Underground coal gasification (UCG), a technique used to recover coal energy by the in-situ conversion of coal into gaseous products, enables recovery of coal energy from the potential coal resources abandoned under the ground for either technical or economic reasons. However, it might be difficult to adopt conventional UCG systems in Japan because of geological conditions that are complicated by the existence of faults and folds. Additionally, it is difficult to control the combustion/gasification area during UCG process because the process is invisible. Therefore, a co-axial UCG system that is compact, safe, and flexible to adopt is suggested with monitoring system by means of acoustic emission as an alternative UCG system. This UCG system has superiority in terms of applicability compared to the conventional one, but 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 develop co-axial UCG system with high efficiency, the model UCG experiment with a large-scale simulated coal seam were conducted. It has been shown that 1) the gasification period can be extended by adopting proper oxygen inflow, 2) it is possible to control the combustion/gasification area and the product gas quality by controlling the position of oxygen inflow, 3) acoustic emission monitoring is an effective technique to evaluate the combustion/gasification area.

Small-scale underground coal gasification (UCG) model tests with a linking hole were carried out using two types of specimens made of either block coal or crushed coal to clarify their characteristics of combustion and gasification. Many similar characteristics were found between both specimens in terms of temperature change and its spatial distribution as well as concentration and heating value of each gas product as long as the crushed coal specimen was sufficiently consolidated. The shape and dimension of the cavity formed in the both specimens were also similar. Texture of the both specimens was changed after the combustion and gasification. Initiation of radial cracks from the linking hole was found in the both specimens. Within the zone with the radial cracks initiation, grains in the crushed coal were bonded whereas cleats in the block coal were healed. The grain bonding and the cleavage healing can be explained by melting and expansion of coal due to temperature increase. The radial cracks are likely initiated after the grain bonding or the cleavage healing due to tensile thermal stress induced by temperature gradient in the coal specimens. It can be concluded that the characteristics of combustion and gasification of the crushed coal and the block coal are similar because both types of coals become similar in texture through combustion and gasification. These results indicate that characteristics of combustion and gasification of coal seam can be mostly estimated from a model test with artificial coal seam made of crushed coal.

Kushiro Coal Mine is located in southeast of Kushiro-City, Hokkaido, Japan and the only underground as well as under seabed coal mine. Paleogene Harutori Coal Bearing Formation is mined over the long period. During the mining, associated methane gas called as Coal Mine Methane (CMM) is extracted for safety reasons. In addition, another type of methane from the Cretaceous is also extracted, and mixed with CMM. Taking these factors into consideration, Kushiro Coal Mine has researched and studied for the development of gas collection technique and effective utilization system. As part of the investigation, Kushiro Coal Mine and Osaka Gas have promoted the effective utilization by gas concentration technique using Pressure Swing Adsorption, and the whole system has operated in 2017. The purpose of this article is to review general design of the gas concentration project of Kushiro Coal Mine.

Coal provides about 40 % of total world primary energy supply now. Coal is one of the most available, affordable and accessible energy resources both in terms of sustainable supply as well as economy. Coal is carbon-intensive fuel and emits a significant amount of carbon dioxide to the atmosphere per unit of heat energy. So it is important to develop coal utilization technologies to minimize environmental impact, so called "Clean Coal Technology". Coal production and consumption trends in the world are changing due to fluctuations in coal prices, policies of governments of various countries, and so on.

This study investigated an effective method to desorb CO₂ from low-concentration (0.2 mol/L) monoethanolamine (MEA) solutions using calcium chloride (CaCl₂) and ultrasound irradiation at 25 ºC. The pH value of the solution had a large influence on the desorption ratio of CO₂ from MEA solution under ultrasound irradiation. CO₂ was successfully desorbed up to pH8.2, and it was impossible to desorb CO₂ at pH over 8.2. It was clarified that CO₂ desorption by ultrasound irradiation is useful for the concentration of MEA solution of up to 2.0 mol/L, because the pH rises above 8.2 when the concentration of MEA solution is increased to above 2.0 mol/L. It also became evident that the addition of small amount of CaCl₂ further increases the amount of CO₂ desorbed during ultrasound irradiation.