The demand for hydrogen (H2) is expected to increase in the coming years, driven by the growth of H2 applications in mobility and investments in H2 infrastructure, such as the announced $8-billion funding from the U.S. Department of Energy (DOE) for regional H2 hubs.
Liquefaction is a critical step in the H2 supply chain because it enables the transportation and storage of pure H2 in an energy-dense form. In addition, liquid H2 may be preferred over other mediums due to the cost-effectiveness of transport and minimal infrastructure investment at the end-use site.
Several cycles have been developed and commercialized for H2 liquefaction, including the Joule-Thomson, Brayton and Claude cycles, each with three main components: a precooling cycle, a cryogenic purification system and a liquefaction cycle. The refrigerant used in the precooling and liquefaction cycles is chosen to minimize the specific energy consumption of the processes. Nitrogen and H2 are the most used refrigerants for the precooling and liquefaction cycles, while helium is common in smaller-capacity liquefiers to reduce capital expenditure.
H2 produced via electrolysis powered by wind and solar necessitates operational versatility due to the variability of renewable energy production. Brayton cycles for both precooling and liquefaction offer the unique advantage of utilizing solely gaseous refrigerants. This enables dynamic operation and control of the liquefier, allowing it to turn down and ramp up to match fluctuations in renewable energy prices and other dynamic factors.
Hydrogen production
Hydrogen molecule
The H2 liquefaction process relies heavily on centrifugal compressors in nitrogen precooling cycles. Reciprocating compressors are commonly used in the primary liquefaction cycle for positive displacement compression of the H2 refrigerant. Cryogenic turboexpanders, which play a central role in refrigeration, are utilized in precooling and primary liquefaction cycles.
Thanks to economies of scale, a H2 liquefier’s capital cost improves relative to increases in size, meaning larger liquefiers can drive down the costs of producing liquid H2. Additionally, larger liquefiers can improve plant performance and reliability due to the scalability of turbomachinery, which keeps the overall unit count to a minimum.
H2 liquefaction plays a critical role in the supply chain by enabling the mass transportation and storage of H2 in an energy-dense form. The Brayton cycle offers operational versatility and dynamic control, and machineries such as centrifugal compressors, reciprocating compressors and cryogenic turboexpanders are critical components in the process.
The reliability of these machinery systems is crucial to ensure the success of H2 liquefiers and driving down H2 costs. Adherence to industry standards and best practices in design, manufacturing, testing and maintenance throughout the machinery's lifecycle is vital to optimize the reliability and performance of the equipment.
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