# Effect of Furnace Structure on Burden Distribution and Gas Flow in Sinter Vertical Cooling Furnace
## 4 Results and Discussion
### Voidage Distribution of Sinter Layer  
Voidage is the volume of voids in a sinter bed per unit volume, and the size and distribution of this value have a significant effect on the distribution of the cooling gas in a furnace. Figure 5a shows the voidage distribution of the existing furnace type and Venturi furnace type when the distribution of sinter was stable. When the Venturi furnace was adopted, in the vertical section, the voidage distribution in the burden had little change compared with the existing furnace. However, in the variable-diameter section, the range of blue and cyan representing low voidage in the contraction part was significantly reduced, while the range of green representing medium voidage was significantly increased, indicating that the Venturi furnace type could improve the voidage in this area. This was due to the different properties of bulk material and gas. When passing through the flow channel with shrinking width, the gas velocity increased as a whole, while the bulk material generated stress inside the material, causing some of the bulk material velocity to increase and some of the bulk material velocity to decrease, resulting in a relative velocity difference within the bulk material. When sinter particles went through the contraction part, the downward movement velocity of the lower sinter particles was larger, while that of the upper sinter particles was smaller, which cannot supplement the voids caused by the downward movement of the lower sinter particles in time, resulting in an increase in the voidage of the burden in this area. Further observation showed that the voidage of the burden decreased in both the vertical part and the expansion part of the variable-diameter section. This was because the expansion part reduced the downward movement velocity of the sinter particles, causing the high-speed particles in the upper layer to squeeze the particles below, thus reducing the voidage in the vertical part and the expansion part. When entering the original vent cowl section and cone section, the voidage of the burden would fluctuate in the same way.  
To quantitatively describe the above changes in the voidage of the burden, the distribution of the voidage at the centerline V1 of the middle area where the burden is most closely stacked is drawn, as illustrated in Figure 5b. Zone 1 corresponds to the (original) vent cowl sections of the two furnace types. In this area, the voidage first decreased and then increased. For zone 2, the voidage at V1 of the existing furnace directly decreased from about 0.36 to about 0.28, while the voidage of the Venturi furnace increased from 0.34 to 0.35 after a slight decrease. For zone 3, the voidage of the existing furnace increased, but this increase was only maintained at about 0.315. The voidage of the Venturi furnace decreased slightly to 0.33, recovered to 0.35, and then began to decline to about 0.31. It can be seen that compared with the existing furnace type, the distribution of voidage in the burden of the Venturi furnace type changed from U-shaped to W-shaped, and the fluctuation along the longitudinal direction was smaller, reducing from 0.28-0.39 to 0.298-0.37. The voidage in the middle area was always maintained at a high level, which was conducive to more cooling gas entering the middle area, thereby reducing the influence of the high-voidage channel in the sidewall and center area.