10 replies to this topic

[sniperel]

Dear friends,

I have to inlet stream (liquids) that have different pressures: one with 2 barg and a low flowrate (3 m^3/h) and the other with higher pressure (4 barg) and a higher flowrate (50 m^3/h).

What will be the best approach to combine these two streams? My approach will be to place a pressure control valve on the stream with high flowrate and pressure to reduce the pressure to 2 barg.

If the pressure of the two streams will vary ( in all cases the pressure with low flowrate will be less then the pressure of the higher flowrate) can I control the pressure valve with a pressure differential controller?

Thank you very much for your support.

[Padmakar Katre]

Hi,
Before commenting on this topic, need some more information such as
1. What are these liquids, specially high pressure stream (concern is flashing after expansion and compatibility of these two liquids)
2. What is the destination pressure requirement after mixing these two streams.
3. Addition to the pressure and flow rates for these two steams can you state the temperatures for both streams (heat of mixing if any)

Waiting for your reply.

Edited by Padmakar S Katre, 20 July 2012 - 12:10 AM.

[Steve Hall]

Sniperel,
A flowsheet would help. You need to describe the two streams from their source to the destination of the mixed stream, preferably from reservoir (e.g., tank) to reservoir. Include any pumps or valves, plus material and energy information. Typically, installing a control valve ("to reduce pressure") will also reduce the flow. So, typically, you'd need to raise the pressure of the small stream with a pump or by pressurizing its source reservoir.
Steve

[sniperel]

Dear all,

Thank you for your answers. I attached a flowsheet with my proposal. I don't have informations about the feed sources, but their destination will be a coalescer separator in order to separate water from the oil. Do you agree with my proposal?

All the best,

[sniperel]

I forgot to add the flowsheet. Please find it at http://www.scribd.com/doc/100897534

[Steve Hall]

Can't you attach your flowsheet to this thread? I seem to only see a portion of it at scribd, and I don't want to create an account or log in there to get the whole thing.

[sniperel]

Dear Steve,

I uploaded here a basic flowsheet with the two streams.

Thank you very much for your support.

[sniperel]

The flowsheet:

Attached Files

•  streams.jpg   38.2KB   26 downloads

[Steve Hall]

Sniperel,
We can't see what is generating your two flows so it isn't possible to give a complete answer to your question. If the 4 barg stream originates at a centrifugal pump then placing any kind of pressure control valve will reduce the flow which seems contrary to your goal. I'll just provide some random feedback; if you can give a more complete flow diagram you'll get a more satisfactory response:

• Unless there is a check valve in the 2 barg line, the pressure in the two streams must always be nearly the same (the only difference would be pressure drop between the junction and wherever the pressure is measured due to friction plus elevation difference). A differential pressure control instrument will NEVER solve your problem.
  
• We can't tell from your diagram why the pressure would be 4 barg (or 2 barg or whatever). Doesn't the oil separator work with an interface control and atmospheric-pressure overflow? Or is it a completely full vessel with no head space operating under pressure as you are suggesting?
  
• If your fluid flow calculations show that the pressure of the 50 m3/h stream is 4 barg at the junction point, then the only way to introduce the low flow stream is to generate sufficient pressure for it to merge in. There are two basic ways to accomplish this: a) with a pump, or an eductor (which effectively lowers the pressure in the primary stream). I don't know if an eductor can perform this much work, but it's something to explore.
  
• Is there any concern with forming an emulsion if too much shear is imparted to the streams? Just something to consider when choosing technologies such as contol valves and pumps.
  
• LPS should enter the top of the exchanger; LPC leaves from the bottom.

Steve

Edited by Steve Hall, 25 July 2012 - 06:12 AM.

[sniperel]

Dear Steve,

Thank you very much for your help. Unffortunately I don't have any informations about the feed sources, the client specified only the pressure of the inlet streams. What would be the best approach to solve this problem since the differential pressure control is not going to work?

The oil-water separator will work under pressure with no head space and coalescer medium. For the emulsion, we consider using a demulsifier.

All the best,

Edited by Art Montemayor, 27 July 2012 - 09:28 AM.

[Steve Hall]

You'll have to ask your client for more information.