Synthetic natural gas

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Synthetic Natural Gas or Substitute Natural Gas (SNG) (colloquially also synthetic natural gas ) is a natural gas substitute that is produced on the basis of coal , especially lignite , or biomass (Bio-SNG or biomethane ) using synthesis gas . In order to be able to replace natural gas, SNG must match it as closely as possible in terms of its composition and properties.

history

Processes for producing SNG from coal were developed as early as 1902 and brought to industrial maturity during the oil crisis in the 1970s. This effort stemmed from the fear that accessible sources of natural gas would not be sufficient to supply industrial nations over the long term. At that time, natural gas provided the main part of the raw material supply for energy production and was to be replaced by cheaply available coal. In 1984 a first plant with a daily production of 3.9 million m 3 SNG in North Dakota (Great Plains Synfuels Plant) started production on the basis of lignite. In this plant, SNG with a thermal output of 150 MW each is produced and methanated in 14 parallel gasifiers . The total production is around 15 TWh / a. No further plants were built due to the high investment costs and new discoveries of natural gas sources.

In recent years in particular, biogas has increasingly been used to produce biomass-based natural gas substitutes, which are known as bio-SNG, bio natural gas or biomethane . The production of Bio-SNG from wood gasification is mainly in the development and testing phase .

technology

Synthetic natural gas on the basis of lignite is produced via coal gasification and on the basis of biomass via biomass gasification to produce synthesis gas . In both cases, the resulting synthesis gas is fed to a subsequent methanation after cleaning of particles, carbon dioxide components and sulfur and chlorine compounds. This takes place exothermically and takes place at temperatures from 300 to 450 ° C and a pressure between one and five bar in the presence of a suitable catalyst. The following reactions take place:

The ratio between hydrogen and carbon monoxide can fluctuate sharply when entering the methanation phase, which means that there is a risk of carbon formation via the Boudouard equilibrium , which can be counteracted by increasing the water vapor content. The resulting gas mixture contains up to 50% carbon dioxide and must be further processed for use as an SNG by separating hydrogen and carbon dioxide.

use

While synthetic natural gas on the basis of lignite has been produced in the USA for a long time and fed into the natural gas network, this has not yet been the case with Bio-SNG. There are only demonstration systems such as in Güssing , where the synthesis gas produced is primarily used for direct thermal use.

Processed SNG, like biomethane obtained from biogas , must correspond to natural gas as much as possible in order to be used as a substitute (see Biomethane # Use ). The SNG produced in North Dakota has the following composition: 96.3% methane, 0.02% carbon monoxide, 1.38% hydrogen, 1.1% nitrogen and argon and 1.2% carbon dioxide.

Storage of wind and solar energy in the natural gas network

In 2010, the Fraunhofer Institute for Wind Energy and Energy System Technology (IWES) published the idea of using SNG to store the irregular wind and solar energy in the natural gas network . For this purpose, hydrogen is generated electrolytically, which is then "in connection with CO 2 (e.g. from power generation with fossil fuels or from the processing of biogas) converted to SNG in a methanation unit and stored in the natural gas network."

In 2013 a plant with a capacity of six megawatts was put into operation.

Colloquially, gas obtained in this way is referred to as " wind gas" or "solar gas" .

Individual evidence

  1. a b SNG synthesis. In: Martin Kaltschmitt, Hans Hartmann, Hermann Hofbauer (Hrsg.): Energy from biomass. Basics, techniques and procedures. Springer Verlag, Berlin and Heidelberg 2009, ISBN 978-3-540-85094-6 , pp. 664-665.
  2. a b c d Heinz Hiller et al .: Gas Production. In: Ullmann's Encyclopedia of Industrial Chemistry , Wiley-VCH, Weinheim 2005, doi : 10.1002 / 14356007.a12_169.pub2 .
  3. ^ "Fraunhofer press release: Electricity-natural gas storage" . Retrieved July 20, 2013.
  4. SNG generation . Retrieved May 6, 2010.
  5. Archived copy ( Memento of the original from April 7, 2016 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. (PDF; 29 kB) Inauguration Werlte. @1@ 2Template: Webachiv / IABot / etogas.com