*3.5. Influence of Tap hole Angles on the Flow of the Main Trough*

Intermittent tapping of a blast furnace must be punched before the tapping and be plugged after the tapping. The angle of the tap hole can change during tapping. Therefore, it is important to understand the influence of the angle of the tap hole to the temperature, velocity and shear stress of the mixture flow in the main trough. Since velocity and temperature distributions are quite similar in Figures 5–11, they are not analyzed any more.

**Figure 10.** Temperature fluctuations of four lines during tapping ((**a**) line 3, (**b**) line 4, (**c**) line 5 and (**d**) line 6, cf. Figure 3b).

**Figure 11.** Temperature distributions from the central plane to plane 3 (cf. Figure 3a).

Generally speaking, the angle of the tap hole changes between 7 to 12◦. Therefore, two values in the interval were selected to highlight the effect of the angle. As shown in Figure 12, with the increase of the tap hole angle, the wall shear stress increases from 0.73 to 0.87 because molten slag and hot metal gets a higher velocity when they fall into the main trough from a bigger angle of the tap hole. The little increase of wall shear stress happens at 15 m due to the fact that the fluid velocity becomes bigger at the skimmer. When the tap hole angle is 7◦, mechanical erosion of the trough has the smallest value. The maximum of wall shear stress is reduced by 16% and the campaign of the main trough is estimated to expand over 5 days, comparing with the tap hole angle of 10◦ and 7◦.

**Figure 12.** Wall shear stress distribution at different angles of the tap hole on line 2 (cf. Figure 3b).

Figure 13 shows temperature changes of line 3 during tapping with different tap hole angles, (a) 7◦, (b) 10◦ and (c) 12◦. With the increase of the angle of the tap hole, change of temperature during tapping is little. But as the location of FPMFT moves toward the direction of the tap hole, the maximum temperature of it increases. During tapping, reasonable adjustment of the tap hole angle can reduce the extent of mechanical erosion in some areas, which is helpful to expand the sieve campaign of the main trough.

**Figure 13.** Temperature fluctuations on line 3 (cf. Figure 3b) during tapping with different tap hole angles, (**a**) 7◦, (**b**) 10◦ and (**c**) 12◦.
