Life cycle concept in greenhouse gas assessment of switchgrass pyrolysis in a vertical auger reactor for bio-oil and biochar production

Abstract

<abstract> <b>Abstract.</b> The pyrolysis of agricultural and forest biomass and the valorisation of co-products could be a sustainable solution for mitigating climate change. However, the environmental impact of the global system from the collection of biomass to the use of co-products is not well known. Thus, the goal of this research study was to assess the greenhouse gas (GHG) emission balance of switchgrass pyrolysis in an auger reactor for biochar and bio-oil production. The life cycle assessment (LCA) approach was used to evaluate the climate change impact of the system from the cultivation of switchgrass on marginal lands to the use of biochar as a soil amendment in a wheat crop to sequester carbon (C) and reduce soil N2O emissions. Moreover, it was considered that bio-oil and syngas were used as an energy source. Two scenarios (A and B) of biochar production were compared. In scenario B, pyrolysis was carried out at a higher pyrolysis temperature (591 °C) and with a longer solid residence time (104 s) than in scenario A (459 °C and 78 s, respectively). Experimental data from pyrolysis experiments, and from an incubation study in which the GHG emission from soil amended with the produced biochars were measured, were used as input data. The results confirmed that biochar production from pyrolysis can be a negative emission technology. The production of one ton of biochar resulted in a net reduction of GHG emission of 2231 and 2772 kg CO2e t-1 biochar for scenarios A and B, respectively. Further research studies should be carried out to evaluate the long-term effects of biochar on C sequestration and soil GHG emissions..