Water distillation method

A method of desalinating water in which a stream of air is saturated with heated water containing dissolved solids and suspended solids. A stream of saturated air is passed through a cooling element to cool saturated air below its dew point, and the water thereby condensed is collected. In preferred embodiments, the cooled air is heated and recirculated through an evaporation screen to saturate the stream of air.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention concerns a method and apparatus for removing dissolved and 
suspended solids from water. It is especially directed towards a method of 
desalinating sea water. 
2. Background of the Invention 
It is known that air is saturated with water when the partial pressure of 
water in the air is equal to the vapor pressure at that temperature. If 
the partial pressure of water exceeds the vapor pressure, the air is said 
to be super saturated. This situation can occur when the temperature of 
saturated air decreases. As the temperature decreases, the relative 
humidity of the saturated air become greater than one-hundred percent and 
the super saturated air cannot hold this much water. The excess water then 
condenses. The temperature at which the partial pressure of water equals 
the vapor pressure is known as the dew point. 
The principle of cooling air below its dew point has previously been 
employed in distilling water. For example, U.S. Pat. Nos. 4,014,751 and 
4,344,826 disclose structures in which liquid is evaporated by being 
heated with a heating element, the evaporated liquid then being passed 
through a condenser to cool the vapor and collect distillate therefrom. 
These prior art structures have the advantage of separating water from a 
dissolved impurity such as salt because the heating elements evaporate 
only water, thereby leaving dissolved and suspended solids such as salts 
behind when the water vapor moves to the condenser. These prior art 
devices, however, require heating water with a heating element in order to 
evaporate the water before it reaches the cooling element. The heating and 
evaporating step requires substantial input of energy because of the high 
specific heat of water. 
Since water boils at lower temperatures at lower air pressures, other prior 
art devices have reduced and the pressure in an evaporator to enhance the 
production of steam as water is heated. An example of such a method is 
shown in U.S. Pat. No. 3,725,206. The development and maintenance of even 
a partial vacuum requires specialized pumps having high energy 
requirements. 
It is an object of the present invention to provide a more efficient method 
of removing dissolved and suspended solids from water by evaporating the 
water without applying heat from a heating element. 
It is a further object of the invention to avoid the necessity for reducing 
air pressure to promote evaporation of the water. 
It is another object of the invention to provide a compact, portable and 
efficient apparatus for desalinating water that is capable of being used 
on offshore structures such as oil platforms. 
SUMMARY OF THE INVENTION 
The aforementioned objects are achieved by a method for desalinating water 
in which a stream of air is saturated with the water by flowing the water 
over an evaporation screen. The saturated stream of air is then passed 
through a cooling element to condense the water therein, the water then 
being collected in a collection pan disposed beneath the cooling element. 
The air which passes through the cooling element is thereafter heated in a 
heating element and recirculated through the evaporation screen over which 
water is flowing. In preferred embodiments, the water flowing over the 
screen is heated before it reaches the screen.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIGS. 1-3, an apparatus 10 is shown for removing dissolved 
and suspended solids such as sodium chloride salt from a raw liquid, such 
as raw water from the ocean. Apparatus 10 includes a closed loop 
refrigeration system comprised of a conduit loop through which a 
refrigerant fluid flows, the system having a cooling portin 12 and a 
heating portion 14 (FIG. 1). A compressor 16 is disposed in the system 
between cooling portion 12 and heating portion 14. Compressor 16 is 
connected to the refrigeration system so that the refrigerant fluid (for 
example Freon.RTM.) flows from cooling portion 12 into compressor 16 and 
thence into heating portion 14. 
An expansion valve 18 (FIG. 1) is disposed between cooling portion 12 and 
heating portion 14 of the system, valve 18 being in fluid communicating 
relationship with both portions 12, 14. 
A counter current, liquid-liquid heat exchanger 20 is disposed in the 
heating portion 14 of the refrigeration system, heat exchanger 20 being 
comprised of a raw water conduit in heat exchanging relationship with the 
conduit of the heating portion 14 of the system, the exchanger 20 being 
provided with an inlet 22 for the introduction of raw water and an outlet 
24. In order to increase the area of contact between the raw water conduit 
and the conduit of the heating portion of the system, the system conduit 
and raw water conduit are arranged in a snake-like series of U-shaped 
loops. 
A rectangular box enclosure 26 has a rectangular base and four upright, 
rectangular walls. Enclosure 26 contains an air saturation sector 28 and a 
condensation sector 30 (FIGS. 2 and 3). Enclosure 26 has an open, 
rectangular top 31 and an open side 32. In the embodiment shown in FIG. 3, 
side 32 has a pair of vertical slats, one on either side of open side 32, 
which enclose therebetween a square opening wich can be covered with a 
filter screen. 
An L-shaped air return conduit is generally designated by the numeral 34 in 
FIGS. 2 and 3, conduit 34 being configured to cover the open top 31 and 
open side 32 of the enclosure 26. Air return conduit 34 is further 
comprised of a first, box-like member 36 and a second box-like member 38, 
the members 36, 38 being perpendicular to one another and having a 
continuous passageway therethrough. The bottom face 40 of first member 36 
is closed, as is the vertical side face 42 of second member 38 (FIG. 2). 
First member 36 is further comprised of a pair of flat, parallel faces 
designated outer face 44 and inner face (not shown). Second member 38 is 
comprised of flat, horizontal, closed outer face 46 and closed inner face 
48. First member 36 closes open side 32 of enclosure 26, the open inner 
face of first member 36 fitting in fluid communicating relationship 
against the opening in open side 32. Second member 38 is of substantially 
the same transverse and longitudinal dimensions as the open top of 
enclosure 26, and fits in closing relationship over the open top 31 of 
enclosure 26. A circular opening 50 is provided in inner face 48 of second 
member 38 for establishing fluid communication between the interior of air 
return conduit 34 and air saturation sector 28 of enclosure 26. Conduit 34 
is secured to enclosure 26 with a hinge (not shown) at the intersection of 
faces 48, 42 to provide pivotal movement of conduit 34 up and away from 
enclosure 26. 
A V-shaped evaporation screen 52 is provided within air saturation sector 
28 of enclosure 26, the V of screen 52 opening upwardly and having first 
and second top edges parallel to the plane of open side 32. Screen 52 is, 
in preferred embodiments, made of a material over which water freely 
flows. Examples of suitable material include open cell foam or fiberglass 
like material used in air conditioner filters. Both of these materials 
serve the function of greatly increasing the surface area over which the 
water flows while permitting air to be blown therethrough. The upper edges 
of evaporation screen 52 enclose opening 50. The width of evaporation 
screen 52, defined as the distance between the parallel upper edges 
thereof, is substantially the same as the width of air saturation sector 
28, defined as the distance between sidewall 54 and baffle 56. The length 
of screen 52 is substantially the same as the length of air saturation 
sector 28. The similar dimensions of the screen 52 and sector 28 permit 
screen 52 to substantially fill sector 28, at least near the open top 31 
of enclosure 26. Screen 52 is suspended from a pair of parallel perforated 
fluid conduits 58, 60 which span the length of air saturation sector 28 
(FIG. 3) and which are mounted in the side walls of enclosure 26 by being 
placed through cylindrical openings through the side walls. Screen 52 is 
mounted on conduits 58, 60 by being looped around the conduits. Conduits 
58, 60 are in fluid delivering relationship to screen 52, while conduits 
58, 60 are also in fluid communicating relationship with outlet 24 (FIG. 
1) through manifold 61 (FIG. 3). 
A centrifugal blow 62 is rotatably mounted in return conduit 34 around 
opening 50. Blower 62 is comprised of a pair of parallel rings (not shown) 
interconnected with a plurality of parallel vanes 64 (FIG. 3) which are 
perpendicular to the rings. Motor 66 is mounted on top of second member 38 
with the shaft of motor 66 projecting through outer face 46 of top member 
38. This shaft, which is not shown in the drawings, rotates blower 62 to 
circulate air from saturation sector 28, through opening 50 and into 
member 38. 
A heating element 68 is shown in FIG. 3 disposed within enclosure 26 
between screen 52 and cooling element 72 (described below). Heating 
element 68 is comprised of a plurality of conduit coils 70 in fluid 
communicating relationship with the fluid in heating portion 14 of the 
refrigeration system. The coils 70 of heating element 68 substantially 
cover a transverse, cross-sectional area of enclosure 26 between screen 52 
and cooling element 72. 
Cooling element 72 is disposed within enclosure 26 between open side 32 and 
heating element 68. Cooling element 72 is comprised of conduit coils 74 in 
fluid communicating relationship with the fluid in the cooling portion 12 
of the system, coils 74 substantially covering a transverse, 
cross-sectional area of enclosure 26 which is parallel and adjacent to 
open side 32. 
Condensation sector 30 serves as a water collection pan beneath cooling 
element 72. In other embodiments, a smaller water collection pan, which 
covers the area of sector 30 underneath cooling element 72, can be used. 
Water collecting conduit 76 conveys water accumulated in the water 
collection pan from sector 30 to a receptacle for the collection of the 
distilled water. 
Since the water in apparatus 10 is being distilled in a very humid 
environment, the growth of bacteria may be promoted. In order to diminish 
the likelihood of such a possibility, an ultraviolet light 78 is provided 
for illuminating the area between screen 52 and cooling coil 72. In 
preferred embodiments, ultraviolet light 78 also illuminates the 
collection area or collection pan beneath cooling coil 72. In especially 
preferred embodiments, additional ultraviolet lights can be added outside 
the enclosure adjacent collecting conduit 76. 
In operation, the refrigerant fluid (Freon.RTM.) in the refrigerant system 
is compressed by compressor 16 to heat the fluid to approximately 
120.degree. F. This fluid is then passed through counter current, 
liquid-liquid heat exchanger 20 (FIG. 1) to bring the fluid into heat 
exchanging relationship with sea water introduced through inlet 22. The 
temperature of water as it enters inlet 22 is typically 75.degree. F., 
that is, ambient temperature. As the raw sea water passes through the 
loops of heat exchanger 20 it is heated by the hot, 120.degree. fluid in 
the system. By the time water emerges from exchanger 20 and enters outlet 
24 the temperature of the water is approximately 120.degree.. The now 
heated salt water flows through perforated conduits 58, 60 and leaves 
these conduits through the perforations therein. Since conduits 58, 60 are 
disposed adjacent the top of screen 52, water flows out of conduits 58, 60 
and into screen 52. A steady flow of water through screen 52 is thereby 
created, and after water flows to the bottom of screen 52 it is collected 
at the bottom of air saturation sector 28 and removed through waste water 
outlet 80. The heated Freon.RTM. fluid in portion 14 of the system then 
passes through heating element 68 to heat coils 70 of element 68, The 
Freon.RTM. fluid in the system raises the temperature of coils 70 in 
heating element 68 to approximately 120.degree.. 
The hot Freon.RTM. fluid in portion 14 of the system then passes to 
expansion valve 18, where it is expanded. Expansion of a fluid reduces its 
temperature, so the fluid in the refrigerant system is now cooled. In the 
preferred embodiment, the fluid in portion 12 of the system is at 
40.degree. F. This cooled fluid now moves through coils 74 of cooling 
element 72 to reduce the temperature of element 72 to approximately 
40.degree. F. The fluid then leaves cooling element 72 and is recirculated 
to compressor 16 where the fluid is once again heated by being compressed. 
Centrifugal blower 62 is rotated by supplying electrical energy to motor 66 
from an energy source (not shown). As vanes 64 of blower 62 rotate, the 
air in evaporation sector 28 moves through screen 52 to the interior of 
blower 62 and thence upwardly into the area enclosed by member 38 of 
conduit 34. The arrows marked with the numerals 82, 84 schematically 
designate the path followed by the air as it flows through the screen and 
into conduit 34. As air passes through screen 54 it is saturatd with 
water, while any dissolved and suspended solids in the water remain in 
solution or in the screen 52. 
The stream of saturated air 86 passes through cooling element 72 to cool 
the saturated air to about 40.degree. F., which is below the dew point of 
the saturated air. The air was heated to approximately 120.degree. F. 
before being passed through screen 52 in a manner to be described below. 
When stream 86 passes through cooling element 72 the water carried by 
stream 86 condenses. The now unsaturated stream of air 88 passes from 
cooling element 72 to heating element 68. Stream 88 is heated as it passes 
through heating element 68, emerging from element 68 at arrow 90 at a 
temperature of about 120.degree. F. This heated air enters evaporation 
sector 28 and passes through screen 52, thereby being recycled back 
towards and centrifugal blower 62. The heated air is thereby recycled and 
directed through evaporation screen 52. Heating air prior to passing it 
through screen 52 increases its capability to carry moisture. 
As water condenses on cooling element 72, it moves downwardlly under the 
influence of gravity. The water then accumulates on the bottom of 
condensation sector 30 or in a collection pan provided for that purpose. 
The distilled water is collected through collecting conduit 76 and stored 
until needed. 
As the saturated air passes from heating element 68 to evaporation screen 
52, it is illuminated by ultraviolet light 78 which destroys bacteria 
which may otherwise thrive in the humid environment inside enclosure 26. 
Additional ultraviolet lights positioned, for instance, at conduit 76 
serve the same function elsewhere in apparatus 10. 
Although a detailed description of the preferred embodiment of the 
invention has been provided in accordance with law, the invention is at 
least as broad as the scope of the following claims.