Versatile LNG carrier series for Malaysia
Bucking the trend, MISC has opted for spherical cargo tanks and steam turbine propulsion in its new stage of LNG carrier fleet development, writes David Tinsley.
Malaysia’s capacity to derive added value from its position as one of the premier LNG exporters is being strengthened by a fleet expansion programme implemented by Kuala Lumpur-based MISC Berhad to meet the long-term needs of parent energy group Petronas.
The commercial significance of the project encompassing five 150,200m3 LNG carriers ordered from Hyundai Heavy Industries (HHI) is complemented by the technical distinction of the chosen design. At a time when membrane-type cargo containment and either dual-fuel/tri-fuel diesel-electric or gas-injected two-stroke machinery predominate in LNGC newbuilds, the MISC quintet endorses the latest advances in spherical tank technology and steam turbine propulsion, the erstwhile most favoured pairing for such vessels.
Marine steam turbines have well-proven operational qualities, not least as regards reliability, and the system chosen for the Malaysian gas carriers promises substantially improved fuel efficiency over previous generations of plant. The cargo loading and transportation arrangements, centred on the Moss spherical tank solution, offer the high degree of trading and deployment flexibility sought by owner and charterer.
Last September’s delivery of the Seri Camellia opened the Seri C-series from HHI’s Ulsan shipyard. The vessel drew her first load at Bintulu, Sarawak, for discharge at Pyeong Taek in South Korea. She was followed in January 2017 by second-of-class Seri Cenderawasih. The third ship, Seri Cempaka, is scheduled for handover this year, while the two remaining newbuilds are to be commissioned in 2018. All five ships have been committed to Petronas on 15-year terms.
Seri Cenderawasih is the twenty-seventh ship in MISC’s LNG tanker fleet, which is predominantly composed of membrane-type tonnage, and is the sixteenth Moss-type LNG carrier to have been completed by HHI for various owners since 1991.
South Korea is the world’s most prolific constructor of LNG carriers, although HHI is the country’s only shipbuilder with a track record in producing both membrane-type and Moss spherical tank-type ships. That dual capability has been enhanced by the adoption and application of the Integrated Hull Structure (IHS) concept in the Seri C quintet.
Used under licence from Aker Arctic of Finland by both HHI and MHI, IHS entails the shielding of the four independent Moss cargo tanks by a continuous cover, integrated with the primary hull structure. This enhances overall hull strength and minimises structural discontinuity, while achieving a reduction in vessel steel weight. The weight saving is in the order of 3% for the Malaysian LNGCs, resulting in improved fuel efficiency.
The unique integrated structure also allows for piping and passageways to be arranged on the tank cover deck, simplifying the layout, improving safety and ease of maintenance.
Each of the cargo tanks is about 42m in diameter. The spherical shape of the Moss tanks ensures that partial loadings do not cause problems with sloshing, such that there are no filling restrictions. Besides conferring increased trading flexibility with partially-filled tanks in adverse weather conditions, the ability to accept any filling level is conducive to offshore loading from floating LNG production and storage vessels. The process of taking on LNG cargoes from ‘floaters’ calls for additional safeguards, due to the forces imposed on a ship’s tanks over the loading cycle in open water conditions prone to rough weather or heavy swell.
The Seri C generation has been dimensioned and designed to enable access to all major LNG terminals worldwide, in line with the charterer’s requirement for the widest operational scope. The hull breadth, at nearly 49m, takes advantage of the increased scale afforded by the development of the Panama Canal with its new locks.
The project provided MHI with its first contract outside Japan for UST plant. The technology combines the sterling qualities of steam turbine machinery, notably as regards reliability, maintainability, power concentration, low noise and vibration levels, and ability to use LNG cargo boil-off as fuel, with a major advance in efficiency. The gain of around 15% in fuel efficiency relative to MHI’s preceding, CST generation of conventional steam turbines, while retaining the well-proven merits of such plant, is claimed to render the UST solution competitive with diesel prime movers.
The key to the enhanced performance of the UST series is the application of the reheat/regenerative cycle. The boilers produce steam at a higher pressure and temperature than in CST plant while adopting a reheat steam cycle.
Main steam is led from the boilers to the high pressure (HP) turbine and then exhausted to the reheaters with decreased pressure and and temperature. Reheat steam is then fed to the intermediate pressure (IP) turbine and subsequently to the low pressure (LP) turbine. By comparison, the steam flow in a conventional installation is boiler-HP turbine-LP turbine.
MHI advised The Motorship at the beginning of July that a total of 17 vessels, including the five Seri C-LNGCs, had been fitted or specified with UST plant.
The maximum continuous power output engendered in the Seri Camellia class is 23,910kW at 81rpm, allowing the ship to make just over 20 knots in loaded condition. A service speed of approximately 19.5 knots is achieved at the same, design draught with the plant turning out 21,519kW at 78.2rpm, the normal continuous rating.
US manufacturer Coffin Turbo Pump provided each shipset of three boiler feed pumps, comprising two steam turbine-driven models and one motor-driven unit. The company has improved the efficiency of its pump and extended the operating range of its turbine design so as to meet the higher temperature and pressure conditions of the UST plant.
Each of the new ships is fitted with a pre-swirl duct and propeller boss cap fin, a device which saves fuel through improved hydrodynamic performance, breaking up the hub vortex created behind the rotating propeller.
The diesel generator is IMO Tier III-compliant by virtue of the incorporation of a selective catalytic reduction (SCR) system to curb NOx emissions. The aggregate is based on a Daihatsu 6DC-32e engine, and the SCR plant is provided by HHI.
MISC ranks among the largest owner-operators of LNG tankers, and its fleet delivered nearly 22m tonnes of LNG in 2016, constituting about 8% of the total trade globally. Five vessels of the Seri B class, ranging from 153,000 to 157,700m3, were brought into service from Mitsubishi Heavy Industries in 2007-2009, following the quintet of Seri A ships of approximately 146,000m3 delivered from Samsung Heavy Industries between 2005 and 2007. Both A- and B-series incorporate membrane containment technology.
In its annual report for last year, MISC outlined key strategic objectives in the LNG sector over the next five years as the pursuance of more third-party long-term charters, and the development of concepts for “non-conventional LNG solutions”.
Malaysia is the world’s third largest exporter of LNG, shipping 25m tonnes last year. Petronas companies control the Bintulu complex, one of the world’s most extensive production facilities, supplied with gas from offshore Sarawak. The recent commissioning of the group’s first floating production and storage vessel (see box) has created a new outlet for Malaysian LNG and strengthened and extended shipment options. Besides marketing LNG on long-term contracts, Petronas is also involved in LNG trading on the spot market.
Malaysia’s floating LNG facilities
On April 1 this year, Seri Camellia inaugurated shipments from the first floating LNG facility deployed by Petronas, the PFLNG Satu, located on the Kanowit gas field in Sarawak waters, some 180km off Bintulu. The LNG carrier took on a full load for delivery into the Asian market.
Contracted through the Technip Daewoo Consortium (TDC), and custom-built by Daewoo Shipbuilding & Marine Engineering to process and liquefy natural gas, and store and offload the LNG, the floater changes the landscape of LNG production in Malaysia. It allows Petronas to effectively unlock reserves in small, remote or ‘stranded’ gas fields once deemed uneconomical to develop and tap.
Currently moored in a water depth of 75m, PFLNG Satu has an LNG production capacity of 1.2m tonnes per annum and embodies a flexible turret design that enables the vessel to be used in different locations at depths up to 200m for up to 20 years without necessitating drydocking. The 204,818gt vessel provides 177,000m3 of LNG storage and 20,000m3 for condensate, within main dimensions of 365m length overall, 300m length between perpendiculars, and 60m breadth.
PFLNG Satu is the first floater to use the dual row containment system, whereby eight GTT No96-type membrane LNG storage tanks are arranged in two rows underdeck, supplemented by a pair of condensate tanks. The central cofferdam structure withstands the high loads imposed by the topside module, and permits a large range of tank filling levels while minimising and accommodating sloshing effects.
Petronas has a second LNG production and storage vessel on order in South Korea. Contracted from a consortium comprising JGC Group and Samsung Heavy Industries, with construction taking place at the latter’s Geoje shipyard, the project-named PFLNG2 will extend Petronas’ deepwater floating LNG capabilities.
Due to be commissioned in 2020, the floater has been designed for operations in water depths between 500m and 1,500m, and will have an LNG processing capacity of 1.5m tonnes per annum. The unit will be assigned to the liquefaction, production and offloading of natural gas from the Rotan field, 240km offshore Sabah. PFLNG2 has been specified with GTT’s Mark III Flex membrane containment system.
PRINCIPAL PARTICULARS -- MISC SERI C CLASS
Steam turbine, geared drive
Propulsion power, MCR
Propulsion power, NCR
Speed, maximum @MCR and design draught, 15% sea margin
Speed, service @NCR and design draught, 15% sea margin
Lloyd’s Register: Seri Camellia, Seri Cenderawasih, and Hull No.2735; ABS: Hull Nos 2731 and 2732.
LR class notations
+100A1, Liquefied gas carrier Ship Type 2G, methane (LNG) in independent spherical tanks Type B, maximum vapour pressure 0.25 bar; minimum cargo temperature minus 163degC; ShipRight (SDA, FDA plus<25, WW>, CM, ACS<B>), IWS, LI, ECO (BWT, IHM), +LMC, UMS
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