Carbon Department manufactures consumable prebake carbon anodes for use in the aluminium smelting process. The Department is made up of three major Sections – the Green Carbon, Carbon Bake and Rodding Room.
Green Carbon: Carbon anode is manufactured by the processing Calcined Petroleum Coke (CPC), Coal Tar Pitch (CTP) and spent anodes (Butts) from the pot lines in a steam jacketed rotary mixer. Spent anodes (butts) are crushed in the Rodding Room and conveyed to Green Carbon to be used as composition of the aggregate for anode manufacture. The CPC 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 –200Mesh) and Butts (+4Mesh to 0.75inches). These aggregates are weighed together with the CTP and conveyed into a steam jacketed rotary batch mixers (10 in number). The sized material is heated to between 165 to 170ºC and mixed for approximately 80 minutes until the proper paste consistency is achieved. Each batch is approximately 8,500 lbs. Nine (9) mixers are normally used with the last being used as a back up to enable PM on the units during normal operating hours. The resultant green paste is dumped and belt-conveyed to one of two Humbolt shaker machines (vibro-compactors), 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 are then cooled in a tunnel of water bath and stacked at any of three green anode storages for Carbon Bake usage.
Carbon Bake: The Carbon bake area consists of three ring type, open top oil fired furnaces where the carbon blocks are baked to about 1150ºC finishing temperature for a period of time (for 288 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 feet in diameter fans. The No. 9 furnace is separately connected to one stack that is powered by one of the two 125 hp approximately 5 ft in diameter fans.
Rodding Room: The rodding department performs two main operations, one is to receive the spent rodded anodes (butts) which is stripped from the rod assembly using hydraulic press and crushed and sized to Green Carbon using primary jaw, secondary cone crusher 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 to ensure good electrical contact in the Cell Lines. The stubs of the rods are then immersed in 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. The unit is fitted with the ability to spray thin layer of aluminium on the surfaces of the rodded anodes. This was then done to help reduce the initial tendency of the air reactivity of the anodes in the reduction cells. This system of anodes spraying is no longer being used as it has been determined that, with adequate covering of the unsprayed rodded anodes in the cells, there is no need for this additional stage of anode layer protection, further reducing operational cost. The rodded anodes are then conveyed to the cell lines with the help of over power and free conveyors. Approximately 350 pieces of rodded anodes of daily inventory is enforced that will assure uninterrupted supply to our customers; Cell Lines.
The safety exposures in these areas are considered to be moderate and the exposures are considered to be common to the industry. In addition, the department ensures strict adherence to all safety processes, rules and regulations. This has ensured enviable safety performance and for that matter a serial winner of interdepartmental safety competition.
