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 decomposition on glass and silica

Ozone decomposition on glass and silica surfaces is studied by means of non‐porous particles in a fixed bed (sand, glass bead, crushed glass bead, silica). Influences of gas velocity, particle diameter and reactor volume are investigated. Ozone is produced by a silent discharge generator. A model considering the geometric characteristics of material is used so that the ozone decomposition rate per unit of surface area is identified. The decomposition reaction is represented by means of an apparent first‐order kinetic constant. The high dependency of the apparent kinetic constant on the surface area, for given flow rates, suggests that the ozone decomposition mechanism is not simple. Due to the values of the apparent first order kinetic constant, the existence of catalytic species produced by the ozone generator, as well as excited ozone and/or oxygen species, are considered, by means of several models, to explain the experimental results.     

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.     

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.     

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.     

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.     

The Basic Clinical Applications of Ozone Therapy

Medical ozone is a mixture of ozone and oxygen, prepared via silent electrical discharge, within a concentration range of 0.05 volume % O₃ to max. 5.0 volume % O₃.

In order to exclude its toxic effect on the pulmonary epithelium, the medical ozone/oxygen mixture is administered so that exposure of the respiratory tract is avoided at all times, i.e., without the disturbing effects of its odor.     

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.     

Catalytic Properties Of Silica Packings Under Ozone Synthesis Conditions

The catalytic effect of dielectric packings inside the discharge gap on the yield of ozone generation was studied under silent discharge conditions. Porous silica of developed internal surface and quartz glass grains were used as the packings. In the presence of coarser grains of both materials, higher ozone concentrations and higher energy efficiency were observed than with the finer ones. Porous silica was found to be more effective than quartz glass. The higher activity of silica arises from the surface structure rather than from its porosity.     

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.     

Comparative Experimental Study between Surface and Volume DBD Ozone Generator

Volume Dielectric Barrier Discharge (DBD) is nowadays considered the most effective way for ozone generation in the industry. Some papers were published only on surface discharge reactors applied for ozone generation. This article describes an experimental investigation for the comparison between these two reactor types of ozone generation. Two surface and volume DBD reactors of cylindrical shape were used in the same experimental conditions. Obtained results showed that although the majority of ozone generators are of volume discharge type, the surface DBD presents significant superiority in terms of ozone generation and energy efficiency.     

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.     

Generation of Radicals using Discharge inside Bubbles in Water for Water Treatment

A new method for a water treatment utilizing radicals produced by a discharge inside bubbles in water is proposed. Radicals with short lifetime (atomic oxygen and OH radical) are used effectively for the water purification because those are generated by discharge inside bubbles in water. OH radical production was confirmed by a light emission of the discharge using the spectroscopic technique. Dissolved ozone concentration of about 0.3 mg/1 was obtained when oxygen was used as a bubbling gas. Decolorization process of indigo solution by a discharge inside bubbles in water was investigated.     

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.     

Studies on the inhomogeneous nature of the silent discharge reactor: Part 3. A multi-zoned flow model

The reaction space of a silent discharge reactor consists of two distinct components, viz. (1) the collection of primary reaction zones (PRZ) or discharge streamers where, under the influence of free electron avalanches, primary electron molecule collisions take place and (2) the remaining reaction space which provides for secondary or quenching reactions between activated species and gas molecules. A flow model based on this concept has been proposed which accounts for the intrinsic chemical activity of the PRZs as well as their random distribution, spatial location, transient nature, and temperature field. Experimental results obtained on laboratory ozonizers have been examined to show the validity of the proposed model.     

Ozone Storage Oriented to Power Load Leveling

This paper investigates the ozone storing properties of silica gel. There are three kinds of storing technologies for ozone at present: First, ozone gas is stored at high pressure in a gaseous state. As ozone is used, it is discharged from the container. Second, silica gel (which stores ozone at low temperatures) is able to adsorb ozone. When the silica gel is heated, ozone becomes detached. Third, silica gel that is stored under high atmospheric pressure can adsorb ozone. To detach ozone, the atmospheric pressure is reduced.

It has been found that it is unnecessary to change the temperature and pressure inside the container when removing ozone from silica gel. This means that ozone can be detached from silica gel using very little energy. This system is proposed for storing ozone in industry, and this system is effective for Power Load Leveling.     

Ozone Production by an Ultra-Short Triggered Dielectric Barrier Discharge.

This work was motivated by the ozone production improvement by a dielectric barrier discharge supplied with a high voltage triggered pulsed generator. Particular attention was focused on the ozone generator cell geometry and on the type of electrical generator. A comparative parametrical analysis on two configurations of reactor was performed: an annular and a surface configuration. This study emphasizes that surface discharges coupled to ultra-short triggered high voltage generators stand out as an efficient process to produce ozone in large quantities.     

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.     

New Generation of Low Pressure Mercury Lamps for Producing Ozone

Producing ozone by means of a low pressure mercury discharge is still limited by such economical and technical factors as efficiency and lifetime of Low Pressure Mercury Lamps (LPMLs). With the introduction of a new “long life coating” technology for LPMLs at Heraeus, these lamps show up as an effective and reliable VUV-light source that can be used in ozone generation. Different coating technologies are compared in terms of radiation losses in the coating and depreciation of the mercury resonance line at λ=185 nm. The parameters of new ozone generating lamps are presented. A simple model with consideration of both the resonance lines at λ=185 nm and λ=254 nm for a practical calculation of ozone concentration in an air flow is proposed.     

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.