Ozone Generation by Hybrid Discharge Combined with Catalysis

In this paper, combining hybrid discharge with pellet alumina catalyst is used for ozone generation. The hybrid discharge including corona discharge (CD), surface discharge (SD) and dielectric barrier discharge (DBD) may happen in the device. Factors that affect the ozone production efficiency and concentration are studied, such as energy density, power, gas flow rate, frequency, peak voltage and catalysts.     

Ozone Generator with Cylindrical Type of Rotating Electrode

An ozone generator using a rotating electrode to improve ozone generation efficiency is proposed. The ozone generator electrode unit consists of a rotating electrode and fixed electrode. The rotating electrode has the grounded 36 pieces of tungsten wires fixed in parallel to the rotation axis on the rotating cylinder surface. A dielectric electrode is used as a fixed electrode located on the inside of the tube of the electrode unit. The width of the apparent discharge gap is 1mm. Alternating current with a frequency of 50 Hz is applied to the electrode unit. The rotation speed can be adjusted from 0 rpm to 1200 rpm by a variable speed motor. Oxygen gas is used as the material gas. Higher ozone concentration and higher ozone generation efficiency are obtained compared with that when the rotation speed is 0 rpm. The gas temperature is measured at the inlet and outlet of the ozone generator, and the rotation speed for the cooling effect is most effective at about 500 rpm. The maximum generation efficiency is estimated to be 61 g/kWh at 800 rpm, and this value is twice as large as in the case of 0 rpm.     

Ozone Production Influenced by Increasing Gas Pressure in Multichannel Dielectric Barrier Discharge for Positive and Negative Pulse Modes

This paper describes the influence of gas pressure on the conversion of O₂ to O₃ and the ozone production efficiency in a multichannel dielectric barrier discharge (DBD) reactor utilizing positive and negative pulses. Results show that conversion of O₂ to O₃ is continuously enhanced by the increase of gas pressure (0.1–0.24 MPa) while the rising speed of oxygen conversion with the increasing gas pressure at fixed specific input energy is reduced above 0.15 MPa. The maximum ozone generation efficiency is increased with increasing gas pressure (0–0.2 MPa) while positive pulse exhibits higher energy efficiency. The maximum ozone generation efficiency is suppressed with further increase of gas pressure (0.2–0.24 MPa) while no significant difference in ozone generation efficiency is observed for two unipolar pulse modes. Results also show that 0.2 MPa is the optimal working gas pressure to obtain the maximum ozone generation efficiency and increasing gas pressure would lead to remarkable increase of ozone generation efficiency for ozone production at high energy densities in multichannel DBD.     

Comparative Experimental Study between Surface and Volume DBD Ozone Generator

Volume Dielectric Barrier Discharge (DBD) is nowadays considered the most effective way for ozone generation in the industry. Some papers were published only on surface discharge reactors applied for ozone generation. This article describes an experimental investigation for the comparison between these two reactor types of ozone generation. Two surface and volume DBD reactors of cylindrical shape were used in the same experimental conditions. Obtained results showed that although the majority of ozone generators are of volume discharge type, the surface DBD presents significant superiority in terms of ozone generation and energy efficiency.     

Simulation of Ozone Synthesis in Oxygen- and Air-Fed Surface Discharge Arrangements

Surface discharge (SD) arrangements are used in commercial ozone generators like conventional arrangements with a gas gap. While in oxygen the characteristics of the ozone production are comparable in both arrangements, the efficiency of ozone production from air is significant lower in SDs. From experimental results it is believed that high temperatures in the discharge cause this “poisoning” of air-fed SD ozone generators. To clarify this, the ozone synthesis from air near atmospheric pressure is investigated with the help of a two-dimensional self-consistent modeling of the discharge development and the relevant plasma-chemical reactions. The temperature in the discharge area is determined from energy densities of electrons and ions and included in the relevant chemical reaction system. The results show a significant temperature increase in front of the metallic surface electrodes combined with an increased concentration of nitrogen oxides.     

Herstellung von metallischen Nanopartikeln in einem asymmetrischen Dielectric Barrier Discharge‐Plasma bei Atmosphärendruck

This paper focuses on the production of metal nanoparticles in a dielectric barrier discharge (DBD) reactor at atmospheric pressure. In the developed reactor only one electrode is provided with a dielectric (alumina), while the point‐shaped counter electrode is not covered and is accessible to the filamentary discharges (asymmetrical DBD). The metallic particles are formed from the material of the open counter electrode, on which the filamentary discharges lead to the formation of craters. A high number of larger nanoparticles (with diameter of some tens of nanometers) are observed in the cold reactor at the beginning of the discharges. After the achievement of the thermal equilibrium in the reactor mainly very small metallic nanoparticles are produced with constant size and number concentration. The produced metallic particles in thermal equilibrium are crystalline and not agglomerated. The mean diameter of the produced particles is about 4 nm. For given operating conditions of the reactor (fixed electrode gap and gas flow rate) the electrode material has almost no influence on the size of the produced particles, but it determines the number concentration.     

Productivity and Efficiency of Ozone Synthesis in Coplanar Discharge Arrangements

In order determine the potential of coplanar discharge arrangements with short electrode distances for the production of ozone, a numerical model of the discharge behavior has been developed. The temporal and spatial distributions of the discharge parameters e.g. those of the field strength, the densities of the charged particles in the gas region and on the dielectric surface and that of the energy release reveal that the ozone production results from the electron phase of the discharge. Quantitative data of the productivity and efficiency of the ozone yield in a certain system are presented, which are in agreement with experimental results.     

Degradation of a textile azo dye by pulsed arc discharge to the surface of wastewater

The pulsed arc discharge to the surface of wastewater was applied to the degradation of a textile azo dye (Acid Red 27). A high-voltage electrode (discharging electrode) was vertically placed above the surface of the wastewater while the wastewater itself was grounded. The pulsed arc discharge occurred between the tip of the discharging electrode and the surface of the wastewater, producing various oxidative species. Oxygen was used as the working gas instead of air to prevent nitrogen oxides from forming. The effect of several parameters on the chromaticity and chemical oxygen demand (COD) removal was examined. The results obtained showed that the chromaticity of the wastewater was completely removed by this process and the COD also decreased significantly. It has been found that ozone formed in the gas phase mainly affects the removal of the dye. The contribution of other effects such as ultraviolet light emission and OH radical formation during the arc discharge to the degradation of the dye was found to be less than 15%. For the present reactor system, the optimum pH, pulse repetition rate and agitation speed were found to be 3.0, 110 Hz and 300 rpm, respectively.     

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.     

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 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.     

Optimal Sizing of a DBD Ozone Generator Using Response Surface Modeling

Dielectric barrier discharge (DBD) reactors used as ozone generators are well known today and widely used for water treatment and air disinfection. The purpose of this article is to propose an experimental procedure based on the response surface modeling in order to optimize the geometrical dimensions of the cylindrical shape ozone generator, i.e., the discharge gap and the electrodes length. Because an effective ozone generator is expected to give high ozone concentration with a minimum of power requirements, the applied high voltage was associated with the geometrical parameters to carry out a composite centered faces design. Obtained results indicate that for an efficient ozone generator, length of the electrodes needs to be optimized while the discharge gap should be minimized.     

Development and Experimental Analysis of a New “Serpentine-Shape” Surface-DBD Ozone Generator—Comparison with a Cylindrical Volume-DBD Ozone Generator

Ozone generators used in the industry for water treatment are almost all based on volume dielectric barrier discharge (DBD). The generation of ozone by surface DBD is also possible. However, there are not enough studies devoted to this solution. The objective of this article is the development of a new patent-pending “serpentine” model in which the gas circulates in a channel having the shape of a serpentine. The developed model is made of 10 parallel channels engraved in a Bakelite plate of 4-mm thickness. The ground electrode is an adhesive aluminum tape placed on the lower surface of the plate, while the high voltage electrode is constituted of narrow tapes of 1-mm width of the same material, placed in the bottom of each channel. The surface DBD is produced inside each channel that measures 1-cm width, 3-mm depth, and 10-cm length. The obtained results showed that the ozone rate (in g/hr) is much higher in the case of surface DBD compared to a cylindrical volume-DBD generator, which is the most used reactor in ozone technology. Furthermore, the energy efficiency of the “serpentine” model is better than the cylindrical model.     

Cooling Conditions of Ozone Generators

The efficiency of ozone generators is determined by many factors. Operating conditions such as feed gas quality and especially cooling conditions are of utmost importance. Cooling of ozone generators is absolutely necessary, since ozone destruction reactions increase exponentially with temperature. The most common way to cool an ozone generator is water flowing in close contact to the electrodes. The heat removal out of the discharge gap depends on different parameters. Electrical input power, cooling water flow conditions, electrode geometry and material properties are some of them. Simultaneously lowering cooling water temperature, applied power density and gap width, leads to a lower gas temperature in the discharge gap and thus to increased ozone production efficiency. Minimizing the temperature difference between the cooling water inlet and outlet improves the ozone production efficiency as well. This measure, however, results in high cooling water flows and requires additional cooling water chilling, resulting in higher operational costs and capital expenses. Cooling associated costs rise disproportionally with increasing cooling water flow. Simultaneously, energy consumption of ozone generators decreases as the average cooling water temperature goes down. As a result, there exists an optimum between the operational and capital expenses for the combination of ozone generator and cooling water system related expenses, offering significant cost savings for the customer.     

不同操作参数下介质阻挡放电的固氮性能研究及机理分析

介质阻挡放电(DBD)是一种典型的低温气体放电等离子体手段,能够在温和的条件下产生大面积的放电等离子体从而进行固氮,具有绿色环保、高效节能等特点。然而目前DBD的固氮能耗偏高,有着相当大的优化空间。探究了调控电压与气流量对DBD固氮性能的影响,以液相固氮的形式考察了总氮浓度TNC和固氮能耗EC的变化情况,并通过分析DBD气相产物变化规律揭示了DBD固氮的反应机理。研究发现,不同条件下的DBD气相产物会处于臭氧模式、过渡模式和氮氧化物模式三种模式之一,而各实验条件下的EC最小值均处于过渡模式,分析其原因在于该模式下可以有效生成NO₂和N₂O₅,提升可溶性氮的占比进而促进了固氮效果。EC的最小值在电压为18 kV、气流量为8 L/min时取得,为31.69 MJ/mol。     

不同操作参数下介质阻挡放电的固氮性能研究及机理分析

介质阻挡放电(DBD)是一种典型的低温气体放电等离子体手段,能够在温和的条件下产生大面积的放电等离子体从而进行固氮,具有绿色环保、高效节能等特点。然而目前DBD的固氮能耗偏高,有着相当大的优化空间。探究了调控电压与气流量对DBD固氮性能的影响,以液相固氮的形式考察了总氮浓度TNC和固氮能耗EC的变化情况,并通过分析DBD气相产物变化规律揭示了DBD固氮的反应机理。研究发现,不同条件下的DBD气相产物会处于臭氧模式、过渡模式和氮氧化物模式三种模式之一,而各实验条件下的EC最小值均处于过渡模式,分析其原因在于该模式下可以有效生成NO₂和N₂O₅,提升可溶性氮的占比进而促进了固氮效果。EC的最小值在电压为18 kV、气流量为8 L/min时取得,为31.69 MJ/mol。     

A Study of the Physical and Chemical Processes Active in Corona Discharges Fed by Carbon Dioxide

Ozone generation in both positive and negative corona discharges DC corona, both operated in glow regime, feed by dry CO₂ has been studied. Higher ozone concentrations were observed in negative corona discharges. Ozone formation was found to be strongly dependent upon both the flow rate of the gas and on the radius of the outer electrode. The physical characteristics of the discharge were monitored through measurement of the discharge current. Small increases in the gas flow rate were observed to cause a significant increase in the discharge current of a negative corona discharge but little/no effect was observed in positive corona.     

Effect of Silica Packing on Ozone Synthesis from Oxygen-Nitrogen Mixtures

The effect of silica packing in an ozone generator fed with oxygen-nitrogen mixtures has been studied. The measurements were carried out in an ozone generator with a double-sided cooled discharge gap, in which silica packing has been placed. In the presence of the packing considerably higher ozone concentrations were achieved than in the ozone generator without packing. An especially clear effect of silica packing was observed in air-fed conditions. It has been found that the increase in the concentration of the obtained ozone coincides with the increase of N₂O in the post-reaction gas.     

介质阻挡放电等离子体特性及其在化工中的应用

阐述了介质阻挡放电（DBD）等离子体的基本特性、放电机理、理论模型、反应器类型及存在问题。评述了介质阻挡放电在物质合成、挥发性有机物处理、汽车尾气净化、材料表面处理、催化剂改性、沉积制膜以及等离子体催化协同作用在环境化工中的应用等方面的研究进展,分析了传统方法在这些方面应用的优缺点,指出通过与催化剂协同可以更好地发挥等离子体的优势。DBD等离子体技术在节约能源、降低成本、安全操作和环境保护等方面都有很大改进,是一种很有前途的新技术,并展望了DBD等离子体技术的发展前景和研究方向。     

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.