project investment was 26.37 %( aftwhere coonversion to methanol was processedtax ) It would take 5 years to recover the investThe off gas from reactor was routed to themencrude methanol separator where crude methanolater and dissolvedd The liquid1.3 Synthesis process of DMEfraction was fed to the dme reactor, whereas theThe dme is industrially produced by catalytic vapor fraction is routed to the recycle compressor todehydration of methanol. This process consists of be re-compressed and recycled To avoid the accucompressoreactor中国煤化工CNMHGFig. 1 Flow diagram for converting excess coal gas to DME2002J. Iron Steel Res. IntVol. gmulation of inert gases a small amount of unreacted a combustion reactor was specially installed in thisgas was purged from the loop before it enters the re- process for the conversion of methane. The convercycle compressorsion was accomplished through partial oxidation ofb After mixing with the unreacted recycling methane under high temperature( about 1 350Cmethanol, the crude methanol was fed to the dmeAccording to the industrial experience the feedreactor where catalytic dehydration of methanol oc- gas for the methanol synthesis should conform to thecurs. The reacted mixture was separated in the following requirement 4l:DME Separator to obtain DME(中H-中o.y中co+中co.)=1.95-2.103 Thermodynamic CalculationTo obtain feed gas with such composition the cokeeven gas should be mixed with appropriate proporIt can be seen from Table 1 that coke-even gas tion of converter gas. Here this proportion was dcontains 57.2 of hydrogen, and 24 of termined by thermodynamic equilibrium of the reac-methane while converter gas contains 80% of car- tions. Table 3 showed that 100 mol coke-even gasmonoxideMethane is an inert gas in the plus 22 mol converter gasand 5. 3 mol oxxygen r canmethanol synthesis and should be converted into hy- produce the gas mixture with a desired compositiondrogen and carbon monoxide beforehand. Therefore for methanol synthesisTable 3 Result of thermodynamic equilibrium calculation at 1 350 C and 60 X 105 PaFeed gas of combustion reactor/molComanen100 mol coke-oven gas22 mol converter gas5.3 mol oxygenCarbon monoxide7.345.5Carbon dioxide1.1OxygenMethane0.77.1Cost of feed gas4 EconomicsFig 2 showed the profits of the process withSeveral assumptions are made as follows in the electricity price ranging 0.2-0.6 Yuan/(kw. h)economic evaluationand coal gas price ranging.2-1.0 Yuan/(kwh)(1) The flow rate of coke-even gas is assumed tobe5.0×104m3/h.Th5 Discussiongthe calculated result in section 45.1 Price of electricity and coal gasFig 2 showed that the profit of the processConsumptione-even5.0×104m3/hConverter gas: 1. 110m/hOxygen:0.27×104m3/hElectricity: 1. 14X10*kWh/hElectrie ily priceProductDME: 500 t/day(2)DME is produced as clean fuel with a priceElectricity priceof 3 000 yuan/t(3)The electricity cost is assumed to be 70 ofthe whole operation cost中国煤化工(4)The operating period is assumed to be 330CNMHGThe profit before tax is calculated accordingthe following equationPrice or coal kas/(Yuan- mProfit =( Sale income )- Operating costFig.2 Profit at different prices of gas and electricityNo. IConversion Excess Coal Gas to Dimethyl Ether in Steel WorksMdepends heavily on the price of coal gas. When the erating costprice of coal gas is higher than 0.9 Yuan/m, the(2)The effective utilization of resources suchprocess will make a loss. According to the interna- cheap electricity oxygen water etc to reduce thetional practices the price of gas was determined byits heating value. If the price of fuel gas is $2.0X10°Btu( about15.7×10°Yuan/kJ), coke-even gas6 Conclusion and suggestionand converter gas can be valued at 0.25 Yuan/m3With the technical development of metallurgicaland 0. 17 Yuan/m', respectively. At such prices of industry more excess gas can be produced in steelcoal gas the process will make a profiworks. Based on the analysis of process the productThe large integrated mills often have their own usage, marketing, profit margin environment5.2 Advantage of DME production inside an iron to practice oaopower stations. Therefore the price of electricity in- friendliness etc, DME production was consideredside the plant may be only 0.2-0.3 Yuan/kwh) promising to utilize excess gas in steel worksor so, much lower than that from market[ about 0.5It is suggested that more research work shouldYuan/(kW. h)]. Using internal power will reducebe carried out on the conversion excess gas intogreatly the operation costdME in steeorks. Joint efforts between facto-ries, institutes and colleges will put this new idea insteel plantReferencesProcess of converting natural gas coal or oil to[1]http:/www.nkkco.jp/en/environment/dme/main.html[2] CUI Shi-chun, HU Li-zhi, ZHU Dong-mao. The Process feis gas mixture of hydrogenMaking dme by CiDehydration of Methanol in Gasand carbon monoxide), synthesis of products andPhase[ J ] Petrochemical Technology 1999, 28(1): 43-45separation of products. Of the total capital inves(in Chinesement and operating cost proportions of the above[3]httpi/hemsina, com/Chinapec Search asp[4] HU Xian-nian, FU Yun-xin, YUAN Zen-gen. Operating Optithree parts are estimated to be 60%, 25, 15nization of Producing Feedstock Gas for Synthesizing Methanolrespectfrom Coking Dry Gas[ J ] Natural Gas Chemical IndustryThe main advantages of converting excess coal000,25(3):33-36( in Chinese)gas to DME inside an iron steel plant are as follows[5] WANG Xian-qing SHEN Shi-kong. Natural Gas Will Becomethe Feed for Synthesis of Clean Fuel and Chemicals in the Next(1)The limination of synthesis gas preparationDecade J ]. Trans Chemical Engineering of Oil and Gas, 1998with obvious reduction of capital investment and op27(4):195-197( in Chinese)中国煤化工CNMHG