Redundant Propulsion Plant by Gas Injection Diesel Engine for LNG Vessels
Koh SASAKI * and Kazutoshi ETOKORO*
Mitsui Engineering & Shipbuilding Co. Ltd.(MES) has researched and developed the GIDE (Gas Injection Diesel Engine) for about twenty years with the intention of applying this very fuel efficient engine to both land electric power generation plants and main propulsion systems of LNG vessels. Six years ago, a pilot GIDE electric power generation plant of 40 MW was built in our shipyard, as the full scale model of I.P.P.(Independent Power Plant) and LNG vessel's main propulsion system.
By the good operation results of this plant, we are convinced that the dual fuel diesel propulsion for LNG vessels is feasible from the view point of not only high fuel economy but also high reliability and maintanability.
This paper presents the result of our latest study of redundant diesel propulsion plant using the well experienced GIDE in view of reliability and maintanability.
Key Words: Dual Fuel Diesel, Propulsion Plant, LNG carrier, Fuel Economy, Redundancy, Environment
The propulsion plants for LNG carriers have special features compared with other merchant ships, because the boil off gas (so-called BOG) vaporizing from the cargo tanks is utilized as fuel to the plants.
Due to the above, the steam turbine propulsion plant with dual fuel boilers has been used until now. However, during the last twenty years, some alternative propulsion plants have been of interest for utilization in LNG carriers instead of the steam turbine plant.
MAN B&W Diesel and Mitsui developed the high pressure gas injection diesel engine (so-called GIDE) as one candidate propulsion for LNG carriers. With the GIDE, the thermal efficiency and output is kept equivalent to that obtained when burning conventional heavy fuel oil. Furthermore, the GIDE has the advantage of being independent, to a large degree, of gas/fuel compositions. In 1994, the world's first large bore GIDE, 12K80MC-GI, was built by Mitsui and installed at Mitsui's Chiba works. Chiba's GIDE has been the commercial power plant as I.P.P. and has verified it's reliability for the next generation LNG carriers.
In 1995, a propulsion system with the GIDE 10K80MC-C- GI was introduced, but it has never been realized yet.
On the other hand, other alternatives, such as the electric propulsion with dual fuel medium speed diesel generator or the low speed diesel propulsion with reliquefaction plant etc. have been discussed.
Therefore, the choice of the propulsion system is one of important factors of initial planning. For the LNG carrier, the propulsion system has to be chosen from the view point of not only economical advantage but also redundancy of the system.
This paper presents a redundant GIDE propulsion plant and result of comparison with other alternatives.
2. PRINCIPAL FEATURES OF GIDE PROPULSION SYSTEM
2.1 Main Particulars of conventional LNG Carrier(ST)
An example of the principal particulars of a 145,000m3 LNG carrier with conventional steam turbine propulsion is shown in Table 1 as a benchmark. The boil off rate (BOR) is assumed to be 0.15%/day during laden voyage and an average speed is 19 knots with a sea margin of 15%. The excess BOG during slow steaming will be burnt by the dual fuel main boiler and excess steam is led to the main condenser and dumped.
The cargo capacity, BOR and average service speed at normal sea going are assumed the same for all plants considered hereinafter.
2.2 Main Particulars of GIDE Propulsion System
2.2.1 Single Main Engine with Single Screw(GIDE1)
The main particulars of the system are shown in Table 1. The system diagram is shown in Fig.1.
* Mitsui Engineering & Shipbuilding Co.,Ltd
Basic Design Dept. Ship & Ocean Project Hq.
1, Yawatakaigan-Dori, Ichihara-City, Chiba 290-8601, Japan