New York City adding 70 electric vehicles to fleet; launches EV educational push
Virginia Governor signs legislation and executive order beginning transition of state vehicles to natural gas, electricity or other alternative fuels

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.



Account Deleted

Today the global market for LNG carriers is growing fast (I believe over 10% per year) mainly as a result of increased LNG production in Qatar (now by far the wealthiest nation on the planet). However, several new and potentially very large LNG exporters will be coming online in the next few decades. Notably Russia, Australia, Norway, Canada, USA, and even Denmark when a significant discovery is made in Greenland.

With regard to USA and Canada the abundance of natural gas resources will primarily come from the expansion of shale gas using horizontal fracking technology. EIA has made a really informative dynamic illustration of how the horizontal shale gas fracking technology has revolutionized the US gas drilling industry since 2004. Follow the link and click on the picture of Dallas and watch for yourselves.

Use of horizontal fracking technology for shale gas exploration

Sometimes a picture tells more than a 1000 words and EIA’s illustration is one of those cases.

Thomas Pedersen

While I realize that the marine industry is quite conservative, 10 MPa @ 560°C is quite mediocre - especially considering the ultra-premium fuel being used. Those steam data are for combined cycle processes, using gas turbines, which btw. are more efficient, powerful and compact than a main boiler system. The GT in a CCGT system also has steeper load gradients because of zero thermal inertia - only thermal stress constraints limit the power output from the GT. The subsequent heat recovery boiler is more sluggish but this is of less importance since it generally supplies only around one third of the power, nominally.

Furthermore, being a ship with ultra-cold LNG on board, there should be a bottoming cycle included to utilize the latent heat in the gas they have to evaporate for propulsion (boil-off gases from heat loss in the tanks is not enough for propulsion).

Also, flue gas condensation has a quite large potential to boost efficiency with such a clean fuel, with a lot of water vapour in the flue gas.

All in all, 60%+ efficiency should be attainable, even when considering the small scale of the power installation.


Combined cycle does seem more efficient for this application. I would rather turn natural gas into liquid fuel at the source. It is easier to transport and the world certainly uses lots of it.


Roger Pham

@Thomas and SJC,
The reason that steam turbine single Rankine cycle is used instead of CCGT is to allow the use of dual fuels, very cheap bunker fuel when far away from shore where SOx emission does not matter, and for use of NG near shore where SOx emission and NOx is strictly regulated. CCGT cannot use dirty bunker fuel.

The UST (Ultra Steam Turbine) design is almost as efficient as slow marine diesel as well as CCGT. The disadvantage of marine diesel propulsion is that NG cannot be used at low load conditions such as on shore and on loading ramp due to poor ignitability of NG, forcing diesel fuel to be used at low loads regime on shore, with resultant much higher SOx and NOx emission in comparison to steam propulsion burning NG.

NG is turned in liquid fuel, as LNG, and this is almost as easy to transport as any other liquid fuel. In fact, methanol has lower energy density than LNG and would be more costly to transport per unit of energy.

Roger Pham

In fact, when petroleum will be more and more expensive than coal, then UST (Ultra Steam Turbine) will have increasing cost advantage in reducing shipping cost. Marine steam turbines are designed to last for 40 years, have fewer moving parts and rubbing surfaces subjecting to wear, hence requires less maintenance than marine diesel.


I mean GTL is easier to transport. The middle east has 5 times the U.S. reserves of natural gas. Turn that into synthetic gasoline, diesel and jet fuel, put it in a tanker and ship it. It is ready to use, no refining required.

Account Deleted

The novelty of Mitsubishi’s design is not their engine which is less efficient than a modern natural gas fired diesel engine. It is the cover for those Moss gas tanks on the deck that seems to make good sense. Replace the steam turbine with two modern diesel engines and twin propellers like in Maersk Triple E class container ships and we have a more fuel efficient ship. Perhaps even more important build a larger ship with a state-of-the-art total tank capacity of 266,000 m3 and sell it in two versions; one standard and another with ice braking capacity so it can be used in the arctic during the winter. In 10 to 15 years we will probably have LNG carriers like that.

As far as I know nobody are making combined cycle gas plants for ships and the reason is that the market is too small with only 50 or so large natural gas burning ships being build each year globally. It is much cheaper to use a standard diesel engine that is modified to burn natural gas. The Maersk Triple E class container ships has two 43000 horsepower engines to propel a 165,000 tonnes, 18000 unit container ship that cost about 180 million USD leaving about 30 million USD for the 86,000 horsepower of engines. A combined cycle would cost perhaps 80 million USD and a coal fired engine would cost 160 million and it would probably need to dump the toxic ashes in the sea along the way. I can’t imagine that coal fired ships will ever return. However, LNG fired diesel engines will be normal in a few years even on non-LNG carriers as LNG cost about half as much as bunker oil. Just wait and see.

SJC your enthusiasm for GTL is based on too optimistic perceptions of what it cost to convert NG to liquid fuels. It cost a fortune and the only place where it is done in scale is Qatar which just started production on their Peal GTL facility. Time will tell us if this is economically viable. I doubt it and it is surely not economical to do GTL on a small scale in remote locations as you imagine. LNG on the other hand is well known and without many of the uncertainties that holds back GTL.


LNG is expensive as well. I am not talking about small scale stranded natural gas. You can express your opinions but stating them as if that is the final word does not help.

Account Deleted

SJC it is beyond any doubt that it cost more to produce methanol from natural gas than it does to produce LNG considering an equal amount of energy. Moreover, as pointed out by Roger it is less costly to transport LNG than methanol as the energy density of LNG is higher than for ethanol.

See for yourselves here

The BP annual report has prices for LNG, gas and oil see page 27

As you can see LNG cost about 11 USD per million BTU compared to 13.5 USD for crude oil. Synthetic oil made from natural gas will cost even more than oil and this is why nobody apart from Qatar is doing it. Qatar is a special case as they can afford to take the risk that their Peal GTL plant fails to be profitable.


You make some good points, but cost is not the only issue.


BTW, I was not referring to synthetic oil but rather synthetic fuels.

Roger Pham

Recently, the rise in the price of petroleum and the reduction in NG price have brought the cost of bunker oil and LNG to be roughly comparable. The prices of these are highly volatile and highly dependent on times and locations, as well as the limited availability of LNG must be brought into consideration.

The advantage of steam turbine is the ability to use a variety of different fuels interchangeably within the same voyage with much lower NOx emission than a diesel engine. A diesel engine may be modified for used with both bunker oil and NG, but such an engine cannot run largely on bunker oil at low load regime at port, where there is restriction on NOx and SOx emission. The UST (Ultra Steam Turbine) design is more efficient that conventional steam turbine and is almost as efficient as marine diesel, thus making a more compelling case for UST. It is doubtful that coal fired steam turbine would be much more expensive to build than a comparable heavy-duty diesel, or else power stations would not have utilized coal-fired powerplants in such large extent as 50% of power generation in the US.


You have natural gas, put it in an SOFC, gas turbine then steam turbine. You will have enough boil off to go where ever you want.

Roger Pham

Correction: A diesel engine may be modified to run on both bunker oil and NG, but such engine cannot run largely on NG at low load regime at or near shore, where there will be increasing restriction on NOx and SOx emission. At low load, ignitability of a very lean Air:NG mixture is very poor, requiring more bunker oil, but such produces a lot of NOx and SOx.

Roger Pham

A LNG carrier will always have access to NG on board, but other non-LNG ships may have problem finding LNG at many ports in the world at the present. The volatility in prices of NG and bunker oil means that a dual-fuel ship will have distinct advantage in using the least-expensive fuel at any time. As more ships will use NG in the future, the price of bunker oil may fall disproportionally low at certain ports, and in that case, it may be more economical to use bunker oil instead of NG. On the other hand, future regulations may limit the SOx emission in deep sea, forcing bunker fuel to have less Sulfur content and that may drive up the price of bunker oil. A ship engine built to last for 40 years should best be able to operate equally on any fuels.


The story is about LNG ships, unless they are running empty I assume they have fuel. Even after off loading they could keep enough for the return trip, natural gas in inexpensive.


This points out the waste in LNG shipping, they return empty. If a freighter ship hauls scrap metal to China and finished goods back, it is used more efficiently. If an LNG tanker carries a load to China, it comes back empty.


Why not operate the world marine fleet with LNG? It burns cleaner and there is plenty of it around. All major ports could easily be equipped with appropriate LNG reservoirs.


That is not a bad idea, but getting shipping companies to retrofit might be a hard sell. Even if you can not get all of them to change it would help. They might do it on the economics of it alone.


The Moss-type tanks are an inefficient use of the enclosed space. It would make more sense to make the two end tanks spherical on the outer ends and cylindrical with flat faces on the inner ends, and the two center tanks cylindrical. The space between tanks could be padded and slightly insulated with something like aluminum honeycomb to allow for differential thermal changes as the tank loadings change unequally. This would also reduce weight, as the tank end walls can exert pressure on each other (esp. if the vapor spaces are manifolded together to equalize pressure) and do not need to be as heavy.

The references and a search do not yield the power rating of the engines, but there are gas-turbine powerplants small enough for these ships. It also seems incredible that NG-fired operation of a marine diesel at low power levels cannot be done using charge stratification. My gut feeling is that the new steam turbine is a low-cost interim offering soon to be supplanted by superior technologies.

Alex Kovnat

I have a question about the reheat-cycle steam turbine propulsion system on the Mitsubishi LNG tankers. Are there any feed water heaters using extracted steam like in fossil fuel power plants? Having worked for a utility consulting firm years ago, I know that coal-burning steam turbine power plants use reheat and have something like 7 or 8 stages of feedwater heating.

The comments to this entry are closed.