CSIRO's model solutions to fit all situations

CSIRO researchers have combined physical (ie water) modelling (top) and computational fluid dynamics (bottom) to simulate the behaviour of a new generation of aluminium cells known as drained cathode cells.

Making process improvements without interrupting production or taking technical risks with new plant design is a perennial challenge for the light metals industry.

However, the Light Metals Flagship offers a proven alternative – using CSIRO’s computer modelling facilities to predict likely impacts.

Computer simulation has already helped Australian alumina refinery operators, including Rio Tinto, Alcan and BHP Billiton, to save $295 million.

These savings resulted from an integrated R&D effort to improve the performance of thickeners in gravity filtration. The research, involving CSIRO and the Parker CRC for Integrated Hydrometallurgy Solutions, included sophisticated computer simulations.

As a result, alumina refineries have been able to process more material, save water, increase operating speeds, obtain a purer mineral stream for subsequent processing, and reduce flocculant use.

While the thickener research was based on computational fluid dynamics (CFD) and physical modelling, CSIRO also offers a new approach known as smoothed particle hydrodynamics (SPH).

Handling free-surface flows
SPH is described as ‘meshless’ modelling, because unlike CFD – which superimposes grids over modelled surfaces to compute fluid behaviour –

One team has used a technique known as SPH to model the filling of dies to minimise air pockets in the cast component.

SPH treats fluids as free-flowing particles, and is ideal for modelling complicated, time-dependent, 3D flows.

A team led by Dr Paul Cleary of CSIRO’s Mathematical and Information Sciences (CMIS) has helped to pioneer the application of SPH to manufacturing processes.

For example, the team has used SPH to model the filling of high-pressure diecasting (HPDC) dies, enabling them to design air vents to minimise the occurrence of air pockets or voids in the cast component.

The CMIS team has also applied SPH to the design of rotating wheels through which molten aluminium is poured into ingot moulds. Excessive splashing of the metal during pouring causes oxidation in the ingots.

The researchers used the modelling technique to reduce ingot oxidation by modifying casting wheel design, an achievement that won them a CAST CRC award. A patent has been lodged on the wheel design.

SPH is being used to assist with stirrer design for magnesium production via a solvent route.

In another application, Dr Cleary’s team is using SPH and physical modelling to simulate a new solvent route for magnesium production.

This will enable Light Metals Flagship researchers to optimise reactor vessel/stirrer design, taking into account magnesia/carbon pellet behaviour, temperatures, reaction time and metal quantities.

CFD a general-purpose tool
At CSIRO Minerals, Dr Phil Schwarz has been applying grid-based CFD modelling techniques to solve process engineering problems for the light metals sector (www.cfd.com.au).

The value of CFD lies in its applicability to a range of production processes – such as multiphase (gas/liquid/particle) interactions, turbulent flow, chemical reactions and heat transfer.

For example, in a Light Metals Flagship project, CFD has been combined with physical modelling to simulate the behaviour of a new generation of aluminium cells known as drained cathode cells (DCCs). Industry collaborator Comalco expects to achieve energy savings of at least 10% compared with current aluminium cell operation.

The data on fluid flows and gas bubble behaviour from the modelling is being used by CSIRO materials scientists to optimise cell design.

CFD is also playing a part in design improvements to a supersonic nozzle and collection chamber at the heart of a Light Metals Flagship project aimed at making magnesium via a carbothermic route.

Approaching real-world complexity
CSIRO’s strength lies in its range of modelling expertise, enabling researchers to provide a customised solution for every process problem.

The combination of computer and physical modelling in particular is a powerful tool for developing robust ‘virtual’ test-beds to evaluate new designs or modifications.

“With the DCC work, CFD models are being progressively extended to encompass the greater complexity in operating smelter cells, including phenomena that are not feasible to physically model,” says Dr Schwarz.

Mechanical engineering angle
CSIRO Manufacturing and Infrastructure Technology brings a different set of skills to bear on the modelling of light metals production processes.

A 30-strong mechanical engineering group, specialising in fluid mechanics and heat transfer, uses both CFD and experimental techniques to model two-phase flows (gas-solid, fluid-solid, gas-liquid).

Hugh Blackburn says his group's capability has been used to improve a number of steps in alumina refinery operations, including desilication tanks, digesters, and precipitation tanks.

CSIRO's laboratory facilities include large impeller-driven mixing tanks, a tiltable slurry pipeline test loop, and state-of-the-art laser-Doppler (LDV) equipment to measure turbulent flow.

Contact:
Dr Paul Cleary
Paul.Cleary@csiro.au

Dr Phil Schwarz
Phil.Schwarz@csiro.au

Hugh Blackburn
Hugh.Blackburn@csiro.au

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In brief...

The Light Metals Flagship is a CSIRO initiative and part of the National Research Flagships program that aims to deliver scientific solutions to advance Australia's most important national objectives. One of the largest scientific initiatives ever mounted in Australia, it aligns closely with the Federal Government's National Research Priorities. The initiative brings together our national research resources to deliver breakthroughs in fields ranging from healthcare to light metals and the environment.

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