Life cycle modelling and environmental impact assessment of energy production supply chains based on a biomass pyrolysis densification process

Biomass has the potential to play a significant role in the world energy scenarios due to its abundance and to the neutral contribution to the CO2 balance when it is used as fuel. Several thermo-chemical processes can be used to produce fuels from biomass. Pyrolysis can be considered a densification process in which the biomass is converted to solid and liquid fractions which may be transported and used for energy production. Nevertheless, the environmental and economic feasibility of a bio-energy supply chain based on this technology and its compatibility with the territory are to be intently investigated. Practical guidelines can be drawn only in a life cycle perspective. The aim of the present study was to perform a LCA study on alternatives biomass-to-electricity (BtE) supply chains based on the slow pyrolysis densification process. Three environmental indicators were included in the assessment: life cycle energy demand, emission of greenhouse gases and land occupation. The application considered co-combustion of coal with solid and liquid products obtained from the slow pyrolysis of different biomass species. Raw biomass co-combustion with coal was selected as comparative scenario. With reference to the set of indicators considered, the co-combustion of the pyrolysis products seems to yield lower environmental burdens than direct co-combustion when long transport distance (i.e. hundreds of kilometres) or high renewable power capacity (i.e. dozens of MWel) are requested. Useful indication for the potential implementation of bio-energy projects on the territory can be obtained from the results of the analysis. The study is moreover a reliable basis for further investigations on other environmental and economic issues and on alternative biomass utilisation routes.