Experimental And Mechanism Investigation On Nitric Oxide Conversion In Pulsed Corona Discharge By Optical Diagnostic Method

The emission of pollutants to the environment is inevitable with the development of economy and society, which results in threats to the environment and health of human being. The pollutants emitted from coal-combustion plants mainly include SO2NOX, Hg, VOCs and PAHs. It is urgent to control the pollutants emission from combustion device as regulation to limit the pollutants emission becoming strict. NOX is an important pollutant and it is urgent to be controlled, so the investigation of NOx conversion process is significant.Pulsed corona discharge is a typical non-thermal plasma form. The radicals such as OH, O, N, H, HO2etc. generated by pulsed corona discharge can react with pollutants so as to decompose them. The multi-pollutants simultaneous removal can be achieved by pulsed corona discharge. The reactions between pollutants and radicals are complicated in the discharge process, so investigation of the mechanism between pollutants and radicals are significant to control the pollutants effectively. However, the lifetimea of radicals are very short, and it is difficult to detect them. The optical diagnostics will not disturb the discharge process since they are non-contant measurements. They are suitable for investigation of pollutants removal mechanism because of the high resolution. NOX was chosen as a typical pollutant, and its conversion mechanism was studied by optical mehods in this thesis.The physical characteristics in the pulsed corona discharge were studied in the thesis firstly. The results show that a little Ar could obviously reduce the threshold voltage; the increase of O? component decreased the discharge current and increased the break-down voltage. The gas temperature in the discharge zone almost equaled the room temperature, but the temperature near the tip electrode was high (more than600K), and the temperature gradient was large. The OH evolution was investigated. The OH decay after discharge can be divided into two periods:fast decay period and slow decay period. The OH density increased with increase of O2conentration and humidity. The OH decay rate in the fast decay period decreasd with increase of O2concentration, and increased with increase of humidty. The OH density decreased as NO was introduced into the reactor. The OH decay velocity was independent with the initial NO concentration. The structure of reactor affect the NOx conversion process in corona discharge. The results show that the intensity of streamer and the NO conversion rate increased with the decrease of curve radius in needle-to-plate discharge; the streamer distribution zone and NO conversion rate increased with the increase of needle tip numbers; in the nozzle-to-plate discharge form, the OH yield and NO conversion increased because of the addition gas. In order to improve the NO conversion further, we represent a new discharge form:separated radical injection discharge, which can increase the collision probability between radicals and NO, and improve the NO conversion rate.The addition gas is an important parameter that affects the NO conversion in pulsed corona discharge. The NO conversion was investigated under different addition gas conditions. First, the effects gas components on NO conversion were studied. The increase of Ar component improved the NO conversion rate and OH yield; the increase of O2component also improved the NO conversion, but decreased the OH yield. Then, the effects of Reynolds numbers on NO conversion were discussed. The NO conversion rate for Re=4138was larger than that for Re=1379. The OH yield and distribution zone also increased with increase of Re number.NOX conversion mechanism in the pulsed corona discharge process was investigated based on the results above. In the process of NO2to NO. the effect of N2is reduction. N and the excited N2were produced in the discharge through the reactions between electron and N2, and then reacted with NO2to generate NO or N2; the effect of O2was oxidation. O, O3and OH radical were produced through the reactions between electron and O2, and then reacted with NO2to generate other nitric oxides. In the process of NO to NO2, the effect of N2and O2were also reduction and oxidization, repectively, which led NO convert to N2or NO2. In the process of NOX formation, there was only NO2produced under the condition of N2/O2/Ar, and the NO2concentration increased with the increase of No or O2concentration. The simulation of NOX conversion mechanism has been done under the same conditions of the experiments.