Experimental investigation on the influence of the pyrolysis operating parameters upon the char reaction activity in supercritical water gasification

Supercritical water gasification of coal is a clean and efficient method for coal utilization which can convert coal into H-2 and CO2. In order to further reduce costs, a novel two-step cascade utilization method was proposed in this study: conducting traditional pyrolysis first and then gasifying the pyrolysis char in supercritical water. The influences of different pyrolysis operating parameters on gaseous products and char gasification in supercritical water were investigated. Quartz tube reactors were used to ensure the complete collection of gaseous products in pyrolysis process. The experimental results showed that both carbon and hydrogen conversion efficiency increased with temperature, and the increasing trend became not obvious after reaction for 5 min. The thermogravimetric curves showed that volatilization removal process was completed at the pyrolysis time of 5 min and higher pyrolysis temperatures were beneficial to the subsequent gasification process. The result also showed that residual weight was 15%-20% of the initial weight. Hydroxyl radicals kept stable during pyrolysis process with the absorption peak intensity increasing first and then decreasing, and mineral substance disintegrated gradually as time increased. As pyrolysis temperature increased, the peak of C-C double bonds decreased, turning into stable functional groups and carbonyl group increased. Dispersive pores occurred at the surface of coal as residence time increased with particle size decreasing, specific surface area and reactivity increasing. The results might be used for the design of a cascade utilization system based on coal gasification in supercritical water. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.