Arc Plasma Torch Research Articles

Selected Properties of High-Frequency Electric Arc Initiators and Stabilisation Oscillators. Part 2. Devices with Compressed Electric Arc

The second part of the overview article discusses general features of the design and operation of selected industrial arc plasma torches. Because of their structural and operating differences, plasma torch power supply systems with internal and partly external arc are discussed separately. Particular attention was paid to the design of electric systems used for the initiation of arc discharges. Because of the fact that the operation of plasma torches with partly external arc is often accompanied by the formation of double arc, the article also presents measures and methods enabling the prevention of the aforesaid unfavourable phenomenon. In addition, the article discusses selected technological properties of plasma torches and micro-plasma torches used for joining, cutting, surfacing and hardening.

Study of double-chamber air arc plasma torch and the application in solid-waste disposal

Arc plasma can be applied in hazardous solid waste disposal for higher temperature than common heating methods, but some practical issues exist in practical engineering application. In this study, an air arc plasma torch with double chambers and magnetic controlling is designed to realize wide variable power and long electrode life. The detailed characteristics and laws of the air arc are studied. The condition parameters of arc current (I), air flow rate (G) and the structure parameters of inlet area ratios and electrode diameters influence both the arc voltage and arc root positions. The arc rotating driven by magnetic field effectively lengthens the electrode life. The gasification process and product of organic wastes by air plasma are influenced largely by the waste compositions and the air flow rate. A furnace structure with more even atmosphere and longer residence time should be considered for better gasification. Oxygen-deficient environment is important to suppress NO x formation during the application of air plasma. Inorganic solid wastes can be melt by the air plasma and cooled down to form compact vitreous structures in which heavy metals can be locked and the leaching rates significantly decrease down.

Plasma chemical synthesis of W-C-Co system nano-sized powders

Parameters have been developed and experimental studies carried out for the synthesis of W-C-Co system nanopowders in a limited jet plasma reactor by interaction of tungsten oxide and cobalt with methane in hydrogen-nitrogen plasma flow generated in an electric arc plasma torch. Nanoscale powders with a specific surface area of about 25 m2/g, consisting mainly of tungsten-carbon phases and cobalt, have been produced.

Optimization of operational parameters for the analysis of metals and alloys by atomic emission spectrometry on a two-jet arc plasmatron using spark ablation

The effect of current strength, pre-batching time, frequency and duration of a discharge pulse, as well as the operational parameters of a two-jet arc plasma (TJP) torch (angle between plasma jets, gas flow) on the value of the analytical signal and standard deviation are studied. The influence of the operational parameters of spark ablation on the morphology and particle size of the resulting aerosol was studied. The optimal conditions for the analysis of steels by the method of TJP-OES with spark ablation were selected. The analytical capabilities of the method are evaluated in the analysis of steels. The limits of detection (LODs) for Cr, Cu, Mn, Mo, Ni, Si, and V during TJP-OES analysis of steels with spark ablation are in the range of n·10−5 ÷ n·10−3% wt.

Mathematical Model of Optimization of Controlled Parameters of the Plasma Surfacing Technological Process of Wear-Resistant Coatings

The dependence of the optimization parameter, which is selected as the clearance of penetration of the base metal of a restored product, is related to several factors: the plasma torch arc current, plasma torch oscillation amplitude, plasma torch displacement speed. It is studied using the methods of mathematical planning of a multifactor experiment and processing the results obtained. As a result of mathematical calculations, the regression equation is obtained in the form of a first-order polynomial characterizing the contribution of each factor to the process of the deposition of wear-resistant plasma surfacing coatings.

Experimental investigations on plasma-assisted wood pellet ignition for the start-up of biomass-fired power stations

The share of power production from biomass-fired plants in the fuel mix energy system is increasing. These plants are responsible to compensate the residual load and therefore need to provide a high level of flexibility. Plasma-assisted ignition for biomass power plants is an alternative start-up technology that offers a carbon-free start-up with high flexibility. The application of an electrical ignition system, using a plasma torch, is investigated in a 400 kW pilot-scale facility at the Institute of Combustion and Power Plant Technology at the University of Stuttgart. A DC arc plasma torch is integrated centrally in a movable block swirl burner which is to be used as a start-up burner. Milled wood pellets are considered for this study to investigate the applicability of the electrical ignition system for cold start-ups of biomass-fired power plants. An evaluation method is developed to characterize the ignition and flame status under various operational conditions. Additionally, the flame stability is evaluated by post-processing the flame images recorded by a high-speed camera. Several operational parameters, such as burner load, air ratio, and primary air flow rate are used to optimize the burner configurations for a successful ignition and a stable flame. The results showed that biomass particles can be ignited at the burner load of 25%, but a rise of 13% in the load is required to produce a stable flame cloud. The flame is formed at the burner mouth with the support of the plasma torch. Nevertheless, when the plasma system is turned off, a flame lift-off is observed in most cases. The investigation of the effect of air ratio on combustion performance highlights the importance of the available heat for the combustion reactions, which is directly related to the burner load.

Investigation of the characteristics of an electric arc plasma torch with an output step electrode

The generalized formulas are obtained in the criteria form for calculating the energy parameters and the discharge chamber of the plasmatron. The calculation results and experimental data for the thermal efficiency and current-voltage characteristics of an electric arc plasma torch with an output step electrode are presented.

Water vapor thermal plasma generation

The results of studies of an electric arc plasma torch for heating water vapor are presented. For the first time, a structural diagram of a steam-water thermal plasma generator with copper electrodes was implemented. The energy characteristics of the plasma torch and erosion of the electrodes reflect the features of their behavior during combustion in a plasma-forming medium of water vapor. The results obtained indicate the promise of the developed design of the steam-water plasmatron.

Design and characteristics of a triple-cathode cascade plasma torch for spheroidization of metallic powders

Arc plasma torch is an effective tool for spheroidization of metallic powders. However, as most conventional plasma torches were not specifically designed for plasma spheroidization, they may exhibit the disadvantages of the radial injection of powders, large fluctuations in the arc voltage, large gas flow rate, and disequilibrium between multiple plasma jets during the spheroidization process. Therefore, this paper presents a triple-cathode cascade plasma torch (TCCPT) for plasma spheroidization. Its structural design, including three cathodes, a common anode, and three sets of inter-electrodes, are detailed to ensure that powders can be inserted into the plasma jet by axial injection, the arc voltage fluctuations are easily maintained at a low level, and the plasma torches can work at a relatively small gas flow rate. Experimental results showed that the proposed TCCPT exhibits the following characteristics: (1) a relatively small arc voltage fluctuation within 5.3%; (2) a relatively high arc voltage of 75 V and low gas flow rate range of 10–30 SLM; (3) easy to be maintained at the equilibrium state with the equilibrium index of the three plasma jets within 3.5 V. Furthermore, plasma spheroidization experiments of SUS304 stainless steel powers were carried out using the proposed TCCPT. Results verified that the proposed TCCPT is applicable and effective for the spheroidization of metallic powders with wide size distribution.

Two-Temperature Chemical Non-equilibrium Modeling of Argon DC Arc Plasma Torch

A 2D two-temperature chemical non-equilibrium model has been developed to investigate the plasma characteristics inside a DC arc plasma torch of argon. In this study the chemical kinetic model is carefully examined in order to properly capture the spatial variations of plasma characteristics, especially near the electrodes and arc fringe, where large gradients of plasma parameters exist. Two different sets of chemical kinetic processes are adopted in the calculation. The first chemical kinetic model [model (a)] includes the ground-state argon atoms, excited argon 4s state, atomic ions, molecular ions, and electrons, while the second model [model (b)] only considers the ground-state argon atoms, excited argon 4s state, atomic ions, and electrons. The predicted exit temperature and arc voltage by model (a) are in better agreement with experimental measurements. A delayed anode attachment with a higher arc voltage occurs in model (a) due to the low electron density in the upstream region of arc-anode attachment. Compared with the wide arc-anode attachment zone of model (b), model (a) exhibits a more constricted anode arc root with higher current density, which leads to a higher heat flux and temperature on the anode. This phenomenon may be explained by the rapid loss of electrons outside the arc-anode attachment zone due to the dissociative recombination of argon molecular ions. Moreover, model (a) produces a longer arc column with slightly higher maximum temperature and velocity on the axis, which is caused by its larger input energy.

Numerical and Experimental Investigation on the Effects of a Nozzle Attachment to Plasma Torches for Plasma Atomization

Plasma atomization technology is able to both melt and atomize a material which is fed into the converging plasma jets as a wire. Temperature and velocity distribution in a plasma jet obtained at the outer region of a plasma torch is very important to melt a solid wire and to disintegrate the liquid metal into fine spherical particles. In this study, a non-transferred arc plasma torch is designed and numerically solved for the determination of temperature and velocity distributions in the plasma jet. A high velocity nozzle attachment is assembled to plasma torches for increasing the jet velocity for atomization purposes. Results of numerical solutions with and without high velocity nozzle attachment are discussed and compared with experimental studies. It is found that high velocity nozzle attachment can be favourable in terms of the higher velocity and temperature distribution in the plasma jet at longer distances from the torch exit.

Radiation energy losses in a single chamber three phase plasma torch with rod electrodes

The paper deals with the results of the study of the plasma energy loss in a chamber of the three phase alternating current arc plasma torch at pressures above atmospheric. It is shown that the loss due to radiation takes the main share. A time-averaged estimation of the radiation power per unit length of the arcs and its dependence on pressure was obtained based on the results of calorimetric measurements of the heat flux into the end part of the plasma torch. The dependence of the fraction of energy loss by radiation versus the total loss in the plasma torch chamber depending on the pressure and gas flow rate are presented. The dependence of the efficiency of the plasma torch versus the gas flow rate and pressure is also given. Studies were conducted on a plasma torch over the power range from 50 to 200 kW. The working gas was nitrogen.

Spheroidization of Fe-Based Powders in Plasma Jet of DC Arc Plasma Torch and Application of These Powders in Selective Laser Melting

Spheroidization of Fe and steel powders in a plasma stream of an DC arc plasma torch is investigated. The possibility of obtaining a product with a spherical particle content of up to 100% is established. The fluidity of the best samples of obtained powder is 13–20 s with a fluidity of the feedstock of 39 s. The bulk density of the initial powder (3.05 g/cm3) during the plasma treatment increases to 4.1–4.4 g/cm3. The nanofraction content in spheroidized powders varied from 0 to 75 wt % and it depends mainly on the enthalpy of the plasma stream, consumption of raw materials, and the organization of the flow of the plasma-forming gas in the discharge channel of the plasma torch. It is established that Fe powders spheroidized in plasma can be used in selective laser melting technology to obtain compact samples whose density reaches 7.86 g/cm3.

Electroplasma Installation for Gasification of Organic Wastes with Obtaining a Fuel Gas

A plasma electrical installation for gasification of various organic wastes has been developed. Its constituent parts are a hydraulic supply of packaged waste to the reaction zone, a gas burner with thermal power of 42 kW, an electric arc plasma torch with power of 50 kW, and a bottom melting ash chamber. In the test mode of electric furnace operation it has been shown that plasma gasification of organic materials produces a synthesis gas suitable for application in heat and electric power engineering. The results of thermodynamic calculations are in satisfactory agreement with the obtained experimental data.

A novel experimental method of investigating anode-arc-root behaviors in a DC non-transferred arc plasma torch

A novel experimental method of investigating anode arc root was presented, and a plasma torch with multiple anodes was designed. With this apparatus, the number of anode arc roots, their position, and movement with changes in plasma current and gas-flow rate were studied. Results showed that multiple anode arc roots can coexist and their number was more related to plasma current than gas-flow rate. The number of anode arc roots increased with increased plasma current. The anode arc root can move forward and backward in the arc plasma jet, and its position was related to current and gas-flow rate. The anode arc root moved forward with increased current, whereas the anode arc root moved forward first and backward with increased gas-flow rate. Based on the finding, a new non-transferred arc model was established. Finally, the anode arc root motion was classified as steady, slight vibration, alternating motion, jumping motion, and multiple arc root modes. These results can serve as a reference for revealing the mechanism of plasma discharge, optimization design of arc plasma jet, and high-quality plasma generation.

Адгезия плазменных покрытий гидроксиапатита

Hydroxyapatite coatings were sprayed with an arc plasma torch argon-nitrogen plasma at a power of 25 kW from a powder with a particle size of 25 – 63 μm at a distance of 95 mm. The samples to which the coatings were applied were preheated in a resistance furnace in an air atmosphere to temperatures in the range of 20 to 600 °C before being sprayed. The adhesion of the plasma coating from hydroxyapatite to the titanium substrate was determined on the pin specimens. The maximum average adhesion value was recorded when the titanium substrate was preheated to a temperature of 550 °C. The results of the study were discussed on the basis of the mechanism for increasing the activity of the titanium substrate during its preheating in order to increase the adhesion of the coating HA and the formation of an equilibrium phase state in the HA coating required for the prolonged use of implants. The received results will be used for formation of optimum structure of the bioactive covering consisting from three-dimensional capillary-porous titanium coatings (3D CP Ti) coating in the form of crests and hollows with porosity of 50% and HA coating applied on its free surface at a temperature of 550 °C. Such process of spraying to provide dense strong and stable a HA coating on implants.

Синтез наноструктур системы Al-B при взаимодействии дисперсного алюминия с бором и дибораном в плазме дугового разряда

Experimental studies of aluminium boride synthesis as a result of interaction of disperse aluminum with diborane B2H6 and disperse boron in a flow of thermal plasma of different composition generated in electric arc plasma torch have been carried out. Experimental work on the synthesis of aluminium boride nanoparticles from elements (a mixture of disperse aluminum and boron) has shown the possibility of obtaining in thermal plasma arc discharge of such phases of the boride as AlB12 and AlB31. The specific surface of the powders obtained is from 3 to 27 m2/g. According to X-ray phase analysis, the powders obtained, except for aluminum boride phases, also contain boron, aluminum, aluminum nitride and boric acid phases. The greatest yield of aluminum boride phases is provided by using the nitrogen plasma with hydrogen and enthalpy 4.5 kWt∙h/m3 in the reactor with increased high-temperature zone. The use of gaseous diborane made it possible to eliminate restrictions on the evaporation of boron particles but did not provide an opportunity to obtain aluminum borides in the plasma-chemical process. It was concluded that it is necessary to perform quenching of high-temperature gas flow containing boron and aluminum vapor to form aluminum borides from the gas phase in plasma-chemical synthesis. Such an approach should ensure that the temperature is reduced to the values at which aluminum borides are stable and that the formation of aluminum boride nanoparticles will occur as a result of condensation from the gas phase under these conditions.

A 2-D Axisymmetric Magneto-Hydrodynamic Model of a DC Arc Plasma Torch and Its Solution Methodology

The behavior of dynamic plasma is governed by the magneto-hydrodynamic (MHD) equation, and the efficient solution is still an open challenging issue in computational electromagnetics. In this article, to efficiently predict the behavior of an engineering direct current (dc) arc plasma torch, a 2-D axisymmetric MHD model is introduced and its solution methodology is proposed. In the methodology, the initial temperature field of the MHD model is estimated based on a predicted trajectory of the plasma arc, determined by using the single-particle orbital theory; a simple yet efficient iterative procedure using a prediction-correction approach to determine the magnetic field and to solve the corresponding 2-D finite-element equations of the mass, momentum, and energy conservations is proposed; and an approach to solve the extremely small conductivity near the electrodes is introduced. Finally, a finite element method code is developed and used to compute the multi-physics fields of the plasmas with promising results.

On the Issue of the Thermal Emission Cathode Resource on the Oxide Films of Hafnium and Zirconium

The article shows the results of research on the destruction of the thermionic cathode of an arc plasma torch when inserting hafnium and zirconium along the trace of the spot of a gas-discharge arc by means of electronic metallography with spectral analysis in the control region. The depth of penetration of the spot into the metal of the cathode insert was determined due to the discrete mechanism of action on the metal at the time of attachment. The erosion rate of zirconium oxide films was experimentally established, the extension of the operating life substantiated while mechanisms for its increase were revealed, and two types of arc contact with a hafnium or zirconium insert - the "contracted" and "diffused" ones - were offered. The theoretical operating life of the cathode is calculated.

Comparison of Reynolds average Navier–Stokes turbulence models in numerical simulations of the DC arc plasma torch

Five turbulence models of Reynolds average Navier–Stokes (RANS), including the standard model, the RNG model taking into account the low Reynolds number effect, the realizable model, the SST model, and the Reynolds stress model (RSM), are employed in the numerical simulations of direct current (DC) arc plasma torches in the range of arc current from 80 A to 240 A and air gas flow rate from 10 m3 h−1 to 50 m3 h−1. The calculated voltage, electric field intensity, and the heat loss in the arc chamber are compared with the experiments. The results indicate that the arc voltage, the electric field, and the heat loss in the arc chamber calculated by using the standard model, the RNG model taking into account the low Reynolds number effect, and the realizable model are much larger than those in the experiments. The RSM predicts relatively close results to the experiments, but fails in the trend of heat loss varying with the gas flow rate. The calculated results of the SST model are in the best agreement with the experiments, which may be attributed to the reasonable predictions of the turbulence as well as its distribution.