A feasibility study carried out by The Glosten Associates for Washington State Ferries (WSF) has revealed that utilising liquefied natural gas (LNG) as a fuel leads to significant economic and environmental benefits, reports Marine Log. The Seattle-based Naval architectural and marine engineering firm built on Glosten’s 2010 study investigating the use of LNG fuel in WSF ships, to determine the feasibility of converting WSF’s 144-car ferry design to LNG propulsion. The conversion is described as both “technically feasible and cost effective, although technical and regulatory challenges remain”.
To support the study, Glosten is reported to have developed a preliminary design for both dual-fuel and single-fuel (LNG only) engines. The operational savings for a single vessel are estimated to be between $900,000 and $1.25 million per year, after an upfront capital cost premium of $8.5 million to $10 million.
In the absence of regulations for LNG-fuelling vessels, the United States Coast Guard’s demonstrated willingness to assist in the development of the design means the project is able to proceed. International Maritime Organisation (IMO) Interim Guidelines on Safety for Natural Gas-Fuelled Engine Installations in Ships, informed by classification society DNV, will guide the process.
Switching to natural gas fuel will significantly reduce emissions of nitrous oxides (NOx), sulfur oxides (SOx), particulate matter, and carbon dioxide (CO2). These greenhouse gases have been identified by the U.S. Environmental Protection Agency (EPA) as significant factors in harming human health, including respiratory illnesses, as well as damaging to the environment.
One significant finding in the report relates to methane slip from LNG-fuelled engines. According to the March 2010 report, “since LNG is nearly pure methane, a small percentage of unburned methane passes up the exhaust which is known as ‘methane slip’. Methane is a greenhouse gas and its release into the atmosphere should be minimized since it has the potential to offset the lower CO2 benefits of LNG propulsion. Engine manufacturers are aware of the methane slip and are continually working to decrease this since it directly impacts fuel efficiency.”
WSF is apparently investigating LNG conversion for other vessels, using similar design features as applied to the 144-car ferry.
Washington State Ferries is the largest ferry operator in the U.S., carrying more than 23 million passengers and 10 million vehicles annually. More than half of the 21 vessels in the Washington State Department of Transportation’s Ferries Division (WSF) are more than 40 years old.