A Study on the Minimization of Energy Cost in the Salt Crystallization Processes

Abstract

In a salt crystallization process, a large amount of energy is consumed for the evaporation of water. Since the amount rises almost proportionately with an increase in the production rate, the strategy for energy saving becomes more important in high-throughput processes. Typically, a reduction in energy cost was achieved by employing multi-effect processes and a heat exchanger network for heat recovery. In this study, a design support system for deriving an energy-efficient salt crystallization process was developed. Simultaneous optimization of multi-effect process and the heat exchanger network was tackled by combining the pinch technology and genetic algorithm. A four-effect process was used as an example process and its optimal design condition was derived using the system. Usually the vapor rising from a crystallizer is used to heat the crystallizer in the next stage. However, the solution indicated that for optimizing the energy efficiency, the vapor should be used to heat the brine or the mother liquor entering the crystallizer. One of the problems of the system was that it was impossible to pose limitations in the number of heat exchangers. Therefore, the system was modified in such a way that the optimal combination of hot and cold streams was derived by an exhaustive search method. The results obtained using the modified system showed a heat exchanger network similar to that obtained using the original system.