A Study of Ozone Synthesis in Coaxial Cylinder Pulse Streamer Corona Discharge Reactors

Synthesis of ozone in coaxial cylinder non-thermal plasma reactors with different structures was investigated in this paper. With digital measuring technology, the absorption energy of non-thermal plasma reactors induced by pulse streamer corona was estimated. In the view of energy absorption of non-thermal plasma reactors, pulse input energy depended on reactor structures, as well as pulse parameters, such as pulse amplitude and DC bias. With coaxial cylinder reactors energized by pulse voltage, the influences on ozone generation of pulse voltage polarity, pulse amplitude, and pulse repetition rate were studied. It was found that positive pulse voltage induced higher ozone generation than negative pulse voltage and higher amplitude pulses generated more ozone. Increasing the pulse repetition rate at a low level increased ozone generation to some extent, but then leveled off with further increasing. A critical repetition rate was found at which the ozone synthesis was the most efficient. Lower pulse amplitude was associated with higher critical repetition rate. Superimposing DC bias on pulse voltage was an effective method to enhance ozone generation. Besides, discharge modes and electrode structures of reactors affect ozone generation. A mixed discharge mode of volume and surface discharges was the most effective mode to generate ozone in all of the experimental discharge modes, namely volume, surface, volume and surface mixed discharge modes. Moreover, helix-cylinder reactors were better than wire-to-cylinder reactors in generating ozone.     

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.     

Kinetic Modeling of Ozone Generation via Dielectric Barrier Discharges

A mathematical model combining chemical kinetic and reactor geometry is developed for ozone synthesis in dry O₂ streams with a wire-tube dielectric barrier discharge (DBD) reactor. Good agreement is found between the predicted ozone concentrations and experimental data. Sensitivity analysis is conducted to elucidate the relative importance of individual reactions. Results indicate that the ground-state oxygen atom is the most important species for O₃ generation; however, ozone generation will be inhibited if the O atom is overdosed. The excited species, that is, O(¹ D) and O₂(b ¹Σ), can decompose O₃ and suppress ozone synthesis. The model developed is then applied to modify the original DBD reactor design for the enhancement of ozone yield. With a thinner dielectric thickness, more than 10% increase of ozone concentration is achieved.     

Optimal Sizing of a DBD Ozone Generator Using Response Surface Modeling

Dielectric barrier discharge (DBD) reactors used as ozone generators are well known today and widely used for water treatment and air disinfection. The purpose of this article is to propose an experimental procedure based on the response surface modeling in order to optimize the geometrical dimensions of the cylindrical shape ozone generator, i.e., the discharge gap and the electrodes length. Because an effective ozone generator is expected to give high ozone concentration with a minimum of power requirements, the applied high voltage was associated with the geometrical parameters to carry out a composite centered faces design. Obtained results indicate that for an efficient ozone generator, length of the electrodes needs to be optimized while the discharge gap should be minimized.     

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.%.     

Basic Parameters of Coplanar Discharge Ozone Generator

Coplanar discharge is a new type of barrier discharge, and has some advantages for high-concentration ozone generation. In this article, basic parameters of coplanar discharge are clarified by experimental and theoretical approaches. Coplanar electrodes consist of many pairs of line electrodes printed on a glass plane, and are covered with dielectric layer. The discharge properties, ozone diffusion process, and surface reaction are discussed. Finally, the scaling rule of a coplanar discharge ozone generator is demonstrated by fabrication of a 3 kg/h ozone generator.     

Enhancement of Energy Yield for Ozone Production via Packed-Bed Reactors

The present work aims to enhance the energy yield of ozone production via packed-bed reactors. It has been experimentally demonstrated that ozone concentration and corresponding energy yield achieved by packed-bed reactors are significantly higher than that achieved by DBD only. The so-called packed-bed reactor is constructed by packing granular dielectric pellets within a DBD reactor. Two kinds of dielectric materials including glass beads and Al₂O₃ pellets are tested. Experimental results indicate that an ozone generator packed with Al₂O₃ pellets results in a higher ozone production compared with one packed with glass beads. The maximum ozone production takes place when Al₂O₃ pellets with diameter of 2 mm are packed. The maximum ozone concentration, ozone production rate, and energy yield achieved in this study are 61 gO₃/m³, 3.7 gO₃/hr, and 173 gO₃/kWh, respectively. The highest ozone concentration and energy yield achieved with the packed-bed reactor are about 8 and 12 times high as those with DBD reactor, respectively. Although the packed-bed reactors have a shortcoming of high temperature, it can be solved by adding a cooling system and the ozone generation can be improved thereof. As a result, the packed-bed reactor is a promising and state-of-the-art technology for ozone generation based on this study.     

Development and Experimental Analysis of a New “Serpentine-Shape” Surface-DBD Ozone Generator—Comparison with a Cylindrical Volume-DBD Ozone Generator

Ozone generators used in the industry for water treatment are almost all based on volume dielectric barrier discharge (DBD). The generation of ozone by surface DBD is also possible. However, there are not enough studies devoted to this solution. The objective of this article is the development of a new patent-pending “serpentine” model in which the gas circulates in a channel having the shape of a serpentine. The developed model is made of 10 parallel channels engraved in a Bakelite plate of 4-mm thickness. The ground electrode is an adhesive aluminum tape placed on the lower surface of the plate, while the high voltage electrode is constituted of narrow tapes of 1-mm width of the same material, placed in the bottom of each channel. The surface DBD is produced inside each channel that measures 1-cm width, 3-mm depth, and 10-cm length. The obtained results showed that the ozone rate (in g/hr) is much higher in the case of surface DBD compared to a cylindrical volume-DBD generator, which is the most used reactor in ozone technology. Furthermore, the energy efficiency of the “serpentine” model is better than the cylindrical model.     

On the Performance of Ozone Generators Working with Dielectric Barrier Discharges

The parameters, which determine the performance of ozone generators, are efficiency and maximum ozone concentration. The efficiency from oxygen has been found to be nearly independent on the kind of barrier discharge arrangement (volume, surface, coplanar), while the ozone concentration saturation level depends on the specific design of the generator. These phenomena are explained with features of the discharge process and the properties of chemical reactions, respectively. The importance of a limit in the energy density of the discharge is highlighted.     

Productivity and Efficiency of Ozone Synthesis in Coplanar Discharge Arrangements

In order determine the potential of coplanar discharge arrangements with short electrode distances for the production of ozone, a numerical model of the discharge behavior has been developed. The temporal and spatial distributions of the discharge parameters e.g. those of the field strength, the densities of the charged particles in the gas region and on the dielectric surface and that of the energy release reveal that the ozone production results from the electron phase of the discharge. Quantitative data of the productivity and efficiency of the ozone yield in a certain system are presented, which are in agreement with experimental results.     

Influence of Field Strength and Energy Distribution of Different Barrier Discharge Arrangements on Ozone Generation

Because of different field strength and energy density distributions in volume (VD), surface (SD) and coplanar discharge (CD) arrangements the ozone yield will differ in general. While in VD configurations the initial field strength distribution is rather uniform, the situation is quite different in CD and especially SD devices. The distributions change during discharge development as well as the energy density in the discharge region and by this the ozone yields. The situation in SD arrangements is discussed in detail and is compared with those in VD and CD configurations.     

The Effect of SF6 on Ozone Generation using Dielectric Barrier Discharge

This paper reports the results of an experimental study of effect of SF₆ on ozone generation within a Dielectric Barrier Discharge (DBD) fed by both pure oxygen and dry air. The chemical reaction mechanisms relevant to the process of ozone generation (and destruction) are discussed. The experimental results show the oxygen source should avoid the presence of SF₆ but the addition of a small amount of SF₆ in an air discharge can improve ozone concentration and ozone produce efficiency.     

Ozone Production Influenced by Increasing Gas Pressure in Multichannel Dielectric Barrier Discharge for Positive and Negative Pulse Modes

This paper describes the influence of gas pressure on the conversion of O₂ to O₃ and the ozone production efficiency in a multichannel dielectric barrier discharge (DBD) reactor utilizing positive and negative pulses. Results show that conversion of O₂ to O₃ is continuously enhanced by the increase of gas pressure (0.1–0.24 MPa) while the rising speed of oxygen conversion with the increasing gas pressure at fixed specific input energy is reduced above 0.15 MPa. The maximum ozone generation efficiency is increased with increasing gas pressure (0–0.2 MPa) while positive pulse exhibits higher energy efficiency. The maximum ozone generation efficiency is suppressed with further increase of gas pressure (0.2–0.24 MPa) while no significant difference in ozone generation efficiency is observed for two unipolar pulse modes. Results also show that 0.2 MPa is the optimal working gas pressure to obtain the maximum ozone generation efficiency and increasing gas pressure would lead to remarkable increase of ozone generation efficiency for ozone production at high energy densities in multichannel DBD.     

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.     

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.     

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.     

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.     

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.     

Ozone and Nitrogen Oxides Generation in Gas Flow Enhanced Hollow Needle to Plate Discharge In Air

Siemens made the first ozone generation system by corona discharge about hundred and fifty years ago. At present mainly two types of atmospheric pressure electrical discharges - corona discharge and dielectric barrier discharge are used for production of ozone. Another type of discharge, which can be used for this purpose, is multineedle to plate electrical discharge enhanced by the gas flow. Contrary to the conventional arrangement when the gas is flowing around the needles we studied the discharge in which the gas was pumped through the needles. Results of studies of ozone and nitrogen oxides production by DC electrical discharge in air at atmospheric pressure with a single hollow needle to plate electrode configuration enhanced by the flow of air through the needle for both polarities of the needle, different airflow rates and currents are presented in this paper.     

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.