Study On PM_2.5 And SO₃ Acid Mist Removal From Wet Desulfurized Flue Gas By Adding Humid Air

Coal-fired power plant is one of the major pollutant sources of fine particles (PM2.5) and SO3 acid mist in atmospheric environment, and the removal efficiency of PM2.5 and SO3 acid mist by dedusting equipment in power plants is quite fow. An investigation was conducted on PM2.5 and SO3 acid mist growth and removal in supersaturated water vapor environment, which was formed by adding humid air into wet desulfurized flue gas.The degree of water vapor supersaturation and the amount of condensable water vapor after mixing the desulfurized flue gas and humid air were calculated and simulated numerically. The results show that the required degree of water vapor supersaturation can be achieved by adding moderate humid air into flue gas with high humidity, and it mainly depends on the temperature and humidity of flue gas and humid air as well as the addition amount of humid air, etc. The degree of water vapor supersaturation and the condensable amount of water vapor increase with the increase of the temperature difference between flue gas and humid air and it increases slightly with the increased relative humidity of humid air. The degree of water vapor supersaturation increases firstly and then tends towards stability and decrease finally as the increase of wet air addition. The numerical simulation results show that the mixing situation of flue gas and humid air is favorable in condensational growth chamber on top of scrubbing tower, the velocity, temperature gradient is higher in the main zone of the chamber, the heat and quality of flue gas and humid air exchanges sufficiently and the higher degree of water vapor supersaturation can be achieved, which is beneficial to the condensational growth and removal of PM2.5 and SO3 acid mist.The removal of PM2.5 and SO3 acid mist by adding humid air into growth chamber on top of the scrubber tower was studied experimentally based on the numerical calculation and simulation, the influences of flue gas properties; humid air temperature and humidity as well as the addition amount of humid air were analyzed. The results show that the removal efficiency of PM2.5 and SO3 acid mist can be increased obviously and the concentration of these two is decreased at the outlet of flue gas by adding moderate humid air. The removal efficiency of PM2.5 and SO3 acid mist increases with the increase of flue gas temperature and the addition amount of humid air, which indicates that it would be appropriate by adding humid air while the desulfurized flue gas temperature is higher (?55?60?).The removal efficiency of PM2.5 and SO3 acid mist increases slightly with the increase of humidity of wet air. When the humid air temperature is fairly fow (?15?), the removal efficiency of fine particles can reach up to 45%.Both of the number condensation of PM2.5 and SO3 acid mist decrease because of the high turbulent motion and coefficient of transmission of impinging stream (IS),and it would be more apparent after humid air addition. Under the same conditions, the removal efficiency of PM2.5 is 30% without humid air addition and 40.8% with adding humid air, and the removal efficiency of SO3 acid mist is 24% and 31% respectively. Besides, the removal efficiency of PM2.5 and SO3 acid mist increases with the increasing temperature and humidity of flue gas and humid air, and it also increases with the increase of the addition amount of humid air. In IS condensational growth chamber, the removal efficiency of PM2.5 and acid mist increases firstly and then decreases as the increasing impinging distance, the optimal value of impinging distance is around 250mm, and it increases with the increasing velocity of IS condensational growth chamber, and best velocity is about 35m/s. Compared with the humid air addition on top of the scrubber tower, the removal efficiency of PM2.5 and SO3 acid mist in IS condensational growth chamber is higher.