As part of NASA’s plan for the first launch of its Space Launch System rocket and Orion spacecraft that will send humans beyond low-Earth orbit, Exploration Ground Systems at Kennedy Space Center is preparing to build the world’s largest liquid hydrogen storage tank incorporating the latest cryogenic liquid control technology developed at the NASA Cryogenics Test Laboratory (CTL), a CSA CSM. The technology will make storing liquid hydrogen for an extended time without loss due to boiloff a practical reality.

Gaining total control over the transfer and long-term storage of cryogenic liquids has been only a dream since the 1950s when industrial scale production and liquefaction of hydrogen began.

Storage tank designs and insulation systems advanced through the 1950s and ‘60s, eventually culminating in the construction of two large (850,000 gallon) liquid hydrogen (LH2) spheres at the National Aeronautics and Space Administration’s Kennedy Space Center (NASA/KSC) around 1965. Looking back at the technology available at that time for handling cryogenic fluids, significant boiloff loss of the hydrogen was accepted as a given, and the operational philosophy and processes were established to accommodate this limitation.

These losses were unavoidable, and were exacerbated by transient operations such as when the LH2 was piped into the storage tank from the delivery tanker truck or transferred on board the launch vehicle.

Without insulation, the liquid would boil away very quickly; with the very best insulation system in the world, the liquid still boils away, just at a slower rate. In any case, for traditional cryogenic liquid storage the tank can either be freely vented to the atmosphere to maintain a desired pressure for long duration storage, or the vent can be closed and the tank allowed to pressurize.

Of course, the latter only provides a temporary reprieve from product loss, as it is limited by the maximum allowable working pressure of the tank; eventually, the vessel must be vented back down.

But now there is a new way. The system approach for complete control over the storage and transfer of cryogenic liquids, including hydrogen, is here. Two new technologies are being incorporated into the design of the world’s largest liquid hydrogen storage tank (4,700 m3 or 1.25 million gallon capacity) at NASA/KSC.

To be built by Precision Mechanical, Inc., Cocoa FL, with support from McDermott International (formerly Chicago Bridge & Iron Company or CB&I) and Chart Industries (CSA CSM), the new vessel will include a thermal insulation system utilizing glass bubbles in lieu of expanded perlite powder, and an internal heat exchanger for a future integrated refrigeration and storage (IRAS) system to enable complete control over the state of the LH2, including zero boiloff.

Glass Bubbles Thermal Insulation System
For large-scale spherical LH2 storage tanks (that is, above about 1,000 m3 or 264,000-gallon capacity), the evacuated perlite powder system has been used for the last 60 years. More recently a new thermal insulation system based on glass bubbles was proven by NASA KSC CTL researchers as a cost-effective, reliable, and superior alternative to evacuated perlite powder systems.

Research and development of glass bubble bulk-fill material for cryogenic tank insulation systems began in the early 1970s by George Cunnington at the Lockheed Palo Alto Research Laboratory, and professor C.L. Tien at the University of California, Berkeley.

In 2004 the CTL team headed by James Fesmire, senior principal investigator for Kennedy Exploration Research and Technology programs, and Jared Sass, cryogenic researcher engineer with KSC Engineering, won major funding from the Space Operations Missions Directorate with a project called New Materials and Technologies for Cost-Efficient Cryogenic Storage and Transfer (CESAT). The job was to prove out the glass bubbles system for large-scale spherical liquid hydrogen tanks.

In 2005 a field demonstration led by Technology Applications, Inc. (CSA CSM) was successfully completed on a pair of vertical 23-m3 (6,000 gallon) cryogenic tanks at Acme Cryogenics (CSA CSM) in Allentown PA.

The CESAT project culminated in 2007 with the publication of several key technical articles covering the thermal, mechanical, materials, and economic details of using the glass bubbles insulation system. The centerpiece of the development was the use of two custom-designed 1000-liter spherical tanks for side-by-side testing of perlite powder and glass bubbles with both LN2 and LH2, led by Zoltan Nagy of the CTL team. The work was centered on using the 3M K1 glass bubbles material for the optimum combination of cost and performance.

Following the success of the CESAT project, an industry partnership project among KSC, Stennis Space Center and 3M, led by Jared Sass of the CTL team, went forward in 2008. Field performance data and cost-effective retrofit of spherical LH2 tanks was the target. A perfect condition 189 m3 (50,000 gallon) LH2 tank was selected. The perlite powder was removed and 3M glass bubbles were installed.

This field demonstration went on to enormous success as three thermal cycles were completed over a six-year period with no vacuum problems and an average 46 percent reduction in boiloff. This result surpassed the 35 percent reduction (compared to perlite powder) found through years of extensive laboratory and sub scale testing with LN2 and LH2.

All the tests showed that the glass bubbles don’t break and they are not difficult to manage. Glass bubbles are far less sensitive to vacuum-level degradation compared to perlite powder, making the field result even better than the idealized laboratory result.

Integrated Refrigeration and Storage (IRAS)
IRAS technology is on the rise as large-scale applications have been proven on a 125-m3 (33,000-gallon) storage tank. This approach provides direct removal of heat energy via an internal tank heat exchanger together with an external cryogenic refrigeration system. Modular, more efficient cryo-refrigeration systems are now available from commercial industry equipment providers such as Linde and Air Liquide, both CSA CSMs. In conjunction with a high performance thermal insulation system, a normal evaporation rate (NER) or boiloff can now be a thing of the past. Conventional assumptions that the boiloff flow stream must be dealt with and/or burned in a parallel process no longer holds true. The IRAS technology can be used for boiloff elimination (zero boiloff), densification (deep thermal storage), or some combination of the two for complete control of the liquid and the most cost-effective long-term operational solution.

From the initial research and development work in IRAS by Dr. William (Bill) Notardonato, principal investigator in Kennedy’s Exploration Research and Technology Program, and Dr. Jong Baik at the Florida Solar Energy Center, in 2001, to the recent field demonstration tests at NASA/KSC led by Notardonato and Adam Swanger, cryogenic researcher engineer with KSC Engineering, the technology development has moved forward to completion in 2017.

The ground test facility, anchored by the 33,000-gallon IRAS storage tank with integral heat exchanger, connected to a modular 900 W cryo-refrigerator unit, demonstrated long duration zero boiloff, zero-loss LH2 tanker off-loads, densification, and liquefaction capabilities.

Conclusion
Integrated Refrigeration and Storage technology in combination with new high-performance insulation systems is the future for energy-efficient control of cryogenic liquids. The energy savings is a fundamental underlying benefit for this technology combination.

It takes only about 14 cents worth of electricity to save one dollar’s worth of LH2 (estimated for aforementioned KSC IRAS ground test). The net result is that the new technology saves hydrogen, saves energy, and saves the planet. The control of the state of the fluid offers unprecedented operational flexibility and enables high performance cryofuel options.

What are the further benefits?

Economics
1. Huge energy (electricity/heat) investment to make the liquid. Consider the holistic perspective (especially for liquid hydrogen and liquid helium), not simply the end monetary cost of the liquid product to the consumer: from prospecting, to extraction, to processing, to liquefaction, to transport, to transfer and storage, the impact in terms of energy, time, money and the environment is monumental!
From this perspective, it can be argued that willful acceptance of boiloff losses at the end of the process, as the norm, is unconscionable! With “zero boiloff” we have the capability to hold the liquid indefinitely.

2. Operational flexibility avoids negative impacts of extra truck deliveries, waiting for deliveries, inclement weather stoppages and other limitations.

Safety
1. Venting can be controlled or eliminated for safe operations.

2. Densified liquid offers “enthalpy margin” so that heat goes into warming the liquid, not boiling it (can make cryogenics “flow like water”); much easier to deal with densified liquid in all aspects of transfer and handling operations.

Process Enabling
All cryogenic liquids are stored for a reason—to supply a downstream process. In the case of the LH2 spheres at the KSC launch pads, the downstream process happens to be a space launch vehicle. And the design of the downstream processes can be a strong function of the cryogenic storage system. In the case of the space shuttle, the dominating feature of the design was a giant LH2/LOX tank, size based upon the maximum propellant density available from the storage tank. Therefore, advancements in storage technologies can provide new opportunities for downstream designs.

1. Densified liquid provides higher performance, more energy-dense fuel (example: SpaceX booster rocket enabled).

2. Operations not constrained to schedule of tanker truck off-loading (example: Space Launch Systems’ vehicle needs capability to go-for-launch on several consecutive days).

The technology provides the capability for the following:
1. Zero boiloff (no losses)
2. Densification of liquid
3. Control, safety and operational flexibility
4. Re-liquefaction
5. Impact on downstream processes (enabling new controls, operation) ■