Life cycle assessment of forest-based biomass for bioenergy: A case study in British Columbia, Canada

摘要

Large quantities of residual forest-based biomass, including harvesting and sawmill residues, are available in British Columbia, Canada. They can be used to generate bioenergy. Currently, harvesting residues are burned to reduce fire hazard, and private and remote sawmills' residues are either burned or landfilled. While previous studies assessed the impact of bioenergy production from residual forest-based biomass on global warming, this life cycle assessment includes a comprehensive set of ten impact categories. Adopting a case study in a region in British Columbia, a life cycle model is applied to three locations considering four combustion and gasification technologies with different capacities (0.5 MW, 2 MW, 3 MW and 5 MW) and product outputs (electricity and/or heat). Most bioenergy supply chain scenarios showed improved environmental performance due to avoided uncontrolled combustion of residues and avoided fossil fuel combustion, particularly in the categories of acidification (+1% to -71%), eutrophication (-2% to -85%), fossil resource depletion (-2% to -84%), respiratory effects (0% to -96%), and photochemical ozone formation (+3% to -59%). Benefits were larger at locations dependent on fossil energy compared to locations dependent on hydropower. In contrast, ecotoxicity values increased in most scenarios (+460% to -11%), due to wood ash disposal. Results confirmed conversion efficiency and wood ash disposal as influencing factors in bioenergy supply chains for the investigated region, but showed a minor influence of the feedstock procurement distance. Moreover, the results emphasized the high contribution of uncontrolled bumings to the overall environmental impact of the forest biomass supply chains.