In ironmaking blast furnace processes, the gas and fines pass a solid particle packed bed during the course of a reduction reaction. It is reported that unreacted fines deposit in the packed bed, causing a local ventilation resistance, which in turn decreases the process efficiency. A three-dimensional simulation combining the discrete element method and computational fluid dynamics (DEM-CFD) was performed to understand the individual behavior of fines in this process. State of the art DEM-CFD simulations were carried out and more than 1.4 million fines were tracked in this study. The searching cells were optimized to increase the calculation speed. A deposition simulation of the gas and fines was performed using this method in a cylindrical packed bed. The fines configuration and the packed bed structure were evaluated for studying the clogging phenomenon. The packed particle to fines diameter ration is given by 7.38 <= D-p/d(p) <= 11.34. At sufficient low diameter ratio (such as D-p/d(p)=7.38), stagnant fines cause cluster formation, and they concentrate at the bottom of the packed bed. Our results show that clogging by the fines depends on the packed bed structure. Stress distribution in the cluster is not constant, and bottleneck particles support the entire cluster. The pressure drop has also been calculated, and the calculation results agree with previous experimental results. (C) 2011 Elsevier Ltd. All rights reserved.