Slag Droplets Research Articles

Modeling of Inclusion Capture in a Steel Slab Caster with Vertical Section and Bending

Particles in molten steel, including argon-gas bubbles, slag droplets, and non-metallic inclusions, are removed into the surface-slag layer or captured by the solidifying steel-shell during continuous steel casting. Captured particles often become serious defects in the final steel product, so understanding particle-capture mechanisms is important for steel quality. Slab casters often have a straight mold and upper-strand prior to a curved lower-strand. The present work investigates particle capture in such a caster using computational modeling with a standard k-ε model for molten-steel flow, a discrete phase model for inclusion transport, and an advanced capture criterion for inclusion entrapment and engulfment into the steel shell. A new postprocessing methodology is presented and applied to predict inclusion-capture rates in commercial cast product. The locations and size distributions of particles captured into the shell, and actual capture rates are quantified. The model predictions are validated with ultrasonic-test plant measurements of the locations of large particles captured in a steel slab. The results reveal how large-inclusion capture accumulates in the beginning of the curved strand, leading to a capture band in the slab inside radius. Finally, the capture fractions and locations due to all capture mechanisms are compared for different inclusion sizes, and the implications are discussed.

Vapor explosion in steel mill industries: Chemical composition analysis on molten slag and coolant

AbstractIt is important to prevent vapor explosion for steel mill industries for the reason that explosions can produce overpressure which cause buildings and facilities to rupture. The spontaneous vapor explosion occurs when a molten slag contacts with coolant. In this research, the molten slag which includes more than 10 chemical compositions produced in actual steel mill industries is employed. Three types of coolant were employed which can be used in real industries such as tap water, freshwater, and yard coolant. Spontaneous vapor explosion occurred when the yard coolant, which has a higher concentration of salt than either tap water or freshwater, was used as coolant. When the vapor explosion occurred, the temperature of the yard coolant was exclusively investigated in the range of 40°C to 55°C. The vapor explosion was independent of the molten slag temperatures employed. The vapor explosion in this work was attributed to the high salt concentration of the yard coolant, which improved the heat transfer to the vapor film around the molten slag droplet. The heat transfer promoted the vapor film to collapse and triggered the spontaneous vapor explosion.

A Microscopic Numerical Simulation of Carbon Dissolution in Different Coke Shapes in the Dripping Zone of Blast Furnace

The carbon dissolution of coke pieces in hot metal mainly influences the carbon content and carbon saturation temperature in the ironmaking process. The liquid metal and slag start to drop down in the dripping zone (DZ) which is located the lower part of blast furnaces. The dissolution of carbon in liquid metal and slag droplets passing the stagnant hot gas flow in the fixed coke bed of the dripping zone were observed by a multi-droplet model based on the Computational Fluid Dynamics (CFD) method. The uniform-coke pattern was set in the model following the preferred distribution of a one-layer packed bed from a water droplet experiment. The different coke shapes relating to the shape factor from 0.75-1.0 were observed in a 40mm-coke bed. For one-time drainage, the carbon dissolution slightly increased after flow in the coke bed zone and showed a high percentage on the coke surface. The concavity and convexity of coke pieces have more effect on the interaction between liquid and coke surface. Besides, the carbon dissolution can be investigated to approach the coke consumption in one coke channel and estimate the carbon content and carbon saturation temperature of liquid metal after draining.

Dynamic behaviors and regime map of a molten blast furnace slag droplet impacting a solid surface

The dynamic morphologies of a molten blast furnace slag droplet impacting a quartz glass surface are studied visually for a wide range of dimensionless initial temperatures (1.604–1.951), Reynolds numbers (17.4–124.4), and Weber numbers (197–1191). Five morphological evolution modes are defined based on the final stage of the slag film as deposition, receding, prompt-splashing, retraction-deposition and retraction-splashing. An impact regime map is established with the Reynolds number and dimensionless initial temperatures as the coordinates and six boundaries dividing the different modes are identified in the regime map. The apparent temperature nephograms of the slag film are extracted by a home-developed optical calibration method. The dynamic spreading processes and temperature distributions of the different regimes are not simply determined by the initial impact parameters, the coupling effect of the flow of the high-viscosity liquid slag and the heat transfer at the interface will obstruct the consecutive morphological evolution. The regulation principle for the centrifugal granulation system is promoted based on the analysis on an energy barrier for the sufficient spreading of the droplet and the impact regime map.

Study of Industrial Copper Matte Converting Using Micrography and Thermochemical Calculations

The converting of copper matte after the smelting process is one of the main steps in the copper-making industry. This work used microstructural analyses of samples collected at different stages of converting and thermochemical calculations to study a real converting batch in a Peirce-Smith converter at Atlantic Copper. The transformation of matte and slag produced during the converting was studied. The use of thermochemical calculations allowed a simulation of non-standard process conditions that provides valuable additional information on converting. The examined non-standard conditions were slag blow carried out in a single blow, the influence of the Fe/SiO2 slag ratio and over-oxidation at the end of the copper blow in the converting process. The micrographical investigation showed two predominant phases formed in the matte matrix after slow cooling, and their proportion varied along the slag blow. The slag presented two fayalitic olivine phases with different Fe/SiO2 ratios, the most abundant being the one with a higher Fe/SiO2 ratio. Magnetite crystals were identified in slags, and some of them were surrounded by fayalitic olivine. The analytical data of samples show that the measured copper in the slag is higher than in the theoretical thermochemical calculations. This indicates that the physical entrainment of matte/copper droplets in slag prevents a complete separation of the matte from the slag (residence time, agitation by blowing and viscosity). The final slag produced at the end of converting contains a high copper content, wherein copper is distributed after slow cooling into cuprite (Cu2O) and delafossite [(Cu,Fe)O] phases.

Investigation of Circulation Flow and Slag-Metal Behavior in an Industrial Single Snorkel Refining Furnace (SSRF): Application to Desulfurization

A combined method of mathematical and physical modeling was used to investigate the circulation flow and slag-metal behavior in industrial SSRF and RH. The circulation flow of molten steel was simulated by using the coupled mathematical model. The results indicate that two different circulation modes are presented separately in SSRF and RH. The incomplete exchange of molten steel was found in SSRF because of the interaction between upflow and downflow in the snorkel, while the molten steel is fully exchanged between the vacuum chamber and ladle in RH. The flow behavior of top slag in the vacuum chamber was further investigated and compared by using cold models. It was found that many slag droplets are generated in the vacuum chamber, and then dragged into ladle by downflow for both reactors. The main difference is that the majority of droplets eventually float into ladle slag in RH, while most of the slag droplets in SSRF is cycled repeatedly, which allows slag droplets to have a longer time to contact with steel. Thus, the slag-steel reaction is more adequate in SSRF. Furthermore, the industrial desulfurization tests were designed to verify the difference in the refining effect between the two kinds of droplet behavior in actual production. The results indicate that the higher desulfurization degree was realized in SSRF with less consumption of argon than that of RH.

The influence of the interaction between the multiple slag droplets on the solidification characteristics in humid air

The solidification characteristics of multiple slag droplets were studied numerically by using the combined evaporation and solidification models. At first, the solidification process for single slag droplet and double molten slag droplets was compared and discussed. Then, the effects of humidity ratio, droplet spacing, droplet diameter, air inlet velocity and relative position of droplets on the solidification characteristics of double slag droplets system were clarified. The results indicate that the complete solidification time of the behind droplet is obviously longer than that of the front droplet. Interface shape of the front droplet is a rough oval, while the behind droplet presents an inverted gourd interface shape. The solidification time for both droplets is decreasing by increasing humidity ratio and droplets spacing. The diameter variation of the behind droplet has little effect on solidification process of the front droplet, while the front droplet with larger diameter has a stronger heating effect on the behind droplet. Increasing the air inlet velocity is effective to reduce the heating effect of the front droplet. The influence of droplet position relation on the behind droplet is significant than that on the front droplet.

Investigation on the control of multiphase flow behavior in a continuous casting tundish during ladle change

The transient multiphase flow behavior in a single-strand tundish during ladle change was studied using physical modeling. The water and silicon oil were employed to simulate the liquid steel and slag. The effect of the turbulence inhibitor on the slag entrainment and the steel exposure during ladle change were evaluated and discussed. The effect of the slag carry-over on the water-oil-air flow was also analyzed. For the original tundish, the top oil phase in the impact zone was continuously dragged into the tundish bath and opened during ladle change, forming an emulsification phenomenon. By decreasing the liquid velocities in the upper part of the impact zone, the turbulence inhibitor decreased considerably the amount of entrained slag and the steel exposure during ladle change, thereby eliminating the emulsification phenomenon. Furthermore, the use of the TI-2 effectively lowered the effect of the slag carry-over on the steel cleanliness by controlling the movement of slag droplets. The results from industrial trials indicated that the application of the TI-2 reduced considerably the number of linear inclusions caused by ladle change in hot-rolled strip coils.

Physical and numerical modeling of liquid slag entrainment in mould during slabs casting

The paper presents results of physical and numerical modeling of liquid slag entrainment during continuous casting of steel slabs process. The main aim of this work was to determine the critical casting speed and also to specify, which entrainment mechanism is most responsible for transport of slag droplets into steel volume. Physical modeling was based on water-oil model of mould, made on reduced linear scale of Sl = 0.4. In mathematical modeling, Realizable k-ε and LES WALE models were used to describe turbulent motion of water and oil, whereas Volume of Fluid model was used to take into account interactions between phases. It was found, that the main cause of slag entrainment is the formation of von Karman vortex in the vicinity of submerged entry nozzle. The results of laboratory experiments and numerical simulations were compared each other. Both method are a useful tools for modeling of slag entrainment. Great agreement was found between laboratory experiments and numerical simulation carried out using LES WALE model, regarding the shape of the oil and oil entrainment as a result of vortex structures formation. However, in the simulation case using Realizable k-ε model, the oil entrainment hasn’t been modeled for the conditions under consideration.

Solidification with crystallization behavior of molten blast furnace slag particle during the cooling process

The centrifugal granulation technique has been considered for the recovery of waste heat retained in molten blast furnace slag while simultaneously obtaining high value slag particles for cement auxiliary materials. During granulation the high wind speed is expected to acquire high vitreous slag particles formed by centrifugal force of the atomizer, but result in significant energy consumption and low-grade heat of the cooling air. To address this problem, we established a two-dimensional symmetrical model to describe the crystallization behavior of blast furnace slag droplets by the enthalpy method via self-programming. The radiation heat transfer between slag particle and the wall was considered as well as non-isothermal solidification, including a narrow temperature interval of crystallization. The results display the evolutions of the local cooling rate and crystal phase content distribution. The effects of the diameter, initial temperature of the slag particle, wind initial temperature and wind speed are also discussed. Furthermore, two correlations of the average cooling rate and final crystal phase content with dimensionless parameters were developed respectively, to predict slag quality under various operational conditions.

Mathematical modelling of slag entrainment and entrained droplets in a continuous casting mould

ABSTRACTThe transient behaviour of the slag layer plays an essential role in the entrainment of slag droplets inside a continuous casting mould. In the current study, a mathematical model using Volume of Fluid-Large Eddy Simulation (VOF-LES) was developed for transient phenomena associated with slag entrainment in a water experiment. The accuracy of the model was verified by comparing the velocities with the available measurement from the literature. The effects of various conditions on free surface fluctuations in the liquid slag layer and transient behaviours of entrained slag droplets were quantified. Finally, the relationships between operating parameters and the size distributions and the amount of entrained slag droplets were investigated using a Fluent User Defined Function (UDF). With increased casting speed, or decreased SEN immersion depth, the size distributions of the slag droplets broadened, and the amounts thereof increased accordingly.

Decarburization of Pig Iron in Synthetic BOF Converter Slag

The paper presents a study on the decarburization of pig iron droplets in synthetic BOF slag. The effects of droplet size and slag composition were studied. The results show evidently that the deca ...

Use of colemanite in ferronickel smelting

Use of colemanite in metal-slag systems aims primarily to decrease the viscosity of slag and, therefore, achieve better metal-slag separation. Enhanced metal-slag separation is helpful to decrease the number of suspended metal/alloy droplets in slag, i.e. the physical losses. In the literature, successful use of colemanite was reported both in steelmaking and copper matte smelting processes. Ferronickel smelting slags contain nickel in the range of 0.1-0.2% and correspondingly, metal-slag distribution ratio values of nickel are reported even above 200. On the contrary, nickel recoveries are hard to exceed 95%. This can be mostly attributed to the physical losses of nickel due to very high slag volume in ferronickel smelters; for 1 ton of ferronickel, 10-15 tonnes of slag are generated regardless of the type of the laterite, which contains significant quantity of gangue components. The authors thought that use of colemanite could be a solution to decrease physical losses. Therefore, the use of colemanite in ferronickel smelting was investigated in the present work. Laboratory-scale smelting experiments were conducted using calcined and prereduced laterites in a vertical tube furnace under different gas atmospheres. The amount of colemanite added was in the range of 0 - 2.5% of the total charge. The experiments were also performed using ferronickel and slag samples obtained from a ferronickel smelter.

Study on the solidification characteristics of molten slag droplets cooled by mixed cooling medium

Numerical studies on molten slag droplets solidification behaviors in humid air were carried out by using the hybrid evaporation and solidification models. The numerical model was firstly validated by the experimental data in the literatures, and then solidification time, temperature distribution, and movement of phase change interface during the solidification process were analyzed. The effects of humidity ratio (content of atomized water), air inlet temperature and velocity, and droplet diameter on solidification behaviors of molten slag were discussed. Finally, a correlation for predicting the solidification time was proposed. The results show that, generally, the solidification time is decreasing by increasing the air inlet velocity and humidity ratio, or decreasing the droplet diameter and air inlet temperature. The solidification rates represent a trend of gradual decline during the solidification process due to the ever-increasing thickness of the solid slag region, and they are normally higher at the upwind side but relatively lower at the leeward side, resulting in an off-center solidification process of a slag droplet. The humidity ratio has significant effect on the cooling air temperature distributions, steeper temperature gradient is observed thanks to the evaporation process of the atomized water. The present work suggests that the operational conditions are: the humidity ratio within the range of 10%∼20%, the air inlet velocity is 1.0 m/s and the air inlet temperature is 303 K, respectively.

Characterization of Slag‐Metal Emulsion and Its Impact on Foaming Behavior and Slopping in the LD Process

In the Basic Oxygen Steelmaking (BOS) process, a heterogeneous emulsion‐solid mix will form, consisting of an emulsion of liquid slag and metal droplets, in which 2nd phase particles of undissolved ...

Experimental visualization and theoretical analysis of the dynamic impact behavior of a molten blast furnace slag droplet on different surfaces

In blast furnace slag dry centrifugal granulation heat recovery systems, the impact of a molten slag droplet on a solid surface is unavoidable because of the device restrictions. To predict the molten slag droplet deposition, the dynamic impact behavior of a high-temperature slag droplet on a solid surface was studied by performing visualization experiments, and the quantitative analysis was analyzed based on the experimental results. Refractory cement and stainless steel were examined as surface materials, and the experimental results from these two surfaces were compared. The droplets spread over a larger area of the refractory cement surface than the stainless steel surface. The refractory cement eroded, and the stainless steel was determined to be a suitable wall material for blast furnace slag dry centrifugal granulation heat recovery systems. On impact, the droplets spread farther if the surface roughness was smaller or if the droplet temperature was higher. A semiempirical model was developed to predict the maximum spreading factor from the initial parameters of the slag droplet. The error of the semiempirical model is within 10%, over a range of Reynold’s numbers (33–110) and Weber’s numbers (220–1301).

Characterization and Recovery of Copper from Converter Copper Slag Via Smelting Separation

Converter copper slag can be viewed as an important secondary resource for valuable metals, considering its high commercial value. The current research investigates the recycling of copper by a combination of theoretical and experimental methods. Based on a modified Stokes equation, it was determined that copper droplets in the molten slag exhibited a low terminal settling velocity of 2.140 × 10−6 m/s. The copper particles will collide with each other during settling, resulting in particle growth. The results from high temperature experimentation, scanning electron microscopy, and energy-dispersive spectroscopy confirm that in the absence of reducing agents, copper droplets are encased in magnetite to form composite ‘Cu droplet–magnetite’ particles. Other copper droplets adhere to magnetite particles which are suspended in the slag in a short-range-ordered array. The study also confirms that in the presence of increasing amounts of anthracite as a reducing agent, the magnetite content of the slag is progressively decreased and the recovery of copper from the slag is significantly improved. Based on the findings from this work, a new processing route is proposed to treat copper slag for the recovery of copper.

Numerical Simulation of Recirculating Flow and Physical Model of Slag–Metal Behavior in an RH Reactor: Application to Desulfurization

Computational fluid dynamics (CFD) techniques and a 1:7.5 physical model of an RH degasser have been used to evaluate the flow of gas and metal inside an RH reactor for vacuum degassing of liquid steel. The effect of gas injection on the gas spatial distribution, steel circulation rate and flow field inside the ladle, snorkels and vacuum chamber have been assessed. N-pentane oil was employed to evaluate the average residence time as well as the slag droplet size distribution. The predicted radial gas distribution and liquid circulation rate have been validated against experimental data from a physical model. The results with incorporation of the virtual mass force coefficient of 0.25 and the turbulence dispersion force showed better predictions of gas distribution in the up-snorkel as well as circulation rate. Full-scale simulations were performed, and the predicted circulation rate was significantly affected by the argon bubble expansion. Data from these simulations were used to analyze the degree of desulfurization performed by the addition of desulfurizing agents inside the vacuum chamber. A model of the kinetics of desulfurization based on the results from the physical model and CFD simulation and on slag dispersion inside liquid steel yields degrees of desulfurization similar to the industrial trials reported in the literature.

Formation of Non-metallic Inclusions of Si-killed Stainless Steel during GOR Refining Process

AbstractThe formation mechanism of inclusions in Si-killed 304 stainless steel was studied by industrial experiments during GOR refining process and thermodynamic calculations. A lager number of CaO-SiO2-MgO-Al2O3-MnO-CrOx liquid spherical inclusions with different size (from 1 μm to 22 μm) had been found after deoxidization of FeSi alloy in 10 minutes. The calculation result of FactSage 6.3 software assisted in confirming that the inclusions in size of less than 5 μm that had less than 30 % CaO mainly came from the deoxidation of FeSi alloy with Ca and Al. The inclusions in size of more than 5 μm that had more than 30 % CaO mainly came from the modification of involved slag droplets through the oxidation of Si and Al and the collision with deoxidation-type inclusions, and the degree of change was bigger for smaller inclusions. The MgO in slag and refractory was reduced by Si and Al in steel, which leaded to the unceasingly increase of Mg content in steel. Subsequently, SiO2, MnO and CrOx in inclusion were reduced by Mg, which resulted in the increase of MgO content in inclusion and the degree of increase of MgO content was greater for the larger size of inclusions.

Numerical Simulation of Slag Eye Formation and Slag Entrapment in a Bottom-Blown Argon-Stirred Ladle

A transient mathematical model is developed for simulating the bubble-steel-slag-top gas four-phase flow in a bottom-blown argon-stirred ladle with a 70-ton capacity. The Lagrangian discrete phase model (DPM) is used for describing the moving behavior of bubbles in the steel and slag. To observe the formation process of slag eye, the volume of fluid (VOF) model is used to track the interfaces between three incompressible phases: metal/slag, metal/gas, and slag/gas. The complex multiphase turbulent flow induced by bubble-liquid interactions is solved by a large eddy simulation (LES) model. Slag eye area and slag droplet dispersion are investigated under different gas flow rates. The results show that the movement of bubbles, formation and collapse of slag eye, volatility of steel/slag interface and behavior of slag entrapment can be properly predicted in the current model. When the gas flow rate is 300 L/min, the circulation driven by the bubble plume will stir the entire ladle adequately and form a slag eye of the right size. At the same time, it will not cause strong erosion to the ladle wall, and the fluctuation of the interface is of adequate intensity, which will be helpful for improving the desulfurization efficiency; the slag entrapment behavior can also be decreased. Interestingly, with the motion of liquid steel circulation, the collision and coalescence of dispersed slag droplets occur during the floating process in the vicinity of the wall.