Submerged Arc Furnace Research Articles

Preparation of High-Quality Silicon with Silicon Cutting Waste by a Carbothermal Reduction Method

Silicon cutting waste (SCW) mainly consists of Si (80 ~ 85 wt%), SiO2 (13 ~ 16 wt%) and other impurities (2 ~ 4 wt%). Nowadays, the Si in SCW is commercially recycled to produce Si ingots by a slag refining method, but the SiO2 in SCW is melted into silicon slag and discarded as waste. In this paper, a carbothermal reduction method has been proposed for recycling Si resources from both Si and SiO2 in SCW to prepare high-quality silicon in a submerged arc furnace. Petroleum coke was selected as the carbonaceous reducing agent. Firstly, the effects of carbon content on the equilibrium compositions of the Si-SiO2-C system were simulated. Secondly, SCW was mixed with petroleum coke under the guidance of thermodynamic analysis results. Finally, the mixtures were charged into furnace and smelted. Thermodynamic equilibrium analysis results showed that the value of n(Si):n(C):n(SiO2) should be controlled as 2.62:0.22:0.44 theoretically. Experimental results revealed that the recovery ratio of SCW was 50% and the purity of Si products was 99.40%. This proposed method provides an effective and industrialized applicable approach for recycling SCW.

Development and Design of the First Industrial Magnetohydrodynamic Slag-Cleaning Reactor From Execution and Analysis of Pilot Plant Tests Through Coupled CFD Simulations

The future challenge for copper smelters is to increase metal yield by reducing copper losses and valorizing the slag as a marketable by-product. This can be achieved through further slag cleaning in a conventional submerged arc furnace (SAF) where remaining metallic oxides are reduced, and metal droplets have more settling time. Nevertheless, a significant amount of copper matte and metallic copper is still present as slight inclusions that cannot settle through the slag layer under simple gravity after SAF treatment. This work presents the development of a new industrial type of slag-cleaning concept, based on the magnetohydrodynamic (MHD) principle, that can be coupled downstream of conventional slag-cleaning technology (e.g., electric reduction furnace). The cleaning efficiency and operating conditions were evaluated in several pilot test campaigns using a SAF supplemented by an externally applied magnetic field (electromagnet), which interacts with electrodes generating Lorentz forces, which are responsible for an MHD stirring effect. In order to simulate experimental conditions and thus understand reaction kinetics and settle mechanisms during pilot tests, this work includes computational fluid dynamics (CFD) models. In order to represent these electromagnetic conditions, the focus of this work is to develop a new coupled CFD model. Numerical simulations showed the interactions between MHD flow field, slag properties, and metal recovery in an industrial slag-cleaning reactor and demonstrated the MHD cleaning effect on non-ferrous slags.

Energy Consumption and Greenhouse Gas Emissions of High-Carbon Ferrochrome Production

This work presents a process model developed based on mass and energy conservation to assess high carbon ferrochrome production from cradle to gate through four supply routes: (1) a conventional submerged arc furnace (SAF), (2) a closed submerged arc furnace with preheating (CSAF+PH), (3) a closed submerged arc furnace with 60% prereduction (CSAF+PR60%) and (4) a direct-current arc furnace (DCAF). The energy requirements are between 40 and 59 GJ/t FeCr (74–111 GJ/t Cr), and the greenhouse gas (GHG) emissions range between 1.8 and 5.5 tCO2-eq/t FeCr (3.3–10.3 tCO2-eq/t Cr). The upgrading of coal-powered SAF process to a closed furnace CSAF+PH and CSAF+PR60% contributes to an emission reduction of 23% and 18%, respectively. Moreover, the use of hydro-powered electricity leads to a further emission reduction of 68% and 47%, respectively. For CSAF+PR process, the GHG emissions can be reduced by 14% when increasing the pre-reduction ratio from 30% to 80% and decreased by 10% when charging hotter feed from 100 °C to 1000 °C. The proposed process model is feasible in generating site-specific inventory data and allowing for parameter studies as well as supporting companies to improve the transparency of the environmental performance in the FeCr value chain.

Investigation of Ultrasonic Velocity and Transmission Losses in Graphite Rods Based on Numerical Simulation and Experiment

The depth of electrodes inserted into the charge plays a vital role in controlling the submerged arc furnace. Therefore, we used ultrasound waves reflected from the electrode tip to estimate the depth of electrodes inserted into the charge. However, graphite’s ultrasonic velocity and transmission loss are the basis for establishing an ultrasonic measurement system. Thus, we expected to improve our understanding of them through numerical simulations and experimental measurements. First, we proposed an ultrasonic detection method to estimate the electrode length by embedding graphite rods in Söderberg electrodes. Then, we developed a 3D finite element model in COMSOL for wave transmission in the graphite rod. The wave transmission through 20 and 40 cm graphite rods was simulated using finite element models. The transmission loss, sound pressure, intensity, and displacement distribution of the sound wave passing through the graphite electrode were calculated. To verify the simulation calculation results, we further conducted an acoustic experiment. The results showed that transmission loss varies significantly with frequency. When the frequency was between 25 and 55 kHz, the transmission loss of the graphite rod was slight. At 47 kHz, the transmission loss was 1.837 dB/m.

Induced Currents in the Lining and Steel Shell of Submerged Arc Furnaces

Numerical models in 2D and 3D are used to study induced currents in the lining and steel shell of large three-phase submerged arc furnaces. The alternating currents supplied through the electrodes cause a significant amount of induced power in the furnace lining and shell. The induced currents flow in three large loops with an accumulation of current near the top of the steel shell between the electrodes. The net result is a thermal loss with heat dissipated at the surface. Furthermore, such accumulation may cause potentially damaging hot spots in the steel. If this persists over a long time, the shell may thin and deteriorate and, in worst-case scenarios, the shell may be cracked or punctured. The influence of an electrically conducting lining and the effect of subdividing the shell in insulated sections have been studied. It is shown that an electrically conducting lining will have a significant shielding effect on the steel shell. The induced currents are considerably reduced in the steel, and “pushed into” the lining. The size of current loops in the shell can be restricted by subdividing the steel into sections with insulation between each section. Such modification is detrimental. Strong opposing currents will be formed on each side of the insulating gaps, leading to higher current concentrations and increasing the risk of hot spots on the steel shell. In addition, the heat loss due to induced currents in the steel will be enhanced.Graphical

Application of Silicomanganese Fume as a Novel Bridging Material for Water-Based Drilling Fluids.

Steelmaking industrial waste, that is, silicomanganese fume (SMF), is one of the byproducts obtained during the steelmaking process in an electric submerged arc furnace at 1500 °C. Millions of tons of such wastes are generated yearly and used in different applications such as road construction, cement mortar, recycling into sinter plant, and so forth. In this study, the application of SMF in the drilling operations was investigated by employing SMF as a bridging material (BM) in water-based drilling fluid (WBF). The SMF samples were collected and dry-sieved, and then, the retained particles on each mesh were examined for elemental analysis. Thereafter, a battery of tests was performed using the WBF-SMF system comprising different SMF grades and mixed grades to investigate their bridging performance. The commercial BM (marble) was used as a reference fluid (WBF-marble system) for comparative investigation. The bridging performance of WBF-SMF and WBF-marble systems was tested and compared at 190 °F and 300 psi testing conditions using 10, 12, 20, and 50 μm ceramic discs. The processing techniques have shown that raw SMF does not require prolonged processing steps like the other waste material requires. All the SMF grades have shown homogenous chemical composition in oxides of manganese, silicon, sulfur, calcium, magnesium, and iron. Moreover, the WBF-SMF system have shown substantial improvement in bridging and sealing performance with average 47, 42, 84, and 75% superior fluid loss performance against 10, 12, 20, and 50 μm ceramic discs, respectively, compared to the WBF-marble system. While comparing the filter cake thickness, the WBF-SMF system has deposited a filter cake with more than 50% reduction in thickness compared to the WBF-marble system for different ceramic-disc sizes. Consequently, this study has introduced SMF as a novel BM with a unique particle size distribution that can be used in WBFs to plug formation pores effectively. In addition, this waste material (SMF) has been investigated as an economical, effortless, readily available, and high-performance material compared to other commonly used BMs.

Pilot-Scale Test of Flue Gas Recirculation for The Silicon Process

Flue gas recirculation (FGR) for the silicon process may facilitate increasing the CO2 concentration in the off-gas, which will be beneficial for potential future carbon capture. Lower oxygen concentration in the combustion gas will also reduce NOX emissions. An existing 400 kVA Submerged Arc Furnace (SAF) pilot setup was modified to be able to recirculate flue gas and equipped with gas analysis to monitor both the flue gas and the mixed combustion gas entering the furnace. Over a running period of 80 h, including 32 h of startup, twelve different combinations of FGR ratios and flow rates were tested using typical industrial raw materials. Increased CO2 flue gas concentrations were successfully demonstrated with concentrations over 20 vol % CO2. Emissions of NOX were shown to be reduced when isolating stable comparable periods within each tapping cycle.Graphical

A Comprehensive Review of Secondary Carbon Bio-Carriers for Application in Metallurgical Processes: Utilization of Torrefied Biomass in Steel Production

This review aims to show the significance of the use of secondary carbon bio-carriers for iron and steel production. The term ‘secondary carbon bio-carriers’ in this review paper refers to biomass, torrefied biomass, biochar, charcoal, or biocoke. The main focus is on torrefied biomass, which can act as a carbon source for partial or complete replacement of fossil fuel in various metallurgical processes. The material requirements for the use of secondary carbon bio-carriers in different metallurgical processes are systematized, and pathways for the use of secondary carbon bio-carriers in four main routes of steel production are described; namely, blast furnace/basic oxygen furnace (BF/BOF), melting of scrap in electric arc furnace (scrap/EAF), direct reduced iron/electric arc furnace (DRI/EAF), and smelting reduction/basic oxygen furnace (SR/BOF). In addition, there is also a focus on the use of secondary carbon bio-carriers in a submerged arc furnace (SAF) for ferroalloy production. The issue of using secondary carbon bio-carriers is specific and individual, depending on the chosen process. However, the most promising ways to use secondary carbon bio-carriers are determined in scrap/EAF, DRI/EAF, SR/BOF, and SAF. Finally, the main priority of future research is the establishment of optimal parameters, material quantities, and qualities for using secondary carbon bio-carriers in metallurgical processes.

Exergy Analysis of Silicon Metallurgy in 22.5 MVA Submerged Arc Furnaces

Exergy Analysis of Silicon Metallurgy in 22.5 MVA Submerged Arc Furnaces

Conceptual Tapping Model of Mn-Ferroalloy Furnaces

The tapping process of submerged arc furnaces, like the Mn-ferroalloy production process, is when you drain the liquid metal and slag from the furnace. The optimal tapping process is when slag and metal is drained from the furnace at the same rate as it is produced, and the slag and metal is being separated in the post-tap hole process. Industrially, this is not always the case. Based on published articles, this paper discusses the total tapping process that contains the consecutive steps of flow from back electrodes to the tap electrode and flow from the tap electrode through the tap hole and runner, and into the ladle system. It focuses on an overall summary of which elements may affect the tapping; however, it should be noted that this is not a mathematical model. The main information is regarding materials and zones in the furnaces, as well as knowledge from computational fluid dynamics (CFD) modeling work.

Characterization of Chromiferrous Pyroxenite and Its Application as Flux in Ferrochrome Production Through an Industrial-Scale Submerged Arc Furnace

Characterization of Chromiferrous Pyroxenite and Its Application as Flux in Ferrochrome Production Through an Industrial-Scale Submerged Arc Furnace

Study of the Physical Behaviour and the Carbothermal Reduction of Self-Reducing Briquettes Developed with Iron Ore Fines, Charcoal and Silica Fume Residues

Self-reducing briquettes made with waste (silica fume, iron ore and charcoal fines) from the FeSi75 industry were studied. The objective was to determine if these briquettes could be used as a complementary load in submerged arc furnaces (SAF). Characterization of this waste was performed and the briquettes were produced without and with binders (Portland cement, hydrated lime, and sodium silicate), in accordance with the proportion of binder (2.50%; 5.00%; 7.50% and 10.00%). These self-reducing briquettes were tested for apparent density, porosity, shatter strength and resistance to hot degradation. To select the best briquettes, pre-established set points were used based on the scientific literature. Within this framework, only two treatments—out of a total of 52—met all the requirements of eligibility. In the two types of briquettes, the binder of solid silicate (5.00 and 7.50%) was produced with 15.00% of water. The briquettes have the following characteristics: apparent density: 1165 kg/m3 and 1247 kg/m3 respectively, porosity: 46.2% and 46.0%; shatter strength (1.50 m): 99.3% and 98.8%; and resistance to thermal degradation: 81.2% and 82.5%. Reduction tests to investigate the self-reducing character, under different heating temperatures (1750, 1800, 1850 and 2000 °C) were performed on these two treatments. The metallic phases that were identified by SEM/EDS analyses were Si, FeSi, FeSi2, thus obtaining the production of FeSi50 and FeSi75, in addition to the formation of the SiC and slag. It was found that the values for SiO gas formation are in the same range as in the industrial FeSi furnace. From the results, it is possible to verify the potential for carbothermal reduction of these residues, but it is punctuated by the need for more research aimed at optimizing the mass percentage in the formulation.

Investigations on the Interaction Behavior between Direct Reduced Iron and Various Melts.

Since the European Union defined ambitious CO2 emission targets, low-carbon-emission alternatives to the widespread integrated blast furnace (BF)—basic oxygen furnace (BOF) steelmaking strategy—are demanded. Direct reduction (DR) with natural gas as the reducing agent, already an industrially applied technology, is such an alternative. Consequently, the melting behavior of its intermediate product, i.e., direct reduced iron (DRI), in either an electric arc furnace (EAF) or a submerged arc furnace (SAF), is of great interest. Based on the conditions in these aggregates, a test series to experimentally simulate the first few seconds after charging DRI was defined. DRI samples with different carbon contents and hot briquetted iron (HBI) were immersed in high- and low-carbon melts as well as high- and low-iron oxide slags. The reacted samples were quenched in liquid nitrogen. The specimens were qualitatively evaluated by investigating their surfaces and cross sections. The dissolution of carbon-free DRI progressed relatively slowly and was driven by heat transfer. However, carbon, present either in the DRI sample or in the melt, not only accelerated the dissolution process, but also reacted with residual iron oxide in the pellet or the slag.

Prereduction Behavior of Manganese Ores With Solid Carbon and in CO/CO2 Gas Atmosphere

The prereduction reactions in the submerged arc furnace (SAF) are highly decisive of the total carbon, and energy consumption of the ferromanganese process. Therefore, understanding the dependency of prereduction behavior on ore characteristics and furnace conditions is of paramount importance. Prereduction behavior of Comilog, Nchwaning and UMK ores with solid carbon was studied in an open 75 kVA induction furnace set up simulating the conditions of an industrial SAF. In addition, the ores were thermogravimetrically studied with non-isothermal heating to 1000 °C in a flowing 70/30 CO/CO2 atmosphere. Gasification of carbon according to Boudouard reaction was considered significant for carbonate ores in induction furnace setup. UMK had a greater extent of prereduction compared to Nchwaning which is low in carbonates and Comilog which is known to have a higher CO reactivity at similar CO contents. TGA rate curves shows that prereduction of UMK ore occurred with two major distinctive steps. The first one was a combination of prereduction reactions and decomposition of carbonates with a peak temperature of 700 °C, and the second peak was the decomposition of calcite at 900 °C. The O/Mn ratio for UMK shows that prereduction is already completed prior to the second decomposition peak at 900 °C. In addition to prereduction reactions, Nchwaning is also characterized by an endothermic step which is decomposition of carbonates at 900 °C. Comilog ore produced the most fines followed by Nchwaning and lastly UMK on decrepitation.

Processing of low grade manganese ore in submerged arc furnace

ABSTRACT This paper presents an innovative technology that has been developed for the smelting of Egyptian low-grade manganese ore to produce low-manganese pig iron and high-manganese slag. This produced slag has a high Mn/Fe ratio, which, therefore, can be used in a second smelting process in the production of manganese alloys. In this developed technology, selective reduction of iron oxides from a ferruginous manganese ore (with Mn/Fe ratio equals 0.68) has been carried out via carbo-thermic reduction, in a 5 kg bench scale submerged arc furnace. The highest metallic yield, iron recovery in the pig iron, and MnO recovery in the manganese-rich slag, equal to 98%, 95.82%, and 94.59% respectively, were achieved at the optimum conditions of 4.5 kVA for pre-reduction power, 15 kVA for smelting power, 0.8 for coke ratio and 0.26 for CaO/SiO2 ratio. The reduction process was applied successfully on a 100 kVA pilot scale submerged arc furnace

Modelling alternating current effects in a submerged arc furnace

Abstract Modelling the production of silicon in a submerged arc furnace (SAF) requires accounting for the wide range of timescales of the different physical and chemical processes: the electric current which is used to heat the furnace varies over a timescale of around $10^{-2}\,$ s, whereas the flow and chemical consumption of the raw materials in the furnace occurs over several hours. Models for the silicon furnace generally either include only the fast-timescale, or only the slow-timescale processes. In a prior work, we developed a model incorporating effects on both the fast and slow timescales, and used a multiple-timescales analysis to homogenise the fast variations, deriving an averaged model for the slow evolution of the raw materials. For simplicity, in the previous work we focussed on the electrical behaviour around the base of a single electrode, and prescribed the current in this electrode to be sinusoidal, with given amplitude. In this paper, we extend our previous analysis to include the full electrical system, modelled using an equivalent circuit system. In this way, we demonstrate how the two furnace-modelling approaches (on the fast and slow timescales) may be combined in a computationally efficient way. Our previously derived model for the arc resistance is based on the assumption that the dominant heat loss from the arc is by radiation (we will refer to this as the radiation model). Alternative arc models include the empirical Cassie and Mayr models, which are commonly used in the SAF literature. We compare these various arc models, explore the dependence of the solution of our model on the model parameters and compare our solutions with measurements from an operational silicon furnace. In particular, we show that only the radiation arc model has a rising current-voltage characteristic at high currents. Simulations of the model show that there is an upper limit on the length of the furnace arc, above which all the current bypasses the arc and flows through the surrounding material.

Tapping Gas from the Silicon Submerged Arc Furnace: An Industrial Measurement Campaign

Producing high-silicon alloys in submerged arc furnaces (SAF) involves the generation of an intermediate process gas, consisting of silicon monoxide (SiO) and carbon monoxide (CO). Combustion of process gas from the taphole can be an environmental challenge. SiO gas burns to fine SiO2 particles which can cause poor working conditions and fugitive particulate matter emissions. The high combustion energy of SiO and CO is a source of high heat load. It is also the source of thermal NOX generation. A measurement campaign was conducted at the Elkem Thamshavn plant in Norway to investigate the composition of tapping gas from a silicon furnace. Over a 3-day period, the gas extracted from the tapping of the furnace was analyzed with Agilent Micro-GC, Protea atmosFIR, and Testo 350. The dust concentration in the gas was measured with a LaserDust instrument from NEO Monitors. Using the plant’s existing flow and temperature measurements, mass and energy flows were calculated. Linear regressions were calculated for three predictors of NOX formation in the taphole gas. From these calculations, the relation between total energy added to the tapping gas and NOX showed the best correlation.

STEEL SMELTING BY OXYGEN CONVERTER METHOD FROM VANADIUM-CONTAINING CAST IRON

The results of BOF steel smelting from vanadium-containing cast iron obtained by smelting metallized pellets from titanomagnetite ore of the Tebinbulak deposit in a high temperature tube furnace (Gero HTRV 200-250/17) are presented in the study. Studies were carried out on devanadization and decarbonization of cast iron under the conditions of BOF process in a vertical high-temperature tube furnace. The study presents a description of the scheme of the experimental setup and the methodology of research, which were carried out on the basis of Research Center of the Montanuniversitaet of Leoben (MUL, Austria, Leoben). The samples of cast iron with different chemical compositions obtained by smelting experimental batches of metallized pellets in submerged arc furnace were used in the tests of BOF process. The temperature was 1450°C in the first quarter and 1550°C in the last quarter of the test. The tests showed that the elements transition from the metal phase to the slag phase according to their standard free energies of oxide formation. The titanium and silicon content decreased to almost null values during the first 12,5% of the total blowing time. The content of manganese and vanadium decreased more slowly, but at the end of the tests they also entered the slag phase. The carbon content can be reduced from 4,5% to almost null values. The quantity of slag was small and as a consequence making it difficult to separate the slag from metallic phase, as a result the slag phase contained about 70% FeO. In similar industrial processes, the FeO content is about 25%, which means that the content of other elements is overestimated by almost three times. The values of vanadium oxide content in the slag obtained during smelting by the oxygen-converter method amounted to 6,2% and 8,41%. The excess of three times is consistent with the vanadium content of about 20% and with 25% FeO in the slag phase. The tests have confirmed the suitability of the vanadium-containing cast iron from titanomagnetite ore of the Tebinbulak deposit in the production of steel by the oxygen converter process.

Evaluation of Coke Resistivity for the Manganese Alloy Market.

The submerged arc furnace (SAF) has become the equipment of choice to produce manganese ferro-alloy. Furnace operators aim to reduce the cost of production by better understanding the role played by the various raw materials involved in the process. Coke is one of the key raw materials fed into the SAF; it plays three key roles in electric furnaces: as a reducing agent, as a source of carbon found in the alloy, and as a resistive element facilitating heat generation in the furnace. The heat generated plays two key functions in the furnace: ensuring both the metal and the slag have a sufficient low viscosity, and providing the heat required to support endothermic reactions. This study investigated the ambient-temperature and high-temperature resistivity characteristics of coke made from single-source coals. The measurement of coke resistivity was performed using the Kelvin (four-point) technique. The results showed a statistically significant difference in mean resistivity between cokes made from different coals. It was observed that coke resistivity generally decreased with increasing temperatures. Raman spectroscopy showed that the structural order of coke changes with increasing temperature.

Effect of carbon material composition on the energy consumption in 22.5 MVA silicon furnace

The influence of various process parameters during silicon production in a 22.5 MVA submerged arc furnace (SAF) was studied to achieve energy-saving effects. This paper analyzed how the main impurities (Fe2O3, Al2O3, CaO) in the main components (fixed carbon, ash, volatile matter, and moisture) of the raw materials used during industrial silicon smelting affected the process using correlation coefficients and contour maps. The results showed that the effect of the main components of the raw materials in a large-capacity furnace was fixed carbon > volatile content > moisture. The effects were significantly reduced compared with a 12.5 MVA. Under the same fixed carbon ratio, coal was more conducive to silicon production than petroleum coke, and the large-capacity furnace had a higher effective utilization rate of raw materials. The falls into order of the influence of metal oxide content on power consumption was Fe2O3 >Al2O3 >CaO.