Experimental Research And Kinetic Analysis Of Nitrogen Oxides Removal By Dielectric Barrier Discharge

Nitrogen oxides (NOx), produced by thermal power plants, not only pollute the environment, but also impose adverse effects on human health. The removal of NOx has become one of the greatest challenges in environmental protection. In order to achieve the goal of developing more effective and more environmentally friendly technologies for controlling NO, some new technologies for decomposing noxious pollutants have received much attention. Dielectric barrier discharge (DBD) plasma actuators, a new plasma technology, have recently attracted significant attention for their potential in the applied fields of NOx removal.This paper experimentally and theoretically analyses the effect of NOx by DBD, the main contents are as follows.1. In order to improve dielectric barrier discharge reactor structure, an experimental study was carried out into its effect on nitric oxide (NO) removal. Different structures were distinguished by electrode connection, diameter, material and shape of inner electrode, and dielectric material, respectively. In coaxial reactor, electrode connection does not affect NO removal efficiency, but a smaller breakdown voltage is required when a high voltage is applied to the outer electrode in the coaxial reactor. As gas gap in the reactor decreases, the electric field in the reactor increases, producing more high-energy electron and active radicals, and finally contributes considerably to NO removal efficiency. When the relative permittivity of dielectric increases, E/N in the reactor increases, producing more active radicals, and the higher the relative permittivity of dielectric, the lower the reactor impedance is, which makes the discharge current higher, producing more active radicals and promotiong NO removal efficiency. When energy density is 440 J/L, NO removal efficiency is 71%, 60% and 52% when inner electrode material is tungsten, copper and stainless steel, respectively. The breakdown voltage by the reactor with a screw electrode is smaller than that with a rod electrode, and NO removal efficiency with a screw electrode is higher than that with a rod electrode.2. Investigations into the effect of O2, H2O, CH4, C2H2, C2H4, CO2 and SO2 on NO removal. When add the O2, NO mainly oxidize to NO2. Hydrocarbons (methane, acetylene, ethyl ene) can make NO removal efficiency increase, and ethylene lead to highest NO removal efficiency. Since CO2 is an electronegative molecules, NO removal efficiency is prevented when add the CO2. H2O can greatly increase the rate of NO removal when the relative humidity of gas is 30%. But NO removal efficiency decrease when he relative humidity of gas increase to 60% and 90%, the breakdown voltage increases as the relative humidity of the gas increases. When the energy density is low, SO2 can prevent NO removal, but the addition of SO2 has no influence on NO removal when the energy density is high.3. Effect of gas temperature on NOx removal by dielectric barrier discharge was investigated. When temperature increases, E/N increases, increasing the ionization rate of gas molecules, when E/N rises from 50 to 150 Td, the electron mean energy increases by 2.3. In NO/N2 system, the rising temperature leads to generate more active particles, promoting NO removal efficiency slightly. In NO/O2/N2 system, an increase in the temperature increases the decomposition of active O3 species, producing a negative effect on NO oxidation.In NO/N2/O2/CH4, NO/N2/O2/C2H2 and NO/N2/O2/C2H4 system, when the temperature increases, the quantity of active species HO2 increases and the NO removal reaction (reaction between HO2 and NO) rate increases, reflecting an obvious improvement in NO removal. And in NO/O2/N2/C2H4/H2O system, when the temperature rises, NO removal is promoted dramatically.4. The plasma reaction model is built and the mechanism is analysed in N2/NO, N2/NO/O2, N2/NO/H2O and N2/NO/O2/H2O system. The model aims to simulate the variation of nitrogen oxides, and calculate the distribution of the major active radicals. The rate coefficients of major reactions are showed in the result.The simulation also reflect the distribution of electron density in the reactor, pionting out the range of the electron avalanche. The research result can provide academic references for the application of plasma technology.