Life cycle greenhouse gas emissions of bio-oil from two-step torrefaction and fast pyrolysis of pine

Life cycle assessment of bio-oil from woody biomass through two pathways was carried out using a one-step pathway that utilizes fast pyrolysis of pine and a two-step pathway that incorporates a torrefaction step prior to fast pyrolysis. A two-step pathway with torrefaction at a temperature of 330 degrees C and pyrolysis at 530 degrees C had a global warming potential of about 6 g CO2 equivalent per MJ of bio-oil compared to about 39 g CO2 equivalent per MJ of bio-oil for a one-step pathway using an energy allocation-based analysis. For a one-step pathway, the size reduction step made the highest contribution of over 50% of the overall global warming potential. Greenhouse gas (GHG) savings of up to 80% compared to heavy fuel oil (HFO) were achieved for a two-step pathway in comparison to a one-step pathway due to savings in size reduction energy. The use of renewable energy sources produced internally to provide process heat either by first burning char and then condensables from torrefaction (oil) or vice versa resulted in similar global warming potential reduction in comparison to use of natural gas to provide process heat. The bio-oil production pathways were found to be more sustainable in comparison to HFO due to relying chiefly on renewable biomass rather than fossil energy. (c) 2016 Society of Chemical Industry and John Wiley & Sons, Ltd