Hydrogen production by non-catalytic partial oxidation of coal in supercritical water: Explore the way to complete gasification of lignite and bituminous coal

Supercritical water gasification (SCWG) of coal is a promising technology for clean coal utilization. In this paper, hydrogen production by non-catalytic partial oxidation of coal was systematically investigated in supercritical water (SCW) with quartz batch reactors for the first time. The influences of the main operating parameters including residence time, temperature, oxidant equivalent ratio (ER) and feed concentration on the gasification characteristics of coal were investigated. The experimental results showed that H2 yield and carbon gasification efficiency (CE) increased with increasing temperature and decreasing feed concentration. CE increased with increasing ER, and H2 yield peaked when ER equaled 0.1. CE increased quickly within 1 min and then tended to be stable between 2 and 3 min. In particular, complete gasification of lignite was obtained at 950 °C when ER equaled 0.1, as for bituminous coal, at a higher temperature of 980 °C when ER equaled 0.2. •Coal is gasified completely in quartz reactors for the first time.•High temperature is a key factor for complete gasification of coal.•Oxidant facilitates complete gasification of coal.•Mass transfer has an important effect on complete gasification of coal.•The chemical equilibrium is difficult to be reached without catalyst.