03_Life Cycle Inventory and Energy Analysis

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Life cycle inventory and energy analysis of cassava-basedFuel ethanol in China

Rubo Leng, Chengtao Wang *, Cheng Zhang, Du Dai, Gengqiang Pu RM330, Mechanical Engineering BLD, Institute of Life Quality via Mechanical Engineering, School of Mechanical and Power Engineering,

Shanghai Jiao Tong University, No. 800, DongChuan Road, Shanghai City 200240, PR China

Received 30 July 2006; received in revised form 7 November 2006; accepted 10 December 2006Available online 9 February 2007

Abstract

The Chinese government is developing biomass ethanol as one of its automobile fuels for energy security and environmental improvementreasons. The cassava is an alternative feedstock to produce this ethanol fuel. Its performance of environmental impacts and energy efciency isthe critical issue. Life cycle assessment has been used to identify and quantify the environment emissions, energy consumption and energy ef-ciency of the system throughout the life cycle. This study investigates the entire life cycle from cassava plantation, ethanol conversion, trans-port, Fuel ethanol blending and distribution to its end-use. Product system of cassava-based ethanol fuel is described and it is divided into six unitprocesses. The environmental impacts and energy consumption of each unit process are quantied and some of the potential effects are assessed. 2006 Elsevier Ltd. All rights reserved.

Keywords: Life cycle assessment; Ethanol fuel; Cassava; Life cycle inventory analysis

1. Introduction

Air emissions from automobiles have become one of themain polluted sources to the cities environment with the in-creasing of the amount of automobile. And it is also themain reason why the environment pollution becomes moreand more serious for many metropolises in the world [1].Many studies have shown that CO 2 emissions from automo-biles are about 14% of the total CO 2 releases, CO and HCemissions are about 50 e 60%, and NO X and PM 10 emissions

are about 30% and 10e

20%, respectively [2]. In China, amongair emissions of metropolises, above 40%, 80%, 70% of the to-tal NO X , CO and HC emissions, respectively, are due to auto-mobiles [3].

China has been a net importer of petroleum since 1993.Imported oil currently accounts for about 25% [4] of Chinastotal domestic needs, and the amount will probably increase to

more than 50% by the year 2015 due to the rapidly risingdemand for oil by the ourishing economy [5,6] .

The Chinese government is developing biomass ethanol asone of its transportation fuels for energy security and environ-mental improvement reasons. Two policies entitled as Dena-tured Fuel Ethanol and Ethanol Gasoline for Motor Vehicleshave been executed in China since 2001, aiming at developinga sustainable energy resource, enhancing domestic energy se-curity, and improving the domestic environment. Ethanol fuelis used by blending with gasoline to produce E10 (10% by vol-

ume Fuel ethanol added to gasoline) nowadays in China.Cassava is a good feedstock to produce ethanol because ithas high starch content and it is abundant in the southern prov-inces of China. Cassava is a starchy material. Starch containedis rst liqueed so that dextrin and subsequently fermentablesugars can be obtained, and, after fermentation and distillation,ethanol of 95.6% w/w comes out, through dehydration, whichis concentrated to 99.5% w/w. Thus cassava-based Fuel etha-nol is produced, and it is usually denatured by small volume of gasoline or other materials added preventing people fromdrinking it.

* Corresponding author. Tel.: 86 21 34206078; fax: 86 21 34206815. E-mail addresses: [email protected] (R. Leng). [email protected]

(C. Wang).

0959-6526/$ - see front matter 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jclepro.2006.12.003

Journal of Cleaner Production 16 (2008) 374 e 384www.elsevier.com/locate/jclepro
mailto:[email protected]:[email protected]://www.elsevier.com/locate/jcleprohttp://www.elsevier.com/locate/jclepromailto:[email protected]:[email protected]


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Like other biomass fuel, ethanol fuel derived from cassavain China is also confronted with two controversial issues.One is whether ethanol fuel is environmental friendly, theother is that does it or doesnt it produce positive net energy?As for the two issues, several studies were conducted in pastdecades. Cal Hodge [7] insisted that ethanol use in US gas-

oline should be banned, not expanded. Because the averageethanol life cycle energy balance indicated more energy isneeded to make ethanol than ethanol gives back, and ethanoluse increases NO X , VOC, and air toxics emissions relative tobaseline gasoline. David Pimentel [8] argued that ethanol fuelbased on corn degraded natural environment and contributed towater pollution and air pollution, and about 29% more energyis used to produce a gallon of ethanol than the energyin a gallonof ethanol. Chambers et al. [9] indicated that the energy ef-ciency is depended on many factors, such as energy-conservingfarming practices, energy-conserving industrial technology,and crop residues. However, Hosein Shapouri et al. [10] con-cluded that corn ethanol was energy efcient as indicated byan energy output:input ratio of 1.34. Seungdo Kim [11,12]also concluded that the ethanol fuel from corn grain producedthe positive energy. As for the US corn ethanol energy balance,in the latest literature, the Consensus of Farrell et al. [13] andvon Blottnitz and Curran [14] is that US corn ethanol hasa slightly positive energy balance.

The purpose of this study is to trace the cassava-based eth-anol fuels eco-prole that synthesizes the main energy andenvironment impacts related to the whole life cycle and toexamine energy conversion efciency. To fulll this purpose,the method of life cycle inventory analysis, including air emis-sions and energy requirement, was carried out for the cassava-

based ethanol fuel.

2. Methodology

The Society of Environmental Toxicology and Chemistry[15] is generally credited for the current LCA methodologicalframework. Recent standards by the International Organiza-tion for Standardization [16] have further formalized LCA.And it denes that life cycle assessment (LCA) studies theenvironmental aspects and potential impacts throughout aproducts life from raw materials acquisition through produc-tion, use and disposal. Life cycle inventory analysis is thephase of life cycle assessment involving the compilation andquantication of inputs and outputs for a given product systemthroughout its life cycle.

2.1. Denition of goal and scope

The rst phase of the life cycle inventory analysis is thegoal and scope denition. Cassava-based ethanol fuel is usedas an alternative automobile fuel in China. The goal of thestudy is to identify the environmental performance and energyefciency of cassava-based ethanol fuel, to search opportuni-ties to improve the environmental aspects at various pointsin its whole life cycle, and to support decision-making of eth-

anol fuel policy for the Chinese government.

The scope of the study includes the holistic life cycle of cassava-based ethanol fuel, which includes cassava cultivationand treatment, transport, ethanol conversion and denaturation,transport of Fuel ethanol, blending of ethanol and gasoline,burning of Fuel ethanol. A traditional inventory quantiesthree categories of environmental releases or emissions: atmo-

spheric emissions, waterborne waste, and solid waste [17] .This study examines atmospheric emissions such as CO 2 ,SO X , VOC, waterborne waste such as BOD and COD, andsolid waste.

A functional unit is a measure of the performance of thefunctional outputs of the product system. The primary purposeof a functional unit is to provide a reference to which theinputs and outputs are related. This reference is necessary toensure comparability of LCA results [16] . The functional unitof this system is to produce 100,000 ton ethanol.

2.2. Product system description

A product system is a collection of unit processes by owsof intermediate products which perform one or more denedfunctions [18].

The life cycle of cassava-based Fuel ethanol includes cas-sava cultivation and treatment, transport, ethanol conversionand denaturation, transport of Fuel ethanol, blending of etha-nol and gasoline, and burning of Fuel ethanol. Fig. 1 showsthe product system in detail.

Based on site investigation, we set some general assump-tions for the product system to produce 100,000 ton ethanolfuel:

d Planting area: 300,000 mu (20,000 ha);d Fresh cassava yield: 2.6 ton/mu (39 ton/ha);d Cassava dry chip conversion rate of fresh cassava: 3:1;d Ethanol (95.6%) conversion rate of cassava dry chip: 2.6:1;d Ethanol (95.6%) annual production: 100,000 ton;d Ethanol fuel (99.5%): 120,100,500 L;d Gasoline e ethanol blends adopted: E10; andd Gasoline consumption: 8 L/100 km.

2.3. Unit processes

Product systems are subdivided into a set of unit processes.Unit processesare linkedto oneanother by ows of intermediateproducts and waste for treatment, to other product system byproduct ows, and to the environment by elementary ows [18].

Fig. 1 shows the detailed system ow diagram for cassava-based ethanol fuel. According to the method of life cycleinventory, the product system is subdivided into six unitprocesses, which are described as the following.

(1) Cassava cultivation and treatmentIn this unit process, it includes eld preparation and

plough, sowing, fertilization, weed, harvesting, pillingand slicing, packing and so on. Fig. 2 shows the unit pro-

cess in detail.

375 R. Leng et al. / Journal of Cleaner Production 16 (2008) 374 e 384


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Based on site investigation, we propose the assumptionfor this unit process:

d The electricity used is recalculated to primary energyfor an average south China electricity production sys-tem, which is based on 40% hydropower and 60%coal fuels.

(2) Transport of dry chipsThe cassava dry chips are transported to ethanol plants

by train or truck. It consists of the following steps:d Transport from the farmers houses to markets;d Transport from markets to ethanol plants; or

d Transport from the farmers houses to ethanol plantsdirectly.

Regarding this unit process, main assumptions are asfollows:d During the transport of dry chips, not only trains but

also trucks consume diesel oil only;d The average transport distance is 200 km by train and

50 km by truck.

(3) Denatured ethanol conversion

Producing denatured ethanol in the ethanol plant, ex-cept for consuming cassava dry chips, consumes coal,electricity and auxiliary materials including amylase,barm, vitriol and water. Fig. 3 shows the unit process indetail. The coproducts are CO 2 , DDGS (Dried DistillersGrain with Soluble, a kind of dried animal food), biogas,and manure.

When denatured ethanol is produced, the coproductsare CO 2 , DDGS, manure and biogas. CO 2 can be usedas a raw material in many industrial processes andDDGS is usually used for animal feeding as a kind of driedanimal food. Biogas from the anaerobic treatment is com-busted in the boiler to generate electricity. Manure is usedto cultivate cassava. Our project teams study the simpliedmass balance for this unit [19], and it is shown in Fig. 4.

In this unit, 126,421,600 L denatured ethanol (95% byvolume anhydrous ethanol and 5% by volume gasoline) isobtained.

Based on site investigation, we propose some of the fol-lowing assumptions for this unit process:

d The electricity used is recalculated to primary energyfor an average south China electricity production sys-tem, which is based on 40% hydropower and 60%coal fuels;

d Electricity generated from Biogas is used as power inthis unit process.

Mixing FuleEthanol and

Gasoline

E10

Denatured FuelEthanol

ChemicalsFarming

Packing

MillingMixing

liquefaction

Saccharification

Separation

DewateringFiltration

powerplant

boilers

RefuelingStation

Transportation

Transportation

Transportation

Supplementary

Liquefaction,Saccharification, and

Fermentation

Milling &Mixing

Distillation

Cassava DryChips

CO2 Production

Denature

E 10 burning

Manure DryingAnd Packaging

AerobicTreatment

DDGS Dryingand Packing Secondary

Fermentation

PostTreatment

AnaerobicTreatment

YeastPreparation

Fermenta

Dehydra-tion

-tionRectifica

-tion

coolingstation

TuberCollection

CassavaTreatment

Pilling& Slicing

PrimaryDistillation

CassavaTuber

Fig. 1. Detailed system ow diagram for cassava-based ethanol fuel.

Field Preparation and Plough

Sowing

Residue Milling/Treatment

Fertilization

Harvesting

Weed

Seed

F a r m I m

pl e m e n t s

a n d T r a c t or s

F e r t i l i z e r

P e s t i c i d e

H e r b i c i d

e s

Pilling & slicing C a s s a v a d r y c h i p s

Insolation packing

Fig. 2. Unit of cassava cultivation and treatment.



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(4) Transport of denatured ethanolThe transportation of denatured ethanol consists of the

following steps:d Transport of the ethanol from the ethanol plant to the

nearest railway station with tank truck;d Transport from the railway station to the nearest railway

station near gas station with tank; and

d Transport from the railway station to gas station withtank truck.

Regarding this unit process, main assumptions are asfollows:d During the transport of dry chips, not only trains but

also trucks consume diesel oil only;

Auxiliary materials

Fermentation

Milling Mixing

Liquefaction & Saccharification

Cassava dry Chips

Rectification

Fuel ethanol

Separation

Dehydration

DDGS

Distillation

Bio-gas

Manure

Denature

Post Treatment

CO 2Electricity

Coal

Solid waste

Water emissions

Air emissions

Fig. 3. Unit of denatured ethanol conversion.

5293 kg Sugar Solution

4443 kg

Water

750 kg

Sugar

100 kg

Other

340 kg Exhaust

2 kgWater

338 kgCO 2

4953 kg Fermentation Broth

4441 kgWater

381 kgEthanol

131 kgOther

Fermentation

4293 kg

Water

Milling

Mixing

1000 kg Cassava Dry Chips

150 kg

Water

765 kg

Starch

85 kg

Other

366 kg

99.5 Ethanol

15 kg

Water

381 kg

95.6 Ethanol4572 kg Effluent

4441 kg

Water

131 kg

Other

Distillation

Dehydration

Liquefaction & Saccharification

Fig. 4. Simplied mass balance for ethanol conversion.



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d The average transport distance is 350 km by train and100 km by truck.

(5) Blending denatured ethanol into gasolineIn this unit process, E10 (90% by volume gasoline and

10% by volume denatured ethanol) is obtained through

blending denatured ethanol into gasoline in the gas station.Fig. 5 shows the unit process in detail.

(6) E10 combustionThe life cycles for ethanol fuel and gasoline come to-

gether at the end-use stage in an urban bus. The amountof ethanol fuel required is dependent on the fuel economyof the bus engine, and the emissions are dependenton many factors, including the type of engine. Thedata used in this study are cited from the GREET model(Table 1 ).

2.4. Data collection and validation of data

Based on on-site investigation, a large amount of data, suchas data related to fertilizers, seed stem, etc. during cassavaplantation, transportation distance, model, and so forth, are ob-tained. Some data come from journals [20,21] and books[22,23] published in China ( Table 2). The net energy andCO2 emissions of CG were taken from the GREET model de-veloped at Argonne National Laboratory [24,25] . The data arereviewed and veried, based on the best knowledge availablein China.

2.5. Allocation

When denatured ethanol is produced, the coproducts areCO2 , DDGS, manure and biogas. Allocating the environmen-tal emissions and the energy uses between the main productand the coproducts is one of the most critical issues in life cy-cle inventory and energy analysis. Market value and replace-ment methods are the most used methods in most studies[8,10] . As for market value allocation, the product energyuses are in proportion to a 10-year average market value of the corresponding product. As for replacement allocation,the energy credits are assumed to be equal to the energy valueof a substitute product that the ethanol coproducts can replace.In this study, the DDGS was replaced by corn (replacement

ratio: 1.077) and soybean meal (replacement ratio: 0.823)[24]. The CO 2 replacement value was based on the energyintensity of corn fermentation in the wet milling process. Itsenergy credit was 1.243 MJ/L [10]. Table 3 shows the alloca-tion results.

3. Results

3.1. Environment impacts

3.1.1. Cassava cultivation and treatment

The unit process of this LCI study involves identicationof the complete environmental ows associated with cassa-vas production. This includes the amounts of chemicals andfuels used on the farm and their associated emissions, aswell as the manufacturing, packaging, and processing of the inputs used to grow cassavas. For example, the energyrequired to mine, process, and transport potash fertilizer tothe eld is estimated. Also, the environmental ows and en-ergy requirements involved in making and transporting pes-ticides, seed, and all other farm inputs are accounted for.These upstream environmental ows are combined withthe ows associated with the actual cassava growing andharvesting to calculate the total emissions associated withcassava agriculture.

In this process, to get 1 ton dry cassava chips, there area large amount of emissions, which are shown in Table 4 .

Table 1The emissions in E10 combustion

Fuel type HC CO NO X PM10 CH4 N2 O

Gasoline 0.129 3.448 0.172 0.021 0.053 0.018E10 0.101 2.759 0.163 0.020 0.048 0.018

Table 2Data resource

Item Data source

Feedstock production Fertilizer, pesticide GREET, eld surveyFeedstock plant,management, andharvest

Field survey

Fuel production Ethanol productiontechnics, energyand emission

Data and report of enterpriseJournal, thesis, book Reference book

Assistant materialproduction (amylase,barm and so on)

Industry unionsData and report of enterprise

Energy (electricity,coal, natural gas, anddiesel oil)

Industry unionsRelated LCI data banks

Coproducts (CO 2 , DDGS) Data and report of enterpriseReference book

Combustion Data Experiment

Industry unions

E10 Blending Unit

Fuel Ethanol

E10

Gasoline

Utilities

Fig. 5. Unit of Blending denatured ethanol into gasoline.



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It can be seen that CO, NO X , CH4 and N2 O emissions areresulted from the burning of cassava haulm, while SO X , CO2emissions are mainly resulted from the production of chemicals.

3.1.2. Transport of dry cassava chipsIn this unit process, emissions are due to the cassava dry

chips distributed to ethanol plant by train or truck. In addition,emissions from the production of fuel, such as diesel oil,which is used in the transport of cassava dry chips, are in-cluded. Emissions from the transport of 1 ton cassava drychips are shown in Table 5 . It can be seen that, in this process,emissions are mainly resulted from the burning of fuel used bytrain.

3.1.3. Denatured ethanol conversionIn this unit process, environmental impacts are related to

several aspects, such as CO 2 which cannot be collected inthe ferment process, emissions from generating electricitywith methane, emissions from electric power used in dena-tured ethanol conversion, water pollution from the treatmentof wastewater in the production of ethanol, and emissionsfrom the fuel of industrial boilers for the production of steam.In this process, emissions from getting 1000 L Fuel ethanol areshown in Table 6 . It can be seen that air emissions and solid

waste are mainly due to coal burning, while water wastesare mainly from the treatment of wastewater for ethanolconversion.

3.1.4. Transportation of denatured ethanol In the unit process, the main emissions consist of air emis-

sions from the fuel burning and the production of fuel. Emis-sions are shown in Table 7 .

It can be seen that, in the process, emissions mainly re-sulted from the production of fuel used in the transportation.

3.1.5. The blending and burning of ethanol gasolineIn gas station, blend denatured ethanol into gasoline to pro-

duce E10 (10% by volume Fuel ethanol added to gasoline),and add it to tank of bus. In the unit process, power consump-tion is 0.7 kWh/1000 L. Emissions are shown in Table 8 .

In addition, the burning of Fuel ethanol causes some emis-sions. It is shown in Table 9 .

Table 3Energy and emissions allocation for cassava-based Fuel ethanol

Allocation method Allocation results (%)

Ethanol Coproducts

Market value 82.30 17.70Replacement value 81.57 18.43

Average 81.94 18.06

Table 4Emissions for cassava cultivation and treatment (g/ton chips)

Item VOC CO NO X PM10 SOx CH4 N2 O CO2 Solid

1 Chemical production 16 102 277 25 252 363 3 201,082 / 1.1 N 3 32 45 4 38 128 1 52,399 / 1.2 P2 O5 3 22 83 7 93 76 0 50,573 / 1.3 K 2 O 2 5 19 2 19 17 0 11,250 / 1.4 Multiple nutrient 2 13 27 2 27 50 0 23,860 /

1.5 Herbicide 6 32 102 9 75 91 1 63,000 /

2 Cassava plantation 40 144 440 24 29 58 200 188,614 a /

3 Transport 0 0 2 0 0 1 0 357 / 3.1 Chemical transport 0 0 1 0 0 0 0 170 / 3.2 Stem transport 0 0 0 0 0 0 0 26 / 3.3 Fresh cassava transport 0 0 0 0 0 0 0 80 / 3.4 Haulm 0 0 0 0 0 0 0 81 /

4 Haulm burning / 180,000 363,000 / / 15,000 21,000 / / 5 Cassava pre-treatment 0 0 0 0 0 0 0 97 5

Total 56 180,246 363,717 49 281 15,421 21,203 12,565 5a

CO2 is taken out of the atmosphere during growth of the cassava.

Table 5Emissions for the transport of cassava dry chips

Item Fuel production Transport Total

Highway Railway

25,943 mmBtu 13,918 mmBtu 12,025 mmBtu

Emission index g/mmBtu g/mmBtu g/mmBtu g/ton

VOC 8.183 4.737 12.729 2CO 13.224 19.273 32.594 4NO X 37.747 78.378 316.559 23PM10 2.702 1.634 8.117 1SO X 18.118 4.903 5.294 2CH4 102.221 14.188 15.693 12N2 O 0.245 0.308 0.332 0CO2 14,496 12,972 13,964 2,787



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It can be seen that, adding ethanol to gasoline increasesVOC emissions, while NO X , PM10 , CH4 and N2 O emissionsdo not change, but CO, SO X , CO2 emissions decrease.

3.1.6. Result Adding up emissions of all aforementioned processes,

we can get the overall emissions. Results are summarized inTable 10 .

Results in life cycle environment impact assessment showthat:

d 90% of VOC emissions are mainly related to the E10burning;

d 95% of CO emissions, over 99% of NO X emissions, almost96% of CH4 and 99% of N 2 O emissions are mainly relatedto the burning of the stem of cassava;

d 89% of SO X emissions are related to the coal burning inthe ethanol conversion process;

d 42% and 57% of CO 2 emissions are from the unit of dena-tured ethanol production and the unit of ethanol gasolineburning, respectively;

d PM10 emissions from E10 burning, coal burn in the ethanolconversion, the production of chemical used in cassavaplanting and cassavas planting have an overall incidentof 41%, 33%, 13% and 12%, respectively;

d Water pollution is related to the treatment of wastewater inthe production of ethanol; and

d Solid wastes are mostly related to the coal burning in theethanol conversion process.

3.2. Energy analysis

The calculation of energy ow in LCA should take into ac-count the feedstock energy and the process energy. Feedstock energy is dened as heat of combustion of raw material inputs,which are not used as an energy source, to a product system. Itis expressed in terms of higher heating value or lower heatingvalue. Process energy is dened as energy input required for

Table 6Emissions for denatured ethanol conversion

Item Category Ferment Electricity generatedfrom methane

Purchasedelectricity

Liquid wastetreatment

Coalcombustion

Total

120,100,503 L 20,473,469 kWh 228,313 kWh 1.08 109 L 1.33164 1012 Btu

Unit kg/1000 L g/kWh g/kWh mg/L g/10 6 Btu kg/year

Air emissions VOC / 0.0160 0.005 / 0.96 1607CO / 0.1999 0.041 / 96.10 132,073NO X / 0.2375 0.532 / 211.40 286,493PM10 / 0.0315 0.053 / 12.66 17,517SO X / 0.0028 1.268 / 600.23 799,637CH4 / 0.0263 0.004 / 1.12 2031N2 O / 0.0121 0.005 / 0.76 1261CO2 158 544 413.452 / 97,050 159,443,505

Water emissions BOD / / / 50 / 5400COD / / / 300 / 324,000HCN / / / 20 / 21,600Tannin / / / 70 / 75,600SS / / / 150 / 162,000

Solid waste / / 20.522 4631 6,171,474

Table 7Emissions for the transportation of denatured ethanol

Item Fuel production Transport Total

Highway Railway g/1000 L kg/year

13,120 mmBtu 5806 mmBtu 7314 mmBtu

Emissionsindex

g/mmBtu g/mmBtu g/mmBtu

VOC 8.183 0.247 1.105 1 117CO 13.224 1.004 2.830 2 200NO X 37.747 4.083 27.487 6 720PM10 2.702 0.085 0.705 0 41SO X 18.118 0.255 0.460 2 243CH4 102.221 0.739 1.363 11 1355N2 O 0.245 0.016 0.029 0 4

CO2 14,496 676 1212 1690 202,977

Table 8Emissions for the blending of ethanol gasoline

Item Electricity consumption:84,630 kWh

Total

Emissions index g/kWh g/1000 L kg/year

VOC 0.005 0 0CO 0.041 0 4NO X 0.532 0 45PM10 0.053 0 4SO X 1.268 1 107CH4 0.004 0 0N2 O 0.005 0 0CO2 413.452 291 34,990

Solid waste 20.522 14 1737



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a unit process to operate the process or equipment within theprocess excluding energy inputs for production and delivery of this energy [18].

3.2.1. Cassava cultivation and treatment

Energy consumption during this unit process includes en-ergy consumption for the production and transportation of fer-tilizers, herbicides, pesticides and so on, energy consumptionfor planting of cassava with mechanical tool using electricity,energy consumption for the treatment of cassava. The value of energy consumption in this unit process is shown in Table 11 .

3.2.2. Transport of dry chipsThe chips of cassava, which are treated by farmer, are dis-

tributed to ethanol plant by train and truck. Energy consump-tion during this stage is shown in Table 12 .

3.2.3. Denatured ethanol conversionThe style of energy consumption during this stage includes

electricity, steam and coal. The electricity is generated by thebiogas which is produced during the treatment of liquid water.And some steam is generated by boiler with coal. Energy con-sumption for each process step is shown in Table 13 .

3.2.4. Transport of denatured ethanol Denatured ethanol is distributed to gas stations by trains

and trucks. Energy consumption during this stage is shownin Table 14 .

3.2.5. Blending denatured ethanol into gasolineIn gas station, blend denatured ethanol into gasoline to pro-

duce E10 (10% by volume Fuel ethanol added to gasoline),and add it to tank of bus. In the process, power consumptionis 0.7 kWh/1000 L.

3.2.6. The total energy consumptionAdding energy consumption during all stages, it gets total

energy consumption for the entire life cycle of cassava-basedFuel ethanol. Total energy consumption and energy consump-tion for each process step are presented in Table 15 .

Table 9Emissions for the burning of ethanol gasoline

Item Emissions forgasoline

Emissions forethanol

Total(g/100 km)

Total(kg/year)

VOC 12.032 2.468 14.500 147,654CO 320.676 -99.988 220.688 2,247,266NO X 15.984 1.203 17.188 175,021PM10 1.918 0.144 2.063 21,002SO X 4.941 2.066 2.875 29,276CH4 4.883 0.368 5.250 53,461N2 O 1.628 0.123 1.750 17,820CO2 22,669 1356 21,313 217,025,643

Table 10Life cycle environmental impacts of cassava-based Fuel ethanol (kg/year)

Item Category Cultivation andtreatment

Denatured ethanolproduction

Transpor t Blending andburning

Total

Air emissions VOC 14,757 1607 548 147,654 164,567CO 46,864,230 132,073 1203 2,247,269 49,244,775NO X 94,566,825 286,493 6597 175,066 95,034,980PM10 12,827 17,517 232 21,007 51,582SO X 73,054 799,637 844 29,384 902,920CH4 4,009,670 2031 4393 53,461 4,069,556N2 O 5,512,720 1261 18 17,821 5,531,820CO2 3,359,848 159,443,505 927,509 217,060,633 380,791,495

Water emissions BOD / 5400 / / 5400COD / 324,000 / / 324,000HCN / 21,600 / / 21,600Tannin / 75,600 / / 75,600SS / 162,000 / / 162,000

Solid waste 1250 6,171,474 / 1737 6,174,461

Table 11Energy consumption during cassava cultivation and treatment stage

Num. Item Energy consumption(Btu/ton dry chips)

1 Chemical production 1,838,4691.1 N 811,7311.2 P2 O5 666,6921.3 K 2 O 148,5001.4 Multiple nutrient 129,2311.5 Herbicide 82,315

2 Plantation 115,208

3 Transport 18,9683.1 Chemical transport 83393.2 Stem transport 63463.3 Fresh cassava transport 4283

4 Cassava pre-treatment 2473

Total 1,975,118



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It can also be seen that cassava cultivation and treatmentand denatured ethanol conversion are the two most energyconsumed processes. The two unit processes consume 27%and 71% of the total energy, respectively. During the stageof cassava cultivation and treatment, the production of nitrog-enous fertilizer and phosphorus fertilizer consumes that of 11% and 9% energy, respectively. In this unit process, nitrog-enous fertilizer and phosphorus fertilizer are consumed as thefeedstock energy. During the process of denatured ethanol

conversion, 70% of the total energy is consumed to providesteam. In this unit process, coal is consumed as the process en-ergy. Life cycle energy consumption is shown in Fig. 6.

Results of life cycle energy consumption assessment showthat the unit process of denatured ethanol conversion is themost energy consumed process. Coal is the main primary en-ergy which is consumed in the whole life cycle.

3.3. Energy efciency analysis

The energy conversion efciency is a key indicator to eval-uate the eco-performance of a renewable energy source. It canbe likely dened as the heating value of 1 L ethanol equivalentto the energy used to produce it during all the life cyclephases.

h qethanol

LCA energy1

Where

qethanol The heating value of 1 L ethanol (Btu);

LCA energy The energy used to produce 1 L ethanol duringall the life cycle phases (Btu).

It can be seen that life cycle energy consumption to produce1 L Fuel ethanol is 15,722 Btu. While the heating value of ethanol is 20,079 Btu/L. Thus, the Fuel ethanol conversionefciency is 1.28.

3.4. Sensitivity analysis

The purpose of the sensitivity analysis is to estimate theeffects on the outcome of a study of the data. In the study,the inuence of increasing and decreasing some productionfactors by 10%, one at a time, was studied. The sensitivityanalysis results are shown in Table 16 .

From Table 16 , we can see that the results except SO X change little with the increasing and decreasing of these pa-rameters. We can also see that the system energy conversionchanges signicantly with coal consumption. The SO X emis-sion is mainly due to the combustion of coal in this system.Therefore, in order to improve the performance of SO X emis-sion and the energy efciency, it is necessary to decrease theuse of coal.

4. Discussion

4.1. Data quality

Because they are impossible to be collected in China, someof data applied in this study are cited from the GREET modeldeveloped at Argonne National Laboratory and Ford company.However, such data may be quite different from the reality inChina, and therefore detailed discussion for this differencemay be important. Because the control for the environment

Table 12Energy consumption for the transport of cassava dry chips

Transport mode Energy density(Btu/ton mile)

Distance(km)

Energyconsumption(Btu/ton)

Train 370 200 46,250Truck 1713 50 53,531Total (Btu/ton) 99,781

Table 13Energy consumption for ethanol conversion

Stage Electricity(kWh)

Stem(ton)

Coal(ton)

Milling and mixing 3,024,000 0 0Liquefaction and

saccharication1,296,000 72,000 0

Fermentation 4,190,400 0 0Distillation 2,424,000 230,400 0Post pre-treatment 7,047,000 79,200 0Supplementary equipment 1,980,000 7,200 72,000Denaturation 740,382 0 0Total 20,701,782 388,800 72,000Self-supply 20,473,469 388,800 0Net energy consumption 228,313 0 72,000Net energy consumption

(Btu/year)

1,334,049,843,715

Table 14Energy consumption for denatured ethanol transport

Transport mode Energyintensity(Btu/tonmile)

Distance(km)

Energyconsumption(Btu/1000 L)

Train tanker 370 350 64,264Tank truck 1028 100 51,015Total (Btu/1000 L) 115,279

Table 15Life cycle energy consumption of cassava-based Fuel ethanol

Stage Energy consumption(Btu/year)

Cassava cultivation and treatment 5.1353 1011

Transport of dry chips 2.5943 1010

Denatured ethanol conversion 1.3340 1012

Transport of denatured ethanol 1.3845 1010

Blending denatured ethanol into gasoline 8.8736 108

Total 1.8883 1012

(15,722 Btu/L)

Heating value of ethanol (Btu/L) 20,079



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and resource use in USA is advanced, the relative environmentreleases are quite lower than in China. Therefore, the environ-mental releases and energy efciency shown in the presentstudy may be better than the reality. With the developmentof technology in China, the difference may become smallerand smaller.

4.2. Allocation method

The allocation procedure in a multi-input/output process isone of the most critical issues in life cycle assessment. Use of different allocation approaches can have signicant impacts oncalculated biomass ethanol fuel-cycle energy use and energyefciency. In this study, market value and replacementmethods are used to allocate environmental emissions and en-ergy for the cassava-based Fuel ethanol system. Table 3 showsthat the allocating results by the two methods are approxi-mately the same.

4.3. Environmental emissions comparison

In this part, we compare E10 with gasoline on their mainemission indexes both in vehicle operation part and wholelife cycle.

- Low emissions during vehicle operation ( Table 17 );- Low life cycle VOC, CO, PM 10 , and GHGs; and- Reasonable increase of SO X and NO X emissions ( Table 18 ).

There are several factors for the higher emissions of someindexes. Firstly, the fuel for industrial boilers in China is coaland emissions from coal combustion are high in China, espe-cially SO X and PM 10 . Secondly, NO X and PM 10 emissionsfrom chemicals like fertilizers and herbicides are high duringthe cassava cultivation in China. Thirdly, many farmers di-rectly burn cassava stem for waste treatment, which causesparticles and gas emissions.

4.4. Potential capabilities to improve the environment

and energy performance

Regarding the results, we can see that it is possible to de-crease CO, NO X , CH4 , and N2 O emissions by using the stemeffectively, such as using it to generate biogas, instead of burn-ing it directly. We can also see that it is possible to decreaseSO X emissions by using low sulfur coal. Adopting the latestequipment in the unit process of ethanol conversion, we cancollect CO 2 as much as possible. It should be stressed outthat these high yields were obtained from unimproved wildpopulations and conventional cultural methods. This indicatesthe great biomass potentiality of this energy crop for thefuture.

5. Conclusion

The present study shows the results of an LCA performedupon cassava-based Fuel ethanol. Cassava cultivation andtreatment, transport of dry chips, denatured ethanol conver-sion, transport of denatured ethanol, blending denatured etha-nol into gasoline and E10 burning are checked. Severalconclusions were drawn from this study.

(1) The energy conversion efciency of Fuel ethanol is 1.28.Contribution of energy consumption from the unit of dena-tured ethanol conversion, its contribution to the total en-ergy consumption by 70%.

119

70

10

0

10

20

30

40

50

60

70

N Production P2O5Production

CoalConsumption

Other

Fig. 6. Energy consumption during life cycle of cassava-based Fuel ethanol.

Table 16Sensitivity analysis results of the system

Changed production factors VOC (%) CO (%) NO X (%) PM 10 (%) SO X (%) CH 4 (%) N2 O (%) CO 2 (%) h (%)

Use of fertilizer ( 10%) 0.25 0.005 0.007 1.26 0.72 0.23 0.09 0.03 2.47Use of fertilizer ( 10%) 0.26 0.005 0.007 1.26 0.23 0.23 0.09 0.03 2.53Cassava average yield (10%) -0.81 -0.012 0.018 2.26 0.73 0.24 0.09 0.002 2.47Cassava average yield ( 10%) 0.99 0.014 0.022 2.76 0.9 0.3 0.11 0.002 3.02Use of coal ( 10%) 0.078 0.026 0.03 3.27 8.85 0.004 0.002 3.39 7.05

Use of coal (10%) 0.078 0.026 0.03 3.27 8.85 0.004 0.002 3.39 7.05

Table 17Vehicle operation emission between E10 and gasoline (g/km)

Item VOC CO NO X PM10 SO X GHGs

Gasoline 0.207 5.517 0.275 0.033 0.085 400E10 0.232 3.531 0.275 0.033 0.046 351Increment (%) 12 36 0 0 46 12



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(2) Contribution of SO X emissions from the unit of denaturedethanol conversion is large, its contribution to the totalemissions by 89%. SO X emissions mainly result fromthe combustion of coal.

(3) Contribution of CO 2 emissions from the unit of denaturedethanol conversion is also very large. To collect CO 2 as co-products in the unit effectively is the available method toimprove the performance of CO 2 emissions.

(4) Contribution of CO, NO X , CH4 and N2 O emissions ismainly related to the burning of the stem of cassava,each contributing to the total emissions by 95%, 99%,96% and 99%, respectively. To use the stem to generatebiogas is the available method to improve the performanceof these emissions.

Acknowledgements

The authors are honored to acknowledge the fth frame-work program of the European Union for funding of Agricul-ture and small to medium scale industries in peri-urban areasthrough ethanol production for transport in China (ICA4-2002-10023).

Acknowledgement is also given to the National Natural

Science Foundation of China (50175070), Ministry of Agri-culture of China, Guangxi Development and PlanningCommittee, Guangxi Xintiande Energy Co. LTD., GuangxiSubtropical Crop Institute. The authors would like to acknowl-edge the efforts of Mr. Rongsheng Huang, Mr. Wei Wang, andMr. Yinong Tian, as well as other data providers.

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Table 18Life cycle emission between E10 and gasoline (g/km)

Item VOC CO NO X PM10 SO X GHGs

Gasoline 0.167 3.483 0.262 0.025 0.079 238.599E10 0.146 2.629 0.265 0.023 0.094 233.827Increment (%) 13 25 1 10 18 2


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03_Life Cycle Inventory and Energy Analysis