Centrifugal peerless pump 1

[redraider33]

Hi all, this is my first post. . . so bear with me. I am a first time intern for a company that deals with moving and processing NGL throughout the Texas Panhandle. I have been assigned a project that deals with a peerless multi stage centrifugal pump that a plant supervisor is wanting replaced. I don't have a lot of info about the pump, and the engineer I am working under is always gone to meetings and is not around to answer my questions. I'm not sure where to start or what questions to ask.
Some information I do know:
The liquid that the pump is moving is located in a spherical tank that is kept at 35-44 psig. On the way to the pump, the liquid is passed through a water phase separator, and then to the pump. I only know a few specifications about the current pump. The flow rate is 30 GPM, the differential pressure is 356 psig and the power is 25 Hp. From what I have been told, the plant wants to have the tank as close to 35 psig as possible, but in doing so, the pump loses head and quits pumping. The operators also told me that they sometimes have problems starting the pump at this lower pressure.

Any suggestions for what data I should collect, or any other advice would be greatly appreciated. I'm trying to learn this stuff as fast as I can. Its a lot different than sitting in a classroom.

Thanks

 

[TenPenny]

Get the serial number of the pump, call your local Peerless rep, and ask for all the serial number data. Then look in your equipment files for the same info.

Also get the motor data, hp you've got, but also check the speed.

When the pump is running, get the tank pressure, find a way to measure the pressure at the suction and discharge of the pump, and also motor amperage load. Check the temp of the NGL as well.

Try to find the data on the water separator as well as the vapor pressure of the NGL.

I think what you'll want to find out is, what is the pressure at the suction of the pump...find out the NPSHr of the pump...I would expect that the NGL is likely vaporizing in the pump suction...but that's just a guess.

 

[redraider33]

When I get the vapor pressure of the ngl and the pressure at the suction of the pump, should one be higher than the other? I should probably know this, but I can't think of which way it needs to be.

 

[SeanB]

If your suction pressure is lower than the vapor pressure then you have vapor at the pump suction. So hopefully, your suction pressure is higher.

 

[wimple]

Some thoughts :

1 - Check the vapour pressure of pumped fluid (poor NPSH available)
2 - I know that some times (Liquefied Natural plants for example), it is installed a booster pump (helix) upstream the main service pump to avoid cavitation
3 - Keep in mind that as general rule, the NPSH required increase when discharge pressure decrease and fluid increase (right of BEP) lowering the NPSH margin

To be safe...check with Mfr. the capability to move to the right of the BEP and discuss with them cavitation risk...

My opinion only

Rgds
Wimple