Overcooling problem during depressuring
Overcooling problem during depressuring
(OP)
Hi,
I'm performing a blowdown calculation in adiabatic conditions for a gas header (mainly methane).
Initial conditions are P=460 bara and T=60°C. The header has to be fully depressurized.
The problem is that overcooling over -10 °C has to be avoided during depressuring (pipeline design temperature).
The flare header backpressure is nearly atmospheric.
Is there a way to perform the blowdown (using several time intervals or whatever) in a way to avoid overcooling?
Thanks for the patience,
best regards,
Francesco
I'm performing a blowdown calculation in adiabatic conditions for a gas header (mainly methane).
Initial conditions are P=460 bara and T=60°C. The header has to be fully depressurized.
The problem is that overcooling over -10 °C has to be avoided during depressuring (pipeline design temperature).
The flare header backpressure is nearly atmospheric.
Is there a way to perform the blowdown (using several time intervals or whatever) in a way to avoid overcooling?
Thanks for the patience,
best regards,
Francesco





RE: Overcooling problem during depressuring
If you're really adiabatic, there's no way that you can heat up the header. Please check my conversion - 460 bara = 6671 psia? Where does such a high pressure come from?
Larry
RE: Overcooling problem during depressuring
Anyone with Ch4 at that high of a pressure must have access to a dynamic simulator like Aspen, right?
Good luck,
Latexman
RE: Overcooling problem during depressuring
of course I'm using a dynamic simulator (OLGA 2000 and Hysys, actually).
Right now my problem is performing a correct simulation of the fluid entering the flare header, where very low temperature can be reached.
The main problem with OLGA seems to come from the PVT table values (P & T range is huge).
Anyone with a good hint?
Tnanks again,
Regards,
FR
RE: Overcooling problem during depressuring
IOWs, the equations of state (EoS) used by OLGA are not predicting PVT accuratly according to a reliable reference table, right? If not, please rephrase, I'm not familiar with these two software.
Good luck,
Latexman
RE: Overcooling problem during depressuring
Larry
RE: Overcooling problem during depressuring
Not sure if the applicable code in your area allows this, but I would check into it before designing a complicated blowdown logic system to limit the rate of depressurization.
RE: Overcooling problem during depressuring
I answer some questions: to use OLGA 2000 without the compositional model you need to supply a property table. I do it via PVTSim.
In the case I'm facing the P&T range, as I said, is really large, so you could get results that are not so accurate.
By the way, Latexman, Hysys 3.1 is from AspenTech. I used its depressuring utility to model what happens to the fluid before the blow down valve while I intended to use OLGA to model the whole scenario.
Kind regards,
Francesco
RE: Overcooling problem during depressuring
I'd call the dP you are looking at gigantic! Seriously, I recommend looking for some real PVT and H data on CH4. A header good for those pressures, must have been expensive, and I wouldn't risk it undergoing brittle fractures as it depressurizes to an EoS without testing it. Either that, or I'd rig up several temperature measurements to stay safe during the depressurization.
Good luck,
Latexman
RE: Overcooling problem during depressuring
I stumbled across a good reference for you. Check this out: http://chumba.che.ncsu.edu/publications/predictions%20o...
Good luck,
Latexman