Ammonia – the answer to shipping’s decarbonisation search?

Malcolm Latarche

Malcolm Latarche · 07 October 2020


Ten years ago or maybe even five years ago, if a shipping professional was asked what they thought about ammonia, the answer would almost certainly have been either a mention of it as a cargo, possibly its role in SCR systems to reduce NOx emissions or just maybe as something to do with fuel cells. Almost certainly the idea of it being used directly as a marine fuel in a diesel engine would not even be considered. Yet today it seems that ammonia is the nirvana as far as decarbonising the shipping industry is concerned and research and projects to explore its potential are underway around the globe.

Except to a chemist, ammonia’s potential as a fuel is probably not obvious. It is well known as a fertiliser and perhaps also as the source of the unpleasant odour associated with some hair dyes and babies’ nappies. However, ammonia (chemical formula NH3) is rich in hydrogen which is a high energy element and along with carbon the two substances that give fossil fuels their energy potential. If decarbonising shipping is the goal, then hydrogen has been accepted as the answer and that could mean that ammonia will take shipping to the place many believe is essential for the sake of the environment.

Wärtsilä is among the leaders in exploring the potential of ammonia as a fuel for conventional engines, and, considering its role in pioneering dual-fuel engines in shipping for over 20 years that is appropriate. ShipInsight spoke to Kaj Portin, General Manager, Sustainable Fuelsin Wärtsilä’s Marine Power division about the potential and practical problems that ammonia has for shipping and the areas being researched.

In June this year, Wärtsilä announced a joint project involving Repsol and Norwegian shipowner Knutsen OAS after having earlier began conducting tests that ‘yielded promising results’. In the new project, the ultimate goal is to develop an engine that can use ammonia as fuel under normal operating conditions. The engine –a four-stroke multifuel engine – will be installed in a Knutsen vessel. Portin said that in the first instance, the ammonia-fuelled engine is likely to be one of four engines on the vessel perhaps on a supply vessel with a diesel-electric power configuration.

Safety and materials come first

At this early stage in the project the focus is on safety and material testing. As far as safety goes, Portin said that there is a huge pool of experience to draw on outside of shipping where ammonia is regularly stored, carried and handled.

As for material testing, this will be more related to the engine than to the fuel storage and delivery system. One area of research is on sealing systems and another concerned with the combustion chamber. There are several ways of dealing with the optimisation of the combustion process, and the possible ventilation of ammonia and unburnt ammonia in the exhaust gases need to be carefully looked a

Some amount of blow by is inevitable in a marine four-stroke and although this should not be any greater, some research will be necessary on the long term effect of ammonia in the crankcase, sump and in the lubricating oil itself and any additives that are being used in the engine.

In terms of fuel storage, there are numerous options according to Portin, as ammonia can be stored as a liquid at 8bar at ambient temperature or refrigerated to -33°C. As yet the IMO’s IGF code does not cover ammonia but there are discussions for it to be included in future. Portin believes that Wärtsilä’s LNGPac system used for most of the vessels with its dual-fuel engines is an ideal solution would be an ideal storage system for ammonia.

In fact, ammonia could very likely be used in many of the existing dual-fuel four stroke engines in service and even conventional diesel engines could be able to use it with modifications. Portin explained that although general perception is that ammonia would be used on its own, there could be benefits in mixing it with LNG or oil fuels and some of the research will be to determine what, if any, mix provides the best results.

Mix and match for best results

Mixing ammonia with diesel would help reduce the carbon output but would not eliminate it unless the diesel was a bio- or synthetic fuel. Mixing fuel could be done in one of two ways; by mixing under pressure before injection into the engine or by having two separate injection systems – one for ammonia and one for the other fuel being used. There are other areas that Wärtsilä’s research will be looking at including the possibility of ammonia slip and its impact on turbochargers and after treatment systems.

Assuming ammonia is proved to be a practical fuel for internal combustion engines, Portin thinks that it will increase the option of fuel choices. Ideally a ship would have tank space for oil fuels and at least two gas tanks with one being reserved for ammonia and the other for LNG or perhaps LPG. Obviously, the fuel choice and bunkering ports would need to be carefully managed, especially for ships not sailing on regular routes and where fuel availability may be limited.

Although ammonia can be mixed with other fuels in the engine, that is not possible in the ship’s tanks. In theory, if there was a very small amount of LNG in a tank and ammonia was loaded on top, the LNG would quickly boil off and be used first. However, the reverse would not be true as the extreme low temperature of LNG when loaded would mean that any small amount of ammonia would solidify creating problems for the fuel system.

As the idea of ammonia’s potential as a fuel for shipping has gained traction, some questions have been raised over whether there is sufficient ammonia produce to meet demand from shipping as well as other industrial users. Portin says that ammonia production could be increased and that where economical so-called green ammonia could be used.

Green ammonia is produced by electrolysing water using renewable energy and mixing the hydrogen produced with nitrogen from the air using the Haber-Bosch process using a catalyst under high temperature and pressure. As Portin points out, “the process for producing green ammonia should not be one that has a higher impact than using fossil fuels and even producing ammonia from LNG could be seen as defeating the object”.

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