Removal of Nitrogen Oxides Contained in Combustion Exhaust Gas by Nitrogen Plasma Injection

Abstract

The purpose of this study is to investigate the method of removing the NO_x contained in combustion exhaust gases by nitrogen plasma injection. Removal characteristics of NO_x are studied under the Zeldovich mechanism. First, the temperature and velocity distributions of the plasma wake were measured along the plasma jet axis. Optimum flow rates of plasma N₂ gas and simulated exhaust gas were determined after consideration of stable plasma operation and the formation of N atoms in arc plasma. Secondly, the simulated exhaust gas (N₂+O₂+CO₂+NO) was mixed with N atoms produced in the N₂ plasma. The Zeldovich reactions for excited N atoms with NO and O₂ will take place. The effects of O₂, CO₂, and H₂O on the reduction of NO_x were studied experimentally. The NO_x removal ratio of 40 to 50% is observed under the condition of O₂ concentration of 3 to 5% and the plasma power of 600 W ; CO concentration generated in the exhaust gas is about 300 ppm. The removal ratio η is highest for a low reaction temperature of less than 500 K. The value of η changes from 100 to 60% due to the addition of H₂O to gas. However, the recovery of the removal ratio is achieved by changing the gas injection site to plasma, as a result of the decrease of OH radical formation. Retention time required for reaction is less than ten milliseconds.