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 Na
₂
SO
₃
chemical scrubber. The flow rate of the flue gas was in the range of 410 - 1480 N·m
³
/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 Na
₂
SO
₃
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 Na
₂
SO
₃
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 ·m
³
/ 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.