6 replies to this topic

[Ritesh Suratwala]

Hi all,

I am performing one excersise on CDU/VDU system simulation and asking your suggestions for good system design.

My points are...

1. Literatures shows GS and BK are suggested thermodynamic models for CDU/VDU system. However I would like to know your suggestions if any of you have experience on this simulation front.

2. Normally we get crude assay upto 70-80% of crude fraction only. This force simulator to predict balance fraction of crude assay and sometimes mis-lead to problem. It may predict falls results mainly for VDU column bottom. How to go about in this situation?

3. I have never simulated vacuum system, so if you have any special tips for vacuum system simulation (like thermodynamic model etc.), let me know.

These are few of the points to share, but I would like to utilise your experience regarding CDU/VDU system simulation that can add to my knowledge.

Thanks.

[joerd]

1. GS is traditionally used for the vacuum column. You'll need (sour) SRK or PR for the overhead system.
2. There is no good way of predicting without data. The only thing I can say is that you need to get better assay data.
3. We commonly have the vacuum system designed by the vendor. The column pressure is fixed, and we add an "air" stream to simulate air leaking in through the flanges (but which also simulates the light cracked components generated in the furnace). This is just a small nitrogen stream entering near the feed tray.

[StealthProg]

You need to get a more detailed assay done if its for vacuum design. Otherwise you can not estimate with any accuracy what the yields will be especially if your going for a deep cut design. A portion of the super heavy material does not boil at any temperature before cracking and extrapolating a curve to the 'end of the assay' is entirely theoretical.

[Padmakar Katre]

Hi all,

I am performing one excersise on CDU/VDU system simulation and asking your suggestions for good system design.

My points are...

1. Literatures shows GS and BK are suggested thermodynamic models for CDU/VDU system. However I would like to know your suggestions if any of you have experience on this simulation front.

2. Normally we get crude assay upto 70-80% of crude fraction only. This force simulator to predict balance fraction of crude assay and sometimes mis-lead to problem. It may predict falls results mainly for VDU column bottom. How to go about in this situation?

3. I have never simulated vacuum system, so if you have any special tips for vacuum system simulation (like thermodynamic model etc.), let me know.

These are few of the points to share, but I would like to utilise your experience regarding CDU/VDU system simulation that can add to my knowledge.

Thanks.

Dear,
First of all let us know what simulator you are using? is it Pro-II by Sim-sci or Aspen Hysys. In case of Pro-II use GS for CDU and BK10 for VDU, but if you are simulating CDU/VDU as a whole go for GS, I did it in past and validated with the plant test run parameters. If you are using the Aspen-Hysys or Aspen-RefSys (preferred for refinery system as you can get an advantage of the Spiral's Crude Manager software as add-on extension and get the extra data needed) use PR. There is another option there with Hysys to characterize crude with Neotec Black oil method and transit the stream to PR in simulation main environment. Apart from this there are plenty of things you have to consider while simulating the system, since it's a huge system and much of heat integration, product quality, certain specific requirements and all. Let us know these things and we can further help you along your simulation progresses. Some points as below to consider,
1.Proper crude characterization,
2. Identifying the key parameters coding the main fractionator theoretical trays and relative locations of the side stripper liquid inlets and vapor outlet return trays, PA from and to trays, Heater COT, flash zone conditions, column pump arounds and overhead condenser duties.
3.Column Delta P.
4.Column operating pressure optimization.
5.Stripping steam rates to main fractionator bottom as well to side strippers in case if they are steam stripped.
6.Side stripper theoretical trays.
7.Transfer line Delta P. (COT and Flash Zone temperature limits)
The same point applied to VDU as well some additional points,
1.Stripping steam rate (accuracy needed as it has major role in column diameter)
2.Fractionator top Pressure and vacuum system
3.Coil steam rate, air ingress (You will find some guidelines in Ludwig)
4.Bottom Quench flow
I hope you can start now and tell us if still find some problems, we are here to guide you.

[Zauberberg]

This thread is 5 years old and there is no point in replying further.

[Padmakar Katre]

This thread is 5 years old and there is no point in replying further.

Dear Zauberberg,
True agreed. Actually I was just finding the new contents and saw the thread has the latest reply of 19th Dec 2010 rather seeing when thread was started. I hope there are plenty of people who search on Google related to CDU/VDU simulation and they can find some info here. Hope you have a nice time there.