Biogas upgrading – Review of commercial technologies - SGC

SGC Rapport 2013:270
Appendix III The GtS cryogenic upgrading process
The Dutch company Gastreatment Services bv (GtS) is the supplier of a modular
cryogenic system for the cleaning, upgrading and liquefaction of biogas. A process
scheme showing the modules can be found on web site of GtS.
In two of the modules (GTP – Gas Treatment Package, and TCR – Total Contaminant
Removal), the gas is essentially compressed to 17-26 bar(a) and then
cooled down for the removal of moisture. Both modules integrate energy recovery
by reheating the dried gas. Because of the low temperature of -25 °C in the TCR
module, also a number of contaminants are removed with the condensate. The
modules can be completed with a SOXIA catalyst to further remove remaining
contaminants.
Following the drying modules, the gas is liquefied in the GPP module (Gastreatment
Power Package). The module consists of two stages which are illustrated in
Figure 1. In the first stage, the gas is further cooled to -50 °C where liquid CO2 is
separated. In the second stage, the temperature is further lowered below the
freezing point of CO2 in two parallel columns. Since CO2 becomes solid at this
temperature, the heat exchangers must be operated batch-wise where one unit is
in operation (online) while the other is defrosted, so the accumulated CO2 becomes
a liquid again and is collected together with the CO2 from the first stage.
The liquid CO2 can either be used for cooling the incoming gas and thereby lowering
the total energy consumption, or be sold as a product. In the case of the production
of compressed biomethane, the upgraded, cold biomethane can also be
used to cool down incoming streams in order to reduce the energy consumption.
Figure 1 The GtS gas upgrading process GPP in the phase diagram for pure CO2.
If LBG is to be produced, the GPP module can be extended by a supplementary
cooling step called GPP+ where the methane is liquefied. This is done by com-
Svenskt Gastekniskt Center AB, Malmö – www.sgc.se 81