Experimental Studies of the Impact of Anode Pre-Heating

The adverse impact of anode setting on the current efficiency (CE) is well known in the aluminum industry, although few published studies exist. When a cold anode is lowered into the bath, it immediately quenches a layer of frozen bath, on the bottom surface, that may extend to the metal pad. It takes time, energy, and bath motion to melt this layer. Until then, the anode current distribution is uneven and the bath motion is disrupted around the newly set anodes. These effects are hypothesized to lead to higher noise and lower CE. The paper summarizes experiments, conducted at Alcoa Warrick, during which anodes pre-heated to 480-510 deg C (bottom surface) were set in a few pots over 60 days. The studies suggest potential to double the rate of load up, reduce energy consumption by 40 kWh/mt, and increase CE by 0.5-1%. Approaches to supply hot anodes are discussed.