NOx concentration using adsorption and nonthermal plasma desorption

The gas flow rates for hazardous air pollutant emissions are generally large and their concentrations are low (in parts per million levels). When we try to directly treat the large flow rate and low concentration exhaust gas, the size of the equipment becomes large, resulting in high operating cost. The objective of this study is to convert the exhaust gas with large flow rate and low concentration into the one with small flowrate and high concentration by desorbing the absorbed gas from the absorbent pellets packed inside a barrier-type packed-bed nonthermal plasma reactor. In this paper, we especially focus on the difficulties of treating NO_x. The absorbent pellets were molecular sieve spheres (MS-13X) made of zeolite with 1-nm pore diameter. The plasma desorption was carried out by applying the high voltage to the plasma reactor using any one of AC 60-Hz, AC 20-kHz, or pulse 210-Hz power supplies. We found out that NO_x could be desorbed effectively in the repeated adsorption and desorption process. Since the surface temperature increased rapidly, the desorption with AC 20 kHz took place not only by the electron impacts but also by the heat addition. In the desorption using the pulse power supply, the concentration rapidly increased and became maximum in a relatively short time. It was effective to close the reactor in the desorption process. It was successful to achieve a nonthermal plasma concentrating desorption of NO_x as the adsorption/desorption was repeated after more than 12 times.