Understanding the mechanism for initial deposition under the coupling effect of sodium and calcium during boiler operation: The first-principles study and thermodynamic analysis

During the boiler operation, ash deposition can result in a decrease in boiler efficiency and an enhanced release of pollutants. To relieve these issues, the formation mechanism for initial deposition triggered by the coupling effect of sodium and calcium was investigated by the first-principles study in this paper. The results indicated that the binding of sodium and calcium deposited on Fe₃O₄(0 0 1) surface is non-covalent interaction. Furthermore, |V|/G values of different particles on the surface are less than 2 and closed to 1. So the reactions of sodium and calcium deposited on the Fe₃O₄(0 0 1) are mainly closed-shell interactions accompanied by partial covalent interaction by Atom-in-Molecule theory. Additionally, the position and form of weak interaction also be further clarified by the independent gradient model. The thermodynamic calculation results showed that Gibbs free energy change is more affected to the change of the temperature under the existence of sodium and calcium. The reaction equilibrium constants is larger than 1, indicating that sodium and calcium are easily combined with Fe₃O₄(0 0 1). Moreover, calcium is more likely to promote a positive reaction than sodium.