| DC corona induced radical shower is a new technique for multi-pollutants removal in flue gas. In corona discharge, the radical production and correlative investigation are quite important for the optimization and improvement of radical shower system. In this paper, the research processes of flue gas cleaning by corona discharge are reviewed, various detection methods of free radical are compared, and the advantage of radical detection by OES is summarized. The mechanism of radical detection by OES in corona discharge is discussed in detail, at the meantime, experimental OES system is set up for corona discharge diagnosisy and radical measurement, and conclusions for optimizing discharge and radical generation are achieved, as follows:Emission spectrums of OH(A2∑+→X2âˆ) and N2(C3âˆu→B3âˆg ) are detected in humid N2 DC corona discharge, the existence of OH radical in DC corona discharge is verified. The spatial distributions of OH(A2∑+→X2âˆ) and N2(C3âˆu→B3âˆg) emission intensity in nozzle, needle to plane discharge are diagnosised. The conclusion is: the light emission of these two transitions focuses in the areas of 10 mm in axial direction and 4 mm in radial direction from the center of discharge nozzle or needle; the emission signals decrease obviously when the detector comes to the farther positions from the nozzle or neelde; the large discharge nozzle leads to a broader OH distribution volume in radial direction, but the change of the discharge gap results in little variation of OH and N2 emission distribution; as the discharge power increases, the radical emission intensity is enhanced and its distribution volume is also expanded.The effect of discharge parameters, gas conditions on emission intensity of OH(A2∑+→X2âˆ) in a nozzle-plane corona radical shower system are experimentally investigated using emission spectroscopy considering the collisional quenching rate. The result is: both the discharge voltage and current have direct influence on OH emission, the OH production increases as discharge power rises; remarkable emission spectrum of OH(A2∑+→X2âˆ) is detected in humid N2 DC corona discharge, but few OH exist in humid air discharge; humidification of electrode gas can enhance the OH emission, and the existence of Ar increases the OH emission, while O2 may reduce the OH emission, the possible reason is that Ar induces the Penning dissociation and the attachment of O2 and free electrons reduces the energy of electrons in discharge space.The Hαtransiton of 656.3 nm is detected in a corona radical shower using Ar as H2O carrier, the intensity of both Hαand OH(A2∑+→X2âˆ) under various discharge power is investigated, and the effect of discharge power on excitation temperature is also studied by the Ar I lines calculation, the excitation temperature increases slowly as discharge power rises. Vibrational temperature of N2 molecule is calculated by Boltzmann plot in N2+H2O corona raidical shower, emission intensity ratio of N2(C3âˆu→B3âˆg,Δv=+1) and N2(C3âˆu→B3âˆg, 0-0) under different vibrational temperature are analyzed, the real emission intensity of N2(C3âˆu→B3âˆg,Δv=+1) band is calculated depending on the detected N2(C3âˆu→B3âˆg, 0-0) emission and vibrational temperature, finally, the integral emission intensity of OH(A2∑+→X2âˆ) is evaluated considering the spectral overlapping of OH(A2∑+→X2âˆ) and N2(C3âˆu→B3âˆg, 0-0). The experimental result shows that the spectral overlapping of OH(A2∑+→X2âˆ) and N2(C3âˆu→B3âˆg,0-0) has little interference on the integral emission intensity calculation of OH(A2∑+→X2âˆ).Laboratory experiments are performed to estimate ozone and OH production under three typical nozzles directions such as vertical, parallel and oblique to plane electrode using O2, H2O as the main radical source, to optimize corona discharge, electrode gas injection and improve active substance production. It is found that the efficiency of ozone production, OH emission intensity and NO oxidization with vertical nozzles show a distinct advantage over that with parallel nozzles. The possible reason is that the discharge zone is quite similar to radical sources enriched region with vertical nozzles, while the corona streamer is focused on the edge of radical source enriched region in parallel nozzles discharge, so the radical production rates are higher in the former condition. Thus the vertical nozzles are the best choice for effective active substance production in a corona radical shower.
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