5 replies to this topic

[abantikag]

Presently i have to find out relief rate for a PSV located in expansion tank in concntrated solar power plant.

 

Expansion tank is used to store thermic fluid.

 

I am attaching one rough sketch showing all inlet and outlet streams on expansion tank.

 

We generally try to maintain 9.65 barg pressure in the expansion tank with nirogen blanketing.If the pressure in vapour space of expansion tank exceeds 9.65 barg pressure vapour will be vented out to primary condenser. 

 

Bottom part of expansion tank is lacated at 10 m height above ground.

 

I do not understand which case will be suitable to find out relief rate for PSV.

 

Please help me.

Attached Files

•  psv_expansion tank.xlsx   14.32KB   38 downloads

[fallah]

abantikag,

 

Considering the elevation of the tank and the sketch and info you provided, appears there is no credible scenario based on which the tank would be subject to over pressure conditions; then putting a small PSV, let say 3/4*D*1 as you mentioned, to meet the code requirement could be adequate...

[abantikag]

Dear Mr. Fallah

 

Thanks for your reply.

 

I just wanted to know whether control valv falure case in nitrogen line or blocked outlet case can be the reasons for overpressure?

 

Please correct me if i am wrong.

[fallah]

abantikag,

 

Because the upstream pressure of control valve in N2 line is lower than the tank design pressure, its wide open condition can't over pressure the tank.

 

Blocked outlet case, if refers to the isolation valve in the pump suction line, causes the pump would be subject to dry running conditions and subsequent severe damage if there would be no safeguard for such situation...

 

How about the pump shut off pressure?

Edited by fallah, 27 December 2014 - 02:57 PM.

[abantikag]

Dear Mr. Fallah

 

Please note  that two of the PSVs located in expansion tanks are set @ 12.07 barg.Can that be designed for valve wide open case in nitrogen line.

 

Further please note that there are four expansion tanks.Manual valves are there at the outlet of each expansion tank as well as at the suction of each pump.Suction valves are equipped with open limit switch which is the start permissive for the pump.So if we close the outlet manual valve of one single tank ,pump will not run dry.

[fallah]

abantikag,

 

Pressure of nitrogen supply source is 11 barg per the info in your sketch and is lower than the PSVs set pressure (12.07 barg). Then such PSVs will not be activated by wide open valves in nitrogen supply line.

 

About the possibility of pump dry running due to inadvertent closing of suction isolation valves, appears there is a protection device via start permissive but the possibility of relevant instrumented loop failure should be analyzed by proper method of risk assessment...