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

Gas discharge plasmas and their applications

In recent decades particular interest in applications of nonequilibrium plasma for the problems of plasma-assisted ignition and plasma-assisted combustion has been observed. A great amount of experimental data has been accumulated during this period which provided the grounds for using low temperature plasma of nonequilibrium gas discharges for a number of applications at conditions of high speed flows and also at conditions similar to automotive engines. The paper is aimed at reviewing the data obtained and discusses their treatment. Basic possibilities of low temperature plasma to ignite gas mixtures are evaluated and historical references highlighting pioneering works in the area are presented. The first part of the review discusses plasmas applied to plasma-assisted ignition and combustion. The paper pays special attention to experimental and theoretical analysis of some plasma parameters, such as reduced electric field, electron density and energy branching for different gas discharges. Streamers, pulsed nanosecond discharges, dielectric barrier discharges, radio frequency discharges and atmospheric pressure glow discharges are considered. The second part depicts applications of discharges to reduce the ignition delay time of combustible mixtures, to ignite transonic and supersonic flows, to intensify ignition and to sustain combustion of lean mixtures. The results obtained by different authors are cited, and ways of numerical modelling are discussed. Finally, the paper draws some conclusions on the main achievements and prospects of future investigations in the field.

/pdf/plasma-assisted-ignition-and-combustion-2i4ybn8440.pdf

Plasma assisted ignition and combustion

The nature of the silent discharge (dielectric barrier discharge) is reviewed. Theoretical models for describing its discharge physics and ensuing plasma chemistry are presented. The phenomena leading to gas breakdown in such electrode configurations at about atmospheric pressure are discussed. The current transport takes place within a large numer of short-lived microdischarges, the plasma conditions of which are investigated. The theoretical predictions are compared to measurements. Two entirely different applications of silent discharges are treated: industrial ozone production and the formation of excimers to generate ultraviolet radiation. The special capability of the silent discharge for large-scale industrial processing is demonstrated. >

Modeling and applications of silent discharge plasmas

A review is presented of plasma chemical processes occurring in the volume part of electrical nonequilibrium discharges. The role of energetic electrons as initiators of chemical reactions in a cold background gas is discussed. Different discharge types of (glow, corona, silent, RF, and microwave discharges) are investigated with respect to their suitability for plasma processing. Emphasis is placed on the requirements of initiating and maintaining the discharge and, at the same time, optimizing plasma parameters for the desired chemical process. Using large-scale industrial ozone production as an example, the detailed process of discharge optimization is described. Other applications of volume plasma processing include other plasma chemical syntheses as well as decomposition processes such as flue gas treatment and hazardous waste disposal. The author only deals with plasmas which are not in equilibrium. >

Nonequilibrium volume plasma chemical processing

A comprehensive model of ozone generation in dielectric barrier discharges is presented. The model combines the physical processes in the micro-discharges with the chemistry of ozone formation. It is based on an extensive reaction scheme including the major electronic and ionic processes. The importance of excited atomic and molecular states is demonstrated. Theoretical limits are given for the ozone production efficiency and the attainable ozone concentration. The most important parameters influencing the performance of ozonisers are identified. All theoretical predictions are compared to measured data.

https://iopscience.iop.org/article/10.1088/0022-3727/20/11/010/pdf

Ozone synthesis from oxygen in dielectric barrier discharges

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.

Ozone Generation from Oxygen and Air: Discharge Physics and Reaction Mechanisms

Method and device for agglomerating particles of opposite electrical charge suspended in gas streams, in which two partial gas streams (3) are provided, in which the particles are alternatingly charged with positive and negative ions in a manner such that sequences of particle clouds (7, 8) with alternatingly positive and negative charge are generated locally, and that the two partial gas streams (3) are brought together in a manner such that the particle clouds (7, 8) of opposite charge impinge on each other and the particles of different sign conglomerate into larger particles. Two corona discharge devices consisting of a point (5) and plate (6) are fed by two transformers wired in opposite phase.

Method and device for agglomerating electrically nonuniformly charged-up solid or liquid particles suspended in gas streams

In the separation of particles, these are heated together with a gaseous carrier medium. Constitutents of these particles thus vaporize, are cooled in a cooler (21) and condense out. An apparatus for carrying out this process comprises a fan (1) and a heating device (7). A continuous process can be used on a large industrial scale. This is achieved when the particles and the carrier medium are mixed continuously and at controlled rates to give a fluidized blend. This blend is heated to a given temperature in a fluidized bed of a heating device (7), with the production of a mixture consisting of a vapor/gas mixture thus formed and of particle constituents remaining in the form of particles. After the mixture has left the heating device (7), the particle constituents remaining in the form of particles are precipitated and a vapor/gas mixture is passed forward in at least one closed circulation.

Process for separating particles and apparatus for carrying out the process

Device for concentrating and agglomerating particles suspended in a gas flow, which is based on the principle of the electrostatic filter, consisting of a T- or Y-shaped channel having two inlet nozzles (1), provided in each case with a charging apparatus, and an outlet nozzle (2) One charging apparatus charges the particles in an opposite fashion to the other The device also consists of means (15, 16), arranged in the central part of the exit nozzle (2), for branching off the component gas flow (14) enriched with particles The removal of the particles is performed in a downstream conventional electric filter Embodiments having negative (5) and positive (6) metal tips as ionisation sources of the charging apparatus and having a metal plate (4) situated on the ground as counter (matching) electrode

Michael Dr. Hirth

Papers

Ozone synthesis from oxygen in dielectric barrier discharges

Ozone Generation from Oxygen and Air: Discharge Physics and Reaction Mechanisms

Method and device for agglomerating electrically nonuniformly charged-up solid or liquid particles suspended in gas streams

Process for separating particles and apparatus for carrying out the process

Device for concentrating and agglomerating solid or liquid particles suspended in a gas flow