Study On The Migration And Transformation Of Soluble Salt During Limestone-gypsum Desulphurization Process

The effect of flue gas purifying equipment on the emission characteristics of particulate matter in flue gas has been increasingly valued with the improvement of pollutant emission standards for coal-fired power plants.The wet flue gas desulphurization process has effects on the concentration and chemical components of particulates,and will change the emission characteristics of fine particulates from coal-fired power plants.Therefore,the study on changes in fine particles,soluble salts,gaseous pollutants,etc.during wet flue gas desulphurization?WFGD?process can provide an important basis for controlling the emission of flue gas pollutants from coal-fired power plants.To investigate the properties of soluble salt particles during the desulfurization process,the experiments were carried out by the self-design simulated wet flue gas desulfurization device and SCR denitrification reactor outlet flue gas generation device.The concentration,particle size distribution,inorganic ion components,morphology of the soluble salt particles and ion components of condensed water were analyzed by meanings of electrical low pressure impactor?ELPI+?,ion chromatograph?IC?,inductively coupled plasma optical emission spectrometry?ICP-OES?and the field emission scanning electron microscope?FESEM?.The effects of desulfurization operation parameters on soluble salt emission were also investigated.The results showed that soluble salt particles are formed during the desulphurization process and the main ingredients are calcium,ammonium and magnesium salts,etc.The entrainment of desulphurization slurry is the main source of soluble salt emission while soluble salt cannot be carried by vaporous water in flue gas.Part of NH₄⁺in the desulfurization slurry will become gaseous ammonia and can be discharged with flue gas.For the NH₄⁺components in soluble salts,the migration and transformation characteristics of ammonium sulfate and escaped ammonia in WFGD system were further studied.The results showed that the emission caused by the evaporation and entrainment of desulphurization slurry and the ammonium sulfate aerosol escaped emission account for 67.29%and 32.71%respectively in the PM₁₀ from the outlet of WFGD system.The NH₄⁺emission from the desulfurization system are mainly caused by the evaporation and entrainment of slurry.Decreasing the liquid to gas ratio,the inlet flue gas temperature and the ion concentration of the desulfurization slurry properly are beneficial to reducing the NH₄⁺emissions from desulfurized flue gas.The impact of the ultra-low emission modification of the tray-tower on the PM_2.5 emission characteristics of the limestone-gypsum wet desulphurization system was analyzed by using coal-fired WFGD platform with industrial desulphfurization conditions.The characteristics of the migration and conversion of NH₄⁺in a typical flue gas purification process were qualitatively analyzed by sampling and analysing the ash and water samples in a coal-fired power plant.The results indicate that the concentration of dust,fine particles and soluble salt ions in WFGD flue gas was decreased with the application of tray-tower WFGD system.The concentration of water-soluble ions in PM₁₀ was reduced by approximately 21.61%compared to that before modification.Decreasing the flue gas velocity properly is beneficial to reducing the emissions of fine particles and soluble salt ions from desulfurized flue gas.The SCR denitrification system will lead to the increase of sub-micron fine particles,NH₄⁺and SO₄^2-emissions from the WFGD system and change the emission characteristics of fine particulates from coal-fired power plants,as the limited trapping capability of ESP and WFGD.