Slag Layer Research Articles

Numerical Analysis of Slag–Steel–Air Four-Phase Flow in Steel Continuous Casting Model Using CFD-DBM-VOF Model

Argon injection is usually applied in the continuous casting mold to prevent submerged entry nozzle (SEN) clogging. However, the stability of the slag–steel interface is affected by the injected gas, even leading to the formation of the slag eye. A computational fluid dynamics–discrete bubble model–volume of fluid (CFD-DBM-VOF) model is established to predict the argon–slag–steel–air four-phase flow in the continuous casting mold. The bubble behavior is treated with the Lagrangian approach considering bubble coalescence and breakup. The movement behavior of the slag–steel interface is analyzed with and without argon blowing, validated with the water model. The results show that the large bubble tends to float up into the slag–steel interface near the SEN with argon injection, resulting in fluctuations in the slag–steel interface near the SEN. The bubble distribution, flow field, fluctuation height of the slag–steel interface and configuration of the slag eye in the mold are analyzed. Furthermore, the effect on the casting speed, gas flow rate and thickness of the slag layer is obtained based on the result. The mathematical prediction results showcase a combination of well-established phenomena and newly generated predictions.

Damage mechanism of postmortem Si-Al2O3 sliding gate adding containing Ti2O3 fused mullite

The Si-Al2O3-fused mullite containing Ti2O3 composite was sintered at 1300 °C in N2 with a solid carbon. O′-Sialon, Ti(C, N)ss, SiC were formed in situ, and there was still free silicon. These non-oxide reinforced phases are not wetted by molten steel/slag and have excellent corrosion resistance. Therefore, the Si-Al2O3-fused mullite containing Ti2O3 after sintering at 1300 °C in N2 with solid carbon is a potential sliding gate material. It was made into a sliding gate and used at steel-making works to explore its damage mechanism. The results show that the postmortem sliding gate can be divided into a slag layer, a reaction layer, a transition layer and an unreacted layer. The reaction and transition layers are very thin, with thicknesses of 1 mm and 6 mm, respectively. In the reaction layer, Si, O′-Sialon and Ti(C, N)ss react with [O]steel to form SiO2 and TiO2 respectively, accompanied by volume expansion to form the dense layer, which inhibits the further penetration of molten steel/slag. In the transition layer, partial and active oxidation of Si occur simultaneously. The damage mechanism model of the sliding gate was established.

Simultaneous nitrate and phosphorus removal in novel steel slag biofilters: Optimization and mechanism study

The simultaneous nitrate (NO3−-N) and phosphorus (P) removal systems are considered to be an effective wastewater treatment technology. However, so far, there are few studies on system optimization to improve NO3−-N and P removal. In this study, nine simultaneous NO3−-N and P removal biofilters (SNPBs) were constructed to treat simulated wastewater. In order to optimize the NO3−-N and P removal, different material loading positions were set: (1) red soil, steel slag, and rice straw (RSR), (2) steel slag, red soil, and rice straw (SRR), and (3) red soil, rice straw, and steel slag (RRS). Results showed that the above three treatments had mean removal efficiencies of 58%–91% for NO3−-N and 55%–81% for TP, with the best N and P removal occurring in the SRR. The TN mass balance indicated that microbial removal was responsible for 78.2% of the influent TN in the SRR biofilter. The key microorganisms were Enterobacter, Klebsiella, Pseudomonas, Diaphorobacter, and unclassified_f_Enterobacteriaceae, which accounted for 61.9% of the total microorganisms. The main P-removal mechanism was the formation of Al–P, Fe–P, and Ca–P in red soil or steel slag layer. In addition, the decrease of SRR effluent pH from 11.86 in 1–7 days to 7.75 in 8–50 days indicated that red soil and rice straw had a synergistic effect on water pH reduction. These results suggest that a reasonable combination of steel slag with red soil and rice straw not only simultaneously removes NO3−-N and P but also additionally solves the problem of high pH caused by steel slag.

CFD-DEM models for matte droplet settling in a flash smelting settler

The flash smelting process is widely used in copper production. In the process, sulfidic feed and flux are oxidized. The heat released in the reactions melts the feed which forms a slag layer through which matte droplets must settle. Understanding the different phenomena affecting the settling is important to minimize losses. Due to the high temperature, simulation methods were employed to study settling. In this work, coupled CFD-DEM was used to study the effect of coalescence and reactions with in-house built submodels and scaled-down geometries. Colliding droplets often coalesce into larger droplets while reactions decrease their size and make them denser. These increase the settling velocity which is further enhanced by the formation of a channeling flow. Channels make the droplet cluster denser causing more collisions. This method enables the phenomena to be studied at the individual droplets' details, although simulating a full-scale process is beyond the available computational resources.

Settling Flow Details in the Flash Smelting Furnace—A CFD-DEM Simulation Study

The flash smelting furnace has previously been simulated using computational fluid dynamics (CFD). A new approach is to combine CFD and the discrete element method (DEM) for more detailed simulations of the different phenomena that occur as copper matte droplets settle through a slag layer. One of the most important phenomena found is the formation of a channeling flow which carries matte droplets faster through the slag. However, such phenomena cannot be directly observed in the flash smelting furnace settler due to the extreme temperatures of the opaque molten slag inside the furnace, therefore alternative methods are required for validating the phenomenon. In this work, the simulated channeling flow is validated with a sphere–oil model. The phenomenon was similar in all of the studied cases, although in the experimental setup the spheres settled faster in the oil model than in the simulations. The differences were most likely caused by the cohesion of the spheres and slight differences in the properties provided by the manufacturer and real properties for the oil and the spheres, and by the fact that simulation ignores surface tension and changing air–oil and water–oil interfaces.

A novel experimental set-up for generating microbubbles for the removal of inclusions from water and liquid metals

ABSTRACT To enhance steel cleanliness, extensive research has been conducted on bubble flotation techniques for inclusion removal. However, effective removal of nonmetallic inclusions smaller than 50 μm remains a challenge during standard liquid metal processing operations. These tiny inclusions have insufficient rising speeds to enable them to float out to the slag layer on their own. Several studies have demonstrated that the use of 500-μm bubbles would be necessary to facilitate the flotation of sub-50-μm inclusion particles from liquid steel within a tundish. Our approach to generating microbubbles in liquid metals uses liquid shearing flows. This method splits forming bubbles into smaller sizes by applying intense shear stresses. As a result, significantly larger surface areas are created, enhancing the interaction between the microbubbles and the inclusions. To test the effectiveness of this approach, a novel setup comprising submerged nozzles within a liquid metal was designed, manufactured, and operated. This setup allowed for experimentation with different rotational speeds and effluent gas flow rates, thereby determining the bubble sizes produced. Microbubbles within the desired size range (400–600 µm) were successfully generated in a Cerrolow 136 eutectic alloy.

Flow and Influencing Factors of Coated Slag in Continuous Casting Mold

In the continuous casting, the protective slag is coated on the surface of the molten steel, which is an important factor affecting the quality of the billet. The liquid slag layer on the surface of molten steel should be kept at an appropriate thickness to ensure a sufficient supply of liquid slag and to prevent slag from becoming entangled in the billet shell. Moreover, the consumption of protective slag should be appropriate to ensure stable liquid slag film thickness and uniform heat transfer between the casting billet and the mold. In this work, a two-dimensional numerical calculation model using volume of fluid method was established for the flow of protective slag, the Navier–Stokes equation was solved for the model, the consumption of protective slag during a vibration cycle was calculated, and the effects of factors such as casting speed, amplitude, and vibration frequency on the consumption of protective slag were explored. The results showed that when the casting speed increased from 1.2 m/min to 1.6 m/min, the consumption of protective slag per unit area decreased by about 4.76%, but the consumption of protective slag per unit length of the casting billet increased by about 26.98% within a vibration cycle. The consumption of protective slag per unit area and per unit billet length within a vibration cycle increased slightly with the increase of amplitude. The variation pattern of the consumption of protective slag with vibration frequency was not obvious. This model can provide theoretical basis and technical guidance for the design of protective slag, thereby improving the quality of steel billets in steel plants.

Investigation of Ash-Related Problem on Sequential Feeding Method for Coal Co-Combustion in Drop Tube Furnace

ABSTRACT In this study, sequential feeding method was conducted due to some coal-fired power plants not being equipped by coal blending facility. Its effect on ash-related problem was investigated using drop tube furnace combustion test and ash particle observation method. AUS coal (low-slagging risk sample) and KT coal (high-slagging risk sample) were used to obtain AK-1 coal and AK-2 coal. AK-1 coal was a coal sample of out-furnace blending method, while AK-2 coal was coal sample of sequential feeding method. AK-1 probe tended to be more similar to AUS coal with only a small spot of ash attached on the probe surface. Meanwhile, AK-2 probe had more ash attached on the probe surface, indicating more severe slagging than AK-1 probe. According to ash morphology, the result indicated that the upper layer of slag tended to be more similar to AUS coal ash, while initial layer of slag of AK-2 coal contained more KT coal ash. Based on ash mineralogy, sodium in AK-2 coal was distributed evenly which was different with AK-1 coal. This result shows that sequential feeding method is not applicable to reduce slagging and fouling risk of KT coal.

Deterioration mechanism of Al2O3–MgO refractory castable in RH refining ladle

The purpose of this work was to investigate the deterioration mechanism of an optimized Al2O3–MgO refractory castable during industrial trials. After structural optimization, the average corrosion rate of every cycle deceased to 0.29 mm/cycle from 0.46 mm/cycle. Corroded microstructure of the optimized Al2O3–MgAl2O4 refractory castable after server 195 cycles was explored. It was indicated that the structural optimization led to an approximate 36% improvement in corrosion resistance than that of comparison one. An adhered slag layer comprising of (Fe, Mg)Al2O4 spinel was observed on the refractory's surface. Iron beans and iron/manganese oxides mainly occurred in the reaction layer, and several penetrating cracks occurred at the corroded interface which would cause potential structural spalling for refractory lining. Based on the observed microstructural characteristics, a corrosion mechanism of refractory lining in a commercial ladle was proposed.

Green synthesis of MgAlON refractories with high strength and excellent slag corrosion resistance

The direct utilization of magnesite to synthesize magnesia-based refractories is a promising approach that not only shortens the mineral processing procedures, but also yields industrial products with high added value. In this work, we attempted to prepare MgAlON refractories with magnesite through a feasible solid-state reaction in a carbon-embedded atmosphere. Afterward, the influence of synthesis temperature and magnesite addition ratio on sintering and mechanical performance of as-synthesized MgAlON refractories was systematically investigated. Besides mechanical performance, the possible oxidation and slag corrosion mechanism of as-sintered MgAlON refractories was proposed. The results indicated that as-sintered refractories featured apparent porosity of 12.98%–39.29%, bulk density of 1.54–2.95 g cm−3, and cold compressive strength of 41.58–221.87 MPa. Additionally, it was found that the high magnesite content accelerated the sintering and densification process through the volume expansion effect. The slag resistance test results showed that the surface of the reacted refractory had a double-layer structure, namely the reacted slag layer and penetrated layer, indicating the slag corrosion process followed the mutual diffusion mechanism. Consequently, this work offers insight into the slag corrosion mechanism, paving the way for the cost-effective and facile synthesis of high-value MgAlON refractories from magnesite.

Flow and Heat Transfer on the Surface of Molten Steel Slag Layer in Continuous Casting Mold

Protective slag is coated on the surface of molten steel during continuous casting, the flow and heat transfer state of the protective slag is a decisive factor affecting the inflow and consumption of liquid slag and is also an important prerequisite for stabilizing and improving the quality of continuous casting billets. Based on the Navier Stokes fluid momentum conservation equation and energy equation, a two-dimensional longitudinal numerical model describing the flow/heat transfer of liquid protective slag on the surface of steel is established. The data comes from the equipment parameters and casting process of an arc shaped slab continuous casting machine in a domestic steel plant. The flow field and temperature field distribution of protective slag are calculated and analyzed, and the effects of factors such as slag layer thickness and shear speed on the flow and heat transfer status of the liquid slag layer are discussed. When the bottom shear velocity increases from 0.005 m/s to 0.2 m/s, the maximum flow velocity of liquid slag from the nozzle to the narrow surface in the center area of the model increases from 0.0012 m/s to 0.0617 m/s, and the average longitudinal flow velocity of liquid slag near the nozzle increases from 0.0012 m/s to 0.0627 m/s. The research results provide reference for investigating the complex metallurgical behavior of protective slag.

Improved slag corrosion resistance of MgO–C refractories with calcium magnesium aluminate aggregate and silicon carbide: Corrosion behavior and thermodynamic simulation

The influence of calcium magnesium aluminate (CMA) aggregate and silicon carbide on the slag corrosion resistance of MgO–C refractories was investigated by the induction furnace tests. The corrosion behavior and the formation of protective slag layer were also comprehensively discussed in present work. The results showed that CaAl2O4 in CMA converted into Al-containing liquid phase when facing the slag, while spinel with better slag corrosion resistance diffused into the refractory-slag interface. The Al-containing liquid phase melted from CaAl2O4 mixed with slag and increased the Al content, increasing the proportion of indirect dissolution, forming more spinel and decreasing the corrosion rate. Furthermore, the spinel and liquid slag formed solid-liquid mixture at the interface, increasing the viscosity and promoting the formation of protective slag layer, which avoided direct contact between slag and refractory. The combined use of CMA aggregate and silicon carbide showed better slag corrosion resistance because silicon carbide increased the oxidation resistance and inhibited the decarburized layer, while the FeSi alloy and higher viscosity also enhanced the slag corrosion resistance of such refractories.

Simulation of Slag Droplet Entrainment by Volume of Fluid and Lagrangian Particle Tracking Coupled Modeling.

The slag droplet entrainment is a common phenomenon in steel refining processes, which may lead to inclusions and defects. In the multiphase flow system, the distinct interface and tiny blobs possess a wide range of spatial and temporal scales and make it hard to be simulated. In numerical methods, the volume of fluid (VOF) approach is appropriate for capturing the interface, but for the unresolvable tiny blobs, the Lagrangian particle tracking (LPT) is preferable. This work newly implements a bidirectional VOF-LPT transformation algorithm for developing a multiscale solver in OpenFOAM to simulate the slag droplet entrainment. The interIsoFoam solver is selected as the main solver to resolve the interface, and the resolution is improved with using the geometric reconstruction and the adaptive mesh refinement (AMR). For capturing tiny droplets, a connected component labeling (CCL) method is adopted for detecting discrete droplets in the VOF field, and then the VOF-to-LPT transition takes place for saving computational costs. Conversely, the LPT-to-VOF transformation for droplets touching the interface is also incorporated to achieve the bidirectional transition. The solver is first validated by a simple case, indicating that the two-way transition algorithm and the Eulerian-Lagrangian momentum coupling are accurate. Then the solver is applied to simulate the slag layer behavior for revealing the mechanisms of slag droplet formation and entrainment. Two main mechanisms of slag droplet formation are identified, and it is found that fewer discrete droplets are generated when the surface tension increases.

Pyrite coupled with steel slag to enhance simultaneous nitrogen and phosphorus removal in constructed wetlands

FeS2-based constructed wetland has garnered increasing interest as an efficient and eco-friendly method for nitrogen and phosphorus removal from carbon limitation wastewater. However, large-scale application is limited due to low nitrogen and phosphorus simultaneous removal performance, slow growth rate of autotrophic denitrifiers and high effluent acidity. This study proposes a novel constructed wetland by coupling with pyrite and steel slag (PSCW) as substrates. The results showed that steel slag addition in PSCW increased total nitrogen removal by 40% ∼ 54%. The higher removal of total phosphorus was mainly attributed to the strong substrate adsorption and metal ions precipitation, which was removed at the pyrite and steel slag layer. The genes involved in denitrification, glycolysis, oxidative phosphorylation and sulfur oxidation were notably enriched in PSCW, indicating the increasing contribution of FeS2-based autotrophic denitrification coupled with steel slag to NO3− removal. The XPS analysis identified the formation of SO42−, S2−, S0, and Fe(III) on the pyrite surface in PSCW. S0 formation and sulfate reducing bacteria enrichment in PSCW were all promoted due to the coupling of pyrite and steel slag, which also maintained higher NO3− removal efficiency. Thiobacillus was specifically enriched in PSCW due to steel slag addition. The toxicity effect of pyrite on root tip can be alleviated by steel slag, which was conducive to nutrients assimilation by roots. The findings of this study provide new insights into the molecular mechanism of carbon, nitrogen, and sulfur metabolism in the pyrite-steel slag based constructed wetland.

Role of self-disintegrating effect produced by decomposition of limestone core on accelerating dissolution of lime in CaO–SiO2–FeOx slag

ABSTRACT The dissolution behaviours of lime, limestone and lime sample with limestone core-lime shell structure in CaO–SiO2–FeOx slag were investigated. The results show that dissolution of lime slows down once 2CaO·SiO2 layer is formed at slag/lime interface. Self-disintegrating effect produced by decomposition of limestone core can accelerate dissolution, but dissolution rate firstly increases, and then decreases with the CaCO3 content of samples increasing. Limestone must decompose to form lime before dissolution, and too much CO2 generated by decomposition of limestone bearing 98.9 wt% CaCO3 blocks the contact between molten slag and lime layer. Thus, limestone hardly dissolves after 60s contacted with molten slag. For lime sample with core–shell structure, the surface of sample is lime layer that can be directly dissolved in molten slag. Meanwhile, self-disintegrating effect produced by decomposition of limestone core enhances slag penetration, and accelerate dissolution. The optimum CaCO3 content in lime sample is 22.7 wt%.

Contaminant release from massive copper metallurgical slags: Insights from long-term monolithic leaching tests

Compared to compliance leaching tests performed on granular materials, leaching experiments on monolithic slags are more suitable for predicting the contaminant release when large boulders or poured slag layers are submerged in water, a specific environmental scenario typical for many smelting sites. We conducted EN 15863 dynamic monolithic leaching tests on massive copper slags over a prolonged period of 168 d. The patterns of the major contaminant (Cu, Co) fluxes indicated an initial diffusion process followed by the dissolution of primary sulfides with the maximum cumulative releases attaining 75.6 mg/m2 Cu and 4.20 mg/m2 Co. A multi-method mineralogical investigation showed that lepidocrocite (γ-FeOOH) and goethite (α-FeOOH) started to form on the slag surface already after 9 d of leaching and partly immobilized Cu (but not Co). Vanadium and other trace elements (Zn, Pb, Cd) were leached to a much lower extent, initially controlled by diffusion followed by depletion and/or sorption to Fe oxyhydroxides. The results of the long-term leaching of the monolithic slag provide new information about the key processes affecting the release of metal (loid) contaminants under specific submerged conditions and have implications for the environmental management of slag disposal sites and/or potential reuse of slags in civil engineering.

Nitrogen removal of decentralized swine wastewater by pilot-scale source reduction – anaerobic baffled reactor – zoning constructed wetlands at low temperatures

The study developed a cost-effective integrated technology to treat swine wastewater at the pilot-scale small pigsty. The swine wastewater, which was separated rinse water after flowing through the slatted floor and the innovatively constructed liquid-liquid separate collection device, was subsequently pumped into an anaerobic baffled reactor (ABR) and then through zoning constructed wetlands (CWs) comprised of CW1, CW2, and CW3. The liquid-liquid separate collection device effectively reduced COD, NH4–N, and TN by 57.82%, 52.39%, and 50.95%, respectively. The CW1 and CW2 enhanced TN removal and nitrification, respectively, through rapid adsorption-bioregeneration of zeolite. Moreover, rice straws were used as solid carbon sources in CW3 to successfully promote denitrification at 16.0 g/(m3·d). The integrated technology (slatted floor-liquid liquid separate collection-ABR-CWs) reduced COD, NH4–N, and TN by 98.17%, 87.22%, and 87.88%, respectively, at approximately 10 °C. Microbial analysis results confirmed that the CWs exhibited apparent functional zoning, with denitrifiers dominating in CW3, nitrifiers dominating in the zeolite layers of CW1 and CW2, and denitrifiers dominating in the brick slag layers of CWs. This cost-effective integrated technology demonstrated significant potential for treating swine wastewater at low temperatures.

Ranking of Injection Biochar for Slag Foaming Applications in Steelmaking

The electric arc furnace (EAF) has the potential to significantly contribute to the decarbonization of the iron and steel industry. However, during EAF steelmaking, carbon still needs to be injected into the molten slag to initiate slag foaming, which is beneficial to the energy efficiency and protection of the furnace. To move away from fossil carbon, biocarbon has gained attention as an injection carbon agent. In this study, two biochar candidates were added to the molten slag layer of an induction furnace for steel melting, to simulate EAF steelmaking conditions. The resultant slag foaming height was measured, and a ranking in comparison to two fossil carbon candidates was developed. The results indicate that the injection biochar sample, in the form of a bio-briquette, has a considerable degree of slag foaming capacity. More work is ongoing to develop a standardized testing methodology of ranking various injection biochar candidates for their suitability and qualification for use on a larger scale.

The Behavior of Direct Reduced Iron in the Electric Arc Furnace Hotspot

Hydrogen-based direct reduction is a promising technology for CO2 lean steelmaking. The electric arc furnace is the most relevant aggregate for processing direct reduced iron (DRI). As DRI is usually added into the arc, the behavior in this area is of great interest. A laboratory-scale hydrogen plasma smelting reduction (HPSR) reactor was used to analyze that under inert conditions. Four cases were compared: carbon-free and carbon-containing DRI from DR-grade pellets as well as fines from a fluidized bed reactor were melted batch-wise. A slag layer’s influence was investigated using DRI from the BF-grade pellets and the continuous addition of slag-forming oxides. While carbon-free materials show a porous structure with gangue entrapments, the carburized DRI forms a dense regulus with the oxides collected on top. The test with slag-forming oxides demonstrates the mixing effect of the arc’s electromagnetic forces. The cross-section shows a steel melt framed by a slag layer. These experiments match the past work in that carburized DRI is preferable, and material feed to the hotspot is critical for the EAF operation.

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.