Combined gasification of coal and biomass in internal circulating fluidized bed

The paper addresses the combined gasification of biomass and brown coal in an internal circulating fluidized bed (ICFB) for generating a valuable producer gas. A primary method for tar abatement and gas improving was adopted, consisting in a Ni-based catalyst in the bed together with sand. The hydrogen concentration in the producer gas was high (up to 35% in the best case, >20% typically) demonstrating the validity of the ICFB process for co-gasification of coal with biomass. Higher H-2 and CO contents and lower tar yields were obtained with greater coal loadings. The tar was reduced by up to three times when changing from inert to a partly catalytic bed, under steam gasification conditions. However, this good figure is contrasted by a rather fast decay in catalytic activity, and a rather low carbon conversion even in presence of the catalyst. A mathematical model based on thermodynamic computations predicts the trend and values of the measured gas concentrations at different steam/fuel ratios, providing useful indications for its optimal choice. The findings of the research reinforce the idea that dual bed gasification is suitable even when a relatively low reactivity fuel is used, such as the brown coal in this study. (C) 2011 Elsevier B.V. All rights reserved.