More about biogas

Bio gas plants and production of biogas

Bio gas plants

In general it is said that there are two types of biogas plants, Landfill- and sewage gas plants. Landfill gas is formed during the natural degradation of organic material in a landfill. The degradation (fermentation) in a landfill requires a long period of time. It is generally said that the main part of the organic material is degraded and the main part of the gas is formed after a period of 20 years. Sewage gas is formed during a controlled degradation (fermentation) process and after 20-30 days the main part of the organic material has been degraded. In a biogas plant the produced biogas is separated from the remaining substance after fermentation for further transport to a utilizer.

Except from gas also a nutritious rest product, is produced in a sewage gas plant. This rest product is commonly called bio manure and can after approved quality control be used as manure on fields.

Production of biogas

As earlier mentioned bio gas is formed when organic material breaks down in an environment free from oxygen (anaerobic conditions) The process is called fermentation. Biogas has a heat value of 5-8 kWh/ Nm3 (normal cubic meter), depending on the content of methane. Normal cubic meter is a standard definition of a gas with the pressure 1013 mbar at the temperature 0°C. Most easy decayable organic material can be used as raw material when producing biogas.

A large part of this material can be found in the agricultural sector partly in the form of manure, partly as waste and other rest products.

Biogas can also be found in the nature in eg. svamps, bogs, and in the stommach of chewing cattle. In the industry the aim is to imitate the process which takes place in the stomach of chewing cattle.