Proceedings

2525thth –– 2727thth November 2007November 2007BratislavaBratislavaSlovakiaSlovakia

EditorsEditors: Juraj Orsz: Juraj Orszáágh, Peter gh, Peter PappPapp, J, Jáán D. Skalný, n D. Skalný, NigelNigel J. J. MasonMason

Universitas ComenianaBratislavensis The Open University Union of Slovak

Mathematicians and Physicists

Proceedings of International Workshop O3zotech Workshop organized by Union of Slovak Mathematicians and Physicists and the Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University in Bratislava (Slovakia), SÚZA, 25th-27th November 2007 Editors: J. Országh, P. Papp, J. D. Skalný, N. J. Mason Publisher: Library and Publishing Centre in collaboration with Department

of Experimental Physics, Comenius University, Bratislava, Slovakia; Union of Slovak Mathematicians and Physicists, Bratislava, Slovakia

Issued: November 2007, Bratislava, first issue Number of pages: 79 Print: 54 pieces URL: http://neon.dpp.fmph.uniba.sk/ozotech ISBN: 978-80-89186-25-9 EAN: 9788089186259

Proceedings2525thth –– 2727thth November 2007November 2007

BratislavaBratislavaSlovakiaSlovakia

EditorsEditors: Juraj Orsz: Juraj Orszáágh, Peter gh, Peter PappPapp, J, Jáán D. Skalný, n D. Skalný, NigelNigel J. J. MasonMason

Universitas ComenianaBratislavensis The Open University Union of Slovak

Mathematicians and Physicists

Welcome to O3zotech !

Werner Von Siemens 1816-1892

150 years ago in the autumn of 1857 Werner Von Siemens, the German philanthropist founder of Siemens & Halske, predecessor of the present international Siemens AG and after whom the unit of electrical conductance is named, published the design and operating characteristics of the first commercial ozone generator1. In the Siemen’s ozoniser a corona discharge was established in the flow of dry air or oxygen by the application of an alternating voltage between two concentric glass tubes lined with tin-foil between which. In his original prototype between 3-8% of the oxygen was converted to ozone, a yield that remains respectable in modern instruments and therefore the Siemen’s ozone generator has served as a model prototype for the majority of electric discharge generators used by a wide variety of industries today.

Werner von Siemens 1857 ozoniser A is the terminal connected to the inner surface; B a terminal connected to outer surface; C the oxygen or the air reservoir; D a calcium chloride drying tube top remove water from the gas flow; a battery and G an induction coil.

This workshop celebrates this landmark paper and reviews the state of our knowledge of ozone formation in corona (and other discharges). Through a combination of modeling and laboratory experiments more energy efficient ozonisers have been developed but remarkably many of the chemical and physical processes in these instruments remain unknown or are largely unquantified. We hope to both review current work and engender debate as to future field of research in this established but still active area of applied research. 1. von Siemens, W.; Poggendorff's Ann. 1857, 102, 120..

Contents

Programme ……………………………………………………………………………... 4

General Lectures ……………………………………………………………………………... 5

U. Kogelschatz History, importance and future perspectives of industrial ozone generation……………………………………………….………………...

6

N. Mason Experimental simulation of ozone production in planetary atmospheres using a corona discharge………………………………..

7

M. Dors Direct and indirect ozone methods for NOx removal………………… 11

F. Pontiga Ozone generation using negative corona discharge: numerical simulation and comparison with experiments…………………………

15

C. Paradisi Corona processing of hydrocarbons in air…………………...……….. 19

J. Skalny Ozone production by corona discharge fed by carbon dioxide……... 20

P. Lukes Generation of ozone by pulsed corona discharge over water surface in hybrid gas-liquid electrical discharge reactor……………..

23

D. Trunec Research of ozone generation at Masaryk University……………….. 27

A. Harling Novel method for enhancing the plasma destruction of environmental pollutants…………………………………………………

28

Progress Reports ……………………………………………………………………………... 31

K. Yanallah Simple modelisation of ozone generation by positive corona discharge………………………………………………………………….

32

F. Krcma Ozone generation in the Practical exercises of applied plasma chemistry course………………………………………………………….

36

G. Horvath Influence of humidity on ozone concentration in negative corona discharge fed by oxygen………………………………………………...

40

J. Országh Temperature effects in positive corona discharge fed by oxygen….. 44

V. Chernyak Features of destruction of organic substances in plasma-liquid systems……………………………………………………………………

48

I. Prisyshnevich Sources of nonequilibrium atmospheric pressure plasma…………... 52

M. Jasinski Stark broadening to determine the electron density in plasmas……. 56

S. Pekarek Non-thermal plasma decomposition of volatile organic compounds – influence of ozone……………………………………………………...

60

Š. Matejčík Ion mobility study of negative corona discharge in mixtures O2/N2.. 64

Z. Stara Water treatment by DC diaphragm discharge………………………... 67

H. D. Stryczewska Experimental investigations of the barrier discharge reactor with mesh electrodes and porous dielectric………………………………...

69

E. Marotta Decomposition of organic pollutants in water induced by dielectric barrier and corona discharge above the liquid………………………..

73

V. S. Taran Ozone sterilizer with ultrasonic cavitation…………………………….. 74

List of Participants ……………………………………………………………………………... 77

Sunday, 25th of November 14:00 Registration Chairman: Jan Skalny

17:00 Ulrich Kogelschatz History, importance and future perspectives of industrial ozone generation

17:30 Nigel J. Mason Experimental simulation of ozone production in planetary atmospheres using a corona discharge

18:30 Welcome dinner Chairman: Cristina Paradisi

20:00 Khelifa Yanallah Simple modelisation of ozone generation by positive corona discharge

20:15 Frantisek Krcma Ozone generation in the practical exercises of applied plasma chemistry course

20:30 Gabriel Horvath Influence of humidity on ozone concentration in negative corona discharge fed by oxygen

20:45 Juraj Országh Temperature effects in positive corona discharge fed by oxygen 21:00 Valeriy Chernyak Features of destruction of organic substances in plasma-liquid

systems 21:15 Irina Prisyshnevich Sources of nonequilibrium atmospheric pressure plasma 21:30 Valeriy S. Taran Ozone sterilizer with ultrasonic cavitation

Monday, 26th of November Chairman: Ulrich Kogelschatz

9:00 Miroslaw Dors Direct and indirect ozone methods for NOx removal 9:30 Francisco Pontiga Ozone generation using negative corona discharge: numerical

simulation and comparison with experiments 10:00 Cristina Paradisi Corona processing of hydrocarbons in air 10:30 Coffee break 11:00 Jan Skalny Ozone production by corona discharge fed by carbon dioxide 11:30 Petr Lukes Generation of ozone by pulsed corona discharge over water

surface in hybrid gas-liquid electrical discharge reactor 12:15 Lunch Chairman: Frantisek Krcma

13:15 Mariusz Jasinski Stark broadening to determine the electron density in plasmas 13:30 Stanislav Pekarek Non-thermal plasma decomposition of volatile organic compounds

– influence of ozone 13:45 Štefan Matejčík Ion mobility study of negative corona discharge in mixtures O2/N2 14:00 Zdenka Stara Water treatment by DC diaphragm discharge 14:15 Henryka D. Stryczewska Experimental investigations of the barrier discharge reactor with

mesh electrodes and porous dielectric 14:30 Ester Marotta Decomposition of organic pollutants in water induced by dielectric

barrier and corona discharge above the liquid 15:00 Tour of Bratislava city center 18:30 Conference dinner in town

Tuesday, 27th of November Chairman: Nigel J. Mason

9:00 David Trunec Research of ozone generation at Masaryk University 9:30 Alice Harling Novel method for enhancing the plasma destruction of

environmental pollutants 10:00 Coffee break 10:30 Round table and closing ceremony 11:30 Lunch & departure

4

General lectures

5

History, Importance and Future Perspectives of Industrial Ozone Generation

Ulrich Kogelschatz Obere Parkstr. 8, 5212 Hausen/Switzerland

(retired from ABB Corporate Research, 5405 Baden/Switzerland)

C. F. Schönbein is credited with identifying ozone, generated in the electrolysis of water, as a new, so far unknown, chemical compound around 1840. Its structure, O3, was established much later by J.-L. Soret in 1865. A practical device generating ozone from air by silent discharges (barrier discharges) was described by W. Siemens in 1857. Soon after the first official documentation of its bactericidal properties (1891) ozone was used for the purification of drinking water. Among the first major ozone installations in municipal water works were those of St. Petersburg, Nice, Chartres, Paris and Madrid, all built between 1905 and 1910. For a long time ozone water treatment was primarily used in Europe, until in 1987 the installation and successful performance of modern medium frequency ozone generators in the Los Angeles Aqueduct Filtration Plant (treating two million m3 of drinking water per day (600 mgd) with an ozone generating capacity of close to 10,000 kg per day) led to major breakthrough of ozone technology also in the United States and Canada.

In addition to drinking water purification ozone has found numerous applications including waste water treatment, pulp and kaolin bleaching, semiconductor manufacturing, and chemical synthesis. In water treatment ozone is used for disinfection or oxidation. Taste and odor control are important issues, as well as color removal. In air pollution control elimination of odor is an important application. Ozone can react directly as a strong oxidant or, in more complex reaction mechanisms, involving hydroxyl radicals and hydrogen peroxide (advanced oxidation processes or AOPs). In water treatment OH radicals are formed from ozone if the pH value is above 10. Presently the largest ozone generating facilities (up to 500 kg ozone per hour) are used in the paper industry replacing chlorine in the delignification and bleaching of pulp and in the treatment of its waste water.

Industrial ozone generation is still mainly based on dielectric barrier discharges (DBDs) as originally proposed by Siemens. Alternatives using corona discharges or VUV radiation are of minor importance. In air- or oxygen-fed DBDs the discharge current is carried by numerous thin, short-lived filaments called microdischarges. The plasma in these microdischarges has many properties of a transient high pressure glow discharge: electron energies of a few eV, gas temperature fairly low, depending on power density and heat removal through cooled electrodes. The physics and reaction kinetics of the microdischarges have been extensively investigated by advanced spectroscopic techniques and by computer modeling and are now reasonably well understood. Ozone formation in oxygen depends primarily on the formation of oxygen atoms by electron collisions dissociating O2 molecules with a subsequent 3 body reaction forming O3. In air discharges approximately half of the generated ozone stems from intermediate reactions involving nitrogen atoms and excited N2 molecules. In both systems the presence of traces of humidity interferes with ozone formation, in air also the accumulation of different NOx species. Since ozone formation from O2 requires less energy and higher O3concentrations can be reached larger ozone generating facilities operate on oxygen. Advanced ozone generators with narrow discharge gaps («1 mm) now reach O3 concentrations up to 20 %wt with an economic optimum around 16 %wt. Small and medium size ozone generators using dry air as feedstock operate at lower O3 concentrations, typically around 2-5 %wt.

It is conceivable that future ozone generators will not only be more efficient but also much more compact. Advanced manufacturing technologies used for microreactors and for modern heat exchangers allow much narrower discharge gaps beneficial for good efficiency at high ozone concentrations and better heat removal from the discharge gap. Recent advances in high voltage and high power semiconductors can revolutionize current power supply units used in ozone generators. Building blocks with insulated gate bipolar transistors (IGBTs) or integrated gate-commutated thyristors (IGCTs) now can switch currents of a few kA at voltage levels in the range of 5-10 kV. They have the potential of completely eliminating the bulky step-up transformers and inductances used for power factor compensation today. In addition, new forms of pulse shaping and impedance matching may lead to considerable power savings in the feeding circuit and increased ozone generation efficiency.

6

Experimental simulation of ozone production in planetary atmospheres using a corona discharge

Nigel J Mason1 and J D Skalny2

1Department of Physics and Astronomy, Walton Hall, The Open University,

Milton Keynes, MK7 6AA United Kingdom 2Department of Experimental Physics, Comenius University, Mlynska dolina F2,

84248 Bratislava, Slovakia

Email n.j.mason@open.ac.uk

The use of a plasma discharge to simulate planetary atmospheres has a long and distinguished history dating from the classic experiment of Urey and Miller in 1953 (figure 1)1-3. In their work a discharge in an atmosphere of water, hydrogen, methane and ammonia was used to simulate what they believed to be a realistic approximation of the gaseous mixture that comprised the early Earth’s atmosphere. After running a spark discharge in this mixture for more than a week they analysed the products and discovered that as much as 10-15% of the carbon within the system had been transformed into organic compounds. Two percent of the carbon had formed amino acids, including 13 of the 22 that are used to make proteins in living cells, with glycine as the most abundant. Sugars, lipids and some of the building blocks for nucleic acids together with other ‘prebiotic’ compounds were also formed though the nucleic acids (DNA, RNA) themselves were not produced. Thus Urey and Miller hypothesized that the building blocks of life were themselves formed in the early Earth’s atmosphere. Subsequently it was determined that the Early Earth’s atmosphere was not as reducing as that proposed by Urey and Miller containing both carbon dioxide and sulphur dioxide and discharges in such mixtures produced a much more diverse set of compounds and smaller quantities of organic/prebiotic species. However Urey and Miller’s original experiment has ensured that in laboratory planetary science discharges are commonly used as a method for simulating chemical processes within planetary atmospheres.

Figure 1; Schematic of the original Urey-Miller apparatus

7

Figure 2; Oct. 11 2006. Cassini captured Dione eclipsing Saturn's moon Rhea. Instruments reveal that these two Saturnian ice covered moons have solid ozone in their ice mantles.

Most recently the Cassini Huygen mission to Saturn and its study of Saturn’s largest moon Titan has led to a series of experiments that use discharges to simulate Titan’s atmosphere. Since the atmosphere of Titan is constantly bombarded by galactic cosmic rays and Saturnian magnetospheric electrons causing the formation of free electrons and primary ions a plasma reactor is felt to be a good simulator for probing the atmospheric chemistry4-6. Such data is now being directly compared with observations from the Huygens probe and is providing valuable clues as to the composition of the particulates that constitute Titan’s famous ‘haze7. Cassini has also revealed evidence for the presence of ozone on the surfaces of at least two of its moons (Rhea and Dione - figure 2)8,9. Ozone has been widely regarded as a biomarker for oxygen production itself a biomarker for photosynthetic activity. The detection of ozone in the ice of Dione and Rhea suggested that ozone must be able to be produced abiotically and could be liberated into a planetary atmosphere by thermal rather than biogenic cycles. The surfaces of Dione and Rhea are mainly composed of water ice with some CO2 (similar to Gannymeade the only Jovian moon to have shown evidence of ozone) thus the ozone is proposed to be formed by electron and ion (from planetary magnetospheres) bombardment. Such results therefore pose the question whether ozone can be formed in planetary atmospheres by similar processes. Ozone is formed in a three body reaction (1) since without a third body to stabilise the product ozone it would rapidly redissociate

O + O2 + M → O3 + M (1)

In an ice the ice itself acts as the third body, M, so whenever a oxygen atom (liberated by photons, electrons ions) is incident upon an oxygen molecule ozone formation is likely. Ozone formation in a planetary atmosphere is less likely since three body collisions are rare. This explains why in the Earth’s atmosphere the ozone layer is restricted to the stratosphere, any higher the pressure is too low for three body collisions to occur with any regularity, any lower and the solar UV flux is to low to break up the molecular oxygen to liberate O atoms.

8

Figure 3; Ozone and CO formation is a corona discharge of pure CO2 as a function of

flow speed through the reactor. Evidence for ozone in other planetary atmospheres is rare. The Martian atmosphere

has traces of ozone which in itself was a surprise since 95.3% of atmosphere is CO2 with oxygen only making up @ 0.13%10,11. Accordingly we have studied ozone formation in a corona discharge of pure carbon dioxide and CO2/O2 mixtures. Ozone is readily formed even in a pure CO2 discharge (Figure 3) albeit in ppm concentrations12. Subsequently we have studied ozone formation for a variety of factors, polarity, flow rate energy input and details will be presented at the conference13,14. Such evidence invites us to revisit the Urey Miller hypothesis and whether a planet may form an ozone layer and thence a UV shield without the need for photosynthetic life. Indeed should an ozone layer form early in a planet history it may play a major role in the evolution of life since it could prevent biomolecules such as RNA and DNA from being destroyed by solar radiation.

However in any life sustaining planet we expect there to be large amounts of water.

Ozone is rapidly destroyed in the presence of water, since photolysis of water leads to the formation of OH radicals which destroy ozone in a catalytic cycle;

OH + O3 --> HO2 + O2

HO2 + O3 --> OH + 2O2

Indeed these reactions may explain the lower yields of ozone found in many ozonisers using air as a feed gas since most air is humid. Using a corona discharge we have shown that water present even in concentrations of 100 -1000 ppm can significantly alter the rate of ozone formation (figure 4)15. Hence it is necessary to consider the role of water vapour in establishing an ozone layer on planetary systems. In particular it suggests that as the oxygen layer developed (from photo-sysnthesis !) on Earth the presence of water may have led to a significant lag in the formation of the terrestrial ozone layer it turn restricting life to the oceans or subsoil and preventing it form colonising the surface. The implications of such research are significant for our understanding of evolution of life on Earth and astrobiology in general and provide an excellent example of how the study of ozone formation in corona (and other discharges) may be used to explore physical and chemical properties of planetary atmospheres. Further discussion will be presented at the meeting.

9

Figure 4. The dependence of O3 concentration produced in a negative corona discharge in CO2 after adding trace amounts of H2O. Acknowledgements; We thank the Royal Society (UK); the ESF (EIPAM) and COST (Action P9) and in furthering this collaboration. This work was also supported by Slovak Science and Technology Assistance Agency under the contract No. APVT-20-007504 and Slovak Grant Agency VEGA 1/4017/07, References 1. S L Miller Science 117: 528. (1953) 2. S L Miller and H C Urey Science 130: 245 (1959) 3. A Lazcano and J L Bada Origins of Life and Evolution of Biospheres 33: 235-242 (2004) 4. T Fujii and N Arai, The Astrophysical Journal 519 858 (1999). 5.H Imanaka, B N Khare, J E, Elsila, E L O Bakes, C P Mckay, D P Cruishank, S Sugita, T Matsui and R N Zare, Icarus 168 344 (2004) 6. J M Bernard ,P Coll, A Coustenis and F Raulin Planet. Space Sc. 51 1003-1011 (2003). 7. J.-M. Bernard, E. Quirico,O. Brissaud,G. Montagnac, B. Reynard, P. McMillan, P. Coll, M.-J. Nguye, F. Raulin and B. Schmitt Icarus 185, Pages 301-307 (2006) 8. B. D. Teolis , M. J. Loeffler , U. Raut , M. Famá , and R. A. Baragiola The Astrophysical Journal, 644:L141-L144, (2006) 9. Ed C. Sittler, R. E. Johnson, S. Jurac, J. D. Richardson, M. McGrath, F. Crary, D. T. Young, J. E. Nordholt Journal of Geophys Research 109, A01214 (2004) 10. S Perrier, J L Bertaux, F Lefevre, S Lebonnois, O Koroable, A Fedorovoa, F. Montmessin Journal of Geophys Research 111 E09S06 (2006) 11. S Lebonnois, E Quémerais, F Montmessin, F Lefevre, S Perrier , J L Bertaux, F Forget, Journal of Geophys Research 111 E09S06 (2006) 12. T Mikoviny, M Kocan, S Matejcik, N J Mason and J D Skalny J. Phys. D: Appl. Phys. 37 64–73 (2004) 13. J D Skalny, S Matejcik, J Orszagh, R Vladoiu and N J Mason Ozone Science & Engineering 29 399 – 404 (2007) 14. J Orszagh, J D Skalny and N J Mason Plasma Processes and Polymers DOI 10.1002 (2007) 15. T Mikoviny, J D Skalny, J. Orszagh and N J Mason J Phys D 40 6646–50 (2007)

10

Direct and indirect ozone methods for NOx removal

J. Mizeraczyk1,2, M. Dors1

1 Centre for Plasma and Laser Engineering, The Szewalski Institute of Fluid

Flow Machinery, Polish Academy of Sciences, Fiszera 14, 80-952 Gdańsk, Poland

2 Department of Marine Electronics, Gdynia Maritime University, Morska 83, 81-225 Gdynia, Poland

INTRODUCTION Direct NOx removal by corona discharge processing

Almost twenty-old years investigations carried out in laboratories and pilot plants showed that removal of NOx from flue gases by corona discharges may be very efficient [1, 2]. However, this is possible when using various gaseous additives [3-9] or combining the corona discharge processing with catalytic methods [10-13]. In “pure” corona discharge and in dry air without any additives NO is oxidized to NO2 and a very small part is reduced to N2 and N2O. As a result, NOx removal efficiency is not higher than several percents. In the presence of water vapor NOx are oxidized to gaseous HNO3 and NOx may be removed up to 90%. Addition of ammonia or hydrocarbons or combination with catalysts result in increase of NOx removal up to 99%. All those results were obtained in laboratories or small demonstration systems. However, scaling-up such systems, in particular power supply, to those required in industry is very difficult. Thus, at the moment there is no commercially available device removing NOx by direct processing with corona discharge.

Indirect NOx removal by ozone processing

Application of ozone in NOx removal process has been studied also for a number of years. The aim of ozone processing is oxidation of NO to NO2 and then to N2O5. NO is the main component of NOx in most practical exhaust gases. Unlike NO having low solubility, NO2 and N2O5 are highly soluble in water. Thus, if NO is converted into NO2 and N2O5, it can be further treated by a wet method.

Nowadays, in contrast to the direct NOx removal, there is at least one commercially available technology named LoTOx™ [14]. In the LoTOx™ system ozone is produced on site and on demand by passing oxygen through an ozone generator. LoTOx™ is a low temperature system, therefore, it does not require heat input to maintain operational efficiency or to prevent treatment chemical slip, like ammonia, as is common with SCR and SNCR systems. Ozone is produced in response to the amount of NOx present in the flue gas generated by the process. There are no adverse effects of acid gases or particulates on the LoTOx™ system and some particulates may even enhance the reaction by producing sites for nucleation of moisture and by catalyzing the oxidation reaction. Ozone rapidly reacts with insoluble NO to form soluble N2O5. The species N2O5 rapidly reacts with moisture in the gas stream to form nitric acid. The conversion of NOx into the aqueous phase in the scrubber allows removal of NOx up to 95%.

In spite of existing commercial technology, some researchers still work on improving indirect NOx removal with ozone application [15]. The aim of these studies is to limit byproducts by reduction of NOx to N2. One feasible method to reduce NOx to N2 is to use a reducing agent such as sodium sulfide (Na2S) [16-18]. Sodium sulfide can reduce NO2 to N2 while it is converted into sodium sulfate (Na2SO4) that is a nontoxic compound. Sodium sulfide can also remove SO2 effectively, which makes it possible to treat NOx and SO2, simultaneously. In order to take advantage of this wet reduction technique, NO in the exhaust gas should be first converted into NO2, prior to contacting with the reducing agent solution. This can be achieved using ozone as the agent oxidizing NO into NO2.

EXPERIMENT AT CPLE IN GDAŃSK In order to compare both direct and indirect oxidation of NOx we carried out our own

experiment involving dc corona discharge processing and ozone processing of air-NO(200 ppm) mixture.

11

Experimental procedure

The working gas (air or air-NO mixture) was processed by a dc corona discharge or ozone only. The working gas was introduced into a discharge reactor in which two electrodes were placed: a stainless-steel plate and either a stainless-steel or brass needle. The needle electrode was polarized positively. The time-averaged discharge current was 40 µA or 50 µA. The operating voltage was varied in the range 26-34.4 kV.

The working gas was air or air-NO(200 ppm) mixture. It flowed through reactor with a flow rate varied in the range 0-2.5 l/min. The temperature of the working gas was 24°C.

The ozone processing of air-NO(200 ppm) mixture was carried out in the same reactor, however, no discharge was applied.

Concentrations of NO, NO2, N2O and O3 in the working gas were measured by absorption spectroscopy method. For the spectra recording a Perkin-Elmer 16 PC FTIR spectrophotometer operating in the infrared range 4400-1000 cm-1 was used.

Results

Results of both the corona discharge processing and ozone processing of air-NO(200 ppm) mixture are summarized in Tab. 1. After the corona processing, in the gas exiting the reactor only NO, NO2 and N2O were detected, and no O3 was observed. However, the corona discharge in pure air produces O3 (Fig. 1). In the case of air-NO(200 ppm) mixture the experimentally observed absence of O3 in the outlet gas may mean that all O3 was consumed in the reactions oxidizing NO and NO2 (Tab.1, reactions 3 and 4) in the duct between the reactor and the FTIR spectrometer (transport time is about 3 s). The absence of O3 in the outlet gas after ozone processing (interaction time about 3 s) of the air-NO mixture (see Tab. 1, B. Ozone processing) confirms that reactions (3) and (4) are very fast (total reaction rate about 200 ppm/s).

Fig. 1. Production of O3 in the dc corona discharge in air.

As can be seen in Tab. 1, the final concentrations of NOx after the corona discharge and

ozone processing were the same when air-NO(200 ppm) mixture was mixed with 211 ppm O3. It may suggests that the removal of NO in the corona discharge is a result of the reaction of NO with O3 only. In such a case concentrations of NO and NO2 should be the same after the corona discharge and ozone processing. However, they were different which may mean that during the corona discharge processing also other reactions are involved in NOx conversion. This speculation is confirmed by the case of processing the air-NO(200 ppm) mixture by the corona discharge and O3 (106 ppm). In this case the corona discharge and ozone processing removed similar amount of NO but the concentration of NO2 was doubled after the ozone processing. It may mean that in the corona discharge nitrogen oxides NOx are removed not only in reactions with O3 (Tab. 1, reactions 3 and 4) but also in reactions with radicals N and O (Tab. 1, reactions 1, 2, 5, 6).

12

Tab.1. Corona discharge processing and ozone processing of air-NO(200 ppm) mixture.

A. Corona discharge processing B. Ozone processing Air-NO

[NO]initial = 200 ppm 40 µA, 26 kV Residence time – 30 s Additional interaction time* – 3 s

Air-NO [NO]initial = 200 ppm [O3]initial = 106 ppm (40 µA, 32.4 kV) Interaction time – 3 s

Air-NO [NO]initial = 200 ppm [O3]initial = 211 ppm (50 µA, 34.4 kV) Interaction time – 3 s

NO removal (ppm)

90 96 154

NO outlet (ppm)

110 104 46

NO2 outlet (ppm)

41 84 103

NO+NO2 outlet (ppm)

151 188 149

N2O outlet (ppm)

7 0 0

Main chemical reactions

NO + O + M → NO2 + M (1) NO + N → N2 + O (2) NO + O3 → NO2 + O2 (3) NO2 + O3 → NO3 + O2 (4) NO2 + N → N2O + O (5)

NO + O3 → NO2 + O2 (3) NO2 + O3 → NO3 + O2 (4)

It may be expected that during the ozone processing of air-NO mixture only one reaction

occurs – oxidation of NO by O3. In such a case the removal of NO should be equal to production of NO2. However, it was observed that concentration of NO2 is lower than expected. This phenomenon may be explained assuming that part of NO2 formed as a result of NO oxidation reacts with O3 forming NO3. The balance of O3 presented in Tab. 2 seems to confirm this explanation. When 106 ppm of O3 was mixed with air-NO(200 ppm) mixture, then 96 ppm of NO were removed which means that in the reaction (6) 96 ppm of O3 were consumed and 96 ppm of NO2 were produced. But the experimentally measured NO2 concentration was 12 ppm lower than that resulted from the reaction (6). If 12 ppm of NO2 reacted with 12 ppm of O3, then total consumption of O3 would be 108 ppm and almost equal to initial O3 concentration. Similar calculation of O3 balance carried out for the initial O3 concentration of 211 ppm results in consumption of 195 ppm of O3. This confirms that the reaction of NO2 oxidation to NO3 is involved in NOx removal in the ozone processing of air-NO mixture. Nevertheless, more accurate experimental verification including the measuring of NO3 concentration is needed for confirming the above speculation.

Tab. 2. Balance of ozone in ozone processing of air-NO mixture.

Air-NO [NO]initial = 200 ppm [O3]initial = 106 ppm Interaction time – 3 s

Air-NO [NO]initial = 200 ppm [O3]initial = 211 ppm Interaction time – 3 s

a) Initial: 106 ppm O3 Consumption:

b) In reaction (3): 96 ppm O3 c) In reaction (4): 12 ppm O3

Total: 108 ppm O3 (close to 106 ppm O3)

a) Initial: 211 ppm O3 Consumption:

b) In reaction (3): 154 ppm O3 c) In reaction (4): 41 ppm O3

Total: 195 ppm O3 (close to 211 ppm O3)

13

CONCLUSIONS Both direct and indirect ozone treatment of air polluted with NO result in the same final

concentration of NOx. However, the ratio of NO/NO2 is different in these methods, what is important for further processing. When direct method is employed then NO exceeds NO2 in the gas leaving a reactor, and a combination with additives or catalysts is needed to enhance NOx removal. Opposite result is obtained after using indirect ozonation of NO. Since concentration of NO2 produced from NO is much higher than initial NO, then conventional wet methods removing NO2 may be used, as it is realized in commercially available LoTOx™ method.

It must be noted that direct method, even combined with catalyst, requires only one reactor, whereas indirect ozonation together with following wet removal of NO2 proceeds in at least two consecutive reactors. Thus, there is a significant difference in size of systems using direct and indirect method of NOx removal.

Another major difference between direct and indirect NOx removal methods is in byproducts and their management. In the direct method two kinds of byproducts are formed: safe gaseous species not requiring further treatment and solid aerosols which usually can be used directly as fertilizers. Indirect method generates waste liquids, which need to be used somehow.

As for energy efficiencies of these two methods, they can hardly be compared since direct method is not implemented yet as a commercially available technique.

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(1994) 856-860 [8] J.Y. Park, I. Tomicic, G.F. Round, J.S. Chang, J. Phys. D: Appl. Phys. 32 (1999) 1006-

1011 [9] K. Onda, K. Kato, Y. Kasuga, JSME International Journal, Series B, 39 (1996) 202-210 [10] H.H. Kim, K. Takashima, S. Katsura, A. Mizuno, J. Phys. D: Appl. Phys. 34 (2001) 604-613 [11] T. Hammer, S. Broer, Plasma Enhanced Selective Catalytic Reduction of NOx for Diesel

Cars (1998), Society of Automotive Engineers Technical Paper Series, No. 982428 [12] T. Hammer, S. Broer, Plasma Enhanced Selective Catalytic Reduction of NOx in Diesel

Exhaust: Test Bench Measurements, Society of Automotive Engineers Technical Paper Series, No. 1999-01-3633

[13] M. Dors, J. Mizeraczyk, Catalysis Today, 89 (2004) 127-133 [14] BOC Process Gas Solutions, Low Temperature Oxidation System Demonstration at RSR

Quemetco, Inc., City of Industry, California, Final Report, 2001 [15] Y.S. Mok, J. Chem. Eng. Jpn., 37 (2004) 1337-1344 [16] T. Yamamoto, M. Okubo, T. Nakao, K. Hayakawa, IEEE Trans. Ind. Appl. 38 (2002) 1168–

1173 [17] Y.S. Mok, Chemical Engineering Journal, 118 (2006) 63–67 [18] Y.S. Mok, H.J. Lee, Fuel Processing Technology, 87 (2006) 591 – 597

14

Ozone generation using negative corona discharge: numerical simulation and comparison with experiments

F. Pontiga1, K. Yanallah2, A. Fernández-Rueda1, A. Castellanos3

and A. Belasri4

1Dpt. Física Aplicada II, Universidad de Sevilla, Av. Reina Mercedes s/n, Spain.

2Laboratoire de Génie Physique, Université de Tiaret, B.P.78, Tiaret, Algeria. 3Dpt. Electónica y Electromagnetismo, Universidad de Sevilla, Av. Reina

Mercedes s/n, Spain. 4Laboratoire de Physique des Plasmas, des Matériaux Conducteur et leurs

Applications, Université d’Oran (USTO-MB).

Ozone generation by corona discharge is the object of a continuous and renewed interest, since this type of electrical discharge is present in a wide variety of industrial devices, such as electrostatic precipitators, air cleaners, laser printers, copiers, etc. Many experimental and numerical studies have been conducted to improve our understanding of ozone production [1-6]. However, precise simulation of corona discharge is a rather sophisticated task since many different problems concur together in the modeling: the hydrodynamics motion of the gas, the chemical kinetics of ozone (as well as many other charged and neutral species) and the physical modeling of the electrical discharge itself.

In this work, the generation of ozone from pure oxygen by negative corona discharge is investigated both experimentally and numerically. The discharge reactor used in the experiments consisted of a wire-to-cylinder coaxial electrode system, with total length L = 5 cm. The cylinder was made of plain steel, stainless steel or aluminium, with inner radius R = 8.5 mm, while the cathode wire was made of tungsten, with radius r = 0.05 mm. The wire was subjected to negative DC high voltage, and the cylinder was connected to ground through a digital multimeter. The discharge cell was fed with high purity oxygen (99.995%), and the flow rate was regulated using a mass flow controller. The discharge cell was placed inside the sample compartment of a UV-visible spectrophotometer and ozone concentration was determined by applying Beer-Lambert's law in the range of wavelengths 190-300 nm. A schematic diagram of the experimental setup used in the experiments is presented in Figure 1.

The corona discharge was numerically simulated using a hydrodynamics model, where continuity equations for every species are coupled with Poisson's equation through charged

Figure 1. Schematic diagram of the experimental setup.

15

species and the electric field dependence of reaction rate constants. The plasma chemical kinetics is incorporated into the model as gain/loss rate terms in the continuity equation. Finally, the effect of Joule heating was also taken into account in the energy conservation equation.

Figure 2 shows the experimental measurements of ozone concentration inside the discharge cell as a function of the current intensity and in the absence of gas flow. Ozone concentration is expressed in ppm in volume (1 ppm ≈ 2.46×1013 molecules/cm3). The results are qualitatively similar using the three different anodes. Initially, the concentration of ozone increases sharply as the current intensity is augmented. Then, a maximum in the ozone concentration is reached, and any further augmentation of the current intensity makes the ozone concentration to decrease. The maximum ozone concentration is obtained when using the plain steel cylinder, for I ≈ 50µA. The results obtained from the numerical simulation have shown that the observed dependence of ozone concentration with current intensity is the result of two combined effects: ozone decomposition on the electrode walls, and the existence of a significant temperature gradient inside the discharge reactor (Figure 3). If none of these effects are considered, the numerical simulation predicts an almost constant ozone concentration, independent of current intensity. However, the existence of reactions between ozone and the electrode walls constitutes an important sink of ozone molecules, particularly in the vicinity of the anode owing to its larger surface. With the inclusion of this effect, the numerical simulation predicts an increasing ozone density with current intensity, which is still unsatisfactory. This behaviour is altered when Joule heating is included into the model, since several important reactions that decompose ozone are activated by temperature. Moreover, Joule heating is more important at higher currents, which helps to limit the growth of ozone concentration with current intensity. If both effects are incorporated into the numerical model, the predictions of the simulation are in qualitative agreement with the experimental measurements, although the numerical simulation tends to overestimate the ozone concentration. When pure oxygen is continuously fed into the reactor, the importance of the above discussed effects becomes less important, since the gas is cooled down by the presence of the gas flow and ozone decomposition on the walls is only acting during the residence time of the gas inside the cylinder. Therefore, the higher the gas flow rate is the weaker both effects will result. Figure 4 shows the experimental measurements and the predictions of the numerical simulation corresponding to two different gas flow rates. The averaged ozone concentration is expressed as a function of Becker parameter, β = IV / Q, where Q is the gas flow rate. The results of the simulation are in good qualitative agreement with the measured data: ozone concentration is

2.5

3

3.5

4

4.5

5

5.5

0 50 100 150 200 250

Ozo

ne d

ensi

ty (

103 p

pm)

Current intensity, I (µA)

steelaluminumstainless steel

Figure 2. Averaged ozone density in the absence of gas flow as a function of the current intensity. Three different materials have been used as the anode.

16

observed to increase with Becker parameter and with a similar growth rate. Quantitatively, the numerical simulation slightly underestimates the ozone density, as the predicted ozone concentration is 35% lower than the actual measured concentration.

REFERENCES

1. C. Monge, R. Peyrous, and B. Held. “Optimization of a corona wire-to-cylinder ozone generator. comparison with economical,'' Ozone Science & Engineering, vol. 19, pp. 533-547, 1997.

Figure 3. Averaged ozone density as a function of current intensity predicted by four numerical models of increasing complexity (num: plain model, num. + temp: including the effect of Joule heating, num. + wall: including the effect of ozone decomposition on the electrodes, num. + temp + wall: including both the effects of Joule heating and ozone decomposition on the electrodes.

15

20

25

30

35

40

45

50

0 50 100 150 200 250

Ozo

ne d

ensi

ty (

103 p

pm)

Current intensity, I (µA)

numericalnum. + tempnum. + wallnum. + temp + wall

Figure 4. Experimental and numerical results of the averaged ozone density as a function of Becker parameter for two different flow rates. Solid line: Q = 75 cm3 / min, dashed line: Q = 125 cm3 / min.

0

1

2

3

4

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2

Ozo

ne d

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ty (

103 p

pm)

Becker parameter, β (J/cm3)

numericalexperimental

17

2. A. Yehia, A. Mizuno, and K. Takashima, “On the characteristics of the corona discharge in a wire-duct reactor,'' Journal of Physics D: Applied Physics, vol. 33, pp. 2807-2814, 2000.

3. J. D. Skalny, S. Matejcik, T. Mikoviny, S. Eden and N. J. Mason. “Ozone generation in a negative corona discharge fed with N2O and O2”, Journal of Physics D: Applied Physics, vol. 37, 1052–1057, 2004.

4. J. Loiseau, F. Lacassie, C. Monge, R. Peyrous, and B. Held, “Numerical simulation of ozone axial and radial distribution in a cylindrical oxygen-fed,'' Journal of Physics D: Applied Physics, vol. 27, pp. 63-73, 1994.

5. J. Chen and J. Davidson, “Ozone production in the positive dc corona discharge: Model and comparison to experiments,” Plasma Chemistry and Plasma Processing, vol. 22, pp. 495-522, 2002.

6. C. Soria, F. Pontiga, and A. Castellanos, “Plasma chemical and electrical modelling of a negative DC corona in pure oxygen,” Plasma Sources Science and Technology, vol. 13, pp. 95-107, 2004.

18

Corona processing of hydrocarbons in air

Ester Marotta,1 Alessandro Callea,1 Milko Schiorlin,1 Massimo Rea2 and Cristina Paradisi1

1Department of Chemical Sciences, Università di Padova, via Marzolo 1,

35131 Padova, Italy 2Department of Electrical Engineering, Università di Padova, via Gradenigo 6/A,

35131 Padova, Italy The corona induced decomposition of model hydrocarbons, n-hexane, i-octane, and toluene,

in air at room temperature and pressure has been studied using a wire/cylinder bench-top corona reactor. The process efficiency, products and reactive intermediates were monitored under different experimental conditions in dry and humid air using –DC, +DC and +pulsed corona. Expectedly, the process efficiency decreases in the order +pulsed > -DC > +DC. Interestingly, for –DC and +pulsed corona, the efficiency of hydrocarbon processing is improved in humid air, whereas the opposite is true for +DC corona. Chemical diagnostics included the analysis of stable products and oxidation intermediates as well as that of short lived species, both charged and neutral. Qualitative and quantitative determination of volatile products and intermediates (CO2, CO, minor quantities of organic byproducts) was performed by GC/FID, GC/MS and on-line FT/IR analysis. A considerable amount of carbon is unaccounted for, especially with +pulsed corona, thus indicating that non-volatile products are also formed. Thus, with +pulsed corona CO2 production increases with energy density also after the complete consumption of the hydrocarbon. Ion analysis data were obtained by means of APCI-MS (Atmospheric pressure Chemical Ionization - Mass Spectrometry) and were matched with current vs voltage profiles measured for DC coronas. Emission spectroscopy measurements yielded the electronic, vibrational and rotational temperatures for the different plasma regimes investigated. The most important neutral reactive species, O(3P) for dry air and •OH for humid air, were also investigated using chemical probes (ozone formation and CO oxidation, respectively). Based on all experimental results, the conclusion is advanced that the decomposition of hydrocarbons induced by –DC and +pulsed corona is initiated by radical reactions, whereas ionic initiation steps prevail in the case of +DC corona.

19

Ozone Production by Corona Discharge Fed by Carbon Dioxide

J. D. Skalný1,2, J. Országh1,2, N. J. Mason2 1Department of Experimental Physics, Comenius University,

Mlynská dolina F-2, 842 48 Bratislava, Slovakia 2Department of Physics and Astronomy, Open University,

Walton Hall, MK7 6AA Milton Keynes, United Kingdom

Abstract The mechanism of ozone formation in DC corona discharges of both polarities fed by pure carbon dioxide in flowing regime has been studied. The influence of ozone concentration on discharge parameters, especially onset voltage, breakdown voltage and the current-voltage (CV) characteristics were investigated. Introduction Ozone is widely used gas especially in various industrial processes (paper and fabric production) and its disinfective and germicidal impacts are also often utilized. Moreover the basic research in the field of astrophysics is also focused to atmospheres of planets where ozone can be present. The study of plasma initiated chemical processes in the discharges fed by gasses present in the atmosphere of these planets can be sometimes applied for the interpretation of effects observed in atmosphere of planets [1-3]. Carbon dioxide is the typical representative of such gases. The concentration of CO2 is very low in atmosphere of Earth, anyway as a good infrared absorber in the Earth atmosphere, the concentration of CO2 considerably affects phenomena known as a greenhouse effect. In contrast the content of carbon dioxide in Martian atmosphere is absolutely dominant. Hence the dissociation of CO2 could be a source for oxygen and ozone production in Martian atmosphere [4]. The idea to use such conversion of CO2 an electrical discharge was appeared recently [3]. Several studies of CO2 decomposition in corona discharges have been published over the last two decades both in pure carbon oxide and/or its mixtures with other gases, predominately air. Recently we have presented study of products contained in pure CO2 and mixtures CO2 + O2 treated by negative corona discharge with particular emphasis on the production of ozone [5]. The discharge current in pure CO2 was found to be highly sensitive to the presence of trace concentrations of molecular oxygen and to changes in the flow speed through the discharge. The ozone concentration increases monotonically with increasing content of oxygen in the mixture with carbon dioxide whereas the CO concentration exhibits a flat maximum for oxygen concentrations around of 4%. The remarkable sensitivity of the discharge current on the flow rate has been ascribed to changes in concentration of ozone produced in the discharge. The goal of presented contribution is to study an effect of ozone formation in DC corona discharge fed by pure CO2 on the properties of the discharges both in positive and negative polarities. Experiment The experimental apparatus scheme is shown in the figure 1. Two cells containing identical coaxial cylindrical electrodes systems (stainless steel inner electrode of diameter 125 μm and stainless steel outer electrode of diameter 16 mm), were used in experiments. Active part length of the discharge tube was 10 cm. DC corona discharge was generated in one of the tubes; the second has been used as a comparative tube. Both were placed into cell compartment of Shimadzu UV spectrometer, which was employed for measurement of the optical transmittance of gas treated in cell containing the active discharge electrodes. The transmittance value was recorded simultaneously with discharge voltage and current by PC. Using Lambert-Beer formula the ozone concentration in the discharge gap was calculated. The flow rate of the gas was kept constant by mass flow controller in the range 5 – 200 cm3/min. Glassman high voltage power supply unit was used to feed the system of discharge electrodes. The measured data of discharge current and the voltage on electrodes have been measured by two multimeters and aquisited by PC. First the onset voltage of corona discharge was detected by jumped appearance of the discharge current of order 0.1 μA. In next the current-voltage characteristic was measured and for each voltage value the transmittance T was registered after stabilisation of the discharge current. Experiments have been carried out at ambient temperature and

20

atmospheric pressure.

Fig. 1. Experimental apparatus scheme. Experimental results and discussion The ozone concentrations reached in the reactor for various gas flow rates and both polarities of the corona discharge are shown in the figure 2. Becker parameter η is an average energy input into unit volume of the discharge gap. If the flow rate is Q and the total discharge current at voltage U is I, the Becker parameter can be expressed as

QP

QI.U

==η . 1

Fig. 2. Ozone concentration dependence on Becker parameter for positive and negative corona discharge. The concentration of ozone at the same value of Becker parameter is only slightly higher in negative corona discharge. The effect of different gas flow rate is similar in both positive and negative polarity. The ozone concentration is higher at lower flow rates as it can be expected. The following reactions are responsible for ozone formation and decomposition in the volume of the reactor:

eOCOCOe 2 ++→+ k1 = f(E/N) (1) [5]

222 COOCOOO +→++ k2 = 1.04 x 10-32 cm6s-1 (2) [5]

MOMOO 32 +→++ k3 = 5.85 x 10-34 cm6s-1 (3) [5]

2-

3 OOOe +→+ k4 = f(E/N) (4) [5]

OOOe -23 +→+ k5 = f(E/N) (5) [5]

1 10 1000

20

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200 cm3/min 100 cm3/min 50 cm3/min 10 cm3/min 5 cm3/min

Ozo

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tion

[ppm

]

η [J/cm3]

positive corona

1 10 1000

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[ppm

]

η [J/cm3]

negative corona

21

2233 OOOP)O( +→+ k6 = 8.5 x 10-15 cm3s-1 (6) [5]

OOO)Δ(OO 22g1

23 ++→+ k7 = 4 x 10-15 cm3s-1 (7) [5] The onset voltage was found to be independent on the gas flow rate in both positive and negative corona discharge. In contrast to this, the breakdown voltage (transition of corona into spark) is decreasing with increasing gas flow rate in the negative corona. In positive corona the breakdown voltage has not been measured, as it was much higher then in the negative corona and the voltage of the power supply was limited. The CV characteristics are shown in the figure 3. The effect of different gas flow rate in the positive corona is not significant. In contrast this effect is evident in the negative polarity. This is caused by the ability of ozone to capture electrons with low energy in the drift region of the discharge which cannot be attached to CO2 because the threshold for this attachment is for electron energy approximately 4 eV. This is resulting into lowering the total discharge current. These processes are expressed by dissociative electron attachment reactions (4) and (5).

Fig. 3. Current-voltage characteristics for both polarities of the corona discharge. Conclusion The ozone formation in DC corona discharge is apparently more effective in the negative polarity discharge. The influence of gas flow rate on CV characteristic of the discharge is evident just in negative polarity. This is caused by the role of dissociative electron attachment to ozone molecule in the drift region of the discharge volume. Acknowledgments

This research project was partially supported Slovak Grant Agency VEGA 1/4017/07, ESF projects COST P9 and EIPAM. This work was supported by Science and Technology Assistance Agency at the contract No. APVT-20-007504. One of the authors (J.O.) is indebted for financial support of project UK /357/2007. References [1] Batanov, G.M., Kossyi, I.A., Silakov, V.P.: Plasma Phys. Reports, 28, 2002, pp. 229. [2] Toumi, R., Houston, P.L., Wodtke, A.M.: J. Chem. Phys. 104, 1996, pp. 775. [3] Dinh, T.H.: Dissertation, Old Dominion University USA, 2002. [4] Vuskovic, L., Ash, R.L., Shi, Z., Popovic, S., Dinh, T., J. Aerospace, 106, 1997, pp.

1041. [5] Mikoviny, T., Kocan, M., Matejcik, S., Mason, N.J., Skalny, J.D.: J. Phys. D.: Appl. Phys.,

37, 2004, pp. 64-73.

4 5 6 7 8 9 100

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nt [μ

A/c

m]

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200 Q = 200 cm3/min Q = 100 cm3/min Q = 50 cm3/min Q = 10 cm3/min Q = 5 cm3/min

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A/cm

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22

Generation of ozone by pulsed corona discharge over water surface in hybrid gas-liquid electrical discharge reactor

P. Lukes1, M. Clupek1, V. Babicky1, V. Janda2, P. Sunka1

1Institute of Plasma Physics, Academy of Sciences of the Czech Republic, v.v.i. Za Slovankou 3, Prague 182 00, Czech Republic

2Department of Water Technology and Environmental Engineering, Institute of Chemical Technology, Technicka 5, Prague 160 28, Czech Republic

Production of ozone generated by the gas phase pulse positive corona discharge above water was investigated for different discharge gap spacing (2.5-10 mm), applied input power (2-45 W), and gas composition (oxygen mixtures with argon or nitrogen). Ozone concentration increased with increasing power input and with increasing discharge gap. The production of ozone was significantly affected by the presence of water vapor formed through the vaporization of water at the gas-liquid interface by the action of the gas phase discharge. The highest energy efficiency for ozone production was obtained using high voltage pulses of approximately 150 ns duration in Ar/O2 mixtures with the maximum efficiency of 23 g/kWh for 40% argon content. Introduction Advanced oxidation water treatment processes that utilize highly reactive radicals such as the hydroxyl radical are of increasing interest for the degradation of organic compounds in contaminated and polluted waters. Various combinations of ozone, hydrogen peroxide, and UV light have been studied as means to produce hydroxyl radicals in water and to effectively degrade many organic compounds. Ozone has typically been produced by electric discharge plasma reactors placed upstream of the water treatment process, and the gas phase ozone thus produced has been sparged into the liquid alone or in combinations with the addition of hydrogen peroxide and UV light. In attempts to bring the ozone generation step closer to the ozone utilization step and to develop plasma reactors that may be suitable for direct water treatment a number of different types of plasma reactors utilizing electrical discharges have been studied. For example, AC, DC or pulsed electrical discharges have been generated in a variety of electrode geometries either directly in the liquid phase or in the gas phase in close proximity to the liquid surface. Electrical discharges generated directly in the liquid were demonstrated to initiate a variety of physical and chemical effects in water including the high electric field, intense ultraviolet radiation, overpressure shock waves and, of particular importance, formation of various reactive chemical species such as radicals (H·, O·, OH·) and molecular species (H2O2, H2, O2, O3). Production of these chemical species has also been reported for electrical discharges generated above the liquid water surface. These reactive species and physical conditions in turn have been shown to be effective at degrading a variety of organic compounds and in the destruction and inactivation of microorganisms in water [1]. Hybrid electrical discharge reactors utilize both the gas phase non-thermal plasma formed above the water surface and direct liquid phase corona-like discharge in the water. The main advantage of these reactors is the production of the same chemical species and physical factors as initiated by the individual gas and liquid phase discharges. Previous experiments have demonstrated the formation of ozone in the gas phase and H2O2 and OH radicals in the liquid phase in these reactors [2,3]. The combined action of these reactive species, as well as possible reaction processes occurring at the gas-liquid interface, can lead to enhancement of the overall efficiency of the electrical discharge process for the removal of pollutants from water [4,5]. In order to optimize the power delivered into the two discharges generated in the gas and the liquid phases and to effectively tune the power supply to the hybrid discharge reactor we have constructed a gas-liquid discharge reactor with separately charged electrodes in the gas and liquid phases using two pulse power supplies, which allow us an independent control of the gas and liquid phase discharges. In the present work, the formation of ozone by the gas phase discharge over the water surface in this hybrid discharge reactor was investigated. The effects of discharge gap spacing, electrical power applied to the reactor and gas phase composition (oxygen and O2/Ar, O2/N2 mixtures) on ozone production was determined.

23

Experimental The discharge reactor is a closed box with Plexiglass walls with outer dimensions of 200×200×200 mm. It consists of two separately charged high voltage electrodes; one placed in the water and one placed in the gas phase above the water. Electrodes are separated by a circular perforated plate made from stainless steel connected with the electrically grounded stainless steel tube of the inner diameter of 160 mm. The high voltage needle electrode in the liquid is made from a mechanically sharpened tungsten wire placed along the axis of the stainless steel tubular ground electrode. The gas phase high voltage electrode is made from RVC disk (diameter 50 mm × thickness 10 mm), which is attached to a stainless steel holder connected to the pulsed high voltage. The distance between the RVC electrode and the ground stainless steel plate submerged in the water is fixed at 40 mm. The gas phase discharge gap between the RVC electrode and the water surface is varied through adjustment of the volume of the aqueous solution used in the reactor. The separate charging of the liquid phase needle electrode and the gas phase RVC electrode is provided by two pulse power supplies that allow for independent control of the gas and liquid phase discharges including separate variation of the input power, voltage, and pulse repetition rate for each phase. Each of them consists of high voltage 0-50 kV DC source, rotating double spark gap giving the maximum pulse repetition frequency of 100 Hz and storage capacitor with variable capacity in the range of 0.2-10 nF. Results and discussion Effect of discharge gap spacing on ozone formation Figure 1 shows the dependence of (a) ozone concentration and (b) ozone production efficiency on the applied power input for different discharge gap spaces between the high voltage RVC electrode and the water surface measured in oxygen. The power input was varied from 11 to 45 W using different applied voltages of positive polarity from 15 to 30 kV at a constant pulse repetition frequency of 50 Hz. The discharge gap space was varied from 2.5 to 10 mm at each applied power input. Reported ozone concentrations are steady state values of the volume fractions of ozone in the output gas, in terms of parts per million (ppmv).

Figure 1. (a) Ozone concentration and (b) ozone production efficiency measured in oxygen as a function of applied power input for different discharge gap spacing. Gas flow rate 2.5 l/min, C=2 nF, discharge gap spacing: , 2.5 mm; , 5 mm; , 7.5 mm; , 10 mm.

It is apparent that for the same power input the ozone concentration and production efficiency increased with the increasing gap spacing. However, when the same discharge gap was used, the ozone concentration increased with increasing power input, opposite to the effect observed for ozone energy yield. For a fixed discharge gap spacing d it can be expected that a higher power input results in a larger average electric field (E=U/d), and higher average power density in the discharge (P/Sd). Increasing the electric field implies increasing E/N and higher mean electron energy in the discharge. Therefore, with a higher power input a larger amount of atomic

24

oxygen can be formed through electron impact dissociation of oxygen, which results in a larger generation of ozone. At the same time, however, a decrease of ozone energy yield with higher applied power input indicates that increases in power density in the discharge can lead to higher power consumption by heat dissipation and subsequently to a larger thermal decomposition of ozone in the discharge [6,7]. In addition to the effects of gap spacing on electric field and power density in the discharge, larger discharge gap leads to the formation of a significantly different kind of discharge. In small gaps (≤ 5 mm) very thin glow-like corona discharge filaments, which homogenously filled the discharge gap above the water surface, were formed during each pulse. With larger discharge gaps smaller numbers of brighter tuft-like corona discharge filaments were formed in each pulse, and in the discharge gap of 10 mm only single bright discharge channels were formed per each pulse. Therefore, as the number of plasma channels decreases with increasing discharge gap, the volume of plasma decreases and the charge transferred in each plasma channel increases for the same applied voltage. This implies higher electron mean energy and gas temperature in the discharge, which could explain the increase of ozone production rate with decreasing energy efficiency observed with larger discharge gap spaces. Consequently, a detrimental effect of water vapor on ozone formation by the gas phase discharge generated above the water should be also taken into account. Since plasma channels formed in the gas are in direct contact with the water surface, the solution can be locally heated and vaporized by the action of the discharge. Typically, the concentrations of water measured in the output gas were 1.5÷2.0 vol.% compared to less than 0.1 vol.% in the inlet gas but even higher concentrations can be expected in the region of the gas phase discharge above the water surface. Thus, the water vapor can absorb a substantial part of electronic energy of the discharge that could otherwise be used in the ozone formation process. H and OH radicals can be formed from water vapor and, consequently, cause reactions that destroy ozone molecules. In addition, O atoms formed through electron dissociation of oxygen can combine with water molecules and their products, preventing ozone formation [8]. Effect of gas composition on ozone formation Figure 2a shows the effects of gas composition on ozone production measured in N2/O2 and Ar/O2 mixtures for different oxygen content. The same total gas flow rate of 2.5 l/min, power input of 20 W (U=20 kV, f=50 Hz, Ep=0.4 J/pulse) and discharge gap spacing of 5 mm were used in each case. It is apparent that the presence of argon and nitrogen in the mixtures with oxygen had different effects on the production of ozone. Figure 2a indicates an improved ozone production in the presence of argon in Ar/O2 mixtures. On the other hand, in N2/O2 mixtures ozone production was considerably suppressed by the presence of nitrogen.

Figure 2. Ozone concentration measured in Ar/O2 and N2/O2 mixtures as a function of oxygen concentration. Gas flow rate 2.5 l/min, discharge gap spacing 5 mm. (a) U=20 kV, C=2 nF, P=20 W; (b) U=30 kV, C=0.2 nF, P=4.5 W.

25

It is known that both nitrogen and argon can have catalytic effects on the production of ozone [6-10]. In the case of nitrogen such an effect is caused by the reactions of nitrogen atoms and electronically excited nitrogen molecules N2(A3Σu

+) and N2(B3Πg) with oxygen, which can produce additional oxygen atoms for generation of ozone. However, at higher specific energy densities in the discharge such a positive effect of nitrogen can be counteracted by quenching of oxygen atoms and destruction of ozone by the relatively high concentrations of nitrogen atoms and nitrogen oxides. In Ar/O2 mixtures these side reactions cannot occur since argon as monoatomic and chemically inert gas cannot serve as a chemical quencher of atomic oxygen and its catalytic effect is mostly due to the involvement of argon as the third collision partner in the ozone formation. Therefore, significantly reduced production of ozone in the N2/O2 mixtures shown in Figure 2a can be explained by the inhibition effect of N atoms and NOx caused most likely by the excessive energy density in the discharge. To decrease both the magnitude and pulse duration of the power delivered into the discharge the charging capacity of 0.2 nF was used instead of 2.0 nF. This resulted in the formation of voltage and current pulses with oscillatory characteristics and with a pulse duration of approximately 150 ns FWHM compared to typical values of about 500 ns FWHM of voltage and current pulses generated using storage capacitor of 2.0 nF. Comparison of the trends in ozone formation in figures 2a and 2b indicates significant improvement in the ozone production efficiency using smaller charging capacitance, especially in N2/O2 mixtures, although the total amount of ozone formation was smaller than for the 2 nF case. Moreover, in Ar/O2 mixtures ozone was formed in larger amounts than obtained in pure oxygen. Figure 2b shows that the production of ozone in Ar/O2 mixtures with argon content in the range of 10-70% was significantly enhanced with the maximum amount of ozone production occurring with 40% argon. This corresponded to the maximum ozone production efficiency of 23 g/kWh. Conclusions In summary, although the efficiency of ozone production was significantly enhanced using high voltage of shorter pulse width, the obtained ozone yields (~10-20 g/kWh) are still much lower than yields reported for ozone production using corona discharges in dry oxygen or air (~50-150 g/kWh) [10-13]. It is apparent that water vapor formed through the vaporization of water surface by the gas phase discharge is one of the most important reasons of this state. However, the formation of OH radicals in water vapor or at gas-liquid phase interface is also desired since they significantly contribute in degradation of organic compounds dissolved in water [4,5]. Thus, a compromise between production of ozone in high concentrations and with high energy efficiency, and production of OH· radicals by the gas phase discharge generated above aqueous solution has to be considered in further development of hybrid gas-liquid discharge reactors. It should be also emphasized that rather than development of a new type of ozone generator the final objective is the most efficient utilization of chemically active species (O3, OH· and O radicals, and other species) formed by the gas phase discharge in the removal of pollutants from water. Acknowledgement This work was supported by the Academy of Sciences of the Czech Republic (No. K2043105). References [1] Locke BR, Sato M, Sunka P, Hoffmann MR, Chang JS Ind. Eng. Chem. Res. 45 (2006) 882 [2] Lukes P, Appleton AT, Locke BR IEEE Trans. Ind. Applicat. 40 (2004) 60 [3] Grymonpre DR, Finney WC, Clark RJ, Locke BR Ind. Eng. Chem. Res. 43 (2004) 1975 [4] Lukes P, Locke BR Ind. Eng. Chem. Res. 44 (2005) 2921-30 [5] Lukes P, Locke BR J. Phys. D: Apl. Phys. 38 (2005) 4074-81 [6] Eliasson B, Kogelschatz U IEEE Trans. Plasma Sci. 19 (1991) 309 [7] Penetrante BM, Bardsley JN, Hsiao MC Jpn. J. Appl. Phys. 36 (1997) 5007 [8] Peyrous R Ozone Sci. Eng. 12 (1990) 19 [9] Mason NJ, Skalny JD, Hadj-Ziane S Czech. J. Phys. 52 (2002) 85 [10] Manning TJ 2000 Ozone Sci. Eng. 22 (2000) 53 [11] Simek M, Clupek M J. Phys. D: Appl. Phys. 35 (2002) 1171 [12] Samaranayake WJM et al. IEEE Trans. Dielect. Elect. Insul. 7 (2000) 254 [13] Ahn HS, Hayashi N, Ihara S, Yamabe C Jpn. J. Appl. Phys. 42 (2003) 6578

26

Research of ozone generation at Masaryk University

David Trunec

Department of Physical Electronics, Faculty of Science, Masaryk University, Kotlářská 2, Brno, 611 37, Czech Republic

The research of ozone generation at Department of Physical Electronics, Masaryk University has a long tradition. In this contribution the results obtained in this field will be summarized. The research of ozone generation at our department started in 1960. Firstly, the influence of different parameters on ozone production efficiency was studied. A new type of ozonizer with a discharge electrode has been developed. Also the ozone generation was studied theoretically. The kinetic model was developed and the ozone production efficiency was calculated. The dependence of ozone production efficiency on the shape of applied electric field was studied. Finally, the so called Atmospheric Pressure Glow Discharge (APGD) was used for ozone generation and it was found that this discharge has better ozone production efficiency than usual dielectric barrier discharge in filamentary form.

27

Novel method for enhancing the destruction of environmental pollutants and odour control

Alice M. Harling1,2, David Glover2, J. Christopher Whitehead1, Kui Zhang2,

1School of Chemistry, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK

2 Plasma Clean Ltd., Broadstone Knowledge Mill, Broadstone Road, Stockport, Cheshire, SK5 7DL, UK

The dielectric barrier discharge (DBD) system is commonly used for producing non-equilibrium plasmas at atmospheric pressure and this technology has been used in industry for ozone generation for over 150 years [1, 2]. Ozone is well known for its ability to oxidise airborne and water borne pollutants and has excellent cleansing, deodorising and disinfecting properties. A novel multistage dielectric packed bed discharge plasma reactor (DPBD) has been developed and is used to destroy environmental pollutants, such as volatile organic compounds (VOCs), and also to produce ozone for odour control applications. In this work we report experimental results on the levels of ozone produced by our DPBD reactor developed in our laboratory. This three cell plasma reactor, operated at ambient pressure and low temperatures, is an effective technology for VOC remediation as well as the production of high levels of ozone, whilst the formation of by-products such as NOx is strongly suppressed. The levels of destruction of VOCs, such as toluene and ethylene are shown elsewhere [3] and the scale-up results will be presented in a future paper [4]. In this work ozone is produced directly from air by a plasma discharge; when three cells are used together in series up to 67 gh

-1 of ozone are produced

which can be used for odour abatement applications. A distinct advantage of plasma technology for removing waste gas streams is the ability to combine this system with catalysts [5, 6]. Plasma-catalysis has been extensively tested to improve the energy efficiency of the system and to restrict the formation of toxic by-products in a plasma reactor [7, 8]. This work combines the ozone produced by a plasma discharge and MnO2 catalysts to further enhance the destruction of VOCs. In this process, a mixture of synthetic air (80 % nitrogen and 20 % oxygen) and the vapour of the VOC pass through the reactor controlled by mass flow controllers (MFC), maintained at a pressure of 1 bar, to give a total flow rate of 1 Lmin

-1. The identities of the products are

determined by FTIR spectroscopy using a long-path gas cell (4.8 m) and a Shimadzu FTIR spectrometer (8300) with a resolution of 1 cm

-1. In this process, NO and NO2 were not detected

by FTIR. An illustration of the multi-cell plasma reactor used is shown in Figure 1. Figure 1 Schematic diagram of the multi plasma cell reactor The DPBD reactor is made up of a plastic box (dimensions 24.81 by 4.8 by 6.5 cm, AAC Eurovent Ltd.) containing three fixed barrier discharge cells (A,B and C). Each plasma cell size is 14.8 by 6.5 by 1.6 cm, and each electrode size in the plasma cell is 13 by 4.5 cm. The plasma cells are made of clear polycarbonate filters perforated on two faces, through which the gas can flow and contain two copper mesh electrodes made from a copper perforated sheet.

A B C

Air in Air out

28

The thickness of the copper sheet is 0.7 mm and the diameter of the round hole is 4 mm, which gives 58 % open area on the copper sheet. The distance between the two copper electrodes is 16 mm. The plasma cell is filled with soda lime glass beads (6 mm in diameter.) Each plasma cell is individually powered by a high frequency, AC high voltage power supply. The distance between each plasma cell is 3 cm. The input voltage to each of the plasma power sources was controlled by a variac connected to the mains. A plug-in power meter was used to monitor the power dissipated to each power source and plasma cell at different input voltages. The output from the transformer was 13.4 kV (pk-pk) with a frequency of 39-43 kHz. Power was applied to all three cells using primary input mains voltages as applied to the transformer. To gain a better understanding of the formation of ozone, air alone was passed through the reactor at 1 Lmin

-1 and the products measured. The results for the formation of ozone, N2O and

NOx, with different plasma cell combinations, are shown in Table 1 and illustrated further by Figure 1. The levels of destruction of toluene are shown elsewhere [3] although to give an indication, one cell (A) gives 0.1 % destruction, two cells (A+C) give 5 % destruction and three cells (A+B+C) give 72 % destruction of toluene. Table 1 Ozone, N2O and NOx concentrations for different plasma cell configurations

0

200

400

600

800

1000

1200

1400

1600

1800

2000

20 25 30 35 40 45

Input voltage (V)

Ozo

ne c

on

ce

ntr

ati

on

(p

pm

)

Figure 2 Ozone concentration at varying input voltages for 2 cells (♦)(A+C) and 3 cells ()(A+B+C)

Input voltage

(V)

Plasma cell configuration

Ozone concentration

(ppm)

Ozone concentration

(gh-1

)

N2O concentration

(ppm)

NOx concentration

(ppm)

25 A 3.9 0.2 0.2 <1

25 C 7.8 0.3 0.2 <1

25 A+B 15.5 0.6 0.2 <1

25 A+C 26.5 1.0 0.4 <1

25 A+B+C 62.7 2.4 0.7 <1

30 A+C 183.6 7.1 2.0 <1

30 A+B+C 1432.5 55.2 33.3 <1

35 A+C 1415.7 54.5 36.7 <1

35 A+B+C 1732.5 66.7 78.3 <1

40 A+C 1545.0 59.5 58.8 <1

29

A novel DPBD reactor has been developed and used to effectively destroy VOCs and produce ozone in order to remove odours from airstreams. Despite its proven ability to destroy waste gas streams the disadvantages of plasma technology for air pollution control include the low energy efficiency and the formation of toxic by-products such as NOx, CO and nitric acid [8]. The advantage of this system is that low concentration of VOCs in air can be converted into CO2 and water without producing other hazardous by-products such as NOx (NO, NO2). It has been shown for the first time that the passage of air in series through a plurality of reactor units in which a non-equilibrium plasma is generated can improve process energy efficiency significantly above that which would be expected by an additive effect of increased residence time. This has significant implications in plasma gas processing, allowing very low power operation of multiple cells to achieve process efficiencies that have previously only been observed with high input energy plasma devices. The synergistic effect that is achieved by combining two or more of the plasma cells in series has its origin in the generation of active species, which impart increased efficiency to the downstream cells. This is also the first known work to remove pollutants using a DBD packed bed reactor but not produce NOx as a byproduct. The basic mechanism for NOx formation in plasma systems is well established and been shown previously [9]. This means that our system effectively removes the NOx that plasma forms and converts it to nitrous oxide (N2O.) We believe that the synergistic effect that is achieved by combining two or more plasma cells in series has its origin in the generation (in the non-equilibrium plasma of an upstream cell) of activated species for example excited states, radicals, ions and long lived intermediates such as ozone which impart increased efficiency to the downstream cells. We believe that the arrangement of the units optimises the production of key intermediates for particular input energies. The effect of a catalyst alongside ozone and the discharge products will be discussed in more detail. Acknowledgments Support of this work by the UK Engineering and Physical Sciences Research Council is gratefully acknowledged. References 1. Kogelschatz, U., B. Eliasson, and W. Egli, From ozone generators to flat television

screens: history and future potential of dielectric-barrier discharges. Pure and Applied Chemistry, 1999. 71(10): p. 1819-1828.

2. Siemens, W., Poggendofls Ann. Phys. Chem. , 1857. 102: p. 66. 3. Glover, D., et al., Novel method for enhancing the plasma destruction of environmental

pollutants by the combination of multiple plasma discharges. In press. 4. Glover, D., et al., Scale-up of novel method for enhancing the plasma destruction of

environmental pollutants by the combination of multiple plasma discharges. In press. 5. Holzer, F., U. Roland, and F.D. Kopinke, Combination of non-thermal plasma and

heterogeneous catalysis for oxidation of volatile organic compounds. Part 1. Accessibility of the intra-particle volume. Applied Catalysis, B: Environmental, 2002. 38(3): p. 163-181.

6. Kim, H.H., et al., Low-temperature NOx reduction processes using combined systems of pulsed corona discharge and catalysts. Journal of Physics D: Applied Physics, 2001. 34(4): p. 604-613.

7. Oda, T. and K. Yamaji, Dilute trichloroethylene decomposition in air by using non-thermal plasma - catalyst effect. Journal of Advanced Oxidation Technologies, 2003. 6(1): p. 93-99.

8. Demidiouk, V. and J.O. Chae, Decomposition of volatile organic compounds in plasma-catalytic system. IEEE Transactions on Plasma Science, 2005. 33(1 II): p. 157.

9. Harling, A.M., J.C. Whitehead, and K. Zhang, NOx Formation in the Plasma Treatment of Halomethanes. Journal of Physical Chemistry A, 2005. 109(49): p. 11255-11260.

30

Progress reports

31

Simple modelisation of ozone generation by positive corona discharge

K. Yanallah1, F. Pontiga2, A. Castellanos3, S. Hadj-Ziane1,

Y. Messlem1 and A. Belasri4

1Laboratoire de Génie Physique, Université de Tiaret, B.P.78, Tiaret, Algeria

2Dpt. Física Aplicada II, Universidad de Sevilla, Av. Reina Mercedes s/n, Spain 3Dpt. Electónica y Electromagnetismo, Universidad de Sevilla, Av. Reina

Mercedes s/n, Spain 4Laboratoire de Physique des Plasmas, des Matériaux Conducteur et leurs

Applications, Université d’Oran (USTO-MB)

Ozone molecule has unique oxidizing properties that are in the base of its many industrial applications, such as air cleaners, water purification, odor control, gas treatment, etc. [1-4]. Therefore, many studies have been devoted to unveil the mechanisms of generation of ozone in electrical discharges [5-7], and to increase the efficiency of ozone production. In this work, we present a numerical study of ozone production by positive DC corona discharge. The electrical discharge occurs between a wire and a coaxial cylinder, and pure oxygen is feed into the discharge cell (Fig. 1). As it is well known, the corona discharge is initiated when the electric field near the wire is sufficiently high to ionize the gaseous species. The minimum electric field is a function of the wire radius, the surface roughness of the wire, air temperature, and pressure [8].

Corona discharge has been simulated by using a hydrodynamics model that combines the physical processes in the corona discharge with the chemistry of ozone formation and destruction in the oxygen stream. Basically, it consists in a set of continuity equations, coupled with Poisson’s equation. The continuity equations govern the transport and the gain/loss balance of every species due to the chemical reactions induced by the electrical discharge. The current-voltage characteristic (CV) measured in experiments is used as input data to the numerical simulation.

Fig. 2 presents the radial distribution of charged species and the electric field for a

positive DC corona discharge from the wire (anode) to the cylinder (cathode) at room temperature (T = 300 K) and atmospheric pressure. The anode and cathode radius are 0.00625 cm and 1.35 cm, respectively, the applied voltage is 8 kV, and the gas flow rate is 100 cm3/min.

Fig.1. Schematic diagram of the positive corona discharge cell.

32

0,01 0,1 1101

103

105

107

109

1011

103

104

105

Den

sity

(cm

-3)

Radial distance, r (cm)

e O2

+

O2- E

(V/c

m)

Fig. 2. Radial distribution of charged species (left axis) and electric field (right axis) in a positive

corona discharge, for V = 8 kV and Q = 100 cm3/min.

The distribution of species is the result of the competition between ionization and electron attachment. Near the wire, the electric field is very high, so ionization prevails over attachment and new electrons are produced. A few millimeters away from the wire, the ionization rate equals the attachment rate. All newly produced electrons attach to oxygen molecules to form negative ions,

e + O2 + M → O2- + M (M = O3, O2, etc.).

Theses negative ions move then towards the discharge wire. Outside the ionization

region, the electric field strength is insufficient to produce electrons. Therefore, positive ions drift into this volume towards the grounded cylinder. The plasma is in a non-equilibrium state and has a low degree of ionization.

0,2 0,4 0,6 0,8 1,0 1,20,0

7,0x1015

1,4x1016

2,1x1016

2,8x1016

3,5x1016

O3(c

m-3)

Radial distance, r (cm)

z=10 cm z=3,6 cm z=0,36 cm z=0,036 cm z=0,0 cm

Fig. 3. Radial distribution of ozone density at five different locations along the cylinder, for V = 8

kV and Q = 100 cm3/min. The radial variation of the ozone density is represented in Fig. 3. As expected, ozone

concentration increases progressively as the oxygen flow advances along the cylinder. Just after the entry of the oxygen gas into the discharge tube (z = 0.0 cm), the radial distribution of ozone is highly inhomogeneous. In that location, the density of ozone has a maximum in the vicinity of the wire, where the active region of the corona discharge is located, and then sharply declines. This decline reveals that ozone diffusion has not had enough time to act in the radial

33

direction. A crude estimate of the diffusion time of ozone gives td ~ 5 s, which is much shorter than elapsed time of flow. As oxygen gas advances along the cylinder, ozone diffuses towards the cathode and its concentration becomes more uniform. Finally, Fig. 4 shows the axial distribution of ozone at a constant radial distance and for two different values of the applied voltage. After a certain entrance length, ozone density is observed to increase linearly along the axial direction for low applied voltages.

The predictions of the numerical simulation are compared with the experimental

measurements in Fig. 5. In that figure, the averaged ozone density has been plotted as function of the applied voltage. The results of the simulation are in qualitative agreement with the experimental measured data. The numerical simulation tends to overestimate the ozone density, as the predicted ozone concentration is 50% higher than the actual measured concentration.

0 2 4 6 8 100

1x1016

2x1016

3x1016

4x1016

O3(c

m-3)

Axial distance, z(cm)

V= 6 Kv V= 8 Kv

Fig. 4. Axial variation of ozone density in the vicinity of the wire (r = 0.01668 cm) for two

different applied voltages and Q = 100 cm3/min.

6 8

1x1015

2x1015

3x1015

4x1015

10

O3(c

m-3)

Applied voltage, V(Kv)

Experimental Modelisation

Fig. 5. Experimental and numerical results of ozone density as a function the applied voltage for

Q = 100 cm3/min.

REFERENCES

[1] C. Gutiérrez-Tapia, E. Camps and O. Olea-Cardoso, “Perturbative method for ozone synthesis from oxygen in a single discharge”, IEEE Trans. Plasma Sci. 22, 979 (1994). [2] A. D. Moore, Electrostatics and Its Applications, John Wiley & Sons, New York (1973).

34

[3] J. A. Cross, Electrostatics: Principles, Problems and Applications, Adam Hilger, Bristol, England (1987). [4] M. L. Balmer, G. Fisher, J. Hoard., Society of Automotive Engineers, Inc., Warrendale, PA, 1999. [5] Skalny J D, “Mass spectrometry of low energy ions extracted from negative corona discharge in air at medium pressure”, Acta Physica Universitatis Comenianae, 28, 161 (1987). [6] M. Laan, J. Aarik, R. Josepson and V. Repän, J. Phys. D Appl. Phys. 36, 2667 (2003). [7] J. F. Loiseau, F. Lacassier, C. Monget, R. Peyrous, B. Held and C. Coste, “Numerical simulation of ozone axial and radial distribution in a cylindrical oxygen-fed ozonizer”, J. Phys. D Appl. Phys. 27, 63 (1994). [8] F. W. Peek, Dielectric Phenomena in High-Voltage Engineering, 3rd ed., New York, (1929). [9] C. Soria, F. Pontiga, and A. Castellanos, “Plasma chemical and electrical modelling of a negative DC corona in pure oxygen,” Plasma Sources Science and Technology, 13, 95 (2004). [10] P. Atten, M. McCluskey, and A. Lahjomri, “The electrohydrodynamic origin of turbulence in electsotatic precipitators,” IEEE Transactions on Industry Applications, 23, 705 (1987). [11] K.Yanallah, S.Hadj-Ziane, and A.Belasri, “Ozone decomposition on walls”, Plasma Devices and Operations, 14, 215 (2006).

35

Ozone generation in the Practical exercises of applied plasma chemistry course

František Krčma, Zdenka Stará

Institute of Physical and Applied Chemistry, Faculty of Chemistry, Brno University of Technology, Purkyňova 118, Brno, CZ-612 00, Czech Republic

Introduction Plasma chemistry is a relatively new scientific discipline that became a part of university study programs relatively recently. This discipline can be studied from two rather different points of view. The plasma chemistry courses for physicists are naturally focused on the basic phenomena in plasmas, the courses for chemists focus more on the use of plasma as an instrument. In both of these conceptions, the plasma chemical technologies plays only a minor role, although a huge increase of plasma chemical technologies has been observed during the last years. Usually, the practical exercises complement the lectures. The practical exercises at universities are normally focused on the basic processes and basic phenomena (studies of DC glow discharge etc.) and on some plasma diagnostic methods. At technical universities, the practical exercises are usually in the form of plasma technology demonstrations without active participation of students. The study programs at our university contain a course in applied low temperature plasma chemistry where students can obtain the basic information about the theoretical description of plasmas and later on about some plasma chemical technologies. This conception raises a serious problem how to present modern plasma chemical technologies to our students because there is only a small chance to see the technologies in specialized laboratories or in industry except during excursions. Due to this fact we prepared a special practical course focused on the applications of low temperature plasma processes. The exercises include various technologies, such as surface treatment, thin layer deposition or decomposition of molecules and also some basic tasks, such as calibration of the measuring devices and characterization of final products. Plasma diagnostics and fundaments of vacuum physics that are not included in any other course at our university are included in our course as well. The diagnostic methods use the apparatus available in our laboratories, so the students can obtain also information about other devices. Finally, most of the experimental plasma devices used in the practical course can be used also during the work on the students’ master and doctoral thesis. This allows in return the continual enlargement and improvement of the exercises. The interesting point of experimental plasma devices used in our course is that these apparatuses are mostly very cheap and also safe to be used by students having more or less no experience with high voltage devices. The study of ozone generation is one of the most complex exercises and thus it is a subject of this contribution. The survey of the other exercises is given below at the end of contribution. Exercise: Study of ozone generation The ozone generation in the low temperature plasma is one of the oldest plasma chemical processes. The experimental set up shown schematically in Fig. 1 uses the silent discharge reactor that is very similar to the original Siemens one. The gas flow through the ozonizer is adjusted by non calibrated flow meter (with the range of 1 Slm), so the first step of the task is its calibration from the known time for filling the given volume at different rotameter marker positions. Both oxygen and ambient air can be used for the ozone generation study. The own ozonizer uses the coaxial configuration with metallic inner cylinder of 27 mm in diameter, the outer graphite electrode is as a surface layer on a Pyrex glass tube (the inner diameter of 30 mm). The total length of the ozonizer is 40 cm with the active part of 30 cm. The power supply constructed in our laboratory uses the car-starting coil giving the voltage amplitude of 10 kV at the frequency of 50 Hz. The input power supply current can be continuously varied between 16 and 34 mA. Due to the use of high voltage, the ozonizer itself is installed in the centre of a Perspex box (10 x 10 x 50 cm). The power regulation is at the low voltage part and therefore it can be placed outside this box.

36

Figure 1: Simplified scheme of the experimental set up. 1 – oxygen bottle or high pressure ambient air source; 2 – rotameter; 3 – ozonizer; 4 – UV absorption measuring unit; 5 – KI double bubbler. The determination of the amount of the generated ozone can be done by two different methods – by UV light absorption and by iodometric titration. The ozone absorption has a wide band in the range of 200 – 300 nm with the maximum at about 250 nm [1]. Due to this fact, the best source of UV light is a low-pressure mercury lamp. The standard side window photomultiplier with an appropriate home made non adjustable high voltage power supply is used as a light detector. The interference filter passable at the mercury line of 253 nm is placed just before the input window of photomultiplier. The signal form photomultiplier is measured by multimeter Metex connected to the PC with rate of 1 sample per second. The UV light absorption is done in the quartz cell with length of 10 cm. Because no imaging is necessary in our case, the cell was made by our glass blower and we don’t use silica windows. Of course, the ozone detection unit is not calibrated so another method which is absolute must be used for the calibration. The best one is iodometric titration that is based on the following reaction:

2 KI + O3 + H2O → I2 + 2 KOH + O2. We use the 0.2 M KI solution. The 2 M solution of HCl is added in the amount of 10 ml/100 ml of KI solution. Titration is done by a 0.05 M Na2S2O3 solution. 1 ml of 0.05 M Na2S2O3 solution is equal to 1.2 mg of ozone [2]. In our case, the generated ozone bubbles in the KI trap for 5 minutes if the generation is done from oxygen or for 10 minutes if the generation is done from air because in this case not only ozone is generated. Due to this fact it is also necessary to calibrate the UV detection line separately in both cases. We use 100 ml of KI solution. The second trap is added mostly for security, only about 1% of generated ozone is destroyed in it. After ozone generation the standard titration is completed and the amount of the generated ozone can be established. As the UV light absorption is more or less linearly dependent on the ozone concentration, usually four points are sufficient for the calibration of UV light detection unit. The ozone generation in the dependence on the discharge current, gas kind and its flow rate are measured by the UV absorption after completing all the calibrations. An example obtained from the students’ laboratory record is given in Fig. 2.

37

Figure 2: The ozone generation as a function of gas flow rate for three power supply currents. Other practical exercises taking place at present Besides the ozone generation another plasma chemical processes and technologies are included in our course. As they are not connected directly to ozone generation, they are only listed here with very short descriptions. - Calibration of pressure gauges

Calibration of Pirani gauge at two different operating temperatures; calibrations of an ionizing gauge in two different gases.

- Optical emission spectroscopy Identification of radiative particles – atoms and molecules; calculation of the rotational temperature; estimation of vibrational distribution or, if possible, the calculation of vibrational temperature. This work is done using two different DC discharge lamps. Study of the high voltage and influence of the slit width on the signal intensity and on the spectra resolution.

- Changes of polymer materials wettability by surface discharge Treatment of a thin polymeric foil (polypropylene, polyethylene, polystyrene) using the surface barrier discharge (UPS 100). The water wettability and surface energy changes are studied using the simple device for contact angle measurement and surface energy calculation (SEE System [3]) as a function of discharge conditions, mainly on the total discharge energy. Besides the direct surface activation by electrons, various radicals and UV radiation, the ozone generated by the discharge in air partially contributes to the surface processes. The influence of the surface ozonization should be added in the future.

- Water permeability enhancement of non-woven textile materials The non-woven polypropylene textile used for the agricultural purposes is treated using the same experimental device as above. The water permeability is measured by the permemeter constructed at Faculty of Science of Masaryk University. The permeability is studied as above as a function of discharge conditions.

- Hydrogen peroxide generation by diaphragm discharge in liquids Diaphragm discharge is generated using DC non-pulsed high voltage in water solution of selected electrolyte. Hydrogen peroxide formed by the discharge in water can be easily determined by colorimetric method (specific reaction with titanium reagent gives yellow complex which absorption intensity is directly proportional to H2O2 concentration). Students observe production of H2O2 in time and determine rate constant of H2O2 creation at particular discharge conditions.

- Organic dyes degradation by diaphragm discharge in liquids This task uses the same device as in the previous case. Moreover, selected organic dye is dissolved in the electrolyte solution and it is treated by the diaphragm discharge. Decrease of the dye concentration is determined by absorption spectroscopy. The dye decoloration is also well observed by the only eye.

- VOC destruction in atmospheric pressure plasma The simply single stage gliding arc reactor is used for the destruction of toluene as a typical example of volatile organic compounds (VOC). As the full analysis of the discharge products is very complicated and time consuming procedure the detector of simple low weight molecular

38

products is applied. The toluene destruction is measured as a function of discharge power, carrier gas composition and total gas flow through the reactor.

- EPR spectroscopy of decaying plasma The generation of nitrogen and oxygen atomic particles in the low pressure microwave discharge in pure nitrogen and oxygen is measured absolutely by in plasma science unique method of electron spin resonance spectroscopy. The absolute concentrations of atomic ground state species are determined in dependence on the discharge conditions as well as on the time during the post-discharge.

Conclusions We have prepared a special practical course focused on applied low temperature plasma physical and chemical processes. The exercises include various technologies, such as surface treatment, thin layer deposition, decomposition of molecules; the exercises are connected with some basic tasks, such as the calibration of measuring devices and the characterization of final products. One of the most educative and complex exercises is focused on the study of ozone generation where students must complete calibration of flowmeter and UV absorption line that is used for the ozone detection. The plasmatic part of the exercises is mostly very cheap and thus the device can be simply installed anywhere. We think the knowledge of the university graduates is not sufficient in the field of practical plasma chemistry. The international interaction and a new practical course can significantly increase the quality and adaptability of graduates in technological practice. Thus the acceleration and the progress in plasma chemical technology applications can be reached in the near future. Acknowledgements This work was based on the results obtained during our the work on various grant projects of Czech Science Foundation, mainly on project No. 202/99/0307 and 202/03/H162 and Czech Ministry of Education, research plan No. MSM0021630501. References [1] R. E. Huffman, Canad. J. Chem. 47 (1969), 1823. [2] W. J. Maeck, G. L. Booman, M. E. Kussy, J. E. Rein, Anal. Chem. 33 (1961), 1775. [3] www.advex-instruments.cz.

39

Influence of humidity on ozone concentration in negative corona discharge fed by oxygen

Horváth, G.1,2, Országh, J.1,2, Skalný, J.D.1,2, Mason, N.J.2,

Chernyak, V.3

1Department of Experimental Physics, Comenius University, Mlynská dolina F-2, 842 48, Bratislava, Slovakia

2Open University, Department of Physics and Astronomy, Walton Hall, Milton Keynes MK7 6AA, United Kingdom

3Radiophysics Faculty, Taras Shevchenko University, Kyiv, Ukraine

Abstract

The ozone generation in negative DC corona discharge fed by pure oxygen has been investigated. The gas was flowing through the reactor at flow rate of 100cm3/min. The influence of discharge power and humidity on the ozone concentration was studied. We have investigated the effect of large values of humidity on ozone concentration before and after the critical value of Becker parameter. Furthermore, the influence of the humidity on the current-voltage characteristics was studied too. The ozone concentration was measured by UV transmittance measurements. Introduction

Corona discharge has been proven to be a reliable ion source for charging objects, such as particles or surfaces in electrostatic precipitators, photocopiers, and laser printers [1]. The production of ozone in the corona discharge is attributed to a series of gas-phase reactions driven by the energetic electrons created in the thin corona plasma layer [2], [3]. Numerous experimental studies by many researchers have examined the dependence of ozone production on the discharge polarity, current level, discharge electrode size, feed gas temperature, velocity, and relative humidity to seek methods to reduce the ozone production [4]–[10].

Experiments indicated that the electrical characteristics of negative coronas change with relative humidity [5] and the production of ozone decreases with increasing humidity [5], [9]. The underlying reasons for the reduction of ozone in the presence of water vapour are not clear.

Experimental apparatus

The experimental apparatus is shown in Figure 1. Discharge tube containing coaxial cylindrical electrode systems (a stainless steel inner electrode of diameter 125 μm and a brass outer electrode of diameter 16 mm) was used in these experiments. The active part length of the discharge tube was 6.5 cm. A regulator of humidity was placed between the discharge tubes and the oxygen-fed bottle. A DC corona discharge was generated in the discharge tubes. The same gas was closed in the comparative cell of the Shimadzu UV spectrometer, which was used to measure the optical transmittance of the gas contained in the discharge. The transmittance was recorded simultaneously with discharge voltage and current. In order to identify ozone produced in the discharge the UV spectrum of the discharge was monitored and ozone identified through the characteristic Hartley Band (centred at 254nm), ozone concentrations can then be derived using the well known Beer-Lambert formula. The ozone concentration was measured as a function of Beckers’s parameter for different levels of humidity. The flow rate of the gas was maintained by mass flow controller at the level 100 cm3/min. A Glassman high voltage power supply unit was used to provide power to the discharge electrodes. The discharge current and the voltage applied to the electrodes were monitored by two multimeters and recorded by computer. The current-voltage characteristics (CV) were measured. For each voltage value the transmittance of UV light (T) was registered. The experiments were carried out at atmospheric pressure. The O2 of technical purity has been used in the experiments.

40

Fig. 1. Simplified scheme of the experimental apparatus.

Experimental results and discussion

The ozone generation in the discharge fed by pure oxygen is relatively simple two-step process. First, the diatomic oxygen is dissociated to the atomic oxygen in a dissociative electron attachment process e + O2 → O- + O. (1) The produced oxygen atom combines with oxygen molecules in a three-body process during which the ozone molecule is created and stabilized O + O2 + M → O3 + M. (2) The third body M, can be any species including a solid surfaces, such as the discharge electrode. The rate of reaction (1) depends on the reduced intensity of electric field E/N. The efficiency of reaction (2) is affected by the discharge parameters which can cause the decomposition of ozone molecules. Ozone dissociates according the reactions O3 → O2 + O (3) O + O3 → 2O2. (4)

Humidity also affects the ozone concentration, both by reacting with ozone molecules as well as by competing for the atomic oxygen radicals, thereby reducing the rate of generation. The presence of water vapour can dissociate ozone according to [9]: O + H2O →2OH* (5) OH + O3 →HO2 + O2 (6) HO2 + O3 →OH* + 2O2 (7) Where OH* is a highly unstable intermediate species.

In the Figure 2 there are dependences of ozone concentration on the Becker parameter for different water vapour concentration shown. The Becker parameter is the amount of energy put by the discharge into the gas volume and was calculated according to the formula

QP

QI.U

==η 1

where I is total discharge current, U is voltage applied on the electrodes and Q is the gas flow rate. As it is shown in Figure 2, in our measurement the minimum ozone production was at the water concentration of 3000 ppm and with increasing humidity the ozone concentration increased, which is in contradiction with experimentally and theoretically obtained results of other authors [5,9], according which the production of ozone decreases with increasing

41

humidity. Moreover, after a critical value of Becker parameter the ozone concentration begins to increase in case of all measured humidity.

0 1 2 3 4 5 6 7 8 90

1000

2000

3000

4000

5000

6000

humidity dry O2

3000 ppm 7000 ppm 11000 ppm 20000 ppm

Negative corona O2 100 cm3/min

Ozo

ne c

once

ntra

tion

[ppm

]

η [J/cm3] Fig. 2. Dependence of ozone concentration on Becker parameter in dry and humid oxygen.

In the Figure 3 there are the dependencies of discharge current on the applied voltage for

different concentrations of water vapour. As it is shown, with increasing content of water vapour the discharge current is lower at the same voltages. It seems that the electron attachment increases with the humidity.

4 5 6 7 8 90.00

0.05

0.10

0.15

0.20

0.25humidity

dry 3000 ppm 7000 ppm 11000 ppm 20000 ppm

I [m

A/c

m]

U [kV]

Negative corona O2 100 cm3/min

Fig. 3. Current-voltage characteristics for different contents of water vapour.

Conclusion

The ozone generation in negative corona discharge fed by oxygen for different contents of water vapour has been investigated. The influence of the humidity on the ozone production and decomposition was emphasized.

The finding of the other authors that ozone generation generally decreases with increasing humidity it was not confirmed. The ozone generation is most efficient in dry oxygen,

42

at water concentration of 3000 ppm the ozone concentration decreased but with additional increasing of humidity the ozone begins to increase. The reasons of this behaviour of ozone generation in discharge fed by oxygen are not clear yet. There is necessary to carry out more experiments in wide scale of humidity to understand these processes.

Acknowledgments

This research project was partially supported Slovak Grant Agency VEGA 1/4017/07, ESF projects COST P9 and EIPAM. This work was supported by Science and Technology Assistance Agency at the contract No. APVT-20-007504 and Slovak Research and Development Agency SK-UA-01906. One of the authors (J.O.) is indebted for financial support of project UK /357/2007. References

[1] J. A. Cross, Electrostatics: Principles, Problems and Applications. Bristol, U.K.: Adam Hilger, 1987.

[2] J. H. Chen and J. H. Davidson, Ozone production in the positive DC corona discharge: Model and comparison to experiments, Plasma Chem. Plasma Process., vol. 22, pp. 495-522, 2002.

[3] J. H. Chen , Ozone production in the negative DC corona: The dependence of discharge polarity, Plasma Chem. Plasma Process., vol. 23, pp. 501-518,2003.

[4] M. B. Awad and G. S. P. Castle, Ozone generation in an electrostatic precipitator with a heated corona wire, J. Air Pollut. Control Assoc., vol. 25, pp. 369-374, 1975.

[5] K. Boelter and J. H. Davidson, Ozone generation by indoor electrostatic air cleaners, Aerosol Sci. Technol., vol. 27, pp. 689-708, 1997.

[6] G. S. P. Castle, I. I. Inculet, and K. I. Burgess, Ozone generation in positive corona electrostatic precipitators, IEEE Trans. Ind. General Appl., vol. IGA-5, pp. 489-496, 1969.

[7] B. Held and R. Peyrous, A systematic parameters study from analytic calculations to optimize ozone concentration in an oxygen-fed wire-tocylinder ozonizer, Eur. Phys. J. AP, vol. 7, pp. 151-166, 1999.

[8] K. Nashimoto, The effect of electrode materials on 0; and NO, emissions by corona discharging, J. Imaging Sci., vol. 32, pp. 205-210, 1988.

3

[9] A. S. Viner, P. A. Lawless, D. S. Ensor, and L. E. Sparks, Ozone generation in DC-energized electrostatic precipitators, IEEETrans. Ind. Appl., vol. 28, no. 3, pp. 504-512, May/Jun. 1992.

[10] T. Ohkubo, S. Hamasaki, Y. Nomoto, J. S. Chang, and T. Adachi, The effect of corona wire heating on the downstream ozone concentration profiles in an air-cleaning wire-duct electrostatic precipitator, IEEE Trans. Ind. Appl., vol. 26, no. 3, pp. 542-549, May/Jun. 1990.

43

Temperature Effects in Positive Corona Discharge Fed by Oxygen

J. Országh1,2, J. D. Skalný1,2, M. Cingel1, N. J. Mason2

1Department of Experimental Physics, Comenius University,

Mlynská dolina F-2, 842 48, Bratislava, Slovakia 2Open University, Department of Physics and Astronomy, Walton Hall, Milton

Keynes MK7 6AA, United Kingdom Abstract The ozone generation in positive DC corona discharge fed by pure oxygen has been investigated. The gas was flowing through the reactor at two different gas flow rates (10 cm3/min and 100 cm3/min). The influence of discharge power on the reactor temperature and subsequent influence of reactor temperature on the ozone concentration were investigated. The ozone concentration was measured by UV spectroscopy and reactor temperature was measured by thermistor (Pt100) built into the outer reactor wall. Introduction The industrial production of ozone is one of the oldest plasma-chemical processes, since there are many technical applications of ozone e.g. sterilization of food and water. Ozone can be produced in most electrical discharges but the corona discharge has been adopted by many industries. The production of ozone in the corona discharge gap is strongly affected by the properties of the discharge. The parameters of the discharge, especially the discharge current, are influenced by the concentration of ozone produced in discharge gap. Several authors have observed a decrease in the discharge current in negative corona discharges fed by air at constant voltage on electrodes. Schwab and Zentner in 1968 [1] stated that the current was decreasing until ozone concentration reached a saturated level. The discharge current can be then 50% of the initial value. This was observed in both pulse and continuous regimes of the negative corona discharge. With increasing volume of the reactor, the saturation level was closer to the initial value and the time necessary to reach this was longer. A similar effect was observed and explained later by Černák, Skalný, Veis and Dindošová [2]. A simple mathematic model expressing the relationship between the discharge current and O3 concentration is presented in that paper. The authors claimed that the basic mechanism, responsible for the observed phenomena, is electron attachment to ozone molecule. Later experiments revealed that process is realized through a dissociative channel. The decrease of the current has been also experimentally observed by Gagarin [3]. According to Gagarin, various small primary negative ions are produced in discharge. Larger secondary ions, having smaller mobility, are formed by consecutive ion-molecule reactions from primary produced ions. In 1999 Rahel, Pavlík, Holubčík, Sobek and Skalný reported the rate constant for an electron dissociative attachment to ozone molecule calculated from the experimentally measured corona discharge current data and the ozone concentration obtained in air and N2 + O2 mixtures [4]. In present study we show the first results of the new reactor equipped by temperature measurement. That is why we are mainly concentrating on the influence of discharge power on the increase of the reactor temperature. Moreover these results are extending the results of the mentioned papers by the temperature effects on the ozone production.

Experimental apparatus The experimental apparatus is shown in Figure 1. Discharge tube containing coaxial cylindrical electrode systems (stainless steel inner electrode of diameter 125 μm and a brass outer electrode of diameter 16 mm) was used in these experiments. The active part length of the discharge tube was 6.5 cm. The Pt100 thermistor was built into the outer wall of the discharge reactor. A positive corona discharge was generated in the discharge tube. The same gas was closed in the comparative cell of the Shimadzu UV spectrometer, which was used to measure the optical transmittance of the gas contained in the discharge. The transmittance was recorded simultaneously with discharge voltage, current and Pt100 resistance. In order to identify ozone produced in the discharge the UV spectrum of the discharge was monitored and ozone identified through the characteristic Hartley Band (centred at 254 nm), ozone concentrations

44

can then be derived using the well known Beer-Lambert formula. The flow rate of the gas was maintained by mass flow controller at the level 10 cm3/min or 100 cm3/min. A Glassman high voltage power supply unit was used to provide power to the discharge electrodes. The discharge current and the voltage applied to the electrodes were monitored by two multimeters and recorded by computer. The onset voltage of corona discharge was determined by observation of a sharp rise in the discharge current (of the order of 10 μA). The current-voltage characteristics (CV) were measured. For each voltage value the transmittance of UV light (T) was registered after allowing the discharge current and thermistor resistance to stabilise and ozone concentrations determined. All the experiments were carried out at atmospheric pressure. The O2 of technical purity has been used in the experiments.

Fig. 1. Simplified scheme of the experimental apparatus. Experimental results and discussion The onset voltage of the discharge was approximately 4.8 kV ± 0.05kV. The current voltage (CV) characteristics of the discharge are shown in the Fig. 2. The influence of the gas flow rate on the CV characteristics of the discharge is negligible.

4 5 6 7 8 90.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

10 cm3/min 100 cm3/min

Dis

char

ge c

urre

nt [m

A]

Discharge voltage [kV]

Fig. 2. Current-voltage characteristics of the discharge for both gas flow rates. Basically the ozone generation in the discharge fed by pure oxygen is relatively simple two-step process. First it is necessary to decompose the oxygen molecule. In the discharge this is usually some kind of electron induced process such as electron dissociative attachment to the oxygen molecule e + O2 → O- + O k1 = f(E/N) [5] (1) The produced oxygen atom can take part in subsequent three-body process during which the ozone molecule is created and stabilized

45

O + O2 + O2 → O3 + O2 k2 = 5.5x10-31 Tg-1.2 cm6/s [6] (2)

where Tg is the gas temperature. There are several different rate coefficients for this reaction reported by other authors (see [5]) but what they have common is the decreasing rate with increasing temperature. So the ozone generation is less efficient with increasing temperature. On the other hand the rate of ozone decomposition processes such as O + O3 → O2 + O2 k3 = 1.9x10-11 exp(-2311.6/Tg) [7] (3) is slightly increasing with the temperature.

In the figure 3 there are dependences of ozone concentration on the Becker parameter shown. The Becker parameter is the amount of energy put by the discharge into the gas volume and was calculated according to the formula

QP

QI.U

==η 1

where I is total discharge current, U is voltage applied on the electrodes and Q is the gas flow rate. In lower gas flow rate the amount of produced ozone was approximately four times higher than in higher gas flow rate.

0 10 20 30 40 50 600

1000

2000

3000

4000

5000

10 cm3/min 100 cm3/min

Ozo

ne c

once

ntra

tion

[ppm

]

η [J/cm3]

Fig. 3. Dependence of ozone concentration on Becker parameter.

22 24 26 28 30 32 34 36 38 40 42 44 460

1000

2000

3000

4000

5000

10 cm3/min 100 cm3/min

Ozo

ne c

once

ntra

tion

[ppm

]

Reactor temperature [°C]

Fig. 4. Dependence of ozone concentration on reactor temperature. In the figure 4 there are the dependencies of ozone concentration on the temperature of the reactor. The ozone is decomposed mostly by heterogeneous processes on the reactor walls. With the increasing temperature these processes become more efficient. The processes of ozone generation and decomposition are competing in the discharge reactor. The maximum of

46

ozone concentration is reached at approximately 30°C (see Fig. 4.). At these temperatures the ozone decomposition starts to prevail over the ozone generation and ozone concentration is decreasing with further increase of energy put into the gas. One would expect that gas flowing thorough the tube is cooling the reactor and that is why these results should be significantly affected by the gas flow rate. Contrary to this suggestion it seems that the cooling efficiency is approximately the same for both gas flow rates because the temperatures of the reactor are similar for both cases. The power supplied by the discharge is similar for both gas flow rates (see Fig. 5). It can be deduced that energy put into the gas by the discharge is used rather for ozone generation and other elementary processes than for increasing the temperature of the gas and subsequently the temperature of the reactor.

0 1 2 3 4 5 6242628303234363840424446

10 cm3/min 100 cm3/min

Rea

ctor

tem

pera

ture

[°C

]

Discharge power [W]

Fig. 5. Comparison of reactor temperature increase for different gas flow rates and discharge polarities. Conclusion The ozone generation in the positive corona discharge fed by oxygen has been investigated. The influence of the discharge parameters on the reactor temperature and subsequent influence of the reactor temperature on the ozone decomposition were emphasized. The conclusions of other authors that ozone generation is increasing with decreasing the gas flow rate was confirmed. The ozone generation is most efficient at the temperatures around 30°C. The reactor temperature is not increasing significantly with increasing the amount of energy put into the gas. The additional energy is rather used for initiating elementary processes in the gas. Acknowledgments This research project was partially supported Slovak Grant Agency VEGA 1/4017/07, ESF projects COST P9 and EIPAM. This work was supported by Science and Technology Assistance Agency at the contract No. APVT-20-007504. One of the authors (J.O.) is indebted for financial support of project UK /357/2007. References [1] A. Schwab and R. Zentner: ETZ-A 89 (1968) 402. [2] M. Černák, J. Skalný, Š. Veis and D. Dindošová: Acta Phys. Slov. 29 (1979) 97. [3] A.G. Gagarin: in Proc. 15th International Conference on Phenomena in Ionized Gases, Part

II Minsk (Soviet Union), 1981, p. 597. [4] J. Rahel, M. Pavlik, L. Holubcik, V. Sobek and J.D. Skalny: Contrib. Plasma Phys. 39 (1999)

501. [5] Eliasson, B., Electrical discharge in oxygen: part 1. Basic data, rate coefficients and cross

sections. Report KLR 83/40 C, Brown Boveri Forschungszentrum, Baden-Dättwil, Switzerland, 1985.

[6] Cenian, A., Cherunko, A., Borodin, V.: Contrib. Plasma Phys. 35, (1995) 273. [7] Hokazono, H., Obara, M., Midorikawa, K., Tashiro, H.: J. Appl. Phys. 69 (1991) 6850.

47

Features of destruction of organic substances in plasma-liquid systems

V.Ya. Chernyak1, V.V. Yukhymenko1, V. Shapoval1, S. V.Olzhevskij1, V.P. Demchina2, V.S. Kudryavzev2 , S. Matejcik3, J.D.

Skalny3,J. Mizeraczyk4, M. Dors4, V.V. Naumov5

1Faculty of Radiophysics, Dept. of Physical Electronics, Taras ShevchenkoKyiv National University, Prospect Acad. Glushkova 2/5, Kyiv 03127, Ukraine;

e-mail: chern@univ.kiev.ua2Institute of Gas, Ukrainian Academy of Sciences, Degtyarevskaya 39, Kyiv

03113, Ukraine3Faculty of mathematics, physics and informatics, Comenius University

Bratislava, Mlynska dolina F2, 84248 Bratislava, Slovak Republic4Centre for Plasma and Laser Engineering, Szewalski Institute of Fluid Flow

Machinery, Polish Academy of Sciences, Fiszera 14, Gdansk 80-231, Poland5Institute of Fundamental Problems for High Technology, Ukrainian Academy

of Sciences, Prospect Nauki 45, Kyiv 03028, Ukraine

1. IntroductionAs is known, interest to plasma-liquid systems in plasma-chemistry first of all is connected to

an opportunity of increase of selectivity action of plasma on substance [1]. Therefore specialinterest represent weakly investigated plasma-liquid systems from the electrical discharge in thegas channel with a liquid wall (DGCLW) and plasma-liquid systems with secondary discharge(PLS SD). Feature of the first (DGCLW) is the possibility of external control of plasma-createdgas compound. Feature of the second (SD) is an opportunity of operating of energy of chargesin a zone of contact plasma - liquid. Examples of technical realization and some properties ofsuch plasma-liquid systems exploited in lab of Kiev University are presented in this paper.

2. Experimental Set-upPlasma-liquid systems of atmospheric pressure for solution treatment are shown on Fig. 1.

Fig. 1 Plasma-liquid systems of atmospheric pressure:a – plasma-liquid system with electrical discharge in the gas channel with

liquid wall; b - plasma-liquid system with secondary discharge.

Air

Outlet of gas

4

H2OInlet

89

4

7

2

6

1

5

3

Air

2

10

H2OOutlet

+(-) Us-(+)

Air

Water

-(+)Ud

+(-)

2

11

a b

48

On Fig. 1 (a) experimental set-up with electrical discharge in the gas channel with liquid wall isshown. It consists of quartz cylinder 1. Top and bottom of the cylinder were hermetically sealedby duralumin flanges 2, in which the system of electrodes was built in. Cylindrical metalelectrodes 3 were placed inside glass tubes 4. Flows of air directed into these glass tubes alongto the top and to the bottom electrodes were colliding and forming stable gas channel, whichconnects two electrodes. Air flow rate was controlled by rotameter. The liquid 6 was input to thereactor through the tube 7 built into the bottom flange. The level of liquid was kept constant byusing the system of communicating vessels. Pressure inside the reactor and communicatingvessels was maintained constant by means of tube 8 built in top flange. Tube 9 built into the topflange was used for outputting gaseous products produced during the plasma treatment ofsolution. DC source was used to supply the discharge 5, which burns inside gas channel withliquid wall. The intensive heat release occurs during discharge burning and leads to the rapidheating of the liquid and walls of the reactor. Therefore the water-cooling system was used.Cold water permanently flows through the cashing 10, which covered the quartz cylinder, andcools walls of the reactor. Flanges were cooled by water-cooling system.

On Fig. 1 (b) experimental set-up with secondary discharge is shown. The primary arcdischarge was burned between two copper electrodes (1) in the flow of air incoming through theinlet nozzle. This blowing arc served as an auxiliary discharge for a secondary (non-self-sustained) discharge with a plasma cathode when the nozzle electrode (2) was introduced intothe arc plasma. So a voltage of the secondary discharge was applied between the electrodes(1) and (2). The treatable water was supplied into the reactor through the nozzle (2). DCsources was used to supply the discharges.

3. Plasma-liquid system for fuel reformingExperimental set-up with electrical discharge in the gas channel with liquid wall (Fig. 1 (a)

was used for conversion of ethanol in synthesis – gas.The power inputs on conversion of ethanol in synthesis – gas were measured. The mass-

spectrometric and gas chromatography techniques for investigation of stable gas-phaseconversion products were used. For formation of the channel in a liquid the modes were used:with a flow of air and without a flow of air. As working liquids were used: ethanol, water and themix of ethanol with water.

The estimation of efficiency of new method of plasma conversion of ethanol by the electricdischarge in the gas channel with liquid wall and other known methods of plasma-fuelconversion was conducted on the basis of thermochemical calculations by the followingparameters: efficiency of conversion of one cubic meter of syngas and hydrogen; productivity ofconversion of syngas and hydrogen; output power of combustion of one cubic meter of syngas.These calculations were made taking into account thermochemical constants of hydrocarbonsand experimental data available in the literature. Comparison of results of our calculations (*)and experimental data are presented on Table 1.

Table 1IHMT,

Belarus[2]

ChosunUniversity,

Korea[3]

DrexelPlasma

Institute,USA[4]

MIT,USA[5]

Instituteof PlasmaPhysics,Czech

Republic[6]

KNU,Ukraine

(this work)

Initial fuelmixture

CH4 +H2O

C3H8 +CO2 +H2O

CH4 +1/2 (O2 +3.76 N2)

Diesel Biomass C2H5OH +0,22H2O +

y(O2 +3.76 N2)

Electric power,kW

2 1.37 0.5÷10* 0.2 107.7 0.1

Conversionefficiency

kWh/m3 syngas

- 2.28* 0.06 0.17* 1.41* ~1.5

Conversionefficiency,kWh/m3 H2

≤ 3 4.09* - 2.19* 1.4* -

49

Productivity H2,m3/h

0.48* 0.26* - 0.091* 28.5* -

Productivitysyngas, m3/h

- 0.60* - 1.2* 76.36* 0.1

Output syngaspower, kWh /m3

- 4.2* 2.9* 4.71* 3.02* 5.3*

4. Plasma-liquid system for destruction of organic substancesStudy of the plasma-chemical degradation of phenol and its products in water solutions after

the plasma processing was carry out on plasma-liquid reactor with a secondary discharge (Fig.1 (b).

The reference solution of 1 mM phenol was prepared by dissolving an analytical-gradephenol in distilled water of crystal quality. Other test solutions were prepared by water diluting.In addition, a small amount of iron sulfate (0.08 mM FeSO4) was added as a catalyst to enhancethe phenol decomposition.

The test solutions were processed in the plasma-liquid reactor at various operational modes:with and without secondary discharge, with positive (+) and negative (-) potentials of the«liquid» electrode in respect of the air arc plasma. The current of auxiliary discharge (I ) was400 mA. The current of secondary discharge (Id) was varied from 100 to 200 mA. Theprocessing time varied from 2 to 10 min.

The content of phenol and its products in water was analyzed by the UV optical absorptionspectrophotometry. The deuterium lamp DDC-30 and xenon flash-lamp served as the sourcesof low-dose UV and visible light radiation.

All test solutions after the treatments were incubated at room temperature for thestabilization, and their properties were monitored during several days. The UV aftertreatmentwas conducted in special quartz cuvettes.

The spectrum analysis of aqueous phenol solutions after the plasma treatment has shown thatthe efficiency of the phenol destruction during the treatment did not exceed 30% (Fig. 2). Then,during the stabilization of the test solutions and their ageing the phenol decomposition reached100%. Noticeable changes occurred during several days. The spectra of output products had amaximum at 300 nm. The phenol destruction in the secondary discharge with the «liquid»cathode is deeper than in case of the «liquid» anode. The addition of the iron sulfate catalyst inthe test solutions before the plasma treatment enhanced the phenol decomposition, especiallyin the mode with the «liquid» anode.

The spectrum analysis of plasma-treated solutions after the additional low-dose UVprocessing has shown that the dynamics of the stabilization of the test solutions depends on theinitial conditions. It has no influence on the phenol solutions with the iron sulfate additions even

Fig. 2. Optical absorption spectra of phenolsolutions in concentration of 1 mM with the0.08 mM iron sulfate additions before (curve 1)and after plasma treatment (curves 2-7) indifferent time moments: 10 min (curves 2, 3), 6days (curves 4, 5), and 12 days (curves 6, 7) fordifferent operational modes: Id =-200 mA (curves2, 4, 6) and Id =+200 mA (curves 3, 5, 7).

Fig. 3. Optical absorption spectra of aqueousphenol solutions in concentration of 1 mM withthe 0.08 mM iron sulfate addition, diluted in 6times by distilled water after the plasmatreatment and additional UV processing indifferent time moments from 5 to 285 min.

50

in case of long-term exposure. Also, the low-dose UV processing of plasma-treated solutionsdid not alter in case of a high phenol concentration (case of optically thick medium d >> k0

-1,where d is the optical path length, and k0 is the absorption at wavelength of 300 nm) thestabilization of plasma-treated solutions. But it has a strong influence on the phenol destructionin the test solutions diluted by water after the plasma treatment in case of optically thin medium(d < k r

-1). It changes not only the rate of the phenol destruction but also the spectrum of outputproducts, if it takes directly after the plasma treatment (Fig. 3). If it takes one day later after theplasma treatment, additional UV processing has no practical influence on the stabilization evenin case of diluted solutions.

Conclusion1. The composition of gas-phase products of plasma conversion and the power inputs on

conversion of ethanol into syngas in the electric discharge in the gas channel with liquid walldepend on the gas that forms the plasma.

2. The main stable gas components in the outlet of the reactor are H2, CO, CH4, C2H4,C2H6 under ethanol conversion.

3. The minimal value of power inputs in the investigated discharge is ~ 1.5 kWh/m3 ofsyngas at the output syngas power ~ 5 kWh/m3. This specifies potential possibility of newmethod.

4. The efficiency of the phenol degradation increases with the deposited discharge energy,particularly with increase of the current of a secondary discharge, and with the treatment time.

5. The properties of plasma-treated solutions are unstable in time after the treatment, andtheir stabilization lasts several days after the treatment independently of the treatment mode.The composition of final products is the same in all plasma-treated solutions.

6. The additional low-dose UV processing of plasma-treated solutions can influence on thephenol destruction in the test solutions diluted by water in case of the optically thin medium, if ittakes directly after the plasma treatment. It changes not only the rate of the phenol destructionbut also the spectrum of output products. If it takes one day later after the plasma treatment,additional UV processing has no practical influence on the stabilization of plasma-treatedsolutions.

AcknowledgmentsThis work is partially supported by the grant No. M/176-2006 of Ukrainian Ministry of Science

and Education (Ukrainian-Slovak project), grant No. 06ÁÏ05203 of Taras Shevchenko KyivNational University, grant No. 34 of Ukrainian Academy of Science (Ukrainian- Polish project).

References1. A.I. Maksimov Physical-chemical properties of plasma- solution systems and opportunity of

their technological applications. M.:Ianus-K. - Encyclopedia of low-temperature plasma. -Vol. XI – 5. – 2006. - pp. 263-309. (in Russian).

2. I.F. Buyakov, V.I. Borodin, et al. Research of conversion process of a mix ÑÍ4- Í 2 Î inplasma of the high-voltage discharge of atmospheric pressure // IVth Minsk internationalforum Heat/Mass Transfer in Chemically reacting Systems. - May, 22-26. - 2000. - V. 4. -pp. 131-137. (in Russian).

3. Young Nam Chun and Hyoung Oon Song Syngas production from propane using gliding arcplasma reforming / Environmental Engineering Science. – 2006. – V. 23, ¹ 6. – pp. 1017-1023.

4. S.K. Cheranjeev, I. Matveev, et al. Transient gliding arc for fuel ignition and combustioncontrol // Drexel Plasma Institute. - http://plasma.mem.drexel.edu/.

5. L. Bromberg, D.R. Cohn, et al. Onboard plasmatron hydrogen production for improvedvehicles // MIT Plasma Science and Fusion Center. – 2006. – 173 P.http://www.psfc.mit.edu/ library1/catalog/reports/2000/.

6. M. Hrabovsky Gasification of biomas in thermal plasma // XVIIth Symposium on Physics ofSwitching Arc. - Brno (Czech Republic). - September 10 – 13. - 2007. – 10p.

51

Sources of nonequilibrium plasma at atmospheric pressure

I. Prysyazhnevych1, V. Chernyak1, J.D. Skalný2, Š. Matejčik2, V. Yukhymenko1, S. Olszewsky1, V. Naumov3

1Physical electronics department, Radiophysical faculty, Kyiv National Taras Shevchenko University, Prospect Glushkova 2/5, Kyiv, 03022, Ukraine

2 Department of Plasma Physics, Comenius University, Mlynska dolina F-2, Bratislava 84248, Slovakia

3Photonics Lab, Institute of Fundamental Problems of High Technology, Academy of Sciences, Prospect Nauki 45, 03028 Kyiv, Ukraine

1. INTRODUCTION

Generators of non-thermal atmospheric pressure plasma, such as: gliding arc GA [1-4],

gliding arc in tornado GAT [4,5], arc in the transverse blowing gas flow (transverse arc TA) [6-8] and discharge in the gas channel with liquid walls DGCLW [9] can ensure simultaneously high plasma density and operating pressure with high level of non-equilibrium. Variation of external gasflow rate allows changing the level of nonequilibrium in such plasma systems that makes it attractive for plasmachemistry applications. They can be efficiently used for different energetic and ecology technologies: reforming of hydrocarbon fuels, plasma-assisted combustion, water and air decontamination, nanoparticles generation, etc.

This work is dedicated to the investigation of plasma properties of the TA and DGCLW at atmospheric pressure and making the comparetive analysis parameters of both discharges with other sorces on nonequilibrium atmospheric pressure plasma known from the literature.

2. EXPERIMENTAL SETUP

Arc in the transverse blowing gas flow differs from the non-stationary GA of Czernichowski

type [1-3] by the fixed arc length. It has also a convective cooling of the plasma column by the airflow but without conductive heat losses at walls since it is a free arc jet. An intensive transverse ventilation of the arc plasma increases its ionization non-equilibrium and non-izothermality. The scheme of the TA discharge in gas flow is shown on Fig. 1a.

a b

Fig.1. Experimental schemata: a− arc discharge in the transverse blowing gasflow (transverse arc TA); b− discharge in the gas channel with liquid walls (DGCLW).

The atmospheric gas flow (air or technical argon) was directed from the nozzle across two horizontal opposite electrodes and formed a bright crescent-shaped electric arc. The rod copper electrodes with diameter d=6 mm and nominal gap between them δ ≈1.5 mm were used. Axially symmetrical nozzle, with inner diameter ∅=1 mm made from stainless steel was maintained vertically perpendicular to the electrode axis at the length L = 20 mm and centred strictly between the electrodes. To regulate the airflow rate G a standard dry air system supplied with the flow meters was used. There was enough high gas-dynamic pressure in the flow to blow out

52

the electric arc downstream. The gasflow rates G=75 cm3/s and G=38 cm3/s and discharge current Id (400 mA in a case of argon flow and 480 mA in a case of airflow) were kept constant. Due to the absence of electrodes cooling, the electric discharge energy was transferred totally to the plasma flow. The arc discharge is powered by the DC source at the ballast resistance R = 2 kΩ in the circuit. Volt-ampere characteristics (VACH) of the investigated transverse arc discharge are shown on Fig. 2a.

Fig.2. a− VA CH of the TA for different rates of the air flow G: 1− G=0 cm

3/s; 2 − G=38 cm

3/s; 3 − G=75 cm

3/s;

b− VA CH of the DGCLW for d istilled water and G=110 cm3/s.

a b

Research of DGCLW was carried out in the reactor, which scema is shown on Fig. 1b and described in [9] in detail. The main advantages of this discharge are large ratio of the surface of plasma-liquid contact to the plasma volume and the possibility of external control of plasma-created gas compound, which specifies its large potential opportunities in plasmachemical applications. Reactor consists of quartz cylinder 1 which is filled by working liquid – distilled water 2. The level of liquid was kept constant by using the system of communicating vessels. Cylindrical copper electrodes 3 of 3-mm diameter were placed inside glass tubes 4 narrowed on the end with outlet of 4-mm diameter. The distance between electrodes was δ ≈10 mm. Flows of air directed into these glass tubes along to the top and to the bottom electrodes were colliding and forming stable gas channel, which connects two electrodes. Airflow rate G was controlled by rotameter. Pressure inside the reactor was maintained constant. DC source was used to supply the DGCLW. Volt-ampere characteristic of the discharge is shown on the Fig. 2b in the case of using distilled water as working liquid. Plasma parameters of DGCLW were investigated for different Id changed from 100 up to 400 mA and for a constant airflow rate G=110 cm3/s. Diagnostics of plasma parameters of both discharges was made by optical emission spectroscopy. Computer operated CCD-based spectrometer SL40-2-3648USB with spectral resolution ∼ 0,73 nm was used for spectra registration in the range of 210-1100 nm. Temperatures, which correspond to the population distribution of the excited electronic states of atoms (electronic temperature T*

e), vibration and rotational levels of molecules (vibration T*v

and rotation T*r temperatures) in investigated plasmas, were determined.

3. RESULTS

Emission spectra of TA and DGCLW plasmas are multi-component and contain 2+-system of N2 (C3Πu-B3Πg: (0-0) 337.1(0-1) 357.7, (0-2) 380.5, (1-0) 316.0 nm etc.), atomic lines H (656.3 nm, 486.1 nm, 434.05, nm), OI (777.1, 844.6, 926.6 nm), Cu I (465.1, 510.5, 515.3, 521.8, 578.2 nm), etc. Intensive UV system of OH (A2Σ-X2П: (0-0) 306.4-308.9 nm) was observed in the spectrum of plasma of the DGCLW. It was shown that population distributions of the excited electronic states of Cu, O and H atoms and of excited vibration levels of N2 molecule (2+ system) in the investigated plasma are close to Boltzmann for used regimes of both discharges. Thus, the electronic and vibrational temperatures were determined from Boltzmann plots. The rotational temperature T*

r≈0,1-0,15eV in TA was evaluated from comparing experimental data with computer simulated molecular band (1-4) of the N2 (C3Πu-B3Πg transition). The temperature dependencies are shown on Fig. 3.

53

Fig.3. Temperature dependences: a− temperature distribution along airflow z in plasma of TA (Id=480 mA, G=38 cm3/s); b− distribution temperatures in plasma of DGCLW on the discharge current Id (G=110cm3/s).

From Fig.3 can be seen, that T*

e of Cu atoms (material of electrodes) is slightly higher then T*

e of O and H atoms. Since the main ions in plasma of lowcurrent arcs are ions from electrodes material, besides the direct electron exitation the additional population of upper excited electronic states of copper atoms can occurs due to the electron-ion recombination. Thus the revealed difference between temperature values can be explained by additional electron-ion recombination mechanism of the upper excited electronic states population of copper atoms, which is almost absent for atoms of a blowing gas. Besides from Fig.3 b was seen, that obtained temperature values almost don’t depend on the Id in the used working regime of the DGCLW. It can be connected with exponencially dependence of the ionization rate on the electron’s temperature (electric field strength). Comparative analysis of plasma parameters of both investigated discharges with other sources of nonequilibrium atmospheric pressure plasma was made and main results are represented in Table 1.

Table 1. Parameters of nonequilibrium atmospheric pressure plasma sources

Type Power input, [W]

Gasflow rate, G

[cm3/s] T*

e , [eV] T*v, [eV] T*

r, [eV]

GA [3]

200-1000 (2-50) ×103 T: 0,52; NT: 0,86

T: 0,27-0,34 NT: 0,17-0,26

T: 0,2-0,34 NT: 0,07-0,18

GAT [4, 5]

90-300 (0,5-2,5) ×103 >0,9 0,17-0,34

TA [6, 7]

220-330 (0,04-0,2) ×103 in air: (Cu) 0,6 (O) 0,35; (H) 0,35

in argon: (Cu) 0,9 (O) 0,3-0,35; (H) 0,4-0,55; (Ar) 0,35-0,38

(N2) 0,35 (N2) 0,1-0,18

DGCLW 260-300 0,11 ×103 (Cu) 0,6 (O) 0,35;(H) 0,35

(N2) 0,3-0,35 (OH) 0,35-0,4

T− thermal regime of gliding arc, NT− non-thermal regime of gliding arc correspondingly [3].

4. CONCLUSIONS

1. It was shown that plasma of the TA is highly non-thermal: T*r(N2)<T*v(N2)<T*e(O, H, Ar)<T*e (Cu) and its non-thermal character varys along the gas flow.

2. Obtained T*e of blowing gas atoms (O and H) are smaller than corresponding values of Cu

atoms (material of electrodes) due to the additional electron-ion recombination mechanism of excited electronic states population of copper atoms, which is almost absent for atoms of a blowing gas.

54

3. It was shown that obtained temperature values almost don’t depend on the Id in the used working regime of the DGCLW.

4. Despite of GA and GAT both investigated in this work discharges generate nonequilibrium plasma stationary in time. It was concluded that investigated discharges are highly non-thermal due to the effective heat and mass transferring with blowing gas. Such high level of non-equilibrium in these discharges can be achieved even with gas flow rates G=40-110 cm

3/s, which are much less that were used in GA and GAT under the similar discharge

power.

Acknoledgements

This work was partially supported by Ukrainian Ministry of Education and Science Grant M/176-2006, by the Kyiv National Taras Shevchenko University Grant 06BP052-03.

References

[1] A. Czernichowski // Pure &Appl. Chem., 1994, Vol. 66, No. 6, pp. 1301-1310 [2] F. Richard, J. M. Cormier, S. Pellerin, J. Chapelle// J. Appl. Phys. 1996, Vol. 79 No.5, p.

2245-2250 [3] O. Mutaf-Yardimci, A.V. Saveliev, A.A. Fridman// J. Appl. Phys.2000, Vol. 87, 4 p. 1632. [4] C.S. Karla, A. F. Gutsol, A.A. Fridman;// IEEE Transactions on Plasma Science, 2005, Vol.

33, .1, p. 32-41 [5] C. S. Karla, I. Matveev, A. Gutsol, A. Fridman;// Elec. proc. of 2004 Technical Meeting,

Central States Section, 21-23 March 2004, Texas, A34.pdf [6] V. Chernyak, L. Kernazhitsky, V. Naumov, et al // J. Mol. Struc. 2005, 744-747, p. 871-875 [7] I.V. Prisyazhnevich, V. Ya. Chernyak, V.V. Naumov, et al //, Proc. of the conference on

Swiching Arc Phenomena, 19-22 September 2005, Lodz, Poland, p. 146-150 [8] V.Ya. Chernyak, V.V. Naumov, V.V. Yukhymenko, et al //, J. Problems of Atomic Science and

Technology. Series: Plasma Physics, 2005, Vol. 11, 2, p. 164-166. (in English) [9] V.V. Yukhymenko, V.Ya. Chernyak, V.V. Naumov, et. al // Bulletin of the University of Kiev,

Series: Physics & Mathematics, 2006, Vol. 4, p. 346-352 (in English)

55

Stark broadening to determine the electron density in plasmas

M. Jasinski1, Z. Zakrzewski2, J. Mizeraczyk1,2 1Centre for Plasma and Laser Engineering, The Szewalski Institute of Fluid-Flow Machinery, Polish Academy of Sciences, Fiszera 14, 80-952 Gdansk,

Poland 2Department of Marine Electronics, Gdynia Martime University,

Morska 83, 81-225 Gdynia, Poland

Abstract. In this paper, we present results of the spectroscopic measurements of the electron density in a microwave surface wave sustained discharges in Ar and Ne at atmospheric pressure. The discharge in the form of a plasma column was generated inside a quartz tube cooled with a dielectric liquid. The microwave power delivered to the discharge via rectangular waveguide was applied in the range of 200-1500 W. In all investigations presented in this paper, the gas flow rate was relatively low (0.5 l/min), so the plasma column was generated in the form of a single filament, and the lengths of the upstream and downstream plasma columns were almost the same. The electron density in the plasma columns was determined using the method based on the Stark

broadening of Hβ spectral line, including plasma region inside the waveguide which was not investigated earlier.

INTRODUCTION

Surface wave sustained plasmas (SWSP) find practical applications in elemental analysis, gas purification, diamond deposition, surface treatment, sterilization. All these applications require plasma sources able to work efficiently under various operating conditions. In the last decades, field applicators for such sources were developed, investigated and implemented in practice [1-3]. In the present investigations we used a surfaguide-type plasma source, based on WR 430 standard waveguide having a reduced-height section. The discharge was generated in Ar and Ne at atmospheric pressure inside a quartz tube cooled with a dielectric liquid. The discharge region consists of two plasma columns outside the waveguide and plasma region inside the waveguide. We present results of the spectroscopic measurements of the electron density in the entire discharge region. To our knowledge, no electron density measurements for the plasma region inside the waveguide (launching region) have been reported so far.

PRINCIPLES OF MEASUREMENT

In this measurement, a small amount (about 0.2 % vol.) of water vapour was added to the Ar

and Ne flow to obtain a detectable intensity of Hβ emission spectral line (486.13 nm) for the electron density measurement. The Hβ spectral line of the hydrogen Balmer series was observed in the emission spectrum due to dissociation of the water vapour in the plasma columns. We checked that the 0.2 % water vapour additive did not change the colour and length of the plasma columns. The electron density in the plasma columns was determined using the

method based on the Stark broadening of Hβ spectral line spontaneously emitted by the plasma. The profile of an emission line can be affected by different mechanisms of broadening [4]:

natural, thermal Doppler, Stark (collisional) broadening, instrumental, etc. Generally, majority of the broadening mechanisms result in the emission lines with the Gaussian profile, except for the Stark broadening, which generates the Lorentzian profile of the emission lines [4]. The convolution of the Lorentzian (Stark) and Gaussian profiles results in the so-called Voigt profile.

In this investigations, the Voigt function was fitted to the measured Hβ line profile in order to estimate the full width at half maximum (FWHM) of the Lorentzian (Stark) profile ∆λStark

(Hβ). The electron density in the plasmas was determined from FWHM using either GKS theory or

Gig-Card theory. In the GKS theory (disclosed in [5, 6]), the Stark broadening is estimated in a quasi-static

approximation using the classic Holtsmark field, resulting in the relation [4]:

ne = [109 · ∆λStark

(Hβ)/(2.5 · α1/2)]1.5 [cm

-3], (1)

where ∆λStark(Hβ) is measured in nm, and the electron density ne is expressed in cm

-3. The α1/2

parameter (fractional semi-half-width) is tabulated in [6]. The simple relation for ne obtained by

56

Goktas et al [7], for the electron temperature in the range of 1-4 eV and electron density between 10

14 and 10

18 cm

-3, is

ne = 1.09 · 1016 · [∆λStark

(Hβ)]1.458

[cm-3], (2)

where ∆λStark(Hβ) is expressed in nm.

The more recent Gig-Card theory (disclosed in [8]) incorporates the ion dynamics to evaluate the Stark broadening of lines spontaneously emitted by the plasma [4]. It results in the relation

between ∆λStark(Hβ), ne and Te as tabulated in [8]. We interpolated the values tabulated in [8],

resulting in a simple relation between ∆λStark(Hβ) and ne in the form of:

ne = 1016 · [∆λStark

(Hβ)]1.55

[cm-3], (3)

where ∆λStark(Hβ) is in nm.

EXPERIMENTAL SETUP

The main parts of the experimental setup used in this investigation were a 2.45 GHz magnetron generator, surface wave launcher of surfaguide-type, microwave power supplying and measuring system, gas supplying and flow control system, spectrograph for emission line analysis equipped with a CCD camera, and a PC computer. As an SWSP source, the surfaguide [1] based on a standard WR 430 rectangular waveguide was used (Fig. 1). The plasma was generated in the form of a plasma column in a quartz tube placed vertically across the reduced-height section of the waveguide. The quartz tube was cooled with a dielectric liquid. The metal shield placed coaxially around the quartz tube protected the personnel and instrumentation from the electromagnetic radiation. The vertical slit in the metal shield made the observation of the plasma column and performing the spectroscopic measurements possible. The circular gap in the reduced-height section of the waveguide made the performing the spectroscopic measurements possible in the wave launching region. The inner and outer diameters of the quartz discharge tube were 1 mm and 5 mm, respectively. The microwave power, up to 1500 W, was fed directly via the waveguide from the magnetron generator at one end of the surfaguide structure while the opposite end was terminated with a movable plunger.

The operating gas (with a small amount of water vapour) flowed at a rate of 0.5 l/min in the quartz tube to be ionized and form the plasma column and finally to exit directly to the ambient atmosphere. The microwave power delivered to the discharge was calculated as PI-PR, where PI and PR are the incident and reflected powers, respectively.

To measure the Hβ spectral line profile, the light emitted by the plasma column was focused onto the entrance slit of the spectrograph [DK-480 (CVI), (1200 grooves/mm)], where the emission lines were selected and then their intensities recorded with a CCD camera. The width

of the entrance slit of the spectrograph was 100 µm. Two horizontal slits (that is, in a plane perpendicular to the plasma column) were placed between the plasma column and the optical lens to collimate the light from a selected section of the plasma column, about 5 mm in height and covering the whole plasma column width.

The instrumental line profile is assumed to be nearly Gaussian. The gas temperature in the plasma column was estimated to be in the range of 1000-2500 K [9], depending on the location within the plasma column. Within this temperature interval, the corresponding Doppler widths of

Hβ spectral line is approximately between 0.010 and 0.017 nm. Hence, we can assume that the Gaussian line profile width is about 0.14 nm.

In all investigations presented in this paper the gas flow rate was relatively low (0.5 l/min), so the plasma column was generated in the form of a single filament, and the length of the upstream and downstream plasma columns were almost the same.

57

a) b)

FIGURE 1. The photographs of the surfaguide shown front view (a) and top view (b).

RESULTS

The fitting to the line profile was made using the Voigt function with a Gaussian line width of

0.14 nm. The resulting value of the FWHM of the Lorentzian (Stark) profile ∆λStark(Hβ) enabled

us to calculate the electron density using the formula (2) [GKS theory] or (3) [Gig-Card theory]. Generally, our results show that the electron density in Ar plasma column ranged from about

5 × 1014 cm-3 up to 4.5 × 1015 cm-3

, depending on absorbed microwave power (200-1500 W) and location along the plasma column. The electron density in Ne plasma column was about 2 times lower at the same conditions. The Gig-Card theory consistently gives lower (by about 20 %) values of the electron densities than the GKS theory. This behavior is in a good agreement with the observations described in [4].

Fig 2a shows electron density ne (determined using Gig-Card theory) as a function of distance z (z – distance along the upstream Ar plasma column measured from the center of the reduced-height section of the waveguide, see the circular gap in Fig. 1) in the upstream Ar plasma column for two values of microwave power (500 W and 1000 W). As seen in Fig. 2a, the

electron density decreased from about 1.5 × 1015 cm-3 to 5 × 1014 cm-3

at microwave power of

500 W and from about 2.8 × 1015 cm-3 to 5 × 1014 cm-3

at microwave power of 1500 W when increasing the distance z from 0 (center of the reduced-height section of the waveguide) to the end of the upper plasma column (z=130 mm and 225 mm). Except for a region inside the waveguide (wave launching region) and close to the waveguide, the electron density decreased approximately linearly.

Fig 2b shows electron density ne (determined using Gig-Card theory) for microwave absorbed power of 500 and 1000 W as a function of the distance l-z, where l is the length of the upstream plasma column. The distance l-z means the distance measured from the end of the upper plasma columns, so the values of l-z = 0 correspond to the end of plasma columns. Values of l-z = 220 mm and l-z = 135 mm correspond to the region inside the waveguide for microwave powers of 1000 W and 500 W, respectively.

Fig. 2b shows, that at microwave powers of 500 W and 1000 W in the range of l-z from 0 to 110 mm, the distribution of the electron densities are the same. It can means that in this range of l-z, the plasmas are almost identical at different microwave powers delivered to the discharges. This behavior of the electron density along the plasma columns at different values of microwave power is in agreement with the theory of surface wave sustained discharges.

In the region, where l-z ≅ 0 (close to the end of the plasma column), the electron densities (~5 × 1014 cm-3

) are the same at different microwave powers. It can means that this value of the

electron density (~5 × 1014 cm-3) is critical value for the sustaining the discharge.

The behavior of the electron density in the region inside the waveguide (launching region) and close to the waveguide is in a good agreement with calculated results described in [10].

CONCLUSIONS

In this paper we presented results of the spectroscopic measurements of the electron density in the surface wave sustained atmospheric-pressure Ar and Ne plasma generated by surfaguide

58

a)

0 40 80 120 160 200 2400.0

5.0x1014

1.0x1015

1.5x1015

2.0x1015

2.5x1015

3.0x1015

Waveguide region

Linear dependances

Ar, Q = 0.5 l/min

Gig-Card theory

ne [cm

-3]

Distance z [mm]

PI = 500 W

PI = 1000 W

b)

250 200 150 100 50 00.0

5.0x1014

1.0x1015

1.5x1015

2.0x1015

2.5x1015

3.0x1015

Waveguide region

Waveguide region

Ar, Q = 0.5 l/min

Gig-Card theory

ne [cm

-3]

Distance l-z [mm]

PI = 500 W

PI = 1000 W

FIGURE 2. Electron density ne in the Ar plasma columns as a function of the distance z (a) and distance l-z (b), where l is the length of the upstream plasma column and z is the distance along the upstream

plasma column measured from the center of the reduced-height section of the waveguide.

cooled with dielectric liquid.

The electron densities in the surfaguide plasma was determined by the Stark broadening method, using both the GKS and Gig-Card theories. The measured electron densities ranged around 10

15 cm

-3, depending on the discharge conditions and the location along the plasma

column. Except for a region inside the waveguide (launching region) and close to the waveguide, behavior of the electron density along the plasma columns at different values of microwave power is in agreement with the theory of surface wave sustained discharges.

Our results include the electron density in plasma generated in the reduced-height section of the waveguide (launching region), which was not measured earlier.

REFERENCES

1. M. Moisan, z. Zakrzewski, J. Phys. D: Appl. Phys. 24 No. 7, 1025-1048 (1991). 2. M. Moisan, Z. Zakrzewski, R. Etemadi, J.C Rostaing, J. Appl. Phys. 83 No. 11, 5691-5701 (1998). 3. Y. Kabouzi, M.D. Calzada, M. Moisan, K.C. Tran, C. Trassy, J. Appl. Phys. 91 No. 3, 1008-1019

(2002). 4. J. Torres, J. Jonkers, M.J. van de Sande, J.J.A.M. van der Mullen, A. Gamero, A. Sola, J. Phys. D:

Appl. Phys. 36, L55-L59 (2003). 5. H.R. Griem, A.C. Kolb, K.Y. Shen, Astrophys. J. 135, 272 (1962). 6. H.R. Griem, 1974 Academic Press New York 316. 7. H. Goktas, A. Demir, E. Hajiyev, R. Turan, A. Seyhan, G. Oke, Int. Conf. Plasma 2003 Warsaw Poland,

2003, p. 81. 8. M.A. Gigosos, V. Cardenoso, J. Phys. B: At. Mol. Opt. Phys. 29, 4795-4838 (1996). 9. M.C. Garcia, A. Rodero, A. Sola, A. Gamero, Spectrochimica Acta Part B: Atomic Spectroscopy 55,

1733-1745 (2000). 10. Y. Kabouzi, D.B. Graves, E. Castanos-Martinez, M. Moisan, Physical Review E 75/1, 016402–1-14

(2007).

59

Non-thermal plasma decomposition of volatile organic compounds – influence of ozone

S. Pekárek

Czech Technical University in Prague, FEE, Technická 2, 166 27 Prague 6 Czech Republic

1. Introduction Environment in the non-thermal plasma produced by electrical discharges in air is strongly oxidizing owing to the presence of energetic electrons and oxygen based reactive species. Electrical energy directed into the process chemistry creates highly reactive free radicals that oxidize/reduce pollutants, fragment pollutants directly, or promote excited-state chemistry. Any kind of volatile organic compounds molecule (VOC) entrained in such an environment can be oxidized according to the following scheme: VOCs + e– →O•, OH•, O3, O3

-, etc. → CO, CO2, H2O ... As it is seen from this scheme, it can be expected that decomposition efficiency of particular VOC in non-thermal plasma will depend on the production of ozone, production of ∗OH radicals and production of other active species. The VOCs such as such as toluene C6H5CH3, trichlorethane C2H3Cl3 or n-heptane CH3(CH2)5CH3 are important part of emission gases from semiconductor, paint or print industries. These VOCs must be removed from the clean-room environment. There are different technologies for decomposition of VOCs. Except of classical technologies as catalytic oxidation, thermal decomposition and carbon adsorption the non-thermal plasma technologies for these purposes are intensively studied [1]. There are several types of non-thermal plasma discharges, which have been tested for VOC decomposition [2-4] or ozone production [5]. Among them are corona discharge (DC or pulsed) and barrier discharge in a confined space. The second category includes packed-bed plasma reactors (discharge takes place among the pellets in the granulated bed) and surface and silent discharges. The corona discharge reactors involve different configurations of electrodes. The most frequent one is wire to cylinder configuration. The other configurations such as corona torch, point to plate and multi-point to plate are also used. In our experiments we chose as a representative of these VOCs the n-heptane CH3(CH2)5CH3 because it is not only a part of organic solvents but also a part of automotive and aviation fuels. It also represents a wide group of saturated hydrocarbons with single bonds; see Fig. 1.

C

C

C

C

C

C C

H H H H

H H H H H H

H

H

H

H

H

H 1

2

Fig. 1. Structure of n-heptane. The most probable reaction channels for n-heptane decomposition are shown in this figure. The first one is the dissociation of C-H bond, see (1) – an average energy per bond is 4.25 eV. The second channel involves the dissociation of C-C single bond, see (2) – an average energy per bond is 3.7 eV. The energies of electrons produced in the discharge are of this range. Subsequent chemical reactions involving products of these processes such as electrons, ions, and excited molecules lead to the formation of additional radical species and reactive molecules (O3, HO2 and H2O2). Thus the presence of n-heptane should therefore influence ozone production and on the other hand the presence of ozone will influence n-heptane decomposition. This is a reason why we performed the study of n-heptane decomposition efficiency together with the discharge ozone production. For this purpose we used hollow needle to mesh DC corona discharge enhanced by the flow of the mixture of air with n-heptane.

60

2. Experimental arrangement The experimental arrangement is shown in Fig. 2. The electrode system consisted from a hollow stainless steel needle N and a mesh M situated perpendicularly to the needle. These electrodes were situated in a discharge tube DT. The needle had an inner and outer diameter of 0.7 mm and 1.2 mm respectively. The tip of the needle was sharpened at the angle 15o (see Fig.2 upper right side). The stainless steel mesh had rhombus cells dimensions 0.60×0.50 mm and thickness 0.15 mm (see Fig.2 bottom right side). Regulated DC power supply provided voltage up to 30 kV. The needle was ballasted by a resistor R = 6.89 MΩ.

Fig. 2. Experimental arrangement, needle and the mesh. Mixture of air with n-heptane, was supplied into the needle. There were two sources from which the air was supplied. They differed by relative humidity of air. In the first case the air was supplied by a compressor through an oil separator OS. In the second case the air was supplied from a cylinder (Linde Gas, a.s.). A mass flow controller MFC adjusted the gas flow through the needle electrode. A needle valve NV controlled precise dosage of n-heptane into the air stream from a bubbler, which contained liquid n-heptane. At the output of the discharge tube, two sensors were placed to detect the temperature T and the relative humidity RH of the mixture. To determine the concentration of n-heptane before and after the treatment a FID total hydrocarbon analyzer HC 51 (measuring range 0-1300 ppm) was used. Calibration of this analyzer on n-heptane was performed using samples of different concentrations of this VOC in air in Tedlar sampling bags. Ozone concentration was measured by the absorption of the 254 nm U.V. spectral line with API 450 ozone monitor (Advanced Pollution Instrumentation, measuring range 1-1000 ppm). The experiments were performed with the flow of the mixture through the needle 1.5 slm, the distance between the tip of the needle and the mesh 12 mm and with the needle biased negatively. 3. Experimental results The n-heptane decomposition by non-thermal plasma represents rather complicated mechanism, which is at present far from being well understood. In spite of the already obtained results [6,7] the detailed study of the principal routes for the decomposition of n-heptane by non-thermal plasma is still required. To clarify the role of ozone in of n-heptane decomposition we performed the experiments in which the discharge ozone production was detected together with n-heptane decomposition efficiency. The results are presented as a function of energy density. The energy density is defined as a ratio of the power delivered to the discharge divided by the flow of the mixture through the needle. The decomposition efficiency is defined as a difference

Exhaust

mA

V

MFC

O

DC0-30 kV

M

d

R

T RH

AIR

NV

N2

n-heptane

HC-51

S

RV

DT

N

61

between the concentration of n-heptane before and after the discharge treatment, divided by the n-heptane concentration before the treatment multiplied by 100. Decomposition efficiencies and ozone concentrations versus energy density for the hollow needle to mesh discharge for relative humidity of the mixture 8 and 20 % are shown in Fig. 3 and Fig. 4 respectively.

0 100 200 300 400 500 600

0

40

80

120

0 100 200 300 400 500 600

0

10

20

30

40

Dec

omp.

effi

c. [%

] O

zone

[ppm

]

Energy density [kJ/m3]

Fig. 3. Decomposition efficiency and ozone concentration versus energy density for hollow

needle to mesh discharge. n-Heptane concentration 49 ppm. Relative humidity 8 %. As can be seen from these two figures the dependence of decomposition efficiency versus energy density can be divided into two regions:

• Low energy densities region (< 200 kJ/m3). • High energy densities region (> 200 kJ/m3.

In the low energy densities region the concentration of ozone produced by the discharge increases with increased energy density. At the point of change from low to high current region the ozone production reaches its maximum. When the energy density is only slightly increased the production of ozone sharply falls to zero. Thus it can be concluded that for higher energy densities the discharge is from the standpoint of ozone production in the state of poisoning, which means that ozone destruction processes prevail over ozone generation therefore no ozone is produced. We think that the existence of the two above-mentioned regions of dependence of decomposition efficiency on energy density could be associated with different reaction mechanisms leading to n-heptane decomposition. We can assume that for high energy densities ozone does not contribute to n-heptane decomposition and this decomposition is mainly determined by reactions involving OH radicals as well as other additional radical species and reactive molecules. Decomposition of VOCs in practical applications usually deals with the ambient air, which usually contains large amounts of water vapors. The results presented in Fig. 3 and Fig.4 show that humidity has similar effects on n-heptane decomposition efficiency and on ozone production.

0 100 200 300 400 500 600

0

40

80

120

0 100 200 300 400 500 600

0

10

20

30

40

Ozo

ne [p

pm]

Energy density [kJ/m3]

Dec

omp.

effi

c. [%

]

Fig. 4. Decomposition efficiency and ozone concentration versus energy density for hollow

needle to mesh discharge. n-Heptane concentration 49 ppm. Relative humidity 20%.

62

As for the effect of humidity on n-heptane decomposition it is seen that for relative humidity 8 % (see Fig.3) the decomposition efficiency is 37.2 % for energy density 513 kJ/ m3. On the other hand for the same energy density and for relative humidity 20% (see Fig.4) the decomposition efficiency is 31.6 %. It can be therefore concluded that that increased humidity decreases n-heptane decomposition efficiency. As for the effect of humidity on ozone production from air with n-heptane admixture it is seen that maximum ozone production for relative humidity 8 % is 133 ppm (energy density 200 kJ/m3). If the relative humidity is increased to 20% the maximum ozone production decreases to 119 ppm (energy density 193 kJ/m3). From this comparison it is seen that increased humidity decreases n-heptane decomposition. 4. Conclusions This work was focused on the study of the role of ozone produced by the hollow needle to mesh corona discharge on n-heptane decomposition efficiency. We found that ozone is involved in n-heptane decomposition for low energy densities, while for higher energy densities the discharge is practically in the state of discharge poisoning. Thus for higher energy densities the n-heptane decomposition can be probably attributed mainly to the presence of OH radicals. As far as the concentration of OH radicals depends on relative humidity, we studied also the role of humidity on n-heptane decomposition and ozone production. We found that increased humidity decreases n-heptane decomposition efficiency as well as the ozone production. Due to the fact that fundamental knowledge of the underlying chemical processes leading to VOCs decomposition is limited the detailed study of the principal routes for the decomposition of n-heptane by non-thermal plasma is still required. Acknowledgement This work was supported by the Ministry of Education, Youth and Sports of the Czech Republic (Research Plan MSM 6840770017 of the Czech Technical University in Prague). References [1] Oda T, Non-thermal plasma processing for environmental protection: decomposition of dilute VOCs in air, Journal of Electrostatics 57 (2003) 293-311. [2] Hyun-Ha Kim, Non-thermal plasma processing for air-pollution control: A historical review, current issues and future prospects, Plasma Proc. Polym. 1 (2004) 91.-110. [3] Pekárek S., Pospíšil M.and Krýsa J., Non -thermal plasma and TiO2 assisted n-Heptane decomposition, Plasma Proc. Polymers 3 (2006) 308-315. [4] Morent R., Leys C., Dewulf J., Neirynck D., Durme J.V. and Van Langenhove H., DC-excited non-thermal plasmas for VOC abatement, J. Adv. Oxid. Technol. 10 (2007) 127136. [5] J. Orsagh, G. Horváth, Š. Matejčík, J.D. Skalný, N.J. Mason, The ozone generation in positive and negative DC corona discharges fed by dry oxygen: Effect of gas flow rate, Proc. 28th Int. Conf. on Phen. in Ionized Gases, July 2007, Prague, CD-ROM 975-978. [6] Curran H.J., Galfuri P., Pitz W.J. and Westbrook C.K., A comprehensive modeling study of n-heptane oxidation, Combustion and Flame, 114 (1998) 149-177. [7] E. Marotta, A. Callea, X. Ren, M. Rea, C. Paradisi, Decomposition of hydrocarbons in air induced by different types of corona: Efficiency, products, ionic intermediates and mechanistic proposals, Proceedings of the 5th ISNTPT, La Vielle Perrotine, June 2006, France.

63

Ion mobility study of negative corona discharge in mixtures O2/N2

1M.Stano, 1,2E. Safonov, 1F. Janky, 1M. Kučera, 1M. Sabo, 2V. Y. Chernyak, 1J. D. Skalný and 1Š. Matejčík

1Department of Experimental Physics, Comenius University, Mlynska dolina F2, 842 48 Bratislava, Slovakia.

2Radiophysical Faculty, National Taras Shevchenko University, Glushkova 2, Kyiv, Ukraina.

INTRODUCTIONIon mobility spectrometry (IMS) is an ion separation method based on individual

velocities of ions as they drift in a weak electric field through an inert gas at ambient pressure. This analytical technique has a variety of applications especially for detection of trace amount of organic compounds in the air [1].

The velocity v of a drifting ion is proportional to the electric field intensity Ev = K.E (1)

where K [cm2V-1s-1] is the ion mobility. As the mobility of ions depends on temperature and pressure of the drift gas, it is usually expressed in terms of reduced mobility K0 which is the mobility of ion at standard conditions T0 = 273 K and p0 = 101 kPa.

K 0= KT 0 pT p 0

(2)

Reduced mobility is characteristic for every combination of ion and a drift gas. In present work we use IMS to study ions formed in negative corona discharge in O2. We investigate mobility of produced ions after introducing CO2, N2 and H2O into discharge.

EXPERIMENTAL SETUPThe work was carried out on a home built ion mobility spectrometer shown on figure 1. It

consists of the corona discharge ion source, reaction part and a drift tube. The corona discharge is realised in a point to plane geometry between a tungsten wire tip (wire diam. 100 μm) and a stainless steel grid. The distance between electrodes is 9 mm and voltage 3 to 5 kV. The gas flows into discharge through a port which is in proximity of the corona electrode.

Fig. 1.Schematic view of ion mobility spectrometer.

64

The ions produced in the ion source drift through reaction region of the spectrometer. The sample gas can be introduced and can react with primary ions in this region. The reaction region of the spectrometer is separated from ion source and from drift tube by appertures with 10 mm diameter. Reaction region contains also gas outlet from the whole spectrometer. Entrance of the ions into the drift tube is controlled by a shutter grid (SG) which is periodically opened for a short time 100 μs. Shutter is a Bradbury-Nielsen type, it is formed by two sets of wires placed in one plane so that every second wire is from the same group. If there is a voltage applied between the wire sets, a tranversal electrical field is formed, prohibiting ions to pass into the drift tube. SG is open when both wire sets are on the same potential. Ions are separeted according to their drift velocities in homogenic electric field along the drift tube. The drift tube lenght is 94 mm and the intensity of electric field is 324 V/cm. The ion current is measured on a collector placed in the end of drift tube. The collector is shielded by an aperture grid.

RESULTSIn the present work we have studied ions formed in negative corona discharge in

oxygen and in mixtures of oxygen with N2. The gasses were added either to corona discharger or into reaction part of the spectrometer. The separation of ions was performed in oxygen. The purity of oxygen used in this work was 5.0.

In the pure oxygen discharge we have observed production of three ions of which the ion with mobility 2.46 cm2V-1s-1 was strongly dominant. The ions with mobilities 2.28 and 2.02 cm2V-1s-1 were observed with much lower intensities. The mobility of the dominant ion is close to 2.55 which was reported for O3

- in O2 by Snuggs et al. [2]. These authors reported similar values of mobility in O2 also for CO3

- 2.50 and for CO4- 2.45 cm2V-1s-1. .

Fig. 2. Ion mobility spectrum of the negative corona discharge in pure O2 (99.999%).

The mixture of oxygen with nitrogen was added to ion source or into reaction part with concentration of N2 ranging from 2.5% to 50%. Presence of N2 in the reaction part did not result in any observable effect except of slight decrease of the dominant ion intensity. The N2 in ion source results in formation of new anionic products with mobilities 2.38 and 2.09 cm2V-1s-1. The intensity of new products is increasing with concentration of N2 and the 2.38 cm2V-1s-1 ion becomes dominant at 50% content of N2 in the gas mixture, see Fig. 3.

65

Fig. 3. Ion mobility spectrum of the negative corona discharge in O2 with addition of N2

into negative corona discharge in O2.

CONCLUSIONSWe have observed that formation of ions in negative corona discharge is strongly

influenced when nitrogen is added into negative corona discharge discharge in O2. The formation of several new anionic products has been observed in addition to that observed in pure oxygen. Formation of these new products was not observed if N2 was added to the reaction part of spectrometer where these compounds may react with ions formed in the ion source. We assume that formation of all new products is initiated by electron induced reaction in proximity of coronating electrode inside the ion source.

ACKNOWLEDGEMENT The work was supported by the Slovak grant agency APVT, project Nr. 20-007504, the

Slovak – Ukrainian project SK-UA-019-06.

REFERENCES1. G. A. Eiceman, Z. Karpas: Ion mobility spectrometry (Taylor & Francis, 2005).2. R. M. Snuggs,D. J. Voltz,J. H. Schummers, D. W. Martin, and E. W. McDaniel, Phys. Rev. A,

3, 477, (1971)

66

67

68

Experimental investigations of the barrier discharge reactor with mesh electrodes and porous dielectric

Henryka Danuta Stryczewska, Grzegorz Komarzyniec,

Ernest Gnapowski

Lublin University of Technology, Faculty of Electrical Engineering and Computer Science, Institute of Electrical Engineering and Electrotechnologies, 20-618

Lublin, 38A Nadbystrzycka Street, Poland

The non-thermal plasma generated by electrical discharges at atmospheric pressure is still the subject of science and industry interests. The dielectric barrier discharges (DBDs) are well recognized and widely used source of atmospheric pressure non-thermal plasma for technological applications [1], [2], [3], [4]. Ozone, O3, being the main product of dielectric barrier discharges in air and/or oxygen, is very strong oxidizing agent but, in contrast with fluorine or chromic acid, oxidation by ozone is much more environmentally friendly because it does not leave any toxic by-products. The main domain of ozone applications is the treatment of drinking water. Ozone not only disinfects and improves the color, taste and odor of water, but it also increase the velocity of filtration and removes non-organic and organic substances dissolved in water. Another large areas of ozone application are: utilization of wastes and sewage, disinfection and sterilization, polluted gaseous treatment. Ozone oxides and removes non-biodegenerable substances from wastes, sewage, soil and polluted gases that cannot be utilized by means of other oxidizing agents [3]. Investigations on the improvement of dielectric barrier discharge plasma reactor’s efficiency are carried out for a long time in many research centers. They are focused on application of new electrodes’ configurations, dielectric materials, reactor’s geometries and electric power supply systems. So-called volume dielectric barrier discharges take place in configuration consisted of two metal electrodes, with one or both of them covered by solid dielectric layer. Another configurations using discharges on the dielectric surface, like coplanar discharge reactors are also studied as ozone sources [5], [6]. The main disadvantage of this kind of ozone generator is necessity to supply the reactor by relatively high voltage, usually higher that 10 kV and worse controllability of ozone concentration in comparison with volume discharge reactor. Novel configurations of glow atmospheric pressure discharges, so called spatially confined discharges, in narrow channels, porous or micro-hollow structures with the presence of perforated or fibrous packing and capillary electrodes have recently been investigated intensively as a promising source of electrons and free radicals chemistry without the flow gas heating [2], [6]. In the configuration of ozone generator, proposed in the paper, the combination of volume dielectric barrier discharges, atmospheric pressure glow discharges in narrow channels of mesh electrode and fibrous dielectric as well as surface discharges on the glass fibers of the wool dielectric and back–corona discharges are expected to occur. Preliminary investigations confirm that in the investigated geometry it is possible to generate atmospheric pressure discharges with quite high intensity and at relatively low value of supply voltage of mains frequency that could be the source of energetic electrons and free radicals. Presence of the wool glass packing in the discharge gap causes an increase of power delivered to the discharge zone and the discharges intensity.

Experimental reactor Characteristics of the discharge are measured in the developed model of the reactor, that allows varying the electrode distance and the thickness of dielectric layer. Sketch of the proposed reactor is presented in Figure 1. In the presented configuration the air or oxygen is flowing through fine mesh metal electrode (#400), 2. In the experiment the second mesh electrode, 1, was covered by polyamide insulating foil, 3. Between electrodes, in the discharge gap, 4, the glass wool packing or other porous or granular dielectrics can be put. The electrodes diameter is 5 cm and the gap distance can be regulated from 1-10 mm. The transparent Teflon’s reactor housing make the observation of discharges possible.

69

Fig. 1. Scheme of the ozone generator, 1, 2 – mesh electrodes, 3 – dielectric, 4- discharge gap, 5- transparent Teflon housing, 7 - air inlet, 6 - ozone outlet, 8- magnifying glass.

Table 1. Experimental conditions

Parameter Setting used

Electrode diameter, mm 50

Discharge gap, mm 1 – 5

Dielectric thickness, mm 0.025, 0.05, 0.075

Flow rate, L·min-1 0.5 – 2

Gas pressure, atm 1

Material gas Synthetic air

Supply voltage value

and frequency 0 – 10 kV, 50 Hz

The experimental set-up consisted of 50 Hz, 230/10000 V transformer with regulated by autotransformer voltage, gas flow meter (EL-FLOW F-202AV-AAD-44-V) and its controller (E-7400-10-01-01-AAA) both produced by Bronkhorst®, as well as ozone monitor BMT 961TC. The applied voltage, discharge current and their courses were measured by a high voltage probe (P6015A) with oscilloscope Tektronix TDS 380, 400MHz, and 2GS/s. The electrical power to the discharge was measured by the voltage-charge Lissajous’s figures - signal proportional to the charge was taken from 0.51μF capacitor connected in series with reactor. Conditions of the experiments are gathered in Table 1.

Results and discussion

Discharges in the configuration with dielectric barrier usually consists of a great number of more or less uniformly distributed filaments in parallel, while atmospheric pressure glow discharges (APGD) are characterized by single current pulse per half period of the AC supply voltage [5], [7], [8]. In the plasma process of sensitive material treatment, local energy of the discharge filament can disadvantageously influence or even damage material structure due to non-uniform heat distribution at its surface. At some conditions, in the same electrode configuration with dielectric barrier, two kinds of discharges can be generated and sometimes they are called as type 1 and type 2 discharges [5]. To stabilize and make the atmospheric pressure glow discharges homogenous the three basic conditions should be satisfied: (i) the presence of solid dielectric material between discharge electrodes, (ii) the suitable kinds of dilution gases passing the discharge gap, (iii) the power supply frequency over 1 kHz [6], [8]. It is relatively easy to generate APGD in such gases like helium, neon and their mixtures, even at 50/60Hz mains frequency of power supply voltage, but in the case of air, nitrogen or argon transition the glow into filamentary discharge is usually observed. Not only the kind of gas but also the mesh electrodes’ presence facilitates generation the APGD and makes discharges more homogenous [7]. As investigations in [9] show, the discharge energy at the presence of mesh electrode is higher than for flat one and the stability of the discharge for fine mesh is much better. Also, the porous or fibrous dielectric can play similar roles to mesh electrode. The purpose of the presented investigations is to check the influence of mesh electrode together with fibrous dielectric on the possibility to generate the atmospheric pressure glow discharges in such a configuration.

70

Fig. 3. Picture of the reactor (a) and gap with the discharge (b); gap lenght - 4 mm, gas flow rate 0.5 l/min, air.

Fig. 4. Waveform of voltage and current of the discharge in the reactor with glass wool packing in air, gap lenght – 3 mm, flow rate- 1l/min.

The discharge observed in the investigated reactor (Figure 3) is like the mixture of barrier discharges and atmospheric pressure glow discharges, which homogenously fill up the gap. The surface discharges have been additionally observed in the presence of the glass wool packing. The discharge is more homogenously distributed in lesser gap. For gaps longer than 5 mm, the sparks have started to occur on the electrodes’ edges, where electric field is not uniformly distributed. Voltage and current waveforms of the discharge are presented in Figure 4 and the Lissajous figures for the reactor with and without glass wool packing are shown in the Figure 5. Figure 4 shows that the polarity of supply voltage influences the positive and negative half cycles of current’s course. That could be explained by different affect of the negative and positive charges on the fibers of the glass wool dielectric packing. The presence of glass wool packing in the discharge gap cause not only the increase of discharge intensity but also increase of power delivered to the discharge, as it can be seen in Figure 5, what is more, it is confirmed by bigger surface of the Lissajous figure. In the paper [9] the bigger surface of the Lissajous figure is also explained by the influence of resistive losses that occur due to partial discharges at the fine mesh electrode. Fig. 5. Lissajous figures for reactor without (a) and with glass wool packing (b) for air at the same conditions of gas flow rate and electrode distance (0,5l/min, gap - 2 mm, 50 Hz, 0,51F series capacitance). As it can be observed from Figure 6, presenting relationship between the discharge power per unit electrode surface and value of the supply voltage, the biggest power density equal to 3500 W/m3 is possible to be obtained in the reactor with glass wool packing in comparison with 3000 W/m3 for reactor operating without glass wool packing at the same conditions.

71

Fig. 6. Discharge power per unit electrode surface versus supply voltage for air at flow rate of 0.5l/min, 50Hz.

Fig. 7. Ozone concentration and power supply voltage for the 1mm and 2mm gaps, at gas flow equal to 2 l/min.

The ozone concentration not only depends on the value of supply voltage and gas flow rate (Figure 7) as it was expected, but also on the gap length and presence of perforated dielectric in the discharge gap. Moreover, presence of the glass wool barrier in the discharge gap would facilitate the occurrence of the so called back-corona discharges that influence the overall discharge intensity and can be effective for decomposition of gaseous pollutants, like VOC, hydrocarbons or nitrogen oxides.

Conclusions The main purpose of the investigation presented in the paper was to check a configuration of ozone generator being the combination of the DBD’s reactor with the porous or fibrous dielectric packing and with mesh electrodes, in which the plasma gas is flowing perpendicularly through the mesh and dielectric. First results show that both presence of mesh electrodes and glass wool packing influence the intensity of the discharge that occurs at lower value of supply voltage in comparison to traditional DBD’s or surface discharge electrodes’ arrangement. Courses of current and Lissajous figures confirm the role of mesh electrodes and fibrous dielectric on the discharge behavior, which is the source of non-thermal plasma being the mixture of volume dielectric barrier discharge plasma, the surface one and micro-plasmas in the mesh holes and micro-channels of the fibrous dielectric glass wool packing. Further investigations should be performed to test out the impact of mesh’s dimension, gas composition as well as the type of porous or perforated material as a packing dielectric on the discharge intensity, ozone concentration, energetic effectiveness of its production and gaseous pollutants destruction efficiency.

Literature

[1]. I. Pollo, J. Adv. Oxid. Technol. Vol. 7, No.1, 2004 [2]. K. H. Becker, U. Kogelschatz, K. H. Schoenbach and R. J. Barker (Eds.): Non-

equilibrium Air Plasmas at Atmospheric Pressure, Taylor &Francis, CRC Press, 2004 [3]. H. Stryczewska, et all, Non-thermal Plasma Based Technology for Soil Treatment,

Plasma Process.Polym, 2005, 2, 238 [4]. U. Kogelschatz, Transaction of the Institute of Fluid Flow Machinery, No. 119, 2007, 55 [5]. L. Hulka, G. J. Pietsch, Plasma Process.Polym, 2005, 2, 222 [6]. A. Bogaerts et al, Spectrochimica Acta, Part B 57, 2002, 609 [7]. S. Okazaki, M. Kogoma et al., J. Phys.D: Appl. Physics, 1994, 1985 [8]. Gherardi N, Gouda G, Gat E, Ricard A, and Massines A, Plasma Sources Sci. Technol.

vol. 9, 2000, 340 [9]. J. Tepper, P. Li and M. Lindmayer, Proc. of XIV Intern. Conference on Gas Discharges

and their Applications, Liverpool, 01.-06. Sept. 2002

72

Decomposition of organic pollutants in water induced by dielectric barrier and corona discharge above the liquid

Ester Marotta1, Milko Schiorlin1, Xianwen Ren1, Massimo Rea2,

Cristina Paradisi1

1Department of Chemical Sciences, Università di Padova, via Marzolo 1, 35131 Padova, Italy

2Department of Electrical Engineering, Università di Padova, via Gradenigo 6/A, 35131 Padova, Italy

We report here a contribution on the removal of organic pollutants in water induced by

different types of non-thermalizing discharges above the liquid. Two different corona reactors were developed and tested for this investigation, the main objective of which is the disclosure of chemical reactions involved in the organic pollutant oxidative degradation in such systems. The first is a dielectric barrier discharge (DBD) reactor composed of a glass vessel (inner dimensions 95x75x60 mm) with the base covered by a film of silver and with two parallel wires of 75 mm length fixed on a teflon cover. The second reactor is a Perspex container (inner dimensions 340x120x37 mm) with a Perspex cover supporting seven parallel wires of 300 mm length which can be energized by positive and negative DC (0-30 kV), positive and negative pulsed (DC bias 0-14 kV, peak voltage 25-35 kV, peak current 40-70 A, maximum frequency 300 Hz) and AC high voltages (0-18 kV, 50 Hz). In both reactors a flow of humidified air or nitrogen is maintained above the solution during the non-thermal plasma treatment.

Phenol was chosen as model compound because it is an important pollutant, widely used in industry and also released in the environment via hydrolysis of pesticides and other precursors. Moreover, it is generally used for testing new reactors. With both reactors and under all experimental conditions investigated, phenol is removed from the aqueous solution, its concentration decaying according to an exponential curve as a function of the energy input. The efficiency is higher for the Perspex reactor probably due to the smaller solution thickness (6 vs 10 mm) and to the better energy distribution owing to the high number of wires. As for the effect of the type of power supply used to energize this reactor, we found that negative DC was the most effective.

The effect of using tap water instead of deionized water was also investigated. Interestingly, under all conditions applied, the best efficiency was found in tap water. Preliminary results of product and reactive species analysis were obtained by means of a combination of various chemical diagnostics including HPLC-UV, HPLC-MS and HPLC-MSn, IC, FT-IR and UV, as well as some specific chemical probes for the determination of ozone, hydrogen peroxide and the OH radical. These results, which constitute a first step towards a thorough chemical characterization of the process, will be presented and briefly discussed.

73

OZONE STERILIZER WITH ULTRASONIC CAVITATION

V.S. Taran, V.V. Krasnyj, A.V. Klosovskyi, T.A. Panas’ko, O.M. Shvets, O.T. Semenova, V.I. Tereshin

IPP NSC “Kharkov Institute of Physics and Technology” 61108, Kharkov, Ukraine Practically in all areas of modern-day science and technology (microelectronics, micro system technology, instrument and machine building, biotechnology, medicine, etc.) there exists a problem of cleaning surfaces of materials from various microbiological objects. If in medicine this is different levels of disinfection and the sterilization and the basic requirements are connected with the low temperature of sterilization, the short duration of process and the high ecological cleanliness of products, then for the articles of electronic and microelectronic engineering one of the key problems is to eliminate bio-corrosion and influence of defects on nano-level (microorganisms, bacterium, viruses, spore, caps, etc.). Presently the basic methods of low temperature sterilization are: a gas method on the basis of ethylene oxide and plasma method on the basis of hydrogen peroxide However, the duration process of these methods and the cost of equipment initiated search of new more simple methods. For the aims of surface cleaning from pollution and disinfection not of high level the ultrasonic washings are used also with addition of chemical ingredients. The ozone technologies with the use barrier glow discharge are one of the promising methods and good alternative for the above mentioned methods [1,2]. In the present work ultrasonic cavitations was used with the simultaneous ozone generation. The high concentration of ozone in water solution was achieved by a two-barrier glow discharge at atmospheric pressure and cool thermo-electric module. The paper presents the results of recent experimental methods of sterilization of different types of microorganisms with the use of ozone and ultrasound [3]. The main aim was optimize the process of sterilization in water solution taking into account the following factors: necessary ozone concentration, power of ultrasonic emitter and water temperature. Sterilizer of a small size, which makes it possible to carry out the process of sterilization at low temperatures (up to 25 °C), without the application of any chemical reagents has been developed. A method of sterilization of instruments is based on operation in ozone- aqueous medium. The functional diagram and common view of sterilizer are presented in Fig. 1, 2. The working bath of sterilizer was filled up with the distilled water. Dried air is forced into the reactor of ozonizer. Generated ozone enters the main, where it is mixed up with the cooled aqueous flow and enters the bath of sterilizer. The continuous feed of water from the bath through the element of cooling into the main is carried out with the help of the anticorrosive aqueous pump. In the given diagram, the reactor of ozonizer was cooled with water. The heat was sequentially removed from the thermoelectric module.

FIGURE 1. The block diagram of the sterilizer FIGURE 2. Sterilizer

74

Ozonizers. Earlier it was carry ouied a study of ozone reactors on the basis of the barrier discharge of different configuration, which made it possible to select reactor for the application in the concrete sterilizer. Were investigated reactors with the application of dielectric coatings from the glass, the mica, the organic film, film Al2O3 and glass enamel [4, 5]. The power supply of the reactor is based on the thyristor converter circuit with the shortening of input pulses on the base of saturable throttle. The power supply scheme is presented in Fig.3.

Reactor

FIGURE 3. Power supply. FIGERE 4. Oscillograms of discharge voltage (upper lines) and current (horizontal scale: 2μs/cm)

0,2 0,4 0,6 0,8 1,00

5

10

15

20

25

30

C,g

/m3

l/min

τpul=8μs τfr=0,7μs τpul=8μs τfr=0,1μs

τpul=0,3μs τfr=0,1μs

0,1 1 10

0

10

20

30

40

1,0

2,0

3,0

4,0Y, (g/h )

l, (l/min)

Y

C

0 6637530,5

C, (

mg/

l)

0,2

FIGERE 4. Dependences of ozone concentration FIGURE 5. Characteristics of ozone (reactor with glass plates) as a function applying generation with glass enamel dielectric voltage. C – ozone concentration Y – yield rate, l – air flow rate. The reactor with flat electrodes covered with dielectric (glass-enamel ε = 12) adapted for this sterilizer. The oscillograms of discharge voltage and current are given in Fig.4. The characteristics of the reactor are shown in Fig.5. Experimental scheme allowed to perform measurements of output ozone concentration is shown in Fig.6. It consists of several blocks: spectrometer MDR-2, ozone monitor, reactor with a pulsed power supply, airflow controller, O3 destructor and CAMAC measuring system with PC [6]

FIGURE 6. Schematic diagram of the experiment. FIGURE 7. Change the temperature of water and concentration of ozone with the periodic work of ultrasonic source.

0 24 48 8418

19

20

21

22

23

T, (

oC)

C, (

mg/

l)

t, (min)

T C

8

4

2

6

00 24 48 84

18

19

20

21

22

23

T, (

oC)

C, (

mg/

l)

t, (min)

T C

8

4

2

6

0

75

Sterilizations. Combination of the factors: ozone, ultrasonic cavitation and the temperature of water made it possible to increase effectiveness with cleaning, disinfections and sterilizations of the surfaces of materials from the microbiological pollution. The conducted earlier investigations on the inactivation of the cryptogamous bacteria Basillus cereus in the aqueous solution with ozone showed their complete destruction with the concentration of 3mg/l in the time of 20 min. [3]. Analogous results were obtained under the influence on strain Basillus Stearothermophilus VKM V -718. Situation is complicated with the inactivation of the mentioned microorganisms of the objects located in the internal cavities. In this case an increase in ozone concentration to 10 mg/litr, with the rare start of ultrasonic source did not lead to the complete destruction of microorganisms. An increase in the periods of the start of ultrasonic source made it possible to conduct complete inactivation with smaller ozone concentration (Fig.7). As a result of applying the developed ozone sterilizer with ultrasonic cavitations the process of the sterilization of medical instrument will obtain the following new preferred properties: - Being the method of cold cleaning, disinfection and sterilization, it may be used for objects rather sensitive to the standard methods of high temperature sterilization; - It allows cleaning from the microbiological contaminations both outer and inner surfaces of objects; - It reduces the cost of the sterilization process; - The sterilization cycle time is reduced (total inactivation time of spore-forming bacterium’s Bacillus Series is of an order 20 min); - Ozone, used as an oxidant, is easy converted into oxygen by the ending the sterilization process; - Minimization of the power consumption for the sterilization process; - It can be used for production of gaseous ozone and ozonized water. References 1. K. Kelly-Wintenberg, Amanda Hodge, J.R. Roth, T. C. Montie et. al. J. Vac. Sci. Technology Surface and Coatings Technology, A17(4), 1999, pp. 1539 – 1544. 2. K. IsIshizaki, N. Shinriki, H. Matsuyama . J. Appl. Bacteriology. 60, 1986. pp. 67-72. 3. V.V.Krasnyj, A.V.Klosovskij,A.S, V.S.Taran et.al. Problems of Atomic Science and Technique, Series: “Plasma Physics” (13), Vol. 1, 2007, pp.188-190. 4. V.V.Krasnyj, A.V.Klosovski, Yu.N.Nezovibatko, D.P.Pogozhev, V.S.Taran, O.M.Shvets. Problems of Atomic Science and Technique, Series: “Plasma Physics” (5), Vol.3, 2000, pp.144-146. 5 V.V.Krasnyj, A.V.Klosovski, A.S. Knysh, O.M.Shvets, V.S. Taran, V.I.Tereshin, International Conference Plasma 2005 comb. With 3 rd GPPD and 5th FPSTPS, Poland, Conference Proceedings, Vol. 812, pp. 345 – 348. 6. V.V.Krasnyj, S.P.Gubarev, V.D.Kotsubanov, D.P.Pogoghev, O.M.Shvets, O.T.Semenova, V.S.Taran, V.I.Tereshin. Problems of Atomic Science and Technique, Series: “Plasma Physics” (7), Vol.4, 2002, pp.121-123.

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List of Participants

Martin Člupek Institute of Plasma Physics AS CR, v.v.i. Pulse Plasma Systems Za Slovankou 3 182 00 Praha 8, Czech Republic clupek@ipp.cas.cz

Miroslaw Dors The Szewalski Institute of Fluid Flow Machinery Centre for Plasma and Laser Engineering Fiszera 14 80-952 Gdansk, Poland mdors@imp.gda.pl

Alice Harling University of Manchester School of Chemistry Brunswick Street M13 9PL Manchester, United Kingdom alice.harling@manchester.ac.uk

Gabriel Horvath Comenius University Faculty of Mathematics, Physics and Informatics Department of Experimental Physics Mlynska dolina F-2 842 48 Bratislava, Slovakia horeszka@gmail.com

Valeriy Chernyak Kyiv National Taras Shevchenko University Radiophysical Faculty Physical Electronic Department Prospect Glushkova 2/5 03022 Kyiv, Ukraine chern@univ.kiev.ua

Mariusz Jasinski The Szewalski Institute of Fluid-Flow Machinery Centre for Plasma and Laser Engineering Fiszera 14 80-952 Gdansk, Poland mj@imp.gda.pl

Ulrich Kogelschatz ABB Corporate Research Obere Parkstr. 8 CH-5212 HausenAG, Switzerland u.kogelschatz@bluewin.ch

Frantisek Krcma Brno University of Technology Faculty of Chemistry Institute of Physical and Applied Chemistry Purkynova 118 612 00 Brno, Czech Republic krcma@fch.vutbr.cz

Milorad Kuraica University of Belgrade Faculty of Physics Studentski trg 12 11000 Belgrade, Serbia kuki@ff.bg.ac.yu

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Petr Lukes Institute of Plasma Physics AS CR, v.v.i. Department of Pulse Plasma Systems Za Slovankou 3 182 00 Prague, Czech Republic lukes@ipp.cas.cz

Ester Marotta University of Padova Department of Chemical Sciences via Marzolo 1 35131 Padova, Italy ester.marotta@unipd.it

Nigel Mason The Open University Physics and Astronomy Walton Hall MK7 6AA Milton Keynes, United Kingdom n.j.mason@open.ac.uk

Štefan Matejčík Comenius University Faculty of Mathematics, Physics and Informatics Department of Experimental Physics Mlynska dolina F-2 842 48 Bratislava, Slovakia matejcik@fmph.uniba.sk

Bratislav Obradovic University of Belgrade Faculty of Physics Studentski trg 12 11000 Belgrade, Serbia obrat@ff.bg.ac.yu

Juraj Országh Comenius University Faculty of Mathematics, Physics and Informatics Department of Experimental Physics Mlynska dolina F-2 842 48 Bratislava, Slovakia juraj.orszagh@googlemail.com

Peter Papp Comenius University Faculty of Mathematics, Physics and Informatics Department of Experimental Physics Mlynska dolina F-2 842 48 Bratislava, Slovakia papp@neon.dpp.fmph.uniba.sk

Cristina Paradisi University of Padova Department of Chemical Sciences via Marzolo 1 35131 Padova, Italy cristina.paradisi@unipd.it

Stanislav Pekarek Czech Technical University in Prague Department of Physics Technicka 2 166 27 Prague 6, Czech Republic pekarek@feld.cvut.cz

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Francisco Pontiga Universidad de Sevilla Física Aplicada II E.U.A.T., Avenida Reina Mercedes s/ 41012 Sevilla, Spain pontiga@us.es

Irina Prisyshnevich Kyiv National Taras Shevchenko University Radiophysical Faculty Physical electronic Department Prospect Glushkova, 2/5 02022 Kyiv, Ukraine priv@ukr.net

Jan Skalny Comenius University Faculty of Mathematics, Physics and Informatics Department of Experimental Physics Mlynska dolina F-2 842 48 Bratislava, Slovakia Skalny@fmph.uniba.sk

Zdenka Stara Brno University of Technology Faculty of Chemistry Institute of Physical and Applied Chemistry Purkynova 118 612 00 Brno, Czech Republic karolinka740@seznam.cz

Henryka D. Stryczewska Lublin University of Technology Institute of Electrical Engineering and Electrotechnologies Nadbystrzycka 38A 20-618 Lublin, Poland h.stryczewska@pollub.pl

Yvonne Sutton The Open University Dept of Physics and Astronomy Venables Building, Walton Hall MK7 6AA Milton Keynes, United Kingdom y.sutton@open.ac.uk

Valeriy S. Taran Institute of Plasma Physics, National Science Center Kharkov Institute of Physics and Technology Akademicheskaya St. 1 61108 Kharkov, Ukraine vtaran@ipp.kharkov.ua

David Trunec Masaryk University, Faculty of Science Department of Physical Electronics Kotlarska 2 611 37 Brno, Czech Republic trunec@physics.muni.cz

Khelifa Yanallah University Ibn khaldoun Tiaret Department of Physics Zarouraa 14000 Zarouraa, Algeria y_yanallah@mail.univ-tiaret.dz

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