Ammonia

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Content – Other fuels

 

Ammonia (NH3) is a compound of nitrogen and hydrogen, which in it´s simplest form, is a colorless gas with a pungent smell.

It has a boiling point at −33.34 °C at atmospheric pressure, so to remain liquid, ammonia needs to be stored under pressure or at low temperatures.

Ammonia is a common nitrogenous waste, contributing significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers.

Around 176 million tons (2014) of ammonia is produced annually, whereas close to 90% is used as fertilizer or as feedstock for fertilizer production.

Even if ammonia primarily is used as a fertilizer or for fertilizer production and other industrial purposes, it could have a potential to be used as a low emission fuel or a storage media for hydrogen.

Since ammonia is both caustic and hazardous in its concentrated form it is classified as an extremely hazardous substance and special precautions needs to be made during storage, transportation and handling.

Currently ammonia is mainly produced from natural gas. However, ammonia can also be produced from water electrolysis where the water is split into hydrogen and oxygen and subsequently the hydrogen and nitrogen from air are converted into ammonia.

Since ammonia holds more hydrogen per volume than liquid hydrogen and due to low cost of nitrogen sourcing it has a potential to be used as a chemical storage medium.

Conversion of ammonia to hydrogen would allow the storage of hydrogen at nearly 18 wt.% compared to ~5 wt.% for gaseous hydrogen under pressure.

The chemical energy of the ammonia could be transformed into thermal energy or electrical energy:

– Ammonia directly used as a fuel for combustion (Gas turbine, other internal combustion engine or furnace)
– Ammonia directly used in a high temperature fuel cell
– Hydrogen recovered from the ammonia (The sodium-amide process) and used in a hydrogen fuel cell.

Combustion of ammonia
Ammonia is not highly flammable but when mixed with oxygen, it burns with a pale yellowish-green flame.

The combustion of ammonia to nitrogen and water is exothermic:

4NH3 + 3O2 → 2 N2 + 6H2O

Since the ammonia molecule (NH3) has a high density of hydrogen and do not contain any carbon it could be well suited to be used as a low carbon fuel for direct combustion or in fuel cells.

Combustion of ammonia does not result in any CO2 emissions but could have issues related to NOx emissions.

Energy content

Weight Based energy content & Volume Based Energy content for some fuels (based on lower heating value (LHV))

FuelWeight Based energy content

(kWh/kg)

Volume Based Energy content

(kWh/Nm3)

Hydrogen (H2)33,333,00
Natural gas (82-93% CH4)10,6 – 13,98,8 – 10,4
Methane (CH4)13,99.94
Propane (C2H5)12,8634,4
Gasoline12,339,1 kWh/l
Diesel12,0610 kWh/l
Ammonia (NH3)5,23,92 kWh/l