Abnormal gas emission in coal mines and a method for its dilution using ventilator control

During coal mining, gas concentration transfinite usually occurs when gas emission increases, and in this paper, we analyzed the reasons that lead to an increase in gas emission. Based on field investigation data, three types of gas concentration transfinite were identified: transitory, continuous, and abnormal fluctuation gas emissions. We draw gas concentration change curves for each type. In the presence of gas concentration transfinite, wind quantity can be increased by varying the frequency of the mine ventilator to dilute the gas. In this paper, we propose two methods for varying the frequency of the ventilator, using a frequency-concentration (f-w) control of the follow-up wind quantity and automatic control of the curve value. The transfer function of the f-w control method and a database of ventilator characteristic curves at different frequencies were established. Using the Da Liuta mine ventilation system, an experimental model for wind quantity adjustment was setup in a ventilation network branch using a variable-frequency ventilator. Considering the fire and explosion risks associated with the real gas, carbon dioxide was instead released to simulate gas emission in the experiment. A carbon dioxide release model was set up using the gas concentration change curves. The experimental results show that the mine ventilator variable-frequency control automatically adjusted the branch wind quantity, which strictly followed the f-w control method and the automatic control of the curve value. Increasing the carbon dioxide concentration caused the mine ventilator variable-frequency controller to increase the branch wind quantity automatically to keep the carbon dioxide concentration under the threshold value. The experimental results demonstrate the feasibility and efficiency of the two methods, and theoretical guidance for adjusting the ventilation branch quantity for a variable-frequency mine ventilator is provided.