M. Jasiński

CFC-11 destruction by microwave torch generated atmospheric-pressure nitrogen discharge

A novel plasma method and its application for destruction of Freons using a moderate-power (several hundred watts) microwave torch discharge (MTD) in atmospheric-pressure flowing nitrogen are presented. The capability of the MTD to decompose Freons is demonstrated using a chlorofluorocarbon CCl3F (Freon CFC-11) as an example. The gas flow rate and microwave power (2.45 GHz) delivered to the MTD were 1–3 litre min−1 and 200–400 W, respectively. Concentration of the CFC-11 in the nitrogen was up to 50%. The results show that the decomposition efficiency of CFC-11 is up to 100% with the removal rate of several hundred g h−1 and energy efficiency of about 1 kg kWh−1. This impressive performance, superior to that of other methods, is achieved without generating any significant unwanted by-products. As a result of this investigation, a relatively low-cost prototype system for Freon destruction based on a moderate-power MTD and a scrubber is proposed.

Hazardous gas treatment using atmospheric pressure microwave discharges

Atmospheric pressure microwave discharge methods and devices used for producing non-thermal plasmas for control of gaseous pollutants are described in this paper. The main part of the paper is concerned with microwave torch discharges (MTDs). Results of laboratory experiments on plasma abatement of several volatile organic compounds (VOCs) in their mixtures with either synthetic air or nitrogen in low (∼100 W) and moderate (200–400 W) microwave torch plasmas at atmospheric pressure are presented. Three types of MTD generators, i.e. low-power coaxial-line-based MTDs, moderate-power waveguide-based coaxial-line MTDs and moderate-power waveguide-based MTDs were used. The gas flow rate and microwave (2.45 GHz) power delivered to the discharge were in the range of 1–3 litre min −1 and 100–400 W, respectively. The concentrations of the processed gaseous pollutants were from several to several tens of per cent. The results showed that the MTD plasmas fully decomposed the VOCs at a relatively low energy cost. The energy efficiency of decomposition of several gaseous pollutants reached 1000 g (kW-h) −1 . This suggests that MTD plasmas can be useful tools for decomposition of highly concentrated VOCs. (Some figures in this article are in colour only in the electronic version)

Production of hydrogen via conversion of hydrocarbons using a microwave plasma

In this paper, results of hydrogen production from hydrocarbons in the atmospheric pressure microwave plasma are presented. As sources of hydrogen, both methane CH 4 and tetrafluoroethane C 2 H 2 F 4 were tested. A new waveguide-based nozzleless cylindertype microwave plasma source was used to convert hydrocarbons into hydrogen. The processed gaseous hydrocarbons were introduced to the plasma by four gas ducts which 2 formed a swirl flow in the plasma reactor. The absorbed microwave power was up to 5 kW. The gas flow rate was up to 212 l min -1. The hydrogen mass yield rate and the corresponding energetic hydrogen mass yield were up to 866 g[H 2 ] h -1 and 577 g [ H 2 ] per kWh of microwave energy absorbed by the plasma, respectively. These parameters are better than our previous results when nitrogen was used as a swirl gas and much better than those typical for other plasma methods of hydrogen production (electron beam, gliding arc, plasmatron).

Numerical Analysis and Optimization of Power Coupling Efficiency in Waveguide-Based Microwave Plasma Source

Three-dimensional electric field distributions in a waveguide-based microwave plasma source (MPS) have been determined numerically. Tuning characteristics of the MPS have been calculated using a direct and newly proposed two-port network method. A method for easy assessment of the quality of a set of the tuning characteristics is presented. Optimization of the plasma source has been performed using these characteristics to ensure good power coupling and stability of the plasma source operation. The calculated tuning characteristics have been compared with experimental ones. Good agreement has been found.

Hydrogen production from ethanol in nitrogen microwave plasma at atmospheric pressure

Abstract Hydrogen seems to be one of the most promising alternative energy sources. It is a renewable fuel as it could be produced from e.g. waste or bio-ethanol. Furthermore hydrogen is compatible with fuel cells and is environmentally clean. In contrast to conventional methods of hydrogen production such as water electrolysis or coal gasification we propose a method based on atmospheric pressure microwave plasma. In this paper we present results of the experimental investigations of hydrogen production from ethanol in the atmospheric pressure plasma generated in waveguide-supplied cylindrical type nozzleless microwave (2.45 GHz) plasma source (MPS). Nitrogen was used as a working gas. All experimental tests were performed with the nitrogen flow rate Q ranged from 1500 to 3900 NL h-1 and absorbed microwave power PA up to 5 kW. Ethanol was introduced into the plasma using the induction heating vaporizer. The process resulted in an ethanol conversion rate greater than 99%. The hydrogen production rate was up to 728 NL[H2] h-1 and the energy efficiency was 178 NL[H2] per kWh of absorbed microwave energy. Graphical Abstract

Liquid fuel reforming using microwave plasma at atmospheric pressure

Hydrogen is expected to be one of the most promising energy carriers. Due to the growing interest in hydrogen production technologies, in this paper we present the results of experimental investigations of thermal decomposition and dry reforming of two alcohols (ethanol and isopropanol) in the waveguide-supplied metal-cylinder-based nozzleless microwave (915 MHz) plasma source (MPS). The hydrogen production experiments were preceded by electrodynamics properties investigations of the used MPS and plasma spectroscopic diagnostics. All experimental tests were performed with the working gas (nitrogen or carbon dioxide) flow rate ranging from 1200 to 3900 normal litres per hour and an absorbed microwave power up to 5 kW. The alcohols were introduced into the plasma using an induction heating vaporizer. The ethanol thermal decomposition resulted in hydrogen selectivity up to 100%. The hydrogen production rate was up to 1150 NL(H2) h−1 and the energy yield was 267 NL(H2) kWh−1 of absorbed microwave energy. Due to intense soot production, the thermal decomposition process was not appropriate for isopropanol conversion. Considering the dry reforming process, using isopropanol was more efficient in hydrogen production than ethanol. The rate and energy yield of hydrogen production were up to 1116 NL(H2) h−1 and 223 NL(H2) kWh−1 of microwave energy used, respectively. However, the hydrogen selectivity was no greater than 37%. Selected results given by the experiment were compared with the results of numerical modeling.

Decomposition of fluorohydrocarbons in atmospheric-pressure flowing air using coaxial-line-based microwave torch plasma

Results of the investigation of decomposition of fluorohydrocarbons C2H2F4 (HFC-134a) and CHClF2 (CFC-22) in atmospheric-pressure flowing air using a coaxial-line-based microwave torch plasma are presented. Concentrations of the fluorohydrocarbons in the flowing air were up to 10 %. The decomposition efficiency of both C2H2F4 and CHClF2 was almost 100 %. This suggests the coaxial-line-based microwave torch plasma can be a useful tool for decomposition of highly-concentrated fluorohydrocarbons in air at atmospheric pressure.

Plasma Sheet Generated by Microwave Discharge at Atmospheric Pressure

In this paper, we present an argon plasma sheet produced at atmospheric pressure using a waveguide-based microwave (2.45-GHz) generator. The unique shape of the plasma sheet is very suitable for surface treatment; thus, it is attractive for industry.

Microwave Torch Plasmas for Decomposition of Gaseous Pollutants

Abstract Results of the study of decomposition of volatile organic compounds (VOCs including Freons) in their mixtures with either synthetic air or nitrogen, and nitrogen oxides NOx in their mixtures with N2 or Ar in low (~ 100 W) and moderate-power (200-400 W) microwave torch plasmas at atmospheric pressure are presented. Three types of microwave torch discharge (MTD) generators, i.e. the low-power coaxial-line-based MID, the moderate-power waveguide-based coaxial-line MTD and the moderate-power waveguide-based MTD generators were used. The gas flow rate and microwave power (2.45 GHz) delivered to the discharge were in the range of 1÷3 l/min and 100÷ 400 W, respectively. Concentrations of the processed gaseous pollutants usually were from several up to several tens percent. The energy efficiency of decomposition of several gaseous pollutants reached 1000 g/kWh. It was found that the microwave torch plasmas fully decomposed the pollutants at relatively low energy cost. This suggests that the MTD plasma can be a useful tool for decomposition of highly-concentrated gaseous pollutants.

Spectroscopic study of atmospheric pressure 915 MHz microwave plasma at high argon flow rate

In this paper results of optical emission spectroscopic (OES) study of atmospheric pressure microwave 915 MHz argon plasma are presented. The plasma was generated in microwave plasma source (MPS) cavity-resonant type. The aim of research was determination of electron excitation temperature Texc gas temperature Tg and electron number density ne. All experimental tests were performed with a gas flow rate of 100 and 200 l/min and absorbed microwave power PA from 0.25 to 0.9 kW. The emission spectra at the range of 300 – 600 nm were recorded. Boltzmann plot method for argon 5p – 4s and 5d – 4p transition lines allowed to determine Texc at level of 7000 K. Gas temperature was determined by comparing the measured and simulated spectra using LIFBASE program and by analyzing intensities of two groups of unresolved rotational lines of the OH band. Gas temperature ranged 600 – 800 K. The electron number density was determined using the method based on the Stark broadening of hydrogen Hβ line. The measured ne rang ed 2 × 1015 − 3.5×1015 cm−3, depending on the absorbed microwave power. The described MPS works very stable with various working gases at high flow rates, that makes it an attractive tool for different gas processing.