When the particles are charged into and discharged from a Paul-Wurth type hopper at a bell-less top blast furnace, the accompanied size segregation phenomenon makes important effect on the burden and gas distribution inside a blast furnace, thereby contributing to the smooth operation of the furnace. Based on the discrete element method (DEM), a three dimensional model is established in the present work. The model is used to investigate the effects of various variables on particle size segregation in and out of the hopper, as well as on the discharging sequence. The studied variables include the mass fraction of small particles in the feed, the burden apex, and the slope of the lower part of the hopper. Results show that particle size distribution in the hopper is most affected by the burden apex. The slope of the lower part of the hopper influences the size distribution only during discharging from the hopper. The discharging sequence also changes at different hopper slopes. It is better to constrain the mass fraction of small particles in the feed to less than 30% in order to obtain a stable particle size distribution in the blast furnace. Additionally, the hopper outlet should be designed close to the centerline of the blast furnace to reduce the particle size segregation. (C) 2013 Elsevier Ltd. All rights reserved.