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Flare Design

flare design

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#1 shashank daksh

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Posted 16 January 2019 - 09:51 PM

I am designing a common flare gas system for Butadiene, Vinyl Chloride and Ethylene.

Flare system used is of carbon steel. SS is not used because of Chloride stress corrosion cracking due to Chloride content.

 

Since Ethylene governing case  relief temp is -78C and if did not considered wind velocity than for its not possible for me to connect this line to carbon steel.

Since my distance is around 350 m so if 1 considered even 1m/s of velocity and ambient temp as 15C my temperature at connecting point to CS piping comes at -5C. Which seems to be Ok.

 

My question is:

 

1) Can I use 1m/s of wind velocity and ambient heat loss.

2) if No than what will the other option I can have to have CS Flare system.

 

Thanks a lot

Shashank

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#2 Bobby Strain

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Posted 16 January 2019 - 11:45 PM

Doesn't seem safe to me.

 

Bobby



#3 fallah

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Posted 17 January 2019 - 02:25 AM

I am designing a common flare gas system for Butadiene, Vinyl Chloride and Ethylene.

Flare system used is of carbon steel. SS is not used because of Chloride stress corrosion cracking due to Chloride content.

 

Since Ethylene governing case  relief temp is -78C and if did not considered wind velocity than for its not possible for me to connect this line to carbon steel.

Since my distance is around 350 m so if 1 considered even 1m/s of velocity and ambient temp as 15C my temperature at connecting point to CS piping comes at -5C. Which seems to be Ok.

 

My question is:

 

1) Can I use 1m/s of wind velocity and ambient heat loss.

2) if No than what will the other option I can have to have CS Flare system.

 

 

Hi Shashank,

 

It's highly recommended using SS; but if you aren't allowed using SS, at least try using LTCS...



#4 breizh

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Posted 17 January 2019 - 03:04 AM

Hi ,

 You should talk to reputable vendors, one is mentioned in the document attached where you can find tips .

 how do you manage the different waste gas for them to reach the flare ( driving force) ? What about the risk of   backflow?

 

Regarding the materials I believe fallah's suggestion is a good one ( CS +liner) or SS .

 

 

my view.

Breizh

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Edited by breizh, 17 January 2019 - 03:04 AM.


#5 flarenuf

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Posted 17 January 2019 - 05:40 AM

Hi Shashank,

you cannot take into account the wind effect, always look at the worse case scenario = no wind 

 

so questions here,

1) is the flow of ethylene a continuous vent flow at -78C or is it a relief valve with limited flow?
2) where does the -78C come from , upstream hi P flashing down or actual LP source temp? your ko drum is CS , so if you vent the -&*C gas into that ...??

3) is the 350m the distance between the LO SS  valve and the KO drum ?
3)does the ethylene flow occur on its own or will the other vents always be flowing as well ( in other words will the cold gas mix with other warmer gases on its way down to the burnpit? and if it does what are the relative flows)

I am trying to determine if you think of this relief dynamically  do actually have  a -78C gas flowing for a time with sufficient "cold" to pull the header KO drum and gas header temp down below -44C  

 

Flarenuf



#6 SawsanAli311

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Posted 18 January 2019 - 12:39 AM

I think you need to perform a more detailed dynamic depressurization study using more accurate theromodynamic based software like the BLOWDOWN software in latest HYSYS version. It helps you to find out the role of the thermal mass inertia of the flare headers and the system's components and to predict more accurately the inner wall temperature of your piping & vessel as well as you bulk fluid temperature. MDMT studies shall be performed on adiabatic considerations with no credit for any external wind convective heat transfer effects.



#7 shashank daksh

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Posted 19 January 2019 - 01:51 AM

Thanks all for your prompt  and valuable reply in such a short time.

I have few point to more clarify the above post :

 

a) -70 is relief due to fire case from a vessel set @ 3.5 kg/cm2. Right now I don't have any KO drum in Ethylene Area and there is no Expected liquid relief.

 b:  I told earlier that I cant use SS material due to chloride cracking, Is there is any code or philosophy which says that we need to consider wind velocity or not. If I did not consider the wind velocity it means there will be no heat transfer no matter how long the pipe is. So for Ethylene I need to consider SS and BD and VCM I need to consider CS, which will increase the cost.

 

Please suggest me the other possible way, my client is concern about money as well as safety.

 

Thanks a lot


Edited by shashank daksh, 19 January 2019 - 01:52 AM.


#8 fallah

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Posted 19 January 2019 - 02:05 AM

 

a) -70 is relief due to fire case from a vessel set @ 3.5 kg/cm2. Right now I don't have any KO drum in Ethylene Area and there is no Expected liquid relief.

 

 

Hi Shashank,

 

Can you upload the fire case calculation leading to -70 C for review checking?



#9 gegio1960

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Posted 19 January 2019 - 02:30 AM

my 2 cents:

1) LTCS (low temperature carbon steel) can be used above -45°C. It is widely used for this kind of services

2) you have a heat transmission also in absence of wind, whenever you have a differential temperature

3) i'm also interested to know the calculation procedures and assumptions leading to a discharge temperature of -78°C (or -70°C)

good luck!


Edited by gegio1960, 19 January 2019 - 02:35 AM.





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