Biogas
Biogas, produced by the fermentation of biomass, is utilised worldwide to supply energy in various ways: by burning it in combined heat and power plants for power generation using waste heat (combined heat and power, CHP), as biomethane fed into the natural gas grid after appropriate processing of the biogas, as fuel for natural gas vehicles or directly for cooking.
The German biogas industry has taken a pioneering role in the field of generation and utilisation of biogas. Germany is both the market and technology leader, particularly in the area of gasification based on organic waste and renewable sources. German companies in the biogas industry cover the entire value chain of biogas technology – from planning and financing to the operation and maintenance of biogas plants – and have many years of experience in process biology and its associated laboratory services. Sophisticated products are also available in the fields of combined heat and power plants, storage and tank systems as well as biogas analysis technology.
BioConstruct GmbH
90 % of the raw material for this biogas plant in Linne, Germany, comes from liquid manure. After fermentation, the digestate is used as high-quality fertiliser for fields
Technologies and applications
Biogas can be extracted from a variety of sources such as organic waste from landfill sites (landfill gas), municipal wastewater (sewage gas), and industrial /domestic / commercial organic waste, as well as from agricultural waste materials and energy crops. The fermenting process of organic substances in an air- and oxygen-free environment uses various anaerobic bacteria, the composition of which depends on their organic feed stock and specific process conditions (temperature and pH level). A decisive factor in the productivity of biogas plants are the microbiological processes that occur during fermentation.
As a rule, agricultural biogas plants use liquid manure as a base material. Renewable sources such as corn, cereal crops and other energy plants such as sunflowers, Sudan grass, sugar beets, oil radishes, sweet sorghum, etc., are increasingly being used to increase gas yields. Commercial plants also process wastewater (from purification plants) as well as waste from food production, food scraps, grease traps and slaughterhouse waste. The extracted biogas is primarily a mix of 50 – 75 % methane and 25 – 45 % carbon dioxide as well as trace amounts of water (2 – 7 %) and gases such as hydrogen sulphide, oxygen, ammonia and hydrogen. Aside from the biogas itself, a digestate is created – a mix of water, minerals and organic substances, which have not decomposed. This by-product can be used as a high-grade fertiliser by farmers, thereby closing the nutrient cycle with the cultivation of energy crops, or it can be sold as mineral fertiliser.
- Using biogas to generate electricity and heat
The stationary use of biogas in combined heat and power plants (CHP plants) for generating power and heat achieves a very high degree of efficiency. The electricity produced can be fed into a public grid or used as an independent power supply for industrial and commercial areas, or even provide power to remote rural settlements with no grid connection. The waste heat can also be utilised in downstream systems to generate additional power, for heating and drying or in the operation of refrigerators. In order to obtain higher power yields from CHP plants, researchers are investigating the use of biogas in fuel cells, which can convert the chemical energy of the processed biogas directly into electricity. Fuel cells have been expensive up to this point, but they work quietly and reach electrical efficiency levels of up to 50 %.
Schmack Biogas GmbH
Biogas upgrading plant in Schwandorf, Germany
If there is no appropriate heat sink at the plant location, the feed-in of biogas into the natural gas grid, after processing into natural gas quality (biomethane, methane content of up to 98 %), is an attractive option. This enables biogas to be used in areas with a high demand for heat and achieves maximum efficiency by producing power (CHP) at the same time. The decoupling of production and utilisation provides, in principle, an opportunity to use the biogas as fuel for natural gas vehicles. In developing and emerging nations, biogas generated from simple biogas plants is primarily used as an economical alternative to electricity, natural gas or wood for cooking.
