Reactivity study of fine discard coal agglomerates

Abstract

In this laboratory study thermo-gravimetric analyses were conducted to determine the influence of the addition of an alkaline metal catalyst (K2CO3 incorporated into a fine discard coal agglomerate mixture by physical mixing) on the CO2 gasification char reactivity of 10 mm coal pellets subjected at high temperatures (900–1000 °C). It was found that catalyst addition significantly increased the reaction rate of the carbon conversion. The reaction rate was doubled for the 5% catalyst addition runs compared to the base case (0% catalyst at 900 °C), 120% faster at 950 °C and, 93% faster at 1000 °C. The temperature influenced the reaction rate, thereby decreasing the reaction time from 6.4 h at 900 °C to 3.4 h at 950 °C and, 1.9 h at 1000 °C for the 5% catalyst addition. The fastest time needed for conversion was with the use of 5% catalyst addition at 1000 °C, which required only 13% of the total time needed in comparison with the base case (14 h). The conversion plots were further analyzed, and it was concluded that the lines followed the homogeneous model (REF) up till a conversion of 50% for the pelletized particles and 20% for the raw coal.The observed activation energy was also found to be lower in the coal pellet catalyzed system when compared to raw run of mine (R.O.M.) coal of the same dimensions as for the coal agglomerates (199 kJ/mol) and was calculated to be 195 kJ/mol, 184 kJ/mol, and 156 kJ/mol for the 1%, 3% and 5% catalyst addition runs, respectively. These results show that there is an opportunity to possibly improve on the fluidised-bed/large particle gasifier throughput by speeding up the time needed for the rate limiting CO2 gasification reaction in a catalysed system comprising of fine discard coal agglomerates containing an alkaline additive