In the joint project "LODYNKON" the liquid steel production in the converter process was optimized by continuous process control with dynamically adjusted oxygen supply. The converter process lowers the contents of the undesired tramp elements carbon, phosphorus and silicon dissolved in the hot metal by top blowing of oxygen and bottom stirring with nitrogen or argon. The oxygen blowing has to be stopped when the target values for the melt temperature as well as the phosphorus and carbon content have been achieved. However, as the status of the steel melt cannot be measured directly, this process results in an undesired combustion of iron and manganese. An increased oxygen content of the melt also leads to an increased consumption of deoxidation aluminium.
The project partners have therefore developed a model for online monitoring of the current heat state evolution, particularly regarding the temperature and the chemical composition of steel melt and slag. A laser optical measurement system is used to analyse the composition of the offgas, in particular its carbon monoxide and carbon dioxide contents. This new technology measures changes in the decarburisation behaviour twice as fast as an existing offgas analysis system. The consequently more prompt and precise detection of the end point of decarburisation prevents an unnecessarily high input of oxygen and reduces the related iron combustion.
Furthermore, the process model is used to predict the expected process behaviour in the course of the further treatment with the scheduled blowing conditions. This allows automatic corrections regarding oxygen supply as well as additions of heating or cooling materials and slag formers.
The application of the dynamic process model combined with the laser-based offgas analysis enables an increase in the metallic yield, saves deoxidation aluminium and reduces the oxygen consumption. It also reduces the refractory wear and the consumption of the stirring gases argon and nitrogen. Based on the yearly crude steel production in Germany of 32 million tons via the converter steelmaking route, this can lead to savings of about 80,000 tons of hot metal and scrap as well as 4,800 tons of aluminium.