The Effect of Biomass Feedstock Type and Process Parameters on Achieving the Total Carbon Conversion in the Large Scale Fluidized Bed Gasification of Biomass

One option for the production of liquid biofuel in Finland is based on fluidized bed gasification of biomass and Fischer-Tropsch synthesis process. The total carbon conversion achieved in the gasifier, operating at temperatures below 1000°C, depends mainly on the reactivity of solid char residue. The reactivity of the char residue is affected by temperature, partial pressures of the reactants H₂O and CO₂ and product gas components (H₂ and CO), which are inhibiting the reactivity. In this reactivity, catalytic active substances, alkaline and earth-alkaline metal compounds play a significant role. Other elements like silicon can react with the metals, leading to losses in the catalytic activity. These elements are naturally occurring in the biomass, and their behavior is individually dependent on the biomass type. The carbon conversion can be improved by increasing temperature, but it should not be too high to avoid ash sintering. By increasing the pressure, the reactivity increases normally, but for biomass it sometimes has no effect or it is even reduced. It was also observed that during the process of debarking and storage of biomass, it remains in contact with water, which can reduce the amount of some alkaline and earth alkaline metals because of leaching that can further affect reactivity and ash sintering. We studied the effects of the above-mentioned factors on various barks, like spruce, pine, birch, aspen, which are the most potential biomass feedstock to be used in the large-scale gasification in Finland. The measurements were carried out in the pressurized thermobalance in the conditions relevant for the pressurized oxygen gasification. Thus, the total pressure range was up to 20 bar, and the partial pressures of the reactants and the product gas components varied respectively. The parameters measured will be used for the development of the gasifier model.