Design And Optimization Of Coupled Mist Eliminator With Perforated And Directing Plate

As the pollution emission standards for coal-fired power plants become more and more stringent,the ultra-low emission technology is gradually popularized in China.The limestone gypsum wet flue gas desulfurization（LSWFGD）system is the tail device in the ultra-low emission technology.The LSWFGD system is of great significance for multiple pollutants control in coal-fired power plants,such as SO₂,particulate matter,and heavy metals.The mist eliminator is widely used in the outlet of LSWFGD system to remove fine particles deeply.With the continuous development of China’s science and technology,the higher requirements are placed on environmental protection.At the same time,more strict requirements are imposed on the performance of the mist eliminator.The mist eliminator required high particle separation performance while particle size in a wide range,and it also required minimizing its system operating pressure loss and energy consumption.Among many types of mist eliminators,wave-plate mist eliminator and wire mesh mist eliminator have the most extensive applications.However,both types of mist eliminators have obvious shortcomings.The particle separation efficiency of the wave-plate demister is undesirable while the fine particles it has;the wire mesh demister has high strict requirements in system loads and is prone to blockage.Based on the above situation,to improve the deficiencies of existing mist eliminators,this work proposes a new type of coupled mist eliminator.The main structure of the mist eliminator includes an internal improved structure of the perforated plate and directing plate inside the mist eliminator,in which the perforated plate serves to strengthen the collection of particulate matter,the directing plate guiding the flow of flue gas and particles.In this paper,the CFD numerical simulation method is used to study the mist eliminator performance of the new coupled mist eliminator,which mainly includes overall particle separation efficiency,particle graded separation efficiency,system pressure drop and economic index of F factor.This article first explores the particle separation performance of the perforated mist eliminator.The research results show that,compared with the traditional wave-plate mist eliminator,mist eliminator with hook plate and foam layer mist eliminator,the perforated plate mist eliminator has the highest performance under the flue gas velocity range and particle load researched.Compared with the traditional mist eliminator,the particle separation efficiency is increased by 14.6%,reaching 93.5%.The system pressure drop can be reduced by 35.6%when the particle separation efficiency of the mist eliminator with hook plate is basically unchanged.Compared with the porous foam layer mist eliminator,the particle separation efficiency of the perforated plate mist eliminator is increased by 2.3%,and the system pressure drop is reduced by more than 27.4%.Due to the interception structure of the perforated plate in the channel of the mist eliminator,it has a higher trapping capacity for the particles entrained by the flue gas,and the porous structure has a lower pressure drop than the hook plate structure of mist eliminator,which is higher than the traditional non-enhanced component mist eliminator.But the pressure drop is still within the acceptable range for industrial applications.To explore the fine particles captured and enhanced mechanism of the perforated plate,we designed and optimized multiple structural parameters of the perforated plate.The results show that the particle separation efficiency and pressure drop are effectively affected by the porosity and the number of porous plates.These parameters will also affect the influence of other structural parameters.The disadvantage of the perforated plate is that the flue gas in the channel of the mist eliminator will shift away from the perforated plate.To improve the flue gas migration phenomenon and further enhance the particle capture ability of the perforated plate mist eliminator,this paper introduces directing plate to induct the flow of flue gas and particles,formed perforated plate and directing plate coupled mist eliminator.The results show that the particle capture is secondarily strengthened while the directing plate introduced.Different structures of the directing plate also have a greater impact on the performance of the mist eliminator,and simulation studies have found that the installation position and angle of the directing plate have a relatively high effect on the fluid flow in the channel of the mist eliminator.The directing plate mist eliminator has the optimal performance while the plate is installed at the start position and the installation angle is 45°.The particle separation efficiency of fine particles smaller than20μm was increased by more than 10%,and the particle separation efficiency of 5～10μm particles was increased by more than 20%.An appropriate structure of mist eliminator should be selected for the different application scenarios.Overall,the above results fully demonstrate the advantages of the new type coupled mist eliminator in different working conditions and its good industrial application prospects.