Energy/exergy analysis of solar driven mechanical vapor compression desalination system with nano-filtration pretreatment

Abstract

The performance of the mechanical vapor compression desalination system is limited due to the required vacuum pressure and associated high temperature scaling problem. Thus, a new solar driven mechanical vapor compression desalination plant with nano-filtration pretreatment operating at atmospheric pressure is developed for a production of 500 m3/day. The electrical and thermal energies of the new system are generated using the integration of solar photovoltaic modules and parabolic trough collectors. To evaluate the performance of the new system, energy/exergy analysis is performed by employing a MATLAB package and a Graphical User Interface (GUI) tool. Also, an economic evaluation for the plant's direct, indirect, and unit product costs ($/m3) is presented. The predicted results are validated with the available measurements. The effects of different design parameters such as feed water temperature, distilled and brine water temperature difference, salt rejection and recovery ratio on plant performance are investigated. The proposed plant's exergy efficiency is found to vary from 14.59 to 20% consistently with design parameters. The enhancement in exergy efficiency is estimated to be 153.7%, 56.3%, 32.63% and 27% compared with Multi-Effect evaporation mechanical and conventional vapor compression, forward feed multi-effect mechanical vapor compression and reverse osmosis systems, respectively. The salt rejection and recovery ratio are found to be the most significant parameters to enhance the plant exergy efficiency. Furthermore, the photovoltaic unit has a significant effect on exergy destruction of the plant with a percentage of 85.79%. The parabolic trough collectors also have high exergy destruction of about 69.53%. The economic analysis reveals that the unit water price for the proposed plant is equal to 1.54 $/m3. Therefore, the developed solar-NF-MVC system suits small scale units for remote communities.