Mathematical And Physical Simulation On RH Vacuum Refining Process

RH vacuum refining is a complicated metallurgical process which involves in multiphase flow, heat transfer and various chemical reactions. By increasing circulation flow rate and shortening mixing time, the RH production rate can be increased in actual system. Therefore, in order to take full advantage of the production efficiency of RH degasser and reduce production costs, it is necessary to have a deep insight into the transport process in RH.In present work, several mathematical models have been developed to study the gas-liquid flow, decarburization process and the collision and growth among inclusions. The transport behavior in RH with traditional side blowing, RH with side-bottom blowing and electromagnetic RH have been investigated by the above mathematical models. On this basis, the mathematical model concerning collision and coalescence among inclusions in gas-stirred ladle has been developed to study the effect of different types of bottom blowing on the inclusion removal process. In addition, the double bottom blowing locations in ladle have been optimized. The results are as follows:I. The transport behavior during RH vacuum refining process(1) A 1: 5.5 scale water modeling of the RH prototype has been developed and the effects of different operating parameters on the circulation flow rate, mixing time, top blowing oxygen absorption and decarburization process have been investigated. By regression on the base of experimental data, the empirical correlations for the circulation flow rate and mixing time are as follows:(2) The side-blowing gas behavior has been studied and the formula for the horizontally blowing gas penetration depth is as follows:A mathematical model of gas-liquid flow in RH degasser has been developed and the numerical results show that the lifting gas flow rate is the key factor to determine the distribution of gas holdup.(3) A three dimensional mathematical model considering different decarburization mechanisms and a homogeneous model concerning the collision and growth among inclusions in RH degasser have been developed to investigate the effects of different operating parameters on the inclusion removal process. By introducing the Stokes collision among inclusions into the inclusion mass and number conservation model, a mathematical model about inclusion behavior in RH degasser has been developed to give the three dimensional spatial distributions of inclusion number density and concentration in RH degasser.II. The transport behaviors during RH with side-bottom blowing and electromagnetic RH(1) For RH with bottom blowing, when the included angle of the line between bottom blowing location and ladle center and the line between two snorkels 0 is zero, the circulation flow rate increases with the increasing distance between bottom blowing location and ladle center L firstly, and then decreases. In addition, the mixing time increases with the increasing L. When L is equal to 0.535m, the circulation flow rate decreases with the increasing 6. In addition, the mixing time decreases with the increasing 9 firstly, and then increases.(2) For RH imposed by traveling magnetic field, with the increasing current density, the circulation flow rate increases linearly and the mixing time decreases linearly. If the current frequency lies in the range of 10～30Hz, with the increasing current frequency, the circulation flow rate increases while the mixing time decreases. If the current frequency lies in the range of 30～60Hz, with the increasing current frequency, the circulation flow rate decreases while the mixing time increases. In order to increase circulation flow rate and shorten mixing time, the most effective measure is to apply the traveling magnetic field near the up snorkel, and the second choice is to apply the traveling magnetic field near the down snorkel if the gas flow rate is smaller than the saturation value. However, such a difference disappears if the gas flow rate is greater than the saturation value. For decarburization and inclusion removal, the most effective measure is to apply the traveling magnetic field near the up and down snorkels, and to apply the traveling magnetic field near the up snorkel has the minor effect.III. The transport behavior in the gas-stirred ladle(1) By introducing the model of inclusion adhesion to gas bubble into the inclusion mass and number conservation model, a three dimensional mathematical model is developed to investigate the inclusion removal process in ladle. The numerical results show that the type of bottom blowing is the key factor for inclusion removal. The triple bottom blowing is the most effective method for inclusion removal, while the double bottom blowing has a minor effect and the eccentric bottom blowing is better than the centric bottom blowing. For inclusion removal, the absorption by the top slag is the main manner, the adhesion to the sidewall is the minor manner, and adhesion to the bottom wall can be negligible.(2) The double bottom blowing locations in ladle have also been optimized and the results show that there is a unique optimum offset of double blowing locations for a particular included angle and vice versa. The correction for the mixing time for the ladle with double bottom blowing can be expressed as:...