Abstract: Systematic design methodologies remain underdeveloped for flue gas desulfurization (FGD) wastewater rotary spray drying systems. Based on traditional methodologies including graphical integration and dryer intensity methods, empirical parameters were determined through single-droplet experiments, rotary atomization tests and operational datasets. The critical particle size and evaporation duration of wastewater droplets during preheating, constant-rate evaporation and falling-rate evaporation were calculated in stages. The impact of wastewater treatment capacity variations on tower dimensions were evaluated by the analytic method. Computational results of tower diameter and height for conventional and concentrated wastewater were compared with actual engineering data. Finally, numerical simulation was conducted on the designed tower structure. Results show that the gas-liquid flow patterns and phase distribution characteristics of the tower structure obtained by the proposed method meet engineering requirements, with actual tower diameters allowing optimization-driven reductions based on computational results.