Abstract: From the perspective view of the practical engineering application, the control system called the single-tower and double-circulation wet flue gas desulfurization (SD-WFGD) system was established. Firstly, the dynamic model was developed by analyzing the impact of the unit frequency change of the absorption tower variable frequency slurry circulation pump on the flue gas SO₂ concentration at different slurry pH during the operation of the SD-WFGD system. Secondly, the direct sulfur balance control (DSC) strategy was proposed based on the desulfurization capacity of the slurry pH. The established dynamic model was then applied as a control model, and a serial control system for the SD-WFGD system was established by combining traditional PID controllers with the DSC strategy. Simulation test results demonstrated that, compared to traditional PID control schemes, the proposed optimized control scheme reduces fluctuations in slurry supply flow and outlet SO₂ concentration, significantly enhancing the control performance of the SD-WFGD system. This model can ensure the safe, stable, economical, and flexible operation of the desulfurization system in the context of flexible operation at coal-fired power stations.