Mathematical Model of the melting of DRI in a slag melt
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Mathematical Model of the melting of DRI in a slag melt Marco A. Ramírez-Argáez1, Carlos González-Rivera1 1 Facultad de Química, UNAM, Departamento de Ingeniería Metalúrgica. Edificio “D” Circuito de los Institutos s/n, Cd. Universitaria, C.P. 04510 México D.F., México. ABSTRACT Melting of Direct Reduced Iron (DRI) pellets in Electric Arc Furnaces (EAF) in steelmaking production is a common practice worldwide. Mathematical models are proper tools to study the phenomena involved in melting DRI. In this work we develop a mathematical model to predict melting kinetics of DRI in a liquid slag bath. The model is successfully validated against experimental results and it is used to develop a process analysis to estimate the effects of DRI size, stirring conditions, and temperatures of the bath and pellet on the melting kinetics of DRI. INTRODUCTION Melting of DRI in Electric Arc Furnaces is becoming a regular practice around the world since scrap prices are unstable and there is a global shortage of scrap. However, electric energy is expensive and the consumption is almost duplicated when the furnace is 100% charged with DRI than when the full charge is scrap. Therefore, it is necessary to understand from first principles the phenomena governing melting kinetics of DRI. Pellets are charged into the EAF through the top by gravity in a steel hot heel. Phenomena governing melting DRI are heat transfer from the bath to the particle. It is well known that when a solid cold particle (a sphere as in the case of DRI) is added to a hot bath, a layer of solid coming from the frozen liquid solidifies and makes the sphere to grow, reaches a maximum size and then gradually decreases its radius until fusion is completed [1]. Several works have been presented that study this melting kinetics by performing experiments in real metallic baths [2]. Those works are able to track the size of the particles and to determine the fusion kinetics as a function of stirring degree of the bath, bath and particle initial temperatures, and particle initial size. Also, several works have been published where mathematical models based on heat and/or mass transfer are developed to predict the melting kinetics [1]. The majority of these articles numerically or analytically solved the energy conservation equation in the particle subjected to a convective (heat or mass) boundary condition at the particle-liquid interphase in a mobile boundary problem. However, these papers considered only the case of a solid addition being incorporated into a melt of equal composition, but in the case of EAF, the porous Fe particle or DRI added at the top does not reach the steel bath but stays in the liquid slag layer, which is on top of the steel. Only Elliot [3] made a first approximation to measure and to predict melting kinetics of DRI in liquid slags. In this paper, a mathematical model is developed to simulate the melting kinetics of a DRI particle in a liquid slag. The model is successfully validated against measurements, and it is used to perform a process analysis
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