Experimenting with CO2 instead of steam for more efficient power generation

Posted: August 22, 2022 by oldbrew in Energy, innovation
Tags: ,

Brayton cycle [image credit: Wikipedia]

Efficiency gains can be made as ‘energy is lost turning steam back into water’, which doesn’t apply to the CO2. Whether the idea can be scaled up to full electricity grid level isn’t yet known.
– – –
Sandia National Laboratories researchers recently delivered electricity produced by a new power-generating system to the Sandia-Kirtland Air Force Base electrical grid, says Green Car Congress.

The system uses heated supercritical carbon dioxide instead of steam to generate electricity and is based on a closed-loop Brayton cycle.

The Brayton cycle is named after 19th century engineer George Brayton, who developed this method of using hot, pressurized fluid to spin a turbine, much like a jet engine.

Supercritical carbon dioxide is a non-toxic, stable material that is under so much pressure it acts like both a liquid and a gas.

This carbon dioxide, which stays within the system and is not released as a greenhouse gas, can get much hotter than steam—1,290 degrees Fahrenheit or 700 Celsius.

Partially because of this heat, the Brayton cycle has the potential to be much more efficient at turning heat from power plants—nuclear, natural gas or even concentrated solar—into energy than the traditional steam-based Rankine cycle.

Because so much energy is lost turning steam back into water in the Rankine cycle, at most a third of the power in the steam can be converted into electricity. In comparison, the Brayton cycle has a theoretical conversion efficiency upwards of 50%.

We’ve been striving to get here for a number of years, and to be able to demonstrate that we can connect our system through a commercial device to the grid is the first bridge to more efficient electricity generation. Maybe it’s just a pontoon bridge, but it’s definitely a bridge. It may not sound super significant, but it was quite a path to get here. Now that we can get across the river, we can get a lot more going.”

—Rodney Keith, manager for the advanced concepts group working on the Brayton cycle technology

Full article here.

  1. Saighdear says:

    Yes, all about Power density of fluids and latent heats … but hot gases leaking – like dry steam, Hmm and the public gets excited about Nuclear stuff ? and nothing new under the Sun, just been forgotten about ( originally proposed and patented by Englishman John Barber in 1791 )

  2. Gamecock says:

    Refreshing to see a report that doesn’t include the requisite “this will save mankind” BS. The word “climate” is nowhere in the report.

  3. oldbrew says:

    Brayton-cycle engines were some of the first internal combustion engines used for motive power. In 1875, John Holland used a Brayton engine to power the world’s first self-propelled submarine (Holland boat #1).


    Brayton Gas engine 1872

  4. JB says:

    Chasing that extra 17%. We’ll see if it goes the way of the Wankel.

  5. catweazle666 says:

    The problem with the Wankel for automotive use was the inefficiency resulting from the surface area and leak path length to volume ratio of the combustion chamber.
    Large (>3 ft across) Wankel engines run very efficiently in petrochemical applications burning flare gas, for example.

  6. Curious George says:

    In a steam engine the steam is not a product of combustion. The flame does heat water and the steam drives the turbine. Here they use a “liquid” (technically, “supercritical”) CO2 instead of H2O. It has some advantages.

  7. stpaulchuck says:

    Gamecock says:
    August 22, 2022 at 11:34 am

    thanks Gamecock, I needed a good chuckle today

  8. pochas94 says:

    We’ll be hearing more about the Brayton cycle, especially with mini-nukes on the horizon and nuclear space propulsion, where there is no water for cooling and you radiate waste heat directly to space.


  9. dscott8186 says:

    It’s not a bad idea per se. The low specific heat of CO2 relative to water would mean much larger equipment to generate the same horsepower. The advantage of water is the Latent Heat storage at the state change from liquid to gas, that 970 BTU/# is a comparatively massive heat density. BTW- regardless of what fluid you use, there will always be something left on the table as it were in Heat Rejected…

    Now, if you wish to take advantage of the low specific heat of CO2, produce a hermetically sealed solar panel for water heating with CO2 outside the water tubes. The low specific heat would cause the temperature of the trapped CO2 to rise dramatically higher than normal air, giving a very fast heat transfer to the water tubes.

    Given the relative simplicity of the equipment, setting up rows of waste nuclear material fan cooled, bathed in a CO2 closed system could extract a significant amount of energy for heating a fire tube or water tube boiler to produce steam. Voila, your nuclear waste is recycled to productive purpose.

  10. oldbrew says:

    What Are Supercritical CO2 Power Cycles?

    Supercritical carbon dioxide (sCO2) is a fluid state of carbon dioxide (CO2), where it is held at or above its critical temperature and critical pressure. CO2 usually behaves as a gas in air at standard temperature and pressure (STP), or as a solid called dry ice when frozen. If the temperature and pressure are both increased from STP to be at or above the critical point for CO2, it can adopt properties midway between a gas and a liquid. At this state, sCO2 can be used efficiently throughout the entire Brayton cycle. Source: DOE, Supercritical CO2 Tech Team

  11. catweazle666 says:

    It is perhaps worth mentioning that at high temperatures and pressures water can exhibit similar behaviour, the Chinese are building ultra-supercritical power stations achieving efficiency >45%.

  12. Graeme No.3 says:

    What effect would the CO2 have on heat transfer. I was thinking of BerkleyLabs experiments in (about 1987) with double glazing, in which CO2 was a poor choice as insulating medium, worse than dry air which was worse than the Rare Gases.

  13. dscott8186 says:

    Graeme No.3 says:
    August 24, 2022 at 11:14 am
    What effect would the CO2 have on heat transfer. I was thinking of BerkleyLabs experiments in (about 1987) with double glazing, in which CO2 was a poor choice as insulating medium, worse than dry air which was worse than the Rare Gases.

    Due to CO2 low specific heat of 0.24 btu/#F @ 441F, the ability to absorb latent heat is therefore low. To continue absorbing heat energy means it must do so in the sensible heat form. Heat transfer rates increase the greater the differential between two mediums. The point being the purpose of the CO2 is not to insulate or inhibit but to transfer heat.

    ( https://www.engineeringtoolbox.com/carbon-dioxide-d_974.html ) I prefer English units over SI

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s