2 replies to this topic

[mykid]

Hi all,

Need a quick advise from all the experts:

 

1) Our existing sonic flare tip is designed for 30 MMSCFD, however it is anticipated that the incoming production flowrate will increase beyond the design rate in one or two years time. What is the consequence if the continuous flaring rate exceeds 30 MMSCFD, ie. 40 MMSCFD? Backpressure for sonic flare tip should remain the same since it's sonic velocity.

 

My interpretation is : higher exit velocity will cause higher noise level and radiation. For the tip design, it will choke at 30 MMSCFD, but  can it relief 40 MMSCFD gas?

 

2) How to determine rated capacity through an oversized PSV?

 

Based on the revised fluid composition, it is calculated that an L orifice is required for blocked discharge on separator. However the existing PSV installed is P orifice, which is 200% overdesigned. To keep the existing PSV, is it really necessary to check the inlet and outlet line loss based on the rated capacity through a P orifice, which is 200% higher than the actual relief flow? This is not practical given that the incoming flow is a lot less than the rated flow.

 

Appreciate for all the time and opinions.

[fallah]

mykid,

 

1) Vendor should deliver flow vs back pressure curve for such flare tip. It might release 40 MMSCFD but at higher pressure (than design value) upstream of the flare tip. Then you should check the capability of the flare header for such higher pressure.

 

2) Having same set pressure and back pressure, the rated capacity of a PSV wouldn't so change. The P orifice PSV with the new conditions you described will chatter due to huge reduction in relief load but appears no need to check inlet/outlet lines losses for new conditions...

[Steady]

In addition to Fallah's reply to your two points; here are my two cents -

 

1) As you say that the sonic flare tip is designed for 30 MSCMD and you are expecting upto 40MSCMD in flare system. First you need to determine your maximum transient peak flow and duration of your peak flow. Then discuss these results with your flare tip vendor.

Exceeding the design flow may result in  -  Higher pressure drop thorugh the tip leading to higher back pressures in the flare system  & Tip may see some damage for a prolonged higher flow.

 

If the maximum flow is 40 MSCMD and it only occurs for a very short duration; this may be okay for the tip. Again discuss with the tip vendor with your expected flow profile in the system.

 

2) Agree with Fallah. 

 Theoretically,  if your existing orifice is P size, then you must determine your inlet & outlet losses for the rated capacity of a P size orifice. Your system may see higher peak flowrate (momentarily) than your actual L orifice rated flow, however this will only result in chattering of the relief valve. In my opinion, no need to check the inlet /oultet line losses for rated P.  

Edited by Steady, 06 May 2014 - 01:58 AM.