Special Focus: Advances in H₂ Production

C. HALL, GenH2, East Granby, Connecticut

Hydrogen (H₂) is taking the lead in the race to renewables. The unlimited supply and eco-friendliness of H₂ positions it as a key element in the transition to advanced clean energy. While H₂ has previously been in the energy spotlight, mainstream adoption of H₂ has yet to take off. In the past, challenges with purity, efficiency and demand have prevented widespread adoption. The good news is that recent technological advances are becoming increasingly viable, especially in small-scale solutions.

Accessible infrastructure is essential to accelerate the H₂ economy. Notable reasons include:

• Every new vehicle, aircraft or fuel cell developed will require small quantities of readily-available H₂ to test products in various environments and locations. 
• Commercial markets will need H₂ available at the point of end use where geographic constraints limit the viability of large-scale systems.  
• Manufacturers in the mobility space must have confidence that infrastructure will be available before launching new H₂-powered modes of transportation. 

H₂ takes on its most efficient form as a liquid due to its enhanced energy density and purity. Liquid H₂ (LH₂) liquefaction, storage and transfer solutions work best with modular designs because modularity allows them to work as stand-alone units, integrate into existing systems or form complete light-scale H₂ systems. Mass-produced, scalable systems also enhance operational efficiency, lower capital expenditure (CAPEX) and speed market entry.

Modular design offers tremendous flexibility to meet the H₂ economy infrastructure. Subsystems can be tailored for any H₂ supply level as needed and integrated with components from other H₂ infrastructure providers to meet commercial market needs. End-use applications include backup power generation, fuel cell supply, clean energy storage and transportation for land, air, sea and space.

The state of small-scale liquefaction and storage. Uses for small-scale systems include expanding H₂ access to remote areas, providing a consistent and reliable power source for disaster relief and fueling large multi-use drones. These light-scale units can also aid small towns or businesses as an integral onsite H₂ system for future LH₂ fueling stations.

Previously, LH₂ systems were only feasible through larger designs requiring a massive footprint. A mobile H₂ liquefaction and storage unit has been developed to demonstrate the LH₂ value chain, including H₂ production, liquefaction, storage, transfer and recovery. The LH₂ technology demonstrator^a is one of the primary systems for a multipurpose LH₂ test platform. The unit tests liquefaction, controlled storage and zero-loss transfer methodologies. It offers 2 kilogram (kg)–20 kg of liquid H₂ and is one of the first infrastructure solutions that demonstrates the complete H₂ value chain—from creation to distribution—in a compact, flexible, modular system.

The liquefaction system is designed to produce ultra-pure liquid from a gaseous H₂ source. The primary subsystems include an electrolyzer, gas pre-cooler, Ortho-para H₂ converter, cryocooler-based H₂ liquefier, portable LH₂ storage tank, ultralight LH₂ fuel tank for aviation application, safety devices and sensors, automated venting system, and associated sensors, instrumentation and control system.

The technology offers large capacity for its process type, high efficiency for its size category and a modular, scalable format that does not require liquid nitrogen pre-cooling. It is important to note that the purity of the gaseous H₂ source determines the ultimate purity produced by the liquefaction system.

Optimized for size and capacity, these units operate with comparable results to larger systems by providing flexible options, offering liquefaction units that function as closed-loop, helium-cooled systems. These dry systems eliminate the need for a liquid nitrogen (LN₂) cooling cycle, with the option to add a pre-cooler to increase the liquefaction rate.

Distributed H₂ liquefaction. A small-scale industrial 1,000-kg/d H₂ liquefaction plant (HLP) is in detailed design and planned for operation in 2024. The plant will achieve localized, efficient H₂ production on-demand in remote locations. It can also be used in transportation where there is a need to simplify logistics, reduce associated costs, and minimize or eliminate losses due to evaporation.

The primary advantages of the HLP are safety, reliability, modularity, accessibility and the ability to increase control of the energy supply. At the heart of the liquefaction plant is the liquefier, which utilizes a closed-loop helium Brayton cycle where temperatures well below the liquefaction temperature can be realized. LH₂ is then stored and maintained at zero loss or densified with a helium side stream taken from the refrigeration cycle. The system utilizes helium at low pressure, making the HLP safer than most H₂ liquefaction systems.

The liquefier is relatively small, with only a few major components inside the vacuum vessel. The system's simplicity increases reliability, affords a high degree of automation and facilitates ease of maintenance to reduce potential downtime. The liquefaction plant is scalable, providing higher or lower production capacities per unit, as necessary. It can also be used to cool mega-scale LH₂ storage tanks. Additionally, since LH₂ pre-cooling is not required, the liquefaction plant can be located in remote areas where electricity is available or local electricity production capability exists, such as natural gas fields.

LH₂-controlled refrigerated transfer. Research supports the necessity of LH₂ to be used for heavy-duty and long-range mobility machines, including trains, ships, aircraft and long-haul trucks. These clean-energy propulsion machines require onboard LH₂ to generate the high energy and consistent power needed to go the distance efficiently and effectively.

However, established storage and transfer methods are problematic due to losses and the systems’ sporadic or on/off nature. Integral servicing system methodology is required for safety and cost affordability through key drivers of time savings, product savings and venting exposures. New designs for controlled storage technology enable quick and effective vehicle servicing at the point of use.

Once H₂ is properly liquefied and stored, an effective distribution system is needed to transport it to the areas of use. Controlled refrigerated transfer systems facilitate the movement of stored LH₂ while creating a zero-loss environment that prevents typical boil-off during the H₂ transfer process.

Vacuum-jacketed transfer lines within this system safely preserve LH₂ since vacuums do not effectively conduct heat and allow for complete energy retention during transfer to the intended recipient. Additionally, isolating the environment within the transfer lines adds a crucial safety layer. Safe and effective dispensing systems are essential for all H₂ systems, as they provide a safe passageway for the LH₂ to reach the machines it fuels.

The author’s company’s system has successfully demonstrated continuous H₂ liquefaction according to the design specification, with the help of an automated control system to maintain the liquid at a desired level without boil-off loss. In addition to liquefaction and controlled storage, the functions of zero-loss transfer, boil-off gas recovery and re-liquefaction were also demonstrated. These systems provide proof-of-concept data points for future LH₂ infrastructure designs and the critical LH₂ refilling and servicing methodology for many H₂ mobility applications.

Takeaway. H₂ is gaining traction as the ultimate replacement for fossil fuels and, as a result, plays a critical role in the global transition to renewable energy. In the past, the lack of infrastructure has been one of the biggest obstacles to H₂’s growth as a clean energy resource. New small-scale infrastructure technology offers the affordability, flexibility and viability to enable the widespread adoption of H₂ with a clear path to a greener environment.H₂T

Notes

^a LS20 mobile system 

About the author

CULLEN HALL is the Vice President of Product Development for GenH2, a technology leader in H₂ infrastructure systems for advanced clean energy. He has more than 20 yr of experience in engineering, cryogenics and H₂, with a specialty in LH₂ infrastructure. Hall’s deep expertise in H₂ infrastructure includes critical components, systems, safety and construction related to cryopumps, compressors, dispensers and refueling stations. He has contributed significantly to accelerating H₂ infrastructure systems throughout his career by commissioning liquid dispensers, developing patented LH₂ pumps and transforming the liquid H₂ refueling station. Hall’s H₂ infrastructure experience spans several H₂ companies in Asia and industry leaders such as Linde’s Praxair and Plug Power.