Renewable energy from shore
5.45 Renewable energy is generated on land using wind generators, hydroelectric plants, geothermal plants, solar-energy plants, etc. Potentially, power from such providers could be harnessed to run ships if a suitable energy carrier was available. However, as long as there is a shortfall of renewable power onshore, there is little prospect for using land-based renewable energy to propel ships. A noteworthy exception is the use of land-generated power while a ship is berthed.
15. Ideally, fuel cells, solar-power, wind kites, etc. are all potential alternative technologies; but they are often seen as auxiliary power sources and not viable replacements for the main propulsion systems on a ship.
14. Other fuel sources may also play a role and bio-fuels can be utilized in operating ships. However, with the amount of fuel used by the maritime industry and the present economic instability, the industry would deem it wise for lawmakers to investigate more clearly the impact of a significant take-up of bio-fuels by such a big consumer as global shipping before arriving at any decisions.
5.2 Present propulsion systems using carbon-based fuels are seen as the only realistic large volume fuel for vessels over the next two decades years and even longer.
Use of natural gas is presently leading in terms of a lower carbon fuel for the short-medium term, either as compressed natural gas (CNG) or liquefied natural gas (LNG). With existing available propulsion equipment, its use could attain around 20% reduction in CO2 emissions in comparison to residual or diesel-oil fuels.
5.3 Ultimately, hydrogen could become a viable source. Sustainable bio-fuel may also have a role to play if enough fuel were provided to shipping. Alternatively, new and radical fuels and/or technologies may play a vital role.
Fuels with lower fuel-cycle CO2 emissions
5.46 Emissions of CO2 can be reduced by using fuels with lesser overall emissions through the full-fuel process (i.e., production, refining, distribution and consumption). The conversion from residual fuels to distillate fuels, implied by the sulphur regulation in the revised MARPOL Annex VI, has already been accepted; hence, there is no point considering the potential benefits and disadvantages of this move on the emission of CO2 now. Other fuel alternatives with bright prospects for cutting the production of CO2 include bio-fuels and natural gas.
5.47 Current-day bio-fuels (also known as “first-generation” bio-fuels) come from sugar, starch, vegetable oil, or animal fats. Many of these fuels can be readily used for ship diesels with no (or minor) alteration of the engine. Bio-fuels can be upgraded (hydrogenated) in a refinery. As such, the end-result is of high-quality and the practical problems mentioned do not apply. This upgrade process requires energy and leads to additional emissions.
5.48 The net benefits on emissions of CO2 vary among many types of bio-fuels. Not all bio-fuels provide a CO2 benefit. Bio-fuels, in fact, have in certain instances led to a 7% to 10% increase in the NO2 emissions.
5.51 In summary, the current potential for cutting CO2 emissions from ships by using bio-fuels is inadequate. This is not only because of technology issues but also of cost, of limited availability and of other factors based on the production of bio-fuels and their use. Moreover, the bio-fuels are significantly more costly today than petroleum fuels.
Liquefied natural gas (LNG)
5.52 Liquefied natural gas is an alternative fuel in the maritime industry. Having a higher hydrogen-to-carbon ratio compared with oil-based fuels, this fuel produces lower specific CO2 emissions (kg of CO2/kg of fuel). Moreover, LNG is a clean fuel since it contains no sulphur; this eliminates the SOx emissions and almost eliminates the emissions of particulate matter.
Furthermore, the NO2 emissions are cut by up to 90% due to decreased peak temperatures in the process of combustion. Unfortunately, LNG use will increase methane (CH4) emissions, thus cutting the net global warming benefit to 15% instead of 25%.
5.54 One of the primary obstacles for LNG use as a fuel for vessels is finding sufficient space for onboard fuel storage. Energy content being held equal, LNG is 1.8-times larger than diesel oil in terms of volume. Nevertheless, the large pressure storage tank needs ample space, and the final volume requirement reaches to three times that of diesel oil.
Shifting from diesel propulsion to LNG propulsion is possible, but LNG is mostly applicable for new ship construction since significant alteration of engines and allocation of addition storage capacity is needed.
5.56 In summary, the current potential for cutting emissions of CO2 from vessels through LNG use is relatively small, since it is generally suited for newly-built ships and because LNG bunkering choices are limited today.
The cost of LNG is currently substantially lower than the cost of distillate fuels, justifying an economic incentive to shift to LNG.
As to alternative fuels, only LNG is a viable competitor for replacing conventional fuels. The problematic issue of on-vessel storage and containment systems and the land-based infrastructure needed for resupply adversely limits the option for this fuel. The operational distance of ships utilizing LNG is constrained by the fuel storage size and boil-off standards. LNG is seen by industry as more fitted to short sea-navigation than the deep ocean trade. In fact, several ferry routes with dedicated land-based supply infrastructure in Scandinavia presently use LNG as fuel for main propulsion.
The shipping industry is a multi-service industry, and provides many various functions for society.
Nuclear energy is technically viable for sea vessels with many instance of nuclear-powered commercial and military ships. Safety and acceptability issues are, naturally, predominant in this ongoing debate. Nuclear powered ships require a delicate infrastructure and disaster response scheme. Due to common apprehensions among countries, nuclear propulsion will not play an important role in commercial vessels. Nuclear power, though put to effective use in the 1960s, would not be viable commercially or acceptable socially. If it were to be considered at all, it would be more acceptably and efficiently used for synthesizing marine fuels on land.
According to a research that IMO commissioned, technologies could cut fuel use and oil consumption by as much as “30–40%”. However, some of these approaches have been applied by merchants and the fall below their expectations.
Non-conventional technologies presently being evaluated for application, for instance, the sky-sail concept, twin-propeller and the under-hull air cushion give serious prospects.
The kite-system developer believes that the system may cut a ship‘s fuel consumption by an average of 10–35% annually, based on wind power availability. However, new tests have shown a low passing grade for this system. Within ideal wind conditions, fuel usage can be cut temporarily by up to 50%. (528.pdf)
5.57 Although CO2 removed by chemical conversion from flue gases, it is not deemed viable. Emission-cutting methods are generally applicable to pollutants within exhaust gases, NO2, SO2, PM, CH4 and NMVOC.
Emission-reduction options for NO2
5.58 NO2 emissions from diesel engines can be cut by using certain measures, such as:
- Fuel conversion.
- Modification of the combustion process.
- Modification of the charge air.
- Exhaust gas treatment (selective catalytic reduction, SCR).
5.59 A fuel’s sulphur content and its deposit-producing tendency can affect the possibilities for other emission-cutting technologies, such as exhaust-gas recirculation (EGR) or selective catalytic reduction (SCR). Usage and quality of water are problems met by options utiizing water.
5.61 LNG fuel usage is both a fuel switch and a combustion-process shift.
5.62 Reduction of NO2 by 15-20% from the present levels can be attained with changes in the internal-combustion process. Currently, cutting NO2 emissions to Tier III limits (~80% reduction) can only be reached by using selective catalytic reduction (SCR) post-treatment or LNG and lean, premixed combustion.
Emission-reduction options for SO2
5.65 Exhaust-gas scrubbing systems can be utilized to cut sulphur dioxide (SO2) levels. Two primary principles apply here: open-loop seawater scrubbers and closed-loop scrubbers. Both scrubber systems may also remove PM and reduce amounts of NO2.
Scrubbing of exhaust gases utilizes energy which is calculated in the range of 1-2% of the MCR.
5.66 Removal of SO2 through scrubbing reduces the exhaust gas temperature. On the other option, SCR technology needs high temperatures of exhaust gas and also produces low sulphur and PM content. Combining SCR with scrubbing to remove SO2 does not seem viable.
5.67 Polluting substances coming from the exhaust is carried by the wash-water.
Sulphur oxides react with seawater to produce stable compounds that are generally common in seawater and not considered dangerous to the environment in many places. However, particulates in the exhaust that are eventually disposed into the seawater may harm the environment. The revised IMO Scrubber Guidelines  establish limits for the effluent, including limits for Polycyclic Aromatic Hydrocarbons (PAH), pH, nitrates, turbidity and other materials. Port State standards for effluent pollutants will have a substantial impact on the possible use of seawater scrubbers. To achieve these standards, an effluent-treatment system must be installed. Normally, the more SO2 and PM removed by the scrubber from the exhaust, the more pollutants will need to be removed from the effluent.
Emission-reduction options for PM
5.70 Some PM emissions from fuels high in sulphur content can be cut by scrubbing with seawater. The potential reduction of PM levels are said to be from 90% to 20%, depending on the source. With low-sulphur fuels, PM emissions can be cut significantly by optimizing combustion to attain greater oxidation of soot and of PM, reducing the use of lube oil and certain additives in lube oil. Burning emulsions of fuel and water can also reduce PM emissions to a certain level.
Emission-reduction options for CH4 and NMVOC
5.72 Engine-exhausts containing methane (CH4) and non-methane volatile organic compounds (NMVOC) are relatively low. Limited reductions may be attained by optimizing the process of combustion. NMVOC can also be oxidized using a catalyst. These catalysts are commonly used in connection with SCR systems, where they oxidize unused ammonia and removing ammonia emissions.
5.73 CH4 emissions can be cut substantially through meticulous design to prevent crevices. However, a little CH4 emission is inevitable. Using a catalyst, this CH4 can be oxidized, although this is not as straightforward as cutting NMVOC levels. Further research and development are required in this area.
5.74 Emissions of CH4 from gas-powered engines can be practically removed through high-pressure gas injection instead of lean premixed-combustion. This alternative principle is believed to be well suited for big two-stroke engines. The disadvantage, however, is that NO2 emission reduction through direct injection is lower than what can be attained with the lean premixed-combustion option.
Alternatives for reducing HFC emissions and other refrigerants
5.75 Hydrofluorocarbons (HFC) emissions are connection to leaks during the operation and maintenance of refrigeration systems. Technical steps to cut down leaks include designs less affected by corrosion, vibration and other stresses, decreasing the effect of leaks by cutting down the refrigerant charge (i.e., by cooling indirectly) and compartmentalizing the piping design in order to isolate a leakage.