6 replies to this topic

[jprocess]

Dear All,
When doing column simulation, which parameters do you consider to set the coumn specifications and help the simulator for faster convergence?

[Zauberberg]

Hello jprocess,

Based on my distillation modeling experience, I think it strongly depends on type of application and available data from process plant, which can serve as model input basis and column convergence specs. Model setup can be quite different, depending on whether you are trying to simulate simple component splitter (De-C3 or De-C4 tower, for example) or complex distillation systems with multiple product draw-offs and pumparound circuits.

However, as a rule of thumb, I observed few things which make the accuracy and convergence of the model extremely difficult:

1. Specifying tower bottoms product flow rate
2. Specifying physical properties of (any) product
3. Setting non-realistic values for tray efficiency

In addition, feed characterization is very important issue. This is not a problem when you have a mixture of true compounds, but it can make your life miserable if you are dealing with various petroleum cuts. Never rely on ASTM D86 distillation, that I can say for sure.
Furthermore, ensure that plant data (temperatures, pressures and flows) are consistent and verified in some kind of plant performance test prior to using them in simulation flowsheet.

Best regards,

[smuk]

Hi JProcess

I think this will depend on the simulator. I have used chemsep for simple multicomponent distillation column. Apart from feed compostion and pressure/temperature, you need to specify reflux ratio and bottom flow rate. Convergence is obtained in less than six iterations. The software takes 10 components and upto 150 stages. The free version can be downloaded from chemsep.org.

Have fun

smuk

[Zauberberg]

You can get HYSYS model convergence in less than 5 or 6 iterations - depending on how stringent are column specs and what is the required accuracy of tower model. But don't forget - it is NOT the simulation software who does the work, it is you. Software is just the tool and - full stop.

If you want your model to give you true data, don't feed it with garbage. Garbage will just come out.


Best regards,

[eilpar]

Hello,

In general I find that specification of product flow rates (all except one) and RR is the simplest specification. I found that it converged in almost all cases. Product purity and recovery are conflicting, so specify one of them. There are several combinations possible (as seen in HYSYS, PRO/II manual) and it depends on what you are looking for. My suggestion is that you go for simpler specification initially to narrow down the operating points and then go for the tough specification to facilitate convergence.

Best wishes

PAR

[dany Oblitas Sotelo]

Hello, I am Peruvian student.
If these using a simulator, are very easy.
for example Hysys.
1ª work with a Shortcut specifying the Keys light and heavy, Pressure of the condenser and reboiler. and an supposed relux ratio, thus you will obtain the number of plates, plate of feeding and reflux

2º with this data from shortcut and soon you use a column.

I hope to have served as aid if what you need it is to design a simulator for distillation write me to ddanielos@hotmail.com.

bye

this is a binary destilation in excel with macros

Attached Files

•  destilacion_exam2.xls   345.5KB   101 downloads

[mohammad reza]

for simulation of column and in order to reach good result it is neceassry to consider following items in secunce:

1. Set the top pressure

Regarding to available utility in the plant and aslo nature of process. for exapmle when you want to design of De-ethanizer tower in LPG recovery unit, regarding to mentioned subject pressure of it maybe vary from 32 bar up to 15 bar.

2. Feed Location

Regarding to your Specification of you Product, to reach the best poit for feed tray location, it is necaaasry to optimize Duty of Reboiler & Condensre.


Mohammad reza