Underground Coal Gasification (UCG) is a promising process for recovering energy from potential underground coal resources as combustible gases such as hydrogen and carbon monoxide. The gasification process that occurs underground is an invisible phenomenon, and the temperature in the underground gasification reaction zone can be over 1,000 °C. Therefore, the visualization/monitoring of the gasification area of UCG plays an important role in the development of a highly efficient, safe , and low environmental impact UCG system. This article reviews the possibility of monitoring high-temperature gasification reaction zones in UCG using Acoustic Emission (AE) technique. AE monitoring can be used as a real time monitoring technique because AE can be detected at the same time when the cracks occur due to the gasification, indicating that it gives an advance warning immediately if the extensive damage occurs. The challenges and future prospects for estimating the gasification reaction area by AE technique are also addressed at the end of article.
