Study On The Monitoring Method Of SO₃ Acid Mist And Its Immigration And Transformation Characteristics During The Wfgd Process

With the rapid development of economy in China,the air pollution is becoming more and more serious.The environmental problems caused by SO₃ acid mist emission from coal-fired power plants have attracted extensive attention.The existing pollutant removal equipment of coal-fired power plants is not efficient to remove SO₃ acid fog.In order to deal with the pollution caused by SO₃ acid mist,the monitoring method and the mechanism of migration and transformation in wet desulfurization are studied in this paper,and a technical method to remove SO₃ effectively is put forward.In this paper,the reheat temperature of flue gas,constant temperature water bath temperature and sampling rate are first developed by using SO₃ generator and simulated flue gas wet desulfurization system.The effect of different sampling parameters such as helical tube size and absorption bottle size on the SO₃ acid mist collection rate is investigated.The results show that when the flue gas reheat temperature is lower than the acid dew point of the flue gas.The SO₃ acid fog collection rate will decrease.Large flow rate should be adopted in sampling by controlled condensation method,serpentine spiral condensing tube with specifications of 400 or 500 should be selected,and condensate tube should be placed in constant temperature water bath with temperature about 65?,and small flow rate should be used when sampling by alkaline absorption method.Three shock absorption bottles have been used to sample in series.The concentration of SO₂ in flue gas temperature and humidity and the coexisting components in flue gas have great influence on the collection rate of alkaline absorption method,but have little effect on the control of condensation method.Therefore,it is more accurate to control condensation for monitoring SO₃ acid mist in wet desulfurization and high humidity flue gas environment.Based on the determination of sampling method and sampling parameters,the migration and transformation mechanism of SO₃ in wet flue gas desulfurization process was studied.The results showed that the concentration of SO₃ acid mist reached 1.1×10⁷1/cm³.SO₃ mist number concentration showed a unimodal distribution with sub micron particles,mainly distributed below0.1?m.With the decrease of inlet flue gas temperature,the increase of fly ash concentration and desulphurization slurry temperature,and the increase of fly ash particle size,the removal efficiency of SO₃ acid mist by wet desulphurization is improved.Metal ions in desulphurization slurry do not directly oxidize SO₂ in flue gas to SO₃.The SO₃ at the outlet of wet desulfurization is mainly derived from coal combustion process and oxidation of SO₂by denitrification unit.The removal effect of SO₃ acid mist by double cycle process is better than that by single tower and double cycle process.In addition,the removal efficiency of SO₃ acid mist by wet desulfurization system can be greatly improved by adding pallet in the desulfurizer.A coupling flue evaporation process for desulfurization wastewater is proposed to remove SO₃from coal-fired flue gas by injecting alkaline substance in the end.This technology can not only effectively remove SO₃ from flue gas,but also realize zero discharge of desulfurization wastewater.The effects of kinds of basic absorbent,injection quantity of basic absorbent,evaporation amount of desulfurization wastewater and concentration of SO₃ in flue gas on the removal efficiency of SO₃ was studied.When the ratio of sodium to sulfur is 2,the removal efficiency of NaOH is higher than that of Na₂CO₃ and NaHCO₃.And the removal efficiency of SO₃ in flue gas can be greatly improved by increasing the evaporation amount of desulfurization water and the concentration of SO₃ in flue gas.However,there is little effect on the removal of SO₃ from the electrostatic precipitator and wet desulfurization system.The choice of nozzle type also has a certain influence on the removal effect of SO₃.