How to Calculate Green Ammonia Bunkering Energy Intensity
Ports planning to handle green ammonia as a bunker fuel must quantify the electricity and emissions associated with each transfer. Pumps, vapor handling, and reliquefaction consume nontrivial energy that determines shore power sizing and the true well-to-wake carbon footprint. This walkthrough provides a concise calculation for energy intensity (kWh per tonne) and total emissions based on delivered tonnage, pump loads, conditioning energy, and the grid emission factor supplying the berth.
The same framework used to evaluate hydrogen compression loads in the hydrogen pipeline compression guide and transport emissions in the sustainable transport emissions calculator applies here: quantify each energy pathway, apply realistic defaults, and validate against measured berth data.
Definition and boundary
Bunkering energy intensity is the electrical energy consumed per tonne of ammonia transferred. It includes cargo pump power, hose handling auxiliaries, boil-off gas management, reliquefaction or chilling, and control systems. It excludes upstream ammonia production and propulsion energy onboard the vessel. When multiplied by a grid emission factor, it yields the direct berth-side greenhouse gas emissions attributable to the operation.
Some terminals may offset energy with onsite renewables or batteries; in those cases, substitute the marginal emission factor for the supplied electricity. If flaring replaces reliquefaction, include combustion emissions separately from the electrical calculation presented here.
Variables and units
Use the following inputs and units:
- M – Delivered ammonia mass (tonnes).
- Epump – Pumping energy per tonne (kWh/t).
- Econd – Conditioning energy per tonne for boil-off handling or chilling (kWh/t).
- g – Grid emission factor (kgCO₂e/kWh).
- I – Energy intensity per tonne (kWh/t).
- Etot – Total electrical energy consumed (kWh).
- mCO2e – Emissions associated with bunkering energy (tonnes CO₂e).
Keep Epump and Econd distinct because pump curves and boil-off strategies vary independently. The grid emission factor should reflect marginal supply during bunkering hours rather than annual averages to avoid understating emissions.
Formulas
Energy intensity and emissions follow straightforward arithmetic:
I = Epump + Econd (kWh/t)
Etot = I × M (kWh)
mCO2e = Etot × g ÷ 1000 (tCO₂e)
If conditioning energy is zero (for example, using nitrogen padding with no reliquefaction), the formula still holds by setting Econd to zero. Keep units consistent in kWh and tonnes to avoid spurious conversions.
Step-by-step workflow
1. Collect equipment data
Gather pump curves, motor efficiencies, and typical flow rates to derive Epump. For conditioning, identify whether boil-off is reliquefied, compressed, or flared. Use historical duty cycles where available; otherwise, start with conservative defaults such as 8 kWh/t for reliquefaction.
2. Confirm delivered tonnage
Use metered transfer mass rather than bill of lading estimates. Tonnage accuracy is critical because it linearly scales total energy and emissions.
3. Select an emission factor
Obtain the marginal grid intensity for the port during bunkering windows. If shore power is supplied via a dedicated renewable contract or virtual PPA, use the contracted residual emission factor and align the accounting with the virtual PPA carbon avoidance guide.
4. Compute intensity and emissions
Add the pumping and conditioning intensities to obtain I, multiply by M for total energy, and then multiply by g to obtain emissions (dividing by 1000 to convert kg to tonnes). Document the calculation for each berth to reveal efficiency differences across equipment sets.
5. Validate against operations
Compare calculated energy use to metered shore power during commissioning. Adjust Econd if boil-off management strategies change, and revisit g whenever the port's marginal generation mix shifts seasonally.
Limits and interpretation
This calculation isolates electrical consumption. It does not include embodied emissions from hose fabrication, vessel auxiliary engines, or upstream ammonia synthesis. Rapid transfer rates may increase Epump nonlinearly due to pump efficiency curves; if operating far from the best efficiency point, recalc using the actual power draw rather than nameplate.
For terminals using battery buffering, apply round-trip efficiency to Etot before multiplying by g. If ammonia purity requirements tighten and chilling energy rises, update Econd accordingly. Always present ranges alongside point estimates when reporting to regulators or financiers.
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Enter delivered tonnage, pumping energy, conditioning energy, and grid emission factor to compute bunkering energy intensity and associated emissions.