Feature 1 | GREEN SHIPPING
been published. However, some technologies are not yet
ready for
shipboard installation and are still at the laboratory stage. Hydrogen-fuelled engines and Plasma Assisted Catalytic Reduction (PACR) are examples of successful technologies at laboratory scale. Although laboratory results of these technologies have been successful, further research is required to prove their viability for shipboard installation. Table 3 presents an overview of reduction potentials of different technologies and measures and Figures 1 to 4 display the performance of these technologies in each category in graphical format. Figure 1 reveals that measures which
introduce water into the cylinder target mainly the reduction of NOx, but not SOx. However, hydrogen and LNG as alternative fuels offer more effective reduction potentials for all the exhaust gas pollutants. Basic engine modification (Figure 2) reduces NOx emission by exchanging conventional fuel valves with low NOx fuel valves, while advanced engine modification optimises combustion, fuel injection and charge air characteristics to gain a greater reduction. Both basic and advanced engine modification are only effective for NOx reduction whereas direct water injection claims to also reduce PM emissions. Figure 3 also shows that post-combustion methods such as selective catalytic reduction and scrubbers are effective at reducing NOx and SOx emissions. Tey both also reduce PM emissions, but have no effect on CO2
.
With the exception of Hydrogen and LNG, none of the measures and technologies in the categories of pre-, during- and post-combustion reduce all exhaust gas pollutants as standalone methods. Interestingly, non-combustion measures, shown in Figure 4, can reduce all four pollutants from ships, the most effective one being OPS (AKA, cold ironing). Te reduction potentials of measures
and technologies presented in the Table 1 suggest that LNG and hydrogen as alternative fuels and onshore power supply are promising measures for the reduction pollution. Hydrogen-fuelled engines, despite their emission reduction capability, are not yet ready for shipboard installation and additionally, worldwide availability, shipboard storage, handling
40
Figure 1: Reduction potential for pre- combustion measures.
Figure 2: Reduction potential for during combustion measures.
Figure 3: Reduction potential for post combustion measures.
and usability as well as economic aspects of it need further research before being considered as realistic option. A study by Levander and Sipilä evaluated the onshore power supply and alternative fuel concepts using dual-fuel auxiliary engines burning LNG at
local areas
for a 7300TEU container vessel. They compared the environmental and economic outcomes of the two concepts and concluded that LNG is an attractive option for
reducing the total, and
especially local, emissions from ships. Regulatory authorities focus on the
local reduction of exhaust gas pollutants such as NOx, SOx and PM because there is a local environmental impact from these emissions. This is not the case for CO2
as it has a direct impact on the
global warming irrespective of the point of emission. Accurate engine models that predict exhaust gas emissions
Figure 4: Reduction potential for non- engine/combustion measures.
when coupled with an environmental model can help understanding and measurement of the possible impact of ships emissions at any part of their commercial profile. Tese models can later be utilised to effectively manage the voyage profile of ships to reduce the impact of emissions.
Predicting exhaust emissions Despite the regulations and a plethora of technologies which target the different emissions with varying degrees of effectiveness, these neglect to account for the actual operating conditions of the vessels, including engines, propeller and hull as a coupled system. Furthermore,
in order to make
operational judgements, whether that be from the tactical point of view of the ship staff on a day-to-day basis, or at a fleet-level to inform strategic decisions on fleet
The Naval Architect May 2012
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