Propulsion: Is LNG the Future?
The world’s first LNG bunkering tanker refuels the world’s largest LNG-powered passenger ship in Stockholm harbor where the tanker Seagas can deliver 70 tons of LNG to the cruise ferry in 60 minutes (note LNG storage tanks on ferry’s stern). Photo courtesy of Linde/AGA.
The move toward using liquid natural gas (LNG) as a marine fuel is continuing to gain momentum as new environmental regulations are enacted and bunkering facilities are expanded. According to a recent forecast by MEC Intelligence, a market insight firm that focuses on the maritime sector, nearly 10,000 vessels could be adopting LNG propulsion by 2020 compared to less than 100 today. Prior to MEC’s forecast, classification society Det Norske had predicted that LNG would become the dominant fuel source for all merchant ships within 40 years. The reason for such growth is strict emission regulations requiring the reduction of sulfur oxides (SOx) and nitrogen oxides (NOx) to 0.1 percent in Emission Control Areas (ECAs) by 2015 and 0.5 percent globally by 2020. The key compliance options available for vessel operators are either adoption of new types of fuel, such as LNG or low sulphur marine gasoil, or by using “scrubber” technology on existing heavy fuel oil (HFO) burning powerplants. LNG, besides becoming cheaper as new sources are opened up through fracking, cuts carbon emissions by about 25 percent, SOx by almost 100 percent and NOx by 85 percent. However, other technologies are also being explored. These include the use of liquid hydrogen as a fuel to generate power within a combined fuel cell and battery system as well as solar panel and automated sail systems. At the same time a new range of extremely efficient low-speed two-stroke diesel engines is being introduced as more operators take up slow steaming.
Latest LNG Ships
To date, LNG use has been restricted to smaller vessels operating rather short runs due to the large size of fuel tanks required and the few bunkering facilities available. Because of this, most development has centered in northern Europe where some LNG bunkering capability was established for the offshore oil industry and local ferry businesses several years ago. In 2011 Sweden’s Tarbit Shipping placed its LNG-burning product tanker Bit Viking in service along the Norwegian coast after repowering the 25,000-dwt ship with Wärtsilä 50DF dual-fuel engines. Last year the world’s first LNG-powered coaster, the 2,650-dwt fish food carrier Høydal, also began operating off Norway. At the same time Stavanger-based Island Offshore christened the 96-meter-long Island Crusader as the world’s first PSV to use fully dedicated LNG-burning main engines. Earlier this year Finland’s Viking Line began operating the 56,000-gt cruise ferry Viking Grace between Turku and Stockholm using dual-fuel main engines burning LNG as the dominant fuel. Later this year Buksér og Berging AS of Norway will place the world’s first LNG-fueled tugboats into operation at Norwegian ports.
Although Norway has been a significant innovator of LNG propulsion the trend has been expanding internationally, with Italy’s Lauro Shipping recently entering into an agreement that will see a series of gas powered passenger/auto ferries developed for Mediterranean use based on Rolls-Royce’s “Environship” program. This will be the first use of the Environship concept in a passenger vessel and the design will include LNG-burning Bergen engines as well as wave piercing bows and combination Promas propeller/rudder systems, the latter to enhance both fuel efficiency and maneuverability.
In Australia, Incat Tasmania Pty Ltd has already completed the world’s first LNG-burning high speed passenger/auto ferry for operation by South America’s Buquebus on the Buenos Aires - Montevideo run. The 50-knot vessel, with a capacity of 1,000 passengers and 140 vehicles, is the first high speed commercial craft to be powered by gas turbines using LNG as the primary fuel, while marine distillate is retained for standby and ancillary use.
In North America, Canada’s Société des traversiers du Québec (STQ) has ordered an 800-passenger/180-car LNG-powered ferry from Italy’s Financtieri for delivery in late 2014. Designed to operate on the St. Lawrence River, it will be North America’s first ferry to be powered by LNG, although Washington State Ferries, BC Ferries and New York’s Staten Island Ferries have all announced plans to begin using the fuel through retrofit programs.
LNG Container Ships
In the commercial cargo sector Seattle’s Totem Ocean Trailer Express (TOTE) surprised the world’s shipping community last year when it ordered two 3,100-TEU LNG-fueled container carriers from the General Dynamics NASSCO shipyard at San Diego. The twin ships will operate on the relatively short run between the US mainland and Puerto Rico when delivered in 2015 and 2016. South Korea’s DSEC, a subsidiary of Daewoo Shipbuilding & Marine Engineering (DSME), is assisting TOTE in the design of the vessels and will provide a patented LNG fuel-gas propulsion system for the ships. This system incorporates the MAN ME-GI dual-fuel main engine, which works by simultaneously burning HFO and LNG. In the minimum fuel and maximum gas mode, around 10 percent of the fuel burned is oil.
DSME has also been working with CMA-CGM of France on the design of a much larger 14,000-TEU vessel that would incorporate the MAN ME-GI engine but with a higher output of 72,285 kW. Capable of being employed on long haul routes, the ship would be fitted with a 22,490-cubic-meter capacity LNG storage tank and a 4,430-cubic-meter capacity heavy fuel tank to give a sailing range of approximately 25,000 miles. Although there would be a loss of cargo space equivalent to about 440 TEUs for the two fuel tanks this would be more than offset by the enhanced fuel economies and lower emissions achieved.
LNG carriers have long been using LNG as a fuel by simply using their own cargo’s “boil off” gas but Dutch shipping company Anthony Veder is now having a pair of 4700-cubic-meter capacity Liquefied Ethylene Gas (LEG)/Liquefied Petroleum Gas (LPG) tankers built in China that will use LNG as a fuel but will not transport it as a cargo. To be completed by China’s Avic-Dingheng Shipbuilding Co. Ltd for operation in the North Sea when delivered toward the middle of next year the twin 99.95-meter by 17.20-meter vessels will make use of a propulsion package being furnished by Wärtsilä in which the main and auxiliary engines will be capable of operating on both LNG and marine diesel. The LNG fuel will be carried in two deck-mounted tanks, each holding approximately 100 cubic meters or about 53,000 gallons. The dual-fuel technology will allow the ships to sail without restriction in Sulphur Emission Control Areas (SECAs) and Nitrogen Emission Control Areas (NECAs).
Wärtsilä is also developing a new 117,000-dwt Aframax tanker design that would be propelled by the company’s heavy fuel oil (HFO) burning two-stroke X62 engine. In this case, an integrated Wärtsilä exhaust gas scrubber would be incorporated, with the main engine, auxiliary engines and auxiliary boilers all exhausting through it in conjunction with a Selective Catalytic Reduction system installed before the main engine turbocharger. These systems would effectively reduce NOx emissions and sulfur oxide (SOx) emissions to such an extent that the vessel could meet the upcoming 0.1 percent sulfur limit to be imposed in 2015, even while burning HFO having a sulfur content of 3.5 percent.
LNG Bulk Carriers
Although no LNG-fueled bulk carriers have been built yet the first order may be just around the corner. Last year Lloyd’s Register gave Approval in Principle (AIP) to a new “Clean Sky” bulk carrier design that would feature a gas-powered propulsion system. The design was drawn up by Chinese shipbuilder COSCO and Greek shipowner Golden Union in cooperation with Lloyd’s. The initial design focus of the project was on a 290-meter-long, 81,000-dwt Kamsarmax bulker that would offer shipowners the flexibility to choose dual, or tri-fuel engines able to burn heavy fuel oil (HFO) or diesel, as well as LNG. The LNG would be carried in a single, 1,160 cubic meter capacity type-C tank that would sit aft on the vessel’s port side. The fuel would be fed to a MAN B&W 6S60ME C-8.2 – GI Tier II main engine that would give a service speed of 14 knots.
Lloyd’s noted that, to date, LNG-as-fuel research, technology development and newbuilding activities have focused on specific niche sectors such as ferries, offshore vessels and short sea or inland trades but that the Clean Sky project “paves the way” for take-up in the deep sea bulk trades. “This moves the industry far beyond the concept stage,” said Nick Brown, Lloyd’s Register Area General Manager and Marine Manager, Greater China, who noted that the AIP came only after exhaustive risk investigations by Lloyd’s into the gas containment and bunkering systems. COSCO, an experienced builder of Kamsarmax ships, feels it is now ready to build an LNG-powered bulker and its first customer may likely be Golden Union.
LNG Cruise Ships
LNG is also being looked at in the cruise sector and Finland’s Wärtsilä has come up with several ship designs that feature LNG propulsion. Last year Wärtsilä introduced the design of a 65,000-gt ship that followed an earlier project, accomplished in cooperation with shipbuilder STX Europe, covering a larger 125,000-gt vessel. The Finnish company said it chose the smaller size this time around because it sees an increasing demand for such tonnage among both large and small operators.
Beyond dual-fuel diesel/electric drive, which would see LNG tanks situated below the ship’s lido area at the stern, and shafted rather than podded drive, the Wärtsilä cruiser would feature a hull beam of 141.5 feet (43.2m) to give better stability and allow the construction of higher cabin decks. However, the superstructure of the proposed vessel would be abbreviated in length, thus requiring only four main fire zones while providing space aft for a low open deck with a large swimming pool. A service speed of 19 knots would be furnished by two 8MW electric propulsion motors driving fixed-pitch propellers. Power would be generated by two Wärtsilä 6L50DF and two Wärtsilä 8L50DF main engines. These would run primarily on LNG, but with marine diesel as a standby.
The Wärtsilä cruise ship’s LNG would be stored in three double-walled tanks, each with a capacity of 465 cubic meters, housed in the stern area below the pool deck and between the tender boats. In this location the 35-meter length of the tanks would not interfere with the ship’s required watertight bulkheads. As the average daily LNG consumption for a typical cruise would be about 45 tons, or 105 cubic meters, the vessel would be able to make a 12-day cruise without refueling. LNG bunkering would be accomplished via the open mooring deck at the stern while tank ventilation would be through a pipe running to the top end of the superstructure and venting at more than 10 meters above the uppermost deck. The stern location for the tanks is considered beneficial from a safety standpoint because there would be no cabins located above the bunkering station and large windscreens around the pool area would prevent passengers from accidentally creating a source of ignition by tossing cigarettes or matches overboard. Nevertheless, Wärtsilä realizes that the technology involved in the LNG bunkering process must be foolproof and that a network of safe LNG bunkering stations must still be created in the proposed operational areas before its LNG-powered “clean cruiser” can head to sea.
A number of LNG-powered platform supply vessels are now being built in the US and a cut-away of one of the new Harvey Gulf boats illustrates the amount of room required for the LNG storage tank, which is situated below the work deck while diesel generator sets are mounted one deck above and forward. Photo courtesy of Harvey Gulf.
First LNG Bunkering Tanker
A prototype operation for bunkering LNG-fueled passenger ships has already started in Europe where the world’s first LNG bunkering tanker, Seagas, has been delivering fuel to the world’s largest LNG-powered ferry, the 2,800-passenger Viking Grace, since February. Prior to its conversion by the Fiskerstrand BLRT yard in Norway Seagas was the local 1974-built car ferry Fjalir. Now equipped with a single 170 cubic meter cryogenic storage tank, the little tanker moves LNG from Linde’s LNG’s processing facility near Nynäshamn, Sweden to the Port of Stockholm where the 56,000-gt Viking Grace is refueled at the end of nearly every round-trip with 70 tons of gas transferred in 60 minutes. Until the arrival of Seagas, refueling of the ferry had been done by road tanker but this was considered an unsatisfactory method due to safety and environmental concerns. While Viking Grace can make three round-trips between Stockholm and Turku, Finland without re-fueling, Seagas has been refueling the ship six days a week.