Co-gasification of Alkaline Black Liquor and Coal in Supercritical Water at High Temperatures (600–750 °C)

Abstract

The catalytic activity of the alkali compounds in alkaline black liquor can be used in supercritical water gasification (SCWG) of coal to lower the reaction temperature and improve the hydrogen production, and the black liquor can be handled simultaneously. In the present study, the gasification features of coal/black liquor blends at high temperatures (600–750 °C) were studied through thermodynamic analysis and experimental study. A synergetic effect was found during co-gasification of coal and black liquor, where both the gasification efficiency and hydrogen production was improved by efficiently using the alkali catalyst in black liquor. The highest improvement of the gasification was found at the blending ratio of about 50:50. Both the thermodynamic analysis and experiments indicated that higher temperature favors the hydrogen production. The gasification efficiency was improved with temperature and the maximum carbon conversion of 79.46% was achieved at 750 °C. The dilution of the black liquor/coal blends favors the gasification by improving the gasification efficiency and H2 production. The prolongation of reaction time enhanced the gasification, but its influence was insignificant when it was above 10 min. The initial pressure of the reactor and the reactant amount impacted the gasification results in different ways. This study may fill the research gaps in SCWG of coal/black liquor blends at higher temperatures and assist in its further development.