The Technology Exists but Compliance Won’t Be Easy
Updated 5 Sep 2019
The IMO’s targets for reducing greenhouse gas (GHG) emissions are clear and well understood throughout the maritime industry – CO2 emissions from ships need to be cut by at least 50 percent by 2050 compared to 2008. What is less clear is how the industry will adapt itself to meet this compliance challenge.
The starting point
Before agreeing on those targets, the energy efficiency design index (EEDI) was the IMO’s main instrument to curtail the contribution of shipping to GHG emissions. This index applies to newbuilds and is aimed at promoting more energy efficient engines and propulsion machinery. The smaller the EEDI, the more efficient the ship design; accordingly, clear reduction targets were put in place by the IMO. Today, ship designers and shipyards are under pressure to come up with designs that comply with the 30 per cent EEDI improvement requirement by 2025, compared to 2008.
During recent years, significant ship design improvements have been made in order to lower the EEDI. Additionally, the installed engine power and the engine’s brake-specific fuel consumption (BSFC) have been reduced. However, there are limits to how small an engine can be, since a ship has minimum propulsion power requirements, and of course there are limits as to how efficient an internal combustion engine can be.
While propulsion efficiency has the knock-on effect of reducing fuel consumption, the EEDI itself doesn’t reflect the actual GHG emissions of a vessel when sailing. Therefore, the IMO has proposed a whole range of additional measures for reducing actual GHG emissions, which include reducing sailing speed, improving operational efficiency through the ship energy efficiency management plan (SEEMP), and the use of low or zero carbon fuels. The SEEMP applies to both new and existing ships and is an operational measure that establishes a mechanism to improve the energy efficiency of the vessel in a cost-effective way.
Reduction of sailing speed
An important consideration when opting for slow steaming is that from experience, we know that there are issues with cylinder liner cold corrosion. Another thing to bear in mind is that at lower speeds and reduced engine output there may not be sufficient steam available for heating purposes. The steam production capability of the exhaust gas boiler is often limited by low exhaust gas temperatures. With modern engines, there are specific tunings available to increase these temperatures at lower engine outputs on account of fuel consumption.
With high main engine efficiency combined with low power output, BSFC optimisation technologies, such as turbocharger cut-off, become less and less attractive. This has further implications should the owner opt to continue using HFO fuel with a scrubber installed in order to comply with the 2020 sulphur cap, because this demands more steam compared to using MGO/MDO.
LNG - the viable fuel
When looking at the alternative fuel options, the most logical choice has to be LNG. While converting to LNG fuel may not be a cost-effective option for existing vessels, it is certainly viable for newbuilds. The global bunkering infrastructure is undergoing fairly rapid development, and as the demand for LNG fuel in marine applications increases, the supply chain is responding accordingly.
The benefit of LNG from the EEDI standpoint is its lower carbon content. The IMO has defined the carbon factors of fuel in its EEDI calculation formula. The carbon factor of LNG is approximately 12 percent lower than that of HFO, meaning that with an engine burning LNG, a ship’s EEDI is some 10 percent lower than when fuelled by HFO.
Another advantage of LNG fuel is that its energy content, or lower heating value (LHV) is higher than that of HFO or MDO. Furthermore, at a similar level of engine efficiency and when considering current LNG bunker prices, fuel costs are actually lower with LNG fuelled engines than with conventional diesel engines.
Methanol and ethanol are also sometimes promoted as alternative fuels, and their carbon factor is even lower than that of LNG. However, because of the production processes involved, the well-to-propeller GHG balance is similar or even higher. The real problems though are the cost of these fuels and their limited bunkering availability, and the only realistic application is to fuel tankers that are carrying methanol or ethanol as cargo. The same is true of LPG.
WinGD X-DF engines
While LNG has clear advantages as fuel in main engines, it has to be said that not all dual-fuel engines capable of burning LNG are equal. WinGD’s X-DF engines operate on the Otto-principle, thanks to the simple low-pressure gas admission technology applied, which enables compliance with all currently known emissions legislation. NOx emissions, for instance, are as low as the current Euro-VI limits for trucks and busses on a g/kWh basis. Thus, the IMO’s Tier III NOx limits can be met without additional exhaust gas after-treatment equipment. Furthermore, with no after-treatment systems to operate and maintain, the ship’s operational costs are that much lower. The sulphur content of LNG is negligible, which also aids compliance with environmental regulations. It is worth noting that, with X-DF engines, prolonged slow steaming ceases to be an issue. This is because of the almost non-existent sulphur content, and that with engines applying the Otto-principle, the liner running surface is typically hotter than with Diesel-principle engines. This means that LNG-fuelled X-DF engines are also the best choice in terms of the speed reduction option mentioned in the IMO’s GHG strategy.
As an engine designer, WinGD is continually investigating or developing technologies for injecting and burning alternative liquid or gaseous fuels for applications where it makes sense. Future synthetic fuels are, therefore, very much part of the R&D landscape. These fuels, which are also known as ‘P-t-X’ or ‘electric’ fuels, are produced with electro-chemical processes. The one with the highest potential to become a zero-carbon fuel for marine engines is e-methanol, and this could possibly over the long-term eventually replace LNG.
However, one needs to bear in mind that any fuel, fossil or synthetic, that contains carbon will create CO2 emissions when burned. Synthetic fuels containing carbon can only be called ‘zero-carbon’ or ‘carbon-neutral’ when the same, or higher, amount of CO2 from the atmosphere is used for their production than the amount of CO2 emitted when burned, and if the electricity needed for the production is generated in a carbon neutral way, i.e. from wind, water, or solar power.
There are synthetic fuels that contain no carbon, such as hydrogen (H2) and ammonia (NH3), which can also be produced.
In addition to alternative fuels and speed reduction in its proposed measures for reducing GHG emissions from ships, the IMO also emphasizes the need to improve operational efficiency. WinGD supports this by offering its ‘WiDE’ engine monitoring system. This enables the actual performance of each individual engine to be compared against its demonstrated initial level. It also assesses the speed at which the engine runs most efficiently and evaluates the causes of any performance deviations.
In fact, the engine monitoring capabilities of ‘WiDE’ are extensive, looking for examples at how fuel quality influences engine performance, and at the load range limits wherein the engine operates. The information provided enables the crew to initiate any necessary adjustments to ensure that the main engine(s) run at optimal efficiency and, therefore, with the lowest possible GHG emissions.
The technologies that will allow CO2 emissions from ships to be within the IMO’s 2050 limit already exist to a large extent. Engine efficiency has developed notably in recent years, and the increasing use of digitalised solutions is promoting even greater efficiencies. The widespread adoption of LNG as the marine fuel of choice also aids this development, though its advantage is greater with SOx and NOx emissions compliance than with CO2 emission reductions.
The greater challenge for ship owners is in making the appropriate choice for compliance. Since it is far easier to achieve optimal efficiencies and low carbon intensity when building a new ship, than it is to convert an existing vessel in order to comply, it may be an option to retire vessels before their normal service life and renew the fleet with new, efficient, environmentally sustainable ships. This is a tough investment decision to make.
The ultimate aim must be to select an engine technology together with a clean burning and low carbon fuel that provides the vessel with both a lower EEDI and greatly reduced GHG emissions. 2050 may seem a long way ahead, but time has a habit of always catching up with us.