Mitigation mechanisms of ash deposition and adhesion by different coatings on heated surfaces at macro and molecular scales

Research on the mitigation of ash deposition on coals rich in alkali and alkaline earth metals using coatings is limited. Existing research methods, mainly focusing on ash composition and melting characteristics, cannot fully elucidate the key mechanisms underlying ash adhesion properties on various coated surfaces. Therefore, this study explored the mitigation mechanisms of nickel and chromium coatings on ash deposition using a drop tube furnace, custom-made ash adhesion strength tester, and molecular dynamics. The results revealed that nickel and chromium coatings effectively mitigated ash deposition, with a more significant effect at temperature less than 1000 °C. Above 1000 °C, the ash melting led to a significant increase in ash adhesion strength, diminishing the inhibitory effect of coatings. The key minerals, Na2SO4, Ca2MgSi2O7, and Ca2Al2SiO7, mainly physically adsorbed onto the NiO(001) and Cr2O3(001) surfaces. The binding energy of these minerals with NiO(001) and Cr2O3(001) was significantly lower than that on α-Fe2O3(110) surfaces. The α-Fe2O3(110) system was more stable, and minerals readily adhered to the α-Fe2O3(110) surface, whereas none of these minerals readily bound to NiO(001) and Cr2O3(001), maintaining their adhesion state. Consequently, nickel and chromium coatings demonstrated excellent resistance to ash adhesion and deposition, with nickel coatings being more effective.