A novel simulation strategy for the modular-based calculation of models describing single unit operations is proposed. It is based on the functional decomposition of the model with further application of the waveform relaxation approach for data exchange and convergence analysis. Compared to convenient simultaneous calculation of units, the proposed approach leads to higher flexibility during model creation and allow simultaneous usage of several solvers and simulation methods. To illustrate the usability of the developed strategy and analyze its efficiency it has been applied for modeling of a fluidized-bed spray granulator. Based on the functional decomposition, the granulator model has been decomposed into six separate submodels connected with information streams for data exchange.