Tadao Imai

Mathematical Plan Model for Longwall Mining in Consideration of Coal-Grade Distribution a Coal Seam.

The purpose of the present study was to develop a mathematical model for effective operation of a longwall working face in an underground coal mine. The model can evaluate the relationship between operating efficiency and working height of the face in a coal seam. The results show that, contrary to a common thought, the working height of the face must be 20-30 % lower than the thickness of the coal seam. As a consequence, low-grade coal near the bed and roof rock remains in the coal seam. The results of this model enable effective operation of the working face and maximum profit in a mine.

Effect of Internal Gas Pressure on Gas Permeability of Coal in Unsteady-State Gas Flow. Study on gas permeability of coal by crack network model (2nd Report).

The purpose of this study is to prove the effect of internal pore pressure on unsteady-state gas flow in coal. Practically, the gas permeation model of coal which consists of the gas permeable and non-permeable crack network was proposed. Then the numerical simulations of gas permeation by this model were carried out by changing the parameters such as inlet pressure in the crack network, confining pressure against coal, closing probability of cracks, etc.The results of these simulations on fluctuations of unsteady-state gas flow were in agreements with the experiments of gas permeation of coal. From these considerations it was found that the above gas permeation model was accurate enough for practically. Moreover, the results of the simulations on unsteady-state gas flow in coal gave an explanation to the deviation from the Darcys law in the relationsbetween gas flow and difference pressure.

Ultrasonic Attenuation in CO2-Air Mixtures.

This paper describes the ultrasonic attenuations in gas mixtures of CO2 and air to investigate the possibility of a CO2 gas concentration monitor using with the ultrasonic attenuations. Three kinds of ultrasonic transducers (40, 215 and 500 kHz) were used for the measurements. Measurements of the attenuation per unit distance of each ultrasonic wave were carried out by varying the length of a test cell of 26 mm in diameter from 30mm to 150mm. From these fundamental results, the practical gas detection cells were designed and the detection method in order to monitor the CO2 gas concentration was developed. Two 215 kHz ultrasonic transducers were installed on the both sides of the gas detection cell of 4 mm in diameter and 70 mm or 40mm long. The attenuation of 215 kHz ultrasonic is the largest of the three ultrasonics. The ultrasonic waves are sent intermittently from the transducer and are propagated through the cell. The sound pressure of the ultrasonic waves are detected by another transducer on the other side. The peak detected value of the sound pressure in the first receiving waves is decayed sharply by introducing CO2 and air mixtures into the cell compared with air. The relationship between the peak detected value;P1 and CO2 concentration; C (%) is presented.The summary of the measurements is as follows:a) The peak detected value of the sound pressure;P1 extremely decreases with increasing CO2 concentration in a range of C=0-20%(Fig. 11).b) The ratio between the peak detected value of gas mixtures and air P1 may be treated to be independent of temperature (Fig. 13).c) The peak detected value is comparatively influenced by adding water vapor into the gas mixtures (Fig. 14).