Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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19283/1 PCT
WATER PURIFICATION ASSEMBLY AND METHOD
The invention relates to a water purification assembly according to the pre-
characterizing portion of claim 1, particularly for the desalination of sea or
brackish water, but also for the treatment of sewage. It also relates to a
method of purifying water.
In addition to reverse osmosis, the most important methods of sea water desali-
nation include distillation, in which the water is evaporated and then
condensed.
Sunlight is being used for the purpose also (see e.g. US 4,329,204 and US
6,821,395 BI). Prior sea water distillation assemblies using sunlight are poor
performers, however, as they provide few liters only of fresh water per day.
The object of the invention is the provision of a water purification assembly
and
method featuring high performance and low building costs.
In accordance with the invention, this object is attained by the water
purification
assembly recited in patent claiml. Patent claims 2 to 12 recite preferred embo-
diments of the inventive water purification assembly. Patent claim 13 is
direct-
ed to the inventive water purification method.
The inventive assembly and method use a solar collector comprising a sunlight
absorber sealed in an upwardly extending enclosure which is transparent, i.e.
transmissive of sunlight, and especially a housing of glass. The absorber,
which may comprise e.g. sheet copper or a sunlight-absorbing coating disposed
in the housing, is coupled for the transmission of heat with a metal tube
extend-
ing through the inside the housing in the longitudinal direction thereof. The
ab-
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sorber and the metal tube preferably are sealed inside the housing in a gas-
tight condition so as to preclude thermal convection with the ambient air.
Each metal tube is partly filled with a liquid, preferably water. At the top,
which
extends from the housing, the metal tube carries a condenser head containing
a cavity which communicates with the metal tube. In this cavity is condensed
the water vapour or steam previously generated by the evaporation of the water
in the metal tube by the heat the sunlight-absorbing absorber provides to the
metal tube.
For example, the absorber may be a sheet of copper or a coat of sunlight-ab-
sorbing metal or a metal-ceramic material disposed inside the housing. For
thermal insulation of the absorber and the metal tube from the environment,
the
housing preferably is evacuated. The metal tube - including the condenser
head - may be copper or a copper alloy.
Solar collectors of this type - comprising evacuated single- or double walled
glass tubing for a housing - are referred to also as vacuum tube collectors
and
are used in building services engineering for heating system support and for
the heating of service water (see the folder published by RZ Solartechnik,
Friedrich-von-Tieck-Str. 20, 89420 Hoechstedt, Germany). In systems of this
kind, the heat of the condenser head is transferred to a carrier liquid which
is
conducted to a heat exchanger.
It was found that condensing the water, which was evaporated in the condenser
head by the incident solar radiation, and the concomitant release of the
evapor-
ation heat may raise the condenser head temperature to 200 C. In accord-
ance with the invention, this temperature of the condenser head is used for
dis-
tilling the water to be purified in the evaporator. To this end, the
evaporator
vessel is provided with an inwardly protruding receptacle adapted to receive
in-
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serted therein the solar collector's condenser head for heat transfer to the
water
inside the evaporator.
In accordance with the invention, this system makes use of a commercially
available solar collector so that the prime costs of the inventive water
purifica-
tion assembly may be kept low.
At the same time, the performance of the inventive assembly features is unusu-
ally high. In contrast to prior distillation systems using solar radiation,
which
simply evaporate the water, the inventive evaporator serves to heat the water
in
it to its boiling point so that the system condensor receives much greater
amounts of water vapour and, thus, of water.
The receptacle provided in the evaporator housing to receive the condensor
head of the solar collector may be designed to be sleeve-shaped, for example.
Large-area contact of the condenser head with the inserted receptacle is de-
sired for high thermal transfer; to this end, the inner cross-sectional shape
of
the receptacle is designed to match the outer cross-sectional shape of the con-
denser head. Further, the receptacle preferably is made of metal so as to en-
sure losses as low as possible when transferring the heat from the condenser
head to the water the evaporator housing holds for evaporation.
With the assembly operating, the evaporator housing is filled in its bottom
por-
tion with the water to be evaporated while the top portion accommodates the
steam that forms. The condenser head preferably extends into the receptacle
to the top water level only, and at any rate only partly to the level of the
steam-
filled region of the evaporator vessel.
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The evaporator housing is provided on the outside with a thermal insulation
suited for the high temperatures that occur in the operation of the assembly -
e.g. mineral wool covered with an aluminum-foil or silicone.
It is preferred for the housing of the solar collector to be tubular in shape.
The
length of the tubular housing may be 1 to 2 meters and its diameter 5 to 10
cm,
for example. It is preferred also to assemble a plurality of tubular solar
collect-
ors - such as 10 to 40 in number - in a parallel side-by-side relationship in
a
common plane, with the condenser heads at their top ends each inserted in a
receptacle in the evaporator vessel.
The evaporator vessel, which extends substantially horizontally across the up-
wardly extending tubular solar collectors, may be formed by a tube, for exam-
ple. The tubular receptacles into which the condenser heads of the solar col-
lectors are inserted may extend crosswise - i.e. from the bottom up - through
the elongated evaporator housing or tube and be sealed at the top by a lid,
for
example.
The receptacles in the evaporator housing for the reception of the condenser
heads of the solar collectors present the heat transfer surfaces for
transmitting
the heat from the condenser heads to the water to be evaporated in the eva-
porator vessel. For increased heat transfer area relative to the amount of
water
to be evaporated in the evaporator vessel, it is preferred for the evaporator
vessel not to be a tube with a constant cross-sectional area. Instead, its
cross-
sectional area should be large enough in the region of the receptacles only to
allow the water to flow around the receptacles, i.e. to flow through between
the
receptacles and the surrounding vessel walls, while the sections of the evapo-
rator vessel between two adjacent receptacles have a smaller diameter.
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To this end, the shape of the evaporator vessel may be designed to match the
sleeve-like receptacles, i.e. to have upwardly extending cylindrical or
prismatic
sectional shapes.
In operation of the evaporator vessel, its bottom portion is filled with the
water
to be evaporated; its top portion accumulates the steam that forms. It is
prefer-
red for the assembly to be operated continuously, i.e. a feed pump is provided
to continuously supply the evaporator vessel with new water to be purified
while
the steam that forms is withdrawn and condensed in the condenser to form
purified distilled water. In addition, the distilled water will be sterile at
least if
distillation takes place at 100 C or higher at normal pressure.
To ensure the evaporator vessel being filled with water to a given level,
means
are provided to regulate that level in the evaporator vessel, with the feed
pump
being turned on or off, for example, when the actual water level is lower or
higher, respectively, than the aforesaid given level.
The feed pump may be powered from a photovoltaic system which may be
connected to a battery. On this basis, it is possible to use the feed pump for
night-time.purges of the evaporator vessel, for example. Where the assembly
is used for sea water desalination, for example, salt deposits, sediments and
the like contaminations may be removed from the evaporator vessel this way.
It is preferred for the water purification assembly to provide tilting means
making possible the emptying of the evaporator vessel of brine before it is
purged (purified). The brine may be conducted to pans for the recovery of sea
salt.
Of additional advantage may be a pump used to draw the steam from the eva-
porator vessel and to conduct it to the condenser. This results in the
formation
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of negative pressure in the evaporator vessel above the water surface, which
promotes the evaporation process. The pump may be powered by the photo-
voltaic system also.
To ensure that steam only, but no water, can reach the evaporator vessel in
the
condenser, the evaporator preferably communicates with the condenser
through a riser conduit.
II
Preferably, pre-heating means are provided to pre-heat the water supplied to
the evaporator. Where the condenser is cooled in counter-current fashion with
water or another fluid for condensing the evaporated water, the heated fluid
conducted in counter-current in the condensor may be fed to the pre-heater.
Also, the pre-heater may be operated with one or several solar collectors of
the
kind used in accordance with the invention for the evaporator. The solar col-
lectors of the evaporator may be designed to be smaller where the water tem-
peratures are higher. In other words: instead of an exemplary solar collector
unit two meters long and correspondingly wide, it would be possible to use a
substantially smaller unit.
The invention will now be explained in greater detail under reference to the
attached drawings, which show:
Figure 1 a front view of the inventive assembly;
Figure 2 a view of a portion of a solar collector in the assembly of Figure 1;
Figure 3 shows a sectional view of part of the evaporator along lines III-III
in Figure 4 including the top ends of the solar collectors of the
assembly in Figure 1, but with a thermal insulation of the eva-
porator vessel omitted; and
Figure 4 a sectional view along line IV-IV in Figure 3, but with the conden-
ser heads or solar collectors omitted.
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As shown in Figure 1, the inventive water purification assembly comprises a
plurality of solar collectors 1 disposed in a parallel side-by-side
relationship in a
common plane, as well as an evaporator 2 extending above and across solar
collectors 1.
Evaporator 2 has connected at one end thereof a line 3 supplying the water to
be purified and at the opposite end a riser conduit 4 which passes the steam
generated in evaporator on to a condenser 5 in which the steam generated in
evaporator 2 is condensed to form purified water or (in sea water
desalination)
fresh water, which exits from condenser 5 at 6.
As shown in Figure 2, solar collectors 1 each comprise an absorber 7 consist-
ing of a material such as sheet copper, for example, and extending from the
bottom up through a tubular glass housing 8. Absorber 7 is coupled in a ther-
mally conductive fashion - by soldering or brazing, large-area contact or the
like
- to a metal tube 9 extending through the housing in the longitudinal
direction
thereof. The top end of metal tube 9 extends outwardly from housing 8, which
is evacuated for thermal insulation.
Solar collectors 1 are disposed in a position such as to be impinged as perpen-
dicularly as possible by the incident solar radiation.
The end of metal tube 9 extending from evacuated housing 8 has thereon a
condensor head 11 also of metal. In its lower portion, metal tube 9 is filled
with
a liquid, especially water.
Incident solar radiation will heat sunlight-absorbing absorber 7, which
transfers
the heat to metal tube 9. This causes the water inside metal tube 9 to be eva-
porated, the steam so generated to condense in condenser head 11 and the
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condensation heat of the water to be released, resulting in condensor head 11
being heated to a temperature as high as about 200 C. The water condensed
in condenser head 11 flows back into the metal tube for cyclic re-evaporation.
In accordance with Figure 3, condenser heads 11 of solar collectors 1 are in-
serted in sleeve-like receptacles 12 extending transversely through evaporator
vessel 13 of evaporator 2. Evaporator housing 13 is filled with water to be
purified up to a level indicated by an arrow 14. The space 16 above top water
level 14 forms the steam space.
The high temperature of condenser heads 11 of solar collectors 1 causes the
water 15 in evaporator vessel 13 to be heated to its boiling temperature, i.e.
to
more than 100 C at normal pressure, so that major amounts thereof will eva-
porate.
For optimum heat transfer, condenser heads 11 should be in large-area contact
with the inside walls of receptacle tubes 12.
In order to get the heat to move from condenser heads 11 along paths as short
as possible and with losses as low as possible via the metal receptacle tubes
12 into the water 15 to be evaporated, condenser heads 11 of solar collectors
1 extend upwards about to level 14 only, i.e. not or only slightly into steam
space 16.
Where evaporator housing 13 comprises a simple tube having a diameter not
greater than the length of a condenser head 11, that head will extend complete-
ly through sleeve-like receptacle 12, of course.
As shown in Figure 1, evaporator vessel 13 is provided with a thermal
insulation
10.
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Tubes 12 receiving condenser heads 11 of solar collectors 1 present the sur-
face areas where heat from condenser heads 11 is transmitted to the water 15
to be evaporated in evaporator vessel 13.
In order to increase these heat-transmissing surface areas, i.e. the area of
the
outer surfaces of condenser heads 11, relative to the volume of the water 15
to
be heated in evaporator vessel 13, the latter vessel is preferably designed to
have a large cross-sectional area in the region of receiving sleeves 12 so
that
water 15 can flow around sleeves 12 on both sides thereof, as indicated by ar-
rows 18 in Figure 4. Between regions 17 holding receiving sleeves 12, evapo-
rator vessel 13 has portions 19 featuring a reduced width, as shown in Figure
4.
In order to further increase the heat-transmitting surface area in relation to
the
volume of water 15 in evaporator vessel 13, regions 17 are matched in shape to
receiving sleeves 12, i.e. to be cylindrical, as shown in Figure 4, or
prismatic, as
shown schematically for the right-hand region 17, for example.
The water to be purified is fed to evaporator 2 via line 3 by means of a feed
pump 21, while the steam generated in evaporator 2 is withdrawn through riser
conduit 4 and condensed in condenser 5 to form purified distilled water. Addi-
tionally, as the water has been heated to 100 C and more in evaporator 2, it
is
sterile.
To ensure that evaporator 13 is filled with water 15 up to level 14 at all
times,
means (not shown) are provided to regulate the level of water 15 in evaporator
13, said pre-determined level 14 being maintained by turning feed pump 21 on
or off, for example.
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The water condensed in condenser 5 exits at 6. As shown in phantom in Figure
1, condenser 5 is cooled in counter-current fashion with water entering conden-
ser 5 at 23 and exiting at 24.
The water to be purified may be fed via line 26 to pre-heating means 25 con-
nected to water supply 3. The heated water used for cooling in counter-current
in condenser 5 and leaving it 24 in a heated condition may be fed into means
25 for pre-heating.
