Recycling helium


By Susan Williamson
Wednesday, 31 July, 2013


Helium is disappearing from the planet and at the current rate of use will potentially run out in 10 years. This has the scientific community concerned because helium is essential for many processes, including medical imaging systems that rely on supercooled liquid helium.

To solve this problem, the ARC Centre of Excellence in Cognition and its Disorders (CCD) at Macquarie University in partnership with the CSIRO has developed a state-of-the-art liquid helium recovery system.

The onsite recovery system enables 90% of spent helium to be recovered from imaging systems such as magnetoencephalography (MEG) machines, which researchers at the CCD use to study children’s brain development.

MEGs measure magnetic fields generated around the currents created by active neurons, providing a non-invasive safe way to study how the human brain functions.

However, for the MEG to operate, liquid helium is needed to cool the SQUID sensors that record the tiny signals generated by the brain. The sensors must be cooled to an extremely low temperature, which requires them to be bathed in quite significant amounts of liquid helium.

“With the current adult and child MEG systems, the CCD uses 200 litres of liquid helium per week,” said CCD Director, Distinguished Professor Stephen Crain, “and the boil-off helium gas is subsequently lost to the atmosphere, so new liquid helium must then be purchased.”

Helium gas (typically 0.3%) is part of the natural gas mixture that has been trapped below the ground. Because helium is lighter than air, once it is lost to the atmosphere it escapes the earth and drifts into space - permanently.

The leak-tight Liquid Helium Recovery System is designed to capture all the boil-off helium gas, pressurise, store and reliquefy it for cryogenic cooling of the superconducting sensors. This provides a more efficient and sustainable use of helium, as well as securing supply for the CCD.

“Helium is a non-renewable resource and rationing is coming,” said Professor Brent McInnes, Director of the John de Laeter Centre for Isotope Research, Curtin University. “It is already being rationed in the scientific industry today.”

Of the 14 helium extraction plants in the world, Australia has one - a new plant that was built in Darwin in 2010. Helium gas is pumped to the plant after being retrieved from natural gas extracted from the Timor Sea.

The Darwin plant has yet to make Australia self sufficient in its helium production. McInnes said Australia remains dependent on the US for helium, which costs $30/liquid litre - a figure that continues to rise as the availability of liquid helium continues to decrease.

Liquid helium has all sorts of applications other than in healthcare. For example, for electrical power, accelerators, high-speed trains, particle accelerators and nuclear reactors.

This collaborative project was partly funded by a New South Wales Science Leveraging Fund (NSW SLF) grant, and partly by the Macquarie University contribution to the CCD.

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