Experimental investigation of tar formation and producer gas composition in biomass steam gasification in a 100 kW dual fluidised bed gasifier

Abstract

Abstract In this study, three types of biomass including corn stover, radiata pine wood and rice husk in the form of pellets were gasified with steam as gasification agent in a 100 kW dual fluidised bed gasifier. Tar formation in initial devolatilization stage and its correlation to the final tar concentration in the producer gas were investigated. In addition, the yields and composition of the producer gas for each type of biomass were also examined. In the gasification experiments, operating temperature was controlled, respectively, at 700 °C and 800 °C. Silica sand was used as the bed material with an inventory of 30 kg. For simulation of the initial devolatilization stage in the steam gasification, N2 was used as fluidization agent. From this study, it is found that there was a positive correlation between tar contents in the devolatilization product gas and those in the final producer gas from gasification. In the devolatilization stage, radiata pine biomass yielded more phenols, while corn stover generated more toluene. Based on the results of this study, tar formation mechanism was proposed which is verified by the observation that more naphthalene was present in the producer gas from gasification of radiata pine while gasification of corn stover produced more biphenyl. The experimental results also show that at gasification temperature of 700 °C, the producer gas yield was the highest for corn stover followed by rice husk and then radiata pine wood. However, for gasification at 800 °C, the trend was reversed with radiata pine having the highest yield followed by risk husk and the corn stover. At both 700 and 800 °C, the radiata pine biomass produced a producer gas with higher contents of H2 and CH4 while the producer gas from rice husk had a higher content of CO and that from corn stover had a higher content of CO2, C2H4 and C2H6. These differences are closely related to the chemical composition of the biomass which was also analysed in this study. Radiata pine had a higher content of lignin (31.96 wt%), rice husk had a higher content of hemicellulose (25.30 wt%) while corn stover was rich in cellulose (69.85 wt%).