Abstrict Desiccant brine is heated and diluted in an air drier by coming
into contact with air to be cooled in an evaporative cooler but
is regenerated by dewatering in a vacuum chamber, from which it
is discharged first into a sump, and then back into the vacuum chamber.
Both the desiccant brine and air are heated in the air drier and
the hot brine when in the vacuum chamber has a temperature above
atmospheric, which provides a higher vapor pressure and its water
is readily vaporized. The higher efficiency reduces the amount of
heat input required, and thereby reduces the extent of heat exchanger
requirement.
Claims The claims defining the invention are as follows:
1. Means for vacuum dewatering of diluted desiccant brine,
comprising a vacuum chamber, a vacuum pump in fluid flow communication
with an upper end of said chamber,
a sump at a level below said vacuum chamber, and an air drier,
a hydraulic flow passage including a valve extending from said
vacuum chamber to said sump,
first and second hydraulic circuits,
said first hydraulic circuit comprising a pump operable to deliver
dewatered desiccant brine through a hydraulic conduit to said air
drier so as to effect drying of air when passing through said air
drier, with consequential aqueous dilution of said brine,
said second hydraulic circuit comprising a second hydraulic conduit,
and means to deliver said diluted brine to said vacuum chamber,
wherein low vapour pressure created by actuation of said vacuum
pump effects dewatering of said diluted brine by evaporation.
2. Means according to claim 1 further comprising a third hydraulic
circuit including a heat exchanger in fluid flow communication with
said vacuum pump in a configuration wherein water vapour removed
from said vacuum chamber by said vacuum pump is condensed as distilled
water.
3. Means according to claim 2 further comprising an evaporative
air cooler, and a hydraulic conduit communicating between said air
cooler and said heat exchanger to conduct said distilled water to
said air cooler for evaporation therein.
4. Means according to claim 2 comprising a second sump located
at a level below said air drier, arranged to receive said diluted
desiccant brine, said second circuit including a hydraulic conduit
containing a first valve extending from said second sump to a lower
portion of said vacuum chamber,
a second valve in an upper portion of said vacuum chamber openable
to ambient air, and
a further hydraulic conduit containing a third valve and extending
from said lower portion of said vacuum chamber to the first said
sump for delivery of dewatered desiccant brine thereto from said
chamber.
5. Means according to claim 2 wherein said first circuit comprises
a hydraulic conduit extending between a lower portion of said vacuum
chamber and said air drier, and said pump is a metering pump in
that said hydraulic conduit.
6. Means according to claim 2 wherein said second circuit comprises
a hydraulic conduit extending from said sump to an upper portion
of said vacuum chamber, said second hydraulic conduit containing
a valve which, when open, allows upward flow of desiccant under
influence of atmospheric pressure from said sump to said chamber
when said vacuum pump is operating.
7. Means according to claim 2 wherein said vacuum chamber comprises
an upper portion, a lower portion, a plurality of pipes extending
between said portions, said second circuit comprising a hydraulic
drain conduit extending from said lower portion, two branches of
said drain conduit terminating one below normal brine level in said
sump and the other above said normal brine level, a respective valve
in each said branch, said drain conduit also having a further branch
extending to said upper portion of said vacuum chamber, and a circulating
pump in said further branch.
8. A method of improving effectiveness of an evaporative air cooler,
comprising
a. passing air through an air drier while simultaneously passing
a dewatered desiccant brine through said drier in contact with said
air, with consequential drying of the air and aqueous dilution of
the desiccant,
b. transferring said desiccant brine to a sump, and from the sump
to a vacuum chamber,
c. actuating a vacuum pump to withdraw water vapour from said vacuum
chamber and thereby dewater said diluted desiccant,
d. passing said water vapour through a heat exchanger to cool and
condense said water vapour into distilled water
e. passing said distilled water to an evaporative air cooler and
humidifying and cooling air by evaporation of said distilled water.
9. A method according to claim 8 further comprising circulating
desiccant brine from said sump, through said vacuum chamber thereby
dewatering said brine, through said air drier, and back to said
sump.
10. A method according to claim 9 further comprising circulating
said brine through heat exchange pipes which join upper and lower
portions of said vacuum chamber, passing air issuing from said air
drier over said heat exchange pipes.
Description This invention relates to dewatering of desiccant brines, utilising
a vacuum technique in lieu of the conventional high energy heating.
BACKGROUND OF THE INVENTION
Air conditioners fall into two general categories, the first being
of the so called refrigerative type which comprises a closed circuit
of refrigerant and lubricant which is pumped by means of a reciprocating
or scroll pump through a condenser wherein the refrigerant is mostly
if not entirely converted to liquid, and is then expanded in an
evaporator wherein the liquid converts back to gas, and thereby
absorbs latent heat to provide the refrigeration. A coefficient
of performance of about 3 is frequently achieved with such refrigerant
type air conditioners, and they are in common use.
A much less expensive type is the evaporative cooler wherein water
passes over an absorbent pad from which it is evaporated by a passage
of ambient air, and is cooled. For relatively dry atmospheres, the
coefficient of performance is very much greater than can be achieved
with more expensive refrigerator type of air conditioners, and consequently
there is much demand for such coolers. However, difficulties are
encountered in the more humid climates, and no evaporation at all
will occur when the humidity of the air is 100%. Furthermore, in
climates where the humidity is high, although not as high as 100%,
the addition of more water vapour to the air is not acceptable and
in some instances there is a requirement for heat exchangers to
separate the cooled but more humid air. However, because of the
relatively small range of humidity within which evaporation can
take place, the temperature differential of the evaporated and unevaporated
air is small and as a consequence, heat exchangers if used need
large surface areas. These problems have been very well recognised
and much effort has been made to solve them, mainly through the
use of desiccants. Hygroscopic material such as lithium bromide
is very effective in absorbing moisture from the atmosphere, but
whereas evaporation of moisture will result in cooling, condensation
results in heating and in prior art evaporative air conditioners
wherein desiccants first dry the air, it has been considered necessary
to use additional heat exchangers. A common method of regeneration
of desiccant is by the application of further heat (for example,
gas flames) but this still further increases the energy input and
further heat exchangers are required. Because of the bulk and cost
of heat exchangers, some efforts have been made to utilise multiple
stages of desiccants, and for example reference can be made to the
U.S. Pat. No. 5170633 Kaplan. Reference can also be made to the
U.S. Pat. No. 4869070 Assaf. Along with Albers (U.S. Pat. No.
5097668), these specifications contain the prior art which Applicant
believes is the most relevant to this specification.
Further relevant prior art exists in the so called "water
refrigerator". Water is said to be quite unsuitable for use
in refrigerators of the type using closed circuits because firstly
of its very low vapour pressure and secondly of its high specific
volume at low temperatures. However, it is well recognised that
it is possible to maintain a high degree of vacuum, and for example,
at about 7.degree. C. (45.degree. F.) the vapour pressure is about
10 millibars (0.15 psi) and the corresponding specific volume of
vapour is about 125 m.sup.3 per kilogram (2000 cubic feet per pound).
This large volume requires removal of vapour if the evaporation
is to be continuous, and in installations where water has been used
as a refrigerant, such as vegetable cooling devices, vacuum pumps
have been supplemented by refrigerant evaporators within a vacuum
chamber which assist in condensation of the water vapour while still
in the chamber. This invention utilises a vacuum dewatering technique,
but without refrigeration. An alternative which has been considered
but as far as is known to the Applicant has not been used, is use
of high pressure steam discharging through a nozzle upstream from
a venturi which is in communication with a vacuum chamber, but this
is not considered viable for air conditioning purposes, and in any
case steam ejector pumps are notoriously of very low efficiency
This invention has for its main object the simplification of desiccant
regeneration, utilising a vacuum dewatering device, but with less
heat exchange requirement. As said, application of further heat
for drying desiccant usually requires association with further heat
exchangers.
BRIEF SUMMARY OF THE INVENTION
In this invention, brine which has been heated and diluted by absorption
of water vapour is dewatered by vacuum created In a vacuum chamber
by a vacuum pump. There are at least two hydraulic circuits, the
first of which includes a pump to deliver dewatered desiccant brine
to an air drier, where it becomes diluted. The second circuit delivers
the diluted brine to the vacuum chamber wherein it is dewatered.
Since dewatering by evaporation is endothermic by about the same
amount that dehumidifying air is exothermic, it is possible to greatly
reduce the amount of additional heat input to regenerate the desiccant,
and consequently reduce the heat exchanger requirements.
This invention is associated with an evaporative air conditioner
wherein air has been separately dried by desiccants, and the dewatering,
or regeneration of desiccant by vacuum. It further relates to recovering
distilled water for delivery to an evaporative cooler through which
dry air is passed. This latter feature is of particular importance
when the evaporation which takes place in the evaporative cooler
is such that with other than distilled water there could be a build
up of salt deposits.
DESCRIPTION OF PREFERRED EMBODIMENTS
Three embodiments of the invention are described hereunder in some
detail with reference to and are illustrated in the accompanying
drawings in which:
FIG. 1 illustrates an installation utilising a vacuum chamber for
rapid evaporation of water from a watery desiccant, and delivery
of warm dry air to be used in an evaporative cooler;
FIG. 2 shows an alternative of the invention wherein air is dried
and cooled before entering an evaporative cooler; and
FIG. 3 shows a further alternative wherein the air is hot and dry
when passing through a water/air heat exchanger employing vacuum
evaporation.
There are at least two, and in these embodiments, three basic hydraulic
circuits, marked CIRCUIT A, CIRCUIT B and CIRCUIT C on the drawings.
Referring first to the embodiment of FIG. 1 a vacuum pump 10 withdraws
moisture vapour from a vacuum chamber 11 which contains a watery
desiccant solution 12 thereby increasing desiccant concentration,
and the vapour removed from the chamber 11 in circuit C is condensed
as distilled water in a heat exchanger 13 and, is subsequently
delivered as pure cold water to moisten the evaporative pads in
an airconditioner (not shown).
In hydraulic circuit A, there is provided a pump 15 which pumps
dewatered, and thereby regenerated desiccant from a sump 16 to an
air drier absorption pad 17 through which the brine percolates to
be delivered to a second sump 18 as a hot dewatered brine. Moist
ambient air is driven by a fan 19 through the pad 17 and the moisture
is absorbed by the desiccant solution so that warm dry air is delivered
to an evaporative air cooler (not shown).
There are provided three valves which control liquid level in chamber
11 between low level (L-L) and high level (H-L). The valves are
designated V1 V2 and V3. The following sequences occur:
(1) V1 open, V2 closed and V3 closed, the vacuum is maintained
in chamber 11 drawing hot watery desiccant solution from sump 18
until the high level "H-L" is reached.
(2) V1 closed, V2 closed and V3 closed, the vacuum pump 10 evaporates
the water thereby dewatering and cooling the hot desiccant solution
12 until the water level drops to "L-L".
(3) V1 closed, V2 open and V3 open, the concentrated desiccant
solution runs in circuit B from chamber 11 into the sump 16.
With this arrangement the dewatering takes place with low energy
input, and the distilled water is likely to be cool thereby partly
offsetting the higher temperature of the dried air emitting from
the pad 17.
In FIG. 2 circuits A, B and C function as in FIG. 1. The desiccant
is again a solution of hygroscopic salt, for example lithium bromide,
and exposed in an air drier 17a to a passage of ambient air by falling
as a stream into sump 16a from where it is drawn upwardly as a cold
watery brine through a valve 21 into a vacuum chamber 11a by a vacuum
pump 10a. Make up water is supplied as in the first embodiment through
a secondary sump 22 being an extension of sump 16a. This is likely
to be hot, and constitute a low grade heat source The metering pump
15a meters brine from chamber 11a to air drier 17a and also it functions
as a valve to separate the low pressure which exists in the chamber
11a from the ambient pressure which exists in the air drier 17a.
After having been subjected to moist air in air drier 17a, the condensation
of the air borne moisture results in heating and sump 16a contains
hot dilute brine which recirculates as the brine is delivered to
the chamber 11a under vacuum, through valve 21. In some instances
it is necessary to incorporate a small heat exchanger between valve
21 and chamber 11a.
The vacuum pump 10a withdraws vapour yielded from the air drier
17a, and that vapour is condensed in heat exchanger 13a and delivered
to an evaporative cooler 23a as distilled water which has been cooled
almost to ambient temperature. Heat exchanger 13a is shown as an
air/water heat exchanger. The dry air which emits from air drier
17a is cooled as it passes through an air/air heat exchanger 24
and subjected to further humidification in evaporative cooler 23a.
The desiccant brine level in the base of the air drier 17a is controlled
by the two probes 26 and 27 which open the valve 21 when water level
falls below the probe 27 and closes it when the water level raises
above probe 26.
With this embodiment it is not necessary to have the very low pressure
in the chamber 11a because of the high temperature which is achieved
in the air drier 17a. As a consequence, the vacuum pump 10a can
be of a simple and inexpensive construction, as can the heat exchangers
13a and 24. Furthermore, the FIG. 2 embodiment illustrates a continuous
process, compared to the sequential process of FIG. 1.
The third embodiment of FIG. 3 is a variation of FIGS. 1 and 2
and corresponding components bear the same designation numerals,
but with the suffix `b`. There is a third "low level"
probe 28 which causes temporary opening of valve 29 to replenish
brine in sump 16b after it has been drained through valve 30 by
pump 15b. Valves 29 and 30 are electrically interlocked to achieve
this. Replenishment of brine into vacuum chamber 11b is effected
basically by vacuum pump 10b, supplemented by circulating pump 15b.
The FIG. 3 embodiment is also continuous. The vacuum chamber 11b
in FIG. 3 includes a plurality of heat exchange pipes 33 between
which ambient air passes, after having been heated and dried in
air drier 17b. This raises vapour pressure within chamber 11b, and
increases vacuum pump efficiency, in turn cooling the air before
it enters the evaporative cooler 23b. Pump 15b causes the desiccant
brine to flow through pipes 33 and that also enhances evaporation.
Pump 34 circulates desiccant brine through circuit A, and the air
drier 17b. Circuits B and C function as in the first and second
embodiments.
In all three embodiments, desiccant 12 is at least warm, if not
hot, when being dewatered, and in the third embodiment the heat
in the chamber 12b is supplemented by hot air passing over heat
exchange pipes 33. This enhances evaporation of water in chamber
11b, and that evaporation is further enhanced by circulation of
watery desiccant through pipes 33. It is not always possible to
avoid further heating, but the requirement is much reduced, with
a consequential cost saving in heat exchanger capacity. |