Experimental And Theoretical Study On NO And SO₂Oxidation By Chlorine Dioxide And Simultaneous Removal Of NO_x And SO₂

With developing requirements and standards of environmental protection, China is facing severe challenges in the flue gas pollution control. Researches of efficient and economical removal technologies become a trend. This paper focuses on oxidation process by chlorine dioxide which can be combined with the absorption process to achieve simultaneous sulfur dioxide and nitric oxide removal. Specifically, the study mainly includes three parts. Firstly, oxidation properties of gas-phase chlorine dioxide with NO and SO2and influence factors are studied experimentally. Secondly, the reactions mechanisms and chemical kinetics in the oxidation system are explored by the quantum chemical method calculation. Thirdly, the removal performance of the absorption technology in the fixed-bed combined with pre-oxidation, its removal factors and their impact mechanisms are researched.The gas-phase oxidation experiment identifies the oxidation selectivity of chlorine dioxide, which means that sufficient SO2oxidation will not been found until the oxidation of NO trends to complete. Temperature is a key factor affecting NO oxidation efficiency. As the temperature rises, the NO oxidation efficiency shows a significant downward trend. Meanwhile, SO2competes with NO in the oxiadation process, oxygen and water vapor promote it in varying degrees. Hg0can be fully oxidized to Hg2+which can be easily absorbed, without impacting the NO oxidation.To develop a more complete understanding of the overall reaction system, quantum chemical method is employed to determine the mechanism and kinetic investigation of SO2oxidation which is the key reaction of the system. NO2is the product of NO oxidation, and it will not be further oxidized to NO3, N2O5such high valence nitrogen oxides. Selective oxidation of Chlorine dioxide is due to the difference of energy barrier between NO and SO2oxidation reaction respectively with OC1O, and their reaction rate constant differ by several orders of magnitude. The rate constant of NO oxidation reaction with OC1O and C1O both decreases with temperature, and SO2is on the contrary. It is speculated that selective oxidation of chlorine dioxide will not be weakened until520℃. The Cl particles as the oxidation product have a strong oxidation of Hg. The calculation results are in contrast with the experimental results. At high temperature, the decomposition consumption of the oxidizing compounds which generates C12and O2is strengthened. In summary, lower temperature and fully mixing of oxidant and flue gas can ensure the selective oxidation of the oxidant and avoid decomposition consumptionIt is an important part of the system to absorb the main oxidation products NO2and SO2simultaneously after NO oxidized effectively. The removal performance of the absorption technology in the fixed-bed combined with pre-oxidation by gas-phase chlorine dioxide, removal factors and their impact mechanisms are researched. When it is not humidified, NO2removal tends through reaction2NO2+SO32-+H2Oâ†'2NO2-+SO42-+2H+, while when it is humidified, NO2removal tends through the reaction with the surface water that producing HNO3. When it is not humidified, SO2removal follows the gas-solid adsorption principles and is severely affected by other competing substances and limited by the capacity of the absorbant. When it is humidified, SO2tends to be removed by dissolution and participate the. ion reaction, and is affected by other products. In the temperature range of60to100℃, the lower the temperature the higher the removal efficiency. In the range of10%-30%, relative humidity promotes NO oxidation at the first, and then inhibites it. The appropriate amount of oxygen can promote NO oxidation and NOx-SO2removal. Without humidification, higher oxygen content causes adsorption competition.