CONTINUOUS IMPROVEMENT OF HOT METAL DESULPHURISATION AT TATA STEEL BOS NO.2 IJMUIDEN

摘要

Optimisation of the performance and reduction of the costs of hot metal desulphurisation at BOS No.2 IJmuiden, is an important subject of continuous improvement activities in which the following aspects of the process have been addressed. Inaccuracies are observed in the prediction of final sulphur levels. As a compensation desulphurisation reagents are added in excess. To improve the accuracy of the predicted final sulphur level, a 6-sigma analysis has been performed. As a result two root causes for scatter were identified and addressed. A dominant root cause was lack of trust in the process model by operators leading to deviation from optimal practise. A better explanation of the process model has led to closer conforming to its advice and less scatter in the final sulphur levels. Another source of scatter proved to be pick-up of slag in the hot metal samples. Improving the construction of the sampling devices and adjusting the sampling routine led to a reduction in rejections and re-treatments of the heat. The overall costs of hot metal desulphurisation could be reduced by optimising the sulphur levels over the entire steel production route. The introduction of steel desulphurisation in the ladle furnace allowed to increase charging of recycled hot metal skulls without compromising steel quality. The final step in hot metal desulphurisation is the removal of the slag layer by raking. This entrains hot metal causing yield loss. Furthermore, raking is time consuming and improper raking causes sulphur pick-up in the converter. The parameters affecting the amount of entrained hot metal and the time required for slag removal were studied with a l/4th scale model.