Applications of Computational Fluid Dynamics (CFD) in iron- and steelmaking: Part 1

Abstract

All operations in process metallurgy involve complex phenomena comprising momentum, heat, and/or mass transport; iron- and steelmaking is not an exception. Transport phenomena, i.e. fluid flows, heat transfer and mass transfer, play a dominant role in process metallurgy since their respective laws govern the kinetics of the various physical phenomena occurring in ironmaking and in steelmaking. These phenomena include such events as three-phase reactions, entrainment of slag and gas in liquid steel, vacuum degassing, alloy melting and mixing, the movements and flotation of inclusions, melt temperature losses, residence times in a metallurgical reactor, erosion of refractory linings, etc. In all these aspects, the evolution in our techniques and abilities to model single and multiphase flows and their attendant heat and mass transfer processes has contributed significantly to our understanding and effectively operating these processes, to designing improvements, and to developing new processes. To be ignorant of these matters can doom a processing operation to the scrap heap of metallurgical failures. Computational fluid dynamics (CFD) and computational heat and mass transfer has been a very effective tool over the last three decades, for modelling iron- and steelmaking processes, starting from the blast furnace up to continuous casting and beyond. With the advent of commercial CFD packages and ever increasing computational power through parallel processing, CFD has now become the dominant approach for predicting various aspects in iron- and steelmaking processes. In Part 1 of this review paper, the applications of CFD in ironmaking processes are thoroughly reviewed, discussed and critiqued. In Part 2, fluid flows and CFD in steelmaking and steel casting processes are similarly reviewed and critiqued.     

Computational Fluid Dynamics (CFD) Investigation of Submerged Combustion Behavior in a Tuyere Blown Slag-fuming Furnace

A thin-slice computational fluid dynamics (CFD) model of a conventional tuyere blown slag-fuming furnace has been developed in Eulerian multiphase flow approach by employing a three-dimensional (3-D) hybrid unstructured orthographic grid system. The model considers a thin slice of the conventional tuyere blown slag-fuming furnace to investigate details of fluid flow, submerged coal combustion dynamics, coal use behavior, jet penetration behavior, bath interaction conditions, and generation of turbulence in the bath. The model was developed by coupling the CFD with the kinetics equations developed by Richards et al. for a zinc-fuming furnace. The model integrates submerged coal combustion at the tuyere tip and chemical reactions with the heat, mass, and momentum interfacial interaction between the phases present in the system. A commercial CFD package AVL Fire 2009.2 (AVL, Graz, Austria) coupled with several user-defined subroutines in FORTRAN programming language were used to develop the model. The model predicted the velocity, temperature field of the molten slag bath, generated turbulence and vortex, and coal use behavior from the slag bath. The tuyere jet penetration length (l _P) was compared with the equation provided by Hoefele and Brimacombe from isothermal experimental work $ \left( {\frac{{l_{\text{P}} }}{{d_{o} }} = 10.7\left( {N^{\prime }_{Fr} } \right)^{0.46} \left( {\rho_{\text{g}} /\rho_{l} } \right)^{0.35} } \right) $ and found 2.26?times higher, which can be attributed to coal combustion and gas expansion at a high temperature. The jet expansion angle measured for the slag system studied is 85?deg for the specific inlet conditions during the simulation time studied. The highest coal penetration distance was found to be l/L?=?0.2, where l is the distance from the tuyere tip along the center line and L is the total length (2.44?m) of the modeled furnace. The model also predicted that 10?pct of the injected coal bypasses the tuyere gas stream uncombusted and carried to the free surface by the tuyere gas stream, which contributes to zinc oxide reduction near the free surface.     

Computational Fluid Dynamic (CFD) Simulations of Liquid Steel Infiltration in Ceramic Foam Structures. Part II: Application to Laboratory‐Scale Experiments

The infiltration of liquid TRIP steel into a porous zirconium dioxide foam ceramics is a possible production line for a new composite material. This composite is currently under investigation and development in the Collaborative Research Center 799. Coupled numerical simulations of the hot infiltration process at the pore scale are presented in the paper. The results of the simulations are analysed in order to study similarities and differences between heat and fluid flow phenomena during the infiltration of the foam ceramics. Among others, temperature distributions in the liquid steel and the ceramics are evaluated for typical casting conditions in a laboratory‐scale experiment.     

Control of slag and inclusions in traditional Japanese iron- and steelmaking

Abstract

In traditional Japanese smelting and forging, three characteristic technologies can be identified that may provide a basis for a new process concept in the production of iron and steel. First, ironsand, the use of which is problematic in modern ironmaking, was used instead of ironstone. The titanium oxide present was effective for keeping the slag fluid and increasing the carbon content of the product, thereby decreasing the activity coefficient of FeO in the slag. Second, two types of operation were carried out with almost the same type of furnace. In one of the operations, mainly molten pig iron was produced and, in the other, steel bloom (>50 wt-% of total product) and molten pig iron. The main controlling factors were the type of raw material (titanium content of ironsand) and the oxidising potential in the furnace, which influenced the degree of carburisation and decarburisation of the iron. Third, it is thought that traditional Japanese steel is the best material for Japanese swordmaking. This was confirmed by an experiment with different materials. In the case of traditional Japanese steel, both the homogeneity of the carbon distribution and the inclusion content in the original material can be improved by the forging process, since the degree of contamination during forging is less. With modern steel, weldability in forging is adversely affected by contamination during forging. This means that the complex combination of material and total process is important for producing the particular product.     

Modelling of Industrial Processes Using Computational Fluid Dynamics

Abstract

Some examples of computational fluid dynamics in modelling and optimization of industrial processes are discussed. Examples include film cooling of turbine blades, gallium arsenide crystal growth, and black liquor recovery boilers. Modelling aspects and numerical techniques used are discussed together with some limitations and possible remedies. © 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.

Résumé

On discut de quelques exemples de calcul par ordinateur de la dynamique des fluides, dans la modélisation et l'optimisation de procédés industriels. Les exemples incluent le refroidissement pelliculaire d'aubes de turbine, la croissance de cristal d'arséniure de gallium et les fours de récupération de liqueur noire. On discute des aspects de la modélisation et des techniques numériques utilisées ainsi que de certaines limitations et de remèdes possibles. © 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.     

Laminar Pipeline Flow of Wastewater Sludge: Computational Fluid Dynamics Approach

A computational fluid dynamics (CFD) technique applied to laminar flow of wastewater sludge in horizontal, circular pipes is presented. The technique employs the Crank-Nicolson finite difference method in conjunction with the variable secant method, an algorithm for determining the pressure gradient of the flow. Head loss (pressure drop) and velocity profile are predicted using the technique. Numerical predictions of head loss and velocity profile for several combinations of flows, pipe sizes, and sludge solids concentrations are compared to exact analytical values, derived from the theory of laminar flow of Bingham-plastic fluids. The predicted values are in good agreement with the exact values. Comparisons are also made to head loss values for municipal wastewater sludge from the literature. The CFD technique has several advantages over the analytical calculations, including ease of use, time efficiency, and the ability to readily change boundary conditions, flow geometry, and the rheological model for the shear stress.     

Coherent Structures in Flat-Bed Abutment Flow: Computational Fluid Dynamics Simulations and Experiments

Numerical computations and laboratory experiments are carried out to investigate the three-dimensional structure of large-scale (coherent) vortices induced by bridge abutments on a flat bed. A finite-volume numerical method is developed for solving the unsteady, three-dimensional Reynolds-averaged Navier–Stokes equations, closed with the k–ω turbulence model, in generalized curvilinear coordinates and applied to study the flow in the vicinity of a typical abutment geometry with a fixed, flat bed. The computed flowfields reveal the presence of multiple, large-scale, unsteady vortices both in the upstream, “quiescent,” region of recirculating fluid and the shear-layer emanating from the edge of the foundation. These computational findings motivated the development of a novel experimental technique for visualizing the footprints of large-scale coherent structures at the free surface. The technique relies on digital photography and employs averaging of instantaneous images over finite-size windows to extract coherent eddies from the chaotic turbulent flow. Application of this technique to several abutment configurations yielded results that support the numerical findings.     

Study of Flow in a Blanket Clarifier Using Computational Fluid Dynamics

This work simulated the flow pattern of the sludge blanket clarifier at the Bansin Water Treatment Plant, Taiwan by multiphase flow, three-dimensional analysis. The following three models were developed individually: One-phase flow (water) in the clarifier—this model acquires the basic water-flow pattern; a homogeneous porous medium at the bottom of the clarifier—this porous medium represents the sludge blanket; and, the Eulerian granular multiphase model, which was utilized to obtain solid effluent flux and to determine the effects of particle size and density on sludge blanket stability. Analytical results indicated that the clarifier has two principal circulations inside and outside the reaction well. A plentiful, dense and thick sludge blanket should exist at the clarifier bottom; otherwise particles could flow out through the gap between bottom of the reaction well and top of blanket surface, resulting in poor water quality. In the multiphase flow model, large particles and a high particle density are positively correlated with sludge blanket stability.     

Computational Fluid Dynamics Modeling of Macrosegregation and Shrinkage in Large-Diameter Steel Roll Castings

Minimizing macrosegregation and shrinkage in large cast steel mill rolls challenges the limits of commercial foundry technology. Processing improvements have been achieved by balancing the total heat input of casting with the rate of heat extraction from the surface of the roll in the mold. A submerged entry nozzle (SEN) technique that injects a dilute alloy addition through a nozzle into the partially solidified net-shaped roll ingot can mitigate both centerline segregation and midradius channel segregate conditions. The objective of this study is to optimize the melt chemistry, solidification, and SEN conditions to minimize centerline and midradius segregation, and then to improve the quality of the transition region between the outer shell and the diluted interior region. To accomplish this objective, a multiphase, multicomponent computational fluid dynamics (CFD) code was developed for studying the macrosegregation and shrinkage under various casting conditions for a 65-ton, 1.6-m-diameter steel roll. The developed CFD framework consists of solving for the volume fraction of phases (air and steel mixture), temperature, flow, and solute balance in multicomponent alloy systems. Thermal boundary conditions were determined by measuring the temperature in the mold at several radial depths and height locations. The thermophysical properties including viscosity of steel alloy used in the simulations are functions of temperature. The steel mixture in the species-transfer model consists of the following elements: Fe, Mn, Si, S, P, C, Cr, Mo, and V. Density and liquidus temperature of the steel mixture are locally affected by the segregation of these elements. The model predictions were validated against macrosegregation measured from pieces cut from the 65-ton roll. The effect of key processing parameters such as melt composition and superheat of both the shell and the dilute interior alloy are addressed. The influence of mold type and thickness on macrosegregation and shrinkage also are discussed.     

Experimental Validation of a Computational Fluid Dynamics Model of Copper Electrowinning

The hydrodynamics that occur in the space between the electrode plates in copper electrowinning (EW) are simulated using a computational fluid dynamics model (CFD). The model solves for the phases of gas oxygen bubbles and electrolyte using the Navier–Stokes equations in a CFD framework. An oxygen source is added to the anode, which sets up a recirculation pattern. The gradients in copper near the cathode lead to buoyancy forces, which result in an uplift in the electrolyte close to the cathode. This study investigates the experimental validation of the CFD model using a small/medium-scale real EW system. The predicted fluid velocity profiles are compared with the experimental values, which have been measured along various cross sections of the gap between the anode and the cathode. The results show that the CFD model accurately predicts the velocity profile at several heights in the plate pair. The CFD model prediction of the gas hold-up and the recirculation pattern is compared with visualizations from the experiment. The CFD model prediction is shown to be good across several different operating conditions and geometries, showing that the fundamental underlying equations used in the CFD model transfer to these cases without adjusting the model parameters.     

Validation of a Three-Dimensional Computational Fluid Dynamics Model of a Contact Tank

A three-dimensional (3D) computational fluid dynamics (CFD) model of a contact tank is presented in this paper. The model results are compared against 3D velocities and flow through curve (FTC) data, representing a tracer concentration profile, from a 1:8 scale physical model. The objective is to demonstrate that CFD models can simulate both the FTC and the 3D velocity field quite well. Simultaneous validation of velocities and FTC is important in ascertaining the predictive capabilities of CFD models, as physical model studies indicate that different baffle arrangements can lead to similar FTCs. Therefore, a good prediction of only FTC, as presented in previous 3D CFD model studies, does not necessarily imply a correct simulation of the flow field.     

Computational Fluid Dynamics Modeling for the Design of Large Primary Settling Tanks

Settling tanks are used to remove solids at wastewater treatment plants. Many numerical models have been proposed to simulate the settling process and to improve tank efficiency. In this research, a three-dimensional (3D) numerical model is developed to simulate large primary settling tanks. In the proposed model, the non-Newtonian properties of the sludge flow in the settling tank are described by a Bingham plastic rheological model. To eliminate the singularity inherited in the rheological model, a modified constitutive relation is used in both the yielded and unyielded regions. Hindered settling of particles in the settling tank is also modeled. Tracer study, where a massless scalar is injected and transported, is done to investigate the tank’s residence time. This numerical model is used to improve the design of the primary settling tanks, which will be built in Chicago. The Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) is in the process of building new preliminary treatment facilities at their Calumet Water Reclamation Plant (CWRP), including twelve 155-ft-diameter primary settling tanks (PSTs) designed to treat flows up to (480?million?gal./day (MGD). The computational fluid dynamics (CFD) model simulated solids removal efficiencies based on a particle size distribution similar to the one observed in the CWRP influent. The results were used to establish the design basis for tank side-water depth, inlet feedwell dimensions, etc., resulting in improved performance and substantial reduction in construction costs.     

Computational Fluid Dynamics Study of a Noncontact Handling Device Using Air-Swirling Flow

The vortex gripper is a recently developed pneumatic noncontact handling device that takes advantage of air-swirling flow to cause upward lifting force and that thereby can pick up and hold a work piece placed underneath without any contact. It is applicable where, e.g., in the semiconductor wafer manufacturing process, contact should be avoided during handling and moving in order to minimize damage to a work piece. For the purpose of a full understanding of the mechanism of the vortex gripper, a computational fluid dynamics (CFD) study was conducted in this paper, and at the same time, experimental work was carried out to measure the pressure distribution on the upper surface of the work piece. First, three turbulence models were used for simulation and verified by comparison with the experimental pressure distribution. It is known that the Reynolds stress transport model (RSTM) can reproduce the real distribution better. Then, on the basis of the experimental and numerical result of RSTM, an insight into the vortex gripper and its flow phenomena, including flow structure, spatial velocity, and pressure distributions, and an investigation into the influence of clearance variation was given.     

Computational Fluid Dynamics Simulation of Supersonic Oxygen Jet Behavior at Steelmaking Temperature

Supersonic oxygen jets are used in steelmaking and other different metal refining processes, and therefore, the behavior of supersonic jets inside a high temperature field is important for understanding these processes. In this study, a computational fluid dynamics (CFD) model was developed to investigate the effect of a high ambient temperature field on supersonic oxygen jet behavior. The results were compared with available experimental data by Sumi et al. and with a jet model proposed by Ito and Muchi. At high ambient temperatures, the density of the ambient fluid is low. Therefore, the mass addition to the jet from the surrounding medium is low, which reduces the growth rate of the turbulent mixing region. As a result, the velocity decreases more slowly, and the potential core length of the jet increases at high ambient temperatures. But CFD simulation of the supersonic jet using the k−ε turbulence model, including compressibility terms, was found to underpredict the potential flow core length at higher ambient temperatures. A modified k-ε turbulence model is presented that modifies the turbulent viscosity in order to reduce the growth rate of turbulent mixing at high ambient temperatures. The results obtained by using the modified turbulence model were found to be in good agreement with the experimental data. The CFD simulation showed that the potential flow core length at steelmaking temperatures (1800 K) is 2.5 times as long as that at room temperature. The simulation results then were used to investigate the effect of ambient temperature on the droplet generation rate using a dimensionless blowing number.     

Hot-Metal Desulfurization Using Calcium Carbide and Calcium Oxide in Transfer Ladle: A Computational Fluid Dynamics Investigation

In this study, a 3D transient computational fluid dynamics (CFDs) model that simulates hot-metal desulfurization (HMD) using calcium carbide and calcium oxide in an experimental-scale ladle with a 70 kg capacity is presented. The model takes into account the efficiency of reagent-particles-penetrating carrier gas bubbles and is validated through experimental work, with an average difference of 7.06%. In this research, the effects of varying reagent particle sizes, hot-metal temperatures, gas flow rates, and ladle design on desulfurization rates are discussed. The results indicate that when particle diameter decreases from 30 to 20.9 and 11.8 μm, desulfurization rates rise from 50.92% to 66.02% and 89.99%, respectively. Regarding hot-metal temperature, a 100° range results in a final desulfurization rate difference of less than 3%. This study also reveals that increasing the carrier gas flow rate from 13 to 15 SLPM reduces the removal rate by 6.10%. As particle gas flow rate increases from 200 to 300 g min⁻¹, the removal rate increases by 9.02%. In the lance arrangement analysis, the duo lance system demonstrates nearly identical desulfurization performance to the single-center lance system, which outperforms the off-center lance system.     

CFD在热轧带钢层流控冷系统中的应用

利用CFD数值仿真技术模拟了层流水冷系统中层流冷却装置复杂的内部流场以及冷却水自由下落后的外部流场,并通过对仿真流场的分析,优化设计了冷却装置内部结构,精确地确定了控制冷却数学模型中强迫对流宽度值,为提高控冷系统的控制精度奠定了基础.     

CFD Benchmark for a Single Strand Tundish (Part II)

In a comparative benchmark, nine participants of the German Steel Institute VDEh working group “Fluid Mechanics and Fluid Simulation” studied the melt flow in a 16‐t single‐strand tundish. Starting with a steady‐state simulation of the melt flow, the transient flow behaviour was simulated for an idealized ladle change involving a sudden jump in temperature and concentration. In addition, the separation of non‐metallic particles to the melt surface was examined. No guidelines and limitations were made regarding the simulation strategy. The predicted flow profiles, temperature and concentration distributions coincide with each other within a good approximation. Systematic differences in the transient temperature and turbulence fields are explained by the selection of the boundary condition at the free surface. All CFD programs reproduce the fundamental flow structure with a good degree of accuracy. The separation rate for non‐metallic particles calculated on the basis of the Lagrange Method are greater than would be expected according to theory and measurement results obtained on the water model.     

CFD Benchmark for a Single Strand Tundish (Part I)

A Computational Fluid Dynamic (CFD) benchmark for the water model of a single‐strand continuous casting tundish was performed by ten members of the newly founded working group “Fluid Mechanics and Fluid Simulation” of the German Steel Institute VDEh. A critical comparison is drawn between laser‐optical velocity measurements and residence time measurements on the one hand and CFD simulations using different CFD programs, turbulence models, boundary conditions, proposed solutions, etc., on the other hand. The validation criteria used include, among others, the turbulence distribution, the position of the recirculation center and the maximum backflow velocity in the tundish which is induced by the recirculation, as well as the residence time distribution. The results show that the flow and turbulence structure can be computed on the basis of the Unsteady Reynolds averaged Navier‐Stokes (URANS) equations with a good degree of accuracy. The relative positional deviation of the recirculation center is ‐12.5% < Δx/L₁ < 5.0%. The characteristic times Θ_min, Θ_max, Θ_20% and Θ_5% , which describe the residence time distribution, are established with a variation of ±15%. The benchmark yields important results for the sensible use of today's commonly used numerical CFD models and contributes to further improving the reliability of CFD simulations in metallurgical process engineering.     

基于CFD的平行流铜电解槽槽型优化设计

以平行流铜电解槽为对象,ANSYS软件为平台,对不同进液方式下电解槽槽内流场分布进行数值模拟。结果表明,进液方式对平行流电解槽极间电解液的流动有重要影响,与下部分段进液槽型和上部交错进液槽型相比,下部交错进液槽型具有较大的极间电解液流动速度与较均匀的速度场。