Biogas is a combustible gas which is produced by fermentation of biomass of any kind. It is produced in biogas plants, including both waste and renewable raw materials are fermented.
The prefix bio points to the " biotic " mode of formation, in contrast to fossil natural gas out, not an origin from organic farming.
The gas can be used to generate electrical energy for the operation of vehicles or to be fed to a gas supply system. For the utilization of biogas is methane content is most important, since its combustion releases energy.
- 7.1 Germany
- 7.2 Switzerland
- 7.3 France
- 7.4 Sweden
Starting materials are biogenic materials such as the following:
- Fermentable biomass-containing waste materials such as sewage sludge, organic waste or leftovers
- Organic fertilizers ( manure, dung)
- Previously unused plants and plant parts (such as cover crops, crop residues, and the like )
- Specially cultivated energy crops ( Renewable Resources ).
Different feedstocks produce different biogas yields and depending on its composition, a gas with variable methane content, as the accompanying table shows.
Much of the raw materials, especially manure and crop residues, generally fall free in agriculture, therefore, represents this industry the most potential for the production of biogas. Quite different are the effects of growing energy crops:
- Production competes with food production,
- Monocultures can cause a depletion landscape.
Advantages of biogas can be with the (possible) disadvantages of energy crops weigh ( " LCA ").
Biogas is produced by the natural process of microbial degradation of organic matter under anoxic conditions. Here, microorganisms decompose the carbohydrates, proteins and fats contained in the main products to methane and carbon dioxide. For anoxic conditions are necessary, so the absence of oxygen.
The process consists of several stages, each of which is carried out by microorganisms of various types of metabolism. Polymeric constituents of biomass, such as cellulose, lignin, proteins are first converted by microbial exoenzymes to monomeric ( low molecular weight ) materials. Low molecular weight substances are degraded by fermenting microorganisms to alcohols, organic acids, carbon dioxide ( CO2) and hydrogen ( H2). The alcohols and organic acids are converted by acetogenic bacteria to acetic acid and hydrogen. In the last stage are formed by methanogenic archaea from carbon dioxide, hydrogen and acetic acid, the end products of methane (CH4 ) and water.
The term biogas is collectively used for energy gases that are formed under anoxic conditions by microorganisms from biotic materials:
- Sewage: the gas produced during the cleaning of waste water
- Digester gas: the produced only in the sludge digestion gas
- Landfill Gas: escaping from a landfill gas
The composition of biogas is very different because it depends on the substrate composition and the operation of the digester. In Switzerland the term is used Kompogas; it is produced exclusively from vegetable waste.
Before the biogas upgrading the gas mixture of methane is the main component (CH4) and carbon dioxide ( CO2). Traces are usually also nitrogen (N2 ), oxygen ( O2), hydrogen sulfide (H2S ), hydrogen ( H2) and ammonia ( NH3) included.
Precious in water- saturated generated biogas, the methane contained about 60% is. The higher the percentage, the more energy the gas. Not used are carbon dioxide and water vapor. The raw biogas are disturbing, especially hydrogen sulfide and ammonia. They will be removed in the biogas processing prior to combustion to prevent hazards to humans, odors and corrosion in engines, turbines and downstream components (such as heat exchanger).
Climate and environmental protection
Methane is an important greenhouse gas. Therefore, testing the tightness of biogas plants and its components are a major contribution to climate protection.
Biogas plants are not completely sealed; also for maintenance they must remain accessible. Therefore, the operation of a biogas plant methane, which is a 25 - to 30 - times stronger that heat up effect on the climate than CO2 released into the atmosphere.
Biogas reached its maximum impact and penetration when it is simultaneously used for electricity and heat production; in the so-called combined heat and power (CHP ), it has the best climate in balance. A generation without heat utilization or the purely thermal use of treated biogas into natural gas thermal baths, however, are expected to be suboptimal, as the agency identified for renewable energies.
The biogas plant uses carbon neutral because the CO2 produced previously bound by plants from the air. But there are factors that can worsen the climate balance of biogas plants by the cultivation of energy crops:
In the production of energy crops, it comes at a high energy input. Is powered by corn silage plant consumed as opposed to waste incineration at all stages of production energy: Saatvorbereitung, seeding, fertilization, protection from pests (pesticide production and use ), harvesting, transport, silage, fermentation under agitation and transport of the Gärrestmenge to the fields. The carbon footprint of the power plant can be improved if the necessary energy requirements for the production itself is covered from renewable energy sources, such as when the agricultural machinery used are also operated with fuels from energy crops or green power.
The case of intensive agriculture caused by nitrogen fertilization nitrous oxide ( also known as " laughing gas ") is must in the climate balance be calculated here. The production of nitrous oxide is made by microbes that make up this oxygen from the air and the excessively supplied nitrogen. Nitrous oxide has an approximately 300 times greater global warming potential than CO2. Also the change of land use must be considered: If pasture is plowed for corn fields, the humus contained therein by contact with air CO2 and other greenhouse gases releases.
The cultivation of corn is environmentally controversial. Maize ( Zea mays ) is a grass of tropical origin. The encoder is mounted so that frost is avoided, so the sowing takes place late in the year, the plants are growing well in May / June and harvesting begins in late September. During most of the year, the area planted with corn fields are thus free and are eroded by wind and rain. This can result in entry of pesticides and fertilizers in nearby waters, but also come into the groundwater. The cultivation of maize in Europe is not possible without these aids. This presents a problem because it can be used both to eutrophication and to silting of water bodies. Likewise, there may be drifts of large amounts of dust from dry fields, which in turn affects soil fertility, because in this way the loss of important soil components; there is long-term risk of desertification, which is best known in the United States.
Due to the large-scale cultivation of maize monocultures for biogas production leads to further environmental impacts. Grasslands and wet meadows are converted into arable land, fallow land used again. This has an impact on birds (eg lapwing, skylark, Stork) and other animals, thus losing the food and breeding areas.
Currently, there are an estimated 180 nationwide biogas plants, which are operated by companies of organic farming. Unlike conventional farms with biogas plants of maize plays only a very minor role as an energy crop for organic farmers. More important, however, are clover grass and waste materials such as slurry and manure. Organic farming also offers suggestions for conventionally working farms, which affects about the cultivation of catch crops and catch crops or the simultaneous cultivation of several plants; as well as conventional farms can benefit for their cultivation of energy crops from the experience of organic farms.
Feeding into the natural gas grid
After a comprehensive biogas processing feeding into the natural gas grid can be done. In addition to the removal of water, hydrogen sulfide (H2S ) and carbon dioxide (CO2), an adaptation of the heating value of natural gas in the respective gas network (conditioning) must take place. Due to the high technical complexity, the processing and feed worth currently only available for larger than average biogas plants. The first projects started to 2007. Developments such as the hollow fiber membrane of Evonik Industries of Essen allow cleaning of biogas with a purity of up to 99 percent and bring it so bring on natural gas quality.
In order to reach natural gas quality following processing steps are necessary:
Desulphurisation The desulfurization is required to avoid corrosion. Sulfur is found as hydrogen sulfide ( H2S) in biogas, and its combustion would arise in the presence of water vapor aggressive acids, namely sulfurous acid ( H2SO3 ) and sulfuric acid (H2SO4 ). Most of the hydrogen sulfide content is low, but can in protein-rich substrate (cereals, legumes, animal waste, and the like ) rise sharply. There are various possibilities for the desulfurization, including biological, chemical and adsorptive processes are possible. If necessary, several steps are necessary as coarse or fine desulfurization.
Drying: Since biogas is saturated with water vapor, would be incurred upon cooling untreated biogas significant amounts of condensate, which can cause corrosion in engines. In addition, the formation of water pockets to be avoided. Therefore, the gas must be dried. This is achieved by cooling the gas to a temperature below the dew point in a heat exchanger, the condensed water can be removed, and the cooled gas is passed through a second heat exchanger and reheated to operating temperature. Simultaneously with the drying, the readily soluble in water, ammonia is removed.
CO2 capture: carbon dioxide (CO2 ) is not oxidized and therefore not contribute to the heating value of the biogas at. For achieving high quality of the natural gas heating value of the natural gas the biogas must be adjusted. Since methane is the energy-yielding component of biogas, whose share by removal of CO2 must be increased. The currently employed methods of methane enrichment by CO2 separation are gas scrubbers and pressure swing adsorption ( adsorption on activated carbon ). Besides, other methods such as the cryogenic gas separation ( by means of low temperatures ), or the gas separation membranes under development.
Conditioning: For conditioning the biogas regarding dryness, pressure and heating value is adjusted to the requirements. Depending on the origin of natural gas has different calorific values , hence the higher heating value of the processed biogas must be adapted to the respective network.
Compression: are to be fed into the natural gas grid, depending on the network operation, low to medium pressures up to about 20 bar is required. Since the biogas after preparation usually has a lower pressure, it has to be compressed in accordance with the aid of a compressor.
More cleaning and preparation steps: Add landfill and sewage gases siloxanes and halogenated and cyclic hydrocarbons may be present. Siloxanes cause greatly increased engine wear. The hydrocarbons lead to emissions of toxic compounds. Siloxanes and hydrocarbons can be removed by gas scrubbing, gas drying or adsorption on activated carbon from the biogas.
Biogas is in addition to the self-use in agriculture as a contribution to the energy mix from renewable sources. This is because it is for a base load, that is, that the biogas in contrast to other renewable energy sources such as wind or solar energy is continuously available, on the other, biomass and biogas can be stored, may be thereby contributing to energy supply during peak periods. Because of this, offers this bioenergy sources to compensate for short-term fluctuations in the power supply of wind and solar energy. So far, most biogas plants are continuous, quasi as a base load power plant, operated. To use the energy contained have the following choices: combined heat and power (CHP) site: Biogas is used in a combined heat and power ( CHP) plants for electricity and heat production (CHP ); the current is completely fed into the grid, heat to 60 percent consumed locally.
The heating value or calorific value depends primarily on the particular methane content and is comparable to that of natural.
Commitment to green power
Although biogas plants can be used for the generation of green power, since they represent a memory, the energy gaps, for example, may close in winter if necessary. Biogas plants are often not controlled according to actual needs, but Farmers operate only as an additional source of income, so that to integrated operation, especially in summer a lot of heat is wasted.
In Germany, the combustion of biogas in combined heat and power (CHP) is most commonly used to in addition to heat to produce electricity to be fed into the power grid.
Since most of the biogas yield is achieved by the sale of electricity, is located at the heat consumers a CHP, which produced as the main product flow to the mains supply and feeds heat, ideally in a local or district heating network. An example of a district heating network is the bioenergy village Jühnde. So far, however due to lack of demand for heat used in most agricultural biogas plants on site, only a small part of the heat, for example, for heating the digester as well as residential and commercial buildings.
An alternative is the transport of biogas in biogas lines via micro gas networks. The electricity and heat production can therefore take place closer to the customer, a long heat network with direct line losses can be avoided.
Other types of use
Biogas can be used as a virtually CO2 - neutral fuel in automotive engines. As a preparation to natural gas quality is necessary, the amount of CO2 must be removed as far as possible. So called bio-methane or biogas has to be compressed to 200 to 300 bar in order to be used in converted vehicles can.
In Switzerland, drive trucks of Walter Schmid AG and the associated company Kompogas since 1995 with biogas, the first trucks reached in summer 2010, its one-millionth kilometer. From 2001, also drove the Migros Zurich with Kompogas and, since 2002 McDonalds Switzerland.
So far, however, recovered biogas is rare in this way. 2006, the first German biogas filling station in Jameln (Wendland) was opened.
Because of the high electrical efficiencies could be interesting in the future also the utilization of biogas in fuel cells. The high price of the fuel cells, which elaborate gas purification and in practical tests yet short life prevent a wider application of this technique.
While biogas has moved in the last 10 years in the consciousness of the European population, the end of the 19th century biogas was used for the energy supply in India already. The economic dissemination of biogas use depends primarily on the world energy policy (eg during the oil glut of 1955 to 1972 and the oil crisis of 1972-73 ) and the respective national laws (for example, the Renewable Energy Sources Act in Germany ) from. Regardless of small biogas plants have been built in countries such as India, South Korea, Taiwan and Malaysia to private energy supply, with about 40 million household plants, most are in China.
From 1999 to 2010 the number of biogas plants of about 700 rose to 5905, producing a total of approximately 11 % of electricity from renewable energy sources.
End of 2011, in Germany around 7,200 biogas plants with an installed plant capacity of approximately 2,850 MW. To replace Germany's biogas farmers more than two nuclear power plants and serve more than five million households with electricity.
For the substrate provision 400,000 hectares of land were needed, which corresponds to 2% of total agricultural land. It is believed that the production of biomethane to 2020Vorlage: Future / can be in 5 years to 12 billion cubic meters annually biomethane expanded. This would correspond to a fivefold increase in capacity in 2007. The Renewable Energy Sources Act ( EEG) ensures compared to conventional power increased and guaranteed 20-year feed-in tariff. For the use of the heat, the plant operator receives an additional one, as set out in the EEG bonus for combined heat and power ( CHP bonus ). The use of heat is promoted by high energy prices and financial incentives, and since January 2009, valid Renewable Energies Heat Act.
Since 2007 in Germany offer gas suppliers increasingly a nationwide supply of pure biogas or blended with fossil natural gas for end customers. Nationwide, gas customers can decide with a biogas mixtures of at least five percent for at least one, but a maximum of ten gas tariffs. In Baden- Württemberg owners of new buildings from ten biogas tariffs per Postal code can choose to upgrade their energetic profile with biogas. In Bavaria, Hesse, Saxony and parts of Lower Saxony gas customers can rely on biogas tariffs of at least seven vendors. Laggards in the competition density, however, are large parts of North Rhine -Westphalia, Thuringia, Brandenburg and Mecklenburg -Vorpommern. Here households can only choose between one and five gas companies.
Of particular importance for the electricity market comes to flexibilised biogas plants that can offer an available balance potential of around 16,000 MW in perspective. Within minutes, this capacity could be throttled in oversupply in the network or powered up with rising demand. For comparison, the capacity of the German lignite power plants is estimated by the Federal Network Agency to around 18,000 MW. These fossil power plants could provide only a few thousand megawatts for the short-term balance of solar and wind power is available because of their inherent delay however.
In Switzerland, pure biogas is usually referred to as Kompogas. Many Swiss gas stations a mixture of Kompogas and natural gas is sold under the name " natural gas ". 2010, there were 119 natural gas filling stations in Switzerland, where natural gas is available with a biogas share of at least 10%. These are located mainly in the west and north of the country.
Since 1 January 2009 in Switzerland is considered the most cost -covering feed (CRF ); related to this is an increased feed-in tariff ( feed-in tariff for electricity produced from biogas electricity) for renewable energy, which also includes biogas. The remuneration consists of a fixed purchase price and an additional so-called agricultural bonus, which will be granted if at least 80 % of the substrates consist of manure. The Swiss model of assistance to the sustainable development in the energy sector accelerate, particularly as they promote the manure -based, and thus sustainable biogas plants.
The Swiss support instrument for renewable energies ( CRF) contributes to the biomass utilization into account the fact that no land available for the cultivation of renewable raw materials. So far, the law has caused no substantial increase in agricultural biogas plants in the use of manure. The low attractiveness of green waste as a co- substrate for agricultural equipment and thus energetically untapped potential has led to design biogas companies to new investment models. Combined with solid manure, food waste or organic waste from communities, new possibilities, without the raw materials to be transported over long distances to centralized systems offer. The simultaneous possibility of manure processing represents a novel concept for generating renewable energy
Pioneer of the Swiss Kompogas was interested in energy efficiency contractors Walter Schmid. On the domestic balcony he assumed after the study of literature in the first trials and was the late 80s convinced to use the gas from organic waste. He took with support from federal and cantonal authorities in 1991 in Zürich in Zurich, the first pilot plant in operation, which was formed in 1992 as the first Kompogas conditioning in the normal operation. The company Kompogas created world more plants and Schmid was awarded the 2003 Solar Prize. In 2011, the Kompogas group was completely taken over by the new energies axpo mentioned department of the Axpo Group as Axpo AG Kompogas.
In January 2011, the first biogas plant in the world started operation, which mostly fermented offal.
France represents a potentially large biogas market, which is handled by German plant producers. The country is characterized by a productive agriculture with various high-yielding substrates and by a stable delivery system for electricity and heat production from biogas and biomethane for injection. In the summer of 2013 there were approximately 90 agricultural biogas plants. The announced in April 2013 development plan for agricultural facilities ("Plan EMAA " ) with a target value of 1,000 plants in 2020 signaled an accelerated market development.
In Sweden, the electricity generation from biogas due to lower electricity prices (about 10 Euro-Cent/kWh ) is currently still unprofitable. The largest portion of the biogas (53%) is used for heat production. Unlike other European countries, such as Germany, the processing to natural gas quality ( biomethane) and use as fuel in gas-powered vehicles with 26% is a common variant in Sweden.