All energy flows were calculated in terms of primary energy (gross energy requirement): the required energy inputs during the extraction, transportation, and ...
Energy balance and GHG emissions in the production of organic sugar and ethanol at São Francisco Sugar Mill Joaquim E. A. Seabra a,*, Isaias de Carvalho Macedo b b
ª College of Mechanical Engineering – FEM/UNICAMP Interdisciplinary Center for Energy Planning – NIPE/UNICAMP
1. Objective and Scope The objective of this work was to raise the carbon inventory (and the greenhouse gases emissions - GHG) associated with the production of organic sugar and ethanol, considering the conditions of production at São Francisco sugar mill (UFRA) for the 2006/2007 season. In this evaluation only the production related to the sugarcane cultivated by the mill (50% of actual total milling) was considered, a sample for which there was a higher quality and quantity of information available (reliability and traceability of data). Because it is closely related to the emissions of GHG, the energy balance involved in the cycle was also estimated to facilitate the calculation of emissions. The evaluation was based on the analysis of “cradle-to-gate of the factory”, including the production of the sugarcane and other inputs, and the industrial stage of the production of sugar and ethanol at the mill (Figure.1). Since part of these products are destined for foreign markets, the energy requirements involved in the transportation to the destinations (USA, EU, and Japan) were also considered. Besides the computation of emissions associated with production, the avoided emissions due to the use of sugar cane products were evaluated: the ethanol substitution for gasoline in Brazil and the sugar in comparison to the sugar produced from sugar beets in Europe. For both products the GHG mitigation due to the commercialization of surplus electricity produced from the bagasse is included.
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Exploration, processing and transportation of raw m aterials: • Fossil fuels Cane processing Production and trasportation of: Energy Land
• • • •
Fertilizers Other agricultural inputs Seeds Machinery
Sugar Ethanol Electricity GHG em issions
• Equipments and buildings • Chemicals Products transportation • Sugar transportation (exportation)
Cane tillage and transportation: • • • • •
Land preparation Ratoon tillage Planting Harvesting Cane transportation
System boundary
Figure 1. Scope of the system considered in this evaluation.
2. Methodology 2.1. Use of Energy and GHG emissions In this evaluation three levels of energy flows were considered for the energy balance and GHG emissions 1. Direct consumption of fuel and external electricity; 2. Additional energy used in the production of chemicals and materials used in agricultural and industrial processes (fertilizers, lime, sulfuric acid, lubricants, etc.); 3. Additional energy necessary for manufacturing, construction, and maintenance of equipment and buildings. All energy flows were calculated in terms of primary energy (gross energy requirement): the required energy inputs during the extraction, transportation, and production of fuel (or electricity) have been considered. The coefficients used for determining the energy consumption and GHG emissions are discussed below. Fuel. Since there are no reliable data for energy consumption and GHG emissions for the production of fossil fuels in Brazil, this study has chosen to use international consolidated data. Brazilian particularities with regard to the extraction (a large part in deep water) and the type of oil (heavy crude) demand more energy for the production of fuel, but the eventual variations relating to international values would not be such to affect this analysis. Table 1 presents the values considered.
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Table 1. Demand of energy and GHG emissions in the production of fossil fuels. Energy demand a
Direct emission b
(MJ/MJc) 1.14 1.16 1.24 1.12 1.00
Total emissions
(g C/MJc)
Emissions in c production (g C/MJc)
18.9 20.2 21.1 15.3 27.5
3.41 3.87 4.95 9.53 -
22.3 24.1 26.1 24.8 27.5
Fuel
Gasoline Diesel Fuel oil Natural gas d Petcoke a. b. c. d.
(g C/MJc)
Eucar (2006). IPCC (2001). Eucar (2006); considering extraction, transport and processing. Considered as residue; emissions related to its production were not considered.
Electricity. Despite investments in the construction of NG thermo-electric power stations, power generation in Brazil is still essentially hydro (>85%). In fact, energy generation from fossil fuel sources amount to less than 10% of the electricity produced in the country (BEN, 2006). Evidently, this low consumption of fossil fuels is also reflected in the GHG emissions. According to evaluations presented by MME (Ministry of Mines and Energy) for determining the baselines of projects of CDM (Clean Development Mechanism) in 2006, emissions in power generation in the Southeast and Midwest Regions are between 78 and 180 CO2/MWh. As a reference, it was considered an emission factor of 130kg CO2/MWh and a specific consumption of fossil energy of 2.300 MJ/MWh. These factors were used only for calculating the associated emissions in the use of (bought) electricity at the mill. In the case of embodied energy of equipment and buildings, the part related to electricity has been disregarded, considering small energy flows involved in the life cycles of the products of sugarcane, Sugar Transportation. Since part of the sugar produced by the mill is destined for foreign markets, fuel consumption related to transportation of the sugar to the harbor of Santos and from there to the final destinations – USA (east and west coasts), EU, and Japan is also considered. As far as Santos, it was considered the transportation by trucks with a specific consumption of diesel fuel of 0.020 L/t .km and for transportation by water, an index of 0.20 MJ/t .km (emission factor of 0.08725kg CO2/MJ; heavy crude oil) JEC, 2006. Embodied energy in agricultural machinery and industrial equipment. For simplification, all materials used in the manufacturing of machinery and equipment have been considered to be metals. According to the Brazilian Energy Balance (2006), the specific consumption of energy in the metallurgical industry in general was 27.2 MJ/t (in 2005). 65% of this was of fossil origin (mainly petcoke and coal). In terms of emissions, Kim and Worrell (2002) estimate a factor for Brazil of approximately 1.25 t CO2/t of produced material, considering specific energy consumption close to the amount used in 2005. Therefore, it has been considered a consumption of fossil energy of 17.7 MJ/t and an emission factor of 1.25 t CO2/t. In the equipment manufacturing, (after production of the alloys) the energy consumption is related essentially to electricity, and it has been disregarded. Energy used in buildings. Consumption of energy in the construction of buildings varies from 3.0 to 5.0 GJ/m2, depending on the type of construction. For the average Brazilian house construction there is an estimated energy consumption of 3.5 GJ/m2, in special the part related to cement production (Tavares, 2005). In the national cement industry (BEN,2006) about 60% of the energy demand comes from fossil sources (mainly petcoke) and for simplification we have applied this relation to all construction. Considering these numbers and types of construction involved at the mill, the values presented in Table 2 have been used for the calculation. For the evaluation of the emissions, the emission factor of petcoke has been considered (100.8 kg CO2/GJ).
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a
Table 2. Embodied energy and emission factors for different buildings at the mill . Edification
Industrial buildings Offices Labs, restore shops Yards a. b.
b
Embodied energy 2 (GJ/m )
Emission factor (kg CO2/GJ)
1.8 2.4 2.4 1.2
100.8 100.8 100.8 100.8
Based on Tavares (2006). Fossil energy.
Energy required for fertilizer production. The data available in Brazil about energy consumption in the production of fertilizers is scarce; however it is very close to the international data. For fertilizers, lime, herbicides and insecticides, the value of the embodied energy and emissions presented in the GREET and EBAMM models have been used; they represent the standards verified in the USA (see Table 3). c
Table 3. Demand of energy and GHG emissions for the production of agricultural fertilizers/pesticides Fertilizer
Nitrogen (N) Phosphorus (P2O5) Potash (K2O) Lime Herbicide Insecticide a. b.
Energy demand (MJ/kg)
Emission factor (kg CO2eq/kg)
56.9 9.3 7.0 0.1 355.6 358.0
3.97 1.60 0.71 b 0.01 25.00 29.00
EBAMM and GREET models. Author’s estimation.
Required energy for the production of chemical inputs. The estimate of energy and emission requirements associated with the production of chemical inputs has been based on general information from the Brazilian chemical industry. In 2005, the specific consumption of energy in the chemical industry in Brazil was of 8.1 MJ/t of product (BEN, 2006), 73% being from fossil fuel sources (essentially natural gas and petcoke). For simplification, this coefficient was attributed to all chemicals used by the mill with an emission factor of 95kg CO2/GJ (associated with the use of natural gas and petcoke). In the case of machinery, equipment, and buildings, the energy and emissions flow was calculated on annual basis through dilution of total value along the useful life (or life cycle) of 1 each component plus the flow related to the annual maintenance rate . These numbers are presented separately in the spreadsheet “Inventario_CO2.xls” (attached file).
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Annual flow of energy related to the maintenance rate was estimated based on annual maintenance expenses divided by costs for each piece of equipment. For agricultural equipment the information used was given by the mill itself, and the values were very close to the ones suggested by Macedo et al. (2004). For the industrial area an index of 4% was used as an additional annual consumption of energy related to maintenance, as proposed by Macedo et al. (2004).
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Besides the use of fossil fuel, the analysis of GHG emissions has included the following items: • •
Emissions of CH4 and N2O from the burning of sugarcane trash during pre-harvest. Emissions of N2O and CO2 from the soil with the application of mineral fertilizers, lime, and residues which are returned to the field.
In all these cases the coefficients were indicated by the IPCC (2006), with the current values of GWP – 100. The emissions of Nitrous oxide from the sugarcane trash and the green manure left on the field, added to the filtercake mud and vinasse (which are industrial residues and carry portion of the nitrogen from the sugarcane) were evaluated according to the values indicated for this category of agricultural residues which are returned to the soil. It is important to note that these values are indicated by IPCC (default values), and they do not represent actual local data, in the case of sugar cane biomass. In the case of manure application, the specific coefficient indicated by the IPCC was used. Table 4 represents the summary of coefficients used. 1
Table 4. Emission factors not related to the usage of fossil fuels. Source Trash burning a N2O b CH4 Nitrogen application (urea) c N2O d CO2 e Lime CO2 f Returned residues (kg CO2/kg N) N2O (stillage) N2O (filtercake mud) N2O (ash) N2O (unburned trash) N2O (green manure) N2O (manure) a. b. c. d. e. f.
Emission factor (kg CO2eq/kg - source)
0.021 0.062 6.163 1.594 0.477 5.698 5.698 5.698 5.698 5.698 6.698
Based on IPCC emission factor (0.07 kg N2O/t dry matter burnt). Based on IPCC emission factor (2.7 kg CH4/t dry matter burnt). 1.325% of N in N-fertilizer is converted to N in N2O. For urea, the emission factor indicated by IPCC is 0.2 kg C/kg urea. Based on IPCC default emission factor for dolomite (0.13 kg C/kg). For manure, 1.425% of the N is converted to N in N2O form; for the others it was considered an index of 1.225%. Nitrogen contents of each residue were provided by the mill.
2.2. Production of energy and avoided emissions The total production of renewable energy from the sugar mill is the sum of the energy in ethanol produced and the generated electricity. The part of the ethanol is estimated through its lower heating value (LHV), while for the electricity it was considered the thermal equivalence of 5.325 MJ/MWh, based on the methodology for carbon credit acquisition proposed by the mill (PDD, 2005).
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The evaluation of avoided emissions depends on the equivalence between renewable fuels (ethanol and electricity) and substituted fossil fuels (including which process) and, evidently, of their emissions in the life cycle. For the ethanol there are innumerable possibilities. Here it was considered its use substituting for gasoline in flex fuel automobiles (the equivalence adopted was of 1liter of ethanol = 0.72liter of gasoline (Joseph Jr, 2005). For electricity, it was considered the value indicated in the methodology for acquiring carbon credits, that is, avoided emission of 267.7kg CO2/MWh (PDD, 2005). This acquired credit was divided between the sugar and the ethanol according to the mix of production at the mill.
3. Results All partial results are presented in detail in the chart Inventario_CO2.xls, as well as the methodology of calculation. Only the final results are presented here with the most relevant details. Figures 1 and 2 represent the sectors of fossil fuel energy consumption and the GHG emissions verified in 2006/2007 season. The consumption of fossil energy for sugarcane production at São Francisco Sugar Mill was approximately 151 MJ/tc, with a GHG emission equivalent to 34.08kg CO2/tc. The sugarcane industrial processing has a relatively low emission level (only 1.11kg CO2/tc) due to the use of sugarcane bagasse as the energy source. The final results are shown for each product on Table 5.
Figure 2. Fossil energy consumption and GHG emissions verified in the 2006/2007 season.
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Fossil energy consumption
GHG emissions 0.3%
63.5%
0.1% 0.3%
0.3% 5.5%
1.8%
4.3% 79.2%
5.4%
8.9%
1.5%
3.0%
3.1%
1.4%
6.4%
0.2%
0.9% 28.1%
Fertilizers
Lime
Diesel
Ethanol
Machinery
Soil emissions
Industrial facility
Chemicals
Electricity
Figure 3. Breakdown of fossil energy consumption and GHG emissions in sugarcane production and processing.
Table 5. Fossil energy consumption and GHG emissions in the production of different products in the mill.
Product
Fossil energy consumption 3 (MJ/t ou m )
Processed cane Sugar - Brazil Sugar - USA (east) Sugar - USA (west) Sugar - EU Sugar - Japan Alcohol
164,5 1.143,4 3.597,3 4.497,3 3.657,3 5.917,3 1.896,7
a.
Emissions 3 (kg CO2/t ou m )
35,19 244,54 454,87 533,39 460,10 657,29 405,64
a
Net emissions 3 (kg CO2/t ou m )
31,97 222,14 432,47 511,00 437,71 634,89 368,49
Considering the avoided emissions due to the electricity surplus.
Comparatively, the values verified for UFRA are considered lower than the average value of emissions in the sector, due essentially to not burning the sugar cane trash and to not using mineral nitrogen fertilizers; however, the great amount of agricultural and industrial residues applied to the soil contributed significantly to emissions. For comparison, considering the usual values (conventional practice) observed in the state of Sao Paulo for the application of nitrogen fertilizers (urea 60kg/ha total) and the burning of sugarcane (70% of the total sugarcane, leading to lower amounts of trash left on the soil), the emissions of GHG in the production of sugarcane would jump from 34.08 to 48.83kg CO2/tc.
This low level of emissions in the sugarcane production is reflected in its products. In the case of ethanol, the verified net emissions for hydrous ethanol was 369kg CO2/m3, including the
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electricity credits. In fact, if we think about the final use of ethanol in substituting for gasoline, we have a net avoided emission of 1.532kg CO2/m3 of hydrate alcohol. Another favorable index is the energy ratio (result of the division of renewable energy produced by consumed fossil energy), that reached 11.6 at UFRA (Sao Francisco Sugar Mill) in 2006. Again, if we consider the usual values for nitrogen application and sugarcane burning, the emissions for ethanol production would reach 539 kg CO2/m3 hydrate, and the energy ratio would be “only” 9.0. For the sugar such logic is maintained. The level of emissions for the production was of 222kg CO2/t, and it would reach 325kg CO2/t if conventional practices were used. In the specific case of sugar exported to EU, total emissions in 2006 reached 438kg CO2/t, due to the great amount of emissions associated to the transportation. Still, sugar from sugarcane is much more competitive in terms of emissions than European sugar produced from sugar beets, 2 which emission is estimated in approximately 900kg CO2/t (see comparisons in Figure 4). This happens because, differently from sugarcane, the processing of the sugar from sugar beets demands great amounts of fossil energy (essentially fuel oil), since the residue of sugar beets is not appropriate for energy use. Consequently, in this case we can say that the consumption of sugar from sugarcane instead of sugar from sugar beets could help reducing GHG emissions in about 462kg CO2/t.
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Estimates of fossil energy use and emissions for the production of sugar from sugar beet vary according to evaluations. Kuesters and Lammel (1999) evaluated the consumption of energy for the sugar beet production as a function of nitrogen fertilizer use, and for the conventional application rate (120 kg/ha) had verified a use of approximately 13 GJ/ha. Brentrup et al. (2001) analyzed the life cycle considering different types of nitrogen fertilizers and obtained averages around 15GJ/ha, with emissions close to 1,600kg CO2/ha, while Styles and Jones (2007) reached a number close to 3,500kg CO2/ha. Dalgaard et al. (2001) proposed a model for evaluating the consumption of fossil energy in agriculture considering both conventional and organic possibilities of cultivation; for the sugar beet, the lower verified consumption was around 14GJ/ha, for conventional culture and 12GJ/ha considering organic culture. In all the above cases, however, transportation of the sugar beet to the mill was not considered. Börjesson (1996) estimated a total consumption of energy 27GJ/ha considering a consumption of 3,1 GJ/ha for sugar beet transportation. At the industrial stage, Krajnk et al. (2007) found an emission of 626kg CO2/t of produced sugar, considering a typical production plant in Europe. Arbitrarily, numbers suggested by Brentrup et al. (2001) were adopted in the comparisons; they were added to those determined by Börjesson for transportation and consumption at the industrial stage determined by Krajnc et al. (2007). Considering these values, we reach a final emission of approximately 900kg CO2/t of sugar and an energy consumption of 14.2GJ/t of sugar.
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GHG emissions (kg CO2/t sugar)
1000 900 800 700
Savings of 462 kg CO2/t
600 500 400 300 200 100 0 Sugar UFRA
Sugar Conventional
Sugar UFRA EU
Beet sugar EU
Figure 4. GHG emissions for different sugars (conventional sugar corresponds to UFRA sugar plus emissions referent to the use of mineral nitrogen and the sugarcane burning, discounting equivalent emissions which would come from the trash left on the soil).
4. References BEN – Brazilian Energy Balance 2006: Base year 2005. Final report/ Ministry of Mines and Energy. Enterprise of Energetic Research. Rio de Janeiro: EPE, 2006. 188 p. Brentrup, F, Küsters, Kuhlmann, H e Lammel, J. Application of the Life Cycle Assessment methodology to agricultural production: an example of sugar beet production with different forms of nitrogen fertilizers. European Journal of Agronomy 14 (2001) 221-233. Börjesson, PII. Energy analysis of biomass production and transportation. Biomass and Bioenergy, Vol. 11, No. 4, pp. 305-318, 1996. Dalgaard, T, Halberg, N e Porter, JR. A model for fossil energy use in Danish agriculture used to compare organic and conventional farming. Agriculture, Ecosystems and Environment 87 (2001) 51-65. EBAMM Release 1.0 – The ERG Biofuels Analysis Meta-Model. December 26, 2005. EUCAR, CONCAWE e JRC/IES. Well-to-Wheels analysis of future automotive fuels and powertrains in the European context. Tank-to-wheels Report; Version 2b, May 2006. 88 pp. GREET 1.6 – Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation. Argonne National Laboratory. Argonne, Illinois, USA. IPCC. 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Prepared by the National Greenhouse Gas Inventories Programme, Eggleston H.S., Buendia L., Miwa K., Ngara T. and Tanabe K. (eds). Published: IGES, Japan, 2006. IPCC. Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change [Houghton, J.T.,Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K. Maskell, and C.A. Johnson (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 881 pp., 2001. Joseph Jr, H. The Use of Ethanol Blends as Regular Fuel for Existing Vehicular Fleets. Report for the Brazilian Ethanol Mission to Japan; UNICA – COIMEX, 2005.
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Kim, Y e Worrell, E. International comparison of CO2 emissions trends in the iron and steel industry. Energy Policy 2002, 30, pp. 827-838. 11
Krajnc, D, Mele, M e Glavi_, P. Improving the economic and environmental performances of the beet sugar industry in Slovenia: increasing fuel efficiency and using by-products for ethanol. Journal of Cleaner Production 15 (2007) 1240-1252. Kuesters, J e Lammel, J. Investigations of the energy efficiency of the production of winter wheat and sugar beet in Europe. European Journal of Agronomy 11 (1999) 35-43. Macedo, IC (organizer). Sugar Cane’s Energy – Twelve studies on Brazilian sugar cane agribusiness and its sustainability. São Paulo: Berlendis & Vertecchia: UNICA, 2005. Macedo, IC; Leal, MRLV; da Silva, JEAR. Balance of greenhouse gases emissions in the production and use of ethanol in Brazil. Secretary of Environment of the State of São Paulo. Project Design Document Form (CDM PDD) - Version 02. Bioenergia Cogeradora S.A. (“Bioenergy”), correspondig to the Santo Antonio Mill (USA – from the Portuguese “Usina Santo Antônio”) and the São Francisco mill (USFR – from the Portuguese “Usina São Francisco”). PDD version number: 11 B. October 14, 2005. Styles, D e Jones, MB. Energy crops in Ireland: Quantifying the potential life-cycle greenhouse gas reductions of energy-crop. Biomass and Bioenergy (2007), doi:10.1016/j.biombioe.2007.05.003. Tavares, SF. Analysis of the energy life cycle in Brazilian residential buildings: Federal University of Santa Catarina (2006).
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