Main turbine drive for boiler feed pump.

[nhlong]

Dear all,

Can anyone help me to answer this question: "Why dont use main turbine shaft to drive BFP instead of steam turbine driv or electri-motor drive?"
This option only need gear box and fluid coupling to drive BFP.
It's simpler than steam turbine drive and more effective than electri-motor drive

Thank u!

 

[RVAmeche]

Seems like that'd be just another thing that could go wrong and screw up your turbine in my opinion. Why mechanically link your pump to the turbine when steam or electric does the job just fine?

I imagine startup would also be an issue. You don't have BFW until the turbine is spinning. How do you get steam for the turbine without BFW.

 

[Raai2015]

Well, i am an boiler process engineer , to the knowleedge of mine between 80 to 360MWe never seen main turbogenerator as a prime mover. but i would give my opinion from the link where i read. Just to summarize,
Advantage of using Turbogenerator as prime mover :
1. Increase in operating pressure leads to the bigger size of the motor which is costly,
2. required higher speeds can be by step-up gears from turbo generator (from1750rpm)
3. steam turbine is itself a variable speed machine , so we dont need VFD or hydraulic coupling.
But the fact remains,
1. hydraulic coupling needs to be used to obtain the variable speed
2. need to install the electric motor driven during start up the boiler.
below facts i didnt understood :
1. para 4th : cross compound unit drive atleast two-half capacity pump
2. Last 2 paragraphs - In my opinion , author says , due to the development of plant effeciency, turbine is condensing turbine and to his knowledge he hasnt seen any sor the pump installation with turn´bine generator

but this principle was in late 1950's & 1960's
Reg
Baskar

https://books.google.de/books?id=63...t use main turbine shaft to drive BFP&f=false

 

[nhlong]

Dear Raai2015, thank for your answer!
Almostly, I agree with your opinion about advantage of main turbine drive(MTD) for boiler feed pump (BFP).
And I have some opinions below:
1. If use secondary steam turbine to drive BFP, you still need to have a small electric motor driven during start up the boiler.
Use MTD is simpler than steam turbine drive (need secondary turbine, steam pipe, control system,...).
This is not disadvantage compared to turbine drive.
2. Cross-compound turbine has space to install 2x50% BFP
In case of tandem-compound turbine, can use 2 paralleling shaft gear units for 2x50% BFP.
3. Condesing turine will increase steam expasion, do more work for drive BFP. But follow author, although condensing turbine was widely used, main turbin shaft drive has not been installed for many years. WHY?

Best regard!

 

[nhlong]

Dear RVAmache,
Due to both of electri motor drive and steam turbine drive have their disadvantages, and main turbine can cover them.
This option can't screw up turbine if install with fluid coupling to start-up no load and control speed.

Best regard!