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Placing our hopes in hydrogren

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World Cement,

Joel Maia, FCT Combustion, explores whether hydrogen is the right method for reducing CO2 emissions in clinker production.

The factors involved in the rapidly-evolving hydrogen industry, seen by many as the ultimate silver bullet for mitigating CO2 emissions, create a very broad topic which needs to be discussed in more detail. Obviously, there is no carbon in the hydrogen. But, is it that simple? The necessity of transitioning to a ‘low-carbon’ economy is a widely accepted concept. Nonetheless, the decarbonisation of human economic activity is a complex matter that can only be responsibly assessed and executed by considering the myriad differences among social and economic conditions of differing nations, and where those are positioned in the hierarchy of needs.

In that context, the utilisation of hydrogen on a large industrial scale has been identified as one of the paths to reducing carbon dioxide emissions, but it is still ‘only one piece of the puzzle’, as highlighted by the International Energy Agency (IEA) in its Global Hydrogen Review 2021 Report.

This article will try to shed some light on the potential role of hydrogen utilisation in the cement industry by breaking down the approach into three main categories: environmental footprint, economics, and specific challenges in clinker production.

Hydrogen’s environmental footprint

The first myth to be addressed is that hydrogen is a clean fuel. Although the straight combustion of hydrogen does not generate any carbon dioxide, most of the hydrogen produced in the world is responsible for a fair amount of greenhouse gas emissions. The IEA estimates that hydrogen production accounts for the formation of 830 million tpy of CO2 (with the current hydrogen production matrix, 1 kg of hydrogen produced generates around 10 kg CO2).

However, there is an important differentiation to be made depending on production processes. Colours are often used to indicate how ‘clean’ the hydrogen production is: ranging from grey (brown or black are also used), to blue, and green, from the least to the most environmental-friendly process.

Grey (brown and black) hydrogen is produced from fossil hydrocarbon-based fuels, typically natural gas (grey hydrogen) or coal (brown or black hydrogen). The fossil fuel components are broken down into hydrogen and carbon dioxide, among other minor components. This method, known as the ‘steam reforming process’ (SRP, or SMR for steam methane reforming, when the hydrocarbon used is methane), releases the same or larger amounts of CO2 per unit of energy when compared to the direct use of the originating fuel (natural gas or coal for example). The reason for this is that this process requires an additional energy source to break the fossil fuel into hydrogen and CO2 and this additional energy source usually comes from fossil fuels.

Blue hydrogen: the production process is similar to grey hydrogen, with the difference being that the majority (80 – 90%) of the CO2 produced by the blue hydrogen process is captured and stored through a carbon capture, usage, and storage (CCUS) unit.

Green hydrogen: the hydrogen is produced using water electrolysis powered by renewable energy such as solar or wind. As a consequence, oxygen is released to the atmosphere (or used for other processes) as a byproduct. From this list, it is clear that green hydrogen is the only truly carbon neutral source of hydrogen (not considering the CO2 generated to produce the solar or wind equipment).

There are other ‘colours’ of hydrogen, depending on the processes, or the power source used to generate it. Up to now, these continue to represent a pretty minor percentage of the hydrogen production environment and therefore will not be discussed.

It means, in a broader context, that the combustion of grey hydrogen has a larger CO2 footprint per unit of energy released than natural gas and fuel oil (Figure 3) and a similar CO2 footprint to coal combustion. Therefore, the use of grey hydrogen as direct substitute for natural gas or fuel oil is actually environmentally detrimental, while even direct coal substitution is barely environmentally beneficial.

As a matter of fact, over 99% of the hydrogen produced in the world is still in the ‘grey’ category – blue/green hydrogen accounts for less than 1% of total production.

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