Hydrogen could decarbonize many sectors by replacing fossil fuels (critical heat, fuel) and by allowing chemical reactions that emit less CO2 (reduction of iron). Nevertheless, we must not believe that it is “magical”: we already consume 70 million tonnes for processes that the economy cannot do without. The question of new uses arises together with the question of hydrogen production.
This article is a part of our dossier on hydrogen, innovation and ecology.
Hydrogen has an extraordinary property: when used to produce energy, it only produces water and can be produced from electricity and water. We have been dreaming since the 1970s of a hydrogen economy, where this gas would replace oil. It is back in fashion, but the technology and the issues have evolved and, beyond the talk of consultants and economists, hydrogen has a real role to play in the ecological transition.
It could credibly be used to decarbonize industrial processes, either by creating heat (cement) or as a reagent (iron reduction) and heavy transport, for which battery storage is not viable. It could also be used as a means of sustainable energy storage (which batteries are not) on a large scale, in particular to absorb variations in intermittent renewable energies.
However, before talking about these new features, we must address a “small” problem: we already use a lot of hydrogen and it is not really “eco-friendly”…
Current uses of hydrogen
We often talk about hydrogen as if it were something new, some kind of recent innovation whose development could change the world. In reality… we already consume more than 70 million tons! The equivalent of a quarter of the world’s natural gas consumption…
We have already talked about the problem of hydrogen production, which is currently produced by very polluting processes (steam reforming of methane and gasification of coal). We can estimate that before developing new uses, it makes sense to start by decarbonizing existing production. In reality, it is more complex. Indeed, old uses are often “integrated” into polluting production methods (especially for the production of fertilizers), switching them to low carbon will be very difficult in the short term. At the same time, incentives for the development of new production methods can be conditional on the low-carbon nature of the hydrogen used. For example, your steel would only be “green” if the hydrogen used to produce it is also. This would strongly promote environmentally sustainable production and allow it to gradually take precedence over polluting processes.
The main statistics of hydrogen consumption
Currently, uses are essentially divided into two poles: refining (~40-50%) and the manufacture of fertilizers. It is also used for the production of methanol, steel (with direct reduction, which we are going to talk about, 3%) and many minor uses (electronics, food industry in particular). Let’s take a closer look at these uses.
Hydrogen and the petrochemical industry
Once extracted from the ground, “crude” oil is a cluster of complex carbon chains and a myriad of components. It cannot be used as it is, it needs to be refined and hydrogen plays a crucial role in this industry.
- Desulphurizing Petroleum: Hydrotreating
Once extracted from the ground, crude oil contains many problematic components, such as sulfur. Once released into the air, it causes health problems and even acid rain. To combat this, the States have agreed on demanding standards imposing a considerable limitation on the presence of sulfur in gasoline and other petroleum products. The operation to desulphurize oil is hydrotreating. This consists of reacting hydrogen with sulfur to form hydrogen sulphide (H2S), which can easily be separated from petroleum. This is called “hydrotreating”.
- “Cracking” heavy oil: hydrocracking
The other major aspect of the refinery is the conversion of the “heavy” parts (i.e. those whose carbon chains are very long) into lighter and more profitable components (diesel, fuel oil, kerosene, heavy or light naphtha , etc.). It is a process that is gaining in importance as oil reserves dwindle. Indeed, we are going to look for oil of less and less good quality (ex: the famous oil sands). Hydrogen is used to break these molecules: this is called hydrocracking.
Ammonia and fertilizer
This is one of the greatest agricultural innovations in history: the Haber-Bosch process, discovered in 1909, makes it possible to “fix” atmospheric nitrogen using hydrogen: N2(g) + 3 H2(g) ⇌ 2 NH3(g) + ΔH. In 2012, 137 million tons of ammonia were produced worldwide. In France, we currently use 220,000 tonnes of gray hydrogen to make ammonia. The hydrogen is produced on site, by steam reforming. The problem is that the facilities are integrated together:
“What the ammonia producers are saying is that we can inject up to 10% green hydrogen without changing the current process. […] If we do 100%, that is to say we completely eliminate steam reforming, we will indeed need a complete restructuring. » (Philippe Boucly)
Various applications of H2
Some players such as CETH2 (Paris, France) are mainly focused on the production of ultra-pure hydrogen for medical or laboratory research applications. The main actors involved are listed in Table 1.Caroline Rozain (2013)
Plus marginaux on utilise aussi du H2 dans les piles à combustible (2 MT), pour le métal (1 MT), le verre et la céramique (0,5 MT), l’alimentation (0,5 MT), l’électronique (0,5 MT), les plastiques (0,5 MT) et les médicaments (0,5 MT).
Hydrogen in the conquest of space
Hydrogen is both the least dense gas (takes up a lot of space) and very dense (contains 3 times more energy per kg than gasoline). It was therefore welcome in the conquest of space, where weight is the most important factor. It is in this context used in liquid form. It is, for example, the fuel for the Ariane 5 space rocket.
Hydrogen in electronics
Hydrogen is used in the electronics industry, in particular for the production of semiconductors, screens and LEDs due to its properties of heat conduction, a reducing and etching agent. The particularity here is that the hydrogen must be of absolute purity. For example, Linde had announced that it would supply an industrial company (Infineon) with hydrogen produced from a PEM electrolyser and, in addition, “purify it to meet the rigorous specifications required by Infineon’s processes”. However, PEM electrolysis is already the process that produces the purest hydrogen natively (source).
Hydrogen is also used in the food industry for the hydrogenation of fats. It is used in particular in the production of margarine.
Possible industrial uses of hydrogen
Hydrogen could decarbonize polluting industrial processes that cannot be electrified. For example, methane produces a type of heat that electricity cannot reproduce. Hydrogen can, under certain conditions, replace this “critical heat”. This would, for example, be its role in decarbonizing cement production. H2 can also be used to replace a polluting chemical reaction, as is the case for iron reduction, a step in steel production.
Replacing coke in steel production
Iron is found in its natural state in the form of oxide (Fe2O3, hematite), it needs, to be transformed into steel, to be deoxidized: this is the reduction of iron. You have two production modes from there: blast furnaces and direct reduction. In blast furnaces, the reduction will be done thanks to carbon C (which gives CO2), brought by the coke (a coal previously emptied of its volatile components) in a furnace whose temperature exceeds 1500-2000°C. This is the ultra-dominant mode of production (93%, excluding recycling). The other is direct iron reduction. Basically, we heat the iron less (1200°C) and expose it to reducing gases (syngas?), which removes the oxygen. Then it is melted in an electric arc furnace. This process still uses a lot of fossil fuels, but can be used with pure hydrogen. Experiments have already demonstrated its feasibility. This is a very promising avenue for which the main steelmakers have announced tremendous investments in the short term.
To go further, you can consult our article on hydrogen to decarbonize steel production.
Hydrogen to decarbonize cement production?
Cement production is a disaster for the climate: it alone represents 7 to 8% of global CO2 emissions. The production of one tonne of clinker (the main component of cement) requires critical heat representing 330 kg of CO2 and 535 kg from the chemical process itself of calcining the limestone. Hydrogen is being considered to decarbonize critical heat generation. This is one of the many solutions that could combine to reduce these emissions (in all seriousness, not the most exciting).
To go further, you can consult our article on the decarbonation of cement by hydrogen.
Electricity production: hydrogen-energy
Hydrogen can be used to produce electricity through fuel cells. The main uses would be in hydrogen mobility and for the management of electrical networks.
Hydrogen fuel cells
It is thanks to fuel cells that we can transform hydrogen into electricity. The principle of heat pumps consists in producing, thanks to the injection of hydrogen (among other things) at the level of an electrode (anode), a reaction which releases electrons. These will seek to join the cathode, but will be blocked by an electrolyte. The latter must nevertheless allow the ions to pass which will migrate from the cathode to the anode.
For example, the reaction for proton exchange membrane fuel cells (PEMFCs) is
- At the anode: 2H2 => 4H+ +4e-
- At the cathode: O2 +4H+ +4e- => 2H2O
Beyond this apparent simplicity, there is an infinity of details that make the whole complex difficult to grasp for laymen. There are many types of technologies, using different electrolytes, different metals for the electrodes, operating at different pressures and temperatures, having different speeds, different inertias, different risks (e.g. the alkaline battery strongly fears CO2 contamination and cannot therefore not use the air as it is, it must have been purified), etc.
To go further, you can consult our article on fuel cells.
Hydrogen mobility: future or fantasy?
It is an eternal chestnut tree: what if hydrogen replaced oil? This is the idea that launched the hydrogen “hype” in the 1970s, in response to the oil shocks. It was the beginning of the “hydrogen economy”. Well, let’s be clear, this is absurd: nothing will replace oil. In terms of mobility, hydrogen suffers from several problems: its physical characteristics, which make it difficult to store and, above all, the poor energy efficiency of the “power to wheels” operation. Indeed, produced by electrolysis, only 25% of the electricity used to produce H2 will be returned to the electric motor. With a battery, this percentage is 90%… Finally, there are the problems of PEM fuel cells: they require rare metals (platinum, etc.) and are expensive.
However, beyond this nonsense, there are many vehicles for which electricity is not an option, such as planes or boats. It could indeed be interesting to develop heavy hydrogen mobility.
To go further, you can consult our article on hydrogen mobility.
Hydrogen to store energy
Finally, the last major use of hydrogen: storing energy. Several renewable energies are intermittent and hydrogen would make it possible to store the excesses. It has strong advantages over batteries: the latter are not suitable for storing large volumes, whereas hydrogen could easily (theoretically). As for traditional storage, thanks to WWTPs, it is already exploited as much as possible.
This approach has three problems:
- Its variations in intensity: alkaline electrolysis does not support them and PEM electrolysis, which supports them, is much more expensive and has a lower yield.
- The time of use of the electrolyzers. they don’t pay for themselves if you don’t use them often enough.
- The overall performance will be poor. (Genvia’s high-temperature electrolysis could change that, but we’re still at the very beginning)
These problems alone are very serious. Added to this are the difficulties associated with hydrogen storage, which is far from being resolved. We often hear about salt caverns, but this technology is still in the experimental stage. Storage in chemical form (eg ammonia) seems more credible. This track will undoubtedly be necessary, but it is hard to imagine it in the short term.
The scale of hydrogen use
Libreich Associates has published an interesting concept, that of a scale of uses. Thus, the production of fertilizer, methanol, hydrocracking and desulphurization would be uses that we could not do without. Conversely, hydrogen cars would be absurd. This scale seems relevant to me (rq: I encourage you to read the article, very interesting):