Transferred Arc Plasma Torch Research Articles

Investigations of Working Characteristics of Transferred Arc Plasma Torch Volume Reactor

A transferred arc plasma torch chemical rector was used to process waste formed from mixtures of dry clay powder and hydroquinone. Such reactors are best suited for the treatment of electrically conductive waste. In these types of reactors, the electric arc moves chaotically throughout the entire reactor volume, making it possible to ensure an even temperature distribution in the reaction zones. An analysis of the literature has shown that there are not many study results related to this type of reactor. The novelty of the work is that the behavior of the operating electric arc inside the reactor was recorded by using a high-speed camera. The distribution of the temperature profile at the cooled reactor wall was investigated. The electrical potential difference inside the reactor was also investigated. To better understand the behavioral properties of the electric arc when the reactor is filled with treated material, hydroquinone-contaminated clay was used. In this case, the movement of the electric arc, as well as the probability of its formation, is the greatest at the location where the thinnest layer of the material to be processed is located. In addition, it has been observed that the use of a graphite anode poses problems because, over time, the anode of such a design deforms due to interactions with the electric arc. While analyzing research results, it can be observed that these types of reactors are very suitable for the treatment of electrically conductive materials and for the treatment of small amounts of nonconductive materials when the material occupies a relatively small part of the reactor. A further development of these studies in the future is planned in order to make the reactors as versatile as possible and as suitable as possible for handling the widest range of materials possible.

Influence of Transferred Arc Plasma Melting Time on the Formation of Phase and Microstructure of Mullite-Zirconia Composite

Transferred arc plasma is an effective and simple technique to synthesis a high temperature reaction ceramic composite material. In this paper, 20 kW transferred arc plasma torch was used to synthesis mullite-zirconia composites through the solid-state reaction of 3:2 mole ratio of ball milled alumina and zircon powders. Dissociation of zircon in a thermal plasma arc is utilized as to prepare mullite-zirconia composites. The ball milled samples are melted for 3, 6, 9 and 12 minutes in transferred arc plasma torch at 20 kW power level with 10 lpm of argon flow rate and cooled by air. The phase and microstructure of melted samples were determined from X-ray diffraction (XRD) and SEM images. The obtained results shows that the processing time significantly influence on the formation of phase and microstructure of the mullite- zirconia composite.

Modelación de una antorcha de plasma de arco no transferido

Las antorchas de plasma se usan para producir el plasma en la manufactura de materiales e industria energética, donde las antorchas de arco de corriente directa representan los componentes principales de los procesos con plasma térmico (plasma spraying, soldadura, corte de metales, tratamiento de residuos, producción de biogás, etc.). En una antorcha de plasma de arco no trasferido, se desarrolla un arco eléctrico aplicando una corriente directa entre el cátodo y el ánodo de la antorcha. Sucesivamente, el plasma se produce calentando, ionizando y expandiendo un gas alimentado a la antorcha antes de la región del cátodo. Los trabajos de laboratorio que usan técnicas de observación y de medición son de difícil aplicación, debido a las características físicas de estos fenómenos físicos. Así las técnicas computacionales pueden representar una herramienta valiosa para investigar los procesos con plasma, aunque el trabajo computacional es extremadamente desafiante, pues estos fenómenos son interdependientes y simultáneos. En este trabajo se propone un modelo computacional para simular una antorcha de plasma bidimensional de arco no trasferido en equilibrio termodinámico local. Se modelan condiciones de estado estacionario para las ecuaciones de conservación de mecánica de fluidos, trasferencia de calor y electromagnetismo en el software Comsol Multiphysics® 5.1. En la trasferencia de calor por radiación, el plasma se asume ópticamente fino y con un coeficiente de emisión neta. El flujo laminar de gas se modela con vórtice libre en la entrada para dos tipologías de antorchas axis-simétricas, respectivamente con argón y nitrógeno como gases de trabajo.

Generalization of the Total Current–Voltage Characteristics for Transferred Arc Plasma Torch With Steam and Air Plasmas Based on the Analytical Anisotropic Model

Total current–voltage characteristics (CVCs) of a transferred arc plasma torch were determined for the case of oxidative plasma type, steam and air, by the application of the anisotropic analytical model to dc electric arc. The model takes into account the arc radiation reabsorption in the approximation of radiant thermal conductivity and is based on the power function approximation of temperature dependence on plasma electrical conductivity with different exponents along the longitudinal and transversal coordinates. The experimental data generalization for a 50-kW plasma torch was obtained in a simple form of dimensionless expression with a high statistically acceptable level. The electric resistance of arc as a generalized function ${\pi _{\rm dep}}$ is mainly affected by convection number of the energy transfer ${\pi _{\rm conv}}$ . This generalized characteristic can be used with subsequent application in the design of steam- and air-transferred arc plasma torches at a wide range of dimensionless numbers: ${\pi _{\rm dep}}$ between 90 and 932, ${\pi _{\rm conv}}$ from $5.16 \times {10^{ - 5}}$ to $1.76 \times {10^{ - 3}}$ , and the Reynolds number from 526 to 2212.

Final treatment of spent batteries by thermal plasma

The growth in the use of wireless devices, notebooks and other electronic products has led to an ever increasing demand for batteries, leading to these products being commonly found in inappropriate locations, with adverse effects on the environment and human health. Due to political pressure and according to the environmental legislation which regulates the destination of spent batteries, in several countries the application of reverse logistics to hazardous waste is required. Thus, some processes have been developed with the aim of providing an appropriate destination for these products. In this context, a method for the treatment of spent batteries using thermal plasma technology is proposed herein. The efficiency of the method was tested through the determination of parameters, such as total organic carbon, moisture content and density, as well as analysis by atomic absorption spectrometry, scanning electron microscopy and X-ray fluorescence using samples before and after inertization. The value obtained for the density was 19.15%. The TOC results indicated 8.05% of C in the batteries prior to pyrolisis and according to the XRF analysis Fe, S, Mn and Zn were the most stable elements in the samples (highest peaks). The efficiency of the paste inertization was 97% for zinc and 99.74% for manganese. The results also showed that the most efficient reactor was that with the DC transferred arc plasma torch and quartzite sand positively influenced by the vitrification during the pyrolysis of the electrolyte paste obtain from batteries.

Zircon dissociation in air plasma through a low power transferred arc plasma torch

Thermal plasma dissociation offers a convenient and attractive route to prepare zirconium oxide from zircon mineral. Transferred and non-transferred arc plasma torches have been used to study zircon dissociation. The major thrust has been to accomplish complete dissociation and make the process simpler and cost effective. Technologically, this has been attempted in argon-fired plasma reactors using higher electrical power. The present work reports a cost effective low power transferred arc plasma (TAP) processing method for dissociating zircon by using air as the plasma forming gas. Phase composition and microstructure formation of the dissociated zircon were examined by XRD and SEM with EDX. Experimental results showed that the torch input power and processing time strongly influenced the dissociation percentage as well as the microstructure formation. Further, obtained results revealed that the air plasma medium significantly improved the percentage of zircon dissociation rather than argon plasma medium at 10 and 15kW power levels. The air plasma gives complete zircon dissociation at 10kW power with 5min of processing.

Inertization of Heavy Metals Present in Galvanic Sludge by DC Thermal Plasma

Galvanic sludge results from the treatment of effluents generated by the industrial metal surface treatment of industrial material, which consists in the deposition of a metal on a surface or a metal surface attack, for example, electrodeposition of conductors (metals) and non conductive, phosphate, anodizing, oxidation and/or printed circuit. The treatment proposed here is exposure of the galvanic sludge to the high temperatures provided by thermal plasma, a process which aims to vitrify the galvanic sludge and render metals (iron, zinc, and chromium) inert. Two different plasma reactors were assembled: with a DC transferred arc plasma torch and with a DC nontransferred arc plasma torch. In this way it was possible to verify which reactor was more efficient in the inertization of the metals and also to investigate whether the addition of quartzite sand to the sludge influences the vitrification of the material. Quantification of water content and density of the galvanic raw sludge were performed, as well as analyzes of total organic carbon (TOC) and identify the elements that make up the raw sludge through spectroscopy X-ray fluorescence (XRF). The chemical composition and the form of the pyrolyzed and vitrified sludge were analyzed by scanning electron microscopy with energy-dispersive X-ray spectrometer (SEM-EDS) analysis, which it is a analysis that shows the chemical of the sample surface. The inertization of the sludge was verified in leaching tests, where the leachate was analyzed by flame atomic absorption spectroscopy (FAAS). The results of water content and density were 64.35% and 2.994 g.cm(-3), respectively. The TOC analysis determined 1.73% of C in the sample of galvanic raw sludge, and XRF analysis determined the most stable elements in the sample, and showed the highest peaks (higher stability) were Fe, Zn, and Cr. The efficiency of the sludge inertization was 100% for chromium, 99% for zinc, and 100% for iron. The results also showed that the most efficient reactor was that with the DC transferred arc plasma torch and quartzite sand positively influenced by the vitrification during the pyrolysis of the galvanic sludge.

Understanding the growth of micro and nano-crystalline AlN by thermal plasma process

We report the studies related to the growth of crystalline AlN in a DC thermal plasma reactor, operated by a transferred arc plasma torch. The reactor is capable of producing the nanoparticles of Al and AlN depending on the composition of the reacting gas. Al and AlN micro crystals are formed at the anode placed on the graphite and nano crystalline Al and AlN gets deposited on the inner surface of the plasma reactor. X-ray diffraction, Raman spectroscopy analysis, single crystal X-ray diffraction and TGA-DTA techniques are used to infer the purity of post process crystals as a hexagonal AlN. The average particle size using SEM was found to be around 30 μm. The morphology of nanoparticles of Al and AlN, nucleated by gas phase condensation in a homogeneous medium were studied by transmission electron microscopy analysis. The particle ranged in size between 15 and 80 nm in diameter. The possible growth mechanism of crystalline AlN at the anode has been explained on the basis of non-equilibrium processes in the core of the plasma and steep temperature gradient near its periphery. The gas phase species of AlN and various constituent were computed using Murphy code based on minimization of free energy. The process provides 50% yield of microcrystalline AlN and remaining of Al at anode and that of nanocrystalline h-AlN and c-Al collected from the walls of the chamber is about 33% and 67%, respectively.

Very low pressure plasma sprayed alumina and yttria-stabilized zirconia thin dense coatings using a modified transferred arc plasma torch

As a novel thermal spray process, very low pressure plasma spray (VLPPS) process has been significantly used to deposit thin, dense and homogenous ceramic coating materials for special application needs in recent years. In this study, in order to enhance low-energy plasma jet under very low pressure ambience, a home-made transferred arc nozzle was made and mounted on a low-power F100 plasma torch to fully melt or evaporate powder feedstock. As a result, thin and dense alumina (Al2O3) and yttria-stabilized zirconia (YSZ) ceramic coatings with an average thickness of 30–40μm were successfully elaborated by the VLPPS process below 1mbar. An optical emission spectroscopy (OES) was used to analyze the plasma jet properties. The microstructures of the coatings were observed by means of a scanning electron microscopy (SEM). It was found that the YSZ coatings displayed a bimodal microstructure which was composed of splats formed by melted particles and a little amount of vapor condensation from evaporated particles. However, vapor condensation could not be observed in the Al2O3 coatings, and only lamellar splats were found. The mechanical properties of both coatings were also evaluated.

Transferred arc plasma processed mullite from coal ash and bauxite

Coal ash disposal is one of the main problems in thermal power plant unit. Currently, a number of waste management systems are being tried for effective disposal of coal ash. In this paper, coal ash from thermal power plant unit was successfully utilized for synthesis of mullite ceramic by using transferred arc plasma processing (TAP) technique. For this purpose, bauxite was added with coal ash by 0, 25, 50 and75 weight ratio. The compositions were thoroughly mixed by ball milling and were melted in the transferred arc plasma torch at 10 kW input power level for 3 min. Argon was used as plasma forming gas. The phase and microstructure formation of the melted samples were investigated by XRD and SEM images. The results show that the additions of bauxite greatly influenced the phase formation of mullite during the processes.

Influence of processing variables on the formation of La 2Zr 2O 7 in transferred arc plasma torch processing

The transferred arc plasma (TAP) torch process has various noteworthy features such as extremely high temperatures, low environmental impact and short processing time which makes it the most suitable technique for synthesizing ceramic composite materials. Furthermore, it is a direct two-step technique which by its virtue of high temperature and power density paves way for high production rate. Hence in this study, an effort has been made to utilize the TAP torch processing technique for the bulk production of La 2Zr 2O 7 with time effectiveness from the mixture of La 2O 3 and ZrO 2 powders (1:2 mol ratios) which were ball milled for 4 h. For this purpose, transferred arc plasma torch was specially designed in laboratory scale level and the operating parameters were optimized in order to achieve maximum La 2Zr 2O 7 formation efficiency. In this study, the phase and microstructure formation of the processed samples was analyzed via X-ray diffraction (XRD) and scanning electron microscope (SEM) images respectively. Moreover, EDX analysis was incorporated to highlight the superior influence of the longer processing time on the stoichiometric ratio of ZrO 2/La 2O 3 in the processed sample as against input power and the gas flow rate.

3D static and time-dependent modelling of a dc transferred arc twin torch system

The transferred arc plasma torch device consists of two electrodes generating a plasma arc sustained by means of an electric current flowing through the body of the discharge. Modelling works investigating transferred electric arc discharges generated between two suspended metallic electrodes, in the so-called twin torch configuration, are scarce. The discharge generated by this particular plasma source configuration is characterized by a complex shape and fluid dynamics and needs a 3D description in order to be realistically predicted. The extended discharge length that goes from the tungsten pencil cathode to the flat copper anode without any particular confinement wall and the fluid dynamics and magnetic forces acting on the arc may induce an unsteady behaviour. In order to capture the dynamic behaviour of a twin torch discharge, a 3D time-dependent plasma arc model has been developed using a customized commercial code FLUENT form in both local thermodynamic equilibrium (LTE) and non-LTE. A two temperature (2T) model has been developed taking into account only the thermal non-equilibrium effects in argon plasma. The main differences between LTE and 2T models' results concern the increased extension of the horizontal section of the discharge and the predicted reduced (of about 60–80 V) voltage drop between the electrodes when using a 2T model.

Synthesis of mullite from sillimanite dissociation through transferred arc plasma torch

The transferred arc plasma process is characterized by extremely high temperatures, low environmental impact and short processing time. By virtue of high temperature and power density it paves the way for a high production rate. Hence an experiment was undertaken to synthesize mullite from the dissociation of sillimanite through thermal plasma processing. For this purpose, a transferred arc plasma (TAP) torch was specially designed on laboratory scale level and the operating parameters were optimized in order to achieve a maximum percentage of mullite with time and cost effectiveness. The phase and microstructure formation of the processed samples were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM) images. The obtained results clearly show that the torch input power and processing time strongly influence the mullite microstructure and phase formation. The present TAP torch processing gives maximum percentage of mullite (95%) through sillimanite dissociation at 15 kW power level with 4 min of processing time.

Plasma arc cutting technology: simulation and experiments

Transferred arc plasma torches are widely used in industrial processes for cutting of metallic materials because of their ability to cut a wide range of metals with very high productivity. The process is characterized by a transferred electric arc established between an electrode inside the torch (the cathode) and another electrode, the metallic workpiece to be cut (the anode). In order to obtain a high quality cut and a high productivity, the plasma jet must be as collimated as possible and must have the higher achievable power density. Plasma modelling and numerical simulation can be very useful tools for the designing and optimizing these devices, but research is still in the making for finding a link between simulation of the plasma arc and a consistent prevision of cut quality. Numerical modelling of the behaviour of different types of transferred arc dual gas plasma torches can give an insight on the physical reasons for the industrial success of various design and process solutions that have appeared over the last years. Diagnostics based on high speed imaging and Schlieren photography can play an important role for investigating piercing, dross generation, pilot arcing and anode attachment location. Also, the behaviour of hafnium cathodes at high current levels at the beginning of their service life can been experimentally investigated, with the final aim of understanding the phenomena that take place during those initial piercing and cutting phases and optimizing the initial shape of the surface of the emissive insert exposed to plasma atmosphere.

Twin step synthesis of mullite and mullite–zirconia composite in low power transferred arc plasma (TAP) torch

Mullite and mullite-zirconia composites were prepared in twin step through low power transferred arc plasma (TAP) torch melting followed by mechanical mixing. The mixture was based on 3:2 mole ratios of alumina and silica; alumina and zircon were ball milled and melted for 3 min in a transferred arc plasma torch at 3 kW input power with 10 lpm of argon flow rate. The phase and microstructure formation of the melted samples was investigated by XRD and SEM respectively. The crystalline behavior of the mullite and mullite–zirconia composite was evaluated by differential thermal analysis. The obtained results clearly showed that the complete mullization was achieved only in alumina–silica system and partial mullization occurred in alumina–zircon system due to the inadequate plasma torch input power.

Characterization and in vitro-bioactivity of natural hydroxyapatite based bio-glass–ceramics synthesized by thermal plasma processing

Natural bovine hydroxyapatite/SiO 2–CaO–MgO glass–ceramics were produced using the transferred arc plasma (TAP) processing method. Homogeneous mixtures of HA/25 wt% SiO 2–CaO–MgO and HA/50 wt% SiO 2–CaO–MgO batches obtained by dry mixing the respective compositions in a ball mill were processed in argon plasma using the TAP torch at 5 kW for 1, 2 and 3 min, respectively. The synthesized glass–ceramic samples were studied for phase composition, microstructure and bioactivity. The phase study of the synthesized glass–ceramics revealed the formation of calcium phosphate silicate with traces of calcium silicate. The structural study by SEM revealed that the prepared samples possessed smooth glassy surface morphology. The in vitro-bioactivity of the TAP synthesized glass–ceramics was examined in simulated body fluid (SBF). The SBF test results confirmed the development of crystalline carbonated apatite phase after 12 days of immersion. The cytocompatibility was evaluated through human fibroblast cell proliferation. The fibroblasts culture results showed that the sample was non-toxic and promoted cell growth.

Twin step synthesis of lanthanum zirconate through transferred arc plasma processing

Low power transferred arc plasma (TAP) processing is a simple and cost-effective method for large amount of ceramic processing in a very short period of time duration. In the present work, lanthanum zirconate (La2Zr2O7) was synthesized by transferred arc plasma (TAP) melting technique followed by mechanical milling. The mixture of La2O3 and ZrO2 powders with 1:2 mole ratio were ball milled for four hours and melted for three minutes in transferred arc plasma torch at 10 kW input power with 10 lpm of argon flow rate. The phase and microstructure formation of the processed samples were analyzed by X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) images.

CaO–MgO–SiO2 glass ceramics: Transferred arc plasma (TAP) synthesis and microstructural characterization

In this paper, synthesis of CaO–MgO–SiO2 glass ceramic using transferred arc plasma (TAP) processing method is illustrated. Homogeneous mixture of 51.6% SiO2, 35.6% CaO and 12.8% MgO prepared by dry mixing in a ball mill was kept in the anode well (which is the melting bed) of the 10kW transferred arc plasma torch. It was melted in plasma at an operating power of 5kW (by varying the processing time for 3, 5 and 8min). The melt was cooled to solidify by applying forced air on it. The resulting samples were characterized for microstructure and phase composition. The phases were identified by scanning electron microscopy (SEM), using the back-scattered electron (BSE) image mode and X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX). The microstructure was examined using optical microscopy (OM) and scanning electron microscopy. The micro-hardness, density and porosity measurements for the synthesized samples were carried out. Differential thermal analysis (DTA) was performed to study the thermal evolution. The results show the formation of diopside phase in the transferred arc plasma melted CaO–MgO–SiO2 glass ceramic system achieved with in a quite considerable short time of plasma processing. The method indicated that TAP technique could be a promising, time saving and one-step manufacturing process for the production of functional bulk glass ceramics.

2-D AND 3-D FLUIDYNAMIC AND PLASMA CHARACTERIZATION OF DC TRANSFERRED ARC PLASMA TORCHES FOR METAL CUTTING

2-D AND 3-D FLUIDYNAMIC AND PLASMA CHARACTERIZATION OF DC TRANSFERRED ARC PLASMA TORCHES FOR METAL CUTTING

Fluid dynamic modelling of electric arcs for industrial applications

Abstract