Arctic Ocean environments are quite delicate, and shipping in Arctic regions has been very limited. Although ships are the most efficient means of cargo transport from an air quality perspective, they are never the less considered large point sources of CO2 and GHG emissions. Recognizing this, local far north Alaskan air quality requirements have called for the use of Ultra Low Sulfur diesel (ULSD) fuels to lessen SOx emissions from engine driven main propulsion systems and other onboard auxiliary machinery. ULSD (limited to 15 ppm or 0.0015% sulfur) exceeds all current requirements for marine diesel fuels to be burned in the proposed Emissions Control Areas worldwide.
There is a price to pay for burning ULSD, as the physical properties of the diesel fuel are changed during the sulfur removal process. In addition, end-product fuel analysis varies depending upon the sulfur content in the feed stock, and the oil refinery used to produce ULSD. Ultra Low Sulfur Diesel is known to have caused engine and component malfunctions due to decreased lubricity, viscosity, and other compositional incompatibilities. This paper (referencing a recently completed project) will highlight the methodology used to prepare a ship for the switch from Marine Gas Oil to ULSD.
Dry docked in the Philippines, a drill ship was undergoing extensive upgrading to ready it for service in Alaskan waters. The proven rig was ideally suited to the location where it was to operate and therefore, an investment decision was made to renew steel, machinery, and all equipment, required for the voyage. The original main diesel engine was to provide the propulsion power for the trip. Electrical power was to be provided by several large Caterpiller diesel engines located in a separate machinery space forward of the centrally located drilling rig. Because of the air quality restrictions in the working area, preparations were being made for the loading and use of Ultra Low Sulphur Diesel (ULSD) in the main propulsion and other auxiliary diesel engine systems. ULSD is known to have caused engine and component malfunctions due to decreased lubricity, viscosity, and other compositional incompatibilities.
The OEM no longer supported the main propulsion engine (although third party support was available), and there was little original, fuel system technical documentation remaining on-board. It wasn't well understood how the main diesel engine would handle the switch over to ULSD. There were also questions regarding several of the auxiliary engines too. For this reason, DNV was invited to perform a risk assessment (RA) on behalf of the vessel charterer to better understand the impact of switching from Marine Gas Oil to USLD. The objective of the exercise was to assess the risk, identify mitigating procedures, and inform the officers and crew.