Whether in bogs and marshes or in the digestive tract of ruminants: biogas is formed everywhere where is decomposed organic material in a humid environment under oxygen conclusion. Various bacteria, including methane bacteria that make the main work. This process is technically reproduced in a biogas plant. The bio gas yield, but also the composition of biogas vary depending on the composition of raw materials and of the procedure and process technology. The energy content of biogas is finally directly depends on the methane content. So has a cubic metres (m ³) methane an energy content of about ten kilowatt hours (9.97 kWh).
With entry into force of the renewable energies Act (EEG) significantly increased the number of biogas plants in Germany. End of 2013 were more than 7,850 biogas plants with an electrical output of over 3,500 MW to the grid and delivered as much electricity as three more nuclear power plants.
The raw materials
Biogas can be produced from a variety of organic starting materials. In agricultural systems, mostly specifically grown energy crops and animal excrements (slurry and manure) serve as substrates. The use of manure and other manures is not only from the perspective of climate protection (emission reduction) and cascade use of great importance, but also has a stabilizing the process action. Renewable raw materials are example maize, cereals, grasses, sunflowers & v. m. in question, where the corn currently occupies the highest production volume as a crop with high mass and gas revenues as well as the least specific cost. Negative the high maize cultivation in some regions can affect but on soil fertility and biodiversity.
Building a biogas plant
An agricultural biogas plant consists of the basic elements before pit/substrate placement, fermenter with agitator, bio gas utilization (such as block heat and power plant or gas processing), gas storage and fermentation residue storage. In the pit before the substrates are stored, if necessary, crushed, diluted and mixed and reach into the heated and insulated fermenter. He is the core of the plant and must be gas - and water resistant as well as opaque. Appropriate mixing technology ensures the uniformity of the fermentation substrate and supports the formation of gas. Biogas into the gas storage while the fermented out substrate in the fermentation rest camp is transported, which typically also serves as Nachgären containers.
The liquid or solid residue of fermentation is called a Digestate or compensation and used mostly as organic fertilizer by farmers due to its high nutrient content. The fermentation process in the fermenter in principle expire in four interdependent steps under anaerobic conditions (without oxygen) in which different groups of micro-organisms are involved. The mixture of gases formed consists mainly of methane (50-75%), carbon dioxide (25-45%) and small amounts of water vapour, oxygen, nitrogen, hydrogen sulphide and other trace gases.
Basically, the four phases take place simultaneously and in parallel. Due to the different environmental conditions of different micro-organisms, therefore a compromise of the optimal parameters, such as in particular fermentation temperature, Ph or nutrient supply, must be found.
Preparation and use - of biogas
Biogas offers a variety of usage options. It can be used both for electricity and heat generation and as fuel and natural gas equivalent. In addition, biogas is can be stored and transported through the natural gas grid, and this at any time and regardless of the source available is. The energy production from biogas is subject to a daily and seasonal or weather fluctuations and can be thus as needed and also continuously.
Thanks to fixed remuneration rates by the EEG for the electricity generation is the generation of electricity and heat directly on the currently primary type of use of biogas biogas plant. You done in block heat and power plants (CHP), one speaking of combined heat power (CHP), because at the same time generate electricity and heat.
Basically, biogas is suitable also as a fuel for fuel cells, Stirling engines, and micro gas turbine. Benefits of these technologies, such as greater efficiency and lower operating costs, are overlaid then one day due to the higher costs.
In recent years the preparation and injection of biogas into the natural gas network is increasingly has become also. End of 2013 more than 140 biogas treatment plants produced approximately 86,000 standard cubic metres of bio-methane per hour. When preparing the desired methane is separated from carbon dioxide and other companion gases and the Biomethane (called also bio natural gas) can be used as a substitute natural gas. Due to the existing infrastructure of the natural gas network, bio methane can then be transported over arbitrary distances and decoupled from production to places with great demand in CHP plant or for the generation of heat used. Also, bio-methane is used as fuel in natural gas vehicles - and rising.