Abstract
In this study, an extraction method and environmental scanning electron microscopy (SEM) are employed to reveal the changes in the occurrence mode of fluorine in a coal-fired power plant in Inner Mongolia, China. The different occurrence states of fluorine during coal combustion and emission show that fluorine in coal mainly assumes insoluble inorganic mineral forms. The results illustrate that the three typical occurrence modes in coal are CaF2, MgF2 and AlF3. The fluorine in fly ash can be captured by an electrostatic precipitator (EPS) or a bag filter. In contrast, the gaseous fluorine content in flue gas is only in the range of several parts per million; thus, it cannot be used in this study. The occurrence mode of fluorine in bottom ash and slag is inorganic villiaumite (e.g., soluble NaF, KF and insoluble CaF2) which is difficult to break down even at high temperatures. The occurrence mode of fluorine with the highest content in fly ash is physically adsorbed fluorine along the direction of the flue gas flow. The insoluble inorganic mineral fluoride content in fly ash is also high, but the gradually increasing fluorine content in fly ash is mainly caused by physical adsorption. Fluorine in the coal-fired power plant discharges mostly as solid products; however, very little fluorine emitted into the environment as gas products (HF, SiF4) cannot be captured. The parameters used in this study may provide useful references in developing a monitoring and control system for fluorine in coal-fired power plants.
Highlights
In recent years, the toxic elements in coal have been research highlights in many countries, especially in China, the largest coal-consuming country in the world
Several types of samples, including pulverized coal, slag, flue gas desulfurization gypsum and Several types of parts samples, including pulverized coal,from slag, the flueShangdu gas desulfurization and fly fly ash, in different of the boiler were collected coal-fired gypsum power plant in ash, in different parts of the boiler were collected from the Shangdu coal-fired power plant in
Extraction rate means that the leaching amount accounted accounted for the proportion of the total content in the sample
Summary
The toxic elements in coal have been research highlights in many countries, especially in China, the largest coal-consuming country in the world. The fluorine in coal is a toxic trace element, with a general content of 100–300 ppm. The average fluorine concentration level in coal in China is 130 ppm [1], 48% higher than that in the rest of the world (the average level in the world is 88 ppm [2]). The reason China is higher than the rest of the world is that the amount in the sample determined by researchers in China is limited, or different determination method was used. The concentration of fluorine in coal is on a ppm level, the emission needs to be paid special attention as the coal consumption increases. A gas product of coal combustion: HF, poses the most harm to humans and animals
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