Vladimir Kopecky

Processes and properties of electric arc stabilized by water vortex

Experimental investigation of an electric arc stabilized by a water vortex was carried out in a DC arc plasma torch for the power range 90-200 kW. Volt-ampere characteristics of the arc as well as the power balance were determined separately for the part of the arc column stabilized by water and for the remaining part between the nozzle exit and the external anode. The temperature of arc plasma close to the nozzle exit was determined by emission spectroscopy. Negatively biased electric probes in the ion collecting regime were used for determination of the plasma flow velocity. The measured temperatures up to 27000 K, and velocities up to 7 km/s are higher than the values commonly reported for plasma torches with DC arcs stabilized by a gas flow. Mass and energy balances within the arc chamber were determined from the experimental results. The radial transport of the energy by radiation was identified as a decisive process controlling the arc and plasma properties. The balance of radial energy transport was studied. The ratio of energy spent for evaporation of the water to the energy absorbed in the evaporated mass is very low in the water stabilized arc. This is the principal cause of high plasma temperatures and velocities found by the measurements.

Steam Plasma Treatment of Organic Substances for Hydrogen and Syngas Production

Gasification of several organic materials in steam plasma generated in a special plasma torch with a water-stabilized arc was investigated. Thermal plasma with very high enthalpy and low mass flow rate is produced in an arc discharge which is in direct contact with water. Biomass and several types of solid and liquid organic waste were gasified by plasma aided reactions of materials with water, carbon dioxide and oxygen. Composition of produced gas, energy balance of gasification process and gasification efficiency were determined from measured data. Synthesis gas with high content of hydrogen and carbon monoxide and very low content of carbon dioxide, light hydrocarbons and tar was obtained for all tested materials. Comparison of measured data with results of theoretical computations confirmed that steam plasma gasification produces syngas with composition which is close to the one obtained from thermodynamic equilibrium calculations.

Visualization of structure of boundary layer between thermal plasma jet and ambient air by moving electric probes

The paper describes how electric probes can be used as a relatively simple and efficient tool for investigation of structure of flow field in thermal plasma jets. A boundary between direct current (dc) arc jet and ambient air was investigated by means of array of moving probes. The process of entrainment of ambient cold gas at the jet boundary and production of separated plasma bubbles surrounded by cold gas was visualized by the applied method.

Dependence of frequency and phase velocity of plasma jet hydrodynamic instability on sound velocity

In this work detailed study of dependence of oscillation parameters of Rayleigh instability on the plasma flow property was performed by analysis of oscillations of light emitted by plasma jet. Plasma flow was generated by a water stabilized or hybrid steamargon plasma torch with an external anode. The frequency and the phase velocity of flow oscillations as well as the velocity of plasma flow and sound velocity were determined for various argon flow rates and various arc currents. The velocity of plasma flow and sound velocity were determined from the streamwise and the counter-streamwise velocity of shock waves propagation, initiated by anode breakdowns in a restrike mode of the anode attachment. It was found that the frequency and the phase velocity of studied coherent oscillations linearly depend on the sound velocity and the phase velocity is about tenth of sound velocity. This dependence is only weakly influenced directly by plasma velocity and mass flow rate.

Erosion of zirconium-based cathodes in an arc

The specific erosion rates of cathodes from Zr and ZrB2 used in the water-stabilized plasma gun PAL 50 were measured. Very good values were obtained for ZrB2, establishing this material as one of the best prospects for such cathodes. X-ray microanalysis of the cross section proved that the emitting surface of ZrB2 contained zirconium oxide.

Steam plasma methane reforming

Summary form only given. To date, methane is the most commonly adopted hydrocarbon for H2 generation. Apart from conventional processes of methane reforming, plasma processing is a new efficient technique, which can be used for converting hydrocarbons and organics into syngas. Most of published investigations on hydrocarbons plasma reforming are based on non-equilibrium, non-thermal plasmas. Comparing with that by non-thermal plasmas, the CH4 reforming by thermal plasma exhibits the significant advantages like large treatment capacity, little byproducts, and relatively high energy conversion efficiency. In this work we studied dry and steam methane reforming in steam thermal plasma with substantially higher arc power than in up now published experiments. Experiments were performed on plasma reactor PLASGAS equipped by plasma torch with a dc arc stabilized by combination of argon flow and water vortex1,2. The measuring system included monitoring of plasma torch operation parameters, temperatures in several positions inside the reactor and calorimetric measurements on cooling water loops. The composition of produced gas was measured on line by a quadruple mass spectrometer at the output of quenching chamber positioned after the reactor. The flow rate of produced syngas was determined from molar concentration of argon when defined amount of argon was introduced into the reactor. Reaction of methane with CO2 and water injected into steam plasma flow was studied for the torch power 88 to 136 kW and methane flow rates 75 to 150 slm. CO2 and water were added to reach molar ratio C/O equal 1 at the input reactants. The output H2/CO ratio could be adjusted by a choice of feed rates of input reactants in the range 1.1 to 3.4. Depending on experimental conditions the conversions of methane and carbon dioxide were 82 - 99.7% and 89 - 93%, respectively; the selectivity of CO and H2 was 87 - 99.9% and 82 - 98%, respectively; and the energy needed for production of one mole of hydrogen was 158 - 528 kJ/mol. Effect of experimental conditions on process characteristics was studied.

Powder particle penetration into steam-argon plasma jet and its relation with particle parameters

Interaction of Al2O3+3% TiO2 particles of diameter in the range 50÷63 μm with the plasma jet generated by de arc plasma torch with hybrid water-argon stabilization was experimentally studied. The plasma jet and particles in the feeding region were photographed by a fast shutter CCD-camera. At spraying distance the particle velocities, temperatures, and fluxes were measured by spray diagnostic system DPV-2000. Relationship between the particles injection parameters, the way of penetration into plasma jet, the particle flux, velocities, and temperatures were investigated at different feeding conditions as well as plasma jet properties. The distribution of temperatures and velocities in particle spray have similar character, the particle flux is influenced by carrying air flow rate and the way of injection. The feeding distance has substantial effect on particle velocity, at higher feeding distance the increase of argon flow rate does not increase particle velocity.

Properties of hybrid water/argon DC arc torch under reduced pressure

Summary form only given, as follows. Hybrid plasma torch is based on a combination of principles of classical gas-stabilized dc arc torch and water-stabilized torch. High enthalpy thermal plasma jet is generated in the torch that is utilized for plasma processing applications like plasma spraying or waste treatment. The torch was attached to the low-pressure chamber and characteristics of the torch and properties of plasma jet were investigated for the pressure range of 10 to 100 kPa. Under these slightly reduced pressures the jet remains subsonic, but both the torch characteristics and plasma jet properties axe substantially changed Pressure inside the arc chamber is reduced as a consequence of reduction of ambient pressure. The boiling point of water is thus decreased and higher evaporation rate from water vortex surrounding the arc column results in increase of an arc cooling intensity of arc column and a rate of absorption of radiation in the vapor sheath surrounding the arc. Consequently the arc voltage, arc power and plasma torch efficiency are increased. Plasma jet properties downstream of the torch nozzle exit were investigated. The fluctuations of emitted light were recorded The intensity of emitted light is substantially reduced due to pressure decrease. This is related not only to a reduction of plasma density but also to a decrease of plasma temperature due to higher evaporation rate in the arc chamber. Characteristic frequency of plasma flow fluctuations as well as phase velocity of propagation of hydrodynamic instability along the jet were substantially increased due to pressure reduction as a consequence of increase of plasma flow velocity in the jet. The results of experiments are analyzed on the basis of simple theoretical model of arc with hybrid stabilization.

Effect of radial energy transfer on characteristics of plasma torch with water-stabilized arc

Summary form only given. Plasma torches with water-stabilized arc used in the industrial scale for plasma spraying, other plasma chemistry applications like waste treatment or CVD are being investigated. The principle of the stabilization of the arc by a liquid vortex offers the possibility of generation of plasma jets with extreme plasma enthalpy and very low density. Plasma is produced by heating and ionisation of the vapor of liquid which confines the arc column. The arc characteristics and properties of generated plasma jet are strongly dependent on the radial energy transfer to the liquid. The paper analyses energy transfer in water-stabilized arc on the basis of a simple integral model. The model is based on a solution of equations describing the transfer of mass, momentum and energy between conducting, arc core, vapor sheath created due to the evaporation of the liquid wall, inner surface of the liquid vortex and the body of the vortex. Radiation energy transfer is described by empirical terms representing absorption in a vapor sheath and absorption in a layer of boiling liquid. An analysis of energy transfer balance is made on the basis of comparison of experimental results with calculations. It is shown that radiation energy transfer play a dominant role in the arc column.