Settling slurries comprise a carrier fluid conveying solid particles. This type of flow
has extensive applications in the mining and mineral processing industries,
where the design of pumped systems must take into account the effect of solids
on pipe friction loss and pump performance.
Simulating the performance of settling slurries is dependant on the solid
density, concentration, particle shape and size distribution, as well as the
properties of the carrier fluid. Selecting the optimum pipeline velocity is
usually the most important factor in the design and operation of slurry systems.
Operating with velocities too high wastes energy, while operating with
velocities too low can lead to pipeline blackage.
Design methods are highly empirical and FluidFlow offers different calculation
approaches:
- Wilson, Addie, Sellgren and Clift (WASC).
- Durand, Condolios and Worster.
- Wasp.
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Carrier and solids input data
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The example opposite shows the Input Editor defined for the
transportation of 1000 tonne/h of sand at a volume concentration of 30%.
FluidFlow will calculate the correct volumetric flowrate to acheive this
requirement. We could have specified flow as total volumetric, or on a carrier
basis only.
Particle size entry requirements depends on the calculation approach selected. WASC requires d50 and d85, Durand requires d50 and WASP requires a particle size distribution which the software allows.
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Pump Deration
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When a pump is used to transport a slurry, the prescence of the
solid particles has a significant effect on the performance of the pump. As the concentration of
slurry increases, the head generated by the pump decreases because of the
greater friction losses that occur in the pump casing.
FluidFlow allows you to select the amount of derating that is applied. This value
may be obtained from the pump supplier, or FluidFlow can estimate the deration
according to Hydraulic Institude guidelines or via other text book calculation
methods.
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Pipeline system curve for a settling slurry
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The system curve for a settling slurry is different to that of a
Newtonian fluid. The friction loss curve for a nickle ore slurry is shown
opposite. A minimum friction loss value is usually observed at or near the
particle deposit velocity. The most economical velocity is usually at this
minimum point.
The curve shown is asymptotic to the equivalent water curve at higher velocities, so essentially the slurry flow calculations are calculations of the "solids effect" of the suspended solids, i.e., the additional pressure loss due to the suspended solids over that for the same volumetric flow of the carrier alone.
Usually, because of the application of safety factors in design methods, pipelines are operated at higher flow velocities than the economic minimum. There are a series of system curves, the exact position and shape of each curve depends on the solid concentration.
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Nickle ore delivery system
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This example shows a pumped slurry system that has been exported to
Excel. The content of the export can be fully controlled.
You can download the xls file produced by FluidFlow by clicking here.
Click on the tabs to display the various Excel pages. Exporting to Excel allows you to customise your reports and provides an excellent method of communicating the results of a study, to a client or colleague. |
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