Upgrading properties of biochar fuel derived from cassava rhizome via torrefaction: Effect of sweeping gas atmospheres and its economic feasibility

Abstract

Torrefaction is a promising biomass thermal conversion technology to produce biochar due to its ease of operation and mild operating conditions. In this study, cassava rhizome (CR) was torrified under various sweeping gas types (nitrogen (N2), carbon dioxide (CO2), mixture gas (N2 + CO2)) and flow rates (50, 150, 250 mL/min) at 200-300 °C for 30 min. The experimental results show that fuel properties of CR were remarkably upgraded after torrefaction. Sweeping gas has less effect on fuel properties of torrified CR than torrefaction temperature. Torrefaction under CO2 atmosphere produced the biochar with minimum ash content. Torrefaction at 300 °C under 50 mL/min CO2 was recommended as the promising condition to produce biochar replacing lignite coal. Thermal properties and chemical functional groups of the derived biochar suggested that torrefaction process removed mainly oxygen and hydrogen contents which could be achieved through decarbonization (DC), dehydrogenation (DH), and deoxygenation (DO) pathways. Economic feasibility revealed that the torrefaction of CR is cost-advantage under the proposed condition.