Study On Improving The Removal Of Fine Particles And SO₃ Acid Mist In Coal-fired Flue Gas By Heterogeneous Condensation

Fine particles and SO₃acid mist have become a prominent problem affecting the environment and human health.Coal-fired power plants are the main emission source of fine particles and SO₃acid mist,while the removal efficiency of fine particulate matter and SO₃acid mist by the traditional pollutant control equipment is not ideal.It is a promising method to promote the condensation and growth of fine particles and SO₃acid mist through heterogeneous condensation,and then the fine particles and SO₃acid mist would be removed by traditional pollutant control equipment.Therefore,it is significance to carry out the removal of fine particles based on the heterogeneous condensation.In this paper,fine particles and SO₃acid mist based on the heterogeneous condensation coupled the optimization of internal structure were studied,and the experiment was carried out through wet flue desulfurization test platform.The results show that heterogeneous condensation could significantly promote the removal of fine particles and SO₃acid mist.The higher the moisture content of the flue gas at the inlet of the desulfurization tower,the more conducive to the formation of supersaturated environment,resulting in a higher removal efficiency of fine particles and SO₃acid mist.A higher liquid to gas ratio is beneficial to the removal of fine particles and SO₃acid mist.The suitable moisture content of flue gas and liquid-to-gas ratio are 83?103g/Nm3 and15?20L/Nm3,respectively.Moreover,the flue gas temperature at the inlet of the tower has a certain influence on the removal performance of fine particles and SO₃acid mist.The heterogeneous condensation in the desulfurization tower can increase the removal efficiency of fine particles from about 45%to about 60%,and the removal efficiency of SO₃acid mist from about 40%to about55%.Additionally,the installation of trays in the desulfurization tower can further promote the removal of fine particles and SO₃acid mist,and the removal efficiency of fine particles and SO₃acid mist can be increased to about 65.0%?70.0%and 60.0%?65.0%,respectively.Based on the single-tower dual-cycle process of coal-fired power plants,the supersaturated environment was established in the desulfurization tower by reducing the temperature of the desulfurization slurry,and then the removal of fine particulate matter and SO₃acid mist by the heterogeneous condensation in the absorption zone of the desulfurization tower was investigated through simulation and experiment.The simulation results show that the decrease of the desulfurization slurry temperature can make the flue gas create supersaturated environment in the absorption zone of the desulfurization tower,and the supersaturation degree increases with the increase of the slurry temperature drop.In addition,the construction of the supersaturated environment in the desulfurization tower is related to the liquid-gas ratio and the flue gas temperature.As the liquid-gas ratio increases,the degree of supersaturation formed increases,which is beneficial to the removal of fine particles and SO₃acid mist.The lower flue gas temperature is not conducive to the removal of fine particles and SO₃acid mist,and the more suitable desulfurization slurry temperature drop is about 8?10°C.Additionally,the decrease of the desulfurization slurry temperature can reduce the evaporation of the slurry.Thus,the moisture content of the flue gas deceases,resulting in the decease of the desulfurization water consumption.The experimental results show that this method can increase the removal efficiency of fine particles from about 40%to about 60%,and the removal efficiency of SO₃acid mist from about 35%to about 50%.In addition,the desulfurization water consumption is decreased to about 65?70%.The relative humidity of the desulfurization flue gas is relatively high,which is beneficial for establishing supersaturated environment.A novel process was proposed to obtain the supersaturated environment by direct heat exchange and indirect heat exchange of the desulfurization flue gas.Direct heat exchange was achieved by spraying atomized cooling water on the desulfurization flue gas,and indirect heat exchange was achieved by installing a fluoroplastic heat exchanger after the desulfurization tower.The simulation results show that in the direct heat exchange process of the desulfurization flue gas,when the spray amount of the atomized cooling water is very small,the desulfurization flue gas can reach supersaturated condition.The suitable atomized cooling water temperature and liquid-gas ratio are 10?20°C and 0.125?0.25L/Nm³,respectively.The experimental results show that this method can reduce the emission concentration of fine particles to about 50%,and the moisture recovery rate in the desulfurization flue gas is close to 40.0%.The indirect heat exchange cooling method of desulfurization flue gas is easy to establish the supersaturated water vapor environment required for the condensation and growth of fine particles,and the suitable cooling range is 4?6°C.Higher flue gas humidity contributes to the formation of the supersaturated water vapor environment,while the temperature of desulfurization flue gas has little influence on the supersaturation.The experimental results show that when the desulfurization flue gas temperature is reduced by about 2?10°C,the removal efficiency of fine particles can be increased from about 10%to about 50%.Moreover,the emission concentration of secondary fine particles is reduced by about 50%,and the water recovery rate can reach about 35.0%.Based on the laboratory research,the actual coal-fired power plant limestone-gypsum wet desulfurization system,the numerical simulation and test research were carried out to vestigate the removal of multiple pollutants and the desulfurization water consumption by decease of desulfurization slurry temperature in the actual limestone-gypsum wet desulfurization system of coal-fired power plants.The power plant uses a two-stage condensing system to separately cool the two-layer desulfurization slurry.The simulation results show that turning on the condensing system can create a supersaturated water vapor environment for the flue gas in the absorption zone of the desulfurization tower.When the temperature of the desulfurization slurry deceases from 55°C to35°C,the supersaturation of the absorption zone of the desulfurization tower can be increased from0.99 to 1.61.The test results show that the decease of the desulfurization slurry temperature can achieve the removal of multiple pollutants.The greater the temperature drop of the desulfurization slurry,the more conducive to the removal of pollutants.This method can increase the removal efficiency of fine particles from about 35.0-40.0%to about 70.0%,the removal efficiency of SO₃acid mist from 35.0%to 70.0%,and the removal efficiency of CPM from condensable particles from 45.0%to 85.0%.In addition,the collection efficiency of mist droplets can reach more than80.0%,and the moisture recovery rate of flue gas can reach more than 40.0%.