4 replies to this topic

[vanlt]

Dear all members,

 

I need your advice.

 

Now I am calcuating the tail piping size and sub-header size by flare net (attached herewith). However, when process run finishes, back pressure of PSV-0105 (98.4 kPag) is smaller than superimposed back pressure (123 kPaG at flare tip). As my understanding that the back pressure of PSV-0105 should be calculated based on built up back pressure (pressure drop of piping) and superimposed back pressure (123 kPaG at flare tip). Is something wrong in this case? Therefore, could you please advise me why the back pressure of PSV-0105 is lower than superimposed back pressure.

 

I am looking forward to hearing your feedback. Thank you so much. 

Edited by vanlt, 16 July 2014 - 09:58 PM.

[flarenuf]

Hello Vanit

please advise me why the back pressure of PSV-0105 is lower than superimposed back pressure

 

it obviously should not be !! check your model  by looking at the pressures back from the tip to your source , are they all lower than 123kg ?

or is there some point at which it drops ?  has the model actually converged properly ?

without looking at the model its hard to say

do a bit of detective work first before coming back

brian

[vanlt]

Hello Flarenuf

the pressures back from the tip to your source , are they all lower than 123kg ?

 

Sorry, I forgot to attach sketch. As you can see in the attachment, pressure back from tip to sub-header is still greater than 123 kPaG. However, from the tee of sub-header to PSV-0105, the pressure back is lower than 123 kPaG.

I also though that the system didn't coverge. But, the solution is not found.

 

Attached Files

•  PFD_Flare model..pdf   454KB   57 downloads

[flarenuf]

comments

1) your flows must be v small to get these sort of Dp's

2) i guess you are looking at static pressures here so what you are seeing is pressure recovery

    small diam  pipe 17   with high velocity + low P into large diam  pipe  130 with low velocity and higher static P
3) if you have any 2 phase flow here then you should be running PR thermo and B&Brill homogeneous options

 

many explanation on this board( from me et al)  for pressure recovery and static vs total pressure  DYOR
 

flarenuf

[vanlt]

Dear Flarenuf,

 

Thank you for your comments.

 

For 2nd comment, it is correct that i am looking at static pressure. However, I didn't understand your meaning. Can you explain more clearly? I wonder what is the reason behind the pressure drop from main header (pipe166) to sub-header (pipe133). In case the reason is un-convergence of software, will increasing of pipe size be a solution?