Numerical Study on the Effect of Material Parameters and Process Conditions on the Melting Time of Hydrogen-Direct Reduced Iron

Abstract The melting time of hydrogen direct reduced iron pellets (H-DRI) is a limiting factor for productivity in electric arc furnace steelmaking for fossil-free steel. The effect of material and process parameters on melting time was evaluated under laminar conditions using computational fluid dynamics. The study found that the melting time of H-DRI is primarily determined by the properties of the slag bath and its movement, with H-DRI properties being secondary. The shortest melting time was achieved by combining high temperature (> 1950 K), high viscosity foam (> 0.1 Pa s), and high thermal conductivity (> 0.9 W m −1 K −1 ) of the slag. With optimal conditions a melting time of 4.56 seconds was observed for a 10 mm diameter H-DRI, although thicker slag with lower terminal velocity was shown to have greater potential for complete melting of the pellet within the slag. Decreasing H-DRI porosity from 65 to 50 pct with maintained mass increases melting time by 4 pct and increasing initial temperature from 300 K to 1100 K decreases melting time by 20 pct. Furthermore, an increased bath temperature from 1850 K to 1950 K results in approximately 55 pct reduction in melting time due to increased superheat. Forced convection in the system was also found to significantly reduce the melting time for H-DRI.