Every kilogram of hydrogen needs nine kilograms of tank to hold it

Tuesday, May 10th, 2022

An ultra-light liquid hydrogen tank design promises to boost the range of hydrogen-powered aircraft to the point where they could fly farther than ordinary kerosene-fueled planes:

Tennessee company Gloyer-Taylor Laboratories (GTL) has been working for many years now on developing ultra-lightweight cryogenic tanks made from graphite fiber composites, among other materials.

GTL claims it’s built and tested several cryogenic tanks demonstrating an enormous 75 percent mass reduction as compared with “state-of-the-art aerospace cryotanks (metal or composite).” The company says they’ve tested leak-tight, even through several cryo-thermal pressure cycles, and that these tanks are at a Technology Readiness Level (TRL) of 6+, where TRL 6 represents a technology that’s been verified at a beta prototype level in an operational environment.

This kind of weight reduction makes an enormous difference when you’re dealing with a fuel like liquid hydrogen, which weighs so little in its own right. To put this in context, ZeroAvia’s Val Miftakhov told us in 2020 that for a typical compressed-gas hydrogen tank, the typical mass fraction (how much the fuel contributes to the weight of a full tank) was only 10-11 percent. Every kilogram of hydrogen, in other words, needs about 9 kg of tank hauling it about.

Liquid hydrogen, said Miftakhov at the time, could conceivably allow hydrogen planes to beat regular kerosene jets on range.

“Even at a 30-percent mass fraction, which is relatively achievable in liquid hydrogen storage, you’d have the utility of a hydrogen system higher than a jet fuel system on a per-kilogram basis,” he said.

GTL claims the 2.4-m-long, 1.2-m-diameter (7.9-ft-long, 3.9-ft-diameter) cryotank pictured at the top of this article weighs just 12 kg (26.5 lb). With a skirt and “vacuum dewar shell” added, the total weight is 67 kg (148 lb). And it can hold over 150 kg (331 lb) of hydrogen. That’s a mass fraction of nearly 70 percent, leaving plenty of spare weight for cryo-cooling gear, pumps and whatnot even while maintaining a total system mass fraction over 50 percent.

If it does what it says on the tin, this promises to be massively disruptive. At a mass fraction of over 50 percent, HyPoint says it will enable clean aircraft to fly four times as far as a comparable aircraft running on jet fuel, while cutting operating costs by an estimated 50 percent on a dollar-per-passenger-mile basis — and completely eliminating carbon emissions.

Hydrogen has an energy density of 140 MJ/kg. Jet fuel (kerosene) has an energy density of 43 MJ/kg.

Comments

  1. Gavin Longmuir says:

    Closest source of naturally-occurring hydrogen is our Sun — although collection of hydrogen from the Sun on a commercial basis is not within our current technological capabilities.

    What we can do is burn fossil fuels in one way or another to manufacture hydrogen from hydrocarbons and/or expensive scarce ultra-pure water.

    Remind me what the advantage of hydrogen is, please.

  2. Bruce says:

    Gavin, it sounds like you have some sort of problem with a fuel that embrittles its valves while being such a small molecule that it oozes out of any container made of other molecules.

  3. Jim says:

    Bruce, lol.

  4. Bob Sykes says:

    Does anyone think regular airport ground crews will be able to handle cryogenic liquid hydrogen? The SpaceX team just had a catastrophic failure in their cryogenic liquid HELIUM fueling system that destroyed the launch rocket on the pad.

  5. Goober says:

    Gavin,

    You see, we need to create solar energy via photovoltaic panels that are super resource intensive and don’t last long enough to pay for themselves, and then use the energy generated from those panels to electrolysis-erate some water that we’ve run through RO filtration to purify it (I’m sure that process is easy, right? No big deal?), so that we can pump it into tanks with valves and structures that are slowly destroyed by the hydrogen (but not really that slowly) so that we can put it in tanks pumped up to like several hundred atmospheres worth of pressure with cryogenically cold liquid that makes any tank it goes into that much more brittle, and then send them up to 30,000 feet above sea level where it’s cold and atmospheric pressure is even lower so the differential between outside and the tanks is even greater, all with them mounted in the struture of the wings of a machine carrying several hundred people through the sky at 500 miles per hour.

    Why are you questioning this obviously sound technology?

  6. Goober says:

    Bob, it’s really not that big of a deal, when you think about it. It’s just a liquid that’s so cold that it will freeze organic material instantly, unless it finds an ignition source, at which point it will incinerate the previously frozen materials, all under so many atmospheres of pressure that a tiny leak would dismember a human that was unlucky enough to get in the way.

    So, essentially no biggie.

  7. Pseudo-Chrysostom says:

    The useful niche of hydrogen in economical transportation was solved a long time ago, which is floating airships. The Hindenburg accident infelicitously stoppercapped the technology unfortunately. Fatality rates in plane crashes are virtually 100% with few exceptions, and more than a few have taken place, but that doesn’t ‘stick’ in people’s minds the same way. Great balls of fire trigger neuron activation in the monkey brain.

    https://www.sparringmind.com/supernormal-stimuli/

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