In this study, heterogeneous combustion of dust clouds containing polydisperse porous iron particles was numerically investigated. The main aim was to develop a discrete three-dimensional model to quantify the effects of particle size, porosity, cloud concentration, and polydispersity on flame propagation speed. The developed numerical model was validated against experimental data to show its promising accuracy. The modeling results show that increasing the cloud concentration increases flame propagation speed significantly, regardless of the particle size distribution, by about 3 times. Increasing the particle porosity can increase flame propagation remarkably, i.e., for particle sizes in the range of 1−3, 1−10, and 1−30 um, flame propagation speed was elevated by up to 24.2%, 36.7%, and 22.6%, respectively, when particle porosity increases from 0 to 0.1. However, increasing the particle size itself was found to decrease flame propagation speed as larger particles tend to be more difficult to ignite. For example, when the particle size distribution changes from 1−3 to 1−30 um, flame propagation speed decreases by a factor of 3.6. These findings serve to improve our understanding of heterogeneous combustion of dust clouds containing polydisperse porous iron particles.