Numerical Study of the Gas Flow and Heat Transfer during Electromagnetic Stirring and Post Combustion in EAFs

Sammanfattning: The effect of electromagnetic stirring on scrap melting and post combustion in two different electric arc furnaces (EAFs) have been studied using numerical modelling. The effect of electromagnetic stirring on melting of a piece of scrap located at the eccentric bottom tapping (EBT) region of an EAF has been studied. The results were compared to a condition in which the only source term for momentum transfer was buoyancy. It was shown that the use of electromagnetic stirring can contribute to a better heat transfer rate at the melt–scrap interface. The Grashof and Nusselt number for both electromagnetic stirring and natural convection were estimated, and were compared with those estimated in previous studies. The post combustion (PC) inside a duct system of an EAF has been studied considering combustion of hydrogen and carbon monoxide. The aim was to study the effect of air leakage through the airgap and fan power on post combustion of the off–gas leaving the furnace. Furthermore, to see how much uncombusted can be captured after the air gap. It was shown a higher off-gas mass flow rate and a higher power of the outlet fan led to a higher combustion of CO and H2. Moreover, a backward modeling of the flow was done to estimate the off–gas composition at the furnace outlet. The post combustion inside the same EAF used in the previous part has been studied. The domain consists of the fluid region above the melt bath. The oxy fuel reactions and combustion of CO were taken into account. The oxy-fuel reactions in a both simplified and a more accurate form (JC) were studied. The results showed less combustion of CO in the latter form. Using the results of the off–gas composition at the outlet, an attempt was made to estimate the flow rate of CO arising from the bath. Different flow rates of CO from the melt and air flow rate through the roof were assumed. In both burner mode and burner + lancing mode, the calculated concentration of CO2 was higher than that calculated in the previous part. The reason could be that the dissociation of CO2 to CO and O2 at high temperatures, and the de-post combustion of CO2 due to the reaction with carbon in the melt and in the electrodes were not considered.