In discharge denitrification, radical production by electron collision with combustion gas is a key process which determines the denitrification process and its performance. In this study N, O, OH and H radical densities have been measured by appearance mass spectrometry in a low-pressure discharge field with parallel electrodes (2 cm gap) under simulated combustion gas flow. Also, electric field, electron number density and electron temperature at the radical sampling position have been measured by the Langmuir probe method. Under constant discharge pressure the radical density (cm −3 ) was about 10 11 -10 12 cm −3 , and the density increased with increasing the discharge current. Under constant discharge current, both the radical concentration [−] and electron temperature increased with decreasing pressure. The radical concentration in the cathode fall region was greater than that for the outer region. Additionally, we measured the concentration change of NO mixed in the simulated combustion gas and observed a little change of the NO concentration.
SUMMARYBy virtue of its comparatively high denitrification (deNOx) efficiency and its compactness, the pulsed-discharge deNOx process is considered to be one of the deNOx processes suitable for combustion gas. However, there has been insufficient clear guidance on the optimum electric field, pulse duration, and pulse repetition frequency, and no clear understanding of pulsed-discharge deNOx process. In this study, we have simulated the pulsed-discharge deNOx process by solving the Boltzmann equation for discharge electrons and the deNOx chemical reaction equations simultaneously, and we have shown the time change of chemical species concentration, extracting the main deNOx reactions. The simulation shows that the pulsed-discharge deNOx process consists of two processes, the reduction of NO to N 2 by N radicals and the oxidation of NO to HNO 3 and HNO 2 by OH and O radicals, and that the amounts of radicals produced and consumed are governed by parameters such as the electric field, pulse duration, and pulse repetition frequency. In our simulation, such parameters are varied widely to examine their quantitative effect on the deNOx energy consumption, NxOy removal efficiency, and reduction ratio in the discharge deNOx process. The preliminary pulsed-discharge deNOx performance is estimated from our simulation, indicating that the discharge deNOx process has almost the same performance as the electron-beam deNOx process.
From comparatively high deNOx efficiency and its compactness, the pulsed-discharge deNOx process is considered to be one of the deNOx processes for combustion gas. However, a clear guidance for optimum electric field, pulse
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