| Gliding arc discharge, as a warm plasma source, combines the merits of thermal and non-thermal plasmas and has wide applications in fuel conversion, surface modification of materials, pollution control and so on. Aiming at its eviromental application, the diagnosis of gliding arc plasma and its application in ammonia removal were studied in this work. As gliding arc plasma possesses a relatively high gas temperature (1500-4000K), emission spectra from different molecules overlap intensively with each other. In this work, firstly, the overlapped emission spectra were resolved and its plasma parameters were obtained. Then, a vortex gliding arc plasma reactor was designed and the temporally resolved diagnoses on the discharge characteristics of the vortex gliding arc plasma with alternating current (AC) frequencies of50Hz and kilohertz were performed. Finally, the kilohertz AC vortex gliding arc plasma was applied in the ammonia removal. The main results are as follows:1. Based on the spectral radiation model of diatomic molecules, simulations of the non-overlapped emission spectra of N2(C-B,Δv=0), OH(A-X,Δv=0) and N2(B-X,Δv=0), and the overlapped emission spectra of OH(A-X,Δv=0) with N2(C-B,Δv=1) and N2(B-X,Δv=0) with N2(C-B,Δv=-2,-3) were performed and auto-fitting calculations were carried out on the experimental spectra of the gliding arc plasma. The fitting results indicated that N2(C-B,Δv=-2) was more reliable for determing vibrational and rotational temperatures, while N2(C-B, Δv=0) could be used to determine the rotational temperature. The rotational temperature from OH(A-X,Δv=0) was about1200K higher than those from N2(C-B) and N2+(B-X) in one discharge cycle. The ratio of number density of OH(A) to N2(C) exhibited a concave profile in each half-cycle of the discharge. Its value was higher than30in the beginning and end of the discharge and was about25in the middle. The ratio of number density of N2+(B) to N2(C) exhibited a dual peak profile in each half-cycle of the discharge, and its value ranged from0.1to0.2.2. The temperal evolution of the50Hz AC gliding arc annular-mode discharge was studied by means of electrical, temporally resolved imaging and temporally resolved emission spectra measurements. The results showed that the discharge process went through the arc-ignition, arc-gliding and arc-extinction stages in each half-cycle of the discharge. During the arc-ignition stage, intensive discharge breakdown process was observed, accompanied with several fast voltage drops and intensive current pulses. Then the discharge proceeded into the arc-gliding stage, the discharge voltage and current varied gently, and the light intensity at the root of the arc cathode was much brighter than that at other areas, exhibiting a glow-like discharge characteristic. The spectral intensity of N2(C-B) during the arc-ignition stage was remarkably higher than that during the arc-gliding stage, while the spectral intensities of OH (A-X) and N2+(B-X) exhibited an opposite tendency. Within the investigated range of the discharge power and water vapor, vibrational and rotational temperatures remained nearly unchanged while decreased with increasing the water vapor contents.3. The dishcarge characteristics of30kHz AC vortex gliding arc plasma were investigated. The results indicated that the light intensity at the cathode arc root of the arc channel was remarkably bright. With increasing the gas flow rate, the gliding mode of the arc channel experienced a transition from an annular mode to a spiral one, and the next discharge occurred around the extinction region of the last discharge not at the narrowest space between the ignition electrode and the outer cylinder electrode. For a given discharge power, with increasing water vapor contents, the spectral intensities of N2(C-B) and N2+(B-X) were not influenced while that of OH(A-X) increased substantially. In the air discharge, the diameter of arc channel was1.1-1.3mm and the electron density calculated according to the current density was (5.5-8.1)×1012cm-3. To verify its reliability, in the4%H2/N2discharge, the electron densities calculated according to the current density and the Stark broadening of the Hβ line were compared and the both were of the same order of magnitude (1013cm-3). Moreover, the electron density in one discharge cycle exhibited a similar trendency with the instantaneous power.4. The application of the30kHz AC vortex gliding arc plasma in NH3removal was investigated. The results showed that the gas flow rate, diameter of vortex outlet and specific energy input(SEI) were three important parameters that affected the gliding mode of the arc channel and the NH3conversion. In the NH3/N2discharge, within the investigated range of diameter of vortex outlet and gas flow rate, decreasing the diameter of vortex outlet or increasing the gas flow rate could get the gliding mode of the arc channel to change from the normal spiral mode (Mode III-A) to the contracted one (Mode III-B), and thus the NH3conversion was improved. Compared with the NH3/N2discharge, with the addition of O2, a high NH3conversion was obtained with a relatively low SEI. With increasing the gas flow rate, the gliding mode of the arc channel changed from the contracted spiral mode (Mode III-B) to the extended one (Mode III-C), leading to the decrease of NH3conversion. With the connection of quartz tube (QT) to the vortex outlet, the gliding mode of the arc channel could return to the contracted one (Mode III-B) and the NH3conversion was further improved. By the comparison between the results of the direct current (DC) and30kHz AC discharges, the both exhibited almost equal NH3conversion at the same SEI. The difference was that the former could provide a higher SEI than the latter. |
