Study on the Coal Underground Gasification Reaction Characteristics Based on the Controlled Retraction Injection Point Gasification Process.

Although modern coal underground gasification technology using the controlled retraction injection point (CRIP) has made significant advancements, several issues remain, such as unstable gas quality, limited process control methods, and an unclear understanding of the distribution and expansion of the gasification reaction zone. This study uses COMSOL Multiphysics software to establish a three-dimensional model of coal seam horizontal well injection underground gasification based on the CRIP process, with a focus on a single backward gasification reaction cycle. The distribution of temperature fields and the heat-affected zone of the combustion cavity during a single reaction cycle are analyzed under three parameters: gas flow rate, oxygen concentration, and gasification pressure. This study also investigates the variation in the coal seam heat-affected boundary and explores the underground gasification reaction characteristics of typical coal types. In this experiment, based on the gas composition and heat-affected zone size, the optimal gas flow rate and oxygen concentration are 0.45 m/s and 60%, respectively, at which the heat-affected boundary thickness is 0.08 m. The heat-affected boundary thickness of the coal seam increases with rising gasification pressure. At the gasification horizontal channel at 1.15 m, the heat-affected boundary thickness is 0.04 m at a gasification pressure of 0.1 MPa, while at 12.0 MPa, the heat-affected boundary thickness reaches 0.23 m, 5.75 times larger than at 0.1 MPa. By understanding the CRIP coal underground gasification reaction characteristics, this study provides scientific evidence to support the control and regulation of CRIP process operating parameters.