Limitations of NOx removal by pulsed corona reactors

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Design and implementation of a compact 20 kHz nanosecond magnetic pulse compression generator

A compact magnetic pulse compression (MPC) topology with only two magnetic cores and a continuous repetition rate of 20 kHz is presented. The demand for higher average output powers of pulsed power systems can be achieved by an increase of the pulse rate frequency (PRF). The PRF is often limited by the switching speed or recovery of the main switch and also the complex behavior of the magnetic materials. With the advent of insulated gate bipolar transistors and the nanocrystalline soft magnetic material, PRFs of tens of kilohertz are feasible if a suitable MPC topology is applied. The presented MPC is based on an existing topology that has been significantly improved to enable high-frequency pulse generation. A design method using 3-D magnetostatic and transient magnetic simulations is introduced to enable optimization of the magnetic switching components. A 20 kHz, 60 kV, and 52 ns full width at half maximum (FWHM) MPC generator is designed, built, and tested for a 100 Ω load. Simulations suggest that a PRF up to 50 kHz is achievable, but continuous operation will likely be limited by thermal management

Energizing a long nanosecond pulsed corona reactor:electrical characterization

\u3cp\u3eIndustrial application of nanosecond pulsed corona technology for air purification requires high volume, high power plasma reactors. Cylinder-wire type reactors require multiple cylinders or very long reactors to meet these demands. In this article, we focus on the characterization of a pulsed corona plasma in a long (4.5 m) plasma reactor. The reactor cylinder acts as a coaxial transmission line wherein high-voltage pulses propagate with close to the speed of light. Interactions between plasma generation and reflection behavior inside the reactor are expected and therefore investigated. A 4.5-m-long corona reactor is constructed and equipped with voltage and current sensors at multiple positions along the reactor length. A lumped element SPICE model is developed to simulate the reflection behavior. Strong reflections at the end of the reactor are observed for pulse rise times which are shorter than the transient time of the reactor. Plasma generation and energy distribution in the reactor, as well as impedance matching between source and reactor, are affected by these reflections. We investigate the role of the input voltage and rise time and analyze the electrical characterization, impedance characterization, and reactor efficiency.\u3c/p\u3

B-dot and D-dot sensors for (sub)nanosecond high-voltage and high-current pulse measurements

In this paper, we present a large-bandwidth, high-current, and high-voltage measuring system for pulse measurements in pulsed power systems. The developed sensors can be easily calibrated, require no extensive (3-D) modeling, are very compact, are inexpensive, and have a bandwidth of up to several gigahertz. Moreover, they can be used in any pulsed power system, where a pulse source is connected to its load by a coaxial cable (without disturbing the coaxial geometry). We developed this sensor system for the use with our nanosecond pulse source system. The type of sensors we used is D-dot and B-dot sensors, which are compactly mounted on the coaxial cable that connects our nanosecond pulse source to its load. This enables us to measure the characteristics of each sensor very precisely with a vector network analyzer. With these characteristics-combined with the characteristics of the measuring cable assembly-we can numerically reconstruct the voltage and current waveforms that passed the sensor positions. Our calibration approach, the mounting on the coaxial cable and the postprocessing of the results makes these sensors very flexible. While we use the sensors for energy measurements, camera triggering, and the general measurement of the pulses, other researchers can use these types of sensors as well in any system, where a (coaxial) cable connects a pulse source to its load

An SDBD plasma-catalytic system for on-demand air purification

\u3cp\u3eSurface-dielectric-barrier discharges (SDBDs) can be applied for a wide range of applications, such as ozone generation, surface treatments, and air-pollutants removal. An important advantage of the SDBD plasma is that relatively low high-voltage (HV) pulses (<10 kV) are needed to generate the plasma. They are effective in removing a wide range of pollutants. Despite their high energy efficiency, plasma decomposition generally results in the reaction by-products and the formation of ozone and nitrogen oxides. This drawback can be overcome by combining the SDBD plasma with catalysis. In this paper, a novel plasma-catalytic topology is proposed for the purpose of on-demand air purification. The main idea of the plasma-catalytic reactor is that both the plasma and the catalytic function are configured as planar structures which are positioned in parallel to each other. The plasma is generated along a planar dielectric structure. We use an SDBD for this purpose. Plates coated with the catalytic material are positioned in parallel to the SDBD plates. The air to be treated is flushed along the plates. There are no restrictions to the type or combination of catalysts used; the catalysts and their specifications can be chosen freely. We have developed a modular plasma-catalytic SDBD reactor to handle large flows, which can be scaled up and scaled down easily. To energize the plasma, an SDBD power modulator was developed. The modulator is able to generate a HV output pulse over an SDBD plasma load with a magnitude adjustable from 4.78 to 6.95 kV. The pulse rise time is about 1μs and its ramp is about 6 kV/μs. The energy per pulse then ranges from 1.1 to 17.4 mJ. The output power can be adjusted up to 48 W at a repetition rate of 5.5 kHz. The maximum possible pulse repetition rate is 22 kHz, but it is limited to 5.5 kHz due to the limited current rating of the available dc power supply. The total energy efficiency of the power modulator is 68%. A single modulator unit can power up to two SDBD reactor plates of 100× 150 mm size, having plasma at both sides of the plate. The operational efficiency of the developed SDBD catalytic reactor has been investigated by studying the removal of NO \u3csub\u3ex\u3c/sub\u3e and ethylene. The removal efficiency of NO \u3csub\u3ex\u3c/sub\u3e and ethylene is determined as a function of energy density and operational parameters, such as their initial concentrations and the gas flow rate. \u3c/p\u3

(Sub)nanosecond transient plasma for atmospheric plasma processing experiments: application to ozone generation and NO removal

In this paper we use a (sub)nanosecond high-voltage pulse source (2–9 ns pulses with 0.4 ns rise time) to generate streamer plasma in a wire-cylinder reactor and apply it to two atmospheric plasma processing applications: ozone generation and NO removal. We will investigate what pulse parameters result in the highest plasma processing yields.\u3cbr/\u3e\u3cbr/\u3eThe results show that for ozone generation, secondary-streamer effects appear to have a slight influence on the ozone yield: if the pulse duration increases and/or the voltage increases in such a way that streamers can start to cross the gap in the reactor, the ozone yields decrease. Furthermore, for NO removal, we see a similar effect of pulse duration and applied voltage as for the ozone generation, but the effect of the pulse duration is slightly different: long pulses result in the highest NO-removal yield. However, the NO-removal process is fundamentally different: besides removing NO, the plasma also produces NO and this production is more pronounced in the primary-streamer phase, which is why the pulse polarity has almost no influence on the NO-removal yield (only on the by-product formation). Moreover, the rise time of the pulses has a much more significant effect on ozone generation and NO removal than the pulse duration: a long rise time results in a lower enhanced electric field at the streamer heads, which consequently reduces the production of radicals required for ozone generation and NO removal, and decreases the streamer volume. Consequently, the resulting ozone yields and NO-removal yields are lower. Finally, the main conclusion is that the plasma generated with our nanosecond pulses is very efficient for ozone generation and NO removal, achieving yields as high as 175 g centerdot ${\rm kWh}^{-1}$ for ozone generation and 2.5 mol centerdot ${\rm kWh}^{-1}$ (or 14.9 eV per NO molecule) for NO removal. In this paper we use a (sub)nanosecond high-voltage pulse source (2–9 ns pulses with 0.4 ns rise time) to generate streamer plasma in a wire-cylinder reactor and apply it to two atmospheric plasma processing applications: ozone generation and NO removal. We will investigate what pulse parameters result in the highest plasma processing yields.\u3cbr/\u3e\u3cbr/\u3eThe results show that for ozone generation, secondary-streamer effects appear to have a slight influence on the ozone yield: if the pulse duration increases and/or the voltage increases in such a way that streamers can start to cross the gap in the reactor, the ozone yields decrease. Furthermore, for NO removal, we see a similar effect of pulse duration and applied voltage as for the ozone generation, but the effect of the pulse duration is slightly different: long pulses result in the highest NO-removal yield. However, the NO-removal process is fundamentally different: besides removing NO, the plasma also produces NO and this production is more pronounced in the primary-streamer phase, which is why the pulse polarity has almost no influence on the NO-removal yield (only on the by-product formation). Moreover, the rise time of the pulses has a much more significant effect on ozone generation and NO removal than the pulse duration: a long rise time results in a lower enhanced electric field at the streamer heads, which consequently reduces the production of radicals required for ozone generation and NO removal, and decreases the streamer volume. Consequently, the resulting ozone yields and NO-removal yields are lower. Finally, the main conclusion is that the plasma generated with our nanosecond pulses is very efficient for ozone generation and NO removal, achieving yields as high as 175 g centerdot ${\rm kWh}^{-1}$ for ozone generation and 2.5 mol centerdot ${\rm kWh}^{-1}$ (or 14.9 eV per NO molecule) for NO removal.\u3cbr/\u3

Oxidative degradation of toluene and limonene in air by pulsed corona technology

The oxidative degradation of two volatile organic compounds, i.e. toluene (fossil fuel based VOC) and limonene (biogenic VOC), has been studied. A hybrid pulsed power corona reactor with adjustable energy density has been utilized for degradation of ppm level target compounds in large air flows. The observed oxidation product range features an energy density-dependent spectrum of oxygen-functional hydrocarbons, which has been qualitatively discussed on the basis of literature studies. Typically, observed stable oxidation products for both target compounds are the biocompatible carboxylic acids acetic and formic acid. Measured degradation G-values are 23 nmol J-1 at 74% conversion of 70 ppm toluene and 181 nmol J-1 at 81% conversion of 10 ppm limonene