Water injection in underground coal gasification with a horizontal hole: A strategy to prevent steel pipe rupture and enhancing hydrogen production reaction

Underground Coal Gasification (UCG) is a technology that enables the extraction of coal energy by converting coal seams into syngas, which mainly consists of H2, CO, and CH4. During UCG, the temperature in the reaction zone can exceed 1300 °C, raising concerns regarding the potential melting of the steel pipes used for oxidant injection. To mitigate this issue, this study investigated the use of water as an injection agent. Water injection serves two key purposes: cooling the injection pipe and enhancing H2 production. To examine the effects of water injection on temperature in gasification zone and product gas composition, a UCG model experiment was conducted. The results show that water injection effectively inhibit melting pipe by decreasing the temperature in the gasification zone without compromising H2 production, although the CO concentration decreases and the CO2 concentration increases. Additionally, the energy recovery loss due to water injection can be estimated based on the amount of water injected, as the heat loss from water evaporation is the dominant factor. These findings demonstrate that water injection is a viable strategy for preventing pipe melting while enhancing H2 production in UCG processes.