Monday, September 18, 2023

Liquid Hydrogen (LH2) Workshop Slides

LH2 Workshop Slides

At the Energy & Mobility conference last week I gave a talk that was awarded best paper and co-taught a full-day workshop on liquid hydrogen (LH2) systems. My workshop slides can be accessed here.

Also moderated a panel session on hydrogen and sustainable aviation fuels (SAF) that included representatives from Boeing, GE Aerospace, NASA, and Aero Mobility. An overview of the panelists and topics discussed can be found here.

A number of interesting topics, questions, and themes related to liquid hydrogen emerged throughout the conference. This post highlights a couple of them.

Misleading Metrics for Boil-off and Liquefaction

There are two commonly misused metrics that came up in several questions and conversations: boil-off per day and liquefaction energy loss. Unfortunately, these metrics are often asserted to be some fixed value that supposedly applies to all liquid hydrogen systems. The truth is both of these metrics are meaningless unless they are tied to a specific system and concept of operation.

In the case of LH2 boil-off losses, properly designed systems can be as low as zero or as high as several percent per day depending on the scale, insulation system, operations, cryogenic fluid management, system requirements, and other parameters. For example, the new 1.25 million usable gallon (4700 cubic meter) LH2 dewar tank at NASA Kennedy Space Center has a passive boil-off rate of less than 0.05% per day which can be reduced to zero with the integrated cryo-refrigeration option.

Liquefaction energy losses are another example of misleading metrics. Various sources place it at 20 to 30% of the energy content of hydrogen. Similar to boil-off rates, the actual value depends on the liquefaction processes used, concept of operation, use of the LH2 cooling capacity, lifecycle energy inputs, and other parameters. To illustrate, consider a system where liquefaction is accomplished by bubbling gaseous hydrogen into the bottom of a liquid hydrogen dewar. There is no electrical energy input for this isolated process, so what is the liquefaction energy loss?

Infrastructure and Microgrids

An interesting theme that came up throughout the conference is the potential synergies possible with microgrids and hydrogen infrastructure. The capability to produce, liquefy, and use hydrogen all in one location with a dedicated renewable energy microgrid is a major paradigm shift compared to legacy fuels. And it eliminates transportation and distribution along with the associated costs and losses.

This scenario has been ignored in many recent authoritative reports as I've lamented in a previous post. Fortunately, a recently published study is shedding light on the advantages of such an approach. Hopefully, new analyses will continue to build on this insight while also tackling the inaccurate boil-off and liquefaction energy loss assumptions addressed above.

Effective trade studies require appropriate assumptions that reflect real-world state-of-the-art systems. With a lifecycle treatment of the entire end-to-end architecture and operations we will get a much clearer understanding of how liquid hydrogen systems can be implemented to build out the necessary infrastructure.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and break-through liquid, slush, and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a co-founder in seven technology startups; and provided R&D and engineering support to many organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management series. He also leads the monthly LH2 Era™ Webinar.