Synthesis of optimal heat-induced separation networks

• Published in: Chemical engineering science Vol. 50; no. 1; pp. 81 - 97
• Main Authors: El-Halwagi, Mahmoud M., Srinivas, B.K., Dunn, Russell F.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 1995; Elsevier
• Subjects: Applied sciences; Chemical engineering; Crystallization, leaching, miscellaneous separations; Exact sciences and technology; Cost minimization; Meshed network; Separation; Theoretical study; Numerical simulation; System synthesis; Pinch method; Phase equilibrium; Optimization; Heat transfer
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/0009-2509(94)00207-8

In this work we introduce the novel problem of synthesizing heat-induced separation networks (HISENs). The essence of HISEN synthesis is to reduce the concentration of a certain component in a number of rich (typically waste) streams from a set of supply compositions to a set of target compositions by using a number of heat-induced separators. A heat-induced separator is any indirect contact unit which employs an energy-separating agent (ESA) to affect separation via phase change. Examples of these systems include condensation, crystallization, vaporization and drying. By combining phase-equilibrium data with enthalpy balances, we develop pinch diagrams that can be used to determine the minimum operating cost of the system. There are two distinctive characteristics associated with the pinch diagrams for the HISENs. First, the location of the pinch point is not restricted to the supply temperatures of streams. Second, heat-induced separators may straddle the pinch point even for networks featuring the minimum cost of energy-separating agents. A systematic procedure is presented to address these characteristics and to synthesize a cost effective network of heat-induced separators. The problem is formulated as an optimization program. A solution procedure that is guaranteed to identify the global solution is devised to solve the problem. In addition, a slightly revised formulation is developed to incorporate the effect of stream bypass/mixing. Several case studies are tackled using the proposed procedures.