One of the first design decisions required is the selection of materials used and it will become increasingly important to determine the recycling capability since the impact of obtaining, processing and manufacturing raw materials is so large. Within the automobile industry the ability to recycle virtually all vehicle components is becoming the trend. Marine structures and equipment require an enormous amount of energy in their construction and future reuse of components should be considered during the concept design stage [1].
The combustion process on-board a vessel contributes to more than 90% of the CO2, CO, NOx, SOx and particulates compared to the fuel production chain. Waste generation for all stages of the life cycle are important with a significant produced during the fuel production process. Vessels have a long operational lifetime and it is necessary to apply cost effective technology and operations that ensures low environmental impact compared to the alternative modes of transport. Johnsen et al concluded from their studies that effort should continue to focus on the reduction of fuel consumption and NOx and SOx emissions [2].
The EU current and planned emissions legislation for road transportation includes significant reduction in CO, NOx, HC, and particulates [4]. It is not too controversial to suggest that the similar pressures will be brought to bear on the marine industry.
3. DEMANDS FOR TECHNOLOGICAL CHANGE
As always, the overriding and most important demand for technological change is the commercial need to remain financially competitive. However, greater emphasis on the environmental impact of marine transportation has resulted from greater social and legislative pressures and these will continue to shape the areas in which technological developments must be made. The following are some of the main marine engineering issues that the industry needs to continue to address [5].
3.1 Fuel Consumption
The reduction in fuel consumption of the powering and propulsion plant will have a significant affect on the LCA, reducing all harmful emissions to air and fossil fuel depletion. A vessels operating speed, hull and propulsion design can minimise resistance and is very important in reducing fuel consumption. Future transportation chain utilisation of shipping will need to balance the demand for high speed and cargo carrying capacity to optimise resistance and improve fuel consumption [6].
Specific fuel consumption for marine diesel engines has reduced by approximately 20-25% since the 1973 oil crisis and similar improvements have been made with road transport diesel engines. However, improvements in fuel consumption figures at this rate are extremely unlikely in the future because of the introduction of increasingly more strict emissions legislation. Measures taking to reduce specific emission species tend to have a negative effect on the fuel consumption of the engine [4].
3.2 Fuel Quality and SOx Emissions
The underlying factor in the performance of any powering and propulsion plant is the type and quality of fuel on which it operates The demand for reduced environmental impact of shipping operating within North European waters has led to some ship operators advocating a move away from heavy fuel oil and the greater use of diesel or gas oil [6]. The total demand for distillates is set to increase across all sectors, not just marine according to Liddy [7]. With the total fuel oil demand predicted to be fairly constant, there is a potential imbalance in the refiner's production that will require correction by further increase in residue conversion processes.
To reduce acidification there has been the introduction of controls on fuel sulphur content as a means to reduce the SOx emissions from shipping. MARPOL Annex VI places a global cap of 4.5% on the sulphur content of marine fuels and also allows for designated SOx Emission Control Areas (SECAs) where the limit is reduced to 1.5%, The 4.5% limit is not a problem for the shipping industry as less than 2% of today's bunker deliveries are above this level. However, a 1.5% sulphur limit used for SECAs will have a major bearing since less than 4% of current bunker deliveries are below this limit. Gas, Low Sulphur HFO, diesel and HFO have a 0.5%, 1%, 1.5% and 3.5-5% sulphur content respectively [6]. Low sulphur fuels are available but extensively consumed by inland users and the shipping industry must be prepared to compete for the relatively small amounts available and meet the price premium.
3.3 NOx Emissions
NOx emissions reduction techniques can be divided into two categories: 'Primary methods', which alter the characteristics of the combustion process within the cylinder, thus reducing the amount of NOx formed, and 'Secondary methods' which focus on exhaust gas after-treatment. Although secondary methods such as Selective Catalytic Reduction (SCR) have demonstrated significant NOx reductions (85%-95%), at present they are more suited to land based applications where space, weight and maintenance requirements are not as critical. Their operation relies on a supply of urea and when conducting a LCA some question the benefits because of the NOx emissions in the production of urea [6].
According to IMO, all engines installed on-board ships with a power of 130kW and above need an Engine International Air Pollution Prevention Certificate (EIAPP Certificate). Emergency diesel engines (generator, fire pump etc,) are excluded. These certificates provide the basis for the International Air Pollution Prevention Certificate (IAPP Certificate) covering the entire ship, which is issued by the flag state authorities or class on their behalf.
Engine monitoring and the regulation of emissions is becoming an increasingly difficult area for the classification societies to control. Emissions measurement is a complex and costly operation. The mandatory inclusion of NOx reduction techniques on new vessels is one thing, however ensuring the use of systems such as SCR plants along deep-sea routes is altogether more difficult.
3.4 Safety
Marine accidents, such as the grounding or loss of a vessel, have potential for enormous social and environmental impact and as a result the safe operation of shipping will remain an important area where improved operational procedures, ship construction, equipment and machinery systems will continue to be demanded.
