Study On Improving Mist Removal Efficiency Of Baffle Mist Eliminator For Fine Droplets

With the frequent occurrence of fog and haze,people pay more and more attention to the flue gas emitted from coal-fired power plants.There are a lot of fine droplets in the flue gas after wet desulphurization.These droplets in the air will promote the formation of PM_2.5,and the mist eliminator is the key equipment to remove these droplets.The baffle demister has been widely used since it has a simple structure and a small pressure drop At the moment,the total defogging efficiency of the mist eliminator is very high,but for the small droplet,its defogging efficiency still needs to be improved.Therefore,based on the theoretical knowledge of gas-liquid separation,this paper analyzes the basic principle of the baffle eliminator and the reasons for the low efficiency of droplet removal,and improves the baffle eliminator.The removal efficiency of fine fog drops is improved by means of blunt body winding.Combined with the actual structure and research conditions of the baffle defogging device,the appropriate experimental method and numerical simulation method were selected to study the mist eliminator before and after improvement.The main contents are as follows:（1）Starting with the basic theory of two phase flow and gas-liquid separation,based on the previous research methods and research results,the basic principle of the demister and the principle of the low efficiency of the fine droplet removal are analyzed.An optimization method for the demister of a baffle plate is proposed in this paper,that is to set a blunt body in front of the baffle.（The improved demister is called the bluff body demister in the later chapters of this article）（2）Using fine particles instead of fine droplets,a demister particle distribution experiment was designed for droplets below 20μm.The experimental results show that the deposition quantity of fine particles in the baffle is different in different positions.The ability to capture fine droplets at corners is greater than that at straight sections.The improved bluff body demister has greatly improved the ability to capture fine mist droplets while maintaining the advantages of a simple baffle structure with reduced pressure,about double the baffle demister.（3）In order to study the performance comparison of demister before and after improvement in actual working conditions,and to provide basis for simulation calculation,the efficiency experiment of the demister is designed in this paper.The experimental results show that the blunt body mist eliminator is much better than the original baffle mist eliminator.For the removal efficiency of fine droplets,the blunt body mist eliminator is much higher than the baffle mist eliminator.For the total defogging efficiency,the blunt body mist eliminator is always greater than 90%,and the efficiency is higher than that of the baffle mist eliminator at different gas velocities.（4）Using the basic theory of computational fluid dynamics,combined with the actual structure and research conditions of the baffle defogger,the Euler method and the Lagrange method are used to numerically calculate the demister.The comparison between experiment and simulation results shows that:The result of the numerically calculation is basically the same as that of the experiment（5）The following conclusions can be obtained through the simulation calculation of the demister:The air flow in the baffle demister is relatively stable,and the entire flow field is approximately streamlined.However,the air flow in the bluff body mist eliminator is relatively disordered and there are many eddy currents.Correspondingly,the movement of the droplets in the baffle demister is also relatively stable while the movement of the droplets in the bluff body demister is relatively disordered.Where there is a vortex,the droplets are in the outer edge area of the vortex structure and the effective flow area becomes smaller.So that the local density of the droplets in the straight section of the inlet and in the first curve is greater than the density of droplets in the baffle demister.That is,the droplets collide more easily with the wall surface.For the removal efficiency of fine droplets,the bluff body demister is much higher than the baffle demister.For a droplet of 15 m,the defogging efficiency of the initial baffle is 35%at 3m/s gas velocity while the blunt body demister is 60%.In the large particle size range,both the bluff body demister and the baffle demister have higher defogging efficiency.The bluff body parameters have a certain effect on the performance of the blunt mist eliminator.When the vertical distance between the center line of the bluff body and the entrance section of the baffle plate becomes larger,the total defogging efficiency of the bluff body becomes smaller Under the research conditions in this paper,at a velocity of3m/s,the efficiency of defogging with a distance of 50mm from the baffle body is less than 8%of the defogging efficiency at a distance of 10mm.The change of blunt body distance has little effect on the classification of fog removal efficiency.Under the condition of this paper,the maximum difference of fog efficiency of three different distance structures is about 20%in the same gas velocity.When the diameter of blunt body becomes larger,the total defog efficiency becomes smaller and the pressure drop becomes larger.Therefore,in the model studied in this paper,a blunt body defogging device with a diameter of 6mm is better than that of a blunt body with a diameter of 8mm and 10mm.