*3.1. Effect of Flue Gas Flow Rate on the Evaporation Performance*

Figure 4 shows the turbulence kinetic energy under different flue gas flow rates. By increasing the flue gas flow rate, the turbulence kinetic energy in the mixing zone of the flue gas and the droplets gradually increases, which indicates more vigorous mixing between the flue gas and the droplets. Figure 5 displays temperature under different flue gas flow rates. A larger flue flow rate corresponds to more heat, which is advantageous to droplet evaporation.

**Figure 4.** Turbulence kinetic energy under different flue gas flow rates (m2/s2).

**Figure 5.** Temperature under different flue gas flow rates (K).

Figure 6 shows the effect of flue gas flow rate on the evaporation performance of the droplets in the spray drying tower. It can be seen that as increasing the flue gas flow rate from 7.792 (case-3) to 11.131 kg/s (case-1), the droplet evaporation time in the spray drying tower significantly decreases, and the distance of complete evaporation greatly decreases from 6.8 to 4.8 m. This can be explained by considering that the increase of the flue gas flow rate introduces more heat into the drying tower, which enhances the droplets evaporation performance. By further increasing the flue gas flow rate from 11.131 to 14.470 kg/s, the droplet evaporation time changes slightly, and the distance of complete evaporation only decreases from 4.8 to 4.7 m. Therefore, higher flue gas flow rate corresponds to shorter droplet evaporation time and shorter complete evaporation distance. Still, if the flue gas flow rate exceeds a certain level, the improvement of the droplet evaporation performance is not apparent. In actual operation, taking the evaporation performance and the safety of boiler operation into consideration, an appropriate amount of flue gas flow should be chosen.
