Plasma Arc Furnace Research Articles

A Computational Magnetohydrodynamic Modelling Study on Plasma Arc Behaviour in Gasification Applications

The application of direct-current plasma arc furnace technology to the problem of coal gasification is investigated using computational multiphysics models of the plasma arc inside such units. An integrated modelling workflow for the study of DC plasma arc discharges in synthesis gas atmospheres is presented. The thermodynamic and transport properties of the plasma are estimated using statistical mechanics calculations and are shown to have highly non-linear dependencies on the gas composition and temperature. A computational magnetohydrodynamic solver for electromagnetically coupled flows is developed and implemented in the OpenFOAM® framework, and the behaviour of three-dimensional transient simulations of arc formation and dynamics is studied in response to different plasma gas compositions and furnace operating conditions. To demonstrate the utility of the methods presented, practical engineering results are obtained from an ensemble of simulation results for a pilot-scale furnace design. These include the stability of the arc under different operating conditions and the dependence of voltage–current relationships on the arc length, which are relevant in understanding the industrial operability of plasma arc furnaces used for waste coal gasification.

Расчет энергофизических параметров плазменной печи с использованием цилиндрической модели дуги Меккера

The method of universal arc characteristics developed for calculating the electrical and thermal characteristics of the cylindrical part of the Mecker model column allows simple algebraic methods to calculate the characteristics of the arc column at a distance from the cathode and, thereby, to concretize the mathematical model of Mecker. The proven conservativeness of the arc as a result of the formation of a spatial layer with increased volumetric viscosity on the surface of the column allows, in accordance with the provisions of the boundary layer theory, to apply a boundary condition of the third kind to the surface of the cylindrical part of the arc column. The method of universal arc characteristics also helps to link the boundary value of the linear heat flux density on the surface of the cylindrical part of the column with the temperature profile of the column and, thereby, to specify the dependence of the electrical, geometric and thermal characteristics of the column plasma on the conditions of arc heat exchange in the working space of the installation with electric arc heating. The proposed method makes it possible, based only on the external voltage characteristics of the arc, to identify the Mecker heat exchange model and calculate by a simple algebraic method the structure and values of the heat fluxes generated by the arc during heat exchange with the plasma torch gas jet in the melting space of the plasma arc furnace. Examples of arc characteristics are given when working on different gases for different stages of melting — at the beginning of melting and during the melting of the charge.

Electroplasma processing of medical and biological waste

The article presents an experimental study of biomedical waste in the form of disposable masks. The study was carried out on a laboratory plasma arc installation with a capacity of 20 kg/h. During the experiments, the most important technological parameters were studied: the composition of the exhaust gases, the dependence of the exhaust gases on the temperature in the chamber of the plasma arc furnace, etc.

Selection of Melting Unit for Fuzed Zirconium Dioxide Production

Data are provided for preparing fuzed and fuzed stabilized zirconia from baddeleyite and synthetic zirconia in induction, plasma, and electric arc furnaces. Results are discussed and prospects for carbothermal preparation of zirconium dioxide from zircon in an electric arc furnace are demonstrated. A favorable effect of oxidation melting in an electric arc furnace on quality and the process of fuzed product preparation is demonstrated. Data are provided for preparing fuzed zirconia from zircon in plasma furnaces.

Исследование сепарации оксидов титана и кремния при плазменно-дуговом плавлении кварц-лейкоксенового концентрата

The aim of the work was investigation of separation of titanium’s and silicon’s oxides during plasma-arc melting of quartz-leucoxene concentrate from Yarega deposit. The melting was proceeded in laboratory plasma-arc furnace in graphite crucible at 16 – 40 kW of arc power. The microstructure and R-x phase analysis of solidified melt were investigated after arc melting. The melt separated on two layers. The upper layer consisted mainly of SiO2 in the form of glass, the lower layer — mainly of cemented titanium oxide particles ≈ 100 μm in dimension. TiO2, Ti8O15, Ti6O11, Fe3TiO3O10, Ti3O5 were observed. These particles formed during melting and moved throw liquid glass to the bottom of crucible with the speed of V ≈ 10–4 m/s. The separation of TiO2 and SiO2 required energy W ≈ 100 GJ/t of concentrate in laboratory plasma arc furnace. The possibility of industrial employment of the arc melting separation was discussed. The estimated energy requirement was about 5 GJ/t in 20-t arc furnace.

Smelting Process of Chromite Ore Fines to Produce Crude Fe–Cr–Ni–N Alloy

The smelting behavior of waste chromite ore fines containing Cr and Ni to produce crude Fe–Cr–Ni–N alloy was investigated in this study. In the experiments, for each heat, liquid steel melt (metal pool 1 kg) was prepared in a 3--capacity laboratory-scale electric arc furnace for the absorption of reduced metals like chromium, nickel, etc., under hydrogen and nitrogen plasma atmosphere at ~ 1600 °C temperature. The result shows the formation of crude alloy containing ~ 13% Cr, ~ 3% Ni along with ~ 500 ppm nitrogen. The highest recovery level of chromium was achieved ~ 63% in 20-min nitrogen plasma exposure. A negligible amount of chromium recovery (14.73%) in case of only hydrogen plasma and improved recovery (60%) for a combination of carbon and hydrogen plasma was observed. Suitable nitrogen level in the Fe–Cr melt can replace the required nickel content for making austenitic stainless steel. Hence, smelting reduction of chromite ore fines in the plasma arc furnace could be feasible to produce crude Fe–Cr–Ni–N alloy. This alloy could be used for making austenitic stainless steel after adopting suitable decarburization techniques.

Формирование анодной области плазменной дуги на вращающемся графитовом тигле

Formation of anode spots on rotating graphite crucible in the plasma arc furnace was investigated. The size and temperatures of the spots were determined by means of photographs and optical pyrometer. Composition of the plasma in anode spot region has been calculated. Cylindrical crucible of 100 mm in diameter with an axial hole of 40 mm in diameter and 28 mm in depth was rotated with the speed of ~100 rpm. Cylindrical cathode of 50 mm in diameter had an axial channel of 24 mm in diameter. Argon was fed through the channel as plasma forming gas. Crucible and cathode were located in the steel water cooled chamber with a volume of 150 liters. The arc was several centimeters long, arc current was 560-630 A. It was shown experimentally that 23-25 kW argon plasma arc can forms contracted or diffuse anode spot. The current density of contracted spot is 1800 A/cm2, while that of diffuse spot is ~250 A/cm2. Contracted spot formation occurs on a cold crucible and accompanied by intensive evaporation of graphite in a spot region. The carbon vapor decreased ionization potential of plasma near the anode and promoted contraction. A uniform heating of the hole in crucible up to 2700 K is needed for transformation of the contracted spot into diffuse one. Such heating was attained by rotation of crucible. Thermal isolation of crucible also promotes diffuse spot formation. Poisson’s equation was solved, and the voltage falls in space charge zones were calculated for contracted and diffuse spots as 10.7 and 1.5 V respectively. It was assumed that the lesser voltage fall promotes the diffuse spot formation.

Effect of Exposure Time, Lining Material and Plasma Gas on the Extraction of Aluminium from Waste by Smelting Reduction

Today’s world has experienced the change in the extraction of metal from its native ore to that from secondary resources. The ash and tailings are such secondary resources for extraction of aluminium. The present investigation shows the effect of furnace lining materials and plasma gas on the extraction of aluminium from the waste material during smelting reduction studies. A laboratory scale plasma arc furnace was used for the reduction studies of bottom ash, iron ore slime with charcoal. Experiments in hydrogen and nitrogen plasma environments were carried out inside magnesite and graphite crucible separately. The rate of reduced metal absorption by the liquid metal bath for a fixed time was determined. The output of aluminium through metal, slag and exit gas was calculated to establish a tentative mechanism of smelting reduction. Combination of nitrogen plasma and graphite crucible showed the optimum recovery level of reduced aluminium in metal. The high-temperature plasma could reduce highly stable oxides of waste materials, and the recovery of volatile aluminium in metal could be possible by using a metal solvent bath.

Quantification of heat transfer phenomena within the melt pool during the plasma arc re-melting of titanium alloys

This paper summarizes the development and application of a mathematical model, based on the commercial Computational Fluid Dynamics code ANSYS-CFX, to describe the transport processes occurring during the heating of a cylindrical slice of Ti-6 wt%Al-4 wt%V (Ti64) ingot with a plasma torch. The model simulates the conditions observed in a test (trial) that was conducted within an industrial scale plasma arc furnace. The test conditions, data, analysis methodology and results, in terms of characterization of the surface heat flux, have previously been published and are only presented in this manuscript in a summary form. This work focuses on the development of a thermal-fluid model of the ingot slice in order to better describe the heat transport processes occurring in the molten pool, which was identified as a shortcoming of the previous work. The model includes heat and fluid transport by diffusion and advection, thermal buoyancy, surface shear resulting from both thermal Marangoni forces and the plasma gas and Darcy damping within the two-phase (solid/liquid) region. A preliminary thermal-fluid model of the plasma plume was also developed as part of the research (not presented) and used to help guide development of a suitable gas shear stress distribution, which was implement using a log-normal approximation. The model was found to be able to reproduce thermocouple and pool profile data collected during the trial. In particular, the prediction of the pool profile was found to be considerably more accurate than had previously been the case with a diffusion-only heat transfer model. A sensitivity analysis conducted with the model showed the liquid pool profile to be highly dependent on the magnitude of the gas shear force and the input power efficiency and distribution. The gas shear was found to have a significant impact on near-surface fluid flow, helping to enhance radial heat transport. In comparison to the Marangoni induced shear, the gas shear was found to be dominant.

Design, Fabrication, and Characterization of an Indigenously Fabricated Prototype Transferred Arc Plasma Furnace

The extraction of metals like Al and Si from bottom ash having alumina and silica requires high temperature for their reduction. Only transferred arc plasma (TAP) furnace could meet this requirement. The TAP furnace was fabricated indigenously for performing experiments in laboratory based on the information available in the literature, related to the furnace design. The furnace was fully characterized for its smooth functioning by observing parameters like arc length, energy, and electrode consumption as well as the generation of sound level. It was found that the required temperature could be achieved by varying arc length, arc current, power rating as well as plasma gases. Arc length could be adjusted by varying power rating and changing voltage for required heat distribution above the melt. The accessories like the charge feeding system, gas purification and its flow system, gas exit system, the pouring system were worked satisfactorily. Sound level could be controlled by controlling arc current with the plasma gas. The thickness of lining was found sufficient to hold liquid metal either in graphite or magnesite crucible. Increased melt temperature (~200 °C) and ~10-dB lower sound level could be achieved by using nitrogen plasma as compared to the normal arc. But, hydrogen plasma produces more ~100 °C melt temperature, and ~5-dB sounds as compared to nitrogen plasma. Based on the results of the operational trial, it could be concluded that the TAP furnace was found to be a suitable tool for melting 2-kg iron and its various attachment were also found to be trouble-free operation.

Calculation of Heat Transfer Characteristics of an Arc in a Gas Stream of Plasma-Arc Furnaces

Within the framework of the heat exchange model of electric arc, the arc characteristics in the gas jet of a melting plasmotron are calculated in the approximation of the interaction of a semi-infinite isothermal jet with a wall. The temperature profile, structure, and values of the heat fluxes of a part of the arc column in the melting space of the plasma arc furnace are determined to a distance from the cathode. For the given power and composition of plasma-forming gas, the electric and thermal characteristics of the plasmotron and its geometry are established. Examples are given of calculation of arc characteristics in argon and argon–hydrogen mixture in the initial period of melting of solid charge with stable arc combustion taking into account the influence of electric circuit parameters. The results on the temperature profile of the arc in a gas jet are presented.

Study of effective utilization of iron ore sinter through arc plasma

Generation of fines is common in mining, sizing, and beneficiation and also in high-temperature metallurgical processes as the disintegration of agglomerate/compact occurs. Extraction of metallic iron from ore fines is one of the challenging aspects of iron making industries as the liberation of fines blocks, the charge burden porosity and hence hinders the reduction rate. Along with size factor, mineral composition plays a vital role in the extraction process; particularly silica. As silica has the very high tendency towards iron oxide, at comparatively low temperature, the activity of silica should be suppressed to prevent silicate phases. Adjustment of such conditions is controlled by addition of lime, but sometimes excessive slag generation increases the cost of production. In the present work, carbothermic reduction of partially reduced iron bearing pellets has been melted through 20 KW DC arc plasma furnace, and a comparative study has been made for considering different slag chemistry approaches. Pellets as aforementioned are made available from Patnaik Steel and Alloys Ltd, Odisha, having high silica content ore fines (of about 8.6%) as obtained from the chemical analysis. X-Ray analysis and optical image analyzer result of sinter thus obtained reveal that fayalite phase has major fractional value. Smelting works were done for sinter with/without adjustment of slag chemistry, where argon and nitrogen were used as plasma forming gases. A range of recovery rates (between 87-94%) is achieved by charge composition, ionizing gases, and smelting duration. It is observed that use of nitrogen as plasma forming gas increases the recovery rate than that of using only argon plasma; due to high energy flux of nitrogen which increases the enthalpy due to its diatomicity. A maximum recovery rate of about 94% is achieved for process duration of 13minutes utilizing nitrogen plasma. Smelting of charge with the addition of hydrated lime targeting melilite as final slag resulted in the formation of metallic iron as confirmed from XRD and XRF analyses. In the other hand, ferrosilicon is liberated in the metallic parts where smelting of charge was done without adjustment of slag chemistry. Both metal and slag thus obtained are characterized by XRD, XRF, microhardness and wet chemical analysis suitably.

Behavior of an indigenously fabricated transferred arc plasma furnace for smelting studies

The utilization of industrial solid waste for metal recovery requires high-temperature tools due to the presence of silica and alumina, which is reducible at high temperature. In a plasma arc furnace, transferred arc plasma furnace (TAP) can meet all requirements, but the disadvantage of this technology is the high cost. For performing experiments in the laboratory, the TAP was fabricated indigenously in a laboratory based on the different inputs provided in the literature for the furnace design and fabrication. The observed parameters such as arc length, energy consumption, graphite electrode consumption, noise level as well as lining erosion were characterized for this fabricated furnace. The nitrogen plasma increased by around 200 K (200 °C) melt temperature and noise levels decreased by ∼10 dB compared to a normal arc. Hydrogen plasma offered 100 K (100 °C) higher melt temperature with ∼5 dB higher sound level than nitrogen plasma. Nitrogen plasma arc melting showed lower electrode and energy consumption than normal arc melting, whereas hydrogen plasma showed lower energy consumption and higher electrode consumption in comparison to nitrogen plasma. The higher plasma arc temperature resulted in a shorter meltdown time than normal arc with smoother arcing. Hydrogen plasma permitted more heats, reduced meltdown time, and lower energy consumption, but with increased graphite consumption and crucible wear. The present study showed that the fabricated arc plasma is better than the normal arc furnace with respect to temperature generation, energy consumption, and environmental friendliness. Therefore, it could be used effectively for smelting-reduction studies.

Comparison of Copper and Graphite Crucibles for Si Extraction from TiO2 - SiO2 System at Plasma-Arc Heating

<p>Plasma arc recovery melting of the quartz-leucoxene concentrate is investigated. Experiments were made in laboratory DC plasma arc furnace in various crucibles. The best results are reached in a cold copper crucible. The temperature field of a pool is calculated in hot graphite and cold copper crucibles. It is shown that in a graphite crucible diameter of an anode spot is more, and density of current and material temperature in a spot is less, than in copper that is the reason of the worst refinements in a graphite crucible.</p>

Quantification of the heat transfer during the plasma arc re-melting of titanium alloys

This paper summarizes the development and application of an Inverse Heat Conduction Code (IHCC) to determine the surface heat flux distribution from an industrial plasma torch applied to heat a sample of Ti-6wt%Al-4wt%V (Ti64) alloy. The test (trial) was conducted within an industrial scale plasma arc furnace and the sample was instrumented with 15 thermocouples embedded below the top surface. The sample was heated for 278 s, which allowed sufficient time for a liquid pool to form within the sample. Following the trial, the sample was sectioned to obtain the liquid pool profile. The IHCC analysis method described in the paper is based on the future time-step approach and uses the commercial finite element code ABAQUS™ as the forward conduction engine. The IHCC analysis was conducted with both isotropic thermal conductivity and anisotropic thermal conductive in the liquid. The later, was used to approximate the effect of fluid flow on heat transport in the liquid. Additionally, the method used linear interpolation to vary the estimated heat flux between the discrete heat flux evaluation points associated with the thermocouple positions. The results indicated that it is critical to account for fluid flow and suggest that the heat flux distribution can be accurately described by two over-lapping Gaussian distributions: one narrow distribution associated with convective heat transfer; and a second, broader distribution, associated with radiation. An overall heat transfer efficiency of 28% was estimated from the heat flux distribution.

Volatilization and leaching behavior of heavy metals in MSW incineration fly ash in a DC arc plasma furnace

Three fly ash samples collected from different waste incinerators were vitrified using a direct current arc plasma furnace at 1250–1400°C. The influence of water-wash extraction and wrapping pretreatment on the volatilization and leaching behavior of heavy metals was investigated. Results showed: After thermal arc plasma treatment, the volume reduction and weight loss of fly ash were in the range of 68.7–82.2% and 23.8–56.7%, respectively. The residual fractions (wt.%) of heavy metals in slag are in the following sequence: Cr<Ni<Cd<Pb<Cu<Zn. Water-washing could reduce the volatilization rate of heavy metals due to some volatile salts removed by washing, while wrapping of fly ash could most effectively resist heavy metals against volatilizing, especially for Zn and Ni. The possible CaO – Al2O3 – SiO2 (CAS) ratio for successful melting of fly ash is suggested to be CaO in range of 20–48%, Al2O3 in range of 10–15%, and SiO2 in range of 40–65%. Moreover, toxicity characteristic leaching procedure results showed that the leaching of heavy metals in slags was much lower than the standard limit of toxicity characteristic leaching procedure (TCLP).

Plasma-arc production of synthetic rutile from leucoxene concentrate

Plasma production of synthetic rutile from leucoxene concentrate with high contents of SiO2 is described. Concentrate was melted with carbon in laboratory plasma-arc furnace. Synthetic rutile with 3.6 % Si was produced. Experimental results and thermodynamic calculations are presented.

Electrotechnology for Silicon Refining: Plasma Generator and Arc Furnace: Installations and Theoretical Base

Electrotechnology for Silicon Refining: Plasma Generator and Arc Furnace: Installations and Theoretical Base

Low Computational-complexity Model of EAF Arc-heat Distribution

The paper presents a computational model and the corresponding algorithm for estimating the arc energy distribution to conductive, convective and radiative heat transfer in an electric arc furnace (EAF). The proposed algorithm uses channel arc model (CAM) in order to compute the distribution of the arc energy through empirical equations (to approximate arc radius), ideal gas law (to approximate arc density) and results of magneto-hydro-dynamic (MHD) models (to approximate arc pressure, temperature and velocity). Results obtained using the proposed algorithm are comparable with other similar studies; however, in contrast to other arc-energy distribution models, this model requires only two input variables (arc length and arc current) in order to calculate the energy distribution. Furthermore, simple algebraic equations used in the algorithm ensure minimal computational load and consequently lead to short calculation times which are approximately one hundred thousand (100 000) times smaller than solving the MHD model equations, making the algorithm suitable for real-time applications, such as smart monitoring and model-based control. The algorithm has been validated by two different approaches. First, the simulation results have been compared to a study dealing with arc-heat distribution in plasma arc furnace; and second, the proposed arc module has been integrated into the frame of a comprehensive EAF model in order to estimate the EAF temperature levels and compare them with operational EAF measurements. Both validations show high levels of similarity with the comparing data.

Experiments on MCCI with oxide and steel

Recently performed experimental programmes at the French VULCANO and the German MOCKA and SICOPS facilities aimed at the further elucidation of various phenomena of molten core-concrete interaction (MCCI). Questions on these phenomena arose during the scientific discussion of MCCI in the last years.The large-scale MOCKA (KIT, Karlsruhe) experiments study the interaction of a simulant oxide (Al2O3, ZrO2, CaO) and metal melt (Fe) with concrete. To allow for a long-term interaction, internal heating was provided by alternating additions of alumino-thermite and Zr metal to the upper oxide layer of the stratified melt. Since the heat generated by the thermite reaction and the exothermal oxidation reaction of Zr is mainly deposited in the oxide phase, prototypic heating of both melt phases is achieved.Recent tests in the MOCKA (KIT, Germany) program are focused on assessing the influence of a typical 6wt.% reinforcement in the concrete on the erosion behaviour. The experiments were performed in siliceous concrete crucibles with an inner diameter of 25cm and a height of 1.3m. In these experiments, the overall downward erosion by the metal melt was of the same order as the sideward one. In addition, the lateral erosion in the overlaid oxide melt region was about the same as in the metal melt region.Experiments with prototypic UO2-containing melts have been conducted in parallel in the VULCANO (CEA, Cadarache) and SICOPS (AREVA, Erlangen) facilities.In VULCANO a plasma arc furnace melts the oxide corium while three 1-L steel induction furnaces melt the steel. All these melts are poured in a concrete cavity where the decay heat is applied to the oxide phase via 40-kHz induction coils. VULCANO VBS tests with oxide and metal have shown an increased ablation in front of the metallic masses. More unexpected results concern a very high steel oxidation (especially in VBS-U1 with limestone-rich concrete in which almost all the steel was oxidised) and the fact that post test examinations did not show the expected horizontal steel layer.Induction heating was also used for decay heat simulation in the laboratory-scale SICOPS tests, using a “cold crucible” technique and a higher frequency of about 1.3MHz. Tests were performed to study the influence of an additional metal phase on the 1D erosion behaviour. For these mixed melt tests, concrete specimen of 10cm diameter, made of siliceous concrete with grain aggregates, were used. Oxide melts were either simulant or prototypic melts. Metallic melt was form by addition of steel (steel 37.1) pellets after oxidic melt has been produced. It was found that the impact of the metal phase depends on heating power and gas release rate. The analysis suggests that the mechanism of concrete attack by metal melt can be understood as a thermal destruction mechanism.