EXHAUST GAS EMISSIONS FROM SHIPS

The marine industry is facing the challenge of adopting new technologies and/or operational practices to comply with stricter international, regional, national and local regulations introduced to reduce air emissions from ships. The adverse effects of exhaust emissions from internal combustion engines and boiler exhaust gases on human beings and sensitive ecosystems have been well documented by the scientific community. The objective of regulations introduced by the International Maritime Organization (IMO), the European Union (EU), the U.S. Environmental Protection Agency (EPA), the People’s Republic of China (PRC), the Government of the Hong Kong Special Administrative region of the PRC and the California Air Resources Board (CARB) is to reduce the negative impact shipping makes on global and local air quality. Critical amongst these regulations are the measures to reduce sulfur oxide (SOx) emissions inherent to the relatively high sulfur content of marine fuels. Ship designers, owners and operators have a number of different routes to achieve SOx regulatory compliance:
• Use low-sulfur marine fuels in existing machinery
• Install new machinery (or convert existing machinery where possible) designed to operate on a lowsulfur alternative fuel, such as liquefied natural gas (LNG)
• Install an Exhaust Gas Cleaning System (EGCS) as an after treatment device

Marine air pollution regulations typically require the use of low-sulfur fuel in order to reduce SOx gaseous emissions and the sulfate portion of the particulate matter (PM) emissions. However, the use of EGCS technology is generally permitted as an alternative means of compliance. While EGCS have limited commercial marine references, they are proven technologies with numerous land-based installations and applications as part of the inert gas systems on tankers. Scrubbers can be effective in complying with regulations that require the use of 0.1 percent sulfur fuel. With regard to meeting the regulatory requirements for emissions of nitrogen oxides (NOx), a typical EGCS provides only negligible reduction in NOx emissions and is not an effective method for obtaining compliance with NOx emission requirements. A number of primary (engine) and secondary (after treatment) techniques for reducing NOx emissions exist. One primary engine technique is the use of exhaust gas recirculation (EGR), which involves the recirculation of a portion of the exhaust gas, typically 20 to 40 percent, back into the combustion chamber. For marine applications, this technique may include an EGCS to prevent engine fouling, corrosion and wear issues because of the relatively high sulfur content in the fuel. IMO is currently in the process of developing guidelines applicable to the bleed off water from EGR systems. Selective catalytic reduction (SCR) after treatment systems may be used as a means of reducing NOx emissions, which have the potential to reduce emissions by up to 95 percent. While scrubbers offer the potential for lower operating costs by permitting the use of less expensive high-sulfur fuels, capital, installation and operational costs associated with scrubbers must be considered on a vessel-specific basis. These costs should be assessed against the alternatives of operating a ship on low-sulfur fuel or an alternative low-sulfur fuel, such as LNG. Fuel switching, an operational practice in which higher sulfur fuel is used where permitted and lower sulfur fuel is burned where mandated, has its own complications and risks but should also be considered during an evaluation of fuel compliance options. The operating profile of the ship will often dictate which compliance option offers the best capital expenditure versus operational benefit. The total cost of ownership for that particular ship should be determined to help reach the best decision.