NOx reduction using nitrogen nonthermal plasma desorption

Abstract

In the flue emission from internal combustion system using diffusing combustion such as coal or oil fuel boiler, incinerator or diesel engine, around 10% oxygen is usually included. It is difficult to reduce the NO/sub X/ in the emission completely using catalysts or plasma alone because the part of NO/sub X/ is oxidized under O/sub 2/ rich environment. In order to overcome these difficulties, we proposed a new after treatment system of NO/sub X/ included in exhaust gas of combustion system using nonthermal plasma (NTP) desorption and reduction. In this system, exchangeable adsorbent columns are equipped. First, the exhaust gas including NO/sub X/ is adsorbed to a NO/sub X/ adsorbent for a period of /spl Delta/T/sub a/. After the period of /spl Delta/T/sub a/ the path of exhaust gas is changed with a pair of rotary valves and NO/sub X/ adsorbent is changed. The adsorbed NO/sub X/ is desorbed from the adsorbent and reduced by applying NTP for a period of /spl Delta/T/sub a/ using N/sub 2/ or low oxygen concentration gas. The exhaust gas is always kept clean by the exchange of adsorbent. Further, total electric energy can be reduced by taking /spl Delta/T/sub d///spl Delta/T/sub a/ smaller because NTP is not applied for /spl Delta/T/sub a/. This system can be operated at atmospheric temperature because no catalyst is used. As an initial step to realize such kind of after treatment system, the basic characteristics of the N/sub 2/ NTP desorption and NO/sub X/ reduction were examined experimentally using a pulse corona NTP reactor. After several adsorption/desorption processes, the amount of NO/sub X/ adsorbed becomes equal to that of NO/sub X/ desorbed, that is, all the NO/sub X/ was desorbed in a single desorption process. It is confirmed that the NO/sub X/ complete reduction using N/sub 2/ NTP desorption is possible not only for a simulated exhaust gas but for a real diesel engine gas. The effective or apparent SED can be decreased down to 29 Wh/m/sup 3/. Further improvement will be obtained by decreasing the ratio of /spl Delta/T/sub d///spl Delta/T/sub a/.