The term “biogas” is used as a generic term for energetic gases, which are formed by microorganisms from biotic substances under anoxic conditions (sewage gas, landfill gas, fermentation gas). Biogas is a combustible gas, produced by the fermentation (anaerobic digestion) of biomass. It is produced in biogas plants by the fermentation of renewable raw materials and/or waste . For the utilization of biogas, the methane content is the most important parameter. The average amount of methane in raw biogas is 60%. If the biogas should be used as fuel or fed into the existing natural gas grid it needs to be upgraded.
Biogas is produced by the natural process of microbial degradation of organic substances under anoxic conditions. The process consists of four stages, each of which is carried out by microorganisms of different metabolic types. For further information, please follow the link.
The used raw materials are biogenic materials, such as the following:
- Fermentable, biomass-containing residues (sewage sludge, biodegradable waste, food residues,…)
- Residues from livestock farming (manure)
- Previously unused plants/plant parts (intermediate fruits, plant residues)
- Energy crops (corn, sugar beet)
The raw materials influence the gas composition and the methane content in the gas. A large proportion of raw materials, in particular manure and plant residues, are generally free of charge, which is why these raw materials have the greatest economic potential for the production of biogas.
The European Standard DIN EN 16723-1:2017-0: Natural gas and biomethane for use in transport and biomethane for injection in the natural gas network - Part 1: Specifications for biomethane for injection in the natural gas network, determines the general framework for quality requirements on upgraded biogas.
The Landfill Directive (2003/33/EC: Council Decision of 19 December 2002 establishing criteria and procedures for the acceptance of waste at landfills pursuant to Article 16 of and Annex II to Directive 1999/31/EC) is the legal basis for the production of landfill gas.
In most installations, biogas is used directly on-site for the production of heat and electricity via a gas engine, generator and heat exchanger. Other options are to upgrade the biogas for either grid injection or direct use in transportation.