US 4,363,703 AGranted

Thermal gradient humidification-dehumidification desalination system

AssigneeInstitute of Gas Technology

InventorsAhmed A. ElDifrawi, Christopher F. Blazek, Bernard D. Yudow

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Abstract

A solar energy desalination process utilizing solar radiation directly for the evaporation of salt water is described. Ambient air takes on water vapor as the air passes through an evaporative medium. It is then directed between a saline water-covered, solar absorbing surface and a solar collecting housing. The resulting heated and moisture-saturated air is cooled in a heat exchange means where condensation of fresh water occurs. Simultaneously, cool salt water is utilized as the cooling water in the heat exchange means, and takes on the heat of condensation given up by the condensing vapor. The heated salt water from the heat exchange means is partially directed over the solar absorbing surface, and at least a portion of it is also directed to wet the evaporative medium. Several optional sub-processes are described for operation of the system during periods of reduced insolation, and an alternative process is described for operation of the process on a floating platform.

Claims30

Dependent claims

A process for the evaporative desalination of salt water to provide fresh water which process fully utilizes the latent heat of condensation to provide additional fresh water, comprising, during periods of isolation:

(a) passing comparatively cold salt water into indirect heat exchange contact with a flow of moisture laden comparatively warm air so that fresh water is condensed from the moisture laden comparatively warm air and the heat of condensation of that fresh water is transferred to the comparatively cold salt water, the temperature of which becomes comparatively warm;
(b) segregating at least parts of the flow of salt water of comparatively warm temperature into at least a first stream and a second stream;
(c) directly contacting only the first stream of the salt water of comparatively warm temperature with the flow of moist air which is subsequently passed into indirect heat exchange contact with the comparatively cold salt water, while simultaneously passing the first stream over a solar absorption surface, and segregating from the atmosphere and heating by solar means both this first stream of salt water of comparatively warm temperature and the flow of moist air to predominantly cause evaporation of water into the air so that the air becomes moisture laden;
(d) wetting an evaporative medium with at least a portion of the second stream of salt water of comparatively warm temperature;
(e) passing ambient air through the wetted evaporative medium so that the air absorbs moisture and becomes the flow of moist air which is directly contacted with the first stream of salt water while both are heated by solar means;
and
(f) collecting at least the first stream of the salt water of comparatively warm temperature in a warm brine collection means;
and further comprising, during periods of reduced isolation:
(g) utilizing the salt water of comparatively warm temperature collected in the warm brine collection means to produce additional fresh water by evaporative desalination.

6 more elements

An apparatus for the evaporative desalination of salt water to provide fresh water which apparatus is designed to fully utilize the latent heat of condensation to provide additional fresh water, comprising:

(a) heat exchange means having a liquid-receiving section with entrance and exit ports and a vapor-receiving section for passing cold salt water contained in the liquid receiving section into indirect heat exchange contact with a flow of moisture laden comparatively warm air contained in the vapor receiving section so that fresh water may be condensed from the moisture laden comparatively warm air and the heat of condensation of that fresh water transferred to the comparatively cold salt water, the temperature of which will become comparatively warm;
(b) means, communicating with the exit port of the liquid-receiving section of the heat exchange means, for segregating at least parts of the flow of salt water of comparatively warm temperature into a least a first and second stream;
(c) means, having air inlet and air outlet ports, for directly contacting only the first stream of the salt water of comparatively warm temperature with the flow of moist air which is subsequently passed into indirect heat exchange contact with the comparatively cold salt water and means for simultaneously segregating from the atmosphere and heating by solar means both the first stream of salt water of comparatively warm temperature and the flow of moist air, including a solar absorption surface in direct contact with the first stream of salt water, to predominantly cause evaporation of water into the air so that the air becomes moisture laden;
(d) an evaporative medium positioned prior to the air inlet of the means for directly contacting the first stream of the salt water of comparatively warm temperature with the flow of moist air, so that ambient air may be passed through the evaporative medium to absorb moisture and become the flow of moist air which is directly contacted with the stream of salt water while both are heated by solar means;
(e) means for conveying at least a portion of the second stream of salt water of comparatively warm temperature into direct contact with the evaporative medium in order to wet the medium;
and
(f) means for collecting and storing at least the first stream of salt water of comparatively warm temperature for utilization to produce additional fresh water by evaporative desalination during periods of reduced insolation.

4 more elements

An apparatus for the evaporative desalination of salt water, utilizing a platform floating on the surface of the salt water, to provide fresh water which apparatus is designed to fully utilize the latent heat of condensation to provide additional fresh water, comprising

(a) a floating platform;
(b) heat exchange means, disposed on the floating platform, said heat exchange means having a liquid-receiving section with entrance and exit ports and a vapor-receiving section for passing cold salt water contained in the liquid receiving section into indirect heat exchange contact with a flow of moisture laden comparatively warm air contained in the vapor receiving section so that fresh water may be condensed from the moisture laden comparatively warm air and the heat of condensation of that fresh water transferred to the comparatively cold salt water, the temperature of which will become comparatively warm;
(c) means, affixed to the floating platform, communicating with the exit port of the liquid-receiving section of the heat exchange means, for segregating at least parts of the flow of salt water of comparatively warm temperature into at least a first and second stream;
(d) means, disposed on the floating platform, having air inlet and air outlet ports, for directly contacting only the first stream of the salt water of comparatively warm temperature with a flow of moist air from the surface of the salt water which is subsequently passed into indirect heat exchange contact with the comparatively cold salt water and means for simultaneously segregating from the atmosphere and heating by solar means both the first stream of salt water of comparatively warm temperature and the flow of moist air, including a solar absorption surface in direct contact with the first stream of salt water, to predominantly cause evaporation of water into the air so that the air becomes moisture laden;
and
(e) means for collecting and storing beneath the floating platform the first and second streams of salt water of comparatively warm temperature for utilization to produce additional fresh water by evaporative desalination during periods of reduced insolation.

3 more elements

Dependencies are inferred from the claim text.