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FluidFlow3 slurry from Accutech

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FluidFlow3 slurry from Accutech will have extensive applications in the mining and mineral processing industries where the design of a pumped system must take into account the effect of the solids on pipe friction and pump performance.

In the screen image below two similar flow systems are compared, one with water only, the other with water containing 20% bauxite solids.

The increased pressure drop or 'solids effect' of the bauxite is evident from the displayed results.

Design method simulating the performance of settling slurries, i.e. a carrier fluid conveying solid particles, is complicated due to the wide range of variables involved, viz particle size and size distribution, solids density and shape, percent solids, mixture velocity etc.

The accepted approach is to determine the solids effect; the extra friction loss caused by the solids content over that for an equivalent flow of the carrier fluid.

The carrier fluid may simply be water if the solids are relatively coarse with no fraction below about 0.4mm but solids smaller than 0.4mm can be held in suspension and create a homogeneous carrier fluid, the friction characteristics of which needs to be determined.

Typical applications will involve water-based settling slurry. A number of inter-related factors then influence the excess pressure drop in a pipeline over the pressure loss for water alone (or the carrier fluid if a fine particle fraction exists).

The two main factors are the solids characteristics and the velocity of flow of the mixture but pipe inclination is also important.

For solids of size less than about 0.4mm and at higher velocities the particles are distributed in a homogenous manner and the head drop can be considered directly proportional to that of water.

At the other end with coarser particles moving only as a contact load, i.e. as a sliding bed with none in suspension, the solids effect is considerable and the pressure loss much greater than for water alone.

This is referred to as fully stratified flow. In between these extremes are two regimes, pseudo-homogenous and heterogeneous.

Pseudo-homogenous flow contains particles between about 0.4mm and 1.5mm and displays a variation of solids concentration with height across the pipe diameter, depending on velocity.

Again the pressure drop is proportional to that obtained for an equal discharge of water.

Heterogenous flow - particle size around 1.5mm to 4mm and lower velocities - exhibits a greater non-uniformity of solids concentration.

The solids are supported partly by fluid suspension and partly by inter-particle contact. The settling velocity of the solids and the percent by volume in the mixture are important factors.

A mining-type slurry may contain a wide particle size distribution and consequently all four regimes of flow - a homogeneous carrier fluid, and pseudo-homogenous, heterogenous and fully stratified fractions - may be present at the same time.

The technique is to estimate the excess pressure drop separately for each of the four regimes and then sum them for the total.

The design method is highly empirical. Slurry transport using centrifugal pumps, by KC Wilson, GR Addie, A Sellgren and R Clift provides reference with a synthesis of the authors' many papers.

Introduction to practical fluid flow by RP King provides a useful summary of the Wilson-Addie-Sellgren-Clift method plus a comprehensive chapter on non-Newtonian slurries.

Chemical engineering fluid mechanics, by Ron Darby provides a useful introduction to all types of flow.

These three references, and a considerable amount of literature research, provided the basis for the development of the settling slurry simulator.

A correction routine for the performance of end suction centrifugal pumps is also included.

Solids database, the solids database allows the physical properties of solids to be entered.

Pump performance correction, the hydraulic performance of an end suction centrifugal pump must be derated when pumping a fluid containing solids.

FluidFlow3 slurry allows choice of two correction methods - fixed reduction ratio or the method according to King.

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