Optimization of the mixing system in biodigesters with computational fluid dynamics (CFD)

Up to 50 % of a biogas plants parasitic energy consumption is actually caused by the mixing system. Therefore the optimization of the mixing-system is an essential method to increase the overall efficiency of the biogas plant. Various influences onto the mixing characteristic such as the type, number, positioning and geometry of the stirrer as well as the (influential) substrate rheology have to be considered. For comprehensive investigations on digester mixing, laboratory experiments in combination with numerical calculations are a promising approach. Under defined conditions, a high flexibility allows various investigations and evaluations. The non-Newtonian, shear thinning behavior of biogas substrate strongly influences digester mixing. While the use of real biogas substrate in laboratory is critical, the creation of a consistent model substrate with similar physical properties, which enables comparable experimental results, should be preferred. The main objective of the presented project, which is funded by the German Ministry of Education and Science, is to optimize biogas digester mixing with highest benefit at lowest cost in general.