7 replies to this topic

[Sara Owens]

what is the point of having a pressure control valve to flare? i already have a relief valve. doesn't the pressure control valve to flare operate the same?

[Pilesar]

Never use safety devices for process control.

[breizh]

hi,

Pilesar is absolutely right , don't mix the 2 applications  process control and safety . One cannot substitute the other .

Probably good to review or perform the hazop .

good luck .

Breizh

[flarenuf]

hi

i dont think the previous two replies  really answer your question here sara.

A pressure control valve is used on a piece of equipment to regulate the pressure in the vessel , say, during startup or shutdown or normal operation. For example starting up a process the gas from a dehydration unit  can be vented totally or partially to  flare via the PCV until the dehydrator has reached full operating status and is producing dry gas. the gas will then be fed to the next downstream equipment and the PCV will close. PCV's can be controlled by instrumentation or operator intervention as part of the normal running of the plant.

A PSV on the other hand cannot be controlled and is there as a last line of protection should the PCV fail, or an operator inadvertently close it when venting. The pressure in the vessel will rise until the PSV set point is reached and then it will open and vent the gas to flare, preventing any further pressure rise and potential vessel failure.

as Breizh says though a PCV is not part of the Safety protection system of a plant. It is however part of the Flare and Relief system and will be considered when designing the Flare headers and tip.

flarenuf

[Ahmed M]

A pressure relief valve and pressure control valve are used for different applications. While a pressure control valve is meant to limit pressure not to exceed a certain value in order not to upset the process, a relief valve is meant to protect a mechanical structure from being exposed to pressures higher than the design pressure. A relief valve basically protects a vessel from failure.

[hameed14]

Hi,

can i ask related question to this topic.

What will be the size of the line this pcv is in? will it sized for full flow as the main process line or there is a rule or something since it is only to reduce the raised pressure?

for example: if main process line effluent from th vessel is 500 kg/hr, what pipe size and flow should be designed for the flare diversion line to the flare?

let say vessel operating pressure is 1 barg and flare operating pressure is 0.1 barg.   

[fallah]

Hi,

can i ask related question to this topic.

What will be the size of the line this pcv is in? will it sized for full flow as the main process line or there is a rule or something since it is only to reduce the raised pressure?

for example: if main process line effluent from th vessel is 500 kg/hr, what pipe size and flow should be designed for the flare diversion line to the flare?

let say vessel operating pressure is 1 barg and flare operating pressure is 0.1 barg.   

 

Hi,

 

The outlet line size of a PV along a gas line to flare is normally bigger than the inlet line size due to gas expansion downstream of that PV and will be sized based on the relevant project's sizing criteria considering the parameters such as gas velocity and density, rho*V2,...

[latexman]

Hi,

can i ask related question to this topic.

 

Hi hameed14.  It is preferred that one starts a new topic, but it is not against the Posting Guidelines.  Posting a new topic should make it easier to find (Search) later, since you will be the author of the original post (OP), can give it a title more relevant to your situation, and post it in a more appropriate Forum.  Enjoy your time here!  It's a great community!