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Control Valve To Flare


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#1 Amar_hb

Amar_hb

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Posted 08 March 2021 - 01:43 PM

Hello everyone,

I would like to know why some units have pressure control TO FLARE instead of main line (gas outlet).
As far as I know, it is bad practice to vent production to flare every time there is high pressure.
If we put PV at main line (gas outlet) does that effect production ? (per exp. the valve would act as a brake of production / accumulation might occur ?)

Attached is a figure for clear understanding.

Thank you.

Attached Files


Edited by Amar_hb, 08 March 2021 - 01:45 PM.


#2 fallah

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Posted 10 March 2021 - 12:59 AM

Hello everyone,

I would like to know why some units have pressure control TO FLARE instead of main line (gas outlet).
As far as I know, it is bad practice to vent production to flare every time there is high pressure.
If we put PV at main line (gas outlet) does that effect production ? (per exp. the valve would act as a brake of production / accumulation might occur ?)

Attached is a figure for clear understanding.

Thank you.

 

Hi,

 

Referring to the attached, in the cases you mentioned there are normally two PVs one along the main overhead line (live line) and another one with the set pressure a little bit higher along the line (NNF) to flare; hence the PV in NNF line just will be opened when there is a partial or fully blockage at downstream of the PV at the main line.

Attached Files



#3 Amar_hb

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Posted 11 March 2021 - 04:45 AM

Hi Fallah, 

In the case I have mentioned, there's only one PV and it is (like you mentioned) flaring the gas in case of High alarm. 
My question is why not put the control valve on the main line (live line) instead of flaring the surplus of gas; as you can see it is disadvantegeous to lose production repeatedly (even small qualities). 
What is the disadvantages of puting a PV on live line ? 

Thank you.



#4 Pilesar

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Posted 11 March 2021 - 05:41 AM

Your diagram snippit shows you have two pressure controllers. There is a bubbled 'PC' just to the right of the valve to flare. Does the dashed line from that PC lead to another pressure control valve? Is the primary pressure controller modulating a valve to the 'main line'? The pressure control valve to flare should only open when the primary pressure control loop is not adequate. You can choose where to send the gas, but you will need a safe place to vent the vessel for system maintenance anyway. Is there a pressure safety valve also routed to flare nearby? So why not route a secondary pressure control valve into the same flare header? If you are 'losing production repeatedly' to the flare, your system is inefficient. The problem is not with the location of the secondary pressure control valve, but with other parts of the pressure control system.






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