Energy consumption balance and environmental benefits from the pyrolysis of switchgrass cultivated on marginal lands with biochar application to soil in China

The pyrolysis of switchgrass on marginal lands with biochar application to soil has the potential to bring environmental benefits through sequestrating carbon and reducing greenhouse gas (GHG) emissions without occupying crop lands. In this study, the physicochemical characteristics of switchgrass was investigated, and the energy and GHG emissions balances of the pyrolysis of switchgrass cultivated on marginal lands suitable for switchgrass cultivation in China with biochar application to soil were calculated and analyzed. Switchgrass has comparable physicochemical properties with typical herbaceous biomasses and has a good potential for thermochemical conversion. Two pyrolysis scenarios for switchgrass pyrolysis were considered, with pyrolysis temperatures of 459 and 591 degrees C and solid residence periods of 78 and 104 s for Scenarios A and B, respectively. If the marginal lands suitable for switchgrass cultivation in China would be utilized to cultivate switchgrass and the pyrolysis of all cultivated switchgrass would require 8.25 and 26.72 million tce y(-1) of energy consumption and could result in the reduction of 173.80 and 147.84 million t CO(2)e y(-1) GHG emissions for Scenarios A and B, respectively. The GHG emissions reductions would account for 1.52% and 1.30% of China's total carbon emissions in 2022 for Scenarios A and B, respectively. Biochar from switchgrass pyrolysis with Scenario B is more stable in soil than that with Scenario A, thus Scenario B is superior over Scenario A from the perspective of the long-term carbon sequestration. Switchgrass pyrolysis conversion presented the highest sensitivity in energy consumption and switchgrass production exhibited the highest sensitivity in GHG emissions. In addition, the combustion of the same quantity of switchgrass was analyzed and the results showed that switchgrass combustion application could provide more energy and lead to more carbon emissions than switchgrass pyrolysis application.