Since April, 2021, the McGill Magnetic Resonance Facilities has a helium recovery system capable of liquefying up to 20 L daily. We now recover 90% of the helium used by our seven traditional NMR magnets, one pumped NMR magnet, and EPR cryostat.
Status
October 25, 2023: We have been consistently recovering about 90% of our liquid helium for at least a year now. As helium is pretty tricky to measure, whether by weight, dipping or the sensor on our production dewar, the best indicator of our recovery rate is the amount of liquid that we have ordered over the past year, which is down substantially.
August 2022: First round of annual maintenance was completed. We checked filter mats for dust in the HR3 compressor unit as well as draining the oil, replacing the oil separator and filter cartridges and filling with fresh oil. After running through a couple of transfers to ensure that any air the was introduced had worked through, the purifier was warmed up and the additional step of pumping to be sure all residual moisture was removed was added it to the usual regeneration protocol. Afterwards a new water filter was installed before returning the system to liquefy mode.
March 8, 2022: We've had a visit from Sébastien Garbarino of Prima Québec today. It was exciting to talk about our cutting-edge system with someone who knows about advanced materials. He was impressed by Québec's lead in implementing a recovery system for an NMR lab that can be maintained in-house.
March 7, 2022: We've had an eventful few months and we think that we are improving our recovery rates. In mid-December, we borrowed a helium sniffer from the John Smeros in the Department of Physics and identified some leaks around flow meters and other connections on our low-field instruments. Then in late December, we realized (with the help of Quantum Technology!) that there was an ice blockage in the level gauge on the production dewar, so we spent the winter break warming it up - no liquefaction. Since starting up again, we have been working on calibrating the production dewar gauge (we aren't convinced that it is linear) by carefully measuring the amount of helium going to the transfer dewar and to medium pressure storage during each transfer out.
August 13, 2021: We have been up for almost six months now! We have discovered that
- our liquefier is very sensitive to chilled water temperature and/or flow - more sensitive than the cryoprobe compressor on the same line. UPDATE: during some scheduled electric work elsewhere in the building and unrelated to our problem we observed that the chilled water flow would stop for almost a minute during a switching event. The cryoprobe compressor could cope with this- the liquefier compressor could not. Ever since the electric work there have been no issues.
- the LN2 purifier can develop significant quantities of ice in a humid room - we use an extension to the outlet and keep a fan trained on the top to help
- the liquefier can manage up to 25 L / day if it has enough helium to liquefy!
- the LN2 purifier should be filled about twice a week UPDATE: once a week is sufficient.
- we are able to identify the end of a magnet helium fill by looking at the pressure in the header - it increases when a magnet is full
July 27, 2021: some sound engineers visited to investigate how noisy the system is. It sounds like it'll be expensive to soundproof properly. Fortunately foam sound panels at the bottom of the liquefier attenuate the sound significantly.
July 25, 2021: We have a loaner dewar so are back in business! And we have a scale to set under our liquid helium transport dewar! It is intended to allow us to track boiloff from this dewar (so that we can, by difference, find out how much is boiling off from our NMR magnets) and to confirm the amount in the dewar after a transfer in. However, it doesn't track small, slow changes in weight! Update August 10, 2021: the vendor helped us configure the settings so that we can turn the scale off, change the amount of helium in the system, and then turn it on and measure the difference.
July 17, 2021: We seem to have overfilled our helium transport dewar last week during a transfer from the production dewar. It had evaporated much less helium than we thought, so we didn't know how much to fill it up by. Now it doesn't hold vacuum.
July 1, 2021: We have a new computer to link to the HMI (touch-screen interface on the liquefier). We can access the computer remotely, allowing us to keep an eye on the recovery system even when we are not in the building.
June 2, 2021: The last low-field system has been connected to the recovery system!
April 30, 2021: Problems with our purifier have led us to suspend liquefaction for a few days. Update May 4, 2021: one of the helium cylinders used to purge some lines contained nitrogen. Regenerating the purifier fixed the problem and we are back online.
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).
Rationale for helium recovery
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.
Funding
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.
Description of system
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 either directs it to a liquefier (this is the route followed during standard boil-off) or compresses it into medium pressure cylinders for storage (this is the route followed during helium fills or transfer of liquid helium from the production dewar to the transport dewar. Our liquefier (production) dewar holds 150 L helium and our transport dewar holds 200 L. The liquefier liquefies 20 L / day maximum. From the liquefier, the gas is 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
Piping
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.
Outreach to classes
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).
Links
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.
