Biochar washing to improve the fuel quality of agro-industrial waste biomass

Abstract

Low energy density and low ash melting temperatures of agro-industrial waste biomass are bottlenecks for their sustainable use in combustion utilities. Torrefaction at low temperature (350 °C for 30 min) for energy density enhancement followed by very simple aqua-washing technique to remove soluble mineral matters from biochar (BC) samples have been employed in this research work to investigate possible improvement of combustion performance of tobacco stalk (TS), sugarcane bagasse (SB), and poultry litter (PL) biomasses (BM). Though the energy density of the BC was significantly higher than their respective BM, the propensity for slagging was also higher, particularly in TS-BC and PL-BC. On char washing, ash content as well as the slagging and fouling tendencies were estimated to be decreased. Energy densification ratio (as compared to biomass) as well as GCV were further increased in washed biochar (WBC). As per the DSC-TGA investigations, combustion reactivity of BC was improved by washing. The significant advantages of BC washing were observed in TS-BC and PL-BC due to the removal of a large amount of soluble materials from respective BCs. As the water extracted material from SB-BC is insignificant, unwashed SB-BC having sufficiently high GCV (20.6 MJ/kg), energy densification ratio (1.5), carbon content (66.7%) can be directly used without washing. Water washing of BC is highly beneficial for TS and PL in respect of combustion performance and a valuable potassium-rich fertilizer material was obtained on evaporation of the leachate depicting unique value-addition of entire process.