Recycle Loops - Technical Information
PRO/II solves recycle loops by performing an iterative calculation around each loop until specified parameters are converged. Initial estimates for the recycle loop are usually not needed, but they are often desirable to enhance the solution convergence. The recycle loops are identified by the PRO/II loop analyzer based on the flowsheet topology and the selected calculation sequence.
See Recycle Techniques for different types of recycle loops and the methods employed to solve them.
PRO/II sets up and solves the largest independent recycle loops first. Nested loops are converged simultaneously and the calculations for units which are outside the loop are not considered until the recycle streams are converged.
Acceleration methods can be employed to speed the convergence of recycle loops with asymptotic convergence characteristics. See Acceleration Methods for more details.
You are allowed to change the default recycle sequence for nested and interconnected loops, apply the acceleration techniques only to selected loops, and also vary convergence tolerances for each loop. The convergence tolerances and the acceleration method for the recycle loops can be selected at the following two levels:
Problem default : You can set the default choices for a simulation problem through the Recycle Convergence and Acceleration Options Window, which is displayed when button is pushed from the Main Window toolbar.
Individual recycle loop : You can override the problem default choices for an individual recycle stream through Individual Recycle Loop Data Window. The starting and ending units, acceleration method and tolerances can be set differently for each of the loops.
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