DC Furnaces Research Articles

Composite (cored) graphitized electrodes for industrial DC and AC steel-melting furnaces

Composite (cored) graphitized electrodes for industrial DC and AC steel-melting furnaces

Композитні (гнотові) графітовані електроди для промислових дугових сталеплавильних печей постійного та змінного струму

Композитні (гнотові) графітовані електроди для промислових дугових сталеплавильних печей постійного та змінного струму

Pilot Tests of Pre-Reduction in Chromium Raw Materials from Donskoy Ore Mining and Processing Plant and Melting of High-Carbon Ferrochromium

Experiments were conducted to pilot the initial reduction in chromium raw materials using the innovative Hoganas technology in a tunnel furnace. To simulate the process, a gas-fired bogie hearth furnace was employed. Technological containers made of silicon carbide crucibles were utilized. Sixteen different combinations of ore and coal mixtures were employed for the initial reduction process. Their total mass was more than 20 tons. Their heat treatment was performed at different temperatures and durations. During the pilot tests, the possibility of achieving chromium metallization was confirmed. Thus, it explains the application of a pre-reduction instead of the sintering or charge heating before the ferrochromium melting, i.e., the power consumption is minimized during the final remelting of the product in DC furnaces. The pilot melting of three batches of the pre-reduced chromium raw materials with various chromium metallization degrees has been tested in the ore-smelting furnace at Zh. Abishev Chemical–Metallurgical Institute (Karaganda). The capacity was 0.2 MVA. To evaluate the technical and economic efficiency of remelting pre-reduced chromium raw materials in commercial DC furnaces, a specific batch of primary ingredients for producing high-carbon ferrochromium, including chromite ore, coke, and quartz flux, was successfully melted in a segregated phase. As a result of the study, it was found that the specific energy consumption for melting high-carbon ferrochromium in the pilot furnace depends on the chromium metallization degree. The researchers tested a range of chromium metallization degrees from 0 to 65% and determined the corresponding specific energy consumption for each degree. Using the data obtained from the study, the researchers were able to assess the melting indexes of high-carbon ferrochromium in a larger 72 MW furnace. They found that by using a pre-reduced product with a chromium metallization degree of 65%, it was possible to reduce the specific energy consumption by half, to around 3.4 MW·h per ton of chromium. Overall, this study highlights the importance of considering the chromium metallization degree when determining the specific energy consumption for melting high-carbon ferrochromium. By optimizing the metallization degree, significant energy savings can be achieved, leading to more efficient and sustainable production processes.

Composition and Cr- and Fe-speciation of dust generated during ferrochrome production in a DC arc furnace

A potential hazard associated with ferrochrome production is the unintentional generation of Cr(VI) in the off-gas dusts produced during smelting. Cr(VI) is a well-known environmental toxin and genotoxic carcinogen. Although Cr(VI) has been identified in baghouse dusts associated with submerged-arc furnaces, its occurrence in DC-arc-furnace dusts has not been previously investigated. In this study, we report the bulk composition and phase make-up, as well as the surface and bulk speciation of Cr and Fe of dusts generated during smelting of chromite ore under basic slag conditions in a pilot-scale DC arc smelter. Dusts are captured from both within the DC furnace as well as along the off-gas handling stream, after passing through the afterburner. The dusts primarily comprise feed material (chromite, flux, reductant), aerosolized slag, and glassy spherules, interpreted as off-gas condensates. Dusts collected from within the furnace, known as freeboard dusts, are dominated by feed materials, with elevated amounts of flux (lime) and lesser amounts of slag and spherules. In contrast, spherules dominate dusts collected along the off-gas handling stream by dust separators that capture the increasingly fine-grained fraction of dust, with the highest proportion of spherules occurring in baghouse dusts. Chromite is the primary host of Cr in all dust samples, whereas the spherules have low Cr contents. Cr(VI) was identified by X-ray photoelectron spectroscopy in the surfaces of dust collected from all parts of the smelter system considered, including from the furnace freeboard, despite the overall reducing conditions present therein. Cr(VI) concentrations are sufficiently high in dusts collected from the off-gas handling stream (post-afterburner, cyclone, and baghouse) to be detected in the bulk dust samples by X-ray absorption spectroscopy. The higher concentration of Cr(VI) in the finer-grained off-gas dusts, especially the baghouse dusts, is consistent with the increased abundance of spherules, the major Cr(VI)-hosting phase, in these samples. Fe is similarly more oxidized in dusts collected down the off-gas handling stream compared to dusts collected from within the furnace, which are dominated by Fe(II). Fe(III) hosted by FeOOH is predominate in dusts collected from all locations along the off-gas handling stream. These results demonstrate that there is sufficient oxygen ingress and sufficiently high temperatures in the closed DC furnace for Cr(VI) to be generated in the freeboard off-gas dusts. Cr(VI) is associated with the finest grained fraction of dusts, underlining the importance of ensuring the continual improvement of dust-capture systems, especially in terms of their ability to target increasingly finer fractions of dust. • Cr(VI) can form in a closed DC arc furnace. • Cr(VI) forms up to about one-third of the Cr species present on particle surfaces. • Fine-grained dusts captured by the baghouse host the highest proportion of Cr(VI). • Spherules are the major Cr(VI)-bearing phase in off-gas dust. • Chromite is the major source and host of Cr in smelter dusts.

Pig Iron Production (Post Blast Furnace Era)

It has become an environmental drive world-wide to reduce the production of Carbon Dioxide (CO2) in the steelmaking process. Alternative reductants other than coal-based materials has been found to be a true replacement with resultant major reduction in CO2, by using “cleaner” reductants like natural gas. Coke consumption in the Blast Furnace requires coke to produce pig iron for which alternative reductant routes are now sought. It has been proven that natural gas is a suitable reductant in the production of Direct Reduced Iron (DRI) in a shaft furnace or a Rotary Hearth Furnace (RHF) process. This DRI can then be used as raw material for pig-iron production in a closed Submerged-Arc Furnace (SAF), (being a circular AC Furnace, DC Furnace, or a large 6-in-line Rectangular Furnace), where a reduced amount of reductant is required for final reduction and introducing additional carbon required for the subsequent steelmaking processes. The SAF also acts as a slag modifier which adds value to this traditional waste product. Instead of producing aggregate, high quality granulated slag is produced which can be used as a clinker replacement material in the classical cement production. This contributes to the reduction of CO2 gasses by reducing traditional cement fabrication. Fossil-based reductant are still required through this process route, but the sum equates to a reduction of fossil-based reductants. The use of renewable energy as a source of electricity further adds to the reduction of emissions adding even more value to the whole production chain. A natural progression from this process step would be the introduction of environmentally friendly Hydrogen (H2) in the future.

Metallurgical Research and Its Contribution to Industrial Development

Metallurgical Research and Its Contribution to Industrial Development

Modelling of the thermal state and the melting loss of a graphite electrode in the conditions of the evaporative cooling in the arc furnace

The cost of the graphite electrodes amounts greater proportion in the final value of the finished product. This calls for finding opportunities to reduce the maintenance costs of AC and DC furnaces used in foundries. The aim of the study is the creation of a mathematical model and the analysis of the efficiency of the evaporative cooling method in reducing the amount of the graphite electrodes used in small capacity arc furnaces. The mathematical model and the computer program allow determining the thermal state of the electrode and the melting loss of the graphite, the model is developed for a primarily cylindrical electrode and takes into account: the current passing through an electrode, the time of the electrode being in the electrified furnace, and the parameters of the water evaporative cooling. The paper presents the received data about the melting loss of the graphite per ton of steel against the water consumption during the evaporative cooling. The graphite consumption in the arc furnaces of 10–12 tons’ capacity is reduced by 40 %. The recommended water consumption for the evaporative cooling of electrodes for all types of foundry furnaces is 0.1–0.2 m3/h.

Current state of ferroalloys production in Russia and CIS

Development of ferroalloy production directly depends on p ress of steel industry. Therefore, an increase in steel production inevitably entails an increase in the production of ferroalloys. Over the past 10 years, global steel production has increased by about 30 %. This article discusses general condition of the ferroalloy sector in the CIS countries and, in particular, in the Russian Federation. The main consumers (among Russian metallurgical enterprises) of ferroalloy products in the domestic market were listed, and the structure of production and consumption in other producing countries (China, India, the EU, USA, Japan) was examined. It was revealed that the overproduction of ferroalloys in the CIS countries is about 400 %. In addition, the ways of development of the ferroalloy field were also considered, aimed at reducing the contribution to the production cost of ore raw materials, reducing agent and electricity, which is achieved through the use of cheaper ore, the use of new types of processes and units, and development of other alternative types of ferroalloys, replacing classic ones. For example, it can be smelting in DC furnaces, which allows the use of small unprepared chrome ore as a raw material for the production of ferrochrome containing scarce lump in combination with small cheap reducing agent (anthracite). Melting in an oxygen reactor is also a promising technology, based on the principle of gaseous oxygen, which results in the reduction of carbon monoxide inside the unit itself. The alternative types of ferroalloy products can be used, such as calcium carbon “KAUR”, which can replace calcium carbide in steelmaking.

Current State of Ferroalloys Production in Russia and CIS

The development of ferroalloys production directly depends on the progress in the steel industry. Therefore, an increase in steel production inevitably entails an increase in the production of ferroalloys. The global steel production has increased by about 30% in the past decade. This article discusses the general condition of the ferroalloy sector in the CIS countries and, in particular, in Russia. The main consumers of ferroalloy products in the domestic markets among Russian metallurgical enterprises are listed, and the structure of production and consumption in other producing economies (China, India, the EU, the United States, Japan) is examined. It is revealed that the overproduction of ferroalloys in the CIS is nearly 400%. In addition, the ways of developing the ferroalloy sector are considered, that is, aimed at reducing the share of ore raw materials, reducing agent, and electricity in the production cost, which is achieved by using cheaper ore, applying new types of processes and outfits, and designing alternative ferroalloys to replace their conventional counterparts. One of such novelties is smelting in DC furnaces, which allows using unprepared fine chrome ore as a raw material instead scarce lump ore in combination with a cheap fine reducing agent (anthracite) for ferrochrome production. Another promising technology is melting in an oxygen reactor by postcombustion with gaseous oxygen released with the reduction of carbon monoxide inside the outfit. In addition, alternative kinds of ferroalloy products can gain ground, such as KAUR calcium carbon which can replace calcium carbide in steelmaking.

Influence of joule heat and heat of electric arc on the vortex flow in DC arc furnace

The paper devoted to the numerical simulation of processes in DC electric arc furnaces with the bottom electrode. These furnaces have shown higher efficiency, low heat loss, lower components wear and higher quality of steel production. The biggest disadvantage of such furnaces is a high rate of fettle wear near the bottom electrode that connected with electrovortex flow. Electrovortex flows appearing under electromagnetic forces as a result of non-homogeneous distribution of the current density through the liquid conductor. This effect can be observed in many technological processes: electro slag remelting process (including DC and AC metallurgical furnaces, electrolysis cells and submerged-resistor induction furnaces), arc welding, processes of semiconductor crystals growing, electro vortex engines etc.

Features of Smelting Carbon Ferrochrome in AC and DC Electric Arc Furnace

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Electrical Conditions of Foundry Operation of DC and AC Arc Furnaces

The electrical conditions of operation of ac and dc 0.5- to 25-t furnaces, namely, the installed, active and net powers, the maximum electric arc voltage, the electric arc operating current, and the electrical efficiency, are considered and compared. The parameters of a dc twin furnace, where one power supply is used for two furnaces and the periods of melting and finishing of a liquid metal in these furnaces are separated in time, are analyzed.

Erratum to: Computational Modeling of Arc–Slag Interaction in DC Furnaces

Erratum to: Computational Modeling of Arc–Slag Interaction in DC Furnaces

Computational Modeling of Arc–Slag Interaction in DC Furnaces

The plasma arc is central to the operation of the direct-current arc furnace, a unit operation commonly used in high-temperature processing of both primary ores and recycled metals. The arc is a high-velocity, high-temperature jet of ionized gas created and sustained by interactions among the thermal, momentum, and electromagnetic fields resulting from the passage of electric current. In addition to being the primary source of thermal energy, the arc jet also couples mechanically with the bath of molten process material within the furnace, causing substantial splashing and stirring in the region in which it impinges. The arc’s interaction with the molten bath inside the furnace is studied through use of a multiphase, multiphysics computational magnetohydrodynamic model developed in the OpenFOAM® framework. Results from the computational solver are compared with empirical correlations that account for arc–slag interaction effects.

Utilization of ferroalloy-production wastes

The problems associated with the ongoing decline in the quality of minerals and the growing volume of industrial wastes generated in ferroalloy production are outlined. Measures proposed for resource conservation and waste utilization are reviewed. It is shown that the lack of waste recycling at ferroalloy plants is partially associated with the low economic efficiency of the available methods, whose capital expenditures and operational costs are high. At the same time, reducing the waste tailings will improve environmental conditions around ferroalloy plants and hence indirectly reduce governmental costs. Ameliorative measures proposed include the construction of new smelting units equipped with up-to-date gas purification and dc furnaces that do not require the use of pelletized materials; and economically appropriate utilization of natural minerals and industrial waste products.

Balance of Raw Input and Energy of Titanium Slag Smelting in Closed High Power Direct Current Electric Arc Furnace

There were two controlling factors, which should be kept balance of raw input and energy during titanium slag smelting in closed high power direct current electric arc furnace, DC furnace for short. The first factor contains compositions and ratio of input raw materials. Compositions of the raw could influence the progress and technical indicators of DC furnace smelting, and on the meanwhile, it could determine the compositions of impurity and contents of TiO2 in titanium slag. On the other hand, the ratio of input infected the compositions of the slag, while too much anthracite would disadvantage to produce high quality slag because of impurity being reduced continually. Meanwhile much more low-state titanium would be generated. The second factor was an important one that energy equilibrium, which influence the production safety of DC furnace. It could keep balance of input and output energy, while the heatloss was 4.971 MVA. While the ratio of anthracite remained the same, the energy would effect slag viscosity and equilibrium of freeze lining directly. The energy input higher than smelting need would result in burnthrough of furnace wall and hearth, on the contrary, lower than smelting need would bring about slagging difficulties. Consequently, raw input and energy must be kept dynamic balance in order to achieve high quality titanium slag and protect freeze lining.

Energy Balance and Offgas Utilization of Ilmenite Smelting in a 30 MVA Direct Current Electric Arc Furnace

Energy balance and offgas utilization of ilmenite smelting in 30 MVA direct current electric arc furnace (DC furnace) of a Yunnan company were investigated to make sure safety production, and to save energy and reduce pollution. The total input energy in the DC furnace was 2,000 kWh per ton of ilmenite, in which 1,003.31 kWh per ton of ilmenite was used to carbothermic reduction and other energy was consumed as heatloss. Based on energy conservation, the whole system heatloss in physical production should be controlled at 1,000 kWh per ton of ilmenite. With high combustion heat, the offgas discharged from furnace after treatment could be used to ilmenite drying, anthracite drying, titanium slag drying, and casting ladle baking. The offgas design flow ranged from 5,000 to 8,000 Nm3/h with the mean of 6,500 Nm3/h. The combustion heat quantity of offgas in the plant was 82,160 MJ per hour, which could save 480,276.8 kWh of electrical energy per day, and thus lower carbon emission of the whole production line.

Dry Sliding Wear of Active Screen Plasma Carburised Austenitic Stainless Steel

Low temperature diffusion treatments with nitrogen and carbon have been widely used to increase the tribological performance of austenitic stainless steels. These processes produce a layer of supersaturated austenite, usually called expanded austenite or S-phase, which exhibits good corrosion and wear resistance. The novel active screen technology is said to provide benefits over the conventional DC plasma technology. The improvements result from the reduction in the electric potential applied to the treated components, and the elimination of such defects and processing instabilities as edge effects, hollow cathode effects and arcing. In this study, AISI 316 coupon samples were plasma carburised in DC and active screen plasma furnaces. The respective layers of carbon expanded austenite were characterised and their tribological performance was studied and compared. Detailed post-test examinations included SEM observations of the wear tracks and of the wear debris, EDX mapping of the wear track, EBSD crystal orientation mapping of the cross sections of the wear tracks, and cross-sectional TEM. Based on the results of wear tests and post-test examinations, the wear mechanisms involved are discussed.

Electrovortex motion of a melt in dc furnaces with a bottom electrode

The effect of the Lorenz force on the origination of the electrovortex motion of a metal melt in dc electric steel furnaces with a bottom electrode is evaluated. The motion of a metal melt is described by equations of magnetic hydrodynamics for isothermal liquid, which are solved by the finite element method. The numerical solution is compared with theoretical results and experimental data of other authors. From analysis of the results obtained, conclusions are drawn that the Lorenz force has a marked effect on the origination of the vortex motion of a melt.

Computational analysis of a twin-electrode DC submerged arc furnace for MgO crystal production

A twin-electrode DC arc furnace has been designed for MgO crystal production and this technique has been found to be another effective method to grow high quality MgO single crystals. Compared with AC submerged arc furnaces, the benefits of DC furnaces are significant. However, the magnetohydrodynamic effects might inhibit the growth of large single crystals. In order to understand the process we present a three-dimensional numerical model of the DC furnace. Coupled with Maxwell's equations, the conservation equations for mass, momentum, and energy are solved with ANSYS. It is found that the shape of the melt–solid interface is significantly affected by the electromagnetic stirring, and the predicted shape of the molten bath shows good agreement with the experiments. It is observed that the environment is more suitable for the crystal growth between each electrode bottom and the shell. These interesting phenomena may be caused by the variation of the flow field which is quantitatively described in the model. Other detailed information including the electric power and the voltage drop distribution is also given approximately by the model to give decision support for the power control system.