10 replies to this topic

[kinetic123]

Please find the attached sketch for the relief valve [RV01] & bursting disc [BD01] on a reactor discharging to a dump tank. (nozzles N1 & N2)

 

All the elbows are long radius [R/D = 1.5] elbows. Please find other info on the attached file.

 

1. RV01 inlet pressure drop is 0.17bar which exceeds [significantly high!] 3%  of set pressure [0.06bar] at the rated capacity [8000kg/hr]. What could be done?
2. What maximum inlet and outlet pressure drop should I allow for bursting disc?

 

 

PS: RV01 outlet pressure drop is OK [within 10% limit]

 

Thanks

Attached Files

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Edited by kinetic123, 07 May 2014 - 10:40 AM.

[fallah]

Hi,

 

1- Generally, you can use pilot operated PSV with sensing line directly from top of the reactor or increase the size of the inlet line.

 

2- Maximum allowable pressure drop of Inlet/outlet lines of the bursting disc would be based on not to cause the relieving load to be less than required value.

[Bobby Strain]

I wouldn't worry about the RV inlet loss. The rupture disk is the real overpressure protection device.

 

Bobby

[kinetic123]

Fallah,

 

Thanks for your input.

I understand that pilot operated relief valve [PORV] is less prone to chattering but if we don't wish to have PORV and if we increase the line size, [say 6"], I understand that relief valve discharge line has to be increased [say 8"] by keeping the 3L4 relief valve as it is? Is this correct?

But in this case 3L4 looks smaller compared to line sizes? is this normal?

Thanks

 

Bobby,

 

Agree what you said, but I would hesitate to put down on the documents saying, inlet pressure drop is significantly higher than 3% and bursting disc is the ultimate protection device. What else you suggest?

Thanks.

[Bobby Strain]

If you size the rupture disk to prevent vessel overpressure without the PSV, then the size and character of the PSV are irrelevant as far as the pressure vessel code is concerned. It's unlikely that even a chattering valve will be a problem since the pressure differential is so low. Don't throw good money after bad.

 

Bobby

[fallah]

 

I understand that pilot operated relief valve [PORV] is less prone to chattering but if we don't wish to have PORV and if we increase the line size, [say 6"], I understand that relief valve discharge line has to be increased [say 8"] by keeping the 3L4 relief valve as it is? Is this correct?

But in this case 3L4 looks smaller compared to line sizes? is this normal?

 

 

Hi,

 

The criteria for PSV discharge lines sizing is irrelevant to that of the inlet line sizing. The pressure loss in discharge line shouldn't be exceeded the allowable overpressure (for single PSV 10% of the set pressure). You may check this matter for your case.

 

Indeed in most cases the PSV size is smaller compared to relevant line size, then it would be considered as normal situation  ....

[kinetic123]

Fallah,

 

Thanks for your reply.

 I have two release cases as listed below

 

1. Case#1: Release rate: 6000kg/hr, molar mass 150, vapour density at relieving conditions 15kg/m3, required vent area 1200mm2.

The rated capacity for this fluid is 8000kg/hr

1. Case#2: Release rate: 3000kg/hr, molar mass 20, vapour density at relieving conditions 2kg/m3, required vent area 1500mm2

            The rated capacity for this fluid is 3000kg/hr

 

Query:

 

In terms of required vent area, Case#2 is the worst case. However, to check the PRV inlet and outlet pressure drop, I believe, I need to check for both cases using their respective rated capacity.  Is my understanding correct?

 

 

Bobby,

 

Thanks for your input. Agree with you

Edited by kinetic123, 08 May 2014 - 04:26 AM.

[fallah]

Hi,

 

A PSV has a unique rated capacity based on which the relevant inlet/outlet lines should be sized within allowable pressure drop.

Edited by fallah, 08 May 2014 - 10:59 AM.

[kinetic123]

Hi Fallah,

 

Sorry, I did not quite get that. 

 

Different vapour/gas has different molecular weight and hence different gas density at a given relieving conditions and hence the different relieving capacity [not unique?] for different fluid. Am I missing something here? 

 

Thanks

[fallah]

 

Different vapour/gas has different molecular weight and hence different gas density at a given relieving conditions and hence the different relieving capacity [not unique?] for different fluid. Am I missing something here? 

 

 

Hi,

 

Yes, but a PSV will be tested with a known test medium (steam, water, air,...) at specified conditions, then its rated capacity measured and reported as name plate capacity but for relevant test medium. This capacity is unique one and could be converted to the capacity for any fluid with any properties.

 

When vendor gets your PSV data sheet would size it for governing case not for all other cases. Then would report the name plate capacity per test conditions for used test medium. Obviously using various fluids with different properties might lead to different rated capacities but when would be converted to test conditions will be terminated to almost same capacities...
 

[kinetic123]

Thanks for your help/advice Fallah..