Performance Characteristics of Pilot-Scale Plasma-Chemical NOx Removal System from Boiler Emission

NO_x removal from a smoke tube boiler flue gas was investigated using a commercial ozonizer for indirect NO oxidation and a Na₂SO₃ chemical scrubber. The flue gas flow rate was in the range of 410~1,480 Nm³/h, the gas temperature of 185~325degC, and NOx concentration of around 40 ppm in city gas firing. Operational and performance data were obtained. The NOx removal efficiency was clearly dependent on the ORP, and increased inversely as the oxidation reduction potential (ORP) in the liquid decreased. To keep the specified NOx removal performance, it is essential to maintain the ORP properly by controlling additional Na₂SO₃ and NaOH solution injection, and to keep the ORP of less than 0 mV and the ORP change rate of less than 0 mV/min. At least, more than 4 kg/h of Na₂SO₃ added to the scrubber should be necessary to sustain the condition. NOx emission of less than 4 ppm was attained at 410 Nm³/h for a 300 minutes system continuous operation by maintaining ORP of -30 mV and pH of more than 7.8.