Numerical Simulation Of Multiphase Flow Movement Characteristics In KR Hot Metal Desulfurization Process

KR desulfurization method has been used on a large commercial scale in our country because of its high efficiency,stable effect,and so on.It will greatly lower production costs to improve the stirring mixing performance and the desulfurization efficiency in KR process.Previous studies have shown that the main factor affecting reaction rate and utilization rate of desulfurizer was the dynamic element in multiphase transmission procedure.Given the complexity of field trials,it is necessary to study the stirring flow field and dispersion behavior of desulfurizer in KR desulfurization process with the numerical simulation method.The objective of this work was to give guidance for improving desulfurization efficiency based on a detaild description of movement characteristics about the multiphase flow.First an unsteady air-hot metal two-phase flow model has been built with Fluent,of which the prototype is a 170 ton-scale ladle in a steel factory.We considered the movement characteristics of flow field and the influence of stirring parameters on it respectively.On the basis of the two-phase flow model,an unsteady air-hot metal-desulfurizer particles three-phase flow model has been built.The movement characteristics of desulfurizer particle in different period of the stirring process have been studied respectively as well as the influnce of sitrring parameters on it.Based upon this work several conclusioons are drawn.A typical radial flow regime of hot metal can be observed during the KR process.Rotation speed has an important influce on the mixing performance and it is suggested to increase the speed as high as possible within the allaowable range.The immersion depth of the impeller is recommended to increase with time from a samll value.Proper distance of offcenter contributes to mixing performance too.In the early stage of mixing,calcium oxide particles float on the surface of hot metal,making a rotary motion with the fluctuating liquid surface.Gradually the particles approach the center of the stirring vortex and some of them will be discharged after entering the intermediate agitation zone with the hot metal under the action of the agitator.In transition period,the calcium oxide particles entering the strong turbulent zone are discharged into the upper circulation or the lower circulation with hot metal.During this period,the calcium oxide particles intersperse in different regions of the ladle through a complex route and finally they reach a stable state.In the last period,the trajectory of calcium oxide particles are basically stable,rotating periodically with the movement of hot metal.It has been found that there are three types of calcium oxygen particles’ tracks after observing a large number of samples.In the first case,the particles make cyclical rotary motion only with the hot metal and are limited to the upper cycle.In the second case,particles aprroach the center of the stirring vertex and then become a part of the middle strong turbulence zone,finally back to the upper cycle after a complicated route.In the third case,particles entangled into the vertex center participate in the lower cycle after a complicated route driven by the middle strong turbulence.Particles which follow the third tracks have a longer resident time in the ladle and thus a higher desulfurization efficiency.The ladle can be divided into three zones,which are upper cycle zone,middle strong turbulence zone and lower cycle zone respectively.Under condition of rotation speed N=80rpm,immersion depth H=1334mm,off-central distance OD=0,the ratios of particles in three regions are 60%,25%,15%respectively when they reaches a steady state of motion.The number of particles in middle strong turbulence zone and lower cycle zone increase along with the rotation speed.The same effect can be achieved under a moderate offcentral distance.Variation of immersion depth has a little influence on the ratio except lower cycle which has a relatively laerge increase.Synthesizing the effect of three stirring parameters,it is recommended to adopt the scheme that using the maxmium rotation speed within the range,a moderate off-central distance and making the immersion depth shallow first then deepen gradually.