Study Of Desulfurization And Denitrification From Fuel Gas Stream Using Oxygen Radicals Injecting

The work is supported by National High Technology Research and Development Program of China (No.2008AA06Z317) "SO2 and NOx Removal from Flue Gas Using Hydroxyl Radical Oxidation" and Project of China Environmental Protection Foundation (No.CEPF200812313) "A New Green Method of SO2 and NOx Removal from Flue Gas to Acid Droplets Using Hydroxyl Radicals Oxidation".With the aim of solving the problems of SO2 and NOx gas-phase oxidation in the process of desulfurization and denitrification from flue gas, this research is carried out around two key things. One is how to produce hydroxyl (·OH) radicals with high concentration and high efficiency, and the other is how to remove SO2 and NOx by radicals oxidation. In the end, these two problems will be solved, and a new gas-phase oxidation method for the removal of SO2 and NOx using strong ionization discharge at atmospheric pressure is found.Using strong electric-field ionization discharge method, water vapor and O2 are ionized, decomposed, and excited extremely into radicals, such as O3,O2-,H2O+,H2O2 and so on. The radicals can transform into·OH, once they are injected into the flue gas. The·OH radicals are generated accompanying a complicated process, which includes lots of plasma chemistry reactions. Being one of the most active radicals,·OH can oxidize SO2 and NOx into H2SO4 and HNO3 on high speed in gas-phase.Basing on the gas discharge physics, plasma chemistry, macrodynamics, the processes of radicals formation and·OH conversation are represented, and reaction mechanics of SO2 and NOx oxidizing by radicals are discussed with mathematics model helping. Experimental system of SO2 and NOx removal using radicals injection has been set up, and effects of operating conditions are discussed in detail, such as mole concentration ratio of oxygen radical to SO2/NOx, gas temperature, gas-flow rate, water vapor concentration, and so on. Moreover, the method of by-produce recycling has been investigated. At last, the optimally conditions of SO2 and NOx removal and recovery have been established.The research results show that in oxygen radicals the concentrations of ozone, positive ion and negative ion are 243 g/m3,2.5×1016/m3,1.7×1016/m3, respectively. This method not only can be applied to single desulfurization or denitrification from flue gas, with the removal rate 90% and 100%, but also the simultaneous desulfurization and denitrification, with the removal rate 68% and 100%. The recovery rates of SO2 and-NOx can reach as high as 68.7% and 77.1%, respectively.The research has solved two difficult problems of production of·OH with high concentration and SO2/NOx oxidation in gas-phase. Therefore, the method for SO2 and NOx removal from flue gas by radical injection without absorbent and catalyst additive, may open a new perspective on resourcify flue gas desulphurization and denitrification.