Torrefaction of Commonly Disposed Agricultural Waste Biomass for anImproved and Sustainable Energy Future: A Review

Abstract

Scientists and policymakers are continuously making techno-economic efforts to close the loop in the agricultural value chain by utilizing and maximizing agricultural wastes and their products. The rising issues of agricultural waste management significantly impact on the ecosystem, and impede to environmental sustainability. Untreated and wrongly disposed agricultural residues are a major threat to health (human and animal), the economy and a significant contributor to greenhouse gas emissions.  However, this review extrapolates a resource efficiency technology to address the energy deficit by converting these sustainable waste resource sources to sustainable energy through a sustainable energy system. The torrefaction technique is a more energy-efficient thermochemical process to upgrade the biomass fuel quality. Studies on readily available and commonly disposed agricultural wastes valorised with their energy values, energy density and physicochemical properties were reported in this study and their performances were compared with fossil fuel (coal and sub-bituminous coal) properties. The assessment brings to the submission that many agricultural wastes can be upgraded into comparable quality in performance via the torrefaction process. It further discovers that the synergy of certain additives and the optimization of process conditions such as residence time, temperature, pressure, and gas carrier could better upgrade the biofuel quality without major compromise on product yield.