Note: Descriptions are shown in the official language in which they were submitted.
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CBB954
WATER PURIFYING APPARATUS AND PROCESS
FIELD OF THE INVENTION
This invention relates to a method of purifying water using a thermoelectric
module and apparatus of use in said process.
BACKGROUND TO THE INVENTION
Thermoelectric modules are small, solid state, heat pumps that cool, heat and
generate power. In function, they are similar to conventional refrigerators in
that they
move heat from one area to another and, thus, create a temperature
differential.
A thermoelectric module is comprised of an array of semiconductor couples (P
and N pellets) cormected electrically in series and thermally in parallel,
sandwiched
between metallized ceramic substrates. In essence, if a thermoelectric module
is
connected to a DC power source, heat is absorbed at one end of the device to
cool that
end, while heat is rejected at the other end, where the temperature rises.
This is known as
the Peltier Effect. By reversing the current flow, the direction of the heat
flow is
reversed.
It is known that a thermoelectric element (TEE) may function as a heat pump
that
performs the same cooling function as Freon-based vapor compression or
absorption
refrigerators. The main difference between a TEE device and the conventional
vapor-
cycle device is that thermoelectric elements are totally solid state, while
vapor-cycle
devices include moving mechanical parts and require a working fluid. Also,
unlike
conventional vapor compressor systems, thermoelectric modules are, most
generally,
miniature devices. A module typical measures 2.5 cm x 2.5 cm x 4 mm, while the
smallest sub-miniature modules may measure 3 mm x 3 mm x 2 mm. These small
units
are capable of reducing the temperature to well-below water-freezing
temperatures.
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Thermoelectric devices are very effective when system design criteria requires
specific factors, such as high reliability, small size or capacity, low cost,
low weight,
intrinsic safety for hazardous electrical environments, and precise
temperature control.
Further, these devices are capable of refrigerating a solid or fluid object.
A bismuth telluride thermoelectric element consists of a quaternary alloy of
bismuth, tellurium, selenium and antimony - doped and processed to yield
oriented
polycrystalline semiconductors with anisotropic thermoelectric properties. The
bismuth
telluride is primarily used as a semiconductor material, heavily doped to
create either an
excess (n-type) or a deficiency (p-type) of electrons. A plurality of these
couples are
connected in series electrically and in parallel thermally, and integrated
into modules.
The modules are packaged between metallized ceramic plates to afford optimum
electrical insulation and thermal conduction with high mechanical compression
strength.
Typical modules contain from 3 to 127 thermocouples. Modules can also be
mounted in
parallel to increase the heat transfer effect or stacked in multistage
cascades to achieve
high differential temperatures.
'These TEE devices became of practical importance only recently with the new
developments of semiconductor thermocouple materials. 'The practical
application of
such modules required the development of semiconductors that are good
conductors of
electricity, but poor conductors of heat to provide the perfect balance for
TEE
performance. During operation, when an applied DC current flows through the
couple,
this causes heat to be transferred from one side of the TEE to the other; and,
thus,
creating a cold heat sink side and hot heat sink side. If the current is
reversed, the heat is
moved in the opposite direction. A single-stage TEE can achieve temperature
differences
of up to 70°C, or can transfer heat at a rate of 125 W. To achieve
greater temperature
differences, i.e up to 131°C, a multistage, cascaded TEE may be
utilized.
A typical application exposes the cold side of the TEE to the object or
substance
to be cooled and the hot side to a heat sink, which dissipates the heat to the
environment.
A heat exchanger with forced air or liquid may be required.
Water in bulk may be purified by a number of commercial methods, for example
by reverse osmosis and by distillation processes.
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Reverse osmosis (R.O.) technology relies on a membrane filtration system that
is
operated under high pressure. While this technology is one of the two leading
technologies of water purification, it suffers from the following main
disadvantages:-
(a) the infrastructure of the system is complex because of the operating
pressure,
typically 8 atmospheres, required to cause the reverse osmosis process in the
membrane;
(b) the membrane is an expensive component that needs to be replaced,
frequently,
depending on the salinity and the purity of the source water, generally, every
4 to
6 months. Also, there is a problem of membrane fouling, if the quality of the
source water is not within certain bounds. The restriction on the water
quality that
is inputted into the system precludes many sources of water or would
necessitate
the utilization of pretreatment systems;
(c) the amount of purified water is very low when compared to the amount of
water
that has to be pumped into the system. Therefore, the cost of pumping and
discharging the rejected water (capital cost to install the required facility
and the
energy cost to operate and maintain it) makes this system very costly;
(d) the quality of purified water obtained by the reverse osmosis process is
inferior to
that of distilled water, in the sense that it leaves small microorganisms and
any
impurities that are small enough to go through the membrane. Also, as the
membrane ages, the water quality does not remain consistent;
(e) the system is feasible from a physical and economical point of view, for
only
large commercial installations. The system is not amenable for use in
household
units or even in small commercial units; and
(f) energy, operating and maintenance costs are high for the R.O. system.
The main disadvantages of distillation technologies, such as the multistage
flashback evaporation systems, are:-
(i) relatively large capital cost needed to assemble and install the system;
(ii) high energy costs to perform the evaporation, provide energy and
equipment for
the vacuum system and the condensation in, literally, three independent
subsystems;
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(iii) significant corrosion problems that necessitate significant pretreatment
of input
water and complete replacement of plant equipment as frequently as every three
to four years;
(iv) the system, generally, needs to be installed only near large power plants
and large
bodies of water; and
(v) the disadvantages listed in item (e) and (f) hereinabove.
There is, therefore, a need to provide a means for producing purified water in
a
safe, reliable, convenient, relatively cheap manner, having low energy
requirements, and
which either eliminates or reduces the aforesaid disadvantages.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and apparatus for
producing purified water in a safe, convenient, reliable and relatively cheap
manner by
means of thermoelectric modules to generate hot and cold heat sinks.
Accordingly, in one aspect the invention provides a process for treating an
impure
water to produce purified water, said process comprising -
(i) electrically activating a thermoelectric element to provide a heated heat
sink in a first chamber and a cooled heat sink in a second chamber;
(ii) feeding said impure water to said heated heat sink, to produce water
vapour;
(iii) transferring said water vapour from said first chamber to said second
chamber;
(iv) contacting said water vapour on said cooled heat sink to effect
condensation to provide said purified water; and
(v) collecting said purified water.
By the term "impure water" is herein meant water containing impurities such
as,
for example, dissolved salts and other matter, and/or suspended particulate
matter which
impure water may be evaporated and concentrated without unwanted carry-over of
such
impurities.
The term "vapour" in this specification and claims includes "steam".
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In a further aspect, the invention provides a water purifier comprising a
housing
having a first chamber and a second chamber; divider means separating said
first chamber
from said second chamber comprising a thermoelectric element having a first
heat sink
5 received within said first chamber and a second heat sink within said second
chamber;
means for feeding water to said first heat sink within said first chamber to
produce water
vapour; transfer means for transferring said water vapour to said second heat
sink to
effect condensation of said water vapour to produce purified water; and means
for
removing said purified water from said second chamber.
Preferably, the apparatus has a vacuum extraction means, forced-air fan or
other
suitable means for enhancing the transfer of the water vapour from the first
chamber to
the second chamber.
Most preferably, the divider has a plurality of the thermoelectric modules
aligned
coplanar within the divider.
Thus, the present invention provides a water purification system which
provides
the advantages o~-
(a) providing both water evaporation and cooling simultaneously within the
same
unit;
(b) being significantly energy efficient because the same amount of electrical
energy
is used to perform evaporation, condensation and chilling; which energy
utilization does not exist in any of the water purification technologies known
at
this time;
(c) recovering all of the water inputted into the system as pure water,
without having
to discharge water with high concentrations of impurities and salt as is the
case in
reverse osmosis technology;
(d) portability of the system and its ability to be scale up over a very wide
range of
dimensions and capacities; and wherein the capacity of the system can be
increased in a modular fashion;
(e) having the ability to energize the system from a very wide variety of
power
sources, such as, for example, operable throughout in the world, including
remote
areas that are not even connected to an energy generation grid; and
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(f) having the ability of the system to handle any type of water regardless of
its
salinity and impurities, while still producing pure water that has the same
quality
as distilled water, which is free from all organic, non-organic and microbial
elements.
BRIEF DESCRIPITION OF THE DRAWINGS
In order that the invention may be better understood, a preferred embodiment
will
now be described by way of example only, wherein
Fig. 1 is a block diagram of a water purifier according to the invention.
Fig. 2 is an exploded, isometric view, in part, of a hot end sink of a divider
plate of use in
the present invention;
Fig. 3 is an isometric view of a divider plate, in part, of use in the present
invention; and
wherein the same numerals denote like parts.
DETAILED DESCRIPTION OF THE INVENTION
With reference to Fig. 1 this shows generally as 10 a water purifying
apparatus
having a rectangularly-shaped container 12 partitioned into a "hot-end"
chamber 14 and a
"cold-end" chamber 16 by a planar divider member shown generally as 18, as
hereinafter
further described. Container 12 has walls 20, base 22 and top 24, thermally
insulated by
a layer of polystyrene 25. Top 24 has a water inlet sprinkler head 26 which
receives a
supply of impure water through a conduit 28.
With reference now also to Fig. 2 divider plate member 18 has a thermally
insulating polystyrene frame 30, within which is retained a plurality of
thermoelectric
modules 32 (PolarTECT"" model PT2-12-30; Melcor Corporation, Trenton, N.J.,
U.S.A.),
each of which is connected to a hot end sink 34 protruding within chamber 14
and a cold
end sink 36 within chamber 16. The modules 32 are essentially in coplanar
arrangement
one adjacent another separated by the intervening patchwork of polystyrene.
Each hot
end sink 34 and cold end sink 36 consists of a rectangularly shaped copper
block spacer
38, which at its "hot" face 40 is abutted to thermoelectric element 32 in a
satisfactory,
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thermally conductive manner. Copper spacer 38 at its coplanar face 42,
opposite its face
40 is bonded to a multi-finned member 44, formed of aluminum having a
plurality of fins
47 extending perpendicularly to divider plate 18. Cold end sink 36 consists of
an
analogous copper spacer and aluminum multi-finned member arrangement bonded to
the
appropriate face of module 32, i.e. its' "cold" face. Sprinkler head 26 is so
arranged as to
operatively direct an appropriate water flow onto finned member 44 as to
effect
vapourization of the water.
Within chamber 16 is suitably located a water level sensor 48 and a thermal
sensor 50, both electrically connected to a microprocessor control unit 52.
Chamber 16
has a water outlet 54 within a wall 20. Within chamber 14 is a water heater 46
for
optionally boiling off any excess water which drips to the bottom of chamber
14. A drain
plug 15 is provided in base 22, for chamber cleaning purposes.
Divider member 18 has an upper portion defining an aperture 56 within which is
an extraction fan 58 for transferring steam from chamber 14 to chamber 16.
DC power is supplied to the thermoelectric element array in divider member 18
from a solar panel 60 and/or 12 volt DC power supply 62 through control unit
52. Water
is fed through conduit 28 and solar panel 60 under the control of valve 64 and
control
unit 52 from water source 66.
In the embodiment shown, container 12 has dimensions of 50 cm length, 35 cm
wide and 30 cm high. Chamber 14 for water evaporation is 15 cm long, while
chamber
16 for steam condensation is 25 cm long. Divider member 18 is 10 cm wide and
in the
embodiment described has six thermoelectric modules having dimensions of 2.5
cm wide
x 2.5 cm long x 0.5 cm thick and 12 V - 2 amp rating, sandwiched between the
hot and
cold heat sinks. The distance between the two heat sinks is increased by
copper spacers
38 to a suitable distance, because the 0.5 cm thickness of the modules offers
low thermal
resistance between the hot and cold sides of the elements. Use of the copper
spacers
enhances the thermal resistance and minimized the effect between the hot side
on the sold
side.
We have found that the use of pump extraction fan 58 or a vacuum pump within
divider member 18 enhances water evaporation and transfer to chamber 16
without the
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need for a boiling temperature of about 100°C. Very satisfactory
evaporation can be
achieved at 70 - 80°C, to result in significant savings in energy.
During a steady state operation the temperature on the hot side of the heat
sink
was between 50 - 60°C while the temperature on the cold side was 10 -
15°C, to provide
a gradient in temperature of 35 - 50°C, which is less then the designed
rate of these
elements (70°C), and consequently, the efficiency of the thermal
electric elements
increases. Under intermediate operations the temperature of the hot side
reached 85°C
and 25°C at the cold side. Water level sensor 48 on the cold side
monitors the water level
and sends a signal when the water level is above or below the desired range.
The thermal
sensor 50 monitors and maintains the temperature of the cold water within
desired limits.
When the temperatures rises above the desired limited, sensor 50 sends a
signal to
processor 52 to turn on thermal modules 32 and cool the water.
Water has been purified at a steady-state rate of 1 litre/hour in the
embodiment
shown.
Several cleaning methods can be implemented for this system. These methods
include, but are not limited to:
1. Jet cleaning.
2. Sonic technology.
3. Chemical cleaning.
4. Manually cleaning (opening a re-sealed lid and scrubbing the tank).
The selection of a particular cleaning method will depend on the size of the
system and the economic considerations for a particular unit.
Although this disclosure has described and illustrated certain preferred
embodiments of the invention, it is to be understood that the invention is not
restricted to
those particular embodiments. Rather, the invention includes all embodiments
which are
functional or mechanical equivalents of the specific embodiments and features
that have
been described and illustrated.
