Biogas upgrading – Review of commercial technologies - SGC

SGC Rapport 2013:270
a very high pressure and can be used in a vehicle fuel filling station with only minor
additional compression. The electricity consumption of the plant, including the
electricity needed for the filling station and further pressurizing to 270 bar(a), is
around 0.4-0.5 kWh/Nm 3 of raw biogas, and the system operates with a methane
slip of 1-3%, all according to the manufacturer.
Due to the high pressure, the components in the system such as absorption and
desorption columns can be built much smaller than in a conventional water scrubber.
However, they need to withstand the high pressure. The footprint of the system
will be smaller as well as the investment cost. The investment cost of a plant
(including dispenser and basic storage) with a capacity of 60 Nm 3 /h is around
380.000 €.
5.2 Rotary coil water scrubber
A method to upgrade biogas in small scale that is similar to a conventional water
scrubber, is to use a rotating coil in which the compression and scrubbing occurs.
This technology is being developed by the Swedish company Biosling. Today, no
commercial units have been sold and delivered to customers, but the product is
available on the market.
The compression of water and biogas is unique for the Biosling unit. Biogas and
water with a pressure of 2 bar(a) are alternately fed into coils of plastic hoses that
are rotating. The rotation increases the pressure up to around 10 bar(g) and most
of the carbon dioxide will be dissolved into the water inside these coils.
As described in Chapter 2, it is beneficial for any type of physical scrubbing to
have a counter current flow of the fluid and the gas, which is not possible for the
coil pump used in the Biosling process. Thus, a product gas with 97% CH4, which
is commonly requested on the market today, cannot be reached by just using the
coils for upgrading. Instead, a conventional water scrubber is used for the final
removal of carbon dioxide. Using only the rotating coil unit, a product purity of 94%
can be reached, according to the manufacturer. Hence, the technology may be
more suited for applications in which a lower product purity is sufficient, as the unit
without the final polishing scrubber would have a lower investment cost. The coil
pump and the columns of the water scrubber can be seen in
Figure 41.
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