Figure 1: Shipping needs to clean up its act [Source: Flickr/Tom Turner, 2009]
One of the problems with carbon emissions is that certain sources of said emissions are often invisible to us. There is as it were a herd of carbon elephants in the room which we tend to ignore because we can’t see them (out of sight, out of mind). And one of those elephants is international shipping. There are an estimated 90,000 commercial cargo ships worldwide, transporting countless millions of tons of cargo on a weekly basis. The ability to move such large quantities of material around the planet, cheaply and efficiently is critical to global trade. Indeed large quantities of the world’s fossil fuels are ultimately move by ship.
Figure 2: If the Global Shipping fleet was a country it would be the 6th largest source of emissions [Source: IMO (2009)]
As figure 2 shows, the global shipping fleet does represent a substantial portion of carbon emissions, more than Germany in fact
. A situation made worse by the fact that shipping has generally avoided the sort of legislation that has applied to vehicles, aircraft or power stations over the last few decades. As a consequence it’s not just the carbon emissions we’re worried about but everything else, notably the very high emission rates for sulphur and NOx from shipping (which until recently was hundreds of times higher than is legal for cars). About 10% of global sulphur and 30% of NOx emissions
are believed to come from shipping. Already legislators in both the EU
and the US
are showing signs that they plan to take action and enact legislation to cut back the emissions
That said, we have to put the emissions from shipping in context. While the overall emissions from a ship can be high, relative to the cargo they carry (i.e. g CO2 per kg per km) shipping cargo results in much lower emissions than via planes or trucks. So eliminating shipping isn’t necessarily a good idea, if we assume said cargo will have to be transported one way or another. Cleaning up the shipping industry’s act is a more sensible option. For as we’ve seen with vehicles and other applications, there are a host of simple ways to cut emissions.
Figure 3: While shipping emissions are high, one has to put those emissions in context of alternative means of transport [Source: Shippingandco2.org, 2012]
All too aware of the way things are heading the IMO has itself brought out a number of reports
which suggest some practical steps to cutting the shipping fleet’s emissions. The DNV has also released a report entitled “shipping 2020
“, which discusses the various options at the disposal of ship owners in order to curb emissions.
Figure 4: A summary of current and upcoming ship emissions legislation [Source: DNV, 2012]
One of the first ideas is slow cruising
. By just cutting the speed of ships, by 20% the emissions generated can go down by as much as 40%
. Of course this is not just a straightforward case of the skipper pulling back on the engine telegraph. Slower speeds means longer transport times, which can be an issue for companies dependant on “Just In Time
” manufacturing strategies. Also its not necessarily good for the engines, as some ships run on two-stroke engines
that are designed to run at a particular speed for minimum wear and maximum efficiency. Hence you end up with more maintenance issues. And of course there are times a captain has to order full steam ahead (to get out of the path of a hurricane, escaping pirates off the Somali coast, etc.).
Also there is the option of changing the fuel used. Currently many ships still use bunker fuel, which is basically the lowest grade of fuel, typically one step up from the stuff that we tar roads with. As you can imagine the pollution generated by such fuels can be considerable. So simply swapping to diesel fuel can have significant benefits, not only lowering sulphur and NOx emissions but potentially greater efficiency and improved flexibility. While it’s difficult to be specific as to carbon emissions (again depends on a host of operating parameters, I nice paper about that here) you are talking about a drop of at least 5-10%.
Figure 5: Diesel v’s Bunker fuel (aka fuel oil) [Source: NOSCA, 2013]
However the major disadvantage is cost, diesel is generally a much more expensive a fuel, hence why some in the industry haven’t given up on fuel oil and are hoping new blends
of the stuff will be sufficient to satisfy NOx and Sulphur abatements by the time they come into force.
Another fuel option is LNG. Already some LNG transporters have dual fuel engines that can consume the boil off gas and use it to power the ship. However the idea is being floated of running entire cargo ships on LNG. While its generally a more bulky fuel than diesel, given that cargo ships tend to have a certain level of free deck space, retrofitting containerised fuel tanks won’t be that problematic for many ships. It is suggested that emissions of sulphur could be cut by 90-95% and carbon emissions by 20-25% by this measure. LNG also happens to be generally cheaper as a fuel than many other alternatives, such as diesel.
Of course there are issues here. Some ship engines are not compatible with using LNG. The cost of retrofitting such ships to run on LNG would likely be prohibitively expensive. There are also safety issues to consider, as some ships carrying hazardous cargo have to be cautious of what they carry, and having a couple of containers of LNG on the deck just might not be a good idea from a health and safety point of view, although one assumes purpose build LNG ships would have adequate safeguards in place to avoid these issues.
Power plant changes
Figure 6: Marine engines tend to be on something of a different scale to any other vehicle! [Source: Wartsila]
Still another option would be to change the powerplant altogether. As noted, many ships still use two-stroke diesel engines
. While it’s a bit of an unfair generalisation to say that four stroke diesel engines are better (this paper
discusses the different performance of engines and fuel types in a little more detail), diesel engines do tend to last a bit longer, provide higher efficiency (thus better fuel economy) and lower emissions. Obviously this would have to be done at the construction stage for ships, although it should be noted that one of the disadvantages with four stroke engines is that then tend to be a good deal more expensive.
Marine Gas turbine engines are another option. This involves putting the same gas turbine engines used on planes or power stations and using it as the main powerplant as a ship or in combination with diesel engines. The benefits are greater power to weight ratio’s and higher fuel economy, but at the expensive of higher capital costs. While such engines have generally been used up until now in relatively small and fast naval vessels, increasingly larger ships are being fitted with them. For example the new UK Aircraft carriers will be powered by Gas Turbine engines as were the previous Illustrious class helicopter carriers.
Civilian operators have been slow to adopt gas turbines, again largely due to cost. But its an idea that is catching on, particularly for cruise ship’s as they tend to have higher electrical demand (the new Queen Mary 2 will use a mix of GT and standard diesel engines). Gas turbines are well suited to this role, as well as supporting dual fuel operation.
This of course brings us to the idea of integrated electrical propulsion, effectively adopting the same idea as hybridisation in cars, where the ships engines are merely used to generate electricity, with electric motors, typically water jets or mounted in Azimuth pods, actually move the ship. It should be noted that the fuel economy benefits of hybridisation, aren’t quite as good as those for automotive…given that ships tend to plot along at 20 knots while cars have to deal with stop and go traffic.
Figure 7: Modern ships increasingly use Electric motors mounted in Azimuth pods to drive the ship [ABB Marine]
However the technical benefits tend to include the simplification of the drive train (e.g. no need for a gear box), improved ship manoeuvrability (some modern ships can practically turn on a dime if needed!) and the fact that the power plant does not need to be located towards the bottom and rear of the ship (as it doesn’t need to be physically connected to the propellers anymore), which allows greater flexibility in terms of ship design.
Streamlining and aerodynamics
And more flexible ship design can have benefits, notably in much the same way the streamlining of trucks and cars has produced greater fuel economy, doing the same with ships can result in fuel savings. This is of course another way to shave a few kg’s off one carbon emissions, use a hull design that’s more streamlined, generating less drag and thus lower fuel consumption .
Figure 8: Ship designers are increasingly looking at more streamlined ship designs to improve fuel economy [Source: Nissan USA]
Obviously a number of the benefits discussed could go a long way towards reducing carbon emissions from shipping, but most generally involve ships that still run on fossil fuels. Could it be possible to propel ships with renewables? After all, before steam power came along most of the world’s trade was carried on wind propelled ships.
Experiments have been carried out using wind power to propel ships
. These include modern sails fitted to a cargo ship, using giant kites
to catch higher altitude winds and so-called rotor sails
(these rely on the Magnus effect
, the same phenomenon that keeps a football spinning in flight).
Similarly solar powered ships have been tested, with and a number of boats of various sizes powered by PV arrays. The large surface area of many ships could well represent a perfect spot for lots of solar cells. In 2012, the Turanor PlanetSolar successfully circumnavigated the globe operating under solar power.
Figure 10: Recent advances in solar cell and litium-Ion battery technology has resulted in solar power ships [Source: planetsolar.org]
That said, to be realistic there are obvious practical problems with this, i.e. what does a ship do when there’s no wind, no sun and it needs to up the speed to get out of danger? One assumes ships will need some alternative form of propulsion as a back-up (the Turanor uses Li-ion batteries to store power overnight). It also seems probable that moving a ship at a decent cruising speed is going to be difficult under renewables power directly, particularly for cargo ships.
Even so renewables can clearly be used to supplement the propulsion of a ship, which helps to lower its overall carbon footprint, much as has been the case with building integrated renewables. Also there is the matter of powering the ship when it is in port. A ship at dock still needs to be powered up, often achieved by running its main engines, using a smaller APU system or connecting up to shorebased power (so called “cold ironing”). Given the new and increasingly stringent legislation mentioned earlier, running the main engines in power is going to become an increasingly difficult (if not illegal) activity and renewables can help to meet these energy needs eliminating the need for APU’s.
Fuel cells, either running on fossil fuels or directly on hydrogen can also help out in this regard and may indeed provide a long term replacement as the primary energy source for ships.
In some respects building a fuel cell powered ship is somewhat easier than a fuel cell powered car. Ships tend to cruise along at a fixed speed for days, while a car has to perform stop go traffic. The issue of power to weight ratio’s tends to be less of an issue with ships. Both of these factors thus allows the use of more robust fuel cell technology such as Solid Oxide fuel cells instead of the super-expensive PEM types favoured for cars. Experiments with fuel cell powered ships have been conducted by the Norwegians (a modestly sized cargo ship, pictured), Iceland (fishing boat sized craft) and various smaller inland craft (such as barges and pleasure craft).
Figure 11: the Viking lady, the world’s first fuel cell powered capital ship ran on LNG [Source: fuelcelltoday.com, 2012]
That said, a fuel cell powered boat will, if powered by hydrogen
, come with many of the same issues mentioned with regard to LNG or CNG, as well as the higher capital costs associated with all electric propulsion. Also at present no fuel cell manufacturer makes fuel cells large enough to power a large ocean going cargo ship, although one assumes existing designs could be just scaled up. There’s also the issue of how a fuel cell will react towards long term exposure to a salty environment such as those at sea. Even so there is at least in the interim a role for fuel cells to play, for example as APU’s
for ships in port.
On paper a ship would appear to be an ideal spot to install a small nuclear reactor. While only a handful of civilian ships have been powered by nuclear power (mostly icebreakers) they have been used for many decades to power naval vessels of all sizes (submarines, carriers, cruisers), so this is proven technology.
However while I hear much enthusiasm for nuclear powered civilian ships from nuclear energy supporters, I rarely hear this from the shipping industry. Perhaps this is because they’ve spent the last 50 years trying to cut down capital costs, maximising cargo capacity of ships, minimise crew size (some are even discussing the possibility of fully automated cargo ships with no crew on board on certain routes) and avoiding getting tied up in pesky government regulations (hence why so many ships operate under flags of convenience).
Nuclear powered shipping involves breaking all of these rules. Nuclear reactors greatly increase the capital costs, reduce cargo capacity, increasing the size of the crew (notably with highly skilled nuclear engineers and the high salaries they command) and one assumes the public will demand that such ships are properly regulated (and one has to question whether flag of convenience nations can adequately do that).
Figure 12: The MV Sevmorput, a nuclear powered cargo ship proved to be a technical success but an economic failure (she is currently awaiting scrapping), the US have seen similar experiences with the NS Savanah [Source: Shipspotter.org]
And on that issue of public acceptance, its worth pointing out that during the cold war many towns and cities declared themselves “nuclear free zones
”, meaning local ordinances forbid the operation or handling of nuclear materials within the city or region. My home town of Cork (a crucial port on the transatlantic route) happens to be one of those
. Convincing locals to relax such rules would probably require high safety standards and strict regulations (both of which have largely rendered civilian nuclear power uneconomic). Else nuclear ships could well find a number of the world’s ports and waterways barred to them.
Consequently I don’t see nuclear powered cargo ships as a possibility unless there is a significant change in the way the shipping industry does business or without a major increase in fuel costs.
A Greener future?
There are as always solutions to the shipping industry’s problems. A host of modest measures taken in concert can produce a significant drop in the carbon emissions and pollution related to shipping. Some of these options can be easily retrofitted or applied to existing ships, others would require more fundamental changes.
Figure 13: A summary of the different options and the cost benefits, according to the DNV 2020 report [Source: DNV, 2012]
The cargo ship of the future could look radically different from those today. Incorporating many new technologies
and concepts, some of which have already been discussed here.
On which point it’s worth noting that the average lifetime age of a cargo ship is only about 25 years, before its run into the sands off Alang
Indeed this is perhaps a final consideration, what is the end of life plan for a ship? There is a need for tougher legislation both to control how ships are dismantled, but also how they are constructed with a view to reducing the environmental impact when they are broken up. One possibility is the idea of adopting similar rules as apply to the car industry, where the manufacturer is obliged to participate in the recycling of the very vehicles they built in the first place.
Figure 15: The end of life and final disposal of ships has to be considered, pictured is the SS American Star, wrecked off the Canary’s [Source: Wollex (2004) via wikimages]
Also one has to consider the more fundamental question – do we really need all these cargo ships?
Making products closer to home, buying locally manufactured goods does go along way to reducing carbon emissions. Thus the future of shipping could well be one with not just cleaner ships, but hopefully less of them.