12 replies to this topic

[raviteja goriparthi]

Hiii all,

 

Please let me help on to find the line size's for PSV . PSV is  conventional type and  sized at

 

The maxium flow capacity is 227.67 kg/hr of natural gas ,

set pressure 6.0kg/cm2 g

operating pressure 2.5 kg/cm2g

Allowable over pressure is 21%

operating temp  57 deg C

releiving  temp 501.78 deg C

max operating pressure is 90% of set pressure 

reveling temp 774.93k

compresaablity factor is 1 and Kb, Kc are 1 resp, and is concated to flare header .

 

My query is in inlet line sizing i can take releving pressure P1 ?and what temp has to take inlet line sizing  condition .And in outlet line sizing calculation what is pressure and temp i have to consider . i gone through Api 520 and Api 521 for outline sizing but i'm able to understand it properly . so plz help to find out the solution.

Thank u . 

 

 

[flarenuf]

ravitija

the inlet line sizing condition will be based on the fluid conditions at relief 501C  and 6.0 x 1.21 = 7.26 kg/cm2g

 

out line will be sized on the pressure  of the gas in the tailpipe , which in turn will depend on the backpressures in the flare header for this scenario

 

flarenuf

[fallah]

^Hi,

^{Inlet line should be sized based on 3% pressure drop limitation due to non recoverable friction loss and PSV rated flow. Because the PSV is connected to flare it is better to size the PSV outlet line including in flare network design by a proper simulation software, let say FLARENET...}

Edited by fallah, 25 July 2013 - 11:02 AM.

[raviteja goriparthi]

THANK U for quick responses.

 I calculated the inlet line sizing by using  7.26 kg/cm2g and 501.68 deg c .

Dear  Fallah, As of now we don't have the FLARENET SOFTWARE  with us can i go with what pressuer and temp i have to take to calculate the outlet line size.

As the PSV vendor provided me  superimpossed backup pressure as 0.5 kg/cm2g and built up back pressure as 0 kg/cm2g and CDTP as 5.8 kg/cm2g.

Can i take the Eq 26 in  section 7.3.1.3.3 API RP 521 for determing the outlet line size. If i'm wrong Please suggest me which pressure and temp i have to take. My PSV  is Full liftCONVENTIONAL  type.

[fallah]

Hi,

 

Suprtimposed back pressure should be specified by the customer. The build up back pressure in your case cannot be 0 kg/cm2 due to connection to flare network. Indeed, it could just be checked and specified after PSV tail pipe sizing.

You can size the PSV tail pipe with isothermal compressible flow equation but it would be accompanied with trial and error due to required checking for build up pressure (10% limitation) and choked flow... 

Edited by fallah, 26 July 2013 - 07:52 AM.

[Balaji Gulgule]

^{Hi Raviteja,}

^{Set pressure in your case is 6 kg/cm2g, relieving pressure would be 6*1.21 = 7.26 kg/cm2g = 8.293 kg/cm2abs , this would be the inlet pressure or starting pressure  for inlet line sizing. The pressure drop allowed for inlet lne sizing is 3% of set pressure = 0.29 kg/cm2a . Based on the relief area required, go to the API 526, Select a orifice area, there you will find the recommended inlet/outlet line sizing along with the orific designation. Start with a recommended inlet line size and check which line size gives you the pressure drop less than 0.29 kg/cm2a. Line sizing should be done for rated flow based on selected area not calculated area.}

^{Outlet Line Sizing:}

^{Start with a outlet line size as recommended in API 526 based on the orifice area required, the mach number for outlet line size should be kept below 0.7.}

^{You need to increase the line size if the mach number is greater than 0.7.}

^{Hope you understood.}  

Edited by Balaji Gulgule, 31 July 2013 - 01:48 PM.

[Bobby Strain]

And, since the fire case relief is 21% overpressure, then the maximum backpressure is 21% of set pressure, too. If you are sizing pipes you should buy proper software from Katmar or Steve Hall.

 

Bobby

[DANA-IF]

^Hi,

^{Inlet line should be sized based on 3% pressure drop limitation due to non recoverable friction loss and PSV rated flow. Because the PSV is connected to flare it is better to size the PSV outlet line including in flare network design by a proper simulation software, let say FLARENET...}

Hi , I was wondering how to find the  line size's for PSV using flare net , as I look into flare net and add a psv , the nominal diameter should be set by user 

Thanks a lot

[fallah]

NADIA BH,

 

If you set the relieving flowrate and maximum allowable mach number you will get the minimum PSV tail pipe size for such conditions...

[DANA-IF]

NADIA BH,

 

If you set the relieving flowrate and maximum allowable mach number you will get the minimum PSV tail pipe size for such conditions...

tail pipe is added after the PSV ?

Do you mean maximumu allowable working pressure ?

[fallah]

NADIA BH,

 

My answers are in red color as follows:

 

 

tail pipe is added after the PSV ?

Yes...

Do you mean maximumu allowable working pressure ?

No, maximum mach number which is around 0.7 for PSV tail pipe...

 

[DANA-IF]

NADIA BH,

 

If you set the relieving flowrate and maximum allowable mach number you will get the minimum PSV tail pipe size for such conditions...

Hi , how to set the maximum allowable mach number because it will be calculated by the software in the summary tab

Could provide more guidance please as I'm new user with flarenet ?

[fallah]

NADIA BH,

 

You can start setting the tail pipe size equal to PSV outlet flange size as an input data and get the mach number as an output data. If the mach number wouldn't be in allowable range, say below 0.7, repeat the simulation by tail pipe size increment till the mach number to be in range.