A flexible model for biogas generation and utilization was developed using simulation tool Aspen Plus. It is based on two interacting submodels, describing the process of biogas generation via anaerobic digestion and biogas utilization. Three possible approaches to model biogas production have been employed - calculation via chemical oxygen demand (COD), calculation according to Buswell's equation, and implementing stoichiometric reactions. For purpose of biogas utilization three paths are included - combined heat and power generation (CHP) by means of a gas engine, a second path which could further be used for biogas upgrading, and adiabatic combustion of generated biogas. The model can be used for a rough estimate whether integration of a biogas process with systems processing organic waste material streams is beneficial or not. An economic approach is no target of this work. This model simply calculates how much biogas can maximal be obtaind out of a specific organic feedstock and how much heat and power can be generated by the use of a gas engine or a simple combustion process. Because of its flexible and simple configuration, the model can be adapted to various types of substrate with respect to model setup. The difference between the calculation methods used have been discussed. The model was evaluated in terms of comparing with results from literature, comparing the results of the model with results of a model from literature, and sensing potential limits by appling several kinds of input data.