Criteria for the Selection of the Feed Gas For Ozone Generation

This paper brings together the requirements and experiences of the supplier of ozone generating equipment and the user of this equipment. The technical requirements of the ozone generator on the feed gas, the main characteristics of the system alternatives, the on-site experience and the development of criteria for future applications are described. The particular application of ozone and the quantities required are detailed to provide a full understanding of the background and environment of the case study and its demands on the system selection. The evolution from an air fed system to an oxygen fed system is outlined. This paper describes the joint evaluation of the choice of feed gas for the Purton Water Works by Bristol Water Plc and Ozonia using the experience gained at the Littleton Works and the technical assessment during the pre-contract stage of the Purton Treatment Works Development Scheme.     

Ozone Gas Scrubbing for Air-Operated Ozone Generation Systems

In laboratory testing as well as in tests using a semi-technical plant it was found that removal of the gaseous N₂O₅ as a by-product of ozone generation from air can be realized from a chemical point of view by gas scrubbing using treated drinking water, and forming nitric acid. At the same time this measure accomplishes a reduction of the trichloronitromethane (TCNM = chloropicrin) concentration in the treated water from Lake Constance by 30%. Surprisingly it was also found that the material used herein (stainless steel DIN 1.4571) will be attacked under conditions such as these.     

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.     

Aspects of Ozone Generation from Air

In many fields of industrial application the usage of ozone is a question of economics. In order to improve the efficiency of especially air-fed ozone generators, fundamental research work on modelling of microdischarges, the chemical reaction scheme, and extensive experimental investigations have been undertaken. By proper choice of the operation conditions like pressure, gap width, and cooling conditions, the efficiency can be improved considerably. The reaction temperature in the process volume and the concentration of nitrogen oxides are the main factors influencing the ozone yield.     

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.     

Exergy Identification Of Energy Utilization Efficiency In an Industrial Process of Ozone Generation

The main objective of the paper is to establish an arrangement of sources of exergy losses (internal and external ones) and to estimate the value of the losses in an industrial ozone production installation. An exergetic model of industrial installation in a system approach corresponding to real conditions has been formulated.     

Effective Ozone Generation in Oxygen Using a Mesh Electrode in an Ozonizer with Variable Linear Velocity

Results of studies on ozone synthesis under discharges proceeding in a metal mesh-ceramic dielectric system have been presented. The experiments were carried out in the reactor with unique reaction space geometry, in which the reacting gas flew with consequently increasing linear velocity. The high voltage electrode was made of a metal mesh, which caused intensification of the gas mixing in the reaction space. Using a simple reactor with one-side cooling of the reaction space, high ozone maximum concentrations (100 g/Nm³) and energy efficiencies (180–200 g/kWh) were obtained at 25 °C.     

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.     

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 Applications The State-of-the-Art in Switzerland

This paper describes the current state-of-the-art for ozone applications in the processes to prepare drinking water in Switzerland. The Author bases this presentation on the collective Swiss experience of ozone use in water treatment spanning five decades and the design and operation of over 40 water treatment plants.     

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.     

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.

     

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.     

Economic and Environmental Benefits of Ozone in Ozone Laundering Systems

Three primary benefits (advantages) of properly designed and operated ozone laundering systems have been proven in successful commercial installations – microbiological kills/inactivation of all microorganisms found in linens to be laundered; economic cost savings and significant environmental benefits. Each of these benefits of ozone laundering is described and quantified in the Ozone Laundry Handbook by Rice et al. (2009 Rice, R.G., Cardis, D., Daniels, R., Tapp, C., DeBrum, M. and Watt, J. 2009. The Ozone Laundry Handbook, A Comprehensive Guide for the Proper Application of Ozone in the Commercial Laundry Industry, San Luis Obispo, CA, , USA: Published by ClearWater Tech, LLC.  [Google Scholar]). In this paper, two of these benefits, Cost Savings and Significant Environmental Benefits are discussed.     

Economics of Treating Waste Gases from an Air Stripping Tower Using Photochemically Generated Ozone

Air stripping towers have been recommended for the removal of volatile organic compounds (VOCs) in drinking water supply and industrial waste treatment systems. This technique removes VOCs economically in the liquid phase. It can, however, create adverse secondary environmental impacts by removing VOCs from the water and discharging them to the air.

A commonly proposed method for controlling .VOC emissions is filtration of the off-gas through adsorption of the stripped organics in the off-gas by granular activated carbon. The high incremental cost of this alternative has produced an interest in alternative control technologies.

One alternative currently available is based on short wavelength ultraviolet (UV) radiation. This technique combines the effects of ozone generation, free radical formation and photolysis of the contaminants to effectively control the VOC emissions. This technique is known as Advanced Photo Oxidation (APO)^R.

The cost for APO is $0.27/m³ for a 3.8 m³/hr contaminated water system. A system of this size is adequate for a groundwater decontamination project where a moderate length of time is available for restoration of the site. The cost of a conventional air stripping tower with Granular Activated Carbon (GAC) adsorption emissions control in this size range would be $0.40 to $0.45/m³ (J.M. Montgomery, 1986).

Additional testing will be required to fully develop design guidelines for different contaminants and larger systems. Another area for additional technical documentation is the application of this technique to the liquid phase oxidation of VOCs.     

The Inhibition of Ozone Generation at Ni/Sb-SnO2 Electrodes in High Concentrations of Dissolved O3

The work reported in this paper investigated the observation that high concentrations of ozone in the electrolyte inhibits the electrochemical ozone evolution process at Ni/Sb-SnO₂ anodes in aqueous sulfuric acid. We show that inhibition does indeed take place and that this inhibition does not affect the current density and hence appears to reflect an increase in the ratio of O₂ to O₃ evolved. A possible mechanism for the inhibition is proposed. It was found that Celgard 2400 membrane was an acceptable alternative to Nafion in the divided electrolysis cell employed.     

Destruction of Ozone Off–Gas by Thermal Catalytic Method

In the operation ofozone treatment plants, one will have to deal with ozone inthe off–gas exhaust air. In higher concentrations in the exhuast air, ozone has the unpleasant property of being detrimental to plant, animal and man.

The normal ozone concentration inambient air should not be more than 1/10of the MAK–value. Insmall treatment plants inEurope the small amount of ozone off–gas can be diluted with atmospheric airso that itis permitted to be discharged into the outside air. For larper plants there isthe choice between a thermal and catalytic ozone destruction, or a process that combines both. In the Lengg Waterworks the exhaust air of the reaction chamber was passed through a thermal destruction systen. From the granular activated carbon (GAC) filters theair was passed into the atmosphere untreated. It was ascertained that during GAC back–washing 1200 PPtl ozone were in the exhaust air. This ozone concentration was much too high.     

Room Temperature,Electrochemical Generation of Ozone with 50% Current Efficiency in 0.5M Sulfuric Acid at Cell Voltages < 3V

The electrochemical generation of ozone by Ni/Sb-SnO₂ anodes immersed in 0.5M H₂SO₄ was assessed in both flow and recycle systems using the same electrochemical cell. The anodes were found to exhibit current efficiencies of up to 50%?for ozone generation under flow conditions at room temperature, with an optimum mole ratio in the precursor solutions of ca. 500:8:3 Sn:Sb:Ni and optimum cell voltage of 2.7V. A comparison of the data obtained under flow and recycle conditions suggests that the presence of ozone in the anolyte inhibits its formation. The minimum electrical energy cost achieved, of 18 kWh kg^?1 compares favorably with estimated costs for Cold Corona Discharge generally reported in the literature, especially when the very significant advantages of electrochemical ozone generation are taken into account.