Renewable Energy – Solutions for application in the communal energy infrastructure

BIOENERGY | 23
Functional principle and design
In the fermenter of a biogas plant, microorganisms
produce methane from biogenic materials, called “substrates”
(e.g. maize, rape, straw, slurry or food waste).
Depending on the climate zone, it may be necessary to
heat the fermenter to around 40°C (e.g. with the waste
heat generated during gas utilisation) so that the microorganisms
can work in an optimal way.
Possible applications and benefits for municipalities:
Biogas is a very versatile energy source that can be used
in a similar way to natural gas and not only reduces
CO 2 emissions but also increases local added value:
The gas produced is collected in a gas storage tank. In
addition to the main component of methane (50 to 70
per cent), it also contains other substances whose proportions
vary depending on the substrate in use. Carbon
dioxide (CO 2 ) is the second-largest component of
biogas, accounting for 35 to 50 per cent. The rest is primarily
nitrogen, water, oxygen and hydrogen sulphide.
• Local generation of electricity and heat in cogeneration
plants (e.g. for operating a dairy with gas
production from cattle manure)
• Use of biomethane for cars, heavy goods vehicles
and ships
• Replacement of natural gas with biomethane, e.g. in
heating systems or power plants
• Flexible power generation to compensate for
fluctuating wind and solar power output
Sulphur and water must be removed in a purification
plant. Then the biogas can be used, for example, in
cogeneration plants or vehicles that have been adapted
to use biogas.
An alternative way is to process the gas into biomethane
in a further purification step. The biomethane can be
used like natural gas in conventional heating systems,
engines and power plants. If it is to be fed into a
natural gas network, the last step is to fine-tune it so
that all the properties – such as its heating value and
dryness – match exactly.
In addition to biogas plants with automatic agitators
and pumps for filling and emptying, there are also very
simple and small models available. These are mostly
used in remote regions. They consist of a simple
container that is filled by hand. These are heated by the
sun. The gas is used, for example, in simple cookers as
an alternative to wood or dung.
Biogas plant with local heating network