The fuel gas supply technology developed by Daewoo Shipbuilding & Marine Engineering (DSME) has helped the shipyard secure significant orders for ships propelled by MAN Diesel & Turbo two-stroke ME-GI dual-fuel engines over the past year. Low-speed ME-GI units have been chosen as the propulsion system for not only many of the latest generation of LNG carriers but also a number of LNG-powered vessels that are not LNG carriers.
MAN’s electronically – controlled M-type gas-injection (ME-GI) engines offer a number of benefits, including high thermal efficiency, low operational and installation costs and the ability to operate over the full range of fuel oil/gas ratios. These engines make use of a high-pressure fuel gas system (FGS) to supply boil-off gas at pressures of 250-300 bar for injection into the cylinders.
In principle there are three different FGS solutions for supplying gas to ME-GI engines, as follows:
(a) a high-pressure boil-off gas (BOG) compressor;
(b) a reliquefaction plant in tandem with high-pressure LNG pumps; and
(c) a reliquefaction plant in combination with a high-pressure BOG compressor.
To date option (b) has been the solution of choice in the majority of cases, thanks to the development by DSME of its own high-pressure fuel gas supply (HP-FGS) system. The Korean shipbuilder offers this system in combination with its own partial reliquefaction system.
In July 2013 MAN Diesel & Turbo signed a patent license agreement with DSME that enables the use of the yard’s HP-FGS package to supply gas fuel to ME-GI engines. The announcement coincided with the specification of the Daewoo HP-FGS and ME-GI engine combination for two pioneering sets of ship newbuilding contracts placed in December 2012. Teekay opted for this propulsion arrangement for two 173,400m3 LNG carriers it had ordered at DSME while Totem Ocean Trailer Express (TOTE) similarly opted for ME-GI engines and HP-FGS systems for a pair of LNG-powered container ships it is building at the NASSCO shipyard in San Diego. The Teekay ships are the first LNG carriers to be specified with two-stroke dual-fuel engines, while the TOTE vessels are the world’s first LNG-fuelled boxships.
The tally of ME-GI/HP-FGS LNG carriers that Teekay has contracted at DSME has now risen to eight and the first of these is due for delivery in the first half of 2016. Furthermore, this propulsion system package helped Daewoo to achieve top ranking amongst the winners of LNG carrier orders in 2014. Of the record 68 LNGCs contracted last year, 41 will be built at Daewoo and 24 of the ships will have ME-GI/HP-FGS propulsion arrangements. In addition, following last year’s order surge, in the early weeks of 2015 several LNGC newbuildings that had originally been contracted with dual-fuel diesel-electric (DFDE) propulsion systems have been respecified with ME-GI engines.
Daewoo developed its HP-FGS system as an alternative to high-pressure BOG compressor fuel gas supply systems which are deemed by many to be too bulky and too power-hungry to make them viable for ship power applications. The shipbuilder states that its high-pressure pump-based fuel system, which was patented in 2007, offers major improvements in terms of the efficient use of power and space and makes dual-fuel two-stroke engines a more realistic commercial proposition. DSME is being assisted in the global marketing of its HP-FGS technology by group affiliate Daewoo Ship Engineering Company (DSEC).
In contrast to BOG compressor-based fuel gas systems, which compress gas to a high pressure, the DSME HP-FGS system compresses LNG and vaporises it into gas form. While this method is still able to supply gas at high pressures of about 300 bar, it requires relatively small amounts of electric power, typically about 100kW for the same amount of gas supply provided by BOG compressors. The pump-based fuel gas system also occupies only a small footprint compared to the large amount of deck space required for compressors. Other advantages, reports Daewoo, are low noise and vibration levels and ease of maintenance.
Daewoo makes use of third party equipment suppliers for key components of its HP-FGS system. Santa Ana, California-based ACD, for example, has engineered and supplied high-pressure LNG fuel gas pump systems for both the LNGCs building at DSME for Teekay and for the HP-FGS systems that the shipbuilder is providing for the two TOTE container ships under construction at NASSCO.
The ACD package features the company’s model MSP-SL high-pressure pumps with gearbox assemblies and electric 150kW inverter duty motors. Also included are an external oil lubrication system and a VWP-190-10 water/glycol vaporiser supplied by Cryoquip Inc, another company in the Cryogenic Industries group. All the equipment is skid-mounted, with integrated piping, control valves and monitoring instrumentation.
In early 2014, following its inaugural arrangement with MAN, DSME agreed to license its HP-FGS technology for LNG-powered ships to five compatriot equipment suppliers, i.e. DongHwa Entec, Daechang Solution, NK, Sunbo Industries and Steel Flower. The new alignments were concluded as part of a drive to localise domestic marine equipment supply as much as possible. DSME is committed to providing design, engineering, commissioning and training support services to all its HP-FGS licensees. MP