Underground coal gasification (UCG) is a technique to recover coal energy by the in-situ conversion of coal into gaseous products. In this study, an application of co-axial UCG system with a horizontal well is discussed by means of the model UCG experiment with a large-scale simulated coal seam which the size is 550 × 600 × 2,740 mm. A horizontal well which has 45 mm diameter is used as an injection/production well. The effect of injection rate is evaluated by using the results of gas compositions, temperature profile, and acoustic emission monitoring. During the experiment, the changes of temperature field and product gas compositions were observed by changing the position of an injection pipe, meaning that it is possible to control gasification area and the quality of product gas by controlling the injection position. Additionally, the increase of injection rate attribute to improve the calorific value of product gas while the higher flow rate may cause to move the gasification area rapidly when the coal with higher ash is gasified.
Underground coal gasification (UCG) is a technique to extract energy from coal in the form of heat energy and combustible gases through the chemical reactions in the underground gasifier. This technique enables to utilize coal resources that remain unrecoverable in underground due to either technological or economic reasons. We are developing a co-axial UCG system that is compact, safe, and highly efficient. The co-axial UCG system uses only well drilling and a double pipe. Gasification agents are injected from the inner pipe to expand the combustion zone. The production gas is recovered from the outer pipe. Until now, various UCG model experiments have been carried out to develop the co-axial UCG system (Hamanaka et al., 2016; Su et al., 2018; Su et al., 2017). However, the recovered energy from the coal is relatively low because the gasification area in a co-axial system is limited around a well. In order to improve the total efficiency of gasification process, an application of co-axial UCG system with a horizontal well is suggested (Fig. 1). Additionally, the range of the gasification area and the quality of product gas are affected by the quality of coal and the injection conditions (Bhutto et al., 2013: Kacur et al., 2014; Stanczyk et al., 2011). Considering those backgrounds, this study investigates the effects of the quality of coal and the injection conditions on the range of the gasification area and the quality of product gas by means of the model UCG experiment with a horizontal well.