The project was financed by the German Bundestag through the Federal Ministry of Food and Agriculture (BMEL) and carried out under the auspices of the Fachagentur Nachwachsende Rohstoffe e.V. (FNR). Its main objective was to markedly increase biogas yield while simultaneously reducing the self‑consumption energy demand of biogas fermenters, with a particular focus on plants that handle highly variable substrate compositions. The effort was organised into three work packages: (1) development of a new generation of impellers with superior suspension behaviour and high axial thrust, (2) creation of a substrate‑dependent drive control system combined with online process monitoring, and (3) formulation of a design methodology to aid plant designers and operators in selecting the optimal impeller technology. The project spanned roughly three years, during which the consortium, including the electronics manufacturer Trilogik, collaborated closely on design, simulation, sensor development, and field testing.
Technically, the team produced an extensive impeller profile catalogue that, together with simulations of the overall fermenter flow, enabled a rapid selection of suitable geometries for varying operating conditions. The influence of dilution on force coefficients was quantified, and key parameters of paddle geometry were identified. A systematic start‑up behaviour was devised, and the overall flow field of the fermenter was simulated to validate the chosen impeller shapes. Laboratory experiments confirmed the simulation results, demonstrating that the new impeller designs achieve improved mixing volumes and flow velocities across a range of substrate mixes. A comprehensive design methodology was then established, providing plant designers with a clear framework for selecting and sizing impellers based on measured flow characteristics.
Parallel to the mechanical development, a robust sensor suite was engineered. The team selected and tested various sensors, including flow‑velocity probes and pressure transducers, in a towing‑tank environment and on moving surfaces using Particle Image Velocimetry (PIV). The sensors were adapted for continuous operation, calibrated, and integrated into an evaluation electronics and software platform. A control algorithm was developed to adjust impeller speed in real time, based on online measurements of flow conditions. This algorithm was embedded into the overall process control and validated under real plant conditions, demonstrating that the system can compensate for flow‑related weaknesses without requiring a complete impeller replacement.
The economic assessment highlighted that the German biogas sector hosts approximately 9,700 existing plants, and that the first‑stage stirring consumes about 25 % of a plant’s self‑generated electricity. By enabling objective, substrate‑independent evaluation of mixing and by providing a systematic optimisation of impeller speed and run‑time, the new technology offers significant energy savings and yield improvements. The consortium envisages that, within two to three years after project completion, Trilogik could manufacture the sensor electronics, thereby securing a market for a mature product. The project’s findings have already been disseminated in scientific forums and applied‑research publications, underscoring both the technical novelty and the commercial viability of the developed impeller and control system.