Why are some locomotive boilers bulging in the middle (verses cylindrical)?

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  • Member since
    July, 2009
  • From: North Saanich, BC, Canada
  • 23 posts
Posted by seafarer on Wednesday, April 11, 2018 11:58 PM


It might make more sense to use gas (combustion) turbines which are perfectly happy to run off natural gas. Ship propulsion would involve a lot less cycling of pwer than locomotive use and improvement in efficiency can be derived from a combined cycle plant or steam injection.


Seventeen cruise ships were built using a combined gas turbine, electric and steam (COGES) system, where gas turbines drove generators to supply electrical power for propulsion and hotel services. The turbine exhaust gases were passed through an exhaust gas boiler to generate steam that was used to power a steam turbo-generator, and to supply steam for hotel services. The electrical power from the steam turbo-generator could be used for propulsion and / or hotel services.

The reduction in the size of the power plant and machinery spaces, compared to a diesel electric or direct drive diesel power plant, meant that up to 45 additional cabins could be fitted, the fares for which helped offset the additional cost of the MGO (marine gas oil) fuel used.

This system was quite efficient and economical until the price of the MGO increased substantially and the economics in favour of the COGES plant over heavy oil burning medium speed diesel electric powered ships was lost.

However, the COGES system is not appropriate for all vessels as not many ships other than cruise ships, have the hotel, or other types of loads to use the additional steam and power generated.

With the advent of international regulations coming into force in 2020, which will effectively ban the use of relatively cheap, but dirty (high in sulphur), heavy fuel oil to power ships in all areas of the world's oceans, all ships will have to move to lighter, and more expensive fuel oil. Today, both the east and west coasts of North America are Designated Emission Control areas in which ships are not permitted to burn fuels contining more than 0.5% sulphur.

For ships trading to N. America, before entering either DEC area (as well as other such areas in the world, such as the coasts of Europe), they must change to a fuel having maximum of 0.5% sulphur content or use an approved method of reducing the sulphur content of the exhaust gases before they leave the funnel. See https://www.maritime-executive.com/article/imo-answers-questions-on-the-2020-sox-regulation#gs.EBajkUM

Which is why so many ship owners are now looking at building, or converting, ships to use LNG as fuel for their diesel engines. One of the problems with converting an existing ship to LNG fueled engine(s) is the volume of space, and the location of that space, required for the one, or more, LNG tanks required, (which impacts the cargo carrying capacity of the ship). This is usually less of a problem for ferries in general, and car ferries in particular, as they normally have several void spaces or compartments below the car deck in which the LNG tanks can be fitted. Cargo ships are a different story.


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