MHI completes development of new-generation LNG carrier; reductions in size and weight, with more capacity and 20% lower fuel consumption than conventional ships
|Top: rendering of the continuous tank cover type LNG carrier Sayaendo Series. Bottom: Conventional Moss-tank carrier. Source: MHI Tech. Review. Click to enlarge.|
Mitsubishi Heavy Industries, Ltd. (MHI) has completed development of a new-generation liquefied natural gas (LNG) carrier marking an evolutionary advance from Moss-type LNG carriers which use independent spherical storage tanks to transport NG.
The new vessel-type dubbed “EXTREM” is a type of the newly developed “Sayaendo” Series (sayaendo = peas in a pod in Japanese), which features a peapod-shaped continuous cover for the Moss spherical tanks that is integrated with the ship’s hull, in lieu of a conventional hemispherical cover. The new configuration enables greater structural efficiency and size and weight reductions, resulting not only in improvements in fuel consumption and operating economy but also in enhancements in terms of compatibility with LNG terminals and maintainability.
|MHI began developing LNG carriers in the 1970s; it delivered its first carrier, the Banshumaru, in 1983. As of September 2010, it had built 42 LNG carriers.|
MHI looks for the EXTREM to become a strategic product that will lead the LNG carrier market. The company is now targeting early order receipts.
In conventional Moss-type LNG carriers, the upper half of the spherical storage tanks above the ship’s deck is covered by a semispherical dome and the lower half under the deck is supported by a cylindrical skirt structure. By contrast, the EXTREM employs a continuous cover integrated with the ship’s hull to house all storage tanks entirely, enabling the cover to be used as hull reinforced material for overall strength.
In the conventional method, pipes, wires and catwalks atop the tanks were supported by complex structures. By covering the tanks with the integrated cover and making those supporting structures unnecessary, the new design improves maintainability.
The continuous cover over the tanks improves aerodynamics by substantially reducing wind pressure which serves as a drag on ship propulsion. Improved aerodynamics contributes to reduced fuel consumption during navigation. At the same time the continuous cover minimizes exposure of support structures and equipments, and it also facilitates reinforcement of overall strength to be effective in resisting ice impact load, thus making the system also suitable for LNG transportation in frigid or icy-water regions.
The new-generation LNG carrier, for which MHI has completed basic design, measures 288 meters (m) in length overall (LOA), 49.0m in width, 26.0m in depth and 11.5m in draft. The ship has cargo tank total capacity of 155,000 m3 using four Moss-type tanks. The ship is projected to respond to anticipated growth in demand for ships in the New Panamax category.
New Panamax is the term for the size limit of ships that will be capable of traveling through the Panama Canal after its planned expansion is completed in 2014: 366m in LOA, 49m in width and 15.2m in tropical freshwater (FTW) draft. Panamax parameters are 295.0m in LOA, 32.2m in width and 12.0m in draft.
Compared with conventional Moss-type LNG carriers of the same size, the EXTREM has the capacity to transport 8,000 m3 more LNG by employing stretched Moss tanks and its steel hull structure is about 5% lighter in weight. The depth of the ship has also been reduced by 1m, enabling better compatibility with major terminals in Japan and other countries in view of cargo manifold and gangway landing arrangement.
|Concept of the UST. Click to enlarge.|
For its main power plant, the EXTREM adopts MHI’s “Ultra Steam Turbine Plant” (UST), a marine propulsion steam turbine plant utilizing reheated steam. UST adopts a medium-pressure turbine, in addition to high- and low-pressure turbines. After the steam from the boiler drives the high-pressure turbine, the exhausted steam is returned to the boiler and reheated for driving to the medium-pressure turbine, and subsequently the low-pressure turbine.
In the world of LNG carriers, electric propulsion ships (DFE ships) using medium-speed diesel engines with gas-firing capability and two-cycle low-speed diesel main engine vessels (DRL ships) have been gaining power in place of conventional steam turbines. To compete with these highly efficient propulsion engines, MHI has developed a UST plant in which highly reliable conventional steam turbines operate at greatly improved efficiency. This plant is designed to improve the efficiency by enhancing the steam conditions from 6 MPa x 515 °C (standard level in the past) to 10 MPa x 560 °C, and leading the steam which is reheated by the reheater to a intermediate-pressure turbine newly provided.—Ohira et al.
Compared with conventional steam turbine plants, the UST cascade facilitates the utilization of thermal energy and enables reductions in fuel consumption of about 15%. Together with downsizing, weight reduction and hull lines improvement, the new ship achieves a substantial 20% reduction in fuel consumption compared to conventional ships.
Moss-type LNG carriers are widely used for their advantages in terms of high-reliability tank structure and strength against possible liquid sloshing inside the tank, features enabling the vessel to achieve swift departure from the pier in case of emergency and permitting safe voyages through rough waters. The EXTREM combines these advantages of Moss-type carriers with energy-saving features and higher LNG cargo transport capacity.
Sai Hiramatsu et al. (2010) Technology Trends and MHI Activities for LNG Carriers. Mitsubishi Heavy Industries Technical Review Vol. 47 No. 3
Hiroyuki Ohira et al. (2007) Key Technologies for Mitsubishi LNG Carrier Now and in the Future. Mitsubishi Heavy Industries, Ltd. Technical Review Vol. 44 No. 3
Makoto Ito et al. (2007) Development of High Efficiency Marine Propulsion Plant (Ultra Steam Turbine) Mitsubishi Heavy Industries, Ltd. Technical Review Vol. 44 No. 3