14 replies to this topic

[evvrista]

Hello, I am currently doing my master's thesis and I am simulating a vacuum column for a petrochemical process. Now I am trying to simulate the head vacuum system made up of 3 exchangers (working with vacuum pressures) in order to study the influence of the flow rate and the temperature of the water used as cooling liquid in the column vacuum. I am using Aspen HYSYS and I see that it is not possible, when configuring the exchangers with vacuum pressures they do not work for me. I am absolutely not going to include the ejectors in the simulation because from what I have been reading they are even more complicated and I cannot even find them in Aspen Hysys v.11. Still could someone provide me with some insight on this? What I can do?

 

 

Evvvrista.

[SilverShaded]

Typically the ejectors pull the vacuum, the exchangers condense the steam/vapours, unless there is a pre-condenser in which case the condenser is helping to pull the vacuum. 

There is an ejector model in Hysys its an extension model you can download from the AT website or i think in recent versions it may have been included.  It's not perfect being based on some simple correlations from perry.  The main effect of cooling water temperature is on the pressure you can condense the vapours at.  You don't say whether it has a precondenser or not which makes a huge difference to what your trying to model.  If there is a pre-condenser then column top pressure is strongly related to cooling water  temperature (dew point - some allowance = cooling water temp).  If its a more modern design with no pre-condenser than pressure is more a function of ejector performance.

 

Edited by SilverShaded, 24 March 2023 - 04:02 AM.

[evvrista]

Sorry, I should have explained better. All three are heat exchangers but effectively the first one acts as a precondenser. In other words, it would not be connected to the ejector system. In this first, the hydrocarbon remains are mainly eliminated and on which the vacuum generated in the column mainly depends. But I don't know how to simulate that system. What equipment should I put? I think it would not be necessary then to simulate the ejectors. I want to do a case study of the influence of temperature and water flow in the vacuum of the column but I don't know what equipment I should put so that it doesn't give me problems.

[SilverShaded]

The problem is you won't condense everything in the pre-condenser, therefore the performance of the ejectors does matter.  The warmer the precondenser, the more vapours the ejectors have to deal with, performance drops and column pressure will increase.

[breizh]

Hi,

A sketch will save words and help to understand.

my 2 cents

Breizh

[evvrista]

Sorry I don't know why I can't share the photo. Click the following link to see or download it:

 

https://umubox.um.es...I5Wbrayt971fguv

 

 

This is a very simple diagram of the vacuum system, is it well understood? How would you do it with aspen hysys?

Edited by evvrista, 27 March 2023 - 12:45 AM.

[evvrista]

Plis, can someone help me?

[Pilesar]

Review the previous responses from this site. https://www.cheresou...-in-aspen-plus/

[breizh]

Hi,

On top of what is shared by Pilesar , consider this document from Graham which should give you some hints on the process side.

Good luck

Breizh 

[SilverShaded]

Its only an academic excerise in effect of temperature on vaccum perfromance you will need to model the ejectors.  Go to the AT support site and download it.  Its not hard to use and good enough for what you are doing.  Alternatively, there are publicay available papers which give the fluidynamics of modelling ejectors, which can be added to Hysys as an extension model  using some appropriate prgramming langauge. VBA/VB.NET/C# etc...

[evvrista]

Thank you so much! Firstly, I'm going to try to get the access to the expansion. But apart from that what can I do to work with a vacuum condenser? Is there any option in hysys for it?

[SilverShaded]

Thank you so much! Firstly, I'm going to try to get the access to the expansion. But apart from that what can I do to work with a vacuum condenser? Is there any option in hysys for it?

 

Depends what level of detail your looking for.  You could use a simple cooler, or use a rigorous EDR representation of a real exchanger (you will need the geometry). 
 

[evvrista]

If I use a rigorous EDR representation is it possible to configure a vacuum condenser? Because I'm not being able to work under atmospheric pressure

[SilverShaded]

Set the pressure, maybe you need some basic hysys training?

[breizh]

Hi,

Let you google :hysys vacuum distillation column.

You will find tutorials.

Sorry I cannot offer more.

Breizh