| With increased concerns over greenhouse gas emission and decreasing fossil fuel supplies, biomass is increasingly seen as an alternative option for energy and chemical production. There are several technologies available to upgrade biomass to useful energy and fuel products, and one of the most promising is gasification. Tar formation is the major challenge for biomass gasification. Formation of tars represents not only a decrease in gasification efficiency, but would cause some operating issues such as fouling and potential clogging due to the condensation of tars as they cool downstream.;The second part of this thesis investigated the potential for the use of catalytic bed materials within a pilot-scale bubbling fluidized bed gasifier at the CANMET Energy Technology Centre (CETC) in Ottawa for air blown gasification of woody biomass. The effects of bed materials (olivine, limestone, dolomite, and a crushed iron ore) and equivalence ratios (ER, 0.20-0.40) on tar formation and syngas composition were investigated with white pine sawdust and crushed peat. All bed materials were calcined prior to gasification within the reactor under combustion conditions. Increasing the equivalence ratio generally led to decreased tar yield. Combustible gas (methane, hydrogen, and carbon monoxide) yields were generally highest at medium ER values (0.25-0.30). Tar and combustible gas yields were lower for crushed peat as compared to pine sawdust for all ER values under similar conditions. Calcined limestone exhibited the highest catalytic activity for tar reduction at all ERs tested, leading to a very low tar yield of 3.5-8.3 g/kg biomass. Other bed materials were similar to each other in terms of tar reduction, though dolomite and iron oxide appeared to be slightly more active than olivine. Dolomite and limestone produced the highest combustible gas yields. Olivine, however, was the most physically/thermally stable bed material. In contrast, limestone, dolomite, and iron oxide all appeared to be inferior to olivine for use as bed materials in a fluidized bed gasifier due to their high rates of fragmentation.;In the first part of this thesis, several impregnated metal ions (iron, cobalt, nickel, and ruthenium) and a locally available raw iron ore (natural limonite) were examined for use as catalysts for gasification of pine sawdust in the media of air/CO2 at 700°C and 800°C. Compared with air, CO2 as a gasifying agent for biomass gasification showed a much lower reactivity. The yields of char and tar both increased with increasing CO2 concentration in the feed gas. A higher temperature and a greater oxygen content in the feed gas led to higher gasification efficiency. It was observed that the addition of iron ore to the biomass feedstock simply by physical mixing did not alter the yields of all products significantly irrespectively of the types of gasification agent and the gasification temperature, which was likely due to the poor contact between the catalyst and the gas/vapor products during the gasification process. All the impregnated metal cations (Fe, Ni, Co and Ru), in particular Ni, Co and Ru, were very effective for promoting the gasification of the woody biomass at 700°C and 800°C, leading to a lower tar yield, a significantly decreased char yield and a greatly increased yield of CO2-free gas. At 800°C, the impregnation of Fe, Ni, Co or Ru led to almost complete conversion of the solid biomass into gas and liquid products, producing an extremely low char yield (<1-4 wt%), and a very high yield of combustible CO2-free gas (ranging from 51.7 wt% for Fe to 84 wt% for Ru). The tar yield also reduced significantly from 32.1 wt% without catalyst to 19-27 wt% with the impregnated metal ions. The addition of all impregnated metal cations significantly enhanced the formation of both carbon monoxide and hydrogen. |
