Use of Liquid Natural Gas (LNG) as Fuel in Offshore Supply Vessels

Terje Nordtun

Wartsila Ship Power Offshore, Norway


Over a period of over 20 years, Wärtsilä has delivered over 1000 gas engines with more than 1.500.000 accumulated engine running hours. The total power installed has reached 4.000.000 kW by the end of 2010. Using LNG as fuel in vessels will significantly reduce exhaust gas emissions. NOx emissions are typically reduced by more than 80% compared to diesel oil (MGO) operation. LNG fuelled vessels can therefore meet IMO Tier III requirements without installing additional exhaust gas cleaning systems. Also CO2 emissions are reduced by 20-25% due to the higher calorific heat value in LNG. And with the present positive price development for LNG compared with MGO, there will also be a significant fuel cost saving potential by operating vessels on gas. This paper will address the experience and operational benefits by using LNG as fuel in Offshore Supply Vessels. It will present the technical solution offered, including the bunkering and onboard gas storage system.

The first two gas powered Offshore Supply Vessels were designed by Wartsila Ship Design (former Vik Sandvik AS) and delivered in 2003. Since then Wärtsilä has accumulated more than 20 years of vessel operation time using gas as fuel in this segment. All Wartsila gas engines delivered to supply vessels are based on the Dual Fuel (DF) type. This means that the engines also can run on MGO as a backup solution with instant change between gas/MGO operation modes. This gives great operational flexibility and redundancy, also without the need for additional redundant equipment and systems to meet DP class requirements. The Wartsila DF engines including the onboard gas tank and gas handling has proven to be a very reliable and safe solution with no incidents and no reported off hire of any vessel caused by gas the operation.

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