Transformation Law And Simulation Study Of Sulfate Ions In Flue Gas Particulates From Coal-fired Power Plants Under Rapid Condensation Conditions

China is the largest consumer of energy by far,accounting for 24.3%of global consumption and more than three quarters of global consumption growth.The consumption of coal in China accounted for 51.7%of the global total consumption,and coal will continue to play an irreplaceable role in the short term.Coal is the main driving force for coal-fired power plants,which produces and emits large amounts of particulate matters during the combustion process.As the main inorganic component of the particulate matters,the contribution of water-soluble ions to fine particulate matter(PM_2.5)and haze weather can not be ignored.There were many studies on the emission and conversion characterizations of water-soluble ions of particulate matters emitted from ultra-low coal-fired power plants.However,less attention has been paid to the internal conversion and influencing factors of typical water-soluble ions such as SO₄^2-in the flue.In this study,the conversion law of SO₄^2-of particulate matters including condensable particle matter(CPM)and filterable particle matter(FPM)emitted from 7 ultra-low emission coal-fired power plants before and after Wet flue gas desulfurization(WFGD)and Wet electrostatic precipitation(WESP)was investigated and analyzed.Moreover,in order to explore the conversion process and influencing factors of SO₄^2-,the self-built device for simulation flue gas was used in the laboratory to explore the influence of condensation temperature,humidity and initial concentration on the conversion process of SO₄^2-from the perspectives of SO₂-H₂O-NOx-NH₃ system and SO₃-H₂O-NH₃ system.Finally,a more complete and comprehensive conversion law of SO₄^2-was obtained through field experimentation and simulation experimentation.In the field experimentation part,the following conclusions can be drawn:First,concentration of SO₄^2-of CPM decreased after WFGD,and the reduction rate ranged from43.12%to 86.84%.The concentration of SO₄^2-of FPM showed an increasing trend,and the growth rate ranged from 22.71%to 180.34%,respectively.Second,the concentration of SO₄^2-of CPM increased after WESP,with a growth rate ranging from 21.05%to 424.65%.The concentration of SO₄^2-of FPM showed a decreasing trend,and the reduction rate ranged from 27.00%to 67.40%,respectively.Thirdly,In the WFGD system,CPM could be transformed into FPM due to its condensation and aggregation with the decreasing of temperature and increasing of humidity of the flue gas.In the WESP system,SO₂ and NO₂and other pollutants existing in the flue gas would combine with water vapor to have a redox reaction to promote the generation of SO₄^2-of CPM through synergistic action.In the SO₂-H₂O-NOx-NH₃ system,taking the low concentration of SO₂ as an example,the following conclusions can be drawn:First,compared with the SO₂-H₂O system,the growth rate of concentration of SO₄^2-was mostly distributed between 10%and 50%in the SO₂-H₂O-NOx system;in the SO₂-H₂O-NH₃ system,the growth rate was mostly distributed between 120%and 220%;in the SO₂-H₂O-NOx-NH₃ system,the growth rate was mostly distributed between 140%and 250%.In other words,the synergistic effect of NOx and NH₃had a better promoting effect on the oxidation reaction of SO₂,and the oxidation effect of NH₃ was stronger than NOx.Second,under the condition of each system,when the condensation temperature reduced to the water vapor saturation temperature,the water vapor condensed in the condenser pipe,which provided a condition for SO₂ dissolved and the related liquid phase reaction,so the concentration of SO₄^2-increased with the decreasing of the condensation temperature and the increasing of the humidity.Thirdly,when the initial concentration of SO₂ became 3 times of the low concentration,the concentration of SO₄^2-also increased to 1?2 times of the original.Besides,the more complex the system was,the smaller the proportion of concentration of SO₄^2-under the condition of high/low concentration of SO₂was.In the SO₃-H₂O-NH₃ system,taking the low concentration of SO₃ as an example,the following conclusions can be drawn:First,compared with the SO₃-H₂O system,the growth rate of concentration of SO₄^2-ranges from 14.10%to 40.74%in the SO₃-H₂O-NH₃system,indicating that NH₃ can promote the oxidation reaction of SO₃ to some extent.Second,under condition of each system,when the condensation temperature was lower than the dew point of the system,the concentration of SO₄^2-in the washing fluid would be lower,and the concentration of SO₄^2-on the filter membrane would be higher.The reason was that when the condensing temperature range was too large,H₂SO₄ vapor directly formed aerosols,which would eventually be captured by the filter membrane.Third,From the point of view of the concentration of SO₄^2-obtained at different condensation temperatures,the closer the condensation temperature to the dew point temperature of the system was,the higher the concentration of SO₄^2-measured would be.Moreover,a layer of filter device behind the condensing pipe was necessary to collect SO₄^2-more completely in the system.