Evolution behavior of mineral structure and trace elements in feed coals from six coal-fired power plants in China

Chemical composition, surface morphology characteristics, and mineralogical characteristics of feed coals from six power plants were studied in this paper, as well as alteration behavior of mineral phase, functional groups, and trace elements during combustion. The apparent morphology of feed coals is different in compactness and order, while sharing a similar lamellar shape. Quartz, kaolinite, calcite, and illite are the main minerals in feed coals. There are obvious differences in the calorific value and temperature range in volatiles stages or coke combustion stages for feed coals. Peak positions for the main functional groups in feed coals are similar. After burning at 800 ℃, most organic functional groups in feed coals were lost in products, but the group of -CH₂ on the side chain skeleton of n-alkane and the aromatic hydrocarbon bond (Ar-H) still existed in the ash, and the vibration of Si-O-Si bond and Al-OH bond in inorganic functional groups was strengthened. During combustion, Pb and Cr in feed coals will be accumulated in the mineral residues, unburned carbon, and residual ferromanganese minerals, along with the loss of organic matter and sulfide or the decomposition of carbonate. Pb and Cr are more easily adsorbed by the fine-graded coal combustion products. Occasionally, the abnormal phenomenon occurred in a medium-graded ash but with the maximum adsorption of Pb and Cr, which is mainly caused by the collision and agglomeration of the combustion products, or the adsorption capacity of different mineral components. The effects of diameter, coal species and feed coal on the forms of Pb and Cr in combustion products were also analyzed in this study. The study has some guiding significance for understanding the behavior track and alteration mechanism of Pb and Cr during coal combustion.