Sedimentation in Slurry Pipelines
Posted on September 29, 2022 Mining Non-Newtonian Flows
When slurries are transported along pipelines and launders, issues can arise from solids settling within the pipe. Such settling behaviour can greatly influence the operability of a system, including increased pressure losses and undesirable wear characteristics, or even plugging the pipe entirely. Management of solids sedimentation is further complicated in systems which experience a wide range of process conditions, such as with mining mineral processing.
The mechanics that dictate solids settlement are complex, as they depend on a multitude of factors including the properties of the solids (size distribution, density, concentration, shape, etc.), and the properties of the carrier fluid (density and viscosity, etc.). Further issues arise when complex mixtures are formed from finer particles, such as clays, integrating with the carrier fluid, which can lead to non-Newtonian rheological effects with the carrier fluid. Water chemistry can also play a large role in rheology. Given all the factors at play, it is notoriously difficult to predict how such systems will behave, and typically requires careful measurement of rheology and characterization of the solid particles.
Depending on the characteristics described above, flow within a slurry hydrotransport line can fall within different regimes. At flow rates that are sufficiently high, velocity fluctuations caused by turbulence in the carrier fluid ensure that the solids remain suspended in a nearly-homogeneous mixture. As velocity is reduced, the distribution of solids becomes heterogeneous, with solids biasing towards the bottom of the pipe, followed by the formation of a moving bed of accumulated solids. If the velocity is further reduced, a stationary bed will form. In this condition, flow can still be maintained along a gap above the stationary bed, although this may also become completely blocked if solids concentration is sufficiently high.
A well-considered characterization of the slurry system and application of available models can help to mitigate these risks.