Strategic Planning for Desulphurization in Integrated Steel Plants
Low sulphur level is required in many steel grades, especially those meant for critical applications. With time, the requirement of sulphur level is expected to become more stringent in the steel products. Implementation of continuous casting process in melt shops and efforts to enhance casting speed, have also contributed to the need for low sulphur level even in the ordinary grades. The newer casting technologies including where the casting speeds are significantly higher than conventional counterparts, requires further reduction in sulphur level. Thus, melt shops are being stretched to refine their unit processes and enhance process capability to meet the exacting demand of producing low-sulphur steels in a cost-effective manner. In addition, unit processes for desulphurization must also meet the requirements of a continuous casting shop – good time and temperature control to enable sequence casting to continue smoothly. Above all, any solution in the form of a new technology and/or operating strategies must be economically viable for successful implementation.
In an integrated steel plant having liquid hot metal production, pre-treatment (desulphurization) of hot metal (HM De-S) allows steelmelting shops to produce grades with low sulphur levels on a consistent basis and in an economically viable manner. In integrated plants blast furnace is the ideal process to remove sulphur. But the hot metal produced still has 10-15% of the input sulphur which under good condition translates to ~0.020 to 0.040% S. This implies that there is a need for liquid steel desulphurization (LS De-S) at the secondary steelmaking stage to meet the requirement of low- or ultra-low sulphur in the final product. Even the requirement of 0.015-0.020% S level does require some De-S at steelmaking stage. Under these conditions, the question that needs to be answered is what combination of HM De-S and LS De-S capability is required to attain the required sulphur levels in the desired time, and in the most cost-effective way.