Modeling of the wet flue gas desulfurization system to utilize low-grade limestone
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pISSN: 0256-1115 eISSN: 1975-7220
INVITED REVIEW PAPER
INVITED REVIEW PAPER
Modeling of the wet flue gas desulfurization system to utilize low-grade limestone Jonghun Lim*,**, Yeongryeol Choi*,**, Geonyeol Kim*,**, and Junghwan Kim**,† *Chemical and Biomolecular Engineering, Yonsei University, 50, Yonsei-ro, Seoul 03722, Korea **Green Materials and Processes R&D Group, Korea Institute of Industrial Technology, 55, Jonga-ro, Ulsan 44413, Korea (Received 25 August 2019 • Revised 15 January 2020 • Accepted 14 July 2020) AbstractWet 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, lowgrade 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, SOX 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. Keywords: Desulfurization, Limestone, Gypsum, Simulation, Flue Gas, Optimization
impurities, such as MgCO3, SiO2, Al2O3, and FeO3, which decreases the desulfurization efficiency and the quality of the final gypsum. Although the total reserves of limestone in the Republic of Korea amount to ~10,690 million tons, high-grade limestone reserves account for only 2,142 million tons, constituting 20% of the total. The use of low-grade limestone would, therefore, be desirable due to the ongoing depletion of high-grade limestone reserves. To date, a number of methods have been developed to improve the limestone quality through pretreatment. Kim et al. [9] developed a firing method to improve the quality of low-grade limestone. Following pulverization of the limestone to achieve a suitable particle size for the firing process, the limestone is purified to caustic lime (CaO) upon firing, and the remaining impurities are separated using crushing machines, such as hammer mill, ball mill, or jet mill. In addition, Ahn et al. [10] developed a technology for improving limestone quality based on the separation of magnetic impurities. In this process, the limestone initially undergoes a firing process, after which the magnetic impurities (FeO3) are removed by magnetic selection. Finally, SiO2 is removed using the differences in weight through an air distribution system. However, since the above-mentioned
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