Limestone of different particle sizes is often calcined together to improve production efficiency, but the calcination effect of mixed particle size limestone is difficult to guarantee. To ...investigate the effect of different particle size combinations on calcination, this study uses a porous media model and a shrinking core model to simulate the calcination process for a single particle size and two mixed particle sizes in a Parallel Flow Regenerative lime kiln (PFR lime kiln). The results of the study show that an increase in void fraction has a small effect on the gas temperature. The temperature also does not change with particle sizes. At the same time, the decomposition is poor near the wall and better the closer to the center of the calcination zone. In addition, when the particle sizes differ by 2 times, the decomposition of small limestone particles had less influence, and the decomposition of large particles was also better. When the particle sizes differ by 3 times, the decomposition of both limestone sizes is more affected, especially for the larger limestone size, where only the outer surface is involved in the decomposition.
•First developed a three-phase coupled model of desulfurization in ESR process.•The MHD thermal flow in the reactor was clarified.•Distributions of sulfur concentration in the three phases were ...demonstrated.•An experiment was carried out to validate the simulation.
A three-phase comprehensive mathematical model has been established to study the desulfurization behavior in electroslag remelting (ESR) process. The solutions of the mass, momentum, energy, and species conservation equations were simultaneously calculated by the finite volume method. The Joule heating and Lorentz force were fully coupled through solving the Maxwell’s equations with the assistance of the magnetic potential vector. The movements of the air-slag and slag-metal interfaces were described by the volume of fluid (VOF) approach. In order to include the influences of the air, the slag and the electric current on the desulfurization, a thermodynamic and kinetic module was introduced. An experiment was conducted to validate the model. The completely comparison between the measured and simulated data indicates that the model can describe the desulfurization behavior in the ESR process with an acceptable accuracy. The sulfur in the metal would be transferred into the slag under the combined effect of the slag treatment and the electrochemical reaction, and is primarily achieved in the period of the droplet formation. The sulfur in the slag then could be transferred into the air because of the oxidation. The maximum calculated removal ratio in the whole process is around 88%.
A one third scale water model experiment was conducted to observe the asymmetric flow and vortexing flow inside a slab continuous-casting mold. Dye-injection experiment was used to show the evolution ...of the transient flow pattern in the liquid pool without and with gas injection. The spread of the dye was not symmetric about the central plane. The flow pattern inside the mold was not stationary. The black sesames were injected into water to visualize the vortexing flow pattern on the top surface. The changes of shape and location of single vortex and two vortices with time had been observed during experiments. Plant ultrasonic testing (UT) of slabs was used to analyze the slab defects distribution, which indicated that the defects are intermittent and asymmetric. A mathematical model has been developed to analyze the time-dependent flow using the realistic geometries, which includes the submerged entry nozzle (SEN), actual mold, and part of the secondary cooling zone. The transient turbulent flow of molten steel inside the mold has been simulated using the large eddy simulation computational approach. Simulation results agree acceptably well with the water model experimentally observed and plant UT results. The oscillating motions of jet and the turbulence naturally promote the asymmetric flow even without the effects of slide gate nozzle or the existence of clogs inside the SEN. The periodic behavior of transient fluid flow in the mold is identified and characterized. The vortexing flow is resulted from asymmetric flow in the liquid pool. The vortices are located at the low-velocity side adjacent to the SEN, and the positions and sizes are different. Finally, the model is applied to investigate the influence of bubble size and casting speed on the time-dependent bubble distribution and removal fraction from the top surface inside the mold.
In ladle metallurgy, the role of argon gas purging in liquid steel is well recognized. One key aspect of this process is the prediction of gas volume fraction and gas bubble diameter. Calculation of ...bubble size is important as it is significantly modified by the injection system and gas flow rate, and it also directly determines the buoyancy which influences the physical mixing process and surface reactions. In this study, a porous plug was used for gas injection as the common practice in the steel industry and a one-third scale water model was established. Then a numerical model based on the Eulerian multiphase model was established and the population balance model (PBM) was used to calculate the gas bubble size distribution. The bubble coalescence and breakage were included and the phase interactions were coupled with the PBM to consider the effect of bubble diameter on the fluid flow. A user defined scalar (UDS) transport equation was added to simulate the solute transport in ladle to study the mixing efficiency. The mixing time, wall shear stress and slag entrapment probability were taken into consideration to find a suitable plug position to balance the mixing efficiency and steel cleanness. The results show that the mixing time decreases with increasing the plug radial distance and the maximum wall shear stress appears when plug radial distance is 0.67 R.
•First time to develop a 3D coupled model of inclusion motion in ESR process.•Inclusion movement during the growing of droplet is demonstrated.•Effects of current, inclusion diameter and density on ...removal ratio are clarified.•Experiment is carried out to validate the mathematical model.
In order to understand the movement of the inclusion in electroslag remelting (ESR) process, a transient three-dimensional (3D) comprehensive mathematical model has been established. The finite volume method was employed to solve the mass, momentum and energy conservation equations as well as the Maxwell’s equations. The volume of fluid (VOF) approach was used to define the redistribution of the metal and the slag. The inclusion trajectory was described by using the two-way coupled Euler-Lagrange method. Experiments were conducted to verify the proposed model. The removal ratios of the inclusions with 1 µm and 10 µm diameters constantly increase with a larger current. The removal ratios of the inclusions with 3 µm and 5 µm diameters first increase with the current ranging from 1000 A to 1600 A, but then decrease if the current continuously increases to 1800 A. The inclusions with 15 µm and 20 µm diameters are almost completely eliminated in the five currents. The increase of the inclusion density would reduce the removal ratio of the inclusion with a larger diameter in different degrees.
A mathematical model has been developed to analyze transient fluid flow and inclusions transport in a slab continuous casting mold, considering the effects of electromagnetic brake (EMBr) arrangement ...and magnetic field strength. Transient flow of molten steel in the mold is calculated by using the large eddy simulation. The electromagnetic force is incorporated into the Navier–Stokes equation. The transport of inclusion inside the mold is calculated using the Lagrangian approach based on the transient flow field. The predicted results of this model are compared with the measurements of the ultrasonic testing of the rolled steel plates and the water model experiments. The transient asymmetrical flow pattern and inclusion transport inside the mold exhibits satisfactory agreement with the corresponding measurements. With electromagnetic brake effect, the velocities around the braking region are significantly suppressed, and the recirculating flow in the lower part drops and tends to develop a plug-like flow. The EMBr arrangement has an insignificant effect on the overall removal fraction of inclusions, especially for larger inclusions. The inclusion removal rate for the flow-control mold (FCM arrangement) reduces instead compared with no EMBr, especially for smaller inclusions.
Quicklime is an essential reducing agent in the steel smelting process and its calcination from limestone is accompanied by considerable energy consumption. As a relatively economical lime kiln, the ...Parallel Flow Regenerative (PFR) lime kiln is used as the main equipment for the production of quicklime by various steel industries. PFR lime kilns generally use natural gas as the fuel gas. Although natural gas has a high calorific value and is effective in calcination, with the increasing price of natural gas and the pressure saves energy and protect the environment, it makes sense of exploring the use of cleaner energy sources or other sub-products as fuel gas. The use of blast furnace gas (BFG) as a low calorific value fuel gas produced in the steel smelting process has been of interest. This paper therefore develops a set of mathematical models for gas-solid heat transfer and limestone decomposition based on a Porous Medium Model (PMM) and a Shrinking Core Model (SCM) to numerically simulate a PFR lime kiln using BFG in order to investigate the feasibility of calcining limestone with low calorific fuel gas and to provide a valuable reference for future development of such processes and the kiln structure improvement.
A transient three-dimensional finite-volume mathematical model has been developed to investigate the coupled physical fields in the electroslag remelting (ESR) process. Through equations solved by ...the electrical potential method, the electric current, electromagnetic force (EMF), and Joule heating fields are demonstrated. The mold is assumed to be conductive rather than insulated. The volume of fluid approach is implemented for the two-phase flow. Moreover, the EMF and Joule heating, which are the source terms of the momentum and energy sources, are recalculated at each iteration as a function of the phase distribution. The solidification is modeled by an enthalpy-porosity formulation, in which the mushy zone is treated as a porous medium with porosity equal to the liquid fraction. An innovative marking method of the metal pool profile is proposed in the experiment. The effect of the applied current on the ESR process is understood by the model. Good agreement is obtained between the experiment and calculation. The electric current flows to the mold lateral wall especially in the slag layer. A large amount of Joule heating around the metal droplet varies as it falls. The hottest region appears under the outer radius of the electrode tip, close to the slag/metal interface instead of the electrode tip. The metal pool becomes deeper with more power. The maximal temperature increases from 1951 K to 2015 K (1678 °C to 1742 °C), and the maximum metal pool depth increases from 34.0 to 59.5 mm with the applied current ranging from 1000 to 2000 A.
A mathematical model has been developed to understand the electromagnetic phenomena, heat transfer and molten steel flow in a continuous casting tundish with channel-type induction heating. Maxwell ...equations are first solved using the finite element method to determine the electromagnetic force and joule heating. Then, the Navier-Stokes equations and energy conservation equation are also solved with the electromagnetic force and joule heating as a source term, respectively. The two-equation RNG k-ε model is used to represent the turbulent mixing. Additionally, the tracer distribution is determined by solving a scale transport equation. The coupled flow field, temperature distribution and concentration distribution are solved by the finite volume method. A non-isothermal water model experiment is performed to observe significantly buoyancy driven flow in the tundish with induction heating. The results indicate that a current loop would be formed by the induced current through the two channels. The electromagnetic force points to the center of the channel generating a pinch effect on molten steel. As skin effect and proximity effect, the electromagnetic force as well as the joule heating in the region closer to the induction coil is greater than that in another region. Therefore, spiral recirculation would occur in the channels when molten steel flows through. After flows through the channels, the molten steel lifts upward under the effect of buoyancy. The heat loss of molten steel can be compensated effectively by the joule heating, and the temperature distribution become more uniform in the continuous casting tundish with induction heating.
Swirling flow tundish was developed to enhance the coalescence of inclusions, so as to deeply clean the liquid steel. Inclusions would gather to the center of the swirling flow by centripetal force, ...due to the density difference between inclusions and liquid steel. Thus, small inclusions can coalesce into larger ones, and then float to the free surface by their self-buoyance. Physical experiments were carried out in a 1/2.5 scale single strand tundish to study the flow characteristics of tundish with swirling chamber. Numerical modeling was developed to simulate the movements of small inclusions in swirling flow. Discrete phase model was employed together with the O’Rourke algorithm to characterize the coalescence of the inclusions in the swirling flow. The removal of inclusions was investigated, considering the absorption by upper slag and trapping by outside wall of ladle shroud. Compared with a turbulence inhibitor, a swirling chamber shows a similar effect on flow improvement, while performs better in inclusion removal, owing to the inclusion coalescence caused by centripetal force. The results revealed that swirling chamber in diameter of 450 mm is an optimized scheme for deep cleaning of liquid steel, with only 1.66% of the inclusions flowing out of the tundish nozzle.
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