Power-to-gas plant put into operation
Key technology to enter sustainable energy era
Methane produced in a biological process using surplus electricity
from renewable sources such as wind and the sun is being fed into
the natural gas grid for the first time at Viessmann's company
headquarters in Allendorf (Eder), Germany. The first system of this
type in the world went into operation in early March. Over the past
few weeks, the necessary technology, equal in size to three
shipping containers, was integrated into the existing biomethane
plant in Allendorf (Eder). Approval has already been given to
expand the system, so that it can generate and process around
400 cubic meters of hydrogen per hour (Nm³/h).
Storage process imitates nature
As the use of wind and solar energy becomes more widespread,
increasingly larger quantities of surplus electricity which cannot be
fed into the power grid will be produced at times when there is a
great deal of wind or sunshine. On the flip side, there may also be
a shortfall in supplies when there is little sun or wind as
conventional power stations are being dismantled for the
sustainable energy era. Developing energy storage systems is
thus one of the greatest challenges of the sustainable energy era.
One interesting approach is the power-to-gas technology which is
now being used at Viessmann. This process can be used to
produce hydrogen from surplus wind and solar electricity using
electrolysis of water. This hydrogen is then either used directly or
mixed with carbon dioxide from a biogas system and converted
into methane gas using a microbiological process.
Generation and consumption separated in time and space
The gas network in Germany has a storage capacity of several
months thanks to its pipelines and underground chambers. The
fuel can thus be stored for a long time and used to supply heat or
to power natural gas vehicles as a climate-friendly fuel source,
irrespective of where the electricity was actually generated. It is
precisely this long-term storage capacity which makes power-togas different from other storage technologies such as batteries,
pump storage systems, or power-to-heat, which mainly provide
economic energy storage over a few days only.
Optimum versatility in absorbing wind and solar power
While existing power-to-gas projects have been using a chemicalcatalytic approach to methanation, the Viessmann Group company
MicrobEnergy has developed a new microbiological process,
which now works on a large scale. This process combines
hydrogen from an external source with the carbon dioxide
generated during fermentation in a biogas plant and converts them
into methane using a microbiological method. A PEM electrolyzer
built by Carbotech, another Viessmann company, is used to
produce hydrogen. Biological methanation impresses due to its
optimum flexibility, making it eminently suitable to absorb
fluctuating quantities of energy produced by wind or solar power.
Micro-organisms produce methane
Highly specialized microorganisms perform the actual
methanation. They absorb the carbon dioxide and the hydrogen in
liquid form through their cell walls, 'digesting' and converting them
into methane. The only thing left over after this process is water.
Reduced costs thanks to use of existing infrastructure
Thanks to the use of existing biogas and sewer gas plants, the
investment costs for power-to-gas plants can be reduced
significantly since transformers, electricity mains connections, and
gas network connections are often already installed.
Funding as part of BioPower2Gas initiative
The plant has been set up in Allendorf (Eder) as a demonstration
power-to-gas plant as part of the BioPower2Gas subsidy program.
The main goals of the project are testing the electrolyzer and
biological methanation with regard to stability for the long and
short term, integrating the system fully into the biomethane plant,
achieving a stable gas quality capable of being fed into the
network and demonstrating process-safe, dynamic operation. The
project also aims to test control energy operation and operation
with varying input gas qualities (CO2, moisture content,
temperature, cycles and seasonal differences). Conformance of
the synthetic methane produced with bio-fuel market requirements
is also being established during cost accounting, verification, and
certification procedures, so that this storage gas can be marketed.
Test results: excellent gas quality
The MicrobEnergy demonstration plant had been in operation at
the Schwandorf sewage works until the end of December 2014.
The test results revealed excellent product gas quality of more
than 98 % methane content with a stable production volume and a
very low proportion of hydrogen at 2 %.
After the plant was relocated to the Allendorf site, the hydrogen
produced there has been methanated using the tested biological
process and fed into the natural gas grid via the existing biogas
feed-in system since early March 2015. The CO2 required is either
taken from the gas processing plant or raw biogas is used directly
with the CO2 that it contains. In this case, the power-to-gas
process is also regarded as an upgrading technology for raw
biogas supplied from biogas and sewage plants.
Background:
The BioPower2Gas (www.biopower2gas.de) research project
funded by the German Federal Ministry for Economic Affairs and
Energy brings partners together who are tasked with expanding
flexible power generation capacities from renewable energies.
These partners are the technology developer MicrobEnergy
GmbH, a Viessmann Group subsidiary, network operator
EnergieNetz Mitte GmbH, utilities company EAM EnergiePlus
GmbH, part of the EAM Group, engineering consultants CUBE
Engineering GmbH, and research body IdE Institut dezentrale
Energietechnologien GmbH (project coordinator). The bioenergy
village of Jühnde an associated partner of the project. The
research is funded as part of the German Federal Ministry for
Economic Affairs and Energy's Bio-mass energy use program with
scientific support provided by the DBFZ (Deutsches
Biomasseforschungszentrum), the German biomass research
center.
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Image: BioPower2Gas demonstration plant
(1) PEM electrolyzer (400 kW) by Schmack Carbotech,
Viessmann Group
(2) Biological methanation, separate pressure tank
(3) Process container: pumps, tanks, gas analysis system,
temperature regulating system
(4) Control container: controls, measurement and control
technology
March 2015