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Air separation is mostly used for chemical processes [1] to isolate certain gases like oxygen or nitrogen. This is what I wrote in my previous comment: > It's

Air separation is mostly used for chemical processes [1] to isolate certain gases like oxygen or nitrogen. This is what I wrote in my previous comment: > It's off the shelf technology for chemical processes. It's not off the shelf technology for energy storage. The while point I'm making in these last few comments is that just because a certain technology is effective for one application doesn't guarantee it's effectiveness for a different application. 1. https://en.wikipedia.org/wiki/Air_separation#Applications https://en.wikipedia.org/wiki/Air_separation#Applications

pfdietz 4y ago
So what if it's used for chemical processes? To make it efficient, there is careful transfer of heat from the input stream to the outgoing streams, with compression/expansion to convert the heat energy back to work. Making this efficient involves just the kinds of components that are needed in a cryogenic energy store.
- Manuel_D 4y ago
  You correctly point out that air separation is made efficient by transferring the heat from the output stream to the input stream. After cooling air enough to isolate whatever chemical is needed (like nitrogen) the cold output stream is run back through the warm input stream to help cool the input stream. This also has the effect of warming the output stream back to ambient temperature. This is fine if you're separating out oxygen to use in a smelter, or nitrogen to be used in the haber process. But you can't do this for cryogenic air storage. The whole point is to produce liquid nitrogen (or liquid air) that can be stored and then reheated later to drive an engine to generate electricity. If you ran the liquid nitrogen output through the input stream like in typical air separation, you'd warm the output stream and turn it back into a gas. So even though the two systems both involve cooling systems they're actually substantially different processes. One of them is separating air's constituent gases, and mixes the input and output streams to achieve efficiency. The other is essentially a big liquid nitrogen plant. Unfortunately the only existing cryogenic air storage plant delivered 15 MWh of storage at a cost of 8 million pounds [1]. That's about $650 per KWh, as compared to ~$130 per KWh for battery storage. Like I said, just because a technology is effective in one application, doesn't mean it's guaranteed to be effective in another one. 1. https://en.wikipedia.org/wiki/Cryogenic_energy_storage#cite_note-11 https://en.wikipedia.org/wiki/Cryogenic_energy_storage#cite_...
  - pfdietz 4y ago
    You tell me: which component of a cryogenic energy storage system is not already in use in some process (air separation or otherwise)? One of the attractions of this sort of thing is it's composed entirely of things that are already quite mature, and that have existing supply chains.
    - Manuel_D 4y ago
      And for the third time, just because the individual components are used in different applications doesn't mean it's going to be cheap or scalable to use them in energy storage. The cost history of existing cryogenic storage plants indicates that no, it's not effective for energy storage it's 4-5x more expensive. We build plenty of flywheels. Does that mean energy storage based on giant flywheels is guaranteed to be efficient at scale because we have experience using flywheels in other applications like automobiles?
      - pfdietz 4y ago
        You're changing the subject now. You were criticizing these for lack of maturity, not for being uneconomical. My point is that your criticism that they aren't mature is misplaced, since the component technologies are all well established. Of course, it could be LN2 or LAir storage doesn't compete.
        Manuel_D 4y ago
        No, my criticism of the lack of maturity of cryogenic air energy storage is still correct. The fact that it shares some components with air separation does not change the fact that cryogenic air storage is not mature technology. Similar deal with ammonia energy storage. We've got plenty of experience with synthesizing ammonia for fertilizer production. We've got very little, if any, experience using synthesized ammonia as a form of energy storage. It was you, not I, that started this tangent about air separation in this comment [1]. I was, from the beginning, talking about energy storage systems. 1. https://news.ycombinator.com/item?id=31760980 https://news.ycombinator.com/item?id=31760980

pfdietz 4y ago

So what if it's used for chemical processes? To make it efficient, there is careful transfer of heat from the input stream to the outgoing streams, with compression/expansion to convert the heat energy back to work. Making this efficient involves just the kinds of components that are needed in a cryogenic energy store.

Manuel_D 4y ago
You correctly point out that air separation is made efficient by transferring the heat from the output stream to the input stream. After cooling air enough to isolate whatever chemical is needed (like nitrogen) the cold output stream is run back through the warm input stream to help cool the input stream. This also has the effect of warming the output stream back to ambient temperature. This is fine if you're separating out oxygen to use in a smelter, or nitrogen to be used in the haber process. But you can't do this for cryogenic air storage. The whole point is to produce liquid nitrogen (or liquid air) that can be stored and then reheated later to drive an engine to generate electricity. If you ran the liquid nitrogen output through the input stream like in typical air separation, you'd warm the output stream and turn it back into a gas. So even though the two systems both involve cooling systems they're actually substantially different processes. One of them is separating air's constituent gases, and mixes the input and output streams to achieve efficiency. The other is essentially a big liquid nitrogen plant. Unfortunately the only existing cryogenic air storage plant delivered 15 MWh of storage at a cost of 8 million pounds [1]. That's about $650 per KWh, as compared to ~$130 per KWh for battery storage. Like I said, just because a technology is effective in one application, doesn't mean it's guaranteed to be effective in another one. 1. https://en.wikipedia.org/wiki/Cryogenic_energy_storage#cite_note-11 https://en.wikipedia.org/wiki/Cryogenic_energy_storage#cite_...
- pfdietz 4y ago
  You tell me: which component of a cryogenic energy storage system is not already in use in some process (air separation or otherwise)? One of the attractions of this sort of thing is it's composed entirely of things that are already quite mature, and that have existing supply chains.
  - Manuel_D 4y ago
    And for the third time, just because the individual components are used in different applications doesn't mean it's going to be cheap or scalable to use them in energy storage. The cost history of existing cryogenic storage plants indicates that no, it's not effective for energy storage it's 4-5x more expensive. We build plenty of flywheels. Does that mean energy storage based on giant flywheels is guaranteed to be efficient at scale because we have experience using flywheels in other applications like automobiles?
    - pfdietz 4y ago
      You're changing the subject now. You were criticizing these for lack of maturity, not for being uneconomical. My point is that your criticism that they aren't mature is misplaced, since the component technologies are all well established. Of course, it could be LN2 or LAir storage doesn't compete.
      - Manuel_D 4y ago
        No, my criticism of the lack of maturity of cryogenic air energy storage is still correct. The fact that it shares some components with air separation does not change the fact that cryogenic air storage is not mature technology. Similar deal with ammonia energy storage. We've got plenty of experience with synthesizing ammonia for fertilizer production. We've got very little, if any, experience using synthesized ammonia as a form of energy storage. It was you, not I, that started this tangent about air separation in this comment [1]. I was, from the beginning, talking about energy storage systems. 1. https://news.ycombinator.com/item?id=31760980 https://news.ycombinator.com/item?id=31760980