An improvement of by-products reuse contributes to reduce the environmental impact of industries and to increase their competitiveness. Within the steel production cycle, several by-products are produced: slags, sludges, scales, dusts. Some of them are directly suitable to the internal reuse, other ones can be separated in fractions that can\ud be used internally or sold for external use. This paper shows an analysis focused on the optimization of by-products reuse in an Italian Integrated Steelworks with a particular attention on the internal recycling in the pelletization process. Starting from previous studies on the selection of suitable by-products and treatments, the paper presents, firstly, the development of a superstructure model using reMIND® software in order to find optimal solutions, considering quality and environmental constraints, and to minimize operating costs. Furthermore, the evaluation and the optimization through laboratory or simulation tests of possible mixtures of by-products to be used in pelletization is also discussed. By-product mixtures were evaluated to the aim of achieving good pellets formation, according to the number, size of pellets and the compression test results. This study shows that a particular scenario is capable to jointly reduce costs and environmental impact as well as to obtain high quality pellets that can maximize the internal reuse in sinter plant of by-products in a particular "winning formula" (BOF slag 65wt%, BOF sludge 27wt%, dolime 1wt%, cement 7wt%). These preliminary results show that a good by-products management could provide\ud important advantages to the companies by contributing to the "zero waste" target

Abstract:In the steel sector water management aims at improving the sustainability of the production cycle, resulting in resource efficiency benefits and in reduced water demand and costs. To be reused, water needs to be cooled and desalinized to avoid salt concentration in water circulation systems. The presented work includes two case studies carried out in an integrated steelmaking plant, respectively, to evaluate the possible implementation of ultrafiltration and reverse osmosis to reduce salt concentration in water streams and to investigate, through modelling and simulation, a process integration solution to improve water efficiency. Results showed that most salts are removed by reverse osmosis and that its coupling with ultrafiltration allows obtaining very high quality water; reuse of desalinated wastewater resulted in being more suitable and economically viable than its discharge. Moreover, modelling and simulation showed that the considered blowdown could be reused without significant changes in the receiving water network area. The industrial implementation of water recovery solutions can lead to a decrease of fresh water consumption, effluent discharge, and to improvement of product quality and equipment service life. The considered desalination technologies are transferable and easily implementable, and modelling and simulation are very useful in order to evaluate process modifications before real implementation.

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Steel industry consumes resources and produces important amounts of by‐products. Process modeling, simulation, and optimization can address field tests for maximizing by‐products reuse. The improvements of a long‐lasting research activity on slag reuse by deepening aspects, only marginally considered in the past, are presented herein. An Aspen Plus‐based model is developed to assess different basic oxygen furnace slag pretreatment configurations or involved techniques. A previously developed superstructure is upgraded, considering more slag pretreatments and qualities. A simplified Aspen Plus‐based model of mixing of the different pretreated by‐products is applied to evaluate the chemical composition of pellets in each scenario, starting from the computed mixtures. The developed tools are exploited to get a holistic view of steelmaking by‐products reuse and make multiobjective optimization studies which provide different results. For instance, the mixture to be pelletized completely changes if final product quality is (or not) considered in the optimization. Regarding the optimization combining all the considered objective functions, the best slag treatment includes a wet high‐intensity magnetic separation stage, and only some slag qualities are considered in the pellet mixture. A preliminary economic analysis confirms that an optimal combination of internal and external recoveries of by‐products can produce noteworthy revenues.

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