I am trying to model water gas shift reactor on Aspen using an Rgibbs reactor. Unfortunately whenever i pass the stream into the reactor(HTS) the amount of CO and H2 both are increasing and C in the system is not balanced. Aspen is not prompting an error regarding elemental balance not being intact. I am confused what should I do

  • $\begingroup$ You should really provide more information. What is the state of the feed stream? What thermodynamic model are you using? What is the state of the reactor. These things will affect the results of rgibbs. $\endgroup$ – Salomon Turgman Mar 26 '18 at 19:35

Without knowing too much about Aspen (I've been looking for a chemical engineering modeling software, so thank you), the documentation data says RGibbs doesn't pay attention to stoichiometry:

The (Rgibbs Reactor) provides reaction calculations without the need for detailed stoichiometry or yield. The calculations are based on minimizing the Gibbs energy for the system as discussed in page 98"

This reactor is intended for systems where the exact reactant composition is unknown but the energy is, such as "crude oil" or "natural gas". As such, this reactor won't notice a change in C concentration. It is probably adding the additional thermal energy to change the concentration of the higher thermal energy products, CO and H2, as it is ignoring the Redox mechanism that would force the consumption of CO to generate CO2 to form H2. A better reactor would be the REquil:

When one or more reactions involved are equilibrium reaction, the REquil block can be used. The block requires knowledge of the reaction stoichiometry, and performs chemical and phase equilibrium reactions.

Using this method would be a better model as the equilibrium constant's dependence on temperature is well documented:

$$K_{eq} = exp(-2.4198 +0.0003855T + \frac{2180.6}{T})$$

Where $T$ is in Kelvins, from the range of 600K - 2000K.


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