repair & maintenance
First gas-fuelled engine conversion to go ahead
T
wo low speed diesel engines in an LNG carrier are to become the first to be converted for gas fuelling in a project that could lead to further conversions. Qatari LNG carrier Nakilat and the country’s LNG producers Qatargas and RasGas have agreed with engine manufacturer MAN Diesel & Turbo to convert the original ME-type engines on one of Nakilat’s Q-Max vessels into ME-GI (M-type electronically controlled, gas injection) versions. These can use LNG as an alternative to heavy fuel oil (HFO). The ship and its sisters are unusual among LNG carriers in that they do not use boil- off gas for propulsion. Instead they reliquefy it, to maintain the cargo’s volume and value. Nakilat’s announcement followed several years of planning, first revealed publicly at the Gastech 2012 conference. At the conference, Alaa Abu Jbara, Qatargas chief operating officer responsible for commercial and shipping, spoke of the company’s intention to use LNG as fuel, citing emissions benefits.
In its statement in January Nakilat echoed those remarks, saying that the project reinforces Qatar’s commitment toward the environment, as it will reduce the ship’s exhaust gas emissions. It also said that the engines would burn more cleanly in their new configuration, which had the potential to increase mean time between maintenance periods.
The statement also referred to flexibility of fuel supply, which Nakilat said would help it react to market changes and reduce bunkering activities, which would in turn reduce operational risks. But it did not mention cost benefits. These must be a factor, given the rise in bunker prices since the original decision to install diesel engines in 2004. At that time, MAN Diesel & Turbo hailed the choice as offering significant cost benefits compared with a traditional steam turbine propulsion plant.
The engine manufacturer based its forecast on a comparison of operating costs for a steam turbine installation and a low speed diesel arrangement. This
showed that Nakilat’s N-Kom yard, where the engine conversion will take place (credit: N-Kom)
much, the economic argument is not so clear, even though LNG values have risen equally steeply in the intervening decade.
The conversion will be carried out by Nakilat- the diesel
installation had higher operating costs. However, once the value of the LNG cargo that would have been lost through boil-off was taken into account, the economic benefit was clearly in favour of the diesel option. But the calculation was based on a fuel cost of US$150 per tonne and an LNG selling price of US$4 per Mbtu. With HFO now costing at least four times as
www.mpropulsion.com
Keppel Offshore & Marine (N-Kom) at its Erhama Bin Jaber Al Jalahma Shipyard facilities in Qatar’s Port of Ras Laffan. A key part of the project has been subcontracted by MAN Diesel & Turbo to the German company TGE Marine Gas Engineering, which provides engineering services for the design and supply of gas carriers and offshore units, mostly to shipyards that build gas carriers. For the Q-Max conversion, it will design and supply the LNG fuel gas package for the converted engines. This includes a modular pre-fabricated fuel gas skid, which is scheduled for delivery in the first quarter of 2015. In developing its contribution to the work, TGE Marine investigated the design of the high pressure fuel gas supply system with its partner ACD, a US company that specialises in cryogenic pumps. The two companies made a complete dynamic simulation of the system that considered all load scenarios, TGE Marine said. In a statement, TGE Marine’s chief executive, Manfred Küver, described the project as a positive indicator. “This project is a signal for the market that the MAN two-stroke ME-GI solution is one of the most economic approaches
for a modern LNG carrier design.” There are 14 ships in Nakilat’s Q-Max fleet of 266,000m3 vessels. At the time of writing in late February the one that will be converted had not been identified. If the conversion yields its expected benefits, further ships may also be converted. There is no indication of when or how that assessment will be made, but Nakilat has said that it has a high level of confidence in the safety and reliability of the propulsion system, adding that
the modification will meet all currently known and planned global emissions regulations. Those additional ships could include the rest of the Q-Max vessels but may extend to at least some of the 31 smaller Q-Flex ships of 216,000m3 capacity. Nakilat owns 11 of these and shares control of the other 20. According to Marine Propulsion’s sister
publication LNG World Shipping, the work is expected to take MAN Diesel & Turbo engineers 40 days to complete at a cost of US$15-20 million. Assessing the payback time will not be easy, the journal suggested in an editorial comment, due in part to the high prices Qatar is obtaining for its gas and to the awaited performance data from the conversion. But gas engine technology has made great strides in recent years, it added, which will have contributed to the decision now to press ahead with this pilot engine conversion. MP
Marine Propulsion I April/May 2014 I 35
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