Kotaro Ohga

Dynamics of Reformation and Replacement of CO2 and CH4 Gas Hydrates

Abstract: The dynamics of reformation and replacement of gas hydrates were studied under nonequilibrium conditions. It was found that the reformation of gas hydrates is largely affected by the state of the gas‐water system and the restarting temperature. This suggests that the effects are caused by changes in the structure of the aqueous solution at a molecular level. Pure samples of CH4 gas hydrate were synthesized from ice crystals and the dissociated solution using the reformation method. Replacement of CO2 gas hydrate is achieved within a short duration in the solid‐phase sample of CH4 gas hydrate, if the pressure and temperature is precisely controlled in a pressure vessel.

Prospect of CO2 sequestration in the Ishikari Coal Field, Japan

This chapter introduces the overall coal-seam CO 2 -sequestration project and presents the results of the laboratory analyses, well-logging, and water-injection falloff tests conducted to date. The data are used to predict the likely results of the future CO 2 huff-and-puff and multi-well tests. The CO 2 -sequestration project entitled “technology development for carbon dioxide sequestration in coal seams” started with a purpose to develop a series of processes that can extract the CO 2 discharged from thermal power plants and other large-scale emitters of CO 2 , and fix it in coal seams in a stable form while recovering methane as a clean energy source. It has introduced the coal-seam CO 2 -sequestration project and presented analytical results for the Y10 coal seam in the Ishikari coal field based on laboratory experiments, well-logging, and water-injection falloff tests. The expected results of future CO 2 huff-and-puff tests and multi-well test have been simulated based on these analyses in order to aid the field-test design. From the simulations, it is estimated that the initial coalbed methane gas production rate is likely to be almost 500 m3/day and that this rate will increase by a factor of two or three once CO 2 is injected due to CH 4 /CO 2 exchange within the coal seam. The adsorbed CO 2 volume is estimated to be 72% of the injected CO 2 for the huff-and-puff field test, and 96% for the multi-well test.

Fundamental Tests on Carbon Dioxide Sequestration Into Coal Seams

Publisher Summary Carbon dioxide injection into coal seams has become a subject of major interest as a method of carbon dioxide sequestration; sequestration into coal seams is more advantageous than other geo-sequestration because carbon dioxide injected into the coal seam is fixed firmly. Furthermore, when carbon dioxide is injected into coal seams, methane can be recovered as a by-product. This will reduce the cost of sequestration. A fundamental research group carried out various laboratory tests—adsorption tests of carbon dioxide and methane, replacement tests of methane by carbon dioxide, and adsorption tests of coal samples treated by carbon dioxide under supercritical condition. Taiheiyo Coal and Akabira Coal were used in these tests. From the results, it became clear that there is a big difference in adsorption volume of methane between Taiheiyo Coal and Akabira Coal, but there is no difference in carbon dioxide adsorption volume between them at low pressure.

Technologies recovering and utilizing coal seam gas in Japan

Abstract In Japanese coal mines the gas drainage is employed in a practical operation in order to keep low level of methane concentration in the ventilation. In 1993, gas of 44.9 million m3 was drained and about 90% of the drained gas was used for power generation and heating. In order to evaluate the utilization possibility of coal seam gas as natural gas resources, the gas resources in Ishikari coal field was estimated. At Taiheiyo coal mine, the long-length boreholes with a length of 500m was developed and used to degas methane from the coal and rock seams. At Sorachi Coal Mine, an auto- controlled gas drainage system to control the flow rate of a gas drainage line from sealed goaf was developed and used successfully in practical operations. This paper summarizes the resources estimation of coal seam gas in Ishikari coal field and recent technologies related to the methane gas drainage in Japanese coal mines.

Characteristics of adsorption and replacement of Shuuparo coals

Publisher Summary Carbon dioxide injection into coal seams has become a topic of major interest as one of the carbon dioxide sequestration methods because the sequestration into coal seam is more advantageous than other geo-sequestration methods. The reasons include the following: (1) the principal of sequestration mainly relies on the mechanism of gas adsorption to the coal, therefore, carbon dioxide injected into the coal seam is fixed firmly and (2) when carbon dioxide is injected into the coal seam, methane can be recovered as a by-product; this reduces the cost of sequestration. To clarify the mechanism of replacement of methane absorbed onto the internal surface of coal by carbon dioxide, the adsorption tests using carbon dioxide and methane and methane replacement tests using carbon dioxide are carried out. To remove the adsorbed gas from coal samples, gas in the reaction vessel is sucked by vacuum pomp at 40°C for 24hours. After that, the temperature of the reaction vessel is decreased to 30°C and gas is injected into the buffer tank and the reaction vessel until the pressure in the reaction vessel is at a certain pressure, and then the adsorption gas volume at that pressure is measured.

COST ESTIMATION OF UNDERGROUND COAL GASIFICATION IN JAPAN

Underground Coal Gasification (UCG) is one of the methods of recovering energy from underground coal seams. In 1970’s and 1980’s, many basic studies and field tests on UCG were carried out in the USA. Although the activity on UCG has been interrupted, because of the recent low oil price in the world energy market, the technologies and concepts developed in this period are remarkable. Since the 1960’s almost no studies on UCG have been made in Japan. The authors made a cost estimation on UCG in JAPAN, applying the new technologies developed in the USA and data obtained in the field tests there. This study includes the selection of the best site for UCG in Japan from the viewpoint of geological conditions, the prediction of product gas component and the cost estimation. Two UCG methods, ELW (Extended Linked Well) and CRIP (Controlled Retracting Injection Point), were taken into consideration for cost comparison. Our assumption was gasification of one million tons of coal within a period of 10 years. The production cost of gases per heating value was estimated to be between US

Countermeasures and Researches for Prevention of Methane Emission into the Atmosphere in a Japanese Coal Mine

0.029/MJ and US

Estimation of Coal Bed Methane Content in Coal Seams.

0.045/MJ. Finally, the authors proposed a boring cost saving UCG method, STRIP (STream Method with Retracting Injection Point) method, for its further technical development.

Problems on the Development of Some Machines assisted by Water-Jets in Japanese Coal Mines

In order to prevent methane emission from underground coal mines into the atmosphere, various technologies are required.

Growth kinetics of CO2 hydrate just below melting point of ice

Various methods of estimation of methane gas content in coal seams have been developed. The direct method of the US. Bureau of Mines is popularly used in the United States, Australia and Europe. Other methods were proposed by French National Coal Institute and German Mine Ventilation Institute. In this paper, the measurement results of some Japanese coal seams based on the measurement method of US. Bureau of Mines are described. Lost Gas were estimated by three methods which are, √t equation, Aieys equation and Darcys equation. In results by three equations, the highest value was one estimated by Aierys equation. The lowest value was estimated by Darcys equation. It can be concluded that the best estimation method of Lost Gas is the method by Aierys equation, though it is impossible to estimate the Lost Gas of some coal samples. Therefore, Lost Gas should be estimated by Aierys equation and √t method. If measurement of desorbed gas can be done several times in the initialstage, the value estimated by√t method will be approximately equal to one estimated by Aierys equation.