*2.1. Spray Drying Tower Description*

The schematic diagram of a spray drying tower without deflectors is shown in Figure 2. The height is 17.9 m, and the diameter is 7.2 m. The flue gas is injected into the spray drying tower through a specially-designed volute structure. In the atomization process, the desulfurization wastewater is firstly sent to the atomizer by the metering pump. The motor drives the atomizing disc to rotate at high speed, and the desulfurization wastewater is thrown out from the channels, thus atomizing into droplets. The droplets are then evaporated under the preheating effect of the flue gas. In this study, the complete evaporation distance (as shown in Figure 2) is defined as the maximum distance from the atomizer in the vertical direction when the droplet particle mass is zero. Table 1 lists the physical parameters of flue gas under full load.

**Figure 2.** Schematic diagram of spray drying tower without deflectors.

