Depressurizing a Natural Gas Vessel

A specially designed automation process can take care of the problem. However much research and safety issues will be required.

just open a valve and it will flow out No need for controls, no need for instruments. The valve should be a globe valve, but a plug valve will work. The temperature will drop about 50 degrees C, so you will see ice form on the line.

I would contact the Fire Department !

Accidents happen !

In your problem you don't state the volumes involved, so it would be impossible to discuss timing issues.

Things to watch out for:

- From 100 bar to 0 bars means youl have 100:1 expansion of the gas before reaching the flare tip. Most of this pressure drop is achieved by shock waves in constrictions in the piping or at sudden openings. Up to 6 shocks waves will develop with 100 bar starting pressure. Most or all will develop at the flare exit, but some can develop within the piping system where you don't expect them.

- you may develop a shock wave at the inlet to the flare knock-out drum or travelling shockwaves up and down the piping. Across the shock wave there is a tremendous volume expansion. If your flare system is not designed for the volume flow that now develops after a shock (i.e. it is undersized for this scenario), too high velocity will develop in the flare knock out drum. A slug of liquid will suddenly fly out of the flare. Since this liquid is water saturated with CH4 to C3H8 hydrocarbons, it can create large flaming globules flying down. It can also extinguish the flare, which opens up more problems.

- Uncontrolled travelling shocks in the piping can cause "waterhammer" like effects, that the ststem may or may not be able to withstand.

In short, a thorough review (hazard and pperability study - HAZOP) should be undertaken of the vessel, piping and flare systems to determine it will handle the flow rates developed during an uncontrolled depressurization. My experience has been that orifices sometimes have to installed at the vessel outlet to ensure the flare system is not ovewhelmed; or the flare system needs to be upgraded.

Cheers,

Steamer Stan