U.S. patent application number 12/500211 was filed with the patent office on 2010-01-21 for heat exchanger tubes, and method for producing heat exchanger tubes.
This patent application is currently assigned to INNOSPIN AG. Invention is credited to Frank Maeckle, Simon Scheidegger, Christoph Toennes.
Application Number | 20100012308 12/500211 |
Document ID | / |
Family ID | 38191243 |
Filed Date | 2010-01-21 |
United States Patent
Application |
20100012308 |
Kind Code |
A1 |
Scheidegger; Simon ; et
al. |
January 21, 2010 |
Heat Exchanger Tubes, and Method for Producing Heat Exchanger
Tubes
Abstract
A method for producing heat exchanger tubes involves applying a
surface coating to the tube through which a fluid medium flows and
which has a number of cooling fins arranged on an outer wall. The
method comprises applying a surface coating to an inner wall and
the outer wall of the tube, the inner wall and the outer wall
comprised of structural steel, the surface coating comprising
copper, nickel, cobalt, chromium, a nickel alloy, a chromium alloy,
a copper alloy, a cobalt alloy or stainless steel. The method
further comprises soldering the number of cooling fins to the outer
wall. The surface coating is configured to facilitate direct
soldering of the number of cooling fins to the outer wall of the
tube and to provide the inner wall with corrosion resistance to the
fluid medium in the tube.
Inventors: |
Scheidegger; Simon;
(Windisch, CH) ; Toennes; Christoph; (Brugg,
CH) ; Maeckle; Frank; (Windisch, CH) |
Correspondence
Address: |
MAGINOT, MOORE & BECK, LLP;CHASE TOWER
111 MONUMENT CIRCLE, SUITE 3250
INDIANAPOLIS
IN
46204
US
|
Assignee: |
INNOSPIN AG
Wettingen
CH
|
Family ID: |
38191243 |
Appl. No.: |
12/500211 |
Filed: |
July 9, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP2008/000166 |
Jan 11, 2008 |
|
|
|
12500211 |
|
|
|
|
Current U.S.
Class: |
165/182 ;
29/890.046 |
Current CPC
Class: |
F28F 19/06 20130101;
F28F 2275/04 20130101; Y10T 29/49378 20150115; F28F 1/126 20130101;
F28F 21/087 20130101; F28F 21/085 20130101 |
Class at
Publication: |
165/182 ;
29/890.046 |
International
Class: |
F28F 1/04 20060101
F28F001/04; B21D 53/06 20060101 B21D053/06; F28F 1/10 20060101
F28F001/10; F28F 1/18 20060101 F28F001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 12, 2007 |
EP |
07000634.1 |
Claims
1. A method for producing heat exchanger tubes comprising a tube
through which a medium flows and which has a number of cooling fins
arranged on an outer wall, the method comprising: applying a
surface coating to an inner wall and the outer wall of the tube,
the inner wall and the outer wall comprised of structural steel,
the surface coating comprising copper, nickel, cobalt, chromium, a
nickel alloy, a chromium alloy, a copper alloy, a cobalt alloy or
stainless steel, and soldering the number of cooling fins to the
outer wall, wherein the surface coating is configured to provide
the inner wall with corrosion resistance to fluid in the tube.
2. The method as claimed in claim 1, wherein the surface coating is
in the form of a cladding or plating.
3. The method as claimed in claim 1, wherein the surface coating is
applied to the inner wall and to the outer wall--comprising the
same material--in one working operation.
4. The method as claimed in claim 3, wherein the tube is produced
by providing both sides of a sheet-metal strip of structural steel
with the surface coating, shaping said strip to form a flat tube,
and welding said strip, wherein a weld seam which is produced
remains free from an iron/aluminum interlayer.
5. The method as claimed in claim 1 wherein the number of cooling
fins are comprised of aluminum, of an aluminum alloy, of steel, of
clad steel or of alloyed steel, wherein the soldering process is
carried out in such a way that a joint between the cooling fins and
the surface-coated tube is free from a continuous iron/aluminum
interlayer as far as the tube wall, and wherein the surface coating
facilitates the soldering the number of cooling fins to the outer
wall.
6. The method as claimed in claim 1, wherein an interlayer which is
formed during the soldering process is rendered ductile by adding
boron.
7. A heat exchanger tube comprising: a tube configured to allow a
fluid medium to flow through it, the tube including an inner wall
and an outer wall comprised of structural steel; a number of
cooling fins soldered to the tube; and a surface coating of copper,
nickel, cobalt, chromium, a nickel alloy, a chromium alloy, a
copper alloy or stainless steel provided on the inner wall and the
outer wall of the tube, the surface coating configured to
facilitate direct soldering of the number of cooling fins to the
outer wall of the tube and for providing the inner wall with
corrosion resistance to the fluid medium in the tube.
8. The heat exchanger tube as claimed in claim 7, wherein the
surface coating, in the form of a cladding or plating, comprises
the same material on the inner wall and on the outer wall.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of
International (PCT) Patent Application No. PCT/EP2008/000166, filed
Jan. 11, 2008, and published on Jul. 17, 2008 as International
Publication No. WO 2008/083971, the contents of which are
incorporated herein by reference, which application claims priority
from European Patent Application No. 07000634.1, filed Jan. 12,
2007.
FIELD
[0002] The present application relates to the field of
thermodynamics. In particular, the application relates to heat
exchanger tubes comprising a tube through which a medium flows and
which has a number of cooling fins arranged on an outer wall, and
to a method for producing such heat exchanger tubes.
BACKGROUND
[0003] Heat exchanger tubes are used, inter alia, in air-cooled
condensers in power plants, refuse incineration plants, combined
heat and power plants and industrial installations with energy
recovery. Known air-cooled condensers of this type--also referred
to hereinafter merely as condensers--perform a similar function to
water-cooled condensers, that is to say they liquefy the exhaust
steam from a steam turbine, which exhaust steam can no longer be
used for energy, and recirculate the condensate produced into the
closed water/steam circuit. By contrast with cooling towers, in the
case of condensers the thermal energy is taken from the exhaust
steam by means of air cooling (fans). Condensers therefore manage
without any cooling water. Nowadays, there is an increased demand
for so-called "dry-cooling condensers" owing to the increasing
water shortage and increased demands and official regulations for
the approval of power plants or industrial installations. The
ecological point of view with regard to water consumption and the
heating of flowing water plays a major role here.
[0004] It is known to provide heat exchanger tubes for condensers
in an A-shaped configuration. DE 690 33 556 T2 shows heat exchanger
tubes produced in this way, and a method for producing them. By way
of example, this is done using round tubes, oval tubes or flat
tubes, each having a fin structure. When steel tubes with any
desired, indicated geometry are provided with a fin structure, the
tubes are initially slotted in helical fashion and flat aluminum
sheets are then drawn in. Another method provides for mechanically
winding up tubes with aluminum sheets in helical fashion.
[0005] Particularly when providing steel oval tubes with a fin
structure, flat steel fins provided with spacers are pushed on and
are then galvanized on the outside and over the surface, and
connected, together with the oval tube.
[0006] Nowadays, flat tubes having a fin structure are produced by
firstly shaping an aluminum-plated flat tube from steel, welding it
and subsequently cladding it with aluminum at the weld seam, then
shaping a fin from a solder-plated aluminum alloy, applying a flux
and fastening the shaped fin on both sides of the flat tube, and
then brazing this fin to the flat tube in a furnace with a
controlled atmosphere at about 600.degree. C. In comparison with
round tubes or oval tubes having a fin structure, flat tubes have
the advantage that they are more resistant to freezing and have a
lower pressure loss on the air side.
[0007] Another important aspect of air-cooled condensers is the
long service life. It is necessary for the condensers to have a
service life of more than 30 years, and sometimes even more than 40
years or more. Since condensers of this type are exposed to
environmental conditions, they have to have high corrosion
resistance. In addition, the inner wall of the condensers is also
exposed to contamination caused by impurities in the fluid flowing
through them. These impurities are already present during
commissioning or arise owing to oxidation or corrosion throughout
the water/steam circuit of a power plant.
[0008] As is known, the inner wall of a flat tube for condensers
consists of unprotected structural steel with no oxidation and
corrosion resistance. However, together with the boiler in the
water/steam circuit of a power plant, the inner surface of an
air-cooled condenser is by far the largest area exposed to the
fluid on the process side. This inevitably results in a
correspondingly high conditioning of the water/steam chemistry as a
result of operation, inter alia to a basic pH value, in order to
protect the heat exchanger tubes against severe oxidation,
corrosion or even rusting through.
[0009] This also means that the condenser has to be cleaned and
rinsed using a time-consuming and costly process before
commissioning, and the deionized water used in the process has to
be disposed of. A similar method with the same disposal of
"consumed" water must likewise be employed following repairs and
before recommissioning. In this case, there is an urgent need for
improvement from an operational and ecological point of view.
[0010] Furthermore, during the ongoing operation of the power
plant, it is necessary to filter out particles of rust that form,
and a complex polisher system is required. Normal operational
stoppages carry the risk of pitting corrosion and rusting through.
Even during transport to the installation site and during assembly
of the condenser, the unprotected surfaces of the heat exchanger
tubes need to be protected by means of covers, shielding gas and/or
drying appliances.
[0011] When producing sheet metal which is plated on one side with
aluminum, after the flat tube is formed by shaping and welding, the
weld seam has to be subsequently clad with aluminum. This is done
by applying aluminium, typically by means of flame spraying, in the
form of 30 mm wide strips. This additional production step may
result in impurities forming or material defects occurring in a
brittle iron/aluminum interlayer which is produced by the welding.
In addition, the sprayed-on aluminum layer has a roughness which
may lead to a reduction in the quality of the soldered joint when
the tube is subsequently brazed to cooling fins, and this in turn
impairs the thermal efficiency of the entire plant. Soldered joints
of limited quality may likewise cause spalling of cooling fins.
[0012] It is also known that joints between aluminum and iron are
comparatively brittle and this results in an increased sensitivity
to thermal/mechanical stresses resulting from operation; this also
applies to impact and/or torsional loading during transport or
assembly. The iron/aluminum interlayer has a low fracture toughness
and ductility associated with a high sensitivity to defects with
respect to pores, sandblasting means, oxides and inclusions. This
low tolerance of the iron/aluminum interlayer to defects results in
a correspondingly high expenditure for production and quality
control.
SUMMARY
[0013] Heat exchanger tubes and a method for producing heat
exchanger tubes are disclosed herein, by means of which the
disadvantages of the known heat exchanger tubes and the methods for
producing them are overcome.
[0014] In particular, by means of the disclosed heat exchanger
tubes and a method for producing them, it is possible to achieve a
significantly improved defect tolerance and corrosion resistance of
the outer wall and of the inner wall of heat exchanger tubes with
respect to the prior art, and also to allow more simple and less
expensive production.
[0015] As disclosed herein, the inner wall and the outer wall of a
tube of a heat exchanger tube, which consists of structural steel,
are provided with a surface coating of copper, nickel, cobalt,
chromium, a nickel alloy, a chromium alloy, a copper alloy or
stainless steel, for directly soldering a number of cooling fins to
the tube and for providing the inner wall with corrosion resistance
to fluid media.
[0016] In this case, it should be emphasized as particularly
advantageous that the surface coating--consisting of the materials
specified--firstly makes it possible to solder the tube to the
cooling fins on the outer wall with outstanding quality and
simultaneously makes it possible to significantly increase the
corrosion resistance of the inside of the tube when it is acted
upon by the water/steam chemistry of a power plant. For the first
time, it is therefore possible to use a cladding or plating
operation to provide a tube for a heat exchanger tube which, in
terms of processability and wear/aging, has a significantly
improved form with respect to the prior art indicated.
[0017] It is not only with regard to the production that
simplifications can be found; at least one embodiment of the
invention also shows an ecological tolerance which is to be
emphasized, in relation to that which is known, with respect to the
ongoing operation of the power plant and the associated
commissioning and recommissioning following stoppages.
[0018] The brazed joint between the cooling fins and the tube is
particularly ductile and tough, and so stresses resulting from
operation or assembly cause no damage to the heat exchanger tube
according to at least one embodiment of the invention; it is
therefore possible to increase service lives and to minimize
maintenance and monitoring work.
[0019] One particularly advantageous embodiment of the invention
provides for the inner wall and the outer wall of the tube to be
clad or plated with one and the same material, as a result of which
only one working operation is required to provide the tube. A tube
is advantageously shaped from a metal sheet, which is clad or
plated on both sides according to at least one embodiment of the
invention and consists, for example, of simple structural steel, to
form a flat tube and then welded directly along the abutting
surface. The weld seam produced in the process is free from any
iron/aluminum interlayer and the flat tube can be directly brazed
to correspondingly dimensioned cooling fins. For good thermal
efficiency, these cooling fins may consist of aluminum or be clad
therewith or may be produced from an aluminum alloy; in any case,
the brazing does not produce a continuous iron/aluminum interlayer,
and so the heat exchanger tube according to at least one embodiment
of the invention essentially still has the ductility and toughness
of the base material of the tube.
[0020] In at least one embodiment of the invention, it is
advantageously provided that an interlayer which is formed during
the brazing process is rendered ductile by adding boron.
[0021] Since all the advantages which apply for the heat exchanger
tube have already been acknowledged when explaining the method for
producing such a heat exchanger tube, repetition is avoided at this
point in order to shorten the text.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The drawings illustrate an exemplary embodiment of the
invention in simplified form, to be precise:
[0023] FIG. 1 shows a sectional illustration through a heat
exchanger tube according to the invention, before a brazing
process, and
[0024] FIG. 2 shows the sectional illustration from FIG. 1, after
the brazing process.
DESCRIPTION
[0025] FIG. 1 shows a sectional illustration of the heat exchanger
tube 8 according to at least one embodiment of the invention,
before a soldering process which brazes a tube wall 1 to a cooling
fin 2. An inner wall 9 and an outer wall 10 of the tube wall 1 are
respectively provided with an outer surface coating 4 and an inner
surface coating 5, which is arranged adjacent to the tube wall 1.
The cooling fin 2 is provided with a fin cladding 3 and makes
touching contact with the outer surface coating 4 of the tube wall
1.
[0026] FIG. 2 shows the heat exchanger tube 8 after the brazing
process, in which the cooling fin 2 is now fixedly joined to the
tube wall 1 by means of an interlayer 6 and brazing 7.
[0027] The method for producing the heat exchanger tubes 8
according to at least one embodiment of the invention provides the
following steps: [0028] 1. Both sides of a core strip, for example
of the steel grade DC01 (EN10130), are provided with supporting
strips by means of roller pressing. The core strip subsequently
constitutes the tube wall 1 shown in FIGS. 1 and 2 and the
supporting strips subsequently constitute the outer surface coating
4 and the inner surface coating 5. [0029] 2. The core strip with
the supporting strips is recrystallization-annealed for several
minutes, and the microstructure is returned to the initial state.
[0030] 3. Subsequent finish-rolling changes the core strip with the
supporting strips into the desired end state, before [0031] 4. the
three strips are joined to one another by metallurgical means in a
homogenization process. This produces a solid and ductile diffusion
layer directly toward the core strip, and this layer is shown as
the inner surface coating 5 in FIGS. 1 and 2. [0032] 5. The
present, plated flat strip made from the core strip and supporting
strips is bent to form a flat tube and closed along a longitudinal
seam of the tube by means of welding. This weld seam is smoothed;
further treatment is not necessary. [0033] 6. A plated strip
consisting of a core strip of an aluminum alloy, which core strip
is provided at least on one side with an aluminum solder alloy, is
provided for producing the cooling fin 2. The cold strip which is
solder-plated in this way is cold-formed in a three-dimensional
cooling fin mold. [0034] 7. After the flat tube and the cooling fin
have been covered with a commercially available aluminum flux, they
are joined to one another by means of a continuous brazing process
to form a heat exchanger tube 8, producing a fixed, gap-free and
pore-free soldered joint between the cooling fin 2 and the tube
wall 1.
[0035] There is now a layer comprising brazing 7 and an interlayer
6, also referred to as a reaction zone, between the tube wall 1 and
the cooling fin 2. This reaction zone comprises an ordered phase
and is distinguished by good strength and very high oxidation and
corrosion resistance.
[0036] According to at least one embodiment of the invention, the
outstanding properties with regard to the solderability and the
corrosion resistance to fluid media (not illustrated in the figure)
in the heat exchanger tube 8 are shown when both sides of the core
strip have a plating by means of the supporting strips and when
these supporting strips consist of copper, nickel, cobalt,
chromium, a nickel alloy, a chromium alloy, a copper alloy, a
cobalt alloy or stainless steel.
[0037] By way of example, on the basis of a nickel alloy, Inconel
Alloy 825 (IN 825), for the supporting strips, the following
material distribution is shown when producing the heat exchanger
tubes 8. After the homogenization treatment of the core strip with
the supporting strips which are made from Inconel Alloy and are
plated on both sides, the diffusion layer--the inner surface
coating 5 of the heat exchanger tube 8--consists of a crystalline
unordered mixed structure, in which primarily the elements iron,
nickel and chromium are uniformly adapted to the respectively
plated alloy. The outer surface coating layer 4 also consists of
Inconel Alloy.
[0038] When the cooling fin 2 is brazed to the tube wall 1, the
reaction zone is produced with an ordered phase of
Al--Ni--Fe--Si--Cr. After the brazing and during operation, this
reaction zone Al--Ni--Fe--Si--Cr is subjected to a slight
compressive stress owing to the deliberately differently chosen
coefficients of expansion of the alloys involved, and this
increases the mechanical integrity of the entire soldered
joint.
[0039] Without departing from the disclosed concepts, all further
materials indicated for the plating by means of supporting strips
show properties which can correspondingly be emphasized with regard
to the good solderability between the cooling fin 2 and the tube
wall 1 and with regard to the corrosion resistance of the inside of
the heat exchanger tube 8 to a fluid medium.
* * * * *