Ecological assessment of integrated bioenergy systems using the Sustainable Process Index

Biomass utilisation for energy production presently faces an uphill battle against fossil fuels. The use of biomass must offer additional benefits to compensate for higher prices: on the basis of a life cycle assessment (using BEAM to evaluate a variety of integrated bioenergy systems in connection with the Sustainable Process Index as a highly aggregated environmental pressure index) it is shown that integrated bioenergy systems are superior to fossil fuel systems in terms of environmental compatibility. The implementation of sustainability measures provides additional valuable information that might help in constructing and optimising integrated bioenergy systems. For a set of reference processes, among them fast pyrolysis, atmospheric gasification, integrated gasification combined cycle (IGCC), combustion and steam cycle (CS) and conventional hydrolysis, a detailed impact assessment is shown. Sensitivity analyses of the most important ecological parameters are calculated, giving an overview of the impacts of various stages in the total life cycle and showing ‘what really matters’. Much of the ecological impact of integrated bioenergy systems is induced by feedstock production. It is mainly the use of fossil fuels in cultivation, harvesting and transportation as well as the use of fertilisers in short-rotation coppice production that impose considerable ecological pressure. Concerning electricity generation the most problematic pressures are due to gaseous emissions, most notably the release of NO_x. Moreover, a rather complicated process (high amount of grey energy) and the use of fossil pilot fuel (co-combustion) leads to a rather weak ecological performance in contrast to other 100% biomass-based systems.