NOx reduction after treatment system using nitrogen nonthermal plasma desorption

In the flue emission from an 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_x in the emission completely using catalysts or plasma alone because part of the NO_x is oxidized under an O₂-rich environment. In order to overcome these difficulties, we proposed a new after treatment system of NO_x included in the exhaust gas of the combustion system using nonthermal plasma (NTP) desorption and reduction. In this system, exchangeable adsorbent columns are equipped. First, the exhaust gas including NO_x is adsorbed to an NO_x adsorbent for a period of Δt_a. After the period of Δt_a, the path of the exhaust gas is changed with a pair of rotary valves and NO_x adsorbent is changed. The adsorbed NO_x is desorbed from the adsorbent and reduced by applying NTP for a period of Δt_d using N₂ or low-oxygen-concentration gas. The exhaust gas is always kept clean by the exchange of adsorbent. Further, total electric energy can be reduced because NTP is not applied for Δt_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 N₂ NTP desorption and NO_x reduction were examined experimentally using a pulse corona NTP reactor. After several adsorption/desorption processes, the amount of NO_x adsorbed becomes equal to that of the NO_x desorbed, that is, all the NO_x was desorbed in a single desorption process. It is confirmed that the NO_x complete reduction using N₂ NTP desorption is possible not only for a simulated exhaust gas but for a real diesel engine gas. The effective specific energy density can be decreased down to 22 Wh/m³.