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Standards Development
This document describes the technical requirements and testing methods for liquid hydrogen pumps used in hydrogen refueling station to meet high pressure onboard storage requirements which is typically with pressure of H35 or H70.
The document is applicable to cryogenic reciprocating pump, including internal type and external type. The pump components include cold-end cylinder assembly, warm-end drive, and cold- and warm- end connection.
The cold-end cylinder assembly consisting of key components such as the piston, piston rings, cylinder, and suction and discharge valves; through which the LH2 passes and is elevated in pressure. The warm-end drive is usually rated for the pressure and flow rate expected for the cold end, is used to drive the cold end and control the piston's forwards and backwards movements via a drive mechanism. The cold- and warm-end connection ensures both correct alignment and transmission of forces, and also ensures that any leakage of cryogenic liquid is kept away from the warm end. It is not applicable to liquid transfer pumps for fuelling liquid hydrogen vehicles.
Liquid hydrogen offers significant advantages in terms of storage density, making it a superior option for the large-scale application of hydrogen energy. Specifically, liquid hydrogen has a much higher volumetric energy density compared to gaseous hydrogen. For example, liquid hydrogen has a density of approximately 70.8 kg/m³ and an energy density of 8.5 MJ/Lwhich is significantly higher than that of gaseous hydrogen at room temperature and pressure. This high density allows for more efficient storage and transportation of hydrogen, especially over long distances.
Employing the liquid hydrogen pressurization and vaporization route during the fueling process can achieve higher efficiency and reduced costs. Liquid hydrogen refueling stations (LHRSs) can significantly reduce energy demand by utilizing cryogenic pumps, consuming only 10–20% of the energy required for gaseous hydrogen compression. Moreover, LHRSs do not require an energyintensive pre-cooling system by utilizing the cold energy of liquid hydrogen. This approach also helps to mitigate the challenges associated with hydrogen storage, such as boil-off losses and the high energy penalty of liquefaction.
The liquid hydrogen pump is a critical component in this process, directly impacting the efficiency and safety of the fueling system. However, liquid hydrogen pumps face several significant challenges. Firstly, liquid hydrogen has complex thermophysical properties. It is extremely cold (around -253°C or 20 K) and has low viscositywhich makes its flow far less predictable compared to other fluids. Secondly, the variability of cryogenic materials is a concern. Hydrogen can cause embrittlement in common industrial pump materials like carbon steel, leading to cracking and reduced mechanical integrity over time. Thirdly, there is an inherent risk of hydrogen leakage. Liquid hydrogen leaks easily, is highly flammable, and when combined with oxygen in the air, it ignites easily and burns with a nearinvisible flame. Additionally, the heat generated during pumping can lead to vaporization of liquid hydrogen, causing rotodynamic instability and boil-off gas losses.
Given these challenges, this document establishes comprehensive technical requirements and performance testing methods for liquid hydrogen pumps, thereby laying a foundation for assessing their reliability and ensuring quality and safety. It provides detailed guidelines on material selection, operating conditions, and sealing to ensure safe and reliable operation.
This is of paramount importance given the escalating demand for liquid hydrogen fueling stations. The development and implementation of a robust liquid hydrogen pump system can significantly improve the efficiency and safety of hydrogen fueling infrastructure. By addressing the challenges associated with liquid hydrogen pumps, we can make hydrogen a more viable and competitive energy source for the future.
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