Aluminum smelters use the Hall-Heroult process, where alumina is dissolved in molten cryolite and reduced in massive “pots” which are large electrolytic cells. Each pot contains a carbon cathode lining that must be kept at around 950C during operation. If the pot cools down, the frozen electrolyte and solidified aluminum contract at different rates than the carbon and steel shell, cracking the lining.
Once it’s cracked, the pot has to be completely cleaned out and relined which takes weeks. A smelter usually has hundreds of pots so this alone takes a while as the liner and anything in it are basically frozen solid and need to be broken apart and torn out. Once relined the pots must be brought back up slowly and the chemistry balanced. The pots also draw a ton of power and are wired in series so they have to all be brought up slowly together (or in batches).
That assumes it was a clean shutdown with nothing else clogged up in the system. “Cleaning” in smelting means that the hardware involved needs to be replaced because it fused to molten metal while cooling down.
I'm sure, like any metal at an industrial scale, it is profitably recyclable. But that is beside the point. This is akin to asking: "My car's engine just threw a rod and is seized. Is it recyclable?" Hopefully you see in this analogy that the car (engine) costs way, way more than the sum of its parts (the constituent metals).
How much of this process is cleaning up from the previous run and how much is purely for starting up the process again? Does it make sense to clean up the system as soon as you can after shutdown, in preparation for restart, whenever that may be?
It’s one and the same. The sodium and other atoms from the molten cryolite intercalate into the carbon cathode structure and swell it by a few percent. Once in use, a cathode is held together by the steel shell and thermal equilibrium of the running pot. Once it cools the cracking is inevitable.
You also can’t fully drain a pot. You can siphon most of the aluminum and cryolite off but at those temperatures they behave like a proper liquid with surface tension and the metal wicks into the pot like solder instead of flowing with gravity.
I'm not sure in this instance, but for industrial plants, the expectation is for them to run 24/7/365 without disruption. They're not designed to be turned off and then on again. When you shut something down, how do you "reset" it to a clean state so production can start again? Think about all the existing stuff still in the pipes, residual, etc.
Aluminum smelters use the Hall-Heroult process, where alumina is dissolved in molten cryolite and reduced in massive “pots” which are large electrolytic cells. Each pot contains a carbon cathode lining that must be kept at around 950C during operation. If the pot cools down, the frozen electrolyte and solidified aluminum contract at different rates than the carbon and steel shell, cracking the lining.
Once it’s cracked, the pot has to be completely cleaned out and relined which takes weeks. A smelter usually has hundreds of pots so this alone takes a while as the liner and anything in it are basically frozen solid and need to be broken apart and torn out. Once relined the pots must be brought back up slowly and the chemistry balanced. The pots also draw a ton of power and are wired in series so they have to all be brought up slowly together (or in batches).
That assumes it was a clean shutdown with nothing else clogged up in the system. “Cleaning” in smelting means that the hardware involved needs to be replaced because it fused to molten metal while cooling down.
Fascinating, and what about the discarded hardware? Is it recyclable in any way?
I'm sure, like any metal at an industrial scale, it is profitably recyclable. But that is beside the point. This is akin to asking: "My car's engine just threw a rod and is seized. Is it recyclable?" Hopefully you see in this analogy that the car (engine) costs way, way more than the sum of its parts (the constituent metals).
How much of this process is cleaning up from the previous run and how much is purely for starting up the process again? Does it make sense to clean up the system as soon as you can after shutdown, in preparation for restart, whenever that may be?
It’s one and the same. The sodium and other atoms from the molten cryolite intercalate into the carbon cathode structure and swell it by a few percent. Once in use, a cathode is held together by the steel shell and thermal equilibrium of the running pot. Once it cools the cracking is inevitable.
You also can’t fully drain a pot. You can siphon most of the aluminum and cryolite off but at those temperatures they behave like a proper liquid with surface tension and the metal wicks into the pot like solder instead of flowing with gravity.
The system is just build for continuous usage and any shutdown does major damage.
To keep it running at reduced capacity will likely be less expensive unless the war goes on for a very long time.
I'm not sure in this instance, but for industrial plants, the expectation is for them to run 24/7/365 without disruption. They're not designed to be turned off and then on again. When you shut something down, how do you "reset" it to a clean state so production can start again? Think about all the existing stuff still in the pipes, residual, etc.
forges are continuous processes - they stay hot while stuff goes in and out
if you make it cold, you'll have to do whole startup sequence again