TPS 2023: Compressing and Pumping Hydrogen - Applications and Technologies

Technical sessions at Turbomachinery & Pump Symposia (TPS) 2023 kicked off on Tuesday, Sept. 26. Speakers from the Elliott Group presented on Applications and Technology for Hydrogen Compression and Pumping.

Marybeth McBain, Manager at Elliott Group, started the technical session with a brief description of blue, green, and pink hydrogens and the methods used to produce each gas: Green hydrogen utilizes curtailed renewable electric power via electrolysis while blue and pink hydrogen require carbon sequestration and nuclear power, respectively. These iterations of hydrogen fuel can be stored for longer periods, but issues regarding cost, wear-and-tear on current pipeline assets, and embrittlement require a careful approach to hydrogen.

Hydrogen Production and Cost

McBain addressed the cost of hydrogen production, as, as of now, even with tax credits, it’s expensive to produce at scale. However, she cited the initial price hikes of LNG in which plant operators were worried LNG was too expensive. But “The industry stepped up and started looking at ways to make power plants more modular to offset construction costs and to standardize equipment to lower manufacturing costs,” McBain said. After which the cost of LNG came down. She encouraged attendees to consider this when it comes to the cost of hydrogen, “and how technology can catch up and give us that cost-competitiveness,” she said.

McBain also addressed secondary concerns regarding what percentage of hydrogen would actually make a meaningful difference in carbon emissions, as using 30% hydrogen doesn’t reduce your use of natural gas by 30%; in fact, it would only reduce natural gas by 15%. She also pointed out the impact hydrogen has on carbon-steel blends (U.S. pipelines are made of several different blends) and compressor requirements—each of which must be considered when transitioning the energy economy to a hydrogen-based model.

Hydrogen Compression

Karl Wygant, Senior Manager at Elliott Group, tackled the challenges presented by the compression of a light gas such as hydrogen. Hydrogen compression typically encounters issues with sealing, embrittlement of materials and coating, and temperature constraints. Titanium is chosen for compression at high speeds for most gases, but hydrogen’s corrosive properties present challenges for titanium, making it unsuitable for hydrogen applications.

“Titanium is very sensitive to hydrogen embrittlement, so it’s not acceptable for hydrogen applications,” Wygant said. “What does work well is some of the aluminum series; they show good resistance to hydrogen embrittlement.”

Wygant detailed the hydrogen-resistant properties of aluminum as favorable for hydrogen compression applications, although the material encounters issues at high temperatures as tip speed increases. Newer impeller designs or advanced material integration may reduce these issues, such as gas corrosion or the lack of materials suited for increased tip speed. Wygant offered a series of potential solutions to the hydrogen compression dilemma, including integrally geared compressors for higher tip speed and the introduction of inter/pre-coolers to manage an increase in temperature. Aluminum may be integrated in favor of titanium with a number of coolers to regulate temperature, addressing a primary challenge when compressing hydrogen for industrial-scale operations.

Pumping Hydrogen

Enver Karakas, Director at Elliott Group, rounded off the technical session with a detailed explanation of pumping hydrogen and ammonia. Hydrogen requires a much lower liquefaction temperature than ammonia, raising the cost of this process in comparison to the liquefaction of other gases. Handling liquid hydrogen presents a host of challenges, as the gas is highly flammable and corrosive, and the minuscule molecular size causes hydrogen to leak from the system into the atmosphere. Karakas offered a number of solutions to counteract the natural properties of hydrogen, such as a submerged motor design and material consistency to minimize stresses on the components within the system.

Liquid ammonia runs into compatibility issues with copper alloys, e.g., bronze bushing, etc. Karakas addressed ammonia leakage by introducing the concept of, although not new, magnetic couplers.

“The way we do handle this is through magnetic couplers. The whole idea is to seal the motor side from the hydraulic side, transferring the torque to the hydraulic side with a magnetic coupler to ensure that no ammonia is leaking into the motor section,” Karakas said.

The director closed the technical session with some final remarks about appropriate liquid expanders and pumps for hydrogen liquefaction. Along with considering magnetic couplers for the sealing of a system, Karakas recommended the use of cryogenic expanders to increase liquid production by 3-5%. Liquid expanders for hydrogen liquefaction achieve higher efficiency through improved cooling and energy recovery systems, counteracting the properties of hydrogen and ammonia that would typically make this process dangerous or ineffective.