Since April, 2021, the McGill Magnetic Resonance Facilities has a helium recovery system capable of liquefying up to 20 L daily. When fully optimized, it should enable us to recovery 90% of the helium used by our seven traditional NMR magnets, one pumped NMR magnet, and EPR cryostat.
April 30, 2021: Problems with our purifier have led us to suspend liquefaction for a few days.
April 22, 2021: The helium recovery system is operational! Following installation by Quantum Technology in April 2021, we are able to collect passive boiloff (boiloff that occurs independently of helium fills) and active boiloff (boiloff during helium fills).
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.
The MMRF is very pleased to have received support from the Sustainability Project Fund at McGill University, the NSERC Research Tools and Instruments program, the Faculty of Science, and the Department of Chemistry.
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 is then purified by passing it through a nitrogen-cooled purifier, and finally it is 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 do not use a balloon to collect helium in our system. Instead, we have medium pressure gas cylinders to store helium before liquefaction when the amount of helium collected is high. Typically, this occurs during transfers of helium into the NMR magnets ("helium fills"). During standard boiloff, the helium flows straight to the purifier for immediate liquefaction.
- during helium fills, when boiloff is highest, helium warms up during passage 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
Each magnet connects to the "recovery header" (the piping bringing the helium from the magnets to the recovery compressor) via a 20' long flexible stainless steel hose with 2" diameter. The header itself is fabricated from 2" copper pipes. Viega ProPress compression fittings, a recognized green technology, are used at the joints and the header has been tested to hold 20 psi helium gas over a weekend. Between the magnet and the 20' stainless steel hose is a valved connection which permits passive boiloff to go through the magnet's standard checkvalve and from there either to the recovery header (standard setup) or to atmosphere (while other magnets are being filled with helium). On the other hand, the main valve is used to direct active boiloff straight to the recovery header without passing through the three-way valve with permits an exit to atmosphere. On the Oxford and Magnex magnets, the checkvalve is also bypassed during helium fills.
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).
We would like to thank the many helpful NMR managers and the AMMRL email list for all of the information and support they provided during the design and use of the system.