Model study of carbonisation of low rank coal briquettes: Effect of briquettes shape

Abstract

Carbonisation is a promising process to upgrade low rank coal briquettes to clean coal, where the shape of briquettes in the carbonisation reactors may be significantly different, including sphere, ellipsoid, cylinder, half-ellipsoid. However, the influence of briquette shape variation on carbonisation performance has not been studied. In the present study, an integrated numerical model is developed and applied to investigate the effect of briquette shape on carbonisation behaviour of low rank coal briquettes in a pilot-scale coke oven. This model integrates a DEM model to simulate packing structure evolution of briquettes in four different shapes; and a CFD model to simulate the carbonisation process. This model is validated against the experimental data. The simulation results indicate that briquettes with different shapes have different packing statuses during the carbonisation in terms of bed height and packing density. Specifically, the half-ellipsoidal and cylindrical briquettes show an upward trend of packing density during the carbonisation, which is opposite to ellipsoidal and spherical briquettes. Moreover, the half-ellipsoidal briquette bed shows the best carbonisation performance in comparison with other shapes of briquettes, as it has a more rapid bed temperature increasing rate and faster devolatilisation efficiency. This work is helpful to design proper briquettes and carbonisation operation for improving carbonisation efficiency in low rank coal upgrading.