주사바늘 전극형 오존발생기 특성 연구

The influence of duty cycle on ozone generation and discharge characteristics was investigated experimentally using volume dielectric barrier discharge in both synthetic air and pure oxygen at atmospheric pressure. The discharge was driven by an amplitude-modulated AC high voltage–power supply producing TON (a single AC cycle) and TOFF periods with a widely variable duty cycle. The experimental results show that the energy delivered to the discharge during each AC cycle remains roughly constant and is independent of feed gas, duty cycle and TOFF. Both average discharge power and ozone concentration show an initial linear increase with duty cycle, and deviate gradually from linearity owing to an increase in gas temperature at higher duty cycles. Nevertheless, ozone yield remains nearly constant (45.7 ± 3.5 g/kWh in synthetic air and 94.7 ± 3.1 g/kWh in pure oxygen) over a wide range of applied duty cycles (0.02–1). This property can be conveniently employed to develop a unique ozone generator with a widely adjustable ozone concentration and simultaneously a constant ozone yield. Additionally, the discharges in synthetic air and pure oxygen have similar electrical characteristics; however, there are observable differences in apparent luminosity, which is weak and white-toned for synthetic air discharge, and bright and blue-toned for pure oxygen discharge.

PurposeThe purpose of this paper is to present a novel numerical algorithm, which can be used to simulate the stationary electric corona discharge in oxygen including some number of ionic species and ionic reactions.Design/methodology/approachDifferential equations governing distribution of the electric field and space charge density for all ionic species have been solved using different numerical techniques: finite element method, method of characteristics (MoC) and donor‐cell method (DCM). Triangular discretization with linear interpolation of solution has been used.FindingsThickness of the ionisation layer in oxygen under normal conditions is in the order of a few hundred micrometers. Most electrons are attached to the neutral oxygen molecules forming negative ions in the drift zone. The current density on the ground plate basically follows the Warburg curve, but the DCM predicts a smooth current density distribution, while in the MoC the current density abruptly drops to zero at some radial distance.Originality/valueThis is the first attempt to solve this problem in the 2D point‐plane configuration. The results can lead to better understanding of all processes occurring in the corona discharge and provide information about density and distribution of different ionic species and current densities.

Ozone generators of dielectric barrier discharge (DBD) are mainly used for water and waste water treatment. Recently, they are also used for cleaning of food product machines, semiconductors processes, pulp bleaching field and so on. It is well-known that ozone concentration composed by DBD type ozone generator decreases with time when high purity oxygen used for feed gas. This is named by us, ozone zero phenomenon (OZP). The causes of the phenomena have been investigated experimentally in the world wide industries us. One of the causes is considered as an electrode material by discharge in the generator metal oxides formed from stainless steel electrode. We have studied the ozone generation characteristics using high purity oxygen as a feed gas and ozone generator of which both electrodes covered with dielectrics. It was found that using only high purity oxygen as a feed gas, ozone concentration decreased from 200g/m3(N) to 54g/m3(N) during about 5 hours. However, adding 0.1vol% of nitrogen into oxygen, ozone concentration increased rapidly over the initial maximum ozone concentration of 216g/m3(N). After that, the concentration of ozone gradually decreased with time. Therefore, adding nitrogen into oxygen has the effect of recovery of ozone concentration in the same generator. The maximum ozone concentration was obtained when 0.1-0.6vol% of nitrogen gas was added to oxygen gas. OZP is caused by ozone generator even when both electrodes are covered with dielectrics. The metal oxide is produced on electrode is not the cause of OZP. Ozone concentration can be increased by adding nitrogen into oxygen.

Pulsed discharge plasmas have been used to treat exhaust gases. Since pulse duration and the rise time of applied voltage to the discharge electrode has a strong influence on the energy efficiency of pollutant removal, the development of a short-pulse generator is of paramount importance for practical applications. In this work, it is demonstrated that the non thermal plasma produced by the 2 ns pulsed discharge has a higher energy efficiency than the 5 ns pulsed discharge plasma for NO removal and ozone generation. Typically, the NO removal efficiency was 1.0 mol kW-1 h-1 for 70% NO removal (initial NO concentration = 200 ppm, gas flow = 10 L/min). Meanwhile, the ozone yield was 500 g kW-1 h-1 for 20 g/m3 ozone concentration in the case of oxygen feeding. These energy efficiencies are the highest in the literature.

Water purification by ozone generator employing non-thermal plasma

Surface states associated with chemisorbed species on zinc oxide

A method for decomposing persistent organic compounds in water by DC corona on water was investigated. The acetic acid as a persistent material was decomposed by corona discharge in oxygen 4 mm away from the surface of the water. The acetic acid in 10 ml solution was a concentration of 9.6-207 mg/l. The number of electrodes where the corona was generated was 4 or 8, the voltage was between 6.2 kV and 9.2 kV, and the current was between 0.09 mA and 0.34 mA. As the voltage and the number of discharge electrodes increased, the decomposition rate increased. The maximum decomposition speed of 4.8 µg/min was obtained with 8 discharge electrodes in initial concentration 20 mg/l of acetic acid. More numbers of the electrode were effective for the decomposition of the acetic acid in the equal discharge power.

This paper studies the influence of inert gases He, Ar, Kr and Xe on ozone generation in a dielectric barrier reactor fed by oxygen feed gas. Results show that inert gas additions would lead to lower applied voltage, discharge power and reduced field. The electron energy distribution function shifts to the right though inert gas addition would lead to a lower reduced field with He, Ar and Kr addition, but it shifts to the left with Xe addition. The effective electron density decreases with inert gas content. With respect to Ar/O2, Kr/O2 and Xe/O2 mixture, conversion ratio of oxygen into ozone and ozone yield would increase with increasing Ar, Kr or Xe content, the growth rates follow the order of Xe > Kr > Ar. Such behaviors can be ascribed to the fact that Ar*, Kr* and Xe* could provide another effective pathway to produce oxygen atom through penning dissociation of O2 and metastable species due to their relatively low excitation threshold and considerable rate coefficients.

Summary form only given. A new atmospheric pressure plasma source has been developed that shows exceedingly high processing rates. For example, kapton films have been etched at 5.0 mum/s using an argon and oxygen discharge with 6.0 vol.% O2 and a temperature of 280degC. The plasma source consisted of a small quartz tube that was capacitively coupled to radio frequency power at 13.56 MHz. The input plasma power could be increased up to 150 W/cm3 without arcing, or forming a streamer like discharge. At this power density, the gas temperature was determined by spectroscopic methods to be 300plusmn30degC. The O atom concentration was measured in the plasma afterglow by nitric oxide titration, and was found to be 1.2plusmn0.6times1017 cm-3 at 150 W/cm3 and 6.0 vol.% O2 in Ar. The concentration of ozone in the downstream region equaled 4.3plusmn0.5times1014 cm -3, as determined by UV absorption spectroscopy. These results were found to be in good agreement with a numerical model of the plasma and afterglow that included the reaction mechanism and the plasma electron density and temperature as calculated from current-voltage measurements

A gradual decrease in the concentration of ozone produced by the continuous operation of a large-scale dielectric barrier discharge-type ozone generator (OG) was observed under the supply of a constant discharge power and high-purity oxygen as the feed gas. This finding was named the ‘ozone zero phenomena’ on the basis of our experiments demonstrating that the ozone molecules disappeared at the surface of the electrodes in the OG, in which both the formation and decomposition of ozone occur simultaneously. To clarify the cause of the phenomena, we performed new experiments with an OG separated functionally into two parts to avoid the effects of the discharge, which also oxidizes stainless-steel and increases the temperature in the generator, although the discharge is indispensable for ozone generation. The first part was an OG supplying ozone to the following part. The second part was an ozone destructor that simulated an OG in which only the ozone zero phenomena occurred. The ozone destructor was an incubator with pipes made of stainless-steel or borosilicate glass in them and maintained at a constant temperature of up to 473 K. The generator and destructor were connected serially with a gas flow line. Ozone–oxygen mixtures with constant ozone concentrations produced by the first part were introduced into the ozone destructor, and the ozone concentrations at the inlet and outlet of the pipes were monitored simultaneously. Using the two ozone concentrations, the decomposition rate of ozone was evaluated as functions of time, the pipe material, the pipe temperature, and the concentration of ozone introduced into the pipe. We concluded that in this model experiment the ozone zero phenomena are induced by the thermal decomposition of ozone in the pipes which is installed in the heated incubator to provide ambient temperature conditions for the conversion of ozone molecules.

In ozone production using plasma generated with pulsed power, the concentration of ozone is not high although ozone is produced with high efficiency. Effect of shortening electrode separation of a coaxial reactor was investigated in order to generate ozone in high concentration in using pulsed power. Ozone concentration and yield increased with decreasing diameter of the reactor because spatial density of plasma would become higher. In these reactors, the ozone yield remained in nearly constant value while the ozone concentration increased in proportion to pulse repetition rate. In reactor of 17 mm, saturation tendency and reduction of the concentration were however seen. In this reactor, the ozone concentration decreases with time after reaching a peak value. Spark discharges with short electrode separation caused temperature elevation of electrodes and gases, so that thermal decomposition of ozone molecules occurred. When oxygen gas containing ozone instead of pure oxygen gas flowed into the reactor, rise of the ozone concentration competed with ozone concentration produced with pure ozone gas. The rise showed potential of plasma for ozone production. Ozone with higher concentration could be obtained by the potential of plasma on an appropriate condition.

During the production of ozone using needle & plate electrodes and a DC current in 99.5% oxygen, we noticed that the concentration of ozone decreased to 0 after several months in which the electrical discharge had produced ozone. The concentration of ozone increased due to the addition of nitrogen into a gas-mixing chamber located behind an electrical discharge. The concentration of ozone increased due to the addition of heat-energy to an anode located in an electrical discharge. The controlled heating cycles showed a change in the density of nitrogen on the surface of the anode. Simulations confirmed this pattern. We used an industrial ozone generator that consisted of ceramic dielectrics and a titanium expanded metal electrode. A change in the temperature of the cooling water led to the characteristic of ozone concentration making a linear line. It follows the formula of van't Hoff. The generator was supplied with 99% oxygen gas and produced ozone. The concentration of ozone increased from 98 g/m/sup 3/ to 120 g/m/sup 3/ under the same conditions. After reaching its peak, the concentration of ozone decreased to zero. Afterward, we produced ozone which was over 20% higher in concentration than primary state ozone due to change in the third element from nitrogen to antimony.

Electrochemical system with moderate ozone generation and catalytic enhancement for efficient organic wastewater treatment.

Passive samplers are often employed to measure ozone concentrations in remote areas such as mountain forests. The potential ozone risk for vegetation is then assessed by calculating the AOT40 exposure index (accumulated hourly ozone concentration exceedances above 40 ppb, i.e. AOT40 = Σ([O(3)] - 40)Δt for any hourly ozone concentration [O(3)] > 40 ppb). AOT40 is customary calculated on the basis of ozone concentrations expressed as a volumetric mixing ratio, while lab sheets normally report ozone concentrations from passive samplers in mass units per cubic metre. Concentrations are usually converted from mass units to ppb using a standard conversion factor taking SATP (Standard Ambient Temperature and Pressure) conditions into account. These conditions, however, can vary considerably with elevation. As a consequence, the blanket application of a standard conversion factor may lead to substantial errors in reporting and mapping ozone concentrations and therefore in assessing potential ozone risk in mountain regions. In this paper we carry out a sensitivity analysis of the effects of uncertainties in estimations of air temperature (T) and atmospheric pressure (P) on the concentration conversion factor, and present two examples from two monitoring and mapping exercises carried out in the Italian Alps. We derived P and T at each site from adiabatic lapse rates for temperature and pressure and analysed the magnitude of error in concentration estimations. Results show that the concentration conversion is much more sensitive to uncertainties in P gradient estimation than to air temperature errors. The concentration conversion factor (cf) deviates 5% from the standard transformation at an elevation of 500 m asl. As a consequence, the standard estimated AOT40 at this elevation is about 13% less than the actual value. AOT40 was found to be underestimated by an average between 25% and 34% at typical elevations of mountain forest stands in the Italian Alps when a correct conversion factor for transforming ozone concentrations from μg m(-3) to ppb is not applied.

In ozone production using streamer discharges by pulsed power, the concentration of ozone is not high although ozone is produced with high efficiency. To improve ozone concentration, we studied the effects of electrode separation in a coaxial reactor using nanosecond pulsed power. We found that ozone concentration and yield increase with decreasing inside diameter of the outer electrode in the reactor. This occurs because dense plasma forms in a small-diameter reactor that has a small electrode separation. As the repetition rate of applied pulses was increased, the ozone yield remained nearly constant, while the ozone concentration increased proportionally. However, in a reactor having a small diameter of 17 mm, the tendency for the concentration to saturate and reductions in the ozone concentration were found to depend on pulse repetition rate. In such a small-diameter reactor, spark discharges occurred owing to the reduced separation of electrodes; these discharges cause the temperature of electrodes and gases to increase. Consequently, ozone molecules thermally dissociated and ozone concentration decreased. The occurrence of spark discharges was affected by not only the small separation of electrodes but also other factors. Potential of a small-diameter coaxial reactor for ozone production were presented and a control of occurrence of spark discharges was paramount.