Feature 1 | GREEN SHIPPING
Exhaust emissions prediction and mitigation
In an extract from a paper delivered at RINA’s Green Shipping conference in February Dr Alan J Murphy, lecturer in Marine Engineering, and Dr Kayvan Pazouki, teaching fellow both at Newcastle University, outline the maritime exhaust emissions conundrum.
Pollution from shipping in European waters amounted to 20 – 30% of the SOx and NOx emitted from all land-based sources in the year 2000 according to an EU report. Despite these concerns demand for
S
global shipping has steadily increased, by 5.5% annually from 2000 to 2007. Increased shipping activity has offset the positive environmental impact of emissions regulations, resulting in a net increase in shipping emissions. Consequently, in 2008 the IMO agreed an amendment of MARPOL annex VI which applies more stringent measures on NOx and SOx emissions from ships. Additionally shipping’s contribution to climate change through CO2
emissions has
received attention from regulatory bodies with estimates suggesting around 3% of the global greenhouse gas (GHG) come from maritime activity. With an anticipated growth in international trade that figure is expected to increase by a factor of 2-3 by 2050 if no action is taken. However, the EU is committed to reducing shipping emissions by 40-50% by 2050, compared to 2005 levels, it said in a recently published transport White Paper. Te IMO has also intensified its work
on regulating GHG emissions from ships and focuses on two areas. Te Energy Efficiency Design Index (EEDI) sets a minimum efficiency standard for new ships and will become mandatory from 2015. Additionally the Energy Efficiency Operational Indicator (EEOI) encourages shipping to reduce CO2
emissions by improving fuel efficiency.
Table1: Reduction performances of mitigating technologies.
38 The Naval Architect May 2012
hipping, despite being a highly efficient form of transport has become one of the world’s major air polluters.
Currently there are some mitigating
measures and technologies available to reduce air pollution from ships. However, some technologies need further development and some may not be economically viable for installation.
Emission reduction methods Much research has been carried out on developing technologies to reduce emissions from ships. Tese abatement measures and technologies can be divided into four main categories as follows:
• Pre-combustion measures modify either air or fuel before admission to
• During combustion measures alter fuel combustion characteristics by
the engine and restrict the formation of NOx and/or SOx. The use of alternative fuels as a mechanism for exhaust gas emission reduction is also included in this category.
either introducing water during the combustion process or through tuning engine timing. These technologies predominantly target NOx formation in the combustion chamber by lowering peak combustion temperatures. Engine modification can, in addition, reduce
* There can be potential reduction of CO2
• Post-combustion technologies clean the exhaust gas using either a scrubber
• Non-engine and non-combustion are measures that concentrate on
and/or by converting pollutants into benign elements by chemical reaction. Tese technologies do not prevent the formation of pollutants during combustion, instead, remove contaminants post-combustion.
managing and optimising shipping activity to reduce emissions. These include optimum maintenance strategies, economic speed and weather routing. Another measure considered in this category is the provision of an onshore [electrical] power supply (OPS) to the ship, when in port. In this case, ship exhaust emissions can be entirely eliminated if all engines are shut down while connected.
These measures and technologies
have been variously investigated and their reduction efficiencies have
depending on the source of supplied energy.
particulate matter (PM) emissions by improving fuel combustion conditions through better atomisation and distribution of fuel.
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