The mixing of powders and granular materials is decisive for the quality of a final product. Simulations of granular mixing via discrete element method are performed. Mixing was done in a vertical cylindrical mixer with two opposed flat blades with 90 degrees rake angle. The effects of packed-bed depth and blade rotational speed on the process of homogenization and on the development of flow patterns were evaluated. The process of homogenization was analyzed at macroscopic scale by global mixing indexes and at microscopic scale by the complex flow patterns with different nature. Macroscopic and microscopic approaches were connected and from flow pattern observation optimal conditions for the best homogenization were predicted.