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Condensate Storage Tank Selection

true vapor pressure floating roof tank reid vapor pressure

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#1 eastorca

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Posted 05 March 2013 - 04:32 AM

Dear friends,

 

Could you please give your advices for condensate storage tank selection operating @ ATM condition.Is there any constrain about true vapor pressure of condensate that it contains to ensure safety operation. In case a internal floating roof tank is selected, is there any specific requirement must be followed? 

 

Thank you so much. 

 



#2 IonCube

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Posted 05 March 2013 - 10:37 AM

  • Vapour pressure constraint can easily be controlled by using good quality auto relief valve
  • A very important aspect is however if the condensate has entrainment of any corrosive material from upstream process...then you have to carefully select MOC (material of construction) accordingly


#3 ankur2061

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Posted 05 March 2013 - 10:56 AM

eastorca,

 

If you plan to use an closed floating roof tank for condensate storage, I don't see any issue as far as safe operation is concerned. Since you are using a closed floating roof tank you don't need any inert gas blanketing.

 

Construct your closed floating roof tank as per the guidelines given in Appendix H of API STD 650 and you should be able to have a safe and good design for storing your condensate.

 

Regards,

Ankur.



#4 paulhorth

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Posted 06 March 2013 - 12:30 PM

Eastorca,

The true vapour pressure at the storage temperature is an important process parameter for liquid stored in floating roof tanks. High vapour pressure can cause vapour breakout under the roof which can cause the roof to tilt or partially sink.

I once had a good paper by an engineer in Chicago Bridge & Iron, who invented the floating roof tank. Unfortunately I can't find my copy, but from memory he advised a maximum TVP of 12 psia at the storage temperature. If you use the search feature on this forum you will find links to earlier posts on the forum on floating roof tanks which will help you.

A fixed roof tank will allow the condensate to go offspec on vapour pressure while production continues. If you use a floating roof tank you will have to carefully consider if you need to build an off-spec tank as well (fixed roof) and route the product there if there is a problem in the stabiliser. You can avoid this by careful online monitoring of the vapour pressure and by having a secure heating utility for the reboiler.

 

Paul



#5 kkala

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Posted 06 March 2013 - 04:25 PM

Criteria for tank selection can be seen at <http://www.cheresour...tank#entry66118> and <http://www.cheresour...-vapour-losses/>, concerning storage of liquid hydrocarbons. Above posts are apparently speaking of such tanks. Mentioned "true vapor pressure to ensure safety" indicates that you rather mean such type of tank.

Note:Seen water condensate tank was of cone roof type, so that escaping steam during a control valve / steam trap failure could pass to atmosphere through a tank vent, sized for worst contingency. The latter concerned escape of low pressure steam from a condensate flash drum, in case that it lost liquid level (unsatisfactory function of its LCV).



#6 ankur2061

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Posted 07 March 2013 - 12:40 AM

Eastorca,

The true vapour pressure at the storage temperature is an important process parameter for liquid stored in floating roof tanks. High vapour pressure can cause vapour breakout under the roof which can cause the roof to tilt or partially sink.

I once had a good paper by an engineer in Chicago Bridge & Iron, who invented the floating roof tank. Unfortunately I can't find my copy, but from memory he advised a maximum TVP of 12 psia at the storage temperature. If you use the search feature on this forum you will find links to earlier posts on the forum on floating roof tanks which will help you.

A fixed roof tank will allow the condensate to go offspec on vapour pressure while production continues. If you use a floating roof tank you will have to carefully consider if you need to build an off-spec tank as well (fixed roof) and route the product there if there is a problem in the stabiliser. You can avoid this by careful online monitoring of the vapour pressure and by having a secure heating utility for the reboiler.

 

Paul

Paul,

 

You are right when you mention the limitations of TVP on floating roof design. Two articles that I read and whose links are provided below, substantiate this:

 

http://smartprocessd...-floating-roof/

 

http://bulktransport...ulations_drive/

 

Regards,

Ankur



#7 fallah

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Posted 07 March 2013 - 01:32 AM

Dears,

 

As far as i know the maximum TVP at storage temperature in a floating roof storage tank should be 11psia.



#8 kkala

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Posted 07 March 2013 - 04:17 AM

This value of true vapor pressure (11 psia) complies with Nelson's "Petroleum Refinery Engineering" (Mc Graw-Hill, 1958), as links of post no 5 (by kkala) indicate. In practice floating roof tanks for liquids of TVP up to 13 psia (1 Atm a =14.7 psia) have been designed here. Critical opinion on this would be welcomed. Regulations on hydrocarbon emissions (VOC) get stricter and stricter with time. 
Mentioned values of TVP are for maximum operating temperature.

Note: Greek legislation recommends floating roof tanks for liquids of flash point lower than (maximum) ambient temperature.






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