As a result of the global transition towards green steel production, integrated steel plants are optimizing the existing processes and/or adopting new steelmaking methods to minimize their carbon footprint. These adjustments affect desulfurization conditions and requirements. The present study examines how the desulfurization is impacted for both hot metal and liquid steel across three routes: the traditional blast furnace (BF) - basic oxygen furnace (BF-BOF) with increased scrap ratio, the direct reduced iron (DRI) - electric arc furnace (EAF) with varying scrap to DRI ratios, and the DRI - electric smelting furnace (ESF) - BOF. This work discusses challenges and possible solutions for each route.

HIsarna reactor is characterized by a high raw materials versatility and is therefore attractive for processing secondary iron sources. Among the materials that can be recycled through HIsarna, zinc-bearing material has drawn a special attention. Based on the plant data, once dust-containing Zinc was injected into the main reactor, a final collected dust with a zinc content of 16% was achieved which opened up possibilities of higher enrichment for direct reuse in Zn smelting as a secondary source and an alternative for Zn ore (the primary source). However Zn vapor can react with iron oxide to form zinc ferrite (ZnFe₂O₄), which is an undesired product. Hence, the main focus of this study is to minimize the formation of ZnFe₂O using thermodynamic (FactSage) and computational fluid dynamic tools. After detecting regions with high potential of ZnFe₂O₄ formation, proper geometrical and operational modifications of the off-gas system is proposed to minimize the formation of zinc ferrite.

In hot metal desulphurisation (HMD) the slag will hold the removed sulphur. However, the iron that is lost when the slag is skimmed off, accounts for the highest costs of the HMD process. These iron losses are lower when the slag has a lower viscosity, which can be achieved by changing the slag composition. A lower slag basicity decreases the viscosity of the slag, but also lowers its sulphur removal capacity, therefore optimisation is necessary. In this study, the optimal HMD slag composition is investigated, considering both the sulphur removal capacity and the iron losses. In part I the theory is discussed and in part II the optimal slag is validated with plant data, laboratory experiments and a thermodynamic analysis.

The optimal hot metal desulphurisation (HMD) slag is defined as a slag with a sufficient sulphur removal capacity and a low apparent viscosity (η_slag) which leads to low iron losses. In part I of this study, the fundamentals behind the optimal slag were discussed. In this part these fundamentals are explored by a Monte Carlo simulation, based on FactSage calculations, plant data analysis and melting point and viscosity measurements of the optimal slag. Furthermore, the applicability of knowing the optimal slag composition for an industrial HMD is discussed.

The slag in the hot metal desulphurisation (HMD) process should have a high sulphide capacity to capture the sulphur and a low viscosity to minimise the iron loss; in particular the emulsion loss. Although the slag composition changes during the HMD process as a result of reagent injection, the initial slag from the blast furnace (BF) is still the main constituent of the slag after HMD. Therefore, an average composition of BF slag is used as a starting point in this study. Using FactSage 7.1 thermochemical software, the influence of slag composition and temperature on the sulphide capacity is calculated. The slag basicity (CaO/(Al2O3+SiO2)) has the strongest influence on the sulphide capacity. Furthermore, the influence of CaO and temperature on the liquid viscosity and solid fraction of the slag is calculated and compared with plant data from Tata Steel, The Netherlands. Although the addition of CaO decreases the viscosity of the liquid part of the slag, neglecting the solid particles, it strongly increases the solid fraction of the slag. Based on the Einstein-Roscoe theory, more CaO leads to a higher slag viscosity and consequently a higher iron loss.