Low-Temperature Solar-Thermal Multi-Effect Evaporation Desalination Systems

As part of a project investigating the productive use of saline land and the development of sustainable desalination systems, the production of potable water from seawater or brackish water using desalination systems powered by low-temperature solar-thermal sources, including salinity-gradient solar ponds and evacuated tube solar collectors, has been studied. A Visual Basic - Excel computer model of solar-powered multi-effect evaporation (MEE) desalination processes was developed to determine the technical and economic feasibility of the system. A small-scale three-effect evaporation desalination system powered by a solar pond, capable of producing up to 2,300 litres of fresh water per day, has been designed using the model. The system has been manufactured and commissioned, and has operated effectively at a first-effect vapour temperature of about 68°C, which is ideal for heat delivery from a solar pond. One of the advantages of the MEE - Solar pond arrangement is the possibility of utilising the discharged concentrated salt solutions from the MEE system for commercial salt production, or constructing additional solar ponds to support additional desalination capacity. The key design and operating parameters controlling the cost of fresh water – distillate production, recovery ratio, thermal energy and solar collection area – were determined from the computer simulation and compared with experimental results. A good agreement between the experimental data and the modelling results has been obtained.