Authors: Faqiang Su,Ken-ichi Itakura, Akihiro Hamanaka, Gota Deguchi and Kotaro Ohga
Abstract: Coal is a major fossil fuel in the world and plays a critical role in the energy field. In the view of the safety and resource efficient utilization, coal is the subject of great expectations to satisfy the rapidly increasing demand for future energy. As a clean coal technology, Underground Coal Gasification (UCG) is used to create a combustion reactor in an underground coal seam, thereby enabling the collection of heat energy and gases (hydrogen, methane, etc.) through the same chemical reactions that are used in surface gasifiers. A typical UCG system has two wells drilled from surface into a coal seam with some separation of injection from production. The wells are connected underground by various linking techniques. Designs of the linking methods are likely to have a strong impact on the extent of gasification. However, it is difficult to apply a universal UCG system directly to an underground coal seam having a complex geological structure. Coaxial UCG proposed in this paper is anticipated for use as a local energy source in small communities because the cost to construct the drill hole and ground plant facility are lower than those for conventional UCG with a linking hole. During the UCG process, fracturing activity inside the coal seam serves an important role for enlargement of the gasification zone because the surface area oxidization increases continuously by coal cracking. For effective coal gasification, fracturing activity must be controlled. Therefore, monitoring and control of fracturing activity in underground constitute key technologies for efficient and safe UCG. To monitor fracturing activity, we used acoustic emission (AE) technology. We introduced the laboratory-scale UCG model experiments conducted with set design and operating parameters. The temperature profiles, AE activities, and product gas concentration were measured successively during gasification. This paper also presents the gas energy evaluation for coal consumption, the production gas quantity and heat value, the application of oxygen element balance in the gasification reaction process, and the gas composition obtained in this study.
Keywords: component; UCG; coaxial model; acoustic emission; energy recovery