Evaluation of Limestone Impurities in the Desulfurization Process of Coal Combustion Gas

Abstract

-Limestones have been used to capture SO2 emitted during the combustion of coal for decades. However, due to the complexities of the variables involved in this process, many issues are still being studied. Some tests were performed in a fluidized bed reactor, which was used to evaluate the performance of the limestones in the bed for flue gas desulfurization, burning low sulfur coal. Metamorphic dolomitic limestones of low cost were evaluated considering the impurity level and need for beneficiation. They were characterized chemically, physically and microstructurally (X-ray fluorescence, X-ray diffraction, laser particle size analyzer, scanning electronic microscope). The data obtained were compared to a calcitic limestone of elevated purity and higher market value. The results showed little effect of the major impurities present in the dolomitic limestones in the calcination and desulfurization processes. Microcrystalline impurities showed a marked effect promoting grain sintering in calcination conditions of TGA/DTA tests in different atmospheres, as shown in SEM images. Dolomitic limestones generate more solid waste and capture less SO2 per kcal (a slightly decrease in the thermal efficiency of the reactor) compared to calcitic limestones. However, due to the lower cost, they were considered to be attractive for the FBC process (2 mg SO2/kcal at Ca/S=3).

Studies on the industrial applications of limestone samples from three geographical regions in Nigeria: Ashaka, Mfamosing, and Nkalagu

“…To be suitable for flue gas desulfurization, limestone must have a CaO content of at least 53%, a CaCO3 content of 95%, less than 3% SiO2, less than 1.5% Al2O3, less than 3% FeO3, and a maximum of 2% MgO (ASTM C911-19, Harrison, 2012;De-Souza and Braganca, 2017) (see Table 4 for details). Limestone samples AS2, MF2, and NK2 (refer to Tables 2 and 3) met these requirements.…”

“…It is a sedimentary rock that is primarily composed of calcium and magnesium (Ayuba et al 2015) and is mostly made up of calcium carbonate (CaCO3) in crystal forms of calcite and aragonite (Azubuike et al 2011;Popoola, 2015). Due to its versatility, limestone has a wide range of industrial applications, including construction, agriculture, and chemical production, which have led to a significant increase in its demand in recent years (De-Souza et al 2017;Siler et al 2018). Limestone's color can vary from white to gray or dark hues, with white deposits indicating high purity, and different shades of gray and dark hues indicating the presence of carbonaceous materials and iron sulfide (Oats, 2011).…”

“…Once this has been established, the mining process can begin, which typically involves drilling, blasting, and crushing the limestone to produce various sizes of limestone aggregates that can be used for different purposes. Limestone is commonly used as a construction material, especially in the form of crushed aggregates, which are used for the production of concrete, asphalt, and road base materials (De-Souza et al 2017). Additionally, it is used in the agricultural industry as a soil conditioner to improve soil quality and crop yields (Siler et al 2018).…”

“…Additionally, it is used in the agricultural industry as a soil conditioner to improve soil quality and crop yields (Siler et al 2018). Limestone is also used in the chemical industry as a raw material for the production of various chemicals, including calcium chloride, calcium hydroxide, and calcium carbonate (De-Souza et al 2017). Furthermore, limestone is a versatile mineral that has numerous industrial applications due to its abundance and chemical properties.…”

Macrokinetic investigations of dry flue-gas desulfurization process using TGA technique

“…The rate of this second step is the important factor in all the pollution-control processes. Depending on the reactor temperature, reaction mechanisms of direct (CaCO3) or indirect (CaO) sulfation of the limestone may occur [11]. It has been demonstrated that indirect sulfation reached the highest efficiency of desulfurization [12,13].…”