*3.2. E*ff*ect of the Velocity of the Blowing Gas on the Cavity Size of the Raceway*

According to the previous analysis, the shape and boundary of the raceway zone are generally stable from the time when the depth reaches the maximum and the time when the air mass begins to drift away from the raceway zone. On this basis, the effects of the different gas kinetic energies of blasting (i.e., airflow velocity) on the shape and size of the raceway zone are considered. Figure 6 shows the volume fraction diagram of the gas phase when the injection angle is four degrees and the gas velocities are 150 m/s, 200 m/s, 250 m/s, and 300 m/s, respectively.

**Figure 6.** Gas phase volume fraction fractions at different blowing velocities.

Combined with the velocity cloud map and the gas phase volume fraction map, it can be seen that the greater the gas injection speed, the deeper the depth of the raceway, and the larger the cavity volume when it is stabilized, which can also be seen from its depth and height. Figure 7 shows the depth variation of the raceway under different gas velocity conditions.

**Figure 7.** Variation of raceway depth with time at different blowing velocities.

Under different gas velocities, the penetration depth is different. With an increase in gas velocity, the depth of the coke layer, through which the gas flows, increases. As can be seen from Figure 7, the cavity depth changes in the four blowing situations are basically the same—that is, both increase from the beginning and finally stabilize. The variation of the depth of the raceway also directly reflects the variation of the volume of the cavity in the raceway. When the raceway zone is stable at 150 m/s, the depth is about 500 mm, at 200 m/s, the depth is about 800 mm, at 250 m/s, the depth is about 950 mm, and at 300 m/s, the depth is about 1200 mm.

The depth and height values of the raceway zone in the stable period at each blowing speed are plotted, as shown in Figure 8. This makes it easier to visually observe how the two change with the injection speed. The main reason for this trend is that the velocity of the blowing gas increases—that is, the kinetic energy of the blast increases, the amount of gas injected per unit time increases, the gas pressure in the cavity increases, and the ability to compress the coke particles also increases. When the gas pressure and the coke layer resistance are balanced, the cavity volume is also large.

**Figure 8.** Variations of raceway depth and height with blowing velocity.

#### **4. Conclusions**

The formation process of the tuyere of the COREX melter–gasifier was simulated by Euler gas–solid two-phase flow theory. The shape and size of the relatively stable period of the raceway were obtained. The influence of the jet velocity on the depth and height of the raceway is analyzed. The main results are as follows.

(1) As the gas continues to inject, the cavity first grows deep into the furnace. After reaching a certain depth, the cavity begins to develop upwards, and the cavity volume increases. The time taken from the start of the gas to the formation of the stable raceway shape is short, and then the depth and height of the raceway and the volume of the cavity are stable for a long period of time.


**Author Contributions:** Conceptualization, Y.S. and R.C.; methodology, Y.S. and Z.Z.; software, G.W. and Y.S.; formal analysis, H.Z. and Y.L.; investigation, X.L. and Y.H.; writing, Y.S. and R.C.; supervision, G.W. and L.L.; funding acquisition, Y.S. and R.C.

**Funding:** This research was funded by the Natural Science Foundation of Liaoning Province (No.20170540476), Liaoning Province Doctor Startup Fund (No.20170520079). Also, special thanks to the project, which is sponsored by the 'Liaoning BaiQianWan Talents Program'.

**Conflicts of Interest:** The authors declare no conflict of interest.
