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Slurry pump iconFlownex Slurry and Non-Newtonian Flow

Flownex models Non-Newtonian fluids such as slow/non-settling slurries and settling slurries. Slow/non-settling slurries are usually well described by non-Newtonian fluid models. However, settling slurries require additional calculation methods which are accounted for in Flownex. This section will give a brief overview of the various slurry types and flow models used by Flownex.

 

Slurry Applications in Industry

The demand for industries to predict/simulate the behavior of slurry pipelines in plant building and maintenance is ever increasing. Slurry flow simulation allows engineers to design and maintain:

  • Ash handling systems in coal-fired power plants.
  • Lime handling systems in flue gas desulphurization plants.
  • Ore transport systems.
  • Tailings transport systems.
  • Backfill transport in deep mines.
  • Hydraulic materials transport.
  • Hydraulic transport of fine ore.
  • Transport of processed ore to tailings dams.

 

What is a Slurry/Non-Newtonian Fluid?

  • Broadly defined as a solid-liquid mixture.
  • First important distinction is whether the slurry is a settling or non-settling solid-liquid mixture.
  • For non-settling slurry – solid particles remain suspended or settle out at very low rates (< 1 mm/s).
  • For settling slurries – solid particles settle out with settling velocity > 1.5 mm/s.
  • Example: Paint vs. coarse sand particles in water (fish bowl).

 

Slurry Types Modeled in Flownex:

In terms of modeling, slow and non-settling slurries are usually well described by non-Newtonian fluid models, while settling slurries require totally different calculation methods. Mixed regime slurries are calculated by combining elements from both settling slurries and non-Newtonian fluids in a specific way. The two main parameters determining slurry characteristics:

  • Slurry particle settling velocity.
  • Solids concentration.

 

Slurries are broadly categorized in three categories, all of which are modeled in Flownex:

  • Non-settling slurries.
  • Slow settling slurries.
  • Settling slurries. 

 

Flownex SE will allow simulation of horizontal flows, inclined flows and vertical flows. Flownex can model: Non-Settling Slurries; Slow Settling Slurries; Settling Slurries and Mixed Regime Slurries.

 

Settling vs. Non-Settling Slurries

 

Slow / Non-settling slurry: 

  • Usually small particles, thumb ruled particle < 75 µm. 
  • Can be treated as homogenous liquid – solid mixture.
  • Concentration does not vary over cross-section.
  • Typically results in Non-Newtonian type flow.

 

Settling slurry: 

  • Usually larger particles, thumb ruled particle > 75 µm.
  • Solid particles settle out unless supported by turbulent mixing.
  • Results in varying solid concentration over cross-section.
  • Moving bed of higher solid concentration at the bottom of horizontal pipe.

 

What is implemented in Flownex?

The Flownex slurry flow module deals with the following three aspects:

  1. Predicting pressure losses in systems operating with non-settling slurries, especially Non-Newtonian mixtures such as mine backfill in pipes.
  2. Predicting pressure losses in systems operating with settling slurries in horizontal, inclined and vertical pipe segments such as ash removal systems on power stations or dredging systems on mines.
  3. Predicting centrifugal pump derating factors for pumps operating with either Non-Newtonian fluids or Settling slurries.

 

Assumptions

  1. For flow and pressure drop calculations, the slurry mixtures are assumed to be homogeneous. 
  2. Mixing is assumed to be instantaneous. 
  3. Settling is not calculated explicitly by way of a mass conservation equation for solids. Rather, the user is warned whenever physically undesirable situations occur, such as settling. Any change in the local concentration is assumed to occur instantaneously.