Synthetic natural gas, also known as substitute natural gas (both usually shortened to SNG), describes a variety of natural gas alternatives that are as close as possible in composition and properties to natural gas. SNG can be derived from coal, (waste) biomass or synthesized using surplus renewable energy. The results of the latter two methods are often referred to as bio-SNG/biogas and e-gas/syngas. Depending on the source fuel, SNG can be a low-carbon or even carbon-free substitute for fossil fuels. Thanks to its composition, it can be mixed and used interchangeably with natural gas in all applications. Liquefied or compressed SNG can be transported or stored in the gas grid.
How do SNG production, gasification and methanation work?
Gasification is a non-combustion heating process that turns solid carbon fuels into hydrogen, carbon dioxide and carbon monoxide. If the feedstock used is plant cellulose, the process is thermochemical SNG production and the resulting gas is called bio-SNG. If the gasification results from the natural anaerobic digestion of organic materials, for example, compost, manure or other waste, it is called bio-SNG or biogas and the process is biochemical SNG production. If the hydrogen is created by electrolysis (usually using surplus renewable energy), the process is referred to as Power-to-Gas or Power-to-X and the resulting product is e-gas or syngas. The following methanation process, a chemical reaction aided by a catalyzer at high temperatures, turns the carbon dioxide and carbon monoxide into methane, the main component of natural gas. After a final cleaning step, it can be used in the same way, transported and stored in the same containers and grids or used to directly power gas engines.
How does SNG production and use reduce CO2 emissions?
The environmental impact of SNG depends on two main factors: the feedstock used to create the synthetic gas and the fuel replaced by the gas in its final application. Replacing heavy fuel oil with syngas from a Power-to-Gas reactor that also captures carbon could – under ideal circumstances – potentially cut 100% of emissions all along the value chain. All forms of SNG share one advantage: they can seamlessly be phased into global gas supplies according to availability. As cleaner, carbon-neutral supplies increase and their production becomes more energy efficient as part of the energy transition, they can slowly take over from natural gas.
SNG as energy storage
Synthetic natural gas is a future fuel and an essential component in the energy transition, which will make several energy-intense industries more efficient and sustainable, while lowering their carbon footprint. More importantly, it is also a flexible, storable and transportable fuel, so it can double as energy storage, ensuring security of supply in a world powered by renewables.
E-gas/Syngas: the Power-to-Gas SNG process
Power-to-Gas may be the energy storage solution of the future – but it has already proven to be viable in the present. In Germany, MAN Energy Solutions successfully constructed one of the most successful examples. A Power-to-Gas reactor for Audi has been successfully operating since 2013 in the car maker’s plant. Renewable energy that cannot be fed into the grid is used to produce hydrogen and oxygen via electrolysis. In the next step, a methanation reactor uses CO2 extracted from the plant’s emissions, making the resulting methane a carbon-neutral SNG. It is fed into the natural gas grid, supplying Audi customers’ gas-powered cars.