A Process Integration Approach to Assessing Possibilities for Improved Material Efficiency in Nordic ore-based Iron- and Steelmaking Systems

Sammanfattning: Iron- and steel production is a material- and energy intensive industrial activity. The production of one tonne of steel commonly results in some 400 kilograms of residual materials such as metallurgical slags, dusts, sludge and scales generated in the processes. Much work is continuously devoted to finding possible ways of using residual materials and minimising landfilled volumes. As these materials often contain considerable amounts of valuable elements such as iron, coal, manganese and calcium, it may be profitable to use them to replace virgin raw materials or to sell them as products that may be useful in other industries and/or processes.  The thesis is based on case studies that exemplify how the use of process integration, through system analysis, can assist in assessing effects and opportunities for different concepts for increased material efficiency in Nordic ore-based steelmaking systems. The process integration approach taken for this research work was the simulation of a specific iron- and steel production system and the use of an optimisation tool for the evaluation of an extended system including the symbiosis between four steel plants. Three different cases were studied including: system effects of increased magnesium oxide content in the lime raw material, investigation of the prospects for vanadium enrichment and slag reduction concept and a study of the logistics perspective for a joint residual material upgrading and recycling venture between four steel plants. The analysed cases present possibilities to improve the material efficiency by:•      Enhanced recovery of residual materials;•      Upgrading of residual materials to products;•      Specific elements recovery;•      Decreased use of virgin raw material;•      Improved quality of residual materials;•      Decreased amounts of materials placed in long-term storage or landfills. From the results of the cases studied, the best scenarios and potential gains by enhanced material efficiency is presented. In the case of system effects of increased magnesium oxide content in the lime raw material, the issue was mainly to obtain maximum usage of metallurgical slags without compromising the quality of the main product. The calculated possibility of increased slag recirculation enabled further a decreased consumption of iron ore pellet and limestone. Regarding the investigation of the vanadium enrichment and slag reduction concept, the best scenario markedly increased the internal slag recirculation in order to enrich the vanadium content in the slag for ferrovanadium production. By the vanadium enrichment and recovery concept, considerable amounts of vanadium would be made useful instead of ending up in long-term storage. The study of a shared Nordic concept for residual materials upgrading and use demonstrated the potential for upgrading the materials to a direct reduced iron product for recovery in blast furnace. The concept showed high potential for significantly reducing the amount of material being long-term stored or deposited to landfill and thus a potential step towards achieving the zero-waste philosophy target. None of the concepts for enhanced material efficiency studied in this thesis work has been implemented; however, they are still of relevance for the Nordic steel industry.