2 replies to this topic

[Miguel]

Hallo,

 

 

This is my first time doing a depressuring calculation. I am trying to calculate the time required and maximum flowrate possible for the depressuring of a pressure vessel from 32 bar to 5 bara to a tank, controlled by a pressure control valve (PCV). The depressuring is regulated through a PCV which has an outlet pressure of 4 bara with a CV at maximum opening of 30.

 

 

The medium to be depressurised is a mixture of Methanol and N2. The process is intended to be kept isothermal by external heating @150 °C.

 

 

For my calculation steps i have firstly assumed a depressuring time of 15 min resulting in a constant pressure drop of 1,8 bar /min (Pinitial-Pfinal/15min). I have max volume of MeOH of 15 tons (1 ton/min).

 

 

Separately i have calculated how much MeOH gas can flow through my control valve at the different time points scenarios, with this information i can then calculate how much time it is required to depressurize per step (each step 1,8bar/min calculation ).

For example, pressure drop from 28 to 26,5 bar a. maximum flow allowed through control valve 3,38ton/min, this results in 1t/min /3,38ton/min which is 0,29 mins.

 

 

- First of all i would like your advice if the calculation process is in the right direction.

 

- I am having trouble determining the right amounts of Methanol which are to be sent in vapor form to the control valve. According to my calculations methanol evaporates @150 ; 14 bara. What happens with the MEOH during the beginning of the depressuring process? i assume that it is in equilibrium with N2 and a small fraction of MeOH is relieved in gas through the control valve to the tank. If the temperature is maintained constant the main part of MEOH should start to evaporate at 14 bar, how could i calculate this ?.

 

-Could you give me orientation on how to calculate the depressuring of a vessel?

 

 

I unfortunately do not have the Hysys depressuring utility, for this calculation, therefore i am trying to do everything manually. This is no typical emergency depressuring scenario, but rather a depressuring of a pressure vessel to another vessel using a control valve at full openning.

 

 

thank your for your advice

 

 

Edited by Miguel, 24 February 2014 - 04:10 AM.

[ankur2061]

Miguel,

 

I have posted a spreadsheet for time-dependent depressuring of gas from a pressure vessel. Do not get confused by the word 'hole' used in the spreadsheet. Ultimately a control valve opening is a 'hole' only.

 

One input that would certainly be needed will be the cross-sectional area at 100% control valve opening which you will need to find out separately. In the input section of the spreadsheet, the opening or 'hole' size is mentioned as diameter.

 

Provide below is the link for the spreadsheet:

 

http://www.cheresour...through-a-hole/

 

Regards,

Ankur.

[Miguel]

Thank you Ankur, i will take a look at it, and come back to you

 

regards,

 

Miguel