4 replies to this topic

[lara1234]

Hello,
Any idea on how to determine the vapor generated from a propane tank during a summer season? The pressure in the tank is controlled by a pressure control valve discharging to the flare. When the pressure reaches a certain set point, this PCV vents to the flare keeping the relief valve closed. Also, how do you calculate the vapor generated while loading to the tank cars. I appreciate any insight you can provide.

Thanks,
Lara

[Art Montemayor]

Lara:

First and foremost, so that my comments can be understood, lets confirm some facts about your Propane storage tank:

1) The Propane stored in it is kept in a SATURATED condition or state;
2) The pressure existing inside the tank is the vapor pressure of the Propane at the temperature the surface of the saturated liquid finds itself in;
3) Your storage tank – like any other industrial Propane (or LPG) tank - should be designed to maintain the liquid product inside it at the saturated pressure corresponding to the temperature it finds itself at. This temperature is directly related – and close to – the ambient temperature where the tank is located. If you find yourself and your tank within the Sahara desert, your tank should be designed to withstand the highest vapor pressure of the Propane corresponding to the highest temperature in the Sahara – which would probably be at noon, during the summer months. I would guess that the Propane temperature could get as high as 125 oF. Maybe a little higher. If your tank is in Antartica, then the tank pressure will be much less.

If your tank has been designed correctly for your location and application, it should not be venting to the flare under normal operating conditions. If it is, something is wrong with the design and the application. Propane storage tanks as well as all LPG tanks are protected from over-pressure by conventional Pressure Relief Valves. These are designed to activate under emergency or hazardous conditions – not continuously.

Therefore, your question: “how to determine the vapor generated from a propane tank during a summer season” has little or no importance for operating or controlling the tank – assuming it was designed and applied correctly. The tank is simply designed and installed to WITHSTAND the highest, normal vapor pressure it generates during the course of its operation.

Some small quantity of Propane vapors may be generated while loading tank cars – rail or truck. However, these normally are handled in a very practical way and never vented to flare or atmosphere. You simply design your Propane transfer system so that there is always an equalization line between the storage tank and the tank car during the loading. The vapor spaces of both the source and the target tanks are equalized so that the pressure is the same in both. When the transfer is finished, you simply shut off the vapor balance line.

I hope this explains what I believe are your misunderstandings on the subject. Since you don’t furnish any background or basic data, I have to make assumptions about just what you have installed and what you are doing.

[ankur2061]

Lara,

Check out the following weblink to understand the mechanism for LP Gas Transfer equipment. It gives a very clear picture of the LP Gas vaporizing and condensing mechanisms:

http://www.corken.co...ining/cp226.pdf

Regards,
Ankur.

[Zauberberg]

Ankur,

That's an excellent link. Thanks for sharing resources.
Best regards,

[lara1234]

Ankur,

That's an excellent link. Thanks for sharing resources.
Best regards,

Hi Art / Ankur,

Thanks for all your input.

Regards,
Lara