Distillation: apparatus – Apparatus – Types
Reexamination Certificate
1999-04-16
2002-08-27
Manoharan, Virginia (Department: 1764)
Distillation: apparatus
Apparatus
Types
C159S016100, C159S903000, C159S906000, C159SDIG002, C159SDIG001, C202S186000, C202S267100, C203S010000, C203S049000, C203S086000, C203S087000, C203SDIG001
Reexamination Certificate
active
06440275
ABSTRACT:
This invention relates to solar stills for producing fresh water, in other words domestic equipment or industrial plant units employing solar energy for producing demineralized water from natural non-potable water. Where this non-potable water is sea water, such stills could also, as a useful by-product, produce brine.
The problems, both economic as well as technical, that sea water desalination installations of different types (distillation and filtration) pose, have been set out in detail in an article by Andy Coghlan, entitled “Fresh water from the sea”, published on pages 37 to 40 of the British journal New Scientist of Aug. 31, 1991. In this article, we are reminded how vital it is becoming to rapidly develop techniques which are both effective and inexpensive for desalinating sea water, in order to meet the exponential requirements for fresh water in dry zones of the earth.
To meet this problem, numerous solutions for distilling sea water have been proposed which call upon the relatively intense and free energy from the sun, as a replacement for the costly energy produced by fossil fuels. The solutions have been the subject matter of numerous patents and articles from which two are of special interest, and are taken as references in view of their particular relevance.
European Patent 0, 612,691 published in 1994, filed by Mitsubishi, discloses a solar unit for producing fresh water of the conventional type, in which a reservoir having a black base, containing sea water, is installed beneath a transparent space having a sloping roof. Two gutters, intended to recover the fresh water which runs down the vertical walls of the space, are arranged at the foot of these walls. In order to prevent drops of fresh water, condensed on the inner space of the roof and which, moreover, reflect a portion of the solar radiation, from falling back into the reservoir, this face is provided with a wettable covering, which is transparent or at least translucent, which prevents water droplets from forming. Additionally, in order to decrease the temperature of the roof of the space and thus improve vapor condensation, sea water is constantly spread over this roof. In this way, the yield of such an installation is improved. At least two disadvantages nevertheless remain: (1) an excessive amount of water is constantly heated by the sun, which decreases the maximum temperature of the mass of water in the reservoir and reduces the degree of evaporation achieved and (2) all the latent heat of the water vapor condensation is lost.
The article from New Scientist cited above carries, on page
39
, a brief description of a piece of domestic equipment for producing fresh water which is original, has a high yield, and employs solar energy. This equipment, developed by P. Le Goff, carries, below a transparent plastic membrane, an orientable mirror that reflects the solar energy towards the front black face of a first aluminium plate, arranged vertically. The rear face of this first plate is coated with a gauze, which is supplied with sea water under gravity. Several identical plates provided with this same hydrophilic covering are arranged in cascade a few centimeters from each other. The solar energy heats the first plate up to a about 94° C., the effect of which is to evaporate a relatively large amount of the water circulating in the lining covering the rear face. The water vapor thus produced in the space separating the first and second plates condenses on the front face of this second plate; the effect of this is to cause it to heat up, leading, in its turn, to evaporation of a large amount of the salt water circulating on its rear face. This goes on up to the sixth plate, which gets heated up to 45° C. The fresh water condensed on the front face of each plate starting from the second one, is collected by a collector. Another collector, which is not shown, collects the brine that appears at the bottom of each lining. The manufacturer announces a daily production of
20
liters of fresh water per square meter of a plate exposed to the sun. Such a high yield is the result of recovery, on the second to sixth plates, of the latent heat of condensation of the water vapor produced by the hot linings, and which are kept constantly humidified, of the first to fifth plates. According to the author of the article, this result compares very advantageously with results (2 to 3 liters a day and per square meter) from sea water solar distillation equipment of the conventional type. This apparatus is effective and suitable for domestic equipment but it is relatively expensive to construct due to some of the components (the heliostat and the aluminium plates) that it includes.
In the text that follows, we shall take the yield of a solar still for producing fresh water to mean the ratio between, on the one hand, the amount of fresh water effectively produced per hour of average sunlight and per square meter of surface absorbing the solar radiation and, on the other hand, the amount of water Q, theoretically evaporated by the heat of the sun, absorbed by this unit of surface area during this unit of time (giving Q=1.5 kg/h.m
2
for an average level of sunshine of one kilowatt/m
2
1
, in dry zones).
The first aim of the invention is to construct improved solar stills for producing fresh water.
The second aim of the invention is to construct such stills having a yield that is as high as possible, while simultaneously requiring a relatively low initial investment and operating and maintenance costs that are particularly low.
The third aim of the invention is to provide solar stills for producing fresh water in which as much as possible of the latent heat of condensation of the vapor is recovered.
The fourth aim of the invention is to provide such solar stills which are readily adaptable to the particular conditions of their implementation.
The fifth aim of the invention is to provide such solar stills for producing fresh water, that are well suited to withstand strong winds.
The sixth aim of the invention concerns industrial solar plant producing fresh water by distillation of sea water and comprising a relatively large number of identical solar stills.
The seventh aim of the invention concerns industrial plant that combines a solar plant for producing fresh water by distillation of sea water and a salt marsh supplied by the brine furnished by this plant.
The eighth aim of the invention concerns a novel composite product, specially adapted to the construction of improved solar stills for producing fresh water according to the invention.
According to the broadest formulation of the invention, there is provided a solar still for producing fresh water comprising:
a device, adapted to absorb solar radiation and to contain water to be distilled;
a condensation surface on which vapor, produced by heating up of water of the device, can condense;
means for collecting the fresh water that trickles down the condensation surface;
characterised in that:
said device comprises an impermeable membrane, that is flexible, kept stretched, of a dark color, exposed to the sun and, arranged in the shade and forming a covering for said membrane, a hydrophilic fleece, supplied with water by capillarity and gravity;
means for recovering brine are arranged at the bottom of said fleece.
It will be immediately noted that the more or less hydrophilic nature of a material is measured by the degrees of capillarity that it has vis-a-vis liquids able to wet it. Under these conditions, a wettable but only slightly hydrophilic fleece will be supplied by gravity, by pouring the water to be distilled on to it. As against this, a highly hydrophilic fleece will be supplied by simple capillarity, by immersing one of the edges thereof in the water. After this, the capillarity, even when this is small, of the fleeces, and the forces of gravity, will ensure spreading, retention and the flow of this water, during its downward travel through the fleeces. For a highly hydrophilic fleece, the throughput, per unit of immersed width, of the water thus pumped,
Baker & Botts LLP
Manoharan Virginia
LandOfFree
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