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Zawartość zarchiwizowana w dniu 2022-12-27

SOLAR POND FOR DESALINATION OF SEA WATER

Cel

To evaluate, using data collected from a relatively large sized solar pond, whether sufficient heat can be economically stored and subsequently used for moderate temperature end use applications. This solar pond is linked with a 10 m3/day vapour compression unit, which may be sized up to 100 m3/day.
Energy savings of 330 toe/yr and a payback of 8 years are expected.
The pond has been filled with bittern by the 1988.
Gradient has been generated at the end of 1988 and the beginning of 1989. The pond has been heated by the harvested solar energy since that time. The desalinator unit has been installed in the summer of 1989 and tested in the autumn of 1989; some tested were carried out using the stored heat into the pond, up to the permitted conditions of the bittern temperature. The desalinator unit has been ran continuously for six months, since end of May through end of November 1990. The demonstration project has allowed to understand the limits of the application from economic point of view, that are strictly related with the scale effect. The most economic size that has been envisaged for an industrial application will be about hundred thousands square meters.
Salt gradient solar ponds are those which have been studied more than any other type of solar pond. Much of the large scale experimental work has been carried out outside of Europe and because expected results are encouraging for particular applications, this project was chosen as the first such demonstration project of its kind.
In salt gradient solar ponds, three strata may be distinguished :
- a shallow, layer on the surface with a low salt concentration. This layer is subject to vertical convection currents induced by the wind and evaporation.
- an intermediate layer with a gradually increasing concentration of salt with depth, thereby preventing vertical convection currents.
- a bottom layer, having a constant high salt concentration, accumulates heat and has convection currents. Therefore the pond contains a certain amount of salts whose concentration approaches the saturation at the depth of 3-4 metres. Total salt content is 15,000 Tons.
Heat is absorbed and stored into thebottom layer which is insulated by the intermediate strata from the atmosphere. The site is most suitable because of availability of salt and water., high level of solar radiation and the flat nature of land. Frequently high wind speeds may induce on the pond surface waves that are suppressed by a buoyant net system. The pond with a clay floor covered by an impermeable plastic liner and of a surface of 25,000 m2, has been linked to a desalination unit producing 10 m3/day of fresh water. The desalination unit has been ran, without any problem, starting from the end of May 1990 up to the end of November 1990. It has been demonstrated by experimental data, that a bigger unit up to 100 m3/day may be ran by the pond of such size.
Heat is extracted by an heat exchanger fed with hot bittern pumped from the bottom of the pond; cooler bittern returns to the pond through a diffuser, installed on a platform in the middle of the basin. The diffuser allows to return the bittern at a determined level under the gradient layers, to avoid gradient perturbations. This technology may become susceptible to be widely adopted for certain application especially in southern Europe.

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Koordynator

ENI SpA- AGIP
Wkład UE
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Adres
VIA EMILIA 1
20097 S. Donato Milanese (MILANO)
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