The rolling granulator is an important device, in which agglomeration of fine particles is used in many industrial processes such as powder metallurgy, iron-making industry, food and pharmaceutical industries. Fine granular materials are prepared and mixed in required proportions, compacted into a granule or tablet and finally sintered to acquire sufficient mechanical strength and toughness needed for subsequent operations. We present a numerical model for the agglomeration process of wet granular materials. The particles interact through capillary liquid bridges, which are modeled by accounting for the cohesive and viscous forces expressed analytically as a function of different parameters such as the distance between primary particles, particle sizes, liquid volume, viscosity and surface tension of the liquid binding. The model also assumes that the liquid is transported homogeneously by the primary particles modeled as agglomerates of finer particles. We find that this model is able to simulate the agglomeration of particles in a rotating drum. Our simulations show that the granule size increases exponentially with the number of drum rotations and in proportion to the amount of liquid. We investigate both effects of process and material parameters such as filling level, the rotation speed of the drum, particle size distribution, friction coefficient between the primary particles and viscosity of the binding liquid on the granule growth, the accretion and erosion dynamics of granule inside the granular flow. We also determine the granulation domains in the relations between the mean particle size, liquid viscosity and the size ratio distribution.