Despite having been thoroughly described in various simple configurations, the study of gas-fluidized systems in a CFD/DEM (Discrete Element Method) formalism becomes challenging as the computational domain size and complexity rise. For a while, attention has been drawn to the design of physical models for fluid-particles interactions, but a recent challenge for numerical tools has been to take advantage from the increasing power of distributed memory machines, in order to simulate realistic industrial systems. Furthermore, unstructured meshes are appealing for their ability to describe complex geometries and to perform local refinements, but lead to significant coding effort involving sophisticated algorithm. In a attempt to design a numerical tool able to cope with these limitations, the methodology presented here proposes an efficient non-blocking algorithm for massive parallelism management, as well as an exhaustive contact scheme to deal with arbitrarily complex geometries, all to be operated on unstructured meshes. The aim is two-fold: (i) To assist larger scale codes in their endeavor to close the solid stress tensor for example, (ii) to pave the way for complex industrial-scale systems modeling using DEM. The methodology is successfully applied to a pilot-scale fluidized bed gathering 9.6M spherical particles and enables to reach interesting physical times using reasonable computational resources.