A novel mathematical model for mixed-feed multi-effect distillation system optimization design

In this work, a novel mathematical model called State-space Superstructure has been developed for the optimization design of a mixed-feed multi-effect distillation (MED) system. The model takes into account complex feeding arrangement relationships and aims to improve the thermal performance of the system. By using this model, novel mixed-feed arrangements have been obtained, which show improved performance compared to forward-feed arrangements in terms of gained output ratio ( GOR ) and specific heat transfer area ( A s ). The GOR is increased by 16 % and A s is decreased by 18 %. Additionally, the number of evaporators and preheaters can be reduced with these mixed-feed arrangements, resulting in a similar freshwater production capacity as a forward-feed MED system. Three optimal design schemes are studied, showing that there is a positive correlation between GOR and A s . Therefore, when optimizing the GOR or A s , it is essential to impose constraints on the optimization objective that is not being prioritized. The optimization scheme focusing on A s and constraining GOR resulted in an 18 % decrease in A s , while the scheme emphasizing GOR and constraining A s led to a 10 % increase in GOR . Overall, this novel mathematical model provides insights for improving the design of mixed-feed multi-effect distillation systems. • A novel mathematical model for mixed-feed multi-effect distillation system design has been carried out • Compared with the forward-feed arrangements, the mixed-feed multi-effect distillation system has better thermal performance with a 16 % increase in GOR and an 18 % decrease in A s • The number of evaporators and preheaters can be reduced with these mixed-feed arrangements, resulting in a similar freshwater production capacity as a forward-feed MED system