Ozone Generation with Narrow–Band UV Radiation

Ozone formation in oxygen at atmospheric pressure following the photodissociation of O₂ molecules in the vacuum UV range is tudied. A new VUV source based on incoherent xenon excimer radiation from a dielectric–barrier discharge provided narrow–band UV radiation at 172 nm with a half–width of 14 nm. The formation of ozone from the initial photodissociation fragments O(³P) and O(¹D) is treated theoretically and compared to measurements.     

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.     

Improvement of a Measurement System for Surface Loss Rate of Ozone

Ozone molecules present in high-purity oxygen as a feed gas interact with surfaces and oxygen molecules in an enclosed container. Therefore, some of the ozone molecules are destroyed and the density of ozone decreases with time. An experimental system has been constructed to monitor the temporal decrease in ozone density in a container based on the HgI 254 nm photoabsorption method. Our investigation is focused on the dependence of the effective lifetime of ozone on the wall material at various gas pressures. During the experiments, distortion of the measured decay curves often caused by instabilities in the mercury lamp intensity. We thus attempted to build a simple setup that eliminates the effect of long-term intensity drift. This setup is based on light source intensity monitoring by a separate photodetector and data correction software. This article describes the setup of the experimental apparatus, the results including some preliminary experiments and the temporal variation of the surface loss rate of ozone by repeated measurement along with inspections of the wall surface by Auger electron spectroscopy.     

The Photochemical Generation of Ozone : Present State–of–the–Art

This paper reflects an investigation of the feasibility of photochemical generation of ozone by irradiating gases containing oxygen with Hg lamps of the highest performance emitting the 185 nm line. Besides the expected photostationary equilibrium, determining factors for practical yields in ozone generation by the 185 nm wavelength are : the reactor and gas temperature, the reactor geometry, and the gas composition, as well as the pressure.

Further developments are expected in the field of lamp construction and also improvement of reactor geometry. A better knowledge of the aging of the lamps is required, as well as of the photochemical reactions of oxygen in the technologies applied.

Systems presently available are most promising for application on small scale or in areas of public water distribution which have no developed structure.

     

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.     

Investigation of Ozone Loss Rate Influenced by the Surface Material of a Discharge Chamber

Decay characteristics of ozone concentration in oxygen in a chamber with three types of wall material (stainless steel, copper, and aluminum) are measured using the 254 nm photoabsorption method. Effective lifetimes of ozone are estimated from decay curves of ozone concentration. These values depend on the wall material: They are largest for stainless steel and smallest for aluminum. The relationship between effective lifetime and gas pressure is investigated precisely to determine three values. The equivalent diffusion coefficient of ozone in oxygen and the reflection coefficient of ozone at the wall correspond to the loss rate of ozone at the wall. The collisional loss (quenching) rate coefficient of ozone in oxygen is also determined.     

Influence of Water Vapor on Photochemical Ozone Generation with Efficient 172 nm Xenon Excimer Lamps

The influence of water vapor on photochemical ozone generation has been investigated. Tests of a coaxial ozone generator driven by an efficient, tubular, 172 nm xenon excimer lamp revealed that ozone saturation concentration strongly depends on moisture concentration in the process gas. In order to adequately model the data, catalytic ozone destruction by OH and HO₂ radicals formed by reactions with trace amounts of water vapor in the process gas had to be included in the photochemical ozone production rate equation system. Based on the model, optimized ozone photoreactor designs for ambient air, dry air and dry oxygen are described.     

Comparison of Economics of Various Ozone Generation Systems

The specific production costs of ozone are presented for a capacity range of 1 to 1,000 kg/h ozone for various plant configurations and air or oxygen as feed gas, and for air preparation, liquid oxygen delivered to site, oxygen produced on–site and/or oxygen recycle systems. The influence of operating parameters such as ozone concentration or on–stream time are studied. Ozone is often considered to be “expensive”. It is difficult to pinpoint the rationale behind this statement. It could be caused by the difficulty to compare a chemical (ozone) which is produced on–site and requires a plant investment, with chemicals (such as chlorine) which are bought as such and delivered to the plant. It is certainly influenced by the fact that the economy of utilizing ozone s i not easily quantified. This paper presents an attempt to quantify the economics of ozone production for a wide range of production capacities, ranging from 1 to 1,000 kg/h. Different operating conditions are compared as well as different plant concepts. In order t o assure a meaningful comparison, certain parameters are common for all cases.     

Ozone Synthesis and Decomposition in Oxygen-Fed Pulsed DBD System: Effect of Ozone Concentration,Power Density,and Residence Time

The process of ozone production in pure oxygen was studied. It was shown how the ozone concentration changes along the discharge gap, both during its generation and decomposition processes. The effect of ozone inlet concentration, power, and gas residence time on ozone concentration was analyzed. It has been shown that concentrated ozone is easily decomposed at very low discharge powers, i.e., when the increase of the average gas temperature in the gap is negligibly small. It was hypothesized that the most intense decomposition takes place in the microdischarge channels, because the process of gas heating in the gap begins inside them.     

Editorial

The dynamics of the ozone formation in an oxygen-fed micro-discharge was studied by observing the dispersed emission from the reacting species. The correlation between the ozone production with the physical factors of a micro-discharge was described by a mathematical model where the distribution of the mean electronic energy is considered. The results showed that the oxygen atom is mostly produced from the oxygen molecule dissociating from the Schumann-Runge band, instead of being produced by direct electron bombardment. This is the reason why pressure has a negative effect role in ozone formation.     

Characterization of the ozone zero phenomenon by infrared spectroscopy

The presence of a small amount of nitrogen in the feed gas is necessary to generate ozone efficiently out of oxygen. Operating an ozone generator with ultra-pure oxygen for extended periods results in highly deteriorated ozone generation efficiency. In extreme cases, when the nitrogen levels in the feed gas are in the lower ppm range, the efficiency of the ozone generation process even drops to zero. In this article, we present our results concerning the correlation between the N₂O₅ concentration in the off-gas and the ozone generation efficiency. After the ozone generator is run for a well-defined amount of time with an oxygen–nitrogen mixture, the N₂ supply is shut off, and the behavior of the system is monitored by near-infrared spectroscopy. Different surface materials lead to different temporal behavior of both the nitrogen oxide levels and the ozone concentration after shutting down the nitrogen supply. The measurements show a good correlation between the evolution of ozone generation efficiency and the changes of the N₂O₅ concentration in the off-gas.     

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%.     

Removal of organic impurities from the silicon surface by oxygen and UV cleaning

We have studied the effect of oxygen and water vapor on the removal of organic impurities from the porous silicon surface under UV irradiation. Infrared spectrum observations of the treated surface suggest that decomposition of oxygen to produce ozone, atomic oxygen, and hydroxyl radical is a rate determination step for the overall cleaning process.     

Research Note: O3 or O2 and Ag: A New Catalyst Technology for Aqueous Phase Sanitation

Silver deposited on an inert surface with a very large area exhibits a strong catalytic interaction with oxygen which results in strong bactericidal activity. This catalytic process is fundamentally different from other known silver-based approaches which deliver low levels of silver ions into water.

Two factors appear to control the rate of this catalytic reaction process: (1) the size and dispersion of the silver crystals and surface area of the supporting bed; and (2) the volume of oxygen in solution. The source of the oxygen can be atmospheric oxygen dissolved in the water or, for a greatly enhanced reaction rate, dissolved ozone produced by an ozone generator. In this process, oxygen molecules absorbed onto the catalyst surface are subsequently transferred to other oxidizable substrates including bacteria and viruses.

These catalytic oxidizing reactions exhibit two properties of significance in the sanitation of water. First, because oxygen on the catalyst surface reacts with both living and nonliving substrates, bacteria or viruses which are in the water flowing over the catalyst-containing medium are killed or inactivated on contact by the oxidizing reactions (i.e., without requiring the release of metals into water). Second, oxygen also is transferred to oxidizable inorganics (such as bromide ion) to generate readily measurable and relatively stable “residual” oxidizers/disinfectants that continue to sanitize water downstream.

Results of this Author's experiments have been independently replicated by sources from the University of Arizona, and at Herbert V. Shuster, Inc. Laboratories in Massachusetts.     

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.     

User Experiences with Ozone,Electrolytic Water (Active Water) and UV-C Light (Ventafresh Technology) in Production Processes and for Hygiene Maintenance in a Swiss Sushi Factory

In a sushi production factory in Vuadens, Switzerland, ozone, ultrasound, electrolyzed water, and UV (185 and 254 nm) radiation are employed to sanitize all production equipment and factory space, including incoming and cooled air, as well as to sanitize the sushi products themselves. Fish, vegetables and rice all are washed with electrolyzed water as ultrasound is applied. Sushi itself is disinfected prior to packaging by fumigation with ozone and UV radiation in a special UV Disinfection Tunnel. Packaging materials (film and trays) are disinfected with gaseous ozone and UV radiation. After sealing of the sushi packages with Modified Atmosphere Packaging (including additional oxygen), UV radiation again is applied in another, longer UV Disinfection Tunnel. This transforms about 12–14% of the oxygen remaining inside the packed tray to ozone, creating an ozone-containing atmosphere. By this Ventafresh technology, the shelf-life of sushi products increases from three to seven days. Plant ambient temperature is maintained at 3°C at all times during processing to provide additional improvement in microorganism control. Cost savings at Sushi are significant, but secondary – only one failure and the plant is shut down. Ventafresh is, at the very least, a technological insurance policy that allows the plant manager to sleep at night.     

Ozone Dissolution vs. Aqueous Methylene Blue Degradation in Semi-Batch Reactors with Dielectric Barrier Discharge over the Water Surface

Ozone accumulation in water was compared with aqueous methylene blue (MB) degradation in a stirred semi-batch reactor. Comparable concentrations of gas-phase ozone, generated by parallel-plate dielectric-barrier AC discharge in high-purity oxygen, were allowed to contact the tested liquid using one of three regimens of ozone generation: (1) dry ex-situ; (2) humid ex-situ; and (3) humid in-situ ( “electroozonation” ). Results from (1) and (2) were similar, whereas in case (3) a slower ozone accumulation rate was contrasted by a three times faster MB degradation. A faster decomposition of aqueous ozone due to an assumed prevalence of free-radical induced MB degradation over direct ozonation in case (3) are indicative of a process similar to glow-discharge electrolysis.     

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.     

Belgian Experiences in the Ozonization of Water

After reviewing the uses of ozone in the preparation of drinking water, high purity water for Pharmaceuticals industries, and swimming pools throughout Belgium, a discussion of technological developments made at the Tailfer plant (serving Brussels) concerning the uses of ozone is presented. These subjects include analytical and monitoring techniques developed for ozone, procedures for ozone contacting employed at this plant, treatment of ozone contactor off–gases, and the use of oxygen–enriched process gas to produce supplemental amounts of ozone required periodically. Capital and operating cost data are presented.     

Using Circular Conduits in Ozone Injection

Dissolved oxygen is the amount of oxygen dissolved in water corresponding to an important water quality parameter in rivers, streams, and lakes. Hydraulic structures can increase dissolved oxygen levels by creating turbulent conditions where small air bubbles are carried into the bulk of the flow. A gated conduit is a hydraulic structure that can be used efficiently in aeration and oxygen transfer. The subatmospheric pressure between the upstream and downstream of the gate is the reason for the air injection. Ozone is an unstable gas comprised of three oxygen atoms, and it can be used for water treatment. Ozone is thermodynamically unstable and spontaneously reverts back into oxygen. Ozone has been widely accepted as an effective disinfectant and a chemical oxidant. In this study a series of experiments was conducted to determine the ozone injection performance of circular conduits. Results showed that circular conduits are very effective for ozone injection.