pipeline and pump design 1

[processengineer1998]

Hi everyone,
We need to design supply and return pipelines from one plant to another plants in order to use existing package in second plant.package will be used occasionally by Only one of two plants.
Because source of liquid is storage tank in first plant ,there is not any concern in designing supply pipeline including pumps and control valve for flow control.
My problem is in return pipeline from outlet of package in second plant to first plant.inside the package and just before sending liquid out of package, there are a vessel ,a pump and a level control valve down stream of pump.but existing package pump could not cover pressure drop in return pipeline.so we need to pump with highter duty.
we have some choices:
1-upgrading existing pump with new pump with higher head(client is not happy with this option and prefer not to change package pump)
2-adding a new pump just after exsisting pump and its level control valve
3-adding a new pump with higher head and its new control valve in parallel of existing pump and control valve.
Now my question is that is choice 2 a logical configuration? can we add a pump after a level control valve?if yes is then required a new control valve after new pump?
Please let me know which choice is preferrable in your point of view.
It should be noted that system is continous.
Thanks in advance

 

[EmmanuelTop]

There should be no control valves between two pumps. You will starve the 2nd pump out of flow and cause significant damage.
Option 1 could be the best, if it is feasible. Option 3 makes no sense - what would be the purpose of the existing pump in this case??

If you want to have a flow-controlled system, you need a surge (feed) vessel upstream of the 1st pump to manage incoming flow variations from the "package".
If you want to maintain a level-controlled system, the LCV needs to be relocated downstream of the 2nd pump.
Mechanical variable speed drive may be the most attractive option depending on how wide are the variations of flow, and whether the system is friction-dominated or elevation-dominated.



Dejan IVANOVIC
Process Engineer, MSChE

 

[processengineer1998]

Dear Dejan
Thanks for your responce,about option 3 it should be explained that as exiting pump and level control valve was already designed and installed for second plants ,if client prefer to do not touch it, actually we should consider new pump and control valve for case when first plant need to use the package.At each time only one plant can use the package.
For option one ,i think we need to change existing pump with new one and in adition we should check that existing level control valve can handle new pressure drop impose by new pipeline between two plants (in different flowrate) as it is big compared to exiting piping system in second plant.

 

[LittleInch]

Option 2 would only work if you made the second pump with a VFD and sensed inlet pressure into the second pump and reduced speed if the flow decreases. The devil is in the details of the system curve and pump curves.

Is there an issue in moving the existing control valve downstream of the new second pump?

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

 

[MJCronin]

I believe that you should consider a small storage tank and an additional set of pumps at process facility #2.

This will make the entire system easier to startup, control and troubleshoot....

Yes, I understand that your MBA master has said that there is no money in the budget for this ...

MJCronin
Sr. Process Engineer

 

[EmmanuelTop]

Posting a sketch with distances, flowrates, pressures etc. would help understand what you need to achieve.

- What are the distances between all facilities involved?
- What are the flowrates and pressures that pump(s) need to deliver?
- What are the characteristics of the pump you already got in the design?
- Modes of operation
- Pipeline diameters etc.

Obviously there is a lot of variables in the play - the solution will depend on the answers above.

Dejan IVANOVIC
Process Engineer, MSChE

 

[processengineer1998]

Dear Dejan
Please find simple sketch as attachment.
Pipeline design is based on maximum flowrate of 40 m3/hr and 40 percent turndown.
Thanks for you help

 

[EmmanuelTop]

The pressures are not so high as they appeared first based on your earlier descriptions. The first pump develops 3 barg at discharge - what is the purpose of this pump in the original design?

If you intend only to pump the product from Plant #2 to Plant #1, then adding another pump in series sounds like the best option to me.

If you intend to pump the product to both locations (to Plant #1 via the pipeline, and within Plant #2 - which you mentioned in your earlier posts but not actually shown anywhere on the sketch), and which never occurs simultaneously, the solution could be as mentioned above - for intermittent operation you might be better off with two separate pumps. One for pumping the product to Plant #1, and the existing one for the original design intent.




Dejan IVANOVIC
Process Engineer, MSChE

 

[LittleInch]

At that level of change, I can't see why your current control valve can't handle both pumps in series. Might not be optimized for it, but flow should be OK.

If you want the option to just pump within plant 2 then just valve the second pump so that you can isolate it and bypass it if all you need is the original pump.

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