The three-dimensional model was developed according to number 4 of the main trough of blast furnace at China Steel Co. (CSC BF4). The
Liquid phase separation plays a central role in a variety of production technologies [
Schematic configuration of main trough: (a) side section and (b) cross section, used in this investigation.
A few investigations were carried out to study the fluid flow characteristics to enhance the separation efficiency. In the laminar flow regime, where Reynolds number [
In the mold of a continuous caster [
As viewed from the above, the active modulation and control of the liquid phase separation are still challenge for high-temperature mixtures of iron and slag. In the present study, we aim to numerically analyze the separation efficiency of melt iron and slag in the main trough of blast furnace through the computer fluid dynamics (CFD) with the different operating conditions and main trough geometry. From the methodology point of view, an effective route to manipulate the separation of iron and slag in main trough of blast furnace depends on the geometry of trough, tapping rate, and the ratio of iron to slag in the fluids. At the present, according to our best knowledge, the computational fluid dynamics are firstly to systematically the parameters of main trough for studying the separation efficiency of molten iron from slag of blast furnace during tapping process.
The main trough of blast furnace number 4 at China Steel Co (CSC BF4) with 7200 tons/day of production capacity was modeled for the three-dimensional computational fluid dynamics (CFD) to investigate the separation efficiency of molten iron and slag in this work. As expressed in the Cartesian (
The physical properties of liquid [
Property | Temperature (K) | Viscosity (kgm−1s−1) | Density (kgm−3) |
---|---|---|---|
Iron | 1773 | 0.00715 | 7000 |
1823 | 0.007 | 6500 | |
Slag | 1773 | 0.2 | 2600 |
1823 | 0.18 | 2000 |
For conservation equations, the following assumptions were made: (1) the chemical reaction [
In addition, conservation of energy is written as
Under the conditions of large capacity of blast furnace equipped with multiple tapholes, interchanging tapping is done at time intervals for batch production of main trough. In the final discharging stage at first batch, the molten iron and slag cannot flow because the liquid levels are not over the iron dam and slag port, respectively, stagnating in the main trough. Figure
The initial level of molten slag and iron in main trough before tapping, as
To simulate that the tapping stream is injected into the main trough from the taphole of blast furnace hearth and solve (
The Eulerian model for a multiphase flow as implemented in the Fluent 6.2 [
Three-dimensional computational domain used in this study.
Computational grid: (a) internal area including upstream and downstream regions and (b) close to outlet at slag port and iron dam of main trough.
The resulting numerical solution was used to calculate the wall shear stress (
For the validation of computational grid, the wall shear stress profile in the
Effect of the computational grid on wall shear stress in the direction of fluid flow at the high of 0.4 m in the main trough.
Figure
It shows the effect of natural convection on the velocity vector in the cross section at buffer region of main trough.
The wall shear stress distribution in the vertical direction in the downstream of trough.
In addition, it was found that the loss rate of molten iron from slag port varying with the flow rate of tapping stream obtained by numerical results is similar to the experimental result, whose water and oil were used to simulate the melted iron and slag, respectively, from literature [
The lost ratio of iron and water from the slag port of trough varying with the velocities of molten slag/iron and oil/water obtained from (a) present study and (b) Kim et al. [
The discharge rates of the molten iron and slag would be significantly changed as the cast proceeds. This is mainly because the size of taphole was enlarged during tapping due to erosion of the refractory material. Figure
The path line of molten iron and slag in terms of the density in the tapping stream with the velocities of (a) 0.0225; (b) 0.0975; and (c) 0.1725 (m/s), respectively, near the slag port of trough.
The effect of main trough geometry on separation efficiency was studied by changing the high difference between iron dam and slag port and the depth of skimmer. The volume rate in main trough is considered for the geometry effect. In the main trough, the interface level of molten iron and slag was influenced by the flow velocity in each stream and the fluid dynamic balance between two phases of fluids, respectively. The molten iron lost from the slag port will be increased when the high difference between the slag port and iron dam is reduced, as shown in Figure
The molten iron lost in terms of the density phase at the slag port varying with the high difference of slag port to iron dam in the main trough of blast furnace: (a) 0.2 m; (b) 0.1 m; and (c) 0.05 m.
Separation efficiency of molten iron from slag phase varying with the height difference between iron dam and slag port.
In addition, as sketched in Figure
Cross section view of velocity vector field varying with the depth of skimmer to the trough bottom: (a) 0.1 m; (b) 0.2 m; and (c) 0.3 m, in the buffer region of main trough.
Separation efficiency of the molten iron from the slag as function of the depth of skimmer to the trough bottom of the blast furnace.
In this study, the full three-dimensional computational fluid dynamics composed from finite volume method and volume fraction equation in the present of natural thermal convection have been successfully developed to analyze the separation efficiency of molten iron and slag in the main trough of blast furnace. As resulting from the sensitivity analysis, particularly, it was evident that the lost rate of molten iron from the slag port is linearly increasing with increasing the velocity of tapping stream due to insufficient retention time of molten iron in the buffer region of main trough, and when the high difference between slag port and iron dam is less than 0.2 m, the separation efficiency of molten iron from slag could be more and more worse, resulting from elevating the liquid level of molten iron in the downstream of the trough. This suggests that the precise control of the high difference between iron dam and slag port is the priority of importance for maintaining the effectiveness of the slag and metal separation in the main trough of blast furnace during tapping process.
The cross area at the inlet [m2]
The cross area at slag port [m2]
The mean specific heat [Jkg−1 K−1]
The specific heat of individual fluid [Jkg−1 K−1]
An empirical constant specified in the turbulence model (0.09) [—]
The gravity acceleration [ms−2]
The turbulence kinetic energy for thermal buoyancy [kgm2s−2]
The turbulence kinetic energy due to velocity gradient [kgm2s−2]
The thicknesses of molten iron layers at the initial stage [m]
The distance from the skimmer bottom to the top of iron dam [m]
The thicknesses of molten slag at the initial stage [m]
Unit vector in the
Unit vector in the
The turbulent kinetic energy [kgm2s−2]
Unit vector in the
The distance from iron dam to the top of main trough [m]
The depth of slag port [m]
The depth of skimmer [m]
Mass flow rate of molten iron at the taphole [kgs−1]
Total mass flow rate of molten iron at the taphole [kgs−1]
Mass flow rate of molten iron at the slag port [kgs−1]
Total mass flow rate of molten iron at the iron and slag ports [kgs−1]
Normal vector [m]
Pressure [Pa]
Index of fluid phase [—]
Time [s]
Temperature [K]
Velocity in the
Velocity vector [ms−1]
Velocity of molten iron at the inlet [ms−1]
Velocity of molten slag at the inlet [ms−1]
Mean velocity fluctuation [ms−1]
Velocity in the
Velocity in the
Coordinates [m]
The criteria defined by equation (
Vector differential operator [m−1].
The fraction of volume [—]
Thermal expansion coefficient [K−1]
Heat conductivity of individual fluid [Wm−1 K−1]
Mean heat conductivity [Wm−1 K−1]
Separation efficiency [—]
The density of molten iron [kgm−3]
The mean density [kgm−3]
Density of individual fluid [kgm−3]
The effective viscosity [kgm−1s−1]
The mean viscosity [kgm−1s−1]
Viscosity of individual fluid [kgm−1s−1]
The turbulent viscosity [kgm−1s−1]
The wall shear stress [Pa].
Phase number indicating air, slag, and iron, respectively [—].
The authors declare that they have no competing interests.
The authors would like to express sincere appreciation to Ministry of Science Technology (MOST: 103-2221-E-005-089) and New Materials Research & Development Department, China Steel Corporation for funding of this study.