5 replies to this topic

[Ghasem.Bashiri]

Dear Process Experts
What is source of recommendation for use of Shutdown valve (on/off) in liquid outlet of hydrocarbon vessel to pump or downstream equipment.
I think it is required based on vessel pressure, liquid content.
Within our P&ID, SDV noted to be minimum from vessel outlet.
GB.

[fallah]

Ghasem,

IMO,the main function of mentioned SDVs is isolation of predefined loop to be depressurized in a fire case.

Fallah

[JaluceroL]

I agrre with fallah. Other reason could be to isolating vessel if there is a great liquid hold up, preventing a pool fire donwstream.

[paulhorth]

Ghasem,

Another reason for the ESDV on the liquid outlet is to protect the downstream vessel from overfilling. The valve would close on High High level on the downstream vessel, which would also stop the pump. You can check these actions on the Cause & Effect diagrams.
If the valve is located on the pump discharge, downstream of the pump recycle, then the pump can continue to run when the valve is closed. This location is best for isolation of the vessel for blowdown as Fallah mentions. If the valve is on the pump suction, then the pump recycle line back to the vessel will not be isolated.

Paul

[Zauberberg]

It could be anything, but you have failed to provide any input data.

In case of amine absorber, loss of liquid level would normally cause the liquid outlet SDV to close and prevent blowing of high-pressure gas into a lower-pressure system.

In case of a feed surge drum, the liquid outlet SDV would close at low-low level in order to protect e.g. multistage centrifugal pump from running dry.

In case of equipment rupture downstream of the corresponding vessel, the SDV on liquid outlet line will go into closed position in order to prevent uncontrolled leak and possible explosion.

Purpose of each and every SDV is - to protect plant personnel and process equipment, and also to limit the inventory (volume) that has to be isolated and depressurized or blown down. If you look at your particular vessel/system, I'm sure you can get a full picture of what the SDV was provided for. Or, as suggested by Paul, have a look at the C&E charts. All the answers should be there.

[JaluceroL]

It could be anything, but you have failed to provide any input data.

Rigth. Also in a ISOMAX unit, first stage separator vessel cannot lose level, then there is a ESDV.