Sedimentation of particulate suspensions under stagnant conditions in horizontal pipes

TL;DR

This study investigates sedimentation in horizontal pipes, demonstrating that sedimentation rates can be predicted with 1D theory, but consolidation behavior requires more complex models, aiding pipeline management.

Contribution

It shows that sedimentation properties are predictable from suspension characterization, but consolidation involves complex stress states not captured by simple models.

Findings

Sedimentation can be accurately predicted using 1D theory.

Consolidation of sediment is not well predicted by 1D models.

Transient effects like gravity currents are negligible in this context.

Abstract

Sedimentation of particulate suspensions in horizontal pipes can lead to formation, growth and consolidation of a solid-like bed which can severely retard pipeline performance. As stagnant flow conditions frequently arise during industrial processes, critical operational questions are: (i) at what rate and extent does sedimentation proceed, and (ii) can the 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, suggesting that the stress state is not 1D and likely involves contributions from the pipe walls. These stagnant cylindrical pipe results provide a basis for the development of methods to predict pipeline sedimentation under more general (laminar and turbulent) flow conditions.