DEM simulation and fractal analysis of particulate fouling on coal-fired utility boilers' heating surfaces

摘要

The microstructure features of particulate fouling on convective heating surfaces play a dominant role on the deposition process in coal-fired utility boilers. Starting with the analysis of the main fouling mechanism, a particulate collision deposition numerical model based on the discrete element method is proposed in this paper. Applying the present method, the numerical simulation of the process of particulate deposition on a tube and a rectangular plate was carried out. The results show that simulated deposition can exactly reflect the microstructure characteristics of real fouling on boilers' heating surfaces, such as porous structure and porosity. The fractal features of the inner porous microstructure and surface morphology of the simulated deposition was further studied in this study. The investigation results indicate that the characteristics of the particle-pore interface and the surface topography, which are heterogeneous and anisotropy, can be quantitatively characterized by the fractural dimensions (FD) of pore contour and surface profile, respectively. The results of FD estimation using a box-counting method show that with decreasing porosity, the FD of pore contour increases and the FD of surface profile decreases. Additionally, particulate diameter plays a role on the fractal features of particulate deposition.