Gas used to power ferry

A low Nox emmission, gas powered car/passenger ferry looks as though it could be the first of many such vessels in Norway.

The first roro/passenger ferry in the world to be powered by LNG entered service with Norwegian domestic operator More og Romsdal Fylkesbatar (MRF) in January. The vessel`s hull was built by Tangen Werft, Norway with Langsten Slip & Batbyggeri AS in Tomrefjord, Norway being responsible for the internal outfitting.

MRF is the largest domestic ferry company in Norway. Its majority shareholder is the county of More og Romsdal operating 26 ferry services and five high-speed passenger boat services all over the More og Romsdal region.

There were two main reasons why LNG was chosen to fuel Glutra, one was political, the other environmental. The Norwegian government believes that the use of LNG in the transport sector makes sense as there is natural gas aplenty sitting on its doorstep in the North Sea. In addition, the reduced NOx and CO2 emissions from the chosen Mitsubishi gas engines provided the environmental benefit. The LNG-fuelled engines on Glutra have produced more than a 90 per cent reduction in NOx emissions, and a 20-25 per cent drop in CO2.

Experience from this vessel will determine how many more will be built. So far this has been very good, with no problems at all, says Mr Rasmussen, technical manager, at MRF. The company has plans to build another vessel in the near future, but only after the evaluation programme is complete on this prototype vessel, he adds. As far as running costs are concerned, for the time being, the price of the LNG has been matched to the cost of diesel fuel, but this will eventually be adjusted, he says.

Glutra operates across a small fjord, between the harbours of Solsnes an Afarnes, with each crossing taking 15 mins. The double-ended configuration of the vessel means that loading/unloading time is only 5 mins. The vessel is in constant operation daily between 05.30 and midnight.

The vessel can carry 300 passengers and 96 private cars, the standard number of vehicles for Norwegian ferries of this size.Vehicles are embarked/disembarked between the main deck and the shore via small shoreside ramps.

The four Mitsubishi GS12R-PTK lean burn main gas engines burn a combination of gas and air and feature both a pre- and main chamber designed for ultra lean gas/air ratio. The pre-chamber technology ensures an even burning of this lean mixture, says Mitsubishi, resulting in very low NOx level.

Mitsubishi says that its gas engine has a thermal efficiency of over 37 per cent at full load, with a lean mixture of gas and air.

Each main engine drives a Siemens IFC453-4 generator rated at 720kVA, and the power is distributed through a Siemens 690V/230V switchboard at 50Hz. The only diesel driven engine on board is a Mitsubishi 6D22T 165kW (224 bhp) emergency generator rated at 168 kVA.

The power is fed to two Siemens 12 pulse drives in 24-pulse configuration, each driving a Schottel STP 1010, 1,000kW thruster unit, one at each end of the vessel. These provide a service speed of 12 knots.

The LNG is stored in two 3m diameter, 30m3 capacity tanks supplied by AGA, located under the main deck on the veseel?s centre line. Each tank is vacuum insulated with a perlite filling, allowing th gas to be stored at a temperature of -163deg C at 1 bar pressure. At 5 bar pressure the temperature -140degC.

Refueling takes place every 5 or 6 days, with the gas being delivered by truck. It takes two hours to transfer 44m3 (17t ) of gas at a time, each tank being filled to the regulation capacity of 85%.