HYSYS Operations Guide

For more information,
refer to Section 2.4.2 -
Parameters Tab.
Column Operations 2-51
This option (when enabled), can help solve columns where some
specifications can be ignored (enabling another) to meet the
rest of the specifications and converge the column.
Both Ranged or Alternate Specs must be enabled and
configured using the Advanced Solving Options Button
located on the Solver page of the Parameters tab before they
can be applied during a column solution.
Specification Tolerances for Solver
The Solver Tolerances feature allows you to specify individual
tolerances for your Column specifications. In addition to HYSYS
converging to a solution for the Heat/Spec and Equilibrium
Errors, the individual specification tolerances must also be
satisfied. HYSYS first performs iterations until the Heat/Spec
(inner loop), and Equilibrium (outer loop) errors are within
specified tolerances.
The Column specifications do not have individual tolerances
during this initial iteration process; the specification errors are
“lumped” into the Heat/Spec Error. Once the Heat/Spec and
Equilibrium conditions are met, HYSYS proceeds to compare the
error with the tolerance for each individual specification. If any
of these tolerances are not met, HYSYS iterates through the
Heat/Spec, and Equilibrium loops again to produce another
converged solution. The specification errors and tolerances are
again compared, and the process continues until both the inner/
outer loops and the specification criteria are met.
Specific Solver Tolerances can be provided for each individual
specification. HYSYS calculates two kinds of errors for each
specification:
• an absolute error
• a weighted error
When the Weighted and Absolute Errors are less than their
respective tolerances, an Active specification has converged.
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