Biomethane

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As bio-methane (synonym Bioerdgas ) is methane referred to, that does not fossil origin, but from biogenic produced substances and part of the biogas is. Both natural and technical processes can be used for production. Biomethane is used for the production of electricity and heat in combined heat and power plants (CHP), gas heat pumps , fuel cells and as fuel for vehicles. Before it is used and distributed, the biogas produced must be processed into biomethane and separated from other gas components.

Emergence

Main article methane

Methane can be produced technically as well as naturally occurring. Biomethane can be produced technically using synthesis gas from biomass gasification. The biomethane produced in this way is also known as synthetic natural gas .

Currently, however, the so-called "biogas" is used more frequently. It is created when organic material decomposes in the absence of oxygen. Technically controlled, these processes take place in biogas plants . The largest fraction of the biogas produced is methane (CH 4 ) with 50 - 75%. In addition, mostly carbon dioxide (CO 2 ) is produced, but also other gases such as N 2 , NH 3 , H 2 , H 2 S , O 2 , volatile organic compounds , siloxanes and thiols . For the production of biogas in biogas plants, energy crops , liquid manure , straw (residues from the grain harvest) and occasionally organic residues are used as substrates . Biomethane also occurs naturally as a component of the biogas in oxygen-free layers under the earth's surface, moors , swamps , anaerobic areas of sediments and rice fields , as well as uncontrolled in landfills , liquid manure containers or through emissions from animal husbandry .

In 2012 the first plant was put into operation in Zörbig ( Saxony-Anhalt ), which can produce 260,000 tons of biomethane annually from (2017) straw . The German Biomass Research Center in Leipzig estimates the potential in Germany at 8-13 million tons, in Eastern Europe at 240 million tons, with 8 million tons corresponding to 2.5 gigawatt hours or clearly the energy requirements of 4 million natural gas vehicles.

processing

Main article biogas upgrading

Before being fed into the gas pipeline network, the raw gases produced by fermentation and saturated with water vapor are upgraded to natural gas quality. This gas treatment mainly includes the removal of water, carbon dioxide and hydrogen sulfide , as well as conditioning and compression . In order for biomethane to be used as a natural gas substitute, the calorific value ( Wobbe index ) must be adjusted . Depending on the technical and economic boundary conditions, various gas processing methods are used and combined with one another.

The first steps of processing and rough cleaning (dehumidification and desulphurisation ) take place in the biogas plant. After these steps, the raw biogas produced contains an average methane content of 50 to 60% and a carbon dioxide content of 35% to 45%. The rest is made up of nitrogen, oxygen and other gases.

In the downstream processing to biomethane, the component carbon dioxide and remaining traces of hydrogen sulfide in particular are removed from the biogas by various physical or chemical processes ( absorption , adsorption or filtration ) and the methane is greatly enriched. The resulting biomethane is conditioned (calorific value adjustment using LPG (liquid gas) such as propane and butane or air) and then compressed for feeding into the natural gas network or for provision as biofuel .

Furthermore, important parameters of the fed-in gas ( calorific value , calorific value , Wobbe index , density, etc.) and the amount of energy transferred (billing calorific value ) must be determined using a gas quality measurement . The aim of these requirements for the gas quality is to provide the same gas quality (especially with regard to the calorific value) for the users and to bill the amount of energy used. In addition for safety reasons the odorization of gas, so that the transparent and odorless gas can be detected via the sense of smell.

Possible processing steps are:

  • Desulphurisation as hydrogen sulphide would lead to corrosion
    • Coarse desulfurization
      • Biological with sulfur-oxidizing microorganisms
      • Chemically with precipitants such as iron oxide, which bind S
    • Fine desulphurisation by adsorption on activated carbon or zinc oxide
  • Gas drying against corrosion through compression and / or cooling
    • Adsorption Binding of water to silica gel or aluminum oxide
    • Condensation by cooling
  • CO 2 separation pressureless amine washing , pressurized water washing , pressure swing adsorption or membrane technology
  • Conditioning Adjustment of the calorific value via gas composition
  • Odorization so that escaping gas is recognized by its smell
  • Compression to line pressure

The processing of biogas / sewage gas under normal pressure and feeding into the natural gas network at a pressure of less than 100 mbar was implemented in Meilen (Switzerland) for the first time worldwide in June 2008 using the BCM process and has proven to be significantly more energetically advantageous than processing under pressure. Since this biomethane is used locally on site, the transport costs for natural gas are also reduced. Compared to processing under pressure, there are significantly lower methane losses with pressureless processing to biomethane. Propane dosing to adjust the calorific value is dispensed with here. Propane can thus be used as a high-quality chemical raw material instead of being burned.

feed

With regard to the biogas quality, there are three standards for the feed-in:

  • Replacement gas (corresponds to natural gas quality; unproblematic feed-in when adjusting the pressure) B. processed biogas (also known as biomethane), processed mine gas or synthetic natural gas
  • Additional gas (limited admixture; different composition and amount of energy to base gas). The possibility of admixture is strongly dependent on the gas quality and the range of uses in the downstream gas network.
  • Purified biogas , which has not yet been adapted to the nature of natural gas by separating CO 2 , is fed into so-called satellite systems in small local networks, usually with satellite CHP units and a heating network via a separate line. There is no mixing with fossil natural gas.

For biomethane to be taken over into the natural gas network, its essential properties must correspond to natural gas . Within the fuel gas family "Methane-rich gases" defined by DVGW worksheet G 260 and the groups L ("low") and H ("high") contained therein, the biomethane must comply with the following values:

  1. Wobbe index of L-Gas: W S, N = 11.0-13.0 kWh / m³, nominal value = 12.4 kWh / m³; may drop to 10 kWh / m³ for a limited time.
  2. Wobbe index of H gas: W S, N = 13.6-15.7 kWh / m³, nominal value = 15 kWh / m³; may be limited to 12 kWh / m³.

Especially within the H group, appropriately processed biogas with extensive carbon dioxide removal with a calorific value of around 10.6 kWh / m³ is only possible as an additional gas. (Without enrichment with e.g. propane , no gas with a higher calorific value than that of pure methane (11.06 kWh / m³) can be generated by processing biogas.)

Spread and Economics

Because of the amount of investment required, biogas processing is only considered economical from a capacity of around 250 m³ to 500 m³ of biomethane per hour. This corresponds to an electrical system output of 1 MW to 2 MW with direct biogas conversion in the combined heat and power plant (CHP). In Germany, 190 plants for biomethane production with a total capacity of 1 billion m³ per year were in operation in November 2017. For 2017, 191 running systems with a capacity of 113,000 m³ / h are expected nationwide. The declared goal of the federal government is for around 60 billion kWh of biomethane to be generated per year in Germany in 2020. This corresponds to the capacity of around 1200 to 1800 biomethane plants and thus a new construction of at least 120 plants per year with an investment volume in plant technology of 10-12 billion €. To provide the energy crops for biogas production, 1.2 million hectares of arable land would have to be available by 2020. In order to achieve the target, biogas production would have to increase by 150% compared to 2007, provided that all biogas is converted into biomethane. If electricity is generated in CHP units, around 4% of the electricity requirement could be covered.

Like biogas, biomethane is subsidized in particular through the Renewable Energy Sources Act . Competitiveness compared to the substitute energy natural gas is neither given nor foreseeable at the moment. Assuming the continuation of the classic oil price indexation of the natural gas price, the economic viability threshold of biomethane would be beyond the (previously unattained) US $ 230 / barrel of Brent crude oil. However, it is questionable whether the oil price link will continue to exist in the future - at least in its current form. On the domestic German natural gas market, wholesale prices are increasingly prevailing , for example the listings on the Leipzig energy exchange EEX , which are usually below the oil-indexed prices.

use

Biogas and biomethane as a link in the sector coupling.

Biomethane can be used for energy either by feeding it into the natural gas network (bio natural gas) or as a biofuel for natural gas vehicles . While feed-in is becoming increasingly important, the use of biomethane as a fuel has so far only been a niche application. In Mecklenburg-Western Pomerania, up to 10 percent bio-natural gas will be added to natural gas fuel from 2011. In November 2010, Stadtwerke München (SWM) had already started adding 50 percent bio natural gas to its seven natural gas filling stations in the city.

Feeding into the natural gas network

When gas is extracted from the natural gas network, the differentiation between natural gas and biomethane is made theoretically. An amount of natural gas equivalent to the biomethane fed in is taken from any point in the network. Individual gas suppliers offer the delivery of natural gas with a biomethane content for a surcharge, as a more environmentally friendly alternative to pure natural gas.

Use for heat and power generation

A large part of the biomethane fed into the natural gas network is used to generate electricity and heat, as some of the operators receive higher electricity payments under the Renewable Energy Sources Act. Various technologies are used to utilize biomethane:

  • Combined heat and power plants (BHKW): A gas engine drives a generator. In decentralized use, the system is operated according to the heat demand, the electricity is used itself or fed into the distribution network.
  • Fuel cells (FC): The biomethane is broken down into carbon and hydrogen and reacts in the FC on a membrane with oxygen to form water and CO 2 . The fuel cell is usually operated with heat. The electricity is used itself or fed into the distribution network. The overall efficiency is higher than with the CHP.
  • Gas heat pumps (GWP): A gas engine drives a compressor. Also heat guided; no power feed. Different temperature levels from the heat pump, engine cooling water and engine exhaust allow a wide variety of applications.

Use as fuel

Comparison of biofuels in Germany
Biofuel Yield / ha Fuel equivalence
[l]		 Fuel equivalent
per area [l / ha]		 Mileage
[km / ha]
Vegetable oil (rapeseed oil) 1590 l 0.96 1526 23300 + 17600
Biodiesel (rapeseed methyl ester) 1550 l 0.91 1411 23300 + 17600
Bioethanol (wheat) 2760 l 0.65 1794 22400 + 14400
Biomethane (with corn) 3540 kg 1.4 4956 67600
BtL (from energy crops) 4030 l 0.97 3909 64000
BtL (made of straw) 1361 l 0.97 1320 21000
  1. ↑ 1 l of biofuel or 1 kg of biomethane corresponds to this amount of conventional fuel
  2. ↑ without by-products
  3. ↑ separate calculation, not based on the other data
  4. ↑ a b c with biomethane from by-products rapeseed cake / stillage / straw
  5. ↑ a b based on FT fuels

Biomethane, like natural gas , can be used as a fuel in motor vehicle engines, but so far biogas has rarely been used in this way. Vehicles that have been converted to run on pure or bivalent natural gas can also run on biomethane. In contrast to natural gas, however, biomethane is almost CO 2 -neutral. When biomethane is fed into the natural gas network, the natural gas used as fuel also contains a proportion of biomethane.

There are currently around 130 natural gas filling stations in Germany that sell 100 percent bio-methane. Of these, 115 are currently being supplied by the biofuel manufacturer Verbio .

The start of the market launch of the fuel cell, the high electrical efficiency that can be achieved and the long service life that has now been achieved make the use of biomethane in fuel cells appear interesting in the future, as electricity and heat are generated from renewable raw materials.

legal framework

The feed-in of biogas is determined by numerous legal regulations, including in Germany the Renewable Energies Act (EEG), the Renewable Energies Heat Act (EEWärmeG), the Energy Industry Act, the Gas Network Fee Ordinance and DVGW regulations . The Gas Network Access Ordinance (GasNZV), which has been in force since April 2008, has made biomethane access to the natural gas network significantly easier. In addition, the ordinance specifies the Federal Government's objective for expanding biogas feed-in: 60 billion kWh of biogas should be fed into the gas network annually by 2020 and 100 billion kWh of biogas by 2030. That would be around a tenth of the 930 billion kWh of natural gas consumed in Germany in 2008.

literature

Individual evidence

  1. ↑ verbio.de
  2. ↑ A. Tilche, M. Galatola: The potential of bio-methane as bio-fuel / bio-energy for reducing greenhouse gas emissions. In: Water Science and Technology. Vol. 57, No. 11, London 2008.
  3. ↑ verbio.de
  4. ↑ AL: Making biomethane out of straw. In: ZfK - newspaper for local economy. April 2012, p. 36.
  5. ↑ S. Rahmesohl et al.: Analysis and evaluation of the possible uses of biomass. Investigation on behalf of BGW and DVGW. Volume 1: Overall Results and Conclusions. Wuppertal / Leipzig / Oberhausen / Essen 2006, p. 23.
  6. ↑ F. Burmeister et al.: New aspects of biogas conditioning. In: GWF, Gas, Erdgas. No. 6, 2008, p. 358 ff.
  7. ↑ S. Rahmesohl et al.: Analysis and evaluation of the possible uses of biomass. Investigation on behalf of BGW and DVGW. Volume 1: Overall Results and Conclusions. Wuppertal / Leipzig / Oberhausen / Essen 2006, pp. 20ff.
  8. ↑ a b Biogas partner - project list Germany ( Memento of the original from March 1, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . @1@ 2Template: Webachiv / IABot / www.biogaspartner.de
  9. ↑ EMPA, Technology and Society Lab, Life Cycle Assessment & Modeling Group on behalf of Erdgas Zürich, October 2009 ( Memento of the original from September 23, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed May 12, 2015. @1@ 2Template: Webachiv / IABot / www.biogaspartner.de
  10. ↑ S. Rahmesohl et al.: Analysis and evaluation of the possible uses of biomass. Investigation on behalf of BGW and DVGW. Volume 1: Overall Results and Conclusions. Wuppertal / Leipzig / Oberhausen / Essen 2006, p. 50ff.
  11. ↑ Institute for Energy Technology IfE GmbH, 2011
  12. ↑ DVGW: G 260 worksheet 03/2013 gas quality ( memento of the original from June 9, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / www.wvgw-shop.de
  13. ^ J. Schiffers, A. Vogel: Final report for the BMBF joint project "Biogas feed". Volume 5: Technical, legal and economic obstacles and solutions when feeding biomethane into the natural gas network from the perspective of a gas company. (PDF; 1.3 MB). E.ON Ruhrgas AG, Essen June 2009.
  14. ↑ biogaspartner.de ( Memento of the original dated December 22, 2017 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.biogaspartner.de
  15. ↑ Use of biogas in rural areas - the contribution of various plant concepts to regional value creation and their environmental performance.
  16. ↑ Development of renewable energies up to 2008 ( memento of October 7, 2009 in the Internet Archive ), statistics and graphics, BMU 2009.
  17. ↑ Sebastian Herold: Bio natural gas between market and state. Münster 2012, ISBN 978-3-00-037292-6 , www.energy-thinker.net .
  18. ↑ Hinrich Neumann: Run on biomethane surprises the industry. (pdf). In: top agrar. 2/2009, pp. 116-120.
  19. ↑ asue.de ( Memento of the original from December 22, 2017 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. . @1@ 2Template: Webachiv / IABot / www.asue.de
  20. ↑ a b c d Biofuels Basic Data Germany, as of October 2009 Fachagentur Nachwachsende Rohstoffe e. V. (FNR), Gülzow, 2009, 14-page brochure, available as pdf
  21. ↑ a b c d Biofuels basic data Germany, as of January 2008 Fachagentur Nachwachsende Rohstoffe e. V. (FNR), Gülzow, 2008, brochure, no longer available as a pdf due to the updated version
  22. ↑ Stadtwerke Rastatt switch to verbiogas. ( Memento of January 14, 2016 in the Internet Archive ) Verbio press release of January 17, 2013.
  23. ↑ fz-juelich.de .
  24. ↑ Gas Network Access Ordinance (GasNZV), Section 41a.
  25. ↑ German Energy Agency: www.Biogaspartner.de - Politics and Law ( Memento of the original from March 1, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . @1@ 2Template: Webachiv / IABot / www.biogaspartner.de

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