Separation of cohesive particulate suspensions under stagnant conditions in horizontal pipes

Sedimentation of cohesive particulate suspensions in horizontal pipes can lead to formation, growth and consolidation of a solid-like bed that can severely retard pipeline performance. As stagnant flow conditions frequently arise during processing, critical operational questions include: (i) at what rate and extent does sedimentation proceed, and (ii) can sedimentation dynamics be predicted from conventional suspension characterisation methods? We address these questions by characterising the sedimentation properties of an aqueous kaolin suspension via batch settling tests and comparing predictions from 1D sedimentation theory with experiments in a horizontally oriented cylindrical pipe. We show that particulate sedimentation can be accurately predicted, indicating that the estimated sedimentation properties are representative material properties, and that transient effects such as gravity currents are not significant. Conversely, we find that the consolidation of the sediment is not well predicted by 1D theory due to shear stresses arising from adhesion of the consolidated suspension to the pipe walls. These findings provide a basis for the development of methods to predict pipeline sedimentation under more general (laminar and turbulent) flow conditions.

水平管道内黏性颗粒悬浮液的沉降过程，会导致类固体床层的形成、生长与固结，进而严重损害管道运行性能。由于工业加工过程中常出现滞流工况，核心工程问题包括：（1）沉降过程的速率与发展程度如何？（2）能否通过常规悬浮液表征方法预测其沉降动力学行为？本研究通过批量沉降试验表征水性高岭土悬浮液的沉降特性，并将一维沉降理论的预测结果与水平圆柱管道内的实验数据进行对比，以此解答上述问题。研究结果表明，颗粒沉降过程可被精准预测，这说明所估算的沉降特性可作为具有代表性的材料属性，且重力流等瞬态效应的影响并不显著。与之相反，由于固结悬浮液与管壁粘附产生剪切应力，一维理论无法准确预测沉积物的固结过程。本研究结果为开发适用于更通用流态（层流与湍流）下的管道沉降预测方法提供了理论依据。