Low-cost US natural gas and ammonia’s advantages as a hydrogen carrier have encouraged the building of intercontinental value chains, with blue ammonia being produced in resource-rich countries, such as the US and Qatar. This is then shipped to Europe and Japan, and converted from blue ammonia to hydrogen via cracking.
However, the lifecycle emissions of this pathway are not low. Upstream natural gas emissions are the largest contributor, although performance varies. The Qatar-Japan corridor consistently produces lower emissions than the US-EU one due to Qatar’s significantly lower upstream intensity.
As presented in the chart below, taken from CRU’s Energy Transition and Decarbonisation Services, the largest contributor to overall emissions is upstream US NG production, including emissions from exploration, flaring, venting and distribution. Under the baseline pathway, heavy fuel oil (HFO) is the one used for blue ammonia shipping and NG fuels the cracker at the destination.
Blue ammonia production contributes a further substantial share, as NG is used both as feedstock and fuel. Steam methane reforming (SMR) converts NG into hydrogen and releases a concentrated CO₂ stream, of which ~95% can be captured and stored. The reaction also needs high-temperature heat, supplied by burning NG. This combustion CO₂ is diluted, making capture significantly harder and more expensive, so most blue ammonia facilities are expected to vent it directly to the atmosphere.
The PSA unit used to purify the hydrogen stream also causes unavoidable hydrogen losses. Some hydrogen leaves through the purge gas used to regenerate the adsorbent, while some remains trapped in the bed’s void spaces during depressurisation. Shipping ammonia from the US to Europe takes several weeks, with vessels consuming HFO throughout, though this adds only a small amount to total emissions. At the EU terminal, NG used to fuel ammonia cracking contributes further, including associated upstream emissions. Finally, hydrogen leakage adds a small final increment.
Ammonia can fuel both maritime vessels and crackers – replacing HFO and NG, respectively – and thereby reducing direct combustion emissions. However, this lowers the hydrogen yield, requiring more upstream ammonia production and associated emissions to deliver the same amount of hydrogen.
Switching shipping fuel from HFO to ammonia, while retaining NG firing at the cracker, slightly increases total emissions. That is, although ammonia combustion produces no direct CO₂ emissions, the additional blue ammonia required for shipping generates upstream NG emissions that exceed the savings from avoiding HFO combustion, which has an intensity of ~0.078 tCO₂/GJ.
Using ammonia to fuel the cracker while retaining HFO for shipping reduces emissions because the displaced natural gas has higher lifecycle emissions than the blue ammonia used in its place, even after accounting for upstream natural gas and carbon capture and storage (CCS) emissions. Ammonia fuel for both shipping and cracking produces slightly higher emissions than this. Therefore, ammonia is preferable for the cracker from an emissions perspective, although costs have not been assessed.
Even in the lowest-emission scenario (‘ammonia-cracker, HFO-shipping’), remains close to the direct plus Scope 3 (i.e. fugitive) emissions intensity of coal. This is because upstream NG emissions and downstream hydrogen leakage remain largely unchanged by fuel choice. Moreover, using ammonia as fuel reduces the cargo available for hydrogen production, requiring additional upstream ammonia and increasing emissions.
Emission outcomes depend on shipping distance and upstream emissions, so the optimal configuration is route-specific. On the Middle East-Japan route, for instance, the lowest-emission scenario would be to use ammonia to both power the vessel and fuel the cracker, unlike the US-EU route. The full client Insight sets out the emission scenarios for both routes and compares them against LNG and coal on a full upstream-inclusive basis, showing that blue ammonia-to-hydrogen conversion can exceed coal under certain configurations. If interested in accessing the full Insight, contact us here.
Further route-level emissions data is available in our Methane Emissions Datapack, which is available to our Premium Energy Transition and Decarbonisation service clients. To learn more about emissions across NG-blue ammonia-hydrogen supply chains, contact us here.
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