Optical Diagnosis Of OH Radical And NO Oxidation In Pulsed Corona Discharge

In order to resolve some disputes on mean electron energy levels, characteristics of OH radical, dominant chemically active species of NO oxidation, and to achieve optimization for simultaneous removal of flue gas multi-pollutants through pulsed corona discharge, optical diagnosis of OH radical and NO oxidation in pulsed corona discharge were carried out based on laser-induced fluorescence (LIF) and optical emission spectroscopy (OES).Firstly, the ratio of emission intensities emitted by the excited molecules and ions of N2was made comparative analysis with numerical simulation to determine average electron energies and electric field distributions. Within2cm distance from wire electrode in horizontal and vertical directions, electric field and average electron energies appear to be in the ranges of11.05～19.6MV/m and10.10～13.92eV; as the distance increases, average electron energies and electric field show a similar trend: first decrease and then increase. Chemically active species, such as OH、O and O3, can be generated through the energetic electron collisions with H2O and O2directly or indirectly.Secondly, characteristics of OH radical were diagnosed by LIF. a) Both Large and small wire-to-plate spacings produce adverse effects on the generation and distribution of OH radical:when the spacing is5cm or6cm, OH radical spreads more widely than2cm spacing, with weaker intensity.3cm or4cm spacing shows better performance in the generation and distribution. b) OH radical is mainly produced in secondary streamer, and distributes in streamer channel of the discharge volume, especially around the wire electrode. c) With increasing O2concentration or relative humidity, OH radical increases and peaks its value at around3%O2concentration or60%relative humidity. d) In humidified Ar, weaker streamer and lower OH-LIF intensity are produced in pulsed corona discharge. e) OH radical density reaches its maximum value approximately3～4μs after the discharge in nitrogen of RH76%, and then decays with a time constant of about7μs, drops considerably low level within135μs. Primary mechanisms responsible for destruction of OH radical after the discharge pulse are collisions with molecules, atoms and ions from the non-thermal plasma generated in pulsed corona discharge.Finally, production of O3with varying O2concentration, OH radical and NO distribution in NO oxidation were diagnosed based on LIF and OES. a) The amount of O3gradually increases with O2concentration and peaks at8%. b) In the NO oxidation, there is no coexistence of NO and O3, whereas coexistence of NO and OH. NO is oxidized by O3or O more efficiently than OH radical.