| With the development of modern machinery,industry,and the increasing demand for high-quality steel,higher requirements for the mechanical properties and corrosion resistance of steel are being proposed year by year.High sulfur content in steel can reduce its quality and performance,making it particularly important to achieve ultra-low sulfur smelting through iron pretreatment.The Mechanical stirring(KR)method is the mainstream desulfurization method in iron pretreatment,which has the characteristics of high desulfurization efficiency,low energy consumption,and low operating costs.It is widely used by many steel companies for deep desulfurization of iron in the iron pretreatment stage,which can greatly reduce the desulfurization cost while effectively improving the desulfurization efficiency of steel enterprises.However,there are still problems in the desulfurization process of the KR method,such as poor desulfurization effect at the bottom of the iron,and the easy breakage of the stirring shaft.The present study employs numerical simulation to investigate the effects of impeller structure on stirring efficiency,free surface deformation of molten iron,and the frequency of impeller vibration.The key findings of this work are as follows:(1)The paper investigates the influence of impeller structure on mixing efficiency,deformation of the free surface,and vibration frequency of the impeller through numerical simulation research.Specifically,the research focuses on four types of impellers,including the helical three-blade impeller,double-layer four-blade impeller,staggered four-blade impeller,and high-low four-blade impeller.The mixing efficiency of these four impellers is studied from three aspects: mixing time of molten iron,axial velocity of molten iron,and distribution of turbulence energy.The results show that the double-layer four-blade impeller has the highest mixing efficiency among the four optimized impellers,with a mixing time 7.3% shorter than that of the traditional four-blade impeller.The analysis of the distribution of turbulence energy and axial velocity of molten iron reveals that the double-layer four-blade impeller has a larger axial velocity in the molten iron and promotes wider diffusion of turbulence energy,resulting in an average turbulence energy of molten iron 28% higher than that of the traditional four-blade impeller.(2)To improve the entrainment effect of desulfurizing agent in the KR desulfurization process and alleviate air entrainment in molten iron,the influence of molten iron free surface was considered.Four optimized impeller blades were selected as research objects,and the formation mechanism of vortex on the molten iron free surface and the deformation of the free surface were studied.The results show that the pressure distribution on the impeller blade plane leads to the vortex on the molten iron free surface,and the trailing vortex on the impeller blade surface determines the final shape of the molten iron free surface.Among the four optimized impeller blades,the double-layer four-blade impeller has a larger low-pressure area on the blade plane,and it’s 7 times larger than that of a traditional four blade propeller,which results in a better entrainment effect and a smaller amount of air entrainment in the molten iron.Moreover,the trailing vortex of the impeller blade is closer to the molten iron free surface.(3)Considering the differences in size and mass of different impeller structures,the inherent frequency of the mixing shaft varies,and the change in the inclination of the free surface of the molten iron caused by the increase in impeller speed also affects the additional mass on the impeller blade,causing the inherent frequency of the mixing shaft to fluctuate.In this paper,the acoustic-solid coupling method is used to simulate and study the resonance problem of the mixing shaft surrounded by molten iron,and the influence of the size of the mixing shaft and the impeller speed on the resonant frequency of the mixing shaft is studied.The results show that although the inclination of the free surface of the molten iron increases by 30% as the impeller speed increases by 50%,resulting in a 6% increase in the resonant frequency of the mixing shaft,the frequency of the force exerted by the molten iron on the impeller blade increases at a faster rate with increasing impeller speed.Therefore,as the impeller speed increases,the frequencies of the two approaches each other,and the risk of resonance also increases.By shortening the cantilever and single span length on the mixing shaft,the resonant frequency of the mixing shaft can be greatly changed,thereby avoiding resonance.Shortening the cantilever length on the stirring shaft by 20% increases the natural frequency of the stirring shaft by about 23%;shortening the single-span shaft length by 20% increases the natural frequency of the stirring shaft by about 12%.Adjusting the stirring shaft size ensures that the natural frequency is greater than the frequency of the fluid action force,thereby avoiding resonance. |
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