Study on a novel spray-evaporation multi-effect distillation desalination system

Abstract

As the negative environmental impacts associated with disposal of brine concentrate become increasingly recognized and attracting public attention, zero liquid discharge (ZLD) is emerging as a technique for desalination plants to minimize waste and recover resources. In this study, an innovative concept of a spray-evaporation multi-effect distillation (SE-MED) system is proposed to achieve ZLD, in which a spray evaporation tank (SET) is used to fully split brine disposal for water and salts. A steady-state mathematical model for the SE-MED process is developed under several simplification assumptions. A five-effect forward SE-MED system with a bleed fraction of 20% is designed based on the mathematical model. A simplified vaporization model is also developed to describe the motion and evaporation behavior of a single water droplet in the SET. The calculated trajectories of the droplet provide guidance to the SET design. Two-phase simulations are performed to provide further insight into spray evaporation performance inside the SET. Results indicate that a high evaporation efficiency of 99.86% is achievable by the modified SET. In addition, the application of the Reaction Engineering Approach in the hindered spray evaporation simulation is discussed and validated for future study.