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Model E-Fuels -Green Hydrogen and Synthetic Green
The problem of the increased CO2 concentration in our atmosphere is arising from man excavating fossil carbon-based fuel – in form of coal, oil or natural gas – and burning it and releasing the contained carbon into the environment. The increased CO2 concentration may lead to global warming. We need to substitute the usage of fossil fuels, in all three energy sectors, by green hydrogen or synthetic green e-fuels.
Fossil fuels provide a constant and reliable energy supply. We want to have our energy sources available at any time when we want it or need it. A substitution technology therefore also needs to be constant and reliable, next to its scalability to live up to the full energy demand.
Usage Route #1 – Hydrogen can either be directly used in industry (e.g. hydrocracking in refineries, production of steel, cement, ammonia) or in new applications in heat and transport (e.g. Fuel Cell Electric Vehicles FCEV). H2 is a highly versatile zero-carbon energy carrier with excellent qualities: it can be burned in heat engines (turbines or combustion engines) and it can be transformed into electricity and heat in fuel cells, zero emission, with only water as exhaust.
Usage Route #2 – H2 can be processed into e-fuels[1], mostly to be used in existing applications in transport (Figure 2, left bottom). Re-usage of the existing infrastructure for transport & storage is a key argument for these fuels. Their drop-in capability allows for a gradual transition from a fossil into a clean world.
H2-powered fuel cells for applications in transport is about twice as efficient as e-fuels powered combustion engines. Therefore, Route #1 requires only about half of the original green electricity. Methane gas blending in gas networks is a further impactful application of H2.
[1] Electricity-based fuels. These are based on green hydrogen. Everything starts with electricity and electrolysis. E.g. SNG, e-LNG, liquid fuels can be produced by synthesizing synCrude and later fractioning into e-gasoline, e-diesel, or e-kerosene. E-methanol or e-ammonia are other examples, also widely discussed in shipping.
Renewable electricity, unless consumed directly because it concurs with current demand, can be transformed into synthetic fuels for long-term storage and, if needed, for long-range transport.
Power-to-gas technologies can transform electricity by electrolysis into hydrogen. As long as we lack a hydrogen infrastructure and because hydrogen is difficult for long-range transport, subsequent methanation or hydrogen-to-liquid technologies may be of advantage. During these processes one adds CO2 or nitrogen (N) to hydrogen. The result of methanation is synthetic natural gas – SNG. It is almost pure and clean methane gas. This resembles natural gas, and is even cleaner because SNG does not contain any residual unwanted substances. If one goes the nitrogen route, the result is ammonia (NH3), which is relatively to handle. It can be liquefied under low pressure or temperature. Ammonia can be used in industry, it can be burned in combustion engines and can be transformed to electricity in special fuel cells.
Renewable electricity can also be transformed into synthetic liquid e-fuels. Again, the first step is to produce hydrogen by splitting water H2O into H2 and O2 through electrolysis. Thereafter comes the synthesis of hydrogen via the Fischer-Tropsch process by adding CO and CO2. This process is a collection of chemical reactions that converts a mixture of carbon monoxide, carbon dioxide and hydrogen into liquid hydrocarbons. The result is synCrude, resembling fossil crude oil. From there one can produce a number of hydrocarbon fuels, as diverse as synthetic e-diesel, e-gasoline, e-methanol or e-kerosene.