Controlling mechanisms in gasification of pulverized coal

Controlling mechanisms in the fuel-rich reaction of pulverized coal with oxygen at atmospheric pressure were investigated through analysis of experimental data and by comparison with predictions of a comprehensive model. Gasification data were obtained for four coal types at various oxygen-steam-coal ratios and effects of coal feed rate, particle size and flame type (premixed, diffusion) were also determined. The results show that coal particle heat-up and devolatilization occur very rapidly (< 60–80 ms) near the coal inlet with up to 70% of the coal consumed. Coal volatiles and oxygen are rapidly consumed through gas-phase reaction, producing high gas temperature and high CO 2 concentrations. Addition of steam plays little role in the coal reaction process, while residual char (typically containing 20–30% of the carbon) is consumed less rapidly (> 200 ms) through surface reaction with CO 2 and H 2O, and possibly O 2 at the onset. This general reaction process varies little among the coal types examined. The surface reactions are controlled in high-temperature regions through oxidizer diffusion to the char surface; however, as the gasifier temperature declines through heat loss and endothermic reaction, heterogeneous char-oxidizer reaction near the particle external surface becomes more important, giving rise to some dependence on coal type.