End of Curves 1

[ghoshtathagata2000]

It is being seen as a trend in the Middle East Oil & Gas companies specification that the drivers shall be designed for the ënd of curve operation. Also I understand that it is common practice to size the driver for end of curve also pumps operating in parallel.

What is the definition of end of curve and how is it achieved in practice? I am sure it is not 120% BEP as defined by the max. allowable flow in API 610 . During a test I witnessed I observed that the OEM described the end of curve even with the discharge valve not fully open which for me is not really the "ënd of curve"

By the way, if the driver is oversized, is there any way the pump operation is limited other than high vibration concerns?

Kindly share your experience

 

[pumpkind]

Before you made the decision, consult with Process Engineers if the equipment will be commisioned with water - it is extremely relevant especially when the process fluid density is much lower that the water

 

[1gibson]

Yeah 80%... If you consider the user's conservative system calculations that are sent out for bids, combined with lack of consideration for "off design" operation, combined with specifications that require silly things, getting it right 20% of the time would be quite impressive.

 

[BigInch]

That's what keeps the VFD market alive.... adjusting rpms to counter design flowrate selection screw-ups.

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

 

[stanier]

Was I really being too optimistic in assuming 20% of engineers knew what they were doing? Does that mean 80% of university professors are not conveying the right message? Its so sad....

Anyway I get a good feed redoing the engineering and pointing out how to reduce the carbon footprint. Who would have thought an old red neck like myself would start using greenie speak? Now the green movement have given me and my bank balance a new lease of life! Revenge is sweet.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[BigInch]

I think profs are getting that right. What else can they say, other than "closest to BEP". Since the "given" was given, no mistakes there either. Since leaving uni, my problem has always been getting accurate information that I could use for stating the "given" facts and keeping those from changing long enough to solve the problem and answer the question. They taught us well enough how to solve the problems themselves, just turns out that in real-world stuff, given has at least a variance of +/- 3[σ] on a good day.

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

 

[TenPenny]

It`s not always `screw ups`; many plants are designed for several operating scenarios, and therefore the equipment needs to cover more than one operating point. This means that compromises have to be made in selections.

If every pump was only ever going to operate at one point, the world would be a simple place.

 

[DubMac]

Amen brother. It would probably put a lot of us pump guys on the street too.

 

[BigInch]

The system can be designed for more than one flowrate even though the pumps only operate at one. Just a matter of paying for and fitting in the tanks, or turning the pump on and off rather than on low, medium, or high.

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

 

[Artisi]

The way round variable flow conditions can in some cases can be dealt with by using a multi-pump installation.

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]

Another good alternative makes 5 ways to avoid VFDs.

1.) BEP flowrate somewhere between avg and max, tank probably needed
2.) On/Off Operations, tank probably needed
3.) n Multiple pumps sized at BEP/n, most common ranges maybe no tanks req'd.
4.) Multiple pumps with BEPs for each different flowrate, probably no tanks req'd.
5.) A combination of the above.


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

 

[stanier]

Also use a control valve for the various conditions. Design the whole system for all conditions and maximise the time the pump and control valve operates at the BEP. Also during selection make sure the pump does not operate in extreme BEP conditions. if it does you have the wrong pump or need a combination of pumps with different characteristics.

If the future is going to hold even more operating conditions check that you can fit a larger/smaller impeller add additional of different pumps.

Whole of life costs involve energy and maintenance costs alongwith prime and future Capex.

“In physical science the first essential step in the direction of learning any subject is to find principles of numerical reckoning and practicable methods for measuring some quality connected with it. I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of Science, whatever the matter may be."

Lord Kelvin [PLA, 1883-05-03]


"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/