Research On Flue Gas SO₂ Absorption Enhancement And Optimal Design Of Desulfurization Absorber

Sulfur dioxide（SO₂）is one of the main air pollutants,which can cause degradation of air quality and serious harm to human health.The main sources of SO₂ include mobile sources such as ships and industrial stationary sources such as power and steel industry.Wet flue gas desulfurization technology is an effective method to control sulfur dioxide emissions for flue gas,and has been widely applied in our country.However,with the continuous tightening of domestic SO₂ emission standards,how to achieve stable and efficient operation of wet desulfurization systems in different application scenarios is an urgent problem to be solved.In view of the requirement of high-efficiency removal of SO₂ for wet desulfurization system under different scenarios,including mobile source and industrial stationary source,it is of great significance to further strengthen SO₂ absorption and develop an efficient absorption tower.In this thesis,the deformation and SO₂ absorption law of droplets during dropping are studied on the scale of a single droplet.The SO₂ absorption model based on different absorbents including limestone and seawater is further established,and the research on efficienct removal of SO₂ is carried out combined with computational fluid dynamics（CFD）method.According to different application scenarios,we proposed the design scheme of the absorption tower by refined design of tower internal components and spray system.The research results provide guidance for the actual engineering design,optimization and operation of the wet desulfurization system.First,in order to explore the influence of droplet motion characteristics and morphological characteristics on the SO₂ absorption performance of droplet during dropping,a gas-liquid multiphase flow and interphase mass transfer coupled model was constructed at the single droplet scale.Based on the model,the deformation characteristics,the revolution of internal and external flow fields and the SO₂absorption process of droplet are studied.The results show that the droplet would deform during dropping and deviate from the standard sphere,which leads to the increase of mass transfer surface area of droplet,about 5.6%under the conditions studied.Meanwhile,the formation mechanism of the internal circulating vortex of droplet is found,and the increase of the relative velocity of gas-liquid phase will accelerate the formation of the vortex and increase its strength.Furthermore,the gas phase mass transfer coefficient curves and correlation under different Reynolds numbers are obtained,and its accuracy is proved by compared with the summarized correlations,which provides a theoretical basis for the construction of SO₂ absorption model at the macro scale.Second,in view of the complex sea conditions and limited space for device layout during the desulfurization process of marine exhaust gas,the research on the high-efficient removal of SO₂ based on seawater is carried out.A high-efficiency SO₂absorption method by enhancing gas-liquid mixing in the scrubber is constructed,and a compact design scheme of marine scrubber based on gas-liquid distribution ring is proposed.We establish a gas-liquid multiphase flow and seawater desulfurization coupled model at the macro scale,and the effects of gas-liquid multiphase flow and distribution characteristics in the scrubber on the SO₂ absorption process were analyzed under different working conditions.The results show that the gas-liquid distribution ring can effectively improve the gas-liquid flow and distribution characteristics in the scrubber,significantly alleviate the deterioration of gas-liquid distribution under inclined condition.By the redistribution effect of distribution ring,the concentration of droplets in the scrubber is promoted 10%-30%,and the desulfurization efficiency is increased by about 6%under vertical or inclined working conditions.What’s more,the operation strategy for marine scrubber by controlling key parameters such as liquid-gas ratio,seawater droplet size and seawater p H value is established,which provides effective guidance for the operation of ship scrubbers.We carried out an engineering application on the EGC system of a container ship with 18.8 MW marine engine.During the test operation,the SO₂ removal efficiency of the ship scrubber could exceed 99%.Third,in view of the flue gas desulfurization process of industrial source,we carry out the research on the high-efficient SO₂removal based on limestone,and propose the enhancement method for SO₂ removal by installing sieve plate and optimizing the spray system in the absorption tower simultaneously.A coupled model of SO₂ multiform absorption including spray absorption and bubbling absorption is established at the scale of macro scale.Based on the model,the changing laws of p H and SO₂ absorption rate during slurry droplets falling are obtained,and the gas-liquid flow,mass transfer and chemical reaction processes in the absorption tower are analyzied.The strengthening mechanism of sieve plate on the desulfurization efficiency is explored,and the optimization for the arrangement of sieve plate and spray system is carried out further.With the proposed enhancement method for SO₂ removal,the desulfurization efficiency of the absorption tower under different working conditions can be increased by 3-8%.The engineering application is carried out in the WFGD of a 660MW unit,and the test results show that the desulfurization efficiency can exceed 98%under different working conditions after using the proposed enhancement method.