Desalination – Vacuum TechnologyHarry
Reference System for Solar Thermal Sea Water Desalination located in Muscat, Sultanate of Oman
The Multi-Effect-Humidification (MEH) method for thermal distillation was developed at ZAE Bayern in close co-operation with T.A.S. GmbH of Munich. Investigations on components in the last years have finally resulted in a system which is designed for 24 hours per day continuous operation. The predicted daily production is up to 800 liters distilled water out of 40 m2 TS 400 evacuated flat plate collectors. The night is bridged by a 3.2 m3 thermal storage tank. Fresh water is used as collector fluid and in the storage tank.
In the spring of 1999 a solar thermal desalination system was constructed at the College of Engineering test area for sea water desalination of the Sultan Qaboos University of Muscat/Oman . The complete plant planned by the ZAE Bayern consists of a field of 40 m2 of TS400 vacuum panel collectors, an isolated 3.2 m3 steel tank and a thermally operated desalination tower (Fig. 2.5.4). Their daily output is approx. 800 liters. Here a distillation method that works at ambient pressure is used that was recently optimized at ZAE Bayern in co-operation with the T.A.S. GmbH company of Munich. Using this method, heated sea water is distributed over a large area evaporator within the desalination module. A convection roller in the module, which is propelled only by the sealing and humidity differences in this thermally isolated box and needs no auxiliary energy, transports moist air over the double polypropylene plate assembly in the module, which act as condensation surfaces. Cold sea water flows through plates, which are heated to higher than 70°C by the condensation of the moist air outside the plates. The geometrical arrangement of evaporation and condensation surfaces makes a material and a heat flow possible, which could otherwise only be achieved in sophisticated multi-chamber systems.
The heat recovery thus achieved during the distillation process decreases the thermal power requirement of the desalination plant to approximately 120 kWh thermally per cubic meter distillate as opposed to the evaporation enthalpy of water of 690 kWh per cubic meter. The heat recovery is thereby only a little under the value reached in more maintenance-intensive and technologically sophisticated vacuum evaporation plants (MSF, MED plants).