Size segregation of pellets in the top bunker (hopper) of a blast furnace is an important factor affecting the radial distribution of the charged burden and indirectly also the distribution of gas in the shaft and cohesive zone. This paper studies size segregation of ternary size pellets during the discharging process of a hopper model through experiments and simulations. The simulations, which are based on the discrete element method (DEM), are first validated using four experimental cases applying different bunker filling methods. The effects of various variables, such as fine mass fraction, particle friction coefficients, diameter ratio of fine to coarse and filling method (random, layered or industrial filling), as well as the interaction with wall (static and rolling friction) on the segregation are investigated. The results show that even though many factors affect the extent of segregation during the discharging process, the most important factors are the filling method, diameter ratio of fine to coarse, wall-particle static and rolling friction, interparticle rolling friction as well as mass fraction of fine particles. Reducing wall-particle rolling or static friction or the fraction of fine particles decreased the extent of size segregation.