Decentralized integrated biogas and bioethanol production

Over recent years, there has been an enormous increase in the number of biogas plants. In parallel, the size of new biogas plants has increased and renewable organic material is predominantly used as feedstock for biogas production. The substantial rise in market prizes of agricultural products makes it quite impossible to operate such a biogas plant economically. The economic situation of a biogas plant can be improved considerably by utilization of the waste heat from the cogenerator. For most biogas plants, which are located in rural areas, it is impossible to feed into a district heating grid. For production of bioethanol, thermal energy is required for fermentation and distillation. Additionally, the stillage can be utilized in the biogas process as feedstock, whereas in industrial bioethanol plants the stillage usually has to be dried, consuming extensive thermal energy. Integrated biogas and bioethanol production is discussed for a 500 kW_el biogas plant and the economics of this process are investigated.