电泳降低煤层气排采中煤粉沉降机理研究

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

  • 摘要: 煤粉堵塞严重影响煤层气高效开发,现有的解堵方法存在效率低、成本高等问题,为此,结合煤在水溶液中的带电特性,提出通过外加电场产生电泳作用驱动煤粉运移解堵。采用自制的电泳改变煤粉沉降特性试验装置,开展电位梯度对不同煤阶煤粉沉降特性影响的物理模拟试验,探究煤粉沉降规律,结合电动电位、接触角测量、红外光谱、粒子图像追踪PIV测试等表征手段,揭示电泳作用机理。结果表明:随着时间的增加,无烟煤、焦煤和长焰煤等3种煤阶煤粉的沉降质量均呈先快速升高、后基本稳定的变化规律;随着电位梯度的增大,3种煤阶煤粉的最终沉降质量均呈反比例函数的变化规律,即先快速降低后缓慢降低至稳定,其中焦煤的降幅最大;试验过程中观察到3种煤阶煤粉均出现聚团现象,且焦煤的聚团现象较明显,这是由于焦煤的羟基含量较高,导致其接触角小,亲水性好,从而使煤粉颗粒之间更易形成液桥;施加电场后,3种煤阶煤粉的运移轨迹类型由快速下降变为减速下降、先降后升的类抛物线或上升等3种,且焦煤的类抛物线和上升轨迹较多,并且加电后3种煤阶的平均运移速率均增大,其中焦煤增幅最大;电泳改变煤粉运移机理是外加电场和液桥2个因素改变煤粉所受合力,一方面外加电场提供电场力使得合力向上,另一方面液桥的存在增大了重力、浮力和电场力,其中浮力增幅比重力大,使得向上的合力增大,并且焦煤的液桥较多,向上合力最大。因此,外加电场可以有效地降低煤粉沉降质量,减少煤粉堵塞。

     

    Abstract: 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.

     

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