Flow Characteristic of Supersonic Jet Related to O₂–CO₂ Mixing Injection Method

The O₂–CO₂ mixing injection method was proposed to mitigate CO₂ emissions and enhance the CO content in flue gas during the BOF steelmaking process. Despite the reported advantages of the O₂–CO₂ mixing injection method, limited research existed regarding the impact of Laval nozzle structures designed by various CO₂ mixing rates on the flow characteristics of supersonic mixing jets. In this research, we investigated four types of Laval nozzle structures designed for varying CO₂ mixing rates through a series of experimental tests and numerical simulations. The results indicated that when the CO₂ additional flow rate increased from 0 to 15 mass pct, the impaction ability of the mixing jet enhanced. However, this increasing rate was gradually suppressed due to the thermo-physical property variations between O₂ and CO₂. Under room and high ambient temperature conditions, the average axial velocity variation within the velocity potential core was 1.58 and 1.68 m/(s·mass pct), respectively. To further validate the metallurgical effects, a pilot test was conducted using a 1.0 ton converter with O₂ and CO₂ blowing rates of 210 and 31.5 Nm³/h, respectively, demonstrating that the Laval nozzle structure designed based on the O₂–CO₂ mixing gas thermo-physical property could achieve superior metallurgical outcomes.