Re: Gas Turbine By V Ganesan Pdf Download
Hilke Mcnally
In this episode, I interview Fourth Power CTO Asegun Henry and CEO Arvin Ganesan, who bring high-profile experience in energy research, policy, and regulation to their new and promising thermal storage startup.
Here on Volts, I do not typically cover companies that are early in the startup game. Sifting through the endless startups and trying to predict which ones will be real and which ones mirages is a recipe for madness, a game I have neither the aptitude nor the desire to play.
First, it uses renewable electricity to heat up a box of rocks to store energy, and listeners, if someone is going to use renewable electricity to heat up a box of rocks to store energy, I am going to cover it. It should be clear by now that I am borderline obsessed with this whole category.
Second, Fourth Power has some extremely impressive names behind it. Asegun Henry, founder and CTO, is a long-time researcher in thermal storage and transfer, at Georgia Tech and then at MIT. He's been a researcher for decades, involved in several cutting-edge discoveries; if this is the company he's going to leave academia to run, I'm going to pay attention.
Arvin Ganesan, CEO, is best known for his five-plus years with Apple, where he led global energy and environmental policy, but he's also familiar with the industry from the regulatory side, having led EPA's regulatory efforts under President Obama. If he's going to leave a global powerhouse like Apple to run a startup, I'm going to pay attention.
Exactly, exactly. Yeah, I mean, molten salt, inexpensive medium to buy, and it really just has to do with chemical interactions. And so what we did, as a starting point for everything that we did, we ultimately said, "what if we start from scratch and rethink the problem from scratch?" and we know corrosion is an issue, and it only gets worse the hotter you go, it's like exponentially worse. We ultimately want to go to really high temperatures. So why don't we just start with materials that we know will work, that experience no corrosion whatsoever. So if we just make that our foundation, like, we're just going to pick materials that are chemically compatible.
There is no corrosion at any timescale. If we start with that, then now we've flipped the problem, and now what we've got to deal with is, how do you make a system out of those materials? But at least one thing we've crossed off is corrosion. There's no corrosion. Right. So that's actually how we started ten plus years ago. We started by saying, "let's flip the problem on its head." Usually the way these things would go is mechanical engineers would go into their room and come up with a system diagram and say, "okay, we want to do this, that, and the third," then throw the problem over a wall to material scientists and say, "can you give me materials that will do these things that I want?"
And when you approach the problem that way, it has produced a number of things that are really challenging on the material science side. And so my background, my PhD, is in mechanical engineering, but a lot of my PhD work, a lot of the postdoctoral work I did, was very heavily rooted on materials. So I have some materials insight and intuition, and my thinking was, we just need to start with the right materials. We need to make it a very boring material science problem, such that there's no chemical interactions. And so tin is special because tin has no chemical interaction with carbon at any temperature, they don't form any compounds, and this is our foundation.
Most of what you're using is carbon. The blocks you're heating up are carbon. The pipes and the pumps that circulate the fluid are made of carbon. So, really, almost everything is carbon and then tin. Is that basically it? And I know carbon, in terms of material supply, is a trivial problem. There's plenty of carbon out there. Is tin at all expensive or rare or difficult? Does that pose any problems at all?
You can also think of, for those that may be familiar with soldering, the little solder beads that are on, like, computer processing boards and whatnot, that's predominantly tin. So, tin is generally considered a very low melting point metal. And there is another choice, which ideally, if you didn't have to care about cost, would be even nicer, which would be gallium, because gallium melts right near room temperature. But 232 degrees C is nothing compared to the temperatures that we're going to. So we are very far above the melting point, or call it the freezing point. So there is an abysmal risk of freezing in our system because we're so far above the melting point.
There are a number of nuclear embodiments for nuclear reactors that are actually cooled by liquid metal. And the reason they're interested in liquid metal is because the extremely high heat transfer rate gives you now this really nice safety net against the meltdown, because you got something that can transfer heat way faster than boiling water. And so in the case of nuclear, most of the focus was on what are called alkali metals. Alkali metals are like sodium, lithium, the elements that are all the way on the left-hand side of the periodic tables. These elements are extremely reactive.
It can touch water, it doesn't explode. Things like sodium, on the other hand, do. And so we wanted to stay away from all the elements that pose significant safety hazards. And so safety was the other key consideration in why we chose tin.
So then you use this radiator to heat up the liquid tin in the pipes. Put the heat in the tin, basically, and then the pipes carry the tin to the next module, which is these big blocks of graphite, basically, big blocks of carbon. And then the pipes circulate the tin around, through the blocks, over the blocks. How does the heat get out of the tin and into the blocks?
Yeah. So think of it as like Legos. So you can stack the blocks. We don't want to have to do additional machining or modification of the blocks straight from the way they're manufactured. We want to keep the cost low. So you can just stack the blocks up and think of it like a lattice. And in between the blocks, you leave gaps. So where the way the blocks are positioned, there's a few-inch gap in between each one. And in between the blocks is where we slide the piping. So the piping carrying the liquid tin sits in between.
And the predominant means of transferring the energy between the, let's say, outer surface of the graphite piping network that's carrying the liquid metal and getting it into the blocks is actually radiation. It's thermal radiation. It's light. And this is actually why we named the company Fourth Power, because we exploit this. We exploit the fact that the amount of light emitted by those pipes scales with temperature to the fourth power.
Absolutely. And just to kind of emphasize this point, because I don't think, unless you've kind of taken a physics class, sometimes this may evade you. When I say fourth power, what that means is suppose you have a given temperature, let's say, where it's orange hot or starting to turn white hot. We'll call that temperature one, and you look at how much light is coming out of the piping. If you now double the temperature, you don't get twice as much light, you get 16 times more light. You get two to the fourth power times more light. So this function of how much light is coming out of something as it gets hotter is such a steep function that we want to push that function as high as we can.
And the reason it matters so much for us is because the hotter you go and the higher you drive this heat flow as the power density goes up, meaning the more light you're emitting per unit surface area of pipe, you're now reducing the total size of the system because for a certain power rating, you now need less equipment.
Yeah, exactly. You can say that the heat transfer rate is substituting for material. And so that's part of the reason we push to such high temperatures, really trying to push it to its extremes to truly take advantage of that. And it's ultimately about saving on cost.
Okay, so the pipes go through the blocks. They light, they emit light. This whole idea that beyond a certain temperature, energy comes back out as light; I've sat with this for months and it still blows my mind a little bit. So they're glowing. They heat up the blocks. And there's not, I don't think, a lot to say about the blocks. They're literally just rectangular blocks of graphite until the rocks themselves are glowing. And that's how you're storing the heat. And so then, if you want to get electricity out of this system, describe the next step, because I'm not totally sure I got this.
As you noted, the next step is after you've got all of this heat now stored in these blocks, now you can turn your heater off, and this big bank of blocks is insulated from the environment so that heat is trapped inside. And when you now want to get electricity back, you're going to use this big bank of blocks as like a giant heater. And so it keeps the liquid metal hot because there's so much energy trapped in the blocks. So what you do is you flow the liquid metal. The liquid metal is going to come out at the peak temperature, which for us is 2400 degrees Celsius.
It then flows over to another subsystem, which is now optimized for converting the heat back to electricity. And so you have liquid metal now flowing through graphite panels or walls that have channels cut in them. As the liquid metal flows through, you can think of it as creating like a furnace or a series of furnaces, many furnaces in parallel. And think of it as like a liquid metal powered furnace. So it's extremely intense light inside the furnace. And we have thermophotovoltaic cells that are mounted onto a heatsink. It's like an aluminum extrusion with water and gas flowing down it.
If you weren't doing storage. But the whole point is storage. So you heat the fluid, it heats the blocks, and then when you need to get it back out, the blocks reheat the fluid, and the fluid goes to the power module, where it is hot and glowing, casting off immense light. There's all these little, sort of look like little tiny furnaces in a row here, where light is coming out of each one from the metal. And then you've got these sticks with TPV panels. And just for listeners who may not know, TPV is thermophotovoltaic, basically, you're harvesting this light that the glowing fluid is emitting with these TPV panels.
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