biogaspartner – a joint initiative.

Value.Chain.of.Biomethane.
Figure: Process steps of raw biogas upgrade.
Source: Fraunhofer UMSICHT (2008).
fine-grade sulphur removal and a drying of the gas may be nec-
essary. For the upgrade of high- or low-methane natural gas, a
separation of Co may also be a required additional step, unless
2
the biogas is to be admixed as accessory gas. In a last step, the
heat value is increased or reduced by admixing LPG (liquified
petroleum gas) or oxygen to adjust the biomethan quality to the
quality of the natural gas in the gas grid.
The upgrade from biogas to biomethane is economically attrac-
tive only starting at medium-sized plants. Existing or planned
smaller biogas plants therefore can make use of the possiblity to
assemble the biogas generated in each plant via micro gas grids
and then upgrade and feed-in the entire quanitity on only one
site.
The figure above provides an overview of the various process
steps of biogas upgrade.
Sulphur removal.
The process of crude sulphur removal can be undertaken either
biologically or chemically.
Biological sulphur removal.
Biological sulphur removal employs microorganisms that consume
hydrogen sulphide. This process is only suitable for crude
sulphur removal. The microorganisms can be placed directly
into the fermenter.
Chemical sulphur removal.
Chemical sulphur removal involves the use of compounds that
bind with sulphur in the fermenter. Iron oxide is the best compound
for this purpose.
34 B I o G a s P a r T n E r – a j o I n T I n I T I a T I v E
Raw biogas from vegetable matter of liquid manure biogas plants
Gross desulphurisation Option: Gross desulphurisation Gross desulphurisation
Fine desulphurisation
Compression
Gas cooling
CO 2 separation adsorption
Calorific value adjustment
with LPG or air
Natural gas H or natural gas L
Compression Fine desulphurisation
Gas cooling Compression
CO 2 separation adsorption Gas drying
Gas drying
Calorific value adjustment
with LPG or air
Supplemental gas
Because some sulphur (specifically hydrogen sulphide) can remain
in the biogas after crude sulphur removal, some preparation
paths may require an additional fine sulphur removal
process before Co separation. The most suitable processes for
2
fine sulphur removal are active carbon adsorption and zinc
oxide adsorption.
Gas.drying..
For the drying of biogas, adsorption and condensation processes
are the methods of choice.
Adsorptive gas drying processes.
The premise of this process is that water vapour adsorbs to
specific compounds (including, for instance, silica gel and
aluminum oxides). Using packed-bed adsorbers, these com-
pounds are passed through the biogas as granulates, thereby
removing water vapour from the gas.
The granulates must be regenerated after adsorption. Here it
is important to note the difference between cold and warm regeneration
processes. If the biogas facility is to feed into the gas
grid on a continuous basis, it is necessary to apply two separate
packed-bed adsorbers so that one may be used when the other is
regenerating.
Condensation processes.
For this process the biogas is cooled, causing the water it contains
to condense. This process is above all intended for drying
biogas for use in motor vehicles. However, the process does not
meet specifications (DvGW G260 and G262) for biomethane
preparation. For this reason, the process is only partially useful
to prepare biomethane for feed-in into the grid.
CO .separation.
2
on the European market, pressure swing adsorption and pressurised
water scrubbing are the most widely used processes for
Co separation. additional processes are currently in the pilot
2
stages; some of these must still be intensively researched. The
following overview provides a short, non-exhaustive description
of some selected Co separation processes:
2