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

Heat Biogas

Project ID 03EI5424

flexigast - Entwicklung und Erprobung eines Verfahrens zur flexiblen Biogasproduktion und optimierten Wärmespeicherung auf Basis gezielter Variationen der Gärtemperaturen


  • 01.02.2021 - 30.09.2023


bue Anlagentechnik GmbH
Am Anger 11
06249 Mücheln

Matthias Bernhardt – project leader
Telephone: +49-(0) 171 6383-048


03EI5424B - ORmatiC GmbH
  • Address:
  • ORmatiC GmbH
    Am Friedrichshain 22
    10407 Berlin
  • Contact:
  • Borko Georgiew – project leader
    Telephone: +49-(0) 30 2250 5478-0

03EI5424C - Technical counseling for systems engeneering
03EI5424D - Magdeburg-Stendal University of Applied Sciences
03EI5424E - GMBU - Environmental Biotechnology, Halle

Associated partners

Cooperation partners



Planned results

  • plant level: procedure, demo plant, retrofitting of existing plants
  • concept level: plant concept
  • data level: models/modeling, test series/-program, software
  • market level: ready for market technologies, transfering pilot-/demo plants to economical application
  • others: best-practice-solutions


In order to counterbalance the fluctuating electricity generation from wind and photovoltaics, biogas plants are increasingly being equipped for demand-oriented electricity production. This so-called "flexibilisation" of biogas plants is accompanied by the installation of additional electrical power through new combined heat and power sytems (CHP) and other necessary measures, which together result in a not insignificant investment. In particular, the large increase of the gas storage volume, which depends on the degree of flexibility, and the installation of heat storage facilities, which may be necessary depending on the heat utilisation concept, should be mentioned here.
For this purpose, a new method (“flexigast”) for demand-oriented biogas production and optimised heat storage based on systematic variations of the fermentation temperatures in the fermenters is to be developed within the framework of the project. If the CHP is switched off according to the electricity schedule, the fermentation temperature is lowered in a targeted manner. When the CHP unit is put back into operation, the temperature is increased. These temperature variations should be combined with flexible feeding. The feeding variations should only be supportive and coordinated in accordance with the targeted temperature changes and should, in addition that, apply to common, practice-relevant substrates or residues with relatively slow fermentation behaviour. In the second half of the project, the method is to be tested on a pilot plant and on a liquid manure biogas plant.
A decrease in the average methane yield and process stability can be avoided by controlled process management. By using a heat pump, the potential and controllability of the required temperature reductions are improved and at the same time the temperature and the usable amount of heat for external consumers are significantly increased.


Key objectives are:

  • The significant reduction of the gas storage volume required for flexibilisation,
  • the avoidance of additional heat storage tanks,
  • the operational optimisation of heat management
  • and an improvement in the effectiveness and efficiency of feeding variations through targeted temperature adjustment.


bue Anlagentechnik GmbH

  • Analysis of current general conditions and specification of requirements, example systems with relevant biogas plant types,
  • Process and plant engineering on the basis of the defined example systems
  • Support of semi-technical trial, large-scale trial on a slurry biogas plant
  • Optimisation of the flexigast process, validation of market potential, conversion plans and handouts for large-scale implementations, technical documentation of the process

ORmatiC GmbH

  • Basic investigations and design of the measurement and control concept for the flexigast process based on the example systems
  • Development of the control on the basis of the example systems and implementation in the pilot plant
  • Planning integration of process and control in automation solutions of biogas plants
  • I&C technical aspects of the transferability, technical documentation of the automation solution

Technical counceling for systems engeneering

  • Basic investigations for combining with innovative technologies of renewable energies and heat utilisation
  • Analysis and adaptation of heat utilisation concepts and of heat management for the example systems to the flexigast process
  • Analysis of optional variants for heat management
  • Test scenarios regarding heat management for model calculations for optimal process parameterisation

University Magdeburg-Stendal

  • Scientific evidence that temperature changes in the digester can be used to control biogas and methane production
  • Design of process monitoring concept; scientific evidence for combination with flexible feeding; gas storage and heat management models
  • Semi-technical testing supported by process biology modelling
  • Scientific evaluation of the semi- and large-scale testing, optimisation of the process monitoring concept


  • Method development for the analytical evaluation of the temperature and load tolerance of the fermenter biology with batch fermentation tests and qPCR
  • Reliable application of the methodical analytical procedures on a laboratory scale in comparison with experimental data
  • Extension of the bioanalytical methods to the half and large scale
  • Documentation of the molecular biological detection procedure incl. validation of the analytical detection procedures on the large-scale trial with a view to practical suitability


bue Anlagentechnik GmbH

  • Process and plant related development and optimisation, planning and coordination of large-scale technical trials

ORmatiC GmbH

  • Development of I&C concept and control system for the flexigast method, implementation for semi-technical testing, planning of integration into automation solutions of biogas plants

Technical counceling for systems engeneering

  • Investigations on the combination of the flexigast method with innovative renewable energy technologies and on the optimisation of heat management in the overall system

University Magdeburg-Stendal

  • Scientific foundation for method development, modelling and simulation and semi-technical testing


  • Microbiological characterisation and molecular biological evaluation of the process biology


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