3 replies to this topic

[Avalon]

Hi All,
I am currently calculating process safety time for a certain pipeline overpressure. The assumptions are:
1) Downstream valve is suddenly closed. No flow out. Pipeline is of fixed volume 30m3, filled with process gas.
2) Incoming gas is at 30t/h, 3.5MPa.

How long will it take for the line to reach 3.5MPa from 3.1MPa, accounting the fact that mass flow rate decreases as differential pressure decreases.

Thank you.

[breizh]

Hi,

Always good to show your work and explain your difficulties. We are not supposed to do homework.

To me this is a simple problem with an initial condition and a final condition.

a)You need to calculate the quantity of moles @ Pi,Ti  within your pipe. 

Same calculation for Pf,Tf 

 

The difference between (b-a )is the increase of moles in the same volume. then you divide this quantity by the moles flowrate (mols/h) and you get your result.

 

The trick is convert all your quantities in moles or moles /hour . To make it simple use the perfect law gas :PV=nRT .

What you need on top of that is the molecular weight of your gas and the temperature for the initial condition and final condition.

I let you the math.

Breizh

[Avalon]

Hi Breizh,

Thank you for your reply. I have already calculated the process safety time required but it is too short. I assumed a linear pressure Vs time relationship in my previous case. In my new case, I was hoping to account for mass flow rate variance with varying pressure difference between P1 and P2. By using ideal gas law, it will not account for the varying mass flow rate.

[breizh]

Hi Avalon,

To get a better support you should share with us process data (material, Temperature) and provide your calculation!

 Better to quantify "Time too short "

Good luck.

Breizh