Biorefinery systems for energy and feed production : greenhouse gas performance and energy balances

Abstract: The current dependence on fossil fuels is problematic because these are a finite resource and because their combustion causes environmental degradation. Biorefineries produce a variety of valuable products from biomass that can replace products from petroleum refineries. Biorefining can also introduce new process technologies and increase the use of biomass resources traditionally not utilised for industrial purposes. Although biomass is considered to be a renewable resource, biomass production and processing are associated with environmental impacts. This thesis examined the environmental impacts of biorefinery systems and products by studying the climate impact and energy balance of two innovative biorefinery systems from a life cycle perspective. These systems were: (1) co-production of ethanol, biogas, electricity and heat in a lignocellulosic biorefinery and (2) processing of faba beans in a green crop biorefinery producing ethanol, protein feed and briquettes. Life cycle assessment methodology concerning biorefinery systems and biomass utilisation was also examined. The analysis showed that increased residue harvesting from agriculture and forestry had a potentially high impact on overall greenhouse gas (GHG) performance, mainly due to soil organic carbon (SOC) changes. Ethanol from the lignocellulosic biorefinery gave GHG savings of 51-84% compared with a fossil fuel reference and used between -0.71 and 0.20 MJ fossil energy per MJ ethanol. Biorefinery processing of whole faba beans marginally decreased the climate impact (-2%), while primary fossil energy use (-119%) and land use (-20%) decreased significantly compared with reference use of the beans as dairy cow feed. On balance, it was concluded that ethanol production from faba bean is not favourable in a climate perspective. The results for GHG performance and energy balance varied significantly depending on method choices, the most influential being handling of multi-functionality and system boundaries, i.e. inclusion of upstream impacts in the form of SOC losses.