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.

http://gcaptain.com/ocean-kites-top-10-green-ship-designs

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.

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.

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 http://en.wikipedia.org/wiki/Energy_density#Energy_densities_ignoring_external_components

The BP annual report has prices for LNG, gas and oil see page 27 http://www.bp.com/assets/bp_internet/globalbp/globalbp_uk_english/reports_and_publications/statistical_energy_review_2011/STAGING/local_assets/pdf/statistical_review_of_world_energy_full_report_2011.pdf

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.

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

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.

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.

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.

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.

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.