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Flame Arrestor For A Pressure Vessel


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#1 chemks2012

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Posted 21 March 2014 - 05:33 AM

Dear all,

 

I want to specify a flame arrestor on the vessel and need your help. See the details of the vessel below.

The main function of this vessel is to pull the vacuum from a reactor before, process starts.

During normal operation, this vessel collects water of about  900kg per batch however, occasionally, it pulls traces of solvent from reactor and hence a need for flame arrestor.

This vessel has 2” vent line and I want to specify an end of line flame arrester on this line.

Please note that we have a relief valve on a separate vent line of size 2” X 3”, set pressure 4barg.

As this is a pressure vessel and not an atmospheric tank, I am not sure, if can use normal inbreathing/outbreathing calcs for gas flowrate.

 

 

Size of vessel:  2m3

Location of vessel: within process building

Design vacuum : full vac

Design pressure: 7barg

Design temperature: 170deg

No insulation applied

Relief valve on a separate independent vent line is designed for a fire case

 

Thanks in advance for your help.

KS


Edited by chemks2012, 21 March 2014 - 05:36 AM.


#2 fallah

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Posted 21 March 2014 - 08:15 AM

Hi,

 

Lack of a detail sketch...

 

Anyway, it seems the flame arrestor is intended to be installed at the end of a free vent on the pressure vessel. This pressure vessel appears to be designed for periodic pressurization due to upstream batch operation. If so, due to existing the relief valve, if this RV is to be designed such that can relieve the load in the case of flame arrestor blockage and is set at vessel design pressure, appears there would be no problem if flame arrestor to be installed there...Final evaluation would depend on adequate info and a detail sketch...



#3 chemks2012

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Posted 21 March 2014 - 09:12 AM

Thanks Fallah,

 

Yes, agree that the vessel in question would not have any issues with regards to vessel protection. But I want to understand following.

 

1) As this a pressure vessel, what code would be applied for gas flow calcs

2) As I understand, flame arresters are not meant for emergency relief and not sure, how do I specify expected maximum gas flowrate.

3) See the location of flame arrester on the receiving vessel in the attached file. I have also provided some more relevant info on the attached sketch.

 

Thanks

KS

 

Attached Files



#4 fallah

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Posted 21 March 2014 - 01:11 PM   Best Answer

Hi,

 

No need to any code for gas flow calculation, just do a material balance around the receiver vessel at the moment of flowing the fluid (appears to be two phase) toward the vessel. In normal operation, gas portion of the mentioned fluid should be go out of the vessel through the free vent terminated by FA. Obviously, resistance of FA against outgoing flow of the gas should be considered in flowrate calculation.

 

PSV relief load would be calculated gas flowrate which has to go out of the vessel in the case of FA blockage...

 

The strange point in the sketch: The set pressure of the PSV on the reactor as source of the pressure for such overpressure scenario, is lower than that of the PSV on the downstream receiver vessel...



#5 chemks2012

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Posted 22 March 2014 - 12:08 PM

Hi Fallah

 

Thanks for your input/reply.

 

Please not that the RV on reactor is designed for vapour release. The reactor has also got an independent 10inch bursting disc, set at 3.5barg for two phase release. However, still the set pressure for reactor is still lower than the receiving vessel. From my preliminary assessment, what i understand is client is considering reactor as a primary release source. 

Just wondering why it is strange.

Thanks,

KS



#6 fallah

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Posted 22 March 2014 - 01:33 PM

From my preliminary assessment, what i understand is client is considering reactor as a primary release source. 

Just wondering why it is strange.

 

 

KS,

 

When the RV on the receiver vessel would activate at 4 barg, because the upstream reactor is the source of pressure then the reractor pressure should be higher than 4 barg means RV on the reactor with set pressure of 3 barg has already been activated but probably with a relief capacity of not adequate for relieving total load. Therefore, remain relieving load has probably left to relieve by the RV on the receiving vessel. It might there would be an isolation valve between the reactor and the vessel for which it is needed to consider a dedicated RV on the reactor, but this RV might being designed so that to relieve total load such that there would be no need having RV on the vessel. Anyway, if it is intended to consider dedicated RVs on the reactor and the vessel, it's logical having at least equal set pressure for both RVs. The RV on the reactor can have a little bit higher set pressure (due to pressure loss between the reactor and the vessel) provided that not to be exceeded to the reactor design pressure...



#7 chemks2012

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Posted 22 March 2014 - 03:04 PM

Hi Fallah,

 

Thanks for your reply.

 

Apologies: My wordings in the previous post were not proper. From my preliminary assessment, what i understand is client is considering reactor as a separate [independent] release source.

 

The reactor is running at maximum 2barg and has design pressure of 7barg. Looking to various release scenarios, the external fire is the worst case.

Again, there are two cases for external fire for reactor

1) External fire & vapour phase release  [very likely]: In this casev RV on reactor set pressure of 3barg is adequate.

2) External fire & two phase release [very unlikely]: In this case, 10" BD on reactor set pressure of 3.5barg is adequate

Both of above scenarios will not lead to pressurisation of Receiving Vessel.

 

Please note that Receiving Vessel has design pressure of 7barg as well. Also looking to various release scenarios for Receiving Vessel, the external fire is the worst case. Here two phase release will not occur and hence the RV on Receiving Vessel set pressure of 4barg is adequate for vapour release.

 

As this is the case, can I not say that both, Reactor and Receiving Vessel are acting as two independent release source and hence the selected set pressure are logical?

 

PS: Agree, that selected set pressure are lower than design pressure of respective vessel but that's due to process reasons.

 

Thanks

KS


Edited by chemks2012, 22 March 2014 - 03:08 PM.


#8 fallah

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Posted 22 March 2014 - 11:23 PM

KS,

 

Having dedicated RV on the reactor and the receiving vessel not only is logical but also is necessary for the code compliance. But if there would be an isolation valve between the reactor and the receiving vessel, it can affect the system analysis in overpressure study and relief load determination standpoints. Obviously if the reactor and vessel are independent release source each of them can be protected against overpressure by a RV with set pressure lower than 7 barg.

 

The info you are provided along with a general sketch isn't adequate for overpressure study and evaluation of such low RVs set pressures. If, as you mentioned, the settings are subject to process requirements...no problem, it's adequate to be lower than the relevant vessel's design pressure...



#9 chemks2012

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Posted 24 March 2014 - 05:48 AM

Thanks very much Fallah,

 

Sorry, could you please elaborate this statement for better understanding? 

 

But if there would be an isolation valve between the reactor and the receiving vessel, it can affect the system analysis in overpressure study and relief load determination standpoints.

 

Regards,

KS



#10 fallah

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Posted 24 March 2014 - 06:21 AM

 

Sorry, could you please elaborate this statement for better understanding? 

 

But if there would be an isolation valve between the reactor and the receiving vessel, it can affect the system analysis in overpressure study and relief load determination standpoints.

 

 

KS,

 

It means, e.g. if there would be no isolation valve there, relief load due to fire case in receiving vessel can be shared between the RV on the vessel and the RV on the reactor. But if there would be an isolation there, one cannot take any credit for mentioned sharing and the RV on the vessel shall be capable to release all relief load due to fire case. As you see being or not being an isolation valve there, affects relevant overpressure study and RVs sizing...



#11 chemks2012

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Posted 24 March 2014 - 08:29 AM

Hi Fallah,

 

Thanks very much for all your info. You are a star!!

 

Yes, I have checked. The line from reactor [through the condenser] to receiving vessel have an isolation valve but that will be normally open. Yes,  RV on both, reactor and receiving vessel are capable of relieving load on their own [i.e. no release load sharing].


Edited by chemks2012, 24 March 2014 - 08:31 AM.





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