Gasification of Wood Pellets in Air and CO2

Abstract

This paper examines the gasification of woody biomass pellets and torrefied wood pellets at different temperatures using air or CO2 as the gasifying agents. The woody biomass pellets were pyrolyzed and gasified in a controlled reactor facility that allowed for the determination of sample weight loss as a function of time from which the kinetics parameters were evaluated. The experimental facility provided full optical access that allowed for in-situ monitoring of the fate of the biomass pellets and the release of gas phase under prescribed high temperature condition. Pellet sample of known weight was placed in a wire mesh cage and then introduced instantly into the high temperature zone of the reactor at known temperature and surrounding gas composition as gasifying agent. The weight loss as function of time was examined for different gasification temperatures ranging from 600–950°C using air or CO2 as the gasifying agent. Significant differences in the weight loss were observed to reveal the fundamental pyro-gasification behavior between the wood and torrefied wood pellets. The results show enhanced gasification with air at low to moderate temperatures while at high temperatures the oxygen evolved from CO2 provided a role in oxidation. The calculated activated energy was lower for woody pellets than torrefied wood pellets and it was lower with air than CO2. These kinetic parameters help in modeling to design biomass gasifiers and combustors for increased conversion efficiency and performance using biomass or municipal solid waste pellets.