Article in the February issue of the GVR: Use of LNG in ships

In the current February issue of the Gas Vehicles Report (GVR), Peter Boisen, Chairman of the NGVA Europe Country Representatives Conmmittee (CRC), in his monthly column wrote a very interesting article about the use of LNG in ships. This is the original text taken from the GVR N°97 (pages 20-21). The complete issue of the GVR published in February is available on www.thegvr.com.

Within the NGV industry we are usually discussing cars and vans with an annual fuel consumption of 1-3 tonnes, or heavy duty trucks and buses with a consumption of 40-100 tonnes. When looking at annual fuel consumption in ships we face another order of magnitude:

LNG carriers
The worldwide fleet of LNG carriers is growing rapidly and would now be around 300 ships. A fairly large share of these ships use LNG for propulsion. Steam boilers are still much more common than dual fuel gas/diesel engines, but Wärtsilä a year ago reported an order stock of 56 LNG carriers fitted with Wärtsilä dual fuel engines. LNG ocean carriers usually have a daily LNG boil-off corresponding with 0.18 % of the full tank contents. This boil-off must either be re-liquefied, or burnt as a fuel.

The British Emerald LNG carrier, built in 2007 (then the world's largest LNG carrier), with a duel fuel gas diesel engine, consumes around 50,000 tonnes annually, whereas a similar sized ship using steam boilers would use around 64,000 tonnes (about 50 % boil-off-gas and 50 % oil).  A third fuelling possibility for the LNG carriers is a conventional oil fuelled engine, but then also including an onboard facility for re-liquefaction of boil-off gas.

The fuel use is the present worldwide fleet of LNG carriers would in the order of 15 million tonnes.

LNG used as a fuel in other types of ships

The use of LNG in other ship types is still very limited. Norway has, however, taken a lead concerning the development of the use of LNG as a fuel for various ships used for relatively short distance traffic (up to seven days sailing without refuelling). These new developments started in the year 2000 with an LNG powered car/passenger ferry by the name of Glutra, and the total Norwegian fleet of smaller LNG powered ships is now already around 15 units with more to come (annual new Norwegian LNG ships projected to réach 40 units within a few years).
The ship in the picture uses cylinders by NGVA Europe member Hamworthy

A Norwegian car ferry for 200 cars and 500 pasengers travelling at 21 knots consumes around 10,000 tonnes annually, on another route at 17 knots around 5000 tonnes annually. Small supply vessels consume around 3500 tonnes, coast guard vessels around 1000 tonnes and small passenger ferries around 200 tonnes. Every new ship obviously represents a huge LNG business potential.

Within Europe other countries along the Baltic Sea and the North Sea are now also looking at the possible future use of LNG. The total fuel used only for RoRo cargo ships and RoPax ferries in the North Sea/Baltic Sea area is 3.1 million tonnes annually.

The main driving force today is the new IMO emission limits for ships which will apply in the area from 2016 with dramatic reductions of SOx emissions and also much tougher limits for NOx emissions. Similar emission limits will also be introduced in other coastal waters and on inland waterways (ECA- Emission Control Areas) , e.g. in North America.

Short distance sea traffic accounts for about one third of all marine transports in the world, and the LNG option must certainly be considered for most of this traffic. Worldwide the regional sea transports consume 113 million tonnes of fuel. For longer ocean transport LNG, on account of size and weight of LNG gas cylinders, would not be quite as interesting.

Ship engines designed to run on natural gas are offered by various suppliers - e.g. Wärtsilä, MAN B&W and Caterpillar (mainly dual fuel), or Rolls Royce and Mitsubishi (mainly lean burn gas engines). The  engines installed in the Norwegian LNG powered vessels are mainly Wärtsilä engines or Rolls-Royce Bergen engines. The ferrry engines usually power propulsion via electric engines.

A RoPax ferry, Ivete Sangalo, for 75 cars and 600 passengers, fitted with a Caterpillar dual fuel engine, was commissioned in Brazil in 2008. demonstrating that the interest  in LNG powered ferries is not limited to Europe.

LNG would also be a perfect fuel for RoPax ferries in the Mediterranean area.

In addition to already mentioned ship types there are also developments concerning fishing vessels with dual fuel gas and diesel engines in countries like Thailand, Norway, and Spain.

The New Hansa project in 2005 studied new ways to handle sea transports in a manner which would reduce pollution. A more recent project was MAGALOG (marine gas fuel logistics) with a final report in December, 2008, and a focus on ships based in Bergen, Gothenburg, Lübeck/Trawemünde. Svinoujscie, and Stockholm. Various ferry lines or passenger cruisers operating out of other Baltic Sea or North Sea ports are also, with or without EU support, investigating future use of LNG (also liquefied biomethane from a planned large production facility in Trelleborg, Sweden, and dealt with in the Baltic Master project). These initiatives have also been discussed at the BALTEF (Baltic Energy Forum)..

In addition to the benefit of SOx emission reductions of 100 % and NOx reductions of 85-90 % the use of LNG will almost completely eliminate particulate emissions, and also significantly reduce CO2 emissions. Reported engine efficiencies for gas powered marine engines range between 43 and 48 %, i.e. on par with oil powered compression ignition engines. This means a 26 % reduction of the CO2 emissions.  Minor emissions of unburnt methane could, however, potentially reduce the net GHG saving to around 15 % expressed in CO2 equivalents.

The total Baltic/North Sea RoRo/RoPax potential of 3.1 million tonnes of LNG annually would reduce CO2 emissions by at least 1.5 million tonnes..

Refuelling of smaller ships can often be arranged via tank trailers parked alongside the berthed vessel (similar to the refuelling of aeroplanes with jet fuel tank trailers). For larger ships one would instead use bunkering tenders collecting LNG from a seaboard LNG storage facility and moving alongside the vessel.

When comparing the choice of conventionally fuelled ships and ships fuelled by LNG things to consider are:

- cost savings on fuel supplies

- avoided tax on ship emissions, or on high sulphur fuel

- some 5-10 % additional ship building costs (mainly LNG storage)

Another consideration, particularly for larger ships, is whether sufficiently large volumes of LNG is available at the ports frequented by the ships. All around Europe there are now some 20 major seaboard LNG terminals, but smaller terminals supplied via small coastal LNG carriers are also being developed.

IMO work on interim guidelines on safety for natural gas-fuelled engine installations in ships developed during 2009 will be included in SOLAS (International Convention for the Safety of Life at Sea), but the new IGF code will not be available until 2014 earliest.

Some earlier attempts concerning the use of CNG (not LNG) in ships or boats:

Whereas CNG may still be an interesting option for smaller pleasure boats LNG is clearly the preferred NG option for larger ships. One single RoRo ferry might annually consume more than 10,000 tonnes of LNG, or as much fuel as 10,000 standard passenger cars or 100-150 city buses. From an  environmental point-of-view the use of LNG instead of marine gas oil or heavy fuel oil in ships used in coastal waters would bring about large benefits.

Author: Peter Boisen
Source: www.thegvr.com

NGVA Europe... for sustainable mobility

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