3 replies to this topic

[LeoLeo]

Hello all,
 
I need to prepare specification for vapor treatment unit and part of the specification is the composition of the vent gas needs to be treated.
 
I need to calculate the vapor composition during pump in to storage tank under nitrogen blanket.
 
Any idea to calculate the vent gas composition from storage tank?
 
Thanks,
 
ARM
 

Edited by ARM, 11 March 2013 - 04:40 AM.

[ankur2061]

ARM,

 

Refer the attached paper for vent losses from tanks. The vent vapor losses are classified as "standing vapor losses" due to tank vapor space breathing and "working losses" due to tank filling. The total vent losses are the sum of the "standing vapor losses" and the "working losses".

 

An instantaneous vapor loss due to filling can also be calculated as an isothermal flash operation from a higher pressure to lower pressure. A process simulator such as HYSYS can be used to perform such an isothermal flash operation.

 

The Nitrogen that you add to the tank will all go out through the vent or in simple terms the inlet N2 flow rate to the tank will also be the N2 outlet flow rate from the tank.

 

Regards,

Ankur.

Attached Files

•  Organic_Liquid_Storage_Tanks.pdf   2.23MB   576 downloads

[LeoLeo]

Dear Ankur,
 
Thank you for the PDF file. I read it and it is mentioned that the calculation is valid when there is no non-condensable in storage tank.
 
I did the simulation in HYSYS already. I wanted to check if the result from HYSYS is correct or not. The worst case I have is pump-in scenario.
 
I assumed;
 
- N2 stream: actual flow rate the same is pump-in flow rate;
- Liquid stream: same as pump-in flow rate;
- both streams connected to a flash vessel
- there is no heating/cooling involved and temperature of both streams is ambient
 
When I check the vapor stream, I then I will have the composition and vapor physical properties. It is the only way that I can think about to simulate it in HYSYS.
 
Cheers,
 
ARM

Edited by ARM, 11 March 2013 - 04:43 AM.

[gregga]

Yes, just run an adiabatic flash with HYSYS, ASPEN or any other simulator with the liquid and nitrogen...make sure you have excess liquid (liquid is coming out of the flash).  The vapor stream will be in equilibrium at T and P with the liquid.  This will give you the composition and phys properties of the vapor.  The actual vapor rate in ACFM will be determined per Mr. Ankur

 

If the liquid is a single component, you can quickly estimate the composition of the vapor space    mole frx in the vapor = vapor pressure/total pressure at the T & P