Liquid biomethane

from Wikipedia, the free encyclopedia

Liquid biomethane , also known as LBM (Liquefied Biomethane), Bio-LNG or Renewable LNG , is a climate-neutral fuel made from liquefied, regeneratively produced methane when fully burned . It enables the transport and storage of large amounts of renewable energy and is the direct replacement for LNG (Liquefied Natural Gas) from fossil natural gas . The problem with the use in engines is i. d. Usually , however, the methane slip , up to approx. 2% of the methane was released unburned into the atmosphere. Since methane is around 20 to 25 times more harmful to the climate than CO 2 , as an alternative fuel in ship engines, it is more harmful to the climate than diesel. This problem should not occur in some 2-stroke engines. In the production of methane-based fuels, however, methane slip is also problematic and should amount to up to 8%.

properties

The liquid biomethane (LBM) produced from regenerative raw materials is a high quality biofuel with a high energy density . It combines the advantages of liquefied natural gas as a fuel with climate neutrality.

Liquid biomethane remains liquid under atmospheric pressure at −162 ° C (boiling point with over 99.6% biomethane content), can be stored and easily transported. The cryogenic energy source opens up the possibility of storing bioenergy for a long time or replacing LNG. The calorific value is 5870 kWh / m³ at −162 ° C. Compared to biogas with, for example, 55% biomethane and only around 5.5 kWh / m³ at 21 ° C, the energy density is around a factor of 1000 higher. Compared to LNG, which contains an average of 98% methane and 2% ethane , liquid biomethane can contain up to 99.8% methane. The rest is carbon dioxide. One standard cubic meter of liquid biomethane contains 600 standard cubic meters of gaseous biomethane. The calorific value in regasified form is up to 11.04 kWh / m³ and in liquid form up to 6622 kWh / m³.

In comparison, gaseous biomethane for natural gas vehicles is compressed by compression up to a maximum of 240 bar (CBM, Compressed Biomethane). In relation to the calorific value , liquefied methane produces 28% less carbon dioxide than diesel fuel . In terms of carbon footprint , LBM and LNG are 28% better than heavy fuel oil for ships. Compared to heavy fuel oil, the energy density of liquefied biomethane and LNG is only about half as great.

Like LNG, LBM produces almost no nitrogen oxide and hardly any particle emissions during combustion. Furthermore, no heavy metal or sulfur oxide emissions are to be expected. If methane escapes during transport, storage or incomplete combustion in the combustion chamber of engines (methane slip), it is up to 30 times stronger in the atmosphere than the greenhouse gas carbon dioxide.

The dangers of refrigerated liquid fuel are the same as with liquefied natural gas. The expansion ratio from liquid to gas is 1: 600. Under atmospheric pressure, the liquid is cooled by the evaporation cold released at the boiling temperature , whereby gaseous methane escapes and should be collected. In closed 40 bar pressure vessels, the liquid can heat up to −120 ° C without danger.

Preliminary products

As with bio-SNG and compressed biomethane (CBM, Compressed Biomethane) , all gases with methane content that arise from waste or biomass can be used as raw materials.

In line with sustainable requirements, preference is given to using biogas, sewage gas and easily accessible sources in the open (landfill gas) for liquefied biomethane. Biomass gasification has the advantage that a lot of biogas can be generated in a small space in a short time, but high temperatures are a prerequisite for this, which reduces the efficiency.

Manufacturing

A prerequisite for an economically sensible liquefaction of biogas with industrial methods has been a volume flow of around 250 m³ / h. The process begins with biogas upgrading , in which vapors and gases are removed before the cleaned gas is cryogenically liquefied .

Small plants for decentralized biogas plants

In order for a liquefaction with a volume flow of 25 m³ / h raw biogas to be economically viable, the effort must be kept small and profitability through the production of marketable dry ice necessary.

This means that no gases or vapors that are not already contained in the raw biogas are supplied during the entire process. Toxic solid materials are also avoided. Consumables are minimized or avoided. Filters and adsorbents should be able to be regenerated as often as possible or taken to normal waste disposal. Any solutions and condensates that arise should be recyclable or reusable. The cryogenic liquefaction plant should be as maintenance-free and simple as possible.

Under these conditions, sulfur compounds, ammonia and water vapor must be completely removed by anaerobic gas treatment. The coarse desulphurisation is already carried out in the fermentation material using an internal chemical desulphurisation process. The fine desulfurization below the detection limit is achieved by a specially adapted activated carbon filter and regenerable iron-containing pellets through adsorption . Ammonia is first reduced in a gas scrubber and the remains are bound in activated carbon. The raw gas has 37 ° C and almost 100% rel. Humidity. The gas is dried by condensation on a cool surface. Residual moisture is absorbed by regenerable silica gel and regenerable zeolites . In a biogas plant with combined heat and power , the raw biogas is processed in a similar way, resulting in synergy effects.

This is followed by pressure-free three-stage cryogenic cooling. In the pre-cooling, the gas is brought to around −78 ° C, which freezes out the last residues of hydrogen sulfide, ammonia and water vapor . In the second cooling stage, the treated BioGas is brought to around −153 ° C. In the process, carbon dioxide resublimates condensation nuclei to form dry ice in the form of flakes or solid crystals. The third and final cooling stage produces liquefied biomethane at around −163 ° C. While the methane condenses, the oxygen and nitrogen remain gaseous and are diverted. It remains liquid biomethane with a purity of 98-99.8%. The rest is carbon dioxide. It seems that 0.2% carbon dioxide cannot be prevented, but higher concentrations indicate too few condensation nuclei or too high a gas flow in the second cooling stage.

Storage and transportation

With the LNG tank and transport infrastructure that has been built up for 60 years, the liquefied biomethane can be stored, transported and marketed worldwide.

The liquefied biomethane must be kept at a constant low temperature. The easiest way to store large amounts of LBM or LNG is to store them at atmospheric pressure in highly insulated cryotanks . The cryogenic temperature is kept at the boiling point by the evaporation cold. The resulting gaseous biomethane, technically called boil-off gas (BOG), is captured. With lossless storage, this biomethane gas is cryogenically reliquefied and returned. This process can take place passively using liquid nitrogen (LIN, boiling point −196 ° C) or actively using a cooling unit. If the boil-off gases are otherwise consumed or flared , storage is lossy.

The liquid biomethane can also be stored in pressure-resistant cryotanks at a temperature of −120 ° C.

A suitable tank truck can transport 14,000 liters of liquid biomethane or LNG.

use

Liquid biomethane (LBM) can replace the LNG (Liquefied Natural Gas) obtained from fossil natural gas without conversion costs. Before use, it regasifies to almost pure biomethane. The main areas of application are:

  • Climate-neutral transport of people and goods by buses, trucks and ships
  • Sustainable power generation
  • Storage of bioenergy
  • Power refinement through planned dispatch or by reacting to the power exchange
  • Injection into the natural gas network as climate-neutral biomethane
  • Climate-neutral heat generation
  • Sustainable energy supply for stand-alone systems

During the regasification of the cryogenic LBM, cold occurs as a by-product. This usually remains unused, but can be used for cooling in air conditioning systems, cold rooms and the like. Ä. Be used further.

Liquid biomethane is burned in pure gas engines , dual-fuel engines and gas turbines . The methane slip is to be minimized through efficient combustion.

Due to LBM / LNG engines in ships, there is hardly any pollution for people in the immediate vicinity, compared to the diesel and heavy oil emissions that are common today . The LBM drive is particularly interesting for the acceptance of port traffic, ferry traffic and inland shipping.

Trucks and buses with LBM or LNG as fuel have twice the range compared to comparable natural gas vehicles with CNG (Compressed Natural Gas) drive.

Biogas plants often deliver base load electricity or electricity at peak consumption times without long breaks in between. The profitability depends on the prices on the electricity exchange. These prices fluctuate depending on whether too much or too little electricity is fed into the grid. Low prices on the electricity exchange indicate an overproduction on the feed-in side. Negative prices are reached several times a year . The storage of biogas in the form of liquid biomethane enables more flexibility in electricity production (electricity refinement) and prevents having to send more electricity into the grid in the event of overproduction. Excess liquid biomethane can be sold.

Individual evidence

  1. ↑ taz from February 7, 2020: New fuel for ships. Pipi for the climate
  2. ↑ Two-stroke ship engine avoids methane slip
  3. ↑ ifeu - Institute for Energy and Environmental Research Heidelberg GmbH: Biomethane as a fuel, a recommendation for action on Biokraft-NachV for practice; Heidelberg 2010
  4. ↑ RP Energy Lexicon: Methane slip
  5. ↑ a b c d e f g h i j k l m Korbinian Nachtmann, Josef Hofmann: Increasing the profitability of biogas plants by converting biogas to liquid biomethane for long-term storage of energy . January 31, 2015 ( infothek-biomasse.ch [PDF; 442 kB ; accessed on January 31, 2020] Conference contribution, IEWT 2015, 9th International Energy Industry Conference - Energy Systems in Transition: Evolution or Revolution? , Vienna University of Technology, February 11, 2015 - February 13, 2015).
  6. ↑ a b c d e f g h Properties of LNG. In: tyczka.de. Tyczka Energy, accessed February 1, 2020 .
  7. ↑ Fachagentur Nachwachsende Rohstoffe eV (Ed.): Basisdaten Biogas Deutschland - Status: March 2005 . Gülzow April 27, 2005 ( istanbullisesi.net [PDF; 309 kB ; accessed on February 2, 2020]).
  8. ↑ a b Data and facts on Liquefied Natural Gas (LNG). In: The DVGW. German Gas and Water Industry Association, accessed on February 1, 2020 .
  9. ↑ a b c d e f g J. Hofmann, et al .: Final report on the research project EW / 14/01 - Production of liquid biomethane from biogas for long-term storage of energy . May 4, 2017 ( 193.175.38.150 [PDF; 3.4 MB ; accessed on January 31, 2020]).
  10. ↑ a b c d e f Sönke Diesener, Dietmar Oeliger, Daniel Rieger: LNG as a marine fuel . Ed .: Naturschutzbund Deutschland (=  Nabu Position ). Berlin May 2016 ( nabu.de [PDF; 154 kB ; accessed on February 1, 2020]).
  11. ↑ a b LNG terminals. In: Linde Engineering. Linde AG, accessed on January 31, 2020 .
  12. ^ A b Korbinian Nachtmann, Sebastian Baum, Oliver Falk: Biogas upgrading to liquid methane and solid carbon dioxide to increase the efficiency and profitability of existing biogas plants. Conference contribution, 11th Biogas Innovation Congress, Osnabrück 2018. In: ResearchGate.net. Researchgate Berlin, May 2018, accessed on February 1, 2020 .
  13. ↑ a b Reliquefaction of boil-off gas at LNG import and export terminals. In: Air Liquide. Air Liquide Engineering & Construction, accessed January 31, 2020 .
  14. ^ André Germann: Environment package for "Viking Glory". In: THB - daily port report. DVV Media Group, October 29, 2019, accessed on February 1, 2020 .