The 19th International Conference on Transport & Sedimentation of Solid Particles (T&S) was held in Cape Town in September 2019 and it was a great success. It's the first time the conference has been hosted in Africa since its inception in 1971 and Paterson & Cooke (P&C) co-hosted the event together with Wroclaw University of Environmental and Life Science in Poland.
The conference was well attended and a total of 43 papers were presented of which two were from Paterson & Cooke.
L to R: Brian Zengeni, Milica Jovanovic (Wroclaw University), Bonang Maja, Dakalo Nekhavhambe, Rene Nsanzubuhoro
The papers presented by P&C were:
"Sensitivity of non-Newtonian Slurry Viscous Properties to Temperature"
Aim: This paper investigated the effect of temperature on the rheological properties (yield stress and apparent viscosity) of a typical non-Newtonian suspension (kaolin clay slurry).
Method: Two samples of kaolin slurry (flocculated and unflocculated) were prepared. Using a rotational viscometer, the rheological properties for the samples were determined at varying temperatures.
Findings: For both samples, the yield stress was found to increase approximately linearly with increasing temperature whilst the absolute viscosity decreased with increasing temperature.
Aim: To evaluate the use of a non-Newtonian two-layer model to predict the bed packing pressure gradient of mixed regime high concentration suspension with a sliding bed in laminar flow conditions.
Method: The two-layer model was fitted to previously published pipe loop pressure gradient data and compared with Electric Resistivity Tomography data to verify the efficacy of determining key parameters such as: the bed packing concentration of the bed, the bed height and the pressure gradients for high concentration mixed regime slurries in laminar flow.
Findings: The two-layer model was found to capture the high concentration mixed regime slurry laminar flow well, provided that stratified flow occurs, i.e. with the coarse solids conveyed as a sliding bed and above is a particle lean upper layer.
Special Address : Allan Thomas
The conference concluded with a special address by Allan Thomas, a leading researcher of tailings pipeline transportation and slurry rheology. In his address, Allan gave a brief summary of the conference and put forward suggestions for future research projects.
Allan alluded to the fact that the common trend is to thicken tailings to a higher concentration in paste thickeners. Consequently laminar flow pumping is increasingly required, resulting in high-pressure gradients ranging from 1.5 to 2 kPa/m which challenges the viability of the required pumping systems.
Lower pressure gradients could be achieved for smaller particles if we were able to predict the pipeline length before settling occurred. However, at present there is no accepted means of predicting this pipeline length for a given pipe size, particle size and pressure gradient. The relationship between these factors could be conveniently studied in small diameter pipe loops.
Other possible research topics suggested by Allan for laminar flow using small diameter pipe loops are:
- Injection of air to help resuspend particles
- Use of pipe with internal spiral ribs to resuspend settled particles
- Dilution of the slurry periodically to achieve turbulent flow to resuspend settled particles
- Addition of a viscosity modifier periodically to achieve turbulent flow
L to R: Bonang Maja, Rene Nsanzubuhoro, Brian Zengeni and Allan Thomas at Cape Point, South Africa
About The Author
Dr Rene Nsanzubuhoro
BSc Eng (Civil), MSc Eng (Civil), PhD
Rene completed his BSc, MSc and PhD in Civil Engineering at the University of Cape Town (UCT) before joining Paterson & Cooke in January 2019 as a Graduate Engineer.
Rene’s PhD research work involved characterising leakage in several bulk water pipelines in the field using: a specially designed test device, the latest knowledge on pipe leak behaviour and a novel theory for the time-dependent pressure behaviour of leaking pipe.