Are ye daft, man? IT’S THROWN AWAY IN THE LIQUIFICATION. There is less than nothing to be ‘returned’ – MUCH less in the case of cryo H2.
(It’s bad enough with LNG ‘cryomethane’ which cannot be direct injected effectively in a positive-displacement piston motor for similar reasons…)
Which structure is that? The burner? The firebox walls (cooled with water)?
Ed
Yes, I see it now, as I envision the various cooling towers and such.
But isn’t that also going to be a problem with cars with hydrogen fuel cells? How do they handle this loss of energy?
Ed
Start with whatever the flame impinges on in the gas path. Did you think both sides of a radiant “water cooled” surface ran at nearly the same temperature? Get your copy of Steam: Its Generation and Use out and review the formulae. You will probably not like what you find for effective gastemps 1000 degrees over that in a Cyclone…
Then we get into differential thermal expansion for irregular flow patterns of high temperature convective/conductive transfer – you will not like what you find there, either.
It’s just taken as a necessary part of the well-to-wheel costs, just as the BFP losses and heating are factored into an ultrasupercritical Rankine cycle.
Those of us who have studied actual hydrogen-carrier-fuel systems over the years know that the energy loss in cryo storage is rolled into the overall system cost, just as hydrogen embrittlement and careful environmental monitoring and so forth have to be. Just as with thorium, there are many engineering reasons the hydrogen miracle has not been embraced as a consumer technology yet.
Hydrogen carrier fuel isn’t really about economics; it’s about realizing one form of zero-carbon when zero-carbon is explicitly mandated as the only applicable solution.
The case was often made back in the go-go days of “clean coal technology” that the ~23-30% cost increase to sequester CO2 would make the technology economically unfavorable (compared to the perceived renewable alternatives, particularly wind or solar). If the reduction in atmospheric carbon is important enough to you, you’ll pay the price (or embrace the alternatives if they are feasible).
The further extension into infrastructure and supply is involved, too. One of the ongoing problems with ‘renewable’ ethanol is that it’s incompatible with existing pipeline distribution of fuels at any great concentration (periodically we see plans to do something with butanol, which doesn’t have that limitation). I don’t see any practical pipeline distribution of cryo hydrogen on a ‘national’ scale, and the energy density is frankly lousy for moving it in the required Dewars even if we dust off the Jughead infrastructure to keep enroute losses minimized. You accept the costs if zero-carbon is the de
Part of it could in the same way that liquid nitrogen has been proposed for energy storage. That is boil LH2 at high pressure using heat from ambient air and expand it through a turbine, reheat the expanded H2 as necessary and expand some more through a turbine.
For an example of how little radiant heat comes from hydrogen combustion, take a look at films/videos of the Space Shuttle main engines at launch and compare that to an Atlas or Saturn at launch.
The chief problem doing this for vehicles is similar in a way to using highly compressed air for vehicle propulsion: enormous circulation of air is needed for the relatively small heat content to support the pressure development to make actual horsepower, and the heat transfer becomes compromised as atmospheric moisture condenses to frost and ice progressively. The combination of large heat-transfer surface, likely requiring heat pipes of some sort, and the power needed to circulate air past the transfer surfaces (remember what an excellent insulator still air can be) may work for large fixed plants where exchanger weight and configuration are not critical design elements. For any road vehicle smaller than Breitspurbahn I’d suspect progressive freezing alone might compromise practical long-term propulsion power generation.
On the other hand, quite a bit of heat balance in a Rankine cycle can be recovered from the subsequent combustion exhaust, as conditions of entropy that prevent heat from doing pressure work do not apply to heat transfer. Proper countercurrent exchange is still likely to be large and heavy, but is limited by the phase transition on the ‘other side’ of latent heat of fusion of water at 32degrees F, a long way, with two bumps in latent heat from phase change along the way, from the oxygydrogen flame temperature (and note we haven’t discussed monatomic hydrogen reaction for part of the combustion yet).
I suspect you’d need to use a ceramic or cermet for turbines working in cryo LH2 expansion, as hydrogen embrittlement would probably affect many superalloys. If you have references for the proposals to use hydrogen expansion for rotary-shaft power, I’d like to have them t