An interesting new choice of bulk-fill insulation for cryogenic tanks could be on the horizon as a widespread commercial alternative, with research suggesting that costly cryogen boil-offs could be reduced.

Tiny glass bubbles, like fine powder and only 65 microns in size, have been developed as a result of a partnership between researchers at the Kennedy Space Centre (KSC), 3M, and Technology Applications Inc. (TAI).

The collaborative project began in 2000 and tested the glass bubbles as bulk-fill insulation for cryogenic tanks. Since then, research has suggested that the material is unmatched in preventing costly cryogen boil-off in large-sized tanks.

September 2008 saw the glass bubbles installed in a 50,000 gallon liquid hydrogen tank at the Stennis Space Centre (SSC), replacing the previous perlite insulation – with considerable cost saving achieved, due to reduced boil-off. In the last four months alone, cost savings have hovered around the 50% range.

Improved performance
Cryogenic storage tanks generally have a thermal insulation system consisting of a vacuum jacket outer shell, filled with an insulation material which is usually perlite powder in the case of larger tanks.

However, with the improved performance and significant cost saving achieved through use of the glass bubbles, this could soon be seen as a competitive alternative – particularly in times of cost-cutting measures and drives towards optimised efficiencies.

James E. Fesmire, Senior Principal Investigator at the Cryogenics Test Laboratory at KSC, told the Cryogenic Society of America’s Cold Facts magazine, “The glass bubbles material, when in a high vacuum environment, is the best bulk-fill insulation material. The apparent thermal conductivity (k-value) is lower compared to perlite.”

“In fact, 3M K-1 bubbles have an even better performance advantage over perlite for ‘degraded’ vacuum levels. Vacuum levels are often degraded bacuase of moisture in the high surface area perlite. This means that comparing a perlite tank at 100 microns versus a retrofitted bubbles tanks at 1 micron, the bubbles would be about 80% better.”

One question that may still remain is, whether the glass bubbles could be used to insulate vessels that store cryogens other than just liquid hydrogen. The answer is a resounding yes.

Fesmire explains, “Could be any cryogen. Could also be any equipment where high performance insulation is needed and bulk-filling of the insulation material is an option.”