11 replies to this topic

[Steve90]

Hi everybody !!

 

I'am simulating an LPG extraction unit from Natural Gas in Aspen Hysys Software but the deethanizer don't want to converge .

 

The specification for the deethanizer are :

 

Component recovery propane 0.93 mole% in reboiler

 

component ratio methane + ethane / propane 1e-5 in reboiler

 

HELP please !!

 

A copy of simulation has been attached !

 

NB :I'm using HYSYS V8.6;

 

I created a Mega file cos i couldn't upload the hysys file :

 

https://mega.co.nz/#!9oUhwLJI!a2ghkjT2B22Mw_DdqH6sSoxDPnFv-db8bNuEDXVQDZ0

[Zauberberg]

You are using the newer version of Hysys than I do. Can you upload the XML file?

[Steve90]

You can find here the XML fIle :

 

https://mega.co.nz/#!0wlDgDxY!mFo26hWBXEL9F5bBCrkA54Uki_zSmr4ZGxIUt6WveDI

[mr-arbdoul]

i am little confused i used aspenone v8.4 to view your simulation but some part didnt appear

[Steve90]

I don't know i uploaded the full simulation with the unconverged deethanizer column ! which part didn't appear ?

[Zauberberg]

For some reason my Hysys crashes when I try to open this XML file. You can try the following with the model:

 

- Remove the spec for C1+C2 ratio in the reboiler. You already have the compositional specification for reboiler (0.93% C3) so forcing the column to satisfy both compositional specs will result in non-convergence.

 

- Try to use another specification, which may be e.g. % C3 in column overheads. If this does not work, try playing with the % C3 in reboiler and tower temperatures in the top section. Once you get the model converged, it is much easier to play with specifications.

 

Let us know where you landed.

[Steve90]

Thanks Zauberbeg !! Before trying the proposed solutions ! i want to clarify that hysys indicates that two liquid phases were found in  the top stream leaving the deethanizer and which is blue (converged) but the entire column is yellow !!

Is this helpful for you to find a solution using my specifications ?

[Zauberberg]

Occurrence of two liquid phases inside the tower is not a showstopper for convergence of the model, but it has made me curious. You can double-click on the column and check liquid composition on each tray. De-C2 feed stream should be water-free. Even if in reality you have 1ppm water or less, you should completely remove water from the column feed stream. Perhaps this is the problem. If the second liquid phase is hydrocarbon, let us know what it consists of.

[Steve90]

you can find here the feed composition :

 

CO2               1,615e-003
Nitrogen         1,188e-003
H2O                9,488e-004
Methane         0,205
Ethane            0,130
i-Butane          8,76e-002
n-Butane         0,1635
i-Pentane        7,911e-002
n-Pentane       7,064e-002
TEGlycol         2,907e-005
n-Hexane        5,209e-002
Propane          0,206

 

and the conditions :

 

Vapour / Phase Fraction    0,1209
Temperature [C]                 -28
Pressure [bar_g]               15
Molar Flow [kgmole/h]    28,993
Mass Flow [kg/h]             1344,3839

[Zauberberg]

I think Glycol and Water are causing this issue. You can remove them from feed by using split unit operation. The problem should disappear afterwards.

[Steve90]

Thank you very much i removed water from the feed stream and the column converged !

[Zauberberg]

By the way, the De-C2 tower pressure seems unreasonably low. These systems usually operate at 30-35 barg. What is the reason for choosing 15 barg for operating pressure?