Burn-off behaviour in alkali-catalysed CO 2 gasification of bituminous coal char: A comparison of TGA and fixed-bed reactor

Abstract

A comparative study has been performed on the kinetics of the alkali-catalysed gasification reactivity in CO 2 of a bituminous coal char (Westerholt) at elevated pressures in a fixed-bed reactor (FBR) and a thermobalance (TGA). Both apparatus essentially yield the same kinetic description, taking into account the integral behaviour of the fixed-bed reactor. The parameters obtained for the kinetic model have physical significance and show good agreement with values reported in the literature. In TGA the intrinsic burn-off profile is observed, because the complete system is gradientless. In the FBR this information is averaged out due to the integral reactor behaviour. The burn-off behaviour of the K 2CO 3/char Westerholt can be described by shrinking sphere gasification based on the grainy pellet model, taking into account catalyst migration. Between approximately 40 and 80% burn-off an apparent order in carbon of − 1 3 is observed, which can be rationalised by the grainy pellet model and a homogeneous dispersion of the catalyst in the grains. Characterization by CO 2 and N 2 adsorption and scanning electron microscopy provide additional support for this model.