Study On The Formation And Distribution Of Micro-bubbles In Tundish

With the increasing requirements for the quality of steel products,the purity requirements of many high-performance steel grades are also getting higher and higher.The key to improving the quality of steel products and producing pure steel is to control inclusions.Using methods such as furnace refining and tundish flow control technology can easily remove inclusions larger than 50?m in molten steel;ultra-fine and dispersed inclusions smaller than 1?3?m can become the nucleation core of intragranular ferrite,refine the grain,and improve the quality and performance of steel.Therefore,the removal of small inclusions of 3?50?m in steel,especially the removal of inclusions less than 20?m,is one of the important issues that must and urgently need to be solved in the steelmaking process.In the tundish metallurgical process,the strong turbulent molten steel brought by the large ladle injection is used to cut the gas blown into the shroud into micro-bubbles,and the key to the technology to remove small inclusions in the molten steel lies in how to obtain uniformly dispersed micro-bubbles and how to ensure the mixing conditions between molten steel and micro-bubbles.Therefore,it is particularly important to deeply study the formation and distribution characteristics of micro-bubbles and the mixing behavior of micro-bubbles and molten steel.This paper will use numerical simulation research methods to study the formation and distribution characteristics of micro-bubbles in the tundish under strong turbulence conditions,and to study the influence of micro-bubbles on the flow behavior of molten steel in the tundish.On this basis,a new method is found.The method is to control the flow pattern of molten steel in the tundish and create good conditions for the full mixing of micro-bubbles and molten steel.The main research content includes the following aspects:A three-dimensional mathematical model of the gas-liquid two-phase flow in the tundish is established,and the influence of micro-bubbles on the flow behavior,temperature distribution and inclusion removal effect of the molten steel in the tundish is systematically studied.Compared with no air blowing,the fluid jet angle in the tundish after air blowing increased from 3°to 17°;the maximum turbulent kinetic energy in the tundish increased from 0.81694 m~2/s~2 to 1.07746 m~2/s~2;the liquid level fluctuation increased from 2.3 mm to 3.1 mm;the average residence time in the tundish has been extended from 511.3 s to 534.2 s,the volume fraction of the dead has been reduced from 21.2%to 16.8%,the ratio of the plug to the dead has been increased from 0.73 to 1.06.Orthogonal experiments are used to study the influence of the nozzle aperture,the number of blow holes and the distribution parameters of blow holes on the average residence time of molten steel in the tundish,flow pattern,temperature distribution and inclusion removal effect.After the first optimization of the blowing method by the intuitive analysis method of the orthogonal experiment,the second optimized blowing method is selected.The obtained second optimal blowing method is that the distribution of blowing holes is 2 rows,the blowing hole diameter is 1.0 mm,and the number of blowing is 6;the second best blowing hole distribution is 1 row,and the blowing hole diameter is 1.0 mm,the number of blows is 12.Then compare the secondary optimization schemes and select the optimal blowing method.Finally,on this basis,the single factor analysis method is used to study the influence of the parameters such as the nozzle aperture,the number of blowing holes,the distribution of blowing holes and the amount of blowing on the formation and distribution of micro-bubbles in the tundish.With the increase of the blowing aperture and the number of blowing holes,the distribution of the formed micro-bubbles in the tundish is more diffuse;the smaller the blowing volume,the more dispersed distribution of the formed micro-bubbles in the tundish.In order to stabilize the dispersion and distribution of micro-bubbles in the tundish and promote the full mixing of micro-bubbles and molten steel,three new flow control devices are designed.The effect of the new flow control device on the distribution of micro-bubbles in the tundish and the gas-liquid two-phase flow behavior of micro-bubbles and molten steel is studied,and a better structure of the new flow control device is obtained.Compared with no new flow control device,No.1 new flow control device has a better effect on improving the flow pattern.The average residence time in the tundish is extended by 32.4 s,and the volume fraction of the dead is reduced by7.2%;the removal rate of 10?m inclusions increased by 20.9%;20?m inclusion removal rate increased by 20.3%.