Comparison of the gasification performance of multiple biomass types in a bubbling fluidized bed

Abstract

he present study investigates the air-steam gasification of ten commercial and alternative lignocellulosic biomass fuels (pine sawdust, chestnut sawdust, torrefied pine sawdust, torrefied chestnut sawdust, almond shells, cocoa shells, grape pomace, olive stones, pine kernel shells and pine cone leafs) in order to evaluate the product gas composition and the process performance in a bubbling fluidized bed gasifier with focus on the different biomass properties. Accordingly, an effort to correlate the biomass characteristics with the gasification results has been done. Pine kernel shell (PKS) was used to test the effect of the gasification temperature (700, 800 and 900 °C), steam to air ratio in the gasifying agent (S/A = 10/90, 25/75, 50/50 and 70/30) and stoichiometric ratio (SR = 0.13 and 0.25) on the product gas composition, combustible gas (H2 + CO + CH4) production, H2/CO ratio, heating value, energy yield and cold gas efficiency of the obtained gas. Results showed that higher temperature and S/A ratio favored H2 production and gasification performance. A higher value of SR slightly affected the gas composition, but led to a higher process efficiency as a consequence of a higher biomass conversion into gaseous combustible products. All the biomass samples of different origin and characteristics were then gasified at the best experimental conditions found (900 °C, S/A = 70/30, SR = 0.25). Gasification of all the biomasses was feasible and H2 and combustible gas concentrations of 30–39 vol% and 59–78 vol% (inert gas-free basis), respectively, were obtained for the biomasses studied, with energy yields of 8–18 MJ/kgbiomass. Torrefied biomass showed similar combustible gas production than the corresponding raw biomass under the conditions studied, but it gave slightly higher H2 production and efficiency results. Possible correlations of the gasification performance parameters with biomass properties were also analyzed. The results showed positive effects of biomass volatile matter content, C content and high heating value (HHV) on the CO and combustible gas contents, calorific value of the product gas, as well as gas and energy yields.