Mechanism of reducing coal powder sedimentation by electrophoresis in coalbed methane drainage

Coal powder blockage seriously affects the efficient development of coalbed methane, and existing blockage removal methods have problems such as low efficiency and high cost. Therefore, based on the charged characteristics of coal in aqueous solution, it is proposed to drive coal powder migration and blockage removal by generating electrophoresis through external electric field. Using a self-made experimental device to change the sedimentation characteristics of coal powder by electrophoresis, physical simulation experiments were conducted on the influence of potential gradient on the sedimentation characteristics of different coal grades of coal powder to explore the sedimentation law of coal powder. Combined with characterization methods such as electrokinetic potential, contact angle measurement, infrared spectroscopy, PIV testing, etc., the mechanism of electrophoresis was revealed. The results showed that with the increase of time, the sedimentation quality of three coal rank powders, namely anthracite, coking coal and long flame coal, showed a trend of rapid increase followed by basic stability; As the potential gradient increases, the final sedimentation quality of the three coal rank powders follows an inverse proportional function, which first rapidly decreases and then slowly decreases to stability, and the decrease of coking coal is the largest; During the experiment, agglomeration phenomena were observed in all three coal rank powders, with coking coal exhibiting more pronounced agglomeration. This is due to the high hydroxyl content of coking coal, which results in smaller contact angle, better hydrophilicity, making it easier for liquid bridges to form between coal powder particles; After the application of electric field, the migration trajectory types of three coal rank powders changed from rapid descent to deceleration descent, first descending and then ascending parabolic trajectory, or ascending trajectory. Among them, coking coal had more parabolic trajectory and ascending trajectory, and the average migration rate of the three coal rank increased after applying electric field, with coking coal showing the largest increase; The mechanism of electrophoretic changes in coal powder transport is influenced by two factors: external electric field and liquid bridge, which change the resultant force acting on the coal powder. On the one hand, the external electric field provides an electric field force that causes the resultant force to increase, and on the other hand, the presence of a liquid bridge increases gravity, buoyancy, and electric field force. Among them, the buoyancy amplification is greater than gravity, causing the upward resultant force to be upward. Moreover, coking coal has more liquid bridges, and the upward resultant force is the greatest. Therefore, the applied electric field can effectively reduce the coal powder sedimentation quality and reduce the coal powder blockage.