Rated flow rates not in 80% to 110% of BEP flowrates

[AspenMech]

Hi all,

I got a quote of a API 610 pump with an efficiency of 38%. I asked the vendor if there are any pumps with an higher efficiency. They have a pump with an efficiency of 48% at the given rate but it is below 80% of the BEP flow rates.

What would be the problems if the flow rate is below 80% of BEP flow rate?

Thanks!

 

[LittleInch]

Larger electricity bill.

But those efficiencies are terrible. What size and diff head are we talking here.

<80% BEP is a lot on the left so doesn't give you much room for less flow without hitting internal recirculation issues.

On the pother hand there is a lot more flow capacity out of the pump than your rated flow. And better NPSH.

But not all vendors provide good coverage for all flow and head combinations. Sounds like you need to spread the net a bit wider.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Besides the obvious hit on economy of operation

https://empoweringpumps.com/some-effects-of-operating-pumps-away-from-best-efficiency-point/

More links here

https://duckduckgo.com/?q=operating...+outside+of+pump+operation+BEP&t=brave&ia=web

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[AspenMech]

The differential head is 149m. The flow rate is 39.7m3/h.

So even if the efficiency of the second pump is higher, but as it is outside of the 80-110% BEP range(69% of BEP), the electricity cost maybe higher?

Why is there suction or discharge recirculation if the flowrates are low?

 

[1503-44]

Definitely will cost to run it. It's important because 150m is a pretty good height. You'll maybe at 3 X your hydraulic power at the power meter.

The pumps impellers want to take more volume than you can give it into the pump.
When you go there with half a glass, the pump would rather fill that glass first. It spills back into suction whatever shortage you arrive with, then it takes it to discharge.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

That's a fairly small pump tbh. Do you really need an expensive API 610 pump? Many cheaper and more efficient pumps would suffice.

The second pump would be less expensive than the first, but still more expensive than the most efficient pump you can gat for the duty.

Having said that about 50 odd percent looks about right for that size of pump when I look at other pump suppliers but you seem to be in a strange place where the head you need is high compared to the flow. Max efficient is maybe 65 to 70% so worthwhile chasing different vendors to see if you fall more into their range of pumps.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[AspenMech]

Thanks all for your responses.

It is the client’s request to have API pumps as the pump is used in refinery plant.

The second one is cheaper but my concern is that it is below 80%of BEP.

 

[1503-44]

It is a bit strange to see these flow rates and relatively high head, outside a domestic water well application.
What is this pump actually doing?


--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[AspenMech]

It is for process condensate in a fertilizer plant.

 

[MJCronin]

Let the guessing games begin !!!

1) Was the pump specified to be able to move solids (solids handling pumps have horrible efficncies)

2) Is this some kind of slurry pump or "chopper pump" ?

3) Is this a "self priming" pump

4) Is this a new pump or "boneyard reused" pump

5) Tell us the pump vendor and model name and we can help you more

MJCronin
Sr. Process Engineer

 

[Artisi]

The application details and the current pump selections, including the performance curve would certainly help to clarify your concerns.

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.)

 

[georgeverghese]

Often, in actual operation, pumps dont operate at design conditions. Flow may be less than design, or developed head may be much lower. In such cases, a variable speed pump will help to reduce power demand. It may be nice to have a pump with a design flow at higher than 80% of BEP, but to me, is not a must have:- the pump min flow recirculation control loop should kick in when required.

 

[1503-44]

The decrease of output head when rpm is reduced to below 50% would require full speed heads of approximately 600m @50%rpm to 1666m @30%rpm. That seemed to make vfd a bit impractical. The pump selection problem gets worse with vfd.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[goutam_freelance]

Nevertheless you can check with pump supplier of 48% efficiency pump to check whether VFD will suit the purpose.

But as the pump head is also lower at a lower speed, you need to check with the system resistance curve also.

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[1503-44]

VFD won't change the 150m head system requirement, but it does change the head the pump can deliver. It will not be this pump that works with VFD. Its of no use here.
VFD just does not usually work for the constant head application so far described here.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[goutam_freelance]

As the pump performance curve for 48% BEP efficiency pump was not available, it was assumed that since the rated flow is larger, the head will be larger too based on the assumption of similar pump characteristics at this size range.

So based on assumption of availability of additional head, VFD was considered as a possibility.

But the process people may know better.



Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[LittleInch]

How many vendors have you sent the enquiry to?

One will have a pump with higher efficiency than the others.

If this pump runs nearly continuously, energy cost difference could easily be higher than the CAPEX difference. Do the numbers.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

As usual, all guess work based on insufficient data, round and round tail chasing - let's get some real information and save everyone's time.

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.)

 

[AspenMech]

The pump is used to increase the process condensate pressure for a preheater. The vendor is the client’s preferred vendor. The lower efficiency pump is RUHRPUMPEN. I don’t have the new quote for the pump that is below the 80% of the BEP yet.

Thanks all for your help. I will check with other vendors.

 

[LittleInch]

If the client accepts the power number then just go with it.

If this is a negligible additional power cost compared to other consumers then just go with it. You just need to make sure the flow can't go much lower than your rated flow without allowing for some sort of recirculation line.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.