Bratislav M. Obradović

A dual-use of DBD plasma for simultaneous NOx and SO2 removal from coal-combustion flue gas

Dielectric barrier discharge (DBD) was investigated for the simultaneous removal of NO(x) and SO(2) from flue gas in a coal-combustion power plant. The DBD equipment was used in either a mode where flue gas was directed through the discharge zone (direct oxidation), or a mode where produced ozonized air was injected in the flue gas stream (indirect oxidation). Removal efficiencies of SO(2) and NO for both methods were measured and compared. Oxidation of NO is more efficient in the indirect oxidation, while oxidation of SO(2) is more efficient in the direct oxidation. Addition of NH(3), has lead to efficient removal of SO(2), due to thermal reaction, and has also enhanced NO removal due to heterogeneous reactions on the surface of ammonium salt aerosols. In the direct oxidation, concentration of CO increased significantly, while it maintained its level in the indirect oxidation.

Decolorization of reactive textile dyes using water falling film dielectric barrier discharge

Decolorization of reactive textile dyes Reactive Black 5, Reactive Blue 52, Reactive Yellow 125 and Reactive Green 15 was studied using advanced oxidation processes (AOPs) in a non-thermal plasma reactor, based on coaxial water falling film dielectric barrier discharge (DBD). Used initial dye concentrations in the solution were 40.0 and 80.0mg/L. The effects of different initial pH of dye solutions, and addition of homogeneous catalysts (H(2)O(2), Fe(2+) and Cu(2+)) on the decolorization during subsequent recirculation of dye solution through the DBD reactor, i.e. applied energy density (45-315kJ/L) were studied. Influence of residence time was investigated over a period of 24h. Change of pH values and effect of pH adjustments of dye solution after each recirculation on the decolorization was also tested. It was found that the initial pH of dye solutions and pH adjustments of dye solution after each recirculation did not influence the decolorization. The most effective decolorization of 97% was obtained with addition of 10mM H(2)O(2) in a system of 80.0mg/L Reactive Black 5 with applied energy density of 45kJ/L, after residence time of 24h from plasma treatment. Toxicity was evaluated using the brine shrimp Artemia salina as a test organism.

Spectroscopic measurement of electric field in atmospheric-pressure plasma jet operating in bullet mode

Atmospheric-pressure helium plasma jet operating in the bullet/streamer mode has been studied using optical emission spectroscopy. Electric field strength distribution is measured using Stark polarization spectroscopy of He I 492.19 nm line. It is shown that the electric field is almost constant along the jet axis. Measured electric field distribution is in agreement with theoretical predictions of streamer propagation in helium jets at atmospheric pressure. Obtained radial distribution of the axial electric field shows that the ring-shaped structure of the light emission is a consequence of such electric field distribution.

Degradation of triketone herbicides, mesotrione and sulcotrione, using advanced oxidation processes

Degradation of two triketone herbicides, mesotrione and sulcotrione, was studied using four different advanced oxidation processes (AOPs): ozonization, dielectric barrier discharge (DBD reactor), photocatalysis and Fenton reagent, in order to find differences in mechanism of degradation. Degradation products were identified by high performance liquid chromatography (HPLC-DAD) and UHPLC-Orbitrap-MS analyses. A simple mechanism of degradation for different AOP was proposed. Thirteen products were identified during all degradations for both pesticides. It was assumed that the oxidation mechanisms in the all four technologies were not based only on the production and use of the hydroxyl radical, but they also included other kinds of oxidation mechanisms specific for each technology. Similarity was observed between degradation mechanism of ozonation and DBD. The greatest difference in the products was found in Fenton degradation which included the opening of benzene ring. When degraded with same AOP pesticides gave at the end of treatment the same products. Global toxicity and COD value of samples was determined after all degradations. Real water sample was used to study influence of organic matter on pesticide degradation. These results could lead to accurate estimates of the overall effects of triketone herbicides on environmental ecosystems and also contributed to the development of improved removal processes.

Spatio-temporally resolved electric field measurements in helium plasma jet

The focus of this paper is on the spatially and temporally resolved measurements of the electric field in atmospheric-pressure plasma jets operating in helium. Using the Stark polarization spectroscopy method, temporal development of the electric field was observed in steps which were in range of 20–500 ns. Such temporal resolution was complemented by the spatial resolution of 0.025 mm. Depending on the plasma jet configuration, the maximal electric field strength in the bullet/streamer head was between 10 and 20 kV cm−1. Electric field measurements are accompanied by the electrical and spectroscopic diagnostics of the discharge evolution. It was found that without the grounded electrode downstream from the nozzle, the jet develops as the cathode directed streamer. Contrarily, when a grounded electrode is present, development of the plasma jet is very similar to the evolution of the single microdischarge in air. Finally, the direct relation between electric field strength and the velocity of the plasma bullet is demonstrated.

Spectroscopic measurement of electric field in dielectric barrier discharge in helium

Spatial distribution of electric field strength in dielectric barrier discharge in helium is determined from the Stark splitting and shifting of two visible helium lines and their forbidden components. Electric field is calculated by using spectral distance between forbidden and allowed components and results are compared to those obtained by using forbidden/allowed intensity ratio. Distributions of electric field, obtained for 200 and 800 mbar pressures, are typical for the glow mode of the discharge.

Doppler spectroscopy of hydrogen and deuterium Balmer alpha line in an abnormal glow discharge

The results of hydrogen and deuterium Balmer alpha line shapes and line intensities study in an abnormal glow discharge are reported and analyzed. The Doppler shifts along line wings are used to determine energies of excited hydrogen and deuterium atoms. For 12 different cathodes, intensity and shape of line wings are examined and dependence upon cathode material is determined. Tentative explanation of line wings intensity dependence is related to the sputtering of cathode material and back-scattering coefficients of incident hydrogen or deuterium ions and atoms from cathode surface. The influence of the light reflected on a cathode surface to the line shape measurements along discharge axis is considered. In hydrogen, deuterium, and Ar+3%H/sub 2/ discharges, basic mechanisms of fast hydrogen generation and excitation are studied. The shape and intensities of the H/sub /spl alpha// line profiles in pure hydrogen and in argon-hydrogen mixture may be correlated with hydrogen atom-carrier gas collision excitation cross sections. In order to assess the importance of reflected fast hydrogen atoms back scattered from the cathode surface, for the Balmer line shape formation, a simulation program is used. The results are in a qualitative agreement with Balmer line shapes observations.

Measurement of electric field development in dielectric barrier discharge in helium

In this paper the diffuse dielectric barrier discharge in helium was investigated using electrical measurements and time–space resolved optical emission spectroscopy. Electric field strength was measured using Stark polarization emission spectroscopy. Investigations were performed at 200 and 800 mbar pressures. It was found that the electric field strength was higher at the higher pressure while cathode fall length was shorter. During the whole discharge development period the length of the cathode fall region decreases. An interesting result is that in the period of current decrease, the maximum of the electric field distribution shifts away from the cathode showing the accumulation of negative charge near the cathode surface. (Some figures in this article are in colour only in the electronic version)

Electric and thermodynamic properties of plasma flows created by a magnetoplasma compressor

A magnetoplasma compressor of compact geometry (MPC-CG) with a semi-transparent electrode system that operates in the ion current transfer regime was constructed and studied. The electric and thermodynamic parameters of the discharge and the plasma flow created in different gases and their mixtures (hydrogen, nitrogen, argon and Ar + 3% H2) have been measured to optimize the working conditions within the 100–3000 Pa pressure range for input energy up to 6.4 kJ. A special construction of the accelerator electrode system shielded by the self-magnetic field results in protection from erosion, which is the main cause of the high current cut-off in conventional plasma accelerators. It was found that the compression plasma flow velocity, electron density and temperature predominantly depend on the energy conversion rate from the energy supply to the plasma, since the current cut-off is avoided. The maximum energy conversion rate for MPC-CG was found when operating in hydrogen. The plasma flow velocity and electron density maximum values are measured close to 100 km s−1 and 1017 cm−3, respectively, for input energy of 6.4 kJ at 1000 Pa pressure in hydrogen. Our results appear in good agreement with existing theoretical and experimental data.

Silver incorporation on viscose and cotton fibers after air, nitrogen and oxygen DBD plasma pretreatment

Dielectric barrier discharge (DBD) pretreatments in air, nitrogen and oxygen plasma of viscose and cotton fabrics with subsequent immobilization of silver were studied. Surface activation of treated fibers was evaluated through subsequent sorption of silver from aqueous AgNO3 solution, after which changes in the surface morphology were monitored and quantity of silver deposition on fabric was measured. The plasma treatment was done in volume DBD discharge with the gap distance between electrodes of 0.5 and 2 mm. Depending on the gas used in pretreatment, significant difference in the way silver bonds to the textile surface was found. Nitrogen plasma pretreatment with gap distance of 0.5 mm led to the homogeneous fiber coating by silver nanoparticles with average size up to 300 nm estimated by SEM, while fibers treated in oxygen plasma adsorbed silver in a form of ions. The plasma pretreatment in air leads to changes that contain features of fibers treated in both nitrogen and oxygen DBD plasma. Distinct difference of used configuration of the plasma source is a use of gap distance 0.5 mm, which is in order of textile thickness. Observed results allow us to report a new way how to immobilize silver nanoparticles onto textile fibers using plasma pretreatment with subsequent sorption of silver from aqueous solution.Graphical Abstract