Slag Layer Research Articles

A Novel Methodology to Quantify the Slag Protective Effect on the Oxidation Behavior of Oxide‐C Refractories

Preventing the oxidation of oxide‐C refractories used as working linings in steelmaking vessels is crucial for maintaining their performance and extending their lifetime. This study introduces a novel methodology for evaluating and quantifying the protective effect that adhered slag can have on the oxidation of the refractory lining of steelmaking ladles. The article details the ad‐hoc methodology itself, including the technique for adhering the slag to the refractory sample and the specifically developed equipment used. The proposed experimental approach includes the evaluation of how the environmental degradation of the slag layer affects the protection it provides to the refractory against attack by environmental oxygen. Finally, the methodology's ability to provide reliable and reproducible results is shown by its application on MgO–C refractories, the most widely used type of oxide‐C products in the steelmaking industry.

Modeling Freeze‐Lining Formation: A Case Study in the Slag Fuming Process

Slag fuming (SF) is a metallurgical process designed to recycle Zn‐containing slags derived from various industrial residues. To protect the reactor from corrosive molten slag, a deliberate as‐solidified slag layer, known as a freeze lining (FL), is formed on the reactor walls using intense water‐cooled jackets. In this article, a computational‐fluid‐dynamics‐based model capable of simulating FL formation in a SF furnace is presented. To capture the complex multiphase flow dynamics, heat transfer, and FL formation during SF, a volume‐of‐fluid model is coupled with a mixture continuum solidification model. Three phases are considered: gas, liquid bulk slag, and solid slag (FL). Moreover, two types of FL are distinguished: one that solidifies on the reactor wall in the bulk slag region and another that solidifies on the reactor wall in the freeboard region owing to slag splashing. Comparisons between calculated FL thickness and heat fluxes and corresponding industrial data demonstrate satisfactory agreement. In this outcome, the robustness of the model is underscored and confidence in its accuracy is instilled. In the simulation results, valuable insights are provided into the evolution of the fuming process, particularly regarding the slag bath temperature, slag splashing dynamics, FL formation, local heat fluxes through the reactor wall, and global net energy balance.

Dephosphorisation behaviour of blast oxygen furnace (BOF) slag due to carbothermal reduction

ABSTRACT The thermodynamic analysis of converter slag by carbothermal reduction was carried out. The laboratory tests of converter slag by carbothermal reduction dephosphorisation were carried out in molybdenum disilicide high-temperature resistance furnace and 500 kg top bottom combined blowing multi-functional test furnace respectively. The results show that the reaction temperature and kinetic conditions have a great influence on the dephosphorisation rate. In the top and bottom combined blowing multi-functional test furnace, coke powder is used as both reducing agent and heating agent. The exothermic reaction between coke powder and oxygen can ensure that the dephosphorisation reaction can be carried out at a higher temperature. At the same time, the good stirring of topblowing oxygen on the slag layer is conducive to further improve the dephosphorisation reaction speed.

Continuous Casting Slab Mold: Key Role of Nozzle Immersion Depth.

Based on a physical water model with a scaling factor of 0.5 and a coupled flow-heat transfer-solidification numerical model, this study investigates the influence of the submerged entry nozzle (SEN) depth on the mold surface behavior, slag entrapment, internal flow field, temperature distribution, and initial solidification behavior in slab casting. The results indicate that when the SEN depth is too shallow (80 mm), the slag layer on the narrow face is thin, leading to slag entrapment. Within a certain range of SEN depths (less than 170 mm), increasing the SEN depth reduces the impact on the mold walls, shortening the "plateau period" of stagnated growth on the narrow face shell. This allows the upper recirculation flow to develop more fully, resulting in an increase in the surface flow velocity and an expansion in the high-temperature region near the meniscus, which promotes uniform slag melting but also heightens the risk of slag entrainment due to shear stress at the liquid surface (with 110 mm being the most stable condition). As the SEN depth continues to increase, the surface flow velocity gradually decreases, and the maximum fluctuation in the liquid surface diminishes, while the full development of the upper recirculation zone leads to a higher and more uniform meniscus temperature. This suggests that in practical production, it is advisable to avoid this critical SEN depth. Instead, the immersion depth should be controlled at a slightly shallower position (around 110 mm) or a deeper position (around 190 mm).

Anti-seepage performance and oxygen barrier performance of the three-layered landfill cover system comprising neutralized slag under extreme climate conditions

For acidic industrial solid wastes, an effective cover system is needed to reduce the rainwater infiltration and oxygen intrusion, thus reducing the generation of acid mine drainage (AMD) from wastes. A three-layered cover using low-permeability neutralized slag (abbreviated as TCNS) at the bottom of the traditional capillary barrier cover is proposed, in line with the novel concept of “waste protecting waste”. This study investigates the anti-seepage performance and oxygen barrier performance of TCNS under extreme climate conditions, through laboratory column test and numerical simulations. The results show that the water content of the neutralized slag (NS) layer remained stable (i.e., changed by less than 0.02) under either extremely wet condition or extremely dry condition. Under extremely wet condition (i.e., heavy rainfall corresponding to a 50-year return period), no water percolation was observed at the cover bottom; under extremely dry conditions, oxygen diffusion was greatly impeded, e.g., after 208 days of column test, the SO42− concentration in the AMD of the exposed (i.e., uncovered) waste rock was 4.6 times higher than that of the waste rock covered by TCNS. Numerical simulations considering two realistic climate conditions (i.e., humid and arid) showed that TCNS were effective in controlling water percolation and oxygen intrusion. The saturated permeability coefficient (ks) and initial saturation degree (Se) of the NS layer have significant effects on the performance of TCNS, i.e., decreasing ks or increasing Se can effectively reduce the water percolation and oxygen flux. In sum, TCNS is an effective barrier for controlling water percolation and oxygen intrusion, even in extreme climate conditions. Consequently, it can effectively minimize AMD leakage and thus reduce geological disasters such as groundwater contamination.

Evolution Mechanism of Blast Furnace Cooling Plate Slag‐Hanging Behavior with Different Cooling System Structure

Based on the 3D heat transfer numerical simulation model, the evolution mechanism of blast furnace cooling plate slag‐hanging behavior with different cooling system structures is analyzed. Cooling plate reduced by 20 mm will not affect its slag‐hanging behavior. Copper cooling plate is best suited for high heat load areas. The vertical spacing of cooling plate is extended by 200 mm, the uniformity of the slag layer decreases by 5%, and the temperature of cooling plate and refractory material increases by 11 and 50 °C. Cooling plate vertical spacing of 510 mm or less can ensure stable slag hanging in the blast furnace. When using a single refractory material, the average uniformity of the slag layer is 95%, 86%, and 79% for graphite brick, semigraphite brick, and sialon‐SiC brick, respectively. Si3N4‐SiC brick cannot operate properly in high heat load areas. The factory can consider setting 125 mm sialon‐SiC brick in the furnace; graphite brick is used outside the furnace lining. The slag layer is well distributed, and the average value of uniformity is about 90%. Even if the slag layer is fully dislodged, the hot surface temperature of the furnace lining is 785 °C, and it can be quickly reslag hanging.

CLSVOF simulations of H2 bubble rising through liquid metal bath covered with a thick slag layer

Abstract The current study presents a fundamental understanding of the behavior of different-sized hydrogen bubbles rising in a new slag – metal system featured with a thick upper slag layer and ever-changing slag thickness and slag physical properties in the H2-based smelting process, based on newly developed CLSVOF model simulations. The evolution of bubble shape, bubble rising velocity, and the formation, collapse and detachment of metal liquid film wrapped on the bubble are predicted. The results show that decreasing the slag layer thickness or the slag viscosity delays the detachment of the metal liquid film from the bubble, increases the bubble rising velocity in the metal layer, but make no difference to the bubble terminal rising velocity in the slag layer. As a result, the bubble has shorter rising time in the bath with a higher slag viscosity. The resistance of the slag – metal interface to the bubble decreases with the increase of the bubble diameter, and small bubble therefore passes through the interface more slowly than the large one. In addition, the bubble shape evolution and bubble breakup in the slag layer are complicated with the increase of the slag thickness, bubble diameter and slag viscosity.

Influence of Different Submerged Entry Nozzles for Continuous Casting of Ultrathick Slab

Controlling the flow activity at the meniscus in the mold during the continuous casting of ultrathick slab is challenging due to the complex flow behavior, which is not extensively documented. Herein, a multiphase transient model of the ultrathick slab mold has been developed to describe the flow of molten steel, velocity distribution, and stream pattern at different submerged entry nozzle (SEN) outlets. The position of impact points and the fluctuation of liquid level are discussed as well. After ejecting from the port, the stream of the S‐shaped SEN splits into upper and lower streams. The upper stream moves to the liquid level, which improves the liquid level activity near the SEN. However, the reduced mainstream momentum alleviates the occurrence of slag layer exposure. Industrial application of the S‐shaped SEN results in uniform slag distribution and smooth casting operations.

Evaluating the efficacy of biogeochemical cover system in mitigating landfill gas emissions: A large-scale laboratory simulation.

Municipal solid waste (MSW) landfills are a significant source of methane (CH4) emissions in the United States, contributing to global warming. Current landfill gas (LFG) management methods, like the landfill cover system and LFG collection system, do not entirely prevent LFG release. Biocovers have the potential to reduce CH4 emissions through microbial oxidation. However, LFG also contains carbon dioxide (CO2) and trace hydrogen sulfide (H2S) depending on waste composition, temperature, moisture content, and age of waste. An innovative biogeochemical cover (BGCC) was developed to tackle these concerns. This cover comprises a biochar-based biocover layer overlaid with a basic oxygen furnace (BOF) steel slag layer. The biochar-based biocover layer oxidizes CH4 emissions, while the BOF slag layer reduces CO2 and H2S through carbonation and sulfidation reaction mechanisms. The BGCC system's field performance remains unexamined. Therefore, a large-scale tank setup simulating near-field conditions was developed to evaluate the BGCC system's ability to mitigate CH4, CO2, and H2S from LFG simultaneously. Synthetic LFG was passed through the BGCC in five distinct phases, each designed to simulate the varying gas compositions and flux rates typical of MSW landfill. Gas profiles along the depth were monitored during each phase, and gas removal efficiency was measured. After testing, biocover and BOF slag samples were extracted to analyze physico-chemical properties. Batch tests were also conducted on samples extracted from the biocover and BOF slag layers to determine potential CH4 oxidation rates and residual CO2 sequestration capacity. The results showed that the BGCC system's CH4 removal efficiency decreased with higher CH4 flux rates, achieving its highest removal (74.7-79.7%) at moderate influx rates (23.9-25.5g CH4/m2-day) and reducing to its lowest removal (27.4%) at the highest influx rate (57.5g CH4/m2-day). Complete H2S removal occurred during Phase 3 in the biocover layer of BGCC system. CH4 oxidation rates were highest near the upper (277.9µg CH4/g-day) and lowest in the deeper region of the biocover layer. In the tank experiment, CO2 breakthrough occurred after 156days due to drying of the BOF slag layer, with an average residual carbonation capacity of 46 gCO2/kg slag after moisture adjustment. Overall, the BGCC system effectively mitigated LFG emissions, including CH4, CO2, and H2S, at moderate flux rates, showing promise as a comprehensive solution for LFG management.

Analysis of the influence of electrode rotation on the desulfurization behavior during electroslag remelting process

A transient multi-physics coupling mathematical model is developed to investigate the influence of electrode rotation on desulfurization in the electroslag remelting (ESR) process. This model incorporates a thermodynamic and kinetic model to calculate the sulfur transfer rate from steel to slag, while simultaneously including the magnetohydrodynamic flow, heat transfer, and species transport. The volume of fluid (VOF) approach is employed to track the slag-steel interface. Experimental validation is conducted to ensure the reliability of the model. Sulfur in steel is primarily removed at the slag-electrode interface and the slag-droplet interface, but the slag-metal pool interface contributes very little to desulfurization. The electrode rotation disperses the molten droplets and enhances the heat convection, resulting in a reduction of the total amount of Joule heat and the temperature within the mold. At the electrode tip, rotating the electrode achieves a higher removal of sulfur, more than 10 % compared to the static electrode. The final removal ratios of sulfur are 78.79 %, 82.01 %, 84.90 %, and 80.81 % with the electrode rotating at 0, 20, 40, and 60 rpm, respectively. The optimal desulfurization is achieved at the rotating speed of 40 rpm, due to the refined droplets, the faster renewal rate of the slag-steel interface, the elevated temperature of the interface, and the longer residence time for droplets passing through the slag layer.

Spatial variation of methane oxidation and carbon dioxide sequestration in landfill biogeochemical cover

ABSTRACT The study investigated the spatial variation of potential methane (CH4) oxidation and residual carbon dioxide (CO2) sequestration in biogeochemical cover (BGCC) system designed to remove CH4, CO2, and hydrogen sulfide (H2S) from landfill gas (LFG) emissions. A 50 cm x 50 cm x 100 cm tank simulated BGCC system, comprising a biochar-amended soil (BAS) layer for CH4 oxidation, a basic oxygen furnace (BOF) slag layer for CO2 and H2S sequestration, and an upper topsoil layer. Synthetic LFG was flushed through the system in five phases, with each corresponding to different compositions and flow rates. Following monitoring, the system was dismantled, and samples were extracted from different depths and locations to analyze spatial variations, focusing on moisture content (MC), organic content (OC), pH, and electrical conductivity (EC). Additionally, batch tests on selected samples from BAS and BOF slag layers were performed to assess potential CH4 oxidation and residual carbonation capacity. The aim of study was to evaluate the BGCC's effectiveness in LFG mitigation, however this study focused on assessing spatial variations in physico-chemical properties, CH4 oxidation in the BAS layer, and residual carbonation in the BOF slag layer. Findings revealed CH4 oxidation in the BAS layer varied between 22.4 and 277.9 µg CH4/g-day, with higher rates in the upper part, and significant spatial variations at 50 cm below ground surface (bgs) compared to 85 cm bgs. The BOF slag layer showed a residual carbonation capacity of 40-49.3 g CO2/kg slag, indicating non-uniform carbonation. Overall, CH4 oxidation and CO2 sequestration capacities varied spatially and with depth in the BGCC system.

Mechanism and interaction of alkaline-earth metal migration induced ash transformation and carbon structure evolution for single coal particle high-temperature gasification

The current study focused on alkaline-earth metal migration induced ash transformation and carbon structure evolution for single coal particle high-temperature gasification, with visualization experiments and surface analysis techniques. The alkaline earth metals were found to aggregate to the peripheral reaction surface, while the rest remained in the initial scattered distribution. A migration index was defined and reached an extreme value in the middle reaction stage and increased with temperature, especially for the Ca element and followed by Mg. Raman spectra show the aggregation of Ca on the particle surface disrupted the carbon structure, leading to an increase in the disordered carbon content and improving the char reactivity. The aggregation behavior led to mineral transformation and melting to a liquid slag layer on the particle surface as a eutectic. Finally, a mechanism of the aggregation behavior of ionic Ca on a single particle scale was proposed in this study.

Corrosion, permeation and mass transfer mechanisms of alkali metals in corundum refractories

During the operation of the waste liquid incinerator, the alkali metal slag might adhere to the surface of the refractory material to form an inhomogeneous solid slag layer, causing the furnace lining to be simultaneously corroded by three phases of alkali metals: vapor, molten salt, and slag. This phenomenon intensifies the damage to the refractory material. Therefore, this paper investigates the mass transfer and permeation process, phase change process and corrosion rate of Na2CO3 inside corundum refractory materials in three phases: Na vapor, molten Na2CO3 and Na-slag. The results showed that alkali vapor penetrated the interior through the pores, and the NaAlO2 and β-Al2O3 generated by the reaction led to the volume expansion and microcracks. Na vapor continued to penetrate the interior along the cracks and eroded the sample, and the higher the temperature the greater Na vapor penetration. In vapor phase corrosion, the effect of corrosion time on the erosion resistance of corundum refractories is less than that of temperature, and the increase in corrosion time does not lead to the formation of additional new phases. In the molten salt corrosion experiments, it was found that the molten salt corrosion was accompanied by vapor phase corrosion at 1100 °C, and the amount of Na2CO3 has a greater effect on the corroded mass than the temperature. Comparing the corrosion of refractory materials by the three phases of Na2CO3, the molten salt corrosion rate was the highest, followed by the vapor phase corrosion, and finally the slag corrosion. It is concluded that the slag layer can effectively prevent the corrosion of the refractory material by alkali metal molten salts and vapors, thus prolonging the service life of refractories.

Corrosion of MgO–C Refractory with Ladle Slags

Herein, MgO–C refractory brick is immersed into the molten ladle slags with various CaO/Al2O3 ratios (located in the range of 0.56–0.78 and 1.99–1.36) and SiO2 addition from 1 to 20 wt%, at two temperatures of 1550 and 1650 °C. After the interaction with the slag with a CaO/Al2O3 ratio range of 0.56–0.78, the MgAl2O4 phase with various sizes is found to form in the solidified slag layer adhering to the MgO–C sample surface, and a layer consisting of MgAl2O4 on the interface of MgO–C brick is observed. For the slag with the CaO/Al2O3 ratio range of 1.99–1.36, a small amount of minor size of MgAl2O4 particle is detected only with 20 wt% of SiO2 addition. Instead of a formation of the MgAl2O4 layer, the Fe phase containing Mn, metallic Ti, and Si is scattered on the side of the solidified slag layer. The corrosion is more pronounced in the slag with a high CaO/Al2O3 ratio and is enhanced via the addition of SiO2 along with the increased solubility of MgO. The increased solubility of MgO in the slag with increasing SiO2 has also been predicted via FactSage.

Uncertainty Quantification in Modeling Mold Heat Transfer in Steel Continuous Slab Casting with CON1D

Computational models are powerful tools to quantify physical phenomena to gain valuable insights into a manufacturing process. Their accuracy is hindered, however, by uncertainty in the input data. Furthermore, when calibrating models with plant measurements, it helps to understand which variables have greatest effect on the critical model outputs. This work applies uncertainty quantification and sensitivity analysis to determine the most influential input parameters in the CON1D model of heat transfer and solidification in steel continuous casting with slag. Results show that the slag rim greatly affects heat flux near the meniscus, so control of its size is important. Heat flux and temperature down the mold depend greatly on velocity of the solid slag layer, and slag solidification temperature, which control the slag layer thickness, which in turn affects the interfacial resistance that controls heat transfer in the process. Scale formation on the mold coldface greatly increases mold temperatures. Based on the results presented here, models of heat transfer in continuous casting such as CON1D would benefit from plant measurements such as slag rim size and solid slag velocity, and lab measurements such as slag viscosity at lower temperatures, to better characterize this important slag property.

Physical Model of Inclusions Removal at Static Steel-Slag Interface.

Inclusions are one of the important factors affecting the cleanliness of molten steel. The current optimization of inclusion removal methods mainly focuses on promoting inclusions to float to the slag-steel interface so that the inclusions can be absorbed and removed by the refining slag. However, the research on the floating removal of inclusions cannot be carried out directly in the ladle, so methods such as mathematical models and physical models were developed. This article uses silicone oil to simulate the slag layer; polypropylene particles; and aluminum oxide particles to simulate inclusions to establish a water model experiment. By changing the viscosity of silicone oil and the diameter of particles, the factors affecting the movement of inclusions at the slag-steel interface were explored. Based on the water model, a mathematical model of the floating behavior of inclusions at the slag-steel interface was constructed, and parameters such as particle diameter and interfacial tension in the water model experiment were studied by the mathematical model for calculation. Both the mathematical model and the water model experimental results show that after the viscosity of silicone oil increases from 0.048 Pa·s to 0.096 Pa·s, the dimensionless displacement and terminal velocity of the particles decreases. When the diameter of the same particle increases, the dimensionless displacement and terminal velocity increases. The dimensionless displacement of polypropylene particles of the same diameter is larger than that of aluminum oxide particles, and the terminal velocity is smaller than that of aluminum oxide particles. This is attributed to the better overall three-phase wettability of polypropylene particle. When the liquid level increases, the dimensionless displacement and terminal velocity of particles under the same conditions show only slight differences (less than 10%).

Antimony and arsenic migration in a heterogeneous subsurface at an abandoned antimony smelter under rainfall

While antimony (Sb) and arsenic (As) co-contamination in subsurface soil systems due to the legacy of Sb smelting wastes has been documented, the role of inherent heterogeneity on pollutant migration is largely overlooked. Herein this study investigated Sb and As migration in a slag impacted, vertically stratified subsurface at an abandoned Sb smelter. A 2-dimensional flume was assembled as a lab-scale analogue of the site and subject to rainfall and stop-rain events. Reactive transport modeling was then performed by matching the experimental observations to verify the key factors and processes controlling pollutant migration. Results showed that rainfall caused Sb and As release from the shallow slag layer and promoted their downward movement. Nevertheless, the less permeable deeper layers limited physical flow and transport, which led to Sb and As accumulation at the interface. The re-adsorption of Sb and As onto iron oxides in the deeper, more acidic layers further retarded their migration. Because of the large difference between Sb and As concentrations, Sb re-adsorption was much less effective, which led to higher mobility. Our findings overall highlight the necessity of understanding the degree and impacts of physicochemical heterogeneity for risk exposure assessment and remediation of abandoned Sb smelting sites.

Influence of Submerged Entry Nozzles on Fluid Flow, Slag Entrainment, and Solidification in Slab Continuous Casting

In this paper, the fluid flow, slag entrainment and solidification process in a slab mold were studied using physical modeling and numerical simulation. The effect of two types of submerged entry nozzles (SENs) was also studied. The results showed that the surface velocity for type A SEN was larger than that using type B SEN. For type A SEN, the maximum surface velocity was 0.63 m/s and 0.56 m/s, and it was 0.20 m/s and 0.18 m/s for type B SEN. The larger shear effect on the top surface made the slag at narrow face impacted to the vicinity of 1/4 wide face, while the slag layer at the top surface was relatively stable for type B SEN. Increasing the immersion depth of SEN decreased the surface velocity and slag entrainment. For type A SEN, the thickness of the solidified shell at the narrow face of the mold outlet was thin (12.3 mm) and there was a risk of breakout. For type B SEN, the liquid steel with high temperature would flow to the meniscus and it was beneficial to the melting of the mold flux. The thickness of the solidified shell at the narrow face of the mold outlet was increased. Furthermore, the surface velocity was also increased and it was not recommended for high casting speed.

Optimal Sensor Placement for Mold Level in Continuous Casting

For high product quality in the continuous casting of steel, it is important that the liquid steel level in the mold remains constant and that its surface is fat. A slag layer on top of the liquid steel surface prevents direct optical measurement of the surface. However, knowing the mold level and surface shape is essential for quality monitoring and feedback control. The current paper addresses the optimal placement of mold-level sensors, given that their number is limited. The actual estimation of the surface shape is performed by an observer that receives mold-level measurements as input. The computed optimal sensor positions are validated based on experimental data from a full-scale laboratory water model of the continuous caster.

Optimize the Operation Parameters in Surging Auxiliary Slag Skimming Process Based on Large Eddy Simulation –Volume of Fluid –Discrete Phase Model Coupled Model

A transient 3D mathematical model is developed to study the surging auxiliary slag skimming process in molten iron ladle. A new mathematical model using the large eddy simulation is built for the gas–metal–slag three‐phase flow in the ladle. The Eulerian volume of fluid model is used for tracking the liquid–slag–air free surfaces, and the Lagrangian discrete phase model is used for describing the bubble movement. The procedure of bubble coming out of the liquid and getting into the air is modeled using a user‐defined function. The results show that optimizing the distance of the lance L and the injection volume Q can better the shape of the slag eye, increase the curvature radius of the slag eye on the side of the iron mouth, and broaden the area of the slag eye. At the same time, it can also improve the fluctuation of the slag layer and the liquid surface of molten iron, and reduce the splashing of molten iron and slag entrapment phenomenon, thus improving the slag skimming efficiency.