Hydrogen Production
Hydrogen is an energy vector, not a primary fuel. It does not exist in pure molecular form naturally on Earth (although hydrogen atoms are estimated to comprise 0.14% by weight of the earth's crust), but must be produced from other sources.
Currently hydrogen is used almost exclusively as an industrial chemical, within which capacity it is applied to a wide variety of uses, including ammonia production (for fertiliser manufacture), refinery use for desulphurisation and other processes, and methanol production. The annual world production is estimated to be around 500 billion Nm3 per annum.
The bulk of hydrogen (almost 50%) is produced by steam methane reforming (SMR), which is the most economical (large scale) route. Partial oxidation of hydrocarbon fuels can be competitive where a cheap source of oxygen is available. Both these processes result in the emission of carbon dioxide and additional measures would be needed to capture and store this carbon dioxide if a truly low carbon energy economy is to be realised by continued use of fossil fuels. However, there are many other potential production chains.Hydrogen production technologies include:
Steam methane reforming (SMR)
Partial oxidation of hydrocarbons
Clean coal gasification (with carbon capture and storage)
Pyrolysis (decomposition of hydrogen in the absence of oxygen)
Electrolysis of water (ideally using electricity generated from low carbon sources such as wind or nuclear)
Photoelectrolysis (splitting of water with sunlight)
Biological production of hydrogen (photosynthetic)
Biological production of hydrogen (fermentation)
Gasification of biomass
Thermochemical cycles (powered by solar or nuclear heat)
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