Structure and combustion characteristics of semi-cokes from a pilot-scale entrained flow gasifier using oxygen-enriched air

Abstract To explore the structural characteristics and further utilization of the semi-cokes obtained from a self-designed pilot-scale entrained flow gasifier at the temperatures of 800–1200 °C with oxygen-enriched air as gasifying agents (21, 50, and 100% O2 in N2), the gasified semi-cokes were characterized by N2 adsorption, scanning electron microscopy (SEM), and X-ray diffraction (XRD) methods, and their combustion performances and kinetic analysis were explored using a thermogravimetric analyzer. Results indicated that the volatile release was significantly enhanced with rising gasification temperature, which would contribute to the rapid development of pore structure in semi-cokes. The increasing oxygen concentration mainly works on promoting both the volatile release and the carbon conversion through enhancing the oxidation reactions with carbon matrix, which would result in the dramatic decrease of both surface area and micropore volume. Thermal analysis showed that the ignition and comprehensive combustion performances of semi-cokes got worse as the gasification temperature and oxygen concentration increased, indicating that the volatile matter is vitally important to promote the ignition as well as maintain the combustion stability. While their combustion intensity and burnout index were more dependent on the pore structure. The activation energy calculated by both FWO and KAS methods increased with the temperature and oxygen concentration and different order reaction models (ranged from 0.8 to 2.1) were responsible for the combustion of semi-cokes. It is notable that the volatile content and pore structure are the key factors affecting the variation of activation energy with conversion degree and the magnitude of the reaction kinetic model.