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.     

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 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.     

The Effect of Relative Humidity on Ozone Production by Corona Discharge in Oxygen or Air – A Numerical Simulation – Part II : Air

The simulation of the temporal evolution of the various neutral gaseous species studied (O, O₃, H, OH, HO₂, H₂O₂, N, NO, NO₂, NO₃, N₂O, N₂O₅, HNO₂, and HNO₃) use corona effects. The physical conditions of the discharge were used. The reactions take place in dry or humid air, after the dissociation of O₂, N₂, and H₂O by an electronic pulse. When water vapor is present, there is a probability of production of H₂O₂, HNO₂, and HNO₃ in air. Temperature and humidity have cumulative effects. With multiple pulses, the O₃ maximal concentration is obtained for a limited number of pulses.     

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.     

The Effect of Relative Humidity on Ozone Production by Corona Discharge in Oxygen or Air – A Numerical Simulation – Part I : Oxygen

The simulation of the temporal evolution of the various neutral gaseous species studied (O, O₃, H, OH, HO₂, H₂O₂) use corona effects. The physical conditions of the discharge were used. The reactions take place in dry or humid oxygen, after the dissociation of O₂ and H₂O by an electronic pulse. When water vapor is present, there is a probability of production of H₂O₂ in oxygen. Temperature and humidity have cumulative effects. With multiple pulses, the O₃ maximal concentration is obtained for a limited number of pulses.     

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.     

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.     

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.     

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%.     

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.     

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.     

Energy Conversion and Temperature Dependence in Ozone Generator Using Pulsed Discharge in Oxygen

A detailed reaction kinetic model consisting of 10 species and 63 reactions is developed to investigate the energy conversion and temperature dependence in an ozone generator using oxygen pulsed discharge. The energy conversion ratios of total electric energy converted into reaction heat, heat carried by gas and heat loss to ambient, namely η_reaction, η_gas and η_loss, are obtained for the first time. The ratio of reaction heat η_reaction decreases substantially with increasing specific energy and inlet gas temperature, which represents how much energy is utilized effectively to synthesize ozone. Correspondingly, η_loss and η_gas increase gradually. η_reaction declines from 55.4% to 27.7% at inlet gas temperature of 298 K when specific energy changes from 0.06 J/cm³ to 0.78 J/cm³. The detailed reaction pathway including the degree of transformation among species for ozone formation is also obtained via kinetics simulation. Meanwhile, sensitivity analysis and rate-of-production analysis for the four most important species O₃, O, O(1D) and O₂(b¹∑) obtained from the reaction pathway are executed to understand quantitatively the temperature dependence of sensitivity coefficient and production rate for each individual reaction. The production rate of ozone via the most important ozone generation reaction O+O₂+O₂ = > O₃+O₂ increases linearly with the increase of gas temperature, as well as the destruction rates of ozone via the most important ozone decomposition reactions O₃+O₃ = > O₂+O₂+O₂ and O₃ + O = > O₂(b¹∑)+O₂.     

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.     

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.