Replacing the ageing LNG fleet

To accommodate the forecasted growth in LNG trade approximately 250 LNG carriers will be needed by 2010, according to UK based Drewry Shipping Consultants. What is more, at least 40-50 of those vessels will have to be ordered in the next few years.

As Keith Bainbridge, director of LNG Shipping Solutions recently said at a Bureau Veritas Gas & Tanker Day: “The LNG fleet is an ageing fleet, with nearly a third of the existing fleet over 25 years of age by 2010”.

There have been a number of changes that have affected the LNG fleet, such as shorter time charters and voyage charters under negotiation. There have also been new entries into the tightly knit club, including Worldwide, Golar, Ceres, and John Angelecousis. There has also been intense activity in the Atlantic Basin and Japanese owners moving west, says Bainbridge. The market rate and the likelihood of increased vetting of older ships are also going to have an effect. There could also be regulatory impacts from the International Maritime Organisation (IMO), Federal Energy Regulatory Commission (FERC) and the US Coast Guard (USCG).

These could be in the form of new environmental legislation governing emissions, efficiency, or oil pollution risks, or could be the result of political pressure or knee jerk reactions, similar to what is happening in the tanker sector.

Bainbridge says that while slow change is the usual style, alternative propulsion systems already on order for new ships will arrive in force. He believes that there will also be diversity in ship size with mid-size ships being used for shorter routes and larger ships for longer routes.

He also predicts that there will be freedom of destination in contract and an increase in spot sales from eight per cent now to maybe 20% by 2008. There also needs to be a realistic assessment of ship life on a case-by-case basis.

In the immediate future Bainbridge sees an increase in ship size, shorter term contracts and greater flexibility, with the LNG trade opening up to new players rather than just the existing ?club?. He also believes that there will be greater input from the host country and new technologies, such as new containment systems, propulsion innovations and possibly a very large LNG (VLLNG). Floating LNG facilities will also push the technology boundaries further and dynamic positioning (DP) systems and podded propulsors are likely to be introduced to enhance manoeuvrability

The industry has developed slowly over the past 40 years and is still reluctant to change. However, the uniqueness of business will always remain but it is fundamentally shipping: therefore there is room for good tanker operators, such as John Angelecoussis. Bainbridge says that 2006 onwards should see most change as the economics of today demand contract rethinks and external factors could dictate new rules to the ?club?.

The majority of orders for LNG newbuildings are in South Korea (29) and Japan (17) with Spain?s Izar having four orders and France?s Chantiers de l’Atlantique, three. Most of the vessels have traditional steam turbine propulsion plants supplied by Mitsubishi or Kawasaki. However, now that Chantiers de l’Atlantique has managed to convince Gaz de France that diesel electric powered LNG carriers are viable, it could open the floodgates for a new breed of these vessels. The yard claims that its carrier design offers a reduction in fuel consumption of almost 40%, thus greatly improving efficiency. Not only do the ships have a new propulsion plant, but they also have a new gas containment system ? the GTT CS1.

French gas distributor, Gaz de France signed a contract for two 74,000m3 LNG carriers with four Wärtsilä 6L50DF dual-fuel engines in a 22 MW electric propulsion plant in February 2002.

The new vessels will operate between Skilda in Algeria and Fos near Marseille in France. The round voyage will take about a week at a service speed of 16 knots, which can be achieved with three of the four generating sets. The vessel is also designed for spot market trading, such as voyages to the USA. For charters of this nature, all four generators will be used and cruising will be at 18.5 knots.

This has since been followed by another order for a bigger ? 153,000m3 LNG carrier ? ordered by Gaz de France for delivery in October 2005. It will transport liquefied natural gas (LNG) from Norway or Egypt, but is also designed for the alternative of trading on the spot market.

The French classification society, Bureau Veritas, helped develop the concepts for the vessels, and developed unique new rules to allow the yard and owners to break new technological frontiers.

Containment systems

The new CS1 membrane cargo containment system developed by Gaz Transport & Technigaz (GTT) combines the best of the two previous membrane technologies. About 80% of the LNG vessels ordered in recent years use one of the two membrane cargo containment systems available on the market ? either the NO96 (Gaz Transport) or MARK III (Technigaz). Both of these membrane technologies are composed of gastight barriers and of insulation layers.

The CS1 technology is the combination of the invar steel plates to form the gastight barriers (NO96 technology) and of the reinforced polyurethane foam to form the insulation layers (MARK III technology). CS1 technology reduces the thickness of the cryogenic by 50%, increases the cargo capacity of the ship by 4,000m3 and cuts in half the number of components requiring assembly compared with previous solutions.

Kvaerner Masa Yards (KMY) is also offering a stretched tank concept for its Moss design which it claims will allow it to build large LNG carriers up to 182,000m3. 2002 also saw the yard integrate the tank cover structure into the hull longitudinal strength allowing what it claims are remarkable improvements. These include the elimination of the negative consequences that result from a large deck of spherical tanks, excellent hull stiffness and an improved hull form. The designers of the concept claim that this will result in 10% lower propulsion power requirements with any type of machinery and significantly reduced construction costs. Maintenance will also be improved resulting in lower operational costs. KMY says that even larger carriers will now be feasible with the concept as it allows for lower freeboard and manifold location, omission of extremely thick steel plates and a stiff and light construction regardless of vessel size.

The designs can be equipped with either a slow-speed diesel or diesel electric drive. Azimuthing electric propulsion can also enhance manoeuvrability. Boil-off gas (BOG) is handled by a reliquefaction plant.

IZAR?s Puerto Real shipyard has delivered its second LNG carrier Castillo de Villalba to Empresa Naviera Elcano. Its Sestao shipyard delivered the first, Inigo Tapias earlier this year to its owner Fernandez Tapias, who is operating it for Gas Natural SDG. Izar Puerto Real has two more LNG carriers under construction for Naviera Fern?ndez Tapias and for Knutsen OAS, while Sestao Shipyard is building another one for the latter.

The Castillo de Villalba has a capacity of 138,000 m3 in four double membrane No96 type tanks.

The Spanish shipbuilder and owners have opted for a more traditional approach to propulsion in the form of a 28,000kW steam turbine Kawasaki-IZAR type, provided by IZAR’s Turbines Factory.

Propulsion plant

When it comes to propulsion plant there are a number of choices, particularly with respect to BOG:

l Burning the BOG in Boilers for Steam

l Burning the BOG in Dual-Fuel Engines

l Dual Fuel Diesel Propulsion

l Dual Fuel Diesel-Electric Propulsion

l Burning the BOG in Gas Turbines

l Burning HFO and Reliquefying the Gas

Then comes the question of machinery layout. This can involve:

l Single or Twin Screw Options

l Steam Turbine

l Dual Fuel Slow Speed Diesel Engine

l Geared Dual Fuel Medium Speed Diesel

Engine options include:

l Geared Gas Turbines

l Electric Motors

l Podded Propulsion Option

The 153,000m3 LNG carrier being built by Chantiers de l’Atlantique for Gaz de France will have gas-electric propulsion, with four dual-fuel engines driving generators to supply electricity for the single propeller plant. The engines will burn boil-off cargo gas with a small quantity of liquid fuel for ignition. They will mainly run on gas with liquid fuel as back up, and can be switched over automatically as the need arises.

There will be three Wärtsilä 12V50DF engines and a single Wärtsilä 6L50DF engine. They have a combined output of 38.5 MW, with the 12-cylinder engines each developing 11,400 kW at 514 rpm and the six-cylinder engine 5,700 kW at the same speed.

Gas-electric propulsion plant was chosen in competition with the more traditional steam turbine plant because it is more compact. This allows more LNG to be carried within the same size hull and thereby increases the vessel?s annual earnings. The Wärtsilä 50DF engines also have clear benefits in terms of fuel efficiency and environmental impact, while multiple engines give valuable safety and flexibility in operation, with the optimum number of engines running to suit the required service speed.

The Wärtsilä 50DF engines make maximum use of the boil-off gas and have a much lower fuel consumption overall and thus lower operating costs than the conventional steam turbine plant. The Wärtsilä 50DF engines also have much lower stack emissions than a steam plant. Their low NOx emissions are about one-tenth those of the equivalent diesel engines. The combination of the engines? low fuel consumption and their maximum use of boil-off gas means the Wärtsilä 50DF engines also have low CO2 emissions.

The 50DF was developed from Wärtsilä?s very successful type 46 diesel engines. The Wärtsilä 50DF engines have cylinder dimensions of 500 mm bore by 580 mm piston stroke and are available in configurations with six, eight and nine cylinders in line, and 12, 16 and 18 cylinders Vee-form. The engines develop 950kW per cylinder MCR at 500 or 514 rev/min for 50Hz and 60Hz electricity generation respectively.

The 50DF engines can be run alternatively in gas mode or liquid fuel mode. The engines are also fully capable of switching over from gas to liquid fuel (marine diesel oil) automatically should the gas supply be interrupted, while continuing to deliver full power.

Gas fuel is supplied at a low pressure (less than five bar) to the engines. In gas mode, the 50DF engines operate according to the lean-burn Otto process. Gas is admitted into the air inlet channels of the individual cylinders during the intake stroke to give a lean, premixed air-gas mixture in the engine combustion chambers. Reliable ignition is obtained by injecting a small quantity of diesel oil directly into the combustion chambers as pilot fuel, which ignites by compression ignition as in a conventional diesel engine.

The Wärtsilä 50DF engines use a “micro-pilot” injection with less than one per cent of the fuel energy being required as liquid fuel at nominal load. Electronic control closely regulates the “micro-pilot” injection system and air-gas ratio to keep each cylinder at its correct operating point between the knock and misfiring limits.

MAN B&W is also advocating the use of diesel engines in LNG carriers and states that more than $3M is lost every year through the funnel of every steam driven LNG carrier. However, instead of using the BOG in a duel fuel engine, the engine manufacturer?s concept for alternative propulsion is based on low speed diesel engines with electronic control and uses the Moss