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42 comments on On the hazards of ignorance of thermodynamics

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wimbi on October 7, 2008 - 9:23pm Permalink | Subthread | Comments top

Thanks, EP, for this good addition. I am too lazy to make any such comments to what struck me as a very uninformed remark. Non-combustion gas turbine not proven!. I remember good Prof Marble at Caltech going on and on about closed cycle gas turbines and their advantages and applications, including nuclear reactors, in 1962.

He said something like - Obey the iron law of thermo that for high efficiency you try to add heat only at the highest temp, and release heat only at the lowest temp in the cycle. So in a closed cycle, you have to get from the low temp to near the highest temp without heat addition, either by a high compression ratio using a complex compressor, or by a counter current heat exchanger, in which the hot turbine exhaust heats the low temp compressor discharge to near the highest temp.

That is, for high efficiency, you take your pick, high pressure ratio compressor , or simple low pressure ratio compressor but a complex exhaust heat exchanger. Either way, you can get good efficiency from some external heat source, whatever that might be, like nuclear or solar. And there is no combustion in the cycle gas, so call it non-combustion if you wish.

Then you can pick the gas you like- helium, hydrogen, nitrogen, carbon dioxide or whatever suits your fancy.

Or, heh, heh, you could go to some other cycle, like, Surprise! A stirling engine. This is what NASA is thinking about for a moon nuclear power source. They are also thinking about a closed cycle gas turbine, but there, they gotta be out of their minds.

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BobE on October 8, 2008 - 5:41am Permalink | Subthread | Parent | Comments top

Helium has very nice thermodynamic properties for heat transfer. But what about Peak Helium?

http://www.energybulletin.net/node/34563

BobE

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fluffy on October 8, 2008 - 5:51am Permalink | Subthread | Parent | Comments top

Is there any particular reason that Neon or Argon could not be used instead? (Neutron activation?)

In any case, technically a nuclear reactor should produce helium as a by product, although goodness knws how you'd go about capturing it..

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DIYer on October 8, 2008 - 6:32am Permalink | Subthread | Parent | Comments top

Argon isn't quite as good. The heavier the atom, the poorer the heat transfer characteristics of the gas. I don't think Argon has much of a neutron cross section, but I'd be guessing on that.

It does make argon useful in those insulating windows, though :)

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wkwillis on October 10, 2008 - 1:09am Permalink | Subthread | Parent | Comments top

Cryogenic plants for Oxygen and Nitrogen produce Argon, Neon, Krypton, Xenon, and Helium, in that order. Argon has a high thermal neutron absorbtion, like Nitrogen, but is widely available. Neon has a low thermal neutron absorbtion, and is available but scarcer. For Fast Neutron Gas Cooled Reactors, Argon is perfectly acceptable and we aren't about to run out.
If we have carbon sequestration rules, then there is also going to be a good deal of byproduct Neon arriving for Pebble Bed Thermal Neutron Gas Cooled Reactors.
Since we have a limited production capability for Pressurised Water Thermal Neutron reactor pressure vessals, the only quick reactor ramp up is going to be Fast Neutron Gas Cooled Reactors. Pebble Bed Thermal Neutron Gas Cooled Reactors don't have to worry so much about pressure surges, so the pressure vessal is simpler and cheaper to build.

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Engineer-Poet on October 10, 2008 - 10:42pm Permalink | Subthread | Parent | Comments top

Thermal-neutron molten salt reactors might be even faster to build than gas-cooled, because the fuel cycle might be started with plutonium from spent PWR fuel instead of enriching raw uranium.  MSR's don't merely dispense with forged reactor vessels, they operate at atmospheric pressure.

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wimbi on October 8, 2008 - 7:57am Permalink | Subthread | Parent | Comments top

Right. that's why, when I think of ways to save the world for heat engines after TSHTF, I restrict myself to nitrogen- (separated air ), or hydrogen (separated water) as the only sane choices for working fluid. Nitrogen is sluggish but ok, and hydrogen is just great, but has bad habits re alloys and such. So, nitrogen. Then you have a big sort of ugly engine, but works well enough. I am talking about the one you put on a tractor train to haul all the neighbors into town for the week end party, using moldy hay as fuel.

Truth of it is that I still can't beat a plain old IC engine running on a wood gasifier. Anybody can do it. Does not take any superannuated dreamers like me.

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Engineer-Poet on October 8, 2008 - 9:13am Permalink | Subthread | Parent | Comments top

Hydrogen is a great coolant, but it reacts with graphite and causes hydrogen embrittlement in metals.

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The_Dude on October 8, 2008 - 9:57am Permalink | Subthread | Parent | Comments top

Very true, not proven. Like most engineering fields, advances in power cycles are getting held back by materials issues.

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Engineer-Poet on October 8, 2008 - 10:43pm Permalink | Subthread | Parent | Comments top

If you think that companies which currently build and sell combustion turbines running at 1380°C firing temperatures would have any difficulty cranking out inert-gas turbines taking a measily 850°C input stream, you're kidding yourself.

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The_Dude on October 9, 2008 - 10:22pm Permalink | Subthread | Parent | Comments top

Well the Helium one should be ok. But you have to remember that the people who sell these turbines, design them to break even after selling a lot of them. There's an inherent resistance to a new working fluid or different working conditions. I heard GE sells a new aircraft engine with the break-even time frame on the order of 5-10 years. I bet GE Energy has lost money on a couple of their combustion turbines. That requires a lot of confidence in the power plant design and market.

A CO2 turbine in the 500-600 C range for a sodium cooled reactor would be a materials nightmare.

The materials problem with the HTGR is the nuclear fuel. Fission product leakage plus the graphite in the fuel might turn the turbine into a combustion turbine if air ever leaked in.

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Engineer-Poet on October 10, 2008 - 11:23pm Permalink | Subthread | Parent | Comments top

But you have to remember that the people who sell these turbines, design them to break even after selling a lot of them. There's an inherent resistance to a new working fluid or different working conditions.

Offsetting this are the mild operating conditions (old, cheap materials and processes will be more than sufficient) and large potential volume.  Certifying one turbine as part of a power reactor (especially one which doesn't compete with other designs for fuel, using e.g. spent PWR fuel and/or thorium) could sell 100 GW of capacity or more in the USA alone.

A CO2 turbine in the 500-600 C range for a sodium cooled reactor would be a materials nightmare.

Sodium is a materials nightmare.  Molten fluorides appear to be much easier to handle.  Neon is more expensive than CO2, but unreactive and with a much more favorable set of thermodynamic properties (ratio of specific heats = 1.67).

The materials problem with the HTGR is the nuclear fuel.

Silicon carbide is sufficient to protect carbon-carbon against re-entry heat on the Shuttle.  It will keep HTGRs from going all Chernobyl on us even if the reactor fills with air.

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Cyril R. on October 14, 2008 - 8:34am Permalink | Subthread | Parent | Comments top

If you think you can get away with comparing apples and oranges like that on this site, you're kidding yourself.

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Cyril R. on October 14, 2008 - 8:54am Permalink | Subthread | Parent | Comments top

Uninformed remark? Hardly. The confusion here stems from a deviation in the definition of what is 'proven'.

The definition of proven I use is not some talks and experiments in 1962, which appears to be the definition you use. There are still no commercial systems operating right now. Half a century later! It's still steam cycles. Proven means systems operating right now, providing real kWhs to real consumers, who are paying real money for them. Oh wait, that last one is a sensitive oxymoron these days.

You can interpret the situation any way you want, but facts are facts and there is no proof in this thread. In the absence of real systems operating today, at the very least we need a detailed engineering/financial report that shows the engineering feasibility and commercial practicality and cost estimates etc, with detailed figures everywhere.

Where is it? One of the topics of this thread was financing. Funny, I don't see any financing at all.

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42 comments on On the hazards of ignorance of thermodynamics

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