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Two Pumps Connection

suction of pump; discharge of pump two pump connection

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#1 Movers

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Posted 08 December 2016 - 07:51 AM

Hi all.

 

I would like to ask what do you think about connection of two pump, where suction line of pump 1 is rooted directly from discharge of pump 2 (process medium flow through air cooler and then part of it is rooted to pump 1)? What disturbances could occur in such configuration? Process medium is diesel oil, about 40 t/h (pump 2) and 15 t/h (pump 1), discharge pressure of pump 2 is about 4 barg.  

 

 



#2 shan

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Posted 08 December 2016 - 09:54 AM

Not "rooted", it should be "routed".

 

It is OK to use your pump 2 as a booster pump.



#3 Bobby Strain

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Posted 08 December 2016 - 12:45 PM

A sketch would help, including valves in the system. Your description is confusing. You should include the type of pump along with suction and discharge pressure of each.

 

Bobby



#4 Movers

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Posted 09 December 2016 - 10:59 AM

Thanks for reply.

 

Please find in attachment a simple sketch. P2 is existing centrifugal pump. P1 is projected new pump (generally the red ones elements are new projected).

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#5 ankur2061

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Posted 09 December 2016 - 12:31 PM

Movers,

 

I have modified your sketch to ensure that you have proper flow split-up by using flow control. See the attached sketch.

 

Regards,

Ankur

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#6 Movers

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Posted 10 December 2016 - 01:34 PM

Thanks for your comments. You are right. I have made only a simple conception without any control devices. I left the rest for the designer. My only apprehension was if this two pumps could work properly in such configuration.

 

Best Regards



#7 Movers

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Posted 23 May 2017 - 07:45 AM

Hi All.

I would like to back to the issue. The designer claims, that such solution will not work properly and may cause big problems with the new one pump. I have no experience with this. Have you ever saw refinery where pumps work in such configuration?

I have never met such arrangement but Also I have never met any standards saying the pumps should not be used this way.


Edited by Movers, 23 May 2017 - 07:46 AM.


#8 Mahdi1980

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Posted 24 May 2017 - 08:56 AM

Movers,

 

Such configuration might be correct.

However, I believe that to control the flow of pump 2, you shall install the flow meter and control valve at discharge of pump 2.

Another important point is the parameter which must be controlled. Flow rate or pressure of diesel oil ?

By the way, what is the discharge pressure of the 1st pump (pump1)?

What is your purpose of using pump 2?

 

Regards



#9 Saml

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Posted 24 May 2017 - 11:17 AM

This type of arrangement, is not unusual. It is done for energy, cost or NPSH.

 

Examples: in some urea plants you need to provide ammonia reflux to a distillation column (low pressure) and feed the reactor (high pressure). It may be better to have a low pressure pump for the reflux and a high pressure pump for feeding the reactor. This way, you avoid the energy needed to pressurize the reflux to the reactor pressure and then wasting that energy in a control valve.  You may say "OK, but you can have them in parallel", what brings us to the NPSH issue.

 

Multistage high pressure pumps, that normally runs at high speed (>3000/3600 RPM) have higher NPSH requirements than a single stage booster pump. So the designer is faced with a few option: more stages and lower speed on the high pressure pump, elevating all the equipment in the suction of the pump (several meters), or installing a booster with low NPSH requirements. Sometimes the later is the best option.

 

Another example are the pumps in reverse osmosis pre filters. If you don't have enough pressure in your water supply, you install a booster pump to feed the pre filters and then you go to the high pressure pumps. Otherwise you would have to design the filters for high pressure.

 

One caveat is that you need to interlock the second pump in case of loss of the first one to avoid damage, and design for the maximum pressure of the first one (suction rating, seals, etc).

 

Also, control strategy should prevent starving of the second pump, and may require a split range or override for the cases where you don't have enough flow in the low pressure pump to feed the required flow in the second (startup, abnormal situations, etc).  And tuning the controllers to avoid interaction/cycling between controllers.


Edited by Saml, 24 May 2017 - 11:19 AM.


#10 Movers

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Posted 26 May 2017 - 06:38 AM

Thanks for response.

 

Mahdi,

I don't know yet the discharge pressure of pump 1, it will be determined, but I suppose that will be c.a. 5 barg (so a liittle bit higher than discharge pressure of the pump 2).

Pump 2 is used for pressurize stream directed to the tower or surge drum



#11 Mahdi1980

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Posted 27 May 2017 - 01:31 AM

Movers,

 

If you give us a complete information about your case, then you may receive the proper response and a good consultation.

Anyhow, I believe that my comment on the previous post would be applicable.






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