Numerical And Physical Simulation On KR Hot Metal Desulfurization Pretreatment

KR hot metal desulfurization pretreatment is one of the hot metal desulfurization technologies which are widely used currently. Especially in recent years,KR desulfurization pretreatment has raised more and more attention and concern among many large steel plants. KR method has a great advantage in deep desulfurization and ultra-deep desulfurization. But because of the stirring mixing feature of KR method,most of the limes which are put into the hot metal will aggregate under mechanical stirring. When the aggregation behavior happen, the desulfurization reaction would occur only on the outside of the limes after aggregation, besides,the dispersion of the desulfurization flux is not ideal and the utilization rate of limes is low, usually only about 10 percent. The low utilization rate caused the consumption of flux increased. In addition, it led to high temperature drop and iron loss.The stirring process of Baosteel plant which is currently used is evaluated and optimized based on Baosteel KR stirring devices and stirring method by combining physical and mathematic simulation. Besides, in order to increase the utilization of the desulfurization flux, decrease the consumption of the limes and improve the KR stirring effect, the laboratory research is carried out from the structure of stirrer, the flux addition method,the stirring vessel structure and the flow control devices on the vessel wall.Results of the numerical and physic simulation optimization on Baosteel stirring process which is currently used show that the insertion depth of stirrer should be 1.65 m and the rotating speed should be 120r/min when using the new stirrer, the insertion depth of the old stirrer should be 1.5m and the rotating speed should be 140r/min. But due to the restriction of Baosteel equipment which is currently used,the insertion depth of the new stirrer should be 1.35 m and the rotating speed should be 100r/min; the changing position stirring method can improve the stirring mixing condition and the kinetics condition in the bath.; based on the final optimization result, the optimization model of the relationship between the best stirring process parameter and the ratio of radius is concluded which is suitable for the Baosteel equipment currently used.Results of the numerical and physic simulation on baosteel KR desulfurization kinetics optimization show that the ratio of stirrer to hot metal vessel should be controled around 0.4 in actual production process; 3 blades abnormal stirrer has a better stirring kinetics condition and the mass transfer coefficient increases to 1.5 times combined with the 4 blades normal stirrer;Combined with the batch flux addition, the continues addition has a better advantage on improving K R desulfurization solid- liquid mass transfer rate; the mechanical stirring method combined with gas blowing can promote the flow in the batch,decrease the mixing time and the area ratio of weak flow zone. In actual production process, the ratio of the liquid level height to the vessel diameter is reasonable to be around 0.9; the addition of baffle can reduce and eliminate the center vortex, suppress the aggregation of flux,enhance the dispersion of flux, increase the utilization of desulfurization and mass transfer rate. The results show that the effect of the addition of long baffles is better than the short baffles and the effect of the addition of 2 baffles achieve the best among all the addition method; after the addition of the baffles, the changing position and constant rotating speed stirring combined process can promote the mixture of bath and the dispersion of desulfurization flux; compared with adherent baffles, the addition of baffles which are away from the vessel wall is better for the flux to be entrained and promoting the dispersion of flux, in actual production process, the gap between the vessel wall and baffle should be controled around 70 to 105 mm.