CO2 supercritical fluid electricity generation

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Power, especially in the form of electricity, is a growing need/concern globally.

I’ve seen mention, a couple times over the last year or so, of using supercritical CO2, a liquid, as the medium to turn turbine blades.

Claude says:
Chaotan 1 (~50 words):
The world’s first commercial-scale supercritical CO₂ power generator, operating at a steel plant in Guizhou, China. Instead of steam, it uses CO₂ compressed beyond its critical point to drive turbines in a closed loop, recovering industrial waste heat and generating over 70 million kWh annually — with half the physical footprint of conventional systems.

This YT describes the tech, and an active site in China.

The video is biased.
The YT suggests China is using this as a primary energy source. And that only China is doing this.
At the END of the YT, it admits it’s a pilot project.
The YT omits any mention of the technology being studied external to China.
It turns out … According to Claude…
That there’s a test project in San Antonio TX.

(. Western Pilot Projects:
Yes — the US has a significant one. The STEP Demo (Supercritical Transformational Electric Power) pilot plant was designed, constructed, and operated at the Southwest Research Institute (SwRI) in San Antonio, Texas, led by GTI Energy in collaboration with SwRI, GE Vernova, and NETL, with $116 million in federal funding. (National Energy Technology Laboratory)
During Phase 1 testing, it achieved full turbine speed of 27,000 RPM at 500°C and generated 4 MWe of grid-synchronized power — enough for 4,000 homes. (GTI Energy) A next phase was planned to reconfigure the plant to a Recompression Brayton Cycle and raise the turbine inlet temperature to 715°C for higher efficiency. (POWER Magazine)
Other countries:
China’s CNNC also launched a separate “Molten Salt Energy Storage + Supercritical CO₂ Power Generation” demonstration project in 2024, expected to complete deployment by 2028. (China National Nuclear Corporation)
Europe has research activity but no announced commercial-scale sCO₂ pilot on par with STEP or Chaotan 1 yet. The US STEP program remains the most advanced Western counterpart to China’s Chaotan 1. )

:rocket:Science is fascinating.
ralph

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Just a couple of nerdy details:

Supercritical carbon dioxide (sCO₂) is a fluid state of carbon dioxide held at or above its critical temperature (31.1 °C) and pressure (1,081 psi). In this state, it acts as a “hybrid”, exhibiting the low viscosity and high diffusivity of a gas, but retaining the density of a liquid.

That is roughly 70 atmospheres (i.e. 70x the pressure at sea level). At atmospheric pressure, you can’t get liquid CO2. And you have to cool it to -78deg C to make it a solid (dry ice, which will sublimate to a gas state without a liquid state at 1 atm). By playing with the pressure you can change those points, and even make it a liquid (as they are doing here). Pretty neat stuff.

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Super critical carbon dioxide is used to decafinate coffee “naturally.” Various solvents can be used but removing last trace of solvent (like hexane ie gasoline or chloroform) is a problem. Carbon dioxide leaves no residue.

High pressure steam is cheap and works very well. What is the advantage of supercritical carbon dioxide?

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I’m not a specialist in this, but DOE says: sCO₂ is increasingly used as a “working fluid” in closed-loop Brayton cycle turbines. It is incredibly efficient at converting heat into electricity and allows for much more compact turbine equipment compared to traditional steam turbines. [1, 2, 3]