Optimization of By-Products Reuse in the Steel Industry: Valorization of Secondary Resources with a Particular Attention on Their Pelletization

Abstract

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

Scenario Analyses for By‐Products Reuse in Integrated Steelmaking Plants by Combining Process Modeling, Simulation, and Optimization Techniques

“…In addition, it can give high‐quality pellets for internal reuse in the sinter plant by selecting, for instance, the best BOF slags to be reused or the best magnetic separation technique (MST). In this way, a further improvement has been obtained with respect to results previously achieved …”

“…Following the previous explained approach and considering the described background, this work deepens the results previously obtained, by providing more detailed indications about BOF slag treatment and by‐products reuse and by providing upgraded or new tools, which are more suitable to make multiple scenario analyses. For this reasons, two software were used, namely, Aspen Plus and reMIND.…”

“…According to this objective, the found amounts of different by‐products (Table ) have been included in the ASP_2 model together with fixed amounts of lime and cement corresponding, respectively, to 1 and 7 wt%, according to the indications reported in a previous work . The simulations give the pellet compositions that are shown in Table ; in this table, also the chemical composition of the “winning formula” of the pellet obtained in a previous work is reported …”

“…In addition, the required additives that allow obtaining a good quality pellets are included (i.e., lime and cement). The model includes some mixers and a “design specification block” that adjusts the quantity of required water to obtain a humidity of the slag mixture of about 14%, representing the humidity that gives the best results in real trials . The flow sheet of the model is shown in Figure .…”

“…One of the main feature of this model is the possibility to consider and compare different magnetic separation solutions at the same time. Furthermore, a renewed software implementing the Method for analyses of INDustrial energy systems ‐ MIND (reMIND) superstructure has been upgraded, compared with the work already done and described . Models developed by the reMIND software are material flow superstructures, implementing results of the treatment models, to evaluate the way to reuse by‐products and coproducts in a more efficient mode and to produce high‐quality raw materials, such as pellets to be used in the sinter plant.…”