EXPERIMENTAL STUDY ON CO-AXIAL SYSTEM WITH A HORIZONTAL WELL OF UNDERGROUND COAL GASIFICATION TO EVALUATE GASIFICATION EFFICIENCY
Underground Coal Gasification (UCG) is a technique to recover the energy of coal by converting coal into gas. One or two wells are drilled from the surface to underground coal seam in order to inject oxidant which consists of oxygen and air for burning the coal seam in situ and recover syngas such as carbon monoxide, hydrogen, and methane in the surface as an energy source. Unused coal resources which have not been recovered for technical and economic reasons are expected to be used in this technology. In this research, a large scale experiment which uses an artificial coal block was conducted, and a co-axial UCG system with a horizontal well was adopted to obtain results of temperature in the coal block and product gas components. Based on the results, the amount of reacted coal and gasification efficiency was calculated in order to evaluate wether the gasification system worked well or not. Moreover, it was compared with past experimental results for evaluation. Regarding the temperature inside the coal block, the area above the coaxial hole had the highest temperature, with a peak value at 1200 to 1400 °C. Furthermore, the peak value at 15 cm above the coaxial hole was 1000 to 1200 °C, indicating that the high temperature had expanded up to 15 cm above the coaxial hole. Meanwhile, the main product gas components are nitrogen, carbon dioxide, carbon monoxide, hydrogen, and methane. Finally, the result of comparing gasification efficiency with those of previous experiments shows that the gasification efficiency was comparable despite the coal quality is lower than that of the previous experiment.