Summary

Synthetic Natural Gas (SNG) can be produced by the methanation of synthesis gas, that is carbon monoxide and hydrogen, which can be produced from biomass via gasification processes. This chemical reaction has been demonstrated as early as 1902 by Sabatier. Methanation is a strongly exothermic process. Thus, heat removal is one of the main problems for the integration of methanation processes e.g. into thermo-chemical biorefineries or other plants. The methanation process has to be catalysed. The methanation catalyst most commonly used is based on nickel, which makes it very vulnerable to poisoning, e.g. by sulphuric components. Poisoning of catalysts leads to catalyst deactivation which should be avoided. Synthesis gas conditioning and cleaning depends on the process conditions and on the catalyst used.
A couple of different concepts are available for the methanation of biomass derived synthesis gas:

• fixed bed cascade concepts with intermediate gas cooling
• fixed bed concepts with recirculation and/or split streams
• fixed bed reactors with internal cooling
• fluidised bed concepts

All of these named concepts have specific advantages and disadvantages, e.g. some of them are technically complicated, but may provide steam on different temperature levels. The optimisation of the heat removal concept is essential for overall plant efficiency. There are strong interdependencies with other units at the refinery or plant as well as with the district heat infrastructure. Thus the qualified design of the methanation unit is essential for overall success.

There are different providers of methanation technologies, including larger companies such as Lurgi (Air Liquide Group) or Haldor Topsøe as well as smaller companies as CTU.

If properly designed, it is possible to provide steam and heat to private and industrial consumers on different temperature and pressure levels. The acid gas and impurities removal system is an important factor in costs and environmental issues, and the utilisation and/or disposal of carbon dioxide and sulphuric components have to be taken into account.

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