Modeling of the wet flue gas desulfurization system to utilize low-grade limestone

Wet flue gas desulfurization was simulated to improve gypsum production using low-grade limestone. High-grade limestone with 94 wt% CaCO₃ content is used for producing gypsum with 93 wt% purity, but owing to the resource depletion of high-grade limestone, low-grade limestone should be replaced as an alternative. However, low-grade limestone with CaCO₃ purity of less than 94% contains impurities such as MgCO₃, Al₂O₃, and SiO₂, which reduce gypsum purity. To resolve this issue, a process involving mixing of both low-grade and high-grade limestone was simulated to predict the quantity of low-grade limestone that could be utilized. Many reactions like limestone dissolution, SO_X absorption, and crystallization were considered and were simulated by different models in Aspen plus. For process optimization, the following constraints were set: 93 wt% gypsum purity, 94% desulfurization efficiency, and 3,710 kg/h total limestone usage, which maximized the mass flow of low-grade limestone. The maximum blending quantity of low-grade limestone for 2,100 kg high-grade limestone that satisfied the constraints was ∼1,610 kg.