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5

Selection Of Whether A Gas Is To Be Flared Or Vented


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#1 muthukmaar

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Posted 15 September 2019 - 01:24 AM

How do we select whether a gas is to be flared or vented in to the atmosphere

#2 breizh

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Posted 15 September 2019 - 03:16 AM

Hi ,

I would say based on regulation in your country  , risks associated with the release of the product ( explosion , health of people  , volume ,nature ,... )

These are the minimum coming to my mind . A good way to answer to your question is to look at MSDS .

 

my view

Breizh


Edited by breizh, 15 September 2019 - 03:17 AM.


#3 muthukmaar

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Posted 15 September 2019 - 04:54 AM

To explain in a bit brief manner. The exhaust of safety relief valve located downstream of LT Shift converter is flared and the exhaust of the pressure control valve at the same location in vented

#4 breizh

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Posted 15 September 2019 - 08:03 AM

Hi ,

Both should be flared !

Most probably the PCV is opening before the PRV (different set points)  therefore I would consider to release to the flare not to atmosphere .

Was it the case at the start up of the unit and / or the flare was installed afterwards ?  

You may have some pointers in the Hazop study or PIDs?

 

note : for the future , consider to go the point in your query to avoid misunderstanding or answer too vague.

 

my thoughts

Breizh


Edited by breizh, 15 September 2019 - 08:07 AM.


#5 Chemitofreak

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Posted 16 September 2019 - 01:32 AM

To explain in a bit brief manner. The exhaust of safety relief valve located downstream of LT Shift converter is flared and the exhaust of the pressure control valve at the same location in vented

 

If the discharge of the safety valve is routed to the flare, then the outlet of PCV shall also be routed to the flare as same material/fluid will flow through them.

 

Having said that what is the composition of the fluid routed to flare/atmosphere 


Edited by Chemitofreak, 16 September 2019 - 01:32 AM.


#6 Pilesar

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Posted 16 September 2019 - 07:59 AM

There are valid reasons why a pressure control valve might be vented to atmosphere when a relief valve at the same location is sent to flare. The air quality permit may have different emission allowances for planned maintenance, startup, and shutdown events. During these events, entire vessels might be evacuated. This may be too much flow for the flare system. So a pressure control valve might be opened to the atmosphere if allowed by permit.


#7 PhilippM

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Posted 16 September 2019 - 08:14 AM

 

There are valid reasons why a pressure control valve might be vented to atmosphere when a relief valve at the same location is sent to flare. The air quality permit may have different emission allowances for planned maintenance, startup, and shutdown events. During these events, entire vessels might be evacuated. This may be too much flow for the flare system. So a pressure control valve might be opened to the atmosphere if allowed by permit.

 

It might also be possible that the gas inside the vessel during normal operation (that is vented to atmosphere) is different from the one during pressure relief, e.g. in the case of vapor breakthrough from an upstream high pressure vapour-liquid separator. The relatively small flow over the PCV might be acceptable to be vented, while the larger flow needs to be flared.



#8 Chemitofreak

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Posted 17 September 2019 - 12:35 AM

 

 

There are valid reasons why a pressure control valve might be vented to atmosphere when a relief valve at the same location is sent to flare. The air quality permit may have different emission allowances for planned maintenance, startup, and shutdown events. During these events, entire vessels might be evacuated. This may be too much flow for the flare system. So a pressure control valve might be opened to the atmosphere if allowed by permit.

 

It might also be possible that the gas inside the vessel during normal operation (that is vented to atmosphere) is different from the one during pressure relief, e.g. in the case of vapor breakthrough from an upstream high pressure vapour-liquid separator. The relatively small flow over the PCV might be acceptable to be vented, while the larger flow needs to be flared.

 

 

I beg to differ, when the system over pressurises, the PCV will open first and then the safety valve, so same material will be relieved via. the PCV and Safety Valve.



#9 PhilippM

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Posted 17 September 2019 - 03:26 AM

 

 

 

There are valid reasons why a pressure control valve might be vented to atmosphere when a relief valve at the same location is sent to flare. The air quality permit may have different emission allowances for planned maintenance, startup, and shutdown events. During these events, entire vessels might be evacuated. This may be too much flow for the flare system. So a pressure control valve might be opened to the atmosphere if allowed by permit.

 

It might also be possible that the gas inside the vessel during normal operation (that is vented to atmosphere) is different from the one during pressure relief, e.g. in the case of vapor breakthrough from an upstream high pressure vapour-liquid separator. The relatively small flow over the PCV might be acceptable to be vented, while the larger flow needs to be flared.

 

 

I beg to differ, when the system over pressurises, the PCV will open first and then the safety valve, so same material will be relieved via. the PCV and Safety Valve.

 

Of course the same material will be released, but let's say only 5 kg/h will be vented over the PCV in normal operation and 10 kg/h during relieving conditions, whereas the relief flow through the relief valve of 1000 kg/h must be flared, because dispersion calculations have shown that this larger flow results in an explosive atmosphere far away from the vessel. Of course this is just an example, if muthukmaar wants an answer what gas needs to be vented or flared, he needs to provide more information.


Edited by PhilippM, 17 September 2019 - 03:28 AM.


#10 muthukmaar

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Posted 17 September 2019 - 11:36 AM

Thank you all so much for investing your valuable time in this regard
Further too add more the relief is set at 28kscg with a capacity of 10tph and the PCV usually has a set value of 24kscg with capacity of 20tph.

#11 muthukmaar

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Posted 17 September 2019 - 11:38 AM

The compostion of that gases are 15% CO2,58% H2,21%N2,.2% CO and remaining argon on a dry basis

#12 muthukmaar

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Posted 17 September 2019 - 11:39 AM

Hi ,
Both should be flared !
Most probably the PCV is opening before the PRV (different set points) therefore I would consider to release to the flare not to atmosphere .
Was it the case at the start up of the unit and / or the flare was installed afterwards ?
You may have some pointers in the Hazop study or PIDs?

note : for the future , consider to go the point in your query to avoid misunderstanding or answer too vague.

my thoughts
Breizh



Thank you so much for your Guidance Sir

#13 Chemitofreak

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Posted 18 September 2019 - 12:59 AM

Thank you all so much for investing your valuable time in this regard
Further too add more the relief is set at 28kscg with a capacity of 10tph and the PCV usually has a set value of 24kscg with capacity of 20tph.

 

I have never seen 'kscg' as a pressure unit, do you mean kg/cm2g, having said that I might be wrong



#14 Chemitofreak

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Posted 18 September 2019 - 01:00 AM

The compostion of that gases are 15% CO2,58% H2,21%N2,.2% CO and remaining argon on a dry basis

 

Considering the PCV capacity of 10 TPH and 58% H2, I would rather flare it than relieve to atmosphere



#15 muthukmaar

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Posted 18 September 2019 - 08:28 PM

 

Thank you all so much for investing your valuable time in this regard
Further too add more the relief is set at 28kscg with a capacity of 10tph and the PCV usually has a set value of 24kscg with capacity of 20tph.

 

I have never seen 'kscg' as a pressure unit, do you mean kg/cm2g, having said that I might be wrong

 

Yes Sir it is kg/cm2.g






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