Study on the monitoring method of cavity growth in underground coal gasification under laboratory conditions

The growth state of the combustion cavity during underground coal gasification (UCG) affects the gasification process's efficiency, stability, and accurate monitoring and control. In this study, a simulation experiment of UCG was performed, and a horizontal coaxial gasification channel was drilled based on the constructed artificial coal seam. Oxygen and air are used as gasification agents to provide a sufficient temperature field to sustain the gasification process. Moreover, the derivation of the gasification zone during UCG was developed using stratified temperature monitoring and acoustic emission damage monitoring. After the experiment, the artificial coal seam was cut to obtain the profile shape of the combustion cavity, which was compared with the temperature and acoustic emission monitoring results. The results show that the temperature distribution results in the coal seam and the calibration results of the acoustic emission source during horizontal coaxial UCG are consistent with the two-dimensional and three-dimensional combustion cavities reconstructed by the profile. Thus, the effectiveness of stratified temperature monitoring and acoustic emission monitoring to infer the gasification combustion cavity is proven. •The data of temperature and acoustic emission during experiment were collected.•The coal sample was cut into pieces to observe the cavities profile.•The 3D constructions of the combustion cavities were built.•The growth mode and influencing factors of combustion cavities were analyzed.•The main components and calorific value of the product gas were analyzed.