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Life cycle assessment of sugarcane ethanol and palm oil biodiesel joint production
b i o m a s s a n d b i o e n e r g y 4 4 ( 2 0 1 2 ) 7 0 e7 9
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Life cycle assessment of sugarcane ethanol and palm oil biodiesel joint production Simone Pereira Souza a, Ma´rcio Turra de A´vila b, Se´rgio Pacca a,* a b
Graduate Program on Environmental Engineering Science, School of Engineering of Sa˜o Carlos, University of Sa˜o Paulo, Brazil Brazilian Agricultural Research Corporation (Embrapa Soja), Brazil
article info
abstract
Article history:
Sugarcane (Saccharum spp.) and palm tree (Elaeis guianeensis) are crops with high biofuel
Received 29 November 2010
yields, 7.6 m3 ha1 y1 of ethanol and 4 Mg ha1 y1 of oil, respectively. The joint production
Received in revised form
of these crops enhances the sustainability of ethanol. The objective of this work was
30 March 2012
comparing a traditional sugarcane ethanol production system (TSES) with a joint produc-
Accepted 22 April 2012
tion system (JSEB), in which ethanol and biodiesel are produced at the same biorefinery but
Available online 30 May 2012
only ethanol is traded. The comparison is based on ISO 14.040:2006 and ISO 14044:2006, and appropriate indicators. Production systems in Cerrado (typical savannah), Cerrada˜o (woody
Keywords:
savannah) and pastureland ecosystems were considered. Energy and carbon balances, and
Biorefinery
land use change impacts were evaluated. The joint system includes 100% substitution of
Ethanol
biodiesel for diesel, which is all consumed in different cropping stages. Data were collected
Biodiesel
by direct field observation methods, and questionnaires applied to Brazilian facilities.
Life cycle assessment
Three sugarcane mills situated in Sa˜o Paulo State and one palm oil refinery located in Para
GHG emissions
State were surveyed. The information was supplemented by secondary sources. Results
Joint biofuels production system
demonstrated that fossil fuel use and greenhouse gas emissions decreased, whereas energy efficiency increased when JSEB was compared to TSES. In comparison with TSES, the energy balance of JSEB was 1.7 greater. In addition, JSEB released 23% fewer GHG emissions than TSES. The ecosystem carbon payback time for Cerrado, Cerrada˜o, and Degraded Grassland of JSEB was respectively 4, 7.7 and 7.6 years. These are typical land use types of the Brazilian Cerrado region for which JSEB was conceived. ª 2012 Elsevier Ltd. All rights reserved.
1.
Introduction
According to the Energy Information Administration (EIA), in 2007 the global liquid fuel production was 13 hm3d1 of which 53% was used for transport. Projections for 2035 indicate a 240% increase in the production of biofuels, and a significant contribution comes from Brazil, where production reaches 210 dam3 d1 in 2035 [1]. Brazil is the second largest ethanol producer in the world responsible for 37 percent (24 hm3) of the global annual production (65.6 hm3) [2,3]. Brazilian ethanol is produced out
of sugarcane, and on average, each hectare of sugarcane yields 80 tonnes of sugarcane, 7.6 m3 ha1 y1 of ethanol [4], 12 t of bagasse (dry basis), and 72e90 m3 ha1 y1 of stillage (liquid effluent of the distillation process). Bagasse combustion fuels cogeneration systems that meet all energy demand of sugar mills. Thus, the direct energy cost of the industrial phase is related to this co-product [5,6]. Although increasing biofuels consumption is supported by energy security and regional development goals, it is undeniable the appeal of this renewable energy carrier because of its greenhouse gas mitigation potential [7]. Nevertheless, the
* Corresponding author. Tel.: þ55 11 3091 8173. E-mail addresses: [email protected] (S.P. Souza), [email protected], [email protected] (S. Pacca). 0961-9534/$ e see front matter ª 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2012.04.018
b i o m a s s a n d b i o e n e r g y 4 4 ( 2 0 1 2 ) 7 0 e7 9
sustainability of sugarcane ethanol is entangled with several factors such as greenhouse gas and energy balance, land and water use, biodiversity loss, employment and income generation, which are extensively discussed in the literature [8e11]. Biodiesel is another biofuel that has been used to meet transportation needs. In 2008, the global biodiesel production was 45.8 dam3 d1, which means a 52% increase in comparison to the previous year [12]. Biodiesel is produced by the reaction between vegetable oil or tallow and ethanol or methanol in the presence of a catalyst. In general, the catalyst used is either potassium hydroxide or sodium hydroxide. This process, which is known as transesterification, produces biodiesel and glycerin [13,14]. Several crops are used to produce vegetable oil. Palm tree is a perennial crop with an average 26 year lifetime [15]. Oil and other co-products are extracted from fresh fruit bunches (FFB) of the palm tree. FFB processing yields, on mass basis, 20e21% of palm oil, 1.7% of kernel oil, 3.5% of kernel cake, 22e23% of empty fruit bunches (EFB), 12e15% of fibers, 5e7% of shells and 50% of palm oil mill effluent (POME) [16]. The POME effluent major sources are: steam and water used in the extraction processes and washing activities of the mill [17]. Therefore, due to the addition of water the total mass yield is greater than 100%. Shells and fibers, which are co-products of vegetable oil extraction, are usually burned for steam and for electricity generation in cogeneration systems. Each tonne of fibers and shells is able to produce 11.5 GJ and 18 GJ of energy on a dry basis (LHV), respectively [18]. Palm biodiesel production is energetically self-sufficient due to the power generation potential of its coproducts [15]. Besides that, the empty fruit bunch can also be used to produce energy; each tonne yields 7.8 GJ [16]. Focusing on the improvement of sugarcane ethanol life cycle, the aim of this study is comparing a traditional sugarcane ethanol production system in Brazil (TSES), with a joint production
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system of sugarcane ethanol and palm oil biodiesel (JSEB). In the latter, biodiesel substitutes for 100% of diesel used in tractors and other machinery required to cultivate sugarcane.
2.
Biofuels joint production Design
The joint production of sugarcane ethanol and palm oil biodiesel portrayed in this study comprises: Use of stillage and filter cake, which are co-products resulting from sugarcane’s processing, for irrigation and organic fertilization. Use 100% of sugarcane bagasse, shells, and fibers from palm tree FFB for steam and electricity generation, which fuels the energy demand of the industrial and the agricultural phases, and yields surplus energy. Use of sugarcane ethanol for oil transesterification (ethyl route) to produce biodiesel. Use of POME and empty bunches resulting from FFB processing, for irrigation and organic fertilization. Due to the water requirement of palm trees, the cultivation on the Cerrado region (Brazilian savannah) needs complementary irrigation. The development of irrigated palm trees in the Cerrado biome was assessed by Embrapa Cerrados [19]. Total displacement of diesel used in transportation, harvesting and other cropping stages by biodiesel without engine replacement [20,21]. The resulting products of the JSEB are: sugarcane ethanol, surplus electricity, glycerin, palm kernel oil, and palm kernel cake. All biodiesel is self consumed by the system. The set up of the system is important to determine GHG emissions allocation, and energy consumption (Fig. 1).
Fig. 1 e Joint production system of sugarcane ethanol and palm oil biodiesel.
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3.
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Methodology
The assessment is based on a life cycle assessment (LCA), according to the guidelines established by ISO 14.040:2006 and ISO 14044:2006. Three LCA’ studies were carried out in parallel, one for the traditional sugarcane ethanol system, another for a palm oil biodiesel system, and another for the joint production system of sugarcane ethanol and palm oil biodiesel. All “well to gate” assessments consider Brazilian underlying conditions; however, the distribution phase of ethanol to the gas station is ignored because it is similar independently of the fuel type. Besides that, the transportation of inputs to the processing units is not assessed because their source varies, and their contribution to the overall emissions is minimal. The life cycle of the traditional system was divided in nine steps. The agricultural stage comprises five sub-systems (Fig. 2), and the industrial stage comprises four sub-systems (Fig. 3). The life cycle of the joint system is similar to the traditional system, but with the replacement of diesel by palm oil biodiesel, and considering the flows shown in Fig. 1. Two scopes describing the life cycle of ethanol were modeled. In scope 1, the function of the system was producing sugarcane ethanol in a traditional system configuration. For scope 2, the system function is ethanol production in a joint system with a palm oil ethyl based biodiesel refinery. The biodiesel is fully consumed in the life cycle of this joint production system. We have assumed that the two scenarios were deployed on Cerrado (typical savannah), Cerrada˜o (woody savannah), and degraded pasture land, which represent the most common land use types of the central Brazilian plains. Regarding land use change impacts, sugarcane expansion historically occurred outside the Amazonian forest, and moreover, an Environmental Impact Assessment Report has to be approved prior to the installation of any new ethanol plant [22]. Therefore, massive deforestation and large carbon debts due to the expansion of sugarcane plantations are unlikely to occur. The functional unit (FU) was based on 7.55 m3 of ethanol, and corresponds to a reference flow of 1 ha of sugarcane for the traditional system, and 1.12 ha of sugarcane plus 0.14 ha of palm trees for the integrated system, because ethanol is used for biodiesel transesterefication. Based on field observations, the power generation system was based on two boilers with 6.6 MPa each, with a combined
Seeds
Production and use of agricultural inputs
output of 500 Mg h1of steam. One tonne of sugarcane yields 0.555 Mg of steam, at 6.6 MPa and 480 C. The power output was 78 kWh Mg1of sugarcane, or 312 kWh Mg1 of bagasse (wet basis). Assuming a low heating value (LHV) of 7.18 GJ Mg1 for the bagasse, the energy production is 43.5 kWh GJ1, which is enough to supply the energy required by the mill itself, and moreover, yields 79% of surplus electricity. Surplus electricity accounted for 11% of the total energy output (ethanol plus surplus electricity). Thus, part of the ethanol life cycle emissions (agricultural and industrial stages) was proportionally allocated to surplus electricity. For energy generation in the palm biodiesel industrial phase the LHV considered for fibers and shells (dry basis) were respectively 11.5 GJ Mg1 and 18 GJ Mg1 [18]. Considering moisture content (65% for fiber and 35% for shell), the available fuel energy of these co-products is 2.76 GJ Mg1of FFB. Steam to fuel input ratio is 65.7%, which corresponds to steam energy of 1.71 GJ Mg1 of FFB (660 kg of steam at 300 kPa) [18].
3.1.
Inventory sources
The ethanol life cycle inventory (LCI) was based on data collected from three mills located in the State of Sao Paulo on areas with characteristics similar to the Cerrado region (Brazilian savannah). Due to the actual sugarcane processing technology and the similarities between different mills, we believe that these case studies could provide evidences on the joint production of ethanol and biodiesel that can be further extended to other mills on the Brazilian Cerrado region. Besides that, according to CONAB, 60% of the new mills will be installed on the Cerrado biome [23]. In the assessment we have considered that 60% of the sugarcane is burned before harvesting and 40% is green harvested. In the case of palm biodiesel, data were collected at Agropalma Company, located on the State of Para in the northern Brazilian region, since there is no experience in commercial production of palm oil on the Cerrado. Details of the life cycle inventory of sugarcane ethanol and palm oil biodiesel are presented in Appendix A, B and C. Palm trees irrigation at the nursery varies between 0.073 and 0.187 m3 ha1 over 12 months. The fertilizer application for N, P, K was 130 g ha1 and Mg was 20 g ha1. According to Embrapa Cerrados, the complementary irrigation of palm trees corresponds to a daily volume of 0.166 m3 per
Cropping practices
Harvesting and Transportation
Manufacture and maintenance of machineries and agricultural implements
Sugarcane System Boundary
Fig. 2 e Agricultural sub-systems considered for the traditional system sugarcane ethanol life cycle.
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Co-products disposal and transportation
Manufacture and maintenance of equipments and industrial construction
Manufacture and use of chemicals inputs
Co-products energy generation
Sugarcane processing
System Boundary
BIOETHANOL
ELECTRICITY
Fig. 3 e Industrial sub-systems considered for traditional system sugarcane ethanol life cycle.
tree during 134 days per year, which results in 3180 m3 ha1 y1 of water, considering 143 plants per hectare [19]. In order to estimate the energy balance and GHG emissions, the energy intensity indicators and GHG emission factors were extracted from life cycle databases in Simapro and Ecoinvent softwares and previously published studies (Annex A). Emissions from sugarcane trash burning which include N2O and CH4 were calculated according to the IPCC Guidelines for National Greenhouse Gas Inventories based on the “Emissions from Managed Soils” section [24]. Both CH4 and N2O emissions due to fiber and shell were assessed according to the IPCC Guidelines for National Greenhouse Gas Inventories based on the “Stationary Combustion” section [25]. During stillage disposal through furrows 0.2% of the carbon content in stillage is emitted as CH4 due to the action of methanogenic soil microorganisms. This estimation is based on the soluble carbon content in stillage of 1%e2% (volume basis) [26]. Besides CH4 emission, 1% of the nitrogen content in stillage and filter cake is emitted after irrigation [24]. Nitrogen contents as N are 280 g m3 of stillage and 5.5 g kg1 of filter cake [26]. The methodology to determine energy demand and GHG emission due to manufacturing and maintenance of tractors, trucks, and agricultural implements was adapted from previous studies [27,28]. The total mass of various machines was collected from manufacturer catalogs, and the lifetime adopted was 5 years for tractors, harvesters, infield wagons, loaders, tows, and 8 years for other equipment. For sugarcane ethanol industrial equipment and construction, the total cement and steel used in a typical ethanol plant, and equipment maintenance energy were estimated according to a previous study [27]. A crushing capacity of 2.0 Tg y1of sugarcane was considered. For palm biodiesel the total steel consumed in a typical plant was based on data in the literature [29] and corresponds to a production capacity of 102 Gg y1 of biodiesel.
3.2. Life cycle greenhouse gas emissions and energy balance Greenhouse gas emissions were quantified for the 100 year CO2e (mass of carbon dioxide equivalent) using CH4 ¼ 23, and N2O ¼ 296 [30].
The following processes were accounted for in order to quantify emission reductions: fossil fuel displaced by palm oil biodiesel in ethanol life cycle e transportation and cropping; gasoline displaced by ethanol and diesel displaced by biodiesel; and grid electricity displaced by surplus electricity based on the GHG of the Brazilian energy mix [31]. Two energy efficiency indicators (EEI) were applied: the net energy ratio (NER), and the renewable energy efficiency (REE). The NER is given by the ratio between the renewable energy output and fossil energy input, as shown in equation (1): NER ¼
Eout;renewable Ein;fossil fuel
(1)
Where, the net renewable energy output, Eout,renewable, includes the total renewable energy produced in biofuel life cycle, which encloses the surplus electricity produced from the co-products (bagasse, fiber, and shell), and the energy content of biofuels (low heating value (LHV) are considered). All values are reported in MJ ha1 y1. The net fossil energy input, Ein,fossil fuel, includes the total fossil energy consumed, MJ ha1 y1. The REE proposed by Sheehan and collaborators [32] and Malc¸a and Freire [33] is given by equation (2): REE ¼
Eout;renewable Ein;fossil Eout;renewable
fuel
(2)
Energy efficiency is related to the ratio between the difference of the net energy output, Eout,renewable (MJ ha1 y1) minus the net energy input from fossil primary energy (MJ ha1 y1) and the output energy (MJ ha1 y1). If the result is between 0 and 1, the fuel is renewable. This renewability is greater if the value is closer to 1 and the fuel is non-renewable for values below zero.
3.3.
Greenhouse gas emission from land use change
Emissions from direct Land Use Change (LUC) were calculated based on the carbon stock on aboveground and belowground of the displaced ecosystem e Cerrado, Cerrada˜o and degraded pasture e and the carbon stock of the biofuel crop e sugarcane and palm trees. The values used are presented in Table 1. The total carbon stock on aboveground and belowground of palm trees is 72 t ha1 [34].
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Table 1 e Above and belowground carbon stock. Ecosystem
Above carbon stock (Mg ha1)
Below carbon stock (Mg ha1)
Total carbon (Mg ha1)
Source (above; below)
33.5 25.5 e 17.0 17.5 e
13.4a 10.2a e 3.08b 3.45b e
46.9 35.7 1 20.08 20.95 72.00
[30,41] [30,41] [34] [41,42] [41,42] [34]
Cerrada˜o e woody savannah Cesrrado e typical savannah Degraded pasture Burned sugarcane Unburned sugarcane Palm
a According to IPCC [30], we added 40% of belowground biomass to the aboveground biomass, which corresponds to the mass of roots. b Dry-root mass in the area without burning is 5.1e7.2 Mg ha1 and in the area with burning is 6.1e7.7 Mg ha1 [42]. According to IPCC [30], the carbon fraction of dry matter is 0.5 Mg (Mg dry mass)1.
The difference between the carbon stocks per hectare in the ecosystems was divided by the time frame adopted in the LCA. The period of analysis considered was 30 years, which is the lifetime of the palm trees. It was considered that 40% of the sugarcane is harvested unburned. The annualized GHG emission due to the land use change is given by equation (3): GHGLUC
tC ha$yr
¼ ðCde Cbe Þ $
1 : tet
(3)
Where, Cde is the carbon stock of the displaced ecosystem, Mg ha1; Cbe is the carbon stock of the bioenergy ecosystem, Mg ha1. For traditional system the Cbe is given by ½ðCbs $fb Þ þ ðCus $fu Þ, where Cbs and Cus are the carbon stocks of burned sugarcane and unburned sugarcane, respectively, Mg ha1; fb and fu are the percentage of burned sugarcane and unburned sugarcane, respectively, 60% and 40%; and tet is the period of analysis in years. The GHG emissions of the integrated system are calculated based on the GHGLUC from traditional sugarcane and the palm tree systems. Therefore, GHG emissions of the integrated system correspond to 94% of the GHGLUC of the traditional sugarcane system plus 6% of the GHGLUC from palm tree system. The percentage 6% is related to the area of palm trees that is required to supply the biodiesel demanded in 1 ha of the integrated system (palm trees plus sugarcane), which was estimated according to the diesel consumption identified in this study. A total GHG emissions scenario, including the LUC effects, is discussed in the results. The presented values take into account the Cerrada˜o biome because it reflects the worst case scenario (the highest carbon content and emissions). This scenario is responsible for greater emissions than scenarios considering indirect land use change effects. Nevertheless, the deforestation of an area is bounded by Brazilian legislation, which prevents the total biome removal. Results considering Cerrado biome and degraded pasture are presented on Table 3. These alternative scenarios yield lower emissions.
In this study, we adapted a method from the literature [34] (Equation (4)). ECPTðyearsÞ ¼
ðCde Cbe Þ GHGLCA;g GHGLCA;e
Where GHGLCA;g , is the mass of carbon, Mg ha1 y1,which is calculated by the total emission factor of gasoline, Mg MJ1 g , (Annex A), multiplied by the energy output of ethanol in terms of its low heating value (LHV), MJe ha1 y1, (Annex A and Appendix A). Therefore, the GHGLCA;g term corresponds to the life cycle GHG emission of gasoline, considering the same energy content of ethanol (LHV). The term GHGLCA;e corresponds to the life cycle GHG emissions of ethanol (Appendix E). The numerator of equation (4) was described in equation (3).
4.
Results and discussion
4.1.
Energy input
Total energy consumed in the TSES life cycle was 20 GJ ha1 y1. The agricultural phase was responsible for 96% of the total energy demand of the traditional sugarcane ethanol life cycle (Fig. 4). The major contribution (48.5%) was associated with fossil fuel used in “Harvesting and Transportation”, “Transportation and Disposal of Co-products” and “Cropping Practices” subsystems, which accounted for 24%, 16.5% and 8% of the total energy demand in agriculture, respectively. The energy demand of agricultural inputs
Table 2 e Avoided emissions due to surplus power electricity from cogeneration system.
Surplus Electricity
a,b
Avoided Emissions
3.4.
Ecosystem carbon payback time
The Ecosystem Carbon Payback Time (ECPT) determines the period required to compensate the carbon stock deficit resulting from LUC. Besides, it takes into account avoided emissions due to the substitution of biofuels for fossil fuels.
(4)
Electricity emissionc
1
1
GJ ha year g kWh1 of CO2e g kWh1 of CO2e % g kWh1 of CO2e
a LCA total emission (ethanol electricity)1. b 1 kWh ¼ 0.0036 GJ [43]. c Brazilian electricity mix [31].
output
TSES
JSEB
19.8 64.6 8.3 11% 73.0
19.8 49.9 23.1 32%
energy
þ
surplus
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Table 3 e GHG life cycle emissions including land use change effects in terms of CO2e (Mg haL1 yL1) Replaced biome
TSES
Palm oil
JSEB
LCA Cerrada˜o (LUC) Total (LUC þ LCA) Cerrado (LUC) Total (LUC þ LCA) Degraded Pasture (LUC) Total (LUC þ LCA)
3.23 3.24 6.47 1.87 5.10 2.37 0.86
1.54 3.07 1.53 4.44 2.9 8.68 7.14
2.5 2.84 5.34 1.47 3.97 2.77 0.27
contributed with 40%, out of which 20% and 10% are attributed to nitrogen and herbicide, respectively. For JSEB, 94% of the total energy demand in sugarcane ethanol life cycle was related to the agricultural stage. However, due to the displacement of diesel, the greatest contribution is attributed to nitrogen and herbicide which accounted for 34% and 18% of the total energy demand, respectively. Consequently, the substitution of palm oil biodiesel for diesel results in a 84% reduction of the agricultural fuel demand (cropping practices, harvesting, transportation and co-products disposal). Energy consumed for seed production was estimated scaling down the total demand of the sugarcane life cycle. It was considered that 12 tonnes of sugarcane seeds per hectare are required over the 6 year adopted cycle, which equates to 2 Mg ha1 y1 of sugarcane. The life cycle energy demand of the industrial subsystem, manufacture and maintenance of trucks, harvester, infield wagon, tows, loaders, tractors, and agricultural implements was not significant. Palm oil transesterification was based on the use of anhydrous ethanol, and this input contributed only to 0.0001% of the total life cycle energy demand. According to Pimentel and Patzek [35], the energy demand for the conversion of hydrous ethanol into anhydrous ethanol is only 38 MJ m3 of product. Thus, the energy demanded for such conversion is negligible because the amount required is only 310 g of anhydrous ethanol for 1 kg of palm oil [29]. The total energy consumption of the JSEB life cycle was 11.6 GJ ha1 y1, which is 42% lower than the TSES life cycle
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energy consumption. A detailed list of energy inputs in the assessed systems is presented in Appendix D. Bagasse burning in the cogeneration system supplies a power demand of 5.16 GJ ha1 y1 to both systems. Because this energy is supplied by bagasse produced in the ethanol life cycle, it is not added to the total energy demand. Energy output is based on the heat content of systems’ products, which comprise sugarcane ethanol and surplus electricity. The energy output is fixed, independently of the system type (JSEB or TSES). Annual electricity generation equals 25 GJ ha1 y1. Because the industrial stage energy demand is 5.2 GJ ha1 y1, surplus electricity equates to 19.8 GJ ha1 y1. Total energy output of either system was 180 GJ ha1 y1.
4.2. Net energy ratio (NER) and renewable energy efficiency (REE) The NER of TSES was 9, which means that for each unit of energy consumed to produce sugarcane ethanol 9 units of energy were obtained. When TSES is compared to JSEB, the NER increases 6.5 units, which is due to high reduction in fossil fuel consumption in the agricultural stage. Macedo and collaborators [36] estimated a NER of 1:9.3 for sugarcane ethanol, which can reach up to 1:11.6 with more efficient boilers. Boddey and collaborators [27] estimated a NER of 1:9.07; however, the considered diesel consumption is 60% lower than the value of this work. The fuel REE of the JSEB and TSEB were similar. The nonrenewability in the TSES is 7% while in the JSEB is 3%. Thus, the difference between the systems is minimal if this indicator is considered.
4.3.
Greenhouse gas emissions
Total CO2 emissions for the TSES lifecycle were 3.23 Mg ha1 y1 or 428 kg m3 of ethanol, ignoring the allocation of surplus electricity and LUC effects (Appendix E and Fig. 5). Fig. 5 shows total emissions considering LUC effects to demonstrate the effect on LCA emissions when this variable is
Fig. 4 e Energy input of the traditional ethanol production system (TSES) and the joint production system (JSEB).
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Fig. 5 e Final ethanol life cycle GHG emissions for traditional system and joint system with and without LUC effects.
considered. However, details of the LUC scenarios are presented in the next session. Excluding LUC emissions, fossil fuel consumed in harvesting (40% of the sugarcane is mechanically harvested), sugarcane transportation, cropping practices, and co-product disposal stages accounted for 25% of the total life cycle emissions. Agricultural inputs such as nitrogen and limestone accounted for 14% and 11% of emissions, respectively. These emissions are attributed to the mineralization of nitrogen and carbon contained in fertilizer and limestone. Emissions attributed to the use of co-products such as stillage and filter cake accounted for 8.6% and 1.7%, respectively. They are both due to methane and nitrogen volatilization. Other emission sources attributed to the agricultural stage are due to the manufacturing of pesticides and agricultural machinery, which contributed to 3.2% and 0.6%, respectively. All values are not including LUC effects. GHG emissions for seed production were estimated scaling down total life cycle emissions of sugarcane. A detailed list of GHG emissions of the assessed systems is presented in Appendix E. For the industrial stage, the GHG emissions accounted for 12% of the total lifecycle emissions, out of which, 9% are related to bagasse burning for cogeneration. Emissions from equipment manufacturing, construction, and industrial inputs were minimal. Considering the allocation, surplus electricity accounted for 11% of the total electricity generated, which corresponds to 356 kg ha1 y1 of total CO2e emissions (Table 2). Therefore, when allocation due to electricity surplus is considered the CO2e emission for TSES is reduced to 0.38 Mg m3 of ethanol. Recent studies published by the “California Air Resources Board” [37] and “Environmental Protection Agency” [38] evaluated the GHG emissions for sugarcane ethanol produced in Brazil. Life cycle emissions of sugarcane ethanol reported by CARB [37] were 26.6 g of CO2e per MJ, without taking into account allocation, transport, and fuel distribution. These emissions ignore surplus electricity from burning bagasse and assume that all sugarcane is burned, that is, no mechanical
harvesting takes place. EPA [38] evaluated sugarcane ethanol emissions based on different scenarios of energy production from co-products and the result was 42 g of CO2e per MJ, considering the use of straw for energy generation and land use change emissions. Different authors presented LCAs without considering LUC effects. Macedo and collaborators [36] and Oliveira and collaborators [39] determined 20 and 24.4 g of CO2e per MJ, respectively. Boddey and collaborators [27] showed the lowest value among these studies, 15 g of CO2e per MJ. In comparison, without considering LUC effects, our study renders a value of 18 g of CO2e per MJ. The agricultural stage of the JSEB was responsible for 84% of the total emissions of the ethanol life cycle. The largest contribution is related to fertilizers, sugarcane straw burning, and methane volatilization from stillage. The displacement of fossil fuel by biodiesel yields 90% reduction in emissions, which include cropping, harvesting, and transportation of sugarcane and its co-products. The industrial subsystem was responsible for 15.6% of the total emissions, and the largest contribution is related to bagasse burning, 12%. These emissions are related to CH4 and N2O. For a LHV of 7.8 GJ kg1 the emissions of CH4 and N2O are 0.215 and 0.029 kg Mg1 of bagasse, respectively [25]. The emissions related to the burning of shells and fibers are not included in this subsystem because they were already included in the biodiesel life cycle. Total CO2e emissions of JSEB life cycle were 2.5 Mg ha1 y1 or 0.352 Mg m3 of ethanol, ignoring surplus electricity allocation (Appendix E). The reduction in life cycle GHG emissions for JSEB, in comparison to the traditional system, was 23%. Considering emissions allocation, in which the surplus electricity is responsible for 0.27 Mg ha1 y1, the final CO2e emission of ethanol for the JSEB is 0.314 Mg m3.
4.4.
GHG emission due to land use change
When LUC emissions are included in the analysis, they are responsible for 50% and 53% of all life cycle CO2e emitted in
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the TSES and JSEB, respectively (Fig. 5). Fig. 5 shows only emissions for Cerrada˜o biome because it represents the worst case scenario as explained in the methodology. Details for other ecosystems’ LUC effects are presented on Table 3. Considering an average between Cerrado and Cerrada˜o biomes, emissions due to LUC for the TSES and JSEB, ignoring the electricity allocation, increased about 1.8 times the life cycle emissions of ethanol. Displacing degraded pastureland reduced life cycle emissions because the carbon incorporated in the sugarcane ecosystem is greater than the carbon stock of the degraded pastureland (Table 3). The emission due to land use change is higher in the TSES because each hectare in this system has just sugarcane whereas each hectare in the JSEB has 6% of palm plantation (see item 3.3). As the palm has more carbon than the evaluated biomes, the little bit of palm area in the ecosystem gives a positive response in the LUC emission.
4.4.1.
Ecosystem carbon payback time
The Ecosystem Carbon Payback Time (ECPT) of the TSES was 9.5 years for Cerrada˜o and 5.5 years for Cerrado displacement. For degraded pasture no emission due to LUC was noticed. Fargione and collaborators [40] estimated an ECPT of 17 years for the displacement of Woody Cerrado (which includes Cerrado and Cerrada˜o) by sugarcane cultivation considering soil carbon, aboveground and belowground biomass. Gibbs and collaborators [34] estimated 12 years, considering Cerrado displacement and above and belowground biomass carbon stocks. In comparison to TSES, the JSEB reduced the ECPT by 27% in the Cerrado case. Considering the Cerrada˜o displacement, 18% of reduction was achieved by JSEB in comparison to the traditional system. For the degraded pasture, there is no carbon debt in either one of the systems. That is, carbon returns to the ecosystem immediately after the sugarcane plantation is established. Certainly the most influential factor for ECPT is the land use change scope. Among the types of biomes the ECPT due to Cerrada˜o displacement was almost two times greater than for Cerrado, in either system.
4.5.
Other considerations
Excluding LUC effects, life cycle GHG emissions of sugarcane ethanol were on average 76% lower than gasoline emissions considering TSES. Considering JSEB, the avoided emissions were 81% of gasoline emissions. The avoided emissions were 88% when diesel is displaced by palm biodiesel, reflecting the results of JSEB. Surplus electricity generation is also an important factor to estimate the avoided emissions due to displaced energy from the Brazilian grid. For TSES the surplus electricity was 19.8 GJ ha1 y1 with related CO2e emissions of 65 g kWh1. 11% reduction was achieved in relation to emission from Brazilian electricity system. Avoided CO2e emissions were more expressive for JSEB. The surplus electricity contributed to 50 g kWh1, which corresponds to 32% of reduction. In short, reductions provided by JSEB were up to 20% higher than avoided emissions by the traditional system (Table 2).
5.
77
Conclusion
The objective of this work was comparing a traditional sugarcane ethanol production system with a joint production system. The propose was evaluating the GHG balance when synergy between sugarcane and palm oil processing refineries is established, including the replacement of biodiesel for diesel and transesterification via an ethanol route (usually methanol is adopted). The LCA of JSEB demonstrates that such alternatives focusing on the sustainability of biofuels might reduce GHG emissions, improve the energy balance, and minimize land use change impacts. The energy balance for traditional sugarcane ethanol system was 1:9 (input:output). The average energy balance of the JSEB was 1:15.5, which corresponds to an increase of 6.5 units in the output energy for each unit in input energy, when JSEB is compared to the traditional system. Life cycle CO2e emissions of ethanol based on the traditional system was 20.2 g MJ1, without LUC emissions. In comparison, CO2e emissions of ethanol produced by the JSEB were 15.6 g MJ1, a 23% reduction in life cycle emissions when compared to the traditional system. For an average between the systems, the displacement of the Cerrado and Cerrada˜o added to the ethanol life cycle CO2e emissions 0.23 and 0.41 Mg m3, respectively. In contrast, the replacement of degraded pasture has contributed to GHG life cycle emission reductions and greater ecosystem carbon stock. The land use change analysis for TSES and JSEB identified that when emissions due to land use change is considered in ethanol sugarcane life cycle, the total emissions increase 1.8 times, considering an average between Cerrado and Cerrada˜o biomes.
Acknowledgments The authors would like to thank the Brazilian National Council for Scientific and Technological Development (CNPq) for the scholarship, Agropalma employees for their interest and patience with this study, Dr. Anand Gopal, Dr. Ralph P Overend, and other 2 blind reviewers for their suggestions.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.biombioe.2012.04.018.
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Available online at www.sciencedirect.com
http://www.elsevier.com/locate/biombioe
Life cycle assessment of sugarcane ethanol and palm oil biodiesel joint production Simone Pereira Souza a, Ma´rcio Turra de A´vila b, Se´rgio Pacca a,* a b
Graduate Program on Environmental Engineering Science, School of Engineering of Sa˜o Carlos, University of Sa˜o Paulo, Brazil Brazilian Agricultural Research Corporation (Embrapa Soja), Brazil
article info
abstract
Article history:
Sugarcane (Saccharum spp.) and palm tree (Elaeis guianeensis) are crops with high biofuel
Received 29 November 2010
yields, 7.6 m3 ha1 y1 of ethanol and 4 Mg ha1 y1 of oil, respectively. The joint production
Received in revised form
of these crops enhances the sustainability of ethanol. The objective of this work was
30 March 2012
comparing a traditional sugarcane ethanol production system (TSES) with a joint produc-
Accepted 22 April 2012
tion system (JSEB), in which ethanol and biodiesel are produced at the same biorefinery but
Available online 30 May 2012
only ethanol is traded. The comparison is based on ISO 14.040:2006 and ISO 14044:2006, and appropriate indicators. Production systems in Cerrado (typical savannah), Cerrada˜o (woody
Keywords:
savannah) and pastureland ecosystems were considered. Energy and carbon balances, and
Biorefinery
land use change impacts were evaluated. The joint system includes 100% substitution of
Ethanol
biodiesel for diesel, which is all consumed in different cropping stages. Data were collected
Biodiesel
by direct field observation methods, and questionnaires applied to Brazilian facilities.
Life cycle assessment
Three sugarcane mills situated in Sa˜o Paulo State and one palm oil refinery located in Para
GHG emissions
State were surveyed. The information was supplemented by secondary sources. Results
Joint biofuels production system
demonstrated that fossil fuel use and greenhouse gas emissions decreased, whereas energy efficiency increased when JSEB was compared to TSES. In comparison with TSES, the energy balance of JSEB was 1.7 greater. In addition, JSEB released 23% fewer GHG emissions than TSES. The ecosystem carbon payback time for Cerrado, Cerrada˜o, and Degraded Grassland of JSEB was respectively 4, 7.7 and 7.6 years. These are typical land use types of the Brazilian Cerrado region for which JSEB was conceived. ª 2012 Elsevier Ltd. All rights reserved.
1.
Introduction
According to the Energy Information Administration (EIA), in 2007 the global liquid fuel production was 13 hm3d1 of which 53% was used for transport. Projections for 2035 indicate a 240% increase in the production of biofuels, and a significant contribution comes from Brazil, where production reaches 210 dam3 d1 in 2035 [1]. Brazil is the second largest ethanol producer in the world responsible for 37 percent (24 hm3) of the global annual production (65.6 hm3) [2,3]. Brazilian ethanol is produced out
of sugarcane, and on average, each hectare of sugarcane yields 80 tonnes of sugarcane, 7.6 m3 ha1 y1 of ethanol [4], 12 t of bagasse (dry basis), and 72e90 m3 ha1 y1 of stillage (liquid effluent of the distillation process). Bagasse combustion fuels cogeneration systems that meet all energy demand of sugar mills. Thus, the direct energy cost of the industrial phase is related to this co-product [5,6]. Although increasing biofuels consumption is supported by energy security and regional development goals, it is undeniable the appeal of this renewable energy carrier because of its greenhouse gas mitigation potential [7]. Nevertheless, the
* Corresponding author. Tel.: þ55 11 3091 8173. E-mail addresses: [email protected] (S.P. Souza), [email protected], [email protected] (S. Pacca). 0961-9534/$ e see front matter ª 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2012.04.018
b i o m a s s a n d b i o e n e r g y 4 4 ( 2 0 1 2 ) 7 0 e7 9
sustainability of sugarcane ethanol is entangled with several factors such as greenhouse gas and energy balance, land and water use, biodiversity loss, employment and income generation, which are extensively discussed in the literature [8e11]. Biodiesel is another biofuel that has been used to meet transportation needs. In 2008, the global biodiesel production was 45.8 dam3 d1, which means a 52% increase in comparison to the previous year [12]. Biodiesel is produced by the reaction between vegetable oil or tallow and ethanol or methanol in the presence of a catalyst. In general, the catalyst used is either potassium hydroxide or sodium hydroxide. This process, which is known as transesterification, produces biodiesel and glycerin [13,14]. Several crops are used to produce vegetable oil. Palm tree is a perennial crop with an average 26 year lifetime [15]. Oil and other co-products are extracted from fresh fruit bunches (FFB) of the palm tree. FFB processing yields, on mass basis, 20e21% of palm oil, 1.7% of kernel oil, 3.5% of kernel cake, 22e23% of empty fruit bunches (EFB), 12e15% of fibers, 5e7% of shells and 50% of palm oil mill effluent (POME) [16]. The POME effluent major sources are: steam and water used in the extraction processes and washing activities of the mill [17]. Therefore, due to the addition of water the total mass yield is greater than 100%. Shells and fibers, which are co-products of vegetable oil extraction, are usually burned for steam and for electricity generation in cogeneration systems. Each tonne of fibers and shells is able to produce 11.5 GJ and 18 GJ of energy on a dry basis (LHV), respectively [18]. Palm biodiesel production is energetically self-sufficient due to the power generation potential of its coproducts [15]. Besides that, the empty fruit bunch can also be used to produce energy; each tonne yields 7.8 GJ [16]. Focusing on the improvement of sugarcane ethanol life cycle, the aim of this study is comparing a traditional sugarcane ethanol production system in Brazil (TSES), with a joint production
71
system of sugarcane ethanol and palm oil biodiesel (JSEB). In the latter, biodiesel substitutes for 100% of diesel used in tractors and other machinery required to cultivate sugarcane.
2.
Biofuels joint production Design
The joint production of sugarcane ethanol and palm oil biodiesel portrayed in this study comprises: Use of stillage and filter cake, which are co-products resulting from sugarcane’s processing, for irrigation and organic fertilization. Use 100% of sugarcane bagasse, shells, and fibers from palm tree FFB for steam and electricity generation, which fuels the energy demand of the industrial and the agricultural phases, and yields surplus energy. Use of sugarcane ethanol for oil transesterification (ethyl route) to produce biodiesel. Use of POME and empty bunches resulting from FFB processing, for irrigation and organic fertilization. Due to the water requirement of palm trees, the cultivation on the Cerrado region (Brazilian savannah) needs complementary irrigation. The development of irrigated palm trees in the Cerrado biome was assessed by Embrapa Cerrados [19]. Total displacement of diesel used in transportation, harvesting and other cropping stages by biodiesel without engine replacement [20,21]. The resulting products of the JSEB are: sugarcane ethanol, surplus electricity, glycerin, palm kernel oil, and palm kernel cake. All biodiesel is self consumed by the system. The set up of the system is important to determine GHG emissions allocation, and energy consumption (Fig. 1).
Fig. 1 e Joint production system of sugarcane ethanol and palm oil biodiesel.
72
3.
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Methodology
The assessment is based on a life cycle assessment (LCA), according to the guidelines established by ISO 14.040:2006 and ISO 14044:2006. Three LCA’ studies were carried out in parallel, one for the traditional sugarcane ethanol system, another for a palm oil biodiesel system, and another for the joint production system of sugarcane ethanol and palm oil biodiesel. All “well to gate” assessments consider Brazilian underlying conditions; however, the distribution phase of ethanol to the gas station is ignored because it is similar independently of the fuel type. Besides that, the transportation of inputs to the processing units is not assessed because their source varies, and their contribution to the overall emissions is minimal. The life cycle of the traditional system was divided in nine steps. The agricultural stage comprises five sub-systems (Fig. 2), and the industrial stage comprises four sub-systems (Fig. 3). The life cycle of the joint system is similar to the traditional system, but with the replacement of diesel by palm oil biodiesel, and considering the flows shown in Fig. 1. Two scopes describing the life cycle of ethanol were modeled. In scope 1, the function of the system was producing sugarcane ethanol in a traditional system configuration. For scope 2, the system function is ethanol production in a joint system with a palm oil ethyl based biodiesel refinery. The biodiesel is fully consumed in the life cycle of this joint production system. We have assumed that the two scenarios were deployed on Cerrado (typical savannah), Cerrada˜o (woody savannah), and degraded pasture land, which represent the most common land use types of the central Brazilian plains. Regarding land use change impacts, sugarcane expansion historically occurred outside the Amazonian forest, and moreover, an Environmental Impact Assessment Report has to be approved prior to the installation of any new ethanol plant [22]. Therefore, massive deforestation and large carbon debts due to the expansion of sugarcane plantations are unlikely to occur. The functional unit (FU) was based on 7.55 m3 of ethanol, and corresponds to a reference flow of 1 ha of sugarcane for the traditional system, and 1.12 ha of sugarcane plus 0.14 ha of palm trees for the integrated system, because ethanol is used for biodiesel transesterefication. Based on field observations, the power generation system was based on two boilers with 6.6 MPa each, with a combined
Seeds
Production and use of agricultural inputs
output of 500 Mg h1of steam. One tonne of sugarcane yields 0.555 Mg of steam, at 6.6 MPa and 480 C. The power output was 78 kWh Mg1of sugarcane, or 312 kWh Mg1 of bagasse (wet basis). Assuming a low heating value (LHV) of 7.18 GJ Mg1 for the bagasse, the energy production is 43.5 kWh GJ1, which is enough to supply the energy required by the mill itself, and moreover, yields 79% of surplus electricity. Surplus electricity accounted for 11% of the total energy output (ethanol plus surplus electricity). Thus, part of the ethanol life cycle emissions (agricultural and industrial stages) was proportionally allocated to surplus electricity. For energy generation in the palm biodiesel industrial phase the LHV considered for fibers and shells (dry basis) were respectively 11.5 GJ Mg1 and 18 GJ Mg1 [18]. Considering moisture content (65% for fiber and 35% for shell), the available fuel energy of these co-products is 2.76 GJ Mg1of FFB. Steam to fuel input ratio is 65.7%, which corresponds to steam energy of 1.71 GJ Mg1 of FFB (660 kg of steam at 300 kPa) [18].
3.1.
Inventory sources
The ethanol life cycle inventory (LCI) was based on data collected from three mills located in the State of Sao Paulo on areas with characteristics similar to the Cerrado region (Brazilian savannah). Due to the actual sugarcane processing technology and the similarities between different mills, we believe that these case studies could provide evidences on the joint production of ethanol and biodiesel that can be further extended to other mills on the Brazilian Cerrado region. Besides that, according to CONAB, 60% of the new mills will be installed on the Cerrado biome [23]. In the assessment we have considered that 60% of the sugarcane is burned before harvesting and 40% is green harvested. In the case of palm biodiesel, data were collected at Agropalma Company, located on the State of Para in the northern Brazilian region, since there is no experience in commercial production of palm oil on the Cerrado. Details of the life cycle inventory of sugarcane ethanol and palm oil biodiesel are presented in Appendix A, B and C. Palm trees irrigation at the nursery varies between 0.073 and 0.187 m3 ha1 over 12 months. The fertilizer application for N, P, K was 130 g ha1 and Mg was 20 g ha1. According to Embrapa Cerrados, the complementary irrigation of palm trees corresponds to a daily volume of 0.166 m3 per
Cropping practices
Harvesting and Transportation
Manufacture and maintenance of machineries and agricultural implements
Sugarcane System Boundary
Fig. 2 e Agricultural sub-systems considered for the traditional system sugarcane ethanol life cycle.
73
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Co-products disposal and transportation
Manufacture and maintenance of equipments and industrial construction
Manufacture and use of chemicals inputs
Co-products energy generation
Sugarcane processing
System Boundary
BIOETHANOL
ELECTRICITY
Fig. 3 e Industrial sub-systems considered for traditional system sugarcane ethanol life cycle.
tree during 134 days per year, which results in 3180 m3 ha1 y1 of water, considering 143 plants per hectare [19]. In order to estimate the energy balance and GHG emissions, the energy intensity indicators and GHG emission factors were extracted from life cycle databases in Simapro and Ecoinvent softwares and previously published studies (Annex A). Emissions from sugarcane trash burning which include N2O and CH4 were calculated according to the IPCC Guidelines for National Greenhouse Gas Inventories based on the “Emissions from Managed Soils” section [24]. Both CH4 and N2O emissions due to fiber and shell were assessed according to the IPCC Guidelines for National Greenhouse Gas Inventories based on the “Stationary Combustion” section [25]. During stillage disposal through furrows 0.2% of the carbon content in stillage is emitted as CH4 due to the action of methanogenic soil microorganisms. This estimation is based on the soluble carbon content in stillage of 1%e2% (volume basis) [26]. Besides CH4 emission, 1% of the nitrogen content in stillage and filter cake is emitted after irrigation [24]. Nitrogen contents as N are 280 g m3 of stillage and 5.5 g kg1 of filter cake [26]. The methodology to determine energy demand and GHG emission due to manufacturing and maintenance of tractors, trucks, and agricultural implements was adapted from previous studies [27,28]. The total mass of various machines was collected from manufacturer catalogs, and the lifetime adopted was 5 years for tractors, harvesters, infield wagons, loaders, tows, and 8 years for other equipment. For sugarcane ethanol industrial equipment and construction, the total cement and steel used in a typical ethanol plant, and equipment maintenance energy were estimated according to a previous study [27]. A crushing capacity of 2.0 Tg y1of sugarcane was considered. For palm biodiesel the total steel consumed in a typical plant was based on data in the literature [29] and corresponds to a production capacity of 102 Gg y1 of biodiesel.
3.2. Life cycle greenhouse gas emissions and energy balance Greenhouse gas emissions were quantified for the 100 year CO2e (mass of carbon dioxide equivalent) using CH4 ¼ 23, and N2O ¼ 296 [30].
The following processes were accounted for in order to quantify emission reductions: fossil fuel displaced by palm oil biodiesel in ethanol life cycle e transportation and cropping; gasoline displaced by ethanol and diesel displaced by biodiesel; and grid electricity displaced by surplus electricity based on the GHG of the Brazilian energy mix [31]. Two energy efficiency indicators (EEI) were applied: the net energy ratio (NER), and the renewable energy efficiency (REE). The NER is given by the ratio between the renewable energy output and fossil energy input, as shown in equation (1): NER ¼
Eout;renewable Ein;fossil fuel
(1)
Where, the net renewable energy output, Eout,renewable, includes the total renewable energy produced in biofuel life cycle, which encloses the surplus electricity produced from the co-products (bagasse, fiber, and shell), and the energy content of biofuels (low heating value (LHV) are considered). All values are reported in MJ ha1 y1. The net fossil energy input, Ein,fossil fuel, includes the total fossil energy consumed, MJ ha1 y1. The REE proposed by Sheehan and collaborators [32] and Malc¸a and Freire [33] is given by equation (2): REE ¼
Eout;renewable Ein;fossil Eout;renewable
fuel
(2)
Energy efficiency is related to the ratio between the difference of the net energy output, Eout,renewable (MJ ha1 y1) minus the net energy input from fossil primary energy (MJ ha1 y1) and the output energy (MJ ha1 y1). If the result is between 0 and 1, the fuel is renewable. This renewability is greater if the value is closer to 1 and the fuel is non-renewable for values below zero.
3.3.
Greenhouse gas emission from land use change
Emissions from direct Land Use Change (LUC) were calculated based on the carbon stock on aboveground and belowground of the displaced ecosystem e Cerrado, Cerrada˜o and degraded pasture e and the carbon stock of the biofuel crop e sugarcane and palm trees. The values used are presented in Table 1. The total carbon stock on aboveground and belowground of palm trees is 72 t ha1 [34].
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Table 1 e Above and belowground carbon stock. Ecosystem
Above carbon stock (Mg ha1)
Below carbon stock (Mg ha1)
Total carbon (Mg ha1)
Source (above; below)
33.5 25.5 e 17.0 17.5 e
13.4a 10.2a e 3.08b 3.45b e
46.9 35.7 1 20.08 20.95 72.00
[30,41] [30,41] [34] [41,42] [41,42] [34]
Cerrada˜o e woody savannah Cesrrado e typical savannah Degraded pasture Burned sugarcane Unburned sugarcane Palm
a According to IPCC [30], we added 40% of belowground biomass to the aboveground biomass, which corresponds to the mass of roots. b Dry-root mass in the area without burning is 5.1e7.2 Mg ha1 and in the area with burning is 6.1e7.7 Mg ha1 [42]. According to IPCC [30], the carbon fraction of dry matter is 0.5 Mg (Mg dry mass)1.
The difference between the carbon stocks per hectare in the ecosystems was divided by the time frame adopted in the LCA. The period of analysis considered was 30 years, which is the lifetime of the palm trees. It was considered that 40% of the sugarcane is harvested unburned. The annualized GHG emission due to the land use change is given by equation (3): GHGLUC
tC ha$yr
¼ ðCde Cbe Þ $
1 : tet
(3)
Where, Cde is the carbon stock of the displaced ecosystem, Mg ha1; Cbe is the carbon stock of the bioenergy ecosystem, Mg ha1. For traditional system the Cbe is given by ½ðCbs $fb Þ þ ðCus $fu Þ, where Cbs and Cus are the carbon stocks of burned sugarcane and unburned sugarcane, respectively, Mg ha1; fb and fu are the percentage of burned sugarcane and unburned sugarcane, respectively, 60% and 40%; and tet is the period of analysis in years. The GHG emissions of the integrated system are calculated based on the GHGLUC from traditional sugarcane and the palm tree systems. Therefore, GHG emissions of the integrated system correspond to 94% of the GHGLUC of the traditional sugarcane system plus 6% of the GHGLUC from palm tree system. The percentage 6% is related to the area of palm trees that is required to supply the biodiesel demanded in 1 ha of the integrated system (palm trees plus sugarcane), which was estimated according to the diesel consumption identified in this study. A total GHG emissions scenario, including the LUC effects, is discussed in the results. The presented values take into account the Cerrada˜o biome because it reflects the worst case scenario (the highest carbon content and emissions). This scenario is responsible for greater emissions than scenarios considering indirect land use change effects. Nevertheless, the deforestation of an area is bounded by Brazilian legislation, which prevents the total biome removal. Results considering Cerrado biome and degraded pasture are presented on Table 3. These alternative scenarios yield lower emissions.
In this study, we adapted a method from the literature [34] (Equation (4)). ECPTðyearsÞ ¼
ðCde Cbe Þ GHGLCA;g GHGLCA;e
Where GHGLCA;g , is the mass of carbon, Mg ha1 y1,which is calculated by the total emission factor of gasoline, Mg MJ1 g , (Annex A), multiplied by the energy output of ethanol in terms of its low heating value (LHV), MJe ha1 y1, (Annex A and Appendix A). Therefore, the GHGLCA;g term corresponds to the life cycle GHG emission of gasoline, considering the same energy content of ethanol (LHV). The term GHGLCA;e corresponds to the life cycle GHG emissions of ethanol (Appendix E). The numerator of equation (4) was described in equation (3).
4.
Results and discussion
4.1.
Energy input
Total energy consumed in the TSES life cycle was 20 GJ ha1 y1. The agricultural phase was responsible for 96% of the total energy demand of the traditional sugarcane ethanol life cycle (Fig. 4). The major contribution (48.5%) was associated with fossil fuel used in “Harvesting and Transportation”, “Transportation and Disposal of Co-products” and “Cropping Practices” subsystems, which accounted for 24%, 16.5% and 8% of the total energy demand in agriculture, respectively. The energy demand of agricultural inputs
Table 2 e Avoided emissions due to surplus power electricity from cogeneration system.
Surplus Electricity
a,b
Avoided Emissions
3.4.
Ecosystem carbon payback time
The Ecosystem Carbon Payback Time (ECPT) determines the period required to compensate the carbon stock deficit resulting from LUC. Besides, it takes into account avoided emissions due to the substitution of biofuels for fossil fuels.
(4)
Electricity emissionc
1
1
GJ ha year g kWh1 of CO2e g kWh1 of CO2e % g kWh1 of CO2e
a LCA total emission (ethanol electricity)1. b 1 kWh ¼ 0.0036 GJ [43]. c Brazilian electricity mix [31].
output
TSES
JSEB
19.8 64.6 8.3 11% 73.0
19.8 49.9 23.1 32%
energy
þ
surplus
b i o m a s s a n d b i o e n e r g y 4 4 ( 2 0 1 2 ) 7 0 e7 9
Table 3 e GHG life cycle emissions including land use change effects in terms of CO2e (Mg haL1 yL1) Replaced biome
TSES
Palm oil
JSEB
LCA Cerrada˜o (LUC) Total (LUC þ LCA) Cerrado (LUC) Total (LUC þ LCA) Degraded Pasture (LUC) Total (LUC þ LCA)
3.23 3.24 6.47 1.87 5.10 2.37 0.86
1.54 3.07 1.53 4.44 2.9 8.68 7.14
2.5 2.84 5.34 1.47 3.97 2.77 0.27
contributed with 40%, out of which 20% and 10% are attributed to nitrogen and herbicide, respectively. For JSEB, 94% of the total energy demand in sugarcane ethanol life cycle was related to the agricultural stage. However, due to the displacement of diesel, the greatest contribution is attributed to nitrogen and herbicide which accounted for 34% and 18% of the total energy demand, respectively. Consequently, the substitution of palm oil biodiesel for diesel results in a 84% reduction of the agricultural fuel demand (cropping practices, harvesting, transportation and co-products disposal). Energy consumed for seed production was estimated scaling down the total demand of the sugarcane life cycle. It was considered that 12 tonnes of sugarcane seeds per hectare are required over the 6 year adopted cycle, which equates to 2 Mg ha1 y1 of sugarcane. The life cycle energy demand of the industrial subsystem, manufacture and maintenance of trucks, harvester, infield wagon, tows, loaders, tractors, and agricultural implements was not significant. Palm oil transesterification was based on the use of anhydrous ethanol, and this input contributed only to 0.0001% of the total life cycle energy demand. According to Pimentel and Patzek [35], the energy demand for the conversion of hydrous ethanol into anhydrous ethanol is only 38 MJ m3 of product. Thus, the energy demanded for such conversion is negligible because the amount required is only 310 g of anhydrous ethanol for 1 kg of palm oil [29]. The total energy consumption of the JSEB life cycle was 11.6 GJ ha1 y1, which is 42% lower than the TSES life cycle
75
energy consumption. A detailed list of energy inputs in the assessed systems is presented in Appendix D. Bagasse burning in the cogeneration system supplies a power demand of 5.16 GJ ha1 y1 to both systems. Because this energy is supplied by bagasse produced in the ethanol life cycle, it is not added to the total energy demand. Energy output is based on the heat content of systems’ products, which comprise sugarcane ethanol and surplus electricity. The energy output is fixed, independently of the system type (JSEB or TSES). Annual electricity generation equals 25 GJ ha1 y1. Because the industrial stage energy demand is 5.2 GJ ha1 y1, surplus electricity equates to 19.8 GJ ha1 y1. Total energy output of either system was 180 GJ ha1 y1.
4.2. Net energy ratio (NER) and renewable energy efficiency (REE) The NER of TSES was 9, which means that for each unit of energy consumed to produce sugarcane ethanol 9 units of energy were obtained. When TSES is compared to JSEB, the NER increases 6.5 units, which is due to high reduction in fossil fuel consumption in the agricultural stage. Macedo and collaborators [36] estimated a NER of 1:9.3 for sugarcane ethanol, which can reach up to 1:11.6 with more efficient boilers. Boddey and collaborators [27] estimated a NER of 1:9.07; however, the considered diesel consumption is 60% lower than the value of this work. The fuel REE of the JSEB and TSEB were similar. The nonrenewability in the TSES is 7% while in the JSEB is 3%. Thus, the difference between the systems is minimal if this indicator is considered.
4.3.
Greenhouse gas emissions
Total CO2 emissions for the TSES lifecycle were 3.23 Mg ha1 y1 or 428 kg m3 of ethanol, ignoring the allocation of surplus electricity and LUC effects (Appendix E and Fig. 5). Fig. 5 shows total emissions considering LUC effects to demonstrate the effect on LCA emissions when this variable is
Fig. 4 e Energy input of the traditional ethanol production system (TSES) and the joint production system (JSEB).
76
b i o m a s s a n d b i o e n e r g y 4 4 ( 2 0 1 2 ) 7 0 e7 9
Fig. 5 e Final ethanol life cycle GHG emissions for traditional system and joint system with and without LUC effects.
considered. However, details of the LUC scenarios are presented in the next session. Excluding LUC emissions, fossil fuel consumed in harvesting (40% of the sugarcane is mechanically harvested), sugarcane transportation, cropping practices, and co-product disposal stages accounted for 25% of the total life cycle emissions. Agricultural inputs such as nitrogen and limestone accounted for 14% and 11% of emissions, respectively. These emissions are attributed to the mineralization of nitrogen and carbon contained in fertilizer and limestone. Emissions attributed to the use of co-products such as stillage and filter cake accounted for 8.6% and 1.7%, respectively. They are both due to methane and nitrogen volatilization. Other emission sources attributed to the agricultural stage are due to the manufacturing of pesticides and agricultural machinery, which contributed to 3.2% and 0.6%, respectively. All values are not including LUC effects. GHG emissions for seed production were estimated scaling down total life cycle emissions of sugarcane. A detailed list of GHG emissions of the assessed systems is presented in Appendix E. For the industrial stage, the GHG emissions accounted for 12% of the total lifecycle emissions, out of which, 9% are related to bagasse burning for cogeneration. Emissions from equipment manufacturing, construction, and industrial inputs were minimal. Considering the allocation, surplus electricity accounted for 11% of the total electricity generated, which corresponds to 356 kg ha1 y1 of total CO2e emissions (Table 2). Therefore, when allocation due to electricity surplus is considered the CO2e emission for TSES is reduced to 0.38 Mg m3 of ethanol. Recent studies published by the “California Air Resources Board” [37] and “Environmental Protection Agency” [38] evaluated the GHG emissions for sugarcane ethanol produced in Brazil. Life cycle emissions of sugarcane ethanol reported by CARB [37] were 26.6 g of CO2e per MJ, without taking into account allocation, transport, and fuel distribution. These emissions ignore surplus electricity from burning bagasse and assume that all sugarcane is burned, that is, no mechanical
harvesting takes place. EPA [38] evaluated sugarcane ethanol emissions based on different scenarios of energy production from co-products and the result was 42 g of CO2e per MJ, considering the use of straw for energy generation and land use change emissions. Different authors presented LCAs without considering LUC effects. Macedo and collaborators [36] and Oliveira and collaborators [39] determined 20 and 24.4 g of CO2e per MJ, respectively. Boddey and collaborators [27] showed the lowest value among these studies, 15 g of CO2e per MJ. In comparison, without considering LUC effects, our study renders a value of 18 g of CO2e per MJ. The agricultural stage of the JSEB was responsible for 84% of the total emissions of the ethanol life cycle. The largest contribution is related to fertilizers, sugarcane straw burning, and methane volatilization from stillage. The displacement of fossil fuel by biodiesel yields 90% reduction in emissions, which include cropping, harvesting, and transportation of sugarcane and its co-products. The industrial subsystem was responsible for 15.6% of the total emissions, and the largest contribution is related to bagasse burning, 12%. These emissions are related to CH4 and N2O. For a LHV of 7.8 GJ kg1 the emissions of CH4 and N2O are 0.215 and 0.029 kg Mg1 of bagasse, respectively [25]. The emissions related to the burning of shells and fibers are not included in this subsystem because they were already included in the biodiesel life cycle. Total CO2e emissions of JSEB life cycle were 2.5 Mg ha1 y1 or 0.352 Mg m3 of ethanol, ignoring surplus electricity allocation (Appendix E). The reduction in life cycle GHG emissions for JSEB, in comparison to the traditional system, was 23%. Considering emissions allocation, in which the surplus electricity is responsible for 0.27 Mg ha1 y1, the final CO2e emission of ethanol for the JSEB is 0.314 Mg m3.
4.4.
GHG emission due to land use change
When LUC emissions are included in the analysis, they are responsible for 50% and 53% of all life cycle CO2e emitted in
b i o m a s s a n d b i o e n e r g y 4 4 ( 2 0 1 2 ) 7 0 e7 9
the TSES and JSEB, respectively (Fig. 5). Fig. 5 shows only emissions for Cerrada˜o biome because it represents the worst case scenario as explained in the methodology. Details for other ecosystems’ LUC effects are presented on Table 3. Considering an average between Cerrado and Cerrada˜o biomes, emissions due to LUC for the TSES and JSEB, ignoring the electricity allocation, increased about 1.8 times the life cycle emissions of ethanol. Displacing degraded pastureland reduced life cycle emissions because the carbon incorporated in the sugarcane ecosystem is greater than the carbon stock of the degraded pastureland (Table 3). The emission due to land use change is higher in the TSES because each hectare in this system has just sugarcane whereas each hectare in the JSEB has 6% of palm plantation (see item 3.3). As the palm has more carbon than the evaluated biomes, the little bit of palm area in the ecosystem gives a positive response in the LUC emission.
4.4.1.
Ecosystem carbon payback time
The Ecosystem Carbon Payback Time (ECPT) of the TSES was 9.5 years for Cerrada˜o and 5.5 years for Cerrado displacement. For degraded pasture no emission due to LUC was noticed. Fargione and collaborators [40] estimated an ECPT of 17 years for the displacement of Woody Cerrado (which includes Cerrado and Cerrada˜o) by sugarcane cultivation considering soil carbon, aboveground and belowground biomass. Gibbs and collaborators [34] estimated 12 years, considering Cerrado displacement and above and belowground biomass carbon stocks. In comparison to TSES, the JSEB reduced the ECPT by 27% in the Cerrado case. Considering the Cerrada˜o displacement, 18% of reduction was achieved by JSEB in comparison to the traditional system. For the degraded pasture, there is no carbon debt in either one of the systems. That is, carbon returns to the ecosystem immediately after the sugarcane plantation is established. Certainly the most influential factor for ECPT is the land use change scope. Among the types of biomes the ECPT due to Cerrada˜o displacement was almost two times greater than for Cerrado, in either system.
4.5.
Other considerations
Excluding LUC effects, life cycle GHG emissions of sugarcane ethanol were on average 76% lower than gasoline emissions considering TSES. Considering JSEB, the avoided emissions were 81% of gasoline emissions. The avoided emissions were 88% when diesel is displaced by palm biodiesel, reflecting the results of JSEB. Surplus electricity generation is also an important factor to estimate the avoided emissions due to displaced energy from the Brazilian grid. For TSES the surplus electricity was 19.8 GJ ha1 y1 with related CO2e emissions of 65 g kWh1. 11% reduction was achieved in relation to emission from Brazilian electricity system. Avoided CO2e emissions were more expressive for JSEB. The surplus electricity contributed to 50 g kWh1, which corresponds to 32% of reduction. In short, reductions provided by JSEB were up to 20% higher than avoided emissions by the traditional system (Table 2).
5.
77
Conclusion
The objective of this work was comparing a traditional sugarcane ethanol production system with a joint production system. The propose was evaluating the GHG balance when synergy between sugarcane and palm oil processing refineries is established, including the replacement of biodiesel for diesel and transesterification via an ethanol route (usually methanol is adopted). The LCA of JSEB demonstrates that such alternatives focusing on the sustainability of biofuels might reduce GHG emissions, improve the energy balance, and minimize land use change impacts. The energy balance for traditional sugarcane ethanol system was 1:9 (input:output). The average energy balance of the JSEB was 1:15.5, which corresponds to an increase of 6.5 units in the output energy for each unit in input energy, when JSEB is compared to the traditional system. Life cycle CO2e emissions of ethanol based on the traditional system was 20.2 g MJ1, without LUC emissions. In comparison, CO2e emissions of ethanol produced by the JSEB were 15.6 g MJ1, a 23% reduction in life cycle emissions when compared to the traditional system. For an average between the systems, the displacement of the Cerrado and Cerrada˜o added to the ethanol life cycle CO2e emissions 0.23 and 0.41 Mg m3, respectively. In contrast, the replacement of degraded pasture has contributed to GHG life cycle emission reductions and greater ecosystem carbon stock. The land use change analysis for TSES and JSEB identified that when emissions due to land use change is considered in ethanol sugarcane life cycle, the total emissions increase 1.8 times, considering an average between Cerrado and Cerrada˜o biomes.
Acknowledgments The authors would like to thank the Brazilian National Council for Scientific and Technological Development (CNPq) for the scholarship, Agropalma employees for their interest and patience with this study, Dr. Anand Gopal, Dr. Ralph P Overend, and other 2 blind reviewers for their suggestions.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.biombioe.2012.04.018.
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