Life-Cycle Assessment of Pyrolysis Bio-Oil Production*

Abstract

As part of the Consortium for Research on Renewable Industrial Materials’ Phase I life-cycle assessments of biofuels, lifecycle inventory burdens from the production of bio-oil were developed and compared with measures for residual fuel oil. Bio-oil feedstock was produced using whole southern pine (Pinus taeda) trees, chipped, and converted into bio-oil by fast pyrolysis. Input parameters and mass and energy balances were derived with Aspen. Mass and energy balances were input to SimaPro to determine the environmental performance of bio-oil compared with residual fuel oil as a heating fuel. Equivalent functional units of 1 MJ were used for demonstrating environmental preference in impact categories, such as fossil fuel use and global warming potential. Results showed near carbon neutrality of the bio-oil. Substituting bio-oil for residual fuel oil, based on the relative carbon emissions of the two fuels, estimated a reduction in CO2 emissions by 0.075 kg CO2 per MJ of fuel combustion or a 70 percent reduction in emission over residual fuel oil. The bio-oil production life-cycle stage consumed 92 percent of the total cradle-to-grave energy requirements, while feedstock collection, preparation, and transportation consumed 4 percent each. This model provides a framework to better understand the major factors affecting greenhouse gas emissions related to bio-oil production and conversion to boiler fuel during fast pyrolysis. This report has been produced as part of the Consortium for Research on Renewable Industrial Materials (CORRIM) Phase I reports on the life-cycle inventory (LCI) and life-cycle impact assessment (LCIA) studies of biofuels. CORRIM’s goal is to provide a database of information for quantifying the environmental impacts and economic costs of biofuels from woody biomass through the stages of collection, fuel conversion, and combustion in the United States. Life-cycle assessment (LCA) has evolved as an internationally accepted way to analyze complex impacts and outputs of a product and the corresponding effects on the environment. An LCA can provide the most comprehensive method to assess net carbon emissions and their associated impacts for fossil and biofuels evaluated under similar uses. The environmental outcomes of an LCA can accurately target the source of impacts, including where, when, and how they occur throughout a product’s life. The LCA process can provide characteristics such as global warming potential (GWP) and fossil fuel use that can be useful on a regional, national, or global scale. Outcomes from LCAs can be used to suggest more ‘‘environmentally friendly’’ products or sustainable production methods and may also provide insights regarding raw material conservation and emissions and waste output reduction. LCIA aggregates the inventory data and classifies them into the type of environmental impact to which they contribute, for example, GWP. Comparisons of the emission outputs of bio-oil with a relevant fossil fuel