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Konferensabstrakt2013

Comparison of LCA methods for evaluating biorefinery products

Karlsson, Hanna; Ahlgren, Serina; Börjesson, Pål; Hansson, Per-Anders

Sammanfattning

Current trends in the development of biofuel production systems are towards maximization of high-value product output as well as an increased focus on the sustainability of biomass feedstock production. Co-production of products such as energy, food and chemicals in so called biorefineries is a promising alternative for optimized utilization of biomass. Lignocellulosic materials such as straw and other agricultural or forestry residues have been identified as attractive alternatives feedstock because of their high availability and lower resource demand. In Sweden both ethanol and biogas are used as transportation fuels, co-production of these fuels increases the biofuel conversion efficiency compared to separate production systems. Biorefineries producing a variety of high-value co-products, pose particular challenges for sustainability assessment methodologies including handling of co-products and definition of functional unit. Therefore there is a need for a discussion on critical methodological issues in LCA, for biofuels in general and specifically for biorefinery systems. Further, LCA as an environmental evaluation tool is increasingly used in policies, with methodological rules for the calculations e.g. as in the EU Renewable Energy Directive (RED) (Directive 2009/28/EC). Using different type of methodology can give large variation of results. With a predicted increasing share of biofuels produced in biorefineries, these methodological challenges needs to be addressed. The present case study analyses the greenhouse gas (GHG) performance of ethanol co-produced with biogas in a large scale hypothetical biorefinery system using straw as feedstock. Additional co-products are electricity and heat. Two calculation methods are applied. Calculation Method I (RED) use the methodology specified in the RED with allocation based on lower heating value (LHV) and excluding the impact from cultivation since straw is considered a residue in the RED. Calculation Method II (ISO) follows the principle of system expansion which is preferred over allocation in the ISO standards (14040/44). This includes alternatives to the generated co-products and soil organic carbon (SOC) changes due to straw removal. The functional unit was set to 1 MJ (LHV) ethanol.The GHG performance of 1 MJ ethanol was found to be 17.4 g CO2e using Method I (RED) and 43.6 g CO2e using Method II (ISO). SOC changes hade the largest impact in Method II (ISO), while the impact from the use of enzymes and were most significant in Method I (RED). The results show that the choice of allocation method was important and significantly altered the results. Generally system expansion can result in large credits especially when high value co-products such as upgraded biogas are produced. Ultimately the importance of the substitution effect will depend on the production mix in the biorefinery. With the introduction of biorefineries with diverse sets of co-products, there might be a need to reconsider the use of energy allocation as the default method in the RED. Energy allocation does not show the benefit of the co-products, which is especially true for products that not are energy carriers. Further, the results indicate that if SOC changes were included in Method I (RED), the ethanol would only meet the current target of 35% reduction from a fossil fuel reference set in the RED. However, SOC change rates are uncertain and depend on factors such as local conditions and time aspects.

Publicerad i

SETAC ... LCA Case Study Symposium
2013, sidor: 50
Titel: SETAC Euprope 19th LCA CAse Study Symposium : LCA in market research and policy: harmonisation beyond standardisation
Utgivare: SETAC of Environmental Toxicology and Chemistry

Konferens

SETAC Euprope 19th LCA CAse Study Symposium