Douyan Wang

Improvement of NO/sub X/ removal efficiency using short-width pulsed power

Pulsed power has been used to remove nitric oxide (NO) in a mixture of nitrogen, oxygen, and water vapor simulating the flue gases from a power station stack. The effect of the pulsewidth at a fixed applied voltage on NO removal concentration was studied. The dependence of the energy efficiency of the removal of NO at a fixed applied voltage on the pulsewidth, on the removal ratio of NO and on the discharge current was investigated. This removal energy efficiency increases with decreasing pulsewidth and decreasing removal ratio of NO.

Propagation velocity of pulsed streamer discharges in atmospheric air

Pulsed streamer discharges have been extensively used in many applications such as control of NO/sub X/ and SO/sub 2/ from exhaust gases, treatment of dioxins, removal of volatile organic compounds, generation of ozone, and laser excitation. An operation with a high energy efficiency is necessary for practical applications. It is very important to know the propagation mechanism of streamer discharges in order to improve the energy efficiency of pulsed discharge systems. In this paper, the emission from pulsed streamer discharges in a coaxial electrode system in air at 0.1 MPa was observed using a high-speed gated intensified charge-coupled display camera. A concentric wire-cylinder electrodes configuration was used. A positive pulsed voltage having a width of about 100 ns was applied to the central electrode. The streamer discharges were initiated at the inner electrode and terminated at the outer electrode. The propagation velocity of the streamer discharges was 1.8-3.3 mm/ns.

Positive- and Negative-Pulsed Streamer Discharges Generated by a 100-ns Pulsed-Power in Atmospheric Air

A Blumlein generator that has a pulsewidth of 100 ns was used to investigate the process of streamer discharge propagation in a coaxial cylindrical reactor using a streak camera. Both positive and negative polarities of the streamer discharges were performed in air at atmospheric pressure. The results showed that the primary and secondary streamers propagated with increasing velocity from the central rod to the outer cylinder electrode in both positive and negative polarities of applied voltages to the rod electrode. The propagation velocity of the streamer heads was in the range of 0.8-1.2 mm/ns for a positive peak applied voltage in the range of 43-60 kV and 0.6 mm/ns for a negative peak applied voltage of -93 kV, respectively. The electric field at streamer onset was calculated to be 12 and 20 MV/m for positive and negative applied voltages, respectively.

Novel dual Marx Generator for microplasma applications

Micrometer size plasmas, or microplasmas, find applications in pollution control, reduction, and prevention. The required nonthermal plasmas can be generated by either an electron beam or an electric discharge. The pulse widths and voltages necessary to generate these nonthermal plasmas are 10/sup -10/-10/sup -8/ s, and 10/sup 3/-10/sup 4/ V, respectively, depending on the application. The required energy is typically in the low 10/sup -3/ J range. This paper presents a novel circuit design to generate high-voltage pulses with variable pulse widths and pulse rise and fall times in the low 10/sup -9/ s regime. The circuit employs two parallel Marx Generators utilizing bipolar junction transistors (BJTs) as closing switches. The BJTs are operated in the avalanche mode to yield fast rise times. The design allows for positive or negative polarity pulses, and can easily be changed to yield higher or lower output voltage.

Influence of gas flow rate and reactor length on NO removal using pulsed power

A short duration of 100-ns pulsed power has been used to remove nitric oxide (NO) in a mixture of nitrogen, oxygen, water vapor, and NO, simulating flue gases from a power station. The effects of the gas flow rate, the reactor length, and the pulse repetition rate on the percentage of NO removal and its energy efficiency are reported. The percentage of NO removal at a fixed gas flow rate increased with increasing pulse repetition rate due to the increased energy into the discharge. At a fixed pulse rate, the removal of NO increased with decreasing gas flow rate due to the increased residence time of the gas in the discharge reactor, thus facilitating the creation of increased radicals of O and N which then decreased NO. The energy removal efficiency of NO (in mol/kWh) decreased with increasing gas flow rate and increasing removal ratio of NO. The removal of NO increased with increasing energy density (J/I), input into the discharge at different reactor length.

Energy Efficiency Improvement of Nitric Oxide Treatment Using Nanosecond Pulsed Discharge

Pulsed streamer discharge plasmas, one type of nonthermal plasma, have been used to treat exhaust gases. Since a pulsewidth of applied voltage has a strong influence on the energy efficiency of the removal of pollutants, the development of a short-pulse generator is of paramount importance for practical applications. In this paper, a nanosecond (ns) pulse generator which has a 5-ns pulse duration in output pulsed voltage is developed, and NO-removal experiments using ns pulsed discharge were conducted. The experimental results of the NO removal showed 100% of NO-removal ratio at 7 pps of pulse repetition rate and the extremely high energy efficiency, which is 0.43 mol/kWh (12.9 g-NO/kWh) for NO removal (initial NO concentration = 200 ppm; gas flow = 2.0 l/min ). The result of deriving energy efficiency for NO removal indicated that the ns pulsed discharge has great advantage in energy efficiency for NO removal to the conventional discharge methods. By this research, the utility of the ns pulse plasma process was proven, and the influence of shorter pulse duration on NO-removal energy efficiency was confirmed.

The reactor design for diesel exhaust control using a magnetic pulse compressor

A magnetic pulse compressor (MPC) was used to control the exhaust gases from a diesel generator employing a wire-to-plate plasma reactor in this work. To obtain efficient NO/sub X/ removal, the energy transfer efficiency from the MPC to the plasma reactor and the pulse streamer discharge physics were investigated by varying the number of anode wires and wire-to-wire distance of the reactor. It was experimentally confirmed that the number of wires and the neighboring wire distance affected the energy transfer efficiency. The optimal reactor design for efficient diesel exhaust processing using an MPC can be achieved by employing large numbers of wires and long wire-to-wire distances for the wire-to-plate reactor.

Production of nitric monoxide using pulsed discharges for a medical application

Nitric monoxide (NO) is widely used in medical treatment of acute respiratory distress syndrome (ARDS). The production of NO is of interest to the medical community. In the present work, NO is generated by pulsed discharges between two rod electrodes in a mixture of nitrogen and oxygen. An arc discharge having a temperature of about 10000 K was produced, which was sufficient to generate NO. Some of the important parameters affecting the production of NO have been investigated. These include the percentage of O/sub 2/ (6-94%) in the mixture of Na and O/sub 2/, the energy of the discharge (0.5-12 J/pulse), the pulse repetition rate (0.54.5 pps) and the flow rate (1.35-5.4 l/min) of the gas mixture. NO/sub 2/ produced in the discharge was successfully changed to NO using a heated molybdenum tube, NO/sub 2/ must be extracted from the gas before clinical inhalation. The concentration of ozone was completely eliminated by bubbling the gas mixture through water. A maximum of NO and a minimum of NO/sub 2/ concentrations were generated when the proportion of O/sub 2/ in the gas mixture was in the range of 20-27%. The concentrations of NO and NO/sub 2/ increased with increasing pulse repetition rate and with decreasing flow rate of the mixture. In all cases, No/sub 2/ was effectively removed using a heated molybdenum tube.

Pulsed Discharge Induced by Nanosecond Pulsed Power in Atmospheric Air

Nonthermal plasmas have been widely used for various applications. Observation of a discharge plasma is an essential aspect for understanding the plasma physics of this growing field. In this paper, the propagation of a general pulsed discharge having a 100-ns pulse duration is observed by taking framing and streak images and spectroscopic measurement. The results showed that two discharge phases exist in the general pulsed discharge, namely, a streamer discharge and the following glowlike discharge. Between these two phases, the electrode gap impedance changed dramatically which could cause impedance mismatching between the power generator and the electrode. In addition, the gas temperature increased about 150 K during the glowlike discharge, which causes further energy loss in plasma-enhanced chemical reactions. Consequently, it was decided to remove the glowlike discharge phase and to only have the streamer discharge. A nanosecond pulsed power generator having a pulse duration of 5 ns was developed, and the observed discharge propagation ended before it shifts to the glowlike discharge. The streamer propagation velocity with the nanosecond pulsed discharge was 6.0-8.0 mm/ns, which is much faster than that of a general pulsed discharge, and showed little difference between positive and negative voltage polarities.

Development of higher yield ozonizer based on nano-seconds pulsed discharge

Abstract Energy efficient generation of ozone is very important because ozone is being used increasingly in a wide range of industrial applications. In this study, ultra-short duration pulsed streamer discharges with a duration of 5 ns hava been used to produce ozone in a wire-to-cylinder electrode reactor. The triaxial Blumlein configuration is used for the nano-seconds pulsed generator. Ozone concentration and ozone production yield were measured at various applied voltages (50 to 70 kV), and pulse repetitions (10 to 60 pps) at atomospheric pressure in oxygen and air. The experimental results showed that the ozone concentration (g/m3) increased with increasing applied pulse voltage and pulse repetition rate. Higher ozone concentrations were obtained in the oxygen-fed ozonizer than in the air-fed ozonizer. The ozone production yield (g/kWh) was high at low ozone concentration, and higher ozone yield was obtained with lower applied voltages. Characterization maps of ozonizers based on different discharge methods (nano-seconds pulsed discharge, DBD, DBD with narrow-gap, surface discharge, pulsed corona discharge, DC corona, superimposed discharge methods and a commercial ozonizer) were presented with oxygenfed and air-fed cases. A nano-seconds pulsed discharge showed the highest ozone yield in the characterization maps for both the oxygen-fed and air-fed cases, where the highest ozone yield were 544 and 239 g/kWh in the oxygen-fed and air-fed cases, respectively.