Supercritical CO2 Turbines: Compact High‑Efficiency Power Shift

Name: The Supercritical CO2 Turbine: Waterless Wonder
Uploaded: 2026-03-29T23:25:32.680941+00:00
Duration: 21 min 17 s
Channel: Asianometry
Description: Summary and key takeaways on The Supercritical CO2 Turbine: Waterless Wonder — Summary, covering Turbine Evolution The power‑generation landscape is shifting

Asianometry

Mar 29, 2026

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21 min video

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3 min read

YouTube video ID: M55XzxjmON0

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The power‑generation landscape is shifting from massive steam‑based Rankine cycle turbines toward compact, high‑efficiency supercritical carbon dioxide (sCO2) turbines. Traditional steam turbines rely on water‑to‑steam phase changes, and their efficiency is limited by the inlet temperature. Ultra‑supercritical steam units can reach 43‑48 % efficiency but demand large, multi‑stage blade assemblies. In contrast, modern gas‑turbine Brayton cycles keep the working fluid in the gas phase and achieve up to 60 % efficiency by operating at inlet temperatures of 1300‑1500 °C. Closed‑cycle Brayton systems recycle the working fluid through heat exchangers; helium is a common choice but suffers from leakage and high compression costs.

Supercritical CO₂ Technology

Supercritical CO₂ offers several advantages over steam and helium. It is stable at high temperatures, non‑toxic, inexpensive, and abundant. Near its critical pressure of 7.38 MPa, CO₂ attains a density about 50 % higher than steam, enabling turbines roughly ten times smaller than their steam counterparts. Because the fluid behaves like an incompressible liquid close to the critical point, the energy required for compression drops dramatically compared with conventional gas compressors.

How an sCO₂ Cycle Works

A simple recuperated sCO₂ cycle compresses the fluid, heats it in a recuperator that recovers waste heat from the turbine exhaust, adds heat from the primary source, expands the hot CO₂ through the turbine, and finally cools it before the next compression stage. A split‑flow variant diverts part of the turbine exhaust to maximize heat recuperation, while the Allam cycle burns natural gas with pure oxygen, produces CO₂ that drives the turbine, and then sequesters the exhaust gas.

Historical Development

The concept of a supercritical power cycle dates back to 1948 with Sulzer Brothers, and engineer Ernest Feher formally proposed it in the 1960s. Early interest faded as open‑cycle systems matured and large fossil‑fuel plants showed little need for the technology. Renewed attention arrived in the 2000s, driven by Generation IV nuclear reactors and the emergence of Small Modular Reactors (SMRs) that benefit from the compact size of sCO₂ turbines.

Applications and Technical Challenges

SMRs under 300 MWe are a natural fit for sCO₂ turbines, but several technical hurdles remain. Small temperature or pressure variations cause large shifts in CO₂ density and viscosity, complicating fluid‑dynamics design. The high fluid density imposes extreme loads on bearings and seals, with windage losses that can reach 2 % of total efficiency. Long‑term material degradation—including carburization, sensitization, and high‑temperature corrosion or erosion—must be managed over 30‑year plant lifespans.

Global Projects and Commercial Status

Pilot and commercial initiatives illustrate growing momentum. The STEP (Supercritical Transformational Electric Power) project in Texas completed Phase 1 testing of a 10‑MWe sCO₂ plant in late 2024. Echogen, partnered with GE Vernova, is developing waste‑heat‑to‑power systems using sCO₂ loops. International efforts include China’s Chaotan One, the first commercial sCO₂ generator at a steel plant; the European CO2OLHEAT project harvesting waste heat from cement plants; and SOLARSCO2OL, which explores solar‑thermal sCO₂ applications.

“These turbines have CO₂ running through their veins instead of steam.”
“The waterless wonder that may be 10 times smaller than their counterparts.”
“Small is beautiful. But the engineering and materials issues are intimidating.”

Takeaways

Traditional steam Rankine turbines achieve 43‑48% efficiency but require massive multi‑stage blades, while modern gas Brayton turbines can reach up to 60% efficiency with high inlet temperatures.
Supercritical CO2 operates near its critical point at 7.38 MPa, giving a density about 50% higher than steam and allowing turbines roughly ten times smaller than comparable steam units.
In a simple recuperated sCO2 cycle, the fluid is compressed, heated by a recuperator and the primary heat source, expanded through the turbine, and then cooled, with split‑flow variants improving heat recovery.
Technical challenges for sCO2 turbines include drastic fluid‑property changes, high bearing and seal loads, windage losses up to 2% of efficiency, and long‑term material degradation such as carburization and corrosion.
Pilot and commercial projects such as Texas’s 10‑MWe STEP plant, Echogen’s partnership with GE Vernova, China’s Chaotan One, and European CO2OLHEAT and SOLARSCO2OL demonstrate growing interest despite remaining hurdles.

Frequently Asked Questions

Why does supercritical CO2 allow turbines to be much smaller than steam turbines?

Because near its critical point CO2’s density increases to about 50 % higher than steam, it behaves like an incompressible liquid. This higher density reduces the volume required for the same mass flow and cuts the energy needed for compression, allowing turbine components to be roughly ten times smaller than traditional steam units.

What is the role of recuperation in a supercritical CO2 power cycle?

Recuperation captures the residual heat in the turbine exhaust and uses it to pre‑heat the compressed CO2 before it reaches the primary heat source. By raising the inlet temperature, this heat‑exchange step improves the thermodynamic efficiency of the cycle and reduces the amount of external fuel needed.

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How an sCO₂ Cycle Works

Helpful resources related to this video

If you want to practice or explore the concepts discussed in the video, these commonly used tools may help.

Thermodynamics Engineering Textbook For Power Cycles Recommended

Provides the foundational physics behind Rankine and Brayton cycles, helping the reader understand the efficiency calculations discussed in the video.

Amazon →

High Temperature Materials Science Reference Book

Covers the metallurgy and corrosion resistance required for components operating at the extreme temperatures and pressures mentioned in sCO2 turbine development.

Amazon →

Industrial Fluid Mechanics And Heat Transfer

Explains the complex fluid dynamics and heat exchanger recuperation processes that are critical to the operation of supercritical CO2 loops.

Amazon →

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Full Transcript YouTube

For over a hundred years, steam turbines 
have generated power using water and steam.
Over the years, that steam got 
hotter and more pressurized. It  
made the turbines more efficient, but 
also made them big and complicated.
Now here comes a different type 
of turbine. Radically smaller.  
Drastically simpler. These turbines have CO2 
running through their veins instead of steam.
In today’s video, supercritical carbon dioxide  
turbines. The waterless wonder that may be 
10 times smaller than their counterparts.
## Spin Up The Turbine
Steam turbines run on the Rankine cycle.
In Rankine-based turbines, water is turned 
into hot pressurized steam inside a boiler.
That steam cools and expands 
when it hits a set of turbine  
blades. Shenanigans and electricity follow.
In the end, we condense the steam 
back into the liquid water phase  
so that the party can get started all over again.
The Rankine's key trait is that it uses 
a liquid as the turbine’s primary working  
fluid - with that liquid changing 
phases to gas and back in a loop.
A heat engine’s efficiency depends on the 
temperature differential of the fluid going  
in and out of said engine. Since the 
outlet temperature tends to be fixed,  
we have to raise the inlet temperature.
So to make our turbines more efficient, 
we - and I mean we as in the human race,  
not me and you personally - have worked 
to make the incoming steam hotter.
As part of this strategy, we now compress and 
heat the water beyond its critical limits to  
make it a supercritical fluid - a weird state of 
matter with traits of both liquids and gases. Once  
supercritical, the water turns directly into steam 
without boiling, letting us heat it up even more.
Today’s top Ultra-supercritical turbines 
have efficiency rates of about 43-48%.
Utilities want efficient turbines 
because it means getting more energy  
for burning the same amount of coal. 
Since their single biggest operating  
expense is the cost of the fuel, 
you want to get the most out of it.
One can argue that the Rankine cycle is 
quite efficient on paper. But achieving  
those efficiencies in reality can be 
tricky. After passing through the blades,  
the steam still has residual energy that can only 
be recaptured with another set of fan blades.
In the end, we only add so many rows of fan 
blades until it gets a bit ridiculous. Some  
Rankine steam turbines have 30+ 
stages of very large fan blades.
## Brayton Cycle
So the Rankine is one of two major philosophies
for running a turbine. But as 
Yoda says, there is another.
The second is the Brayton cycle - or 
Joule cycle as some like to call it.
It is the basis of jet engines and the 
gas-fired turbine. The key aspect of  
the Brayton is that the working fluid remains 
in the gas phase throughout the whole cycle.
The gas turbine takes in air, compresses it, 
and then adds the natural gas as fuel. Then we  
ignite that sucker using a combustor 
to bring it to a high-energy state.  
The high-energy air hits the turbine blades - 
losing pressure and cooling down in the process.
After passing the turbine, the hot 
gas is often expelled out the back  
like a bad customer. So the gas-fired 
turbine is an open cycle Brayton system.
There is a variant of this system 
called the Combined Cycle Gas Turbine,  
where the exhaust's residual heat 
is used as a heat source for an  
attached Rankine steam turbine to 
garner yet more efficiency gains.
I should also note here that we 
have a whole rogues' gallery of  
Brayton variants - all with their own tradeoffs.
The use of gas has certain 
benefits. With steam turbines,  
the superhot steam can degrade the metals in 
the turbine blades due to moisture-induced  
oxidation and "creep" - where the steel 
deforms over time due to extreme stresses.
Dry gas is more forgiving on the blades at higher 
temperatures. And thus indeed, modern gas turbines  
can operate with inlet temperatures 
between 1300 and 1500 degrees Celsius.
Such incredibly high inlet temperatures let 
gas-based Brayton cycle systems operate at  
higher efficiencies. Up to 60%, higher than those 
of top Rankine-based ultra-supercritical turbines.
## The Closed-cycle Brayton
In addition to the rather 
common Open-cycle Brayton,  
there is the closed-cycle 
Brayton. Which is a bit rarer.
In a closed cycle Brayton, the gas is 
compressed and heated up indirectly by  
some heat source via a heat exchanger. And 
after passing through the turbine blades,  
it is sent back to the heat exchanger 
to extract some heat before being put  
back into the fold like how Mufasa 
tells it in the Circle of Life.
A closed-cycle Brayton can use any gas as 
its working fluid. One of the most closely  
studied gases is helium. The pluses 
of Helium is that it is safely inert,  
conducts heat much better 
than air, and flows cleanly.
Helium has serious downsides though. It 
has a low molecular weight, which means it  
easily leaks through shaft seals, imperfect 
welds, and even small cracks in the casing.  
Since it is also kinda expensive, we need 
some extra engineering to keep it sealed.
The gas's low density also means it takes quite 
a bit of energy to compress. Power-hungry gas  
compressors inflict a considerable penalty on the 
helium Brayton turbine's real-life efficiency.
Hence to compensate, the Helium Brayton system 
needs very high inlet temperatures of something  
in the neighborhood of 900 degrees Celsius to 
achieve efficiency rates comparable to that of top  
Rankine turbines. Certainly possible for an open 
cycle system but for a closed cycle a lot tougher.
## Supercritical Carbon Dioxide
So despite helium's strong advantages, people 
have shifted their attentions to carbon dioxide.
Carbon dioxide is well studied - particularly 
since it was used as a coolant for early  
era nuclear reactors - so 
people are familiar with it.
It is quite stable at turbine-level 
temperatures of 1,500 degrees Celsius  
or more. It is also non-toxic, 
less likely to leak than helium,  
and is cheap and abundant. Perhaps a 
bit too abundant nowadays. But yeah.
When supercritical, carbon dioxide's fluid 
density is 50% higher than that of steam.  
Depending on your assumptions, that implies 
a turbine to be some 10 times physically  
smaller than a Rankine-cycle turbine 
due to smaller parts and fewer stages.
Another important thing is that 
carbon dioxide's critical pressure  
limit of 7.38 mega-pascals is just 
about a third that of water’s.
Moreover, carbon dioxide’s density rises as 
it approaches that critical limit - making  
it more incompressible like a liquid. Which is 
a big deal because it is easier to compress an  
incompressible liquid than a low-density 
gas. In Rankine steam turbine systems,  
pressure is applied with simple water pumps.
Since gas compressors like I said use so 
much energy, CO2 getting more liquid-like  
as pressures approach the critical point 
means that the gas compressors can work less.
So all in all, a supercritical CO2 turbine can 
be just as efficient with inlet temperatures of  
550 degrees Celsius as a helium Brayton turbine 
with inlet temperatures of 900 degrees Celsius.
## How It Works
The simplest supercritical CO2 Brayton 
system goes as we talked about earlier:
A compressor first compresses the 
CO2 to near the critical limit.
Then the CO2 is heated up. First, 
heated up inside the recuperator  
with heat from the gas exiting the 
turbine later on down the line.
And then heated up secondly from 
the primary heat source - nuclear  
or otherwise - indirectly 
via a primary heat exchanger.
The carbon dioxide then enters 
the turbine where it expands  
and cools. The turbine turns the 
generator. Electricity results.
Now we must recuperate heat from the carbon 
dioxide exiting the turbine. We send it to  
the recuperator system to transfer its 
heat to the gas exiting the compressor.
Then it goes back to prepare for the 
cycle to restart all over again. We  
call this the "simple recuperated 
supercritical CO2 power cycle".
Note how the gas travels in a 
single flow throughout the cycle.  
This single flow works and is simple enough,  
but frankly is not all that efficient because 
the temperature difference between the gases  
exiting the compressor and turbine is not that 
great. We are not recuperating enough heat.
So engineers have developed a 
variant called the split-flow.  
They split the CO2 gas flow exiting the turbine 
into two, running the twins through additional  
components like a compressor to maximize 
heat recuperation and thus efficiency.
There are so many variants, all tailoring the  
cycle to fit certain applications 
or circumstances. For instance,  
they might blend the CO2 with additional gases to 
tweak the cycle's overall commercial viability.
And then there is the Allam cycle, which is an 
interesting expansion on the concept. In it,  
we burn natural gas and pure oxygen 
together to get carbon dioxide. This  
carbon dioxide is all captured and run 
through a supercritical CO2 turbine to  
generate power. After that, the 
gas is sent to be sequestered.
## Supercritical History
The idea of using supercritical carbon dioxide 
for a closed-cycle Brayton dates back to 1948.
That year, a Swiss industrial engineering firm 
called Sulzer Brothers filed a patent for a  
Brayton turbine utilizing supercritical carbon 
dioxide. They never did anything with it however.
Then in the 1960s, an American engineer 
at Douglas Aircraft named Ernest Feher  
published a series of papers that led him 
to propose the supercritical power cycle,  
choosing carbon dioxide as the working fluid.
The supercritical power cycle is similar 
to the Brayton cycle. The carbon dioxide  
operates throughout the whole system at above 
its critical limit. To sidestep the challenge  
of pressurizing carbon dioxide gas, we 
compress it to near the critical point.
Other individuals working on the supercritical 
cycle or something like it in the late 1960s  
include D.P. Gokhshtein and G.P. Verkhivker 
of the Soviet Union and G. Angelino of Italy.
All of their work showed that 
supercritical CO2 turbines have  
generally higher thermal efficiencies 
than existing Rankine steam turbines:  
Anywhere from 48 to 50%, which 
is an impressively high number.
Plus, their smaller size and simpler 
designs make them favorable for  
constrained environments like 
ships or nuclear power plants.
Unfortunately, interest in developing 
supercritical CO2 closed-cycle Brayton  
systems petered out. Open-cycle systems were 
more mature, with far higher temperatures and  
efficiencies. Closed-cycle systems were 
still working out their technical issues.
And inside a terrestrial thermal power plant,  
the technology’s potential size advantages 
were not all that relevant. Fossil fuels also  
generate higher temperatures, which more 
favors steam turbines or Helium Braytons.
## The Nuclear Opportunity
Fortunately, the technology was found to hold 
interesting potential for nuclear energy.
Nuclear power plants share similar technical 
traits with fossil fuel thermal plants. As in  
they both heat up water to turn a turbine. 
But their economics are quite different.
A fossil fuel plant's biggest operating 
cost is that of the coal or oil fuel. So  
utilities add certain complexities 
to their steam turbines like reheat  
cycles to squeeze as much energy 
as possible out of their coal.
But with nuclear energy, the cost of 
the uranium fuel is small compared to  
the plant's immense upfront cost. About 30% 
of that is the turbine. So the supercritical  
CO2 turbine’s potential simplicity and 
smaller size can impact those build costs.
There are also potential safety benefits 
with a closed-cycle turbine - as the  
sealed cycle could possibly prevent the 
accidental release of any fissile material.
In 1970, Feher collaborated on a small 
150 kilowatt-electrical supercritical  
CO2 loop. Not a full turbine but a 
loop. Evidently to investigate its use  
for nuclear energy generation. So people 
recognized the potential very early on.
The problem that people hit at the 
time was that supercritical CO2  
turbines achieved their ideal thermal 
efficiency with inlet temperatures of  
about 550 degrees Celsius. But the light 
water reactors of the 1960s and 1970s  
produced temperatures between 200-300 
degrees. So short of what was ideal.
## A 2000s Revival
The technology gained new energy in the 
late 1990s and early 2000s due to a general  
revitalization of nuclear energy thanks to 
high oil prices and US government support.
Technology changes also played a factor. New 
energy sources were emerging. Most notably,  
the Generation IV nuclear reactors.
Stuff like the molten salt reactor or very 
high temperature reactor. These can achieve  
temperature ranges of about 550 degrees Celsius 
or higher - which is the turbine's sweet spot.
Researchers also identified synergies with the 
Small Modular Reactor, the ever-so-memed SMR.  
SMRs are smaller advanced fission reactors with 
power capacities under 300 megawatt-electrical,  
but can be prefabricated in a 
factory and integrated into a site.
Supercritical CO2 turbines jive with 
the SMR's overall goals for simplicity,  
smaller size and lower capital costs without 
compromising too much on thermal efficiency.
## Technical Challenges
Supercritical CO2 technology 
is not alien. The oil and gas  
industry already compresses and pumps 
carbon dioxide, so there is a precedent.
But there are major technical challenges.  
Perhaps the most foreboding one being 
understanding and handling the changing  
physical characteristics of the carbon dioxide 
as it transitions inside the turbine machinery.
Small changes in gas temperature and pressure 
can lead to big changes in the CO2's density,  
viscosity and compressibility. This 
has major consequences on the machine's  
components like its compressor - which 
tend to be designed for fixed conditions.
The supercritical carbon dioxide flowing 
throughout the turbomachinery is dense,  
putting immense loads on the 
machinery's bearings and seals.  
Broken seals cause leaks and what are 
called windage losses - significant  
efficiency losses that can be as 
large as 2% of the whole thing.
Another challenge concerns the 
turbine’s materials - same as  
with advanced steam turbines. Metals 
have to maintain their integrity in  
a high-heat environment over the 
30 or so years of its lifetime.
Studies on how stainless steel and nickel alloys 
will perform in such conditions are limited.  
Risks include carburization - where carbon 
diffuses into the metal; Sensitization - where  
carbon reacts with steel elements like chromium; 
As well as high-temperature corrosion and erosion.
## Projects
There are a lot of supercritical 
CO2 turbine projects around the  
world. We have been developing this 
stuff since the 1960s, remember.
The first post-2000 projects began in the 
United States with collaborations between  
MIT and national government labs like 
Sandia. Many were test loops that were  
too small to show the true physics and 
mechanics of scaling to commercial size.
After 2015, Sandia realized that they needed 
to go bigger - and they sponsored projects  
to build a 10 megawatt-electrical 
turbomachine power system, hoping  
that one of these machines fulfill 
a non-nuclear commercial use case.
Some of these designs have been called 
"ingenious", including one where the  
turbine rotors, the compressor, and the 
recompressor are all assembled on one shaft.
This project - referred to as 10-MWe 
Supercritical Transformational Electric Power,  
or STEP eventually built a pilot 
plant in Texas. In end of 2024,  
it recently finished Phase 1 testing - 
generating electricity for the first time.
There are also multiple startups. A notable one 
is Echogen. Founded in 2007, they partnered with  
turbine maker GE Vernova to produce some of the 
first commercial supercritical CO2 power loops.
They are selling waste-heat-to-power systems 
which convert waste heat from industrial  
sources like gas turbine exhaust for extra 
electricity. They lack a combuster and all,  
but do use supercritical CO2. I say it counts.
Others include NET Power, which is 
working on a practical Allam cycle;  
Arbor Energy, which recently raised $55 million 
in a series A; and Peregrine Turbine Technologies,  
which is making modular turbines for any 
heat source and has little to do with birds.
Shifting to things abroad, there are 
major projects across Asia and Europe  
as well. The South Koreans and Japanese 
are building turbines at Korea Institute  
of Advanced Science and Technology 
and the Tokyo Institute of Technology.  
Both are pretty advanced, but have hit upon 
challenges relating to seals and components.
The Chinese only recently initiated technology 
development but are advancing rapidly. In  
December 2025, they opened what they called the 
first commercial supercritical carbon dioxide  
power generator at a steel plant, Chaotan One. It 
generates power from waste heat in a steel plant.
And the Europeans are working on this 
as well. Their CO2OLHEAT project is  
building a CO2 turbine to harvest waste 
heat from a cement plant in Czechia. I  
love Czechia the country, so 
I was pleased to learn this.
And something else that caught my eye is 
SOLARSCO2OL, an European technology development  
project that seeks to use supercritical 
CO2 turbines for solar thermal systems.
These focus solar energy into heat which can 
then be used to warm up a working fluid to do  
work. The idea behind this project is to help such 
solar thermal power plants become more economical.
## Conclusion
In the end, the turbine's key compelling benefits
are clear: It can offer high thermal 
efficiencies in a way smaller package.
The potential is there. But there 
is something to be said that the  
core academic principles of the technology 
have been largely developed since the 1970s  
and we still don't have a full live 
system in a commercial environment.
It seems that - for all of its failings and 
inefficiencies - the steam turbine spins on  
because it is massive, relatively forgiving, 
and has 140 years of proven history behind it.
For the supercritical carbon 
dioxide turbine on the other hand,  
the sweet spot seems to be as 
before: Small is beautiful. But  
the engineering and materials issues are 
intimidating. I hope they figure it out.