Plasma Torch Operating Research Articles

CO[formula omitted] dissociation using a lab-scale microwave plasma torch: An experimental study in view of industrial application

Under laboratory conditions, microwave plasma torches are known to be an energetically very efficient CO2 conversion technology, for pressures ranging from 100mbar up to atmospheric pressure. However, issues relevant for industrial application such as the total energy efficiency, including the power consumption of peripheral equipment, the performance for impure CO2 streams (such as directly from carbon capture facilities) and the stability at long-term operation are usually not addressed. To fill that gap, a lab-scale plasma torch and the corresponding vacuum pump are connected to an energy meter system. Measured wall-plug energy efficiencies yielded values up to 17.9%, corresponding to an electrical power consumption of 19.6kWh per produced Nm3 of carbon monoxide. Experiments with controlled amounts of impurities (Ar, N2, O2, real air and synthetic air) in the feed gas stream are performed. It is shown that small amounts of nitrogen can even increase energy efficiency whereas humidity in the CO2 stream might have an extremely detrimental effect on CO2 decomposition. Finally, a durability test over 29h was performed, demonstrating that microwave plasma torch operation is very reproducible and stable in all figures of merit with short ramp-up times, making it a promising technology for intermittent operation on industrial scale.

In-Flight Mechanisms in Suspension Plasma Spraying: Issues and Perspectives

Suspension plasma spraying has aroused much research efforts over the two last decades to describe and understand the in-flight mechanisms of suspension plasma processing by developing advanced diagnostics and models. This research field has highlighted the intricate and prevailing dependence of the coating properties, and especially the rich variety of attainable microstructures, on the thermal and dynamic histories of the submicron particles in the plasma jet. This paper gives an overview of the major key points to control from the plasma torch operation up to the coating build-up. The main diagnostics methods are examined and the most advanced models as well. The perspectives focus on the key issues to improve the basic understanding of the in-flight phenomena. They also insist on a necessary multiscale approach to combine the diagnostics and the models in order to form relevant data flows for machine learning algorithms and better process prediction and reliability.

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.

Тепловые характеристики столба дуги в зоне стабилизации ламинарного плазмотрона, работающего на воздухе

The method of universal characteristics of an electric arc is described as a mathematical basis for the heat exchange model of an electric arc in the processes of electric arc heating in electrical engineering. Application of this method for calculation of the temperature characteristics of an arc column compressed by the walls of the discharge channel in the stabilization zone of a laminar plasma torch operating in air is considered. An example of the temperature profile calculation of a wall-stabilized arc for a plasma generator with a discharge channel diameter of 5 mm operating in air at an arc current of 60 A is presented. Calculated results are compared with the results of experimental studies of this plasma generator.

Control of the Arc Motion in DC Plasma Spray Torch with a Cascaded Anode

Two common concerns in DC plasma torches are stability of plasma jet and anode erosion. The challenge is how to get a stable plasma jet with minimal anode erosion. This study tackles this question by using either a swirling gas injection or an external axial magnetic field applied to the Oerlikon SinplexPro™ plasma torch. A 3-D, time-dependent MHD model of the plasma torch operation was used to predict the value of the external magnetic field and its effect on the heat flux to the anode and plasma jet stability. The special feature of the model is to couple the gas phase and electrodes that makes it possible to follow the anode temperature evolution. For specific operation conditions (anode of O9 mm, 500 A, Ar 60 NLPM), the model predicted that the maximal value of the azimuthal self-magnetic field inducted by the arc current was 0.055 T; it also showed that an external magnetic field of 0.05 to 0.1 T could make it possible to limit the anode erosion without noticeably disturbing the plasma jet issuing from the plasma torch. We expect this approach to help to better understand the arc behavior in commercial plasma torches and control anode erosion

Numerical simulation of high power RF–RF hybrid plasma torch

In this paper the possibility of operation of a high-power RF-RF hybrid plasma torch for materials processing is shown with help of numerical simulation. That kind of plasma torch consists of two coaxial ICP/RF torches connected in series. A mathematical model is presented which includes assumptions, basic equations, a computational domain with main sizes. The results of the calculation i.e. the temperature distributions inside the plasma torch for two modes of operation are shown. In the first mode the power is fed only to the first plasma torch (P1=40 kW, P2=0), in the second mode the both parts of the RF-RF hybrid plasma torch (P1 = 40 kW, P2 = 600 kW) operate. The obtained results can serve as a basis for further analysis of the operation of a high-power RF-RF hybrid plasma torch.

A non-stationary model of the AC plasma torch

Modelling of a single-phase two-channel AC plasma torch with a calculated power of 1.1 kW at a current value of 6 A is presented in the paper. A model of the plasma torch operation on argon at a flow rate of 0.69 g/s is considered. A 35-millisecond operation of the plasma torch has been simulated. The obtained temperature distributions and arc voltage drops allow us to evaluate the simulation results at a qualitative level.

Numerical simulation of the flow characteristics inside a novel plasma spray torch

A novel direct current non-transferred arc plasma torch that can generate a long, stable and silent plasma jet of over 350 mm in length into ambient air is studied by numerical modelling. Numerical simulation of the plasma torch operating in the current of 160 A with a mixture of 70% nitrogen and 30% argon in volume at three different gas flow rates (8.5 SLPM, 10 SLPM and 14 SLPM) are performed in a 3D domain. The renormalization group method is employed to model the turbulent flow inside the plasma torch, particularly the torch’s novel channel structure. The results show that a narrow circular gap at the boundary layer of the cathode led to a region of high flow constriction and large pressure and velocity gradients. The anode counts with a novel trumpet-like structure that separates the flow in the channel and induces turbulent fluctuations in the direction transverse to the flow, which can disrupt and decrease the cold boundary layer around the arc column. The arc attachment position that obtained in simulation is in agreement with the experiment observation. The maximum velocity at the torch nozzle in simulation is increased and the length of the plasma jet in experiment is decreased with the increasing of the total gas flow rates from 8.5 SLPM, 10 SLPM to 14 SLPM. However, the maximum temperature at the torch nozzle in three different gas flow rates are varied slightly. Our results suggest that generation of a long and stable plasma jet downstream of the nozzle exit should not only focus on a relatively low gas flow rate, but depend instead on the aerodynamic characteristics of the channel flow, particularly in the anode region and downstream of the anode.

INFLUENCE OF MODE AND GEOMETRIC CHRATERISTICS ON HIGHT-FREQUENCY INDUCTIVE PLASMA TORCH WITH REVERSE VORTEX FLOW

The analysis of aerodynamic and heat structure of flow in high-frequency inductive plasma torch has been carried out. The range of plasma torch power is measured in dozens of kilowatts. The numerical simulation methods of the turbulent flow in the plasma torch affected by high frequency electromagnetic field without considering the chemical kinetics are used during the research. The data of temperature field and induced current density in the plasma torch depending on current amperage and frequency are obtained. Also, these data are obtained depending on the flow scheme in the operated on argon and air plasma torches. The inductive plasma torches can be applied to solve a wide range of tasks such as activation of coal-dust mixture with its further gasification, coating process for the stabilization of combustion processes as well as for the recycling processes at the mobile seaport recycling complexes. The calculations demonstrated convincingly the advantage of the operation of plasma torches with reverse vortex flow over plasma torches with “direct” vortex flow. Moreover the obtained data allow executing the assessment of thermal efficiency of inductive plasma jet and obtaining its optimal operational modes.

Study of the operation of high-voltage plasma torches with rod electrodes

Study of the operation of high-voltage plasma torches with rod electrodes

Operation of High-Voltage Plasma Torches with Rod Electrodes

The paper deals with single-phase AC plasma torches with rod electrodes made of iron-copper composite material, with air as the plasma-forming gas and an life time of ~200 h. The construction peculiarities of this type of plasma torch and its power-supply systems is described. The experimental results, in particular, the current-voltage and the voltage-flow rate characteristics of the plasma torches, as well as the typical current and voltage oscillograms, are presented.

Development of the arc plasma torch operation mathematical model for spheroidization of fine-dispersed powders

Brief review of the fine-dispersed powders production technologies for additive laser technologies is presented in the paper. Non-stationary mathematical model of DC plasma torch operation and stationary model of the reactor operation for powder spheroidization have been developed. Air is used as the plasma-forming gas. The influence of the transporting flow and compressing gases on the characteristics of the plasma flow is analyzed. Verification of the non-stationary mathematical model of DC plasma torch operation is based on experimental studies. Radial temperature distributions obtained from the results of numerical simulation and spectral diagnostics of the plasma torch PN-V1 are presented. The results of the experimental study describing plasma flow behavior for given parameters of the fine-dispersed powders spheroidization process are presented in the paper.

Application field and ways to control alternating-current plasma torch with rail electrodes

The paper deals with the investigation of parameters of the high voltage alternating-current plasma torch with rail electrodes. Usage of the injector and its variation allows controlling of operation of the ac plasma torch with rail electrodes. Also the possibility to protect the electric arc chamber without protective gas has been studied. It was found that increasing in the injector power causes the repeated breakdown at lower voltage and hence the arc dimensions decreases. The results of experiments are presented in the paper.

Supersonic Plasma Spray Deposition of CoNiCrAlY Coatings on Ti-6Al-4V Alloy

Plasma spray is a versatile technology used for production of environmental and thermal barrier coatings, mainly in the aerospace, gas turbine, and automotive industries, with potential application in the renewable energy industry. New plasma spray technologies have been developed recently to produce high-quality coatings as an alternative to the costly low-pressure plasma-spray process. In this work, we studied the properties of as-sprayed CoNiCrAlY coatings deposited on Ti-6Al-4V substrate with smooth surface (R a = 0.8 μm) by means of a plasma torch operating in supersonic regime at atmospheric pressure. The CoNiCrAlY coatings were evaluated in terms of their surface roughness, microstructure, instrumented indentation, and phase content. Static and dynamic depositions were investigated to examine their effect on coating characteristics. Results show that the substrate surface velocity has a major influence on the coating properties. The sprayed CoNiCrAlY coatings exhibit low roughness (R a of 5.7 μm), low porosity (0.8%), excellent mechanical properties (H it = 6.1 GPa, E it = 155 GPa), and elevated interface toughness (2.4 MPa m1/2).

Main Issues for a Fully Predictive Plasma Spray Torch Model and Numerical Considerations

Plasma spray is one of the most versatile and established techniques for the deposition of thick coatings that provide functional surfaces to protect or improve the performance of the substrate material. However, a greater understanding of plasma spray torch operation will result in improved control of process and coating properties and in the development of novel plasma spray processes and applications. The operation of plasma torches is controlled by coupled dynamic, thermal, chemical, electromagnetic, and acoustic phenomena that take place at different time and space scales. Computational modeling makes it possible to gain important insight into torch characteristics that are not practically accessible to experimental observations, such as the dynamics of the arc inside the plasma torch. This article describes the current main issues in carrying out plasma spray torch numerical simulations at a high level of fidelity. These issues encompass the use of non-chemical and non-thermodynamic equilibrium models, incorporation of electrodes with sheath models in the computational domain, and resolution of rapid transient events, including the so-called arc reattachment process. Practical considerations regarding model implementation are also discussed, particularly the need for the model to naturally reproduce the observed torch operation modes in terms of voltage and pressure fluctuations.

Investigation of the AC Plasma Torch Working Conditions for the Plasma Chemical Applications

The presented design and parameters of a three-phase AC plasma torch with the power up to 500 kW, flow rate of air 30–50 g/s (temperature up to 5000 K) could be used in different plasma chemical processes. Range of measured plasma temperature is 3500–5000 K. The paper presents investigations of the plasma torch operation modes for its application in plasma chemical technologies. Plasma chemical technologies for various purposes (processing, destruction of various wastes, including technological and hazardous waste, conversion or production of chemicals to obtain nanoscale materials, etc.) are very promising in terms of the process efficiency. Their industrial use is difficult due to the lack of inexpensive and reliable plasma torches providing the desired level of temperature, enthalpy of the working gas and other necessary conditions for the process. This problem can be solved using a considered design of a three-phase alternating current plasma torch with power of 150–500 kW with working gas flow rate of 30–50 g/s with mass average temperature up to 5000K on the basis of which an industrial plasma chemical plant can be created. The basis of the plasma torch operation is a railgun effect that is the principle of arc movement in the field of its own current field. Thanks to single supply of power to the arc, arcs forming in the discharge chamber of the plasma torch move along the electrodes under the action of electrodynamic forces resulting from the interaction of the arc current with its own magnetic field. Under the condition of the three-phase supply voltage, arc transits from the electrode to the electrode with change in the anodic and cathodic phases with frequency of 300 Hz. A special feature of this design is the ability to organize the movement of the arc attachment along the electrode, thus ensuring an even distribution of the thermal load and thus achieve long time of continuous operation of the plasma torch. The parameters of the plasma jet of the plasma torch and the single-phase three-phase plasma injector for use in a plasma-chemical unit for production of nano-dispersed materials are described in the paper.

Methods for increasing the service life of electrodes in the arc plasmatorches

Results of experimental studies of electrode erosion in high-current arc discharges are presented. Available data on the service life of electrodes in the arc plasma generators sometimes are contradictory and do not give the whole pattern on the relationship of specific erosion of the electrode material with the basic determining parameters of the plasmatorch. The real ways to increase the duration of plasmatorch operation before electrode replacement have been proposed.

The Main Issues to Address in Modeling Plasma Spray Torch Operation

The modeling of plasma torch operation has advanced greatly in the last 15 years due to a better understanding of the underlying physics, development of commercial, open-source computational fluid dynamics softwares, and access to high performance and cloud computing. However, the operation mode of the electric arc in plasma torches is controlled by dynamic, thermal, electromagnetic, acoustic and chemical phenomena that take place at different scales and whose interactions are not completely understood yet. Even though no single model of plasma torch operation fully addresses these phenomena, most of these models are useful tools for parametric studies, if their use is reinforced by knowledge of torch operation and the model predictions are validated against experimental data. To increase the level of predictability of the current models, several further steps are needed. This study examines the issues remaining to be addressed in the modeling of plasma spray torch operation and the current critical aspects of these.

Coherent and incoherent Thomson scattering on an argon/hydrogen microwave plasma torch with transient behaviour

A new method of processing time-integrated coherent Thomson scattering spectra is presented, which provides not only the electron density and temperature but also information about the transient behaviour of the plasma. Therefore, it is an alternative to single-shot Thomson scattering measurements as long as the scattering is coherent. The method is applied to a microwave plasma torch operating in argon or a mixture of argon with hydrogen at atmospheric pressure. Electron densities up to m−3 (ionization degree above 10−3) were observed, which is more than two times higher than presented in earlier works on comparable discharges. Additionally, a parametric study with respect to the argon/hydrogen ratio and the input power was carried out and the results are discussed together with earlier Stark broadening measurements on the same plasma.

Application of DC plasma torch for synthesis of carbon nanostructured materials

The results of the synthesis of carbon nanostructures at high temperatures using a DC plasma torch are presented. Plasma was generated by introduction of argon, nitrogen and helium into the plasma torch with an anode in the form of an expanding channel. Sustainable modes of the plasma torch operation have been achieved by simultaneous tangential input of a plasma gas with a carbon source. Obtained solid products were studied using electron microscopy, thermogravimetry, Raman spectroscopy and X-ray diffraction to characterize their properties and morphological structures.