Measuring duct offgas temperatures to improve electrolytic cell energy efficiency

A process for controlling operations in a cell for producing aluminum by electrolysis of alumina wherein said cell comprises a chamber containing a molten electrolyte comprising cryolite and alumina, said electrolyte being at least partially covered by a solid crust, said process comprising

• a) establishing a standard rate of addition of aluminum fluoride to said electrolyte,
• b) establishing a target temperature for a duct carrying offgas from said chamber,
• c) measuring an actual temperature in said duct, and
• d) in response to the actual temperature measured in step (c), performing at least one of:
• 1) when the actual temperature is greater than the target temperature, inspecting said crust for a crust hole and when a crust hole is observed repairing it, and
• 2) varying an actual rate of addition of aluminum fluoride to said electrolyte in response to the actual temperature measured in step (c), by increasing said actual rate of aluminum fluoride addition above the standard rate when the actual temperature is greater than the target temperature and by reducing said actual rate below the standard rate when the actual temperature is less than the target temperature.