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Supercritical CO2 Turbines a Leap in Efficiency

11/01/2023 4:42 PM

"Supercritical CO2 pilot aims to make steam turbines obsolete"

The 10 MW supercritical carbon dioxide turbine

..."Steam turbines still produce most of the world's power, but supercritical carbon dioxide promises to be much cheaper, and 10% more efficient as a medium than water, using 10X smaller turbines. A US$155-million pilot plant is now complete in San Antonio.

Ribbons were cut at the Supercritical Transformational Electric Power (STEP) pilot plant in Texas on October 27 as it was declared "mechanically complete" by project partners Southwest Research Institute (SwRI), GTI Energy, GE Vernova, and the U.S. Department of Energy.

The device in the image above is the world's first supercritical carbon dioxide turbine. Roughly the size of a desk, is a 10-megawatt turbine capable of powering around 10,000 homes. Ten megawatts is pretty small potatoes in the energy business, but to do it with a turbine this tiny? That could prove to be a revolutionary feat.

Carbon dioxide goes supercritical when the temperature and pressure are above about 31 °C (88 °F) and 74 bar (1,070 psi), respectively. At this point, it stops acting like a gas or a liquid, and instead starts acting something like a gas with the density of a liquid. Past this point, relatively small changes in temperature can cause significant changes in density."....

https://newatlas.com/energy/supercritical-co2-turbines/

Hey smaller footprint, higher output, what's not to love....Looks good for those megawatt chargers we're going to need...

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#1

Re: Supercritical CO2 Turbines a Leap in Efficiency

11/01/2023 5:24 PM

Wow. Who wuddah thunk that carbon dioxide was good?

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#2
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Re: Supercritical CO2 Turbines a Leap in Efficiency

11/01/2023 5:32 PM

Probably some plants already knew....

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#4
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Re: Supercritical CO2 Turbines a Leap in Efficiency

11/01/2023 5:34 PM

Neat flower. Thanks !

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#5
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Re: Supercritical CO2 Turbines a Leap in Efficiency

11/01/2023 5:38 PM

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#6
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Re: Supercritical CO2 Turbines a Leap in Efficiency

11/02/2023 2:48 PM

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#7
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Re: Supercritical CO2 Turbines a Leap in Efficiency

11/02/2023 8:49 PM

" . . . if you do doubt your courage or your strength, come no further, for death awaits you all with nasty, big, pointy teeth."

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#3

Re: Supercritical CO2 Turbines a Leap in Efficiency

11/01/2023 5:34 PM

What has made this possible is the research done on metals compatibility...

https://www.osti.gov/servlets/purl/1807235

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#14
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Re: Supercritical CO2 Turbines a Leap in Efficiency

11/05/2023 2:07 AM

I always wondered what the obstacle was...

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#8

Re: Supercritical CO2 Turbines a Leap in Efficiency

11/02/2023 11:33 PM

Guess I'm always skeptical about such promises. Has it been peer-reviewed? How much power does it take to get CO2 to that pressure? Like, is the 10 MW the net power produced?

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#9
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Re: Supercritical CO2 Turbines a Leap in Efficiency

11/03/2023 12:09 AM

GE has built prototypes, and based on the performance achieved they can expect about a 50% extraction rate or 50% efficiency rating, about a 10% improvement over steam turbine...they also have a much faster startup time of just 2 minutes, as opposed to steam which takes about 30 min...

Increasing the density of your expander fluid is the holy grail of turbine generation...like the waste heat recovery units Organic Rankine cycle used in industry today, and for probably 50 years or more....

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#10
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Re: Supercritical CO2 Turbines a Leap in Efficiency

11/03/2023 3:47 AM

This is the actual size of the 10MW Supercritical CO2 turbine ...

https://www.popularmechanics.com/technology/infrastructure/a20359/ge-minirotor-co2-powered-turbine/

There are many different for purpose turbine designs made by several companies...

https://www.turbomachinerymag.com/view/steam-is-here-to-stay-demand-grows-for-small-and-medium-sized-steam-turbines

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#11
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Re: Supercritical CO2 Turbines a Leap in Efficiency

11/03/2023 4:55 AM

..."As a working fluid, supercritical carbon dioxide is ideal – at the right temperature and pressure it behaves like a dense fluid (denser than water), allowing the Brayton cycle to work at higher efficiency – much higher than can be achieved via the Rankine cycle. Because supercritical carbon dioxide is so dense, the size of the turbine can be reduced, and simplified, from the size of a semi-trailer to something that could sit on an office desk."...

..."The carbon dioxide is recycled – and since we are no longer making steam, our water usage goes down tremendously (80-90%). Water use for energy production accounted for 583 billion cubic meters – 15% of the world’s water withdrawals. In the U.S. over 40% of all freshwater withdrawals are for thermal power generation. Seems to me freeing up this much water for other uses, especially in dryer areas, might be very welcome…."

Figure 1 The Rankine Cycle.

The Rankine cycle is normally operated with a change in phase (water to steam). We’ve long known that a different cycle, called the Brayton cycle, is more efficient.

Figure 2 The Brayton Cycle.

The Brayton cycle uses what we might call a gas turbine. It operates solely within the gas phase. The reason the Brayton cycle is more efficient is it lacks the phase change of liquid water to steam which ultimately robs some of your energy output.

For the Brayton cycle, the density of your working gas makes a big difference in your energy output. Supercritical fluids (gases heated and compressed until they behave like liquids) are much easier to compress….because of that the amount of work done during the compression phase is reduced; and the energy saved there greatly contributes to the turbine’s overall efficiency.

https://euanmearns.com/every-big-bit-helps/

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#17
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Re: Supercritical CO2 Turbines a Leap in Efficiency

01/08/2024 6:42 AM

The Brayton Cycle diagram doesn't show the operating temperatures and pressures but I wonder if the heat taken out in the 'cold region' could be returned to contribute to the heat input using technology similar to the heat recovery used in air handling units?

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#12

Re: Supercritical CO2 Turbines a Leap in Efficiency

11/03/2023 8:37 PM

A description of supercritical fluid...

https://stirlingengineforum.com/viewtopic.php?t=1168

Supercritical CO2 is used for producing decaffeinated coffee (an oximoron, if you ask me...)

https://www.coffeereview.com/coffee-reference/coffee-categories/decaffeinated-coffee/carbon-dioxide-methods/

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#13

Re: Supercritical CO2 Turbines a Leap in Efficiency

11/05/2023 2:02 AM

This is actually very old technology. See E.G. Feher: THE SUPERCRITICAL THERMODYNAMIC POWER CYCLE (Douglas paper <unreadable> 1967) and (same author and title) Energy Conversion, Vol. 8, pp. 85-90. Pergamon Press, 1968.

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#15

Re: Supercritical CO2 Turbines a Leap in Efficiency

12/20/2023 6:54 AM

Hi

A couple of things occur to me:

  • If these devices were in general use, would pulling the CO2 out of the atmosphere significantly decarbonate it?
  • If the heat transfer fluid has to be heated, are you not still going to add CO2 to the atmosphere?
  • would this technology have a future in SMRs?

OK, three things.

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#16
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Re: Supercritical CO2 Turbines a Leap in Efficiency

12/20/2023 2:26 PM

This is not a significant amount of CO2 ....What is gained here is efficiency in heat to power generation, a significant improvement...so with efficiency gains the amount of heat required (btu's) to generate per kwh is reduced, thus reducing pollution....Add to that the reduction in water use, also a significant amount, and we have a win win situation...

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