Direct Current Plasma Torch Research Articles

Reduction of an Ilmenite Concentrate by Using a Novel CO2/CH4 Thermal Plasma Torch

Plasma technology has emerged as a very helpful tool in a variety of sectors, notably metallurgy. Innovators and scientists are focused on the problem of finding a more ecologically friendly way of extracting titanium and iron metal from natural ilmenite concentrate for industrial applications. A direct current (DC) plasma torch operating at atmospheric pressure is used in this study to describe a decarbonization process for reducing an ilmenite concentrate. The plasma gases employed in this torch are CO2 and CH4. The molar ratio of the gases may be crucial for achieving a satisfactory reduction of the ilmenite concentrate. As a result, two molar ratios for CO2/CH4 have been chosen: 1:1 and 2:1. During torch operation, a thin layer of graphite is formed on the cathode to establish a protective barrier, prolonging the cathode’s life. The material was analyzed using X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). The output gases were analyzed using mass spectrometry (MS). In addition, a thermodynamic analysis was performed to predict the development of thermodynamically stable phases. An economic assessment (including capital expenditures (CAPEX) and operating expenditures (OPEX)) and a carbon balance were developed with the feasibility of the piloting in mind.

Investigation of Upgraded Technology for Plasma Spraying of Bronze Powder Using the Combined Process with Hydrocarbon Additions

The object of the research is thermal spray process for the formation of metal coating from bronze powder in plasma-fuel variant, using direct current (DC) electric arc plasma torch, on steel samples. The aim of the work was to investigate and develop the technology for plasma-fuel spraying of functional coatings (for wear-resistant and antimicrobial applications) on machine-building and medical purpose pieces with increased process capacity and moderate energy consumptions in a comparison with conventional thermal spray technologies with use of inert and oxygen-free gas media. During the study, using experimental and thermodynamic estimation methods, the thermal and chemical parameters of the process under the spraying conditions at ambient pressure were characterized, which made it possible to determine the area of preferred regimes of the developed technology. On the modernized testing unit for plasma spraying of metal powders with power of up to 40 kW, operating using a controlled combination of three types of gases – technical nitrogen and propane-butane (LPG) with compressed air, the measurement and optimization of the operating and constructive/assembling parameters of the system for aluminum bronze coating spraying were established. In this case, the experiments were carried out using the designed fuel intensifier, which is joined with the PP-25 arc plasma torch, as well as additional technological equipment (protective shroud). For samples of the resulting coatings with a thickness of 100 to 450 mm from the bronze material, testing of phase composition and some parameters of the resulting coatings on steel products was carried out. Operating capacity of the proposed process reaches 7–15 kg/h for bronze powder when using a moderate power of the torch – up to 35–40 kW and a limited flow rate of hydrocarbon gas (for example, LPG of the SPBT grade) – 0.1–0.35 kg/h. Analysis of the energy efficiency parameters of the developed technology, as well as its calculated technical characteristics, in a comparison with plasma and combined equipment of a similar purpose, showed that it has an advantage in terms of target indicators, in particular, in terms of energy consumption and total energy efficiency of the spraying unit, not less than 20–30 %. This makes it to proceed later to the stage of application of this technology into production based on a new process for the metal coating formation, in particular with antimicrobial properties, with improved energy efficiency of the process.

Eliminating ciprofloxacin antibiotic contamination from water with a novel submerged thermal plasma technology

Thermal plasma is successfully used to degrade the model pharmaceutical wastewater ciprofloxacin (CIP) under submerged operating conditions at atmospheric pressure. The model aqueous solution is prepared for two different concentrations (10 and 25 mg/L) and treated separately at 7 kW discharge power with two different plasma-forming gas compositions, Ar/Air and Ar/CO2. A direct current (DC) hollow cathode plasma torch produces a thermal plasma jet inside the solution. The effect of plasma gas compositions on the CIP degradation process is investigated, and the corresponding degradation and mineralisation efficiencies for different treatment times are systematically compared using high-performance liquid chromatography (HPLC) and total organic carbon (TOC) analysis, respectively. Submerged Ar/CO2 plasma shows higher degradation and mineralisation efficiency than the Ar/Air plasma. Energy yields of 74.32 mg/kWh and 176.98 mg/kWh are achieved for a 5-min treatment by Ar/CO2 submerged thermal plasma at concentrations of 10 mg/L and 25 mg/L, respectively. The degradation of CIP by submerged plasma shows a resemblance with first-order reaction kinetics having reaction rates 0.149 min−1 and 0.073 min−1 for Ar/CO2 and Ar/Air, respectively. Density Functional Theory (DFT) calculations are used to identify the various reactive sites on CIP, and the results are consistent with the formation of various intermediates detected through liquid chromatography-mass spectrometry (LC-MS) analysis. These findings suggest that reactive species formed through thermal and photochemical processes in submerged thermal plasma play a significant role in the degradation of CIP. This study also offers a possible way of using CO2 gas in wastewater treatment using submerged thermal plasma.

Design and Experimental Jet Characteristics of an Optimized DC Plasma Torch

Due to their favorable jet characteristics, direct current (dc) thermal plasma torches have been used to meet the different requirements of variety applications. For obtaining more favorable jet characteristics and longer service life, variety design considerations of thermal plasma torches, e.g., cascade anode, multicathodes, and multianodes, have been used and studied by experiments and simulations. However, how the design considerations influence the jet characteristics and how about the coupling relationships of the working conditions should be studied systematically. Therefore, some key design tips have been discussed and applied to optimize a home-made thermal plasma torch first. Then, the experimental setup and methods for obtaining the jet characteristics of the optimized plasma torch have been introduced in detail. Finally, the experimental jet characteristics of the optimized plasma torch and the coupling relationships of the working conditions have been obtained and discussed. The study results show that: 1) the thermal plasma torch could obtain good jet characteristics and long service life by adopting the design tips and 2) the coupling relationships of the working conditions have been obtained and discussed, which could be helpful for predicting the jet characteristics of a thermal plasma torch.

Study on CO2 based thermal plasma torch and its effective utilization for material processing in atmospheric pressure

Reuse of greenhouse gases is one of the promising approaches towards controlling global warming to some extent. As a part of that, an attempt has been made to utilize CO2 gas as one of the primary gases to form a thermal plasma jet for material processing. For that purpose, a unique direct current (DC) non-transferred arc thermal plasma torch was designed and its current-voltage characteristics and electro-thermal efficiency with different discharge currents and gas compositions were studied. The torch is made of rod type cathode and a nozzle type anode, which can produce a stable thermal plasma jet under different gas compositions. CH4 was used as a secondary mixing gas in an Ar-CO2 gas composition to produce a carbon-rich thermal plasma with high electro-thermal efficiency. The maximum electro-thermal efficiency of 73 % were reached while the torch operated at 100 A current with 6 slpm of CH4 flow along with 15 and 20 slpm of Ar and CO2 gas flow, respectively. Torch efficiency decreased to 12 % with increase in discharge current from 100 A to 200 A. Optical emission spectrum of the plasma jet was recorded at the exit of the torch nozzle to understand the emission characteristics of the plasma and estimate temperature and electron density. Temperature of the plasma increased from 13,400 to 17,800 K with respect to the discharge current. Thermodynamical studies were carried out for the given experimental conditions to understand the thermal decomposition of CO2-CH4 gas mixture and select the suitable condition for the material processing. Under the selective conditions, plasma torch was utilized for the spheroidization of tungsten metal powder and carburization of the AISI 316 L stainless-steel coupons in atmospheric pressure without using any shielding gases. Results showed that around 85 % of the metal powders were spheroidized perfectly at 15 kW input power. Plasma carburization results showed that the microhardness of the steel surface reached 605 HV with a short processing time of 3 min which was 4 times higher than the untreated steel surface. This work provides useful insight for the utilization of CO2 as primary plasma forming gas to generate thermal plasma for material processing.

Numerical modelling of a direct current non‐transferred thermal plasma torch for optimal performance

AbstractA laminar steady‐state 2D axisymmetric model of a direct current (DC) thermal plasma torch using a magneto‐hydrodynamic approach has been developed. The model takes into account the entire torch system comprising the plasma gas injection, the inner region of the torch, and the jet exiting into the ambient environment. Numerical results are obtained for two different power inputs chosen from published experimental data. The temperature predictions at the torch exit are found in good agreement with experimental results. Velocity analysis of the plasma jet has been presented and the impact of electromagnetic force on jet velocity is analysed. The Lorentz force arising due to the coupling of fluid motion and electromagnetic forces shoots up the jet velocity to significantly high values near the cathode tip. Temperature and velocity profiles are in good agreement with the characteristics of a long laminar plasma jet. An operating value of heat transfer coefficient (h) has been suggested for optimal torch operation, thus ensuring a low anode erosion rate and acceptable thermal efficiency. The argon torch has the maximum temperature and longest jet length among the plasma gases considered.

Experimental study of the effect of argon on the restrike characteristics of nitrogen arc

The arc restrike process is a typical mode of operation within a direct current arc plasma torch. By using a transfer arc device with a planar anode parallel to the gas flow direction, the effect of argon addition on the disappearance of downstream old arc roots, the overall arc downstream movement process and the generation of upstream new arc roots of the nitrogen arc restrike process is experimentally investigated. The experimental results show that for pure nitrogen arc, the restrike frequency is very high and the old arc root disappears very quickly. The addition of argon will significantly decrease the temperature of the arc root and prolong the coexistence time of the old and new arc roots. This phenomenon is caused by the rapid decay of charged particle density in the nitrogen arc, because the recombination process of charged particles in the nitrogen arc is faster than that in the argon arc. The breakdown field strength at the upstream location where the new arc root occurs is calculated by combining the measurements of arc voltage, arc grayscale image and temperature. The results show that as the percentage of argon increases, the boundary layer thickness becomes thinner and the critical electric field strength required for arc breakdown decreases, leading to the generation of new arc roots more likely to occur toward the upstream location. This study improves the understanding of the effect of argon on the nitrogen arc restrike process.

Comparative Study of Plasma Torch Characteristics Using Air and Carbon Dioxide

The plasma torch is the key component of the thermal plasma-assisted material processing system. Particularly, direct current (dc) nontransferred arc plasma torch is widely used in high-temperature material processing applications. The characteristics of the thermal plasma jet emanating from the plasma torch depend on many factors, including arc current, type of plasma forming gas, gas flow rates, gas injection configuration, torch geometry, and so on. This experimental study focuses on the comparison between the effects of CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and air on the arc voltage, electrothermal efficiency, and specific enthalpy of the plasma torch operated at the atmospheric pressure. For this purpose, a low-power dc plasma torch consisting of a rod-type thoriated tungsten cathode and the copper anode was customized. CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and air were used as the plasma forming gases along with a feeble amount of argon (15 lpm). The plasma torch was operated over a wide range of current (100–175 A) with fixed gas flow rates. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula> characteristics and the electrothermal efficiency of the plasma torch were measured, and results were compared. The maximum electrothermal efficiency and specific enthalpy of the plasma torch when operated with CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> were reported as 70% and 1900 KJ/Kg, respectively, which is higher than the same torch operated with air as the plasma forming gas. The electron number density and electron temperature of the air and CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> plasma jet were measured by optical emission spectroscopy (OES). The calculated electron number density and electron temperature of the plasma jet with CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> were <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.89\times 10\,\,^{\mathrm{ 16}}$ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> and 8598 K, respectively, which is higher than air plasma jet. It was found that CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> has a stronger influence than air on the arc voltage fluctuation, electrothermal efficiency, and operating regime of the plasma torch.

Computational fluid dynamics evaluation of conditions before impact of particles in plasma spraying process

Plasma Spraying is one of the most sophisticated and versatile thermal spray techniques. In Plasma Spraying, powdered material is injected into a plasma jet, which is generated from a plasma torch. Upon contact with the plasma jet, the particles are melted and propelled forward onto a substrate to form an adherent coating which modifies the properties of the substrate. The modifications to the substrate can, for example, increase its resistance to other extreme operating conditions such as wear, abrasion, and corrosion. However, the phenomena governing the formation of the plasma jet inside the plasma torch and its subsequent interaction with injected particles are not fully understood. This paper provides a detailed report on steps taken for the development of a comprehensive numerical model to simulate plasma jet development inside a direct current plasma torch. The heat flow and mass exchange of ionized gas with injected solid particles were followed in three dimensions by using a Computational Fluid Dynamics (CFD) method. A cylindrical energy source term which was defined as an increasing linear function dependent on time as a variable, was included to reproduce the effects of an electric arc on the gas flow. For optimization purposes, it was sought to investigate the effects of the particles’ injection angle and inlet velocity, as well as the effects of particle size distribution on the particle temperature and velocity histories.

Validation of computational fluid dynamics method through experimental investigation of the plasma spraying process

Numerical modelling has emerged as a powerful predictive tool to enhance plasma sprayed coatings quality and process efficiency. In the present work, a comprehensive Computational Fluid Dynamics model of a gas heating inside a direct current arc plasma torch, is developed, using the simulation software Ansys Fluent. It is therefore sought to test its accuracy and limitations by comparing its predictions to actual data generated in the South African Nuclear Energy Corporation plasma spraying laboratory. In this regards, titanium powder of respective size distributions, 0-63 μm, and 63-75 μm, is sprayed onto a metal piece work. The transport medium is an argon-nitrogen plasma jet, generated from a direct current torch running under an induced power of 12.8 – 13.1 kW. The spraying distance and powder carrier gas flow rate are varied throughout the experiment, from 75 to 85 mm, and 3.9 to 5.8 kg/h, respectively. Comparison of laboratory and simulation-based results were mostly in agreement, in terms of the plasma jet shape, the effect of power increase on the torch exit temperature, the effects of particle size distribution, and carrier gas variation on particle melting and trajectory.

Basic Characteristics of Plasma in Atmospheric Non-Transferred Direct-Current Plasma Torch

Basic Characteristics of Plasma in Atmospheric Non-Transferred Direct-Current Plasma Torch

Theoretical and experimental approach of fuel gas and carbon black production from coal tar pitch by thermal plasma process

ABSTRACT The processing of coal tar pitch (CTP) to produce clean fuel gas and carbon black (CB) is studied in a plasma reactor equipped with a direct-current plasma torch. The composition of the gas produced and energy costs were estimated theoretically for the CTP pyrolysis and gasification processes by two oxidants, namely oxygen and water vapor. We have found that the main gaseous compounds obtained in the pyrolysis and gasification processes are hydrogen (H2), carbon monoxide (CO), and very often carbon dioxide (CO2). For the pyrolysis case, the mean value of the synthesis gas concentration reaches a major value of 98 vol.% (H2 – 81 vol.%, CO – 17. vol.%). However, only 23% of the initial CTP is transformed into gas phase at 1100 K and its content increases up to 37.4% at a temperature of 3000 K. For oxygen gasification, the syngas quantity is little less compared to the pyrolysis case and attains 96.6 vol.% (H2 – 26.5 vol.%, CO – 70.1 vol.%) for T > 1100 K. An intermediate syngas content for the water steam gasification is 97.8 vol.% (with H2 – 55.8 vol.% and CO – 42.0 vol.%). The CB produced was composed of well-defined spherical particles of 30-nm size. Furthermore, it is composed of carbon (98.2%), and followed by oxygen (1.8%) with a surface area of 97 m2 g−1. The thermal plasma system shows high efficiency in conversion of CTP into high-value-added products.

A Study on Direct Current Arc Plasma Torch Design with Preserve Nozzle for Perfluorinated Compounds (PFCs) Decomposition in Cement Kiln

A Study on Direct Current Arc Plasma Torch Design with Preserve Nozzle for Perfluorinated Compounds (PFCs) Decomposition in Cement Kiln

Graphene Flakes for Electronic Applications: DC Plasma Jet-Assisted Synthesis.

The possibility of graphene synthesis (the bottom-up approach) in plasma and the effective control of the morphology and electrical properties of graphene-based layers were demonstrated. Graphene flakes were grown in a plasma jet generated by a direct current plasma torch with helium and argon as the plasma-forming gases. In the case of argon plasma, the synthesized graphene flakes were relatively thick (2–6 nm) and non-conductive. In helium plasma, for the first time, graphene with a predominance of monolayer flakes and high conductivity was grown in a significant amount using an industrial plasma torch. One-dimensional (1D) flow modeling shows that the helium plasma is a less charged environment providing the formation of thinner graphene flakes with low defect density. These flakes might be used for a water-based suspension of the graphene with PEDOT:PSS (poly(3,4-ethylenedioxythiophene): polystyrene sulfonate) composite to create the structures employing the 2D printing technologies. Good structural quality, low layer resistance, and good mechanical strength combined with the ability to obtain a large amount of the graphene powder, and to control the parameters of the synthesized particles make this material promising for various applications and, above all, for sensors and other devices for flexible electronics and the Internet of things ecosystem.

Effect of the Plasma Gas Composition on the Properties of Graphene

Theoretical and experimental studies of the synthesis of graphene with the introduction of nitrogen into a jet of helium plasma generated by a direct-current plasma torch with a power of to 40 kW at a pressure of 350 Torr have been performed. A propane–butane mixture was used as a source of carbon. As found by scanning microscopy, Raman scattering, and synchronous thermal analysis, the morphology of the synthesis products changed from graphene flakes to carbon nanotubes upon the addition of nitrogen in a ratio of 1 : 1.22 to the jet of helium plasma. The numerical modeling of the process showed that cyanopolyyne molecules, HC9N and HC11N, containing many carbon atoms appeared instead of C60 and C80 in the jets of helium upon the addition of nitrogen.

Plasma Disposal in Problems of Ecology (Review)

The current state and issues of plasma disposal are discussed. Various types of plasma torches used for disposal, the technological schemes of existing plasma systems, a plasma torch with an expanding output electrode, equipment characteristics, diagnostic methods for the design of an effective low-temperature plasma generator, and the studying of the effects of a high-enthalpy plasma jet generated by a direct-current plasma torch on a solid target material are described. The results obtained via high-speed imaging, micropyrometry, laser profilometry, spectroscopy, and stereoscopy methods are presented. The data on spatial and temporal changes of the temperature field on the sample surface, the dynamics of material loss, and changes in the parameters (temperature and electron density, temperature of heavy particles) of the plasma-jet incident on the sample are analyzed. The collected theoretical and experimental results and engineering solutions can be used to design various low-temperature plasma generators with a power of up to 1 MW and higher.

Spectroscopic Study of a Helium Plasma Jet with Hydrocarbon Additives

The results of a spectroscopic study of the conversion of acetylene and methane in a helium plasma jet produced by a direct current plasma torch are presented. The operating mode of the plasma torch corresponds to conditions that provide a high yield of carbon nanostructures. In the emission spectra recorded during the transverse observation of a 20-mm jet section following the outlet of the anode channel of the plasma torch, high-intensity Swan bands of the С2 molecule are the dominant component in the visible wavelength range. The spectra show atomic hydrogen lines of the HI Balmer series from Hα to He, numerous CI carbon lines from ultraviolet 247.9 nm to infrared 962–966 nm, and a number of HeI helium lines. The axial temperature values of the plasma jet were spectrally determined by the observed ionized carbon CII lines 283.7 nm, 392.0 and 426.7 nm. A joint analysis of the emission spectra and the mixture composition calculated in the Saha–Boltzmann approximation revealed the nature of the spatial heterogeneity of the studied He : C : H plasma jet. It is manifested by the difference in the electron temperature of the axial region of the jet, which is measured with ionized carbon lines CII (Te(0) = 12 000–14 000 K) from the vibrational and rotational temperatures of C2 molecules (TV = TR ≅ 5000 K) that emit intensely at the jet periphery. The electron density measured along the Hβ and Hγ line widths, which varies in the range of the observed jet region of ne = (4–2) × 1016 cm–3, corresponds to the ionization equilibrium in a plasma He : C : H mixture with an electron temperature close to Te measured by carbon-ion lines.

Distinctive Features of Graphene Synthesized in a Plasma Jet Created by a DC Plasma Torch.

Synthesis of graphene materials in a plasma stream from an up to 40 kW direct current (DC) plasma torch is investigated. These materials are created by means of the conversion of hydrocarbons under the pressure 350–710 Torr without using catalysts, without additional processes of inter-substrate transfer and the elimination of impurities. Helium and argon are used as plasma-forming gas, propane, butane, methane, and acetylene are used as carbon precursors. Electron microscopy and Raman imaging show that synthesis products represent an assembly of flakes varying in the thickness and the level of deformity. An occurrence of hydrogen in the graphene flakes is discovered by X-ray photoelectron spectroscopy, thermal analysis, and express-gravimetry. Its quantity depends on the type of carrier gas. Quasi-one-dimensional approach under the local thermodynamic equilibrium was used to investigate the evolution of the composition of helium and argon plasma jets with hydrocarbon addition. Hydrogen atoms appear in the hydrogen-rich argon jet under higher temperature. This shows that solid particles live longer in the hydrogen-rich environment compared with the helium case providing some enlargement of graphene with less hydrogen in its structure. In conclusion, graphene in flakes appears because of the volumetric synthesis in the hydrogen environment. The most promising directions of the practical use of graphеne flakes are apparently related to structural ceramics.

Influence of Temperature Profile on the Composition of Condensed Carbon in a Plasma Jet

Graphene materials are synthesized in a thermal plasma jet without using size forming catalysts. The synthesis was performed on a direct current plasma torch operating at 28–30 kW with a pressure of 100–710 Torr. The synthesis products are studied by electron microscopy, X-ray diffraction, and dynamic light scattering. It is found that structures formed in the plasma jet have a flake morphology regardless of the type of the carbon bearing source. Thermodynamic calculations testify a correlation between the temperature profile in the plasma jet and the composition of condensed carbon (redistribution between C60 and C80). The application areas of flaky structures are discussed.

Effect of helium/propane–butane atmosphere on the synthesis of graphene in plasma jet system

An experimental and theoretical study was performed on helium/propane–butane plasma, which enabled assembly of advanced carbon nanostructures, such as multilayer graphene flakes. A plasma jet was created at pressures ranging from 350 to 710 Torr, and with direct current plasma torch powers from 28 to 35 kW at varying mass ratios of helium to propane–butane 1:7.5 to 1:5. Graphene production was confirmed by different analytical techniques. The non-catalytic synthesis in the plasma jet volume provided the graphene purity. As a result of numerical simulation, the kinetic mechanism of the formation of carbon phase precursors in the gas phase, namely, C2 dimers, was studied. The concentration of C2 was determined, depending on the temperature and compared with the literature data on the pressure of saturated carbon vapours at temperatures ranging from 2500 to 5000 K. It is shown that the C2H-involving reactions provide additional C2 production, leading to the formation of supersaturated vapour from C2 molecules at temperatures of 2500 to 3500 K.