Engineering context

Settling slurries carry coarse, heterogeneous solids that drop out of suspension if velocity falls too low, so they need dedicated treatment rather than being modelled as a plain liquid. The first decision is classification — settling versus non-settling — because that choice determines how the slurry is modelled.

Settling slurries don’t behave like conventional liquids — friction loss does not rise monotonically with velocity, and as velocity falls through the moving-bed regime it can increase with decreasing velocity. FluidFlow handles them within its steady-state pipe network solver, detecting pipe orientation, applying the chosen correlations automatically, and derating centrifugal pumps for solids friction.

Engineering workflow

1. Classify the slurry as settling. If slurry test data is available, use it — scale-up testing confirms settling behaviour. Without test data, solids mostly 75 microns and smaller indicate a non-settling slurry, which may exhibit non-Newtonian characteristics depending on concentration and solids type; coarser or mixed solids are treated as settling.
2. Define the solids in the fluid database — store the solids’ properties in FluidFlow’s fluid database as required.
3. Configure the settling correlations — choose one method per category using engineering judgement: deposition velocity, inclined-pipe adjusted deposition velocity, horizontal friction-loss correlation, and vertical friction-loss correlation. FluidFlow detects pipe orientation and applies the methods automatically.
4. Define the boundary conditions — add the boundaries and set the inlet boundary fluid type to heterogeneous settling so the solids data is defined there. Choose the pressure model correctly — stagnation for vessels, static for pipes.
5. Build and connect the network — add pipes, fittings, elevations, and equipment, including any centrifugal pumps.
6. Model the system as a liquid system with centrifugal pump solids derating — enable the option to derate centrifugal pump performance for the additional friction loss that coarse solids impose on the pump internals.
7. Solve, then analyse as a typical liquid system — review pipe velocity, capacity, and NPSH margin.
8. Analyse the slurry-specific results — check pipes for deposition issues (velocity against deposition velocity), pressure losses, specific energy consumption, slope impact, and the drop in pump performance due to derating.

Why the full system matters

Velocity is the critical variable in a settling slurry system. If velocity falls below the deposition velocity, solids settle and blockage risk rises. But friction loss in a settling slurry does not behave like a liquid — in the moving-bed regime, friction loss can increase as velocity falls, producing behaviour that a standard liquid model cannot reproduce. Pump performance is also derated by solids, so the duty point, flow distribution, and NPSH margin must be evaluated in the connected slurry system, not from liquid-only calculations.

How FluidFlow helps

FluidFlow models settling slurries within its steady-state pipe network solver: solids are defined in the fluid database, the inlet boundary fluid type is set to heterogeneous settling, and deposition-velocity, inclined-pipe, and horizontal/vertical friction-loss correlations are selected per system. It detects pipe orientation, derates centrifugal pumps for solids friction, and reports velocity, deposition margin, pressure drop, specific energy consumption, and NPSH across the network.

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