To reduce the country’s dependence on gas imports, Germany wants to strengthen the use of biogas plants. To this end, the national government has suspended the limit on maximum annual production and is supporting research into making the production of biogas more profitable. In this context, an interesting new innovation from the Münster University of Applied Sciences has recently picked up the Bernard Rincklake Award.
For his doctoral thesis in 2020, Sven Annas focused on the efficiency of the agitator (the large, paddle-like device) in the fermenter basin. The stirring apparatus accounts for around 60 percent of total energy consumption at a biogas plant. Based on his investigations, he was able to develop a uniquely effective agitator that could save plant operators as much as EUR 30,000 annually.
The substrate in biogas plants is very viscous, a similar consistency to wallpaper. "Long-fibre forage like grass tends to float to the top and different layers form. Ideally, however, we want to keep the mass homogeneous," Annas explains in a . First he looked at the speed, positioning and filling levels and found that the usual position of the agitators (for making assembly easier) actually increases mixing time significantly. He simulated the stirring and mixing processes digitally, then modelled operations in the department's fluid mechanics laboratory.
Finally, working with an agitator manufacturer, he was able to test and verify the results in a new biogas plant in the UK. Annas is now supervising two follow-up projects as a junior professor at the university’s Department of Mechanical Engineering. Since the publication of his thesis, an operator of a large plant in northern Germany has realigned its agitators accordingly and estimates it could save EUR 30,000 a year – far exceeding even Annas’ expectations.