10 replies to this topic

[Abdessamed1961]

Hello everyone!

I'm currently working on a project in which i want to reduce the pressure of a gas that has the followng properties ( T= 80 - 120 °C ; P1 = 350 - 260 bar.a; the flow varies between 1 to 10 Millions Sm3/day), i want to reduce it to achieve P2= 240 bar.a (as shown in the scheme attached).

My question is :

1- Can i control the pressure and the flow at the same time for example, i want to transfer 1 Millions Sm3/day and setting the pressure at 240 bar and then switch to another flow 5 Millions Sm3/day and keeping the same set pressure at 240 bar.a.

2- Installing  FCV + PCV close to each other is it feasible, they won't affect each other?

 

Thanks in advance for your help.

Attached Files

•  Scheme control valves.jpg   49.28KB   1 downloads

Edited by Abdessamed1961, 14 December 2025 - 04:30 AM.

[Pilesar]

I do not understand the diagram with the arrow from the PCV pointing to the FCV, but I don't see a problem with the proposed scheme of FCV upstream of PCV. You should have other similar pipeline control systems to use as a go-by. The choice of valves will make a difference. I have usually left the specific valve details to the instrument engineer since they rarely make the choice I would have made yet they keep their jobs so must know what they are doing.

[Abdessamed1961]

I do not understand the diagram with the arrow from the PCV pointing to the FCV, but I don't see a problem with the proposed scheme of FCV upstream of PCV. You should have other similar pipeline control systems to use as a go-by. The choice of valves will make a difference. I have usually left the specific valve details to the instrument engineer since they rarely make the choice I would have made yet they keep their jobs so must know what they are doing.

thanks for your answer, the objective of making those arrows is to set a cascade or override control, i was trying to put the PCV as Inactive as long as the downstream pressure doesn't exceed 240 bar.a. 

[breizh]

Hi,

I'm not sure I understand what you are doing. Where are located the FT and PT?

Generally, you have an internal set point and an external set point, one being a linear combination of the internal set point and the outlet signal. 

As Pilesar said talk to your Instrument engineer. Time delay should be considered.

Good luck

Breizh

[Pilesar]

There is no need for cascade or override control. Set the downstream pressure control setpoint to 240 bar. If the upstream pressure is lower than that, then the PCV will open all the way.

[Abdessamed1961]

Thank you for your answers , i will attach another image for better understanding.

what i'm worry about is the feasability of regualting the flow like i want without having an influence on the pressure which must be kept between 190 and 240 bars maximum

Attached Files

•  fcv pcv.PNG   153.49KB   0 downloads

[breizh]

Hi,

My understanding:

You need to keep the pressure within limits, which is fine according to your schematic (PIC loop) .

Why do you need to adjust the Flow rate (mass flowrate based on your set up), should not be only a FI?

If the pressure is dropping, due to higher demand, the PCV will open to compensate thus the flow rate. I don't think you need a FCV unless you want to keep the flowrate within limits.

 

Breizh

[Abdessamed1961]

Hi,

My understanding:

You need to keep the pressure within limits, which is fine according to your schematic (PIC loop) .

Why do you need to adjust the Flow rate (mass flowrate based on your set up), should not be only a FI?

If the pressure is dropping, due to higher demand, the PCV will open to compensate thus the flow rate. I don't think you need a FCV unless you want to keep the flowrate within limits.

 

Breizh

Hi,

1- according to the instrument engineer, there are some flowmeters that need a correction to get an exact value of flowrate ( like a conversion between Nm3/ Sm3 / m3....) 

2- yes i would have put only a PCV but the thing is we must disptach the gas according to demand ( the flowrate is variable from 1 to 10 miilion Sm3/day) which is why i included a FCV too.
 

[latexman]

Do the users set the flow through their demand? If so, I see no purpose for your FCV. Just provide product at specified pressure range.

[Abdessamed1961]

Do the users set the flow through their demand? If so, I see no purpose for your FCV. Just provide product at specified pressure range.

yes they do set the flow through their demand, so only a PCV will do the job?

[latexman]

 

Do the users set the flow through their demand? If so, I see no purpose for your FCV. Just provide product at specified pressure range.

yes they do set the flow through their demand, so only a PCV will do the job?

 

Yes, only a PCV will do the job.  You may want a total flow indicator (FI) for process information and troubleshooting in the future, as well as FI's at each user to charge them for the product, but you are not controlling the flow, they are.  You are providing a flow range capability for on demand users.