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Description
Direct Reduced Iron (DRI) particles present high porosity, between 40 and 70% with a bi-modal pore size distribution around 1 and 7 µm, as seen in Figure 1. Their melting in an Electric Smelting Furnace (ESF) slag displays complex behaviour involving chemical reactions, heat transfer, and fluid-solid flows, resulting in rheological changes in the porous DRI matrix such as a reduction in porosity due to iron sintering [1] or slag infiltration through the DRI pores [2]. The slag flowing through the pore channels of the particle impacts significantly heat transfer by modifying the DRI's effective thermal conductivity. It also contributes to an increase in particle density which can determine whether the particle floats or sink at the slag interface, as seen in small-scale melting experiments.
A description of local heat and mass transfer between slag and DRI is crucial for understanding the ESF process. In this work, Computational Fluid Dynamics (CFD) are used to describe the particle-scale melting of a single DRI particle in an ESF slag. The results are compared to various experimental data. The final goal of this work is to obtain a representative melting model to couple with a large-scale numerical model of the ESF.
The free code platform Basilisk, containing a DNS code using dynamic adaptive mesh refinement and developed at Sorbonne University, is used to model the DRI melting process. A first study is conduced with a simplified isentropic configuration to investigate the slag infiltration evolution in the particle during its heating. Mean physical parameters are introduced using local porosity and slag saturation in the pores. Solids and liquids are differentiated using temperature-driven properties, determined with in-house thermodynamic calculations. Flow through the pores is modeled using Darcy’s law, with capillary pressure acting as the driving force, thanks to a small contact angle and high surface tensions. Results highlight that infiltration is limited by temperature diffusion in the particle, as slag solidifies rapidly in the pores around the colder iron matrix.
In a second time, the flow of air, slag, and metal is considered in the domain representing a DRI particle in a crucible of similar dimensions to the ones used in the experiments. Using the results from the first study, slag infiltration is supposed to depend only on temperature diffusion, thus allowing the determination of local slag saturation in the pores using only local temperature, without solving Darcy’s equation.
This model was used to simulate the melting of a single H-DRI. The evolution of temperature distribution within the DRI presented in Figure 2 matches experimental data found in the literature [3]. Sinking time of particles reported in Figure 3 match with experimental data, showing a good determination of slag infiltration time scales by the model.
New simulations are to be conducted at the pore scale as the flows of air, slag and metal will be considered in the domain representing the porous matrix. This will enable a more detailed analysis of the local phenomena responsible for rheological changes, such as slag solidification in the pores.
| References | [1] J. Li, M. Barati, Kinetics and mechanism of decarburization and melting of direct-reduced iron pellets in slag, Metallurgical and Materials Transactions B, 40, 17–24 (2009). [2] J. Huss, A. Vickerfält, N. Kojola, The Melting Mechanism of Hydrogen Direct Reduced Iron in Liquid Slag, Steel research international, 95, 2300325 (2024). [3] R.J. O’Malley, The heating and melting of metallic DRI particles in steelmaking slags, PhD Thesis, Massachusetts Institute of Technology (1983). |
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| Country | France |
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