Speaker
Description
Insulation systems are critical to liquid hydrogen storage tank thermal performance. Storage tanks in the capacity range of 100 to 1,000 cubic meters are typically shop built and designed with evacuated multi-layer insulation (MLI), whereas storage vessels larger than 1,000 cubic meters are typically field-erected and supplied with evacuated bulk fill insulation. Field-erected vessels use bulk fill insulation because MLI installation is impractical in the field and requires a controlled shop environment to achieve the optimum cleanliness level needed. MLI systems require high vacuum (HV) to fully utilize the insulating properties, while bulk fill systems only require moderate vacuum (MV) for full effectiveness. For large field-erected vessels, the two types of bulk fill insulation available are perlite and glass bubbles. The selection of either material is driven by a tradeoff between CAPEX and OPEX, such as the construction cost versus operating thermal performance and maintenance. In either case, the vacuum level needed to achieve optimum thermal performance is likely to drive the field testing and commissioning portion of the construction schedule. The goal of this paper is to present practical experience and standard data for both warm vacuum pressure (WVP) and cold vacuum pressure (CVP) levels. Recommended WVP levels needed for cooldown of large-scale liquid hydrogen storage tanks consider both perlite powder and glass bubbles. The pumping time expected to achieve the target vacuum level, considering insulation filtering, vacuum pumping equipment, pipe sizes, and installation requirements, is also discussed. Recommendations for a standard practice in vacuum-jacketed tank commissioning are based on historical NASA data, and those collected during recent projects completed at Kennedy Space Center and in Houston, Texas.
