Centrifugal Pump efficiency 1

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We have a API std centrifugal pump installed in our plant with following details as given by vendor:-
Capacity-13.36 m3/hr
Total Head- 163.9 m
Speed-3550 rpm
Sp. Gravity-0.5370
Viscosity-0.1109 cp
Efficiency-24.5%
BHP-13.05 kw
Shut off- 182.25 m

My question:: Is it recommended to use this pump with above efficiency.
Currently we are facing high vibration problem, and we suspect some design problem. We have replaced power end, mechanical seal, but still have high vibrations in the pump.

 

[petrochemical87]

I have also seen a single stage centrifugal pump with a datasheet stating rated head of 180 m at 22 m3/hr with efficiency of 29 percent. I guess its not uncommon. Our pump is working fine.

 

[BigInch]

Are you pumping condensate with that?

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[bingopin]

I have seen problems pumping butene with a low efficiency pump. Wonder what the heat rise is across the pump?

 

[petrochemical87]

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After looking at the numbers you have posted I wanted to ask whether sufficient NPSH is available to the pump. Was it designed to pump butene at 60 degC?

 

[DubMac]

I think Petrochemical87 has nailed it. Pumping condensate is (along with tower bottoms) probably the toughest service for any pump in refinery. Mainly due to the typically very low NPSHA.

Most often a long vertical can pump handles this service since the first stage can be sunk to whatever elevation below grade is needed to provide adequate NPSHA. It is not uncommon to see 20-30 stages on a condensate service.

If this is a single stage centrifugal at ground level, it owuld be wise to study the NPSH profile of the pump and the installation.

 

[BigInch]

Nobody's going to "nail" anything with that little bit of evidence. BTW cavitation was not mentioned. They can't even tell you what BEP is and they are tearing down the pump trying to "fix it". I would guess they are not operating it correctly (nowhere near BEP) and until they learn how to do that, they will keep on tearing it down.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[Artisi]

The OP said that vibration was the problem, well, I would be interested in knowing how vibration was linked to efficiency.

As most of us would know, vibration can caused by 100 and 1 things starting with mis-alignment -- and we still haven't been given any clear info to work from, well next year we might have the missng detail.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[BigInch]

Is not vibration linked to far away BEP flow, and hence indirectly to efficiency too.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[Artisi]

Yes / maybe, if this particular unit is running well away from BEP - which is still an unknown.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[DubMac]

Simply saying, that from the information we do have available, insufficient NPSHA would a prime suspect. Using single stage overhung pump at grade for condensate service instead of a vertical canned pump just raises a flag in my mind. Running at 3550rpm raises the NPSHR significantly as well.

If NPSH margin is in fact O.K., then next I might consider wear ring clearances?? Light hydrocarbons are notoriously bad lubricants. Usually clearances are opened up somewhat to accomodate low lubricity; if that is the case here, would help explain operating off BEP.

It would be nice to have curves, technical data, pictures of the pump and installation, teardown/inspect report of the last repair before performing diagnosis on the patient.

Of course we want this; but as the saying goes, "people in Hell want ice water". Quit whining and shine your balls some more.