Large Scale Solar Desalination
Using Multi Effect
Humidification
Summary
A theoretical proposal is outlined for large scale solar
desalination using multi effect humidification. It involves the use of a large area solar collector,
multi effect distillation and boiling at reduced pressure. The configuration devised is a circular tank of one
kilometre diameter containing water to a depth of 10 metres
with a sealed double glazed dome, operating at 0.1
atmosphere pressure with a working temperature below 50°C. A solar
absorber placed just above the water level, abundantly
perforated but covering the entire area, sets up convection
currents that evaporate the sea water and condense the
vapour. Incoming seawater recovers energy from outgoing clean water and brine
in a counter current heat exchanger. Water flow is driven by solar distillation and
hydrostatic pressure. It is estimated that the structure would have 95% energy
efficiency and a gained output ratio of 20. In sunbelt countries with average isolation of 6kwh/m2/day
the desalination plant would produce 100,000 m3/d
distilled water at a speculative cost of $0.28/m3.