CARBON

Carbon department is where the consumable carbon anodes are manufactured.

The carbon anode is manufactured by the processing of calcined petroleum coke, Coal tar pitch and spent anodes (butts) from the Cell Lines in a steam jacketed rotary mixer.  Spent anodes (butts) are crushed in Rodding Room and sent to Green Carbon to be used as part of the aggregate for anode manufacture. The Petroleum coke and Butts received are processed  in the Green Plant and sized using Roll crushers, Vibrating screens and two Ball mills into Coarse(-4Mesh to +20Mesh), Fines (+20Mesh to –325Mesh) and Butts (+4Mesh to 0.75inches). These aggregates are weighed together with pitch and conveyed into a steam jacketed rotary batch mixers (10).  The sized material is heated to between 165 to 170ºC and mixed for approximately 80 minutes until the proper consistency is reached. Each batch is approximately 3856 kg. Nine mixers are normally used with the last being used as a back up to enable preventive maintenance on the units during normal operating hours.  The resultant green paste is dumped and belt-conveyed to one of two Humbolt shaker machines, that compacts the paste into an anode block (green anode).  Normal capacity of the shaker unit is about 28 anodes per hour. The carbon blocks (green anodes) weighing about 1000Kg/anode are then cooled in a tunnel of water and stacked at any of the three green anode storages for Carbon Bake usage.

The Carbon Bake area consists of three ring type oil fired furnaces where the carbon blocks are baked to about 1150ºC finishing temperature for a period of time (for 240 hours at 48 Hours Baked Cycle Time), for curing and hardening of the blocks.  The carbon blocks are then cooled, removed from the furnace and transferred to either in-house warehousing or to the rodding department.  A normal 2 week supply of baked anodes and an additional 2 week supply of green anodes are maintained.  The Nos. 7 and 8 furnace ductwork (exhaust) are connected together and exhaust into one stack which uses one of the four 125 hp exhaust fans available, approximately 5 ft in diameter fans.  The No. 9 furnace is separately connected to one stack.

The Rodding department performs two main operations, one is to receive the spent rodded anodes (butts) from Cell Lines which are stripped from the rod assemblies using hydraulic press and crushed and sized to Green Carbon using primary jaw, secondary cone and a final roll crusher. The rod assembly is straightened, the thimbles stripped from the rod and one side of the copper rod sanded using a rotoblast for good electrical contact in the Cell Lines. The stubs of the rods are then immersed in a graphite slurry  and conveyed to the Casting station. The second function is at the Casting station where the processed rod is mated with baked anodes from Carbon Bake and molten cast iron metal from Ajax Magnerthermic Induction furnaces  poured to fill the annular space around the stubs of the rod assembly in the baked anode. On cooling the rodded anode assembly is conveyed to the spray station where molten Aluminium metal is sprayed onto the anode at a temperature of about 860oC.

The sprayed anode is then conveyed to Cell Lines for use to complete an electrical circuit between the anode and cathode (reduction cell), to produce molten aluminium. Approximately 220 rodded anodes are used per day, at 300 Cells level, with an in process inventory maintained.

The safety exposures in these areas are considered to be moderate and common to the industry.

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