Step washing: A modified pretreatment approach for industrial applications to improve chemical composition of agricultural residues

To improve the efficiency and applicability of the washing pre-treatment for combustion, pyrolysis and gasifi-cation, a modified approach was developed in the present study. Two novel washing approaches were tested using wheat straw and empty fruit bunches of oil palm: multiple-step washing with fresh water (SWFW) and wastewater recirculation (SWWR). SWFW showed the high removal of K (<68%), Cl (<99%), S (<80%), N (<58%), and ash (<52%) reducing fouling, slagging, and corrosion propensity of the biomass. Furthermore, with one-third the amount of water used in SWFW, SWWR showed similar to higher efficiency than SWFW with relatively better energy (98%) yields. Industrial-scale pilot testing was also conducted for the validation of the SWWR approach, which showed similar findings as the lab-scale results. The effect of a high washing temper-ature and pressing on washing efficiency and characterisation of wastewater was also determined. Overall, SWWR with pressing is recommended for industrial applications.

Automated summary

Two novel washing approaches, SWFW and SWWR, were developed in this study. SWFW showed significant reduction in fouling, slagging, and corrosion of biomass, while SWWR achieved similar to higher efficiency with better energy yields. Industrial-scale testing confirmed the applicability of SWWR, making it recommended for industrial applications.