5 replies to this topic

[Xiao]

Dear All

 

I have some problems regarding to the size my pressure relief valve of liquid/supercrical CO2 delivery line.

I am going to pump liquid CO2 to a line at up to 250 barg at room temperature (say 20 to 35C), and I want to put a pressure relief valve after high pressure pump (at this area, CO2 pressure is ~250 barg) to protect the system. So the state of CO2 could be liquid or supercritical depending on room temperature.

 

The discharge of pressure relef valve is atomsphere water tank. So I assume at the discharge port of pressure relief valve, there are going to be two phases: gas CO2 and solid (dry ice). As the formation of dry ice has potential to block the valve. I wonder if anyone has experience on the sizing of this kind of valve or solving this problem. Any other recommendations/cautions for the system design are also very welcome and appreciated.

 

Regards,

[fallah]

Xiao,

 

The heat tracing of the PSV discharge line might remove the possibility of the valve blockage due to ice formation...

[Bobby Strain]

You should route the discharge directly to atmosphere.

 

Bobby

[Art Montemayor]

 

 

At 30 ^oC and 250 barg, CO₂ starts to go into the supercritical phase.

 

I’ve been there many times and can tell you that you will have PSV problems if you have a relief.  Dry Ice snow will form in your PSV and prevent it from re-seating.  The best thing(s) you can do are:

• Don’t allow for a relief to occur in the first place;
• If a relief occurs, shut the system down and isolate it until you get everything back into operating condition without the PSV leaking;
• Install a heating system (as Fallah recommends) – electrical tracing works; steam tracing will not work because the -109 ^oF temperature of Dry Ice will freeze the condensate formed and plug the system.

My practice was to shut down such a system and isolate it.  250 barg is an exceptionally high pressure operation and you should not - in my opinion - plan on continuing the operation during a PSV discharge.  If something has caused a hazardous over-pressure, you should want to immediately shut it down and find out what caused it.

[Xiao]

Xiao,

 

The heat tracing of the PSV discharge line might remove the possibility of the valve blockage due to ice formation...

Thank you for your useful recommendation, fallah.

[Xiao]

 

 

At 30 ^oC and 250 barg, CO₂ starts to go into the supercritical phase.

 

I’ve been there many times and can tell you that you will have PSV problems if you have a relief.  Dry Ice snow will form in your PSV and prevent it from re-seating.  The best thing(s) you can do are:

• Don’t allow for a relief to occur in the first place;
• If a relief occurs, shut the system down and isolate it until you get everything back into operating condition without the PSV leaking;
• Install a heating system (as Fallah recommends) – electrical tracing works; steam tracing will not work because the -109 ^oF temperature of Dry Ice will freeze the condensate formed and plug the system.

My practice was to shut down such a system and isolate it.  250 barg is an exceptionally high pressure operation and you should not - in my opinion - plan on continuing the operation during a PSV discharge.  If something has caused a hazardous over-pressure, you should want to immediately shut it down and find out what caused it.

 

 

Thank you for your excellent experience. If it is the case that we definitely have dry ice solid formation. Can I just treat it as two-phase flow (like gas and solid phase) and size the pressure relief valve based on two-phase situation?