Analysis on Availability of the Carbon Element in Alcohol Production

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 2006Analysis on Availability of the Carbon Element in Alcohol ProductionGUO Su-rong(郭素荣)，JIANG Da-he(蒋大和)，KOU Liu-xiu(寇刘秀)，LU Yong-sen(陆雍森)(College ofEnvironmental Science and Enginering, Tongi Universit, 1239 Siping Road, Shanghai 2002 China)Abstract: According to the concept of circular economy, the mass integration of alcohol production was investigated thoughthe analysis of the catbon element contained in raw material cassava. Through the mass integration, the ditillage wastewaterturmed into carbon resource and produced a great deal of by-product biogas while its chemical oxygen demand (COD) wasreduced fom 50000 mg/L to not more than 300 mg/L, the local secondary efluent standards, and other by-products such asCO2 (liquidized) and fusel oil were recovered. n the way, the consumption of raw material was only 2.2 tons cassava toproduce 1 ton alcohol (96%, ) in the case study, much lower than the average level 2.92 t in China. The carbon elementbalance for production of alcohol was made through testing the concentations of the carbon element of all mass flows. Theresults showed that the mass integration helped the availability of the carbon element increased from 44.74% to 64.75%。Key words: alcohol production; cassava; carbon element; circular economyCLC No.: X7Document Code: AArticle ID: 1009- -606X(2006)03- -0435-041 INTRODUCTIONresources. These will help to close the economy loop.Contrary to circular economy, conventionalAlcohol ditillery is an industrial sector, whichindustrial economy is a one-way linear economy, whichconsumes great amount of raw material, water andis 'resource- + production- + consumption- > disposal'.energy. The average consumptions of one ton alcoholUndoubtedly, this linear economic development is based(96%, q) are 2.7~3.1 tons of raw material, 102 tons ofon the cost of 'high exploitation, low utilization andwater and 217 kW.h of electricity, meanwhile 10~12severe pollution'.tons of the distillage with COD as high as 50000 mg/LAccording to the principle of circular economy,are obtainedl.2The alcohol output reached 3 million tons in Chinabased on an intensive mass integration in Xintai Alcoholin 2004. It meant more than 30 million tons of theDitillery in Taicang (Xintai, as follows), the case studydisillages were resuted. It would be serious problem ifon the availability of the carbon element contained inthey were discharged directly. Under the pressure of theraw material cassava was researched.laws of environmental protection, many small alcohol3 MASS INTEGRATION OFdistllries have been closed since 1990s because theyALCOHOL PRODUCTIONcould not solve the severe pollution.3.1 Background of the Case Study2 CIRCULAR ECONOMYBefore 1998 the wastewater ditilage of XintaiThe circular economy and many similar conceptswas discharged directly into a river, sharing 70% totalpractised in different countries are evolved fromamount of COD discharged by all local industrialdecades of worldwide efforts in searching for economicsectors. When the national project on renovating Taihudevelopment that is in harmony with naturaldrainage area was launched in 1998, Xintai began to setenvironment, its principles are 'reduction, reuse andup the ditilage treatment system, consisting ofrecycle'B)digestion tank, upflow anaerobic sludge blanket (UASB)Reduction is a method aiming at reducing the inputnd sequential biological reactor (SBR) to reuse thematerial and energy flows into the production andcarbohydrates contained in it and eliminate pollution. Inconsumption processes. Reuse is a method concerning2003 it consumed 133000 tons of cassava to produceprocessing. We should try to use natural resources and45500 tons of alcohol, and obtained 20000 tons ofproducts in every possible way. Recycle is a methodliquid中国煤化工meters of biogas.concerning output. Tuming wastes to secondaryiY片CNM H Gng alcohol include5resources reduces the wastes for final disposal insteps: mlling, cooKing, saccnarnlication, fermentationvolume and decreases the consumption of naturaland ditllation.Xintai possesses two auxiliaryReeived dat: 2005-10-10, Acepted date: 2005-12-19Biognpby: GUO Su-rong(1962-), female, native of Longyan City. Fuyjian Proince, Ph.D. candidate, asistant poessor, research on envionmental science.436过程工程学报第6卷installations, one is cogeneration power station,production; another is the distllage treatment system, asgenerating electricity and vapor for its alcoholshowed in Fig.l.[ Mlling ]- -Cooking -→[ Scarication F -Fementation ]H Disilation ]H- ProductElectricity「VaporDisillageCassavaWater CoalCogenerationBiogasDigestion. UASBpower stationSludgeTankSBRTail gas, Waste water, AshDischarged waterFig.1 The flow chart of alcohol production in Xintaiand will result in photochemical effect. Collecting fusel3.2 Mass Integrationoil brought about the benefits of economy and3.2.1 Input reduction of raw material cassavaenvironment.The cassava is roughly made up of 65% starch,In milling process, usually alcohol distllery uses20% vegetable fibre, and 15% other things, includingdry process with the apparatus of 1, 2 and 4 (see Fig.2)water, protein and soil. It is usually considered that theto separates cassava powder by pneumatic-conveyor gas.starch with small part of fbre is fermented into alcohol,After separated by cyclone collector (1), the powder (S)and the rest is decomposed into various kinds of otherat the bottom of collector (1) is mixed with spentorganic compounds, which are the main pollutants ofcooling water (L) for cooking, and the gas coming outthe distillage. The reaction equations are shown ason the top of collector (1) drawn by exhaust fan (3) andfollows:discharged as G2.Starch →CHO。→2C,H,0H+ 2CO2↑. (1)Dry methodSide-reaction:Wet method的-Some part of fibre .→CgH20。-→2CH,0H+2CO2↑，(2)G231▲Other carbohydrates of cassava-Drspaen +itilge. (3)1Taking the advantage that some yeast coulddecompose more vegetable fibre into glucose, Xintaimixed the cassava residues, from which the starch wasextracted but rich in fbre, with raw material cassava toproduce alcohol.To cookingConverting the cassava residues into cassava input,ProcessXintai only consumed 2.22 tons cassava to produce11. Cyclone cllector 2. Crashing tower 3. Exhaust fanton alcohol (96%，). In this way, natural resource of4. Mixing tankcassava was saved, and the waste of starch-productionG1. Pneumatic-conveyor gas for carying powderG2: Discharged air L: Spent cooling waterfacility was reused as secondary resource.LS: Washing water containing cassava powder3.2.2 Reuse and recycle of by-productss: Cassava powderIn the fermentation process, a great deal ofCO2 isFig.2 Dry/wet methods for separating cassava powder from gasgenerated according to Eq.(1). Such CO2 is a safeauxiliary substance for drink and food production.中国煤化工ollig technique, wetRecycling CO2 is not only profitable, but also helpful toproceCH.CNMH Gapplied to finish thereduce CO2 emission, which results greenhouse effect.same uask (C ng.c). nius iaring cyclone collectorXintai collected and liquidized 20000 tons of CO2 in(1), the gas flows into crashing tower (2) and is washed2003.by spent cooling water (I), and discharged throughDuring the ditillation process, about 600 kg/dexhaust fan (3); at the same time, the washing waterfuseI万i为数据ined. It is a kind of organic compoundscontaining cassava powder (LS) flows out at the bottom第3期GUO Su-rong, et al: Analysis on Availability of the Carbon Element in Alcohol Productionof crashing tower (2), and flows into the mixing tankcomposition of the biogas and the concentrations of the(4).carbon element in all mass flows were tested by theCompared with dry process, the advantage of theapparatus of SHIMADZU GC-14B and SHIMADZUwet process is taken to make exhaust gas cleaner andTOC-VCPN. The experimental results are shown incollect more cassava powder, and its disadvantageTable 1 and Table 2.resulting secondary pollution of water is avoided,Table 1 Composition of the biogas (%)because the powder contained in exhaust gas is notCHCOHOOthersuseless and harmful pollutant but valuable raw material.6922.6.90.05The wet process helped Xintai reduce the input ofTable 2 Concentrations of the carbon elementcassava and eliminate the dust of exhaust gas._Cassava mixture (9%)37.543.2.3 Recycle at the pipe endingDry sludge (%)36.52There are a lot of carbohydrates in the distllage.Fusel oil (mg/L)6.45x10*On one hand, they are pollutants; on the other hand,Dischanged water (mg/L)285.7Alcohol (%, @)96they would be resources if they were utilized.CO2(L)(%,0)99.9With the help of the distillage treatment system(Fig.1), the carbohydrates are digested into biogas, thenMaking the element balance, the ratios of theUASB and SBR continued to decompose carbohydratescarbon elements are calculated and the results are shownin anaerobic and aerobic conditions to decrease COD toin Table 3.less than 300 mg/L, the local secondary efluentTable3 Ratios of carbon element in all mass flowsstandards. Xintai yielded 37 m' biogas per ton of theSubstanceMass flow rate (d) TC (vd)TC(%)distillage, much higher than the average level of 23 m/tCassava mixture50168.9100in Chinal4. It obtained 40000 m'/d biogas and 100 t/dAlcobol15475.64.74sludge, which were used as energy resources.CO2 (iquid)452.37.26Fusel oil0.50.273.2.4 Integrated utilization of carbobydrates of cassavaCO2 ofbiogas450 (kmold).43.19All mass integrations carried out in Xintai areDischanged water1100.30.1Biogasludge4.3summarized in Fig.3.CH ofbiogas1149 (kmold)3.88.16Note: TC means total carbon amount.CO: produced by femeolatien ad digstionAtmosphereTable 3 shows that the sum of calculated amountsBy product Co:(山)Input:l Proceuleaving the system was 68 13%. So it could be assumedCasr+( Alcobol I Product Alcoholthat the rest (31.87%) exhaled from the fermentationprodurtioOutput:and digestion diffuses into the atmosphere. Based on theBy product: Fuel oilassumption, the balance chart of carbon components isconI ElatricitPuseloldrawn in Fig.4.(Ri( PowerTC in Co2 cxhalig fom the fermenaton and昆\同digestion dffusing into the atnospbere .31.87RiverToOC in discherged waterTC in acohol product, 4.74色TC in fusel oil, 0.27Fig.3 Integrated utilization of carbohydrates of cassavaTC in discharged water,0.19Figure 3 shows that the raw material cassava is目|reduced, recycled and reused in alcohol production;N Tc i ChloNopa,816only a small part of materials is discharged into waterTC burmod into CO2. dischargedand atmosphere in the forms of total oxygen carbon中国煤化工v(TOC) and CO2.YHCNMHG4 ANALYSIS ON AVALIABILITYOF THE CARBON ELEMENTFig.4 Carbon element balance of alcohol productionIn order to analyze the availability of cassava, the438 .过程工程学报第6卷was changed into CO2 according to the reaction Eq.(1),5 CONCLUDING REMARKSand in the whole process 42.32% of carbon elementbecame CO2, but only 7.26% of CO2 was recovered,(1) Achievements of circular economy on mass35.06% else emitted into the air. Limited by Eq(1), itintegrationseems impossible to avoid a part of the carbon elementBy reducing, reusing and recycling raw materialbecoming CO2 unless a new reaction equation is found.cassava in every possible way, the cassava consumptionBut there is a possibility to increase the conversion2.22 tUt for production of alcohol in the case study wasrate of fibre into alcohol, for instance, finding some newmuch less than the average level 2.92 tUt and the bestbiologic enzyme from cows or sheep. If it could be done,level of 2.78 tVt. In adition, although the averagethe utility of carbon element would be improvedconcentration of starch in the feedstock was decreasedsignificantly, because among the total carbon element,due to addition of cassava residues, the total amount of44.74% changes into alcohol product, 22.37% becomescarbohydrates was increased, that helped Xintai obtainCO2, the rest 32.89% is regarded as fibrous carbonmore 14 m' biogas per ton of the distillage, andelement and goes into wastewater distllage. Now onlyincreased the availability of the carbon element by12.48% in the disillage is used in energy forms of3.19%.(2) A‘zero emission' model for the alcoholbiogas and sludge, and another part (20.31%) escapesinto the air. That means that one fifths of cassava isdistillerywasted.With the help of the ditillage treatment system,almost all organic wastes were recycled in forms ofREFERENCES:mass and energy. Only 0.19% carbon element was[1] KimJ S, KimB G Lee C H, et al. 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