Aggregation and sedimentation experiments of coal fines with different particle sizes during CBM development
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摘要: 在煤层气开发过程中，煤粉聚集及沉降会堵塞煤层气运移通道及导致卡泵、埋泵等事故。为了查明不同粒度煤粉的聚集及沉降特征，选取粒度>140目（<106 μm）、>70~140目（106~<212 μm）和>50~70目（212~<300 μm）3种粒度范围的煤粉，开展了在去离子水中煤粉的聚集及沉降实验，从煤粉聚集及沉降特征观察、悬浮液中煤粉含量及煤粉粒度分布探究不同粒度煤粉在去离子水悬浮液中的聚集及沉降特征。结果表明，随着静置时间的增加，各粒度煤粉悬浮液的颜色均不同程度地变浅，逐渐出现分层，其中，粒度>140目的煤粉悬浮液最先出现分层。煤粉粒度越小，煤粉悬浮液顶部漂浮的煤粉量越多；煤粉粒度越大，其下沉到煤粉悬浮液底部的煤粉量越多。不同粒度煤粉悬浮溶液中煤粉含量均随着静置时间的增加呈现不同程度的降低，在停止搅拌后3 min内，煤粉含量下降最快，粒度为>70~140目的煤粉悬浮液中煤粉含量最大。根据不同粒度煤粉悬浮液中煤粉粒度分布曲线，将煤粉聚集及沉降过程分为3个阶段：单峰变双峰阶段（煤粉快速上浮及沉降）、双峰变单峰阶段（煤粉快速聚集及沉降）和单峰阶段（煤粉缓慢沉降）。粒度>140目的煤粉在悬浮液中最先达到缓慢沉降阶段，粒度>70~140目的煤粉在悬浮液中最后到达缓慢沉降阶段。从煤粉的受力、扩展的DLVO理论及煤粉的有机分子结构方面探讨了煤粉聚集沉降的机理：煤样含有大量的脂肪烃和芳香烃等疏水性基团，疏水性强，润湿性低；随着煤粉粒度的减小，其比表面积显著增大，煤粉表面吸附大量空气，形成气膜；同时，煤粉颗粒间相互吸附聚集，内部形成很多微孔隙，导致粒度小的煤粉易聚集漂浮在悬浮液面上。实验得到的不同粒度煤粉的上浮、下沉及悬浮情况，为后期煤层气开发中煤粉管控措施提供依据。Abstract: During the development process of coalbed methane, the aggregation and sedimentation of coal fines can block the migration channel of coalbed methane and lead to accidents such as stuck pump and buried pump. In order to find out the aggregation and sedimentation characteristics of coal fines with different particle sizes, the aggregation and sedimentation experiments of coal fines with the particle size>140 mesh(<106 μm), 70 to 140 mesh(106-212 μm) and 50 to 70 mesh(212-300 μm) in deionized water were carried out. The aggregation and sedimentation characteristics of coal fines with different particle sizes in deionized water suspension were investigated from the suspension observation, the concentration characteristics of coal fines and the particle size distribution of coal fines in suspension. The results show that with the increase of the time, the color of coal fines suspension becomes lighter to different degrees, and the stratification of coal fines suspension gradually appears, and the suspension of coal fines with the particle size more than 140 mesh was the first to stratify among three suspensions. The smaller the particle sizes of coal fines, the more coal fines float on the top of the suspension, and the larger the particle sizes of coal fines, the more coal fines sink to the bottom of the suspension. The concentration of coal fines in the suspensions decreased to different degrees with the increase of the time. The concentration of coal fines decreased the fastest within 3 minutes after stopping the stirring. The concentration of coal fines with the particle sizes of 70 to 140 mesh in suspension was the largest among three suspensions. According to the particle size distribution curves, the process of aggregation and sedimentation of coal fines was divided into three stages: single peak to double peak(rapid floating and settlement of coal fines), double peak to single peak(rapid accumulation and settlement of coal fines) and single peak(slow sedimentation of coal fines). Coal fines with particle size more than 140 mesh in the suspension was the first to reach the stage of slow sedimentation, and coal fines with particle size of 70-140 mesh in the suspension reached the stage of slow sedimentation at the latest among three suspensions. The mechanism of aggregation and sedimentation of coal fines was discussed from the aspects of the force of coal fines, the extended DLVO theory, and the organic molecular structure of coal fines. The coal samples contain a large number of hydrophobic groups, such as aliphatic hydrocarbon and aromatic hydrocarbon, therefore, they have strong hydrophobicity and low wettability. With the decrease of particle sizes of coal fines, its specific surface area increases significantly, and a large amount of air is absorbed on the surface of coal fines, forming an air film. At the same time, particles of coal fines are adsorbed and aggregated with each other, and many micro pores are formed inside, resulting in that coal fines with small particle size is easy to aggregate and float on the suspension surface.
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Keywords:
- CBM /
- coal fines /
- particle sizes /
- aggregation /
- sedimentation /
- suspention liquid
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