Second-Order Correction Methods for Chemical Process Optimization


Mark Hoza and Mark A. Stadtherr


When successive quadratic programming methods are used in connection with the sequential-modular or simultaneous-modular approaches to chemical process optimization, substantial reductions in calculation time can be achieved by reducing the number of derivative evaluations. We present here methods for achieving such a reduction; these include two second-order correction techniques and a selection strategy. One second-order correction technique is a variation of the method of Fletcher. The other involves a correction quadratic program (QP) with a Broyden-updated constraint Jacobian. This correction step solves a QP subject to the next quasi-Newton approximation to the solution of the currently active constraints. The selection strategy forces the methods to work together to provide the most progress in a given iteration. An iteration could involve only a basic step, a basic step plus either second-order correction step, or a combination of the basic step and both correction steps. Backtrack capabilities allow the program to abandon a nonproductive correction step and recover the base QP step. Tests on both general problems and flowsheeting problems show these techniques to provide a reduction in the number of derivative evaluations required in most cases.

Comput. Chem. Eng., 16, 901-915 (1992)

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