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Authors: Vincent Kenny [2015] and Stephen Lenzini [2015]

Steward: Jian Gong and Fengqi You



Process simulation is extremely beneficial to engineers, allowing them to further understand the process, identify process advantages and limitations, and provide quantitative process outputs and properties. Modeling reactors and their corresponding reactions is difficult by nature but can be rewarding if done correctly. This page provides essential information on the topic of reactor simulation using the computer program Aspen HYSYS.

Aspen HYSYS Reactor Simulation Basics

The HYSYS program allows the user to define reactions primarily based on desired model outputs and available information. After defining process components, the user can choose a reaction type as listed in the section below. HYSYS includes a number of different reactor models for the various reaction types, desired outputs, and specification limitations as well as standard PFR and CSTR models as described in this section.


Because simulation requires reaction characteristics, parameters, and other information, it is important to conduct background research appropriate to the reaction of interest before beginning the actual simulation. If theoretical or empirical data do not exist for the reaction, it may be difficult or impossible to conduct a computer simulation (see Additional Options). Of course, the phase of the reaction must be known; unfortunately, however, HYSYS does not support solid phase modeling[1] and thus a different approach must be chosen.



Fluid Package

Defining Reaction Characteristics

HYSYS Reactions


Conversion Reaction

Equilibrium Reaction

Heterogeneous Catalytic Reaction

Kinetic Reaction

Simple Rate Reaction

Managing Reactions

HYSYS Reactors[2][3][4]

Plug Flow Reactor (PFR)

Continuous Stirred Tank Reactor (CSTR)

Equilibrium Reactor

Conversion Reactor

Gibbs Reactor

Yield Shift Reactor


Degrees of Freedom[5][6]

A degree of freedom analysis will assist in reaching a state of convergence for the reactor and downstream units. For a reactor,


in which the number of degrees of freedom is expressed as the number of unknown variables plus the number of reactions occurring minus the number of material balances able to be performed on the system. In order for the simulation to converge, the user must specify as many variables as existing degrees of freedom. The simulation will then calculate unspecified variables.


Additional Options


  1. ^ AspenTech, "FAQ: Solids Modeling in AspenPlus", 2014
  2. ^ G.P. Towler, R. Sinnott, Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. p.186-194, Elsevier (2012).
  3. ^ AspenTech. HYSYS 2005.2 Simulation Basis. Chapter 9 (2005).
  4. ^ Rice University Chemical Engineering Department, "Reactions in HYSYS"
  5. ^ R.M. Felder, R.W. Rousseau, Elementary Principles of Chemical Processes. 3rd edition, Wiley (2005).
  6. ^ "Introduction to Chemical Engineering Processes: Degree of Freedom Analysis on Reacting Systems"