Determination of optimal temperature and amount of catalysts based on alkali and alkaline earth metals for steam gasification process of bituminous coal

The subject of this study was to analyze the influence of catalysts addition on the kinetics of 'Janina' coal gasification with steam. Thermovolumetric, isothermal measurements were performed at 800 °C, 900 °C, 950 °C, and 1000 °C at a pressure of 1 MPa. Samples of coal, and then coal with various amounts (1, 3 or 5 wt%) of calcium, potassium, and sodium cations were gasified. Based on the obtained results, the formation rates of main gaseous products as well as their yields and percentage share in the resulting gas were determined. Moreover, the influence of the amount of catalyst and operating temperature on the half times and rate constants of CO and H2 formation reactions, as well as their kinetic parameters (the activation energy Ea and/or the pre-exponential factor A), were specified based on the isoconversional method, the grain model and the random pore model. The obtained results confirmed the positive effect of catalysts addition as well as increasing their amount but only to a certain level and at the temperature range of 800-900 °C. The optimum amount of catalyst for Na+ was 3 wt% and for K+ and Ca2+ it decreased along with an increase in temperature. Moreover, selectivity of the catalysts towards specific gas components was observed (Na+ resulted in a high H2 content; K+ in a high CO content). In addition, the values of kinetic parameters (Ea and A) were reduced along with the increase in the amount of catalysts. However, while analyzing the catalytic gasification one should also take into account other parameters defining the process (half times and rate constants of gasification reactions at specific temperatures).