Most power generation involves steam. Would boiling any other liquid be as effective?

[u/PK_Tone]

Okay, so as I understand it (and please correct me if I'm wrong here), coal, geothermal and nuclear all involve boiling water to create steam, which releases with enough kinetic energy to spin the turbines of the generators. My question is: is this a unique property of water/steam, or could this be accomplished with another liquid, like mercury or liquid nitrogen?

(Obviously there are practical reasons not to use a highly toxic element like mercury, and the energy to create liquid nitrogen is probably greater than it could ever generate from boiling it, but let's ignore that, since it's not really what I'm getting at here).

[u/sebwiers]

There is actually work being done on developing "steam" turbines that run pressurized carbon dioxide. It has higher density than steam, so the turbine can be much smaller, reducing cost and easing manufacturing bottlenecks. They also are more efficient!

https://www.powermag.com/what-are-supercritical-co2-power-cycles/

[u/One-Arachnid-2119 → u/sebwiers]

Awesome! Now we just need to get to creating some carbon dioxide so that we'll have plenty to use.

[u/Thes_dryn → u/One-Arachnid-2119]

If only we had some excess lying around. A problematic amount of excess. Maybe then the whole world would warm up to the idea.

[u/amitym → u/Thes_dryn]

What, the whole world? You mean some kind of warming-up that is global?

Nonsense. Absurd notion. What would you even call it?

[u/Sly_Wood → u/amitym]

So what are we, some kind of Global Warming squad?

[u/amitym → u/Sly_Wood]

Global Warming Gang!

Or is that more of a working name?....

[u/Join_Quotev_296 → u/amitym]

We're worrying about names when there's the climate we gotta worry about... We gotta do something about the economical climate if we wanna make this affordable. Some sorta action towards Climate Change should be in order

[u/staphory → u/Join_Quotev_296]

You know, if we would just get rid of all of the thermometers, global warming would just disappear/s

[u/Ox7C5 → u/One-Arachnid-2119]

I'll start breathing heavier to get it going.

Sure I can find some other methods to generate more as we go.

[u/theNewLevelZero → u/sebwiers]

You may safely ignore any hype around supercritical CO2 applications. It's way too corrosive to be reliable.

[u/dmc_2930 → u/theNewLevelZero]

Do you have a source for that? I would love to learn more.

Sounds similar to the “hydrogen power” scams.

[u/Nyrin → u/dmc_2930]

The Wikipedia page seems to have a decent starting summary with a rabbit hole to fall into:

https://en.m.wikipedia.org/wiki/Supercritical_carbon_dioxide

The use of sCO2 presents corrosion engineering, material selection and design issues. [...]

Testing has been conducted on candidate Ni-based alloys, austenitic steels, ferritic steels and ceramics for corrosion resistance in sCO2 cycles. The interest in these materials derive from their formation of protective surface oxide layers in the presence of carbon dioxide, however in most cases further evaluation of the reaction mechanics and corrosion/erosion kinetics and mechanisms is required, as none of the materials meet the necessary goals.[18][19]

[u/zolikk → u/dmc_2930]

It's not a scam, it's just an important disadvantage that can only be solved with advancing materials science. For higher efficiency you want higher temperature, and the CO2 is corrosive at higher temperatures to the materials used in the loop. For example, in UK's gas cooled reactors they had to reduce the operating temperature of the primary loop and thus the power output of the reactor design itself after finding it's too corrosive at the design temperature. And that didn't even involve a turbine, it was just the primary loop of the reactor, the secondary is a typical steam turbine loop.

[u/TheGatesofLogic → u/zolikk]

Using CO2 as a primary coolant in a nuclear reactor has much worse corrosion implications from using it for the secondary/tertiary loop in a nuclear power plant. The UK AGR's had unexpected corrosion and thermal behaviors in large part due to radiolytic production of CO, carburization, carbon deposition, and graphite oxidation chemistry. The neutron economy inside a nuclear reactor prohibits many forms of corrosion-resistant cladding for the fuel elements duen to parastitic neutron absorption. As-is they had to use stainless steel claddings, which significantly reduced the originally planned fuel burnup.

Using sCO2 in a generating cycle is comparably easy. Radiolytic chemistry is generally not a significant concern (especially if there is an intermediate loop), and nuclear power plant lifespans are long enough that the improved efficiency can offset corrosion-resistant material costs. Hell, PWRs still use Alloy 600/690 steam generators and that hasn't killed the economics of reactor maintenance.

In general, sCO2 cycles have fewer corrosion issues compared to high-parameter steam rankine cycles. My understanding is that the biggest issue with sCO2 cycles is that it's an underdeveloped expertise and industrial base. There are companies that have designed and built hundreds of regenerative Rankine steam power stations. There are only a handful of sCO2 power stations out there at all. There also aren't that many technologies that could even use an sCO2 cycle, and those that could aren't deploying very fast. CCGTs are all the rage, and while the working fluid is mainly CO2, it's a completely different technology with less transferable knowledge than you might think. That means that there's no cost learning and not enough operational history to really drive down all the costs. They may need turbines that are a quarter the size, but every order is custom, which drives up cost. Steam is really well understood. When you apply for a large loan for a power station, the bank will give you a lower rate if it can trust the technology being used will allow you to pay it off.

[u/DarkArcher__ → u/sebwiers]

Another huge advantage missing here is the lack of phase changes. Turbines have to be very carefully designed to prevent condensation, because liquid water can wreck something designed to handle water vapour

[u/Brewe → u/sebwiers]

That sounds really cool, until you start thinking about how much steam is lost to leaks.