Understanding the interaction mechanism of iron and calcium during Zhundong high-iron coal combustion by the experimental study and molecular dynamics simulation

In order to obtain widespread applications for Zhundong high-iron coal, the interaction characteristics of calcium and iron during the Zhundong high-iron coal combustion were investigated experimentally in one-dimensional furnace and further explored via molecular dynamics (MD) simulation. The properties of raw coal and formed ash deposition were analyzed by XPS, ICP-OES, XRD and SEM-EDX, and MD simulations were mainly employed to dig the microstructural characteristics and viscosities of the slag systems. The results indicated that the main forms of iron in Zhundong high-iron raw coal are sulfide iron, carbonate iron and silicate iron, which account for about 46.6%, 34.5% and 18.9%, respectively. The spherical and irregular lumpy deposited samples will bond with the increase of the temperature, signifying that more iron-containing minerals in the flue gas begin to melt and react with other minerals to form a low-temperature eutectic. The hollow ash spheres are produced during the combustion process, due to the decomposition of anhydrite under higher temperatures. Meanwhile, the interaction of Fe, Ca, Al, and Si for forming a low-temperature eutectic can result in the enhanced smoothness of ash deposited surface. The MD simulations results indicated that the reaction between iron and calcium is one chemical interaction, and the appearance of multiple peaks verifies the occurrence of the slag melting phenomenon. In addition, the viscosity of Zhundong high-iron coal is relatively lower, and decreases with the increase of the temperature. The slag body burning Zhundong high-iron coal can exhibit a good fluidity, aggravating ash deposition issues.