Capture of liquid hydrogen boil-off with metal hydride absorbers

Abstract

Standard operating procedure at the Kennedy Space Center (KSC) for the Space Shuttle Program requires the storage and transfer of substantial quantities of liquid hydrogen. Vaporized liquid, routinely lost during these transfer operations, is vented to the atmosphere or burned and represents a significant fraction of the total amount of hydrogen fuel used for each launch. Of the five normally occurring sources of boil-off vapor the loss associated with the off-loading of liquid tankers during dewar refill was identified as the most cost-effective and readily achievable recovery. In this report a procedure which uses metal hydrides to capture some of this low pressure (less than 17 lbf in −2, 0.117 MPa) hydrogen for subsequent reliquefaction is described. The design, fabrication and testing of a capture device operating at a rate that is commensurate with the evolution of vapor by the target stream to test the above idea is described. Liberation of the captured hydrogen gas at pressures greater than 30 lbf in −2 (0.207 MPa), the typical liquefier compressor suction pressure, was also demonstrated. A payback time of less than three years is projected.