Yes, Blue ammonia should play an important role, whether it’s a role as a transition or it’s a role as part of the long-term energy mix.Ammonia—a renewable fuel made from sun, air, and water—could power the globe without carbon. The potential use of ammonia as a carbon-free fuel, and covers recent advances in the development of ammonia combustion technology and its underlying chemistry. Ammonia on the other hand, comprises 17.8% of hydrogen by mass and can be produced from renewable hydrogen and nitrogen separated from air.

.

Dear Medhat Elkelawy this is indeed a very important technical question which is certainly of broad general interest to many RG members. Even though we are inorganic chemists, this issue was more or less new for me. Personally I'm absolutely skeptical about hydrogen technology because of the highly flammable and potentially explosive nature of elemental hydrogen. In the case of ammonia, the trick seems to be to regulate the combustion such that no toxic nitrogen oxide by-products are formed. Ideally the ammonia combustion yields only nitrogen and water as products. If this became possible, it would certainly be a very promising new technology. For some good overview about this please have a look at the following potentially useful articles:

Is ammonia the fuel of the future?

https://cen.acs.org/business/petrochemicals/ammonia-fuel-future/99/i8

(published March 8, 22021)

In this article the color scheme for ammonia is nicely explained (e.g. blue ammonia, gray ammonia etc.). Interestingly, this scheme, which describes the carbon intensity of the different methods for manufacturing ammonia, also applies to hydrogen.

A perspective on the use of ammonia as a clean fuel: Challenges and solutions

Article A perspective on the use of ammonia as a clean fuel: Challen...

Unfortunately this paper is not freely available as public full text on RG. However, it is a very recent article (2020) and both authors have RG files. Thus there is a good chance that you can request the full article directly form one of the authors via RG.

Good luck with your work and best wishes, Frank Edelmann

I am not sure if it is more important to come up with an alternative fossil fuel, or to simply say we are allowing any fuel to come up (of course make sure it is stable)

Ammonia works out 32% cheaper than hydrogen. Hydrogen requires excessive costs for transport. Ammonia is expected to have low production, storage, and transport costs compared to other carbon-neutral fuels, and the stable fuel supply is possible as the large-capacity ammonia synthesis technologies are already mature.

https://splash247.com/ammonias-advantages-detailed-in-new-report/

Hydrogen and ammonia are not supposed to be used in " various combustion applications such as internal combustion engines and turbo engines." The thermodynamic efficiency of such engines are too low. The storage of hydrogen is the main unsolved problem. Hydrogen has a very low energy density. The production of H2 and NH3 should not have any carbon dioxide footprints. In addition, the production of NH3 uses H2. In this sense, the future of NH3 as a fuel is far from bright.

There are some substances that could be used to store and/or generate hydrogen. Ammonia, metanol are some of then among others. The Journal of Materials Chemistry (Royal Society of Chemistry) has a collection of artciles dealing with this subsject, Materials chemistry for hydrogen storage and generation. https://pubs.rsc.org/en/journals/journalissues/jm#!issueid=jm018020&type=archive&issnprint=0959-9428.

I worked with metanol steam reforming to generate hydrogen because of the possibility of store metanol at ambient pressure. And the CO2 used could be green as that one generated in ethanol fermentation or gasification of biomass.

Please let me draw your attention to the fact that combustion of hydrogen does not need to result in increased NOx generation. We are applying Flameless Oxyfuel combustion and the NOx levels are same as when using, for example, natural gas as a fuel. It should, furthermore, be noted the NOx generation from Flameless Oxyfuel combustion is substantially lower than with air-fuel combustion.

Ammonia has the potential to become the future green fuel. In the case of hydrogen, it is difficult to use due to its explosion and other properties including difficulty in storage, transportation, and distribution. In contrast, ammonia has already a good infrastructure. However slow reaction kinetics and high NOx emissions from ammonia combustion is still major challenge. Ammonia burning intensity can be increased by mixing with higher reactive fuel or injecting the partially dissociated ammonia into the combustor. However, to reduce NOx emission, two-stage combustion or steam-assisted combustion or plasma combustion can be used. These processes are still in the nascent stage. You can go through the following papers

Article Chemical Kinetic Modeling of the Autoignition Properties of ...

Article Chemical kinetic analysis on influence of hydrogen enrichmen...

Yurii V Geletii This really depends on what you use the H2 and NH3 for. It's true that internal combustion engines are rather inefficient, but modern combined-cycle gas turbine power plants are not. If you look at industrial furnaces or boilers, they usually also achieve very high efficiencies.

There are also other things to consider than just efficiency: Long-distance transmission of electricity isn't great, chemical energy carriers are much better suited to this. So, if you transport H2 or NH3 from sunny and windy places to regions with high energy demand, why not burn H2/NH3 where it makes sense to do so.

Kindly please read article as below

https://arxiv.org/abs/2102.00439

1. Consider the safety and material strength, it is impossible to create a cheaper system for H2 combustion.

2. Is ammonia combustible in several conditions? Because as far as I know, ammonia has better utilization for refrigerant rather than combustible fluids.

Edo Widi Virgian concerning your first point: What makes you think that? There are already combustion systems for various applications which can be run with pure hydrogen, both for residential and industrial applications and even (smaller) gas turbines.

Dear Medhat Elkelawy

It is well known that renewable resources such as solar, wind, and tidal suffer from intermittency and generation capacity. In this sense, energy storage broadly appears as an essential step in overcoming this inherent intermittency. Chemical energy storage in energy-dense fuels (e.g., hydrogen, ammonia, methane) provides the capability of storing large quantities of energy for a long time with broad distribution compared to the other approaches. Despite hydrogen's advantages, challenges associated with its storage, distribution, and infrastructure remain. Liquid hydrogen has a density of 8 MJ/L, whereas gasoline has a density of 32 MJ/L. This indicates the low volumetric energy of hydrogen compared to other fuels. Thus, converting hydrogen into other fuels with higher volumetric energy densities may be a viable solution to reduce the cost of transportation and comply with existing infrastructure capabilities. In this sense, ammonia is very attractive as a carbon-free energy carrier and a high-density hydrogen energy vector

see the following recent review article:

Article Review on the recent advances on ammonia combustion from the...

Dear A. M. Elbaz , everything is fine with ammonia except one thing. How to make ammonia from solar energy? I could imaging only one way, namely, to use H2 from solar driven process to reduce N2 to ammonia. Why not to reduce CO2 by H2 to liquid fuel?

Dear Yurii V Geletii

Thank you for your comment, Green, Grey, or Blue NH3 are produced from H2 (it depends on the H2 source), my comment was to emphasize that, it will be easy to handle NH3 than H2, however at the endpoint, it could be cracked or partially cracked into H2 or H2/NH3 blends.

Hydrogen and gaseous ammonia (NH3) are being considered as potential alternative fuels for internal combustion engines and fuel cells. They have several advantages that make them attractive as potential replacements for fossil fuels, including their high energy density, low emissions, and the ability to be produced from various feedstocks.

Hydrogen is a highly efficient fuel that can be used to power fuel cells, which convert the chemical energy of the hydrogen into electricity with high efficiency. Fuel cells are quiet, clean, and efficient, making them attractive for various applications, including vehicles, portable electronics, and stationary power systems. However, hydrogen fuel cells still face some challenges, including the high cost of production and the lack of a widespread hydrogen fueling infrastructure.

Gaseous ammonia has also been proposed as an alternative fuel for internal combustion engines. It has a high energy density and can be produced from various feedstocks, including natural gas, coal, and renewable energy sources. Ammonia is also relatively easy to store and transport, making it a potentially attractive alternative to other fuels. However, there are still some challenges to be addressed to make the widespread use of gaseous ammonia as a fuel practical, including the development of efficient and durable engines that can run on ammonia and the need to establish a distribution infrastructure for the fuel.

Overall, hydrogen and gaseous ammonia have the potential to play a significant role in the future energy mix. However, there are still challenges to be overcome to make their widespread use practical and sustainable.