5. Dripping zone and hearth

Due to the lack of appropriate experimental data for the melting of iron-bearing material by a hot gas in a real condition occurring in a CZ, the melting of a packed bed of ice particles in a solid– liquid system is selected. The simulation setup is shown in Figure 7. Figure 8 compares the predicted results with experimental data [51] of the mass loss history for a packed bed exposed to an water mass flow of a velocity of 0.1 m/s. The comparison shows that the predicted mass

Figure 6. The effect of Young's modulus on structural rearrangement of the packed bed of pellets.

134 Iron Ores and Iron Oxide Materials

Figure 7. Schematic representation of the packed bed of particles used in the simulation [50].

Figure 8. Comparison between experiments and predictions of the mass loss history of a melting packed bed.

The liquid iron and slag produced in the cohesive zone trickle down through the packed bed of coke particles towards the hearth in a zone known as the dripping zone. It is located deep inside the blast furnace where measurements are not easy to perform. It highly affects the production rate, the quality of hot metal and process efficiency [53]. In this region, the two liquid phases descend slowly and hot gas introduced through the tuyeres ascends upwards

while exchanging heat and mass with the particles. The presence of solid particles besides the fluid phases makes the coupled discrete-continuous methods suitable for this application. In our previous study [54], the XDEM approach has been validated by comparing the numerical results with the experimental data [55] for a case representing the dripping zone. The experimental setup and the simulation domain are shown in Figure 10. A liquid distributor is located on the upper part, which is indicated as a mass source for some cells in the simulation domain in order to produce the same amount of liquid as the experimental study. The gas phase is introduced through a nozzle in the experimental study, which is specified as fixed uniform inlet velocity boundary condition in the modelling, while no slip boundary condition was used for the walls and the total pressure for the outlet boundary condition. Results obtained under these conditions are shown in Figure 11. The total absolute mean error of 3.27% was achieved, which shows the robustness of the XDEM for modelling of such cases. This model has also been applied to the trickle bed reactors [56].

In this regard, the model is applied to the lower part of the blast furnace including both dripping zone and hearth shown in Figure 12. The domain is randomly filled with non-uniform particle sizes of dp¼1�0:1 cm since the coke particles do not have the same sizes in this particular part. The molten iron and slag produced in the cohesive zone have completely different properties, thus showing different flow behaviours. Most of the previous studies considered only one liquid phase with either slag properties or iron, whereas in this study, both liquid phases are considered, and their mutual effects are studied. Therefore, the simultaneous downward flow of molten iron and slag through a packed bed of coke particles with the upward flow of gas phase is investigated. Despite the existence of several forces, drag force is the only force considered between each pair of phases. In this figure, the calculated porosity field is also illustrated. A predefined cavity is considered right in front of the gas inlet in order to avoid numerical instabilities as shown in Figure 12.

The liquid saturation, which is defined as the volume of the fluid per volume of the void space for both liquid iron and slag, is illustrated in Figure 13 over time. An incline mass source representing

Figure 11. The XDEM results (unfilled) versus the experimental data (filled) for constant liquid mass flow rate of 650 cm<sup>3</sup>=min

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where the gas flow rates are (a) 0:08 m<sup>3</sup>=min, (b) 0:14 m<sup>3</sup>=min, (c) 0:28 m<sup>3</sup>=min and (d) 0:34 m<sup>3</sup>=min [54].

Figure 12. The simulation domain and the porosity distribution.

Figure 10. Experimental set-up [53] (a) and simulation domain (b).

Figure 11. The XDEM results (unfilled) versus the experimental data (filled) for constant liquid mass flow rate of 650 cm<sup>3</sup>=min where the gas flow rates are (a) 0:08 m<sup>3</sup>=min, (b) 0:14 m<sup>3</sup>=min, (c) 0:28 m<sup>3</sup>=min and (d) 0:34 m<sup>3</sup>=min [54].

Figure 12. The simulation domain and the porosity distribution.

while exchanging heat and mass with the particles. The presence of solid particles besides the fluid phases makes the coupled discrete-continuous methods suitable for this application. In our previous study [54], the XDEM approach has been validated by comparing the numerical results with the experimental data [55] for a case representing the dripping zone. The experimental setup and the simulation domain are shown in Figure 10. A liquid distributor is located on the upper part, which is indicated as a mass source for some cells in the simulation domain in order to produce the same amount of liquid as the experimental study. The gas phase is introduced through a nozzle in the experimental study, which is specified as fixed uniform inlet velocity boundary condition in the modelling, while no slip boundary condition was used for the walls and the total pressure for the outlet boundary condition. Results obtained under these conditions are shown in Figure 11. The total absolute mean error of 3.27% was achieved, which shows the robustness of the XDEM for modelling of such cases. This model has also

In this regard, the model is applied to the lower part of the blast furnace including both dripping zone and hearth shown in Figure 12. The domain is randomly filled with non-uniform particle sizes of dp¼1�0:1 cm since the coke particles do not have the same sizes in this particular part. The molten iron and slag produced in the cohesive zone have completely different properties, thus showing different flow behaviours. Most of the previous studies considered only one liquid phase with either slag properties or iron, whereas in this study, both liquid phases are considered, and their mutual effects are studied. Therefore, the simultaneous downward flow of molten iron and slag through a packed bed of coke particles with the upward flow of gas phase is investigated. Despite the existence of several forces, drag force is the only force considered between each pair of phases. In this figure, the calculated porosity field is also illustrated. A predefined cavity is considered right in front of the gas inlet in order to avoid numerical instabilities as shown in Figure 12.

The liquid saturation, which is defined as the volume of the fluid per volume of the void space for both liquid iron and slag, is illustrated in Figure 13 over time. An incline mass source representing

been applied to the trickle bed reactors [56].

136 Iron Ores and Iron Oxide Materials

Figure 10. Experimental set-up [53] (a) and simulation domain (b).

the cohesive zone was specified to investigate its effect on the movement of liquid phases as well as the gas phase. The figures on the left are showing slag saturations and on the right the molten iron saturations. Higher saturations are calculated for the slag, which is due to the higher viscosity and lower density. The slag properties create higher resistance due to the solid particles and in consequence higher saturations. Therefore, the liquid iron flows with higher velocities and lower hold ups through the packed bed. The velocity difference of the two liquid phases causes a slip velocity, which accelerates the slag movement and decelerates the iron downward flow.

Within this concept, the stratification of liquid iron and slag can also be studied. The liquidliquid interface affects the mass and heat transfer rates between liquid iron and slag and thus, determines the final product quality. The molten iron with higher density is settling at the bottom where the slag floats on the top of it.

The effect of the gas phase due to the drag force on the deviation of the liquid phases from the raceway zone, which leads to the formation of the dry zone, is shown in Figure 14. The gas phase tends to replace the liquid phase at the entrance of the gas phase. This behaviour creates a dry zone, whose size is proportional to the gas inlet magnitude [54]. It can also be concluded that the liquid iron is pushed more towards the centre than the slag phase due to the larger drag force between liquid iron and gas phase. Although constant properties are considered for all phases, it should be noted that the fluid properties are not constant while moving through the blast furnace. They are mainly function of temperature, pressure and composition.

The gas phase stream lines for gas inlet velocity of 30 m=s are illustrated in Figure 15. The gas velocity loses its energy dramatically as it touches the particles. The recirculation of the gas phase in the raceway besides the redirection of the stream lines in the cohesive zone is

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observed.

Figure 14. Formation on the dry zone.

Figure 15. The gas phase streamlines.

Figure 13. The slag (left) and the molten iron saturation (right) at different time instances.

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the cohesive zone was specified to investigate its effect on the movement of liquid phases as well as the gas phase. The figures on the left are showing slag saturations and on the right the molten iron saturations. Higher saturations are calculated for the slag, which is due to the higher viscosity and lower density. The slag properties create higher resistance due to the solid particles and in consequence higher saturations. Therefore, the liquid iron flows with higher velocities and lower hold ups through the packed bed. The velocity difference of the two liquid phases causes a slip

Within this concept, the stratification of liquid iron and slag can also be studied. The liquidliquid interface affects the mass and heat transfer rates between liquid iron and slag and thus, determines the final product quality. The molten iron with higher density is settling at the

The effect of the gas phase due to the drag force on the deviation of the liquid phases from the raceway zone, which leads to the formation of the dry zone, is shown in Figure 14. The gas phase tends to replace the liquid phase at the entrance of the gas phase. This behaviour creates a dry zone, whose size is proportional to the gas inlet magnitude [54]. It can also be concluded that the liquid iron is pushed more towards the centre than the slag phase due to the larger drag force between liquid iron and gas phase. Although constant properties are considered for all phases, it should be noted that the fluid properties are not constant while moving through

the blast furnace. They are mainly function of temperature, pressure and composition.

Figure 13. The slag (left) and the molten iron saturation (right) at different time instances.

velocity, which accelerates the slag movement and decelerates the iron downward flow.

bottom where the slag floats on the top of it.

138 Iron Ores and Iron Oxide Materials

The gas phase stream lines for gas inlet velocity of 30 m=s are illustrated in Figure 15. The gas velocity loses its energy dramatically as it touches the particles. The recirculation of the gas phase in the raceway besides the redirection of the stream lines in the cohesive zone is observed.

Figure 15. The gas phase streamlines.
