There are numerous refinery and chemical reactor processes which can be modeled with ProMax reactors. The degree of model detail depends on the complexity of the reactions, the availability of any required kinetic or equilibrium information, and the availability of required input information.
Gibbs Minimization
The Gibbs Minimization reactor has the advantage that stoichiometric equations are not required. Equilibrium is determined from the free energy and the heat of reaction is calculated automatically. The method is completely general and predictive. Processes which come to equilibrium or close to equilibrium may be modeled with this technique. ProMax allows the user to choose which components are reactive and which are inert. Setting components reactive and inert is an important aspect in modeling sulfur plants. In the refinery, a hydrogen plant may be modeled using two Gibbs Minimization reactors for the reformer and shift converter. In the higher temperature reformer most or all components are allowed to react. The temperature in the shift converter is lower and only the components in the water-gas shift reaction (CO + H2O = CO2 + H2) are allowed to react.
Equilibrium
Like the Gibbs Minimization reactor, the Equilibrium reactor also calculates chemical equilibrium. However for this reactor stoichiometric equation information must be entered by completing the data for a Reaction Set. The required equilibrium constant may be determined by one of two options. ProMax can calculate the equilibrium constant from the Gibbs free energy or it can be entered by the user as a function of temperature. A temperature approach to equilibrium can be specified based on pilot plant data or plant experience. Isomerization reactors for paraffin or xylene isomerization are often be modeled as equilibrium reactors.
Plug Flow
Plug flow reactors can be used to model tubular flow reactors in which there is no mixing in the horizontal direction and perfect mixing in the radial direction. Kinetic information must be known and the reaction does not have to come to equilibrium. Reaction set data must be completed which includes stoichiometric equations, reaction order information for some combination of forward, reverse, and equilibrium reactions, rate constant information including pre-exponential and activation energy in a Arrhenius type expression, adsorption term information, and concentration type and units. In addition, heterogeneous catalysis reactions may have the rate specified per mass rather than per volume and require the catalyst particle density. Catalytic reformers are often modeled as a plug flow reactor. A lumped model may be used where a naphtha feed is represented by model paraffinic, naphthenic, and aromatic compounds and reaction equations for naphthene dehydrogenation, paraffin cyclization, and hydrocracking are included.
Conversion
Conversion reactors can be used to quickly calculate reaction products. The conversion of a specified reactant is described by an equation which can be a function of temperature. A conversion reactor might be used in place of a plug flow reactor with multiple
reactions inside a recycle loop in order to save time. The actual plug flow reactor calculations would be done once the recycle is converged and conditions are more finalized. Another situation where conversion reactors are useful is when product yields are known but detailed kinetics may not be available. Many refinery reactors, including hydrotreating, alkylation, catalytic cracking, coking, and others can be modeled with conversion reactors.
Stirred Tank
The Stirred Tank (CSTR) reactor models the flow reactor which is perfectly mixed. The composition of the product is assumed to be the same as that in reactor volume. The Stirred Tank reactor requires the same kinetic information as plug flow reactors. Reaction set data must be completed which includes stoichiometric equations, reaction order information for some combination of forward, reverse, and equilibrium reactions, rate constant information including pre-exponential and activation energy in a Arrhenius type expression, adsorption term information, and concentration type and units. In addition, heterogeneous catalysis reactions may have the rate specified per mass rather than per volume and require the catalyst particle density. Stirred tank reactors are used in many chemical processes and the production of polymers and pharmaceuticals.