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Blanketing Estimation For Hot Oil Expansion Drum


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#1 Butterfly

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Posted 31 October 2011 - 04:37 AM

I now there are many related topics, but I cannot find the exact information.

I have a hot oil close circuit. Oil comes out the expansion vessel and is pumped through a WHRU. It then enters some reboilers, and goes back to the expansion drum.

This drum has blanketing using natural gas. Its volume is 725 ft3, and the blanketing consumption estimated by the engineering company is 270000 ft3/day. Since hot oil is continually flowing through the reboilers where it is used, I cannot see how they calculated such a big amount of fuel gas for blanketing. I just would like to have a way of doing a quick estimation.

Design/operating pressure of the vessel are 125 psig/5 psig

Thanks in advance

#2 proinwv

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Posted 31 October 2011 - 07:04 AM

From your explanation, it seems that the gas consumption (and expulsion) would be directly related to the outflow and inflow cycles. This assumes a constant oil temperature.

#3 fallah

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Posted 31 October 2011 - 08:01 AM

From your explanation, it seems that the gas consumption (and expulsion) would be directly related to the outflow and inflow cycles. This assumes a constant oil temperature.


Butterfly,

One topic in two different forums! One in Industrial Professional and another in Tank Blanketing and Venting!

Paul,

Don't you think due to continious operation of the mentioned system, as a closed loop, the gas consumption couldn't mostly be related to the in-flow/out-flow cycles?

Fallah

#4 proinwv

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Posted 31 October 2011 - 08:43 AM

Well if truly is continuous (and a constant level) then we would expect no consumption of gas.

I have assumed that there is some cycling or variation in the liquid level and that would be indicative of the need to have some replacement gas. Also, there is the likelihood of gas leakage which would require the addtion of gas. Last, heat transfer could result in cooling of the vapor space.

The problem is that it will be difficult to quantify these amounts. If I knew more about the details of his system and the construction possibly I could "estimate" that but I don't and even so I don't feel willing to cross the bridge from general advice to specific details to design a system that I will never see.

If it were mine, I would start with investigating the cycle and estimating the volumetric changes, the volumetric change due to temperature cycling, and the leakage of gas out of a small hole (simulating a gasket or other type of leak). These I would add together and consider a multiplier for a factor of safety.

Next I would calculate the amount of gas needed to provide a cold start up of an empty vessel, and then use the larger as my gas needs.

Agree?

#5 Butterfly

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Posted 31 October 2011 - 09:33 AM

Thanks for your help, and sorry for the multi-forum post, my mistake

#6 proinwv

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Posted 31 October 2011 - 09:38 AM

You are welcome.

One more comment. Don't be concerned with calculating/estimating a higher gas flow. Your system will only take what is required. However, gross oversizing could lead to regulator instability especially with small volumes. Your drum is large enough that I would not expect that to be an issue.

Have our comments been helpful?

#7 Butterfly

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Posted 31 October 2011 - 10:44 AM

Yes, they have. This drum has no level control valve, so as per your indications the main contibutor should be the volumetric changes due to temperature plus gas leaks.

#8 fallah

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Posted 01 November 2011 - 01:34 AM

Well if truly is continuous (and a constant level) then we would expect no consumption of gas.


Paul,

The level may vary due to temperature changes and also gas leaks would be contributed in fuel gas consumption.

Butterfly,

Don't you think the consumption of fuel gas for above mentioned issues is out of order and it may be due to sweeping application?

Fallah

#9 proinwv

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Posted 01 November 2011 - 06:49 AM

Fallah, I do agree with what you say, but I am not sure what you mean by "sweeping application".

#10 fallah

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Posted 01 November 2011 - 08:09 AM

Fallah, I do agree with what you say, but I am not sure what you mean by "sweeping application".


Paul,

I meant using continious gas passing through the drum from the source of gas to, let say, flare system as "once through" in order to keep space at the top of the drum continually saturated with mentioned gas.

Fallah

Edited by fallah, 01 November 2011 - 08:15 AM.


#11 proinwv

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Posted 01 November 2011 - 08:32 AM

Thanks, I understand. Then it may well consume a large quantity of gas.




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