NASA institutes full-scale study of 3M™ Glass Bubbles for cryogenic insulation
The major problem was that of boil-off or loss of cryogen from the tank. At Kennedy Space Center, it was noted that Pad A experienced a loss of 300-350 gallons per day, while Pad B showed a loss greater than 800-900 gallons per day. NASA initiated a program to determine the cause of pad B boil-off being greater than pad A. Pad A and Pad B both housed identical 850,000 gallon tanks manufactured by CB&I. Through their studies, NASA determined that the compaction of the perlite used for insulation was a key factor in boil-off. One approach to address this issue was to replace the perlite with 3M™ Glass Bubbles K1. Other options considered included aerogels and multi-layer insulation (MLI).
NASA contracted with the engineering firms Sierra Lobo and TAI to investigate the bulk insulative, mechanical, compaction, and thermal cycling properties of 3M Glass Bubbles K1, aerogels, and MLI versus the current insulative material, perlite. Sierra Lobo subsequently contacted 3M requesting technical assistance on the properties and material handling for 3M glass bubbles.
As a bulk material, 3M glass bubbles K1 were directly compared to the performance of perlite. Results showed significant improvements in performance in both insulative capacity and mechanical properties. Based upon this improvement, NASA approved the retrofitting of a 50,000 gallon cryogenic tank at Stennis Space Center, Mississippi. This is the first large scale application to validate both insulative and mechanical performance data.
Thermal performance of 3M™ Glass Bubbles shown to be 27% better for liquid nitrogen and 34% better for liquid hydrogen in 1000 liter demonstration tanks.
Retrofitting the Cryogenic Tank
The team at Stennis purged the system of all cryogen, opened the tank and removed the perlite which had been in place for approximately 50 years. Surprisingly, most of the perlite was still free-flowing and was easily removed from the tank. Once the perlite was removed, the Stennis team inspected the annular space of the tank. Small amounts of residual perlite (hardened deposits) were removed and necessary maintenance on the support structure was completed. Ports located on the top surface on the sphere were set-up to accept three inch hose for transferring and venting the 3M glass bubbles. Additionally, vacuum gauges and inert gas purge valves were installed. Once completed, the cryogenic tank was ready to receive 3M glass bubbles.
Dust Collection System
3M designed a unique portable dust collection system specifically for this application. The equipment was supplied by Donaldson Company, Inc. of Minneapolis, Minnesota. This system was designed to collect and contain any airborne 3M glass bubbles that were conveyed during the loading and venting process. This equipment performed efficiently, collecting all airborne glass bubbles with no release to the surrounding environment. This portable system is available for all on-site cryogenic tank refurbishments.
||3M designed a unique portable dust collection system specifically for this application. The equipment was supplied by Donaldson Company, Inc. of Minneapolis, Minnesota.
Bulk Delivery and Installation
3M uses a bulk delivery system using PD (pressure differential) trailers designed specifically for 3M™ Glass Bubbles. The 2,600 cubic foot trailer holds approximately 9,000 pounds of 3M™ Glass Bubbles K1. A three inch static dissipative smooth bore hose and sweep 90 degree piping was specified for the conveying of the 3M glass bubbles. Based upon the annular space of the cryogenic tank at Stennis, it was determined that four trailer loads of glass bubbles would be required, totaling 33,100 pounds. Minimal pressure, 1.5 psi line pressure and 3.0 psi tank pressure were used in order to maximize the volume of glass bubbles going into the annular space and to minimize the volume of glass bubbles going to the dust collector. Each of the four trailer loads required between 1 and 1.5 hours to unload. The delivery was scheduled to receive and unload two trailers per day thus allowing the glass bubbles to settle overnight.
Topping Off and Completion
In order to ensure that the annular space was completely filled, large boxes of 3M glass bubbles K1 were conveyed using vacuum pulled on the annular space. A total of three large boxes (210 pounds each) were required to top off the tank. The Stennis team then welded the ports closed, thereby sealing the system. After the system was closed, vacuum was pulled to achieve 50 millitorr with a target of 10 millitorr. This process took several weeks. Once vacuum was achieved, cryogen was transferred into the tank and data and measurements were collected. Long term, it is the intention of the Stennis team to calculate boil-off rates, to use thermal cycling to study 3M glass bubble K1 compaction, and to use infrared thermography to locate and measure “hot spots”.
||50,000 gallon liquid hydrogen cryogenic tank being filled with 3M™ Glass Bubbles K1 from a pressure differential trailer.
To learn more contact our development team today.