6 replies to this topic

[mohammadhosseinzadeh]

Dear colleague:
1-Due to limited capacity of flare system we have to sequentially depressurize gas trains and also some other units through flare system.
Max capacity of each gas train/other units and flare tip capacity is available.
Could U advise me regarding procedure for this calculation?
2- if there is a vessel with specified V, p1&T1 which contain compressible gas fluid, if it starts depressurizing to p2. Is it possible to calculate outlet flow rate during depressurizing? How?

[joerd]

There is a nice article that contains all info you need and more, "How to predict temperatures during gas depressuring", by G. Montgomery, Hydrocarbon Processing, April 1995, p. 85-88.
It is all pretty straightforward, using gas law, heat transfer equations, mass balance considerations, and valve flow equations. I am sure you could even figure it out by yourself.

[Shahnawaz Makroo]

It is quit possible with fundamental equations:
But you have to give on more variable that is crossetional area (A)of piping to depressurisation.

Loss in pressure energy during depressurusation = Kinetic energy of gas releiving with certain velocity.

Allowable Velocity can be calculated by limiting mach no 0.3 to 0.4.

Q (m3/h) X (p1-p2) =1/2 m v2

substitute value Q = v x A

=> m =2*(p1-p2)*A/v (kg/hr)


Calculatiom of v.

V sonic =(KT/Mw)^.5
V allovable = 0.4*v sonic



Formulae to be checked from any text for unit consistancy


Regards
Shahnawaz

[mbeychok]

Mohammad:

I suggest that you read this article:

http://en.citizendium.org/wiki/Accidental_release_source_terms

It provides the the correct equations for use in the choked flow and the non-choked flow of gases for use in accidental gas releases or in routine depressurization of gas-filled vessels or pipes.

Milt Beychok

[mohammadhosseinzadeh]

thanks all for useful information

joerd:

could you please send me this article:
How to predict temperatures during gas depressuring", by G. Montgomery, Hydrocarbon Processing, April 1995, p. 85-88.
Email:m.hosseinzadeh.78@gmail.com

[joerd]

Sorry, it is copyrighted. You can request it at http://www.hydrocarb.../hp-photos.html
or give it a try at your local university library. Good luck,

[steamreformer]

It is quit possible with fundamental equations:
But you have to give on more variable that is crossetional area (A)of piping to depressurisation.

Loss in pressure energy during depressurusation = Kinetic energy of gas releiving with certain velocity.

Allowable Velocity can be calculated by limiting mach no 0.3 to 0.4.

Q (m3/h) X (p1-p2) =1/2 m v2

substitute value Q = v x A

=> m =2*(p1-p2)*A/v (kg/hr)


Calculatiom of v.

V sonic =(KT/Mw)^.5
V allovable = 0.4*v sonic


Dear mr shahnawaz ,plz explain teh meaing of KT you used in above equation for Vsonic..,r they soem contants ..if yes then plz give there vaules.



Formulae to be checked from any text for unit consistancy


Regards
Shahnawaz