Biogas is coming out of the anaerobic digesters saturated with water vapour. At the usual digester temperature of mesophilic anaerobic digesters of around 30°C, this means that the biogas contains about 5% water, or about 50 g/Nm³ biogas. If the temperature of the biogas subsequentely drops, some of that water will condense into liquid.

In case the biogas pipeline from the digester(s) to a biogas burner(s) is long, with many ups and downs, and/or has certain part of its trajectory under ground or in a culvert below grade, then this condensation will give rise to the build-up of water pockets, resulting in pressure fluctuations and surges which will disturb or trip the biogas reuse system.

In case the biogas is used as fuel in electrical power generators, there are limits imposed on the humidity of the biogas at the inlet of the engines (usually 70 – 80%), in order to avoid damage to the engines.

As a solution for these problems, GWE, in collaboration with its long time partner DWS (Belgium), has developed a biogas drier system called GASODRIX™.

The GASODRIX™ biogas drier package unit used consists of a stainless steel biogas/refrigerant heat exchanger and a refrigerant cooling group with a compressor, a condenser, a storage tank, and an evaporator.
The biogas at typically 30 – 40°C is cooled to 5 – 10 deg C, after which ca. 60 – 70% of the water vapour (about 35 g/m³) condenses to water, which is separated from the gas in and after the heat exchanger.

The remaining moisture in the biogas is about 10 – 15 g/m³, and acceptable, considering the fact that the biogas is heated again in the biogas compressor and then cools off to ambient temperature which in subtropical and tropical climates is mostly between 15 and 35 deg C.

In case the application is in cold countries, the refrigeration drier might not be sufficient, especially in winter. For this case, and also for very large biogas flows, GWE/DWS have developed an alternative using absorption of the water vapour by glycol in an absorption tower. The absorbed water is then removed from the glycol in a recovery column (by heating, using some of the biogas), after which the glycol is returned to the absorption tower.