Modeling Of Gas-liquid Two Phase Flow And Decarburization In RH Degassing Vessel With Swirling Flow

Secondary refining is one of the most important technologies in modern steelmaking process. Now, most researches focus on improving the efficiency of secondary refining system and quality of molten steel. RH refining system is widely used in secondary refining, but there are still some problems, such as life of up-leg is short, utilization rate of argon is low, decarburization is not enough and so on. These problems restrict the improvement of the quality of production.In the present work, some methods were put forward to improve the efficiency of secondary refining process on the basis of physical rules. A 3D mathematical model including ladle, up-leg, down-leg, vacuum vessel has been developed to analyze motion of Ar gas bubbles and to understand how electromagnetic improve the efficiency of refining .RH vacuum degasser is a multi-function metallurgical reactor; Deep decarburization, inclusion removal are the key technologies of it. On the basis of flow field, decarburization and particle motion models have been built to understand the decarburization process, non-metal inclusion motion behavior in RH system with swirling flow.(1) Improve utilization rate of argon applying swriling flowUtilization rate of argon is main factor that affect the efficiency of RH system. In the present work both water model experiments and numerical simulation were developed to show the transient distribution and trajectory of the gas bubbles. A novel process was found to get larger number of bubbles and disperse the coalescence bubbles using the difference of centrifugal forces between gas and liquid in swirling flow. This phenomenon was called "bubble curtain", it is very useful to improve the utilization rate of argon and circulation flow rate of RH system. But, with the increase in swirling number, bubble column appear at the centre of up-leg, then the utilization rate of argon decline.(2) Develop gas-liquid two phase flow model on the basis of population balance model Population balance model is widely used in chemical industry and nuclear science. The population balance approach can better describe and understand complex flow systems, especially with the consideration of bubble coalescence and breakup mechanisms. In present work, Population balance model was used to simulate bubble distribution in RH system. The results show that the bubbles with large Sauter diameter appear at the zone near the wall of up-leg in RH system without swirling flow. The Sauter diameter of the bubbles become smaller and more uniform when swirling flow was used. And, with the increase in swirling number, bubbles with larger Sauter diameters appear at the center zone of up-leg.(3) Study the trajectories of gas bubbles in swriling flowNonmetallic inclusions removal is another important function of RH system. Nonmetallic inclusions such as alumina and silica can be captured by gas bubbles and floated up to the free surface in RH system. The development of these processes has been focused on achieving two conditions: number of gas bubbles and chance for both bubble and inclusion to meet with each other. So it is important to understand the behavior inclusions in RH degasser considering electromagnetic stirring. Molten steel is stirred through horizontal swirling flow driven by rotating magnetic field, particles such as nonmetallic inclusions contained in molten steel, which densities are small compared with the density of the molten steel, are moved towards the central area of the reactor because of the difference in the centrifugal force. Numerical results for inclusion motion showed that trajectories of non-metal inclusion are the spiral, and it can prolong the trajectories of the non-metal inclusion particles in the RH degassing vessel using the swirling flow. The viscous drag force is important for small inclusions in the RH degassing vessel, which have the trend to flow with molten steel. Therefore, some inclusions cannot move up to surface of bath.(4) Decarburization in RH system with swirling flowDeep decarburization is one of important metallurgical functions of RH system. On the basis of the flow field, a coupled mathematical model was developed to analyze decarburization process with swirling flow. Numerical results show that the decarburization process without swirling flow is in agreement with experiments in literature. At the first stage of the reaction, when magnetic flux density is 0.04T, the decarburization rate of RH system with electromagnetic stirring is 15% larger than that without electromagnetic stirring, with increase of the magnetic flux density the decarburization rate obviously rise. The carbon content converges at the last decarburization process.