Comparative performance evaluation of LT-MEE desalination systems with three feed configurations

摘要

Horizontal-tube falling-film evaporator has been widely applied in the low-temperature multi-effect evaporation (LT-MEE) desalination system because of its unique advantages. Research shows that the spray density has a significant effect on the heat transfer effect of this kind of evaporator and it is closely related to the feed configuration. Therefore, this paper focused on the feed configurations suitable for the large-scale LT-MEE desalination plant based on a reasonable spray density, which include the parallel feed and mixed feed. Based on the mass and energy conservation equations, the corresponding mathematical models were established, which consider the thermodynamic losses including boiling point elevation (BPE), non-equilibrium allowance inside evaporators/condensers and distillate flashing boxes, and flow resistances from evaporation to condensation. Validity of the model was verified through comparison between the industrial data. The effects of heating steam temperature and number of effects on the performance parameters were investigated. The comparison of performance and scaling tendencies between various feed configurations was accomplished. Results show that the mixed feed system presents a better performance than the parallel feed systems, while scaling risk of the combination of backward and parallel feed configuration is the highest. This comparison illustrates the logic behind choosing each feed configuration.