Ozone Production in a High Frequency Dielectric Barrier Discharge Generator

Factors that affect the performance of an expanded-mesh dielectric barrier discharge ozone cell were investigated. A gas feed pf 94% O₂, 4% Ar and 1% N₂ was used. An improvement in the productivity (g ozone/kWh) of about 20 % was achieved by doubling the gas flow rate through the cell. Decreasing the cell operating frequency (in the range 72 kHz to 19 kHz) increased the productivity of the ozone generator at constant power. The ozone production increased approximately in proportion to the input power; however productivity did not vary significantly with power above a minimum level. As the cell voltage was increased the dependence of productivity on power or frequency was reduced. Changing the feed gas temperature between ? 5^°C and + 42^°C had no effect on productivity. Finer meshes drew more power than coarser ones for a given voltage. Using a thinner mesh for the centre electrode increased productivity. The best results were obtained with a 6 × 3 × 1.86 mm titanium mesh giving a productivity of 110 g ozone/kWhr at 30–60 W, 1500–1900V and 23 KHz.     

Ozone Production in a Dielectric Barrier Discharge with Ultrasonic Irradiation

Ozone production has been investigated using an atmospheric pressure dielectric barrier discharge in pure O₂ at room temperature with and without ultrasonic irradiation. It was driven at a frequency of either 15 kHz or ～40 kHz. The ozone production was highly dependent on the O₂ flow rate and the discharge power. Furthermore, powerful ultrasonic irradiation at a fundamental frequency of ～30 kHz with the sound pressure level of ～150 dB into the discharge can improve the ozone production efficiency, particularly when operated at the frequency of 15 kHz at the flow rate of 15 L/min.     

Ozone Production by an Ultra-Short Triggered Dielectric Barrier Discharge.

This work was motivated by the ozone production improvement by a dielectric barrier discharge supplied with a high voltage triggered pulsed generator. Particular attention was focused on the ozone generator cell geometry and on the type of electrical generator. A comparative parametrical analysis on two configurations of reactor was performed: an annular and a surface configuration. This study emphasizes that surface discharges coupled to ultra-short triggered high voltage generators stand out as an efficient process to produce ozone in large quantities.     

Optimizing Factors on High Concentration of Ozone Production with Dielectric Barrier Discharge

The gap distance, electrode material, voltage and gas flow velocity were optimized with gas pressure variation of dielectric barrier discharge (DBD) for producing high concentration of ozone. There exists an optimum gas pressure at which the highest ozone concentration is produced with other parameters being fixed. This optimum gas pressure value changes accordingly as the other parameters changed. As the discharge continues at the optimum pressure, the ozone concentration could increase or decrease slowly. This aging effect has different characteristics with the metal electrode material and the impurity level of the oxygen gas used for ozone generation. The aging effect is supposed to be related with the catalytic effect of metal oxide, which is generated in the discharge zone. The change in the characteristic of optimum pressure by the other parameters, indicate that the ozone concentration is deeply related with the filament self-organization characteristics of DBD. At the final optimized condition, the ozone concentration was higher than 22.5 wt.%.     

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.     

Enhancement of Energy Yield for Ozone Production via Packed-Bed Reactors

The present work aims to enhance the energy yield of ozone production via packed-bed reactors. It has been experimentally demonstrated that ozone concentration and corresponding energy yield achieved by packed-bed reactors are significantly higher than that achieved by DBD only. The so-called packed-bed reactor is constructed by packing granular dielectric pellets within a DBD reactor. Two kinds of dielectric materials including glass beads and Al₂O₃ pellets are tested. Experimental results indicate that an ozone generator packed with Al₂O₃ pellets results in a higher ozone production compared with one packed with glass beads. The maximum ozone production takes place when Al₂O₃ pellets with diameter of 2 mm are packed. The maximum ozone concentration, ozone production rate, and energy yield achieved in this study are 61 gO₃/m³, 3.7 gO₃/hr, and 173 gO₃/kWh, respectively. The highest ozone concentration and energy yield achieved with the packed-bed reactor are about 8 and 12 times high as those with DBD reactor, respectively. Although the packed-bed reactors have a shortcoming of high temperature, it can be solved by adding a cooling system and the ozone generation can be improved thereof. As a result, the packed-bed reactor is a promising and state-of-the-art technology for ozone generation based on this study.     

Experimental Study on Ozone Synthesis via Dielectric Barrier Discharges

The characteristics of ozone generation using a dielectric barrier discharge reactor were investigated experimentally. Results indicate that ozone concentration increases with increasing applied voltage and gas residence time. In addition to applied voltage, ozone generation rate varies with reactor configuration as well. Optimum ozone generation rates can be reached at the specific gas residence time for a given applied voltage and gas composition. At the same applied voltage, the reactor with a single dielectric barrier results in a higher ozone generation rate in comparison with the reactor having double dielectric barriers. Given a constant N₂/O₂ ratio in the feed gas, NO_x concentration increases as applied voltage and gas residence time increase. Results indicate that maximum NO_x concentration is reached when the N₂/O₂ ratio of feed gas is 4.     

Physicochemical Investigation of Homogeneous Pulsed Discharge in N2/O2 for Ozone Production

The purpose of this work is to draw attention to the plasma kinetics in a nitrogen-oxygen mixture. The model includes the plasma chemistry module and the circuit module investigating the electrical and the physical characteristics of high-pressure homogenous pulsed discharge. The fundamental chemistry governing ozone generation developed in this work is based on a full set of processes regrouped in 117 reactions involving 19 charged particles, atomic, and molecular species. The results of simulations show the temporal variation of the discharge electrical parameters and the effect of the voltage applied to ozone production. The role played by different reactions and species is also given by analyzing the time evolution of species concentrations, as well as the ozone production and loss terms.     

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.     

Ozone Generation from Argon-Oxygen Mixtures in Presence of Different Packing Materials within Dielectric Barrier Discharge Gap

Assessments of ozone yield and concentration in Dielectric Barrier Discharge of argon-oxygen mixtures in presence of various packing materials are discussed. These include zeolite molecular sieve 13X pellets, Pyrex beads, Pyrex wool, and porous TiO₂-beads, which presented differential reactive surfaces, nano cavities, photo-catalysis, and dissimilar ionic environments. Their utility was evaluated in conjunction with varied gas composition, flow rate, and electrical inputs. In a mixture of 3–21% O₂ in argon, the ozone concentration ranged between 16–980 ppm, simultaneous measurements of in situ energy dissipation revealed its yield, G(O₃) to change independently from 0.002 to 2.020 μmol J^?1. TiO₂ packing emerged as the most versatile material to produce O₃ in high concentration and yield.     

Generation of Active Oxidant Species by Pulsed Dielectric Barrier Discharge in Water-Air Mixtures

Experimental research into the electrical and optical parameters of pulsed dielectric barrier discharge (PDBD) was undertaken. PDBD was applied to humid air containing water droplets as a means of water oxidative treatment with short-living species generated in the discharge zone. In spectral analysis of PDBD, only small concentrations of nitric oxides were detected at the resulting electric field strength and electron mean energy sufficient for generation of OH-radicals. The water droplets served as electric field strength concentrators: PDBD was ignited close to the water droplets' surface.     

Analysis of Plasma Reaction for Decomposition of CHF3 in a Dielectric Barrier Discharge

The decomposition of CHF₃ in a mixture with O₂ and Ar was investigated in a coaxial dielectric barrier discharge at atmospheric pressure. CHF₃ decomposition increased linearly in regard to specific energy input (SEI), whereas energy efficiency decreased. The main product was CO_2, and its selectivity increased with high SEI and the presence of O₂ in the feed, but an increase of O₂ in the feed led to a decrease in decomposition rate. An increase in total flow rate led to an increase of the absolute amount of CHF₃ decomposition and energy efficiency; however, the decomposition of CHF₃ decreased. A complete CHF₃ decomposition occurred under an SEI of 1.54 kJ/L with the selectivity of CO₂ and CO as 89.87% and 7.00%, respectively. Optical emission spectroscopic analysis could explain the available reaction pathways for CHF₃ decomposition in the CHF₃/O₂/Ar atmospheric plasma and show the possibility of F₂ and HF formation.     

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.     

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%.     

Analytical Approach to estimate and Predict the CO2 Reforming of CH4 in a Dielectric Barrier Discharge

CO₂ reforming of CH₄ to syngas was investigated in a coaxial dielectric barrier discharge reactor immersed in an oil bath. An analytical model was suggested to estimate and predict the reaction phenomena. The model had input parameters as predictor variables (applied voltage, ratio of CH₄/CO₂, and total flow rate in the feed), output parameters as observed variables, the molar flow rates of reactants (CH₄, CO₂, CO, H₂, and by-products), and energy efficiencies. More than 70% of the output parameters variance could be explained by the input parameter. The model for the CO₂ reforming of CH₄ in a dielectric barrier discharge reactor would be useful to optimize the experiments. A comparison between input parameters suggests that the reaction should be performed under high total flow rate or low applied voltage to obtain greater energy efficiency; whereas at high applied voltage and total flow rate, the reaction obtains a greater absolute amount of reactant conversion and products, but lower energy efficiency.     

Development of Catalyst-Sorbents for Simultaneous Removal of SO2 From Flue Gas by Low Temperature Ozone Oxidation

One technological process employing ozone and heterogeneous catalyst-sorbents was proposed for removal of SO₂ from flue gas. The catalyst-sorbents were developed and tested especially for adsorption and oxidation of SO₂. Alternative catalyst-supporters including γ-Al₂O₃, permutite, silica gel, activated carbon and diatomite combined with different metal oxides (MnO₂, Cr₂O₃, Fe₂O₃, CuO, CoO and NiO) were evaluated and tested. It was found that γ-Al₂O₃ doped with MnO₂ can be considered as removal-effective sorbent for adsorption and oxidation of SO₂. The synergetic effect between ozone and catalyst was found to be dominated. Effects of catalyst preparation parameters like calcination temperature, metal loaded and reaction temperature, etc. were investigated based on the MnO₂/Al₂O₃ catalyst-sorbents. Results show that γ-Al₂O₃ combined with 8% Mn, calcinated under 573 K and reacted at 413 K are the optimal parameters for removal of SO₂. Extra NO in flue gas can slightly enhance the capture efficiency of SO₂.     

Dielectric,magnetoelectric and magnetodielectric properties in CMFO-SBN composites

The paper reports synthesis of Sr_0.5Ba_0.5Nb₂O₆ (SBN) and Co_1.2−xMn_xFe_1.8O₄ (CMFO) via ceramic and hydroxide co-precipitation routes respectively. The nanopowders of SBN-CMFO0.1 (MSBN0.1) and SBN-CMFO0.3 (MSBN0.3) are compacted to form the desired magnetoelectric (ME)/magnetodielectric (MD) composites. The Bi₂O₃ is used as a sintering aid. The Bi₂O₃ at three weight percent is observed to cause agglomeration of SBN and CMFO particles and improve the magneto-mechanical coupling. The composites are investigated for their ferroelectric, ferromagnetic, dielectric, magnetoelectric (ME) and magnetodielectric (MD) properties. The results on the magnetocapacitance (M_c) are observed interesting and could be correctly understood in terms of the stress induced variation in the dielectric constant. The MC is observed to remain fairly constant between 10 to 500 kHz and possess a useful magnitude of M_c nearly 4%.     

Hydrogen Production by Steam Reforming of Commercially Available LPG in UAE

Steam reforming of commercially available LPG using Ru/Al₂O₃ and Ni/Al₂O₃ catalysts has been studied at temperatures between 573 and 773 K. Ru/Al₂O₃ catalyst showed higher rates of reaction and lower activation energies of the three main components of LPG, compared with Ni/Al₂O₃. However, Ni/Al₂O₃ catalyst showed a better H₂:CH₄ selectivity. The activation energy of n-butane was the lowest over Ru/Al₂O₃, whereas over Ni/Al₂O₃, propane had the lowest activation energy. The activation energy of i-butane was always the highest over both catalysts, which suggests that both catalysts performed better with unbranched molecules. A slight increase in activation energy was observed, when each component of the LPG mixture was studied separately as a pure gas, compared with being mixed in LPG. At a constant temperature of 773 K, hydrogen production yield and H₂:CH₄ selectivity were determined using Ru/Al₂O₃ at different steam:carbon (S:C) ratios and LPG flow rates. It was found that the yield and selectivity increased with the increase in S:C ratio and the decrease in the flow rate. The highest yield of 0.64 was achieved using S:C ratio of 6.5 and a LPG flow rate of 50 mL min^?1. The work provides valuable information on steam reforming of pure components of LPG, compared with when they are in the mixture. The comparison is done using conventional steam reforming catalyst, Ni/Al₂O₃, and compared with Ru/Al₂O₃. The observed trends and variations in reaction rates, in pure and mixed gases, indicated that the mechanism of steam reforming of a hydrocarbon mixture depends on its composition.