The effect of slag properties (thickness and viscosity), have been evaluated in terms of mixing time, exposed surface or ladle eye and energy dissipation. A nozzle configuration defined in terms of the number of nozzles, its radial position and gas flow rate has been employed to describe the influence of the top layer on mixing phenomena. It has been found a negative effect of both slag thickness and slag viscosity on mixing time, on the other hand, the same properties are useful to decrease the exposed surface or ladle eye.An empirical approach using water modeling is suggested to evaluate the average velocity of the bulk liquid. The method was used to define the fraction of stirring energy consumed by the top layer. The result is in agreement with a previous investigation.
Recent Electric Arc Furnaces are equipped with ultra high power transformers to provide maximum values of electric power and minimize the melting time. The active power is increased by increasing arc length and arc voltage, however in these conditions energy losses due to radiation can also be increased with a consequent decrease in thermal efficiency. The energy radiated from the electric arcs is transferred to the walls inside the EAF promoting hot spots which represent a catastrophic operational condition. This work reports a radiation model which describes the formation of hot spots as a function of arc length and foamy slag height in an industrial EAF of 210 ton. of nominal capacity. Temperature profiles on the surface of the water cooled panels and values for the incident radiation were computed as a function of foamy slag height, used subsequently to define conditions to eliminate the formation of hot spots.
A computational fluid dynamics model coupled to a lagrangian model of melting/solidifying particles has been developed to describe the melting kinetics of metallic particles in an industrial Electric Arc Furnace (EAF), assuming that liquid steel occupies the entire computational domain. The metallic particles represent Direct Reduced Iron (DRI). The use of two previous models, an arc model and a fluid flow model has made possible to evaluate the melting rate of injected DRI in a three phase-EAF, evaluating the influence of the initial particle size, the initial DRI temperature, feeding position, feeding rate, arc length and some of the metallurgical properties of DRI. The frozen shell formed in the early stage of the melting process has also been evaluated in this model. KEY WORDS: DRI melting; CFD; melting rate. 9© 2010 ISIJ that the thickness of the frozen shell is negligible in comparison with the radius of the particle, therefore, in the thermal balance the radius employed is not the radius at the liquid-particle interface but the initial particle radius, as follows:.............. (1) Sato et al. 6,7) reported laboratory experimental results from the melting of pre-reduced pellets in liquid steel and in molten slags. They found an increase in the melting rate by increasing metallization of pellets and by increasing the temperature of the molten bath, however, once the temperature reaches 1 570°C a further increase has no significant effect on the melting rate.Aboutalebi et al. 8) reported the influence of particle size, temperature and stirring conditions on the melting rate of metallic particles in a ladle. In this work the formation of the solid shell was neglected. They concluded that the melting rate increases by decreasing the particle size and by increasing both superheat temperature and stirring conditions. Similar results have been reported by Jiao and Themelis 9) and Ji et al. 10)Zhang and Oeters 11) described a mathematical model to represent the melting process of ferromanganese particles thrown into a steel ladle. They found a short time, less than 1 s, to reach the terminal velocity inside the melt and such velocity was used to compute the heat transfer coefficient. A melting distribution time to represent the melting rate of all particles was used to define the melting time of a variable particle distribution. It was found a higher melting rate as both the terminal velocity and melt temperature increases.Several works have been reported on scrap melting in Electric Arc Furnaces (EAF). Matson and Ramirez 12) investigated the melting process of scrap assuming spherical iron particles. Gaye et al. 13) suggested a maximum scrap size of 120 mm in the converter to avoid unmelted scrap at the end of the blow. Szekely et al. 14) attributed a key role to carbon dissolved in liquid steel to facilitate scrap melting. Li et al. 15) used steel bars with various sizes to describe scrap melting.An integral approach coupling heat, mass and fluid flow phenomena to understand the DRI melting and dissolu...
In this work, the effects of equal (50%/50%) or differentiated (75%/25%) gas flow ratio, gas flow rate, and slag thickness on mixing time and open eye area were studied in a physical model of a gas stirred ladle with dual plugs separated by an angle of 180°. The effect of the variables under study was determined using a two-level factorial design. Particle image velocimetry (PIV) was used to establish, through the analysis of the flow patterns and turbulence kinetic energy contours, the effect of the studied variables on the hydrodynamics of the system. Results revealed that differentiated injection ratio significantly changes the flow structure and greatly influences the behavior of the system regarding mixing time and open eye area. The Pareto front of the optimized results on both mixing time and open eye area was obtained through a multi-objective optimization using a genetic algorithm (NSGA-II). The results are conclusive in that the ladle must be operated using differentiated flow ratio for optimal performance.
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