5
LIFE-CYCLE ANALYSIS OF ALTERNATIVE FUELS
Alternative fuels will play a dominant role in the decarbonization of the marine and offshore sectors and are expected to yield the most benefits for reducing greenhouse gas (GHG) emissions. The current regulatory framework is focused on vessel emissions (tank-to-wake) rather than the overall life-cycle emissions of a given fuel (well-towake). However, it is recognized throughout the industry that the life-cycle carbon footprint of fuels provides the most complete description of their environmental impact. This section presents comparative analyses of some of the alternative marine fuels and their life-cycle emissions, with the objective of offering a holistic view of the challenges associated with adopting low- and zero-carbon fuels. The fuels include: • Liquefied natural gas (LNG) • Liquefied petroleum gas (LPG) • Methanol (CH3OH) • Liquefied hydrogen (LH2) • Ammonia (NH3) The adoption of alternative fuels will require changes to ship designs in order to accommodate storage tanks, as well as fuel-containment and gas-supply systems. The table below offers some key indicators to compare the fuels and to understand some of the design implications. For comparison purposes, very low sulfur fuel oil (VLSFO) is used as the reference. Fuel Type
LHV (kJ/kg)
Density (kg/m3)
Storage Volume Ratio
Vessel Specific GHG Emissions (g/kWh)1
VLSFO (ref)
41,600
944
1.0
568 (ref)
LNG
50,000
420
1.9
Diesel Cycle: 424 (-25%) Otto Cycle: 492 (-13%)
LH2
120,000
71
4.6
0 (-100 %)
LNH3
18,800
674
3.6
102 (-82%)
LPG
46,000
448
1.9
500 (-12%)
Methanol
19,900
796
2.5
533 (-6%)
Table 1: Summary of characteristics for fuels produced from hydrocarbons. Lower Heating Value (LHV, MJ/kg) — Mass-based energy content of the fuel. Density (kg/m3) — Defined at storage conditions, as it relates to tank-volume requirements. Storage Volume Ratio — Defined as the product between the density and LHV referenced to VLSFO. For comparison purposes, it is assumed that all other variables to vessel performance, such as engine and propulsion-system efficiency, range, etc., are kept constant.
ABS | VIEW OF THE VALUE CHAIN | PAGE 40
