Potlines
Overview of a Pot

Aluminium production is a continuous process which extracts pure aluminium metal from alumina, the powdery white oxide of aluminium.
The chemical equation for aluminium smelting is 2Al203 +3C = 4Al + 3C02.
A "potline" is a long building or two buildings which contain a series of "pots", or large electrolytic cells, in which aluminium is made.

Each pot is a large rectangular cell, lined with carbon blocks and insulating bricks. The "pots" are connected electrically in series so that direct electric current flows through one pot, then on to the next and so on, to the end of the line.

Inside the pot, alumina is dissolved in a "bath" of molten cryolite (sodium aluminium fluoride) and other materials. As the electric current is passed through the bath it generates the heat to keep the bath molten and causes the alumina to separate into two constituent elements, aluminium and oxygen.
A special feature of the pots is that they have been designed to allow alumina to be added to the pot from feed hoppers mounted above each pot. This means that the pot can be replenished with alumina without the pot hoods having to be opened, thus ensuring a highly effective collection of pot fumes.
These fumes are drawn off and treated in a "dry scrubber"
Each pot is fitted with a microprocessor (a small computer) which continuously monitors the pot to maintain optimum operation conditions.
Each of the pot rooms has a number of special multi-purpose pot-tending machines used for tapping molten metal from the pot, for changing anodes, for replenishing alumina feed hoppers and other production operations.
For every tonne of aluminium produced a smelter consumes approximately two tonnes of alumina and half a tonne of carbon products.
Molten aluminium formed in the pots is syphoned off, taken to holding furnaces, tested and then poured into various casting machines.

Cast house

Molten metal is carried from the potline to the Cast house in transport ladles on specially designed vehicles.

Overhead cranes are used to lift the ten tonne ladles and pour the molten aluminium into holding furnaces where it is mixed with specific amounts of alloy materials to produce special qualities and strength according to customer requirements.
This alloyed aluminium is poured from the furnaces into continuous and semi-continuous casting machines which produce 22kg Gautschi and 25kg Brochot mould ingots, tee ingots, rectangular slabs and circular extrusion billets.

Electrodes

Carbon anodes, made from petroleum coke and pitch, are manufactured on site in the Electrode Department. They are used to conduct electricity into the smelting cells/pots in the pot room.
Anodes are consumed in the smelting process and the remaining portions (known as butts) are recycled.

Anode blocks are baked in a natural gas fired baking

furnace for several weeks. Petroleum coke is crushed, mixed with liquid pitch and vibrated into a rectangular block weighing approx. 1250kg.
These anode blocks are baked in a natural gas fired baking furnace for several weeks.
Anodes are attached to rods and suspended into the electrolytic cells in the pot room. where they are slowly consumed in the aluminium process. They are replaced on a rotating schedule about every three weeks.


Reference
Web site: http://www.tomago.com.au

Back