Numerical simulation methods have a very high utility in the description of relevant processes. Over the years, a wide range of numerical simulation methods have been developed for different applications, such as aerosol processes, separation processes, breakage of agglomerates, and fluidized beds. The interaction of small particles or droplets with the fluid flow is often difficult to measure. Numerical simulation of the fluid flow and the Lagrangian tracking of particle trajectories can help to understand and optimize a process. In addition, the discrete element method is essential for the accurate description of particle-particle and particle-wall interactions. For more complex particle/fluid flows, a CFD-DEM coupling is the method of choice. This allows dynamic processes, such as a silo discharge, to be accurately predicted. Our choice of software for simulation and modelling is not limited to commercial providers in our experience, open source software often offers a good alternative. A CFD-DEM software DNSLab® developed at the institute, which is specifically designed for filtration processes, completes our simulation experience.