DeNOx Characteristics Using Two Staged Radical Injection Techniques

Ammonia radical injection using pulsed dielectric barrier discharge (DBD) plasma has been investigated as a means to control NOx emissions from combustors. When DBD plasma-generated radicals (NH2, NH, N, and H) are injected into a flue gas containing nitrogen oxide (NOx), NOx is removed efficiently by chain reactions in the gas phase. However, because the percentage of NOx removal gradually decreases with increasing oxygen concentrations beyond 1% O₂, improvement of the DeNOx (removal of nitrogen oxide) characteristics at high O₂, concentrations was necessary for commercial combustors. A two-staged injection of the DeNOx agent was developed based on the detailed mechanisms of electron impact reactions and gas phase reactions. A concentration of H radical was observed to play an important role in NOx formation and removal. The effects of applied voltages, oxygen concentrations, and reaction temperatures on NOx removal were investigated under normal and staged injection. NOx removal was improved by approximately 20% using staged injection at O₂, concentrations of 1 to 4%.