A brine evaporative cooler/concentrator for autonomous thermal desalination units

摘要

In recent years growing attention has been paid to the problem of brine disposal due to the raisingudawareness of significant environmental issues related to the use of desalination processes forudfresh water production. This is particularly relevant when desalination units are located in remoteudsites, characterised by major complexity in the construction and management of intake and outfalludstructures. In the present work a novel device, named brine evaporative cooler/concentrator (BECC,udpatent pending), has been developed for coupling with small-scale thermal desalination plants inudorder to reduce the problem of brine disposal. Such device fulfils two different functions: i) coolingudof the recirculating brine (which is often mixed with cold seawater to feed the unit, acting firstudas a cooling medium for the condensation of the vapour) and ii) concentration of the brine to deuddisposed. The BECC device is based on the principle of evaporative cooling, i.e. a primary liquidudstream is cooled by means of a secondary liquid stream (by-pass stream), which in turn evaporatesudin contact with atmospheric air, thus being cooled naturally. The two streams are separatedudby a heat-conductive surface, through which heat is transferred from the primary stream to theudcooling-evaporating by-pass stream. A lab scale BECC pilot unit has been designed, constructedudand tested. Geometrical and operating features have been studied in order to allow the operationudwith concentrated brines, to minimise problems of corrosion, scaling and fouling. The first resultsudhave demonstrated the feasibility of the technology and a larger scale prototype unit has beenuddesigned for the installation within a 5 m3/d solar membrane distillation unit to be constructed inudPantelleria Island, Italy.