Milan Hrabovsky

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

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.

Production of high quality syngas from argon/water plasma gasification of biomass and waste.

Extremely hot thermal plasma was used for the gasification of biomass (spruce sawdust, wood pellets) and waste (waste plastics, pyrolysis oil). The plasma was produced by a plasma torch with DC electric arc using unique hybrid stabilization. The torch input power of 100-110 kW and the mass flow rate of the gasified materials of tens kg/h was set up during experiments. Produced synthetic gas featured very high content of hydrogen and carbon monoxide (together approximately 90%) that is in a good agreement with theory. High quality of the produced gas is given by extreme parameters of used plasma--composition, very high temperature and low mass flow rate.

Thermal Plasma Generators with Water Stabilized Arc

Electric arc stabilized by a vortex of liquid, mostly water, is used in a special type of plasma torch for generation of thermal plasma jet with extreme plasma parameters. The paper presents analysis of properties and processes of water stabilized arcs and discusses differences from common gas stabilized arcs. Plasma torch utilizing stabilization of arc column by combination of gas flow and liquid vortex is described and its properties are presented.

Numerical Investigation of Supersonic Hybrid Argon–Water-Stabilized Arc for Biomass Gasification

This paper presents a numerical simulation of temperature and flow fields in the discharge and near outlet regions of the hybrid argon-water-stabilized electric arc. The calculations for an argon mass flow rate of 0.450 g ldr s-1 reveal the transition from a transonic plasma flow for 400 A to a supersonic one for 600 A with the maximum Mach number of 1.57. The comparison with available experimental data for 400 A shows satisfactory agreement.

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.

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.

Thermal Plasma Gasification of Biomass

Since the 1980s applications of thermal plasmas experienced an important increase. In the 1990s fundamental research led to great progress in the understanding of the basic phenomena involved, and to a renewed interest in applying thermal plasmas to material processing and waste treatment. The application of plasma torches for environmental purposes is a relatively new process. Thermal plasma offers unique capability of carrying extremely high energy by small amount of plasma and ensures high heat transfer rates to treated materials. All materials can be decomposed if they are brought into contact with plasma. Generators of thermal plasma (plasma torches) operate simultaneously as a plasmachemical and a thermal apparatus. The electrical energy of the torches goes into the plasma which transfers its energy to the substances to be treated, thereby triggering a dual simultaneous reaction process in the plasmachemical reactor: the organic compounds are thermally decomposed into their constituent elements (syngas with more complete conversion of carbon into gas phase than in incinerators), and the inorganic materials are melted and converted into a dense, inert, non-leachable vitrified slag, that does not require controlled disposal. Therefore, it can be viewed as a totally closed treatment system. While decomposition of waste and dangerous materials in thermal plasmas has been intensively studied in the last decade and industrial scale systems for treatment of various types of waste has been installed, plasma gasification of biomass is newly appearing application. For this application, the principal goal of the technology is production of fuel gases, principally mixture of carbon monoxide and hydrogen, called syngas. Thermal plasma offers possibility of decomposition of biomass by pure pyrolysis in the absence of oxygen, or with steichiometric amount of oxygen (gasification) to produce high quality syngas, with high content of carbon monoxide and hydrogen and minimum presence of other components. As production of fuel gas is the main goal of the technology, an energy balance of the process is thus much more important than in case of waste treatment, where the principal goal is material decomposition. Gasification is a process by which either a solid or liquid carbonaceous material, containing mostly chemically bound carbon, hydrogen, oxygen, is reacted with air or oxygen. The reactions provide sufficient exothermic energy to produce a primary gaseous product containing mostly CO, H2, CO2, H2O(g), and small content of higher hydrocarbons. Heat