NO<italic>x</italic> Removal Performance of a Wet Reduction Scrubber Combined With Oxidation by an Indirect DBD Plasma for Semiconductor Manufacturing Industries

Abstract

A wet packed-bed scrubber combined with dry oxidation by an indirect dielectric-barrier-discharge plasma for the conversion of NO to NO2 and wet reduction with two reduction agents of Na2S and Na2SO 3 to remove NO2 was developed at room temperature for semiconductor manufacturing industries. The design and operation parameter for the wet scrubber such as gas concentration, liquid-to-gas ratio, reducing agent concentration, residence time, and pressure drop were investigated at 2 m3/min and 200 ppm of pure NO gas. Na2S solution was more suitable than Na2SO3 with less chemical consumption and liquid-to-gas ratio. The removal efficiency of over 80% was achieved with the liquid-to-gas ratio of 10 L/m3, reduction agent solution of 0.1% w/w, which corresponds to oxidation and reduction potential of −310 mV and pH of 12.3, residence time of 2 s, and pressure drop of 25 mmAq/m, respectively. Finally, a demonstration test of the wet scrubber was conducted for 1 month with an exhaust gas from the perfluorinated compounds gas scrubber at the rooftop of a semiconductor manufacturing plant in Korea. In order to suppress H2S as byproducts of the wet scrubber, pH over 12 was carefully controlled with NaOH solution because commonly highly acid gases such as HF and HCl were fed from the manufacturing process. The NO x removal efficiency was 83.8% on an average, which was very similar to those obtained from the lab tests. These results indicate that the combination of the dry oxidation and wet reduction method could be a promising solution to remove NO x from semiconductor manufacturing industries.