Analyzing energy and resource efficiency measures in the steel and zinc industry combining flowsheet simulation with a linear material and energy flow model

The German metal industry is confronted with an enforcing international competition, rising prices of energy and commodities, the increasing relevance of sustainable economy, political demands and incentives such as emission trading. To meet these challenges it is essential for companies to further improve resource and energy efficiency and to reduce CO2 emissions. Usually, efforts concerning these objectives focus on new or improved single processes. In contrast, the presented approach extends the considerations to the inter-company perspective and considers multiple processes from ferrous and nonferrous metals industry which are linked by material flows. Our considerations focus on residue flows in the iron and steel as well as the zinc industry. Steel production in integrated steelworks or electric steel plants involves the formation of large amounts of by-products, e.g. dusts, sludges or slags. These contain valuable substances such as iron or zinc and can be further processed by internal re-feeding or external recycling, e.g. by specialized companies, particularly Waelz kiln plants or the DK process. The latter produce zinc concentrates for the zinc industry. Changes in the modes of operation of one or more process can therefore affect the connected processes. We investigate strategies to further reduce landfilling and to efficiently allocate by-products to internal and external recycling options within the scope of the sketched network. We develop flowsheet models for representative processes within the regarded industries in Germany. With an Electric Arc Furnace (EAF), an integrated steelworks, two recycling companies, and a hydrometallurgical zinc plant the major processes of the German iron, steel and zinc industries are considered. We derive linear input-output functions for each of the processes by means of multiple linear regression analysis which we apply on results of systematically varied flowsheet simulation runs. These functions are used in a system of linear equations, forming a material and energy flow model of the regarded network. The model is applied to identify and assess strategies and measures to enhance resource and energy efficiency and to reduce climate relevant CO2 emissions by scenario and sensitivity analyses. Thus, technical and economical barriers of inter-company measures can be overcome by identifying strategies which are technologically feasible and favorable with regard to the named objectives.