As helium prices go through the roof, NIST embarks on an ambitious recycling technology.
The recycling of helium could be the next big sustainability and cost efficiency trend. A high-profile consumer of liquid helium, the National Institute of Standards and Technology (NIST) has determined that recovery and re-liquefaction of the gas promises significant long-term returns. Helium recovery reduces vulnerability to shortages and supply disruptions. Furthermore, recycle systems are easily installed, and when maintenance is performed on such a system, the ongoing supply of helium is maintained by providing bulk helium as a backup. The NIST story that unfolds in the following is insight into how a research institution has opted for adaptive change that not only improves its balance sheet but also sets an example for an entire industry. It is the kind of change that beckons to both public and private organizations. Whether it is an engineering or physics department at a university, a research institute or government institution, any organization that uses a significant quantity of liquid helium as a coolant can now consider recovery and re-liquefaction as a step toward a more secure future.
Because it is an inert gas, helium is used in applications as varied as arc welding, semiconductor production and thermo-acoustic refrigeration. Because the gas has the lowest melting point and boiling point of any element, liquefied helium (LHe) is used to cool infrared detectors, certain types of nuclear reactors, fiber optics during production, sub-atomic particle detectors, superconductive material, and high energy physics research to provide cooling for super-conducting magnets in particle accelerators. Most critical for NIST, liquid helium is an irreplaceable element in cryogenic applications below the temperature of 17 K; in this application there is no substitute for liquid helium.
The proposed recovery and re-liquefaction system will eliminate most of NIST’s liquid helium purchase requirements.
A non-renewable resource
The National Helium Reserve is a strategic reserve of the United States holding more than 1 billion cubic meters of helium gas. The helium is stored at the Cliffside Storage Facility about 12 miles northwest of Amarillo, Texas, in a natural geologic gas storage formation, the Bush Dome reservoir. The reserve was established in 1925 as a strategic supply of gas for airships, and in the 1950s became an important source of coolant during the Space Race and Cold War.
The facilities were located to be close to the Hugoton and other natural gas fields in southwest Kansas and the panhandles of Texas and Oklahoma. As the natural gas in these fields contains unusually high percentages of helium— from 0.3 to 2.7%—they constitute the largest source of helium in the U.S. The helium is separated as a byproduct from the produced natural gas.
After the Helium Act Amendments of 1960, the U.S. Bureau of Mines arranged for five private plants to recover helium from natural gas. For this helium conservation program, the Bureau built a 425-mile pipeline from Bushton, Kansas to connect those plants with the government’s partially depleted Cliffside gas field. This helium-nitrogen mixture was injected and stored in the Cliffside gas field until needed, when it was then further purified.
By 1995, a billion cubic meters of gas had been collected and the reserve was $1.4 billion in debt, prompting Congress to phase out the reserve. The resulting “Helium Privatization Act of 1996” directed the U.S. Department of the Interior to start liquidating the reserve by 2005.
By 2007, the federal government was reported as auctioning off the Amarillo Helium Plant. The National Helium Reserve itself was reported as “slowly being drawn down and sold to private industry.” However, by early 2011, the facility was still in government hands. In May 2013, Congress voted to continue the reserve under government control.
NIST’s plan for helium recovery and re-liquefaction
The NIST project team developed bridging documents for a helium gas reclamation system across its campus of eight buildings that house more than 40 LHe users, such as superconducting magnets, cryostats, neutron traps, probes and instrumentation. The new system, which will encompass both present and future users of LHe, will include helium recovery, storage and transport piping and a helium re-liquefaction system using a turbo-expander-type helium re-liquefier and purifier. The liquefier includes a “cold box” with turbines, single stage oil-injection screw compressor, oil management system, dryers and controls. The helium recovery auxiliary system includes gas bladders and compressors to transfer helium from the users to the liquefier building, 2,000 psi high-pressure compressors and storage cylinders, a process chiller for liquefier cooling, and a thermal conductivity purity meter, analyzer and hygrometer. The design also includes comprehensive control, monitoring and metering of the helium recovery process. A two-level, 3,000-square-foot building will house the re-liquefaction equipment. To appreciate the choices that designers face when considering helium recovery systems, it is helpful to understand the basic steps through which any system must channel helium in its gaseous form. Recycling the gas is a three-step process.
1) Gas capture. When the helium is used, the liquid helium boils away and is released to the atmosphere. Once it enters the atmosphere, there is no economical way to recover it. Capturing a waste helium stream in closed systems like those in the NIST labs makes recovery a straightforward task. Instead of venting the gas into the atmosphere, it is collected in the gas bladders and pumped to liquefier equipment.
2) Purification. Nearly all applications that use LHe cooling have stringent purity specifications.
3) Returning recovered gas into the process. The third step presents the greatest economic challenge because gas re-liquefaction is expensive. Helium liquefiers fall into two general categories: turbo expander and reciprocator. Each comes with its own opportunities and risks.
The SSOE team based the following comparisons on two liquefier types, a turbo expander and a reciprocator, that have maximum production rates of 70 liters of liquid helium/hr.
On the plus side, a turbo expander has impressive advantages. It employs the most current methods and technology and permits longer operation times between major maintenance, resulting in longer sustained production cycles. The turbo expander is highly reliable and not subject to mechanical wear. Hot gas bypass on this liquefier allows turndown of the system at low load. On the down side, the turbo expander costs twice as much as a reciprocator and it is more susceptible to damage from impurities or operator error. Its repairs are generally more expensive, and repair parts have long lead times.
The advantages of the reciprocator are that it costs half as much as a turbo expander, it is a proven and reliable technology, repairs are less complex, repair parts are cheaper and more readily available, it is less susceptible to failure and damage from impurities and operator error, and its internal gas purifier can handle approximately 5% water vapor. The reciprocator, however, is known to require more regular maintenance than the turbo expander, creating a higher lifecycle cost than the turbo expander.
Long-term cost savings
The SSOE project team provided a lifecycle cost analysis computer model comparing current NIST LHe purchases with three configurations of investment for helium recovery system—see Table 1.
NIST opted for the turbo expander to liquefy helium because of the lower life cycle cost, current technology and availability of the equipment from more than one manufacturer.
Conserving nonrenewable natural resources such as helium makes good business sense in both the public and private sectors. These benefits will accrue to any university engineering or physics department, research institute or government institution that uses a significant amount of liquid helium. Through its future-focused design for helium recovery, NIST is acting as both a template and a real-time evaluation environment for the many other organizations that are faced with increasing global competition for this precious resource.