Project meeting of STEP at the site of the company ATS - Agro Trading & Solutions in Hardegsen (Photo: DBFZ)

Power Biogas Biomass technologies

Project ID 03KB152

FlexPump - Development and demonstration of a pump-based mixing concept for the flexible, efficiency-optimized and multifeed-capable operation of biogas plants

Development of an external pumping system for hydraulic reactor mixing (source: Fraunhofer IKTS)


  • 01.01.2019 – 31.12.2021


Fraunhofer Institute for Ceramic Technologies and Systems IKTS, Mixing Processes and Reactor Optimization
Winterbergstraße 28
01277 Dresden

Anne Deutschmann – project manager
Telephone: +49 351 2553-7685

Dr. Karin Jobst – former project manager



03KB152B - Vogelsang GmbH & Co. KG
03KB152C - A & U Service- und Vertriebs GmbH

Associated partners

Cooperation partners



Further expansion of the regenerative-operated electricity system requires economical and optimized flexible operation of existing and newly constructed biogas plants. Taking into account the given advantages such as reliability, controllability and the variety of possible applications, efficient concepts and technologies have to be developed which ensure long-term, sustainably profitable operation independent of state support. An immense potential lies in optimizing the mixing of the fermentation substrates, combined with an efficient and targeted technique for substrate introduction and pre-treatment.


Through targeted coupling of the substrate pre-treatment and the return of internal process water streams with an intelligent pump system, an overall system for the hydraulic mixing of biogas reactors will be developed and tested and optimized under practical conditions on a pilot scale. With the additional development and testing of a multifeedstock-capable plant concept and the development of a complex control system for the adaptation of the hydrodynamic process flows, a practicable and sustainable profitable system solution for the flexible and demand-oriented biogas production for a broad circle of users shall be available.



  • Based on the requirements of flexible biogas production, different substrates, primarily biogenic residues such as grass silage and straw are included in the considerations. For the realization of a comprehensive parameter variation, first process tomographic investigations on a small scale are planned. As a function of strongly varying substrate properties, different feed regimes and circulating flows to be adapted, the resulting flow rates and mixing grades in the reactor are evaluated and functional relationships are established between the process variables and the process result. The parameter studies to be performed are supplemented by flow simulations.


  • In addition to the dependencies to be determined between substrate properties, the process variables to be varied and the mixing result, the knowledge of the flow conditions forming in the pump system is an essential prerequisite for the development of the control concept to be created. To derive optimized design and operating parameters of the process, the flow behaviour in the pump system is evaluated by means of numerical flow simulation. The main focus of the subproject is to adapt the criteria for the design and operation of the pump system to the requirements of multifeedstock-capable plant operation and to develop a concept for the regulation of the overall process as the basis for automated, flexible and needs-based operation of biogas plants. The developments to be made are then transferred to the pilot scale and tested.

A & U

  • The realization of a multifeedstock-capable plant operation for demand-oriented biogas production requires process control adapted to the substrate properties. In addition to substrate pre-treatment, the fluid dynamic properties in the fermenter and thus the mixing process are significantly influenced by internal cycles (digestate, process water). The sub-project plans systematic investigations to optimize the overall biogas production process chain. Taking into account different plant concepts, the influence of the process water produced during fermentation residue dewatering, conditioned and recycled process water on the resulting suspension properties in the fermenter and their effects on the mixing and biogas process will be investigated. Another focus of the subproject is installation and process evaluation of the hydraulic mixing system in the bypass of a large-scale fermenter.



  • Development of a process concept for the use of an external pumping system
  • Evaluation of the mixing process by means of process tomography and numerical flow simulation


  • Adaptation and optimization of the design and process parameters of the pumping system
  • Concept development to regulate the overall process

A & U

  • Integration of the pump-based mixing system in a biogas plant
  • Evaluation of the mixing system under practical condition


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