Page 61 - Process simulation and control using Aspen

2

C H A P T E R

Aspen Plus Simulation

of Reactor Models

2 . 1 BUILT-IN REACTOR MODELS

In the Aspen Plus model library, seven built-in reactor models are available. They
are RStoic, RYield, REquil, RGibbs, RCSTR, RPlug and RBatch. The stoichiometric
reactor, RStoic, is used when the stoichiometry is known but the reaction kinetics is
either unknown or unimportant. The yield reactor, RYield, is employed in those cases
where both the reactions-kinetics and stoichiometry-are unknown but the product
yields Eire known to us. For single-phase chemical equilibrium or simultaneous phase
and chemical equilibrium calculations, we choose either REquil or RGibbs. REquil model
solves stoichiometric chemical and phase equilibrium equations. On the other hand,
RGibbs solves its model by minimizing Gibbs free energy, subject to atom balance
constraints. RCSTR, RPlug and RBatch are rigorous models of continuous stirred tank
reactor (CSTR), plug flow reactor (PER) and batch (or semi-batch) reactor , respectively.
Eor these three reactor models, kinetics is known. RPlug and RBatch handle rate-
based kinetic reactions, whereas RCSTR simultaneously handles equilibrium and rate-
based reactions. It should be noted that the rigorous models in Aspen Plus can use
built-in Power law or Langmuir-Hinshelwood-Hougen-Watson (LHHW) or user defined
kinetics. The user can define the reaction kinetics in Fortran subroutine or in excel
worksheet.
One of the most important things to remember when using a computer simulation
program, in any application, is that incorrect input data or programming can lead to
"
solutions that are " correct based on the program's specifications , but unrealistic with
regard to real-life applications. For this reason, a good knowledge is must on the reaction
engineering. In the following, we will simulate several reactor models using the Aspen
Plus software package. Apart from these solved examples, interested reader may
simulate the reactor models given in the exercise at the end of this chapter.

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