Energy Efficiency of Corona Discharge Reactor Driven by Inductive Energy Storage System Pulsed Power Generator

Characteristics of a pulse corona reactor driven by an inductive energy storage (IES) pulsed power generator are described in this paper with focusing on the influence of streamer-to-glow transition on NO removal efficiency. A pulsed high voltage with a short rise time of under 30 ns is employed to generate streamer discharges homogeneously in whole the discharge region. Fast recovery diodes are used as semiconductor opening switch (SOS) to shorten the rise time. The various resistors are employed as dummy load to clarify a suitable circuit parameter such as the capacitance of a primary energy storage capacitor and/or the inductance of a secondary energy storage inductor. The energy transfer efficiency of the pulsed power generator has a maximum value of 50% at 714 Omega dummy load resistance. A co-axial cylinder type discharge chamber was used as the corona discharge plasma reactor driven by the IES pulsed power generator. The pulsed power generator supplies 30 kV pulse with 300 pps repetition rate. The co-axial cylinder plasma reactor consists of 1 mm diameter tungsten wire and 19 mm i.d. copper tube with 30 cm length. NO removal from the simulated diesel engine exhaust gas (N₂:O₂=9:1, Initial NO concentration=200 ppm) increased with input energy into the reactor. The energy efficiency for NO removal was obtained to be 25 g/kWh at 30 % removal in gas flow rate of 2 L/min. However, the energy efficiency decreased to 5 g/kWh with increasing capacitance of the primary capacitor from several hundreds pF to several nF. This decrease was caused by a streamer-to-glow transition. The efficiency was affected by oxygen concentration in the gas mixture.     

Reticulated vitreous carbon electrodes for gas phase pulsed coronareactors

A new design for gas phase pulsed corona reactors incorporating reticulated vitreous carbon (RVC) electrodes is demonstrated to be effective for the removal of nitrogen oxides from various gas mixtures containing O₂, N₂, water vapor and ethylene. The reactor consists of either a Plexiglass or glass cylindrical tube with macro-porous RVC electrodes placed perpendicularly to the cylinder axis. Streamers propagate between the RVC disks providing a uniform exposure of the flowing gas stream to the electrical discharge. This mode of operation provides for convenient reactor scale-up while maintaining the interelectrode spacing in a moderate range, thus allowing scale-up without the need for higher voltage power supplies. It is further envisioned that the reactor can be operated with multiple sets of electrodes placed in series down the length of the reactor in order to facilitate high efficiency removal of air pollutants     

Formation of chemical species and their effects on microorganismsusing a pulsed high-voltage discharge in water

The primary mechanism for sterilization of microorganisms by high-voltage pulses has been considered to be an electrical breakdown of the cell membrane. However, it is expected that many kinds of chemically active species would be generated by an electrical discharge in a needle-plate or rod-rod electrode system. Therefore it is necessary to identify the chemical species produced by the discharge and to investigate lethal effects of the active species on microorganisms. In the present study, the formation of active species in water (without O ₂ flow) and their effects on yeast cells were investigated using needle-plate electrodes. In the presence of the streamer discharge, H and OH radicals were detected by means of emission spectroscopic analysis of the discharge light. Hydrogen peroxide (H₂O₂) was also detected by absorption spectrophotometry using a reaction of peroxidase and catalase. The effect of the electrical conductivity of the water on the formation of the active species was investigated. Maximum ·OH and H₂O₂ concentrations were obtained at a water conductivity of about 10^-5 S/cm. The H₂O₂ formation mechanism was considered to be a recombination reaction of ·OH. The lethal effects on beer yeast of ·OH and H₂O₂ generated by the pulsed electrical discharge in water were also investigated. It was found that ·OH had almost no effect in reducing the survivors. However, the H₂H₂ did kill the yeast cells: the logarithm of the survival ratio decreased linearly with increasing H₂O₂ concentration     

A novel plasma reactor for NOx control usingphotocatalyst and hydrogen peroxide injection

The authors have developed a new type of plasma reactor combining discharge plasma with a photocatalyst (TiO₂) which improves the performance of NO_x removal. This reactor is designated as a plasma-driven catalyst (PDC) reactor. The authors found that hydrogen peroxide (H₂O₂) is a very effective additive in this PDC reactor and the formation of undesirable by-product (such as O ₃, N₂O) was reduced significantly. Comparative test results showed that the combination of discharge plasma with TiO ₂ catalyst is a very effective method in NO_x, removal over a conventional wire-cylinder reactor. NO_x was effectively oxidized to HNO₃ on the TiO₂ catalyst and trapped on the catalyst surface. Specific energy consumption of this de-NO_x process is significantly reduced, in particular, with the injection of H₂O₂     

Industrial experiments on pulse corona simultaneous removal of NOx and SO2 from flue gas

The corona-induced simultaneous removal of NO_x and SO ₂ from flue gas is based on the application of narrow voltage pulses to an electrode structure similar to that of an electrostatic precipitator. The free electrons of the corona discharge, having energy up to 20 eV, originate active radicals which lead to the transformation of NO_x and SO₂ into their acids which can be neutralized to salt particulate by adding to the gas a basic compound such as ammonia and calcium hydroxide. The process has been investigated with a test rig installed in the slipstream of the flue gas duct of a coal-fired thermal power plant. The experiments were performed with three reactor modules of different geometries. Further experiments are necessary to assess the effect of different electrode geometries of the reactor, the efficiency of the process attainable with an improved coupling of narrow pulse power set to the reactor, and the practical ways for integrating the DeNO_x and DeSO₂ corona process with the solid particle collection system     

Diesel engine exhaust treatment with a pulsed streamer coronareactor equipped with reticulated vitreous carbon electrodes

Reticulated vitreous carbon (RVC) has been shown to be useful for high-voltage and ground electrodes in gas-phase pulsed streamer corona reactors. RVC disks with large macroscopic porosity are placed perpendicular to the gas flow and the main axis of a cylindrical corona reactor. This electrode geometry produces streamers that propagate in the direction of the gas flow and are uniformly distributed in the cross section of the reactor. This highly electrically conductive material has large macroscopic porosity, thus allowing for gas flow through the electrodes with low pressure drop. Previous work has considered the effects of RVC electrodes on NO/NO_x removal from various test gases containing air, water vapor, and ethylene. The present studies show removal of NO/NO_x from the exhaust of a 5 kW diesel engine. Under cold reactor operating conditions (12°C) 81% NO and 53% NO_x could be removed at an energy yield of 4.8 g/kWh (based on NO). Furthermore, experiments with the combination of TiO₂ or γ-Al₂O₃ catalyst particles placed in the region between the high-voltage and ground electrode disks gave NO removal at energy yields of 29 g/kWh and 9 g/kWh, respectively, at about 100°C, and significant fractions of the nitrogen were recovered as NO₃^- deposited on the catalyst surface. The RVC electrode system without catalysts was found to lead to efficient ozone production (55-70 g/kWh) in dry air at room temperature     

All-Solid-State Power Modulator for Pulsed Corona Plasma Reactors

Atmospheric pressure pulsed corona plasma (PCP) reactors of wire-plate design offer novel solutions to environmental issues and to a number of industrial processes. Emerging applications include indoor air sterilization and odor removal in air conditioning systems, chemical synthesis in non-thermal plasmas, and plasma reforming of gaseous fuels. We previously reported on experimental investigations of a laboratory size, wire-plate plasma reactor for pulsed corona treatment of gas flows. Operation with gas flow, at pulse repetition frequencies of between 10 pps and 200 pps, has been achieved at pulse voltage amplitudes of between 10 and >30 kV, at pulse durations of around 0.3 mus (FWHM). High efficiencies of up to 70 g/kWh have been reported using an all-solid-state pulse generator. In this work, we report on the development of all-solid-state power modulators for use with nonlinear loads like pulse corona plasmas. The pulse generators are based on a fast thyristor switch discharging pulse capacitors, a pulse step-up transformer, and one or two stages of magnetic pulse compression. At pulse repetition rates of up to 200 pps, amplitudes of > 30 kV into a resistive-capacitive load (1 kOmega200 pF) have been achieved, at risetimes of about 80 ns and a pulse width of 0.3 mus. The pulse generator is insensitive to load variations, in particular to sparking in the reactor. An advanced generator version uses two magnetic pulse compression stages resulting in even shorter rise times. The modulator and its performance concerning experimental results will be described in detail when driving a pulsed corona reactor.     

Gas cleaning with semi-wet type plasma reactor

An experimental study on the removal of NH₃, NO, NO_x in concentration of 10-40 ppm in air has been carried out using plasma chemical reactions in a streamer corona discharge. The results of the performance of dry type and semi-wet type reactors are compared. The effects of different type of applied voltages such as rectangular pulse, 60-Hz sinusoidal, and 18-kHz alternating voltages are investigated. During NO removal, O₃ and NO₂ are produced. NO₂ can, partially, be removed with higher power input into the discharge. Another undesirable pollutant, namely N₂ O, is also produced, especially, in case of dry reactors having long residence time (~2.4 s). N₂O production decreases, essentially, to zero at 0.6-s residence time while using a semi-wet reactor. In general, higher removal efficiency has been obtained with pulse voltage in a semi-wet reactor. NH₃ in air appears to produce ozone and ammonium nitrate in a discharge. The performance of semi-wet reactors an the removal of submicron dust particles has also been investigated and very high removal efficiency (~93% at 0.6-s residence time) has been obtained     

The effect of residence time on the CO2 reduction fromcombustion flue gases by an AC ferroelectric packed bed reactor

An experimental investigation was conducted to reduce CO₂ from combustion gases using an AC ferroelectric packed bed reactor. This ferroelectric packed bed reactor consists of two mesh electrodes packed with ferroelectric particles between them. An AC voltage is applied to the reactor to generate partial or spark discharges. The results show the following: the CO₂ gas reduction rate increases with increasing flue gas residence time and primary applied power; the CO₂ gas reduction rate increases with decreasing gas flow rate and dielectric constant of packed ferroelectric particles; and the CO₂ concentration is reduced by up to 18000 ppm, and 108 g of CO₂ are removed by 1 kWh of primary applied energy used in the packed-bed reactor     

Reduction of NOx from natural gas combustion flue gasesby corona discharge radical injection techniques [thermal power plantemissions control]

An experimental investigation has been conducted to reduce NO_x in natural gas combustion flue gases by means of corona-discharge-activated ammonia/methane radical injection methods. Multihole-type corona radical injectors are used in the present investigation. Experiments were conducted for the simulated natural gas combustion flue gas (N₂:O₂:CO₂:NO=83.96:8:8:0.04) flow rate from 1 to 200 L/min, the activation voltage (DC or pulse) from 0 to 40 kV, and the Ar-ammonia or Ar-methane mixture gases flow rate from 0 to 200 mL/min. The results show that the NO_x reduction increases with increasing activation voltage and nonmonotonically depends on ammonia/methane stoichiometry     

Optimization of a low jitter, 50 kV, 100 Hz triggered spark gap with high pressure gas mixtures

Recent research efforts at Texas Tech University on impulse antenna phased array has needed to develop a reliable high voltage, high repetition rate switch that will operate with ultra low jitter. An ideal jitter of a small fraction of the risetime is required to accurately synchronize the array to steer and preserve the risetime of the radiated pulse. In [1], we showed the initial test system with sub-ns results for operations in different gases and gas mixtures. This paper discusses in detail 50 kV, 100 Hz switch operations with different gases. The effects of gases and gas mixtures have on switch performance which includes recovery rate and in particular jitter will be investigated. Gases tested include, dry air, H², N², and SF₆, as well as H₂-N₂, and N₂-SF₆ gas mixtures. Switch jitter as a result of triggering conditions is discussed, also including a comprehensive evaluation of jitter as a function of formative delay in the various gases. The temperature of gas and its effects on switch jitter is also documented in this paper. A 50 Ω, 1 nF pulse forming line is charged to 50 kV and provides the low inductance voltage source to test the different gases. Triggering is provided by a solid state opening switch voltage source that supplies ~150 kV, 10 ns risetime pulses at a rep rate up to 100 Hz in burst mode. A hermetically sealed spark gap with a Kel-F - PCTFE (PolyChloroTriFluoroEthylene) lining is used to house the switch and high pressure gas.     

Destruction of living cells by pulsed high-voltage application

Destruction of living cells in liquid has been formed by pulsed high-voltage application to the liquid. S. cerevsaie (yeast cell) or Bacillus natto, dispersed in deionized water and one- and three-percent NaCl solution, were used in this experiment. Four different electrodes (plate-plate, needle-plate wire-cylinder, and rod-rod electrode) were tested. The survival rate of cells was measured against peak electric field E_p pulsewidth T _W, and pulse application number N. The experimental results indicate that the survivability roughly follows Weilbull distribution. Yeast cells dispersed in deionized water could be almost completely destroyed when the wire-cylinder electrode was used with E_p=20 kV/cm, T_W=100 μs, and N=200. The energy input to a unit volume of the liquid to complete the cell destruction, however, differed significantly with the electrode type. The wire-cylinder electrode required above 10-30 cal/cm ³ to destroy the yeast cell in deionized water to 10^-6 survivability. This value was less than that required more than 70 cal/cm³. Using the rod-rod electrode contained in a pressure vessel, an arc discharge was generated to produce an intensive shock wave, which also destroyed the cells by its mechanical force. In this case, 5-10 cal/cm³ of energy was required to decrease the survivability of yeast cells in deionized water to 10^-6. Though further studies are necessary, this results indicate a possibility of the cell destruction by pulsed high voltage to be used as an energy-efficient sterilization process     

Pulse energization system of electrostatic precipitator forretrofitting application

A pulser module has been developed for electrostatic precipitators for upgrading the performance of existing plants. The module is inserted between the existing DC power supply and corona electrodes. A sawtooth voltage appears on the corona electrodes at a switching frequency, including at its leading edge a transient LC oscillation with a very sharp first peak and fast-decaying amplitude. This acts as the submicrosecond pulse energization, producing very active negative streamers in uniform distribution along the entire length of corona wires of the conventional construction. The average of the sawtooth voltage produces a DC field between the corona and the collecting electrodes. This direct-coupled pulse energization indicates in present laboratory tests exactly the same collection performance as the hitherto most effective submicrosecond pulse energization using a coupling capacitor and a DC bias voltage. A specific feature of the present pulse energization system is its simplicity in construction and low initial and operating costs     

An ultra compact back-lighted thyratron for nanosecond switching applications

An ultra-compact back-lighted thyratron (BLT), which is also named as mini-BLT, with effective volume of 15 cm^{3 was developed to serve as a high voltage switch in compact transient plasma ignition systems. The mini-BLT can hold off 40 kV and was used to conduct a peak current up to 4.5 kA. A 30 ns switching delay with 2 ns jitter was achieved when triggered by a 70 mJ, 355 nm laser pulse. Delay and jitter increase as the photon energy of the trigger pulse decreases. The plasma density in the switch measured at a peak current of 3.2 kA is 9×1014 cm-3. The mini-BLT was successfully used as the switch in a 100 ns, 60 kV pulse generator for generation of streamers in a plasma ignition system.}     

Decomposition of benzene using alumina-hybrid and catalyst-hybridplasma reactors

In order to investigate the effects of alumina and metal ions in plasma discharge, plasma reactors packed with a mixture of BaTiO₃ pellets and porous Al₂O₃ pellets (alumina-hybrid reactor), and with a-mixture of BaTiO₃ pellets and metal-supported Al₂O₃ pellets (catalyst-hybrid reactor) were examined for oxidation of dilute benzene in air. It was found that the oxidative decomposition of benzene was enhanced by concentrating benzene on the Al₂O₃ pellets and the catalyst pellets. Furthermore, the selectivities to CO ₂ in the alumina-hybrid reactor and the catalyst-hybrid reactors were higher than those in the plasma reactor packed with BaTiO ₃ pellets alone. In particular, the selectivities to CO₂ in the catalyst-hybrid reactors using Ag, Co, Cu and Ni/Al₂ O₃ were higher than those from the alumina-hybrid reactor. In addition, the presence of the alumina and catalysts suppressed the formation of N₂O     

Measurements of Pulsed Corona in Coaxial Electrode Structures

A low-inductance pulse generator is used to deliver a high-voltage short-duration pulse to an air-filled coaxial electrode configuration. When the voltage is below the sparkover value, the pulse energy is delivered to a diffuse corona which visually appears to fill the Interelectrode region. Energy transfer, current distribution, and pulse shape are measured for variations in electrode diameters, air temperature, and voltage. Over a range of voltages up to sparkover, the entire stored energy is delivered to the corona. Pulse rise times are approximately 0.2 ?s, the maximum peak voltage is 92 kV, peak currents equal approximately 400 A, and pulse energies range up to 1.6 J.     

Frequency conversion of Ti:sapphire-based femtosecond laser systemsto the 200-nm spectral region using nonlinear optical crystals

We review the linear and nonlinear optical properties of crystals transparent near and below 200 nm and suitable for up conversion of femtosecond Ti:sapphire laser sources, β-BaB₂O₄ , the crystal with the largest birefringence of all presently available materials, is investigated experimentally as a quadrupler by mixing the fundamental and the third harmonic both using a 1-kHz repetition rate Ti:sapphire regenerative amplifier and a 82-MHz mode-locked Ti:sapphire laser. Milliwatt average powers near 200 nm are achieved in both cases. The sub-200-fs pulses at the fourth harmonic are almost bandwidth limited. Sum-frequency generation as a method for upconversion of femtosecond pulses is experimentally studied by mixing the fourth harmonic generated down to 189 nm by the regenerative amplifier with a parametrically generated femtosecond pulse in the infrared. Pulse energies at the microjoule level are produced with LiB ₃O₅ above 180 nm. Li₂B₄O₇ shows superior performance in the 170-180-nm range, and the shortest wavelength achieved with KB₅ O₈·4H₂O is 166 nm     

脉冲电晕法中的双脉冲电源的研制

研制设计了脉冲电晕法脱硫脱硝重要组成部分的双脉冲电源 ,它由高压发生、控制、火花间隙开关 3部分组成 ,可产生 6 0kV的脉冲高压 ,改变电容器容量可改变脉冲宽度。该实验所选电机转速 4 0 0 0r/min ,容性负载 30pF ,脉宽 <2 0 0ns,上升沿 <5 0ns,频率调节范围 0 相似文献   

AC particle-triggered corona discharge in low pressure SF/sub 6/ gas

This paper deals with AC particle-triggered corona discharge as a follow-up to our previous research with DC voltage to clarify the particle-triggered corona discharge process in SF₆ gas. Corona current pulses, charges associated with a corona current pulse, and corona light pulses were observed with an aluminum ellipsoidal particle suspended in a parallel plane electrode system under a SF₆ gas pressure range of 30 kPalesPles50 kPa by changing the particle position. Corona mode, phase (Phi)-charge (q) characteristics as well as corona discharge processes were discussed and the following results were obtained. AC corona mode depended on the instantaneous applied voltage, voltage gradient as well as the particle position and then, the Phi-q characteristics were also affected by those parameters. Charges flow into the floating particle due to coronas on the both tips of particle and excite field fluctuations around the opposite side of particle in addition to the applied AC field. The field fluctuation in SF₆ gas by the corona charges was about 4% of the applied field and much lower than that in air gap which was about 70%. That is, the corona development was suppressed effectively by high electron affinity of SF₆ gas even in the case of floating particle. The less effective interference between coronas on the both side of particle in SF₆ gas results in an obscure local minimum in the breakdown voltage characteristics as the particle is in the vicinity of electrode as contrasted with a drastic fall in the breakdown voltage by the particle in air     

Energy and Spatial Distribution of Traps in SiO2/Al2O3 nMOSFETs

The energy and spatial profiling of the interface and near-interface traps in n-channel MOSFETs with SiO₂/Al₂ O₃ gate dielectrics is investigated by charge-pumping (CP) measurements. By increasing the amplitude as well as lowering the frequency of the gate pulse, an increase of the charge recombined per cycle was observed, and it was explained by the contributions of additional traps located higher in energy and deeper in position at the SiO₂/Al₂O₃ interface. In addition, CP currents, acquired after different constant voltage stress, have been used to investigate the trap generation in this dielectric stack