The Sulfite Oxidation, NO_x And Mist Removal In A Wet Discharge Reactor And NO_x Generation

Multi-pollutants control in coal-fired flue gas is important for improvement of Chinese air quality. The traditional coal-fired flue gas emissions control process is a simple connection of various devices in series with low efficiency, high energy consumption and large coverage area. High-voltage discharge could produce a large amount of high energy electron and active species, The integration of ammonia- flue gas desulfurization (FGD) and non-thermal plasma can remove the particles, SO2 and NOx in flue gas simultaneously, control ammonia slip after FGD and produce fertilizer byproducts. The wet discharge reactor between FGD and stack in an this process could capture slipped ammonia and oxidize ammonium sulfite simultaneously.Based on the integrated process, this thesis aims at the sulfite oxidation, aerosols capture, and NOx absorption in the wet discharge reactor. Two homemade high-flow rate NOx generators are made for NOx generation from air by arc discharge. The experiments provide basis for the wet dischargte reactor design and sizing. The NOx generator could produce high concentration of NOx.In a wet discharge reactor, ammonium sulfite could get oxidation by air, diacharge and NOx. To clarify their contribution, the oxidation rates are measured by sulfite titration and gas analysis. At the sulfite concentration of 1 mol/L, oxidation rates by air, discharge, NO2 and NO are 7.25、 82.46、1.5 和 0.13 mol/(m2·h), respectively. The oxidation rates are affected by the sulfite or NOx concentration, pH value and discharge power. The air and discharge oxidation rate increase first and then decrease as sulfite concentration and pH get higher, and reach to a peak at 0.5～0.8 mol/L and pH of 7 or 9, respectively. The more energy injected into the reactor, the quicker sulfite get oxidized. The oxidation rate of NOx increases with sulfite or NOx concentration. Compared to NO, the NO2 oxidized less sulfite in acidic solution than in alkaline solution. Different cations would not affect the oxidation process.The thesis measures the dissolved oxygen concentration in sulfite solution by a fluorescence sensor and the hydroxyl radical concentrations in liquid phase by bromophenol blue spectrophotometry. The performances of corona and spark discharge, positive and negative discharge are compared. Dissolved oxygen in ammonium sulfite solution at concentration higher than 0.001 mol/L is lower than 0.1 mg/L. The low dissolved oxygen limits the air forced oxidation rates. Oxidation rate of corona and spark discharge are 0.33 and 2.46 mol/(m2·h), respectively(0.6 J/L). The amount of hydroxyl radicals transitted into liquid phase is 1.34×10-8(corona) and 2.72×10-9(spark) mol/min corresponds to 1～10×10-9 mol/J. Despite corona discharge can generate more radicals, still more NOx produced by spark discharge could also oxidize sulfite. Postive discharge oxidize sulfite at a rate 20 times of that by negative discharge for higher OH yield rate.The removal rates of aerosols in the exhaust from ammonia-FGD by discharge and falling film flow are tested. By simultaneous discharge and falling film flow, the removal efficiency of water mist, ammonium sulfte solution and ammonia aerosols is 36%、55% and 96%, respectively. Collection efficiency of ammonia slip by discharge is similar to that by simultaneous removal. The capture of aerosols in the diameter of 0.1～1 μm is better than other size. Falling film performs better on ammonia capture than on sulfite or water mist. The number of latter would even increases. The solid ammonium sulfite crystal is hygroscopic and would easily adhere to the reactor surface.The kinetic models of ammonium sulfite oxidation of air, discharge and NOX are analysed. The simulation results show that the air forced oxidation is controlled by dissolved oxygen and sulfite concentration; the discharge oxidation is limited by dissolved oxygen, sulfite concentration and discharge power; the NOx oxidation is affected by NOx and sulfite concentration. The model could guide the wet discharge reactor design and predict the operating performance. The pilot demonstration, in which a wet discharge reactor was installed, could control the SO2, NOx and particle emissions under 9～25、1～30 and 15～20 mg/m3, respectively.To produce high concentration NOx under high flow rate, a NOx generator is designed and manufactured. The NOx production by AC arc discharge and its influence factors are investigated by flue gas analyzer, FTIR, thermal imaging, and high-speed camera. In the homemade prototype reactor, NO and NO2 concentration could reach 3500 and 2000 ppm, respectively at the flow rate of 0～10 L/min. The ratio of NO to NO2 could be adjusted between 2～30. In a lab scale reactor, through which 55～108 m3/h of air could flow, the peak NO and NO2 concentration is 2000 and 400 ppm, respectively.