Slurry optimisation

Efficient pumping of thickened or viscous slurries

by Dr Chris Vernon

Reducing water usage and slurry dilution is a high priority for many operations, due to the ever-growing cost of water, and growing environmental and regulatory pressures.

Many mineral processing operations are increasingly pumping thickened materials or slurries with elevated viscosities, to increase throughput while reducing water consumption.

While this option helps to solve the problem of high water usage, it can have a range of operational, financial, and environmental implications.

Many operations see it as the only option, as there have so far been few other viable alternatives (beyond using larger positive displacement pumps, which come at a high cost and a sometimes-low ability to handle abrasive slurries).

Slurry transport is a complex process, and optimisation requires a good understanding of slurry rheology.

Issues facing the industry, while costly and potentially dangerous, have driven the development of more innovative slurry transport solutions.

Some of these are already having success at operating scale and are enabling the efficient pumping of thickened slurry with minimal cost and risk.

Pumping challenges

Transporting thickened materials or slurries with elevated viscosities can be problematic due to increased friction losses in the pipe which may exceed the pumping capacity.

This can be particularly acute with clay-bearing ores or slurries containing rheologically-active fines. These perturbations can be spasmodic, making smooth operational control difficult and unpredictable in the plant.

The end result can be:

• bogging, blockages and unplanned stoppages
• increased maintenance costs
• reduced production and adverse impacts on downstream processes
• excessive water use and costs, and
• in extreme circumstances, failure of tailings dam facilities

These outcomes are common and are faced by global operations on a daily basis, resulting in reduced production and increased operational downtime.

These issues are only set to become more problematic as further legislative changes are applied to the management of tailings facilities, further reducing water use.

Drag Reduction technology (DRT) offers a potential solution

We originally developed DRT to assist pumping of concentrated tailings.

The key innovation is a simple single-point water injection concept whereby pipe friction is reduced by providing a lubricating layer along the pipe wall.

The lubricating fluid can be water, or other process fluids with or without additives.

 

The device has a number of internal grooves to make distribution of the injected water uniform at the pipe wall.

It’s a simple, cheap, compact design and can be readily inserted between pipe flanges.

While originally developed with tailings in mind, it became clear that it would also be viable to use this technology to assist transporting feed slurries into reaction vessels, particularly pumping slurries into autoclaves.

Application of DRT at Murrin Murrin Operations (MMO)

MMO operate an acid pressure leaching plant in WA to treat nickel laterites.

Concentrated ore is pumped to a storage tank ahead of the High Pressure Acid Leaching (HPAL) autoclaves – a high solids concentration is required.

Sometimes the slurry viscosity can be high causing a drop in pumping capacity.

Water injection was traditionally used to maintain the full pumping flow, by (counterproductively) diluting the slurry.

In a routine site visit to MMO by our process engineers, operating staff mentioned the issue of capacity drop and the desire to find a solution other than water dilution.  We suggested our DRT technology may alleviate the pumping problem.

Based on data supplied by MMO, tests were conducted at our unique and fully instrumented Pipe Loop Facility, where slurries can be pumped through pipes (50-150 mm ID) in lengths up to 3000 times the pipe diameter under a range of operating conditions (flow rate, pulp rheology/viscosity, pulp density, and pipe tortuosity and inclination) enabling real-world slurry transport conditions to be optimised at scale.

The pipe loop testwork indicated that by using DRT, a significant reduction in pump pressure loss could be achieved with just 1.5% w/w water injection.

Significantly more water was required to achieve the same pressure loss reduction, if by simple dilution, giving MMO the confidence for a plant trial of DRT.

A DRT unit was designed and fabricated for testing on site, and installed in 2015 at the discharge side of the paste thickener underflow pump between two pipe flanges with a 25 mm water inlet connection.

Plant tests were conducted comparing the effect of dilution water with and without DRT.

The plant trails showed dilution water was reduced by a factor of 4 with DRT compared with the original dilution system to maintain a steady 500 m³/h slurry flow.

These results have been maintained, with the unit still in operation six years on and maintenance free.

This successfully demonstrates that DRT is useful for paste-like/high viscosity slurries over 300-400 metre pipeline distances.

Suitable applications include autoclave feed slurry pipes and tailings discharge pipes, especially on the suction side of the pump where the tailings pump is some distance from the thickener underflow discharge.

Partner with CSIRO to achieve optimised slurry transport

With increasing focus on mitigating disasters associated with tailings and the use of thicker slurries becoming more critical, more innovative and long-term solutions will need to be considered and implemented in mineral processing plants.

As the cost of water becomes higher – particularly in arid areas – devices like DRT are going to be more in demand to provide a solution.

Our Fluids Engineering Team offers science-led expertise, facilities and technology to assess and optimise slurry transport in your operation with a focus on increasing productivity.

We can offer:

• expertise in the physical handling and processing of particle suspensions in mineral processing and tailings treatment
• laboratory and pilot scale facilities leading to commercial plant trails
• measurement, simulation and modelling of multiphase flows and solid-liquid separation processes through advanced rheological understanding and physical experimentation, and
• world leading technologies such as DRT with proven commercial track records.

Improving slurry pipeline capacity means improved slurry management and operational efficiency via increased productivity. This in turn offers financial benefit and a stronger bottom line.

If you are facing slurry transport challenges, contact our team on +61 407 882 355 or email my colleague, Warren Bruckard, at Warren.Bruckard@csiro.au to take the next step in analysing your fluids-based processes to determine areas for optimisation.

We are also open to discussing manufacturing partnerships for this technology.

Please visit the CSIRO Commercialisation Marketplace for more information.