Lyophobicity and slagging resistance mechanism of h-BN based coating for coal-fired boilers

Abstract

Sodium reacts with sulfur oxide to form molten Na2SO4 during combustion of high-sodium coal (HSC). The resulting sticky inner layer captures ash to form slag, which inhibits heat transfer and flow of combustion gases. A novel water-based ceramic coating with hexagonal boron nitride (h-BN) as the main component has been recently developed to address the slagging problem in boilers that burn HSC. In the present study, wettability tests were performed to show that, compared with uncoated steel, the coating was completely lyophobic to molten Na2SO4. Density functional theory was used to study the adsorption of Na2SO4 on coated and uncoated steel at the atomic level. The calculated adsorption energies, electronic density of states, and Bader charges of Na atoms adsorbed on h-BN(0001) and Fe2O3(110), representing the coating and steel, respectively, indicated that the interaction of Na atoms with h-BN(0001) is significantly weaker than that with Fe2O3(110). Therefore, the ceramic coating could effectively inhibit the formation of the sticky inner layer composed mainly of Na2SO4 and alleviate the slagging of HSC-fired boilers.