During the underground coal gasification (UCG) process, fracturing and cracks occur
inside the gasification zone and surrounding rocks as the underground coal cavity evolves.
Although fracturing activity and crack extension directly affect gasification efficiency and
have environmental impacts, little research to date has focused on their effects. This study
discusses the application of acoustic emission (AE) analysis for the evaluation of distinctly
designed UCG models and operational parameters and describes the gasification process
based on its results. We studied the cavity growth, fracturing mechanism, and the effects of
various design and operational variables, such as linking-hole type, gas feed rate, and
gasification agent. We found that the AE activity was closely related to the temperature
change occurring inside the coal, with AE generation apparently resulting from crack
initiation and extension around the coal gasification area, which occurs as a result of
thermal stress. UCG modeling showed that the location of AE sources reflects the size of
the gasification area and the cavity growth. In addition, the quantitative information on the
located AE sources can be obtained. The introduction of a process control system into
UCG modeling along with AE monitoring allowed for the real-time monitoring of the
fracturing and cavity evolution inside a combustion reactor. Together, these processes have
the potential to significantly reduce field risk in UCG by enabling the timely adjustment of
operational parameters. Thus, AE monitoring is useful for maintaining a safe and efficient
UCG process.
Monitoring of coal fracturing in underground coal gasification by acoustic emission techniques
AE_189_142-156
(1.7MB)
