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.