Nitrogen+Syngas 369 Jan-Feb 2021
31 January 2021
Shades of green
It can’t have escaped anyone’s notice that the question of the carbon intensity of ammonia and downstream nitrogen compound production has been one of the main industry talking points for the past year. Everyone seems to be talking about ammonia of different colours – green ammonia, blue ammonia, and all shades of turquoise in between. If you are confused, it may not be surprising, as these words have come to cover a wide variety of different methods and technologies for producing ammonia, and their green credentials consequently come in a whole range of different shades.
“Scale is the issue, and for scale you need money”
What most people mean when they talk about green ammonia these days seems to be conventional Haber-Bosch production using hydrogen generated from electrolysis powered by renewable electricity. This is certainly the least carbon intensive method, albeit with issues from fluctuation of power source to the cost of hydrogen generation. But what about biomass gasification to generate syngas? Is that ‘green’? Or conventional production using methane emitted from the breakdown of organic waste (‘biogas’)? Both are generating carbon dioxide, though, depending on the source, they may not be emitting any additional CO2 beyond what the breakdown of the organic matter would have produced anyway.
‘Blue’ ammonia, on the other hand, tends to mean it has been produced from conventional fossil fuel feedstocks, probably natural gas (though some coal-based ones are also proposed), but that the carbon dioxide generated has been captured and somehow sequestered. However, there are shades of blue as well, according to how much of the total carbon fraction is actually captured – it is by no means always 100%. Sometimes the carbon captured is used for downstream urea production, but the urea will release the CO2 again in the field when it hydrolyses, so was it ever really captured? And even when all of the CO2 ends up underground, there are vanishingly few carbon capture installations where the CO2 has been used for anything other than getting more oil and gas out of an existing well via enhanced oil recovery (EOR). How green (or indeed blue) that really is as a process can be a matter of debate. Saudi Arabia claimed to have shipped the world’s first cargo of blue ammonia in September 2020, but again the carbon dioxide from its production had been used for EOR.
And then there is Monolith Materials, who have what they describe as a ‘turquoise’ methane pyrolysis process which converts natural gas into hydrogen and carbon black. While they claim it produces ‘carbon free’ ammonia, in fact would generate 530 kg of carbon for every tonne of ammonia, but admittedly not as a carbon oxide. The carbon black market runs to about 15 million t/a, so there is room for more supply, but not on the kind of scale that would make a dent in the current 180 million t/a of global ammonia production.
Scale is of course the issue, and for scale you need money. Lots of money, if you are building an electrolysis-based plant. For this reason, most renewable-based plants that have been built so far have been small scale pilot or demonstrator units. But there are signs that this is now changing. As noted in our news section, Yara is considering moving to fully convert its 800,000 t/a Porsgrunn ammonia plant to electrolysis-based production, and Air Products’ NEOM project in Saudi Arabia, which will produce green ammonia from various renewable sources, aims to produce 1.2 million t/a of ammonia, albeit at a capital cost price tag of $5 billion – several times that of a conventional plant, even if the power source is ‘free’.
Of course this is still a developing area for ammonia production. Capital costs will come down, as more innovations in electrolysis and economies of scale in production and installation start to be realised, but for the moment large scale government funding is needed to get these projects off the ground. That being the case, it looks as though for the moment, most low carbon ammonia is going to be ‘blue’. That was the conclusion of a report by HSBC published just last week, which puts the cost of converting a 1.2 million t/a gas-based ammonia to carbon capture and storage at $500 million – one tenth of that of the comparable sized NEOM project. HSBC believes that hydrogen production is heading towards a ‘tipping point’, and that the cost of ‘pure’ green hydrogen production (i.e. renewable/electrolysis-based) will fall below the cost of conventional (gas-based) hydrogen production some time between 2030 and 2050. But for the next decade, most low carbon ammonia will likely be blue.
