Moaning about ammonia

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I am a bit disappointed, to be honest. I thought my commentary a few days ago about on-board carbon capture would have garnered more feedback than it did, but there is still time: there is a click-through link to my email address at the end of it for you to tell me what you think. There is also a link at the end of this item for you to respond to these further comments.

I was not surprised that the one reaction I did get came from one of the two people behind the scheme that I mentioned in my discussion: Paul Wilson, whose PMW Technology has been given a UK government grant for a six-month study into its potential.

He felt I should have said more about how carbon-capture compares with other low-carbon solutions, against which his technology will be competing. He’s right: I didn’t go into that detail because ShipInsight has published a lot of articles about those fuels and because my article was long enough as it was. Perhaps it was too long for most readers; lesson learned.

Paul’s reply particularly mentioned ammonia and made a point I had not looked into before: the amount of storage space it needs. He guided me to a detailed study published in late January by the Korean Register (KR) called Forecasting the alternative marine fuel, which has a particular emphasis on ammonia.

In my commentary about carbon capture, I had made a big thing of the space needed for both bunker tanks and CO2 receiving tanks and calculated that, for an HFO-fuelled ship, they would together take up nearly four times the space of the bunker tank on its own. I now learn from the KR study that because ammonia has a relatively low energy density, it requires 4.1 times the bunker volume than the equivalent conventional fuel, with a corresponding reduction in cargo space.

Unlike my carbon-capture comparison, the KR figure takes account of the insulation needed to keep the ammonia at -33.6°C and 10 bar pressure so, in practice, the extra volume needed to replace an HFO fuel system with an ammonia alternative is probably about the same as for the carbon-capture concept. But Paul told me that his work “has already established that ammonia is likely to impact cargo capacity to a greater extent than carbon-capture,” so his comparison is probably based on an LNG-fuelled vessel – such as the car carrier Siem Confucius that he is using as a case study – since LNG produces a lower volume of CO2 per tonne of fuel than HFO does.

We reported last month (26 March) that Wärtsilä has started combustion trials using ammonia to help it “prepare for the use of ammonia as a fuel that can contribute to reducing both the shipping’s and energy sectors’ greenhouse gas emissions.” It is a long-term project, with engine tests involving shipowners not anticipated until 2022 followed by fuel cell tests in 2023.

Dutch naval architect C-Job is also looking at ammonia fuel cells for future ship designs and its lead naval architect Niels de Vries won the Dutch Maritime Designer Award in November for his work in this area. “Ammonia is proving itself to be one of the most feasible alternatives available” for meeting IMO’s GHG reduction targets, the company’s website says.

Meanwhile, MAN Energy Solutions and other companies are working on engine technology suitable for ammonia and I look forward to hearing how all this research goes because the KR report sets out some of the problems that engine designers face. These include ammonia’s “poor fuel properties” because of its high flash point, very high minimum ignition energy and slow flame speed, so “it is difficult for conventional engines to use pure ammonia,” KR notes.

It reports that the solutions being studied by all those exploring ammonia’s potential are based on dual-fuel arrangements to enhance ammonia’s combustion properties and we quoted Kaj Portin, general manager, fuel and operational flexibility at Wärtsilä Marine, saying that its initial tests “have yielded promising results and we will continue to optimise combustion parameters.”

Another factor that will have to be tackled is ammonia’s NOx emissions; it may be carbon-free, but it obviously produces more nitrogen oxides when it burns than other fuels. We have the technology to address that by using SCRs, which use ammonia and there will be no shortage of that on board. But engine designers have previously been able to meet IMO’s NOx limits through machinery modifications and that may not be sufficient when they are burning ammonia, making SCRs essential for ammonia-fuelled vessels.

In summary, then, using ammonia for fuel poses a number of challenges that I had not considered before. Not that you would know that from the Ammonia Energy Association’s report in February about KR’s publication. “KR makes a notably explicit and complete case in ammonia’s favour,” it gushed.

It was selective in its reporting, just as I have been in mine. So I encourage you to follow the link above to read the KR report and join me in following progress in Wärtsilä’s experiments and the work that MAN Energy Solutions is doing on the same topic.

If we are to have a carbon-free future for shipping, ammonia is likely to play a role in it. But there is a long way to go before it becomes a practical reality.

• What do you think about ammonia’s potential contribution to decarbonising shipping? Email me now with your views.