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5

Snuffing At Vent Stack


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#1 farid.k

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Posted 19 September 2019 - 09:48 PM

Hye. I need to design a snuffing system at vent stack that release flammable gas. Anyone has an example calculation and any spacial devices required i.e. Purging nozzle? I don't have any experience before.

Planning to use N2 gas for snuffing gas.


Edited by farid.k, 20 September 2019 - 11:55 AM.


#2 muthukmaar

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Posted 20 September 2019 - 10:43 AM

We are using 12kg/cm2 saturated steam to snuffing purpose

#3 farid.k

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Posted 20 September 2019 - 11:51 AM

We are using 12kg/cm2 saturated steam to snuffing purpose

hye muthukmaar,

 

any reason behind for 12kg/cm2? actually why kg/cm2? i expecting mass flow rate i.e. 12 kg/h? but 12 kg/h too small



#4 breizh

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Posted 20 September 2019 - 06:45 PM

farid ,

kg/cm2  is  a unit of pressure  still in use in some part of the world.

 

Breizh



#5 farid.k

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Posted 20 September 2019 - 07:29 PM

farid ,
kg/cm2 is a unit of pressure still in use in some part of the world.

Ok then. But the statement still too generic for me to design . Is it 12 kg/cm2 at downstream of orifice (in case they use orifice). My concern is i don't know how much steam flow or n2 flow required.
Breizh



#6 breizh

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Posted 20 September 2019 - 08:25 PM

Hi ,

Let you consider the document attached to start with.

Good luck

Breizh

Attached Files



#7 farid.k

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Posted 20 September 2019 - 09:47 PM

Hi ,
Let you consider the document attached to start with.
Good luck
Breizh


Thanks so much sir for the material. It helps

#8 breizh

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Posted 21 September 2019 - 08:46 PM

https://www.eng-tips....cfm?qid=163305

 

Hi farid,

Consider this link to support.

Note : Using your favourite engine your will find a lot of info , key words Snuffing  vent stack .

 

Breizh 



#9 gegio1960

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Posted 23 September 2019 - 03:11 AM

further reading...Attached File  1774.pdf   225.38KB   22 downloads



#10 muthukmaar

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Posted 23 September 2019 - 04:27 AM

This is used based on its availability as 12kg/cm2 saturated steam is generated by the FLash drum in the CBD of Boilers



#11 farid.k

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Posted 23 September 2019 - 08:55 AM

https://www.eng-tips....cfm?qid=163305

Hi farid,
Consider this link to support.
Note : Using your favourite engine your will find a lot of info , key words Snuffing vent stack .

Breizh


Thanks so much for your support

#12 farid.k

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Posted 23 September 2019 - 08:58 AM

further reading... 1774.pdf


Hye. Thanks so much for the material..

Just thinking.. What if they don't calculate, just simply connect the pioing and throttle manually maybe 5-7 % opening

#13 gegio1960

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Posted 23 September 2019 - 09:12 AM

you shall verify the residual O2 concentration and tune the valve opening in accordance.

if you open too much, you'll loose money.

if you open too little, you'll be unsafe.

better to make preliminary estimations and then verify in field: it's not difficult!

good luck!



#14 farid.k

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Posted 26 September 2019 - 06:08 AM

you shall verify the residual O2 concentration and tune the valve opening in accordance.
if you open too much, you'll loose money.
if you open too little, you'll be unsafe.
better to make preliminary estimations and then verify in field: it's not difficult!
good luck!


How to verify? Especially to get know required n2 to flow? So that i can sizing accordingly i.e orifice size

#15 gegio1960

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Posted 26 September 2019 - 09:22 AM

farid,

i think the answers are already in the supporting materials provided to you.

another source is NFPA 69.

when you'll provide some data aboit your process, maybe it will be possible to improve the help.

just for example: you propose to throttle to 5-7% opening of what? (inert, size, conditions, configuration....) against what? (flow, composition, conditions, size, duration....)



#16 gegio1960

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Posted 26 September 2019 - 09:26 AM

ok, your inert is N2!



#17 farid.k

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Posted 26 September 2019 - 09:54 PM

farid,
i think the answers are already in the supporting materials provided to you.
another source is NFPA 69.
when you'll provide some data aboit your process, maybe it will be possible to improve the help.
just for example: you propose to throttle to 5-7% opening of what? (inert, size, conditions, configuration....) against what? (flow, composition, conditions, size, duration....)

Thanks. I will refer to relevant nfpa accordingly. Its actually N2 purging across 99.9% ethylene gas that release to atmosphere (via vent Stack) during overpressure scenario. Rated ethylene capacity to atmosphere is 11 T/h.

Edited by farid.k, 26 September 2019 - 09:55 PM.


#18 gegio1960

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Posted 26 September 2019 - 11:47 PM   Best Answer

my 2 cents....

going back to #8 by breizh, the calculation procedure shown in https://www.eng-tips....cfm?qid=163305 , would say:

- LEL: 2,7 %v in air (for C2H4 in GPSA physical properties table)

- RL = (100-LEL)/LEL = 36.04

- RST = 3/.21 = 14.29 (stoichiometric, .21 is the fraction of O2 in air))

- RXS = RL-RST = 21.75

- NE = 1 (for nitrogen)

- RI = RXS/NE = 21.75

- FOS = 1.5

- RSN = RI*FOS = 32.63

 

C2H4 load in kmol/h is 11000/28.05 = 392.16

N2 min snuffing flow should be 392.16*32.63 = 12796 kmol/h or 358.3 t/h (MW N2 = 28)

 

it seems a lot....


Edited by gegio1960, 26 September 2019 - 11:49 PM.


#19 breizh

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Posted 27 September 2019 - 01:58 AM

farid ,

Find someone knowledgeable in your organization to support your work. You cannot release to atmosphere a cloud of ethylene . You should review with local safety bureau what is the requirement in term of process safety . By the way you should take a look at the Hazop .

A good habit is to look at the MSDS to evaluate the risks and then come with a technical solution to mitigate them.

I don't think that dilution is a realistic one , based on LEL , quantity of N2 required and cost of nitrogen .

Did you consider other technologies?

Good luck

Breizh  



#20 farid.k

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Posted 27 September 2019 - 09:05 AM

farid ,
Find someone knowledgeable in your organization to support your work. You cannot release to atmosphere a cloud of ethylene . You should review with local safety bureau what is the requirement in term of process safety . By the way you should take a look at the Hazop .
A good habit is to look at the MSDS to evaluate the risks and then come with a technical solution to mitigate them.
I don't think that dilution is a realistic one , based on LEL , quantity of N2 required and cost of nitrogen .
Did you consider other technologies?
Good luck
Breizh


This has been practised 1990. Final overpressure released is to ATM. i know it is highly flammable. Even i do compared 2 ethylene technologies provider and both release to atm. And all have snuffing.

#21 farid.k

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Posted 27 September 2019 - 09:06 AM

farid ,
Find someone knowledgeable in your organization to support your work. You cannot release to atmosphere a cloud of ethylene . You should review with local safety bureau what is the requirement in term of process safety . By the way you should take a look at the Hazop .
A good habit is to look at the MSDS to evaluate the risks and then come with a technical solution to mitigate them.
I don't think that dilution is a realistic one , based on LEL , quantity of N2 required and cost of nitrogen .
Did you consider other technologies?
Good luck
Breizh


And for information also, 1st release is to flare. Final release is to atmospheric

#22 PhilippM

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Posted 27 September 2019 - 09:34 AM

 

farid ,
Find someone knowledgeable in your organization to support your work. You cannot release to atmosphere a cloud of ethylene . You should review with local safety bureau what is the requirement in term of process safety . By the way you should take a look at the Hazop .
A good habit is to look at the MSDS to evaluate the risks and then come with a technical solution to mitigate them.
I don't think that dilution is a realistic one , based on LEL , quantity of N2 required and cost of nitrogen .
Did you consider other technologies?
Good luck
Breizh


And for information also, 1st release is to flare. Final release is to atmospheric

 

What do you mean by "1st release" and "Final release" ?



#23 farid.k

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Posted 27 September 2019 - 07:59 PM


farid ,
Find someone knowledgeable in your organization to support your work. You cannot release to atmosphere a cloud of ethylene . You should review with local safety bureau what is the requirement in term of process safety . By the way you should take a look at the Hazop .
A good habit is to look at the MSDS to evaluate the risks and then come with a technical solution to mitigate them.
I don't think that dilution is a realistic one , based on LEL , quantity of N2 required and cost of nitrogen .
Did you consider other technologies?
Good luck
Breizh

And for information also, 1st release is to flare. Final release is to atmospheric
What do you mean by "1st release" and "Final release" ?

2 relief valve set in staggered. 1 low setting pressure release to flare, 2nd higher release to atm

#24 Bobby Strain

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Posted 27 September 2019 - 10:49 PM

Low and higher have no meaning to us. One must always assume that the vent will ignite. Then you must consider flame radiation affecting people and equipment. You don't have any steam available?

 

Bobby



#25 farid.k

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Posted 27 September 2019 - 11:40 PM

Low and higher have no meaning to us. One must always assume that the vent will ignite. Then you must consider flame radiation affecting people and equipment. You don't have any steam available?

Bobby


Have. Why? Steam better than n2?




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