Understanding the Competition Mechanism between Na 2 O and CaO for the Formation of the Initial Layer of Zhundong Coal Ash

The contents of alkali and alkaline earth metals are higher in Zhundong coal, and there are serious problems of slagging and fouling during the combustion process. Therefore, it is of great significance to reveal the mechanism of slagging and fouling in the boiler of Zhundong coal. In this paper, first-principle calculations based on density functional theory are used to study the competition mechanism of alkaline metal oxides during the combustion process in Zhundong coal by establishing the Na 2 O(110)/CaO(100)-SiO 2 (100) double-layer interface model. The results show that the bond lengths of the surface of Na 2 O(110) and CaO(100) with SiO 2 (100) after adsorption were generally lengthened and the value of bond population became smaller, which formed a stable binding energy during the reaction. The electron loss of Na is 0.05 e, the electron loss of Ca is 0.03 e, and the electron loss of Na 2 O is greater than that of CaO. The charge transfer on the surface of Na 2 O with SiO 2 is obviously higher than that of CaO and the orbital hybridization on the surface of CaO with SiO 2 is weaker than that on the surfaces of Na 2 O with SiO 2 . Na 2 O is easier to react with SiO 2 than CaO. The adsorption energies on the surface of Na 2 O and CaO with SiO 2 are −5.56 eV and −0.72 eV, respectively. The adsorption energy of Na 2 O is higher than that of CaO, indicating that Na 2 O is more prone to adsorption reactions and formation of Na-containing minerals and other minerals, resulting in more serious slagging. In addition, the XRD analyses at different temperatures showed that Na-containing compounds appeared before Ca-containing ones, and the reaction activity of Na 2 O is stronger than that of CaO in the reaction process. The experimental results have good agreement with the calculation results. This provides strong evidence to reveal the slagging and fouling of Zhundong coal.