Computational fluid-dynamics simulation of postcombustion in the electric-arc furnace
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Computational Fluid-Dynamics Simulation of Postcombustion in the Electric-Arc Furnace YUN LI and RICHARD J. FRUEHAN To obtain insight on the characteristics of postcombustion (PC) inside an electric-arc furnace (EAF), a three-dimensional computational fluid-dynamics (CFD) model was developed. Simulations of the process, including the PC reactions, radiation heat transfer, and de-PC reactions have been conducted. Dissociation reactions of the PC products were also considered in the PC model. The predicted temperatures are realistic because of the inclusion of radiation and the dissociation of CO2. Based on gas/liquid and gas/solid interfacial reaction kinetics, a de-PC reaction model was developed and successfully integrated into the CFD model to simulate the reactions between O2/CO2 and carbon in the liquid metal, the electrodes, and the scrap. It was found that the de-PC reactions decrease the net heat generated by reactions in the furnace and decrease the PC ratio. The rate of oxidation of the electrodes was also calculated. Radiation was found to be the main heat-transfer mechanism from hot combustion gas to the metal and furnace wall. Under a flat-bath condition, the heat-transfer efficiency is very poor; most of the heat generated by PC is transferred to the furnace wall. When a low-temperature scrap pile exists in the furnace, the heat-transfer efficiency is improved significantly. Air ingress from the slag door significantly decreased the PC ratio and the heat-transfer efficiency.
I. INTRODUCTION
IN steelmaking processes, carbon monoxide is produced when oxygen is reacted with carbon, releasing energy. The CO gas can be further oxidized to CO2 if mixed with oxygen before leaving the furnace. If CO2 is produced, it releases about 3 times the energy released by oxidation of carbon to CO. In electric-arc furnace (EAF) steelmaking, more carbon and scrap substitutes containing carbon are being charged than previously. In a typical heat in the state-of-the-art EAF–flat-rolled plant, about 1.5 kmol of CO is generated per ton of steel, which, if combusted to CO2, represents 425 MJ of energy. The potential use of this energy and the corresponding increase in productivity is the economic driving force behind postcombustion (PC) technologies. Two goals must be achieved to get the maximum benefit from PC. First, the way of introducing oxygen and the amount of oxygen introduced must be optimized to achieve a high PC ratio. Second, the heat generated from PC must be efficiently transferred to the solid scrap or liquid metal and not leave the furnace as high-temperature gas. The heat transferred to the furnace wall must also be minimized. Because of the high temperature involved, it is difficult, if not impossible, to do a physical study on the characteristics of the flow, combustion reactions, and heat transfer inside the steelmaking furnace. With the availability of increasing computing power and development of commercial codes for computational fluid dynamics (CFD), a number of numerical studies have been carried out
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