Combined removal of SO2 and NOx from exhaust gas by using dielectric barrier discharge and absorption-reduction techniques

Dielectric barrier discharge is an easily available method to produce ozone that is a strong oxidant. When ozone is injected into the exhaust gas, NO, which is the main component of nitrogen oxides (NOx), is rapidly oxidized to NO2. The NO2 that forms can be reduced to N-2 by a reducing agent, such as sodium sulfide or sodium sulfite, in the next step. These chemical reagents are also able to remove SO2 effectively. In this paper, a two-step process consisting of an ozonizing chamber and using an absorber containing sodium sulfide or sodium sulfite solution is proposed to remove NOx and SO2 simultaneously. When the exhaust gas passed through the ozonizing chamber and the absorber sequentially, more than 95% removal efficiencies of NOx and SO2 were observed. The rate of depletion of the reducing agents during the treatment of the exhaust gas was much faster than expected from the reaction stoichiometry, obviously because of oxygen in the exhaust gas. Compared to sodium sulfite, sodium sulfide maintained its reduction capacity much longer. The amount of sodium sulfide required was ca. four times the amount of NOx and SO2 removed.