Rapid Gasification of Nascent Char in Steam Atmosphere during the Pyrolysis of Na- and Ca-Ion-Exchanged Brown Coals in a Drop-Tube Reactor

Several recent student on In situ steam gasifieation of coal suggest a possibility of extremely fist steam gasification of char from rapid pyrolysis of pulyerized brown coal. The unprecedented rate of char steam gasification can be achieved by exposing nascent char, that is after tar evoluation (temperature range > 600 degrees C), but before devolatilization (<900 degrees), to steam in the presence of Na and/or Ca dispersed in/on the char. In this study, we conducted rapid pyrolysis experiments using ion-exchanged Loy Yang brown coal samples, that is, H-form coal with Na/Ca contents <0.001 wt%, Na-form coal with Na content = 2.8 wt% and Ca-form coal with Ca content =3.2 wt %. These samples were pyrolyzed in and atmospheric drop-tube reactor at a temperature of 900 degrees C, inlet steam concentration of 50 vol %. and a particle residence times of 2.8 s. The char yields from the pyrolysis of Na-form and Ca-form coals were as low as 12 and 33% on the respective coal respective coals at 900 degrees C .The chars from the Na-form and Ca-form coals also acted as catalysts for steam reforming of tar, which was evidenced by significant negative synergitic effects of blending of H-form coal with Na-form coal or Ca-form coal on the tar and soot yields.