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I have a existing system where there is a control valve at the inlet of gas scrubber and RV is provided on the scrubber. To determine whether the RV can stand if control valve failure - fail open, I check the control valve fail-open case (100% open), the flow is huge and the RV is size is inadequate. The thing that confuse me is the actual gas production now is less than the maximum flow thru case, please advise which flowrate should i use to make a conclusion of this RV because if based on actual gas prodcution, the RV is adequate.
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Sizing Case
Started by Guest_Rangga_*, Apr 07 2003 12:08 AM
3 replies to this topic
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#2
pleckner
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Posted 07 April 2003 - 07:08 PM
Sorry but you must take into account the flow through the control valve. The problem is not what happens a few seconds after the control valve fails opened but the instantaneous flow you get. This can be enough to over pressure the system and cause a catastrophic failure.
Also, one misconception people have is that a relief valve calculation is really a volumetric calculation and not a mass calculation. Therefore, even a small amout (by mass) of gas can expand with enough force to rupture a vessel.
But let's look at some things that hopefully will help.
1. Did you make sure that the flow you are calculating through the control valve is based on the maximum upstream operating pressure minus the relieving pressure (set pressure + 10% over pressure)?
2. It sounds like the control valve is way oversized. You may want to investigate this and make this valve smaller.
Also, one misconception people have is that a relief valve calculation is really a volumetric calculation and not a mass calculation. Therefore, even a small amout (by mass) of gas can expand with enough force to rupture a vessel.
But let's look at some things that hopefully will help.
1. Did you make sure that the flow you are calculating through the control valve is based on the maximum upstream operating pressure minus the relieving pressure (set pressure + 10% over pressure)?
2. It sounds like the control valve is way oversized. You may want to investigate this and make this valve smaller.
#3
Guest_Rangga_*
Guest_Rangga_*
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- guestGuests
Posted 08 April 2003 - 08:35 PM
Mr.Pleckner,
Can you elobrate further about the RV calculation as you said, is it the misconception about the RV sizing is a mass calculation or volumetric calc.
Can you elobrate further about the RV calculation as you said, is it the misconception about the RV sizing is a mass calculation or volumetric calc.
#4
pleckner
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- ChE Plus Subscriber
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- 564 posts
Gold Member
Posted 10 April 2003 - 06:10 PM
What I am getting at is that a gas will expand to fit the volume so the initial release has nothing to do with the actual amount of gas generation.
The relief valve calculations that can be found in API RP520 and numerous vendor cataloges and books repersent both mass and volumetric flow. Any equation can be used as they are all the same. However, the derivation of the base equation is based on volumetric flow not mass flow. A relief valve is actually an isentropic nozzle, not an adiabatic orifice.
The relief valve calculations that can be found in API RP520 and numerous vendor cataloges and books repersent both mass and volumetric flow. Any equation can be used as they are all the same. However, the derivation of the base equation is based on volumetric flow not mass flow. A relief valve is actually an isentropic nozzle, not an adiabatic orifice.
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