Note: Descriptions are shown in the official language in which they were submitted.
~3~
SOLAR DISTILLATION APPARATUS
.
The present invention relates to solar distillation
apparatus and more particularly to apparatus for the solar
distillation of water.
In United States Patent No. 4,134,393 issued January
16, 1979 of which I am a co-inventor and the sole assignee,
and in United States Patent No. 4,194,949 issued March 25,
1980,of which I am sole inventor, solar energy distillation
apparatus are disclosed in which a par~ of the heat of conden-
sation of the condensing liquid is recovered. In the disclosed
embodiments in those applications, the heat of condensation is
transferred to a fluid in a fluid lens. The fluid lens is
disposed over the liquid to be distilled and is inclined to
provide an inclined bottom surface on which the evaporated
liquid is condensed and along which the condensate may flow to
be discharged from the lower end thereof. However, in order
to provide a suitable flow and discharge of condensate along
the bottom surface of the fluid lens the inclination of the
fluid lens should preferably be between about 10 to about 20.
The lens is also inclined to increase collection
of solar energy and in some locations, however, an inclination
of up to about 45 is desirable. At locations where a lens
inclination of greater than 20 is desirable to increase
collection, the system operates at reduced efficiency since
~13925S
the fluid lens i5 limited to angles of inclination of less
than about 20-. For example, at a latitude of 35 S, the
optimum angle of inclination for the lens will be about 45-
and a system with a lens inclined at about 20' will collect
less solar energy than a system with a lens inclined at the
optimm angle of 45-.
Additionally, the focal distance and concentration
of fluid lenses suitable for use in solar distillation
apparatus are competing factors. A large fluid lens is
desirable to provide a high concentration factor but the
focal distance of the fluid lens increases with its aperture.
Therefore, a comprise must be reached between the concentra-
tion factor and focal distance of the fluid lens in which the
concentration factor of the lens may not be as high as
desired in order to reduce the focal distance of the lens,
and the focal distance may be longer than desired to increase
the concentration factor of the lens. Moreover, since
the fluid lens must be placed at a greater distance from the
liquid than otherwise desired in order to increase its
concentration, there is a large volume, which is undesirable,
between the lens and the liquid to be distilled.
The spacing between the lens plates of the fluid
lens is determined by the lens characteristics desired and
the lens fluid used. The greater the spacing of the lens
plates, the lower the transmission efficiency of the lens.
For example, with a lens plate spacing of only about two
inches at the center of a lens having a convex upper plate
~139;~SS
and a flat lower plate, there are important transmission
losses through the lens. Transmission efficiency through the
fluid lens is also dependent upon the particular lens fluid
chosen. For example, when distilling salt water, salt water
may be chosen as the lens fluid and circulated through the
lens to preheat the water. However, there are also impGrtant
transmission losses through the salt water. Additionally,
when salt water is used as the lens fluid, deposits of salt
and minerals will accumulate within the lens requiring clean-
ing thereof.
In accordance with the present invention, these
drawbacks are substantially overcome and improved solar
energy distillation apparatus are provided.
It is an object of the present invention to provide
solar energy distillation apparatus of improved efficiency in
which a substantial part of the heat of condensation of the
condensed, distilled liquid is recovered.
It is another object of the present invention to
provide solar energy distillation apparatus of improved
efficiency in which a substantial part of the heat of conden-
sation of the condensed, distilled liquid is recovered and an
increased amount of solar energy collected.
These and other objects of the present invention
are accomplished by providing solar distillation apparatus in
which the solar energy is concentrated in the liquid to be
distilled and conduit means including a heat exchange fluid
therein are provided to condense the evaporated liquid vapor
~392S5
--4_
on a surface thereof, the conduit means being disposed
intermediate t'ne liquld to be distilled and means for concen-
trating the solar energy in the liquid.
In accordance with the invention, the apparatus
comprises lens means disposed above the liquid to be distilled
for concentrating the solar energy therein; conduit means for
passing a fluid therethrough disposed intermediate the lens
means and the liquid to be distilled and comprising an
inclined, lower wall having a smooth outer surface and having
a lower end; a fluid in said conduit means in a heat exchang-
ing relationship with said lower wall; and container means
disposed below said lower end for receiving condensed liquid.
The concentrated solar energy causes the liquid to evaporate
with the vapor impinging and being condensed upon the outer
surface of the lower wall, the condensed liquid flowing along
the outer surface of the lower wall to the lower end thereof
and falling therefrom into the container means, a substantial
part of the heat of condensation o~ the condensing vapor
being absorbed by the fluid in the conduit means.
The conduit means is transparent at least in part
and the solar energy is passed through the transparent
portions into the liquid to be distilled, the conduit means
and the lens means being superposed at least in part.
In the di,sclosed embodiments, the conduit means is
a flat conduit comprised of transparent upper and lower walls
sealingly joined, for example welded, to form the conduit.
According to one embodiment of the invention, a
~1392SS
plurality of sets or series of Fresnel-type lenses are
arranged over a container holding liquid to be distilled.
Each set of Fresnel lenses includes a plurality of individual
Fresnel lenses arranged end to end to provide an elongated
narrow focus. The series of Fresnel lenses are inclined with
respect to the horizontal. The container includes a plurality
of baffles dividing the container interior into a plurality
of distillation compartments for the liquid to be distilled.
The container bottom is inclined in the same direction of the
Fresnel lenses so that the compartments are offset in height.
The elongated focus of each series of Fresnel lenses may
therefore be located in and along a different compartment.
Interposed between the Fresnel lenses and the dis-
tillation compartments is a flat plate conduit containing a
heat exchange fluid. The flat plate conduit is inclined at
approximately 5 to 20 degrees with the horizontal and located
above the compartments so that evaporated vapor is condensed
on the lower surface of the conduit. The container also
includes a collection compartment for the condensate dispo~ed
adjacent the lower side thereof which is disposed below the
lower end of the flat plate conduit. The condensate flows
along the lower plate of the conduit to the lower end and i9
discharged therefrom into the compartment.
An expansion tank for the heat exchange fluid in
the conduit is located so as to provide minimal pressure
within the conduit.
A heat exchanger is also provided to transfer the
113~ZSS
--6--
heat recovered in the heat exchange fluid circulated in the
conduit to the liquid being introduced into the container to
preheat the liquid. The heat exchanger is also located to
minimize pressure in the conduit. Another solar energy
system may be utilized to further preheat the liquid to be
distilled, for instance to 75'C in the case of water, before
the liquid is introduced into the container.
In accordance with the invention, more fluid is
circulated in the conduit means than the quantity of liquid
introduced into the distillation compartments, evaporated
therefrom and condensed on the conduit means in order to
carry away the released heat of condensation while maintaining
the temperature of the fluid below that of the condensing
liquid vapor.
In the case of the distillation of salt water, the
quantity of fluid circulated through the conduit to absorb
and carry the heat of condensation released by the condensing
water vapor, will greatly exceed, for example, by 10 times,
the quantity of water evaporated, condensed and distilled by
the apparatus. Much more fluid is circulated in the conduit
to maintain the fluid temperature below that of the condens-
ing water vapor.
The liquid concentrated with impurities (in the
case of salt water, concentrated brine at for instance, 80-C)
may be recycled one or several times in separate distillation
unitq or in the distillation channels or compartments of the
same unit, the liquid concentrated with impurities (or the
~39%~;S
brine) being introduced into the distillation compartments to
take the place of at least some of the liquid to be distilled
which would otherwise be introduced into the compartments.
Thus, the heat of the liquid concentrated with impurities
(brine) may be recovered and the concentration of thereof may
be increased in successive compartments and units, allowing a
more economical extraction of, for example, salts from the
brine.
A separate heat exchanger using a fluid heated,
for instance, to 150-C by solar energy in a separate solar
energy unit can be used to preheat the liquid to be dis-
tilled, increasing its temperature, in the case of water to,
for instance, 75-C, before introducing the liquid into the
distillation compartment.
In accordance with another embodiment of the inven-
tion, the sets of Fresnel lenses are arranged so that the
elongated focus of at least one set is substantially parallel
to the axes of the compartments in the container and the
elongated focus of at least one other set is arranged so that
the elongated focus is transverse to the axes of the compart-
ments. According to this embodiment, the focus which is
transverse to the axis of the compartments extends into
varying depths of liquid in the container. The two sets of
Fresnel lenses are arranged at an angle to each other so that
they meet along an apex with each set having a lower end.
The conduit system on which vapor condenses is made up of two
flat plate conduits disposed at an angle along an apex with
~392S~
each conduit having a lower end disposed above compartments
for the distilled liquid.
In still another embodiment of the invention, a
composite system is provided made of of individual, adjacently
arranged units.
The Fresnel lenses may be replaced by fluid lenses,
if desired. However, the Fresnel lenses are preferred for
the reasons discussed above.
According to the present invention, production of
distilled water from salt water is substantially higher than
by conventional solar ponds. The cost of producing distilled
water may be reduced to zero in certain locations when salt
(NaCl) and/or magnesium chloride sulfate are extracted from
the concentrated brine.
According to another aspect of the invention, the
bottom of the compartment containing the liquid to be dis-
tilled is blackened preferably by flexible blackened material
which is impermeable to the liquid. In the case of water,
Esso Butyl or a similar material may be used. This allows
absorption of solar energy and enhances the heating of the
liquid, and also seals the bottom of the compartment.
Alternatively, the compartment bottom can be the ground
surface covered by the material instead of concrete, for
example.
In accordance with another embodiment of the
present invention the relatively large and deep distilla-
tion compartments are replaced by an undulated plate or
~1392SS
plurality of adjacent plates on top of an insulating base.
In accordance with a further feature of this embodi-
ment of the present invention, a single panel or plurality
of adjacent panels made of blackened flexible plastic or the
like, such as isobutyl, are disposed over all or bottom part
of the plates. They are to be attached to the plates in a
removable manner which will permit taking them out to remove
deposits which may form on them.
Furthermore, it is preferred that the undulated
plates be placed above the focal area of maximum concentration
obtained from the Fresnel lenses. This permits a wider
spread of the heat converging from the lens on the undulated
plates so that a wider area of the plates is heated. Another
feature of this embodiment is to allow the fluid circulating
between the double plates located between the Fresnel lenses
and the distilling basin with undulated plated to spread all
along the surface between the double plates and to selectively
regulate the quantity of fluid circulating, thus controlling
the temperature of the fluid by restricting the bottom
passage of the section at an extreme end of the plates
leaving a small opening for releasing the fluid.
In the same type of system, in accordance with
another feature of the present invention photovoltaic cells
are installed in one or more bottoms or valleys of the
undulated plates ~t the locations where the focus area of
the Fresnel lens are most concentrated. As in my previous-
ly disclosed systems, the lenses are supported for movement
~392S~
--10--
to track the location of the sun using either the systems
described in my previous applications or systems to be
described in more detail herein. Again, as with my other
system, although Fresnel lenses are preferred f`or a number of
reasons, liquid lenses may also be used.
With such an arrangement the photovoltaic cells
will produce electricity at the minimal additional cost
avoiding the cost which would be associated with a separate
solar installation for producing electricity. Furthermore,
where concentration of solar energy is used as is the case
with the present invention, the production of electricity can
be up to for instance 40 times that which it would be without
concentration. For example, the average yearly production of
electricity with concentration will be, for example 3 Watts
per cell for example, 5cm x 5cm compared with about 0.06
Watts per cell for cells exposed to the sun without concentra-
tion. Cost estimates have shown that installing an array of
photovoltaic cells in a distillation unit of the present
invention permits saving all of the cost of the solar system
otherwise required by the photovoltaic cells. Put another
way, it reduces by about half the total cost of the photo-
voltaic cell system when the solar need to concentrate the
solar energy is considered. Thus, the present solar energy
system uses a single concentrating means, i.e., lens system,
which supplies energy both for distillation and for generating
electricity.
Furthermore, the absorption of infrared rays by the
11392SS
fluid in the conduit means and by the water being distilled
which circulates above and around the photovoltaic cells
permits the production of electricity at higher efficiencies.
As temperature goes up the efficiency of silicon photovoltaic
cells goes down. At a temperature of 200-C the efficiency is
zero, and the cells melt. However, because of the absorption
of the infrared radiation by the circulating fluid and by the
water being distilled, temperatures are maintained lower.
The photovoltaic cells can preferably be encap-
sulated in a transparent plastic or glass cover of similar
shape either rectangular or round so as to protect the cells
from saline water which will flow above such covers. The
cells can also be enclosed in a transparent tube in which
distilled water such as cooled condensate produced by a
distillation unit can circulate and further absorb heat
generated by the infrared rays. Such a heat exchange can
reduce the temperature of the condensate from about 75-C to,
for example, about 30-C. With this arrangement, heated salt
water will not flow around the photovoltaic cells and form
deposits thereon. And, furthermore, the cells instead of
being surrounded by fluid at a temperature of up to 75 C,
will be surrounded by fluid at a temperature of only, for
example 40-C. The efficiency of the electricity production
is generally reduced by about 0.4% for every degree C increase
in temperature above, for example, 30-C. By encapsulating or
enclosing the cells and circulating cooling water around them,
the cells will be maintained at their optimum temperature for
i~3g25~
-12_
efficiently producing electricity and at the same time the
cells will be protected from any corrosion effects of the
salt water or salt deposits.
According to another aspect of the invention
involving distillation of salt water, a chemical such as
barilium chloride may be added to the salt water to prevent
the formation of otherwise insoluble deposits such as calcium
sulfate or unstable sodium bicarbonates which may form in the
salt water. Barilium sulfate may deposit during the nights,
for example, and can be extracted and sold for use in the
petroleum industry for drilling oil wells.
These and other aspects of the present invention
will be more apparent from the following description of the
preferred embodiments thereof when considered with the
accompanying drawings.
The present invention is illustrated by way of
example and not limitation in figures of the accompanying
drawings in which like references indicate similar parts and
in which:
Fig. 1 is a vertical cross-section schematic view
of solar distillation apparatus according to the invention
showing two ad~acent sets of Fresnel lenses arranged above a
container holding water to be distilled, a transparent
plate-like conduit on which vapor is condensed being inter~
posed between the container and the lenses, the plate-like
conduit and the lenses being inclined at about the same angle
to be substantially parallel;
255
-13-
Fig. 2 is a top plan schematic view, partly broken-
away, of the solar distillation apparatus of Fig. 1;
Fig. 3 is a vertical cross-section schematic view
of solar distillation apparatus according to the invention
similar to that shown in Fig. 1 with the Fresnel lenses being
inclined at a greater angle than the plate-like conduit;
Fig. 4 is a top plan view, partly broken-away, of
the solar distillation apparatus of Fig. 3;
Fig. 5 is an end elevation schematic view, partly
broken~away, of the solar distillation apparatus of Fig. 3;
Fig. 6 is a vertical cross-section schematic view
of solar distillation apparatus according to still another
embodiment of the invention showing two sets of Fresnel
lenses arranged above the container for the water to be
distilled with an inclined transparent plate-like conduit on
which vapor is condensed interposed between the len~es and
the container, one set of lenses extending generally parallel
to the axis of container and one set of lenses extending
transverse to the container axis, the two sets of lenses
being ad~acent and inclined with respect to each other
and with respect to the container and plate-like conduit;
Fig. 7 is a top plan schemati¢ view of the solar
distillation apparatus of Fig. 5;
Fig~ 8 is a vertical cross-section schematic view
of a compo~ite solar distillation apparatus utilizing a
plurality of ~ystems of the type shown in Figs. 6-7; and
Fig. 9 i~ a top plan schematic view of the composite
. ,. ~
~13~5S
-14-
system of Fig. 8.
Figure 10 is a cross-sectional elevation view
through the first embodiment of distillation apparatus
according to the present invention.
Figure 1Oa is a perspective view of the double
plate system of Fig. 1.
Figure 11 is a perspective view of the unit accord-
ing to Fig. 10, showing the installation of photovoltaic
cells.
Referring more particularly to the drawings, appara-
tus for the solar distillation of water are illustrated. In
Fig. 1, the distillation apparatus 10 includes a Fresnel lens
system 12 to concentrate the solar energy, a transparent flat
plate conduit 14 on the bottom of which water vapor is
condensed, and a container 16 having compartments 18a,b,c for
the water to be distilled and a compartment 22 for distilled
water which is discharged from the bottom of the conduit 14.
The sides 26, 28 of the container are offset in height and
the lens system 12 extends inclined along the sides of the
container between the ends 30, 32 thereof, the lens system
closing the top of the container and being supported by the
sides and ends of the container. Compartment 18a in the
ontainer is formed by the slde 26 of the container, a baffle
34 and the ends of the container; compartment 18b by baffles
34 and 36 and the ends of the container, and compartment 18c
by a partition 38 and the ends of the container. The parti-
tion 38 separates the compartments 18a,b,c holding water to
`` ~139ZS5
--15--
be distilled from comp2rtment 22 holding the distilled w2ter.
Compartments 18a,b,c extend parallel to the elongated axis of
the container.
The bottom 40 of the container is inclined down-
wardly from side 26 to side 28 at an angle A with respect to
the horizontal. The heights of baffles 34 and 36 are substan-
tially equal to provide the inclined container bottom 40 with
stepped compartments 18a,b,c so that during normal distilla-
tion operation, the maximum depths of the water to be dis-
tilled in compartments 1Ba,b,c are substantially equal. The
water to be distilled is introduced into compartment 18a and
overflows therefrom into the other compartments. The height
of partition 38 is higher than the heights of baffles 34, 36
so that the water to be distilled does not flow into compart-
ment 22. Since compartment 18a is separated from the other
compartments, the introduction therein of the water to be
distilled does not directly cool the heated water in the
other compartments.
The lens system 12 is inclined downwardly, extend-
ing from the higher side 26 to the lower side 28 of the
container substantially parallel to the container bottom 40
at approximately the angle A with the horizontal. The lens
system 12 includes two series 42, 44 of adjacently disposed
Fresnel lenses 46, each ~eries extending substantially
parallel to the elongated axes of the container and compart-
ments 18a,b,c. The inclined, parallel lenses are spaced by,
for example, one inch to prevent shadowing of adjacent
1139255
-16-
lenses. Two series of lenses are shown and each series oflenses is shown to include six lenses; however, one or three
or more series of lenses and more or less than six lenses may
be utilized per series depending upon the size of the
installation and the quantity of distilled water desired.
Each Fresnel lens comprises longitudinally extending prisms
47 which provide an elongated narrow focus. The series of
lenses are arranged to provide spaced parallel elongated
composite foci 48, 50. The composite focus 48 of lens series
42 is located in the water in compartment 18a while the
composite focus 50 of lens series 44 is located in the water
in compartment 18b, each focus extending substantially
parallel to the elongated axis of the respective compartment.
Offsetting the height of the compartments, i.e. providing an
inclined lower surface of the container and spaced baffles,
permits the foci of the inclined lens system to be located in
the different compartments.
Interposed between the lens system 12 and the top
of the container is the transparent flat plate conduit 14.
Conduit 14 is inclined downwardly from side 26 substantially
parallel to the inclination of the lens system, i.e. at
approximately angle A, and includes spaced opposed transparent
plates 52, 54 which extend downwardly from side 26 to above
the compartment 22 for the distilled water. The flat plate
conduit 14 is substantially co-extensive with the lens system
and extends between ends 30 and 32 and from side 26 downwardly,
terminating short of side 28 of the container. The flat
-16~ 25~
plate conduit and the Fresnel lenses are disposed to have a
minimal air space therebetween to reduce transmission losses
through the lenses and conduits and to reduce heat losses.
In the embodiment shown in Figs. 1 and 2, angle A has a
maximum value of about 20-.
The transparent plates 52, 54 are made for example
of glass or plastic and are sealed along the peripheries
thereof to be fluid-tight and thusly form the conduit 14.
The plates may be sealed at their peripheries by, for example,
welding or with a sealant such as silicone. A frame may be
provided in which the edges of the plates are mounted fluid-
tight using, for example, a silicone sealant. The plates 52,
54 are planar or flat, as mentioned, and are parallel, being
spaced by a distance of from about 6mm to about 12mm.
Openings are provided to the interior of conduit 14 to permit
the evacuation of air therefrom and for the circulation of a
fluid through the conduit 14. The lower plate 54 forms a
vapor barrier over the container.
The plates forming the conduit 14 may alternatively
be co-extensive in length and width with each Fresnel lens
series or each lens, with the plates being adjacently disposed
and sealed and the lower surfaces of adjacently sealed plates
forming a vapor barrier over compartments 18a,b,c to prevent
escape of vapor therepast. A frame and/or a sealant may be
used to sealingly join adjacent plates.
The lower end 56 of the conduit is supported by
frame means and is spaced from the top of partition 38 to
il39~5
--17--
provide the only opening through which vapor may pass from
the compartments. However, the spacing is small and the
escape of vapor therethrough is negligible. Water vapor
evaporated from compartments 18a,b,c rises and impinges upon
the bottom of the conduit 14 and condenses thereon. The
condensate flows downwardly past the opening between the
partition 38 and the conduit towards end 56 of the conduit
and is discharged therefrom into compartment 22 for the
distilled water. Thus, the opening between the partition 38
and the bottom surface of the conduit need only be large
enough to permit the condensate to flow therepast.
As mentioned, the plates are mounted fluid-tightly
to form conduit 14 with the lower surface of the conduit
forming ~ vapor barrier. The plates are thus mounted to form
a fluid-tight, elongated, generally rectangular enclosure
through which a heat exchange fluid may be circulated. As
mentioned, water vapor impinges upon the bottom of the conduit
and is condensed thereupon. Upon condensation of the water
vapor, the heat of condensation thereof is released and heats
the bottom plate or plates of the conduit. The bottom plate
or plates are also heated by the sensible heat Or the vapor
and condensate. A heat exchange fluid is c~rculated through
the conduit to recover a substantial part of the heat of
condensation and the sensible heat and to cool the bottom
platets) of the conduit to enhance condensation thereon.
The interior of the conduit 14 is connected to the
coil 59 of a heat exchanger 60 by conduits so that the heat
1~39:255
--18--
exchange fluid may be circulated through the conduit 14 and
the heat exchanger 60. An expansion tank 62 for the heat
exchange fluid is provided between the conduit 14 and the
coil of the heat exchanger, conduit 61 connecting conduit 14
to the reservoir. The expansion tank is located at approxi-
mately the same height as the conduit 14 to minimize pressure
in the conduit. Preferably, the heat exchanger is located
within about 50cm vertically from the expansion tank to pro-
vide a small height difference in the levels of the heat
exchange fluid, thereby requring a low pressure to circulate
the fluid. Angle A may be changed to further reduce the
pressure required to circulate the fluid. Thus, the conduit
need not withstand high pressures. The heat exchange fluid
may be circulated by pump 64 about a closed circuit which
passes through the conduit 14, conduit 61, the expansion
tank, conduit 63, the coil 59 of the heat exchanger and
conduit 67. Water to be distilled is introduced through
inlet 68 into a chamber 69 in the interior of the heat
exchanger so that the water in the chamber and the fluid in
the coil are in a heat exchanging relationship. The chamber
is connected to compartment 18a by conduit 70. Thus, the
water to be distilled may be pumped by pump 72 through the
heat exchanger and discharged into compartment 18a of the
container. Conduits 61 and 67 have been shown to include
only one conduit each. However, it is understood that each
may comprise more than one conduit depending upon the size
of conduit 14 and the quantity of fluid circulated there-
1~392~S
19-
through.
In operation, solar energy is concentrated by lens
series 42, 44 in elongated foci 48, 50 located in the water
in compartments 18a, 18b respectively. Water is introduced
into the container in compartment 18a and upon overflowing
baffle 34, enters compartment 18b; upon overflowing baffle
36, the water enters compartment 18c. As the water moves
from compartment 18a to compartment 18c, it is progressively
heated in compartments 18a and 18b by the concentrated solar
energy and a substantial portion thereof is evaporated. Since
the water overflowing into compartment 18b has been heated
in compartment 18a by the solar energy concentrated along
focus 50, the water in compartment 18b will reach a higher
temperature than the water in compartment 18a so that evapor-
ation from compartment 18b in the central part of the con-
tainer is accelerated. Heated water overflows into compart-
ment 18c from compartment 18b with evaporation continuing.
The water vapor rises and impinges upon the bottom plates of
the conduit and is condensed thereon. The condensate flows
downwardly along the bottom plates and is discharged into
compartment 22. Distilled water is removed from compartment
22 through conduit 74. The water in compartment 18c is a
concentrated brine also containing other minerals such as
magnesium chloride and magnesium sulfate and is removed
through conduit 76.
A clear heat exchange fluid is circulated through
the flat plate conduit, as mentioned, to recover a substan-
~139ZSS
-20-
tial part of the heat of condensation of the condensing
liquid and to cool the bottom plates of the flat plate con-
duit to enhance condensation. The heat exchange fluid is
circulated through the heat exchanger and the heat removed
from the heat exchange fluid is transferred to the incoming
water to be distilled to preheat it. Thus, a substantial
portion of the heat of condensation is recovered and used to
increase the efficiency of the system.
The heat exchange fluid circulated in the conduit
may be Therminol 66, a clear liquid available from Monsanto,
or a similar liquid, or distilled water which may have a
product such as glycol added thereto to raise the boiling
point of the distilled water and lower its freezing point.
According to the invention, the flat plate conduit
is used to condense the water vapor and accordingly the
plates thereof are spaced and the heat exchange fluid therein
is chosen to permit maximum transmission of solar energy
therethrough while accomplishing condensation of the water
vapor and recovery of a substantial part of the heat of con-
densation. The fluid circulating in conduit 14 is also
heated by the absorption of solar energy transmitted through
the Fresnel lenses and from solar energy reflected to the
fluid in the conduit from the water in the container.
In the embodiment shown in Figs. 1 and 2, the
Fresnel lenses 46 can, for example, be about 84cm wide by
about 250cm long and have a concentration factor of about 40
and a focal width of about 2cm; the container can, for
~3925S
exa~ple, be about 168cm wide by about 125cm long and the
height of baffles 34 and 36 can, for example, be about 50cm.
The width of the compartments can, for example, be about 40cm.
The water depth in the compartments can correspondingly be
about 5cm to about 50cm, which is relatively shallow. The
apparatus lO is arranged with its longitudinal axis in the
east-west direction and the lens system facing South. Prefer-
ably, the bottoms of the compartments are blackened by a
flexible dark sheet 131 such as Esso Butyl or a similar
material which is also water tight and is capable of with-
standing temperatures of up to 100-C and will absorb heat and
transfer it to the water to be distilled to increase the
temperature thereof. This will allow use of levelled earth
instead of concrete for the bottom of the channel, thereby
reducing the cost of the installation. The temperature of
the water introduced into compartment 18a is about 55 C and
can gradually reach about 85 C therein.
The quantity of fluid circulated in the flat panel
conduit 14 is much larger, for instance, by 10 times, than
the quantity of distilled water obtained through evaporation
and condensation of vapor on the conduit. This large quantity
of fluid is required to carry off the recuperated heat of
condensation while maintaining the temperature of the fluid
below that of the condensing vapor. Thus, condensation of
the water vapor continues on the bottom plate of conduit 14.
Referring now to Figs. 3-5, the solar distillation
apparatus 80 includes a container 82, a Fresnel lens system
1~39;;~
- 22 -
84 and a transparent flat plate conduit 86 similar to that
shown in Figs. 1 and 2 and described above. The container
bottom 88 and the Fresnel lens system 84 are each approxi-
mately inclined at an angle B with the horizontal while the
transparent flat panel conduit is inclined at the angle A, as
in Figs. 1 and 2. Angle B is in the range of from about 25,
to about 60. The higher side 90 of the container includes
a shoulder 92 to support the Fresnel lens system and space
it from side 90 so that the focus of lens 46a is located in
compartment 18a, as in Figs. 1-2. The transparent flat plate
conduit is spaced from the lens system since the lens system
and flat plate conduit are inclined at different angles with
the horizontal, the lens system and flat plate conduit being
inclined with respect to each other at an angle of B-A. The
lens system and conduit are therefore separated. The blaffles
34 and 36 are of unequal height, baffle 36 being higher than
baffle 34 to provide a greater depth of water in compartment
18b.
Apparatus 80 also includes a separate solar heater
92 which is illustrated to be of the type disclosed in United
States Patent 4,134,393 issued on January 16, 1979. The
collector 94 of heater 92 includes two conduits carrying fluids
therein heated by solar energy concentrated by lens system 96.
The coil 59a of heat exchanger 60a is connected to one of the
conduits, preferably the outer conduit 97 and a heat exchange
fluid is circulated through the outer conduit and coil 59a. Conduits
1139~55
--23--
98-100 complete the circuit with the fluid being pumped by
pump 101. Conduit 102 connects the chambers of the two heat
exchangers, and conduit 70 cornects the chamber of exchanger
60a to compartment 18a. Heater g2 is used to assist in pre-
heating the water to be distilled which is introduced into
compartment 18a of apparatus 80. The water to be distilled
passes first through heat exchanger 60 as described for Fig.
1, and then through heat exchanger 60a before being intro-
duced into compartment 18a through conduit 70.
Apparatus 80 operates similar to apparatus 10 and
provides additional heat from heater 92 to preheat the water
introduced into container 82. Additionally, the lens system
is inclined at an optimum angle towards the south to collect
additional solar energy. A fluid as described for conduit
14 of Fig. 1 is circulated through heater 92 and can be
heated to about 280 C. The heat exchanger 60 transfers heat
recovered by the fluid in conduit 14 to the water to be dis-
tilled. In apparatus 80, the water is preheated and intro-
duced into compartment 18a at a temperature which can reach
about 75 C.
Other details of apparatus 80 are similar to
apparatus 10. Only two Fresnel lenses have been shown for
apparatus 80 for clarity, but it is understood that the lens
system may comprise series of lenses as for apparatus 10.
In Figs. 6-7, solar distillation apparatus 104
includes a lens system 105, container 106 and a flat-plate
transparent conduit system 107. Container 106 includes sides
il3~32~5
-24-
108, 109 and ends 110, 111 which with support 112 support the
lens system 105. The container 106 comprises partitions 113,
114 disposed in the container adjacent walls 108, 109 to form
compartments 115, 116 for the distilled water. Each compart-
ment is formed by the bottom 118, sides and portions of the
ends of the containers and the partitions. Baffles 120-122
are also provided in container 106 extending substantially
parallel to the partitions to form with partitions 113 and
114 and portions of the container end, compartments 124a,b,
c,d for the water to be distilled. The heights of the
baffles 120-122 are less than the heights of the partitions
113, 114 so that the water to be distilled will not overflow
into compartments 115, 116 during normal distillation
operation.
The lens system 105 includes lens series 126 and
128 of Fresnel lenses 46. The lenses of series 126 are
arranged with their longitudinal axes and the axes of the
refracting prisms 47 extending parallel to the longitudinal
axes of the compartments. The lenses of series 128 are
arranged with their longitudinal axes and with the axes of
the refracting prisms 47 of the lenses extending substan-
tially transversely to the longitudinal axes of the compart-
ments. Lens series 126 and 128 are inclined with respect to
each other with the two lens series meeting over the con-
tainer and forming an apex 130 thereabove. Lens series 126
extends from apex 130 downwardly at an angle C with the hori-
zontal and is suppoted by side 108 of the container. Lens
11392SS
series 128 extends from apex 130 downwardly at an angle D
with the horizontal and is supported on side 109 of the
container. Support 112 extending at the apex supports the
lens system thereat. Side 108 is higher than side 109 and
the apex 130 is located closer to side 108 than side 109.
Therefore, angle D is greater than angle C. The bottom 118
of the container is inclined at an angle E with the~hori-
zontal, the water to be distilled being introduced into
compartment 124a and overflowing into com?artments 124b-d.
Concentrated brine is removed from compartment 124d.
Each of lenses 46a,b,c of lens series 128 has an
elongated focus 132a,b,c extending transverse to the axes
of the compartments (Fig. 6) and extending through varying
depths of water. Each of lenses 46d,e has an elongated focus
132d,e extending within compartment 124a with the axes of
foci 132d,e extending substantially parallel to the axis of
compartment 124a, each focus extending through a substan-
tially con~tant water depth with the two foci being at
different water depths.
The transparent conduit system 107 includes trans-
parent conduits 14a, 14b inclined with respect to each other
along apex 136, each extending downwardly at the angle A, as
described for Fig~ 5, towards sides 108 and 109,
respectively. Supports suspend the transparent conduits
above the container with the lowermost ends of the conduits
being above compartments 115, 116. Each conduit lower surface
forms a vapor barrier as described for conduit 14 in Figs.
~13~255
-26-
1-5 and the lower surface of the apex is sealed fluid-tight
so that the conduit system 107 forms a vapor barrier above
the container. The circuit for the fluid in the conduits 14a
and 14b passes serially through the conduits and the heat
exchanger 60. The water to be distilled passes serially
through heat exchanger 60 and heat exchanger 60a. The angles
of inclination of the lens series exceeds angle A and there
is a space between the conduit system and the lens system,
as described for Figs. 3-5.
Apparatus 104 also includes the heat exchanger 60a
and the solar heater 92, as described for Figs. 3-5. More-
over, two conduits 14a, 14b are provided and two compartments
for the distilled water are provided to increase the produc-
tion of distilled water.
Apparatus 104 is arranged so that the compartments
extend generally east-west and operates similar to apparatus
10 and 80. Apparatus 104 includes the intersecting lens foci
which serve to heat the water at different depths transverse
to the axis of the compartments as well as substantially
parallel to the axes of the compartments. Additionally, the
lens system 105 includes lens series which can be tilted to
the north and to the south at, for example, 10- and 30',
respectively to collect more solar energy than the apparatus
of Figs. 1-5. The temperature of the water in compartments
124a-d can gradually reach about 85 C.
While the lens series 126, 128 have been shown to
include three and two Fresnel lenses, respectively, it is
-27-
understood that each series may comprise more or less lenses
having the same or different sizes so that the lens sy.stem
extends over substantially the entire top of the container.
Although not shown, means may be provided to move
the lens systems to track the sun to further increase produc-
tion of distilled water.
Mirrors may be disposed along selected portions
of the prisms of the Fresnel lenses to further concentrate
the solar energy in the liquid to be distilled.
Excess water vapor not condensed in the distilla-
tion apparatus may be removed and superheated in a heat
exchanger using a heater such as solar heater 92. The super-
heated steam at 250-C for example, can be expanded in a
turbine to obtain power and condensed to obtain additional
distilled water.
Referring now to Figs. 8 and 9, a composite dis-
tillation system 140 is shown which comprises a plurality
of individual, adjacently arranged systems 104a-104d. Each
system 104a-104d is similar to system 104 with adjacent
systems having common compartments 115a for receiving dis-
tilled water. Each system 104a-104d is individually supplied
with water to be distil'ed and heat exchange fluid for cir-
culating in the conduit system of each system 104a-104d.
Common conduits, however, may be u~ed to supply and withdraw
the water and fluid.
The brine which is athigh temperature and at a
higher concentration than the water (salt water) to be dis-
~139255
-28-
tilled, can be serially fed to one or more successive dis-
tillation units. Moreover, a countercurrent arrangement may
be set up within a single unit or among several units in
which the concentrated brine of downstream compartments is
supplied to the upstream compartments. Thus, the heat in
the brine at about ôO-C, for instance, can be recuperated
and used to enhance evaporation of water in other compart-
ments or units. Additionally, the brine will be concentrated
and allow a more economic extraction of salt and/or other
chemicals such as magnesium chloride, magnesium sulfate, etc.,
therefrom.
Fig. 10 is a cross-sectional view of another embodi-
ment of solar distillation apparatus according to the present
invention. The distillation apparatus 210 of Fig. 10 includes
a Fresnel lens system 212 supported base structure 218, hav-
ing a front wall 220, a bottom wall 222 and a rear wall 224.
On the base structure is a container 219 including an insulat-
ing base plate 226 which rests on walls 220 and 224, a bottom
end wall 221 and a top end wall 223. The Fresnel lens are
supported by supports 214 and 216 which are attached to end
walls 221 and 223 respectively. The container will, of
course, have appropriate side walls, not shown on the figure.
On top of this insulating base plate 226 i9 an undulated
plate system 228 which can be made up as a single system or
made up a~ a plurality of plates. The height of each of the
undulations 230 should be, for example, 90 mm (about 3.5
inches). The distance between undulations should be, for
~139ZSS
-29-
example, 120 mm (about 5 inches). The Fresnel lens system
212 is tilted to an angle of, for example 30 and base plate
226 with the plate system 228 thereon tilted, in the illus-
trated embodiment, to an angle of 20-. Interposed between
the Fresnel lens 212 and the plate system 228 and parallel
to base plate 226 is a double plate conduit 232. In this
double plate conduit, having a lower plate 231 and upper
plate 233, a fluid 35 circulates in the manner described
above. Salt water 237 which is to be evaporated is sup-
plied to upper end of the plate system 228 through end wall
223 and flows downward over the undulations 230. In the
process, heat from the sun which is concentrated by the
Fresnel lens system, in the illustrated embodiment includes
a Fresnel lens 212a and a Fresnel lens 212b, evaporates some
of the water in salt water flowing over the invention in
order to spread the solar energy over a larger area, the
focal points of the Fresnel lenses 212a and 212b designated
as points 234 and 236, respectively, are located below the
insulating base 226. Typically, for example, if the focal
distance of the lens is 105 mm [42 inches], i.e., where there
is a distance of 42 inches from the lens to the maximum area
of concentration, the plates will preferably be located at,
for example, 90 cm [35.5 inches] from the lens. The evapor-
ated water vapor 239 which will typically be about 75-C rises
and is condensed on the bottom plate 231 of conduit 232 which
contains a fluid 235 typically at 30 C. The condensate 241
runs down the inside of the plate and is collected in a com-
~13~; :S~i
3o -
partment 238 from which it flows through an opening 239 to
a compartment 252. The fluid 235 flowing between the plates
231 and 233 of the conduit 232 is collected in a compartment
240. Brine 243 which results from the evaporation of the
water from the salt water flows through an outlet 242 of the
plate system 228 through plate 226 to a compartment 248.
The plates of the plate system 228 are preferably
made out of metal such as steel, stainless steel or coper,
having a thickness of, for example, 1 mm. It is preferred
that they be covered by a black paint or chrome black. The
paint or other agent used should be of an anti-corrosive
material and provision should be made, if necessary, to pro-
vide cathodic protection for the metal structure to prevent
the damage which could result from electrical currents caused
by the reaction between the metal surfaces and existing
chemicals in an electrolytic solution in the water.
As an alternative to metal, undulated asbestos
fiber, glass or plastic plates can be used. Metallic
undulated plates are preferred since they will conduct heat
to all sides of the plates, from the location of the striking
solar rays in the focal area.
As the water being distilled flows over the undula-
tions, it will be in cavities which are only about 90 mm deep.
The thinness of the water in the cavities between the undula-
tions 230, coupled with the thin layer of water which flows
over the undulations 230 will result in fast heating and
evaporation of the water.
1139;~5
Since deposits can form on the plate system 228,
a single panel of plurality of adjacent panels made of
blackened flexible plastic or the like such as isobutyl can
be used to cover the wall or the bottom plate system and be
attached thereto in a removable manner so that the plastic
oovering can be taken out and the deposits thereon removed.
The double plates 231 and 233 are partially obstructed at
the extreme ends (see Fig. 1Oa) by silicone or other means
leaving a small outlet 233a for the release of the fluid to
compartment 240. This is done so to allow the fluid 235 to
spread all over the surface between the plates 231 and 233.
A valve 233b at the upper end of the double plate system 232
permits selectively controlling the flow of the fluid 235.
The fluid 235 will flow to a collector 43 at the inlet to
the double plates 232 from a tank 233c at a height of, for
instance 40 cm (about 17") above the collector 243 so as to
allow a maximum pressure between the plates 231 and 233.
In accordance with another feature of the embodi-
ment of FIG. 1, storage areas are located beneath the insulat-
ing plate 226. Shown is a storage area 248 for brine 242,
a storage area 250 for the fluid 235 circulated in the double
plate conduit 232, a storage area 252 for the condensate 241
and a storage area 254 for concentrated brine. By storing
the various fluids beneath the insulating base, further
insulation and retention of heat within the system is
obtained. Circulation of the various fluids can be carried
out in the manner described above. Basically the fluid
~39;;~5S
-32-
collected in the compartment 40 which normally starts out at
30-C and is then heated up to approximately 65 C by the vapor
at 75 C is circulated to a heat exchanger 251 where it trans~
fers heat to the incoming salt water and in the process is
cooled back down to 30-C. It is then recirculaed to a con-
tainer 233c and flows through valve 233b entering the double
plate system through end wall 223. Condensate from compart-
ment 252 can also be circulated th rough heat exchanger 251.
In addition, recirculation of the brine for concentration
thereof and removal of additional heat therefrom in the manner
described above may be carried out as shown. Salt water from
heat exchanger 251 along with additional preheated saltwater
from another solar system 253, such as that of my previous
application or as described below, enters plate system 228
through opening in end wall 223.
Fig. 3 is a perspective view of a system such as
that shown in the Fig. 1. Once again, the insulating base
226 is shown as is the plate system 228 with its undulations
230. The two Fresnel lenses 212a and 212b are shown as is
the double plate conduit 232. However, in this embodiment,
at the bottom of the plate system above the points 234 and
236 where the solar energy is concentrated (See Fig. 1),
there are installed arrays of photovoltaic cells 259. Photo-
voltaic cells 259 produce electricity from the visible solar
rays only, i.e., those form 0.4 to o . 8 microns. The infrared
rays will be mostly absorbed by the fluid flowing in the
double plate system 232 and by the water being distilled
1139255
--33--
which circulates above and around the photovoltaic cells.
By using such an arrangement a separate photovoltaic cell
installation in order to produce electricity is not neces-
sary. Furthermore, because of the concentration of the solar
energy by the lenses, a production of electricity up to, for
instance, twenty times that can only be produced with concen-
tration. For example, the average yearly production of elec-
tricity may be increased to about three watss per cell with
the concentration as compared with about 0.061 Watt per cell
without concentration.
This arrangement offers many advantages since it
allows concentrating the energy on the cell and, at the same
time, removing infrared energy, which should otherwise heat
up the cell and reduce its efficiency. The infrared energy
is absorbed by the water 237 being distilled and by the fluid
235 in the dual plate conduit 232 and the distilled water
around the cells circulating in the tube enclosing the cells
are shown herein, whereas the visible light is utilized to
generate electricity. Thus, simply for the additional cost
of the cells themselves, a system which is both a distilling
and an electrical generating unit is provided. Without such
cooling, the temperature wou,d be higher reducing the
efficiency of the silicon voltaic cells and if the tempera-
ture exceeded 200-C, the efficiency would drop to 0 and the
cells could melt.
The array of photovoltaic cells can be installed
in a transparent square encapsulate protecting the cells
~1~9~55
from the saline water and over and above which saline water
is circulated.
The advantages of the present invention, as well
as certain changes and modifications of the disclosed embodi-
ments thereof, will be readily apparent to those skilled in
the art. It is the applicant's intention to cover by his
claims all those changes and modifications which could be
made to the embodiments of the invention herein chosen for
the purposes of the disclosure without departing from the
spirit and scope of the invention. Protection by Letters
Patent of this invention in all its aspects as the same are
set forth in the appended claims is sought to the broadest
extent that the prior art allows.
