1 reply to this topic

[Freester999]

Hi all,
I am a summer intern trainee at an Oil and Gas company.
The situation is a pressure relief valve on a wet gas pig launcher.Assuming an unwanted situation of fire and blowdown occurs.The gas is entering at 120barg and 19 Deg C and mass flow 9430kg/h through a 0.11in2 orifice.I have calulated the Joule thompson cooling through PRV to be -60Deg C at 1 atm (using HYSYS).This gas is routed to a tie in to a flare KO drum .But the pipeline to KO drum is designed for -40Deg C only.So I need to calculate what length of pipe is required to warm up the gas to a temp around -40Deg C.
Other physical ppts of gas at inlet condition are
mass heat capcity 3.775 kJ/kg C
mass density 175.7 kg/m3
Thermal cond 0.053 w/mK
viscosity 0.02014 cp

also the ambient temp is 5Deg C and no wind .assuming no heat transfer by radiation.
Assuming length of pipe =1m and bulk temp is Tb=55Deg C
I tried to calculate the heat transfer coeff using formula h=k/D*Nu
where Nu=0.023*(Nre^0.8)*(Pr^0.3)

and calculated q=h A (To-Ti) where To =(-50Deg C outlet temp assumed) and Ti inlet (-60 deg C)

using this Q value,I calculated the To using mass balance,
Q=mCp(To-Ti)-
To? but the calculate To value would give a value close to Ti(60Deg C)
so my assumption is wrong.
If it were correct,I would do more iterations and plot Temperature Vs Length and the legth corresponding to -40Deg C would be my pipe length.

But I feel I'm missing something and my answers and predictions are not correct.
Please help

freester

[JoeWong]

freester,

Suggest you an article.

S. Kumar, "Material Selection for low temperature application", Hydrocarbon Processing, July 2004.

Good luck.