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Depressurization Rate


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#1 farid.k

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Posted 28 September 2016 - 01:51 AM

hye guys.

 

just want to know on how to calculate depressurization rate calculation. I've tried to searched but not so clear on calculation methodology and most of them using simulation like HYSYS.

 

the condition is like this, I have hydrogen cylinder with 50 liter capacity at 200 barg. This Hydrogen cylinder need to supply to reactor which operate at 36 barg with consumption maximum 200g/h.

 

How to know how long the cylinder can supply the H2 gas? personally just calculate how long the time it takes to drop pressure from 200 barg to 36 barg.

 

anyone can advised previous link/example/how to simulate using HYSYS

 

 



#2 breizh

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Posted 28 September 2016 - 02:01 AM

Hi Farid ,

Let you consider the search engine in this forum . This topic has been discussed several times .

If I remember well , same discussion at Chemwork .

 

Hope this helps

 

Breizh



#3 farid.k

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Posted 28 September 2016 - 04:12 AM

most of them discussed about the blowdown sizing using hysys. nevermind, I will try to search again.



#4 MrShorty

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Posted 28 September 2016 - 01:34 PM

Is there enough information given to solve the problem? You list a maximum rate of H2 consumption (200 g/hr). Is that close to the typical flow rate? Or are you considering a "worst case" scenario (how long will the H2 last at the maximum flow rate?)?

 

As phrased, you are asking about calculating how quickly the pressure drops -- you want to find dP/dt. Could you do something like:

 

Choose your favorite EOS for H2. P=f(T,V,m)

from EOS, you should be able to determine dP/dm

take your given typical or maximum (or other desired) mass flow rate -- dm/dt

Chain rule should allow you to compute the rate of change for the pressure dP/dt=dP/dm*dm/dt

Integrate dP/dt between Pmax and Pmin to get total time.

 

If I were looking at this problem, I would wonder if the rate of change in pressure is really that important. I might solve the problem like this:

From EOS, compute m H2 at max P, T, and V

From EOS, compute m H2 at min P, T, and V

The difference of those two is the mass of H2 available to the reactor

from typical or maximum or other mass flow rate, determine time needed to consume the available mass of H2. This computation would usually assume that dm/dt is constant, independent of pressure (only you would know if that is a good assumption). If that is a good assumption, then this is probably simpler than the previous.



#5 walidd_23

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Posted 29 September 2016 - 03:21 AM

Hi

 

you can use Depressurization Utility in Hysys  to see  the flow rate Profile, put the back pressure as 36 barg, the time required is when the pressure of vessel stabilize to 36 barg. However the maximum Flow rat is depended directly with the valve CV (orifice area) that must  be selected to achive 200 g/h as maximum flow rate.

 

 

Regards

 

 

Walid 



#6 farid.k

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Posted 29 September 2016 - 05:48 AM

Hi

you can use Depressurization Utility in Hysys to see the flow rate Profile, put the back pressure as 36 barg, the time required is when the pressure of vessel stabilize to 36 barg. However the maximum Flow rat is depended directly with the valve CV (orifice area) that must be selected to achive 200 g/h as maximum flow rate.


Regards


Walid

Yea, i tried to do so but still got error as i don't have experience in depressuring modelling in hysys. I quite not clear on how to set the parameter especially cv of the valves..

#7 serra

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Posted 30 September 2016 - 07:51 AM

it is basic thermodynamics as discussed by MrShorty,

you know Initial mass (t1, p1) and final mass (t2, p2) of hydrogen in cylinder,

at each time step you know P, T (in cylinder) and P (delivery)

if you wish to model a CV there are ISA formulations,

perhaps a good book of thermodynamics could be more useful than a operating manual of a software...



#8 aqassam

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Posted 30 September 2016 - 02:38 PM

Disclaimer: I work at AspenTech

 

We just released a new technology here at Aspen Technology that is easier to use than HYSYS DPU (my opinion, obviously). We have a video and lots of content on how to use this at support.aspentech.com. 

 

If you want to use DPU, support.aspentech.com also has content to show you how to use the tool. 

 

Of course -- you can get any tool to tell you anything. So you should do your research (read API 521, CCPS, and other guidelines out there to get a background on the phenomena of depressurization). 

 

Also, we have an upcoming webinar that will show exactly how to use this tool (it is more rigorous, and more complex than DPU).  I recommend checking out the recording (now posted)

 

http://www.aspentech...wn-oct/?src=cer


Edited by aqassam, 03 November 2016 - 11:21 AM.


#9 ezralh

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Posted 12 January 2017 - 10:05 AM

Salam Farid,

 

This how I calculate

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