Energy Fuels 2010, 24, 1720–1730 Published on Web 02/24/2010
: DOI:10.1021/ef901432g
Can Rape Seed Biodiesel Meet the European Union Sustainability Criteria for Biofuels? T. Thamsiriroj†,‡ and J. D. Murphy*,†,‡ †
Department of Civil and Environmental Engineering, University College Cork, Cork, Ireland, and ‡ Environmental Research Institute, University College Cork, Cork, Ireland Received November 24, 2009. Revised Manuscript Received February 8, 2010
The European Union (EU) Renewable Energy Directive stipulates that only biofuel systems that achieve greenhouse gas emission savings of 60% will be eligible to be considered for the 2020 target of 10% renewable energy in transport. Rape seed biodiesel is a very popular indigenous European biofuel; however, this 60% target is very challenging for the biofuel produced. Tropical biofuels such as palm oil biodiesel tend to be sustainable, due to use of residues and byproduct to satisfy parasitic energy demands. This paper explores, through life cycle assessment methodologies, the whole rape seed system and the potential to improve sustainability. Allocation by energy content attributes almost half the greenhouse gas emissions to rape cake (a coproduct). Indeed rape cake as animal feed displaces imported soybean from Latin America and potential destruction to rain forests. Together with use of glycerol as a source of heat, greenhouse gas savings of 75% maybe attained, indicating a sustainable system. Furthermore use of rape straw pellets in lieu of the environmentally unsound practice of using peat produced from Irish Bogs as a source of domestic heating can lead to a 135% savings on diesel. Interestingly, rape cake as a source of biomethane greatly improves the energy balance of the system but is of little benefit to emissions. biodiesel to offset the carbon released by ploughing of the grassland.5,6 There has been a 4-fold increase in land growing oilseed rape in Ireland as an energy crop between 2004 and 2007 (2.2-8.2 kha).7 This has been encouraged by the premium funded to farmers under the Energy Crop Scheme and Bioenergy Scheme.8 The limited arable land in Ireland is already fully employed; allowing for the fact that oilseed rape is a crop rotated 1 year in 4 or 5; its maximum extent is of the order of 2% of agricultural land providing 2% of energy in transport.3 Biofuels produced in Ireland only replaced 0.5% of transport fuels in 2007, with rape seed biodiesel as one of the primary biofuels. To achieve the renewable energy target of 10%, importing biofuels or ready blended biofuels is almost certainly unavoidable. The recently published EU Renewable Energy Directive1 includes sustainability criteria for biofuels. For a biofuel to be counted toward national targets it must effect a minimum GHG reduction in comparison to the fuel it replaces of 35% post 2010 rising to 60% post 2017. The Directive provides a default value of 38% for rape seed biodiesel. The biofuel producer will therefore need to ensure that the 60% reduction may be effected before investing in a biofuel production facility. Previous work by the authors suggested that rape seed biodiesel was inferior to palm oil biodiesel when considered under two parameters: energy production per hectare and GHG savings.3 Furthermore, a GHG saving of only 28% was calculated for the rape seed biodiesel system using a noallocation methodology
1. Introduction 1.1. Biofuels and Biodiesel in the European Union (EU) and Ireland. The EU has set a target of 10% renewable energy in transport by 2020.1 Ireland responded with the introduction of biofuels obligation2 with an obligation level of 4% renewable energy (measured by volume) by 2010. Rape seed oil is the only energy crop in Ireland used to produce biodiesel. Previous work by the authors indicated that 1% of agricultural land is required to satisfy 1% substitution of transport fuel by rape seed biodiesel.3 Over 90% of Irish agricultural land is under grass; less than 10% is arable and available to production of energy crops.4 Conversion of permanent grassland to arable land is not an option. It has been shown that if grassland was converted to arable land growing oilseed rape, it would take about 49 years for the greenhouse gas (GHG) saving from substitution of diesel by rape seed *To whom correspondence should be addressed. Telephone: þ 353 21 490 2286. E-mail: jerry.murphy@ucc.ie. (1) Official J. Eur. Union Directive 2009/28/EC of the European Parliament and of the Council of 23 April on the promotion of the use of energy from renewable sources and amending and subsequently repealing Directives 2001/ 77/EC and 2003/30/EC. June 5, 2009, http://eur-lex.europa.eu/LexUriServ/ LexUriServ.do?uri=OJ:L:2009:140:0016:0062:EN:PDF (accessed July 2009. (2) Department of Communications, Energy and Natural Resources. Government White Paper: Delivering a Sustainable Energy Future for Ireland, March 2007. http://www.dcmnr.gov.ie/NR/rdonlyres/54C78A1E4E96-4E28-A77A-3226220DF2FC/27356/EnergyWhitePaper12March2007. pdf (accessed June 2009). (3) Thamsiriroj, T.; Murphy, J. D. Is it better to import palm oil from Thailand to produce biodiesel in Ireland than to produce biodiesel from indigenous Irish rape seed? Appl. Energy 2009, 86, 595–604. (4) Murphy, J. D.; Power, N. M. An argument for using biomethane generated from grass as a biofuel in Ireland. Biomass Bioenergy 2009, 33, 504–512. (5) CONCAWE, EUCAR. Well-to-wheels analysis of future automotive fuels and powertrains in the European context. European Commission. Well-to-tank Report, version 2b; May 2006. (6) Stephenson, A. L.; Dennis, J. S.; Scott, S. A. Improving the sustainability of the production of biodiesel from oilseed rape in the UK. Process Saf. Environ. Prot. 2008, 86, 427–440. r 2010 American Chemical Society
(7) Central Statistics Office Ireland (CSO). http://www.cso.ie (accessed June 2009). (8) Department of Communications, Marine and Natural Resources. Report on measures taken to promote the use of biofuels or other renewable fuels to replace diesel or petrol: Compliance with Directive 2003/30/EC (Article 4); July 2005, http://ec.europa.eu/energy/res/legislation/doc/biofuels/member_states/2005_rapports/2003_30_ie_report_en.pdf (accessed June 2009).
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: DOI:10.1021/ef901432g
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1.2. Life Cycle Analysis. Life cycle analysis has become an essential tool in assessing the sustainability of biofuel systems. In a life cycle analysis, the goal, scope, and functional unit are initially defined followed by a definition of the system boundary.9 Of issue and a driver for this paper is the wide range of results, which may be produced from the same defined biofuel system. This is primarily due to the allocation methodology and the methodology employed when considering coproducts, byproduct, and residues in the system.10 There are a number of allocation approaches that may be applied to the life cycle analysis. In general, these include the no-allocation approach, allocation by physical relationship (e.g., mass, volume, energy content), allocation by economic value, substitution approach, and the mixed approach.11,12 Many works on biofuel systems recently have focused on the substitution approach.12-17 The method is claimed to be the most appropriate, especially when the impact from a specific change in the total fuel production system to end uses is of interest.17 A study of the literature reveals a number of studies of rape seed biodiesel systems utilizing different allocation methods.3,6,17-19 The results depend significantly on allocation methodology employed and on what substitutions are applied to rape cake, glycerol, and rape straw. For example, Bernesson et al., when investigating a large-scale rape seed biodiesel system, showed that calculated GHG emissions differ by 30% using the substitution approach as opposed to allocation by energy content.17 Stephenson et al. when assessing a small-scale system showed that the GHG emissions may change by 92% if rape cake is used for combined heat and power production (CHP) rather than for use as animal feed.6 1.3. Calculation Method for GHG Emissions from Biofuel Systems. The EU Renewable Energy Directive provides a
methodology (eq 1) to calculate the GHG emissions from biofuel systems in the Annex V Part C of the Directive.1 The functional unit is specified in grams of CO2-eq MJfuel-1. The equation allows for the global warming potential (GWP) of CO2, CH4, N2O. EB ¼ eec þ el þ ep þ etd þ eu - esca - eccs - eccr - eee ð1Þ where, EB is the total emissions from the biofuel; eec is the emissions from the cultivation of raw materials; el is the emissions from the land use change; ep is the emissions from processing; etd is the emissions from the transport and distribution; eu is the emissions from the biofuel in use; esca is the emission saving via the improved agricultural management; eccs is the emission saving from the carbon capture and geological storage; eccr is the emission saving from the carbon capture and replacement; and eee is the emission saving from excess electricity from cogeneration burning of agricultural crop residues. In order to assess the sustainability of the biofuel, the calculated GHG emissions are converted to the GHG saving compared to fossil fuels. The Saving is calculated using eq 2. ð2Þ Saving ¼ ðE F - EB Þ=E F where, EB is the total emissions from the biofuel and EF is the total emissions from the fossil fuel comparator. The highlight of the methodology is that it allows for both the allocation by energy content and the substitution approach to be included. Parameters including eec, ep, and etd are allocated to the main product, coproducts, and byproduct based on their lower heating values. The substitution approach is allowed through the parameter eccr when applied to the use of coproducts, byproduct, and residues from the biofuel system. 1.4. Objective of Paper. This paper has an objective in ascertaining whether rape seed biodiesel may be classified as a biofuel in the EU after 2017. Two clauses exist in the EU Renewable Energy Directive relating to sustainability. The first relates to the aforementioned GHG savings. The second clause states that no damage maybe done to sensitive eco-systems in growing biofuels (such as conversion of grassland to arable land to grow biofuels). In this paper it is not proposed to grow rape seed outside the existing arable land base in Ireland; thus damage to sensitivity ecosystems is not associated with the rape seed crop. The life cycle assessment (LCA) methodology used in this paper thus follows the approach suggested in the Directive and is primarily concerned with GHG savings. In particular this paper focuses on applications of coproducts, byproduct, and residues from the rape seed biodiesel system, which will allow improvement in the energy balance and the sustainability of the whole system. The analysis takes into account the energy and emission credits from rape cake, glycerol, and rape straw.
(9) Guin ee, J. B. Handbook on Life Cycle Assessment: Operational Guide to the ISO Standards. Eco-Efficiency in Industry and Science, Vol. 7, Kluwer Academic Publishers: Dordrecht, The Netherlands, 2002. (10) Singh, A.; Pant, D.; Korres, N. E.; Nizami, A. S.; Prasad, S.; Murphy J. D. Key issues in life cycle assessment of ethanol production from lignocellulosic biomass: Challenges and perspectives. Bioresour. Technol. 2009, DOI: 10.1016/j.biortech.2009.11.062. (11) Roundtable on Sustainable Biofuels. Annex 1 to Paper 3: Pros and cons of substitution and allocation. EPFL Energy Center, May 16, 2008, http://cgse.epfl.ch/webdav/site/cgse/users/171495/public/Paper3_Annex1_Pros%20and%20cons.pdf (accessed July 2009). (12) Thamsiriroj, T.; Murphy, J. D. The impact of the life cycle analysis methodology on whether biodiesel produced from residues can meet the EU Sustainability Criteria for biofuel facilities constructed after 2017? Submitted to Renewable Energy, July 2009. (13) Smyth, B. M.; Murphy, J. D.; O’ Brien, C. What is the energy balance of grass biomethane in Ireland and other temperate northern European climates? Renewable Sustainable Energy Rev. 2009, 13 (9), 2349–2360. (14) Murphy, J. D.; Power, N. M. How can we improve the energy balance of ethanol production from wheat? Fuel 2008, 87, 1799–1806. (15) Liska, A. J.; Yang, H. S.; Bremer, V. R.; Klopfenstein, T. J.; Walters, D. T.; Erickson, G. E.; Cassman, K. G. Improvements in life cycle energy efficiency and greenhouse gas emissions of corn-ethanol. Res. Anal. 2008. DOI: . (16) (S&T)2 Consultants Inc. An examination of the potential for improving carbon/energy balance of bioethanol. IEA Task 39 Report T39-TR1, February 2009. (17) Bernesson, S.; Nilsson, D.; Hansson, P. A. A limited LCA comparing large- and small-scale production of rape methyl ester (RME) under Swedish conditions. Biomass Bioenergy 2004, 26, 545–559. (18) Kaltschmitt, M.; Reinhardt, G. A.; Stelzer, T. Life cycle analysis of biofuels under different environmental aspects. Biomass Bioenergy 1997, 12, 121–134. (19) Reijnders, L.; Huijbregts, M. A. J. Biogenic greenhouse gas emissions linked to the life cycles of biodiesel derived from European rape seed and Brazilian soybeans. J. Cleaner Prod. 2008, 16, 1943–1948.
2. Rape Seed Biodiesel Scenarios 2.1. Rape Seed Biodiesel Facility: Base Case. A small-scale biodiesel plant with a capacity less than 1 million tonnes per annum is considered; this is a typical size for a farmcooperative scheme in Ireland and was used in a previous paper by the authors3 comparing palm oil to rape seed as a source of biodiesel. The harvested rape seed is treated locally; the oil press (cold press) and biodiesel plant are combined. Rape seed oil obtained from the oil press is directly mixed 1721
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: DOI:10.1021/ef901432g
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Table 1. Scenarios Considered in the Study
Table 2. Allocation Factors to Rape Seed Oil and Rape Cake
rape seed rape cake glycerol rape cake, rape straw to to to glycerol to to biodiesel animal feed heat biomethane pellets base case scenario 1 scenario 2 scenario 3 scenario 4
X X X X X
X X
X X
X X X
product
LHV (GJ t-1)
yield of product (t ha-1a-1)
rape seed oil rape cake
37.0a 14.82b
1.23 2.85
total energy (GJ ha-1a-1)
allocation (%)
45.51 42.24 total
51.87 48.13 100
a From the EU Directive 2009/28/EC.1 b On the basis of the ultimate analysis of compositions by the authors, estimated using Sheng’s formula.20
X
Scenario 1. This differs from the base scenario in that rape cake is used for animal feed and glycerol is combusted in a boiler to produce heat for an industrial use. (The glycerol produced in a rape seed biodiesel facility in Cork, Ireland, is used in a boiler specially made for glycerol feed to provide thermal energy). Scenario 1 is the expected typical rape seed system in Ireland. The calculation of net energy and GHG emissions are based on allocation by energy content method. GHG saving credits from rape cake and glycerol are accounted for via the parameters eccr in eq 1. The cradle for rape cake is defined as the cultivation of oilseed rape (parasitic demands and emissions are allocated between biodiesel and rape cake in proportion to oil production for biodiesel and cake production for feed; refer Table 2); the grave for rape cake is its use as animal feed. For glycerol (considered a residue), the cradle is the collection of glycerol from the biodiesel plant; the grave is the combustion of glycerol in an industrial boiler. Scenario 2. This differs from scenario 1 in the use of rape straw to produce pellets for heat. It is assumed that the pellet production facilities are located close to the biodiesel plant. Parameters eccr and eccs are applied to rape straw. Normally, rape straw in Ireland is ploughed back to the land providing carbon sequestration to the soil (eccs). The use of rape straw for pellets production removes this GHG saving credit but adds the credit of replacement of fossil fuel heating (eccr) to the system instead. The cradle for rape straw is the collection of straw from the field. The grave is combustion of pellets for heat production. Scenario 3. In scenario 3, rape cake and glycerol are used for biomethane production through an anaerobic digestion process. It is assumed that a nearby anaerobic digestion facility complete with upgrading facilities is in place already digesting other feedstocks. The biomethane is used as a transport fuel. The GHG saving credit (for displaced fossil vehicular fuel) is included via the parameter eccr. The cradle for biomethane is defined as the cultivation of oilseed rape in the case of rape cake and the collection of glycerol from the biodiesel plant in the case of glycerol. The grave is the use of biomethane as a transport fuel. Scenario 4. This scenario adds an option of rape straw for pellet production to scenario 3. The calculation of the emission saving credit for rape straw is as explained in scenario 2. 2.3. Functional Units Used to Compare Scenarios. Energyrelated figures are denoted as GJ ha-1 a-1; GHG emissions as kg of CO2-eq GJbiodiesel-1. An important issue for the functional unit is the denominator of the emissions. Thus, for example, when biomethane (from rape cake and glycerol) is produced and the energy production increases, the energy in the biomethane product is accounted for in the term eccr only. In effect, the functional unit is directly proportional to kg of CO2-eq ha-1 a-1.
Figure 1. Processes involved with different scenarios in this study; units of inputs and outputs are per hectare per day.
with methanol in the biodiesel processing unit. The energy requirement of a small-scale biodiesel plant based on rape seed oil is considered low, as the oil does not need pretreatment and biodiesel separates from glycerol through density differential. 2.2. Scenarios. Five scenarios are assumed in this study as indicated in Table 1 and Figure 1. While rape seed oil is used for biodiesel production, there are choices for the uses of rape cake, glycerol, and rape straw. Base Case Scenario. This considers only one energy output: biodiesel production. The calculation of net energy and GHG emissions are based on no-allocation. None of the GHG saving credits from coproducts or byproduct is considered. The cradle of the system is the cultivation of oilseed rape in the field. The grave of the system is biodiesel fuelling cars. The processes considered include agriculture, transport of rape seed to oil press, oil pressing process, biodiesel production, and biodiesel distribution to customers. 1722
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: DOI:10.1021/ef901432g
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released to the atmosphere if straw is combusted as a fuel in lieu of ploughing back to the land. 3.3. Glycerol for Heat Production. Scenarios 1 and 2 involve combustion of glycerin. Crude glycerol obtained from biodiesel plants can vary in composition and energy content. An ultimate analysis test was performed by the authors on a glycerol sample from a rape seed oil biodiesel plant in Cork. The lower heating value was estimated using Channiwala’s formula22 as 19.2 GJ t-1. The glycerol sample contained 16% methanol, which indicated some fossil-derived CO2 emissions released from the combustion of glycerol. The estimation of the fossil-derived CO2 from glycerol according to Thamsiriroj and Murphy3 is 0.77 kg of CO2-eq GJbiodiesel-1. Glycerol is assumed in the analysis to be used for heat production replacing light oil, which has a primary energy of 41.8 MJ L-1 and emission factor of 75.19 kg of CO2-eq GJ-1 primary energy.
Table 3. Result of the Batch Experiment for Anaerobic Digestion of Rape Cake and Glycerol methane yield 3
-1
m of CH4 kg wwb
feed type rape cake glycerola 94.7% rape cake þ 5.3% glycerol
0.243 ( 0.048 0.384 ( 0.044 0.284 ( 0.004
m3 of CH4 kg-1 of VSaddedc 0.289 ( 0.041 0.445 ( 0.051 0.336 ( 0.005
a 0.27 ( 0.031 L of CH4 g-1 CODremoved. In experiments it was noted that 1.42 kg of COD is produced per kilogram of glycerol. Thus, methane yields of 0.384 ( 0.044 m3 CH4 kg-1 ww. b ww is wet weight. c VSadded is volatile solids added.
3. Experiments Carried Out To support the analysis a number of experiments were carried out. The experiments and the rationale for the experiments are explained in the following sections. 3.1. Anaerobic Digestion of Rape Cake and Glycerol. Scenarios 3 and 4 include digestion of rape cake and glycerol. A batch anaerobic digestion experiment was performed using rape cake and glycerol as feedstock sourced from the same biodiesel plant in Cork, Ireland. The anaerobic digestion unit was an Armfield W8 anaerobic digester, which was modified to work with a high solids content feed. A mixer was installed and connected to a motor with a rotational speed of 60 rpm. Feedstock was fed to the 5 L reactor tank once and left to be digested for a 25 day period. The amount of feed was in the range 3-5 g of volatile solids (VS) liter-1 of reactor volume to avoid pH adjustment. Inoculums were nongranulated sludge taken from the Camphill anaerobic digestion plant in Kilkenny, Ireland. This digester uses cow manure and food waste as the main feeds. Gas compositions were analyzed for CH4 and CO2 using the infrared portable gas detector, model PGD3-IR, supplied by Status Scientific Controls Ltd. Three subexperiments were performed including digestion of rape cake-only, glycerol-only, and a mixture of rape cake and glycerol. The mixture was 94.7% rape cake and 5.3% glycerol, which corresponds to the ratio of actual production (i.e., 2.85 t ha-1 a-1 for rape cake and 0.157 t ha-1 a-1 for glycerol). Each subexperiment was duplicated three times in order to calculate the average and variance (Table 3). The digestion occurred rapidly with up to 100% of biogas produced in the first 15 days in most cases. The retention time for energy crop digesters is of the order of 60 days,13 thus addition to energy crop digesters should result in full contribution from the biodiesel byproduct. 3.2. Carbon Released When Rape Straw Is Combusted. Scenarios 2 and 4 involve combustion of straw. The yield of harvested rape straw surveyed in Ireland varies significantly between 1.5 and 7 t of dry solids (DS) ha-1 a-1, with a mean value of 4.2 t of DS ha-1 a-1.21 Straw samples were collected locally (Cork, Ireland). The moisture content of the sampled straw was found to be 15%. An ultimate analysis was carried out both on fresh straw and the ash after combustion. The carbon content in the fresh straw was 45.57% of DS; that in the ash was 0.18% of DS. Thus, (1) carbon losses in combustion 1.9 t of C ha-1 a-1 ((4.2 t of DS ha-1 a-1)(45.39% C)); (2) global warming potential of 7 t of CO2-eq ha-1 a-1 (1.9 t of C ha-1 a-1/0.273 t of C t-1 of CO2-eq); (3) 156 kg of CO2-eq GJbiodiesel-1 (7 t of CO2-eq ha-1 a-1/44.87 GJ ha-1 a-1). This carbon dioxide will be
4. Rape Seed Oil for Biodiesel Production (All Scenarios) 4.1. Previous Work. The authors previously compared palm oil biodiesel with rape seed biodiesel.3 The energy balance and GHG saving were based on the no-allocation approach. The results suggested that the GHG saving of rape seed biodiesel was 28.8%. In that study, lime application to soil was not included.3 However, in many parts of the U.K. and Ireland, soil conditions are acidic, necessitating pH adjustment through the use of lime. Thus, in this paper lime is considered. This results in a reduced net energy production per hectare and a reduction in GHG savings. 4.2. Effect of Lime. The base case scenario in this paper is based on the data from the authors’ previous work with the addition of lime input to the system. In Munster (a province of Ireland) lime requirement was surveyed to be an average of 1.8 t ha-1 a-1 (7.3 t ha-1 over 4 years between 1993 and 1997).23 However, this is the mean figure that includes grassland and arable land, with different soil pH. Optimum pH for grassland is 6.3, for cereal crops is 6.5, and for oilseed rape is 7.0.24 Farmers in Cork, (Munster, Ireland) apply lime at about 2 t ha-1 a-1. Lime requirement can be widely variable depending on soil conditions, farming practice, and crop rotation in specific areas. This study will assume the lime application to the analysis as follows: (1) 2 t ha-1 a-1 of lime for rape seed production and (2) 1.6 t ha-1 a-1 of lime for barley production (rape cake used as a substitute for barley in cattle feed) In addition to the large quantity of lime applied, the GHG emissions released from lime are also very high. Lime reduces soil acidity by changing some of the hydrogen ions in soils into water and CO2. The pH increases because the hydrogen ion concentration reduces. A tonne of agricultural lime (ground limestone) releases 440 kg of CO2-eq based on stoichiometry. In this study, the emission factor for lime is divided in two: 432 kg of CO2-eq t-1 from the chemical reaction and (22) Channiwala, S. A.; Parikh, P. P. A unified correlation for estimating HHV of solid, liquid and gaseous fuels. Fuel 2002, 81, 1051–1063. (23) Coulter, B. S.; McDonald, E.; Murphy, W. E.; Lee, J. Visual environmental data on soils and landuse. End of Project Report ARMIS 4496, Teagasc, Johnstown Castle Research Centre: Wexford, Ireland, May 1999; http://www.teagasc.ie/research/reports/environment/4496/eopr4496.asp (accessed August 2009). (24) Coulter, B. S.; Lalor, S. Major & micro nutrient advice for productive agricultural crops. Teagasc, Johnstown Castle Environment Research Centre: Wexford, Ireland, April 2008. (25) Mitchell, C. C. Soil acidity and liming (Overview). Homepage of the Department of Entomology, Soils and Plant Sciences, Clemson University Extension Service, http://hubcap.clemson.edu/∼blpprt/acidity2_review.html (accessed July 2009).
(20) Sheng, C.; Azevedo, J. L. T. Estimating the higher heating value of biomass fuels from basic analysis data. Biomass Bioenergy 2005, 28, 499–507. (21) Keogh, B.; Shalloo, L. Forage crops to reduce winter feed costs. In Moorepark’ 09, Moorepark Dairy Production Research Centre, 2009 http://www.teagasc.ie/publications/2009/20090618/MooreparkBook2009. pdf (accessed July 2009).
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Table 4. Energy Balance and Greenhouse Gases from Rape Seed Biodiesel with No-Allocation Approach and Lime Application Included (Adapted from Reference 3)
Table 5. Crude Protein in the Two Feed Options ration 1: barley ration 2: barley and soybean meal and rape cake
greenhouse energy gases balance (GJ ha-1a-1) (kg CO2-eq GJbiodiesel-1) gross value from combustion of biodiesel 46.5 Parasitic Demands cultivation of oilseed rape 14.15 (excluding lime) lime 2.34 transport of rape seed to 0.1 oil press oil extraction (cold press) 2.32 transesterification 0.95 methanol usage 3.49 NaOH catalyst usage 0.16 biodiesel distribution 0.04 total parasitic demands 23.55 net value from life cycle of biodiesel
22.95
barley grains, 99 g of CP kg-1 fresha 90% soybean meal, 469 g of CP kg-1 fresha 10% rape cake, 320 g of CP kg-1 freshb total crude protein (CP) 13.6%
3.81
85% 15% 13.2%
a From Keane.32 b From personal communication with Gro-oil Ltd., Ireland.27
49.05
production cannot fully support the herd and throughout the winter period when housed.29 Soybean meal is the most frequently used supplementary protein source among a range of sources (such as distillers grains, corn gluten, brewers grains, cottonseed, copra, and rape seed).30 Therefore, the use of local rape cake to feed animals reduces the importation of soybean meal and earns the carbon capture and replacement credit (eccr). 5.2. Rape Cake As a Substitute for Soybean and Barley. This study focuses on rape cake to be used as a farm-mixed feed. One of the ration mixes recommended is 90% barley grains mixing with 10% soybean meal, which gives approximately 13% crude protein in the feed. An alternative to this ration is 85% barley grains and 15% rape cake providing the similar crude protein content (Table 5).31 As a result, 1 kg of rape cake may replace 0.67 kg of soybean meal and 0.33 kg of barley grains. Barley is commonly grown on arable land in Ireland, but the domestic production is not adequate and importation is required. Soybean, on the other hand, cannot be grown in Ireland, but there is a large demand for soybean meal in the livestock feed industry. Around 89 172 t of barley and byproduct were imported to Ireland as opposed 607 367 t of soybean in 2007.33 Brazil and Argentina are the main exporters of soybean to the EU countries. About 60% of imports are in the form of soybean meal, with the remainder as raw soybean to be crushed in the EU.34 The analysis in this study is based on barley grains produced in Ireland and soybean meal imported from Brazil. Parasitic energy in the production of barley is estimated as 3.01 GJ t-1 grains, and greenhouse gases are 500 kg of CO2-eq t-1 grains (Table 6).
21.25 0.17 3.65 1.45 3.87 0.11 0.06 79.61 83.42
43 kg of CO2-eq t-1 from transportation yielding 475 kg of CO2-eq t-1 of lime. The emission factor for the chemical reaction is slightly less than the stoichiometric value as pure CaCO3 product is not generally available. With the no-allocation approach included for lime application, the net energy is calculated as 22.95 GJ ha-1 a-1 and GHG emissions are 83.42 kg of CO2-eq GJbiodiesel-1 (Table 4). The previous work3 indicated the net energy and GHG emissions using the no-allocation approach (without lime) as 25.29 GJ ha-1 a-1 and 58.35 kg of CO2-eq GJbiodiesel-1, respectively. In terms of greenhouse gases, the increase is 25 kg of CO2-eq GJbiodiesel-1, equivalent to an increase of 43%. Lime is thus a very significant factor to the GHG life cycle study of rape seed biodiesel. When considering the production of 87.3 kg of CO2-eq GJdiesel-1 on a whole life cycle of fossil diesel,3 the green house gas saving for the biodiesel system with lime addition is 4.4%. 4.3. Allocation Methodology. Allocation by energy content differentiates rape seed oil from rape cake based on the lower heating value (LHV) and yield of the products. The allocation factors are estimated to be 51.87% and 48.13% for rape seed oil and rape cake, respectively (Table 2). As such, the parasitic energy and related greenhouse gases in processes including oilseed rape cultivation, transport of rape seed, and oil pressing are allocated to the two products.
(29) Casey, J. W.; Holden, N. M. Analysis of greenhouse gas emissions from the average Irish milk production system. Agric. Syst. 2005, 86, 97–114. (30) Stacey, P.; O’Kiely, P.; Rice, B.; O’Mara, F. P. Experiment 2.5: A note on the on-farm moist grain storage and feeding practices in Ireland. In Beef Production from Feedstuffs Conserved Using New Technologies to Reduce Negative Environmental Impacts. Beef Production Series, No. 82; Teagasc: Wexford, Ireland, December 2007. (31) Fitzgerald, L. Cattle farm management notes: April 11, 2008: Looking at feed value in beef rations. Agriculture and Food Development Authority (Teagasc), 2008. (32) Keane, M. G. Comparison of barley and sugar beet pulp with and without added protein as supplements for weanling steers. In Beef and sheep production research, Research Report 2004; Teagasc: Wexford, Ireland, 2004 (33) O’Callaghan, M. The transition to GM-free meat and dairy production in Ireland - The food island. Presentation to the Second International Non-GMO Soy Summit, Brussels, Belgium, October 7-9, 2008, http://www.gmfreeireland.org/feed/documents/SoySummit2/GMFISoySummit2008.pdf (accessed June 2009). (34) van Gelder, J. W.; Kammeraat, K.; Kroes, H. Soy consumption for feed and fuel in the European Union. A research paper prepared for Milieudefensie (Friends of the Earth Netherlands). Final version October 28, 2008. (35) Rice, B. How the farmers’ world will change - new problems, new crops, new opportunities. In Before the Wells Run Dry: Ireland’s Transition to Renewable Energy; The Foundation for the Economics of Sustainability: Dublin, Ireland, 2003.
5. Rape Cake for Animal Feed (Scenarios 1 and 2) 5.1. Rape Cake and Concentrate Animal Feed. Rape cake extracted by cold press comprises 35-38% of crude protein (CP) in the dry matter (DM).26-28 Because of the high protein content, rape cake is used as an ingredient in concentrate feed production. It is also used as the protein source in farm-mixed feed rations. In Ireland, animal rations are required in the early spring and late summer when grass (26) Ferchau, E. Equipment for decentralised cold pressing of oil seeds. Folkecenter for Renewable Energy, November 2000. (27) Rape cake composition factsheet. Personal communication with Gro-oil Ltd. Bandon, Cork, Ireland, 2007. (28) Huuskonen, A. The effect of cereal type (barley versus oats) and rape seed meal supplementation on the performance of growing and finishing dairy bulls offered grass silage-based diets. Livestock Sci. 2009, 122, 53–62.
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Table 6. Energy Demand and Greenhouse Gases from Barley Grains, Soybean Meal, and Rape Seed Productions barley grains process agriculture (total) direct (fuel use) indirect (fertilizer and lime) N2O from fertilizer use conversion of vegetation land to arable land raw material processing transportation (total) raw material product grand total
rape seede
soybean meal
process energy GHG emissions process energyd GHG emissions process energy GHG emissions (GJ tgrains-1) (kg of CO2-eq tgrains-1) (GJ tmeal-1) (kg of CO2-eq tmeal-1) (GJ tseed-1) (kg of CO2-eq tseed-1) 2.94 0.65a 2.29b
494.49 48.67 329.99 115.83c
1.3 0.71 0.59
840.32 53.3 64.35
4.01 1.0 3.01
786.1 72.92 584.96 128.22
0.02
1.87
0.02
1.87
4.03
787.97
722.67
0.07
5.47
0.07
5.47
3.01
0.71 2.64 0.05 2.59
500
4.65
53.3 198.32 3.95 194.37 1092
On the basis of an energy demand of 4.1 GJ ha-1 a-1.35 b On the basis of the average fertilization of 140 kg N ha-1 a-1, 28 kg P ha-1 a-1, and 63 kg K ha-1 a-1 (adapted from Coulter et al.36) and lime application of 1.6 t ha-1 a-1. c On the basis of the N2O emission factor of 5.24 kg of CO2-eq kg-1 N fertilized (adapted from Abdalla et al.37) d Process energy adapted from Cavalett and Ortega38 for the Cerrado region, Brazil, and transportation model adapted from Lehuger et al.39 e Adapted from Thamsiriroj and Murphy3 with a lime application of 2 t ha-1 a-1 included and rape seed transported to the oil press. a
5.3. Soybean and Associated GHG Emissions. Soybean is produced on a large scale in the Central West (Cerrado) and South of Brazil; these areas produce approximately 90% of all vegetable oils in Brazil.40 The Cerrado region produces 75% of soybean in Brazil.38 The expansion of exportoriented soybean cultivation is one of the principle reasons for deforestation in Latin America.41 As such, the greenhouse gases related to the conversion of forest and/or pasture land to arable land is necessary to be included in the analysis. The figure of 65 t of CO2-eq ha-1 is estimated for greenhouse gases from the clearing of Cerrado pasture land to cultivation of soy.42 Considering a common plantation period of 25 years,19 the greenhouse gases may be assessed as 2.6 t of CO2-eq ha-1 a-1. The parasitic energy in the production of soybean meal is estimated as 4.65 GJ t-1 soybean meal and the greenhouse gases are 1092 kg of CO2-eq t-1 soybean meal (Table 6). It is noted that the allocation between soybean oil and soybean meal are based on the energy content, with the allocation factors of 36.1% and 63.9% for soybean oil and soybean meal, respectively. The production yield of soybean oil is 510 kg ha-1 a-1, and that of soybean meal is 2300 kg ha-1 a-1.38 Nitrous oxide emissions (N2O) are an important
Figure 2. Daily mass balance of anaerobic digestion.
factor in agriculture that influences the result of greenhouse gases calculation due to its high global warming potential. However, soybean is categorized as a nitrogen-fixing crop. As a common practice in Cerrado, the application of N fertilizer is not required.38 Direct N2O emissions is therefore omitted in this study. Indirect N2O emissions (soil N2O emissions) are beyond the scope of this paper. However the discussion examines the sensitivity of N2O on the results obtained. 5.4. GHG Saving Associated with Rape Cake As a Feedstock. As previously noted 1 kg of rape cake substitutes for 0.67 kg of soybean meal and 0.33 kg of barley grains. Thus the greenhouse gases substituted by 1 t of rape cake are 896 kg of CO2-eq ([(0.67 tmeal)(1092 kg of CO2-eq tmeal-1)] þ [(0.33 tgrains)(500 kg of CO2-eq tgrains-1)]). From Table 2, 2.85 t of rape cake is produced in one hectare, thus the saving may be expressed as 2.55 t of CO2-eq ha-1 a-1. This hectare also produces 44.7 GJ of biodiesel; thus the savings may be expressed as 57 kg of CO2-eq GJbiodiesel-1 (Table 9).
(36) Coulter, B. S.; Murphy, W. E.; Culleton, N.; Quinlan, G.; Connolly, L. A survey of fertilizer use from 2001-2003 for grassland and arable crops; Teagasc: Wexford, Ireland, July 2005. (37) Abdalla, M.; Wattenbach, M.; Smith, P.; Ambus, P.; Jones, M.; Williams, M. Application of the DNDC model to predict emissions of N2O from Irish agriculture. Geoderma 2009, 151, 327–337. (38) Cavalett, O.; Ortega, E. Energy, nutrients balance, and economic assessment of soybean production and industrialization in Brazil. J. Cleaner Prod. 2009, 17, 762–771. (39) Lehuger, S.; Gabrielle, B.; Gagnaire, N. Environmental impact of the substitution of imported soybean meal with locally-produced rape seed meal in dairy cow feed. J. Cleaner Prod. 2009, 17, 616–624. (40) Stattman, S. L.; Bindraban, P. S.; Hospes, O. Exploring biodiesel production in Brazil: A study on configurational patterns in an evolving policy domain, Report 199, Plant Research International B.V.: Wageningen, The Netherlands, August 2008. (41) Upham, P.; Thornley, P.; Tomei, J.; Boucher, P. Substitutable biodiesel feedstocks for the UK: a review of sustainability issues with reference to the UK RTFO. J. Cleaner Prod. 2009. DOI: 10.1016/j. jclepro.2009.04.014. (42) Bringezu, S.; Sch€ utz, H.; Arnold, K.; Merten, F.; Kabasci, S.; Borelbach, P.; Michels, C.; Reinhardt, G. A.; Rettenmaier, N. Global implications of biomass and biofuel use in Germany - Recent trends and future scenarios for domestic and foreign agricultural land use and resulting GHG emissions. J. Cleaner Prod. 2009. DOI: 10.1016/j.jclepro.2009.03.007.
6. Rape Cake and Glycerol for Biomethane Production (Scenarios 3 and 4) 6.1. Model of Biogas Facilities. Rape cake and glycerol are assumed to be fed to a two-stage continuously stirred tank reactor (CSTR) as a codigested feed. The dry solids content 1725
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in the reactor is below 12%, recirculation of liquid from the second tank back to the first tank facilitates control of solids content. Biogas production is assumed to be 80% and 20% from the first and second tanks, respectively. The figure of 0.284 m3 of CH4 kg-1 ww (wet weight), which corresponds to 0.336 m3 of CH4 kg-1 VS added obtained from the laboratory experiment (Table 3) is considered as the methane yield from the biodiesel byproduct in the digester. A mass balance of the modeled facility is outlined in Figure 2, adapted from Smyth et al.13 The total methane produced is 2.215 m3 of CH4 ha-1 d-1 (808 m3 of CH4 ha-1 a-1). Electricity demand in the biogas plant is assumed to be from the electricity grid, and thermal demand is met by natural gas from the gas network. Electricity demand in anaerobic digestion includes 10 kWeh t-1 slurry for mixing13,43 and 0.694 kWeh t-1 circulated liquid for pumping.13,44 Heat demand is required to raise the temperature by 28 °C on average. A boiler efficiency of 85% is assumed; heat loss of 15% from the digester is assumed.13 Emission factors for electricity and natural gas are given as 538 kg of CO2-eq MWeh-1 and 205.6 kg of CO2-eq MWh-1 natural gas, respectively.45,46 The electricity generation efficiency in Ireland is on average 45%.47 Biogas losses are kept to a minimum using extended digestion periods in the second reactor; losses of 2% are assumed. This is a conservative analysis; the considerable benefits of digestate as a substitute for mineral fertilizer are not considered in this analysis. 6.2. Biomethane for Transport. It is assumed that biogas is upgraded to biomethane (g97% methane) on site, and the biomethane is injected to the natural gas network and used as a transport fuel. Compressed natural gas service stations along the gas grid are used to dispense the biomethane (compressed to 250 bar). Diesel is the fossil fuel displaced. Upgrading of biogas to biomethane requires 0.35 kWeh m-3 of biomethane.13,14,48 Compressing and fuelling processes demand for 0.61 kWeh m-3 of biomethane.5 Methane losses in upgrading and compressing are in the range 0.2-2%;49 1.5% is chosen in this study.13,48 Methane losses in the gas grid are negligible;50 energy required for gas distribution is also negligible as compression provides for distribution.5 In Table 7, it is calculated that rape cake and glycerol could produce 804 m3 ha-1 a-1 of biomethane equivalent to
Table 7. Energy Balance and Greenhouse Gases from Biomethane As Transport Fuel greenhouse quantitya energy gases kg of 3 -1 -1 -1 -1 m ha a GJ ha a CO2-eq ha-1 a-1 gross value from biomethane
833.3
30.54
Parasitic Demands heat demand for anaerobic 3.11 digestion electricity demand for 0.85 anaerobic digestion biogas losses in anaerobic 16.7 0.61 digestionb electricity demand for 1.03 biomethane upgrading methane losses in 12.2 0.45 upgrading energy demand for biomethane distribution methane losses in biomethane distribution electricity demand for 1.77 compression/fuelling methane losses in included compression/fuelling total parasitic demands
28.9
net value from biomethane 804.4
177.68 57.25 265.44 69.2 195.1
119 included
7.82
883.67
22.72
883.67
Quantity of biomethane at 97% CH4 ha-1 a-1. b Biogas losses are calculated as follows: 1 kg of CH4 dissipated produces 23 kg of CO2-eq. The density of CH4 is 0.714 kg m-3; thus, 1 m3 of CH4 generates 16.4 kg of CO2-eq. Biomethane is 97% CH4. a
804 L of diesel. It is assumed that 1 m3 of biomethane displaces 1 L of diesel. This may be supported analytically by noting that biomethane at 97% CH4 has an energy value of 36.6 MJ m-3 ((0.97)(37.78 MJ m-3)) and that diesel has an energy value of 36 MJ L-1. 7. Rape Straw for Heat Production (Scenarios 2 and 4) 7.1. Rape Straw Use and Implications for Carbon. Rape straw has a relatively high lignin content when compared to grass and cereal straw (rape straw 19-22%; grass 3-7%; cereal straw 6-21%).51,52 Therefore, it is a good source of thermal energy. In Ireland, cereal straws are commonly used for bedding; however, rape straw is ploughed back to the land. If rape straw is utilized for thermal energy, the carbon sequestration benefit from ploughing into soil is removed. Carbon losses from arable soil in Europe average 0.84 t of C ha-1 a-1 (3.08 t of CO2-eq ha-1 a-1).53 However, allocation of carbon losses from soil to specific crops is difficult to ascertain particularly as arable land is rotated.19 According to Schulze and co-workers,54 the balance for all greenhouse gases across Europe’s terrestrial biosphere is near neutral as
(43) Murphy, J. D.; McKeogh, E.; Kiely, G. Technical/economic/ environmental analysis of biogas utilisation. Appl. Energy 2004, 77, 407– 427. (44) Berglund, M.; B€ orjesson, P. Assessment of energy performance in the life-cycle of biogas utilisation. Biomass Bioenergy 2006, 30, 254– 266. (45) The Commission for Energy Regulation. Fuel mix and CO2 emission factors disclosure 2007. November 7, 2008, http://cer.ie. (46) Homepage of Sustainable Energy Ireland. http://www.sei.ie/ Publications/Statistics_Publications/Emission_Factors/ (accessed July 2009). Gallach (47) Dennehy, E.; O oir, B.; Howley, M. Energy efficiency in Ireland. Sustainable Energy Ireland, May 2009, http://www.sei.ie/ Publications/Statistics_Publications/EPSSU_Publications/Energy_Efficiency_ in_Ireland_2009/ (accessed June 2009). (48) Murphy, J. D.; Power, N. Technical and economic analysis of biogas production in Ireland utilising three different crop rotations. Appl. Energy 2009, 86, 25–36. (49) B€ orjesson, P.; Berglund, M. Environmental systems analysis of biogas systems-Part II: The environmental impact of replacing various reference systems. Biomass Bioenergy 2007, 31, 326–344. (50) McGettigan, M.; Duffy, P.; Connolly, N.; O’Brien, P. Ireland: National inventory report 2006. Greenhouse gas emissions 1990-2004, Reported to the United Nations Framework convention on Climate Change. Environmental Protection Agency: Wexford, Ireland, http:// coe.epa.ie/ghg/nirs/NIR_2006_IE.pdf (accessed August 2009).
(51) Kamm, B.; Kamm, M.; Schmidt, M.; Hirth, T.; Schulze, M. Lignocellulose-based chemical products and product family trees. InBiorefineries-Industrial Processes and Products: Status Quo and Future Directions, Vol. 2, Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2006; pp 97-149. (52) Gill, M.; Beever, D. E.; Osbourn, D. F. The feeding value of grass and grass products. In Grass-Its Production and Utilisation; Blackwell Scientific Publications: Oxford, U.K., 1989; pp 89-129. (53) Vleeshouwers, L. M.; Verhagen, A. Carbon emission and sequestration by agricultural land use: a model study for Europe. Global Change Biol. 2002, 8, 519–530. (54) Schulze, E. D.; Luyssaert, S.; Ciais, P.; Freibauer, A.; Janssens, I. A.; et al. Importance of methane and nitrous oxide for Europe’s terrestrial greenhouse-gas balance. Nat. Geosci. 2009, 2, 842–850.
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Table 8. Energy Content and Emissions of Solid Fuels emission factor for combustion fuel types
LHV (GJ t-1)
kg of CO2-eq kg-1
kg of CO2-eq GJLHV-1
coal sod peat peat briquettes
27a 13.1b 18.6b
2.55b 1.377b 1.852b
94.6c 105.1d 99.8d
a Calculated from emission factors in kg of CO2-eq kg-1 and kg of CO2-1 GJ in this table. b From Kenny and Gray.60 c From SEI homeLHV eq 46 d page. Calculated from LHV and emission factor in kg of CO2-eq kg-1 in this table.
the CH4 emissions from feedstock and N2O emissions from arable agriculture are fully compensated for by the CO2 sink provided by forests and grasslands. In Ireland, carbon density in arable soil has not changed significantly over decades. Comparing 1970 to 2000, the carbon density to a depth of 30 cm was 42.9 Tg C (1970) as opposed to 43.6 Tg C (2000); for a depth to 100 cm, the carbon density was 64.4 Tg C (1970) as compared to 65.4 Tg C.55 As a result, the traditional system in which rape straw is ploughed back could be referred to as a carbon neutral system, providing net zero CO2 emissions to the atmosphere. Therefore, the use of rape straw to produce pellets gains the emission saving from the replacement (eccr) but removes the emission saving from the carbon capture and geological storage (eccs). Pellets produced from rape straw are assumed to be used in fireplaces and boilers, replacing solid fuels, i.e., coal, sod peat, and peat briquettes. Section 3.2 deals with the carbon release when rape straw is combusted. 7.2. Substitution of Peat with Rape Straw Pellets. The pellet production plant is assumed to be installed near the oil press and biodiesel plant. Fuels used for straw handling (including windrowing, baling, storage, and transport) were estimated as 6.5 L t-1 straw.56 Straw can be pelletized without major difficulties. Straw is ground in two steps: first a scarifying process and then a fine-chopping into smaller particles. Generally, straw is delivered with a moisture content below 20%, bypassing the drying stage, which is the most energyconsuming stage. The same pellet mills can be used for straw and wood pelleting, producing straw pellets with the LHV of around 15.5 GJ t-1.57 Energy demand for the production varies with scale. For a medium scale of about 2200 t pellets a-1, the electricity demand is 128.5 kWh t-1 pellet for raw material grinding and pellet milling processes.58 In Ireland, solid fossil fuels used for residential heating include coal, sod peat, and peat briquettes. The energy consumption of such fuels in 2007 was 208, 186, and 85 ktoe, respectively (1 ktoe = 41.9 GJ).59 The energy content of straw pellets (15.5 GJ t-1) is similar to that of peat but
Figure 3. Net energy result of different scenarios.
different to that of coal (Table 8). Thus straw is proposed as a replacement for sod peat and peat briquettes for open fires, stoves, and boilers. Peat (which will be substituted) is described in this paper as a combination of sod and briquettes in proportion to use in 2007 (sod 186 ktoe; briquettes 85 ktoe). This generates a LHV of 14.43 GJ t-1 and an emission factor of 103.4 kg of CO2-eq GJLHV-1. The full life cycle of the peat must be taken into account. In terms of energy (including for fuel extraction, processing, and transport) the rise is relatively small; from 14.43 GJLHV t-1 to 14.88 GJprimary energy t-1 (adapted from Cleary et al.61). However for GHG emissions, the rise is significant; 103.4 kg of CO2-eq GJLHV-1 to 136.9 kg of CO2-eq GJprimary energy-1 (adapted from Styles and Jones62). Rape straw produces 4.45 t ha-1 a-1 of pellets (4.2 t DS ha-1 -1 a are produced at 15% moisture content, which is equivalent to 4.94 t ha-1 a-1 “as is”; 10% losses occur in baling and pelletting) and 68.9 GJ ha-1 a-1 ((4.45 t ha-1 a-1)(15.5 GJ t-1) of pellets). Peat substitution is 4.8 t ha-1 a-1 (68.9 GJ ha-1 a-1/ 14.43 GJLHV t-1). Thus, the emission credit eccr is calculated to be 9.7 t of CO2-eq ha-1 a-1 [(4.8 t ha-1 a-1)(14.88 GJprimary energy t-1)(136.9 kg CO2-eq GJprimary energy-1)]. With allowance for 44.7 GJbiodiesel a-1, this equates to 217.7 kg of CO2-eq GJbiodiesel-1. 8. Results 8.1. Energy Balance. The results of net energy balances are shown in Figure 3. For scenarios (base without lime, base with lime, 1, 2, 3, 4), the net energies are 25.3, 23.0, 38.0, 102.9, 48.8, and 113.7 GJ ha-1 a-1, respectively. From an energy perspective, it is better to use rape cake and glycerol to produce biomethane for transport than to use rape cake for animal feed and glycerol for heat (scenario 1 vs scenario 3). The net energy benefit is 16.7 GJ ha-1 a-1 (scenario 3, biomethane) as compared to 5.9 GJ ha-1 a-1 (scenario 1, feed and heat). Use of rape straw for thermal energy is extremely advantageous in comparison to ploughing back to the land. The benefit is 64.9 GJ ha-1 a-1 of net energy; this is where the majority of energy lies. The net energy from straw is more than twice the net energy from biodiesel. It is thus considered
(55) Eaton, J. M.; McGoff, N. M.; Byrne, K. A.; Leahy, P.; Kiely, G. Land cover change and soil organic carbon stocks in the Republic of Ireland 1851-2000. Climate Change 2008. DOI: 10.1007/s10584-0089412-2. (56) Nilsson, D. Energy, exergy and emergy analysis of using straw as fuel in district heating plants. Biomass Bioenergy. 1997, 13, 63–73. (57) Passalacqua, F.; Zaetta, C. Pellets in Southern Europe. The state of the art of pellets utilisation in Southern Europe. New perspectives of pellets from agri-residues, 2nd World Conference on Biomass for energy, Industry and Climate Protection, Rome, Italy, May 10-14, 2004. (58) Thek, G.; Obernberger, I. Wood pellet production costs under Austrian and in comparison to Swedish framework conditions. Biomass Bioenergy 2004, 27, 671–693. (59) Homepage of Sustainable Energy Ireland. http://www.sei.ie/ Publications/Statistics_Publications/Energy_Balance/ (accessed July 2009).
(60) Kenny, T.; Gray, N. F. Comparative performance of six carbon footprint models for use in Ireland. Environ. Impact Assess. Rev. 2009, 29, 1–6. (61) Cleary, J.; Roulet, N. T.; Moore, T. R. Greenhouse gas emissions from Canadian peat extraction, 1990-2000: A life-cycle analysis. Ambio 2005, 34, 456–461. (62) Styles, D.; Jones, M. B. Energy crops in Ireland: Quantifying the potential life-cycle greenhouse gas reductions of energy-crop electricity. Biomass Bioenergy 2007, 31, 759–772.
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Table 9. GHG Emissions (kg of CO2-eq GJbiodiesel-1) from Different Components in the Integrated Rape Seed System
released emissions cultivation, eec processing, ep transport, etd fuel in use, eu total released emissions
rape seed to biodiesela
rape cake to animal feed
36.46 7.32 0.15 3.81 47.74
33.83 1.76 0.33
emission savingsd geological storage, eccs replacement, eccr total emission savings net released emissionsc
47.74
glycerol to heat
0.01 0.77 0.78
35.92
rape cake and glycerol to biomethane
rape straw to pellets
33.83 21.53 0.08
9.14 0.39
55.44
9.53
-57.02b -57.02
-5.88 -5.88
-56.54 -56.54
156.32 -217.75 -61.43
-21.1
-5.1
-1.1
-51.9
a
Greenhouse gases are allocated to rape seed biodiesel based on the energy content (see Table 4 for full GHG figures). b A total of 10.62 kg of CO2-eq GJbiodiesel-1 from barley and 46.4 kg of CO2-eq GJbiodiesel-1 from soybean meal. c Net released greenhouse gases = total released - total saving. d Negative sign represents the GHG saving, while positive sign represents the GHG released.
(5) Scenario 4, scenario 3 plus straw for thermal energy, provides a GHG saving of 106.0%. 9. Discussion 9.1. Lime. In a previous paper,3 the authors evaluated the GHG savings of rape seed biodiesel using a no-allocation approach and found a 28% savings as compared to diesel. The savings are reduced to 4.4% when lime application to acidic land is included in the analysis. The effect of lime on the energy balance and GHG emissions is significant. In terms of crop production, it is responsible for 14% of energy and 30% of GHG emissions (Table 4). 9.2. Allocation. Allocation by energy content (from biodiesel to coproducts, in particular rape cake) while ignoring credits (rape cake to animal feed, straw to thermal energy) improves the GHG emissions savings to 45% (Figure 4). GHG savings from European rape seed biodiesel systems using an allocation by an economic value yielded results of 32-33%.6,19 Bernesson and co-workers17 arrived at a figure of 54% GHG savings based on an allocation by energy content; using a no-allocation approach they arrived at a 0% GHG savings, very similar to the result here of 4% 9.3. Nitrous Oxide. A review of the literature on N2O emissions is complicated and contradictory due to site specific characteristics, management practices and environmental conditions. Indirect N2O emissions in relation to the biological nitrogen (N2) fixation by grain legumes (i.e., soybean) are not well understood.63 N2 fixation by legumes as a source of N2O emissions has been excluded from the national inventory calculations due to lack of sufficient evidence.64 The use of grain legumes in crop rotation increases soil fertility and crop yields.65 In such a case, N2O emissions from N2 fixation should be allocated to other crops in rotation. Crutzen and co-workers66 in a recent publication
Figure 4. GHG saving from different scenarios.
as the major factor that improves the sustainability of the rape seed system. 8.2. GHG Emissions. Biodiesel in the Allocation Approach. Rape seed biodiesel, with the allocation of GHG emissions by proportion to rape cake and biodiesel, is responsible for 47.74 kg of CO2-eq GJbiodiesel-1 (Table 9). Rape Cake and Glycerol. The GHG analysis yields a totally different viewpoint on rape cake and glycerol use to the energy analysis. Rape cake used for animal feed coupled with glycerol for heat provides a GHG saving of 26.2 kg of CO2-eq GJbiodiesel-1, while rape cake and glycerol for biomethane production provide a saving of only 1.1 kg of CO2-eq GJbiodiesel-1 (Table 9). Rape Straw. The GHG analysis agrees with the energy analysis on the benefits of the use of rape straw to produce pellets for thermal energy. This provides the highest GHG saving among the options, offering a saving of 51.9 kg of CO2-eq GJbiodiesel-1. The system is greatly enhanced by the displacement of the environmentally unsound practice of producing peat from bogs for combustion; eccr is 40% greater than eccs. 8.3. GHG Saving. GHG savings from different scenarios are summarized in Figure 4. The GHG savings are determined from eq 2, using the fossil fuel comparator figure of 87.3 kg of CO2-eq GJdiesel-1.3 (1) The base case scenario without lime and the base case with lime provide the lowest GHG saving at 28.0% and 4.4%, respectively. (2) Scenario 1, base case with lime plus rape cake for animal feed and glycerol for heat production, generates a GHG saving of 75.3%. (3) Scenario 2, scenario 1 plus straw for thermal energy, generates a GHG saving of 134.8%; this is the best option. (4) Scenario 3, base case with lime plus rape cake and glycerol for biomethane, provides a GHG saving of 46.6%.
(63) Zhong, Z.; Lemke, R.; Nelson, L. M. Nitrous oxide emissions associated with nitrogen fixation by grain legumes. Soil Biol. Biochem. 2009, 41, 2283–2291. (64) IPCC. IPCC guidelines for national greenhouse gas inventories. In Agriculture, Forestry and Other Land Use, Prepared by the National Greenhouse Gas Inventories Programme, Vol. 4; IGES: Kanagawa, Japan, 2006. (65) Lupwayi, N. Z.; Kennedy, A. C. Grain legumes in northern Great Plains: impacts on selected biological soil processes. Agron. J. 2007, 99, 1700–1709. (66) Crutzen, P. J.; Mosier, A. R.; Smith, K. A.; Winiwarter, W. N2O release from agro-biofuel production negates global warming reduction by replacing fossil fuels. Atmos. Chem. Phys. 2008, 8, 389–395.
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highlighted the reduction in GHG savings associated with N2O release from agro-biofuel production. However, it was argued that they did not conduct a life cycle study and a life cycle study is needed to properly account for relevant factors.67 Kim and Dale68 examined the regional variations in GHG emissions associated with soybean in the United States. They concluded that even though a very small quantity of nitrogen fertilizer was applied during soybean cultivation, N2O emissions from soil were one of the largest GHG sources because of nitrogen fixation during soybean cultivation. Metay and co-workers69 indicated that the conversion of native ecosystems of Cerrado to agricultural uses also increased N2O emissions. 9.4. Carbon Stocks. Bayer and co-workers70 showed that with a no-till system, carbon stocks in Brazilian Cerrado soils increased with a mean rate of carbon sequestration of 1.28 t of CO2-eq ha-1 a-1 when compared to tillage. This is confirmed by Metay and co-workers.71 However Metay and co-workers69 stated that N2O emissions from soils also increased as a result of no-till. This effect reduced the carbon sequestration balance to around 1.17 t of CO2-eq ha-1 a-1. This does not reduce the magnitude of GHG emissions resulting from the conversion of Cerrado pasture land to arable land (65 t of CO2-eq ha-1 in this study; section 5.3). 9.5. Land Use Change. Dalgaard et al.72 estimated GHG emissions associated with soybean meal from Argentina as 721 kg of CO2-eq tmeal-1. This did not include for deforestation. GHG emissions increased to 5700 kg of CO2-eq tmeal-1 when the deforestation effects were included.72 Our value considering conversion of grassland to arable land generates a figure of 1092 kg of CO2-eq tmeal-1. This highlights the importance of land use change. A variation in magnitude of GHG emissions due to conversion of grassland to arable land is found in the literature. Reijnders and Huijbregts19 reported a range between 92 and 103 t of CO2-eq ha-1 compared to 65 t of CO2-eq ha-1 (Bringezu et al.42) used in our study. Rapeseed is presently grown in a 4 year rotation on arable land in Ireland. It is used as a break crop in a cycle which includes wheat and barley. The authors do not envisage ecosystem or habitat destruction as it is not proposed to convert pasture land or forestry to arable land. 9.6. Sensitivity. The Irish biodiesel system is benefiting from reduced habitat destruction in Latin America. This is a controversial argument, which must be included under
land use change. The displaced importation of soybean by rape cake as a feedstock is beneficial when GHG emissions and reductions in C sequestration due to conversion of pastureland are taken into consideration. If the factor associated with indirect N2O emissions were to be included in the life cycle analysis, the GHG saving for rape cake replacing soybean would be of a higher magnitude. Nobre73 measured an increase in N2O emissions up to 1.2 g of N2O-N ha-1 d-1 within the first 100 days of crop establishment probably due to an increase of biological N fixation by the crop. If the figure was applied to our analysis, the GHG saving for rape cake replacing soybean meal could increase by 11%. On the other hand, if the GHG emissions associated with conversion of pastureland were omitted from the analysis, then the benefit of GHG saving from the replacement would be entirely removed and it would then be better to produce biomethane from rape cake and glycerol. 9.7. Biomethane. It was expected by the authors in advance of the work that biomethane would be a very favorable option. This was proved true from an energy perspective (scenarios 3 and 4, Figure 3) but not so from a GHG perspective. The reason for the low GHG saving in the biomethane scenario is the high energy input associated with rape cake as a proportion of energy output. In the allocation methodology, rape cake is responsible for 33.83 kg of CO2-eq GJbiodiesel-1. The GHG saving for the biomethane system is from displaced diesel. Approximately 804 L of diesel is displaced (30 GJ ha-1 a-1). Attributing GHG emissions of 87.3 kg of CO2-eq GJdiesel-1,5 the savings are 56.5 kg of CO2-eq GJbiodiesel-1. Thus the emissions associated with the rape cake are 60% of the emission savings. 9.8. Straw Substitution for Peat. The greatest source of energy and GHG savings is associated with use of straw as a thermal energy source. In particular, the substitution of peat briquettes as a source of thermal energy in Ireland pushes the GHG savings over 100%. Again the biodiesel system is benefiting from reduced habitat destruction 9.9. Can Rape Seed Biodiesel Meet the EU Sustainability Criteria for Biofuels? To comply with the GHG saving limit after 2017 of 60%, the rape seed biodiesel system should at a minimum include rape cake for animal feed (allowing for displaced soy importation with associated habitat destruction in Brazil) and glycerol for heat production. For an optimum system, rape seed biodiesel should include combustion of rape straw as a source of thermal energy substituting for peat.
(67) Dale, B. Calculation of Direct and Indirect N2O emissions and other Procedures in the EPA Draft Regulatory Impact Analysis: A Critical Evaluation, http://www.ncga.com/files/pdf/N2OemissionsinEPAdraftreport_dale.pdf. (68) Kim, S.; Dale, B. E. Regional variations in greenhouse gas emissions of biobased products in the United States-corn-based ethanol and soybean oil. Int. J. Life Cycle Assess. 2009, 14, 540–546. (69) Metay, A.; Oliver, R.; Scopel, E.; Douzet, J. M.; Moreira, J. A. A.; Maraux, F.; Feigl, B. J.; Feller, C. N2O and CH4 emissions from soils under conventional and no-till management practices in Goi^ania (Cerrados, Brazil). Geoderma 2007, 141, 78–88. (70) Bayer, C.; Martin-Neto, L.; Mielniczuk, J; Pavinato, A.; Dieckow, J. Carbon sequestration in two Brazilian Cerrado soils under no-till. Soil Tillage Res. 2006, 86, 237–245. (71) Metay, A.; Bernoux, M.; Boyer, T.; Douzet, J. M.; Feigl, B.; Feller, C.; Maraux, F.; Oliver, R. Storage and forms of organic carbon in a no-tillage under cover crops system on clayey Oxisol in dryland rice production (Cerrados, Brazil). Soil Tillage Res. 2007, 94, 122–132. (72) Dalgaard, R.; Schmidt, J.; Halberg, N.; Christensen, P.; Thrane, M.; Pengue, W. A. LCA for food products: Case study: LCA of soybean meal. Int. J. LCA 2008, 13, 240–254.
10. Conclusions This paper highlights the importance of allocation methodology and substitution effects on a rape seed biodiesel system. In a no-allocation approach, the rape seed biodiesel system including lime only affects a 4.4% savings in GHG emissions as compared to diesel. However allocation by energy content (distributed between biodiesel and rape cake) softened this detrimental effect. In particular the use of rape cake as a feed stock for animals, reducing imports from Latin America of soybean meal, is a significant plus to the system, especially when land use change is associated with the production of soybean. Together with use of glycerol as a source of (73) Nobre, A. D. Nitrous oxide emissions from tropical soils. Ph.D. Dissertation, University of New Hampshire, Durham, NH, 1994.
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heat, this is now a sustainable system resulting in GHG emission savings of 75%. Use of straw pellets to substitute for the environmentally unsound practice of producing peat from bogs also greatly enhances the system; coupled with use of rape cake as a substitute for soybean the GHG savings are 135%.
Acknowledgment. The authors acknowledge The Higher Education Authority (HEA) under the HEA PRTLI Cycle 4 ERI program for funding the research. Nicholas Korres, Anoop Singh, Beatrice Smyth, Abdul Sattar Nizami, John Buckley, Richard Kearney, and Brian Nixon are acknowledged for their advice, brainstorming sessions, conversations, and critiques.
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