Development of Heat-Integrated Evaporation and Crystallization Networks for Ternary Wastewater Systems. 1. Design of the Separation System

Abstract

This paper considers the optimal design of an evaporation and crystallization network for separation of a ternary wastewater stream with two salts and is the first part in a two part series on evaporation and crystallization networks. A crystallization and evaporation design is compared with previous work on condensation within the framework of a heat-induced separation network design. Detailed mathematical expressions are listed for complete material and energy balances, pinch equations, and unit sizing and cost of the evaporation and crystallization network. Some generic structures are proposed for heat integration of a typical evaporation and crystallization network. Several graphical insights are listed that allow one to use the representation of evaporation and crystallization operations on a ternary triangular composition diagram and to avoid mathematical complexity. Graphical insights enable reduction of the search space and allow solution of the problem in a computationally efficient manner. A graphical solution strategy and algorithm are described to converge to the optimal design. The solution algorithm requires the identification and bounding of certain critical design variables. A case study is solved to demonstrate the broad applicability and value of the proposed approach.