Effect of water washing on fuel properties, pyrolysis and combustion characteristics, and ash fusibility of biomass

In this study, six biomass fuels are washed with deionized water at different temperatures, by a well designed test setup. The effects of water washing on fuel properties, pyrolysis and combustion characteristics, and ash fusibility of biomass fuels are studied via fuel analysis, thermogravimetric analysis and ash fusion temperature measurements. A better method for evaluating the removal efficiency of element contained in biomass has been proposed. The results show that potassium, sulfur and chlorine contained in biomass, which may be harmful to boiler operation, can be effectively removed by washing. After washing, the hemicellulose and cellulose peaks move apart in the derivative thermogravimetric profile and the devolatilization begins at a higher temperature during pyrolysis and combustion processes. Washing also delays the char combustion. Except for candlenut wood and rice hull, washing significantly increases the ash fusion temperatures for biomass fuels. As water temperature increases, the removal efficiencies of potassium, amorphous silica and ash increase for all the six biomass fuels, and the temperature intervals between the deformation temperature, softening temperature and fluid temperature decrease only for washed samples of wheat straw and corn stalk. ► Water washing improves fuel properties for all the six biomass fuels. ► The removal efficiencies of K, SiO2 and ash increase as water temperature rises. ► Water washing delays the devolatilization and the char combustion. ► The temperature intervals between DT, ST, and FT decrease as water temperature rises. ► Suggestions for industrial application of water washing are given.