Emission Abatement Methods
According to Directive (EU) 2016/802, the use of Emission Abatement Methods (EAM) as an alternative to traditional marine fuels, should be allowed in ships of all flags in ports, territorial seas and economic exclusive zones of the EU. Ships using EAM’s in these areas shall continuously achieve reductions of sulphur dioxide emissions that are at least equivalent to the reductions that would be achieved by using marine fuels (Annex I).
According to the Directive (Article 4c) the following EAM have to be considered:
-Mixture of marine fuel and boil-off gas (BOG) for LNG carriers
-Exhaust Gas Cleaning Systems (EGCS), commonly known as ‘scrubbers’
-Biofuels (andmixtures of biofuels and marine fuels)
and, where applicable...
-On-shore power supply
-Alternative Fuels e.g. LNG, Methanol.
At the international level, the use of EAM is regulated by the MARPOL Annex VI (Regulation 4). According to this regulation, the Administrations of Party shall allow a fitting, material, appliance, apparatus or other procedures, alternative fuels, or compliance methods used as an alternative to that required by MARPOL Annex VI.
Mixture of marine fuel and boil-off gas (BOG) for LNG carriers
Liquefied natural gas (LNG) Carriers are ships frequently fitted with dual fuel boilers, using boil-off gas and heavy fuel oil for propulsion and cargo-related operations. In order to meet the requirements of the Sulphur Directive most LNG Carriers calling at EU ports can use emission abatement technology employing a mixture of marine fuels and boil-off gas to produce sulphur emissions equal to or lower than 0,1 % sulphur fuel emissions. The provisions for BOG as an Emission Abatement Method are laid in Commission Decision 2010/769/EU on the establishment of criteria for the use by liquefied natural gas carriers of technological methods as an alternative to using low sulphur marine fuels meeting the requirements of Article 4b of Council Directive 1999/32/EC relating to a reduction in the sulphur content of certain liquid fuels as amended by Directive 2005/33/EC of the European Parliament and of the Council on the sulphur content of marine fuels
Commission Decision 2010/769/EU establishes the framework criteria for the use of boil-off gas as a primary fuel at berth, producing even lower sulphur emissions than those which would be achieved through the limits on sulphur in fuel specified in the Directive.
Exhaust Gas Cleaning Systems (EGCS)
Exhaust Gas Cleaning Systems (EGCS) represent, in particular for ships in service, a technically and economically viable solution that can be considered as a strategy to comply with sulphur emissions limitations, using otherwise non-compliant fuel.
Different EGCS technologies exist that can be considered:
- Wet medium EGCS (wet scrubber), comprising of EGC systems able to operate in “open-loop”, in “closed-loop” or even on a combination of these two modes, on what is commonly called “hybrid-mode”. The wet scrubbing systems, regardless on the details of the operating mode, use water (seawater or fresh water with additives) directly spayed against the exhaust gases in such a way that the absorption of SOx molecules is promoted before exhaust release to the atmosphere.
- Membrane Scrubbing, where in a similar approach to “wet scrubbers” a basic liquid absorbent is used to react with the acidic sulphur dioxide gas. When compared to “wet scrubbing” technology the key difference of membrane scrubbing is that the liquid absorbent is not sprayed into the exhaust stream to mix with the exhaust. Instead, the liquid absorbent is suspended in membranes to come in contact with the exhaust but not to mix with it, leading only to the absorption of sulphur dioxides.
- Dry Scrubbing, relying on de-sulphurization process in dry medium where a reactor filled with granulate of calcium hydroxide in the exhaust line is responsible for the gas cleaning. No water is involved in the process and no water discharges or process circuits are considered.
None of the technologies above are without their challenges. From the de-sulphurization technique down to the system integration onboard, either for a retrofit project or for a newbuild, existing and potentially innovative technologies can be considered to have different technical aspects that require substantial engineering design. Notwithstanding the potential for a significant number of currently available EGC concepts, the technology present in the largest number of onboard applications is the “wet scrubbing”. Significant build-up experience has been gained from an increasing number of onboard installations, making of this technology an important example as an Emission Abatement Method.
Wet based EGC systems, as mentioned above, depending on their specific engineering arrangements, can be operated in either “open-loop” or “closed-loop”. Systems that can be operated in both modes are called “hybrid”.
Sea water scrubbing is based on the natural alkaline characteristics of seawater, it is used to neutralise the acidic exhaust gases. Further to the absorption of the SOx molecules by the seawater, the water is then discharged back into the sea after being treated and ensured that all criteria for its discharge are met. Any resulting sludge from this treatment must be stored on board prior to final delivery to a shore reception facility.
Alternative fuels, and as specially considered in the Sulphur Directive, Biofuels (and mixtures of biofuels and marine fuels), are obvious alternatives to the use of conventional oil fuels of higher sulphur content.
Sulphur is a naturally occurring element in hydrocarbon fuels. It is associated with asphaltenic fuels and correlated with vanadium content. Sulphur generally occurs in large aromatic molecules. Because of this, it is concentrated in residual oils or HFO. Fuels of a simpler molecular composition can be considered as cleaner fuels, avoiding complex carbon molecular content that is responsible for a large spectrum of pollutant emissions.
What are Alternative Fuels? The particular definition of Alternative Fuels in Directive 2014/94/EC can be used to answer this question. ‘Alternative fuels’ means fuels or power sources which serve, at least partly, as a substitute for fossil oil sources in the energy supply to transport and which have the potential to contribute to its decarbonisation and enhance the environmental performance of the transport sector.
Some of the examples of cleaner alternative fuels are:
-Biofuels as defined in point (i) of Article 2 of Directive 2009/28/EC
-Synthetic and paraffinic fuels,
-Natural Gas, including biomethane, in gaseous form (compressed natural gas (CNG)) and liquefied form (liquefied natural gas (LNG)),
-Liquefied Petroleum Gas (LPG);
-Ethyl/Methyl alcohols (also known as “ethanol” or “methanol” fuels)
Amongst the typical challenges with Alternative Fuels in shipping are:
-Energy Content of the Fuel, measured through Specific Energy or Energy Density, (KJ/Kg or KJ/m3) is in many alternative fuels lower than that of oil based fuels. For typical ship applications this leads in the majority of the cases to increase fuel tank volume requirements, for similar operating profiles.
-Safety, with many of the fuels having low flashpoints (lower than 60C) and leading to the need of addressing different safety aspect of their storage and use onboard. Different risk reduction mitigation measures are designed for different alternative fuel applications, resulting from safety assessment.
-Availability. In comparison with the wide spread market penetration of oil based fuels, alternative fuels have, presently, much more limited availability as a ship’s bunker fuel.
Shore-side electricity facilities can serve maritime and inland waterway transport as clean power supply, in particular in maritime and inland navigation ports where air quality or noise levels are poor. Shore-side electricity can contribute to reducing the environmental impact of sea-going ships and inland waterway vessels.
EMSA participates in IMO Committees and Correspondence Groups and acts as technical Secretariat for the ESSF - European Sustainable Shipping Forum (Working Groups on LNG, EGCS). Technical studies were conducted to develop the understanding and promote the use of different alternative fuels. (e.g. with the studies on the Potential of Biofuels for Shipping 2012, Standards and Rules for LNG bunkering 2013, Use of Methanol as alternative fuel – 2015, and more recently, already in 2016, with the Study on the use of Fuel Cells in shipping).