In this paper, the flow of fly ash in fluidized dense phase pneumatic conveying through a section of pipeline having uniform pipe diameter has been modeled and analyzed using Computational Fluid Dynamics (CFD). Besides considering a single solid phase with the mean particle diameter, several solid phases based on the particle size distribution (PSD) have been incorporated in the developed CFD model. For the CFD simulation, particle size distribution with the Euler–Euler approach is adopted for analyzing the behavior of the flow of fly ash in the dense phase. The validity of the developed CFD model has been evaluated under different operating parameters of pneumatically fly ash flow in the horizontal pipeline. The results of the simulation demonstrated an excellent matching with experimental pressure drop data with an error margin of ±15%. Furthermore, variations of pressure drop, air velocity and void fraction along downstream of flow, and distributions of solid volume and void fractions spatial profiles have been presented and discussed. Then, the flow regimes have been investigated under the effects of conveying velocity, solids loading ratio and PSD. The numerical observation showed that the dense regime is mainly dominated by the behavior of large-sized particles while the fine particles control the dilute regime and there is intense contact between these two regimes through the intermediate regime. © 2020 Taylor & Francis Group, LLC.