O. Chumak

Properties of Hybrid Water/Gas DC Arc Plasma Torch

A new type of plasma torch with combined stabilization of electric arc by water vortex and gas flow was investigated. This hybrid water/gas stabilization offers the possibility of adjusting plasma jet parameters within a wide range from high-enthalpy low-density plasmas typical for liquid stabilized torches to lower enthalpy higher density plasmas generated in gas stabilized torches. The torch was operated at an arc power from 22 to 130 kW with an exit centerline plasma velocity from 2 to 6.5 km/s and a plasma temperature from 14 000 K to 22 000 K. Moreover, gas flow in the cathode part protects a cathode tip and thus a consumable carbon cathode used in water torches could be replaced by a fixed tungsten cathode. The characteristics of the electric arc with combined gas/water stabilization were measured and the effect of gas properties and flow rate on plasma properties and gas-dynamic flow characteristics of the plasma jet were studied for argon, and mixtures of argon with hydrogen and nitrogen

Plasma gasification of refuse derived fuel in a single-stage system using different gasifying agents.

The renewable evolution in the energy industry and the depletion of natural resources are putting pressure on the waste industry to shift towards flexible treatment technologies with efficient materials and/or energy recovery. In this context, a thermochemical conversion method of recent interest is plasma gasification, which is capable of producing syngas from a wide variety of waste streams. The produced syngas can be valorized for both energetic (heat and/or electricity) and chemical (ammonia, hydrogen or liquid hydrocarbons) end-purposes. This paper evaluates the performance of experiments on a single-stage plasma gasification system for the treatment of refuse-derived fuel (RDF) from excavated waste. A comparative analysis of the syngas characteristics and process yields was done for seven cases with different types of gasifying agents (CO2+O2, H2O, CO2+H2O and O2+H2O). The syngas compositions were compared to the thermodynamic equilibrium compositions and the performance of the single-stage plasma gasification of RDF was compared to that of similar experiments with biomass and to the performance of a two-stage plasma gasification process with RDF. The temperature range of the experiment was from 1400 to 1600 K and for all cases, a medium calorific value syngas was produced with lower heating values up to 10.9 MJ/Nm(3), low levels of tar, high levels of CO and H2 and which composition was in good agreement to the equilibrium composition. The carbon conversion efficiency ranged from 80% to 100% and maximum cold gas efficiency and mechanical gasification efficiency of respectively 56% and 95%, were registered. Overall, the treatment of RDF proved to be less performant than that of biomass in the same system. Compared to a two-stage plasma gasification system, the produced syngas from the single-stage reactor showed more favourable characteristics, while the recovery of the solid residue as a vitrified slag is an advantage of the two-stage set-up.

Experimental study of anode processes in plasma arc cutting

Anode processes taking place during pilot arc and cutting phases of plasma arc cutting (PAC) are experimentally studied. The experiments are carried out on commercial equipment so as to bring the studied conditions close to real operating conditions in application areas. The obtained results show the significant role of anode attachment in both process phases. In the pilot arc phase long residence time of the anodic spot results in electrode wear. An increase in the flow rate of the plasma medium facilitates anodic spot movement. In the cutting phase, the anode attachment significantly affects the kerf shape and surface morphology. Lack of its movement deeper inside the kerf leads to different heat transfer conditions at the top and bottom of the material and results in different surface roughness values. Facilitating the anodic spot movement towards the plate bottom is desirable to improve the cut quality.

Characterization of Plasma Jet Structure and Fluctuations by Statistic Processing of Photographic Images

A couple camera-computer provides a possibility of simple characterization and monitoring of plasma jets. This paper demonstrates another way of characterization of plasma flow structure by statistical processing of plasma jet images. The processing is based on an analysis of variations of local brightness in a sequence of images recorded by fast shutter camera. Resulting pictures show space distribution of plasma jet brightness fluctuations.

Effect of arc power and gas flow rate on properties of plasma jet under reduced pressures

DC plasma torch with argon-water stabilization of are was attached to vacuum chamber, in which pressure was varied from atmospheric down to 4kPa. Properties of the plasma jet were strongly affected by plasma generating conditions. Influence of plasma generation parameters, namely chamber pressure, are power and plasma gas flow rate on temperature and velocity profiles in plasma jet were studied. Present the measurements were performed using enthalpy probe connected to mass spectrometer. Such arrangement allows simultaneous measurement of the plasma temperature and velocity as well as composition of the plasma gas.

Digital Image Processing in Investigations of Plasma Flow Structure

This paper demonstrates the use of digital image processing for investigations of a plasma flow development. Two examples are presented. In the first, the postprocessing of shadowgraph images emphasizes objects of interest and makes the image clearer. The second processing method, based on a statistical analysis of photographs of a fluctuating jet, generates a map of fluctuation intensity in the plasma.

Multi-viewpoint imaging based simulations of sensors for APS jet monitoring

Test results are presented for different configurations of newly developed optical sensors consisting of several narrow-collimated photo detectors pointed at a plasma jet along different directions in its cross section. The sensors are capable of detecting time-variations of the position, width and asymmetry of a plasma jet. Two plasma torches with different plasma forming gas, air and argon/water vapor mixture, were used in our experiments under typical atmospheric plasma spraying (APS) conditions. The tests are based on fast, side-on imaging of the plasma jet from two or three angles (viewpoints). Reference values for the jet center coordinates, width and maximum brightness were deduced by processing the full information in the images. Next, data from small areas were processed to obtain values of the same parameters that simulate the sensor actual performance. It is commented that the accuracy of the new sensors seems reasonable for the purpose of on-line control of APS.

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.