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Gas Boot Sizing Upstream Of Fwko Tanks




Gas Boots are provided upstream of a Crude Oil Dehydration tank in order to degass the crude oil before it enters the dehydration tank. Entrained gas in crude oil disturbs the settling process in a dehydration tank and it's removal is required to ensure quick and effective settling for separating bulk water in crude oil dehydration tanks also referred commonly as "Free Water Knockout" (FWKO) tanks.
 
It is important to note that Gas Boots are very effective up to a Gas-Oil-Ratio (GOR) of 10 Nm3/m3. Above the aforementioned GOR, a conventional gas-liquid separator is recommended.
 
In a gas boot the downward liquid velocity should not exceeed 0.1 m/s.
 
Attached Image
 
Gas boots are generally designed as a piece of piping in the inlet piping to the FWKO just uptream of the inlet connection to the FWKO. Today's blog entry provides a quick sizing method in terms of the diameter of the gas boot pipe and the wet and unstabilized crude oil nominal flow rate based on a reputed company guideline.
 
Refer the attachment for the sizing of gas boots.
 
Any comments are welcome.
 
Regards,
Ankur.
 
 




Photo
ogpprocessing
May 29 2014 11:40 AM

Dear Ankur,

 

1. Based on the sketch you have provided, the outlet gas stream is connected to top of FWKO. Is this acceptable to let the gas to enter the top space of storage tank after getting separation from oil? Isn't it better to route it to gas outlet line from FWKO?

 

2. Regarding to the sizing of gas boots some clients ask to include slug volume of feed pipeline into gas boot volume. Is this part of gas boot function such that can handle any slug volume from feed line?

 

Thanks a lot.

Thnaks for this criteria. appreciate if you could provide a reference so that we can authentically use it.

Dear Ankur,

 

1. Based on the sketch you have provided, the outlet gas stream is connected to top of FWKO. Is this acceptable to let the gas to enter the top space of storage tank after getting separation from oil? Isn't it better to route it to gas outlet line from FWKO?

 

2. Regarding to the sizing of gas boots some clients ask to include slug volume of feed pipeline into gas boot volume. Is this part of gas boot function such that can handle any slug volume from feed line?

 

Thanks a lot.

1. Gas outlet connection is connected to top of FWKO tank. The FWKO tank vent is connected to flare. Ultimately the vent of the gas boot is connected to flare and in no way effects the degassing action of the gas boot.

 

2, This blog entry only deals with a degassing boot. The sizing does not include any allowances for slug volume, The name is self-explanatory "Gas Boot".

 

Regards,

Ankur

Thnaks for this criteria. appreciate if you could provide a reference so that we can authentically use it.

The reference is "Dehydration Manual" of Shell.

 

Regards,

Ankur

 

Thnaks for this criteria. appreciate if you could provide a reference so that we can authentically use it.

The reference is "Dehydration Manual" of Shell.

 

Regards,

Ankur

 

Dear mr.Ankur,

I am new to this community. Your posts are very help ful for us. I just want to know from where we will get Guidelines for the Process design of Gas boot and associated Dehydration tank. I couldnt find Dehydration manual online.

Regards,

Jayesh

 

Thnaks for this criteria. appreciate if you could provide a reference so that we can authentically use it.

The reference is "Dehydration Manual" of Shell.

 

Regards,

Ankur

 

Dear Ankur,

 

Could you please tell what is the manual number? for instance Glycol Dehy system manual number is 20.04.10.10.. In this way could you please let me know the number?

 

Regards,

G

 

 

Thnaks for this criteria. appreciate if you could provide a reference so that we can authentically use it.

The reference is "Dehydration Manual" of Shell.

 

Regards,

Ankur

 

Dear Ankur,

 

Could you please tell what is the manual number? for instance Glycol Dehy system manual number is 20.04.10.10.. In this way could you please let me know the number?

 

Regards,

G

 

G,

 

This content is from Shell's Dehydration Manual 1.0, Page 42, Fig A 4.3.5, Page 42.

 

Regards,

Ankur

Wow Ankur Sir, That was quick response.. Very much appreciated and thanked.. I was just curious to know the exact number as i am generating a calc. report and was struck as i couldn't quote the equation numbers, thanks again for this.
 

One last question if you think it's valid, as far as my limited knowledge, Shell has an Standard numbering philosophy for their manuals, so wondering if it's just "Shell Dehydartion manual 1.0" or would it be something like "DEP xx.xx.xx.xx".

 

Sorry for asking too much on this, as i am creating a calc report, i need some references which the client would take a look into based on my report.. I am totally new to Shell standards and have been relying on GPSA and API for these sizing things..

 

Thanks again 

G

Wow Ankur Sir, That was quick response.. Very much appreciated and thanked.. I was just curious to know the exact number as i am generating a calc. report and was struck as i couldn't quote the equation numbers, thanks again for this.
 

One last question if you think it's valid, as far as my limited knowledge, Shell has an Standard numbering philosophy for their manuals, so wondering if it's just "Shell Dehydartion manual 1.0" or would it be something like "DEP xx.xx.xx.xx".

 

Sorry for asking too much on this, as i am creating a calc report, i need some references which the client would take a look into based on my report.. I am totally new to Shell standards and have been relying on GPSA and API for these sizing things..

 

Thanks again 

G

G,

This manual is not part of the DEPs. It is an old design manual (1999) used by Shell and it's affiliate companies.

 

Regards,

Ankur.

That's it Sir, thanks so much for your guidance and inputs, I will quote "Shell Dehydration manual 1.0" onto my report and await further question from clients, if any..

 

Best Wishes,

G

Dear Ankur,

 

A Question again, now related to Crude Dehy Tank which is downstream of gas boot.

 

I am being asked to verify the tank volume which in my case is an API 650 tank. Is there a retention time for the tank that i should be keeping in mind while checking it's volume? In my case the feed rate of liquids out of gas boot would be roughly 7500 cu.m/day and the tank is volume of tank is 2150 cu.m. Is there any standards (Shell or others) that speak about this. Kindly enlighten me..The Crude and water ratio is roughly 50:50 by volume. 

 

If you think, this post here would be irrelevant (as the post was opened to teach about gas boot sizing), i will move the post to appropriate section.

 

Thanks,

G

Dear Ankur,

 

A Question again, now related to Crude Dehy Tank which is downstream of gas boot.

 

I am being asked to verify the tank volume which in my case is an API 650 tank. Is there a retention time for the tank that i should be keeping in mind while checking it's volume? In my case the feed rate of liquids out of gas boot would be roughly 7500 cu.m/day and the tank is volume of tank is 2150 cu.m. Is there any standards (Shell or others) that speak about this. Kindly enlighten me..The Crude and water ratio is roughly 50:50 by volume. 

 

If you think, this post here would be irrelevant (as the post was opened to teach about gas boot sizing), i will move the post to appropriate section.

 

Thanks,

G

G,

Is your crude oil tank designed for crude oil-water separation or in other words as a dehydration tank? This question is relevant since a dehydration tank has lot of features different from a normal storage tank in terms of the design of tank internals. Please note that the API STD 650 design code maybe applicable for both Dehydration tank as well as a normal crude storage tank. The difference is in terms of internals only.

 

Normal crude storage tanks (without internals) are drained periodically to remove accumulated water and sediment from the bottom. A crude tank designed as a dehydration tank is generally designed for continuous removal of produced water,

 

Regards,

Ankur

Dear Ankur,

 

It's been called as Dehydration tank and it has internals. It has floating oil collector with vortex breaker. I think It's designed for continuous removal of water and crude as it has a 50:50 vol. of water and crude.

 

Is there any specific reason why a particular volume has been sized? or would it be a general operational constraint. Seeing the vol. of tank and inlet flow-rate it has a retention time of roughly 8 hrs. and on seeing this makes me to believe that it would be more of an operational constraint, but want to make sure from you, if there would be any codes guiding this (on retention time)?

 

Thanks,

G,

 

For dehydration tanks, the key to the design is to provide internals which will minimize turbulence and prevent channeling. Retention time is not a criteria in the real sense since water is being drawn-off continuously.

 

Regards,

Ankur.

OK Sir, many thanks again for your support. I will ask the clients in what context should i be checking the volume for the tank.. And as usual i will comeback to the forum if i get some question back.

 

Regards,

G

Dear Ankur Sir,

 

I am going to trouble you again by asking a few more question, now coming back to gas boot again and the question is on the height of Gas boot.

 

In my design i am not keeping any height for 'hold ups' consideration, the question is truly from the figure of Shell. What i see from the figure are two different heights

 

1. The total height is sum of (HH level of Dehy tank) + (diameter of inlet nozzle of gas boot)+(1m above which i assume should be for vapor space or something)

 

2. The total height of Gas boot is 1.33 times level of HH in crude Dehy tank.

 

My questions to you are:

 

Q1. Of these two things which one should i take up for height? Should i take up the one that gives me more height? .

 

Q2. Assumed if i consider point 1 for my height, should my inlet nozzle of Gas boot be located immediately at the HH level of the crude dehy tank's height or should I give some additional clearance for the same?

 

Thanks,

G

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