Coal pyrolysis under synthesis gas, hydrogen and nitrogen

Chinese Xundian and Mongolian Shiveeovoo lignites, and Khoot oil shale were pyrolyzed under synthesis gas (SG) at temperature ranging from 400 to 800°C for the lignites and from 300 to 600°C for the oil shale with a heating rate of 10°C/min in a fixed bed reactor. The results were compared with those obtained in pyrolysis under hydrogen and nitrogen. The results show that higher liquid yields with lower yields of char and gas are obtained in pyrolysis of oil shale under SG and H2 than under N2, but the differences are slight. It is found that the pyrite S can be easily removed and partially converted to organic S under various gaseous atmospheres. The total sulfur removal for oil shale is considerably less than lignite, which may be related to its high ash content. The higher total sulfur removal and the less organic S content in the presence of SG in comparison with that under N2 and also under H2 in pyrolysis of Xundian lignite may result from the action of CO in SG. However, CO does not show its function in pyrolysis of Khoot oil shale, which may also be related to the high ash content. The results show the possibility of using synthesis gas instead of pure hydrogen as the reactive gas for coal hydropyrolysis.