Increased yield and enhanced steel quality by improved deslagging and slag conditioning (OPTDESLAG) : final report

The objective of the project was to improve deslagging processes during two process steps of liquid steelmaking by applying image sensors and process models to control deslagging operations. The two process steps that were investigated are: after hot metal desulphurisation at SSAB EMEA AB, Sweden; before secondary steelmaking at Saarschmiede GmbH Freiformschmiede, Germany. In both steelworks suitable imaging sensors were installed - CCD and IR at SSAB, CCD at SAARSCHMIEDE. Based on new information from custom made image analysis about the deslagging efficiency, a dynamic model-based control of the slag conditioning process was developed by Swerea Mefos AB, Sweden, and VDEh-Betriebsforschungsinstitut GmbH, Germany. At SSAB a model was implemented to calculate the possible remaining slag amount to go into BOF regarding the Sulphur requirements. At SAARSCHMIEDE a dynamic model was implemented to calculate online the actual slag condition with respect to composition and weight throughout the following secondary steelmaking processes, together with a heat-individual calculation of the amount of slag formers to be added for conditioning of the slag. Continuous online monitoring of melt bath surface during deslagging became an essential tool for the operators at SSAB and SAARSCHMIEDE. Together with the additional information (possible slag amount to remain on hot metal, remaining slag amount on liquid steel) the operators are supported in determining the optimal point to finish deslagging. This results in less hot metal loss and mechanical refractory wear at SSAB and in less remaining slag amount and decreased duration of deslagging processes at SAARSCHMIEDE. At both steelworks the improved process control led to reproducible performance of deslagging processes. At SAARSCHMIEDE the amount of added slag formers was on the average reduced without deteriorating the performance of the metallurgical operations.