Application of Process Integration for Electric Arc Steelmaking

Sammanfattning: About one third of the total steel production is produced by electric arc steel making today. It is a very energy intensive industry but for the total cost of the final product the raw material stands for a dominating part. A global trend for the manufacturing industry is to produce more energy effective products by using low alloyed steels which in return affects the scrap based steel industry. An increased need of iron ore based metallic, such as direct reduced iron (DRI) and hot briquetted iron (HBI), as scrap supplement is then needed for maintaining low levels of trace elements in the produced steel The selection of raw materials is a matter that affects the conditions for the production system, such as the product properties, slag, off gas and dust generation, energy consumption and processes downstream. For the integrated iron and steel industry and also for other energy intensive process industry, process integration research field has shown good results regarding energy consumption and material utilization. The application of process integration as a method for the scrap based industry, and in particular for Höganäs AB:s production system, is discussed in the thesis. Mixed Integer Linear Programing has been used to develop system models for optimization and evaluation of costs and energy consumption. Also processes not present in Höganäs current production system has been developed for analyzes of future raw material scenarios. The current system models include six main process steps: a direct reduction process, an electric arc furnace, a ladle furnace, a continuous casting process and a hot rolling mill. Among the presented result in the thesis it could be mentioned the ability to predict and constrain product quality in an improved way and potential cost- and energy savings for the modeled production system. Also the ability to minimize cost and energy consumption for sequences of different product qualities, taking stock levels in consideration, has been showed. Prices, the composition of the raw materials and the availability are changes and fluctuating over time. System modeling has been showed as a good tool for being flexible and taking advantage of the market fluctuations to keep low conversion costs and energy consumption levels.