Study on the evacuation of gas in bulk-fill insulation materials used in large-scale LH2 storage tanks

Large-scale hydrogen storage is crucial for advancing liquid hydrogen technology. Due to liquid hydrogen's ultralow boiling point and low heat of vaporization, effective insulation is necessary to minimize boil-off loss. Larger storage vessels use bulk-fill insulation like perlite and hollow glass microspheres (glass bubbles) operating at moderate vacuum (MV) levels. The choice of insulation material affects the construction schedule, capital cost, and operating costs of storage tanks. Therefore, studying evacuation properties of bulk-fill insulation materials is essential to advance hydrogen-based energy infrastructure. This study aimed to quantify and compare the pumpdown times for 3MTM Glass Bubbles K1 and cryo-insulation grade perlite and to identify physical properties influencing pump-down times. Perlite, with its porous structure and low bulk density, was expected to enable faster gas evacuation, while glass bubbles were thought to hinder it. However, our research shows that dry 3MTM Glass Bubbles K1 have faster nitrogen evacuation rates.