Optimization of mechanical mixing of anaerobic digesters using computational fluid dynamics (CFD)
Date
2018-09Author
Abstract
To keep biogas production competitive against alternatives in the energy sector, reducing the
operating costs is a major challenge for biogas applications. Up to 50 % of the energy
consumption in biogas plants is contributed by the digester mixing. Therefore, the
optimization of the digester mixing system is a promising approach to increase the overall
efficiency of biogas plants. The main objective of the presented thesis is to optimize digester
mixing to achieve the highest benefit at the lowest cost. Investigating the mixing process in
digesters is a necessary precursor for successful design, operation, and increased efficiency in
biogas plants. However, observation of mixing in digesters under real conditions is complex
and cost intensive. With an adapted mixing system, a reduction of the operating costs of up
to 30 % is possible. Process disturbance and maintenance costs can be minimized and the
biogas production within a given digester volume can be maximized. The work shows the
process and results of a simplified approach to simulate the mixing dynamic in a common
cylindrical digester with computational fluid dynamics (CFD). The CFD simulation is verified by
laboratory experiments. Based on the theory of similarity, at the Institute of new Energy
Systems of the Technische Hochschule Ingolstadt, a 1:12 scale digester model was set up and
an artificial chemical substrate was selected to mimic the rheology of real biomass. Different
mixing regimes were configured using propellers and paddle stirrers located in varying
positions. Optical and acoustic techniques were employed to observe the fluid dynamics in
the laboratory experiment. In this thesis, the laboratory setup and the results on the flow
velocity and torque on stirrer shaft developed during mixing are presented and discussed. The
experimental are used to validate the similar numeric computational fluid dynamic study.
Description
Collections
- MPhil [36]