2 replies to this topic

[shvet]

Hi, forum

 

Is here anybody who works/worked in Aspen Plus and Aspen EDR v. 8.X? Could you help please or may be you know any dedicated forum? Any thoughts / reply would be greatly appriciated.

 

I started to simulate an existing distillation column and I have some trubles and questions.

 

1. I use "HeatX" block in Aspen Plus for existing condenser (air cooled) check. I made air cooler model in Aspen EDR and linked this EDR-file with HeatX block in Aspen Plus. As I understod I can't specify inlet temperature and LMTD in Aspen Plus. Instead of this I have to specify air flow and inlet temperature. Is this right. Or I can't notice any obvious thing?

 

2. Who can help me with RadFrac block? Question is about option lists "Trays Rating" and "Efficiencies". How are they interconnected? If I specified real trays in "Trays Rating" how does it affect on option list "Efficiencies":

- does Aspen Plus calculate tray efficiency according to "Trays Rating" inputs and "Efficiencies" unputs are ignored?

- or Aspen Plus calculates tray efficiency according to "Trays Rating" inputs and in addition corrects them according to "Efficiencies" unputs?

- or Aspen Plus does not calculate trays efficiencies and just applies user's inputs from "Efficiencies"? Then what about this parameters?

 

3. Did anybody try to connect reboiler to column using HeatX block and EDR-file. I connected column with HEatX block as reboiler but Aspen Plus again and again increases inlet flow to reboiler up to infinity. If I connect column reboiler with HeatX block using pseudostream all is OK, but in this way I have to specify vapor fraction in reboiler outlet. This way is not so good because I can't see reserve of area in heat exchanger.

 

4. Can block "Design Specifications" work well? What have I to do to force it not only to increase variable but for example to change it on sinusoid?

 

5. Has anybody met this kind of bag - this button does not work at all? Some kind of "Error with ActiveX ..."

 

6. Can Aspen EDR (and HeatX block in Aspen Plus) allow to specify different numbers of rows in one bundle? For example I have this layout of tube rows in air cooler - 3+2+1. But as I understood Aspen EDR can't adjust such structure.

[Pilesar]

My thoughts for what they are worth:

1. I would model the column in AspenPlus with an integrated condenser and reboiler. This will be much easier column to converge. Use Pseudo streams to get the composition, conditions and flow rate of the feed stream to the exchangers. The column calculates the duty, so put the pseudo stream to an exchanger and specify the duty. You can add air at the inlet conditions for the cold stream of the exchanger and vary the quantity until you get a reasonable outlet air temperature. The air flow is just a guess that you will iterate to solution in EDR.

2. 'Trays Rating' and 'Efficiencies' are not interconnected. Tray rating is done after the column is converged. Efficiencies are used when converging the column. AspenPlus does not calculate trays efficiencies and just applies user's inputs from 'Efficiencies'. (I could not view your 'parameters' link.) I recommend you use theoretical stages in your model and avoid the 'Efficiencies' input completely.

3. See point 1 above. Use pseudo streams. Yes, you have to specify vapor fraction in reboiler outlet, but you can go back and update this after EDR calculates vapor fraction based on piping and exchanger dimensions.

4. 'Design Specifications' works pretty well if you know what you are doing. Consider using the Calculator block to model complex variable responses. Design Specifications can use a Calculator result in the calculations.

5. I could not view your button link.

6. Aspen EDR has limitations, of course. You can get advice from their Help Desk or try to work around the limitations by modeling something similar and using engineering judgment to assess accuracy.

[shvet]

Thank you a lot, Pilesar