Note: Descriptions are shown in the official language in which they were submitted.
CA 02605884 2007-10-12
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Method for Cleaning the Tubes of a Heat Exchanger Using an Abrasive
and a Device Suitable for the Method
This is a divisional of Canadian Application Serial No. 2,473,145 filed July
7, 2004.
The present invention relates to a method for cleaning a heat exchanger by
using an
abrasive and a device that is designed for using the method. From time to time
it is
necessary to remove deposits from heat-exchanger tubes. Even though there are
many
chemical cleaning methods available, these require a major technical outlay
because of
the large number of heat exchanger tubes and the correspondingly large number
of
openings that are involved. For this reason, exchanger tubes are mainly
cleaned by
mechanical means. In addition to cleaning with brushes, in many instances
blast
cleaning methods are used; in such methods, an abrasive is blown through a
tube with
the help of a nozzle that is applied to one end of the tube. Such a method is
described,
for example, in DE 195 "46 788 Al. As an example, steel or carborundum
particles are
used as the abrasive. The particles that emerge for the other end of the tube
are collected
in a trap and returned to the abrasive cycle. DE 198 37 683 C2 describes such
a trap. As
is shown in Figure 1, in a conventional cleaning method two jet nozzles 2 that
are
mounted on a carrier 1 are attached, for example, to the inlet side 3 of a
heat exchanger
4. The ends of the jet nozzles 2 that point in the direction 5 of the jet are
constricted to
form a cylindrical connector that is introduced into the end 7 of the tube. At
their other
15 end, which faces against the direction 5 of the jet, the nozzles have an
inlet opening that
is connected to a delivery line 8. A venturi jet with a choke point 13 is
disposed between
the outlet opening 10, which is surrounded by the front end of the connector
6, and the
inlet opening 9.
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It is the objective of the presznt invention to describe an alternative method
and an
altematively configured device for realizing the method described in the
introduction
hereto, which permits, in particular, more efficient cleaning of a heat
exchanger.
This objective is achieved according to one aspect of the invention, in that
an
unchoked nozzle is used, it being preferred that the outlet opening of this be
of equal size
or slightly smaller than the internal cross-sectional area of the tube. This
configuration
makes it possible to act on a tube that is to be cleaned with a large flow of
abrasive. This
is not possible to the same extent using the usual nozzles. In such a case,
the velocity of
the abrasive in a delivery line that is connected to the nozzle is greatly
increased because
of a relatively small constriction in a. vcuturi nozzle. The consequence is
that particles of
abrasive are emitted with a large amount of kinetic energy. However, these
particles are
decelerated within a relatively short section of line. Then, only an abrasive
flow with a
low concentration of particles is available for cleaning the tube. This is not
the case with
the present invention, in which-because there is no choke effect or
constriction in the
nozzle-an abrasive flow with a very high concentration of particles and a
concomitant
high degree of abrasiveness is available. A configuration that permits large
outlet
openings ensures that the nozzle is pressed against a face of the delivery
line with a
contact surface that surrounds the outlet opening. In contrast to this, in the
prior art, a
constricted connector is inserted into one end of the tube, when the outlet
opening of the
connector must be reduced by an amount that at least corresponds to its wall
thickness
relative to the cross-sectional area of the tube.
The time required for the cleaning method can be reduced in that a plurality
of tubes is
cleaned simultaneously. This is effected in that a plurality of nozzles that
are held iii a
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30146-23D
carrier in the tube grid of the heat ex.chancer is used, Wiiereas, in the case
of
conventional methods and devices, the position of the nozzles is fixed in that
a
constricted connector of the nozzle is introduced into an end of a tube,
according to the
present invention a locating pin that protrudes in the direction of the jet is
provided, and
tlus is inserted into one tube end during the cleaning process. This can be
done without
any problems if the locating pin is disposed on the carrier in a position that
corresponds
to the tube grid.
A cllolce-free nozzle can be realized in that a duct that is defaled by an
inlet opening and an outlet
opening passes through the nozzle, in the region adjacent the outlet opening
said duct being of a
diameter that is esseitially constant and having a cross-sectional area that
corresponds approximately to
the size of the outlet opening. As described heretofore, the outlet opening is
surrounded
by a contact surface that, during the cleaning process, is pressed against the
end face of
the tube that is to be cleaned. It is preferred that this contact surface be
enclosed by a
collar that is disposed radially on the outside and projects axially. The
contact surface
and the collar form a receptacle for the end of a tube. This configuration
permits better
sealing of the end area of the tube and also provides an additional way by
which the
device can be fixed in position on the heat exchanger. This prevents a carrier
that
supports a plurality of nozzles fronz twisting around the locating pin as an
axis of
rotation. In orie preferred enibodiment of the present invention, in order to
enhance the
seal between the end of the tube and the nozzle, provision is made such that
the area that
contains the receptacle and the outlet opening is of an elastomer. In
addition, this also
makes it possible to conipensate for tolerances and unevenness in the face
area of a tube
end. In order to provide a measure of inechanical protection and to prevent
the collar
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that encloses the face area of a tube being made wider by
the pressurized stream of abrasive, this collar is
surrounded by a reinforcing sleeve that is of a rigid
material such as a metal. It is preferred that the
elastomer area be formed by an end piece that resembles a
section of tube and is positively connected to the nozzle.
In accordance with an aspect of the present invention, there
is provided a method for cleaning the tubes of a heat
exchanger, in which a nozzle is set on one end of a tube
wherein the nozzle has an outlet opening of a size that is=
equal to or slightly smaller than the inside cross-sectional
area of the tube and air that contains an abrasive is blown
through the tube, wherein an unchoked nozzle is used.
In accordance with another aspcct of the present invention,
there is provided a jet device for cleaning the tubes of a
heat exchanger wherein the jet device comprises an unchoked
nozzle, wherein the nozzle blows air containing an abrasive
through a tube of the heat exchanger, wherein the jet device
carries out the method as defined herein, wherein a flow
channel that is delimited by an inlet and an outlet opening,
passes through the nozzle, the flow channel being of an
essentially constant cross-sectional area that approximately
corresponds to the size of the outlet opening, and wherein
the outlet opening is surrounded by a contact surface that
extends in the plane of the opening and functions in
combination with the face end of a tube.
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In accordance with yet another aspect of the invention,
there is provided a blasting nozzle for delivering a
pressurized air mixture containing an abrasive to a tube of
a heat exchanger, the heat exchanger tube having an internal
diameter, the blasting nozzle being connectable to a supply
line providing the pressurized air mixture, the supply line
having a conduit through which the pressurized air mixture
may flow, the blasting nozzle comprising: a nozzle body
having an outer surface, a first end, an opposed second end
and a channel defined therethrough extending between the
first and second ends; the first end of the nozzle body
having an inlet opening defined therein for receiving
therethrough the pressurized air mixture from the supply
line; the second end of the nozzle body having an outlet
opening defined therein through which the pressurized air
mixture may exit the nozzle body; the channel having a first
diameter at the inlet opening and a second diameter at the
outlet opening, the second diameter being sized to
correspond substantially to the internal diameter of the:
heat exchanger tube, the first diameter being sized at least
as large as the second diameter, and the nozzle body further
having at the second end thereof a third diameter defined by
the outer surface, the third diameter being at least as
large as the internal diameter of the heat exchanger tube.
In accordance with yet another aspect of the invention,
there is provided a blasting nozzle head assembly for
delivering a pressurized air mixture containing an abrasive
to a plurality of heat exchanger tubes, each heat exchanger
tube having an internal diameter, the blasting nozzle head
assembly comprising: a carrier, and a plurality of blasting
nozzles held by the carrier, each blasting nozzle of the
plurality having: a nozzle body having an outer surface, a
first end, an opposed second end and a channel defined
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therethrough extending between the first and second ends;
the first end of the nozzle body having an inlet opening
defined therein for receiving therethrough the pressurized
air mixture from a supply line; the second end of the nozzle
body having an outlet opening defined therein through which
the pressurized air mixture may exit the nozzle body; the
channel having a first diameter at the inlet opening and a
second diameter at the outlet opening, the second diameter
being sized to correspond substantially to the internal
diameter of the heat exchanger tube, the first diameter
being sized at least as large as the second diameter; and
the nozzle body further having at the second end thereof a
third diameter defined by the outer surface, the third
diameter being at least as large as the internal diameter of
the heat exchanger tube.
In accordance with yet another aspect of the invention,
there is provided a method for cleaning heat exchanger tubes
using a pressurized air mixture delivered from a supply
line, the pressurized air mixture containing an abrasive,
the method comprising: providing at least one blasting
nozzle, the at least one blasting nozzle having: a nozzle
body having an outer surface, a first end, an opposed second
end and a channel defined therethrough extending between the
first and second ends; the first end of the nozzle body
having an inlet opening defined therein for receiving
therethrough the pressurized air mixture from the supply
line; the second end of the nozzle body having an outlet
opening defined therein through which the pressurized air
mixture may exit the nozzle body; the channel having a first
diameter at the inlet opening and a second diameter at the
outlet opening, the second diameter being sized to
correspond substantially to the internal diameter of the
heat exchanger tube, the first diameter being sized at least
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30146-23D(S)
as large as the second diameter; the nozzle body further
having at the second end thereof a third diameter defined by
the outer surface, the third diameter being at least as
large as the internal diameter of the heat exchanger tube;
connecting the first end of the nozzle body of the at least
one blasting nozzle to the end of the supply line; coupling
the second end of the nozzle body of the at least one
blasting nozzle to the end of the heat exchanger tube to be
cleaned; and urging the flow of the pressurized air mixture
from the supply line through the at least one blasting
nozzle and into the heat exchanger tube to be cleaned.
The present invention is described in greater detail below
on the basis of an embodiment shown in the drawings appended
hereto. These drawings show the following:
Figure 1: A conventional device positioned on a heat
exchanger, in a longitudinal cross section;
Figure 2: A device according to the present invention,
corresponding to Figure 1;
Figure 3: The device shown in Figure 2, in cross section at
a greater scale;
Figure 4: A detail from Figure 3;
Figure 5: A perspective view of-the device shown in
Figure 2.
The device shown in Figure 2 to Figure 5 comprises a nozzle
head with a carrier 21 in which two nozzles 22 are
supported. It is, of course, possible to have nozzle heads
that incorporate only one or more than two nozzles.
Essentially, the carrier 21 is formed from a hollow, cuboid
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housing 23. Two parallel bores 24 that each accommodate a
nozzle 22 pass through the housing 23. A nozzle 22 is
essentially formed as a housing 25 in the form of a section
of tube. The housing 25 has three different longitudinal
sections, a middle section 26 being of a greater diameter
than the other two sections; namely, a front section 27 and
a rear section 28. The transition between the middle
section 26 and the narrower sections 27, 28 is formed in
each instance by a radial shoulder 29, 30. A stop flange 32
extends radially inward from the wall of the bore 24.
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The sirle of this stop tlange that is proximate to a middle section 26
functions with. the
radial shoulder 29 to fix the axial position of the housing 25. The radial
shoulder 30 of
the housing 25 rests against a cover plate 33 that closes off the rear of the
carrier housing
23. Between the cover plate 33 and the rear section 28 of the of the nozzle 22
there is an
0-ring seal 3 1. An elastomer seal 34 that encloses the periphery of the
section 27 is
installed is the area of the bore 24 that extends away from the stop flange 32
and
surrounds the section 27. In the front face of the nozzle housing 25 there is
a swallow-
tail groove 35 and one end of the essentially tubular-section end piece 36
that is of
elastomer material is inserted into this so as to form a positive fit.
A duct 37 passes through the front section 27. The mid-line longitudinal axis
38 of the
duct simultaneously forms the mid-line longitudinal axis of the nozzle housing
25. The
duct 37 is limited at the front by an outlet opening 39 and at its other end
by an inlet
opening 40. In the region adjacent the outlet opening 39, the duct 37 is
essentially of
constant cross-sectional area or constant diaineter 42.
The cross-sectional area or the diameter 42 eorrespond to the cross sectional
area or the
diameter 43, respectively, of a supply line 46, an external thread of which is
screwed
into the internal thread 45 of the middle section 25. The front face end 47 of
the supply
line 46 abuts against a radial shoulder 48 in the transition area between
section 26 and
section 27. A wedge-shaped projection 49 that encloses the inlet opening 40
like a ring =
protrudes from the radial shoulder 48 in the axial direction and this digs
into the
e].astozner material of the supply line 46. This enhances the..seal between
the supply line
46 and the housing section 26. The diameter 50 of the inlet opening 40 is
slightly
greater than the diameter 43 of the supply line 46, The difference in the
diameter is to be
such that that it coz7esponds to a wideniilg of the diameter 43 that occurs
when the hose
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is acted upon by a pressurized flow of abrasive. This ensures that the flow of
abrasive
does not encounter an edge of the housing that protrudes into the flow
channel. The area
52 of the flow channel 37 that is adjacent to the inlet opening 40 is slightly
tapered
conically, approximately as far as its inid-poiiit, a cylindrical section of
the cllannel of
diaineter 42 adjoining the .area 52. The nozzle may be considered to be
unchoked or
choke-free even when it includes such a taper.
As is shown in Figure 2, in order to carry out the cleaning method, the
carrier 21 is
arranged in front of the inlet side 53 or in front of the outlet side of a
heat exchanger 54.
If the heat exchanger is part of a-nuclear power station, the carrier 21 will,
as a rule, be
held by a manipulator (not shown herein) to which the carrier 21 is attached
by means of
a mounting device 55 (Figure 5). The tubes 56 of a heat exchanger are arranged
in a
regular grid pattern, and their ends pass through a retaining plate 57. The
end sections
58 of the tubes 56 protrude through the retaining plate 57. The nozzles 22 are
so spaced
apart from one another on the carrier plate 21 that they can be positioned on
the face
ends 59 of two tubes 56b that are separated by a tube 56a. To this end, the
end piece 36
has a contact surface 60 that functions in conjunction with the face end 59
and surrounds
the outlet opening 39. The contact surface 60 extends transversely to the mid-
line axis
3 8. Tlae contact surface 60 is also surrounded by a collar 62 that extends in
the axial
direction, or in the direction of flow 5. The collar 62 is of a wedge-shaped
cross section
and has an inclined surface 63 that is oriented radially inward, and an
inclined surface 61
that is oriented radially outward. The inclined surface 63 serves as an
inclined surface
that simplifies insertion vvhen the nozzle 22 is installed on the end of a
tube. During the
cleaning process, this tube end is accommodated in a recess 64 that is
enclosed by the
stop surface 60 and the collar 62, a cylindrical edge section 63 of the collar
62 I;~ing
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against the outside periphery of a tube 56b. The inclined surface 63 lies
snugly against a
welded seam 66 by which the tube 56 is attached to the retaining plate 57. The
collar 62
thus acts as a sealing lip that functions in conjunction with the outer
periphery and the
welded seam 66 of a tuber 56b. In order to ensure that the collar can.not
widen radially
when under pressure, it is completely surrounded by a reinforcing sleeve 67. A
flange
68 that extends radially inward from its end that is proximate to the carrier
21 lies in a
radial groove 71 in the end piece 36. The face end of the reinforcing sleeve
67 that is
applied to the flange 68 is inclined, and together with the inclined surface
61 of the
collar 62 forms a flush inclined surface 69. The bevel of the end piece, in
the form of
the inclined surfaces 61 and 69 prevents it from coming into contact with a
welded seam
66a of an adjacent tube 56a, and under certain circumstances preventing an
effective seal
being formed between the end piece 3 and the tube 56b that is to be cleaned.
Between
the section 27 of the nozzle housing 25 and the reinforcing sleeve 67 there is
a radial
groove 70 in the end piece 36 that increases its elasticity in the axial
direction.
On the front side of the carrier 21 there is a locating pin 73 for fixing the
position of the
carrier 21-from which the section 72 of the nozzles 22 protrades-on the
retaining
plate 57, and this retaining pin extends from the carrier 21 in the direction
of the mid-
line axis 38. A threaded section 74 of the locating pin 73 is screwed into a
threaded bore
75 in the carrier 21. Its front end, which is remote from the threaded section
74, is
tapered conically. The longitudinal section adjacent to the tapered section is
of a
5 diameter that is slightly smaller than the inside diameter of a tube 56,
During the
cleaning process, the locating pin 76 extends into a tube 56a that is disposed
between
two tubes 56b that are to be cleaned. The carrier is prevented from rotating
about the
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locating pin 73 as an axis of rotation by the positive combined function of
the tube ends
with the end pieces 36.
A mechanical distance sensor is disposed on the front side of the carrier 21.
This
ensures that the carrier 21 can be moved into a predetermined position with
respect to
the retaining plate 57 with the help of a manipulator (not shown herein).
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Reference Numbers
1 Carrier
2 Nozzle 39 Mid-line axis
3 Inlet side 39 Outlet opening
4 Heat exchanger 40 Inlet opening
Direction of jet 42 Diameter
6 Connector 43 Diameter
7 Tube end 44 Outside thread
8 Supply line 45 Inside thread
9 Inlet opening 46 Supply line
Outlet opening 47 Face end
12 Venturi 48 Radial shoulder
13 Choke point 49 Projection
21 Carrier 50 Diameter
22 Nozzle 52 Area
23 Housing 53 Inlet side
24 Bore 54 Heat exchanger
25 Housing 56 Tube
26 Middle section 57 Retaining plate
27 Front section 58 End section
28 Rear section 59 Face end
29 Radial shoulder 60 Contact surface
30 Radial shoulder 61 Inclined surface
31 0-ring seal 62 Collar
32 Contact surface 63 Inclined surface
33 Cover 64 Recess
34 Elastomer seal 65 Cylindrical wall section
35 Groove 66 Welded seam
36 End piece 67 Reinforcing sleeve
37 Flow channel 68 Flange
8a
CA 02605884 2007-10-12
69 Inclined surface
70 Radial groove
72 Protruding section
73 Locating pin
74 Threaded section
75 Threaded bore
76 Front end
77 Distance sensor
8b
