Theory And Experimental Research On Dielectric Barrier Discharge Treatment Of Nitrogen Oxides

Reducing nitrogen oxides (NOx) emissions from coal-fired power plants has already become an urgent task faced by the electric power industry, because the coal-fired power plants are the second largest source of NOX emissions in the world and NOX causes a wide variety of health and environmental problems. Some emissions control strategies have been implemented, among which selective catalytic reduction (SCR) technology dominate the market of the coal-fired power plants applications in recent years. However, the problems of SCR appear to be the narrow temperature operation band, catalyst poisoning, ammonia leakage and the high cost. Presently many emerging technologies are focusing on systems capable of controlling NOX emissions and overcoming the problems of SCR, among which dielectric barrier discharge (DBD) technique in this paper is one of the most promising. The contents of this paper include:(1) The Boltzmann transport equation subject to a rapidly time-varying excitation field for DBD has been given. Based on the Boltzmann equation, a electron collision kinetic model for ionized gas has been established. Elastic, excited, and ionized cross sections data of gas mixture consisting of dilute concentration of NO in N2 have been found. Electron energy distribution function, dissociation reaction rate, and electronic mean drifting velocity of the non-thermal plasma in a common DBD reactor have been calculated, based on which it produces 0.346 N radical per 100 eV.(2) The chemical kinetics model has been established and the reaction mechanism and thermodynamic data of gas mixture consisting of dilute concentration of NO in N2 have been attained. United the electron collision kinetic model and the cross sections data, a DBD processing of NOX model has been established. The reaction rates as a function of the input energy density has been calculated. The calculation indicated:by research using the gas mixture consisting of dilute concentration of NO in N2, it is suitable to examine the effect of reactor design on the DBD processing of NOX.(3) A benchtop experimental apparatus of DBD processing of NOX has been set up. Experiments were conducted and the parameters investigated included length, frequency, gap distance, and gas flow rate in the DBD reactor. Results show that: An ideal reactor needs the length to match the demand of discharge power. The gap distance has little effect on the electrical energy consumption for DBD processing of NOx when the gap distance is equal or greater than 3 mm. Altering the supply frequency almost does not affect the electrical energy consumption for DBD processing of NOx when the frequency is less than 1 GHz. The gas flow rate has little influence on nitrogen oxides removal efficiency when the input energy density is identical.(4) Experiments were conducted in the presence of the individual components, such as N2, O2, O3, Ar, and C2H4, as well as the mixture of these, will be presented. Results show that:NO cannot completely convert to NO2 in the presence of O2 without any handling. Only relying on the Ar existing in the flue gas or adding a small quantity of Ar in the flue gas can not improve the NO removal effect. O3 could remove the NO efficiently, but O3 today is not cost-effective, due in part to relatively high manufacturing costs. NO can successfully convert to NO2 in the presence of C2H4. The preferred concentrations of C2H4 shuold be 2 times of the NO.