How is a Hall-Herault aluminum smelting cell started up
and shut down?
All the descriptions and diagrams I've seen show it in
steady state operation, with no hint how the electrolyte
is melted initially, nor how it's tapped off before cooling
so the structure of the cell doesn't turn into a big rock
on cooldown.
Link 1 below has an abstract and references for a chapter called "Cell Preheat/Start-up and Early Operationon", in a book on light metals production. Springer wants $29.95 for a pdf of the chapter, or $319
for the book but the chapter's references are in publications
engineering libraries might have on hand.
Gas preheating using heater
assemblies on wheels seems to be common.
About getting the aluminum
out, per wikipedia (link 2) "The liquid aluminium is removed from the
cell via a siphon every 1 to 3 days in order to avoid having to use
extremely high temperature valves and pumps. Alumina is added to the
cells as the aluminum is removed." Of course, then aluminium is being siphoned out, they usually stop short of getting it all because the
molten cryolite that floats on the molten aluminium needs to be left
in the cell. But if the cell is being shut down for cathode changing,
they probably need to siphon everything out.
1. <https://link.springer.com/chapter/10.1007/978-3-319-48156-2_107>
How is a Hall-Herault aluminum smelting cell started up
and shut down?
All the descriptions and diagrams I've seen show it in
steady state operation, with no hint how the electrolyte
is melted initially, nor how it's tapped off before cooling
so the structure of the cell doesn't turn into a big rock
on cooldown.
Thanks for reading, and any hints!
bob prohaska
James Waldby <j-waldby@no.no> wrote:
Link 1 below has an abstract and references for a chapter called "Cell
Preheat/Start-up and Early Operationon", in a book on light metals
production. Springer wants $29.95 for a pdf of the chapter, or $319
for the book but the chapter's references are in publications
engineering libraries might have on hand.
A bit spendy for a matter of curiosity. I'm surprised there's not more online.
Gas preheating using heater assemblies on wheels seems to be
common.
That's very much a surprise. Given that aluminum smelters run
on electricity I expected an electric preheat, maybe using
SiC resistance elements in the cell walls. Gas seems alien.
About getting the aluminum out, per wikipedia (link 2) "The liquid
aluminium is removed from the cell via a siphon every 1 to 3 days
in order to avoid having to use extremely high temperature valves
and pumps. Alumina is added to the cells as the aluminum is
removed." Of course, when aluminum is being siphoned out, they
usually stop short of getting it all because the molten cryolite
that floats on the molten aluminium needs to be left in the cell.
But if the cell is being shut down for cathode changing, they
probably need to siphon everything out.
Perhaps that's the answer to my shutdown question. Just tap off all
the aluminum, and then keep going. I guess it depends on how the
siphon is arranged.
1. <https://link.springer.com/chapter/10.1007/978-3-319-48156-2_107>
The link worked, but the pdf preview wouldn't download, reporting one
page requested and three as minimum.
On Sat, 2 Oct 2021 01:50:34 -0000 (UTC), bob prohaska
<bp@www.zefox.net> wrote:
How is a Hall-Herault aluminum smelting cell started up
and shut down?
"Presently there are two main preheating methods being used, i.e.
gas preheating/baking and resistor bed heating/baking."
The resistor bed method is based on using a layer of coke or
graphite particles between the anodes and cathode block surface
to provide ohmic voltage drop and act as a heating element
. Some plants use shunts to deflect a part of the electric
current directly to the next pol without passing through the
resistor bed. The shunts will enable a more gentle start of the
preheating period and by gradually increasing the load passing
through the resistor bed the preheating time is extended
A typical gas or fuel bake equipment consists of either two large
propane, LNG or oil burners or multiple small gas
nozzle/bumers . Preferably, steel sheets are used to protect the
cathode surface from direct flame exposure
"bob prohaska" wrote in message news:sjbdga$gm7$1@dont-email.me...
The mental picture is coming together. Preheating with fuel-air
flames, granulated coke resistors and pre-melting the cryolite
before pouring it into the preheated electrolytic cell were all
things I didn't think of.
----------------
How will you power this project?
I've been looking into loads that utilize alternate energy efficiently as it's generated and so far the only practical one for me is DC refrigeration, with an Alpicool freezer.
Heating water is out because the elements in an
electric water heater can fail by shorting to the water and thus the tank, which I've seen happen without tripping the breaker, and could possibly put 120VAC on my otherwise Low Voltage (<50V) solar panel wiring.
Carbon fiber mat has low electrical resistance and excellent high
temperature properties and might make a good distributed heating element.
The sample I got from a vacuum oven maker's scrap heap measures 3 - 5 Ohms through its 1" thickness.
"bob prohaska" wrote in message news:sjbdga$gm7$1@dont-email.me...
The mental picture is coming together. Preheating with fuel-air
flames, granulated coke resistors and pre-melting the cryolite
before pouring it into the preheated electrolytic cell were all
things I didn't think of.
----------------
How will you power this project?
I've been looking into loads that utilize alternate energy efficiently as it's generated and so far the only practical one for me is DC
refrigeration,
with an Alpicool freezer.
Heating water is out because the elements in an
electric water heater can fail by shorting to the water and thus the tank, which I've seen happen without tripping the breaker, and could possibly
put
120VAC on my otherwise Low Voltage (<50V) solar panel wiring.
Carbon fiber mat has low electrical resistance and excellent high
temperature properties and might make a good distributed heating element.
The sample I got from a vacuum oven maker's scrap heap measures 3 - 5 Ohms through its 1" thickness.
Heating water is out because the elements in an
electric water heater can fail by shorting to the water and thus the tank, which I've seen happen without tripping the breaker, and could possibly
put
120VAC on my otherwise Low Voltage (<50V) solar panel wiring.
Due to surrounding trees and the orientation of my roof I've found semi-permanent homes for only about 150W of panels. If needed I can quickly set up another 400W in the yard or driveway and manually re-aim them every few hours. If the sky is clear that appears to be enough to support my low winter electricity demand, since my wood stove provides heat, cooking and
hot water, even for laundry and showers.
Using the solar power as DC instead of AC would eliminate the ~50W constant loss in the inverter, reducing battery cost by decreasing the nighttime
depth of discharge and the number of batteries required. My compact refrigerator consumes about 100W half the time so the inverter doubles the overnight drain. Panels have fallen below $1/Watt and it's the cost of batteries that makes my solar more expensive than grid power.
If the inverter could power up when it senses load demand its loss would be halved, but my (free) APC 1400 UPS doesn't support turn-on from idle in its command set and would require hacking the circuit board to accomplish it. Tripp Lite inverters can sense load if you have to buy. Apparently all true-sine inverters have significant no-load power demand and the cheaper, more efficient square wave ones aren't suited to refrigerator compressors, other AC motors or capacitive-input (light weight) power converters. A scope shows that "modified sine" means a pulse-width-modified square wave.
I'd like to create a low cost home solar system that someone else could assemble from purchased or salvaged components without needing electrical engineering and technician skills. So far mine is cheap and effective, but not simple or easy and I don't operate some parts of it unattended or overnight.
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