Resource-saving and sustainable production of high-quality steel by enhanced on-line control of stirring efficiency in vacuum degassing (SUSPRISE Joint Call)
The production of steel is connected with an extensive consumption of raw materials, energy and other resources. This is especially true for quality steels with high percentages of expensive alloying elements. To produce steel grades with highest quality and cleanness demands, a vacuum tank degassing (VD) plant is often used. Within this process, liquid steel is treated under a low pressure of about 1 mbar to remove the undesired elements hydrogen, nitrogen, sulphur and for some grades also carbon. Furthermore non-metallic inclusions have to be removed from the liquid steel to achieve a high cleanness. The performance of these metallurgical operations is significantly influenced by the intensity of Argon gas bottom stirring. At present, the rating of the actual stirring intensity is normally left to the subjective judgement of the operator which, in turn, may lead to a failed estimation of the actual stirring intensity. In such cases the aims of the metallurgical operations are often not achieved. The vacuum treatment has to be prolonged or completely repeated, which means a significant loss in energy, raw materials and productivity. In the worst case heats have to be downgraded, so that valuable alloy materials have been added in vain.
Main objective of the project is to overcome the problems caused by an undefined stirring intensity during vacuum degassing treatment of liquid steel, leading to improved process reliability with less consumption of raw materials and energy. This shall be achieved by development and application of an enhanced on-line monitoring and control system for reliable operation of VD treatment.
A suitable thermo camera and data acquisition system for on-line recording of the melt surface during vacuum tank degassing process will be developed and installed at a VD plant. For reliable assessment of stirring intensity, and for prediction of slag slopping during VD treatment, appropriate image analysis software will be newly developed and optimised during extensive plant trials. Operational trials at the VD plant will be performed to investigate the interactions between stirring intensity and removal of non-metallic inclusions, degassing, as well as slag foaming and slopping. Existing dynamic process models for degassing of hydrogen and nitrogen, and inclusion removal shall be extended and adapted to the considered VD plant. Thereby, information provided by thermal image analysis will be incorporated as additional and completely new input for the model calculations. Based on data and recordings of operational trials, a closed-loop control of the stirring gas rate and a new control strategy to avoid slag slopping during vacuum degassing will be developed. Joint application of new thermal imaging based monitoring and control of Argon bottom gas stirring and improved dynamic process models will lead to an enhanced and integrated on-line monitoring and control system for VD treatment with a reliable control of stirring intensity, leading to an improved performance of main metallurgical operations during the vacuum degassing process. This system and its performance will be tested, improved and validated in long-term operational trials at the VD plant.
Expected benefits are improved quality and cleanness of liquid steel, connected with significant savings of raw materials (e.g. alloys, slag formers, refractories), resources (e.g. argon stirring gas, steam for vacuum generation) and energy (electrical and chemical), achieved by reduced treatment times and less failure heats. Furthermore the productivity of the steelmaking process will be improved. Moreover, the well-aimed control of stirring will lessen the problems with slag foaming and slopping, and will reduce the risk of potentially dangerous slag overflow.
VDEh-Betriebsforschungsinstitut GmbH, Düsseldorf, Germany
Project or cooperation partner
- Böhler Edelstahl GmbH & Co KG, Kapfenberg, Austria
- InfraTec GmbH, Dresden, Germany
Dr.-Ing. Bernd Kleimt
40237 Düsseldorf, Deutschland
Dipl.-Ing. Robert Tanzer
Böhler Edelstahl GmbH & Co KG
8605 Kapfenberg, Österreich