Reaction submodels for the Bosen-Engels approach

To properly use the Bosen-Engels approach for electrolyte fluids, you must create a reaction submodel that includes equations for the rate constant and the reaction rates. The equations depend on the empirical reaction data that you have gathered for your reaction system.

In most cases, you can use the following generic equilibrium reactions and equations to define your reaction system. If your reaction contains more products or reactants than the generic equilibrium reaction, you must add more equations for each species so that your reaction submodel accurately defines your reaction kinetics.

The following equations give a generic equilibrium reaction along with a generic equilibrium constant equation.

where

ka is the equilibrium constant

a, b, c, and d are the stoichiometric coefficients

A1, B1, C1, D1, and E1 are dimensionless coefficients

T is the temperature

We can calculate equilibrium constants for all the reactions in the system in this way. If your system contains more than one equilibrium reaction, you should add equations and variables for all the equilibrium constant equations to your reaction submodel.

For electrolyte reactions, we can simplify the products of the dissociation into a single complex consisting of the ion and solvent molecules. For example, the reaction equation scheme for an H2SO4-H2O system is as follows:

where

C± represents the combination of two different ions (H3O+ and SO4--*2H2O)

For simplicity, the model does not differentiate between positively and negatively charged complexes. We can formulate the equilibrium reaction with an equilibrium constant according to the following equation:

where

Xi is the liquid mole fraction of component i in the solution

gi is the activity coefficient of component i

We can calculate ka according to the following equation, as before:

We highly recommend that you write your equilibrium reaction submodels in a dimensionless form. If you expect some of your process streams to approach nearly pure water, we also recommend that you add the water auto-ionization reaction to your reaction submodels. See Understand reaction submodels for equilibrium reactions for more information.

After you configure your reaction submodel with all the required rate constant equations and reaction rate equations, you can then add it to a Fluid to use the reaction submodel in all model instances that use the Fluid. You also use the reaction submodel as a replaceable submodel in a reactor model, such as the CNVR, EQR, CSTR, and PFR models in the Process Library, as well as in the Source from the experimental Electrolytes Library. The Source in the Electrolytes Library propagates the reaction submodel throughout the simulation. Please contact AVEVA Technical Support if you would like a copy of the Electrolytes Library.

You can also use the Reaction Generator to generate reaction submodels for equilibrium reactions. When you use the Reaction Generator to model equilibrium reactions, you must set the Reaction Type to Equilibrium. See Reaction Generator for more information.