It's Happening - China Launches World's First Supercritical CO2 Turbine

I, like a lot of you, saw articles on my timeline a few weeks ago claiming that China has just killed the steam engine. And if you saw my video last month about small modular reactors, which honestly could have been titled a video essay on why steam engines are kind of disappointing, you will understand why this headline grabbed my attention. But what is it that has everyone so convinced that this might be putting the nail in the coffin of the 140year-old workhorse of industrial civilization for good? And what even is a supercritical CO2 turbine? More importantly, is this the moment we finally move beyond Victorian thermodynamics or are we just renaming it? Let's dive in. — Turbine to speed. — Roger. Ready to move out. — In December, the China National Nuclear Corporation announced that it just switched on what is calling the first commercial grid connected super critical CO2 power unit. Not attached to a fancy nuclear plant, but bolted onto a waste heat system in a steel works in Jesu. Not the flashy entrance into the world that maybe this new technology deserves or wanted. It is a pair of 15 megawatt waste heat turbines called Cheton 1. And honestly, while the technical details are a little sparse, the numbers that are being thrown around are pretty impressive. According to the announcement, swapping out the existing steam turbine for this new superc critical CO2 system boosted energy generation efficiency by over 85% while delivering more than 50% more net power from the same heat source. On top of that, they're claiming that the whole setup is 50% smaller overall. And the bottom line is that the plant will now be able to generate more than 70 million kwatt hours of electricity per year, which they are saying translates to about 4. 3 million US in extra revenue into the pocket of the steel works. So what is so special about these super critical CO2 turbines that means that this announcement is getting so much attention? To understand that, we first need to look at what is a superc critical fluid. We've known about supercriticality since the early 1800s when Baron Charles Canard Deato observed that if you increase the temperature and pressure of a system. The distinction between a liquid and a gas starts to disappear. I usually explain this as a supercritical fluid is a gas, meaning the molecules are so hot the intermolecular forces that usually hold a liquid together can no longer lock the system into a stable condensed phase. but that the density of this gas, the number of molecules in any given volume, is so high that it is still basically the same density as a liquid. The question that you might have is why CO2? Why can't you do this with just something like water? When people hear water, they think of something harmless. But water is one of the most chemically active fluids used in large scale engineering systems. At room temperature, it readily dissolves ions and promotes electrochemical reactions. and it supports corrosion processes in most structural metals. Under power plant conditions, that chemistry becomes far more aggressive. When supercritical, water's dialectric constant drops from around 80 at ambient conditions to below 10 near the critical point. That change means it no longer behaves like a strongly polar solvent, meaning the metal oxides that are usually stable and resist corrosion in subcritical water start suddenly to dissolve and corrode when water is at supercritical conditions. By comparison though, super critical CO2 is chemically far more stable. It doesn't support the same electrochemical corrosion mechanisms because it lacks the ionic conductivity of water. But maybe the deeper advantage comes from something much more fundamental. The intermolecular forces between CO2 molecules are just really weak. Where water has strong hydrogen bonds, CO2 has kind of feeble Vanderwal's forces. For water, that means the critical point is at 374° C and 22 megapascals, reasonably extreme conditions. For CO2, though, this critical point is down at just 31° C and 7 megapascals. In practical terms, that means that just accessing this superc critical state in CO2 is dramatically easier, and you don't need extreme temperatures or pressures. And once you do cross that critical point, CO2 becomes dense like a liquid but flows like a gas. And that becomes really powerful if you try to do something like spin a turbine. In a turbine, power is generated by moving mass past a series of turbine blades. The more mass flow that you can drive through per second, the more momentum that you can extract and the more electrical power that you can generate. And we'll get to why that is important, but first I have to thank today's sponsor, ODU. 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While the exact geometry of the Chaitton 1 isn't public, all supercritical CO2 turbines follow the same basic closed Brighton architecture. You begin with CO2 at roughly 30° C, just below its 31° critical point, where it's already dense, typically around 600 to 800 kg per cubic meter. Here, it enters the compressor and is pressurized to around 20 megapascals or around 200 atmospheres. Because CO2 near the critical point is so dense, its specific volume is incredibly low. That's important because compressor work scales with specific volume. So compressing supercritical CO2 requires dramatically less energy than compressing conventional gas. In practical terms, compressor work in a supercritical CO2 cycle can be less than a third of what the equivalent open braen gas turbine would require. That high-pressure fluid is then passed through a recuperator where it absorbs heat from the turbine exhaust. The exhaust is still hot, typically 350 to 500° C. So instead of dumping that heat into the environment, the system recycles it internally. This is much harder to do in steam plants because there the low pressure exhaust is often only 40 to 60° C and is partially condensed. So there is far less usable high-grade heat available for this recovery step. After recuperation, the CO2 may already be 300° C even before it reaches the primary heat source. In this main heater, whether it's nuclear gas, coal, or concentrated solar, it raises the supercritical CO2 to over 700° C before injecting it into the turbine. Within the turbine, it underos rapid expansion through the turbine system. As it expands from roughly 20 megapascal down to perhaps 10 megapascal, enthalpy is converted into shaft work. Here, the dense exhaust gas transfers its momentum into a series of compact turbine blades spinning at tens of thousands of revolutions per minute, which drive a generator to produce electricity. Because CO2 is far denser than steam in most of the cycle, often by 1 to three orders of magnitude, depending on the state point, the volutric flow rate required for the same power output is dramatically lower. This allows that turbo machinery to be up to 10 times smaller than the equivalent steam system. Here, what's important is that centrifugal stress scales directly with the radius of the blade. This means that these machines can spin significantly faster without exceeding their material limits. The overall result is that you produce a power block that is smaller, potentially cheaper per megawatt, and capable of thermal efficiencies approaching 45 to 50%. That makes them in theory significantly more competitive by comparison to things like steam plants, which run according to the ranking cycle and typically cap out around 35% efficiency. This means that on paper, pound-for-pound, supercritical CO2 outperforms steam across size, density, and thermodynamic efficiency, which naturally raises the question, if it is smaller, denser, and more efficient, why isn't it everywhere? — This planet has an incredibly dense molecular structure. — Building a system capable of maintaining temperatures of 700° C and operating at pressures of 20 megapascal, it turns out, isn't that gentle on the engineering. The first barrier that we encounter is materials. Above 550 degrees C, conventional steels under sustained load begin to deform through a process called creep. At the same time, oxygen diffuses into the metal surfaces and forms oxide scales that can crack or spool away under thermal cycling. Steam turbines face the same problems too, which is why modern high temperature power plants typically rely on nickelbased super alloys with names like Incanel 718 or Hannes 230. These alloys are carefully engineered at the microscopic level using elements such as chromium, aluminium, and malibdinum to form protective oxide layers around the materials that allows them to survive at temperatures where ordinary steels would simply start to fail. But using superc critical CO2 as a different degradation mechanism between roughly 500 and 700° C, iron and nickel based alloys can absorb carbon from highpress CO2. That carbon diffuses along the grain boundaries and forms brittle carbides in a process known as carburization. Over time, that can reduce the ductility of a material and can initiate cracking. We're starting to get to the point where we have sufficiently well-designed super alloys that can start to slow this process. But we simply don't have the

multi-deade data on how well these materials behave after 20 or 30 years in dense CO2 environments. You can also imagine that these alloys aren't that trivial to work with. The very microructure that prevents things like creep makes them difficult to machine. And they can cost tens of times more per kilogram than structural steel before you even start taking into account things like specialized castings, heat treatments, or the fabrication process. The second major problem is the recuperator. The efficiency and advantage of the entire superc critical CO2 cycle depends on how efficiently you recycle heat from the turbine exhaust back into the compressed inlet stream. Without incredibly high recuperation effectiveness, typically above 90%, the efficiency benefit largely disappears and that puts you in a difficult design constraint where you need to transfer enormous thermal loads across incredibly thin walls while maintaining pressures approaching 20 megapascal. Most of the designs that we're seeing at the moment achieve this using diffusion bonded printed circuit heat exchangers. Stacks of chemically etched metal plates that are fused together into a monolithic block containing thousands of tiny microchs that run through them. They become incredibly compact, strong, and highly efficient. But they also are incredibly difficult to inspect. Basically impossible to dissemble and incredibly expensive to manufacture. And if micro cracks start to develop inside the bonded core that's operating at 200 atmospheres and it starts to fail, everyone has a bad time. The third major challenge, even though we initially posited it as a positive, is the turbo machinery. Because CO2 is dense, the turbines can be much smaller than steam's equivalent. But smaller rotors must spin faster to achieve the same tip speeds, typically tens of thousands of revolutions per minute. And actually, that can be a major drawback. At these levels of RPM, even tiny friction forces generate significant amounts of heat. And that means that you can't do things like use conventional bearings because the speed and heat would cause the lubricant to break down, leading to potentially catastrophic failure. In some of the most recent academic test rigs and demonstrators that I've seen back in 2022 in places like Germany, teams have been switching to things like magnetic bearings that support the rotating shaft without physical contact. No mechanical contact means in theory these things have very long shelf life, but that comes at the expense of complexity, requiring constant power, which means you need backup bearings in case you ever get a power failure. And that all means that you simply have much higher capital costs. There are a few other demonstrators out there that I've seen like hydrostatic or hydrodnamic bearings. They float on a cushion of fluid and these have been proven in steam and gas turbines in the past using the CO2 itself as the working fluid. But that also means that your bearings need to operate and support 200 atmospheres of pressure. And again, these systems are in development and in early works, particularly in places like Korea. But they're not yet at a point where we're seeing the mass rolled out. All these teething problems broadly bring us back to what is the Chetton 1 and how excited should we actually be? If the Chaitton 1 is genuinely running at high temperature and pressure with stable recuperation and reliable turbo machinery, then it represents something more important than incremental efficiency or extra revenue for the steel plant. It signals that manufacturing tolerances, material science, and system integration challenges might all finally be coming to a point where they're starting to converge, at least sufficient to start running them in somewhat commercial test settings. That is interesting. But the test setting that they have chosen to run it in also tells us a lot. This isn't bolted on to a big flashy nextG nuclear reactor. It is being deployed on something much more ordinary and arguably less exciting that is just waste heat. If supercritical CO2 turbines were sufficiently mature, you would be expecting to see these things integrated directly into advanced nuclear designs or maybe just as primary energy generation mechanisms in coal and other existing plants cuz that's where the efficiency gains would actually matter most. But nuclear projects are already pretty high risk and highly regulated. and in new nuclear or in existing power plants, you don't add a relatively unproven turbo machinery platform into the mix unless you're pretty confident that it will behave predictably over at least a 10 to 20 year time horizon. So to me, the Chetton 1 being tested in these kind of nice to have settings tells us behind the scenes where the technology and confidence and market readiness actually are enough to start to win early feasibility and pilot type projects, but not yet at the point where this energy revolution is on the cusp like it's kind of been packaged as. That is at least until we have the depth of data that this first sort of pilot might provide us. Then maybe sure everything does start to change. What I do find still slightly amusing is that what we're talking about when we're saying leaving the steam age behind, well, the steam engines and the ranking cycle that underpins it dates back to 1859. And the Braen cycle that the super critical turbines rely on, we first formulated in about 1872. So, after 150 years of progress, we've upgraded by about 13 years. I guess every little helps. If you enjoyed this video and want to support my team making this sort of content, we would love it if you

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