Dielectric-barrier discharges (silent discharges) are used on a large industrial scale. They combine the advantages of non-equilibrium plasma properties with the ease of atmospheric-pressure operation. A prominent feature is the simple scalability from small laboratory reactors to large industrial installations with megawatt input powers. Efficient and cost-effective all-solid-state power supplies are available. The preferred frequency range lies between 1 kHz and 10 MHz, the preferred pressure range between 10 kPa and 500 kPa. Industrial applications include ozone generation, pollution control, surface treatment, high power CO2 lasers, ultraviolet excimer lamps, excimer based mercury-free fluorescent lamps, and flat large-area plasma displays. Depending on the application and the operating conditions the discharge can have pronounced filamentary structure or fairly diffuse appearance. History, discharge physics, and plasma chemistry of dielectric-barrier discharges and their applications are discussed in detail.

https://www3.nd.edu/~sst/teaching/AME60637/reading/2003_PCPP_Kogelschatz_dbd_review.pdf

Dielectric-barrier Discharges: Their History, Discharge Physics, and Industrial Applications

Major industrial plasma processes operating close to atmospheric pressure are discussed. Applications of thermal plasmas include electric arc furnaces and plasma torches for generation of powders, for spraying refractory materials, for cutting and welding and for destruction of hazardous waste. Other applications include miniature circuit breakers and electrical discharge machining. Non-equilibrium cold plasmas at atmospheric pressure are obtained in corona discharges used in electrostatic precipitators and in dielectric-barrier discharges used for generation of ozone, for pollution control and for surface treatment. More recent applications include UV excimer lamps, mercury-free fluorescent lamps and flat plasma displays.

https://iopscience.iop.org/article/10.1088/0741-3335/46/12B/006/pdf

Atmospheric-pressure plasma technology

Ozone in the gas phase and hydrogen peroxide in the liquid phase were simultaneously formed in hybrid electrical discharge reactors, known as the hybrid-series and hybrid-parallel reactors, which utilize both gas phase nonthermal plasma formed above the water surface and direct liquid phase corona-like discharge in the water. In the series configuration the high voltage needle-point electrode is submerged and the ground electrode is placed in the gas phase above the water surface. The parallel configuration employs a high voltage electrode in the gas phase and a high voltage needle-point electrode in the liquid phase with the ground electrode placed at the gas-liquid interface. In both hybrid reactors the gas phase concentration of ozone reached a power-dependent steady state, whereas the hybrid-parallel reactor produced a substantially larger amount of ozone than the hybrid series. Hydrogen peroxide was produced in both hybrid reactors at a similar rate to that of a single-phase liquid electrical discharge reactor. The resulting concentration of H/sub 2/O/sub 2/ in the hybrid reactors, however, depended on the pH of the solution and the gas phase ozone concentration since H/sub 2/O/sub 2/ was decomposed by dissolved ozone at high pH.

Hydrogen peroxide and ozone formation in hybrid gas-liquid electrical discharge Reactors

Abstract The widespread applications of ozone technologies are established on the basis of large-scale manufacture of ozone generator and chemical reactivity of ozone. It is hence necessary to summarize the principles of ozone generation and to analyze the physicochemical properties of ozone, which are of fundamental significance to indicate its technical developments and practical applications. This review presents a summary concerning ozone generation mechanisms, the physicochemical properties of ozone, as well as the applications of ozone in water treatment. Ozone can be produced by phosphorus contact, silent discharge, photochemical reactions, and electrochemical reactions, principally proceeding by the reaction of oxygen atom with oxygen molecule. There are side reactions to the generation of ozone, however, which are responsible for ozone depletion including thermal decomposition and quenching reactions by reactive species. The solubility of ozone in water is much higher than that of oxygen, suggesting that it may be reliably applied in water and wastewater treatment. Based on the resonance structures of ozone, one oxygen atom in ozone molecule is electron-deficient displaying electrophilic property, whereas one oxygen atom is electron-rich holding nucleophilic property. The superior chemical reactivity of ozone can also be indirectly revealed by radical-mediated reactions initiated from homogenous and heterogeneous catalytic decomposition of ozone. Owing to the reliable generation of ozone and its robust reactive properties, it is worthy to thoroughly elaborate the applications of ozone reaction in drinking water disinfection and pre- or post-treatment of industrial wastewater including cyanide wastewater, coking wastewater, dyeing wastewater, and municipal wastewater. The structural characteristics of ozone reactors and energy requirement of applied technologies are evaluated. In addition, future directions concerning the development of ozone generation, ozone reactivity, and industrial wastewater ozonation have been proposed.

Ozonation in water treatment: the generation, basic properties of ozone and its practical application

A new theoretical model for ozone generation from air is proposed. This model considers the dependency of the ozone dissociation rate by electron impact on the electric field strength, in addition to ozone decomposition processes through the reactions with nitrogen oxides. Assuming a stationary and uniform discharge in time and space, ozone concentrations obtained experimentally under various discharge gap widths and gas pressures are in good agreement with the analytical results. It is concluded that the discharge condition of a narrow gap and accordingly an optimized high gas pressure is one of the most effective means of efficient ozone generation for an air-fed ozone generator.

https://iopscience.iop.org/article/10.1088/0022-3727/32/23/309/pdf

Analysis of ozone generation from air in silent discharge

Experimental and theoretical investigations have been carried out on the ozone generation characteristics of oxygen-fed ozone generators with various discharge gap lengths. In this paper, a new theoretical model considering the dependence of ozone dissociation rate by electron impact on the electric field strength is suggested. Assuming a stationary and uniform discharge in time and space, ozone concentrations obtained experimentally under various discharge power densities and gas pressures are well explained by this model. It is concluded that the operation under a high electric field has a potential advantage in producing high-concentration ozone efficiently because of the reduction in the population density of low-energy electrons which decompose generated ozone.

https://iopscience.iop.org/article/10.1088/0022-3727/30/17/011/pdf

J Kitayama

Papers

Analysis of ozone generation from air in silent discharge

Theoretical and experimental study on ozone generation characteristics of an oxygen-fed ozone generator in silent discharge