U.S. patent application number 13/156958 was filed with the patent office on 2011-09-29 for method and device for cleaning the water-trickling surfaces in an air/water heat exchanger.
Invention is credited to Paule Blokbergen, Michel Degrange, Remi Gomez, Nicolas Laurent, Jean-Marc Meurville.
Application Number | 20110232695 13/156958 |
Document ID | / |
Family ID | 37547534 |
Filed Date | 2011-09-29 |
United States Patent
Application |
20110232695 |
Kind Code |
A1 |
Gomez; Remi ; et
al. |
September 29, 2011 |
METHOD AND DEVICE FOR CLEANING THE WATER-TRICKLING SURFACES IN AN
AIR/WATER HEAT EXCHANGER
Abstract
A method of in situ scale removal from a heat exchange body
suspended in a wet cooling tower, wherein the method generates at
least one air blast by a generator implementing controlled
expansion via a nozzle of a mass of compressed gas in a nozzle
towards a zone of the body, the generator being opened at a
distance (H) from the zone, and the method consisting in repeating
the operation after moving the generator under the body outside the
zone.
Inventors: |
Gomez; Remi; (Paris, FR)
; Laurent; Nicolas; (Poix, FR) ; Degrange;
Michel; (Paris, FR) ; Meurville; Jean-Marc;
(Nailly, FR) ; Blokbergen; Paule;
(Clermont-Ferrand, FR) |
Family ID: |
37547534 |
Appl. No.: |
13/156958 |
Filed: |
June 9, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12307222 |
Dec 31, 2008 |
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PCT/FR2007/001114 |
Jul 2, 2007 |
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13156958 |
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Current U.S.
Class: |
134/37 |
Current CPC
Class: |
F28G 13/00 20130101;
F28C 1/00 20130101; F28G 7/00 20130101 |
Class at
Publication: |
134/37 |
International
Class: |
B08B 7/00 20060101
B08B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 3, 2006 |
FR |
06 05983 |
Claims
1.-13. (canceled)
14. A method of in situ descaling an element body covered in a
deposit, and present in a wet bag cooling tower, wherein the method
consists in generating at least one air blast of large quantity of
low pressure by means of a generator causing a mass of compressed
air to expand towards a zone of the element so as to create a flow
in said element that is substantially parallel to the surfaces of
walls constituting it, the generator being open at a distance (H)
from said a zone, and said operation being repeated after moving
the generator along the element.
15. The method according to claim 14, wherein the generator is
moved continuously under the heat exchange body and a succession of
blasts are emitted during the movement.
16. The method according to claim 14, including a stage of heating
the zone concerned of the body by a flow of hot air.
Description
[0001] The present invention relates to a method and a device for
cleaning water-trickling surfaces in an air/water heat exchanger,
such as those present for example in the lateral or horizontal
packing of a cooling tower or in droplet separators.
BACKGROUND OF THE INVENTION
[0002] In cooling towers, the water of a secondary condensation
circuit is cooled, for example, mainly by evaporating a fraction of
the water to be cooled, which water trickles over surfaces that are
provided for this purpose and that are swept by a flow of air
flowing in the opposite direction to the trickling, and it is
cooled to a lesser extent by the convection that occurs on the heat
exchange surface within the water itself.
[0003] These surfaces are carried by a heat exchange body, commonly
referred to as "packing" and constituted by sheets made of PVC in
particular, which sheets are assembled to one another so as to form
a cellular structure. Each cell of the structure is in the form of
a tube that is about 1.5 meters (m) long, with the mean dimension
of its section being of the order of a few centimeters. The walls
of the cells are fine (a few tenths of a millimeter) and they are
pierced by numerous orifices.
[0004] The heat exchange bodies are suspended in the cooling tower
between an installation for sprinkling the water that is to be
cooled and a bottom basin for recovering the cooled water, droplet
separator or capture means also being located higher up in the
tower in order to retain as much as possible the water droplets
that are entrained by the cooling air. It is important not to
exhaust this water into the atmosphere since it can carry germs
that proliferate readily in the tower since it operates at a
temperature that encourages such proliferation.
[0005] In use, the heat exchange body and the droplet separators
become covered in a deposit of mineral salts because of the
evaporation that occurs on the trickling surfaces. This deposit
grows over time and, in the packing, it can reach a weight that is
as much as ten times the weight of the body itself in certain
installations. This deposit presents numerous drawbacks: it
constitutes an obstacle to trickling and thus to the effectiveness
of heat exchange, it constitutes a nest for retaining various germs
that are present in the water under conditions that encourage their
proliferation, it constitutes a very significant extra load on the
structure supporting the heat exchange body since it is generally
suspended inside the tower, . . . .
[0006] At least in theory, there are several ways of remedying that
drawback. One consists in chemically treating the water for cooling
so as to remove salts therefrom, thereby avoiding scaling of the
heat exchange surfaces. That cannot be envisaged in the cooling
towers of power stations, whether nuclear or fossil fuel.
[0007] It is also possible to dissolve the scale chemically using
appropriate solutions. That technique raises difficult problems of
effluent treatment and therefore has an economic impact on
operating costs.
[0008] Finally, it is possible to envisage shaking the heat
exchange body with any appropriate mechanical means; on being
tested, that method has led to so much deterioration of the heat
exchange body as to render it practically unsuitable for subsequent
use.
[0009] Finally, it is possible to clean the heat exchange body
mechanically after it has been disassembled, but that constitutes
an operation that is extremely expensive given the large volume of
the body (10 cubic meters (m.sup.3) to 12,000 m.sup.3 in units of
about 2 m.sup.3.
OBJECT OF THE INVENTION
[0010] A solution is therefore sought that enables the drawbacks of
existing or potential solutions to be avoided, while nevertheless
cleaning heat exchange bodies used in the cooling towers of power
stations, in particular of nuclear power stations.
SUMMARY OF THE INVENTION
[0011] To this end, in a first aspect, the invention provides a
method of in situ descaling a heat exchange body present in a wet
cooling tower (the body being in the form of horizontal or lateral
packing) or descaling a droplet separator (with scaling necessarily
taking place on the fins thereof), which method consists in
generating at least one air blast in large quantity and low
pressure (e.g. of the order of 2 bars to 12 bars) by means of a
generator serving to expand a mass of compressed gas towards a zone
of the heat exchange body or towards the fins of the droplet
separator in order to create a flow in said body or said separator
that is substantially parallel to the surfaces of the walls
constituting it, the generator being open at a distance from said
zone, and the method consisting in repeating said operation after
moving the generator along the heat exchange body or the separator
through a step of determined size.
[0012] The gas blast generated by the generator progresses inside
the cells or channels of the heat exchange body, giving rise as it
passes to a kind of expansion of the inside channels of the element
to be descaled and thus giving rise to local elastic deformation of
the walls of said channels, the deformation being of an amplitude
that is sufficient for the scale, which is hard or brittle, to
become detached therefrom. During testing, it is found that a cloud
of dust is formed beside the wall as though the particles of scale
had been suddenly separated from the wall surface in a direction
normal thereto. The flow of gas inside the element for cleaning
suffers significant head loss such that the blast progresses into
the inside of the body over a depth that corresponds to
substantially half the total thickness of said element when it is a
heat exchange body, and this is advantageous since it is
specifically in this half of the body where the greatest amount of
deposition takes place. The generator is presented to the face of
the heat exchange body that corresponds to the outlet for the
trickling water. When used with droplet separators, the length of
the channels between sheets is short so the head loss to which the
flow is subjected stems essentially from the baffle-shape of these
channels, for ensuring that the sheets constitute obstacles that
are effective in trapping the droplets that are entrained by the
cooling air. The flow of gas tends to entrain at least some of the
detached particles inside the channels, and it is found that they
have an abrasive effect that increases the cleaning power of the
method. Depending on the rate of "firing" and on the spacing
between generators along the elements to be cleaned, it is possible
to organize a kind of cycling for the detached particles in a
plurality of successive flows.
[0013] Given that the section of such a heat exchange body can be
as much as several thousand square meters, it will be understood
that it is not possible to provide a blast generator capable of
covering the entire area. The method of the invention thus consists
in treating the bodies in question zone by zone. Thus the method
consists in moving the generator continuously underneath the heat
exchange body and in generating a continuous succession of blasts
as it moves.
[0014] In order to improve the effectiveness of the treatment, it
is possible to proceed with a stage of heating the zone in question
by means of an element for blowing hot air. Since the walls of the
channels constituting the elements are made of thermoplastic
material (typically PVC), heating tends to make these walls more
flexible and therefore to increase the difference in stiffness
between the wall and the deposit. It will be understood that when
the blast goes past under such conditions, the scale is separated
more easily from the walls.
[0015] In a second aspect, the invention provides a device for
implementing the above-described method, in which the
above-mentioned generator comprises: [0016] a source of compressed
gas; [0017] at least one tank having an inlet communicating with
said gas source through a cock with controlled opening and closing,
and an outlet communicating with the outside atmosphere via the
seat of a valve member with controlled opening and closing; and
[0018] control means for controlling the cock and the valve member
to isolate the tank from the outside atmosphere while it is in
communication with the compressed gas source, and for isolating it
from the source when it is open to the outside atmosphere.
[0019] In an embodiment specially adapted to descaling packing
(whether horizontal or vertical), in which the heat exchange
surfaces define channels of small section, the outlet seat from the
gas tank is extended by a nozzle in which the air flow expands
progressively.
[0020] The structure of the device enables communication to be
established quickly from the tank to the outside atmosphere and
thus enables gas expansion to be obtained that leads to a blast
being created that is powerful but at low pressure (2 bars to 12
bars) and that propagates from the outlet of the tank, or of the
nozzle when a nozzle is provided, towards the face of the element
next to which it opens out. It is found that the device should not
be located immediately under the body, but should be at a distance
therefrom so that the material constituting the channels is not
damaged by a gas pressure that is too high and too localized. This
distance needs to be of the order of a few tens of centimeters
(e.g. 15 cm to 50 cm).
[0021] It has also been observed that with a device having a
nozzle, it is advantageous for the free end of the nozzle to be
situated inside a cylindrical sleeve that is spaced apart radially
from said end. The gas leaving the nozzle generates suction in the
gap between the wall of the nozzle and the sleeve, thereby creating
a kind of tubular fluid sheath that contains the outgoing stream of
gas in a direction that lies substantially on the axis of the
channels. This sheath prevents the outgoing gas stream from
diverging and reaching the cells at an angle of incidence that
causes the kinetic energy of the stream to apply pressure to said
walls and deform them to breaking point. This is particularly
desirable with packing.
[0022] In a particular embodiment of this device, the valve member
is mounted to slide on a stationary rod inside the tank and
co-operates with said rod to define a variable-volume chamber
suitable for being connected selectively to the compressed gas
source and to the atmosphere for the purpose respectively of
closing and opening the outlet of the tank. In addition, the rod is
hollow; it is in permanent communication with the source of gas
under pressure and it possesses openings putting its inside volume
into communication with the tank, while the valve member is shaped
as a jacket with a wall that is suitable for covering said openings
when the valve member is spaced apart from its seat so that, in
this position, the tank is isolated from the gas source. These
means make it easy to obtain rapid opening of the outlet from the
tank via a flow section that becomes large very quickly. These
means also enable the movement of the various moving parts to be
synchronized mechanically in simple manner so as to feed gas and
exhaust gas at relatively high frequencies, as is necessary to
ensure that the treatment of a heat exchange body, for example, can
be performed in a length of time that is compatible with the
industrial operating requirements for a cooling tower.
[0023] Advantageously, the device of the invention includes a
source for blowing hot air towards the element to be treated. This
may be constituted merely by a blower serving to heat the plastics
material forming the body to be descaled prior to the "campaign" of
shots to which it is subjected on a continuous basis, for
example.
[0024] Finally, the device of the invention may be provided with a
hopper for collecting the particles of scale that are detached by
the treatment and that fall under the effect of gravity, in
particular when operating under horizontal packing. Other collector
means, e.g. suction means, could be implemented with the device of
the invention.
[0025] Other characteristics and advantages of the invention appear
from the description given below of an embodiment.
BRIEF DESCRIPTION OF THE DRAWING
[0026] Reference is made to the accompanying drawing, in which:
[0027] FIG. 1 is a schematic diagram of a shockwave generator
implemented in the invention; and
[0028] FIG. 2 shows the implementation of the method in accordance
with the invention in treating horizontal packing.
DETAILED DESCRIPTION OF THE INVENTION
[0029] FIG. 1 shows a tank 1 having an outlet opening shaped to
constitute a valve seat 2 suitable for being closed or opened by a
valve member 3. The tank is generally cylindrical in shape with a
longitudinal axis X on which the seat is centered. On this axis the
tank includes a stationary internal rod 4 made in the form of a
tube that is closed at its end inside the tank and that passes
through the wall of the tank opposite from the seat 2. The valve
member 3 is constituted by a tubular jacket 3b and a head 3a at the
top of the jacket, the head being of a profile that is adapted to
close the seat in leaktight manner while presenting an annular
thrust surface around the seat that can be acted on by the pressure
that exists inside the tank.
[0030] The valve member 3 is slidably mounted on the rod 4 and
co-operates with the closed end thereof to define a variable-volume
chamber 5 into which a duct 6 opens out, the duct 6 being inside
the rod 4 and being isolated from the inside volume thereof.
[0031] The side wall of the rod 4 is provided with a plurality of
openings 7 at a level such that they are completely uncovered by
the jacket 3b when the valve member is pressed against its seat,
while being covered by the jacket when the valve member 3 is moved
away from the seat 2.
[0032] Outside the tank 1, the inside volume of the rod 4 is
connected via a duct 8 to a pressure source 9 that may be a
manifold fed by a compressor or one or more cylinders of compressed
gas (air). The duct 6 is connected to the same compressed gas
source 9 via a duct 10 and a rotary plug cock 11 with a drive shaft
that is referenced 12 in the figure. In the position shown, the
cock establishes communication between the source 9 and the duct 6,
and thus the chamber 5. In the opposite position, after the plug of
the cock 11 has been turned through half a turn, it isolates the
chamber 5 from the source of pressure and puts it into
communication with the atmosphere via an exhaust orifice 13
opposite from the duct 10. The plug of the cock is coupled by its
drive shaft 12 to a gearwheel 14 forming part of a rotary drive
transmission system for transmitting drive from a motor that is not
shown in the figure and that includes, for example, a cog belt 15
for driving the gearwheel 14. In an example that is not shown, the
rotary plug cock could be replaced by any suitable solenoid
valve.
[0033] Finally, there can be seen in this figure a nozzle 16 that
diverges away from the outlet orifice of the tank 1. Outside the
nozzle, the device includes a cylindrical sleeve 17 that surrounds
and extends the outlet from the nozzle into the atmosphere.
[0034] The above-described device operates as follows.
[0035] It is assumed that the first state of the device is that
shown in FIG. 1. In this state, the chamber 5 is full of gas under
pressure, thereby tending to press the valve member 3 against the
seat 2 surrounding the outlet opening from the tank 1. In this
position, the skirt 3b of the valve member lies above the openings
7, and the inside chamber of the tank 1 is in communication with
the source 9 of gas under pressure.
[0036] The plug 11 is turned, e.g. being driven to rotate
continuously. During the first portion of this rotation, the
chamber 5 is isolated from the source 9, and then the channel
through the plug reaches the exhaust orifice 13.
[0037] The chamber 5 is then vented and the pressure that exists
inside the tank 1 bearing against the annular surface of the valve
member around the seat 2 is no longer opposed by the pressure that
exists inside the chamber 5. The valve member is thus moved away
from the seat 2. The volume inside the tank 1 is thus connected to
atmospheric pressure via the outlet orifice surrounded by the seat
2, while the jacket 3b of the valve member 3 overlies the orifices.
The expansion of the gas in the nozzle 16 that extends the outlet
orifice causes a blast to be formed that propagates towards the
outlet of the nozzle 16 along the axis X of the device.
[0038] Inside the nozzle, the flow of gas leads to a drop in
pressure, and at the outlet from the nozzle 16 the flow is
channeled by the presence of the sleeve 17, thereby establishing
therein, by the Venturi effect, a peripheral tubular flow that
constitutes means for confining the divergence of the stream
leaving the nozzle. The flow of gas outside the nozzle is thus
maintained substantially parallel to the axis X of the device.
[0039] As it continues to rotate, the plug returns the device to
the state shown. At this moment, the chamber 5 is no longer
connected to the atmosphere, but is once more in communication with
the gas source 9. The valve member 3 is then pressed once more
against the seat 2, thereby serving firstly to isolate the inside
chamber of the tank 1 from the atmosphere, and secondly, once the
openings 7 have been uncovered, connecting the chamber to the
source of gas under pressure. The cycle thus begins again so long
as the gearwheel 14 is driven in rotation.
[0040] FIG. 2 is a diagram showing a battery of devices of the kind
described above being implemented in an operation for cleaning a
heat exchange body 20 suspended in a cooling tower, e.g. in a power
station. A frame 21 carries a plurality of blast generators 22 with
their nozzles pointing upwards under the heat exchange body 20.
[0041] The distance H between the outlets from the nozzles and the
bottom end of the suspended body is of the order of 15 cm to 30 cm.
The frame also carries a source of gas (air) under pressure,
constituted in this example by a compressor 23 and a manifold 24.
Each generator 22 possesses a rotary plug valve coupled to a
transmission system 25 driven by a motor 26. This transmission
system is constituted by a belt driving all of the controlling
gearwheels of the valve synchronously. By having each plug
angularly offset relative to all of the others, the generators are
organized to fire their "shots" successively over time; for
example, if the frame carries six generators, an angular offset of
60.degree. between plugs enables six successive shots to be
obtained during the time taken by a plug to perform one revolution.
If solenoid valves are used, then they are triggered to execute the
sequence by a controller.
[0042] The frame 21 is shown as being mounted on an elevator
platform 27 (or a crane) that may be self-propelled and that serves
to adjust the distance H between the heat exchange body 20 and the
nozzles. The travel speed of the platform under the heat exchange
body is adjustable, e.g. around a few centimeters per second.
[0043] In operation, the release of gas under pressure on each
opening of a valve member creates a blast that propagates into the
channels formed through the heat exchange body by fine sheets of
PVC, deforming the elements of the heat exchange body and breaking
up the deposit on the surfaces of said elements. The scale that has
become deposited uniformly on the sheets of PVC is hard and
brittle, while its support as constituted by the fine sheets of PVC
is very flexible, so the scale breaks into pieces when its support
is deformed under the effect of the shockwave. Once the scale has
cracked or broken up, it is more inclined to separate from its
support.
[0044] In addition, the stream of air simultaneously sweeps
intensely over all of the volatile elements contained in the
channels as it passes therethrough. The pieces of scale that are
initially loosened from the sheets of PVC by the shockwave are then
swept along by the stream of air and they contribute to cleaning
the channels by abrasion.
[0045] The device shown in FIG. 2 includes a device for heating the
heat exchange body 20, which device is represented diagrammatically
in the form of a hot air blower 28. Provision is also made to fit
the top assembly with a detached scale collector, e.g. in the form
of a hopper surrounding the frame 21 and not shown in order to
ensure the drawing is clear. The bottom outlet from the hopper may
be connected to a suction source.
[0046] The method of the invention and the device used for
implementing it in a modified embodiment different from that shown
in the figures can be used for treating other scaled elements such
as lateral packing in certain forms of air-cooled towers, or
droplet separators that are also deployed in such towers to
minimize the quantity of droplets that are entrained into the
atmosphere by the air leaving the tower. Such separators are not
heat exchange bodies and rather they form physical barriers
(baffles) for the droplets contained in the air stream, which
baffles are necessarily subjected to scale formation that is less
than that on the heat exchange bodies but still sufficient for it
to become necessary in the long run to treat them in order to
restore their initial performance.
* * * * *