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Hydrate Formation During Depressurizing

depressurizing hydrate

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#1 Ghasem.Bashiri


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Posted 11 August 2021 - 10:27 AM

Hydrate formation during depressurizing calculation should be tracked based on good engineering practice such as shell DEP. However, during depressurizing calculation we exposed to high velocity of process fluid in flare netowork with minimum dead points. Therefore, it is not clear for me possibility of hydrate formation. Thermodynamically simulation software predicts hydrate formation (hydrate dissociation point). 

However, quantity of water may not enough to have stable hydrate phase to for blockage of flare header. within a forum here with following subject, I found this text: 


Effect Of Depressuring Time On Hydrate Formation Probability At Flare


In general, the answer on your question is: Yes, because hydrate formation is a kinetic-driven process as well. That is why you'll see in some installations (particularly wellheads) - where hydrate formation cannot be avoided - a provision for MEG and Kinetic Hydrate Inhibitor injection. In other words, since we are already within the hydrate formation region (thermodynamically speaking: pressure and temperature), the only thing we can do to suppress hydrates is to affect the process kinetics.

For evaluating blowdowns, you can try to do the following (I did it on few occasions and it works good): obtain the pressure and temperature profile downstream of BDV/orifice during depressurization, and check if these values are within the hydrate formation envelope. You'll see that, probably at the beginning of depressurization and a certain time period after initiating blowdown, you'll be within the hydrate formation conditions (that will depend on P, T, and gas composition). If you see that the period of high likelihood of hydrate formation is more than just a few seconds, go for hydrate inhibitor injection. It doesn't need to mean that you'll get hydrates if there is no inhibitor injection (again, the kinetics plays an important role) but it's better to have a backup solution instead of facing the possibility to have plugged blowdown line in cases when you need it the most.




Above statement is clear for me but I dont know is it possible to rely on such recommendation for ...."few second". Please advice if there is some more qualitative rule for such checking. 




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