16th International Conference
on Microwave and High Frequency Heating

18-21 September 2017, Delft, The Netherlands
15:45   Microwave and RF plasma applications
Chair: Marco Garuti
15:45
15 mins
MODELLING OF CO2 DISSOCIATION IN NON-EQUILIBRIUM MICROWAVE PLASMA
Sergio Moreno, Javier F. de la Fuente, Andrzej Stankiewicz, Georgios Stefanidis
Abstract: Microwave plasma reactors have the potential to enable storage of green renewable electricity into fuels and chemicals. There are, however, some challenges to overcome before this technology can be implemented in large scale industrial applications. Among others, the increase of energy efficiency and scalability of the reactors are two well-known challenges hindering the development of the technology. Purely experimental techniques have proven to be insufficient to cope with these challenges and therefore numerical models are becoming essential to get insights into the process for optimization purposes. Plasma chemistry in non-equilibrium conditions is usually the most challenging and complex component of the model due to the large number of species and reactions involved. Recently proposed reaction kinetics models for CO2 dissociation in non-equilibrium microwave plasma consider more than a hundred species and thousands of reactions. Therefore, a reduced kinetic model was developed to enable the implementation of such complex chemistry into multidimensional simulations. The reduced set captures the dissociation and vibrational kinetics in 44 reactions among 13 species. The next step in the construction of the reactor model is the implementation of energy and momentum conservation equations, along with a validation of the model with reported experimental results.
16:00
15 mins
IMPROVING CHEMICAL CONVERSION IN A SURFACE-WAVE MICROWAVE PLASMA REACTOR FOR CO2 REDUCTION WITH HYDROGEN (THE REVERSE WATER-GAS SHIFT REACTION)
Javier F. de la Fuente, Sergio H. Moreno, Andrzej Stankiewicz, Georgios Stefanidis
Abstract: A novel surface-wave microwave discharge reactor configuration to generate syngas (CO and unreacted H2) via gaseous CO2 reduction with H2 (non-catalytic Reverse Water-Gas Shift reaction) is studied in the context of power-to-chemicals concept. Improvement of CO2 conversion to maximize CO production is explored by adding an external cylindrical waveguide downstream of the plasma generation system. We show experimentally that CO2 conversion is increased by 50% (from 40% to 60%) at the stoichiometric feed ratio H2:CO2 equal to 1 when using the waveguide. At higher H2:CO2 ratios, the effect of the waveguide on the reactor performance is nearly negligible. Optical emission spectroscopy reveals that the waveguide causes significant increase in the concentration of O atoms at a ratio H2:CO2=1. The effects of the operating pressure and cooling rate are also investigated. A minimum CO2 conversion is found at 75 mbar and ratio H2:CO2 = 1, which is in the transition zone where plasma evolves from diffusive to combined operation regime. The cooling rates have significant impact on CO2 conversion, which points out the importance of carefully designing the cooling system, among other components of the process, to optimize the plasma effectiveness.
16:15
15 mins
NEW APPLICATIONS OF MICROWAVE PLASMA GENERATED AT ATMOSPHERIC PRESSURE
Ryszard Parosa, Andrzej Brożyński, Krzysztof Kowalczyk, Marek Natoński, Michał Radziwon, Piotr Zietek, Janusz Zytkiewicz
Abstract: Ryszard Parosa, Andrzej Brożyński, Krzysztof Kowalczyk, Marek Natoński, Michał Radziwon, Piotr Ziętek, Janusz Żytkiewicz PROMIS-TECH Ltd, (PROMETEUS Ltd) Wrocław, POLAND Keywords: microwave plasma, discharge cavity, plasma application Atmospheric pressure plasma excited by microwave energy has found several applications in chemistry, semiconductors technology, ozone production and many other processes. New specific applications of microwave plasma are presented: for enriching of water with nitrogen compounds and for treatment of pyrolitic gases. Enriching of water by nitrogen compounds allows to produce specific liquid nitrogen fertilizer which efficiently support fast growth of green plants - then can have an important application in agriculture. In the presented solution microwave plasma is excited inside of long quartz tube crossing rectangular waveguide and is supplied by 3 kW microwave generator (2,45 GHz). Quartz tube with plasma column inside is immersed into the tank fulfilled with water and at the bottom of tank - this tube is connected to special construction of gas bubble system. Atmospheric air is pressed by compressor, directed to the discharge cavity, and next in plasma zone air is excited and ionized. Due the specific conditions in non equilibrium plasma the nitrogen compounds like NOx and nitrogen radicals are formed. Such a modified gas formed as small bubbles flows by the water and the synthesized nitrogen compounds are dissolved into the water. Experimentally relationship between level of NOx , nitrogen radicals and pH factor was determined – what practically helps to control the process of nitrogen fertilizer production. Another solution of multi cavity microwave plasma system was developed for treatment of pyrolitic gases. In this application main goal is to “produce” long plasma column of hydrogen and hydrocarbon gases (like methane, butane etc.). Mutlicavity system contains first plasma waveguide cavity with strongly concentrated electric field density and three other waveguide cavities located along of the quartz tube. Distance between cavities is determined for different plasma gases: cavities are very close in case of hydrogen and/or hydrocarbon gases and are unfolded for nitrogen, air and noble gases plasma. Each cavity is supplied by 3 kW, 2,45 GHz microwave power supply with small ripples of microwaves. Main goal in this application is plasma decomposition of heavy hydrocarbons to hydrogen, CO and simple hydrocarbons, like methane, butane etc.
16:30
15 mins
DESIGNING OF A NOVEL RIDGED WAVEGUIDE FOR GENERATING ATMOSPHERIC MICROWAVE PLASMA
Wei Xiao, Kama Huang, Wencong Zhang
Abstract: This work presents a novel ridged waveguide used for producing atmospheric microwave plasma. Dimensions of the ridged waveguide are optimized to acquire strong electric field intensity in the discharge region. The excitation process of argon plasma is simulated here with fluid approximation method. Compared with the conventional tapered waveguide, plasma in the proposed ridged waveguide has better performance in electron density, electron temperature and gas temperature. Moreover, the energy utilization efficiency is 17.3% higher than that in the tapered waveguide at the same input microwave power.
16:45
15 mins
DEVELOPMENT OF SOLID-STATE MICROWAVE PLASMA SOURCES FOR INDUSTRIAL AND LABORATORY APPLICATIONS
K Achkasov, L Latrasse, Marilena Radoiu, J Lo, L Chauvet, C Muja, P Guillot
Abstract: Microwaves (MW) are frequently used to produce high density plasmas for industrial and laboratory applications presenting several advantages when compared to RF and DC discharges such as high reactive species density and no need for electrodes. Technological advances over the last few years calls for large-scale processing with high density and uniform plasma at reduced pressure. To meet these industrial requirements Aura-Wave [1], an electron cyclotron resonance coaxial plasma source and Hi-Wave, a collisional plasma source, have been designed. Multiple sources can be distributed together in the same reactor. Using the solid-state technology allows the sources to be self-adapted [2] on a wide range of operating conditions: gas type,pressure, MW power. Atmospheric plasma sources are widely requested in applications such as surface functionalization, elementary analysis, creation of radicals and reactive species as well as a broad use in medicine (sterilization/disinfection, treatment of chronic wounds, etc.). For these purposes, a compact plasma source S-Wave has been developed. It can operate in the range of a few 10-2 mbar to atmospheric pressure and is able to create and maintain plasma columns with variable lengths. An ignition system based on dielectric barrier discharge allows to breakdown easily even at atmospheric pressure.