Centrifugal Pump efficiency 1

[zipped]

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.

 

[Artisi]

Why is it always the pump that gets blamed, most of these units have been round for years running in all types of conditions usually without any problems. Look at the system or the application of the pump, also a pump curve might help plus the actual site performance - not the design criteria - from this you mighty get some useful feedback.

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]

No. Running at that efficiency would indicate that you are not operating near BEP and consequently you should expect to have maintenance problems of one kind or another.

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

 

[JJPellin]

You really don't provide enough information to say for sure. It is a simple economic analysis to find the value of a higher efficiency pump. Determine the amount of energy it could save and compare that to the cost of conversion.

If BigInch is correct and you are running well away from BEP, then you have a reliability penalty in addition to the energy penalty. However, it is also possible that you have a pump that is designed with low efficiency even close to BEP. We have examples in many parts of our plant. Sundyne pumps are notoriously low efficiency. We have fully-lined slurry pumps in our FCC bottoms service that are inefficient. Because of their design, the efficiency cannot be increased by much. If this is a service where some other priority (non-clog, erosion resistance, compact size, etc.) is more important that energy efficiency, then you may have few options.


Johnny Pellin

 

[1gibson]

Service conditions are not unreasonable, this looks like a clean light hydrocarbon:

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

The question "Is it recommended to use this pump with above efficiency." doesn't seem to blame the pump, instead it questions the application. You are correct to suspect a design problem: with a system that uses that pump in the listed conditions.

What % of BEP are you running at, less than 40%?
What is the suction pressure and how does the pump handle it in terms of thrust?
Product temperature, vapor pressure, are either of these higher than the original design conditions?

Missing quite a few pieces of the puzzle but once we get them all, I still don't see them fitting together very well...

 

[SNORGY]

Upon first inspection, I wouldn't immediately suspect that this is a pump issue. It would appear that even at this low efficiency point you are still operating at a point that gives you another 11% rise to shut-off. However, 59 USGPM @ 538 ft implies, to me, that you probably have a multi-stage pump. In that case, your "overall pump" characteristic curve would be expected to be steeper than the "head per stage" curve, so even if it (upon first inspection) *looks like* there is healthy rise to shut-off, you might well be far enough left of BEP that you have some form of flow instability going on.

When one thinks about it, it wouldn't be in any pump manufacturer's best interests to have e = 24.5% @ BEP.

In conclusion, then, without knowing or seeing anything otherwise, you probably have a multi-stage pump running well left of BEP. Or, so it would appear based on what I see.

Regards,

SNORGY.

 

[SNORGY]

My above post said, I acknowledge JJPellin's comments that some pumps are notoriously inefficient - Sundynes and slurry pumps among them. I just reviewed some Galighers that operate at BEP @ 35%, for example.

Regards,

SNORGY.

 

[TenPenny]

As others have said, without knowing the BEP, it's hard to answer your question. This could be a low-flow model, which are notoriously inefficient, but designed to run at low flows.

 

[BigInch]

A slurry with an SG of 0.57? For an "API standard centrifugal" pump, it's pretty clear that either the flowrate is wrong, the pump is wrong, or it has been totally trashed.

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

 

[SNORGY]

I don't think the OP mentioned a slurry pump. JJPellin and I just included them in our short list of examples of pumps that are typically inefficient.

Most slurry pumps won't be designed or built to API anyway.

Sorry about us (me) creating the misunderstanding.

Regards,

SNORGY.

 

[Artisi]

Everyone shut down their crystal ball until such times we hear more from the OP.

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.)

 

[rmw]

But we are so good (or should I say practiced) at crystal ball gazing.....

rmw

 

[Artisi]

yep, and I hope Santa brings me a new one this Christmas, the old one is just about worn-out.

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]

No problem. Just trying reemphisize some consistency with the very little evidence presented.

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

 

[zipped]

Hi everyone.
Thanks all for your responses. Sorry for the late reply. Let me clarify your doubts.

1. This is a single stage centrifugal pump.
2. This is not a slurry pump. Pumping fluid is Butene. Pumping temperature is 60 deg C with vapour pressure as 7.813 bara.
3. BEP of this pump is 25.5% at flow rate 18.4 m3/hr. That implies the pump is running close to its BEP.
4. Suction pressure is 7 bar g. Discharge Pressure is 15.6 bar g.

 

[BigInch]

At BEP (nothing is implied by your above data, except that you are NOT anywhere near BEP) you should certainly have efficiencies above 60%, if not higher.

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

 

[Artisi]

As most of the guys / gals here deal in facts, posting a pump curve, advising pump size and model etc, would certainly go a long way to helping with getting to the root cause of your problem

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]

Or at least telling us what BEP is, but it seems that you don't know. It should be found on the pump's nameplate data, if you can still read it.

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

 

[Pumpsonly]

""3. BEP of this pump is 25.5% at flow rate 18.4 m3/hr. That implies the pump is running close to its BEP.""

25% as BEP is not uncommon for pump of the low folw/ high head = low Ns type. Especially from Sundyne and also the PEP series by FindeR pompe.

 

[BigInch]

If he's got one of those, then maybe no problem. Those makes aren't in my standard centrifugal line up ... for painfully obvious reasons.

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