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Carbon anodes - whether produced on-site or purchased froma specialist manufacturer - are the highest consumable cost in any aluminium smelter. Maximising anode use by carefully controlling butt thickness is a key process parameter.
Damage or disruption to the anode whilst in the pot means reduced production efficiency and the additional cost of removing a partially used anode and replacing it with a new one. By far the most common disruption is the formation on the underside of the anode of spikes, sometimes referred to as mushrooms.
The practice of removing and discarding anodes under which spikes have formed is still followed by many smelters, inevitably increasing carbon consumption and operating cost.
Numerous investigations into anode spikes have been documented over the years. Their formation has been attributed to many factors, of which the most significant are undoubtedly cell carbon dust and anode to cathode distance (ACD).
When a spike forms on the underside of an anode it has a considerable effect on cell performance - typically current efficiency drops by around 2%, energy consumption increases by 1,52,0%, and net carbon consumption increases...