Simulations on the liquid-phase absorption of NO

There is a huge difference between using only a reactor and also a distillation tower; radfrac should be used to set up reactive distillation

Reply to 2# dawnchuck: Reactive distillation? Is it about adding chemical reactions in RADFRAC? I don’t know much about the tower; there are no exact figures. How are the number of trays and the size of the tower determined?

The number of plates and other parameters are determined through simulation and trial and error; the size of the tower cannot be determined by Aspen. Are you planning to convert NO into nitric acid? All of this requires data obtained from pilot or scale-up experiments.

Reply to 4# dawnchuck: Well, it’s mainly due to chemical reactions. If the kinetic parameters of the reaction have been set, is it possible to specify only the reaction time without setting the size of the tower?

For now, it seems that the dynamic parameters cannot be found

Reply to 5# Yihe: Define the reaction and its kinetic parameters in the reaction section, and then call this reaction from the Radfrac section. For a reactive distillation column, first determine which trays are involved in the reaction; in this case, it should be all of the trays. It is possible to define the conversion rate for each tray. If it is assumed that the conversion rates are identical, then no values need to be set in the column – in such cases, the conversion rate specified in the reaction section is used directly. For example, if 50% is set as the conversion rate in the reaction section, then each tray in the distillation column will have a conversion rate of 50%. Note that the overall conversion rate of the column will be greater than 50%, with the exact value depending on the number of trays. 2. Use the holdup mode; this is likely the calculation method desired by the original poster, which calculates the conversion rate based on the residence time set for each tray.

This post was last edited and replied to by Recalling the Lotus on 2010-10-8 at 12:41. Reply 7# dawnchuck (Check the post below; this one doesn’t cover everything). Thank you for such detailed guidance. :) I still have some doubts regarding the conversion rate issue. Since several reactions take place in the tower, how can one determine its conversion rate on each tray? If 50% is set in the reaction, does it mean that the conversion rate for each reaction on each tray is 50%? Also, when setting up the reaction, there are two parameters: holdup and residence time. What is the difference between them?

Reply to 7# dawnchuck: Thank you for such detailed guidance. :) I still have some doubts regarding the conversion rate issue. Since several reactions take place in the tower, how can one determine its conversion rate on each tray? If 50% is set in the reaction, does it mean that the conversion rate for each reaction on each tray is 50%? Also, when setting up the reaction, there are two parameters: holdup and residence time. What is the difference between them? There’s one more thing I don’t understand: why is it necessary to specify both the reaction conversion rate and the conversion time? Because if the conversion rate and the number of theoretical plates are given, then the conversion rate of the overall reaction can be determined. And how can one use the conversion time to calculate the conversion rate?

Regarding the issue of conversion rates, I have conducted some research on this topic and have gained some insights, which I would like to share here. Please feel free to point out any mistakes. 1. In Aspen, there are two places where conversion rates can be entered: one is during the definition of the reaction. However, this approach is too simplistic; in reality, the conversion rates vary for different reaction stages in a distillation column. In such cases, it is possible to specify the conversion rate for each individual tray within the column. 2. If conversion limits are specified for certain trays in the tower, then the set values in the reaction are overridden, and they only apply to the trays in the tower for which no conversion limits have been specified. 3. Only the conversion rate per tray can be specified; the overall conversion rate of the entire tower is calculated based on that of each tray. The formula is quite simple. Let’s derive it briefly: assuming that the conversion rate is the same for each tray, we have Cao(1-x) = Ca1 and Ca1(1-x) = Ca2. From this, it follows that Cao(1-x)^n = Can. Once Can is determined, the overall conversion rate of the tower is (Cao – Can)/Cao. Those who have studied reaction engineering know that this approach does not take into account the issue of reaction order at all. In fact, the conversion rate for each tray is determined by the initial concentration Ca on that tray and the reaction time; setting a fixed conversion rate is essentially a simplified method. For greater precision, one needs to use the terms \"hold up\" or \"residence time\"; in reaction engineering, these correspond to the concepts of space-time and residence time respectively. The tray flow rate = hold up/residence time. In this way, Aspen can calculate the conversion rate based on the known reaction time, the calculated Ca value for each tray, and the reaction order specified in the reaction. Note that the calculation of the overall tower conversion rate here is somewhat complex; it is equivalent to a series calculation using CSTR reactors. As a brief hint: assuming it is a first-order reaction, t1 = X1/, and t2 = (X2 – X1)/. Here, t represents the residence time on a single tray. If t1 = t2, then X2 = X1² – 2X1 + X1 = 0; from this equation, X2 = 2.5 can be determined. If there are multiple reactions occurring simultaneously on a single tray, the situation becomes even more complex, depending on whether these reactions occur in parallel or in series. For the specific calculation methods, refer to textbooks on reaction engineering – this requires some knowledge, and I need to consult books to recall them. If these reactions are unrelated to each other, then it’s no different from a single reaction.

Reply to 10# dawnchuck: Dude, I’m currently working on a desulfurization simulation, and it’s really tough. I’d like to ask you some questions. My email address is shikm1984@163.com