Understanding the mechanism for the formation of initial deposition burning Zhundong coal: DFT calculation and experimental study

Zhundong coal as a high quality steam coal has not been widely utilized due to severe slagging and fouling problem during combustion. It is crucial to reveal the slagging and fouling mechanisms in a boiler burning Zhundong coal. In the article, the properties of Ca and Na particles adsorbed on iron oxide film were studied by quantum chemistry. Furthermore, two representative ash deposits at rear water wall and final superheater in a 330 MW utility boiler were also verified the calculation results. These results indicated that alpha-Fe2O3 (1 1 0) is selected as the adsorption substrate. The binding energies of Na or Ca on alpha-Fe2O3 (1 1 0) is - 12.44 eV and -13.73 eV, respectively. The charge transfer of Ca on alpha-Fe2O3 (1 1 0) is significantly higher than that of Na, and the orbital hybridization of Na on (1 1 0) surface can be weaker than that of Ca on (1 1 0) surface. Thus, Ca would combine with the oxide film more easily than Na. This indicates that compared with other coals with a high sodium, Ca burning Zhundong coal plays a critical role on severe ash deposition. In addition, the binding energy of Ca adsorbed on Fe or O defect surface for alpha-Fe2O3 (1 1 0) is -15.13 eV or - 4.16 eV, respectively. The amount of charge transfer for Ca adsorption on Fe defect surface may be significantly higher than that on O defect surface, and the orbital hybridization of Ca adsorption on Fe defect surface can be stronger than that on O defect surface. Therefore, Fe defect surface have a higher propensity to Ca. Finally, the result of experiments is in accordance with calculation results.