A Study of Ozone Generation by Negative Corona Discharge Through Different Plasma Chemistry Models

The Steady radial distribution of chemical species in a wire‐to‐cylinder ozone generator filled with pure oxygen has been computed by applying four different plasma chemistry models of increasing complexity. The most complete model considers ten species (e, O₂ ⁺, O₂ ^?, O₃ ^?, O^?, O₂, O₂(¹Δ_g), O₂(¹∑_g ⁺), O and O₃) and 79 reactions, including ionization by electron impact, electron attachment and detachment, electron-ion recombination, charge transfer, etc. The chemical model is coupled with the electrical model through Poisson's equation. The spatially averaged ozone density has been computed as a function of the current intensity and compared with the experimental values obtained by UV spectroscopy.     

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.     

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%.     

The Effect of Gaseous Diluents on Ozone Generation from Oxygen

Ozone generation in a negative corona discharge has been experimentally investigated using both a pure oxygen and in binary mixtures of oxygen with several gases. The concentration of ozone (O₃) in such mixtures is found to be dependent both on the input energy density η, dissipated in unit volume of gas mixture and on the type and the concentration of the additives. The experimentally measured dependencies of ozone concentration on the input energy density (O₃) = f(η) have been fitted using the Vasiliev–Kobozev–Eremin formula and the specific rate coefficients for ozone formation K_f and ozone decomposition K_d have been calculated. Using Ar, N₂ or CO₂ as admixtures, an increase in the specific rate coefficient for ozone generation was observed for increasing concentrations of added gaseous impurity into oxygen. In contrast, admixtures with SF₆ or CCl₂F₂ caused a substantial reduction of K_f values. The absolute values of ozone concentration at constant input energy density were observed to decrease with decreasing concentrations of oxygen in all mixtures.     

Possibility of Improvement on Ozone Production by Using the Back-Corona Effect

Electrostatic precipitators’ problems and experimental results in point-to-plane or wire-to-cylinder systems indicate that the presence of a thin layer of porous dielectric material on the electrodes increases the discharge current for the same applied potential. This socalled Back-Corona effect, which generally reduces the sparking potential, depends on the active electrode polarity; nature, and thickness and porosity of the insulating layer; and position on the active or passive electrode of the deposited particles or insulating layer. In laboratory experiments in a point-to-plane device, with a dielectric porous layer on the plane, the current may be many times higher than its “normal” value (clean electrodes). In a DC negative wire-to-cylinder system, where the ozone concentration depends quasi directly on the discharge current, it appears possible to increase the ozone production, for the same running conditions (gas flow, electrical circuit, etc.).     

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.     

Investigations on the Effect of Ozone as a Disinfectant of Egg Surfaces

The feasibility of gaseous ozone to reduce the number of microorganisms on the shell surface, of Salmonella Enteritidis (S.E.) in particular, of avian hatching eggs was investigated. Shell eggs were externally contaminated with S.E. to contain either 10²–10⁴ or 10⁵–10⁶ cfu/shell. Subsequently, the eggs were exposed to several ozone concentrations ranging from 0.5% to 5% wt/wt in combination with two relative humidities (< 30, > 70%) at room temperature. Exposure times varied between 20 minutes and 24 hours. A complete inactivation of 10²–10⁴cfu S.E./egg shell was reached by using an ozone concentration of 1% (wt/wt) for 120 min. Considering higher concentrations of S.E. on the shell ozone treatment caused approximately a 6 log₁₀ reduction. This demonstrates that gaseous ozonation is suitable for applications in hatcheries provided that high-power ozone generators are available. The parameters should be verified in large ozone cabinets.     

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.     

Corrosion Resistance of Ozone Generator Electrode

Materials used for the discharge tubes of ozone generators and also their method of production are examined, focusing on the conductive film characteristics. In comparison with the aluminum hot spray method, the stainless steel sputtering method can form a thinner and denser amorphous conductive thin film with corrosion resistance. It has higher durability exposed under discharge species than other materials ever before used.     

Microbiological Environmental Monitoring After the Use of Air Purifier Ozone Generator

The work aimed to evaluate the indoor microbiological air quality after using the purifier ozone generator (Brizzamar®), by counting the total viable microorganisms. The plates containing the culture media were exposed on pre-defined locations for 10 min at the times 0 h (without purifier), 1, 2 and 3 h (with purifier). The results showed significant decreases in the microorganisms after using the purifier, reaching a reduction up to 80% of the fungi and bacteria in the environment after two hours. The amount of ozone in the atmosphere was kept at 0,01 ppm, which is considered non-toxic to human exposure. The purifier significantly improved the air quality in indoors.     

Effect of Ozone Injection on the Catalytic Reduction of Nitrogen Oxides

The improvement in the catalytic reduction of nitrogen oxides (NO_x) by means of the ozone injection into the exhaust gas was investigated. Nitric oxide (NO) in the exhaust gas was first oxidized to nitrogen dioxide (NO₂) by ozone, and then the exhaust gas containing the mixture of NO and NO₂ was directed to the catalytic reactor where both NO and NO₂ were reduced to nitrogen. The ozone injection method was very efficient for the oxidation of NO to NO₂ in a wide range of temperatures, and the increase in the content of NO₂ by the ozone injection remarkably improved the performance of the catalytic reactor.     

Study of the Sonication/Ozone/Argon Process for Saturated Free Fatty Acids Degradation in Aqueous Solution

In the present work, study of the sonication process was investigated for saturated fatty acids degradation. Saturated fatty acids are the most hard-degradable compounds of FOG (fats, oils, and greases) wastewater contaminants. The influence of various conditions (probe immersion level into the liquid, simultaneous ultrasound irradiation and bubbling of Ar, O₂, air, and O₃) on the sonochemical and energy efficiency of the sonication process were studied. According to our experimental data and the state of the art, the most appropriate conditions were selected on purpose to decompose hydrophobic compounds, such as saturated free fatty acids. The most effective degradation treatment method for saturated free fatty acids was the simultaneous sonication (with high probe immersion level into the liquid) and argon bubbling (at low flow rate) under controlled temperature.     

Power Evaluation of the Los Angeles Oxygen–Fed Ozone System

The Los Angeles Department of Water and Power (LADWP) operates a 600 mgd (2,270 ML/day) direct filtration water treatment plant which includes a 7,900 lb/day (149 kg/hr) ozonation system. Ozone is applied as a preoxidant for the purposes of disinfection and microflocculation. The ozonation system is unique in that high purity oxygen is generated on–site and is used as the feed–gas in a once–through system. The process was selected through competitive bids and evaluated for total present worth from 20–year life cycle costs which included capital plus energy expenses. Power consumption (and penalty) was valued at $6,500/kW. System power demand was measured at nine ozone production rates. A minimum specific energy of 6.5 kWh/lb (14.3 kWh/kg) of ozone was observed when generating ozone at a concentration between 5 and 6 % (wt) [65 and 80 g/m³; where the standard temperature and pressure are 70F (21.11 C) and 1 atm, respectively]. The test methodology and data assessment considerations were developed jointly by the owner and manufacturer, and produced results with practical significance beyond the performance testing objective.     

The Benefits of Small Quantities of Nitrogen in the Oxygen Feed to Ozone Generators

This paper reports the ozone generation in pulsed multichannel dielectric barrier discharge. The influence of nitrogen addition (0.1%–10%) on ozone concentration and ozone generation efficiency in nitrogen–oxygen gas mixtures is studied. Results show that adding 0.1% N₂ would not seriously increase the ozone production. Meanwhile, 1% N₂ content exhibits the highest ozone production efficiency in low SIE (J/L, defined as the ratio of power to gas flow rate) region (0–200 J/L) while adding 0.3% N₂ would lead to the highest ozone generation efficiency in high SIE region (300–800 J/L). The increase of ozone production induced by N₂ addition is more significant in low SIE region compared with that in high SIE region. At 100 J/L, ozone production efficiency increases 26.9% to 201.6 g/kWh with 1% N₂ addition when compared with that in oxygen. At 18 J/L, the observed maximum ozone generation efficiency reaches 252 g/kWh at 1.3 g/Nm³ with 1% N₂ addition. An increase of ozone production can be obtained with 0.3%–2% N₂ addition in all explored SIE ranges.     

Development of a Practical Method for Using Ozone Gas as a Virus Decontaminating Agent

Our objective was to develop a practical method of utilizing the known anti-viral properties of ozone in a mobile apparatus that could be used to decontaminate rooms in health care facilities, hotels and other buildings. Maximum anti-viral efficacy required a short period of high humidity (>90% relative humidity) after the attainment of peak ozone gas concentration (20–25 ppm). All 12 viruses tested, on different hard and porous surfaces, and in the presence of biological fluids, could be inactivated by at least 3 log_10, in the laboratory and in simulated field trials. The ozone was subsequently removed by a built-in catalytic converter.     

The Ozone Laundry Handbook: A Comprehensive Guide for the Proper Application of Ozone in the Commercial Laundry Industry

Applications of ozone in commercial laundry systems began in the late 1980s–early 1990s. Early installations showed promise for ozone to save considerable energy over conventional (thermal) systems. However, inconsistent performances of ozone equipment of that period coupled with a lack of in-depth understanding of how ozone was performing hindered commercial acceptance of ozone. With continued study and testing, these early misunderstandings about ozone have been overcome, and today many thousands of commercial laundry systems are using ozone successfully in many parts of the world. For example, more than 2,000 ozone laundry systems are operating in commercial laundry systems in the USA and another 2,000 commercial ozone laundry systems in the United Kingdom alone! Based on proven performance data obtained from many of these successful applications of ozone in commercial laundry systems, the authors have developed an Ozone Laundry Handbook, intended to be a summation of current knowledge and a guide to the laundry owner/operator considering the use of ozone. The Handbook contains 10 chapters, including discussions of the economic, environmental and microbiological benefits of ozone in commercial laundries, a discussion of ozone technologies as they apply to laundry systems, a comparison of traditional vs ozone laundry formulations, methods of applying ozone for laundering, operator training and ozone safety, a discussion on facts and fallacies about ozone for laundering, and finally a chapter on the future of ozone for laundering. The Handbook also contains a Glossary of Ozone Terms, Indices, and an Index.     

Kinetic Study of Ozone Decay in Homogeneous Phosphate-Buffered Medium

The ozone decomposition reaction is analyzed in a homogeneous reactor through in-situ measurement of the ozone depletion. The experiments were carried out at pHs between 1 to 11 in H₂PO₄^?/HPO₄^2– buffers at constant ionic strength (0.1 M) and between 5 and 35 °C. A kinetic model for ozone decomposition is proposed considering the existence of two chemical subsystems, one accounting for direct ozone decomposition leading to hydrogen peroxide and the second one accounting for the reaction between the hydrogen peroxide with the ozone to give different radical species. The model explains the apparent reaction order respect of the ozone for the entire pH interval. The decomposition kinetics at pH 4.5, 6.1, and 9.0 is analyzed at different ionic strength and the results suggest that the phosphate ions do not act as a hydroxyl radical scavenger in the ozone decomposition mechanism.     

Cooling Conditions of Ozone Generators

The efficiency of ozone generators is determined by many factors. Operating conditions such as feed gas quality and especially cooling conditions are of utmost importance. Cooling of ozone generators is absolutely necessary, since ozone destruction reactions increase exponentially with temperature. The most common way to cool an ozone generator is water flowing in close contact to the electrodes. The heat removal out of the discharge gap depends on different parameters. Electrical input power, cooling water flow conditions, electrode geometry and material properties are some of them. Simultaneously lowering cooling water temperature, applied power density and gap width, leads to a lower gas temperature in the discharge gap and thus to increased ozone production efficiency. Minimizing the temperature difference between the cooling water inlet and outlet improves the ozone production efficiency as well. This measure, however, results in high cooling water flows and requires additional cooling water chilling, resulting in higher operational costs and capital expenses. Cooling associated costs rise disproportionally with increasing cooling water flow. Simultaneously, energy consumption of ozone generators decreases as the average cooling water temperature goes down. As a result, there exists an optimum between the operational and capital expenses for the combination of ozone generator and cooling water system related expenses, offering significant cost savings for the customer.     

Control of A Fully Automated Ozone Application System

A fully automated system is controlling a two-stage ozonation system treating 140 × 10³ m3/h (6.4 mgd) of potable water in a full-scale water treatment plant. A supervisory computer has a data communications path to each of six ozone generators and a direct link to the ozone destruct system. Total ozone requirement is calculated, the most power-efficient equipment configuration is selectedt and the flow of ozone to each contactor is controlled. Inaddition, graphic display ofequipment status and process variables is provided system events are logged, and strip charts and reports are produced.     

A New Device for the Measurement of Ozone in the Gas Phase

This paper presents a new device for the dosage of ozone in the gas phase. This device measures the concentration of ozone according to the isothermal differential pressure procedure. In principle, this procedure achieves a totally physical ozone measurement without requiring calibration using a chemical method. A comparison is made between the physical results and chemical results obtained by the iodometric standard method (IOA, 1987). There is satisfactory agreement between the two series of measurements in the range of ozone concentration where the chemical method is applicable (with a standard error of estimate of 4.4%).The method and the device are perfectly reliable based upon the strict measurements of temperature and pressure and a convenient choice of constitutive materials.