In sewage sludge incineration plants, fly ash can adhere to the surfaces of both the incinerator and dust filter and then accumulate over time. Since this grown layer can potentially block the gas flow and damage the filter, thus preventing stable and long-term operation of incineration plants, fly ash adhesion must be monitored carefully and suppressed as much as possible. Herein, we used three different fly ash samples to demonstrate that the merger of experimental and theoretical approaches enabled a rational choice of additive that could suppress fly ash adhesion. The tensile strength of ash powder beds provided a benchmark for the adhesive properties, which were further studied by thermodynamic calculations. Experimental and theoretical results suggest that the use of alumina nanoparticles is a promising approach to suppress the adhesion of fly ash containing a relatively high concentration of phosphorus components.