Optimization of wet flue gas desulfurization system using recycled waste oyster shell as high-grade limestone substitutes

Wet flue gas desulfurization, which is performed in many thermal power plants, has a high desulfurization efficiency and produces desulfurized gypsum as a by-product. Currently, high-grade limestone with a CaCO₃ content of 94 wt% or more is used to produce desulfurized gypsum with a purity of 93 wt% or more. However, high-grade limestone resources are depleting, so new substitutes to this are required. The objective of this work is to optimize the wet flue gas desulfurization system using recycled waste oyster shells as high-grade limestone substitutes. The process model was developed for predicting the optimal blending ratio of waste oyster shells to limestone with constraints of desulfurization efficiency and purity of desulfurized gypsum. A mathematical model was addressed for optimized process costs, which was a nonlinear programming problem that minimizes the total annualized cost (TAC) by considering the total product cost (TPC) and equivalent annual cost; these vary according to the blending ratio. The optimal blending ratio of waste oyster shells is 16.160 wt% or 599.536 kg/h, TPC and TAC are reduced by $ 840,721 and $ 760,543, respectively. The waste oyster shell can be utilized 4,901 t/y, which is about 20.66 wt% of the total landfilled waste oyster shell. The results of this study suggest waste oyster shells, which pose landfill and odor problems, can be used as excellent substitutes for high-grade limestone for high economic and environmental benefits.