Hydrogen as a raw material
Hydrogen is the lightest and most abundant element in the universe. On Earth, it's most commonly found in water, but it exists in every living thing and burns with an invisible flame. Hydrogen occurs commonly in compounds (e.g., H2O), and this makes its production possible. Despite being a colorless gas, it comes in different colors - sort of. Depending on the method used to produce it, it’s referred to as green, blue, grey, or brown hydrogen. More hydrogen colors exist - turquoise, pink, yellow - but they’re not widely used.
The first in our two-part series about hydrogen will take a closer look at what those colors represent and explain the basics of hydrogen as an energy carrier.
The many shades of hydrogen
Hydrogen is viewed as a promising energy carrier for several reasons:
- Usability in a wide range of industries
- Energy storage potential
- Diverse supply sources
Fossil fuels, as well as low-carbon and renewable resources, can be converted or harnessed for hydrogen production. This includes, among others, gas, coal, biomass, wind, and solar. Even certain microbes have the ability to produce hydrogen or extract it from biomass. At the time of writing, hydrogen is produced almost exclusively from fossil fuels - over 99% in 2020, according to Wood Mackenzie.
Hydrogen is typically generated from natural gas through a process called steam-methane reforming. The result is grey hydrogen, named as such because the process is environmentally damaging, albeit less so than the production of brown/black hydrogen from lignite or bituminous coal. The carbon byproduct is not captured in either process. The production of one kilogram of grey hydrogen emits about 9.3 kg of CO2.
Source: Wilton International
Blue hydrogen involves the capture of carbon during the steam-methane or autothermal reforming process and subsequent storage underground (via carbon capture and storage). It’s generally described as a carbon-neutral energy source, but “low carbon” is a more accurate term, as roughly 10-20% of the generated CO2 can’t be captured.
The most environmentally friendly option is green hydrogen, also called clean hydrogen. Produced through electrolysis (the process of splitting hydrogen from water molecules) using energy from renewable sources such as solar or wind power, green hydrogen currently accounts for less than 1% of global hydrogen production. However, this number is expected to grow as the cost of renewable energy continues to decrease. Since renewables can’t generate energy at all hours of the day, green hydrogen is considered a good option for storing surpluses and feeding them back to the grid when needed. Additionally, green hydrogen can contribute to the decarbonization of industries like the chemical and transportation sectors.
Going underground
Saline rock formations and depleted natural gas and oil reservoirs are the ideal geological storage sites for carbon capture. At depths below 800 meters (the average depth of reservoirs is about 1,500 meters), CO2 is trapped in the subsurface as a supercritical fluid, i.e., a highly compressed fluid that has the properties of both liquids and gases. But at such depths, temperatures and pressures are so high that CO2 changes its characteristics in a way that allows for much greater volumes to be stored there than at the surface.
On the move
Whenever hydrogen is transported, from the point of production to a storage site or point of use, it travels via pipelines or super-insulated cryogenic tanker trucks specially designed to carry liquid hydrogen. Gaseous hydrogen is first liquefied (i.e., cooled to below -253°C, only twenty degrees above absolute zero, the coldest temperature theoretically possible) and then stored in large tanks at the liquefaction plant until transportation. However, the shipment of liquid hydrogen is still in its infancy. Compared to the transport of liquefied natural gas (LNG), it’s an enormous technological challenge that requires a new generation of vessels to keep the hydrogen chilled at -253°C. Susio Frontier, the world’s first ship to transport hydrogen, was built by Japan’s Kawasaki Heavy Industries and took its maiden voyage in early 2022. Other countries have also launched pilot projects, but it'll likely take a few more years until large-scale sea transportation of liquid hydrogen becomes a reality.
Hydrogen, particularly the green variety, is expected to become a significant component of future energy systems. In part two of our hydrogen series, we'll discuss use cases, power-to-gas technology, sector coupling, and more.
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