Investigation of K sub(2)CO sub(3)-Catalyzed Pyrolysis and Steam Gasification of Coal Char

Pyrolysis and steam gasification experiments of coal char with and without K sub(2)CO sub(3) were performed using a thermogravimetric analyzer to investigate the effect of catalyst loading method on gasification reactivity at different temperatures (650-800 degree C), and an additional redox cycle experiment of catalyzed char-steam gasification was conducted in a fixed-bed reactor. The results showed that, at low temperature, the solution impregnation method had a larger effect on the gasification reactivity than the physical blending method; at temperatures above 700 degree C, the differences of two methods diminished due to the high mobility of potassium. In catalytic pyrolysis, the release of CO and CO sub(2) indicated that K sub(2)CO sub(3) reacted with carbon. The redox cycle experiments suggest that the potassium reacted with carbon to produce intermediates of the form K sub(2)O sub(2)--C, K sub(2)O--C, and K sub(2)--C. The K sub(2)--C intermediate may help to explain the release of more H sub(2) during the initial period of catalytic coal char-steam gasification. New redox cycle: In this study, the process of potassium-catalyzed steam gasification of coal char is divided into two parts and a new redox cycle is proposed. At low temperatures, the K sub(2)O--C or K sub(2)--C reacts with H sub(2)O to release H sub(2) without CO, and upon heating the reactor, the K sub(2)O sub(2)--C reacts with K sub(2)CO sub(3) to release CO. The reaction mechanism could explain the release of more H sub(2) in the initial period of gasification.