Energetics of Brazilian ethanol: Comparison between assessment approaches

Energy Policy 39 (2011) 4605–4613

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Energetics of Brazilian ethanol: Comparison between assessment approaches Carlos Ariel Ramı´rez Triana n ´, Postal Code 110231, Colombia Faculty of Bussiness Administration, Economics and Accounting, Polite´cnico Grancolombiano, Calle 57 3-00 Este, Bogota

a r t i c l e i n f o

abstract

Article history: Received 14 February 2011 Accepted 1 May 2011

As with any other bioenergy product, bioethanol production requires fossil fuel inputs; hence the alleged benefits of energy security and carbon mitigation depend on the extent to which these inputs are capable of drawing a substantive bioenergetic yield. Brazilian ethanol, made out of sugarcane, has been reported as the most efficient gasoline substitute that is commercially available nowadays. For that reason it has been the object of several analyses on the energetics, i.e. energy balances. These studies surprisingly vary widely according with the scholar approach and are not fully comparable among them due to divergences in the assessment method. This paper standardises results of the four most prominent authors in the field, establishing a point of comparison and drawing some light on the energetics studies on biofuels. The main result is shown in Table 5, which homogenises the outcomes for referred studies in terms of unit of assessment in the energy input analysis. Subsequently, this information is also charted (Fig. 2) explaining the source of divergence among authors. This work ends with a short reference and comparison to some energy balance studies carried out on feedstocks of diverse nature, highlighting the potential that sugarcane-based bioethanol represents nowadays. & 2011 Elsevier Ltd. All rights reserved.

Keywords: Brazilian ethanol Energetics Energy balance

1. Introduction Liquid biofuels production has emerged as alternative of fossil fuels use for transportation purposes. Mitigation of carbon emissions, energy security and agricultural development are the main drivers behind these sorts of bioenergy projects. In contrast with these advantages, some nuisances may come to light, since under bad planning, biofuels can create food threatening (Boddiger, 2007; Tenenbaum, 2008), environmental negative impacts (Randerson and Watt, 2008; Tilman et al., 2009; Mol, 2007), and lately the energy balance is under scrutiny among different stakeholders (Dias De Oliveira et al., 2005; Pimentel, 2003; Ulgiati, 2001). Ethanol, made out of biological material, or the so-called bioethanol, is a versatile substitute for gasoline since it can be used directly in its hydrous form in modified combustion engines; and it can be blended with gasoline, in its anhydrous version, in existing engines without any modification, for levels inferiors to 25% ethanol. Recently under flex-fuel technologies that limit is not a problem and any mix of alcohol gasoline can be placed in the engine (Coelho, 2005a). Having understood the use and scope of ethanol, the real problem remains in the source of it. Feedstock used for bioethanol varies widely. For instance, nowadays some materials rich in sugars or starch, i.e. food crops such as sugarcane, sugar beet, corn, and

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cassava among others are being used. When ethanol is elaborated following this way is classified within first generation biofuels. However, ethanol production can include other wider source of materials with high content of lignin and cellulose, such as perennial grasses and agricultural waste such as woodchips, bark, branches or co-products like bagasse. These sources are the base of second generation biofuels and beyond.1 At first glance second generation biofuels are very promising; however the technological route to reach the sugars embedded in the cellulose is very complex and the cost is still prohibitive for the implementation of these technologies at a commercial scale. Giving that a solution for gasoline market is currently required, the need of temporary answers rest under responsible production of first generation ethanol. Under current commercial technologies sugarcane-based ethanol has been reported as the most efficient one (Goldemberg, 2007) and it has been object of several studies creating a broad spectrum of results (Luo et al., 2009; Shapouri et al., 2002; Macedo et al., 2008; Pimentel, 2003). Brazil is by far the most experienced country in sugarcane–ethanol production in the world, being the main exporter and second largest producer after the United States. Secondly, its

1 In the literature it has been identified up to fourth generation biofuels as will be explained in the subsequent parts of this paper. Is additional info is required see Ramı´rez Triana (2010) Biocombustibles: seguridad energe´tica y sostenibilidad. Conceptualizacio´n acade´mica e implementacio´n en Colombia [Biofuels: energy security and sustainability: Academic discussion and its implementation in Colombia]. Punto de Vista 2, 43–79.

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2. Routes to Brazilian ethanol: history and technical process As the purpose of this paper is to understand the energetics of the ethanol production, it is important to follow the path traced by the sugarcane processing industry from its origins, mentioning the drivers that justify the founding of this bioalcohol industry. This encompasses political decisions, mechanical aspects and economic policies. Though, beyond the history, it is equally important to break down the ethanol elaboration technical process in different stages, in order to establish input assessments, and try to recognise their contribution in the different energy balances presented in the second section. 2.1. Sugar and ethanol industries’ establishment in Brazil: brief overview According to FAOStat, in the year 2008, sugarcane was the main item in the Brazilian agricultural production in terms of weight with more than 645 million MT and the second in terms of income (it was worth more than 13 billion USD at international prices) right after indigenous cattle meat. By that time, Brazil was

Sugarcane production and Brazilian share 2,000 Brazilian share Brazil World

1,800 1,600 1,400 1,200 1,000 800

41.0%

37.2%

34.0%

33.6%

32.0%

31.0%

28.7%

200

27.3%

400

27.3%

600 26.1%

geographic position and natural conditions are comparably similar to countries that have tried to follow the path traced by this Brazilian experience and may become potential ethanol exporters in the near future. Several tools have tried to capture the net energy impact of ethanol based on different sources and some scholars have applied life cycle assessment, LCA and different sorts of balances to establish an output/input ratio that allows justifying the implementation of this kind of bioenergy projects (von Blottnitz and Curran, 2007; Shapouri et al., 2002; Luo et al., 2009). Actually, it is possible to find some contrast among different studies, including different sources of feedstock, places, output and technologies (Menichetti and Otto, 2008; Larson, 2006), and not just applied to ethanol production. This ratio between different authors can be compared because, regardless of the units used in the study, it always answers the same question: how much bioenergy units can be obtained from a unit of fossil energy? What causes curiosity is the difference between authors and it can be seen that they take diverse approaches to calculate the ratio, specifically the amount of fossil fuel used, i.e. the energetic input. For this purpose, every one of them breaks down the analysis in different stages at different levels. At the end it was found that the common stages were the agricultural contribution, the industrial process and the distribution stage in some cases. The problem is that the assessment in every case was taken based with heterogeneous units, which represents a barrier in order to compare results. Therefore, final aim of this paper is to cover divergences in studies on the energetics applied to the Brazilian ethanol, unifying unit assessment between different scholars. This work will enable the reader to understand in detail the magnitude and reasons of discrepancy, in particular, with the energy input evaluation and it will encourage further analysis on the same area applied to any kind of biofuels an even other alternative energies of diverse nature. The structure of this document is as follows: it starts with a first section where an overview of the domestic feedstock industry in general and ethanol industry in particular are presented. Therefter, in a second section an introduction of the energy ratio is presented in the context of LCA analysis, showing the importance of the study on the energetics of ethanol. The final and third section, before conclusions, unifies four assessment approaches of the net energy balance of Brazilian ethanol making comparable the impact of fossil fuel that was used in its elaboration.

Million Metric Tonnes

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0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 Fig. 1. Elaborated by the author. Data source: FAOSTAT (2010).

the main sugarcane producer in the world, followed by far for India and China with 348 and 124 million MT correspondingly. In the last decade Brazil has increased its sugarcane production, reaching by 2009 more than 40% of the world supply and tripling the level shown in 2000 (see Fig. 1). Nonetheless these results in the sugar sector are not new whatsoever and they have a long history behind their success as it is presented as follows. The Brazilian role model programme for sugar, and later on, for ethanol production is the outcome of the introduction of sugarcane by Portuguese colonisers, a profound need of fossil fuels during the oil crisis and an incredible government vision, as it is explained below. Sugar cane became the first large-scale plantation at the beginning of the 16th century. Soon after, the plant was brought from the island of Madeira by a Portuguese expedition. This crop was equally important as other colonial crops such as coffee and rubber. After the colonial period, slaves provided the manual labour required by the industry (Schwartz, 2005). Then European immigrants, since 1883, have secured a cheap labour provision for the sugarcane industry and have consolidated it as one of the most prominent industries in the country nowadays (Boddey et al., 2008). Back in 1933, the Sugar and Alcohol Institute was founded and the first ethanol blend trial in petrol engines took place. Succeeding efforts were made in order to enlarge the scope of the ongoing project, but it was not until 1973, during the oil crisis when the Brazilian military government decided to fully support an exclusive bioethanol development, launching 2 years after the National Alcohol Programme, PROA´LCOOL (Xavier, 2007; Coelho, 2005a). Under such programme, special engines were designed to run purely on hydrous ethanol and mandatory blends were set by the Government for gasoline—run vehicles. Not only the demand side was boosted, but supply was greatly assisted by an economic package that included tax and investments favouring the industry; allowing new construction and enlargement of distilleries, at the same time that sugarcane farming suffered an important expansion. By the early 1990’s, direct subsidies for bioethanol were eliminated, but an elevated gasoline taxation combined with a wide supply of ethanol-based cars, created strong incentive to consolidate the market. However, at the end of the decade two simultaneous facts embodied an important drawback on the consumers’ confidence: ethanol suppliers, due to a drought, struggled to provide enough fuel for domestic consumption, and cheap oil prices put pressure on the programme performance (Martines-Filho et al., 2006). Under those circumstances, despite mandatory blendings were impose since the beginning of the programme (Puerto Rico, 2007), the government decided, in 2000, to set up mandatory blends

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with petrol, adding between 20% and 24% of anhydrous ethanol to all gasoline (Martines-Filho et al., 2006). More recently, in 2003, flex-fuel technology was developed specifically for local conditions, admitting any combination of hydrated ethanol (E100) with a blend of gasoline with 20–25% anhydrous ethanol. Bear in mind that North American and European flex-fuel vehicles are designed to run on a maximum blend E85 fuel. This limit in the ethanol content is set to reduce ethanol emissions at low temperatures and to avoid cold starting problems during cold weather, at temperatures lower than 11 1C (Davis et al., 2000). Flex-fuel vehicles have been gaining popularity, among Brazilians although small problems have manifested when pure gasoline is used. However this situation only occurs during trips to other South American countries. So far, it has been shown that Brazil has a strong agricultural industry around sugarcane. This industry has been favoured by historical conditions plus government and private sector initiatives. As outcome of this sector are drawn at least two emblematic products that contribute to the domestic labour and the potential exports income: refined sugar and alcohol. However, as the aim of this paper is to understand the energy balance of sugarcane-based ethanol, a detailed explanation of its elaboration process is required and presented below. 2.2. Brazilian ethanol production process Ethanol production can be broken down in different stages. In this document the author will follow the same approach proposed by Boddey and his team, i.e. the whole process will be divided into three separated phases: agricultural stage, transportation stage and industrial stage. In the Brazilian case, the crop cycle is quite standardised and is the driver for the agricultural operations. The plant is sowed every 6 years and it yields, after year and a half, one direct harvest from the initial plantation. This is followed by 4 additional harvests from ratoons every 12 months. Land is left fallow for six months before the whole process is started again (Macedo, 1998). This kind of information is crucial in order to calculate an average ethanol yield per annum, due to decreasing sugar content according to the harvest. Boddey et al. (2008) do a detailed explanation of the rest of the process that is summarised as follows. At the initial stage, before the planting process, a heavy tillage is applied. This of course leads not only to diesel consumption, but also to a reduced soil organic matter accumulation. It also releases a great deal of GHGs to the atmosphere. Recently, a Zero tillage technique is being introduced in the sugarcane crop in few areas, but albeit the potential environmental benefits the fuel consumption is similar to mechanised production, because herbicides are utilised instead of the harrowing operation. In both cases the formation of furrows requires machinery. After tillage, a fertilisation stage begins. The setts, once planted, are covered with filtercake. As these filters are used to separate suspended material from cane juice, they have several nutrients accumulated that are absorbed by soil. In addition, in order to improve results, a fertiliser known as 4-24-24 (which is a combination of 20 kg of nitrogen, 120 kg of phosphorus pentaxide and 120 kg of potassium oxide) is used for ratoons in further harvesting stages. As occurs in other agricultural practices, nitrogen (N) is broadly used in fertilisers; however, it seems that some cane varieties in Brazil were bred in low N soils, resulting in lowering N needs, hence fuel consumption, and more importantly, N negative impact on the atmosphere (Boddey et al., 2001, 2008; Lima et al., 1987). Harvesting finalises the so-called agricultural stage. Particularly in sugarcane crops, it is quite common to burn the field before this is harvested. By doing this, workers diminish their exposure to poisonous animals and avoid cuts by sharp cane

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leaves. Such practice has improved workers’ productivity threefold. However, there is evidence that pre-harvest burning threatens human health. As a consequence of this, policymakers have created a law for the State of Sao Paulo in order to eliminate this practice by the year 2022 on those lands that have less than 12% slope (Sao Paulo State, 2002). Such principle was effectively applied to 20% of Sao Paulo crop fields (Coelho, 2005b). A regulation like that could bring several changes, in terms of energy balances and ultimately to LCAs since costs can encourage mechanised harvesting, dropping respiratory hazards and carbon emissions from burning (Boddey et al., 2008; Arbex et al., 2007). On the downside, the share of labour could drop enormously, because these harvesting technologies are able to substitute 80–100 men. Therefore, more machinery and corresponding fossil fuel should be acquired. Nevertheless new agricultural waste can be used in the cogeneration systems to produce power or even as raw material for second-generation biofuels production, raising consequently energy ratio. A second stage is transportation which should include all the moving of different consumable goods, like machinery, fuel, and different inputs to sugarcane fields and sugar mill and also the carrying of the cane itself once is harvested to the plant (Boddey et al., 2008). The third stage (industrial) summarises all the processes (cane crushing, pumping water and juice clarification, among others) needed to make the cane become ethanol fuel. This stage is highly energy-intensive. Most of the direct or internal energy needs of the plant come from burning bagasse creating steam power/ electricity, so in that sense, the majority of sugar industry is energy self-sufficient (Coyle, 2007; Martines-filho et al., 2006). In fact there is an energy surplus that can be exported to the local grid. Regardless of the common practice of building the distillery attached to sugar mill, by 2008 a third of Brazilian distilleries were working independently from the sugar industry and nowadays are exclusively dedicated to ethanol production (EPE [Empresa de pesquisa energe´tica], 2008). However, some external inputs such as chemicals, yeasts and enzymes, for fermentation and distillation processes are needed, in the same way that all the materials to build the plant for instance cement and steel are indispensable and energy demanding. The subsequent steps are described by the Cooperative of Sugar and Alcohol Producers of Brazil, Copersucar (COPERSUCAR, 2010). After the yeast is applied in the fermentation process, it is recovered using centrifuge equipment that takes apart fermented juice, which is directed to distillation stage done in three different columns, to end up with obtaining hydrated ethanol (i.e. biofuel has 5% of water). Some ethanol is commercialised in this way in Brazil, which counts on a fleet with vehicles capable to run with pure ethanol, as discussed above. However, water excess must be eliminated from hydrated ethanol for the compulsory blends. The alcohol passes through a dehydration process, where benzene is added concentrating the alcohol, which suffers a final distillation. Benzene is almost fully recovered from the mix using a special column. After this separation, anhydrous ethanol is ready to be stored.

3. The problem of the energetics Biofuels have emerged as an alternative that, according to its promoters, not only helps to tackle the problem of energy security, in the transportation sector, but also has the potential to curve climate change and also might have positive effects on rural development (Dale, 2007; Mathews, 2007; Goldemberg, 2007). Based on those assumptions, several policies have been recently adopted around the globe. Liquid biofuels in particular ethanol and biodiesel, have received great attention by researchers, politicians,

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farmers, entrepreneurs and NGOs, and are occupying priority places in the international and local agendas and academic discussions (Hertel et al., 2008; Groom et al., 2008; Van Thuijl and Deurwaarder, 2006; FAO, 2008; Koizumi and Ohga, 2007; Banse et al., 2007). However, the path covered so far by ‘‘green oil’’ has not been comfortable. Some critics of bioenergy (Pimentel, 2003; Searchinger et al., 2008; Brown, 2008) have documented that implementation of aggressive biofuels production programs, as a result of ambitious policies, unveils environmental flaws that include biodiversity loss, air quality degradation, direct and indirect land use changes (LUC), water depletion and pollution. Nevertheless, these questions have been clarified by some scholars, showing that the results obtained from Searchinger or Pimentel studies are not applicable to a wide spectrum of technological conditions and feedstocks, but contrarily to a very specific corn-based ethanol production in the US (Mathews and Tan, 2009; Dehue, 2010). It is worth noting that in ECOFYS report, Searchinger’s results are extremely high in comparison with other studies of the same nature. For instance, Searchinger points out that the (I)LUC of corn-based ethanol accounted for 140 g CO2/MJ whereas the same impact for sugarcane-based ethanol calculated by the Environmental Protection Agency (EPA) was just 30 g CO2/MJ (Dehue, 2010). In addition, as land and biomass are required to produce biofuels, other sort of social and economic criticisms come forward. Competition with food/feed sources, and its consequential impact in prices, is probably the highest barrier that first generation biofuels have to overcome (FAO, 2008; Boddiger, 2007; Koning et al., 2008; Banse et al., 2007), and this is precisely the category used to classify sugarcane-based ethanol. In spite of the aforesaid, as it happened with (I)LUC, the food controversy has been refuted as well: it has been rejected the hypothesis that ethanol production would cause an increase in food prices, via diversion of agricultural commodities from food to fuel (Zhang et al., 2009). On the other hand a second generation of biofuels is being developed, but albeit a promising future, given by high ethanol yields per hectare (van den Wall Bake et al., 2009) and a huge feedstock diversification, nowadays its implementation is still economically expensive and technologically complicated (Suurs and Hekkert, 2009; Charles et al., 2007). Given the duality and controversy of the aforementioned topics a scientific eco-balance analysis is required. Aiming in that direction, several Life Cycle Assessment studies, LCAs, have been carried out by scholars in order to evaluate the possible benefits or unfavourable side effects of biofuels. The LCA methodology is a quite comprehensive cradle-to-grave analysis of a particular product, in terms of inputs requirements and outputs achievements. The evaluation starts with raw materials extraction, followed by a processing stage, and, subsequently, by distribution and commercialisation phases. A complete LCA finalises when the selected product reaches its disposal stage but in several cases ends with its final use (Udo de Haes and Heijungs, 2007; Hunkeler and Rebitzer, 2005). LCAs are not designed exclusively to study bioenergy, but in this case they are usually broken down into three components: greenhouse gas (GHG) assessment, Health and Environmental impact, and finally, Energy Balance. In the first component, the aim is to establish how neutral bioenergy production is, regarding climate change (von Blottnitz and Curran, 2007). In order to do that, the analysis is focused mainly in CO2 flows, i.e. carbon released through fossil fuels use, during bioenergy production, minus carbon captured during crops growth. In extended studies the inclusion of other major GHGs that result from fertilisers use, such as methane and nitrous dioxide, enriches the scope of analysis. These inclusions are not

just important, but necessary given that the global warming potential are 21 and 310 times those of CO2, for CH4 and N2O, respectively (von Blottnitz and Curran, 2007). An ideal LCA study on bioenergy should also include a wide range of variables like toxicity potential (either human toxicity or ecotoxicity, or both), abiotic resources depletion, impact on photochemical smog creation, eutrophication and acidification potential. All these elements make part of health and environmental impact assessments. Repeatedly, LCA’s studies leave out partially or completely this component. This is mainly due to the fact that the information required is not ample enough or the inventory data are not available. Sensible conclusions from a contrast of studies of this nature are then very unlikely to obtain, because they diverge in goal and scopes, and assumptions are not clearly reported (Menichetti and Otto, 2008). Nonetheless, there is no evidence that points out consent on the environmental or health benefits of bioethanol, beyond the possibility to avoid GHG’s emissions in comparison with other fossil energy carriers (von Blottnitz and Curran, 2007; Reinhardt and Uihlein, 2002). Finally, a LCA study for bioenergy must conduct an energy balance or an analysis of the energetics. This concept is understood as the flow and transformation of energy within a particular system, which in this case implies transformation of a combination of solar energy captured trough a photosynthetic process and fossil fuels used as agricultural input, resulting in a transportation energy carrier biomass ethanol (after biochemical conversion) and potential electricity/power as by-product. The conversion of biomass to ethanol, or any other kind of bioenergy, involves additional energy inputs, most often supplied in some form of fossil fuel. However, there is no reason to undertake an active support to a bioenergy industry if the latter is not capable to lower the amount of fossil fuel needed to propel vehicles without incurring in major modifications to the existing transportation gasoline-based fleet. As it was mentioned above in some cases LCAs are rarely completed to their full extension, but it is quite usual to see partial studies that make and approximation to at least the energy balance component. Those are the object of this analysis. Two main indicators are taken into the account in these sorts of studies. The first one is Energy yield ratio, which is also found in the literature as EROI (energy return over investment) and is expressed as the ratio between the quantity of energy supplied and the quantity of energy used in supply process (Cleveland and Costanza, 2008). Numerator and denominator are expressed in energy units, and according to the available information, this could be Btus, joules, calories or any other energy equivalent. EROI can be read as the amount of energy, bioenergy in this case, that can be produced out of 1 unit of fossil energy. The second one is the net replaced fossil energy, which is measured as either the effect that determined biofuel has on transportation (e.g. kilometre driven) or as being relative to the land area used. This one, however, is not often reported. To capture the input for energy balance is required to divide energy inputs in different categories as is referred by Smeets et al. (2006) and Boddey et al. (2008): fossil fuels (mainly diesel), as it was described in Section 2.2, are needed in order to undertake the first stage which is comprised by several agricultural operations, such as ploughing, fertilising, harvesting, etc. Afterwards, in a second stage, raw material should be transported using lorry with various loading capacities for further processing at the mill/ distillery. The final stage is carried out at the factory before ethanol reaches the market. Different inputs along the chain, such as fertilisers and material for building the plants, are intensive in energy use as well; hence, they should be taken in consideration for a net energy balance.

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Table 1 Pimentel and Patzek (2008). Energy ratio analysis. Inputs per 1000 L of 99.5% ethanol produced from US and Brazilian sugarcane USA

Brazil

Quantity Inputs Agricultural inputs Sugarcane Sugarcane transport Agricultural inputs Industrial inputs Water Stainless steel Steel Cement Steam Electricity 95% ethanol to 99.5% Sewage effluent Distribution Sub-total industrial inputs TOTAL INPUTS Output Ethanol fuel TOTAL OUTPUTS

kcal  1000

Quantity

12,000 12,000

kg kg

1828 490 2318

12,000 12,000

kg kg

612 490 1102

21,000 3 4 8 2,546,000 392 9 20 331

L kg kg kg kcal kWh kcal/L kg BOD kcal/L

90 165 92 384 0 0 9 69 331 1140 3458

21,000 3 4 8 2,546,000 392 9 20 331

L kg kg kg kcal kWh kcal/L kg BOD kcal/L

90 165 92 384 0 0 9 69 331 1140 2242

1

L

5130 5130

1

L

5130 5130

Energy ratio Output/input

1.48

Several authors have studied the Brazilian sugarcane-based ethanol production case. In the following section a comparison between four prominent authors is presented in detail, and some other studies are included for reference purposes.

2.29

Table 2 Macedo et al. (2008). Energy ratio analysis. Fossil energy consumption (MJ/t cane) in the production of ethanol including agricultural and industrial stages Item

4. Brazilian net energy balance: a review and comparison of previous studies Brazil is by default, a reference point in terms of literature about bioenergy. As a matter of fact, Brazil was, for a long time, the major ethanol producer in the world, recently surpassed by the United States. However, this outstanding and long-lasting Brazilian performance has attracted the interest of scholars, who have carried out LCA’s amid other sort of studies. The sample of studies for this section is formed by the more recent job released by the most cited authors in Brazilian bioenergy: (a) (b) (c) (d)

kcal  1000

Pimentel and Patzek (2008). Macedo et al. (2008). Boddey et al. (2008). Dias de Oliveira et al. (2005).

Pimentel and his colleague present an analysis on the energetics based on the conversion of sugarcane to ethanol comparing Brazilian and American practices. In this study, it is assumed that production facilities are exactly the same (see industrial inputs in Table 1). In both cases, energy ratio is positive and greater than 1, implying that for every kcal of fossil energy used it was possible to obtain 1.48 and 2.29 kcal of bioenergy for American and Brazilian cases correspondingly. Although the productivity (ton/ha) was higher in Louisiana, as were its energy inputs, it drew a lesser energy ratio, playing in favour of the Brazilian case. In this work, the use of bagasse as energy source for electricity is acknowledged, but the surplus that goes to the grid is not taken into account, diminishing the potential of the ratio. Macedo and his team, in contrast with Pimentel’s work, have been focusing exclusively on the Brazilian case from several years

Agricultural inputs Agricultural operations Harvesting Cane transportation Inputs transportation Other activities Fertilisers Lime, herb., insect. Seeds Machinery Subtotal Industrial inputs Chemicals and lubricants Buildings Equipment Subtotal Total inputs Output Ethanol Bagasse surplus Electricity surplus Total outputs Energy ratios Ethanol only Ethanol þ bagasse Ethanol þ bagasse þelectricity

2002

16.4 21.7 39 4

2005/2006

2020

66.5 19.2 5.9 29.2 201.9

13.3 33.3 36.8 10.9 38.5 52.7 12.1 5.9 6.8 210.3

14.8 46.9 44.8 13.5 44.8 40 11.1 6.6 15.5 238

6.4 12 31.1 49.5 251.4

19.2 0.5 3.9 23.6 233.9

19.7 0.5 3.9 24.1 262.1

1921.3 168.7 0 2090

1926.4 176 82.8 2185.2

2060.3 0 972 3032.3

7.64 8.31 8.31

8.24 8.99 9.34

7.86 7.86 11.57

Adapted from Macedo et al. (2008).

ago. In the most recent publication, they calculated energy ratios for current practices (2005/2006) and also included a forecast for a scenario in 2020 where it is assumed that mechanisation is enhanced in agricultural activities, and pre-harvest burning has been phased out giving the opportunity to use waste as fuel for

C.A. Ramı´rez Triana / Energy Policy 39 (2011) 4605–4613

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electricity production and optimising the use of bagasse as well. A previous study was also brought in for comparison purposes. Energy results are shown in Table 2. Interestingly, Macedo foresees an energy ratio reduction by 2020 if just neat alcohol is taken into consideration, and there is an obvious explanation, given that more diesel fuel would be needed to run new agricultural machinery. But the inclusion of the energy co-production system, using bagasse and waste shows increments by current and future scenarios. Boddey’s study took a different approach: here, calculations were made revising the whole process and drawing what it takes to process 1 ha of sugarcane into ethanol. Maybe this work is not representative of the average production facility since data were taken from a modern plant; but at least it establishes an updated and detailed reference point for Brazilian ethanol potential. In Table 3 it is possible to see that energy ratio is actually similar to those obtained by Macedo’s team, indicating that 15.3 GJ of fossil energy are required to process into ethanol a hectare of sugarcane; releasing a biological-based product that has 8.8 times that energy content. Just like Pimentel and Paztek, in this paper the inclusion of energy surplus in the form of electricity is not taken into consideration. Finally, Dias de Oliveira and his colleagues compared American corn-based ethanol to the Brazilian sugarcane experience. Just the Brazilian case was taken into account for this document because its production is based on the feedstock object of this study, i.e. sugarcane. Again, self-sufficiency of the plants is acknowledged, but there is not a meticulous separation of the harvesting and processing steps, avoiding a clear identification of different

Table 3 Boddey et al. (2008). Energy ratio analysis. Source: Boddey et al., 2008. Fossil energy input, total energy yield and energy balance of bioethanol produced from sugarcane under present day Brazilian conditions

Input Field operations Labour Machinery Diesel Nitrogen Phosphorus Potassium Lime Seeds Herbicides Insecticides Vinasse disposal Transport of consumables Cane transport Total transport Total field operations Factory inputs Chemicals used in factory Water Cement Structural mild steel Mild steel in light equipment Stainless steel 95% ethanol to 99.5% Sewage effluent Total factory inputs Total all fossil energy inputs Output Sugarcane yield Total ethanol yield Final energy balance

Quantity

Unit

128.0 155.4 22.3 56.7 16.0 83.0 367.0 2000.0 3.2 0.2 180.0 820.0 24.7

h kg L kg kg kg kg kg kg kg m3 kg L

11.5 28.1 23.1 4.0

MJ/unit

MJ/ha/year

7.84 8.52 47.73 54.00 3.19 5.89 1.31

1003.5 1785.6 1064.4 3061.8 51.0 488.9 478.9 252.2 1445.3 87.3 656.0 276.8 2058.0 2334.8 12,709.7

451.66 363.83 3.64 47.73

487.6 0.0 75.9 841.8 693.5 287.1 225.3 0.0 2611.2 15,320.9

L kg kg kg

0.0

76.7 6281.0

mg/ha L/ha

Energy values expressed on a per ha per year basis.

21.45

134,750.4 8.8

Table 4 Dias de Oliveira et al. (2005). Energy ratio analysis. Energy balance of ethanol production from sugarcane in Brazil Input

GJ/ha

Agricultural sector Industrial sector Distribution Total Outputa Energy ratio

35.98 3.63 2.82 42.43 154.4 3.64

a

Assumption: 1 ha sugarcane ¼6.4 m3 of ethanol¼ 5.17 GJ.

energy uses. On the contrary, a high diesel lump is presented having a big impact on the agricultural sector (it accounts for 23 GJ/ha, which is 54% of total energy input). This assumption was criticised, due to the fact that this work uses a calculation of emergy and not energy input in diesel fuel (Smeets et al., 2006). These two concepts are different and energy can be a sub-set of emergy. The latter refers to all embodied energy used in the work processes to create a product or service (Odum et al., 2000); thus an overestimation of the net energy impact is very likely to occur. A summary of this work is shown in Table 4. There is not problem comparing these four studies in terms of energy ratios; because regardless of the used unit, the ratio is going to express the same. However, it is complicated if a transversal analysis along the common elements is done. As the less comprehensive and detailed report was given by Dias de Oliveira, it is going to be used as representative items and units, breaking down the analysis in three stages: the first one refers to agricultural phase (it includes field operations and transport to the mill), the second one makes reference to industrial step (from cane crushing to ethanol storage), and finally there is distribution stage (transport from distillery to biofuel retailer).2 In Table 5, the original data from Tables 1 to 4 are arranged in panel A. It is necessary to have a common unit to do any sort of comparison among stages, so all four works are presented in panel B as GJ/ha. In every case all stages are calculated by weighting their share in total energy input from panel A. To obtain the conversion for Pimentel and Paztec’s results the following information was taken into consideration: 1000 L of ethanol need 2240 kcal  1000 (or 9.38 GJ) of fossil fuel. To produce that amount, according to the authors, it is required between 12 to 14 tons of fresh cane (it was assumed 14). That draws 0.67 GJ/ton and it was reported an efficiency of 77 ton/ha, giving a total input of 51.59 GJ/ha. In Macedo’s paper the data supplied is a yield of 77 tons/ha whereas in his work it is reported a total energy consumption of 0.23 GJ/ton. That makes an energy input of 18.01 GJ/ha. Boddey’s work just needed the conversion of energy units from MJ to GJ, and Dias de Oliveira did not require any particular change. See the final result in Fig. 2. A recalculation of the energy output was made to standardise results. It was assumed a production of 82 L of hydrous ethanol from a ton of cane (MAPA, 2007), and a productivity of 77 ton/ha giving 6314 L/ha. The calorific value of a litre of ethanol is

2 The reader should bear in mind that in this case agricultural stage comprehends both agricultural and transportation activities as were described in Section 2.2, and this was made only for comparison purposes among these studies. In addition, transport from distillery to biofuels retailers is exclusively considered a distribution stage and it is not part of the transportation stage. For gasoline such distribution energy expenditures are never considered; however, this stage was included in Pimentel and Paztek, and Dias de Oliveira reports reducing the energy ratio.

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Table 5 Comparison of energy ratio studies on Brazilian sugarcane-based ethanol. Study

Pimentel and Patzek (2008)

Macedo et al. (2008) (case 2005/2006)

Boddey et al. (2008)

Dias de Oliveira et al. (2005)

(A) Original unit

kcal  1000/m3 ethanol

MJ/ton

MJ/ha

GJ/ha

1102 809 331 2242

210.3 23.6

12,709.7402 2611.2

233.9

15,320.9

35.98 3.63 2.82 42.43

2.29

8.24

8.80

3.64

Input according to stage Agricultural Industrial (without distribution) Distribution Total Original energy ratio (B) Standardised units

GJ/ha

Input according to stage Agricultural Industrial (without distribution) Distribution Total input

25.36 18.62 7.62 51.59

16.19 1.82 0.00 18.01

12.71 2.61 0.00 15.32

35.98 3.63 2.82 42.43

(C) Assumed output Recalculated energy ratio

135.44 2.63

135.44 7.52

135.44 8.84

135.44 3.19

Recalculated fossil energy inputs for sugarcane-based ethanol production (GJ/ha) Oliveira et. al. 2005. Boddey et.al. 2008. Macedo et al 2008. (case 2005/2006) Pimentel & Patzek. 2008 0 5 10 15 20 25 30 35 40 45 50 55 Agricultural Industrial (without distribution) Distribution Fig. 2

21.45 MJ (Pimentel, 1980), so a hectare of sugarcane after processed can draw 135.4 GJ. Comparing the obtained energy ratios with the original ones it is possible to find just small discrepancies,3 so it is assumed, on those bases that a further contrast between the studies is absolutely valid. Under those circumstances, it is possible to make a comparison between these studies: Boddey and Macedo obtained the two most favourable O/I ratios, but these studies did not cover distribution stage. If the worst scenario presented here is assumed (i.e. Pimentel and Paztek) the including of distribution stage would represent an additional energy input of 17.3% over other inputs and that would reduce O/I to 6.4 and 7.5 to Macedo and Boddey correspondingly. If the addition is made under Dias de Olivera’s supposition the extra energy input would reach 7.1% and O/I ratios would draw 7 and 8.25 indicating that, albeit distribution stage could reduce the energy ratio its contribution is not significant. In Pimentel and Patzek there is an evident impact of the industrial stage accounting for more than 35% of the total input, whereas the other cases the same variable barely surpass 17%. It is possible a short life time period was assumed for the plant overestimating some of the embedded energy of some materials like cement and steel (see again Table 1). For instance, in this report the impact of cement

3 That could be explained by divergences in the original assumptions, for instance in Macedo’s it was assumed a productivity of the crops of 81 ton/ha and a processing rate of 85.4 L/ton.

accounts for more than 1/3 of total factory energy inputs, whereas in other studies (Macedo and Boddey) this input reaches approximately 0.25% (average) of factory energy inputs. There is no agreement on the use of steel (structural steel for buildings and steel for equipment) across these studies: the calculations show over 16%, close to 70% and 22% of factory energy inputs for Macedo’s, Boddey’s and Pimentel and Patzek’s reports correspondingly (see Tables 1–3). The only coincidence across these studies was the major importance of the agricultural stage sharing more than 80% of the total energy inputs in three of them.

5. Comparison between energy balance studies based on different feedstock It has been pictured the remarkable sugarcane-based ethanol Brazilian case so far. However it is not until the former is compared one can realise the real potential of this industry. Fig. 3 shows the results of several energy ratios using feedstock from different nature: in order to create the contrast some kinds of cereal (wheat and corn), wood, sugar beetroot, among others were taken into account for ethanol production. It is noteworthy that for all cases energy ratio drew a number higher than 1, confirming the potential of biomass as energy source. All alternatives, among first generation technologies, provided an energy balance lower than the one obtained by Brazilian sugarcane. It is important to bear in mind that lignocellulosic processing technologies face barriers that make difficult to lower product costs at commercial scale; however it is expected to reach a better scenario in the very near future, and several pilot plants are already running trials in Canada, the United States of America and Europe. Given the aforementioned, the fact is that Brazilian sugarcanebased ethanol provides a great energy alternative currently and it could be replicated by those countries with similar natural, political and social conditions. 5.1. Conclusions and final remarks A comparison among four recent energy studies for sugarcanebased ethanol has been shown. All of them provide an O/I energy ratio greater than one, implying that for every unit of fossil fuel used in the whole process is created more than 1 unit of bioenergy equivalent fuel. On one hand Pimentel and Paztek, and Dias de

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C.A. Ramı´rez Triana / Energy Policy 39 (2011) 4605–4613

Bio-Ethanol O/I ratio according to selected feedstock in different studies Cited in Goldemberg (2007). Lignocellulose * Macedo et al (2008). Sugarcane Boddey et al (2008). Sugarcane Macedo et al (2008). Sugarcane D. de Oliveira (2005). Sugarcane Cited in Woods and Bauen (2003). Cereal Cited in Woods and Bauen (2003). Wheat straw Pimentel & Patzek (2008). Sugarcane Cited in Woods and Bauen (2003). Wood Cited in Woods and Bauen (2003). Beet * Durante and Miltenberger (2004). Dry Corn Pimentel & Patzek (2008). Sugarcane Shapuori et al (2002). Corn 0.00

2.00

4.00

6.00

8.00

10.00

12.00

Fig. 3. Sources: Goldemberg (2007), Macedo et al. (2008), Pimentel and Patzek (2008), Durante and Miltenberger (2004), Shapouri et al. (2002), Boddey et al. (2008), Dias De Oliveira et al. (2005) and Woods and Bauen (2003). White bars indicate Brazilian case and *includes co-products.

Oliveira show some scepticism of the benefits of fuels made out energy crops, however some miscalculations were shown and they are arguably the cause of such wide variety of results. On the other hand, Macedo et al. and Boddey et al., with research in situ and updated data, have highlighted the potential of Brazilian experience, giving substantial positive results either by working under current circumstances (I/O: 8.24–8.80), or even better by introducing cleaner production technologies, avoiding air pollution and enhancing the role of bagasse in ethanol (not electricity) production (I/O: 8.99). In any case, if energy balance is compared along current technologies applied for another sort of feedstock around the world, Brazilian sugarcane provides the best results as it can be seen in Fig. 3. Lignocellulosic technology has an even greater energy potential, however has limitations to reach commercial implementation. It is important to keep enhancing the efficiency of ethanol, through several ways: feedstock productivity enlargement, where the introduction of better agricultural practices is crucial, given the importance of this factor and its impact on the energy input; dissemination of flex-fuel technologies that creates incentives for the market without generating stress over the consumer, and finally improvement of available processing technologies that seize the potential of lignocellulosic material. However, at the end of the day, it is a fact that sugarcane-based ethanol, under Brazilian circumstances, provides one of the best options among the current technologies for transportation fuel. In addition, several nations in Latin America with similar natural conditions are likely to enter in the world market increasing the supply and spreading the benefits of sugarcane–ethanol in the near future.

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