3 replies to this topic

[PTSHeng]

Good morning all,

I would like to ask any pump specialists as this is my first time doing this and I want to ascertain if my steps are correct.

My boss has asked me to size an RO for a pump recirculation line. There are 2 cases which I have to take into account which are attached in the picture.

These are my procedures:

1) Size for bore for case 1

2) Use bore size calculated in case 1 and input the DP of case 2 to find the flowrate at Q2 for case 2. (The flow for case 2 in the other line will not affect the flow through the orifice in case 2 due to the flow rate through the RO being controlled by the DP)

Thanks to all for help in advance!



 

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Edited by YiHeng, 19 March 2014 - 04:05 AM.

[ankur2061]

YiHeng,

 

Some questions you need to answer:

 

1. What is the basis for the recirculation flow rate of 33 m3/h? Is it the minimum safe continuous recirculation flow for the pump? Has it been provided by the pump vendor?

 

2. What is the design or rated capacity of your pump? Logically, if the flow Q2 is equal to the minimum safe continuous flow of the pump and you know the rated or design forward flow (Q1), then the pump rated or design capacity should be Q1 + Q2. In such a case, the RO should be sized for Q2 m3/h and there is no actual need to do any other calculations.

 

The Differential Pressure (DP) for in the above case will be:

 

DP = (Pump Rated Discharge Pressure - Dynamic Line Losses @ pump rated capacity / pump rated discharge press., up to the tap-off point for the recirculation line - Dynamic Line Losses @ Q2 m3/h and pressure at recirculation tap-off point for RO up to RO inlet) - (Pressure at termination point of recirculation line + Dynamic Line losses from RO outlet to recirclation line termination @ Q2 m3/h)

 

Knowing the DP as calculated above and the flow rate Q2, the RO size can be calculated.

 

Hope this clarifies the approach for RO sizing.

 

Regards,

Ankur.

[PTSHeng]

Hi Ankur,

Thank you very much for your feedback. The 33m3/h is indeed the minimum pump recirculation flow.

With regards to your 2nd point Ankur, for case 2, does it mean that the pump has a designed capacity of 33+70m3/h and that  the sizing for case 1 will also be applicable to case 2?

I have discussed with my head what you said and he said that your points were all correct, thank you very much!
 

Edited by YiHeng, 19 March 2014 - 10:06 PM.

[ankur2061]

YiHeng,

 

The design or rated capacity of any centrifugal pump with a minimum safe continuous recirculation flow should always be the sum of the minimum safe continuous flow plus the design or rated forward flow. To know more about the various schemes for minimum safe continuous flow refer the link below:

 

http://www.cheresour...trifugal-pumps/

 

Regards,

Ankur. 

Edited by ankur2061, 19 March 2014 - 11:51 PM.