Experimental analysis of mixing-processes in biogas plants

The aim of this paper was to develop a deeper understanding of the mixing processes in biogas plants and to explore potentials for optimization with respect to efficient mixing. Since slow-running agitators have a higher energy efficiency than high-speed submersible mixers, the focus was placed on paddle agitators. In order to achieve more effective mixing, different agitator positions were compared. The risk of stagnation zones was identified by a current condition analysis with optical velocity measurements. By using different agitator positions stagnation zones can be decreased. In order to evaluate an increase in efficiency, mixing times were determined by conductivity measurements. The results showed that complete mixing can be achieved even at significantly lower speeds if an optimal agitator position is used. With higher viscosity and shear thinning sensitivity of the fluids, the energy-saving potential also increases and the mixing times can be reduced by a factor of 10.(c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).