LNG as Marine Fuel
• Liquefied natural gas (LNG) is natural gas that has been cooled to a liquid state, at about -162C, for shipping and storage.
• LNG contains less carbon per unit of energy than conventional marine fuels, which means that burning it emits less carbon dioxide (CO2).
• LNG contains less carbon per unit of energy than conventional marine fuels, which means that burning it emits less carbon dioxide (CO2).
• LNG is less expensive than Marine Gas Oil (MGO) and is now in some regions cheaper than heavy fuel oil (HFO).
• LNG is emerging as a cost-competitive and cleaner transport fuel, especially for shipping and heavy-duty road transport.
LNG is odorless, colorless, non-toxic and non-corrosive. The volume of natural gas in its liquid state is about 600 times smaller than its volume in its gaseous state.
LNG typically contains more than 90% methane. It also contains small amounts of ethane, propane, butane, some heavier alkanes, and nitrogen.
Natural gas is found in deep underground rock formations or associated with other hydrocarbon reservoirs in coal beds and as methane clathrates.
It can also be produced using biomass waste's anaerobic digestion and is called Bio-LNG.
E-LNG or Green LNG is produced by the synthesis of green hydrogen and CO2 captured from the air and is a type of e-fuel or electrofuel.
Volumetric density of LNG is lesser than conventional marine fuels like HFO, so volume of the ship required to accommodate storage tanks is larger.
The storage tanks must be kept insulated to keep away heat and avoid boil-off. Any boil-off must be carefully regulated by flaring or reliquification to avoid over pressuring the tanks.
LNG handling is well understood and there is sufficient infrastructure worldwide for LNG bunkering.
LNG can be burned directly in a diesel engine with slight modifications as a standalone fuel with pilot injection system or as a dual-fuel engine. 2 and 4 stroke LNG combustion engines are readily available and it can also be used in a gas turbine. LNG based fuel cells are also in early development but could provide higher efficiencies if commercialised.
Unburnt methane in the exhaust gas is called 'Methane Slip' and poses a serious issue as methane has much higher GHG potential than CO2.
LNG can significantly reduce pollution from nitrogen oxides and particulate matter compared with conventional marine fuels, while cutting emissions of sulphur oxides by more than 90%, helping to meet regulatory requirements.
Over a 100-year time frame, the maximum life-cycle GHG benefit of LNG is a 15% reduction compared with MGO, and this is only if ships use a high-pressure injection dual fuel (HPDF) engine and upstream methane emissions are well-controlled. Methane slip is expected to reduce as engine technology advances. Existing LNG infrastructure can also be easily converted to use low carbon future fuels once they are developed.
Over a 100-year time frame, the maximum life-cycle GHG benefit of LNG is a 15% reduction compared with MGO, and this is only if ships use a high-pressure injection dual fuel (HPDF) engine and upstream methane emissions are well-controlled. Methane slip is expected to reduce as engine technology advances. Existing LNG infrastructure can also be easily converted to use low carbon future fuels once they are developed.