Energy Efficiency Improvement
Ladle preheating gas consumption in the smelter
As most people know, Australia has abundant reserves of natural gas. Natural gas is considered to be a fossil fuel and consists mainly of methane that was formed by the decomposition of plant matter millions of years ago. This gas, when burned, releases energy in the form of heat, which in turn can be used by domestic and industrial users for cooking, heating, drying, etc. Using this natural resource has therefore become a regular part of almost every Australian’s daily life.
Simcoa uses natural gas in several applications, one of them being to cure and heat refractory-lined ladles before they are used. Ladles are basically large steel “pots” that are lined with bricks and cement composed of various substances known as oxides, for example alumina (Al2O3) and silica (SiO2). These oxides are able to resist the very high temperatures of the molten silicon metal so that the silicon can be transferred from the furnace taphole to the area in the smelter building in which it is cast into ingots. The refractory lining in the ladles needs to be cured and pre-heated before use so that it can perform correctly and not cause the molten silicon to freeze in the ladle.
During the gas crisis that occurred on Varanus Island in June 2008, Simcoa was forced to drastically reduce the amount of gas used for several months due to the limited amount of gas available. This included the amount of gas to be used for ladle preheating. During this “gas crisis”, Simcoa were successfully able to reduce the amount of gas consumed to roughly one seventh of the usual consumption by preheating the ladles for a shorter period and not always having a ‘stand-by’ ladle continuously being preheated. Surprisingly the reduced preheating had little impact on production losses. When the gas supply went back to normal again after the gas crisis had been resolved, Simcoa decided to continue using natural gas at the vastly reduced rate for ladle preheating as part of our commitment to environmental impact improvement and an energy efficiency improvement opportunity.
In the last quarter of 2009 a formal trial with closely monitored performance was done. The results showed that, during the trial period, up to fourteen times less natural gas was consumed for ladle preheating than would have been using the pre-crisis practices. There was also very little impact on production losses. These improved ladle preheating practices are now part of the normal daily operation in the smelter.
There is a cost saving associated with reducing natural gas consumption, but the biggest advantage of the new ladle preheating practices is knowing that we have greatly reduced our consumption of a limited natural resource.
Simcoa is the world’s most energy-efficient silicon producer and every improvement, no matter how small, will ensure that we keep this title. This gas crisis and the unforeseen consequences it had on ladle preheating are proof once again of that old saying ‘necessity is the mother of invention’.Jürgen AchleitnerSenior Metallurgist
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