Pump running at end of curve

[SENGUTTUVAN]

For a vertical submersible pump ( closed drain drum pumps of Vs4 type) , the vendor has given the allowable operating region upto the end of its curve . Is it advisable to run a centrifugal pump continuously at its end of curve? Will there not be any impact on its effective life of the components. However the selected drive motor power is suitable for this operation. Thanks to clarify.

 

[BigInch]

Is it advisable to run a centrifugal pump continuously at its end of curve?
NO.

Will there not be any impact on its effective life of the components.
Most certainly there will be.

However the selected drive motor power is suitable for this operation.
If end-of-curve operation is not required, the motor might actually be oversized, so check that,

it is not oversized,
properly sized for BEP and
that the BEP point was actually specified and/or selected using the correct average and anticipated ranges of operation.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[TenPenny]

The vast majority of time, the motor is selected to cover end-of-curve operation. That what most specs I see call for.

But actually operating there for any extended period of time will result in a shortened life, shafts and bearings are usually the first to go.

Also, your use of the term 'VS4' sounds like an API service - note that 610 limits acceptable operating range to, what is it 105% of BEP or something like that?

 

[JJPellin]

I agree with both previous answers. Running at end of curve comes with a reliability penalty. If you want to quantify that penalty, there are a few details that you could consider. As previously mentioned, running well above the best efficiency point is not recommended. You may want to calculate how far out end of curve would take you. Divide the flow at end of curve by the BEP flow. If that is above 105%, you have reason for concern. If it above 120% you should expect a severe reliability penalty. Other concerns with end of curve operation in this application could include NPSH margin and submergence. You should evaluate the NPSH required at the higher flow rate as compared to the NPSH available. The lower the ratio of available over required, the lower the expected reliability. And even if the NPSH margin looks acceptable, you could still have a submergence problem. At the higher flow, you require a greater submergence to avoid the possibility of votexing and ingesting gas. At the higher flow rate, you have higher velocity. If there are any solids in the product, you could experience accelerated erosion. If you have corrosion mechanisms, they could be accelerated by the higher velocities and possible high temperatures because of the inefficiency. In short, there are a lot of ways this could hurt you.

Johnny Pellin

 

[BigInch]

If your motor, power distribution and piping system are prepared to do it, go for it, but have your checkbook handy.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[SENGUTTUVAN]

Thanks to all for keeping replying. I would like to explain the scenario further to get additional comments from you all . Actually this pump is to be installed in the refinery plant for one of the closed drain pump to empty the flare knockout drum within two hours and works intermittent . Two cases given in the process data sheet (Case 1: 95m3/hr at 54M head& Case2: 95m3/hr at164 M head). The 2 cases are for 2 battery limits .Case 2 oper conditions will be in normal operation & Case 1 oper conditions will be when reqd. For the above 2 cases the vendors are accepting to offer for Case 2 only and cannot offer a pump that can satisfy both cases. We are planning to accept for a higher Head pump . If the Higher Head pump is used for Case 1 also , the pump will go for end of curve oprn to max flow. It is to be noted that the vendors have given the allowable operating range upto the end of curve flow. It is aruged that this pump is only going to empty the drain drum and if it empties quickly ( earlier than 2 hours) it is fine and the pump is for intermittent operation only. Thanks for clarifying.

 

[JohnGP]

Can you stick a valve in the discharge line that can be partially closed for Case 1 operation, to increase the head seen by the pump?

 

[BigInch]

With 1 pump, supplied to the case 2 reqirements, you must be able to set up the boundary conditions for the case 1 scenario using appropriate control, otherwise any fixed speed pump without such controls will simply operate at the intersected point of the pump curve with the system curve, wherever that happens to be. JohnGP reasonably suggests you use a control valve to effectively change the system curve to give you that intersection point at 95m3/h & 54 m head.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[SENGUTTUVAN]

Thanks a lot JohnGP and Biginch. The offered pump have 120 metres head at EOC and even control system at the discharge cannot give the required head of 54M. I think the only available option now is that the process has to put a note in the PDS that for case 1 operation the discharge valve needs to be closed to control the flow to the requirement so that it does not operate at EOC. Is this OK?

 

[JohnGP]

I think what BigInch meant to say was that, with a control valve in the discharge, you could change the system curve such that it intersected the pump curve at 95m3/h and 164m head for Case 1. If he was to clarify, he would probably also say that you don't need to have the valve shut in that much though - enough to increase the head somewhere above 120m (EOC), say in the range mentioned by JJPellin above.

So yes, if your operating procedures can handle it, shutting in the discharge valve for Case 1 operation should get the pump off the end of its curve. Otherwise add a control valve.

Regards,
John

 

[BigInch]

Thanks John. I was on the way out the door and wanted to finish that .... apparently a little too fast. Owe you one.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[JohnGP]

No problem, maybe you can go easy on me when I have one of my foot-in-mouth moments.

 

[BigInch]

Deal.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[SENGUTTUVAN]

Thanks a lot Biginch and JohnGP.