Synthesis of flexible heat exchanger networks. II, Nonconvex networks with large temperature variations

Abstract New features have been incorporated to the systematic algorithmic approach presented in Part I to make it capable of solving nonconvex HENS problems with large temperature disturbances. They permit detection of pinch-jumps and evaluate the intermediate temperatures at which the discontinuities arise. At pinch-jump conditions, a pair of simultaneous pinch temperatures are observed, requiring further units to reach maximum energy recovery. Additional partitioning of the process streams at such temperatures make it possible to reach the energy target everywhere. Application of the method to the solution of several nonconvex examples yields networks comprising the fewest number of units to always minimize the utility usage. Because they are built-in, feasibility tests are not required. The efficiency of the method remains remarkable even for a seven-stream problem.