6 replies to this topic

[Dilu]

Hi

 

I am working on flare-net model attached. I have a problem while modeling i have considered 12" flare header dia. but pipe 7 and pipe 20 shows different results i.e. Mach no.  .255 and 1 respectively.

 

As mach no. is dependent on dia it should be same as flow rate in both pipes are same.

 

Length for pipe 7 is 6m while for pipe 20 192m.

 

Kindly tell me whats wrong..

 

 

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[fallah]

Dilu,

 

Nothing is wrong...The density of incompressible flow is decreased along the header from pipe 7 toward pipe 20 and following that the mach number is increased....

[Dilu]

Fallah

 

I get that as pressure decreases with distance density also decreases and thus increasing mach no. But as per standards we have to size header for 0.5 or 0.7 mach no. so in this case it is one. What should I do.

[fallah]

Dilu,

 

If the mass flow rate is fixed try to reduce the length of pipe 7/pipe 20 or enlarge their size...

[Dilu]

Dear Fallah

 

I am checking adequacy of existing header (12 ") , so in my case length is fixed which is 200 m. The worst case scenario is blocked gas flow of 120 MMSCFD at 54 barg set pressure. According to flarenet the results are shown above by considering 12" header having mach no. 1 which seems inadequate.

 

So in my case i cant change length of piping, so I have changed flare header to 18" at that mach no was 0.67, which meets criteria. But i am not sure that 18" header is common for such flows.

 

According to your experience is that size right for such flows at given set pressure.

[fallah]

Dilu,

 

Lack of complete info, but if rho*v2 and mach number are ok, then the 18" header appears to be acceptable for mentioned flow...

Edited by fallah, 22 September 2014 - 01:57 AM.

[Dilu]

yes mach no is below 0.7 and rho*v2 is below 200000.