木薯燃料乙醇的碳效应分析

March 2012Journal of resources and ecolog.Vol 3 No. 1J Resour. Ecol. 2012 3(1)055-063RepDo:10.5814/issn1674764X201201009www.jorae.cnCarbon Balance of Cassava-based Ethanol fuel in ChinaYANG Hailong, 2, LV Yao*and FENG ZhimingI Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China2 Graduate University of Chinese Academy Sciences, Beijing 100049, ChinaAbstract: Considering energy security and greenhouse gas emission, many governments are developingbio-liquid fuel industries. The Chinese Government advocates the development of a fuel ethanolindustry with non-food crops such as cassava. However, scientists debate the carbon emission of thesebio-liquid fuels. The focuses are the influence of soil carbon pool destruction and by-product utilizationThis study built a carbon balance analysis model, and assessed carbon emission of cassava fuel ethanolacross its life cycle. The results show that the carbon emission of cassava fuel ethanol per kilogram inits life cycle was 0.457 kg under new technical conditions and 0.647 kg under old technical conditionsCarbon emission mainly came from the use of nitrogen fertilizer(9% of total emissions, the destructionof the soil carbon pool(29%)and fossil energy inputs(50%). Taking gasoline as a reference the carbonemission of cassava fuel ethanol was 90% of that of gasoline This percentage would drop to 64% if soilcarbon pool destruction was avoided Therefore in order to promote the development of cassava fuelethanol in China, farms should apply fertilizer properly grow cassava on marginal land and not alterland use patterns of woodland, grassland and other environments. In addition, we should exploit effcientfuel ethanol conversion technologies and strengthen the use of by-productsKey words: fuel ethanol; life cycle assessment (LCA); carbon impact; carbon balance analysis; cassava1 Introductionethanol has great significance in reducing CO2 emissionsfrom transportation. In recent years, the bio-fuel ethanolThe reduction of greenhouse gas emission is a shared industry has developed rapidly and the Chinese Governmentglobal challenge. The Chinese Government promised at also gives great support to this developing bio-fuel ethanolthe Copenhagen Climate Change Conference in 2009 that industry. Considering food security, the GovernmentChina would endeavor to reduce its carbon dioxide emission promotes bio-fuel ethanol from cassava, sweet potato, sweetper unit of GDP by 40%45% by 2020 compared with 2005 sorghum and other non-grain cropslevels(http://www.chinanews.com/cj/cj-hbht/news/2009/11-Therearemanydifferentviewsoncarbonemissionfrom26/1986490. shtml). The CO, emission of China from oil bio-fuel ethanol production. International Energy Agencyconsumption has amounted to 12.95 x10 ton in 2010 (IEA (IEA) and Food and Agriculture Organization(FAO2011), and more than 30% of total emissions come from assessed the greenhouse gas emission of bio-fuel ethanotransportation. Therefore, exhaust gas from automobiles is globally(FAO 2008), and found that despite variation inan important source of greenhouse gas emissions. Bio-fuel benefits, bio-liquid fuels were able to reduce greenhouseethanol as a substitution for gasoline can effectively reduce gas emission to some extent(Revin 2001; Hu et al. 2003vehicle greenhouse gas emission from burning fossil fuels. Hu et al. 2004). However, recent researches have shownConsequently, the study of the carbon balance of bio-fuel that carbon emissions from bio-fuel ethanols are almost the中国煤化工Received: 2011-11-23 Accepted: 2012-01-20Foundation: the National Natural Science Foundation of China(40971270)ICNMHGCorresponding author: LV Yao Email: 13651221336@ 126 con56Journal of Resources and Ecology Vol 3 No. 1, 2012same as those of the oil(farrell et al. 2006; Renton et al. fuel ethanol industry in China2007; Zhang et al. 2006). Conversely, if energy crops weregrown in tropical rain forest, peatland, savanna or grassland,2 Methods and datacarbon emissions would be even worse Joseph et al. 2008; 2.1 Life cycle assessment and carbon balance modelAdler et al. 2007; Elsayed et al. 2003; Searchinger et al. The methodological framework applied in this study is2008based on the life cycle assessment(LCA) methodologyCarbon emission from bio-fuel ethanol is affected by Ideally, the lCa methodology makes it possible to accountcomplicated factors such as plant management, for all materials and energy flows associated with thelevels, land use types, converting technology anproduction system while keeping track of outputs(products,by-product processing. The most significant reason for energy and waste materials)along the production cycle(Figthe discrepancies is the ignorance of carbon emissions 1)arising from land use change and by-product distributionThe carbon balance model of bio-fuel ethanol is asAdditionally, the uncertainty of the system boundary and followthe difficult accessibility of some indirect factors also leadto different results. The destruction of the soil carbon poolCnet= Fossil+ Csoil+ Substituteand how to use by-products are essential when assessing where, Cnet is net carbon emissions; Fossil is carboncarbon emission. For instance, cassava dregs can be used as emissions from fossil energy input in the life cycle of themanure or materials for generating power, namely "avoiding cassava-based fuel ethanol; Csoil is the carbon emissiongreenhouse gas emissions, and these have enormous impact from the destruction to soil carbon pool when plantingon evaluation resultscassava;Cswbstirute is the reduction of carbon emissions dueIn this study, applying life cycle assessment(LCA)and to the secondary utilization of by-products, the so calledestablishing a fuel ethanol carbon balance model we(i)"substitution effect". For instance, generating biogasbring the impact on the soil carbon pool when growing cogeneration by cassava residue can reduce fossil energycassava and the substitution effect of by-products into the input and thereby reduce carbon emissionsresearch system,(ii) analyze thele cassava-bascarbon emissions in China, and(i) provide a basis for 2.2 Date collectiondecision-making for the development of a cassava-based Primary data was mainly collected from field surveys andAtmosphericPetrochemicalCultivation andExploitationMaof crude oillProcessing andRefining andTransformationcarbon fromcarbon fromConsumptionConsumptionEqualFossil fuelearth crust中国煤化工 nalysis frameworkbalance in lifeCarbon impact of bio-fuel ethanol in life cycleCNMHYANG Hailong, et al. Carbon Balance of Cassava-based Ethanol Fuel in Chinapublished literature. Besides, official databases were alsoimportant data sources. In order to obtain primary data,X XMCthe authors went to Guangxi Zhuang Autonomous Regionthree times in October 2010, March and August 2011 to where, X, is the quantity of nitrogenous fertilizer consumeddo surveys and administer questionnaires. We took detailed during the cassava cultivation(calculated as N); a is therecords of energy input-output involved in cassava planting. proportion of N, 0 due to the nitrification of nitrogenousWe visited enterprises to collect data on the processing and fertilizer, in this study, the value of a is 0.18%(Zhang ettransformation of bio-fuel ethanolaL. 2010); GWPN,O is the global warming potential index3 Resultsof N2O and its value is set to 296(IPCC, 1996); M, is the3.1 Carbon emission from cassava cultivationatomic weight of nitrogen and its value is 14; and Mc is theatomic weight of carbon and its value is 1Cultivation, management and transportation of cassavaconsume a lot of chemicals such as fertilizers, pesticidesC,=D×mExBand fuel. The carbon emissions due to the production ofAthese chemicals should be included in the analysis. Besides, where, D, is the average transportation distance; TE,is thethe original equilibrium state of the soil environment wasdestroyed because local farmers reclaimed wasteland in afuel consumption intensity of transporting cassava and TEFllarge-scale to grow cassava, which also caused great carbon is the carbon emission coefficient of transport fuelemissions. Consequently, carbon emissions caused by soilThe main fossil energy inputs for sowing, andcarbon pool destruction should be included in the analysismanagement(including transportation and storage) ofsystemcassava are nitrogen, phosphate, potash, pesticides,herbicides and mechanical fuel. Considering the actual3.1.1 Carbon emission from fossil energy inputsituation we took the average value after doing fieldCarbon emissions of fossil energy inputs are as follows:research. From the investigation results we obtained theaverage value of transportation distance as 4 km, the diesel=C+(2)L( and the yield of cassava is 41 t ha ! Thus, dieselwhere, C, is carbon emissions from fossil energy input consumption for transporting cassava is 9.84 L per hectarefor planting cassava; C, is carbon emissions from fossilTaking into account the fuel consumption for cultivationenergy input of harvesting and transporting cassava. C wa(34 L ha), we derive that the total fuel consumption forcalculated as followsplanting cassava per hectare is 43.84 L. Because cassava'swater requirements are met mainly by rainfall, the powerC=元×∑XxEFconsumption of irrigation is zero. Seed investment is(3)negligible because farmers kept the seed themselvesannually. According to formula(2) 5), we can calculatewhere,X, is the quantity of i material consumed in planting the carbon emissions from fossil energy input per hectarecassava; EF, is the carbon emission coefficient of i material; (including cassava transportation)(Table 1)A is the cassava planting areaAs shown in Table I and Fig. 2, total carbon emissionsAs the warming effect of N2o is obvious, the from fossil energy input during cassava cultivation areconsumption of nitrogen fertilizer during cassava cultivation 429.44 kg per hectare. Nitrogen is the main source of carbonneeds a separate discussion. The formula is as follow:emissions and accounts for 42% of total emissions. the useof plastic film also plays a great role, which takes up 10%of total emissions, followed by diesel fuel and pesticidesTable 1 Carbon emissions of fossil energy inputs per hectareInput(unit) Coefficient(kg C urCarbon emission(kg C) Proportion(%)210(kg)08571799741.91Phosphate(P2O5)146(kg)0.16524.09561Potash(K,O)178(kg)0.12021.36Pesticide8(kg)4.93239.469.19Herbicide7(kg)4.70232.917.Diesel(cultivation/harvesting/transporting0.8493736Plastic film30(kg)46944.0710.26o(kW-h)Gasoline for transportation0853中国煤化工0.00EffectCNMHG 11.69427.++100Journal of Resources and Ecology Vol 3 No. 1, 2012Plastic filmnitrogen(Nno effectPhosphate(P,O)4.97%9.19%0Potash(KO)760PesticideHerbicidePhosphate(P,O,)Plastic filmN-effect(N O)10.26%0204060801001201401601804191°Fig 2 Carbon emissions of fossil energy input(both 9% of the total emissions). In order to reduce carbonLP= NPP-CPemissions, we should adopt advanced cultivation technology Fi o(carbon flux from litter to humus inand scientific fertilization methods that reduce nitrogen lossequilibrium)=kxLPoand ultimately reduce carbon emissionsFia o(carbon flux from litter to atmosphere in3.1.2 Carbon emissions from soil carbon pool destructionequilibrium=(I-k)xLPFhs. o(carbon flux from humus to soil inWe built a model to calculate carbon emissions caused byequilibrium)=k×p×LPosoil carbon pool destruction. Some parameters should be Fha. o (carbon flux from humus to atmosphere indefined firstequilibrium)=k×(1-φ)×LP(10)Lo: carbon stored in the litter pool in equilibrium at timeFsa o(carbon flux from soil to atmosphere inequilibrium=kxoxLPoL: carbon stored in the litter pool at time tAccording to the formulas(6 (11), the carbon flux fromHo: carbon stored in the humus pool in equilibrium atlitter to soil to atmosphere ultimately follows a dynamictime oequilibrium. However, the dynamic equilibrium of th esolSo: carbon stored in the soil pool in equilibrium at time 0. System is destroyed in actual practice which causes largeH(: carbon stored in the humus pool at time t;carbon emissions from the soil carbon poolS(o): carbon stored in the soil pool at time t;LP= NPP-CP-LNP+LRE= LP,-LNP+LRE(12)LP: carbon content in annual litter production inFi(carbon flux from litter to humus in actual practiceequilibrium at time 0;L×kLP (t): carbon content in annual litter production at time t; Fia (carbon flux from litter to atmosphere in actualNPP: annual net primary production(14)CP: annual harvest of cassavaFhs(carbon flux from humus to soil in actual practice)LNP: the amount of removed plant waste whenreclamation:Fha(carbon flux from humus to atmosphere in actualLRE: annual amount of cassava straw returningFsa(carbon flux from soil to atmosphere in actual(16)practice)=H×khk: share of the carbon flux out of the litter pool thatenters the humus pool [(l-k)is emitted to thepractice)=s×k(17)atmosphere];The following equations for the carbon mass balance ofp: share of the carbon flux out of the humus poolthe three pools have to be solvedthat enters the soil pool [(1-p)is emitted to thetmospheredl= LPo -LNP +LRE-kiaxL-kinXL (18)kla: carbon flux fraction from litter to atmosphere;k,a: carbon flux fraction from humus to atmosphere=k, xl-kxh-kxHksa: carbon flux fraction from soil to atmosphere(19)k,: carbon flux fraction from litter to humuskhe: carbon flux fraction from humus to soil中国煤化工The system is assumed to be in equilibrium at time 0,thereforeCNMHGWith thar'equinorium une proportionality factorsYANG Hailong, et al. Carbon Balance of Cassava-based Ethanol Fuel in Chinakxy can be calculatedliterature where NPP=5.3 t C hay"(Atay et al. 1979),dL/dt=0; I-Lo; k=[(l-kxLPo]/Lo; kn=(kxLPo)LosCP-1.8tC ha"y, LP -NPP-CP-35 t C ha"y", LNP-12tdH/dt=0; H==Ho; kha=[(l-o)xkxLPo]/Ho,C hay, LRE-03t C hay, Lo-26.8tC ha, H=692t Cha, S/53.7 C ha, k=0.25, and -0 1(Schlamadingerk=(φ×kxLP)/het al. 1995), After substituting these valdS/dt=0; S-So; k,a=(oxkxLPo)/Soequations 24 to 27, the parameters are described as beloAccording to k,y and equations(18),(19)and (20)L()=6901+199dLP-LRE-Lf×(L/L)(21)L()=197e012-1.el"+514e0oyS()=50.802-1.81+0.02e0+4.6e0d t=LP×kx[(L/L)-(H/H0Caos)-12985.02e01119.7e02-560x50.8c000+1.8e00y=LP×kxx(H/H0)-(S/S0According to the above equations, CLoss (10. 7 t C=700 kgSolving differential equation(21)C; CLoss(5)=0.1 tC=100 kg C; CLoss(6--0.01 tC-10 kg C040 kg CL=ce 4+5(P-INP LRE)(C, is arbitrary constant)(24) Carbon emissions caused by soil carbon pool destructionare 700 kg after one year of cassava planting; this is 1.6Solving differential equation(22)times more than carbon emissions caused by fossil energy4C1H0×k,H(LP-LNP+LRE而input. As most of the plant waste is removed duringreclamation, the original balance of the soil carbon poolxk-His broken, and leads to a massive release of soil carbon.(Ch C? are arbitrary constants)(25) Meanwhile, the soil humus layer decreases because of theSolving differential equation(23)reduction in raw materials on the surface layer which leadsto a reduction in soil carbon accumulation. After years ofS=CC2Soxo Rstcassava growing carbon emissions from the soil carbon poolH×φ-Swill gradually decrease, and the soil carbon pool will be ina new dynamic equilibrium again in the sixth year. If moreCLS2×k2xcassava straw is returned to the fields, many ycars later,(L×k-H0)(L0×kxφ-S)such as the tenth year, soil carbon storage will be greaterthan the carbon emittedHSx叭(LPB=LNP+LRE),Among all the carbon emissions during cassava planting,LP0(Hxφ+S)soil carbon emissions are 700 kg which accounts for 62%of the total carbon emissions Therefore in order to reduce(Cr, C2, C3 are arbitrary constants)(26) carbon emissions, we should not significantly change landSo, the carbon emission equation isuse types, particularly for woodlands and grasslands. Weshould instead make full use of woodland and grassland forCloss o=Lo+ Ho+ So-L(o-H(o-S(o(27)Most of the local soil is lateritic red soil. the thicknessof the humus of the topsoil is 10-20 cm before reclamation;3.2 Carbon emissions from cassava-based fuel ethanolwe regard the average value as 15 cm in this paper. Theproductionproportion of organic matter is between 4% and 6%( from Carbon emissions from bio-fuel ethanol are correlatedsurvey data). The conversion coefficient which describes with technological process. In particular, the secondarythe organic matter transformation into organic carbon is utilization of by-products is a key factor which affects058(SSAACC, 1989). The homogeneous layer thickness carbon emissionsis 0.5-2 m. Cassava cultivation layer is generally between15-30 cm, and we took the mean value 0. 25 m as the depth3. 2. 1 Carbon emissions from fossil energy input during theof soil disturbance. The soil bulk density is about 1.59roduction(WBS, 2008). Soil organic matter content is 2.3%(Wei et Coal consumption accounts for 76.7% of total energy1. 2007). Soil organic carbon content is 1. 35%(Ni et al. consumption in China. Thermal power accounts for 82.98%2007). Accordingly to these data, we can estimate Ho=69.2 of total generating capacity (NBS. 2009). Thus, we believetC ha, S,=53.7 t C ha". This value roughly approximates the power cessava-based fuelto the FAO-UNESCO soil classification(5.7-16.9 kg m") ethanol is th中国煤化 nt types of energy(Batjes et al. 1996)should be coCNMHGand then carbonSome data is accessible from the survey data and emissions calculated. The main energy inputs and theJournal of Resources and Ecology Vol 3 No. 1, 2012Table 2 Main energy inputs and carbon emissionsItemInput(unit)Data sourceOld technology New technology Technology insmall and medium-sizedenterprises8-10tt ethanol 3-4tr' ethanol 12-15tt ethanol Survey and reference(fresh waterSteam4.5-5.2ttl2.2t t" ethanolSurvey and referenceethanolPower250 kWh t180 kWh t300 kWh t" ethanolSurvey and referenceethanolNatural gas0.9mt 'ethanol1.2Lt'ethanolChemical reagent1.98 kg" ethanol 1.56 kg ethanol(H, SO4 etc.Microbial preparation3.75 kg t"ethanol 3.34 kg t" ethanolSurveamylase etc.Fungicide (penicillin etc.0.08 kg t ethanolSurveyEquipment depreciationTotal energy consumption 19.67 MJ kg13.35 MJ kg25.24 MJ kg ethanol Survey and reference19.82 MJ"ethanol°0. 67 kg k0.46 kgkg0.86 kg kgConvertingstandard coalethanolCarbon emission0.75590.75590.7559IPCCcoefficient of standard coaCarbon emission0.51 kg kg0.35 kgkg0.65Convertinga: Reference(Hao et aL. 2009); b: Reference( Dai et al. 2005); c: Reference(Dong et al. 2008)carbon emissions are shown in Table 2are cooking/liquefaction, distillation and dehydration. NewAccording to Table 2 carbon emissions from the three technology greatly reduces carbon emissions from thesedifferent technologies are 0.51 kg, 0.35 kg and 0.65 kg sources. Carbon emissions from cooking/liquefaction,per kilogram of bio-fuel ethanol respectively. This shows distillation and dehydration were reduced by 32.7%,that improvements in production technology are essential 37.0% and 19.6% respectively when using new technologyto reduce carbon emissions. Carbon emissions can be compared with old technology. Therefore, the enterprisesreduced by 31.4%after utilizing new technology. Small should introduce new technology to radically reduce carbonand medium-sized enterprises have the greatest potential to emissionsreduce carbon emissions by introducing new technology.As shown in Fig 3, the main sources of carbon emissionsPretreatment of raw materialsTotal carbon emissFermentationWaste distiller disposalDistillationDehsdrmtie42.29%■ DehydrationWaste distiller disposDistillation22.29%FermentationRaw matenals pretreatment05010015020025030035040045050550600650700Carbon emission (kg C I ethanol中国煤化工New technologyCNMHFig 3 Carbon emission of cassava-based ethanol in different technical conditionsYANG Hailong, et al. Carbon Balance of Cassava-based Ethanol Fuel in China3.2.2 Substitution effect of by-products secondaryadopting new technology. The cassava growth cycle andutilizationcassava fuel ethanol processing are the two main carbonemission sources. Carbon emissions from these two linksThe main by-products are cassava dregs. Dregs can be used accounts for 47%and 50% of total emissions. Carbonas manure or the materials for biogas and power. Using emission caused by the soil carbon pool destruction is thecassava dregs as manure would reduce carbon emissions key factor during the cassava planting linkto some extent. Cassava dregs are used to generate biogas Fig. 5 shows life cycle carbon emissions of different bioor power which also replaces a certain amount of electrical fuels under different technical conditions. Carbon emissionenergy and thermal energy consumption. All of these effects from maize bio-fuel ethanol is greater than that of other fuelshould be removed so that we can objectively assess carbon ethanol. The highest emission of maize bio-fuel ethanolemissions throughout the life cycle.is two times more than gasoline. Carbon emission fromCompany research showed that cassava dregs were maize bio-fuel ethanol in the most advanced technolog.mainly used for cogeneration, which per kilogram bio- is even higher than that of gasoline. This indicates that itfuel ethanol would generate 0.47 kW.h power. The current is not rational to produce maize fuel ethanol using currentthermal power generating efficiency is about 0.334 kg technologystandard coal kW h"' in China. It is equivalent to substitute Sugarcane fuel ethanol industry is mature in Brazil. Its0.16 kg standard coal consumption. In other words, it equals carbon emission only takes up 17. 4%of that of gasoline. Ita reduction of 0. 12 kg in carbon emissionsbenefits from a wealth of sugarcane resources and advancedIn small and medium-sized enterprises cassava dregs are processing technology. The sugarcane fuel ethanol industrymainly used for generating biogas or manure. This equals in Brazil has long existed. After decades of development,a reduction of 0.09 kg in carbon emissions. In summary, this industry chain is mature and greatly reduces carbonunder new and old technical conditions carbon emissions emissionsduring cassava processing and transformation are 0. 23 kg Carbon emission from herbaceous cellulose fuel ethanoland 0.42 kg respectivelyin America is 3. 16g C MJ. Taking herbaceous cellulose3.3 Carbon emissions of cassava-based fuel ethanolas raw materials to produce bio-fuel can effectively avoidacross the life cyclecarbon emissions during planting raw material speciesHowever, this technology is not mature and it cannot beCarbon emissions during the transportation and used in large-scale commercial production. Technicalconsumption link are mainly generated by the fuel problems hamper the development of this industryconsumption of transport vehicles. Based on survey data, however, the cellulosic fuel ethanol industry has potentialthe distribution range of cassava fuel ethanol is about 300 once technical breakthroughs are achieved.km, and the fuel consumption intensity of the diesel truck Considering food security, some countries such as Chinais about 0.06L tkm. The carbon emission coefficient of and Thailand, advocate the production of bio-fuel ethanoldiesel is 20.2 t C(TD(IPCC 1996), namely 0.777 kgC from non-food crops like cassava and sweet sorghum. Fig.5L'. Thus the carbon emission during the transportation and shows that the highest carbon emission of cassava bio-fuelconsumption link is calculated as 14 kg per ton cassava fuel ethanol is 33. 53 g C M. The lowest emission is 12.44 g Cthe Mr, which only accounts for 65.8% of that by gasoline. InIt is shown in Fig 4 that total carbon emissions across the this study, the life cycle carbon emission of cassava bio-fuellife cycle are 0.647 kg and 0.457 kg respectively in the old ethanol under old technical conditions is 24.16 g C Mjand new technical conditions. It is reduced by 29.4% after which is higher than that produced by gasoline. However,PLastic filmTotal emissonHerbicidePesticideSou carbonPlanting link(P2O3)Soul cartonEFfectFig. 4 Life cycle carbon emission of cassava-based fuel中国煤化工mckg'chmethanol in different technical conditionsCNMHGournal of Resources and Ecology vol 3 No. 1. 2012Casoline 4Cassarva-new technologyCassava 3. ThailandCassavaMaize 3.AmericMaize 2Fig. 5 Life cycle carbon emission of differentMaizebio-fuels in different technical conditions1: reference(Zhang ef aL. 2009); 2: reference(CREDSRG2008): 3: reference(Thu et al. 2007); 4: referenceCarbon emission(g CMJ"')(IPCC1996)emissions decrease to 16.93 g C M 'after the application cannot effectively reduce carbon emissions comparedof new technology, lower than that of gasolinegasoline. The carbon emission of herbaceous cellulose4 Conclusionsfuel ethanol in America is lower than that of gasoline. Butthe technology is not mature, and cannot be used in largeThis study assessed carbon emissions from cassava bio-fuel scale commercial production. Cassava fuel ethanol inethanol across its life cycle in China. Comparative analysis China will achieve positive environmental benefits if thewith other bio-fuel ethanol was also done. The main carbon emissions caused by soil carbon pool destructionconclusions are as followsare avoided. Additionally, it is noteworthy to emphasize1)Carbon emissions during the cultivation link were that many benefits of cassava fuel ethanol cannot bemainly generated from the emission of fossil energy input, captured adequately by our analysis. They are(i)reducingespecially nitrogen fertilizer and the destruction of the soil oil imports and saving foreign exchange, (ii) enhancingcarbon pool. Carbon emission from nitrogen fertilizer and technological development, (ii)stimulating domesticsoil carbon were 0.043 kg and 0 132 kg per kilogram fuel agricultural production and expanding the market forethanol respectively, accounting for 9% and 29% of the domestic agricultural commodities, and (iv) generatingtotal life cycle carbon emissionsrural employment and improving farmer income. If these(2)Carbon emission during the processing link differs benefits are taken into account in a green gas abatement costacross different technologies. Carbon emission in this link analysis, the cost would be more favorable to cassava fuelis reduced 3 1%after the application of new technology ethanolwhich are from 0.51 kg to 0.35 kg. New technology mainly 6 Acknowledgmentsreduces the energy consumption of raw material cooking,distillation and dehydration, while enhancing secondary This research was supported by the National Natural Scienceutilization of by-products. All these improvements Foundation of China(40971270) The authors would like to thankeffectively reduce carbon emissionthe officers and farmers for help in cassava farming data collection()Carbon emissions during the transportation link in Wuming County, Guangxi Zhuang Autonomous Region.Thanksare negligible because they only account for 2% to 3%are also extended to Wei Xuebing and other technicians at Jiaolongof total emissions. The cassava bio-fuel ethanol industrAlcohol Energy Ltd. Co. for providing cassava bio-fuel ethanolin China is developing fast, but carbon emissions acrossprocessing-conversion data. We are also grateful to an anonymoushe whole life cycle are higher than that of gasoline, with reviewer for useful comments and suggestionscurrent processing technology. Therefore, improving Referencesproduction technology is the key point to achieve positive Adler P, Del S J and Parton WJ. 2007. et greenhouse gas flux of bioenergyenvironmental benefitscropping systems using DAYCENT Ecology Application, 13(8): 345-352(4)It should be noted that we have considered carbon Atjay G L, Ketner P and Duvigneaud P. 1979. Terrestrial primary productionemissions caused by land use change. However, these and phytomass. In: Bolin B, Degens E T, Kempe S, Ketner P(eds).Theemissions can be avoided if we plant cassava on marginalland. 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Environmental Science, 27(4): 616-619content change of betula alnoides plantation in hot areas of Yunnan木薯燃料乙醇的碳效应分析杨海龙12,吕耀,封志明1中国科学院地理科学与资源研究所,北京1001012中国科学院研究生院,北京100049摘要:出于能源安全的考虑及对温室气体减排的关注,世界各国近些年大力发展生物液体燃料,我国政府提倡以木薯等非粮作物为原料生产燃料乙醇。但一直以来科学家们对生物液体燃料的碳效应争论激烈,争论的焦点在于原料种植对土壤碳库的影响及不冋技术条件下副产品利用的评估。本文通过建立碳平衡分析模型,将原料种植对土壤碳库影响及副产品利用的替代效应纳入研究体系,评估了我国木薯燃料乙醇生命周期内的碳排放,研究结果显示:我国每生产单位质量(1kg)木薯燃料乙醇在新旧两种技术条件下的碳排放分別为0457kg和0.647kg。碳排放主要来自于氮肥的使用、木薯种植对土壤碳库的破坏及木薯燃料乙醇加工转化过程能源投入,在新技术条件下分别占总排放量的9%、29%和50%。以汽油的碳排放为参照,在旧技木条件下我国木薯燃料乙醇碳排放呈现负效益,在新技术条件下其碳排放为汽油的9%,倘若能避免对土壤碳库的破坏,劓这一比例将下降到64%。因此,为了促进我国木薯燃料乙醇的发展,首先应该引导农民合理施肥,利用边际土地种植木薯,不转换林地、草地等土地类型的利用方式;此外,要开发高效节能的燃料乙醇转化技术及加强对副产品的二次利用。关键词:燃料乙醇;生命周期分析(LCA);碳效应;碳平衡分析;木薯中国煤化工CNMHG