Helium is a precious noble gas that has become invaluable for leak detection, as well as cooling down magnets in medical equipment. This is why consumption of this essential industrial resource is increasing and its price is rising rapidly. To combat a looming shortage of this increasingly scarce resource, new methods of helium recovery are becoming more important than ever – as are specialized compressors for the same purpose.
A Noble and Versatile Gas
Due to its characteristic properties, helium is used for a large variety of industrial applications. With the lowest boiling point of all gases, it is used in cryogenic research for example, as a coolant for magnets found in computer tomography.
Because of its small atomic diameter, it is able to permeate even the smallest openings. This is what makes the gas an ideal choice for leak testing. The fact that it is inert and almost non-reactive makes it extremely versatile.
Helium is also used for quenching in metal working as a superior alternative to oil. The noble gas prevents discoloration from oxidization. In addition, it eliminates the need for subsequently cleaning the work pieces, thus increasing efficiency and improving cycle times.
Exploring New Ways of Recovery and Reuse
Helium is mostly derived from natural gas, in which it is contained in low concentrations. Rising natural gas prices have contributed to helium becoming increasingly expensive over the last few years. The trend is expected to continue since the gas is growing scarcity and there are no viable alternatives for helium production.
This requires a new approach. For a long time, helium, when used as a tracer gas for example, was simply expelled into the atmosphere after serving its purpose. Today, an entire industry is looking into ways of recovering and reusing the precious resource.
Specially designed recovery systems store the helium in large balloons after its use in leak testing. A compressor siphons the helium and compresses it to 2900 psi. In this state it can easily be bottled and stored for later use.
Breathing Air Compressors Not Up to the Task
Many manufacturers sell breathing air compressors used in diving equipment for compressing helium. However, these compressors are not sufficiently gas-tight to prevent costly helium leakage. In addition, with an average service life of 200-1000 hours, breathable air compressors are not made for long-term use. Actual helium compressors are designed to operate for up to 7,000 hours per year.
Helium compressors require accurate testing. Photo courtesy of Sauer Compressors.
Special Measures Help Prevent Costly Leakages
The unique properties that make helium ideal for technical applications are the same properties that complicate its compression. Given the low atomic size and viscosity of the gas, special valves and gaskets are necessary in helium compressors. The use of adhesive sealants further helps prevent costly leakages.
Oil-lubricated compressors in particular tend to have shaft-sealing rings installed to prevent oil and gas leakage. However, these seals only provide one-way leak tightness. The risk of contamination from the outside remains high when using standard air compressors. To counteract this, compressors designed for helium applications are doubly sealed. Two opposed shaft lip seals prevent both oil and gas leakage and keep contaminants from entering. Helium compressors are equipped with enclosed safety valves at each compressor stage. When they close, the superfluous gas is not expelled into the surrounding air, but instead, redirected to the compressor's priming chamber connected to the safety valves.
The condensate separator in standard air compressors proves another difficulty when it comes to compressing helium, as it not only expels condensate but also gas that then needs to be recovered. For this reason, helium compressors have condensate drains that enable recirculation of the gas.
Accurate Testing Required for Helium Compressors
In order for helium compressors to meet the requirements of the demanding gas, thorough testing is required. Many manufacturers only measure a static leak rate by subjecting the compressor to overpressure during standstill. However, this is not enough to get reliable test results and to ensure sufficient gas tightness.
Sauer Compressors, based in Kiel, Germany, has devised an extensive 16-hour test procedure for its helium compressors that is unprecedented in the industry. The goal: maximum leak tightness for the lowest possible loss of helium and the highest attainable gas purity.
Instead of using air for testing, Sauer’s specialized helium compressors are fully tested with the gas itself. First, a bubble test is performed to ensure that no gas is leaving the compressor. To do so, the compressor is subjected to overpressure and completely immersed in water. If a leak is present, it can be discovered via the emerging bubbles.
The compressor is then subjected to a vacuum in a pressure-rise test to ensure protection from contaminants from the outside. Finally, Sauer employs a pressure-decay test in a hermetically sealed helium cycle. This measures a possible loss of helium during operation at final pressure of 3335 psi, for example. The results of this extensive testing are helium compressors with a maximum leakage rate of only 0,1 mbar x l/s.
Specially Designed Compressors Remain Invaluable
Besides helium, the recovery of other noble gases with similar characteristics, such as argon and neon, will become increasingly relevant in the coming years. In order to ensure an economic use of these resources, specially designed compressors will remain invaluable in the long term.
About Sauer Compressors
Industries worldwide rely on Sauer piston compressors for pressures of up to 7,250 PSI to control process and production using high-pressure air or gas. Our starting and working air compressors have proved highly successful in a variety of demanding markets and are among the most modern and efficient in the world. We place great importance on comprehensive and proficient customer support backed by the Sauer Lifetime Warranty. We assist our customers from the initial project phase through after-sales service with specialist consultation for the complete solution while ensuring the best possible efficiency over the entire life-cycle of the compressor. By complementing the supply of compressors with added value accessories, engineering services and assembly, Sauer makes entire solutions possible, ranging from modules to complete turnkey plants. For more information, visit www.sauerusa.com.
About the Author
Stelios Flessas is a Business Development Manager for J.P. Sauer & Sohn Maschinenbau GmbH. For more information, visit www.sauerusa.com, www.sauercompressors.com, www.iter.org, www.airliquide.com.
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