Helium, an elixir of research
In many laboratories all over the world research only works with helium. ETH Zurich and the University of Zurich also depend on a regular and reliable supply of helium. After its use in the laboratory, helium it is recovered and reused in various processes to ensure that as little as possible of the valuable gas is lost. A new and more efficient plant for helium liquefaction has now gone into operation at ETH Zurich on Hönggerberg.
Why do researchers need helium?
Helium is indispensable to many technical applications. Magnetic resonance imaging (MRI) systems, for example, cannot be operated without helium. These devices work with strong magnetic fields generated by superconducting coils. These work at extremely low temperatures of minus 269 degrees Celsius, which are generated by liquid helium. It is the only substance that does not solidify even at absolute zero (0 K or -273.15 °C) under normal pressure. Basic research in physics, materials science, biology and chemistry also requires such low temperatures for their experiments, some of which take months.
What happens during a shortage of supply?
Only experiments that are continuously kept at temperatures close to absolute zero produce useful results for research. Without these results, success in key research fields such as quantum research would not be possible. That's why the technical department services in the department of Physics, ETH Zurich — which is supplying the entire ETH and the University of Zurich with liquid helium — does everything it can to ensure that there is never a supply bottleneck. In addition to experienced specialists, this requires stable facilities, flawless logistics and foresight.
How does helium become liquid?
We know gaseous helium from fairs since childhood. But the process of liquefying the gas is anything but child's play. The helium obtained from natural gas is procured externally and then reused in a cycle with as little loss as possible. A highly engineered labyrinth of pipes in the underground of the campus ensures that the helium, which becomes gaseous after use, is recovered as loss-free as possible. The gas liquefaction plant can therefore be imagined as a heart connected to a large circuit and continuously supplying all affiliated research centres and laboratories with newly processed liquid helium. In the gas liquefaction plant, the gas is pumped through heat exchangers at high pressure generated by a compressor and expanded by turbines until it is cold enough and becomes liquid. Pre-cooling of the gaseous helium with nitrogen additionally increases the output of the liquefied gas.
The new gas liquefaction plant
For 2.2 million Swiss francs, one 20-year-old liquefaction plant was replaced by a new one over the course of a year. It has a capacity of 100 l/h, three times more than the previous one. The second one was previously serviced and equipped with new control valves, new controls and new gas management. This guaranteed the permanent supply of the laboratories during the construction phase. The cold box of the new plant is equipped with more efficient turbines and even larger heat exchangers and requires considerably less energy than the old one. However, the just-installed machine is also not quiet. It will probably still take some time before the technicians can reduce the sometimes high-pitched operating tones, which is relevant because the specialists are always working in the immediate vicinity of the machines.
Mainly safety-relevant building elements of the HEZ unit at Hönggerberg, where the plant is located, where additionally renewed. Working with gases in rooms can be dangerous, which is why appropriate air supply is of great importance.
Emergency management and remote control
The plants are constantly monitored because also at night they produce at full speed. Until the entire system is well established, a false alarm will cause a sleepless night every now and then for the one responsible in the "gas liquefaction" team. In the future, both systems will also be controlled from home via a Remote Monitoring and Control System (RMCS). In certain cases, to ride to the Hönggerberg in middle of the night can be avoided. But anyhow, you can't really get back to sleep after an emergency.
A long-proven team
René Keller, Beat Helbling and Richard Lauener, who oversaw the conversion and now operate the new plant, have been a well-rehearsed team for 10 years. René Keller has been working in the gas liquefaction team at Hönggerberg for 27 years and hears how well things are going listening to every tone of this large system. He heads the group and is also responsible for the management tasks. A lot of experience is needed before the recovery of the gaseous helium, the preparation of the helium for storage in cylinders, the gas management and the entire liquefaction process by means of expansion turbines can run smoothly. This is the only way to ensure reliable delivery of the liquid helium to the laboratories. The liquid helium from the liquefaction plants is filled into "dewars", medium-sized insulation tanks on wheels. (For details, see see Downloadthis schematic (PDF, 537 KB).)
Fundamental service for research
Thanks to the new facility and increased building security, even in the event of increased demand the Department of Physics can guarantee its services for the entire ETH and the University of Zurich without interruption and of the highest quality. Also, the researchers themselves are responsible for ensuring that this remains the case, because only by using helium sparingly, enough can be recovered. Prices for this non-renewable gas have recently risen from 8 to 20 Euros per cubic metre on the world market. In addition, the Asian market supplies the ordered quantities only unreliably. When visitors enter the ETH Hönggerberg campus, they notice nothing of all this. The technical heart, which is central to many research areas, pumps in secrecy — so naturally that one almost forgets.