The McGill Magnetic Resonance Facilities are having a helium recovery system installed! When complete, it should enable us to recovery 90% of the helium used by our seven traditional NMR magnets and one pumped NMR magnet, as well as permit us not to lose the helium used to cool our EPR cryostat.
Helium is the second-most abundant element in the universe. On earth, it is generated by radioactive delay, and if it is trapped in deposits in the earth's crust, it can be extracted, purified, and used. Usually this happens as a byproduct of natural gas extraction. However, because it is very light, it is difficult to prevent it from escaping the earth's atmosphere. This makes it a nonrenewable resource. Furthermore, helium is only found in certain locations, and it must be trucked or shipped to its final location. Recycling helium on site substantially reduces greenhouse gas emissions generated in extraction and transport.
Helium is used by all eight NMR magnets and the EPR spectrometer (when the cryostat is cooled). For NMR, it is used to keep the metal in the magnet cold so that they are superconducting. For EPR, it keep the sample cold. This helium boils off during normal usage, and it boils off at a significantly faster rate during helium refills, when liquid helium is transferred into the NMR magnet dewars. Normally, this helium evaporates into the atmosphere and from there dissipates into space. However, with the helium recovery system, it flows through copper pipes to a compressor which compresses it into medium pressure cylinders for storage. The gas will then be purified by passing it through a nitrogen-cooled purifier, and finally it will be condensed to liquid helium via a cryocompressor. At this point, the cycle can be completed by transferring the recovered liquid helium into the NMR magnets or the EPR cryostat.
A couple of noteworthy points:
- we will not be using a balloon to collect helium in our system
- during helium fills, when boiloff is highest, helium will warm up through an extra long line before entering the collection pipes, so as to reduce pressure changes down the line
- all magnets are located on the same floor, with the seven standard NMR magnets and the EPR instrument located at approximately 100 m from the helium recovery system. The pumped magnet is located about 15 m from the recovery system
The copper pipes used have a 2" diameter. Compression fittings are used and the pipes have been tested to hold 20 psi helium gas over a weekend.
As part of the SPF project, information about helium and helium recovery system is being shared with various classes, especially CHEM 429 (Chemistry of Energy) and CHEM 462 (Green Chemistry).