Spontaneous combustion of coal is one of the major problems in the coal mine. The fire may occur due to exogenous and endogenous causes, by which coal liberated heat to the air or heat absorbed into it. It causes loss...Spontaneous combustion of coal is one of the major problems in the coal mine. The fire may occur due to exogenous and endogenous causes, by which coal liberated heat to the air or heat absorbed into it. It causes loss of production, as well as economical or financial losses and polluted the environment. If, the heat liberated during this process is allowed to accumulate, the rate of reaction increases exponentially and there is a further rise in temperature that generates the flame and produce CO, CO<sub>2</sub>, CH<sub>4</sub>, N<sub>2</sub>, O<sub>2</sub> etc. In addition, the heat generated within coal affected by different factors such moisture, ash, volatile matter etc. of coal. This paper deals with the oxidation and spontaneous combustion risk in Barapukuria underground longwall coal mine, Dinajpur, Bangladesh. In this study, the laboratory analyses (proximate analyses) shows the inherent and the total moisture content value is average 2.73% and 5.82% to 12.75%, respectively. It indicates that these moisture contents are moderately liable to self heating. The less ash content value (av.13.2%) shows, it is less liable to spontaneous combustion. In addition to this, the temperature and concentration of some mine gases (CO, N<sub>2</sub>, O<sub>2</sub>) were monitored to calculate the Graham’s ratio. According to Graham’s ratio, the longwall faces have high oxidation risk and medium combustion risk. Therefore, the actual control of spontaneous combustion of coal is important to save coal mine from mine fires and also provides a real opportunity to improve the financial performance of the overall organization.展开更多
In this study, finite element analysis based on an Ansoft Maxwell software was used to reveal the temperature stability of a magnet ring and the equivalent structural periodic permanent-magnet（PPM） focusing system. ...In this study, finite element analysis based on an Ansoft Maxwell software was used to reveal the temperature stability of a magnet ring and the equivalent structural periodic permanent-magnet（PPM） focusing system. It is found that with the temperature increasing, the decrease rate of magnetic induction peak（Bz）maxof single magnet ring is greater than that of remanence Brof magnet in the range from room temperature to 200 °C, however,the PPM focusing system do have the same temperature characteristics of permanent-magnet materials. It indicates that the magnetic temperature properties of the PPM system can be effectively controlled by adjusting the temperature properties of the magnets. Moreover, the higher permeability of the magnets indicates the less Hcb, giving rise to lower magnetic induction peak （Bz）′max： Finally, it should be noted that the magnetic orientation deviation angle θ（／15°） of permanent magnets has little effect on the focusing magnetic field of the PPM system at different temperatures and the temperature stability. The obtained results are beneficial to the design and selection of permanent magnets for PPM focusing system.展开更多
文摘Spontaneous combustion of coal is one of the major problems in the coal mine. The fire may occur due to exogenous and endogenous causes, by which coal liberated heat to the air or heat absorbed into it. It causes loss of production, as well as economical or financial losses and polluted the environment. If, the heat liberated during this process is allowed to accumulate, the rate of reaction increases exponentially and there is a further rise in temperature that generates the flame and produce CO, CO<sub>2</sub>, CH<sub>4</sub>, N<sub>2</sub>, O<sub>2</sub> etc. In addition, the heat generated within coal affected by different factors such moisture, ash, volatile matter etc. of coal. This paper deals with the oxidation and spontaneous combustion risk in Barapukuria underground longwall coal mine, Dinajpur, Bangladesh. In this study, the laboratory analyses (proximate analyses) shows the inherent and the total moisture content value is average 2.73% and 5.82% to 12.75%, respectively. It indicates that these moisture contents are moderately liable to self heating. The less ash content value (av.13.2%) shows, it is less liable to spontaneous combustion. In addition to this, the temperature and concentration of some mine gases (CO, N<sub>2</sub>, O<sub>2</sub>) were monitored to calculate the Graham’s ratio. According to Graham’s ratio, the longwall faces have high oxidation risk and medium combustion risk. Therefore, the actual control of spontaneous combustion of coal is important to save coal mine from mine fires and also provides a real opportunity to improve the financial performance of the overall organization.
基金financially supported by the National Natural Science Foundation of China (No. 61001120)
文摘In this study, finite element analysis based on an Ansoft Maxwell software was used to reveal the temperature stability of a magnet ring and the equivalent structural periodic permanent-magnet（PPM） focusing system. It is found that with the temperature increasing, the decrease rate of magnetic induction peak（Bz）maxof single magnet ring is greater than that of remanence Brof magnet in the range from room temperature to 200 °C, however,the PPM focusing system do have the same temperature characteristics of permanent-magnet materials. It indicates that the magnetic temperature properties of the PPM system can be effectively controlled by adjusting the temperature properties of the magnets. Moreover, the higher permeability of the magnets indicates the less Hcb, giving rise to lower magnetic induction peak （Bz）′max： Finally, it should be noted that the magnetic orientation deviation angle θ（／15°） of permanent magnets has little effect on the focusing magnetic field of the PPM system at different temperatures and the temperature stability. The obtained results are beneficial to the design and selection of permanent magnets for PPM focusing system.
