Numerical simulation of fumes evacuation in steelmaking plants

Evacuation systems in steelmaking plants contribute to the security of the operators around the furnace and help to gain the emission levels stated in the environmental regulations, furthermore play a major role in the mass and heat balance of the factory. The aim of the dissertation is to study both primary and secondary emission capture systems of an electric arc furnace steelmaking plant by means of 3D computational thermal fluid dynamics calculations. The overall performance of the post-combustion chamber, and consequently the primary line, is controlled by the size of the gap downstream the fourth hole of an electric are furnace. The impact of the opening coefficient (ratio between the gap area and the total area) on the post-combustion chamber performance has been investigated by means of a comprehensive 3D steady CFD simulation comprising radiative heat exchanges and detailed chemical reactions. It was found that there is not a unique value of the opening coefficient capable of optimizing all the relevant quantities of the evacuation process. A value of the opening coefficient in the range 0.40-0.52 appears advisable. The impact of the (mostly unknown) boundary conditions was also assessed and inefficiencies of the assumed post-combustion geometry have been highlighted. The secondary line's capturing efficiency during the charging phase was simulated with both transient and steady-state solvers with different turbulent models, namely the standard k-e and the Large Eddy Simulation models. The results revealed that steady-state simulations provide sufficient information for designing and optimizing the geometry of the secondary capture system. The simulations also pointed out several geometries, which cause significant pressure drop and, as a result, diminish capturing ability of the canopy hood and the additional evacuation system. The boundary conditions were imposed with the help of experimental measurements in the simulated steelmaking factory.