BFW NPSH available problem 6

[flinana]

Hi,

I am having a problem keeping my BFW pumps from having to stop due to low NPSHR.

50MW solar powered plant. 4 BFW pumps, 3 normally maintaining level in Steam generator drum, 1 stdby.
The pumps NPSHR at 100% (3300 rpm) is 3 m. We are having great troubles in having a NPSHA above 3 at high loads. We have implemented an interlock to protect the pump so when the NPSHR is below NPSHA we trip the pump leading of course a a Turbine trip when we are around 47 MW.

Normally the pressure drops at the pumps suction is derived by an increase in energy from field causing a cold flow of condensate into the deaerator causing a or large movement from the HP bypass valve, pressure drop while the temperature remains stable due to the inertia of the system. This pressure drops lead to a drop in NPSHR tripping the pump.

How can I control this???, We have tried being very careful with sudden changes in flow, slowing closing ST HP bypasses, Slow increase in field energy, all to no avail, somehow we cant get to 50 MW because of NPSH. It is driving me crazy. Please anyone help? ideas? I can send more info of course

 

[rmw]

Flinana,

Without all the details, it didn't seem right that 22 meters of NPSHa went to 3 meters, but stranger things have happened. Glad to hear that you are getting a handle on it.

I would like to take a look at the formula if you would post it.

rmw

 

[flinana]

thanks, find the formula attached. Its in spanish but its easily understood. asp = suction. Disponible =available

 

[flinana]

forgot the attachment! here it is

 

[rmw]

Gracias,

Hablo espa~nol. Lo tengo.

rmw