AC/DC/pulsed-power modulator for corona-plasma generation

Gas-cleaning techniques using nonthermal plasma are slowly introduced into industry nowadays. In this paper, we present a novel power modulator for the efficient generation of large-volume corona plasma. No expensive high-voltage components are required. Switching is done at an intermediate voltage level of 1 kV with standard thyristors. Detailed investigations on the modulator and a wire-plate corona reactor will be presented. In a systematic way, modulator parameters have been varied. Furthermore, reactor parameters, such as the number of electrodes and the electrode-plate distance, have been varied systematically. The yield of O radicals was determined from the measured ozone concentrations at the exhaust of the reactor

Novel modulator topology for corona plasma generation

Gas cleaning using plasma technology is slowly introduced into industry nowadays. Several challenges still have to be overcome: increasing the scale, safety, life time and reducing costs. In 2006 we demonstrated a 20 kW nanosecond pulsed corona system. The electrical efficiency was > 90%. O-radical yields were found to be very high (3-7 mole/kWh). However, to be competitive, high costs of the pulsed power technology are still a major hurdle. Here we present a novel modulator for efficient generation of large volume corona plasma. Only a small amount of expensive high voltage components are required. Switching is done at an intermediate voltage level of 1 kV with standard thyristors. At the high voltage side, only a diode and a pulse transformer are needed. The estimated costs are about 5 kEuro/kW, whereas for state of the art pulsed power technology these costs usually are about 20-30 kEuro/kW. Detailed investigations on the modulator and a wire plate corona reactor will be presented. Modulator parameters have been varied systematically as well as reactor parameters (number of electrodes, electrode-plate distance). The O-radical yield was determined from the measured ozone concentrations at the exhaust of the reactor. With a detailed kinetic model, ozone concentrations could be calculated back to the initial O*-yields. The following conclusions will be discussed: for all parameters, an electrical efficiency of > 90% could be obtained. With fast imaging, the average streamer width was found to be ~ 737 µm and an estimate for the plasma volume was made. The obtained yields of O-radicals (1-4 mole/kWh) are excellent. The conditions to obtain high yields will be discussed