SFI Smart Maritime Report by Dr E. Lindstad
Previous studies on fuels and engine technologies have tended to focus either on the emission impact of the fuels covering GHG and local pollution in a well-to-wake (WTW) perspective, or on alternative engine technologies in a tank-to-wake (TTW) perspective. In contrast, the motivation for the present study has been to investigate alternative engine technologies with focus on fuel flexibility, potential GHG reductions and energy utilization.
The motivation for the present study has been to investigate alternative engine technologies with focus on fuel flexibility, potential GHG reductions and energy utilization. When diesel outcompeted coal on ships 100 years ago, it was simply because it reduced the weight and the volume of the fuel to a tenth, it was easier to handle and required less manpower on-board. Today, none of the new alternative fuels have any advantages regarding volume, weight or handling. In best case they increase volume 2 to 3 times and weight with 30% – 50% for LNG and LPG. While in worst case weight and volume increase 3 to 5 times for ammonia and from 7 to 20 times for pressurized hydrogen at 350 bar.
Both hydrogen and ammonia doubles the energy consumption on a well-to-wake basis compared to conventional fuels, even when made from Green electricity, which makes them more costly if we simply assumes that there is a link between energy usage to produce the fuel delivered on the ship's fuel tank and its price.
Based on this study and its findings the following recommendations can be given:
1. Reducing fuel consumption per ton transported, will be a key requirement to:
- Reduce the carbon intensity of the vessel, even without a fuel switch.
- Enable use of fuels which will come at a higher cost per TOE than conventional fuels such as ammonia and hydrogen.
- Avoid that the fuel occupies to much of a vessel available volumes and weight capacity, i.e. enable use of ammonia, hydrogen or electricity stored in batteries.
2. Replacing conventional fuels with fossil-based hydrogen or ammonia (as produced today) will increase the annual well-to-wake GHG emissions of a ship.
3. Hydrogen and ammonia can only reduce a ships well-to-wake GHG emissions if they are produced with Green renewable electricity or alternatively with steam reforming of natural gas and carbon capture technology.
4. Batteries charged with Green renewable electricity from the land-based grid gives the best energy utilization and is a technology under rapid development. In addition, batteries also give fuel and GHG savings in hybrid setups with combustion engines, even when charged by the engine(s) on boards (Lindstad et al, 2017; Lindstad and Bø, 2018).
5. With a dual-fuel Diesel-engine, the ship can burn nearly any fossil and biofuel with a high thermal energy efficiency and the lowest GHG (CO2eq.) emissions per kWh (Lindstad, Eskeland and Valland, 2020). Moreover, if Green renewable ammonia becomes available within the first part of the ship's lifetime, it can be converted to run on ammonia.
6. If sustainable biodiesel becomes available for shipping, it will be a good GHG reduction option, especially for smaller ships with their standard diesel engine.
7. For existing medium and larger ships, HFO in combination with scrubbers and buying CO2 quotas to offset the ships GHG emission, might be the best option both to reduce global GHG emissions and cost-wise for the operator.
8. Lower prices of natural gas, in combination with the EEDI benefits of LNG, might become a strong driver for increased use of dual-fuel engines in general, especially if the LNG price in some regional areas stays bellow the HFO price.
(Updated version 14.04.2020)