A question about distillation simulation
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When simulating the distillation column (for calculations), I can achieve the desired separation effect by adjusting the number of theoretical plates (which yields results similar to those in the given process package, regarding the light and heavy components). However, the temperature at the top of the tower is much different. For example, the actual number of plates is 24, while the ASPEN theoretical number of plates is 6; the composition of the materials at the top and bottom of the tower as well as the packing data are roughly the same, but the temperature at the top of the tower differs significantly. What causes this? Is it true that the greater the number of trays, the greater the heat transfer loss, and that this is not reflected in the ideal model? If that’s the case, how should it be resolved? Thank you!
The question is too general. What are the pressures at the top and bottom of the tower, and are they equal? Also, by \"almost the same,\" how much of a difference does that mean? Moreover, the process package data you mentioned is very likely theoretical data as well; so where does the concept of heat loss come from? It would be best to provide the data along with the ASPNE model so that everyone can analyze and discuss it
The pressure and everything else are the same. The data in the package shows 1.7 degrees; my simulation indicates around 7 degrees. I can adjust the number of theoretical plates so that various parameters such as the pressure components at the top and bottom of the tower remain consistent with those in the package, but only the top temperature data will differ. Strangely, the first tower has basically identical values for all parameters (with an error of less than 2%), while the temperature at the top of the second tower differs significantly. It simulates the ethane-propane/propylene separation (main components). Ethane is the light component, and the rest are considered heavy components.
How about adding a few more distillation plates? Increase it up to 1.7°C at the top of the tower, and see whether the error is smaller or larger compared to that in the process package; if it’s smaller, it indicates that the composition still has an impact, while if it’s larger, the accuracy of the process package should be questioned
I admire the expert! I tried it using your method; by increasing the number of theoretical plates, it is indeed possible to bring the top temperature closer to the target value of 1.7 degrees, but the composition becomes worse as a result. I believe you are right, but I still don’t quite understand the details of it. Could you give me some guidance?
But the worse the composition, the greater it becomes. ?Is the difference between it and the process package growing larger? The boiling point is related to the composition; the more theoretical plates there are, the higher the content of the light components. For a given amount of distillate, the higher the content of light components, the lower the temperature at the top of the tower
When both the reactor and the top of the process package were producing 1485 KG/H of ethane, the temperature at the top of my model was 6.9 degrees, while it was 1.7 degrees for the process package. When I increased the number of theoretical plates so that the top temperature was 1.7 degrees, the proportion of the light component ethane in the overhead distillate was much higher than the value given in the package (by nearly 15%). Does it mean there is an error in the data inside the package?
It’s possible; the process package may not be entirely correct either. Of course, first you need to verify whether your input parameters are correct, such as the equation of state, and it’s best to consult some literature on the topic
Perhaps the model built is not exactly consistent with the package.
It should be consistent; there’s no problem with the first tower. It’s the second one, alas. Take another look