How EnPot Works
The EnPot system places up to 60 intricate heat exchangers against the side of each pot and connects them to an external ducting system. The airflow to each exchanger can be varied by using a series of precisely controlled extractor fans allowing the exchangers to cool or insulate the pot, depending on what is needed.
The EnPot technology was first developed and patented by a specialist team of researchers at the Light Metals Research Centre at The University of Auckland, which has long been acknowledged as one of the preeminent aluminium smelting research institutes in the world.
Dr. Pretesh Patel, Chief Engineer for Energia Potior Ltd, was a key member of the team charged with converting the original research and prototype into the practical design and application of the technology into smelters, explains how the EnPot System works.
“The process of making aluminium is an electro-chemical process that requires an electric current as the driving force for the reaction to occur.
“Basically in laymen’s terms, we run a powerful electric current through large carbon-lined steel furnace pots filled with metal oxide and molten electrolyte kept at close to 1000 ̊C. The electric current breaks the molecular bonds of the oxide, and the resulting heavier metallic aluminium then collects at the bottom of the pot, ready for siphoning off and casting.
Dr Patel says the difficult bit is that the molten electrolyte is a compound called cryolite, which in its liquid state will dissolve virtually anything. In fact the only thing proven to contain hot molten cryolite, is cooler solid cryolite.
“It's a bit like a burning candle. The solid wax around the outside will contain the hotter molten wax that forms around the flame in the centre.
“So to contain the molten cryolite in the middle of the pot and to stop it from melting through the outer pot wall, we use a solid ledge buffer of colder cryolite, Dr Patel says.
“But now comes the really difficult bit.
“The electro-chemical process used to make aluminium produces a massive amount of heat as a by-product. How heat is dispersed through the pot from the centre to the outside is critical. If the outer part of the pot gets too hot, the solid cryolite will melt and then dissolve the carbon sidewall lining and the steel shell of the pot, ultimately leading to a pot failure.
“If on the other hand the temperature drops too much, then the cryolite liquid material will solidify and effectively freeze the pot. All smelters are built with a very narrow temperature window for the molten bath, usually only about 30°C, and hence why they must consume power at a very consistent rate.
Dr Patel says that if you want to increase production, you have to remove heat from the outside of the pot faster to prevent pot failure, and conversely if you want to slow down production you have to insulate the pot to keep it from cooling.
“To do both has been impossible before now, but over the last decade the teams at Energia Potior, Yunca Engineering and the Light Metals Research Centre have perfected the EnPot System so that it can both cool or insulate.
"We achieved this by placing up to 60 intricate heat exchangers against the side of each pot and then connecting them to an external ducting system.
"The airflow to each exchanger can then be varied by using a series of precisely controlled extractor fans, which allows the exchangers to either act as an air-conditioner to cool the pot down, or a thermal blanket to keep the pot warm, depending on what is needed.
“While it sounds theoretically straight forward, it took over a decade of research and the development of some significant patents to make it work, but now the dynamic control that it gives smelter operators enables a smelter to significantly vary its electricity use and production output,” Dr Patel says.