Ozone Generation in Air by a DC-Excited Multi-Pin-to-Plane Plasma Source

In the fields of material processing and environmental technology, atmospheric pressure non-thermal plasmas embrace a broad range of applications. Ozone generation is one of them. This paper discusses a DC-excited atmospheric pressure glow discharge in a multi-pin-to-plane electrode configuration for the production of ozone in air. The influence of discharge current, temperature, flow rate and air humidity is investigated. A simple model is proposed to predict the experimental results for the ozone production and ozone concentrations.     

A Study of the Physical and Chemical Processes Active in Corona Discharges Fed by Carbon Dioxide

Ozone generation in both positive and negative corona discharges DC corona, both operated in glow regime, feed by dry CO₂ has been studied. Higher ozone concentrations were observed in negative corona discharges. Ozone formation was found to be strongly dependent upon both the flow rate of the gas and on the radius of the outer electrode. The physical characteristics of the discharge were monitored through measurement of the discharge current. Small increases in the gas flow rate were observed to cause a significant increase in the discharge current of a negative corona discharge but little/no effect was observed in positive corona.     

Ozone Generation from Oxygen and Air: Discharge Physics and Reaction Mechanisms

Industrial ozone generation uses a special high pressure, low temperature electrical discharge which is referred to as the dielectric barrier discharge or silent discharge. The filamentary structure of this discharge and the properties of individual microdischarges are discussed. The main reaction paths for the excited atomic and molecular species in oxygen and air are identified. Possible approaches to obtain high power densities, high ozone generating efficiencies or high ozone concentrations are discussed.     

Ozone Generation by Hybrid Discharge Combined with Catalysis

In this paper, combining hybrid discharge with pellet alumina catalyst is used for ozone generation. The hybrid discharge including corona discharge (CD), surface discharge (SD) and dielectric barrier discharge (DBD) may happen in the device. Factors that affect the ozone production efficiency and concentration are studied, such as energy density, power, gas flow rate, frequency, peak voltage and catalysts.     

Simulation of Ozone Synthesis in Oxygen- and Air-Fed Surface Discharge Arrangements

Surface discharge (SD) arrangements are used in commercial ozone generators like conventional arrangements with a gas gap. While in oxygen the characteristics of the ozone production are comparable in both arrangements, the efficiency of ozone production from air is significant lower in SDs. From experimental results it is believed that high temperatures in the discharge cause this “poisoning” of air-fed SD ozone generators. To clarify this, the ozone synthesis from air near atmospheric pressure is investigated with the help of a two-dimensional self-consistent modeling of the discharge development and the relevant plasma-chemical reactions. The temperature in the discharge area is determined from energy densities of electrons and ions and included in the relevant chemical reaction system. The results show a significant temperature increase in front of the metallic surface electrodes combined with an increased concentration of nitrogen oxides.     

Optimizing Factors on High Concentration of Ozone Production with Dielectric Barrier Discharge

The gap distance, electrode material, voltage and gas flow velocity were optimized with gas pressure variation of dielectric barrier discharge (DBD) for producing high concentration of ozone. There exists an optimum gas pressure at which the highest ozone concentration is produced with other parameters being fixed. This optimum gas pressure value changes accordingly as the other parameters changed. As the discharge continues at the optimum pressure, the ozone concentration could increase or decrease slowly. This aging effect has different characteristics with the metal electrode material and the impurity level of the oxygen gas used for ozone generation. The aging effect is supposed to be related with the catalytic effect of metal oxide, which is generated in the discharge zone. The change in the characteristic of optimum pressure by the other parameters, indicate that the ozone concentration is deeply related with the filament self-organization characteristics of DBD. At the final optimized condition, the ozone concentration was higher than 22.5 wt.%.     

Ozone Production in a Dielectric Barrier Discharge with Ultrasonic Irradiation

Ozone production has been investigated using an atmospheric pressure dielectric barrier discharge in pure O₂ at room temperature with and without ultrasonic irradiation. It was driven at a frequency of either 15 kHz or ～40 kHz. The ozone production was highly dependent on the O₂ flow rate and the discharge power. Furthermore, powerful ultrasonic irradiation at a fundamental frequency of ～30 kHz with the sound pressure level of ～150 dB into the discharge can improve the ozone production efficiency, particularly when operated at the frequency of 15 kHz at the flow rate of 15 L/min.     

Experimental Study of Ozone Generation by Negative Corona Discharge in Mixtures of N2 and O2

Ozone generation by negative DC corona discharge in N₂-O₂ mixtures has been experimentally investigated using a coaxial wire-cylinder corona reactor operating at room temperature and atmospheric pressure. The experiments have been carried out under different gas flows (15 cm³ min^?1 to 200 cm³ min^?1) and gas compositions (5% to 90% of O₂), and the effect of these parameters on the corona current, the ozone density and the efficiency of the ozone generator have been analyzed. The global rate coefficients for ozone formation and destruction have also been evaluated, and their values compared with those reported by other authors. The maximum efficiency for ozone production was found in gas mixtures with oxygen content about 70–80%.     

A Study of the Physical and Chemical Processes Active in Ozone Generation by Carbon Dioxide Fed Corona Discharges

Ozone generation in both positive and negative corona discharges DC corona, both operated in glow regime, feed by dry CO₂ has been studied. Higher ozone concentrations were observed in negative corona discharges. Ozone formation was found to be strongly dependent upon both the flow rate of the gas and on the radius of the outer electrode. The physical characteristics of the discharge were monitored through measurement of the discharge current. Small increases in the gas flow rate were observed to cause a significant increase in the discharge current of a negative corona discharge but little/no effect was observed in positive corona.     

Dimensional Analysis of Detrimental Ozone Generation by Negative Wire-to-Plate Corona Discharge in Both Dry and Humid Air

A semi-empirical equation is derived to provide a correlation between the ozone generation rate of a negative wire-to-plate corona discharge in both dry and humid air and a series of design/operating parameters. A basic correlation is first derived by applying dimensional analysis on negative wire-to-plate corona discharge in dry air. Further development on the basic correlation is carried out by integrating the influence of humidity. The derived equation is validated by previously reported experimental data and numerical model. The new semi-empirical equation is comprehensive and useful in guiding the design/operation of indoor corona devices under actual ambient operating conditions.     

Response Surface Methodology Applied to Ozone Generation

In this work, a strategy is presented to optimize the ozone generation by response surface methodology. A dielectric barrier discharge ozone generator was developed in which it is possible to control electrical current frequency and gas flow entering the generator. Response surface methodology was used to identify ozone generator optimum operational conditions, that is, those that permit considerable ozone productivity and high concentration of ozone gas.     

Ozone Production in a High Frequency Dielectric Barrier Discharge Generator

Factors that affect the performance of an expanded-mesh dielectric barrier discharge ozone cell were investigated. A gas feed pf 94% O₂, 4% Ar and 1% N₂ was used. An improvement in the productivity (g ozone/kWh) of about 20 % was achieved by doubling the gas flow rate through the cell. Decreasing the cell operating frequency (in the range 72 kHz to 19 kHz) increased the productivity of the ozone generator at constant power. The ozone production increased approximately in proportion to the input power; however productivity did not vary significantly with power above a minimum level. As the cell voltage was increased the dependence of productivity on power or frequency was reduced. Changing the feed gas temperature between ? 5^°C and + 42^°C had no effect on productivity. Finer meshes drew more power than coarser ones for a given voltage. Using a thinner mesh for the centre electrode increased productivity. The best results were obtained with a 6 × 3 × 1.86 mm titanium mesh giving a productivity of 110 g ozone/kWhr at 30–60 W, 1500–1900V and 23 KHz.     

Removal of Toluene,Chlorobenzene, and Benzene by a Needle‐to‐Net Corona Discharge Reactor

A corona discharge reactor consisting of a hollow needle cathode and a net anode was used to remove benzene, toluene, and chlorobenzene in a synthetic air stream. Two gas flow directions were adopted to examine the contributions of the separated reaction zones, a high‐energy corona zone at the needle cathode tip and a relatively large zone outside it. The target gas was fed in the corona zone through the needle cathode and exhausted through the net anode. Inversely, the gas was fed in through the net anode and exhausted through the needle cathode. It was observed that the removal efficiency of these components did not depend on the gas flow directions, indicating that the spatial distribution of the reactivity was not influential on the removal efficiency of the three target gas species. This means that the high electric field zone around the needle cathode tip would overwhelm the surrounding low‐energy zone. In addition, the contribution of ozone reaction was observed as insignificant. Considering a reported ozone distribution, this result also indicates that the main reactive zone is the corona zone at the cathode tip.     

Medium frequency pulse train ozone generation

In this paper an ozone generation system that uses square bipolar pulses at 1900 Hz frequency (carrier signal) modulated with low frequency square wave is presented. The optimization of the carrier was done by sweeping the frequency from 500 to 2400 Hz and the duty cycle from 20 to 100 %, obtaining the best results at 1900 Hz and 80 % respectively. The experiment was done using a corona discharge generator with glass dielectric, 2 mm gap, water‐cooling at 26 °C and oxygen as the feed gas. Different levels of ozone production were obtained by changing the duty cycle of the modulator signal. The modulator signal works on a discrete way with whole numbers of pulses. The priority of the pulse polarity can be set so the beginning of the pulses may be either positive or negative. A dead time between pulse trains is always present with a minimum value of 10% of the modulator signal. The dead time contributes to the generator cooling because no energy is applied.

A comparative study between the proposed system and a 60 Hz traditional source generator shows an increase in the ozone concentration and ozone production rate, as well as a reduction of the voltage required to produce the corona discharge by using a pulse train at medium frequency.     

Ozone Generator with Cylindrical Type of Rotating Electrode

An ozone generator using a rotating electrode to improve ozone generation efficiency is proposed. The ozone generator electrode unit consists of a rotating electrode and fixed electrode. The rotating electrode has the grounded 36 pieces of tungsten wires fixed in parallel to the rotation axis on the rotating cylinder surface. A dielectric electrode is used as a fixed electrode located on the inside of the tube of the electrode unit. The width of the apparent discharge gap is 1mm. Alternating current with a frequency of 50 Hz is applied to the electrode unit. The rotation speed can be adjusted from 0 rpm to 1200 rpm by a variable speed motor. Oxygen gas is used as the material gas. Higher ozone concentration and higher ozone generation efficiency are obtained compared with that when the rotation speed is 0 rpm. The gas temperature is measured at the inlet and outlet of the ozone generator, and the rotation speed for the cooling effect is most effective at about 500 rpm. The maximum generation efficiency is estimated to be 61 g/kWh at 800 rpm, and this value is twice as large as in the case of 0 rpm.     

Ozone Production: Economical Operation of a Cold Plasma Reactor

For a fixed value of the reduced electrical field, the economical operation of a cold plasma reactor generating ozone is determined by a particular value of the energy supplied by the field per molecule of reactant. Evidences are given in the ozone formation from air and oxygen. Moreover, influence of the flow and reduced electrical field upon the production is emphasized.     

Production Of Ozone in an Electrical Discharge Using Inert Gases as Catalysts

The catalytic role of using inert gases to increase the efficiency and lower the power cost of producing ozone (O₃) from high purity oxygen (O₂) in a process incorporating an electrical discharge is demonstrated. Three inert gases (Ar, Ne, He) and N₂ are individually mixed with O₂ and the results presented. The increase in ozone production is partially attributed to the increase in electron density provided by the ionization of the inert gas in the discharge.     

Ozone Generation Using Plate Rotating Electrode Ozonizer- Effect Of Electrode Rotation And Discharge Analysis Method

An attempt to explain the phenomenon of the effect of electrode rotation on the ozone generation process is presented. A discharge photography method was applied and computer analysis method was used to find discharge differences between electrode rotational and non-rotational cases. The research presented shows that with electrode rotation the discharge was more uniform and the ozone generation efficiency increased about 15% compared to an ozonizer with a non-rotating electrode. In addition, during the research, the most suitable electrode rotational speed for the ozone generation process was estimated.     

Gas Phase Reactions in Silent Electric Discharges. Part I: Exact Calculation of the Charge Passed Through the Discharge Chamber and the Electric Field Using the Electrical Parameters of the Circuit

The rate of a chemical reaction occurring in a silent electric discharge is dependent on the electric charge passing through the gas. In the knowledge of the electrical characteristics of the circuit and its elements (i.e., the ohmic resistance and capacitance), the composition and the pressure of the gas, the electric charge involved in the discharge can be calculated. The application of a purely sinusoidal alternating current to the system allows deduction of the time dependence of the voltage drops across various circuit elements and also the time dependence of the current. Experiments were conducted with two reactor types (static and tubular flow) and their electrical characteristics were varied to test the results of the calculations, which were thereby confirmed.     

High Frequency Testing and Modeling of Silent Discharge Ozone Generators

This paper deals with high frequency modeling of silent discharge ozone generators (OGs). The electrical characteristics of two simple silent discharge OGs operated at low and high frequency are analyzed and compared. An equivalent electric model is proposed for the operation of the OG at high frequency. This model can be used to optimize the electronic power converter used to supply silent discharge OGs at high frequency. Experimental results measured in the laboratory for two particular OGs are presented to validate the proposed model.