Thermodynamic efficiencies and GHG emissions of alternative desalination processes

摘要

Three alternative approaches to desalinating seawater were evaluated with respect to theirnthermodynamic efficiencies and greenhouse-gas emissions. The technologies considerednwere multistage flash distillation (MSF), reverse osmosis (RO), and membrane distillation (MD).nThe analysis was based on published stream data from large-scale operational MSF and ROnfacilities and experimental-scale data for the MD process. RO was found to be the mostnexergy-efficient (30.1%) followed by MD (14.27%) and MSF (7.73%). RO and MD required lessnpower consumption to produce water (3.29 kWh/m3 and 5.9 kWh/m3, respectively) comparednto MSF which had a much higher energy demand (16.7kWh/m3). Similar results were obtainednwhen comparing equivalent carbon dioxide emissions from each process; MD and RO accountednfor 5.22 and 2.91 kgCO2eq/m3, respectively, whereas MSF generated three to four times thatnamount. The results indicate that MD has potential as a commercially viable techniquenfor seawater desalination provided a source of waste heat is available. This study providesnan overview of the use of thermodynamic efficiency analysis to evaluate desalinationnprocesses and provides insight into where energy may be saved with developed desalinationnprocesses and areas of research for emerging desalination techniques.