H2 production enhancement in underground coal gasification with steam addition: Effect of injection conditions

Hydrogen is a clean energy source, and its use helps to mitigate climate change. Underground coal gasification for hydrogen production is a promising method for countries with abundant coal resources and high hydrogen demand. However, the existing coal-to-hydrogen process underground exhibit low production efficiency. This work proposes the use of swirl flow injection to improve hydrogen production efficiency, and also explores the influence of other injection conditions (oxygen flow rate, steam mass flow and steam temperature) on hydrogen production. For straight flow injection, the effect of steam addition on gasification performance depends on the oxygen flow rate, and the highest H2 production is 14.6 L under 1 L/min oxygen and 1 g/L steam. With a swirl flow injection, H2 production increases with steam addition for both 1 L/min and 2 L/min oxygen, which shows a larger H2 production than straight flow injection. The highest H2 production for swirl flow injection is 19 L under 2 L/min oxygen and 1 g/L steam. An increase in steam temperature barely affects the composition of products but apparently increases the amount of products. The fracture effect of high temperature steam might cause a sudden increase of H2 and CH4 at the late stage.