Slag Flow Research Articles

Effect of process parameters on dry centrifugal granulation of molten slag by a rotary disk atomizer

Dry centrifugal granulation (DCG) experiments for blast furnace slag (BFS) were performed by means of a rotary disk atomizer since water quenching method can create a series of problems. The results showed that the DCG method can granulate the BFS, but the results are easily affected by the slag flow rate, disk rotating speed, disk radius, disk material and slag falling height. The granulating parameters with an excessive flow rate, low rotating speed, SiN–SiC disk, stainless steel disk and low slag falling height are detrimental to the granulation process. The most suitable parameters for granulation are a slag flow rate of 5.1 × 10−5 m3/s, a disk rotating speed of 1500–2300 r/min, a slag falling height of 0.8 m and a smooth graphitic disk with the radius of 0.1 m. In the absence of an off-center flow, the overall best granulating effect produces round particles with mean diameter of 3.43 mm without creating slag fiber. The vitreous content of the BFS particles granulated by graphite disks is 92%, which meets the requirements of cement raw materials. The Bond work index of dry granulated BFS is 18.4 kWh/t, and the grindability of dry granulated slag and water-quenched slag is similar.

Investigation of Molten Liquids Flow in the Blast Furnace Lower Zone: Numerical Modelling of Molten Slag Through Channels in a Packed Bed

Slag flow behaviour is critically important in the lower zone of the ironmaking blast furnace, and is closely related to the selection of charged raw materials, coke bed permeability, process stability and hot metal quality. To better understand the effect of slag properties on flow behaviour in the coke bed, a numerical approach was applied to characterize the slag flow through funnel analogues. These analogues were used to represent molten slag flow through the inter-particle voids of a coke packed bed. A critical funnel neck size, through which no slag flowed was experimentally established and confirmed by numerical modelling. The influence of slag wettability on the occurrence of blockage was also determined via numerical modelling. An increase in either contact angle or surface tension can make the occurrence of blockage easier. For a constant neck size, the relationship between surface tension and contact angle is non-linear. The status of the remaining slag in the funnel corresponding to different slag wettabilities was differentiated in terms of the blockage in the upper part and hanging in the lower part of the funnel. Modelling was also undertaken of slag flow through the inter-particle void between spherical particles to evaluate empirical correlations for predicting the remaining slag in the packed bed. These results show that the numerical approach is very useful in providing some level of guidance to help understand and predict the slag flow behaviour in the blast furnace ironmaking process.

A 1D Analytical Model for Slag Infiltration during Continuous Casting of Steel under Non-Sinusoidal Mold Oscillation

A 1D analytical model for slag infiltration during continuous casting of steel is developed to investigate the slag behavior in the mold–strand gap. The superposition principle and Fourier expansion are applied to obtain the analytical solution for transient slag flow under arbitrary mold oscillation including non-sinusoidal oscillation mode. The validated model using literature data partially explains several controversies such as slope of slag film channel, mechanism of non-sinusoidal mold oscillation, and timing of slag infiltration. The model shows that a converging slag film into the casting direction is required to open the mold–strand gap if compression is applied in between. Also, model calculations imply that higher slag consumption is achievable from non-sinusoidal mold oscillation by means of the increase of film thickness through longer positive pressure with higher peak pressure. The model demonstrates a time difference between slag flow and pressure near the meniscus and the discrepancy in timing of infiltration between previous works is attributed to the mismatch. The model provides a concise but reliable tool to understand slag infiltration behavior and design mold oscillation settings.

Modeling Study of the Slag Behaviors and SiC Refractory Wall Corrosion on the Top Cone of a Membrane Wall Entrained-Flow Gasifier

The slag behaviors on the top cone are significant characteristics that relate to the refractory wall corrosion and safe operation in a membrane wall gasifier. The slag flow and heat transfer model...

Direct observation and numerical simulation of molten metal and molten slag behavior in electroslag welding process

The electroslag welding process involves high heat inputs and high deposition rates. In this process, the weld region is surrounded by the base metal and/or devices; therefore, it is difficult to observe the phenomenon and understand the mechanism of weld formation. In this study, we directly observe the molten region formed during the process and construct a numerical model to discuss the phenomena especially the construction of the molten region, the flow field of the molten region, and the metal transfer. A device for direct observation was constructed, and the molten region was observed. The molten slag flows from the wire tip to the molten metal interface, and the direction of flow is changed to the side at the interface. The molten metal flows from the center to the side region at the interface of the slag and metal. The penetration depth is governed by the behavior of the molten metal. In addition, droplet transfer from the wire is observed, and this transfer occurs in the spray or rotating mode. The simulation results indicate a tendency similar to that deduced via direct observations. Thus, the mechanism of penetration can be elucidated more clearly using these tools.

Modification of tundish design to improve quality of slabs, casted at CCM No. 4 of EVRAZ NTMK

A technology of continuous casting of steel has a large effect on its contamination. In particular, proper organization of metal flows in tundish and mold is very important. After completion a series of casting through a tundish and drop of metal level in it, it possible, that the slag flows from the surface layers of the tundish to capture the metal. An analysis of results of ultrasonic control of finished strip showed, that the basic number of the revealed defects was obtained during strip rolling out of the last slabs of the last heat in a series for a tundish. Metallographic studies determined, that the defects were located in the slab axis zone and filled by macro-inclusions of complex composition. To determine the actual distribution of metal flows, a water simulation of them was accomplished for the existing design of the EVRAZ NTMK tundish. It was determined, that at the drop of metal level in a tundish, a capture of slag from the metal reservoir and its transfer into the main bath of the tundish takes place due to whirligig flows. Following the weight metal consumption, the zone of slag inclusions distribution enlarges. Besides, denudation of the metal mirror in the metal reservoir takes place, resulted in metal secondary oxidation. Based on the results of the simulation, it was proposed to modify the design of the “turbostop”, which is installed in the metal reservoir of the tundish. Besides, it was proposed to remove the dividers installation in the tundish. It was noted, that the proposed steps enable to ensure a minimal level of rejections.

Slagging behavior modeling in coal gasifiers using two-way coupled slag model with CFD

In pulverized-coal gasifiers, wall slagging behavior is an important issue associated with ash handling and discharge. Numerical methods have been widely employed to predict the slag flow and heat transfer on the gasifier wall. However, most of the analytical models are only one-way coupled with the simulation of the gasification reactor. In the present study, the slag model was integrated into a commercial computational fluid dynamics (CFD) solver to achieve two-way coupling. The coupled mass, momentum and energy equations were solved iteratively until convergence. The simulations of a simplified gasifier show that the solid slag thickness was seriously affected by the heat flux from gas to slag surface. The proposed two-way coupled slag model was able to give more reasonable predictions compared with other offline slag models since the heat transfer between the gas and the slag could be modeled more accurately. Through analyzing the energy balance in the slag layer, it is found that most of the heat flux from gas was extracted by the cooling water. However, the effect of the heat flux absorbed by the flowing liquid slag became important under high gas temperatures and ash deposition rates.

Film fragmentation mode: The most suitable way for centrifugal granulation of large flow rate molten blast slag towards high-efficiency waste heat recovery for industrialization

In molten slag centrifugal granulation heat recovery technology, the centrifugal granulation process is crucially important to realize efficient heat recovery as well as high-quality resource utilization. Facing the actual large-scale industrial application, the film fragmentation mode is likely to be the suitable operational mode for centrifugal granulation due to its ability to handle large discharged slag flow. However, the fragmentation phenomena and mechanism in film fragmentation mode are unclear since most of the existing experiments scale is too small to reach this mode. Here, the authentic molten slag is employed as the working fluid to investigate the centrifugal granulation characteristics in film fragmentation mode. A unique perforated disintegration of extended free slag sheet in film fragmentation mode is observed, and the good granulation performance is proved through the comparison with that in ligament fragmentation mode. The effects of operating conditions and structural parameters including granulator rotating speed, molten slag mass flow rate, initial slag temperature, rotary cup diameter, and granulation chamber radius are discussed on the particle size distribution and average particle diameter. Finally, the predictive correlation of granulation performance is put forward. For the industrial applications, the rotary cup diameter is recommended between 86 mm and 126 mm, and the granulation chamber radius should be set at least larger than 1.36 m if the granulator rotating speed is designed lower than 1800 rpm.

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.

Modeling and simulation of coal gasification on an entrained flow coal gasifier

In this paper, the recent researches and developments on coal gasification modeling and simulation are described. Numerical models for the three chemical processes such as devolatilization, char gasification, and gas-phase reaction are reviewed and discussed for further development to improve accuracy. Recently the devolatilization models to describe the coal chemical structure with a simple expression have been proposed and validated on the laboratory-scale flames. It is essential to precisely model char gasification reaction as a rate-determining step and the formulation of the active sites sharing by the mixture and the pore structure formation are important in the modeling. It will become significant to take the elementary reactions into account in the gas phase reaction model. Large-eddy simulation of coal gasification on the laboratory-scale entrained flow gasifier is performed to demonstrate the numerical procedure. Results show the predicted temperature distribution qualitatively agrees with the experiment. Moreover, the gas-liquid-solid three-phase reacting flow simulation is preliminarily performed to capture the molten slag flow behavior within the gasifier. It is revealed that the three-phase simulation can give insight into the complex multiphase and multiphysics phenomena taking place within the gasifier to assess the design and the operating condition.

Two-dimensional comprehensive mathematical model for electroslag remelting process with pipe electrode

Taking the electroslag remelting with pipe electrode (ESR-PE) and electroslag remelting with solid electrode (ESR-SE) as the research objects, a two-dimensional steady-state mathematical model of coupled electromagnetic field equation, energy equation, and flow equation was established. The distribution of its current density, Joule heat, flow field, and temperature field was compared and the difference of their molten metal pool was analyzed. The results show that compared with those of ESR-SE, current density distribution and Joule heating area of ESR-PE are mainly concentrated in the inner and outer wall areas of the electrode tip, while the Joule heat generated in the central area of the slag pool is less. In the ESR-PE, the slag flows from the outside of the electrode to the hollow area of the electrode, which makes the temperature distribution in the slag pool is more uniform. Affected by the Joule heating area and flow field, the heat of ESR-SE is concentrated below the electrode in the slag pool area and it transfers from the center to the periphery. However, in the ESR-PE, the heat is concentrated near the inner and outer walls of the electrode tip, and the heat is transferred from the periphery to the center of the slag pool. The molten metal pool depth of ESR-SE is 0.1188 m and that of ESR-PE is 0.0962 m. Compared with that of ESR-SE, the molten metal pool of ESR-PE is shallower and flatter.

Research on Measurement Method of High Temperature Slag Flow Rate Based on Image Identification

<p>A method for the measurements of the flow rate of high temperature molten slag using image identification was proposed. Image of molten slag could be acquired by high-speed camera. The flow rate of molten slag was calculated by the diameter, which was obtained by the edge detection, and the velocity of the feature points obtaining by threshold segmentation. Feature points could be found on the liquid column of molten slag by photo graphing, which showed that the method is feasible. Then glycerite was used to study the influences of different shooting parameters on the measurement accuracy. The effects of exposure time, frame rate and focal length on measurement accuracy were obtained. At the same time, it was found that the selection of location and length of feature region would also have a significant impact on the measurement accuracy.</p><p> </p>

Modelling of slag flow and prediction of corrosion state of refractory bricks in an entrained-flow gasifier

The corrosion rate of refractory brick is a key factor for long-term and stable operation of a gasifier. In situ measurement of refractory brick corrosion was always a challenging topic due to the extreme temperature and pressure in the gasifier. In this paper, numerical simulations were adopted to accurately predict the corrosion depth of the refractory brick. Models for slag flow and refractory brick heat transfer were built, and various models of refractory brick corrosion rate were derived in detail. Heat transfer and brick corrosion models were validated with available industry data and the prediction accuracies of the different models were compared and discussed. Results showed that the external diffusion model could accurately predict the corrosion state, and the correlation coefficient with industry data was 0.998. The slag shear rate on the surface of the refractory brick was a key control parameter for corrosion, especially for a top single-burner down-flow gasifier.

Numerical simulation of bubble formation behavior in oxygen coal combustion melting and separating furnace

AbstractIn order to improve the mass transfer efficiency of the high‐temperature molten pool area in the oxygen coal combustion melting and separating furnace, water model experiment and VOF model were used to study the mechanism of bubble formation in the area, investigate the changing rules of oxygen lance parameters on the shape and frequency of bubbles. The results show that the basic law of bubble generation is the transition from lateral injection to longitudinal growth, and the bubble generation frequency is 7.5 Hz under standard conditions. Increasing the oxygen lance mass flow will reduce the generation frequency, but the local bubble distribution is more compact. Increasing the oxygen lance inclination angle increase the generation frequency, but it will cause local gas phase accumulation, if too close to the bottom of the furnace. Small oxygen lances diameter is beneficial to increase the generation frequency and enhance mass transfer efficiency. Increasing the oxygen lance immersion depth is conducive to increasing the generation frequency, the gas‐liquid interface and improving molten and separation efficiency. On the other hand, it will weaken the effect of “adherence to the wall” and reduce the erosion of furnace lining by inhibiting the flow of bubbles and slag.

Droplet Formation and Dripping Behavior during the Electroslag Remelting Process with Two Series-Connected Electrodes

The formation and dripping behavior of droplets in the process of the electroslag remelting with two series-connected electrodes (TSCE-ESR) has an important influence on the optimization of power supply parameters and the purity of the electroslag ingot. In this article, through numerical simulation based on the VOF (volume of fluid) model, combined with the transparent experimental device for physical simulation, the mechanism of metal droplet formation and the effect of the filling rate on its droplet behavior were studied. The results showed that the proximity effect, instead of the skin effect, is a major factor influencing droplet formation in TSCE-ESR process. The proximity effect makes the region inside the two electrode tip melt first, and the molten steel converges at the electrode tips to form a droplet source. The process of droplet formation and dropping can be divided into three stages: formation of molten layer, droplet stretching and necking, and detachment. In the stage of droplet stretching and necking, the increase in the contact area between the droplet and the slag and the instantaneous increase of the current provide good thermodynamic and dynamic conditions for the removal of non-metallic inclusions. After the droplet drops into the slag pool, it promotes the flow of slag and improves the heat and mass transfer efficiency of the slag/metal interface. The relatively large filling rate can form smaller and dispersed droplets, which improves the refining effect. At the same time, the increase of the filling rate can improve the input power and the electrode remelting rate.

Investigations on Crystallization Processes of Three Oxidic Gasifier Slag Systems

Abstract In entrained flow gasifiers, the production of oxidic slag accompanies the gasification process. This slag forms a layer on the refractory walls, flows downwards gravitationally, and is collected in a water quench. Hence, the slag flow must be constant, since a slag blockage represents a worst-case-scenario. Crystallization of the slag increases slag viscosity, subsequently leading to a possible slag blockage. Therefore, crystallization processes in oxidic slags need to be understood and hence investigated. In this study, three artificial, coal ash related oxidic slag systems were analyzed on their crystallization behavior. Therefore, their melt behavior was investigated via hot-stage microscopy and differential thermal analysis (DTA). Additional thermochemical calculations were performed to predict crystallized phases. Subsequently, quenching experiments were conducted to generate supercooled crystallization in the slag samples. These samples were analyzed afterward via X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the morphologies of crystals were characterized/described. In-situ observations on crystallization growth were performed by using a confocal laser scanning microscope (CLSM). Finally, crystallized phases were compared with results obtained from thermochemical calculations, and the impact of kinetics on the distributed phases was discussed. The knowledge on the crystallization behavior of various phases can be transferred to other slag systems and can improve general crystallization predictions made by thermochemical calculations.

Transient flow and mold flux behavior during ultra-high speed continuous casting of billet

Ultra-high casting speed is an important development feature for efficient continuous casting of billet. A mathematical model which addresses the high flow rate of molten steel in the billet mold is presented, coupling slag flow with heat flux and solidification. The model is then applied to investigate the correlation between transient steel flow, slag infiltration and heat transfer in the mold-shell gap during ultra-high casting speed. The results show that the meniscus level experiences a hump near the mold wall and a valley near the nozzle as a result of the recirculating flow in the upper mold. The liquid slag around the mold wall infiltrates preferentially into the gap to be consumed quickly, whereas those near the SEN flows to the mold with a low speed. Severe fluctuations in meniscus level will disturb the slag infiltration, which in turn causes the formation of uneven slag films, leading to intensified heat flux fluctuations in the mold-shell gap, especially in the area of 20−60 mm from the mold corner.

Numerical Study of Binary Trickle Flow of Liquid Iron and Molten Slag in Coke Bed by Smoothed Particle Hydrodynamics

In the bottom region of blast furnaces during the ironmaking process, the liquid iron and molten slag drip into the coke bed by the action of gravity. In this study, a practical multi-interfacial smoothed particle hydrodynamics (SPH) simulation is carried out to track the complex liquid transient dripping behavior involving two immiscible phases in the coke bed. Numerical simulations were performed for different conditions corresponding to different values of wettability force between molten slag and cokes. The predicted dripping velocity changes and interfacial shape were investigated. The relaxation of the surface force of liquid iron plays a significant role in the dripping rate; i.e., the molten slag on the cokes acts as a lubricant against liquid iron flow. If the attractive force between the coke and slag is smaller than the gravitational force, the slag then drops together with the liquid iron. When the attractive force between the coke and slag becomes dominant, the iron-slag interface will be preferentially detached. These results indicate that transient interface morphology is formed by the balance between the momentum of the melt and the force acting on each interface.

Numerical Simulation of the Magneto‐Hydrodynamic Two‐Phase Flow and Heat Transfer during Electroslag Remelting Hollow Ingot Process

The electroslag remelting hollow ingot process is a new technology, which is considered a promising method to manufacture the superior hollow ingot. Herein, a coupling multiphysical fields mathematical model is developed to investigate the magneto‐hydrodynamic two‐phase flow and heat transfer phenomena. A laboratory scale experiment is conducted to validate the model. The results indicate that the molten slag flows around the electrodes at the edge of slag bath. Under the electrode tip, the flow of molten slag is dominated by the dropping of metal droplets, with a maximum velocity of 0.12 m−1 s−1. The temperature is not uniform in the circumference direction due to the nonuniform arrangement of the electrodes. The behavior of metal droplets is similar to that in a traditional electroslag remelting process, with a final velocity of 0.44 m−1 s−1 and a final temperature of 1858 K. In addition, the heat flow at the ingot/external mold interface is 3–5 times larger than that at the ingot/inner mold interface. The heat flow at the slag/metal pool interface takes 42.6% of total power input, and the heat of metal droplets takes 28.6% of that, both of which are the main heat resources for metal pool.

Slag corrosion-resistance mechanism of lightweight magnesia-based refractories under a static magnetic field

Slag corrosion resistance of lightweight magnesia-based refractories with micro/nano-sized pores under a static magnetic field is investigated. They exhibited excellent slag resistance under static magnetic field of 8.5 mT with an isolation layer composed of solid phases formed at the refractory/slag interface. The static magnetic field generated a “magnetic brake effect” that suppressed the infiltrating flow of the molten slag and decreased the dissolution rate of MgO grains. Moreover, it also limited the thickness of the isolation layer by reducing the extent of the refractory-slag interaction, which can be applied to further improve the slag resistance of refractories.