Biogas plant

Our society is faced with the fundamental task of securing a reliable and sustainable supply of energy. Renewable energies already contribute considerably towards this. In the future, they will form a secure guarantor for alternative energy supplies. With our biogas plant in Hillerse, we would like to make our own contribution to this.

In our biogas plant, we use the energy plants cultivated in our irrigation areas for the CO2-neutral production of biogas. The plant nutrients left behind during the biogas production are thereby fed back into the natural cycle of matter. Via a 20-kilometre-long pipeline, the Abwasserverband Braunschweig delivers the biogas to the local energy supplier BS | Energy, who produces electricity and heating for several thousand households in Braunschweig.

Our reasons for building the biogas plant at a glance:

  • Production of climatically-neutral energy and considerable savings on CO2
  • Conservation of finite resources
  • Stabilisation of the waste water utilisation concept (Braunschweig model)
  • Production of high-quality organic fertiliser
  • In contrast to wind and sun, biogas is a weather-independent, storable energy carrier and a sustained production of electricity and heating is possible.

What is biogas and how is it produced?

Biogas is obtained through the processing of biomass. For the input material, special “energy plants”, such as maize and rye, are used, which are characterised by a high biological usability. In order to produce biogas, organic material must pass through a multi-stage fermentation process in an oxygen-rich environment (anaerobic digestion). Through the efforts of bacteria and other micro-organisms, the input material is initially decomposed and then, in intermediate stages, transformed into methane (CH4), carbon dioxide (CO2) and trace gases (incl. hydrogen sulphide) and water.

How does the biogas plant in Hillerse work?

For decades, waste water from the city of Braunschweig has been purified in the treatment plant Steinhof and then used to irrigate the Association’s fields in order to improve the ground yield. These fields are now used to cultivate renewable raw materials such as maize and rye, which are fermented in the Association’s biogas plant.
These raw materials (substrate), which are cultivated and harvested specially for the Hillerse plant, are homogenised and heated to 45°C in the biogas plant. The substrate is then pumped in liquid form into the fermenter. The biogas process takes place here.
Fermenters, the biomass is split into ever-decreasing molecules during a multi-stage reaction process. From carbohydrates, proteins and fats, simple organic acids are formed. Each of these chemical reactions takes place in the metabolism of various strains of bacteria.

In the final reaction stage, methane gas is developed. In order to optimally utilise the produced gas (approx. 1,200 cubic metres/hour) both profitably and ecologically, the majority of it is transported via a gas dehumidification and compression facility through an underground gas pipe to Ölper in Braunschweig.

Here, BS | Energy has constructed two gas engines (2 x 1 MWel) and uses the biogas for both the production of electricity and the supply of heating for Braunschweig households. The biogas is also used for own requirements and for the additional production of electricity at the biogas plant. The resulting electrical energy of 20.1 million kilowatt hours per year provides 6,000-7,000 households with electricity and 1,000-1,500 households with heating.

The biogas production per day amounts to 26,500 cubic metres.
The electricity production per day amounts to 55,000 kilowatt hours.

Numbers, data, facts

  • Commissioning: 09/2007
  • Block heating and power station with gas Otto engines (2 x 1 MWel BS|Energy power station in Ölper, 1 x 600 kWel power station in Hillerse)
  • Silage slabs (4 x 3,200 m² + 1 x 2,500 m²)
  • Fermentation containers (2 x 5,000 m³)
  • Secondary fermentation container (3,500 m³)
  • Fermentation residue storage (1 x 6,000 m³, 3 x 3,500 m³)
  • Gas foil roof (4 x 1,500 m³)
  • Separate gas storage (500 m³)
  • Company building (740 m²)
  • Input materials: maize (105 t/d, 38,000 t/a), rye whole-crop silage (24 t/d, 9,000 t/a)
  • 1,000 hectares agricultural area under cultivation
  • Utilisation of 28,000 t fermentation residue (liquid or dehydrated)
  • Production of 9.7 million Nm³ biogas per year, production of 20.1 million kWh electricity per year