Performance Characteristics of Pilot-Scale Indirect Plasma and Chemical System Used for the Removal of $\hbox {NO}_{\rm x}$ From Boiler Emission

The process of removing NO_x from the flue gas emitted from a smoke-tube boiler was investigated using an ozonizer, which is used for carrying out the indirect oxidation of NO, and a Na₂SO₃ chemical scrubber. The flow rate of the flue gas was in the range of 410 - 1480 N·m³/h, its temperature was in the range of 185°C- 325°C, and the concentration of NO_x was approximately 40 ppm during the combustion of city gas. Operational and performance data were obtained from the experiments. The efficiency of the NO_x removal process was clearly dependent on the oxidation reduction potential (ORP), and it increased with a decrease in the ORP of the scrubbing solution. To effectively remove the requisite amount of NO_x, it is essential to maintain the ORP by controlling the injection rates of the Na₂SO₃ solution and maintaining an ORP of less than 0 mV and the rate of change in ORP to less than 0 mV/min. More than 4 kg/h of Na₂SO₃ must be added to the scrubber in order to sustain the aforementioned ORP condition of the scrubbing solution. The amount of NO_x emitted from the flue gas was maintained as less than 4 ppm at a flue gas flow rate of 410 N ·m³/ h during a 300-min continuous system operation by maintaining an ORP of -30 mV and a pH of more than 7.8 for the scrubbing solution.