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.
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.
Anything made of steel or aluminum is recyclable because they can just melt it down and easily separate the metals, but the carbon lining and anything nonmetal is basically slag afterwards. Aluminum, electrolyte, and random atoms seep in everywhere and destroy it.
The smelting process I described above is actually the more expensive process to used to produce aluminum from raw bauxite. Recycling aluminum is cheaper and a significant fraction of the world’s aluminum produced every year is from recycled feedstock (over two thirds in the US, last I checked). Same goes for steel and most other metals.
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).
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.
Android users will at some point next year not be able to install software unless the developer has paid and registered itsef with Google, and Google has approved the developer and the software (for an uncertain amount of time).
I get the interest, and the review process. What I mean is, is this a hobby where someone is passionate about soothing, or does some employers allow people to work on side projects?
I feel my life is mostly about direct value, and I don't really understand where I went wrong in the path for meaningful knowledge.
Any philosophical help will be very welcome, as you correctly guest I'm a bit lost.
It sounds like you're too focused on outcome and not enough on experience.
It is a miserable life to treat everything like a chore done to earn some know, expected, concrete reward.
I suspect the author got curious, did some reading, realized they understood something, and thought it would be fun to write up the result. Likely all in their free time.
I remember R. Feynman wrote that at some point in his life he reached the end of his achievements, and it was a pretty sad time. For many years he couldn't produce anything valuable anymore. So over time he gave up trying and just kept on living, doing stuff just for fun, not for value. One day he saw someone juggles a kitchen plate throwing it into the air, spinning. He got interested, why does the plate "waves" exactly twice less than rotation speed. He started computing it, just for fun. Because he was already a failure, so who cares. Over time that pointless kitchen plate computations grew up to quantum calculations, for which he much later was awarded a Nobel.
Unless you're supremely lucky, this kind of stuff is a hobby. One wishes that weren't the case, but capitalism is what it is...
I'd encourage you to generally ignore whether something has direct value or not because that's not how knowledge works. For example, I once spent well over a month implementing the NthWeekday function using nothing but basic arithmetic operations. This would allow us to calculate all federal holidays for a given year at runtime instead of precalculating the values and storing them in a table (which I hated, because it meant that someone had to maintain that table). This hyper-specific problem has near-zero direct value, but it was THE project that sparked my passion for maths.
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