4 replies to this topic

[Goldenboy]

A sphere is design for 65psig, but during the summer time isobutane flare. Why does this happen during the summer time, and will the same thing happen during the winter?. Also the sphere design for 75psig with normal butane does not flare

[Art Montemayor]

Golden:

 

I think you are repeating the same basic topic in different threads.   If you don't understand the responses to the other threads, please say so and our members will surely try to explain in a manner you can understand - if you are a graduate engineer.

 

If the PSV or relief valve on your 65 psig sphere is set at what you call the design pressure (65 psig) and it is opening, then you probably don't have what you say you have inside the sphere: pure butane saturated liquid.  You probably have "lights" - such as ethane & propane - mixed with it.  Pure butane liquid exists at the saturated temperature of  130 oF and 65 psig.  If you really had "pure" (100%) butane in the sphere then the temperature would have to be 130 oF in order for the internal pressure to reach 65 psig.  I believe what you say about it relieving, so it is obvious that it isn't what you thing it is because you would have to be in a very intolerably hot area of the world to achieve that kind of temperature.  Insulation would probably help or cure the relieving situation, but you don't give us much basic data like the composition of the contents, your ambient max. temperature, the MAWP of your sphere, its dimensions and wall thickness, etc. etc. - so we can't comment any further.

 

If you are a degreed chemical engineer, you should know the vapor pressure curve of the liquid contents or calculate it with a simulation program.  By inputting the actual composition of the contents, you should be able to find the saturated vapor pressure inside the tank when at max. local ambient temperature.

[Goldenboy]

I don't have a degree yet, and the IC4 composition is mixed with ethane and propane and the RV is set for 55psig

[Art Montemayor]

A pressure relief valve (PSV) is (according to the API and ASME) supposed to be set to relieve at the Max. allowable working pressure (which is usually a higher value than the design pressure of the vessel in question.

 

Therefore, by setting the PSV at the design pressure you are being conservative.  However, you seem to be setting the PSV at a pressure below what you identify as the design pressure.  This would explain the venting of the sphere.   You can set the PSV at the design 65 psig instead of the reported 55 psig.   Having said that, I have to trust a non-degreed individual in reporting the correct design and PSV set pressures.  I would feel a lot safer if I were communicating with an experienced, professional engineer.  Designing and resolving relief scenarios is a very important and critical step and should be done by experienced engineers because the consequences of a mistake or error can be catastrophic disasters.

[breizh]

http://encyclopedia....orPressureGraph

 

Consider this resource from air liquide  in particular the vapor pressure graph vs temperature to support your study and the Boiling Point  of the components  .

 

 

Hope this helps

Breizh

Edited by breizh, 28 July 2013 - 11:45 PM.