booster pump design 1

[chunk8]

I have a pump application where the npsha is less than the npshr. process specs given below:
npsha = 7.5 ft
npshr = 18 ft
sg = 0.6
vis = 0.36 cp
liquid at bubble point
suction p = 350 psig
discharge p = 4200 psig

I realize that there are other ways to increase the npsha other than installing a booster pump (i.e. raise vessel height, etc.) but at this point I am only interested in how I would even begin to spec out or design a booster pump to get the npsha on the main pump up to the required npshr. Can anyone provide me with the equations, as well as the theoretical and practical knowledge on how to do this?

Thanks.

 

[BigInch]

Try a can pump as a booster.

I don't really understand the numbers you're giving. You say 350 psi at suction. What is that? It can't be the expected suction pressure, that would give you a 1346 foot head.. well above 18ft. What is that?

http://virtualpipeline.spaces.msn.com

 

[JJPellin]

The vapor pressure is equal to the static pressure in the supply vessel. The only head available to the pump is elevation head. That is why the NPSH(a) is so low even with such a high suction pressure.

The simplest way to find a suitable booster pump is probably to contact the major pump manufacturers that you are most comfortable working with. You have the flow rate and the suction pressure. All you need to do is estimate how much discharge pressure you want from the booster and that is all the conditions that the pump company will need to recommend a pump. If you want to be certain to avoid cavitation on the larger pump, I would suggest sizing the booster to provide 3 or 4 times the NPSH(r) for the larger pump. So, for the sake of argument, I would select a pump with perhaps 50 or 70 feet of head. Try to get a pump that will be running at 1800 rpm rather than 3600. Try to get a pump sized to run very close to BEP flow.


Johnny Pellin

 

[BigInch]

Must be it.

http://virtualpipeline.spaces.msn.com

 

[djack77494]

I like Johnny Pellin's suggestion. Make sure that the booster pump can deliver adequate capacity under ALL conditions. The choice of how much head needs to be supplied by the booster pump is somwhat arbitrary; it can be anywhere from just enough to meet the main pumps NPSHr all the way up to the required discharge pressure (in which case you wouldn't need the booster at all). I like the idea of a slower rpm pump operating near BEP, as Johnny said. For the booster, you should have the luxury of selecting a pretty common inexpensive pump.
Doug

 

[BigInch]

Yes, Mssr. Pellin is totally right... as always. I did not catch the liquid's vapor pressure as EQ suction pressure.

http://virtualpipeline.spaces.msn.com