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:: New Transport Options for Minerals Processors, the Petrochemical Industry & Food Manufacturers
By L.J.W. Graham and L. Pullum
New research facilities at CSIRO Building Construction and Engineering at Highett in Melbourne have opened up the potential for manufacturers in diverse processing industries to investigate new options for transporting high concentration suspensions and pastes by pipeline.
A long term objective of the work is to develop techniques for reliable transport of these materials based on an understanding of the complex flow regimes inherent in these flows.
The recently constructed pipeline test loop for fundamental and applied research into the use of hydraulic transport for complex, high concentration suspensions at CSIRO Building Construction and Engineering (BCE’s) Advanced Fluid Dynamics Laboratory in Melbourne offers industry the chance to overcome problems associated with pipeline transport.
For example many of the materials currently transported by pipeline are actually two or more phases such as pastes and suspensions or oil-water-gas mixtures and many also exhibit non-Newtonian rheology in contrast to simple fluids like water.
This makes the design of piping systems a difficult task since mathematical models of these complex high concentration suspensions are lacking. By comparison the techniques for designing pipe networks for simple Newtonian fluids like water are well established.
BCE’s research will consider fundamental aspects of the flow of complex fluids and suspensions in order to develop a more comprehensive understanding of the flow of these concentrated suspensions under a range of flow conditions. This understanding can then be used to develop a design methodology for pipeline systems where complex fluids or suspensions are conveyed.
This would include recommendations as to optimum particle size ranges for maximum throughput and pump types. This should be of substantial industrial benefit since more confident design of piping systems should lead to lower operating and capital costs and more energy efficient transport.
The pipeline facility is also available for testing and development. Pipeline equipment manufacturers can test their equipment in a more controlled manner than would be possible in an industrial situation.
A typical example would be the testing of slurry pump designs in a range of known slurries or non-Newtonian fluids which would lead to better design and performance predictions. Other equipment such as flow meters and valves for slurry flows can also be tested in a removable module in one of the loops. A photograph of the mixing tanks and pumps for the pipeline loop are shown below:
One of the measuring devices available for the pipeline facility is a Magnetic Resonance Imaging (MRI) system. This device is similar to those used for medical imaging but is smaller and fully dedicated to engineering research in granular solids and suspension flows. MRI provides non-invasive fluid velocity and particle concentration measurements even in opaque suspensions. Other instrumentation includes laser based flow velocity measurement techniques for use in transparent simulated fluids or suspensions as well as the normal instrumentation required to obtain the gross transport characteristics of these materials. Several rheometers are also available for characterisation of fluids.
A graphic illustration of the complexity of these seemingly simple systems was afforded by an experiment to investigate the behaviour of particles in a non-Newtonian carrier fluid. The carrier fluid was a long chain polymer dissolved in water to provide a rheology similar to that of some mineral slurries. Screened sand particles of a known size distribution were added to the carrier fluid. Under static conditions or in a mixing tank the fluid held the particles stably in suspension. When the mixture was pumped through the pipeline the MRI results revealed that the particles had fallen out of suspension as shown in the images below:
The velocity map shows the existence of a low velocity region at the bottom of the pipe consistent with a moving bed of solids. This is confirmed by the concentration image. Thus suspensions which appear to be stable and homogeneous under static conditions may stratify under shear as can occur during pipeline transport. This has implications for piping system design where pastes and suspensions are often assumed to be homogenous. Further research into these phenomena is continuing with this new pipeline facility with the aim of developing technology that can successfully exploit such behaviour.
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