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Although generally hydrogen is only mentioned within the context of transportation and energy storage, by far the most useful applications are found in industrial applications, including for the chemical industry, the manufacturing of steel, as well as that of methanol and fertilizer. This is illustrated by how today most of all hydrogen produced today is used for these industrial applications, as well as for applications such as cooling turbo generators, with demand for hydrogen in these applications rapidly increasing.
Currently virtually all hydrogen produced today comes from natural gas, via steam methane reformation (SMR), with potentially methane pyrolysis making natural gas-derived hydrogen a low-carbon source. The remainder of hydrogen comes from coal gasification and a small fraction from electrolysis of water. The hydrogen is often produced on-site, especially at industrial plants and thermal power plants. So aside from any decarbonization efforts, there are many uses for hydrogen which the public appears to be generally unaware of.
This leads us to the somewhat controversial hydrogen ladder.
Some among us may already have come across the clean hydrogen ladder, as popularized by Michael Liebreich. This is similar to the clean hydrogen pyramid in that it tries to capture the most essential and most economical hydrogen applications. For example with the primary industrial uses highlighted, we get the following:
The controversial part of this hydrogen ladder comes mostly from the placement of categories such as ‘Long-term storage’ and ‘Off-road vehicles’, with a CleanTechnica article series (part 1, part 2) by Michael Barnard and chemical process engineer Paul Martin going into some level of detail here. As far as long-term energy storage using hydrogen goes, this is a topic that we have covered in a previous article on energy storage systems, along with an article on more practical grid-level storage technologies.
When we just focus on the ‘A’ and ‘B’ line categories that are highlighted in this image, it is important to remember that these categories contain essentially all major forms of current hydrogen usage, along with a number which were mentioned earlier, such as the use as coolant, but which are not covered in this image. The biggest use of hydrogen by far, however, is that for ammonia (NH3) production. Ammonia is used in solvents, household cleansing agent, as an antiseptic, as a refrigerant (R717), in sulfurous oxide (SO2) and nitrous oxide (NOx) scrubbers, but perhaps most essentially in the production of fertilizer.
A more controversial application of ammonia is that as a fuel, since the combustion of NH3 in an oxygen-containing atmosphere produces various pollutants, including N2O (nitrous oxide), as noted in recent studies by Juan D. Gonzalez et al. (2017) and S. Mashruk et al. (2021). Nitrous oxide, also known as laughing gas, is a potent greenhouse gas, and is neurotoxic, being an NMDA receptor antagonist. Due to such issues, ammonia as a fuel is unlikely to see significant use where alternatives exist.
Among gaseous coolants, hydrogen is a popular choice, as it has significantly higher thermal conductivity relative to other gases, has high specific heat capacity, low density and thus very low friction in applications where this really matters, such as in generators. This is why turbo generators are usually cooled with hydrogen gas, with the heated gas passed through a gas-to-water heat exchanger before it is recirculated. The maintenance of these hydrogen-cooled turbo generators also leads to one of the more exciting features of hydrogen: its ability to combust in air at hydrogen concentrations between 4% and 74%.
Combined with hydrogen’s auto-ignition point at 571 °C, this makes it essential to prevent leakage of air into the generator and vice versa. Before any maintenance can be performed on the turbo generator, the hydrogen has to be purged, which makes it a trade-off between increased efficiency and ease of maintenance. And as noted earlier, most power plants have an on-site electrolyser to generate replacement hydrogen when they need to.
Hydrogen’s thermal conductivity is also why it is used in some welding gases, with certain studies claiming that it improves weld quality on even lower quality steel. When looking at the various blends from a single manufacturer, Linde HydroStar shielding gas, these are argon/hydrogen blends with the hydrogen percentage ranging from 2% to 35%. In the absence of an oxygen atmosphere, TIG welding using hydrogen as part of the shielding gas is not risky, though it makes the need for constant ventilation even more important than with argon/CO2 and other blends.
As long as all of the requirements for a violent hydrogen explosion are not met, it is after all perfectly safe and a very useful gas, especially when it comes to welding tricky materials, such as stainless steel. Which ties into a fairly new and still developing use of hydrogen, in the reduction of iron oxide and the production of so-called ‘green steel’.
As ubiquitous as steel is in modern-day society, the production of this material from iron ore has change little from the 17th century, when the invention of the blast furnace first expedited the production process and made it into a commodity. Originally these blast furnaces used mostly charcoal as the carbon source, but this later got replaced with coke as the Industrial Revolution kicked off. This is essentially what we’re still using today in modern day blast furnaces.
The iron ore is generally mined in the form of an iron oxide such as magnetite (Fe2+Fe3+2O4) or hematite (Fe2O3), which is then reduced in the blast furnace by exposing the iron oxide to a substance such as carbon, with which the oxygen binds more readily than with iron. This redox reaction leads to the production of pig iron, which is iron with a relatively large (3.8 – 4.7% typically) percentage of carbon, as well as some further impurities. The carbon content of steel is generally between 0.002% and 2.14%, requiring a few more processing steps of the pig iron to produce the various grades of steel.
Where hydrogen comes into play is in this redox step, where instead of carbon, hydrogen can be used as a redox agent. This process is detailed in a 2019 literature review paper in Steel Research International by Daniel Spreitzer and Johannes Schenk.
What’s interesting about the use of hydrogen for the iron oxide redox reaction is that it has better diffusion behavior than the carbon monoxide (CO) that is the redox agent in a coke-fueled blast furnace. This means that even with worse porosity in the iron ore, hydrogen should be more effective at stripping away oxygen as it can diffuse more readily into the ore. The same low viscosity that makes hydrogen an ideal cooling gas is also useful here.
As with all large-scale production processes, the devil is in the details. Since CO and H2 are not the same molecule, and thus will behave differently in the conditions of a blast furnace, there is nothing intrinsically more complicated about using hydrogen as a redox agent with iron oxide, and so-called ‘green steel’ manufactured using hydrogen rather than coke are already available on the market, albeit in limited quantity.
Can’t Get Enough
Due to the rapid increase in demand for hydrogen from not just the fertilizer industry but also steel and other industries, more and lower-carbon sources of hydrogen are needed. Here the economics behind the sources of the hydrogen become an important factor, with hydrogen from natural gas via SMR costing around $1/kg, with hydrogen from an electrolyser run by only renewable energy costing well over $4.40/kg. For nuclear sources (electrolyser or thermolysis), levelized costs range between $0.69 – $4.80 depending on the reactor type, making this a viable green hydrogen option alongside methane pyrolysis.
Whichever options we end up picking in the end, it’s hard to deny the importance of hydrogen to our civilization, and the need to produce much more of it. Whether we’ll one day have so much of it that we can use it for transportation and the production of e-fuels remains to be seen, currently industrial applications such as the shift of the steel industry from coke to (low-carbon) hydrogen. Here we can see for example Norwegian Blastr investing in a new steel plant in Finland that will use an on-site hydrogen plant powered by local hydropower.
With the price of hydrogen having to be below $2/kg to make ‘green steel’ viable if it wants to compete with conventional steel, the search for cheap hydrogen will intensify, along with its demand. This does make one wonder why there is talk of ‘switching to a hydrogen economy’ when it seems we have been living in one for at least a century now, even if it wasn’t quite the one from the glossy marketing brochures.