18 August 2009
Sohar, which started production in June 2008, has the world’s largest potline, which consists of 360 pots and produces up to 360,000 tons of aluminum a year. Qatalum will be the world’s largest aluminum smelter with a production capacity of 585,000 tons a year and 704 pots when the plant starts up in late 2009.At the heart of each smelter are five ABB rectiformers, each weighing more than 400 tons and each designed to enable the plants to operate in all conditions, including worst-case scenarios.Rectiformers are critical components in the aluminum production process. They control and convert the alternating current delivered by the power grid or onsite power plant into the required direct current that powers the electrolytic process and produces the molten aluminum in the pots. The potlines have to be constantly supplied with power. If the power conversion station fails, the lines will shut down and the molten aluminum in the pots will solidify and incur massive costs of as much as $100 million or more. For many years the voltage limit of rectiformers was stuck at 1200 volts DC. In the past few years ABB has extended the voltage limit first to 1500 V DC, then to 1650 V DC for Sohar and soon after to 2000 V DC for Qatalum (although the plant will operate at 1750 V DC).This enables the rectiformers to convert and deliver substantially more power than was previously possible. As a result, each smelter requires only five rectiformers instead of the six that would have been necessary at the lower voltage limit.In addition to eliminating the need for a sixth rectiformer, the increase in energy efficiency achieved by the solution is claimed to be equivalent to 18 per cent. This will represent a good saving for plants that consume as much electrical energy in a year as 300,000 homes.
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