Valorization of Agricultural Waste: Comparative Study with Focus on Improving the Heating Value of Biomass

Abstract

Agro-based biomass is a viable alternative to fossil fuels, but problems such as ash slagging, fouling, and heated-surface corrosion impose negative impacts on the process of thermal conversion of biomass. Demineralization is a pretreatment process that can be used to alleviate these problems by decreasing the ash content of biomass feedstock. In this research work, rice husk (RH) and cotton stalk (CS) were leached with three different acid solutions (H2SO4, HCl, and CH3COOH) to investigate the potential effects on the fuel characteristics of the biomass. The leaching agents dissolved the minerals present in the biomasses and reduced the ash content; however, the percentage reduction of ash content in RH (∼29%) was lower than that in CS (∼58%). The high heating value (HHV) of both demineralized biomasses increased due to the increase in overall carbon content; however, the percentage increase in HHV in CS was greater than that in RH. The HHV of treated RH samples increased to 16.48, 16.20, and 15.97 MJ/kg when treated with H2SO4, HCl, and CH3COOH, respectively, compared with raw RH (15.41 MJ/kg). In the CS samples, the HHV of H2SO4-, HCl-, and CH3COOH-treated samples increased to 19.80, 19.20, and 18.90, respectively, compared with raw CS (18.38 MJ/kg). The thermogravimetric characterization of leached biomass showed that the demineralization with acid solutions increased the thermal stability. Fourier-transform infrared spectroscopy and scanning electron microscopy analysis illustrated that the acid leaching induced significant physiochemical structure changes in the treated biomasses. The study demonstrated that demineralization has the ability to reduce the ash content of the biomass, which improved the energy value of the biomass.