Crude Pump Selection Low NPSH

[rotaryguy]

I have Crude Transfer pump application. Design duties are as below.

Flow rate=25000 gpm
Diff head=360 ft
NPSHA=5.7 ftMax/Rated Suction Pres.: 19.31 psia
Vapour Pressure= 12.5 psia
Fluid= Crude
SG = 0.80
Temp= 80 °F
Viscosity = 1.50

Any body has suggestion which type of pump should be able to do this. constraint is low NPSHA.

 

[DubMac]

Try a big splitcase, just as the ones used for years in pipeline service; I believe now called BB1?? You can always get two pumps rated at 12,500 each.

Check out Flowserve, Goulds, Ruhrpumpen, etc. Will have to be massive and run slow. If you absolutely can't find anything large and slow enough to meet the NPSH, consider dropping it in a hole to "buy" NPSHR. Just a thought.

 

[GHartmann]

Sulzer also has similar pumps. Both Flowserve and Sulzer have application software you can use to select pumps; but you will need a business e-mail and not a private one (i.e. yahoo, g-mail, etc).

Your problem definitely is going to be obtaining the necessary NPSHr.


Sulzer

 

[GHartmann]

Here is a link to the Ruhrpumpen design. It has a double suction that helps minimize the NPSHr.

Ruhrpumpen

I will let other posters with more direct experience comment on the merits of the various models.

A couple of points to consider:

Do you have a common manufacturer for your facility in question?

When discussing the application with your pump sales representative, make sure the pump they select has references in applications similar to your service.

 

[BigInch]

Can pumps are good for low NPSHa.

http://www.gouldspumps.com/pump_VIC/

you must get smarter than the software you're using.

 

[JJPellin]

This is a classic problem in any oil refinery. We use a vertical turbine pump at the tank as the primary pump. This delivers low head, high flow to the crude booster pumps which are two stage, double suction, split case pumps. It works very well.

Johnny Pellin

 

[1gibson]

Use a vertical can pump (API VS6.) You won't need (or want) double suction, the double suction first stage impeller will just increase the barrel size for a small decrease in length.

 

[GHartmann]

Now that you have all these answers aren't you glad you asked?

It appears to me that your flow/head requirements exceed the range of the Goulds VIC coverage range:

Goulds

I am not sure about the Ruhrpumpen equivalent:

Ruhrpumpen

It looks like the Flowserve VPC might meet your application (see attachment).

As you can see you will have to make some pretty fair preliminary investigations just to find proper pump coverage. If you can access the pump selection software from the various manufacturers you can at least eliminate those that cannot provide adequate coverage.

As far as pumps in series, I am not a fan of that arrangement (it will cost maybe 2 x more total installed cost).

Let us know how you make out with your preliminary investigations.

 

[LittleInch]

Rotaryguy,

At those sorts of NPSHA levels (<2m), you're really going to struggle to find something that works reliably, so maybe a re-think is worthwhile to either reduce your friction losses or increase head (lower pump, can pumps etc). Be aware that meeting the NPSH number does not guarantee lack of cavitation. Often the onset of cavitation is above the NPSH curve by anything up to 2m head so you need to specifically ask the vendors if this pump will not cavitate at your inlet NPSH level. Generally the slower the pump and the more to the left of the pump curve you are the better, but nothing is guaranteed.

At that flow you probably need at least two pumps in parallel to increase your availability of pumps.

good luck and let us know how you get on.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[DubMac]

Either a splitter or a vertical can pump; take your pick. Plenty of manufacturers make them; these will be specials and most likely not in any catalog. Your NPSHA, if you can't increase somehow, may force you into can pump design.

The main difference between the 2 designs will come down to what your folks (especially Maintenance) are used to. The volume makes the can pumps huge diameter, but the head is easily handled by adding stages (deeper hole). The head will require the splitcase selection to have a huge wheel (or two), but flows can be easily handled.

You might want to check out using 3 pumps with 2 running and one standby to reduce overall size of the selection. The scale of cost going to one pump at 25K gpm is going to go almost exponential (think how large the seals would be).

As tempting as it will be to find the smallest (read cheapest) pump possible, the slower this baby runs, the longer it will last and the cheaper to maintain.

Wear increase = speed increase cubed!