# Steam Turbines with Reheat



## Fritz Basset (Aug 29, 2021)

I'm a new poster here but have long been intrigued with steam plant efficiency. The Japanese are finally installing steam plants on LNG carriers with reheat, which really is superheat twice, and has been a feature of land based power plants for decades. It raises the thermal efficiency somewhere into the 30+% range - at least somewhat comparable to diesel. Why wasn't reheat employed on the FRANCE or QE2 so that they didn't gobble hundreds of tons of fuel daily? FRANCE burning 800 tons per day in the '60s is much the same as MAJESTIC in the '20s, although she achieved higher speed. Could reheat have helped here?


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## Tim Gibbs (Apr 4, 2012)

Fritz Basset said:


> I'm a new poster here but have long been intrigued with steam plant efficiency. The Japanese are finally installing steam plants on LNG carriers with reheat, which really is superheat twice, and has been a feature of land based power plants for decades. It raises the thermal efficiency somewhere into the 30+% range - at least somewhat comparable to diesel. Why wasn't reheat employed on the FRANCE or QE2 so that they didn't gobble hundreds of tons of fuel daily? FRANCE burning 800 tons per day in the '60s is much the same as MAJESTIC in the '20s, although she achieved higher speed. Could reheat have helped here?


 Like lots of things, once you get to the 65bar/515degree steam condition it's a lot of added complication for relatively small efficiency gains


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## Burntisland Ship Yard (Aug 2, 2008)

What is the difference in terms of thermal efficiency between reheat and what was on the Danish class extractions from the Stal Laval Turbines to feedwater circuit heaters?


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## Ian860B (Dec 17, 2015)

I remember being told in college in the 70's that there were ships out there that used reheat, the efficiency quoted was around 40%, Control of the boiler was tricky the reheat being bypassed during slow and standby conditions. The efficiency of conventional high pressure high temperature boilers with regenerative air heaters was certainly in the 90's %, these ships should have managed mid 30's overall efficiency.
IanB


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## captainconfusion (Aug 13, 2020)

I am unsure of my ground here: However in the 70's Stal Laval at Finspong where producing marine turbine Sets for container ships and large tankers, I do not recall reheat cycles being installed on these ships,
Stal Laval were turbine main engine manufactures in principle, and did not provide ship owners/builders with small powered turbines for Alternator/Generator or feed pump and cargo pumps.
The large engine high powered marine steam Turbine sets had gear sets (CYCLIC) provided by Allens, which in general worked well, but were never proven at full output? Maybe on Containers ships as at the time 'THE SUEZ CRISIS' and tankers slow steaming around the CAPE OF GOOD HOPE.
The engine plant-boilers/condensers/feed heaters/feedpumps apart from the Main Engine either single shaft or multishaft of some where in excess of 45,00KW, where not designed as a single unit by Stal Laval, but by the ship builder.
Stal Laval produced large shore based Power Units for ''POWER STATIONs' but these were Stal Laval-LUNGSTROM Turbine designs.
AS stated previous comments 'stand By and reduced speed' may have caused the shipping industry to discourage the use of STEAM REHEAT Turbine cycles. Our own RN were at the time developing the gas turbine as a main propulsion unit.
It is a long way from the old 'Up and Downer' Scotch Boiler, with a parsons exhaust turbine.
Oh, to read those old Marine books on the orals for engine types. memories??? Just a dream???


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## Tim Gibbs (Apr 4, 2012)

Ian860B said:


> I remember being told in college in the 70's that there were ships out there that used reheat, the efficiency quoted was around 40%, Control of the boiler was tricky the reheat being bypassed during slow and standby conditions. The efficiency of conventional high pressure high temperature boilers with regenerative air heaters was certainly in the 90's %, these ships should have managed mid 30's overall efficiency.
> IanB


Some boilers have separately fired reheat sections making making control easier but I still think it's a lot of faff for small gains. However I'm much attracted to the idea of gas fired marine boilers as there would be little to worry about in the furnace leaving only the water side to worry about!


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## FuzzyGolfito (Oct 3, 2015)

Tim Gibbs said:


> Some boilers have separately fired reheat sections making making control easier but I still think it's a lot of faff for small gains. However I'm much attracted to the idea of gas fired marine boilers as there would be little to worry about in the furnace leaving only the water side to worry about!


I sailed as 2A/E in the S/S Flor ex Beth Flor (sister Beth Tex) built in the late '40's with a 1,500 Pound Steam Plant with 3 turbines and 2 external reheaters....As I understood the hulls were originally laid down as Aircraft Carriers.
Later I was 1A/E on the S/S Bayamon, there were a few of these built for Transamerica Trailer Transport, Single 1,1500 pound plant with an internal reheater.....
I know that the reheat steam plant has been around for quite awhile!
Glenn Klima
US Chief Engineer Steam and Motor Unlimited Retired


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## triumphguy (Jan 20, 2011)

My ship, USS Joseph Strauss (DDG-16) was powered by a steam plant operating at 950 deg. (F) and 1200 psi (82 bar). The boiler included a superheater in the uptakes to extract as much energy as possible from the steam. The US Navy developed a lot of expertise with high-pressure steam plants during WWII and the following years, and the 1200 lb. plant was ubiquitous from the mid-50s on, powering everything from 3,500 ton frigates to 90,000 ton aircraft carriers. However, it was a very high-maintenance plant with high manning requirements and once the equipment started to wear, they were very difficult to keep operating. The pressures and temperatures required specialized materials and training. Throughout the 70s, many Navy destroyers and cruisers with 1200 lb. plants were pierside for long periods because they had been rode hard and put up wet during the Vietnam war and much maintenance had been deferred due to operational requirements. Many of the plants could not be operated safely, both due to their material condition, and as a result of the lack of trained operators; my ship had contractors from Combustion Engineering aboard for weeks at a time, trying to get our plant working.

I think the 1200 lb. plant pushed the available technology a little farther than was feasible, but the Navy had such a huge investment in those plants that they continued to patch them up and ran them as long as possible.

The launching of the Spruance class destroyers in 1974, with 4 LM2500 gas turbines and controllable pitch propellers, represented a sea change in the Navy’s approach to destroyer propulsion; those plants proved themselves in the Spruance class destroyers (now all decommissioned) and are now found in the Arleigh Burke class DDGs and Ticonderoga class cruisers, as well as many other vessels. On my ship, the engineers would have to come aboard 2 or 3 days before we got underway to get the plant up to operating temperatures and pressures; the Arleigh Burkes turn the key, crank the starter (Just like your Toyota) and start up their gas turbines 15 minutes before they cast off lines.

I think steam is still as viable choice for propulsion and power plants, but as Tom Gibbs suggested, you reach a point at which the effort required to extract that extra bit of energy exceeds the benefit realized.
Cheers,
Patrick Cherry
Ojai, California USA


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## FuzzyGolfito (Oct 3, 2015)

triumphguy said:


> My ship, USS Joseph Strauss (DDG-16) was powered by a steam plant operating at 950 deg. (F) and 1200 psi (82 bar). The boiler included a superheater in the uptakes to extract as much energy as possible from the steam. The US Navy developed a lot of expertise with high-pressure steam plants during WWII and the following years, and the 1200 lb. plant was ubiquitous from the mid-50s on, powering everything from 3,500 ton frigates to 90,000 ton aircraft carriers. However, it was a very high-maintenance plant with high manning requirements and once the equipment started to wear, they were very difficult to keep operating. The pressures and temperatures required specialized materials and training. Throughout the 70s, many Navy destroyers and cruisers with 1200 lb. plants were pierside for long periods because they had been rode hard and put up wet during the Vietnam war and much maintenance had been deferred due to operational requirements. Many of the plants could not be operated safely, both due to their material condition, and as a result of the lack of trained operators; my ship had contractors from Combustion Engineering aboard for weeks at a time, trying to get our plant working.
> 
> I think the 1200 lb. plant pushed the available technology a little farther than was feasible, but the Navy had such a huge investment in those plants that they continued to patch them up and ran them as long as possible.
> 
> ...


I am just enjoying my retirement, but on the S/S Flor as 2 A/E I had to maintain the Boilers, I don't remember the manufacturer, they were still 1,500 when I sailed on her, but I do remember Diamond Air Puff Soot Blowers ! When I sat for my C/E license there were several questions which I protested involving them....but as I had to make the parts to maintain them, I passed easily

Glenn Klima
San Francisco de Rivas,
Perez Zeledon,
Costa Rica!


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## Tim Gibbs (Apr 4, 2012)

triumphguy said:


> My ship, USS Joseph Strauss (DDG-16) was powered by a steam plant operating at 950 deg. (F) and 1200 psi (82 bar). The boiler included a superheater in the uptakes to extract as much energy as possible from the steam. The US Navy developed a lot of expertise with high-pressure steam plants during WWII and the following years, and the 1200 lb. plant was ubiquitous from the mid-50s on, powering everything from 3,500 ton frigates to 90,000 ton aircraft carriers. ............
> 
> I think steam is still as viable choice for propulsion and power plants, but as Tom Gibbs suggested, you reach a point at which the effort required to extract that extra bit of energy exceeds the benefit realized.
> Cheers,
> ...


One positive from reheating - it does keep the steam in the LP turbine dry and reduces blade erosion, but how big problem is that compared with the issues ?! I often wonder about turbines taking steam from pressurised water reactors as, with the low stream inlet conditions, it must be pretty wet by the time it gets near to the condenser !!


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## williamjshaver_4263 (Nov 25, 2021)

thought some of the canadian built lake ships had this... john inglis plants.


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## Burntisland Ship Yard (Aug 2, 2008)

captainconfusion said:


> I am unsure of my ground here: However in the 70's Stal Laval at Finspong where producing marine turbine Sets for container ships and large tankers, I do not recall reheat cycles being installed on these ships,
> Stal Laval were turbine main engine manufactures in principle, and did not provide ship owners/builders with small powered turbines for Alternator/Generator or feed pump and cargo pumps.
> The large engine high powered marine steam Turbine sets had gear sets (CYCLIC) provided by Allens, which in general worked well, but were never proven at full output? Maybe on Containers ships as at the time 'THE SUEZ CRISIS' and tankers slow steaming around the CAPE OF GOOD HOPE.
> The engine plant-boilers/condensers/feed heaters/feedpumps apart from the Main Engine either single shaft or multishaft of some where in excess of 45,00KW, where not designed as a single unit by Stal Laval, but by the ship builder.
> ...


Must dig out my "Reids" books for a refresher.......


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## Ian860B (Dec 17, 2015)

Burntisland Ship Yard said:


> Must dig out my "Reids" books for a refresher.......


I worked in a power station in Australia that had a number of the Stal Lungstrom Radial turbines, the smaller 7.5 MW units were quite reliable but not greatly efficient. the larger units had an axial blade section to boost efficiency which it did but reliability suffered with blade failure. I was not a fan of the Stal Laval marine units not as reliable as Parsons or G.E.
Jock


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## Varley (Oct 1, 2006)

Tim Gibbs said:


> One positive from reheating - it does keep the steam in the LP turbine dry and reduces blade erosion, but how big problem is that compared with the issues ?! I often wonder about turbines taking steam from pressurised water reactors as, with the low stream inlet conditions, it must be pretty wet by the time it gets near to the condenser !!


When pondering the topic wikistike says BWR plant use re-heat to dry before lower pressure turbine stages. I had imagined PWR pressurised water circuit temperature allowed superheating of steam in secondary circuit for a conventional turbine train. If not, then perhaps re-heat is used also?


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## Tim Gibbs (Apr 4, 2012)

Varley said:


> When pondering the topic wikistike says BWR plant use re-heat to dry before lower pressure turbine stages. I had imagined PWR pressurised water circuit temperature allowed superheating of steam in secondary circuit for a conventional turbine train. If not, then perhaps re-heat is used also?


Can't get steamed up about it 😎


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