Use of exergy tools in renewable energy driven desalination systems

Abstract

Desalination technologies can utilize various forms of energy to produce freshwater. The first law of thermodynamics (energy) analysis is used commonly to determine the process efficiency, which is not a true measure of the process performance because it does not account for all losses of energy. The second law of thermodynamics (exergy) is an efficient tool to evaluate the performance of desalination systems. This method accounts for all forms of available energy in the process streams and energy sources with a reference environment to identify the major losses of exergy destruction to aid in resource-efficient desalination system design. Due to changing climate concerns and dwindling conventional energy sources, renewable energy has been identified as a sustainable alternative to supply the energy demands for desalination processes. Desalination processes can be powered by solar, wind, geothermal, and tidal energy sources depending on the process type and configuration.This paper elaborates on use of exergy tools to evaluate renewable energy powered desalination processes to evaluate their thermodynamic efficiency. Illustrations are provided to identify the major components and process streams that contribute to major exergy destruction and to suggest suitable operating conditions that minimize exergy losses. Well-established MSF, MED, RO, Solar distillation and membrane distillation technologies were discussed with case studies to illustrate their exergy performances. Single (water only) and dual (water and power) purpose desalination plants were discussed. Cogeneration, trigeneration (water, power, and heating/cooling) and polygeneration schemes and their exergy performance were also included.