Insight into fouling mechanisms on inclined tube banks in molten salt heat exchangers for coal-fired boiler

Coupling coal-fired boilers with molten salt thermal energy storage is a critical technical pathway for flexible peak shaving of thermal power units. As the core component, the flue gas-molten salt heat exchanger (MSHE) requires inclined tube bank arrangements to achieve gravity-driven molten salt drainage and anti-solidification, while the fouling characteristics and underlying flow mechanisms of inclined tube banks remain poorly understood. In this study, a numerical model is established for dust-laden flue gas flowing across an aligned inclined tube bank. The Eulerian-Lagrangian approach coupled with a dynamic deposition-removal model is adopted to investigate the regulatory effect of inclination angle on particle deposition behavior, as well as the influences of flow velocity and Stokes number. Results indicate that fouling mass decreases with rising flow velocity and Stokes number, due to enhanced near-wall shear and increased rebound and removal probability of high-inertia particles. The inclined configuration induces asymmetric oblique vortex shedding, leading to significant spanwise differences in particle impingement parameters and aggravated deposition non-uniformity compared with horizontal tube banks. The total fouling mass shows a non-monotonic first-increasing-then-decreasing trend with inclination angle, with the deposition peak at 3°-4°. For balanced flow and heat transfer performance and ash fouling mitigation, the MSHE tube bank design inclination angle is recommended to be controlled within 3° to avoid the peak fouling range, and 5° can be adopted under high dust-loading conditions. This study provides theoretical basis for anti-fouling optimization of inclined tube bank heat exchangers under dust-laden flue gas conditions.