Reply to post: Re: scaling up is the answer?

Hotter than the Sun: JET – Earth’s biggest fusion reactor, in Culham

bombastic bob Silver badge
Boffin

Re: scaling up is the answer?

(regarding the post by 'The Man Who Fell To Earth')

Uh, I visited the first link and did not see any of that information. The 2nd one was interesting [keep in mind I was talking about steam plants, not gas turbines].

I might as well give a bit of background on max efficiency:

Carnot Efficiency: https://www.e-education.psu.edu/egee102/node/1942

Here are some calculations based on Carnot efficiency.

For a 1200 psi steam plant, appx 550 deg F with 60F rejection temperature - that would be 1010R and 520R, approximately. Yeah I'm using deg R. deal with it. Would you prefer an El Reg unit?

max efficiency = (1010R - 520R) / 1010R, approximately 44.5%

That's the theoretical maximum assuming 100% efficiency everywhere else. A bit better than I expect, actually.

Of course In actual practice it's considerably lower than this. So achieving better than 30% is actually VERY good, so I won't doubt your claims outright.

But if you assume ~30% total efficiency instead of ~25%, you STILL end up using a third of that electricity just to run the fusion reactor. And THAT was my point, along with pointing out that Tokomak is probably NOT the best design for an actual power plant.

As for overall plant efficiency, you have turbine blade efficiency, the effects of condenser vacuum [or lack of it], delta-temperature across the condenser, generator efficiency, secondary steam systems, superheaters, and power required to run all of the support equipment (in particular all of the pumps, like cooling water pumps, and primary coolant pumps for a nuke plant).

And when you consider that 70% of the thermal energy goes out through the cooling system, those pumps have gotta be BIG. A high 'delta T' on the condenser would reduce its efficiency even more, so the flow rate for the cooling water has to be MASSIVE to keep efficiency up. Big pumps, with big electricity consumption, in other words.

Again, I've been out of the industry for a while. I remember what I've worked with. So kudos to steam plant makers who've squeezed an extra few percent efficiency out in the last 30 years. Well done.

Of course gas fired plants would have higher efficiency than steam plants, because they're not limited by the physics of steam.

But good luck transferring a bunch of gamma energy into a gas.

Nuclear aircraft were tried, at one time, and that one big problem of transferring nuke heat into air for a jet engine's turbine cycle became impractical. Sure, you COULD do it, if the heat transfer surface were 'big enough'. You'd need something that could absorb gamma AND neutron radiation, and would tolerate the higher temperatures. And pressurized water would land you back in the same realm as a fission plant. So there ya go.

And that was my point all along [so thanks to everyone for all of the thumbs down, a testament to your ignorance of practical applications in the realm of power plant engineering].

In answer to another question, the only reason they don't hire _ME_ is because I don't have their "lovely academic pedigree". After all, a paper pedigree makes you SO smart these days... [academic arrogance, yeah]. And yet I see it often enough, where "those who can't, teach". In the IT realm, professors who call themselves 'programmers' generate some of the most impractical, inefficient, and unmaintainable code I've ever seen. In Python. [used to be BASIC]

Question: how many people in this forum have ACTUALLY OPERATED a nuclear reactor or even a steam plant? (I have, just sayin')

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