Boiler Feed Pump NPSH at Hot Start 3

[swapanburo]

There are many articles on Boiler Feed Pump transient NPSH analysis during load throw-off. Can anyone inform me about similar study for Hot Start situation ?

 

[bimr]

Review this chapter:

http://85.185.231.196/mekanik/CD_3/pump handbook/steam power piants.pdf

 

[PumpSmart]

Swapanburo,

Do you work on power plan or what kind of industry?
What is the service?
What type of centrifugal pump it is?
What is the temperature and fluid?

Please specify some details in your question.

There is a lot of literature, but please be a little more specific.

 

[swapanburo]

I work in Consulting Engg. firm, specialised in Power plant engineering
I am discussing Boiler Feed Pump in Utility Scale power plant of above 300 MW rating.
Barrel type pump
Deaerator temperature around 9 bara, temperature around 350 deg.C

I am interested to know about the Cavitation scenario at the hot restart condition after a plant trip. After a plant trip the pressure and temperature of deaerator drops. However the temperature of water at pump suction near the pump may be at higher temperature. So when the pump is started at hot restart there is possibility of flashing and cavitation. I was looking for some literature on this issue.

 

[rmw]

Good link bimr. It think I'll add a star for you.

Swapanburo, the answer lies in how much the DA pressure decays. Look at figure 9 in bimr's attachment. Using that example, if the pressure lowers enough so that the saturation pressure of the water at or near the pump suction is 51 psig, you will have flashing in the water at the pump suction, running or not. Even if it stops decaying at that point, now your fluid stored in piping at the impeller eye is saturated. You can't pump it. It will flash the second you start the pump.

Two solutions are given in the paragraph's numbered 1 & 2 below figure 9.

I have a third one and one probably easier to do than 1 & 2. If the decay in pressure stops and the pressue equalizes, then you can drain water at the pump until water at the saturation temperature of the DA vessel arrives at the pump suction from the DA storage tank and that fluid will be subcooled with respect to the pressure on the surface of the liquid in the vessel due to the head contribution of the piping. Now you can start the pump.

rmw