Solar distillation of foamed saline water to recover fresh water

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Drawing sheet — no readable text.

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United States Patent Office Patented Feb. 18, 1969

vices, such layers prevent efficient thermal exchange and 3,428,529 thus the efficiency and useful lifespan of the installations SOLAR DISTILLATION OF FOAMED SALNE are reduced unless descaling methods are applied. These WATER TO RECOVER FRESH WATER methods are more or less expensive and complicated and Ricardo Salcedo Gumucio, Madrid, Spain, assignor to increase the cost of producing for instance fresh water Instituto Nacional de Industria, Madrid, Spain from saline or sea water.

Filed July 18, 1966, Ser. No. 565,780 It is therefore an object of the present invention to over Claims priority, application Spain, July 17, 1965, 315,400 come the above-discussed difficulties and disadvantages.

U.S. C. 203-10 10 Claims It is a further object of the present invention to provide Int, C. C02b 1/06, 5/06; B01d3/34 10 a method and device for the distillation of liquids, par ticularly aqueous salt solutions and sea water, which method can be carried out in a relatively simple and effec

ABSTRACT OF THE DISCLOSURE tive manner and which device is also relatively simple and A distilling method which comprises the steps of con inexpensive.

verting a liquid to be distilled into a foam, and subjecting 5 Other objects and advantages of the present invention the thus formed foam to solar heat so as to evaporate at will become apparent from a further reading of the de least a substantial portion of said foam; and a distilling scription and of the appended claims. device for distilling a liquid by utilizing solar heat, which With the above and other objects in view, the present comprises foam forming means for converting a liquid invention contemplates a distilling method, comprising into a foam, solar distilling means for exposing the thus 20 the steps of converting a liquid to be distilled into a foam, formed foam to solar heat so as to vaporize at least a and subjecting the thus formed foam to solar heat so as portion of the liquid of said foam, condensing means to evaporate at least a substantial portion of the foam. operatively associated with said solar distilling means for The present invention is also concerned with a distilling condensing the vaporized portion of said liquid, and con device for distilling a liquid under utilization of solar heat, duit means for passing foam from said foam forming 25 comprising, in combination, foam forming means for con means to said solar distilling means. verting a liquid into a foam, solar distilling means for ex posing the thus formed foam to solar heat so as to vaporize

at least a portion of the liquid of the foam, condensing

The present invention relates to a distilling method and means operatively associated with the solar distilling means device and, more particularly, the present invention is 30 for condensing the vaporized portion of the liquid, and concerned with distilling liquids such as sea water or conduit means for passing foam from the foam forming aqueous salt solutions by utilizing solar heat as the source means to the solar distilling means. of energy for evaporating the liquid. Thus, according to the present invention, the above The importance of industrial processes for converting discussed difficulties and disadvantages of prior art meth saline water and sea water into fresh water is well known. 35 ods are overcome and rapid evaporation is achieved with These processes may be classified as thermal processes an optimum energy exchange between the solar heat and or as electrical processes. The most important thermal the saline water or the like and, at the same time the processes are those that use high efficiency evaporation of formation of scales or crusts is avoided. saline water or the like, for instance by multistage distill According to the present invention, the saline water or lation, the thermal compression process, instantaneous 40 the the like prior to being distilled is converted into a foam evaporation, etc. It has also been proposed to purify or a more or less colloidal dispersion which is produced saline water and the like by cryoscopic or freezing by adding a conventional detergent or foaming agent to processes. the liquid and then passing a gas such as hot or com The electrical processes include those in which elec pressed air or another suitable gas through the same so trodialysis is applied and, more recently, electrodialysis 45 as to convert the liquid into a foam, and the thus formed through ion exchange membranes. However, these proc foam is then exposed to solar heat. esses are suitable only when the salt content of the water According to another embodiment of the present inven is below a certain limit and thus they cannot be used di tion, instead of blowing gas into the detergent-containing rectly for desalting sea water. liquid, the latter is stirred and thereby converted into a Present efforts are frequently aimed towards improving 50 foam. It is of course also possible to combine stirring saline water evaporation by better heat exchange between and gas introduction.

the heat source and the water which is to be evaporated, It will be easily understood that the distribution of the as well as by considerably increasing the evaporation sur water which is to be distilled throughout the very large face. In addition, it is generally necessary to provide a surfaces represented by stable foam, and the very thin system or process for the recovery of at least a part of 55 layers of liquid formed thereby will considerably facilitate the condensation heat, in order to obtain adequate effi evaporation. In addition, the solid residues which will be ciency with respect to the utilization of energy. formed during evaporation, i.e. the salt content of the One of the more modern processes which is carried out original liquid, will be finely divided and no scale forma "without boiling' is the rapid distillation process accord tion or the like will take place. ing to which the water to be treated is distributed over a 60 Thus, the present invention will achieve a large evapora large hot surface by centrifugal force so that a liquid film tion surface and a very thin film of saline water which is formed which is in very close contact with the heated is subjected to evaporation under the influence of solar Surface. In this way, an efficient thermal exchange and heat, which film is so thin that it may be passed through practically instantaneous evaporation are achieved and by solar infrared radiation.

the formation of saline crusts on the heat exchange sur 65 The novel features which are considered as characteris face, which tend to insulate the liquid from the heat source, tic for the invention are set forth in particular in the are minimized. appended claims. The invention itself, however, both as However, all of the known processes of saline water to its construction and its method of operation, together distillation are connected with serious problems with re with additional objects and advantages thereof, will be spect to corrosion, salt occlusion, crust formation, etc., 70 best understood from the following description of specific the latter producing insulating layers on the heat exchange embodiments when read in connection with the accom or evaporation surfaces. Upon prolonged use of the de panying drawing, in which:

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FIG. 1 is a perspective view, partially in cross section intended to be comprehended within the meaning and of a solar heat foam distilling device according to the range of equivalence of the following claims. present invention; and What is claimed as new and desired to be secured by FIG. 2 is a cross-sectional view through the device Letters Patent is:

illustrated in FIG. 1 taken along the line II-II. 1. A method for recovering solvent from a solution The present invention will now be described by way of comprising a solvent and a solute, comprising the steps example and with reference to the drawing, however, with of admixing to said solution a foaming agent in a quantity out limiting the invention to the specific details of the ex sufficient to cause foaming of said solution upon agita emplary description. tion thereof; agitating in the presence of a gaseous FIG. 1 shows the entire distilling device and FIG. 2 10 medium the thus formed foaming-agent-containing solu is a cross section therethrough taken in a direction from tion so as to cause foaming of the latter; subjecting the east to West, in other words, the inclined surfaces C and thus formed foam to solar heat so as to cause evaporation C face east and west, respectively, so as to obtain maxi of at least a substantial portion of the solvent constituent mum exposure to Solar radiation. of said foam; separating the thus formed solvent vapors; A represents a sea water container to which sea water 5 and condensing the thus separated solvent vapors. is fed through tube a. A dissolved detergent is introduced 2. A method as defined in claim 1, and including the through tube b in an amount such that the detergent con step of condensing said solvent vapors.

centration in the Sea water container A will remain sub 3. A method as defined in claim 1, wherein said solu stantially constant. Only very small and economically in tion is an aqueous salt solution.

significant amounts of conventional detergents are needed 20 4. A method as defined in claim 3, wherein said solu for operation of the device. tion is sea water.

Foaming is carried out by introducing through conduit 5. A method as defined in claim 1, wherein said agitat c, terminating in a nozzle head, a suitable gas such as ing of said foaming-agent-containing solution is carried compressed air into the liquid located in container A. In out by blowing a gas therethrough. troduction of the compressed air or the like will cause 25 6. A method as defined in claim 5, wherein said gas foam formation of the detergent-containing liquid and a is compressed air.

stable foam will be produced which passes through con 7. A method as defined in claim 1, wherein said agitat duit d and overflows from there onto the surfaces B of the ing of said foaming-agent-containing solution is carried distilling device, whereon the foam is exposed to solar out by stirring.

heat radiation passing through transparent inclined sur 30 8. A distilling device for distilling a foamable solution faces C and C, thereby causing evaporation of the thin liquid films forming the individual foam bubbles. The including said a solvent and a solute by utilizing solar heat, device comprising, in combination, foam-forming thereby obtained vapors condense into troughs D and D' means including means for agitating in the presence of and flow from there through conduits E and E' into col a gaseous medium said foamable solution so as to convert lecting devices such as tanks E. 35 at least a portion of the solution into a foam; solar dis It is well known that foam is a dispersion of a gas in a tilling means for exposing the thus formed foam to solar liquid and thus formation of a foam represents a way heat so as to vaporize at least a portion of the solvent of increasing the boundary surface between liquid and constituent of said foam; condensing means for con gas. In the present case, the gas preferably is air so that, densing the vaporized portion of said solvent; and conduit if the foam represents a fine dispersion of quasi-colloidal means for passing foam

from said foam-forming means type, the active evaporation surface per unit of volume is to said solar distilling means. increased to an extremely large extent. 9. A distilling device as defined in claim 8, wherein Since the evaporation surface in a conventional solar said foam forming means comprise a vessel adapted to distiller depends on the surface area of the liquid film hold solution to be distilled; introducing means for intro which is subjected to solar radiation, generally the larger ducing solution into said vessel so as to fill the same up the installation the greater the amount of vapors which to a predetermined level; and gas introducing means for can be produced in a given period of time. introducing gas into said vessel at a point below said On the other hand, when, in accordance with the pres ent invention, a saline foam is exposed to solar radiation, predetermined level.

the active evaporation surface depends only on the extent 50 said10.foam A distilling device as defined in claim 8, wherein forming means comprise a vessel adapted to of air dispersion in the liquid, and thus the geometrical hold solution to be distilled; introducing means for intro surface of the entire installation can be and will be consid erably smaller than the actual surface of the liquid film of to ducing solution into said vessel so as to fill the same up the dispersion which is subjected to solar heat. a predetermined level; and stirring means for stirring For these reasons, the present invention permits the use 55 said solution so as to foam the same. of relatively very small solar distilling installations and References Cited the efficiency of these devices is significantly increased by UNITED STATES PATENTS evaporating the saline foam, instead of a layer or con tinuous film of saline water which is directly supported by 863,031 8/1907 Lehnert.

a surface portion of the distilling device. 60 1,753,429 4/1930 Rice ------------ 252-359.5 X In addition, the depth of penetration of solar rays is 2,027,115 1/1936 Oman et al. -------- 203-20X considerably greater in a foam than in a non-foamed saline 2,616,839 11/1952 Ames ------------- 202-187 liquid, this again may be primarily due to the very small 2,782,162 2/1957 Liddell ----------- 203-20X thickness of the foam bubbles-forming films, and thus 2,981,629 4/1961 Ginnette et al. the evaporation is accelerated and the efficiency of the 85 3,282,327 11/1966 Hardy et al. -------- 159-1X operation is increased. FOREIGN PATENTS Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can 1,336,794 7/1963 France. by applying current knowledge readily adapt it for vari NORMANYUDKOFF, Primary Examiner. ous applications without omitting features that, from 70 F. E. DRUMMOND, Assistant Examiner.

the standpoint of prior art, fairly constitute essential char acteristics of the generic or specific aspects of this inven U.S. C. X.R. tion and, therefore, such adaptations should and are 159-1; 202-234; 203-50