Retrofit of a steam turbine ship for 'green' combined cycle operation

[Sheps75]

A project has been funded to rescue a somewhat dilapidated mid-60s ship (once a car ferry) now 'sunk' (only in about six foot of water) at the North-east of England port.

The main points of the power engineering are that the ship is to remain at least part 'steam' but refitted to 21st century standards. A very well known, international turbine engineering/power firm are pencilled in to supply up-to-date electrically-coupled steam turbines as part of an exercise for their apprentices, and some PR.

The initial idea was to fire the boilers (keeping the original units, I believe) with a green 'bio-oil' for her demonstrator journeys around the English Channel.
But, due to a number of factors (and 'politics'), a more involved design using a number of half-MW gensets (bio-diesel, 4-stroke) is being developed with an HRSG being integrated to form a

Our company is to supply the gensets, but we need to provide estimates of how much heat recovery is possible from each unit, as a whole integrated system can then be designed in one go.

The original ship was fitted out with a strange combination of around a dozen or so smallish diesels, with each one dedicated to a particular ancillary purpose on the ferry, whilst two large boilers fed two pairs of steam turbines, each pair on a gearbox to each of the two props.

The idea now is to have instead, a single electrical backplane that all prime movers tie on to, and distributed electric machines where mech work is required. Ideally, only two of the four ST's will be replaces and our diesel units will create part of a 'smart micro-grid' where the waste heat will be a great enough asset to provide saturated steam for the new turbines, prior to the superheater(s).

For a kick-off I was wondering if there is a good rule of thumb for the amount of saturated steam that can be raised for each kW(shaft power) installed in gensets?
Thanks kindly!

 

[EdStainless]

Depends a lot on the specific engines.
There have been many paper published on heat recovery from diesels (Wartsila has done a lot of this on ships).
Look up some of those case studies to help with your approximations.

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Plymouth Tube

 

[MintJulep]

The short answer is not enough to do anything useful.

 

[willard3]

You can also check the mfg of the gensets as they've done stack heat recovery.....they sell the hardware.

 

[davefitz]

It might be off-subject, but the latest "combined cycle" powering technology for ships is to use a gas turbine, and the waste heat is recovered in a supercrtical CO2 powered cycle- the footprint of the CO2 cycle is much smaller than that of a steam cycle. All shaft powser is used to generate electricity, and electric drive for ths ship is employed.

"Nobody expects the Spanish Inquisition! "

 

[crshears]

Hello Sheps75,

One of my older books on Diesel engines contains the following basic information:

It is realistically feasible to capture about 50% of the heat contained in the exhaust gas stream of a Diesel engine operating at full rated load; the amount of energy available for extraction diminishes rapidly as the engine loading falls from rated.

Four-stroke cycle Diesel engines at full rated load are reported to have an average engine exit temperature of 750°F, whereas two-stoke cycle engines will have an exhaust temperature of only 550°F; since condensation and corrosion concerns limit the HRSG exit temperaure to no lower that about 300°F, the former type of engine is clearly a more favourable candidate for exhaust heat recuperation.

Unfortunately, Diesel gensets will reject a fairly large proportion of their waste heat in the coolant, most of which it appears will be unrecoverable in your application...

Is there a desire to emulate the vessel's original configuration? Or would those funding the project consider instead using a combined cycle harnessing a gas turbine/HRSG unit or units? Your vessel, being steam-turbine-driven, would not have the problems of oily exhaust that I'm dealing with [see threads 341551, 342485 and 343198].

BTW: are the two steam turbines connected to one propellor shaft identical, or is one high-pressure and one low-pressure?
Are there thoughts of removing one of each of the turbines and converting the vessel's drive into a combined steam and electric propusion plant?

Hope this helps.

Carl

 

[EdStainless]

The other option for a bottoming heat recovery cycle is to not use steam, but an organic with a lower boiling point. This is common with geothermal energy where you have fairly low temperature sources.
There is a ORC unit out there that uses a rotary screw expander (instead of a turbine). It has been shown to be reliable and efficient.

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Plymouth Tube

 

[Sheps75]

Thank you all for sharing your expertise on this matter.

I should make it clear that due to the historic nature of the ship, and the way its restoration is to be funded, the design criteria are limited to having to stick with about half the propulsion power originating from steam in essence, otherwise much of the 'good will' and therefore the cash will dry up.... it's unfortunate, but there it is.

I had hoped to have some figures to better expand on the power demands, and the operating parameters of the primary diesel engines by now, but (due in part to the way the project is backed) extracting further information is somewhat painful.

CRShears, I'd like to particularly thank for offering some ballpark figures on the recoverable limits for differing diesel types; I've passed them on to the 'steam side' boys whilst I await more on the diesels. I hope to discover soon whether the updated turbines are destined to be supplied in a HP/LP pair, but it would fit with what's there currently.
My expectation is that, being of the 'high-speed', 4-stroke type machines, the gensets that we are proposing to supply will be on the upper end of the figures quoted (750°F/400°C), but clearly the most important figure to discover is the -quantity- of hot gases (their saturation, H2O, appears a critical factor too) available for heat recovery.

Sorry I can't offer more to work with at this point, but I mostly just wanted to say 'Thanks so far guys!'.