Microwave torrefaction of biomass waste: Fuel property evaluation and life cycle impact

Abstract

The investigation of microwave torrefaction for solid biofuel production is significant for biomass waste conversion and environmental sustainability. In this study, a comprehensive analysis of microwave torrefied biochar fuel property and life cycle assessment is employed. The Chinese medicine residue is selected as the feedstock for biochar preparation, and its fuel property and environmental impact are evaluated. The obtained results suggest that with the increasing torrefaction severity, the fuel performance gradually becomes better. Concerning the proximate analysis, the values of volatile matter, fixed carbon, moisture, and ash content are 57.93–81.23%, 13.77–35.59%, 1.65–2.36%, 2.64–4.83%, respectively. A severer torrefaction condition would arise a better decarbonization and deoxygenation effect. Good linear relationships are obtained between torrefaction severity index (TSI) and carbonization index and TSI and deoxygenation index, with the correlation coefficient of 0.8683 and 0.8600. The life cycle assessment (LCA) result indicates that microwave torrefaction process would arise the environmental impact on greenhouse gas (GHG) emission, human toxicity, ionizing radiation, land use, and water environment pollution. Specifically, over 20% improvement in heating value and reduction in GHG emissions are achieved via microwave torrefaction process. However, lab-scale microwave torrefaction (10 g/batch) with gate-to-gate LCA shows 20% GHG reduction but excludes full-scale impacts. Totally, the obtained results are helpful for the cognition of fuel property variation and environmental impact of the Chinese medicine residue conversion and solid biofuel production, and thus for better waste-to-energy process to achieve biowastes valorization.