magnets:
SYNTHESIS OF HEAT EXCHANGER NETWORKS BY SEQUENTIAL OPTIMIZATION

A. Ciric, A. Katohwala, S. Zhang, C. Floudas and I.E. Grossmann

 
Screen Shots:
initial screen
Data input
Output
Network structure
 




MAGNETS is an interactive program for the synthesis of heat exchanger networks. It has the capability of synthesizing networks that exhibit:

  • minimum utility cost,
  • fewest number of units,
  • minimum investment cost

The strategy employed is sequential optimization. The program consists of three major phases:

  • minimum utility calculation,
  • determination of matches for minimum number of units,
  • network derivation for minimum investment cost.

The first involves a linear programming (LP) transshipment problem, the second a mixed-integer linear (MILP) problem, and the last a nonlinear programming (NLP) problem that optimizes a superstructure that has embedded all the options of flow patterns for the selected matches. MAGNETS generates automatically the mathematical formulations and interfaces with LINDO for the first two, and with MINOS for the last.

Important capabilities of MAGNETS include handling of multiple utilities, options for selection of pinch points for network partitioning, specification of constraints on matches and handling of stream splitting. The constraints on the stream matches can be handled by forbidding them, imposing them with a minimum heat load, or restricting the heat load in a match.

Stream data must be supplied through data files, but these can be edited during a run with MAGNETS. The information that must be supplied are units, min. temperature approach, inlet and outlet temperatures, Fcp's for process streams, cost coefficients for utilities.

MAGNETS code was written by the senior undergraduate students at Carnegie-Mellon, Amy Ciric and Alok Katohwala for VAX/VMS operating system and transfered to IBM / AIX by Sue Zhang under the supervision of Ignacio E. Grossmann .

References for MAGNETS:

  • Floudas, C. A., A.R. Ciric and I. E. Grossmann, Automatic Synthesis of Optimum Heat Exchanger Network Configurations , AIChE J., Vol. 32, p. 276 (1986).
  • Papoulias, S.A. and I. E. Grossmann, A Structural Optimization Approach in Process Synthesis. II:Heat Recovery Networks , Computers and Chemical Engineering, Vol. 7, p.707 (1983).