Speeding up container shipping's transition to clean energy has become a priority. In this article, we review the different fuel and propulsion options which will enable the sector to attain the objectives set by the International Maritime Organisation.
The transition to cleaner energy is under way in the container shipping industry. It is being carried out at a fast march as the industry comes under pressure from the International Maritime Organisation (IMO) as part of a deliberately ambitious timetable set by numerous supra-national bodies, including the European Commission in Brussels. The IMO's initial strategy on the reduction of greenhouse gas emissions was adopted in 2018 and a number of new amendments were proposed in late 2020.
How can the IMO's objectives be met? It would seem at this stage that the response to this question will involve a combination of different solutions. We can draw a parallel with the transformation of the merchant fleet at the end of the 19th century. Sail and steam-powered navigation continued to exist alongside each other until steam technology finally forced the last clippers out of service. It is a good bet that this hybrid scenario will apply until one technology establishes itself as the definitive clean energy solution.
We have deliberately excluded all-electric battery and engine solutions from this survey even if there are already river ferries, barges and port vessels which use these technologies. Because of the energy storage constraints they involve, they can only be considered relevant for small vessels which are regularly immobilised so that they can be recharged - not for long haul vessels.
1/Is it possible to completely do without an internal combustion engine?
To produce energy, internal combustion engines necessarily give off exhaust gases. Three well-tried technologies show that alternatives exist but they are not necessarily suited to all uses and are not without disadvantages.
This technology uses NEOLINE-type sailing vessels and Magnus effect-driven turbo-sail vessels, with autonomous, auxiliary electrical propulsion.
Advantages: This technology undoubtedly offers the best overall carbon performance, taking account of both shore-based energy and energy produced aboard ship.
Disadvantages: This technology does not fit in well with regular line schedules unless substantial auxiliary combustion engines are also fitted. It is not very suited to very big ships.
This technology, which has been well tried and tested for 50 years in the military field, depends on the generation of steam aboard ship to drive turbines. There are no exhaust emissions apart from steam. The civil nuclear industry is currently moving towards series production of mobile micro-reactors suitable for use aboard ship.
There are few examples of civil vessels using nuclear propulsion but one is provided by Russian ice-breakers.
Advantages: This propulsion mode meets the specifications of the IMO and produces no greenhouse gases at all. It also enables ships to enjoy greater autonomy.
Disadvantages: Nuclear propulsion raises the problem of the environmental impact posed by waste processing, as well as that of its political acceptability. It also poses security problems.
This solution involves storing hydrogen aboard ship to feed a fuel cell which produces the electricity necessary for propulsion.
Advantages: This technology meets the CO² emission reduction targets for seagoing vessels.
Disadvantages: It does not resolve the problem posed by the production of hydrogen, 95% of which is manufactured from fossil fuels in shore-based facilities. Some also have reservations about the stability of hydrogen stored aboard ship.
2/ Which fuels offer the best prospects for emissions reductions from internal combustion engines?
For the next 30 years, it is most likely that ships will continue to be propelled by internal combustion engines. It is nevertheless possible to improve their performance by using different fuels. The subject is an exciting one and research into it intense. A first major step was taken through last year's implementation of the IMO 2020 regulation, which bans the use of heavy fuel oil by ships without scrubbers. The regulation brought an immediate, positive impact in the form of reduced carbon and sulphur emissions.
Research on cleaner fuels is moving towards combined solutions. In the short term, LNG + MGO technology is the most compatible with shipping greenhouse gas emission reduction objectives. This option was the one adopted by the CMA CGM group. In the medium-term, however, ammonia + MGO seems to be leading the field.
This fuel has been known about since the beginnings of the internal combustion engine. It has not so far been brought into mass production, however, because of its toxicity and low flammability level. The most promising trials of this technology have used a 70% ammonia and 30% marine gas oil (MGO) mixture.
Advantages: Compared to hydrogen, ammonia is much easier to store. It is also more readily available in ports. Production costs per tonne are very low and it can enable shipping companies to meet IMO targets.
Disadvantages: It is a toxic product which presents risks when it is stored in liquid form in great quantities. Also, it is largely produced using fossil fuels, which does not solve the environmental problem. Finally, it needs to be mixed with a more volatile fossil fuel in combustion chambers to enable it to produce an acceptable performance.
- LNG and MGO - "flex fuel"
Liquefied natural gas allows fuel and carbon emissions to be reduced drastically, which is its main attraction.
Advantages: It only needs minor modifications of existing propulsion technology, which means that emission reduction targets can be attained rapidly and at limited cost. Another sizeable advantage is that MGO can used alone if LNG is temporarily unavailable.
Disadvantages: Apart from needing huge amounts of lubrication additives, this technology has few disadvantages even if though it relies wholly on fossil energy resources.
- New generation MGO blends
These involve the use of growing proportions of biofuels, mainly ethyls, or recycled oil products such as used engine oil or recycles vegetable oils.
Advantages: The second option above can allow some waste to be recycled by bringing it back into the fuel chain.
Disadvantages: Production is costly if it is not subsidised because of the collection and recycling it requires. Its impact on emissions is low, moreover. Also, as regards agriculturally produced fuel, the ecological cost of production is a subject of controversy because it involves massive use of water and difficult choices regarding the end use of crops.