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Energies 2018, 11(4), 898; https://doi.org/10.3390/en11040898

Evaluation of a Compact Coaxial Underground Coal Gasification System Inside an Artificial Coal Seam

1
School of Energy Science and Engineering, Henan Polytechnic University, 2001 Century Avenue, Jiaozuo 454-003, China
2
Department of Earth Resources Engineering, Kyushu University, Motooka 744, Nishi-ku, Fukuoka 819-0395, Japan
3
Graduate School of Engineering, Muroran Institute of Technology, 27-1 Mizumoto, Muroran 050-8585, Japan
4
Underground Resources Innovation Network, Non-Profit Organization (NPO), Higashi-ku, Sapporo 007-0847, Japan
5
School of Materials Science and Engineering, Henan Polytechnic University, 2001 Century Avenue, Jiaozuo 454-003, Henan, China
*
Authors to whom correspondence should be addressed.
Received: 10 March 2018 / Revised: 5 April 2018 / Accepted: 8 April 2018 / Published: 11 April 2018
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Abstract

The Underground Coal Gasification (UCG) system is a clean technology for obtaining energy from coal. The coaxial UCG system is supposed to be compact and flexible in order to adapt to complicated geological conditions caused by the existence of faults and folds in the ground. In this study, the application of a coaxial UCG system with a horizontal well is discussed, by means of an ex situ model UCG experiment in a large-scale simulated coal seam with dimensions of 550 × 600 × 2740 mm. A horizontal well with a 45-mm diameter and a 2600-mm length was used as an injection/production well. During the experiment, changes in temperature field and product gas compositions were observed when changing the outlet position of the injection pipe. It was found that the UCG reactor is unstable and expands continuously due to fracturing activity caused by coal crack initiation and extension under the influence of thermal stress. Therefore, acoustic emission (AE) is considered an effective tool to monitor fracturing activities and visualize the gasification zone of coal. The results gathered from monitoring of AEs agree with the measured data of temperatures; the source location of AE was detected around the region where temperature increased. The average calorific value of the produced gas was 6.85 MJ/Nm3, and the gasification efficiency, defined as the conversion efficiency of the gasified coal to syngas, was 65.43%, in the whole experimental process. The study results suggest that the recovered coal energy from a coaxial UCG system is comparable to that of a conventional UCG system. Therefore, a coaxial UCG system may be a feasible option to utilize abandoned underground coal resources without mining. View Full-Text
Keywords: acoustic emission (AE); underground coal gasification (UCG); coaxial UCG model; energy recovery acoustic emission (AE); underground coal gasification (UCG); coaxial UCG model; energy recovery
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Su, F.-Q.; Hamanaka, A.; Itakura, K.-I.; Deguchi, G.; Zhang, W.; Nan, H. Evaluation of a Compact Coaxial Underground Coal Gasification System Inside an Artificial Coal Seam. Energies 2018, 11, 898.

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