VAPOUR PRESSURE

[cesvalsar]

I have a problem with design of a 1000L container (IBC) for carryng gasoline (UN1203) with a steam pressure VP15 = 0,3 barA at 15ºC and 1,3 barA at 55ºC. Initial loading condition 90% (maximum filling rate) at 15ºC; so I have a gas chamber of 100L.
Container is closed after filling (equilibrium condition has been reached before closing). In this case final pressure 1,013barA = VP15 + AP15 (AP15 is partial pressure due to air = 1,013-0,3 = 0,713barA).

Now I have to calculate final pressure at 55ºC (extreme service condition of container).
VP55 = 1,3 barA
AP55 = 0,713 * (273+55)/(273+15) = 0, 812 barA
Final pressure = 2,112barA; so the setting of safety valve should be minimum 1,112 bar in order to prevent gas leaks
(I have not considered the thermal expansion of liquid)


Now my problem is: I am designing according ADR&IMDG CodeS (point 6.5) that determines a maximum setting pressure of maximum 0,65bar and minimum the total inner pressure at 55ºC (according my calculation over 0,65bar!)

Are my calculation wrong?

 

[rbcoulter]

What do you mean by "steam pressure"?
It appears as though you are saying that the gasoline has a boiling point between 15 C & 55 C. Which seems unusually low. Is your gasoline vapor pressure data correct?

 

[cesvalsar]

Sorry.It is a translation mistake. I should better said vapour pressure instead steam pressure

You have got the reason. I have mentioned gasoline but really I am designing for carrying also another substances. The maximum vapour pressure for every substances that can be carried in these container is 1,3 bar at 55ºC

-Absolute vapour pressure at 15ºC = 0,3 barA
-Absolute vapour pressure at 55ºC = 1,3 barA

Boiling point(temperature at which absolute vapour pressure reachs 1,013 barA)is not relevant in this case
my problem is: If I fill container at 15ºC opened to atmosphere. When I finish and I close container I have a total pressure of 1,013= 0,3 + 0,713 barA.

If I raise temperature at 55ºC I will have a final pressure of 1,3 + 0,812 = 2,112barA.
(0,713 * (273+55)/(273+15) = 0, 812 barA)
If I mount a safety valve with a opening pressure of 0,65bar according regulations; I think the valve will open in normal service condition range (15..55ºC); relieving flammable gases to atmosphere

My doubt is if I am calculating correctly the final pressure (I am not sure).

I am stopped. I will very grateful with every aid

Thanks

 

[rbcoulter]

The calculation does not appear to be the problem here. The problem appears to be that your vapor pressure data is closer to an LPG. Gasoline would be expected to have a VP less than 1 bar at 55 C. Your standard is probably meant for liquids that are still liquids at 55 C (VP less than 1 bar). You should probably be using a standard for LPGs. For example, propane or butane.

 

[StoneCold]

cesvalsar
You have the wrong container. As rbcoulter suggests you need to switch to a higher pressure rated container and then try to apply the codes that are relavent to the new container.
I feel for you. I have a lot of DOT code problems with things we ship as well.

StoneCold