Climate Impact and Energy Balance of Emerging Biorefinery Systems
Sammanfattning: Use of fossil fuels is the main contributor to anthropogenic emissions of greenhouse gases (GHG). Biorefineries, which are facilities that produce a set of valuable products from biomass, have been suggested as alternatives to fossil refineries, for the production of fuels, chemicals and materials. Emerging biorefineries are introducing new technologies, which can lead to increased use of biomass not previously utilised for industrial processes, such as harvesting residues from agriculture and forestry. Biomass is a renewable resource, but production and processing of biomass are associated with environmental impacts.This thesis examined the climate impact and energy balance of emerging biorefinery systems, paying particular attention to the use of residues as feedstock. Three biorefinery systems were assessed and compared, all producing transportation fuels in combination with different co-products. These systems were: (1) co-production of ethanol, biogas, electricity and heat from straw in a lignocellulosic biorefinery; (2) co-production of ethanol, protein feed and briquettes from faba bean in a green crop biorefinery; and (3) co-production of biodiesel, biogas and electricity from straw in a lignocellulosic biorefinery. The analytical method used was life cycle assessment (LCA). Methodological issues when using LCA for assessing the climate impact of biorefinery systems were also discussed.Ethanol and biodiesel produced from straw and forest residues in emerging biorefinery systems were found to have a lower climate impact and better energy balance than fossil fuels. Moreover, the biorefinery system producing ethanol and co-products from straw had a lower climate impact and more beneficial energy balance than that producing biodiesel and co-products. However, when using residues from agriculture and forestry or when harvesting the whole crop as biorefinery feedstock, specific consideration of effects on soil organic carbon is needed. The study on faba bean showed that using a biorefinery feedstock that is currently used for other purposes, such as feed, can cause indirect effects that affect the overall climate performance of the system. To improve the potential value of LCA studies on biorefinery systems, selection of functional unit, allocation method and treatment of biogenic carbon fluxes over time need further attention.
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