Journal of MMIJ

Special Edition for Coal Energy Technology; Development and Utilization of Coal Energy

Published: January 01, 2016 Updated: January 01, 2016

Displaying 1-7 of 7 articles

Volume 131 (2015) Issue 5 Pages 171-176 Published: January 01, 2016
Coal Policy in Japan
Akira YASUI

Based on the New Basic Energy Plan and the Japan Growth Strategy, Coal will continue to be an important from a viewpoint of the energy mix. For future stable supply of coal, Japanese government will advance ①diversification of the coal supply countries ②improve and promote coal power generation efficiency by advancing technology development ③promote the coal power generation investment in developing countries.
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Volume 131 (2015) Issue 5 Pages 177-182 Published: January 01, 2016
Current Status and Issues of Coal Sector in the World
Hirofumi FURUKAWA, Takashi NAKAMURA, Shinji TOMITA

The world produced over 7.8 billion tonnes of coal in 2012. The world relies on coal for about 30% of the primary energy consumption and is consumed by 41% of electric power as fuel. Although the production and consumption are concentrating on China, the U.S., and India, especially China consumes about 48% of the total amount of coal produced in the world. On the other hand, in China, investment was supplied to coal industry and oversupply has occurred. In recent years, the structure of coal supply-demand, such as competition with alternative energy, rise of concern about global environment problems and the U.S. shale-gas revolution, rise of resource nationalism, a jump in oil price, a shortage of skill, and a nuclear problem, is changed dramatically.
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Volume 131 (2015) Issue 5 Pages 183-188 Published: January 01, 2016
Coal Mine Safety Management in Vietnam
Takehiro ISEI

Vietnamese coal industry is now increasing the production at a higher rate of around 15 percent a year that is almost double of the economic growth. Their coal production of 12 million tons in 2000 had been increased up to 48 million tons in 2011, most of which are anthracite, namely four times increase in ten years. During this time, depending ratio on underground production increased from 33% to 45% and in the near future underground production inevitably exceeds the production from open pit coal mines. In contrast with production increase, safety record has not been improved in the past 10 years, for example, fatality rate per one million tons of underground coal mine stays around one since 2003, namely, safety of underground coal mine had not improved not so much in spite of much effort of relevant people in Vietnam. From the experiences of technical advices for coal mine safety management in Vietnam for more than 10 years, the author had found five key important factors which relate to the safety management of underground coal mines, and which are (1) safety check during weekend and holidays, (2) ineffective utilization of monitored data, (3) production overemphasis mine design, (4) non-feasible coal mine safety regulations and (5) organizational structure for coal mine safety management. In this report, those five factors are introduced in concrete manner and some proposals for improvement would be discussed.
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Volume 131 (2015) Issue 5 Pages 189-194 Published: January 01, 2016
Estimation of Gas Emission from a Long-Wall Panel
Le Trung Tuyen, Kotaro OHGA, Toyoharu NAWA

Gas explosion in underground coal mines is a major hazard in coal production. Here, to evaluate gas emission increases in anthracite coal mines in Vietnam, estimated gas emissions from a long-wall panel were calculated by scale models of Mine Gas Stress (MGS) and Mine Gas Flow (MGF) for various depths of longwall panels with various gas contents. These calculated results suggest that it will be difficult to dilute the emitted methane gas by conventional ventilation even when gallery cross sections are enlarged in deeper coal seams containing much gas. The calculation results showed the necessity of gas drainage prior to actual mining to ensure the safety in coal exploitation. The paper also reviews gas explosion accidents in light of the calculated results of gas emissions and finds that many accidents occurred at the preparation stage of the coal mining panels, supporting the calculated results.
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Volume 131 (2015) Issue 5 Pages 195-202 Published: January 01, 2016
Development of Underground Coal Mine from Toe of Open-cut Highwalls in Indonesia
Takashi SASAOKA, Akihiro HAMANAKA, Hideki SHIMADA, Kikuo MATSUI, Masatomo ICHINOSE

The surface mining method is generally considered to be more advantageous than the underground mining method, especially in recovery, grade control, production capacity, economics, flexibility, safety and working environments. Therefore, the surface mining method is common in major coal producing countries. Most of coal is produced from open-cut mines in Indonesia. However, the conditions of their surface mines are worsening each year: The stripping ratio is approaching to the value of break even stripping ratio, the regulations of environmental protection become to be tighten, and the infrastructure for transportation of coal from inland mining areas is insufficient for such intense mining operations. To meet the demand for coal in Indonesia and the rest of the world, underground mines have to be developed in the near future. Under these circumstances, the development of underground coal mines from the toe of open-cut highwalls is being planned in several mines in Indonesia. However, if the conventional mining systems and designs introduced in US, Australia and European countries are applied, several geotechnical issues can be expected to arise due to weak geological conditions in the mines. This paper describes the conditions and geotechnical issues for underground coal mines developed from the toe of open cut highwalls in Indonesia and addresses problems associated with the weaker rock strata. From the results of on-site investigation and numerical analyses, the mechanisms of the roof fall have been clarified. It was concluded that the current roof support system is not sufficient to maintain the stability of the roadways. In order to develop an appropriate roof support design and code of practice for this mine, further data such as that for geological conditions, mechanical properties of roof rock, the behavior of rock around the roadways, etc. have to be collected and studied. Additionally, as underground water flow is a major problem in this mine, drainage systems should be introduced immediately.
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Volume 131 (2015) Issue 5 Pages 203-218 Published: January 01, 2016
Evaluation of Energy Recovery from Laboratory Experiments and Small-scale Field Tests of Underground Coal Gasification (UCG)
Faqiang SU, Ken-ichi ITAKURA, Gota DEGUCHI, Koutarou OHGA, Mamoru KAIHO

Cavity growth occurring with crack extension and coal consumption during UCG processes directly influences the gasification efficiency and the estimated subsidence and gas leakage to the surface. This report presents an evaluation of the gas energy recovery, coal consumption, and gasification cavity estimation using a proposed stoichiometric method to analyze the coal gasification reaction process. We defined the evaluation parameters of rate of energy recovery and investigated the effects of different parameters using UCG trials conducted with coal blocks and coal seams, adopting different Linking-hole methods and operational parameters. Analyses of results obtained from laboratory experiments and small-scale field trials using V-shaped and L-shaped linking holes, and Coaxial-hole UCG models show that the gasification of Linking-hole models yielded average calorific values of product gas as high as 10.26, 11.11 MJ/m³ (lab.), and 14.39 MJ/m³ (field.). In contrast, the Coaxial-hole models under experimental conditions yielded average calorific values of product gas as: 7.38, 4.70 MJ/m³ (lab.) and 6.66 MJ/m³ (field.). The cavity volume obtained with Coaxial models was about half of the volume obtained from Linking-hole models. Results obtained for these UCG systems show that the feed gas and linking-hole types can influence coal consumption and product gas energy. Fissure ratios were also investigated. Results confirmed major factors underpinning gasification efficiency. Linking-hole types strongly influenced the development of the oxidization surface and fracture cracks for subsequent combustion in the gasification zone. Estimated gas energy recovery results support experimental observations within an acceptable error range of about 10%. Moreover, this stoichiometric approach is simple and useful for evaluating the underground cavity during UCG. Based on these results, we proposed a definition of the energy recovery rate, combined with the obtained volumes of gasification cavities that provide a definition of energy recovery and UCG effects.
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Volume 131 (2015) Issue 5 Pages 219-225 Published: January 01, 2016
Hydrothermal Treatment of Lignite for CO₂ Gasification
Moriyasu NONAKA, Tsuyoshi HIRAJIMA, Satoshi KUMAGAI, Keiko SASAKI

Hydrothermal treatments of lignite, Loy Yang Coal, having high water content of about 60 % were conducted at temperatures ranging from 200 ℃ to 380 ℃. The solid products were examined from various angles like fuel characterization, equilibrium moisture content, solid state VACP (Variable Amplitude Cross Polarization)/ MAS ¹³C-NMR spectroscopic study and thermogravimetry. As a result, the treatment produced upgraded solid fuel; the rising treatment temperature yielded increasing carbon content, fixed carbon, fuel ratio and carbon aromaticity. The advantages of the solid products obtained at harsh condition, 300 ℃ or higher, were low moisture content, high calorie and their slight variation regardless of wide variety in humidity. On the other hand, mild hydrothermal treatments at 250 ℃ or lower demonstrated advantages in terms of energy recovery and solid yield. Addition of a small amount of alkali at hydrothermal treatment improved the gasification reactivity of the solid phase in the successive gasification stage more than twofold, rather decreasing the ash content. Further alkali dose may influence the coal structure that leads to a decrease in the slope of the Arrhenius plot.
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