What is ALPHA in distillation column algorithms?

In the IO column, ALPHA is reported for each iteration in the inner loop calculations.  ALPHA is the multiplier used to modify the stripping factors (shortcut thermo) for the next inner loop calculation, and can be either positive or negative.  A value of ALPHA equal to 1.00 indicates that the enthalpy balances and product specifications are converging well in the inner loop.

In the SURE column, ALPHA and ALPHA MAX are reported for each iteration.  Since the SURE algorithm uses a Newton-Raphson technique, a set of derivatives is developed with respect to the independent variables to determine the appropriate step size to be taken at each iteration.  Limits are set on the maximum allowable predicted change of the independent variables, and if any variable falls outside this range then the factors needed to reduce the derivatives to fall within the range are computed.  The most limiting factor, which is ALPHA MAX, is selected and used to scale all the derivatives for the next step.  If the predicted solution appears to be diverging, this value is further reduced for that iteration and now termed as ALPHA.  If the predicted solution appears to be converging, ALPHA and ALPHA MAX are equal.

In the CHEMDIST column, ALPHA has a similar role to that in the SURE column.

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