Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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me purpose of the inventlon is an atmospheric cooling
plant, also called an atmospheric cooling tower~ used to cool a
potentially corrosive liquid co~taining substances capable of
precipitation.
Many processes for cooling solutions exist in industry~
and in the case of electrolysis, it is known to cool solutions by
means of coils through the interior of which co~ water flows, said
coils being su~merged in baths of electrolyte. However~ this
type of cooling does not provide good efficiency, because it is
indirect, and because the coils are rapidly covered by salts, further
and considerably reducing the heat-transmis~ion; moreover, these
coils take up too much space in the baths of electrolyte and have
a poor resistance to corrosion.
An atmospheric cooling plant, on the other hand, is an
installation in which a liquid, generally an aqUeo4s solution flows
by gravity between the level where it is finely distributed and the
level where it is collected, generally the water-level of a reservoir
provided for this purpose~ During this journey, the liquid is in
direct contact with a flow of atmospheric air; the overall relative
movement of these phases is substantiallyeither counter-flow,or
cross-flow~ although frequently both types of overall relative
movements are provided, the air entering horizontally into the
apparatus and emerging vertically, whereas the overall movement of
the liquid is generally substantially vertical; in the cases when
the liquid is finely distributed in the cooling fluid by nozzles
projecting it upwards, there is, above the level of the nozzles,a
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portion of the contact which takes place in parallel-flow
circumstances.
The atmospheric airflow is ~et in motion preferably
by blower~, which blow external air into the body of the cooling
plant, but thi~ may also be achieved by blowers which extract from
the cooling system the air which has finished its contact with the
liquid, ejecting it into the atmosphere where it may be removed
by the natural draught of a chimney, or all known combinations
of blowing and extracting fans, or by a chimney a~sisted by
blowing or extracting fans.
Where there is nolri~k of the liquid forming serious
deposits or incrustations, the thermal interchange between the
liquid and the air takes place in exchange members generally
made up of flat or corrugated plates or sheets, or various types
of grid, over which the liquid runs and splashe~. On the other
hand, when there is a ris~ that the liquid will form serious
deposit~, and thus will rapidly clog the channels (orifices or
passages) of the exchanger memhers, these latter may no longer
be used. In these cases, the liquid is atomised by nozzles, and
fills the interior space of the cooling plant in the form of
a large number of droplets which are violently agitated by the
airflow, and which con~tantly collide with one another until
they fall into the reservoir.
During the thermal exchange between liquid and air,
the air i~ heated, without, however, ever exceeding the temp-
erature of the liquid at the input to the cooling system, and
its humidity approache~ that with the same water-vapour pressure
a~ the liquid to be cooled, without the relative humidity, however,
ever being ab~ve lOO~o.
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As regards the liquid, generally an aqueous liquid, it
cools; if it is heavily charged with dissolved substances~ or if
these substances are not very soluble,~cooling brings the temperature
below the precipitation threshold. Depending on the nature of the
dissolved substance~ muds or flakes or even other types of precipita-
tion may form.
In certain cases, which are particularly difficult,
incrustations form, deposits adhering to all the rigid walls against
which the supersaturated liquid comes in contact~ This is particularly
notable during cooling of electrolytes in the zinc industry.
Such solutions are both extremely corrosive and lead
to severe incrustation. Their pH, which is close to zero, due to
the sulphuric ac1d (for example, 150 gm of H2S0~ per litre),
necessitates the use of special materials such as stainiess steels
and organic polymers (plastics) of suitable properties. As to the
incrustations, they occur on the walls; these are in effect subject
to the constant splashing of the solution. These deposi~s of
gypsum rapidly grow~ by several centimetres per month , necessitating
frequent, minute and difficult maintenance work, entailing immobi-
lisation of the installation. Scaffolding must be periodically
assembled inside the cooling plant, to permit the maintenance per-
sonnel to remove the incrustations and drop them into the reservoir
which has been emptied for this purpose. By the date of the
bi-monthly maintenance, the incrustations have reached thicknesses
of about 10 cm~ but blocks, saturated with acid , of a thickness
of 15 cm are by no means rare. Any accidental falling of these
represents grave danger during the maintenance work, and may often
damage the walls of the cooling plant.
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The conventional atmospheric cooling plant, particularly
suitable for cooling a potentially corrosive liquid containing
substances capable of precipitation, cQmpriSeS an enclosed space
having on its upper portion means of causing a descent of the
liquid in droplets, and at its lower portion a blower designed
to blow between the lateral walls of the enclosure an atmospheric
flow of air capable of cooling the liquid and causing eddies of air
$n the enclosure, the cooled droplets and the precipitated solid
matter being collected in a reservoir provided at the base of the
enclosure.
According to the invention, the lateral walls of the
enclosure are protected from the splashes of liquid and solid
incrustations by smooth waterproof cloths whose lower edges are
submerged in the reservoir, and which are suspended a slight distance
in front of the walls, and are constantly moved by the eddies of
air, thus detaching, during their formation, the deposited solids,
which then fall into the reservoir.
Each cloth is suspended by any suitable means, such as
hooks or cords wound around bars or tubes, and is stretched by
any suitable mean5 of ballasting,such as sand or bars of lead~ the
tension thus created being insufficient to immobilise the cloth,
which would allow serious solid incrustations to form.
Cloths suitable for use with liquids containing mineral
salts and acids, such as electrolyte during zinc refining, are
preferably made of glass fibre-reinforced polyester with a coating
of polyvinyl chloride.
The interior walls of the cooling plant are preferably
hung with a single cloth made up of several smaller cloths welded
together before assembly in the cooling plant.
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A rapid and inexpensive method of cleaning the internal
walls of an atmospheric cooling plant according to the invention,
during the short ~tst ~ d~ periods of the ~ consists in
removing the incrustations by manually shaking the cloths, this
technique is of great advantage, as it is obvious that these
cloths may thu~ be shaken much more energetically than could be
achieved by eddies of air.
In accordance with one aspect of the present invention,
there is provided an atmospheric cooling plant for cooling a
potentially corrosive liquid containing substances capable of
precipitation, formed by an enclosure having lateral walls and
comprising on its upper portion means for causing the fall of
the liquid in droplets, and in its lower portion a blower
~uitable for blowing in the body of the enclosure, i.e. between
its lateral walls a current of atmospheric air capable of cool-
ing the liquid and of creating movement of the air within the
enclosure, the cooled droplets and precipitated solids being
collected in a basin provided at the base of the enclosure,
characterised in that the lateral walls of the enclosure are
protected from splashes of liquid and incrustations of solid
matter by waterproof smooth cloths which, their lower edge being
submerged in the basin, are suspended a short distance in front
of said walls, and are constantly moved by the movement of the air,
thus detaching as they form, the deposited solids, causing them
to drop into the basin.
In accordance with a further aspect of the present
invention, there is provided a rapid and inexpensive method of
cleaning the internal walls of an atmospheric cooling plant for
cooling a potentially corrosive li~uid containing substances
capable of precipitation, formed by an enclosure having lateral
walls and comprising on its upper portion means for causing the
fall of the liquid in droplets, and in its lower portion a blower
suitable for blowing in the body of the enclosure, i.e. between
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its lateral walls a current of atmospheric air capable of
- cooling the liquid and of creating movement of the air within
the enclosure, the cooled droplets and precipitated solids being
collected in a basin provided at the base of the enclosure,
the lateral walls of the enclosure being
protected from splashes of liquid and incrustations of solid
matter by waterproof smooth cloths which, their lower edge
being submerged in the basin, are suspended a short distance
in front of said walls, and are constantly moved by the movement
of the blown air, thus detaching as they form the deposited solids,
causing them to drop into the basin, the method being carried out
during short stopping periods of the blowing and characterised in
that the incrustations are removed by manually shaXing the cloths.
The accompanying drawings show by way of example an
embodiment of the invention.
Fig. 1 is a plan view of a conventional atmospheric
cooling plant, whose internal walls are protected from splashes
of liquid by an assembly of protective cloths suspended from the
ceillng,
Fig. 2 is a perspective view of the cooling plant in
'' 20 Fig. 1, without the protective cloths,
Fig. 3 shows on a larger scale one of the liquid-dis-
tributing nozzles or jets mounted on the ceiling,
Fig. 4 is an overall view of the assembly of the pro-
tective cloths, and
Figs. 5 and 6 show the assembly of the cloths respect-
ively along section lines 5-5 and 6-6.
The cooling plant 10 (Fig. 1) is an enclosure of
substantially parallelepipedic shape, whose small sides 11, llA
and large sides 12, 12A are made up of self-supporting panels 13,
either flat (Fig. 2) or corrugated (Figs. 4 - 6), fixed to a
concrete base 14, the panels are advantageously made of a high-
quality polyester reinforced with glass fibre, and are reinforced
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,
either by vertical ribs 13A (Fig. 2), or by vertical spars
13B ( Figs . 4-6 ), supported by horizontal spars 13C .
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The base is in the form of a rectangular basin 15 (Fig.1,2)
intended to collect the corrosive liquid charged with precipltates
after cooling of the latter. The basin is covered either with lead
or anticorrosive brick, or also with a high-quality reinforced
polyester. In addition, as corrosion is normally at its most intense
at the liquid-air interface~ a hydraulic seal 16 (Fig.2) or flap is
provided , made of the same polyester material, in order to ensure
contact between the walls of the cooling plant and the basin.
One of the walls 11 (Fig.l), situated on one of the two
small sides, has an inspection door 17, while the other, opposite
wall llA~ contains a circular orifice 18 (Fig.2) into which is
insert~d the edge of an annular guard or ferrule 19 of a blower
fan 20. This latter~ which is mounted on the exterior of wall llA
on columns 21 of galvanised or painted steel~ has vanes 22 of
polyester~ and a hub 23 of painted or galvanised cast metal~which
is rotated by an electric motor 24 coupled to a reduction gearing
25; th3 external protective grille 26 for the fan is made of
stainless steel of type 316.
The fan is also protected from falls of precipitate by
a protective covering 27 of polyester which fits the orifice
18 on its upper portion~ and is then elongated ~ertically (Fig.l~
5, 6).
The atmospharic cooling plant is enclosed at the top by
a ceiling made up of distinct layers 28 and 28A (Fig.2), of
lamellar polyester, known as vesicular entrainment extractors, capable
of capturing the drops of liquid while at the same time allowing
the cooling air to be diffused to the exterior. These extractors
, ~ f ~1'5
are supported by transverse profilcd column_ 29 and 29A with an
H or T cross-section, and made of stainless steel of type 316,
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the two terminal columns supporting each stage of extractors
rèspectively 30 and 30A, which have a U cross-section.
A main duct, or hot-liquid cQllector 31, made of stainless
steel of the same type, is mounted beneath the spars 30 in the
longitudinal direction of the cooling plant, on either one side
(Fig.2) or the other (Figs.1~ 5, 6) of the fan; it is connected
by ties 32 to transverse secondary ducts 33, supported by spars 3
mounted parallel with the collector.
~ ach of the secondary ducts 33 is provided with several
nozzles or ~ets 35 (Figs 2~3) ~ capable of emitting hot liquid 36
downwards.
Parts made of stainless steel or flat sheet 37 (Figs. 5,6)
connect by means of welding the spars 29 to the collector 31~ in
order to helps~po~lng it; plates 38 connect by means of weld~ng
the spars 29 to spars 3~ with the purpose of supporting the secondary
ducts 33.
For ease of assembly and maintenance of the installation7
the ends of the collector consist of sleeves 39, 39A with ties,
which pass through the walls of the cooling plant (Figs.l~ 5 and
Fig.2), one of the two being closed, and the other being supplied
with liquid at high temperature, for example in the direction of
arrow ~0 (Figs.l, 2, 5).
It is self-evident that the collector 31 and the lateral
ducts 33 could also be made of a synthetic material such as polyvinyl
chloride, reinforced if necessary by polyester, for example~ and
in this case, of course~ the ducts would not be supported by
welded plates.
The atmospheric cooling plant may be equipped with a
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ladder 41 (Fig.2 ), and a catwalk 42 (Figs.2 , 5) of protected
steel.
In order to obtain the maximum degree of droplet cooling
in a hot aqueous solution , the configùration and proportions of
the enclosure, the dimensions and power of the blower fan, and
the characteristics and output of the jet have all been carefully
calculated; careful account has been taken not only of the initial
temperature of the blown air and of the hot liquid, but also
of other factors such as density, specific heat and vapour pressure
of the liquid. For example, it was discovered that, when the
electrolyte to be cooled is an aqueous solution of zinc sulphate,
the total available surface for contact between the air and the
droplets must be almost twice as great as that for the water of
a conventional wet cooling tower.
Naturally, when the atmospheric cooling plant described
above is used to cool sea water, brine, concentrated acid or
alkaline aqueous solutions, etc.~ the steps taken to prevent
corrosion may be sufficient (stainless steels and special
polyesters~ conventional coverings, etc.)~ In the case of the
hot electrolyte arising from zinc refining, on the other hand, as
this contains about 200 g of ion sulphate per litre and 5~ of
fluorine, and which precipitates on cooling gypsum saturated
with sulphuric acid, the splashes of liquid attack the glass in the
reinforced polyester, forming hYdrofluoric acid, and incrustations
with all the risks and drawbacks enumerated above~
In order toprevent such a liquid coming into contact
with the walls of the cooling plant, it is necessary to protect
them. According to the invention, they are hung with smooth
waterproof cloths made preferably of glass fibre reinforced
107559~3
polyester coated with polyvinyl chloride. These cloths~ before
being freely suspended a short distance ~n front of the walls,
are sewn together to form a continuous screen.
The walls 12 and 12A (Fig.l) of the cooling plant are
concealed by cloths 43 and ~3A (Figs.l, 5, 6) whose upper edg~ is
perforated in order to accommodate the lower leg of S-shaped hooks
4~ (Figs.4, 5, 6) , the upper leg being placed on bars or tubes
~5 fixed to the top of spars 29 with a T or H cross-section;
indeed , the ends of these spars are free of the lamellar
extract~ layer 28 (Fig.2).
Each cloth ~3~ 43A (Figs.5, 6) is submerged beneath the
surface 46 of the cooled liquid ~7 collected in basin 15, and the
lower edge 48 of the cloth is provided on the interior with a
ballasting material such as sand or lead, in order to prevent the
flow of air blown in~o the enclosure from exposing the protected
walls.
One cloth 49, seen in plan view (Fig.6) and in elevation
(Fig.5) at the point of its seams connecting it to cloths ~3 and
43A, is placed in front of wall 11 so that the lower edge is
submerged in the basin like the adjacent cloths; the upper edge
is fitted with S-shaped hooks 50 , as are the other cloths, but
the upper leg of the hooks rests on the upper part of the U-section
spar 30.
A cloth 49a (Figs.l , 5, 6~ intended to cover wall ~,
is suspended~ l1ke cloth 49, to the corresponding U-section spar 30,
but the lower edge of the cloth is located just above the polyester
protective element 27 of the blower (Figs.5, 6) and is fitted with
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a ballast system 48A~ analogo~s to that of the adjacent cloths.
The part of the wall llA surrounding the blower need not be protected
by the cloths, as the blown air blows the rain of droplets towards
the interior of the enclosure.
When the atmospheric cooling plant is in operation, the
continually renewed movement of air causes cooling of the droplets
of liquid, coming from the jets, the cooled liquid dropping with
the precipitate into the basin~ and the heated air leaves the
enclosure through the ceiling of lamellar polyester~ any droplets
carried along being captured by the latter. The splashes of liquid
are stopped by the cloths~ and precipitate which might tend to form
incrustations is constantly eliminated by the movements of the
cloth due to the air in motion.
During the short stopping periods of the installation,
the maintenance personnel vigorously shake the cloths by hand, thus
detaching any precipitates which might still be adhering thereto.
Naturally, the invention is not limited to the
embodiment which has been described and illustrated by way of example,
and any modifications thereto would not go beyond its scope.
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