Vanguard Magazine

26 FEBRUARY/MARCH 2018 www.vanguardcanada.com the requirements are called "energy effi- ciency" they are linked to carbon dioxide emissions, and so the carbon content of the fuel is an element of the calculation. IMO requirements are implemented by the Flag States but also enforced by the Port States – the countries where the ships load and unload, or visit for other reasons. For Canadian coastal traffic, Transport Canada plays both roles. In the U.S., the Coast Guard and the En- vironmental Protection Agency are both involved in compliance. Compliance options As noted earlier, exhaust emissions can be cleaned up by scrubbers and other af- ter treatment systems, and engine com- bustion cycles can be tweaked to reduce NOx. A disadvantage of all these is that they reduce the engine efficiency by vari- ous percentages, making it more difficult to meet EEDI targets. Ships can also move to different fuels. Nuclear is perfect from an air emission standpoint, but runs into other concerns and has never been proven to be cost- effective in commercial shipping. Hydro- gen is a potential fuel of the future but will require a range of new technologies. Battery power is an increasingly useful supplement to other sources but does not have enough energy density to be the main source for anything beyond very short range vessels such as some ferries and passenger vessels. From a practical standpoint, in the short to medium term future, the most viable options remain al- ternative hydrocarbons such as biofuels, methanol, and natural gas. Biofuels are by definition renewable. They can include biodiesel, alcohols (ethanol and methanol) and biogas. Only in a few parts of the world are these available to meet more than a small part of the necessary energy supply for transportation or other requirements, and boosting the supply can cause other environmental problems. Methanol can also be generated from fossil natural gas and is seen by some as a potential major marine fuel option. However, most at- tention is currently focused on the di- rect use of natural gas (NG) in liquefied (LNG) or compressed (CNG) forms. NG is predominantly methane, with typically some heavier gas fractions and low levels of other contaminants. Most of these are quite easy to remove. marine fuels Figure 2: EEDI Requirements Table 1: Typical Emission Reductions with LNG ULSD MGO/HFO LNG Cases UNITS Engine Type Medium Speed Slow Speed Medium Speed Slow Speed CO2 600 577 460 430 g / kWH CO2-E 617 581 552 480 g / kWH NOx (Assumes Tier III) 2.5 3.4 1.3 1.2 g / kWH SOx 0.0 0.4/3.5 0.0 0.0 g / kWH PM 0.25 0.30/0.62 0.04 0.04 g / kWH HC 0.8 0.2 4.4 2.3 g / kWH Natural gas While still a fossil fuel, NG is relatively clean burning and has a much lower car- bon content than diesel or heavier fuels. With some engine combustion cycles, it can lead to great reductions in NOx emis- sions. Table 1 presents typical values for the reductions in various emissions in moving from conventional marine fuels to NG. The great disadvantage of natural gas is that – it is a gas. Its natural energy density is much lower than that of liquid fuels, and so storage on a ship or elsewhere requires huge volumes. Two main approaches exist to mit- igating this drawback: compression and liq- uefaction. Compression to 235 bar pressure increases the energy density at ambient tem- perature by around 250 times. Liquefaction at ambient pressure, and at a temperature of -160oC increases energy density by around

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