A tiny supercritical carbon dioxide turbine can power 10k homes
cleantechnica.com
cleantechnica.com
Where do these improvements come from [1].
> CO2 has a relatively low critical pressure of 7.4 megapascal (MPa) and a critical temperature of 31C ... A consequence of this is that it can be compressed directly to supercritical pressures and readily heated to a supercritical state before expansion. In a heat engine, this can facilitate obtaining a good thermal match with the heat source. The critical temperature is also sufficiently high for ready heat rejection from the cycle at terrestrial ambient temperatures. Therefore, the system has a great potential for high efficiency since a large temperature difference is available ... CO2 near its critical point becomes more incompressible and hence, the compression work can be substantially decreased leading to high cycle efficiency.
> The high density and volumetric heat capacity of sCO2 with respect to other working fluids make it more energy dense, meaning that the size of most system components such as turbine and pump can be considerably reduced, which leads to a smaller plant footprint and possibly lower capital costs.
[1] https://www.powermag.com/what-are-supercritical-co2-power-cy...
Nevertheless, the circuit must also include heat exchangers and those are not reduced in size as much as the turbines and the pumps.
Therefore the very small sCO2 turbine will be accompanied by much larger heat exchangers, so the reduction in size of a complete system is not so impressive as the shrinking of the turbine.
Even so, the sCO2 system has another advantage over the traditional steam turbines, when used for the recovery of the waste heat from a gas turbine, or when using any other high-temperature heat source, like a nuclear reactor. Because the steam generation happens at a constant temperature, which must be relatively low for reasonable pressures, the heat transfer from a high-temperature source is inefficient. Due to this, for the recovery of the waste heat of a gas turbine are used typically 3 steam turbines whose steam generators work at different temperatures and pressures, not a single turbine.
Supecritical CO2 can be heated with a heat exchanger having a gradient of temperature along it, which allows a single sCO2 turbine to replace 3 steam turbines in a combined-cycle power plant.
Nuclear (fission) reactors really aren't high-temperature heat sources. The working fluid inside reactors is itself liquid water, which doubles as a neutron moderator. That severely limits their temperature range (<374° C), so, there's no downside to limiting yourself to steam on the energy conversion side as well.
The linked articles make brief mention of a nuclear/sCO2 combination, but, to be clear, they're talking about radically different types of nuclear reactors. Not types that are currently commercialized/mature technology. Types where you replace the working fluid on the nuclear side with higher-temperature compatible substances—molten metals, molten fluoride salts, or inert gases like CO2 or helium.
edit: Also applies to nuclear fusion, I guess. IIRC, the proposed working fluids for those are molten lead/lithium, or molten lithium fluoride—both match with the sCO2 temperature range. (Lithium is the common factor, because the overriding concern of the working fluid is to transmute lithium into tritium, using the fusion reactor's neutron flux, to hopefully allow a sustainable fuel cycle).
There are fission reactor designs with different working fluids that operate at much higher temperatures.
Nevertheless, for the future reactors it is desirable to use higher temperatures in order to increase their energy efficiency. This requires the use of other cooling fluids, as you also mention, and for such high-temperature nuclear reactors sCO2 turbines are preferable to steam turbines.
I suppose you can compensate by incorporating energy storage, which also has the side benefit of allowing the plant to be self-sufficient for cold-start.
This is just a natural gas powered generating plant using a different working fluid. The goal is to get from current efficiencies approaching 48% to somewhere above 50%.
The record for a natural gas powered plant is 68% efficiency.[2] That's a gas turbine. Indirect heating, with combustion to working fluid to turbine, is less efficient. However, if CO2 as a working fluid results in a smaller plant, it might be worth it for some applications.
[1] https://netl.doe.gov/project-information?p=FE0028979
[2] https://www.power-eng.com/gas/ge-powered-plant-awarded-world...
From a grid standpoint, peaker gas turbines can go from 0 to 100% in a few minutes. Combined cycle turbines can take a couple hours. They are precision machines and need to warm up to operating temperature much slower.
[1] https://www.ge.com/gas-power/products/gas-turbines/lm6000
It's not a great fixed power plant, but if it's smaller, it might be useful when you need a few megawatts of portable generating capacity. Caterpillar sells a megawatt Diesel in a shipping container. Here's a megawatt gas turbine in a small trailer.[1] Maybe this is useful in that niche.
[1] https://turbinepowersolutions.com/1mw-compact-generator/
For some grounding context: gas turbines are also century-old technology, and supercritical CO2 as the working fluid is pretty obvious and was extensively looked at in the 1970's [a] (and perhaps earlier). There's no qualitatively new stuff here; it looks more like a reopening of old and simple ideas due to shifting economics.
I'm definitely not trying to assign a pro-/con- valence on the tech—I just prefer clearly-grounded discussions, not puff pieces.
[a] e.g., https://ntrs.nasa.gov/citations/19760016593 ("Energy Conversion Alternatives Study (ECAS), General Electric Phase 1. Volume 2: Advanced Energy Conversion Systems. Part 2: Closed Turbine Cycles" [1976])
NET Power's approach has some significant differences from the DoE's. In their cyclical approach, natural gas and pure oxygen (obtained from an on-premises air separator) are combusted to form high-pressure CO2 and water. This mixture goes through a turboexpander, which generates electricity and lowers the pressure of the CO2-water mixture. After passing through a heat exchanger, the water is separated out as byproduct, and some amount of CO2 is also pumped out as byproduct. The remaining CO2 passes through the heat exchanger, brought back to high-pressure, and returns to the start of the cycle.
It's a quite incredible all-byproduct, no-emission energy generation process.
Even a hydrogen-fueled car has an emission of water, or a "waste product" [2]. And that's the key to understanding it: waste product, which is really what the term emission means.
What I talked about has virtually no waste product and therefore no emissions, though perhaps "no emissions" is too optimistic. The NET Power website says "NET Power’s patented technology captures over 97% of CO2 emissions from power generation", so it's darn good but not "no emission".
[1] https://www3.epa.gov/airquality/emissns.html
[2] https://www.latimes.com/business/story/2023-08-16/hydrogen-f...
For ground applications, I don't think this is enough beneficial, to be alternative to classic turbines.
Wow
"the new turbines are powerful enough to generate the electricity equivalent of 10,000 typical homes"
Average home power consumption is about 1kW... 10MW output in a turbine the size of desk/refrigerator/pony/credenza/golf cart??
Wind turbines are 10-20 MW and just the generators are around 150 tons... or 300 ponies
Making fuel from solar and wind seems key to me. Because you need long term energy storage and batteries don't cut it.
But you're right that we definitely need something better than batteries for certain applications, particularly transport.
As a locally generated process input, H2 appears to make sense, say for steel production or yes, ammonia. But H2 is hard to store; best is to do so cryogenically which uses a lot of energy and is heavy. storig higher temperature H2 is more difficult (those crafty molecules are tiny!). The economics likely work for many industrial processes, but not for transport, much less grid power generation. The "fuel" part doesn't pencil out; I believe H2 fuel story are just a subsidy to the fossil fuel companies in order to get legislation passed.
Compared to other fuels Ammonia isn't especially energetic, but for a large vessel with a lot of space it can work. But it's really toxic and harder to manage safely than buker fuel or jet fuel. "Sustainable" doesn't mean just its production but its overall risk to human life. It lacks adequate energy density to drive something like a car much less a plane, even if you were willing to have something as nasty as NH3 in your fragile, weight-sensitive vehicle.
Don't take my word for it: Maersk, who is famously commissioning ammonia (and methanol) vessels, has publicly stated that these are not long term solutions but rather (they hope) a way to push the green agenda forward.
> What fuels do you think are sustainable?
I really don't think we know yet (for transportation). The fuels we have are highly energetic (in particular by weight) because a lot of energy went into them to generate those tight bonds. Transportation fuels need a lot of important factors: energy density at a system level (energy per weight including storage), general safety at STP, etc.
There have been some efforts to make ptroleum products from captured CO2, which might be a temporary bridge (by definition it's GHG neutral and can use renewable power) but burning these fuels produces other pollution beyond GHGs (thus are't sustainable) so they still need to be eliminated.
Fortunately batteries appear viable for the middle of the curve, most wheeled vehicles. But at the extrema (ships, planes, and rockets), we need something that performs closer to what we have today and I don't see anything on the horizon.
What I am concerned about is energy storage for power grids or microgrids.
Do you want to claim that hydrogen and ammonia can't work for this use case either, and that there is nothing viable? Implying that the most sustainable option is to just continue using fossils fuels.
What I think is that there a ways to make both hydrogen and ammonia and other options very viable not only for grid storage but also for transportation. What's holding it back is a lack of critical thinking. This is because most people's views are dictated by social circumstances and then they subconsciously find ways to rationalize them. In other words, it's hard to get people on board with solving new problems related to using different energy sources, and so executives will invent reasons it can't work.
What sort of fuel do you think makes sense to pursue for long term (months) energy storage?
I don't think you've reached your opinion on the basis of adequate reasoning.
So, no.
Unless the air is 600C or something. In which case, have you checked to make sure you’re not on fire?
I'm on the side of efficiency, note vote harvesting, and it doesn't need to part of the discussion; handle it elsewhere.
Claiming disagreements are "just identity politics" is a way of shifting an argument from factual debate to "you don't like me because I don't agree with you."