The homotopy option is an aid to converging problems where the specification is difficult to meet by virtue of the value of the specification (as opposed to the type of specification). This was designed for Reactive Distillation where convergence is more complex but it may be used for any Column Algorithm.
Systematically increasing tray volumes to very large values is particularly useful for determining the equilibrium compositions for reversible kinetic reactions.
The homotopy option allows you to solve the problem with an initial value for the specification and then automatically move to the desired final value in a set number of steps. The column is converged at each step.
The Specification name and the Final Value entered in the Column Specifications and Variables Window are shown in the table for all column specifications.
To use the homotopy option for any specification, you must supply the Initial Value of the specification and the Number of Intervals to use in moving from the initial value to the final value. You cannot change the Final Value in this window.
The homotopy option may be used for a specification which is varied by a controller or optimizer. If Initially is selected (the default), the homotopy iterations will be carried out to meet the given column specification. If the specification value is then changed by another unit operation, the column will solve without homotopy iterations. If Always is selected, the homotopy iterations will be carried out every time the column is reconverged after the specification has been changed. In this case, the Initial Value will be the last converged specification value, not the supplied value.
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