Online measurement in biogas fermenters for automated digestion control

Electricity production from biogas power plants is an important part of a renewable energy system. The main advantage compared to other renewable energy sources is capability to provide base load to the electricity grid. This is possible since biogas production is quite predictable and can be influenced to some degree by feeding the biogas fermenters accordingly. Nevertheless, there are still some open issues for biogas usage. The fermentation process and hence the gas production is difficult to control since the lack of understanding of the fermentation process and the missing measurement equipment make it impossible to set up a closed control loop. Apart from that, biogas is used in block heat and power plants. This is only efficient if the heat is used, meaning there are different demand profiles for heat and electricity. The goal of the ongoing research is to make the biogas power plant and hence the fermentation process controllable with a fast reaction to changes and high flexibility on the input and the output side. This would lead to a smart biogas power plant with the capability to provide peak load to the grid. Furthermore, the smart biogas power plant allows optimization and efficiency gains. One core issue for this goal is the provision of online measurement tools directly in the fermenter (in situ or in process). We present recent research on the selection of measurement parameters, the usage of digestion process models in controller design and the development of online measurement equipment for biogas fermenters.