Newbie seeking help with the selection of property methods for ammonia synthesis in Aspen and regression of interaction parameters
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This post was last edited by Spring Orange on 2009-10-21 at 18:29. I studied mechanical engineering, but now I have switched to chemical engineering; as a result, I am not very familiar with many concepts in chemical thermodynamics. For my graduation project, I used ChemCad and Aspen to simulate the ammonia synthesis process. My questions are as follows: 1 For a polar molecule like ammonia, is it inappropriate to use the RKS property method for simulation? Is it more accurate to use activity coefficient methods such as Uniquac, Unifac, Wilson, and NRTL? But a doctor in the department told me that in this process, it doesn’t matter whether the molecule is polar or not. Is what he says correct? 2 The gases simulated are all very simple and common low-boiling-point gases, such as N2, H2, CH4, NH3, Ar. However, the interaction parameters for models like UNIQUAC and NRTL for these gases are virtually not available in ChemCAD and Aspen, nor can they be found in DECHEMA’s data collection. Why is this? 3 If I want to use the gas-liquid equilibrium data from the literature to regress the UNIQUAC interaction parameters for this 5-component mixture, can I simply enter the gas-liquid equilibrium data for each pair of components in Aspen to carry out the regression? Or is it necessary to have the gas-liquid equilibrium data specific to this 5-component mixture? I’ve been using ChemCAD and Aspen for less than 2 weeks, so the questions I ask might be rather naive and stupid; please feel free to offer your guidance.
For the property-based methods of ammonia synthesis, you can refer to the built-in example ammonia.bkp in Aspen
For the ammonia synthesis process, property equations such as BWR and SRK can be selected.
This post was last edited by hu688 on 2009-10-22 at 10:45. The ammonia.bkp file included with Aspen seems to be an example of ammonia dissolved in water, and the property method used is ELECNRTL
Thank you, guys from LS. Who can answer my question 3?
The example included with 4# hu688 Aspen V7.0, namely ammonia.bkp, is a comprehensive process example related to gasification, purification, methanation, and ammonia synthesis. The ammonia synthesis uses RKS-BM
5# Spring Orange: The UNIQUAC method is not suitable for these gases. Local constitutive equations are suitable for medium- and low-pressure non-ideal solutions, while equation of state is more appropriate. The binary interaction parameters for VL of NRTL/UNIQUAC are effective for predicting the vapor-liquid equilibrium of multicomponent mixtures. If there is no vapor-liquid data for a pentavalent component, binary interaction parameters can still be used; however, having data for the pentavalent component yields more satisfactory simulation results.
Ammonia synthesis is a high-pressure process – why isn’t predictive thermodynamics PSRK used?
Could you please tell me how to view Aspen’s built-in examples? Thank you for your help!
Reply to 9# A Pine tree – open---favorite; there are quite a few examples available there, worth taking a look at.
Support is good. . . . . . . . .