DESCRIPTION
STEEL COVERING LAYER AND METHOD OF SURFACE TREATMENT OF
HEAT TRANSFER TUBE
Field
5 [OOOl] The present invention relates to a steel covering
layer and a method of surface treatment of a heat transfer
tube, used for treating the surface of a pipe in a heat
exchanger.
Background
10 [0002] For a great number of heat exchanging tubes (heat
transfer tubes) provided in a shell (body) of a heat
exchanger, carbon steel is mainly used in view of heat
transfer efficiency and material cost. There are a baretype
and a fin-type for heat transfer tubes. The fin-type
15 is used for a heat transfer tube since the fin-type has
higher heat transfer efficiency.
[0003] The heat exchanging performance of the heat
exchanger is deteriorated by ash and soot adhering to and
depositing on the heat transfer surface of the heat
20 transfer tube during continuous operation. When ash and
soot included in flue gas adhere to and deposit on the
surface of the heat transfer tube, the ash and soot form a
bridge in a gap between heat transfer tubes. The bridge
narrows the flue gas passage between the heat transfer
25 tubes, thereby obstructing the flow of the flue gas flowing
through the group of heat transfer tubes, resulting in the
rise of pressure loss of the flue gas. Further, moisture
(mist) in the flue gas adheres to the heat transfer tube,
wetting the heat transfer tube, which is one of causes of
30 corrosion.
[0004] There are methods for removing the ash and soot
adhering to the heat transfer tube such as a method of
shaking off the ash and soot adhering to the heat transfer
Docket No. PMHA-13017-PCT
tube by the impact of a fallen steel ball hitting the heat
transfer tube, a method of forcibly burning the soot
adhering to and depositing on the outer circumferential
surface of the heat transfer tube using a heating wire
5 attached to the outer circumferential surface of the heat
transfer tube, and a method of removing the ash and soot
adhering to the surface of the heat transfer tube by
blowing steam or air by a soot blower (e.g., see Patent
Literatures 1 to 3).
10 [0005] There are methods of preventing corrosion of a
heat transfer tube by covering the heat transfer tube using
a resin tube or a method of applying a coating on the heat
transfer surface of the heat transfer tube (e-g., see
Patent Literature 4).
15 Citation List
Patent Literature
[0006] Patent Literature 1: Japanese Laid-open Patent
Publication No. 5-133695
Patent Literature 2: Japanese Laid-open Patent
20 Publication No. 7-63495
Patent Literature 3: Japanese Laid-open Patent
Publication No. 2010-117067
Patent Literature 4: Japanese Laid-open Patent
Publication No. 2005-98666
25 Summary
Technical Problem
[0007] However, in the method of removing the ash and
soot adhering to the heat transfer tube using the impact
made by a fallen steel ball, the steel ball might be stuck
30 between heat transfer tubes. In the methods using a
heating wire or a soot blower, an additional apparatus for
arranging the heating wire or the soot blower is necessary,
resulting in the rise in cost. Further, using only a soot
Docket No. PMHA-13017-PCT
3
blower is not enough to remove the ash and soot tightly
adhering to the heat transfer tube.
[0008] Since a resin tube is used so as to cover the
heat transfer tube, a resin tube cannot be used for
5 preventing corrosion of a fin-type heat transfer tube,
although the fin-type heat transfer tube has high heat
transfer efficiency. Besides, when coating is applied to
the heat transfer surface of the heat transfer tube, a
thick coating layer deteriorates heat transfer efficiency.
10 [0009] The present invention is made with regard to the
problem mentioned above. The object of the present
invention is to provide a steel covering layer and a method
of surface treatment of a heat transfer tube, which
suppress adhering of ash, soot, or the like included in
15 flue gas to the heat transfer surface of the heat transfer
tube.
Solution to Problem[0010] According to a first aspect
of the present invention if order to solve the above
problems, there is provided a steel covering layer
20 including a surface layer formed of a low surface energy
material and formed on a surface of a heat transfer tube.
[OOll] According to a second aspect of the present
invention, there is provided the steel covering layer
according to the first aspect further including a binder
25 layer formed of an inorganic glass-based material and
formed between the heat transfer tube and the surface layer.
[0012] According to a third aspect of the present
invention, there is provided the steel covering layer
according to the second aspect, wherein a thickness of the
30 binder layer is 10 pm or less.
[0013] According to a fourth aspect of the present
invention, there is provided the steel covering layer
according to any one of the first to third aspects, wherein
Docket No. PMHA-13017-PCT
4
the low surface energy material includes at least one of a
(CH4)3-Si structure, a F3C structure, and a silane coupling
reactive group.
[0014] According to a fifth aspect of the present
5 invention, there is provided the steel covering layer
according to any one of the first to fourth aspects,
wherein a thickness of the surface layer is 1 pm or less.
[0015] According to a sixth aspect of the present
invention, there is provided a method of surface treatment
10 of a heat transfer tube including: applying a solution
including a low surface energy material to a surface of a
heat transfer tube; and performing heat treatment to cure
the solution to form a surface layer.
[0016] According to a seventh aspect of the present
15 invention, there is provided the method of surface
treatment of a heat transfer tube according to the sixth
aspect, wherein a binder layer formed of an inorganic
glass-based material is formed between the heat transfer
tube and the surface layer.
20 [0017] According to an eighth aspect of the present
invention, there is provided the method of surface
treatment of a heat transfer tube according to the seventh
aspect, wherein a thickness of the binder layer is 10 pm or
less.
25 [0018] According to a ninth aspect of the present
invention, there is provided the method of surface
treatment of a heat transfer tube according to any one of
the sixth to eighth aspects, wherein the low surface energy
material includes at least one of a (CH4)3-Si structure, a
30 F3C structure, and a silane coupling reactive group.
[0019] According to a tenth aspect of the present
invention, there is provided the method of surface
treatment of a heat transfer tube according to any one of
Docket No. PMHA-13017-PCT
5
the sixth to ninth aspects, wherein a thickness of the
surface layer is 1 pm or 1ess.Advantageous Effects of
Invent ion
[0020] According to the present invention, adhering of
5 ash, soot, or the like included in flue gas to the heat
transfer surface of a heat transfer tube can be suppressed.
Brief Description of Drawings
[OO21] FIG. 1 is a schematic view illustrating a steel
covering layer according to a first embodiment of the
10 present invention.
FIG. 2 is an explanatory drawing illustrating a
coupling status of a silane coupling reactive group and a
heat transfer surface of a heat transfer tube.
FIG. 3 is a schematic view illustrating another
15 configuration of the steel covering layer.
FIG. 4 is an explanatory drawing illustrating an
example of ash and soot in flue gas adhering to a heat
transfer tube.
FIG. 5 is a schematic view illustrating a steel
20 covering layer according to a second embodiment of the
present invention.
FIG. 6 is an explanatory drawing illustrating a
coupling status of a binder layer and a heat transfer
surface of a heat transfer tube.
25 Description of Embodiments
[0022] The present invention will be described below in
detail referring to the drawings. Note that, the present
invention is not limited to the embodiment described below.
The component of the embodiment includes a component which
30 is included within the meaning and range of equivalency,
that is, a component which those skilled in the art can
easily conceive or a component substantially the same as
that of the embodiment. Further, components disclosed in
Docket No. PMHA-13017-PCT
6
the embodiment can suitably be used in combination.
First Embodiment
[0023] The case in which a steel covering layer
according to a first embodiment of the present invention is
5 applied to a great number of heat exchanging tubes (heat
transfer tubes) provided in a shell (body) of a heat
exchanger will be described referring to the drawing. FIG.
1 is a schematic view illustrating a steel covering layer
according to the first embodiment of the present invention.
10 As illustrated in FIG. 1, a steel covering layer 10A
according to the embodiment is formed as a surface layer 12
on a surface lla of a heat transfer tube 11.
[0024] The surface layer 12 is formed of a low surface
energy material. For example, silicone resin compositions,
15 fluoro resin compositions may be used as the low surface
energy material. The silicone resin composition preferably
has a water-repellent or water-and-oil-repellent
(hereinafter referred to as "water/oil-repellent") (CH4)3-
Si structure. The fluoro resin composition preferably has
20 F3C structure as a terminal substituent. Specifically, for
example, silicone resins (produced by Shin-Etsu Silicone
Co., Ltd. ) , Unidyne (produced by Daikin Industries, Ltd. ) ,
Fluoro Surf (produced by FluoroTechnology Co., Ltd), or
Lumiflon (produced by Asahi Glass Co., Ltd.) may be used.
25 The surface layer 12 may be formed of one of or a plurality
of low surface energy materials mentioned above.
[0025] By forming the surface layer 12 using silicone
resin compositions or fluoro resin compositions mentioned
above, the surface energy of the interface can be lowered,
30 suppressing adhesion of ash, soot, or the like and thereby
suppressing contamination of the surface of the surface
layer 12. Further, even when ash and soot adhere to the
surface of the surface layer 12, the surface layer 12 is
2 8 AUG 20\1
Docket No. PMHA-13017-PCT
7
enhanced with the effect of separating the ash and soot.
[0026] The surface layer 12 preferably includes in a
molecule thereof, a silane coupling reactive group
{(RO)nSi-) for coupling with the base material by covalent
5 bond. FIG. 2 is an explanatory drawing illustrating a
coupling status of the surface layer 12, including the
silane coupling reactive group, and the surface of the heat
transfer tube 11. As illustrated in FIG. 2, the silane
coupling reactive group { (R0)nSi-} included in the molecule
10 forms a covalent bond (-0-Si-0-) by dehydration reaction
with an OH group on the surface of the heat transfer tube
11. In this manner, a bridging layer is formed between the
surface layer 12 and the surface of the heat transfer tube
11, strongly bonding the surface of the heat transfer tube
15 11 and the surface layer 12.
[0027] The low surface energy material is preferably in
a form of liquid which can be coated by spraying, painting,
dipping, or the like. By applying a solution including the
low surface energy material and then heat treating and
20 drying the solution, the surface layer 12 is obtained.
[0028] As mentioned above, an organic material such as
silicone resin compositions and fluoro resin compositions
is used as a raw material of the surface layer 12, so that
the organic material can easily be applied to an object
25 such as the heat transfer tube 11 to form a thin film.
Further, by simply applying an organic material such as
silicone resin compositions and fluoro resin compositions,
the surface layer 12 can be reformed on the heat transfer
surface of the heat transfer tube 11. So that even when
30 the surface layer 12 has degraded, the surface layer 12 can
easily be reformed by applying the raw material for forming
the surface layer 12 on the heat transfer tube 11.
[0029] The surface layer 12 is preferably a
2 8 AUG 2014
Docket No. PMHA-13017-PCT
8
monomolecular film with the thickness ranging from 10 nm to
1 m . Specifically, for example, Fluoro Surf produced by
FluoroTechnology Co., Ltd is used as a monomolecular film.
The monomolecular film has a molecular structure in which a
5 reactive group is at one end and a water/oil-repellent
group is at the other end, which allows forming of a
monomolecular film between heat transfer surfaces of heat
transfer tubes. By forming the surface layer 12 with a
single molecular film, a coating can be provided on the
10 heat transfer tube 11 without deteriorating thermal
conductivity.
[ 0 0 3 0 ] Further, the steel covering layer 10A according
to the embodiment is formed simply as the surface layer 12
on the surface of the heat transfer tube 11. However, it
15 is not limited to the configuration. As illustrated in FIG.
3, the steel covering layer 10A according to the embodiment
may be configured to have a primer layer 13 provided on the
surface, opposing the heat transfer tube 11, of the surface
layer 12. By providing the primer layer 13 on the surface,
20 opposing the heat transfer tube 11, of the surface layer 12,
the contact between the heat transfer tube 11 and the
surface layer 12 can further tightly be provided and
adhesion between the surface layer 12 and the heat transfer
tube 11 can be improved.
25 [0031] As described above, since the steel covering
layer 10A according to the embodiment is formed as the
surface layer 12, adhesion of ash, soot, or the like to the
surface of the steel covering layer 10A according to the
embodiment can be suppressed. Further, by providing the
30 primer layer 13 on the surface, opposing the heat transfer
tube 11 side, of the surface layer 12, the adhesion of the
surface layer 12 to the surface of the heat transfer tube
11 can further be improved.
Docket No. PMHA-13017-PCT
9
[0032] Since adhesion of ash, soot, or the like to the
surface of the heat transfer tube 11 can be suppressed, the
heat transfer tube 11 can stably maintain the heat transfer
efficiency. As illustrated in FIG. 4, when a great number
5 of heat transfer tubes provided in a shell of a heat
exchanger are used without any treatment as in the prior
art, the ash and soot included in flue gas 15 passing
through the heat transfer tubes 11 in the first stage
adhere to the heat transfer tube 11 in the first stage and
10 harden to form a deposit 16. This narrows the flow passage
between the heat transfer tubes 11 in the first stage, and
thereby the flue gas 15 including ash and soot is likely to
be concentrated to flow toward the front side, opposing the
gas flow, of the heat transfer tube 11 in the second stage.
15 When a large amount of ash and soot included in the flue
gas 15 adhere to the front side, opposing the gas flow, of
the heat transfer tube 11 in the forward stage, the flue
gas 15 including ash and soot is likely to be concentrated
to flow toward the front side, opposing the gas flow, of
20 the heat transfer tubes 11 provided in downstream stages.
Therefore, the ash and soot included in the flue gas 15
similarly adhere to the heat transfer tube 11 provided in
the downstream stage causing deterioration in heat transfer
efficiency, resulting in deterioration in the heat
25 exchanging efficiency of the whole heat exchanger.
[0033] Contrarily, when the steel covering layer 10A
according to the embodiment is provided on the surface of
the heat transfer tube 11, adhesion of ash, soot, or the
like to the surface of the steel covering layer 10A
30 according to the embodiment can be suppressed, thereby
suppressing deterioration in heat transfer efficiency of
the heat transfer tube 11. In this manner, the
deterioration in heat exchanging efficiency of the whole
Docket No. PMHA-13017-PCT
10
heat exchanger can be suppressed, enabling stable operation
of the heat exchanger.
Second Embodiment
[0034] A steel covering layer according to a second
5 embodiment of the present invention will be described
referring to the drawings. FIG. 5 is the schematic view
illustrating a steel covering layer according to the second
embodiment of the present invention. As illustrated in FIG.
5, a steel covering layer 10B according to the embodiment
10 includes the surface layer 12 and a binder layer 21. The
binder layer 21 is formed on the surface lla of the heat
transfer tube 11 and the surface layer 12 is formed on the
binder layer 21.
[0035] The binder layer 21 is formed between the heat
15 transfer tube 11 and the surface layer 12, forming a fine
film. The binder layer 21 is formed of an inorganic
material having high reactivity with the surface layer 12.
As an inorganic material, a silane coupling agent, a glass
coating agent composed of a Si-0 structure may be used.
20 Specifically, a silane coupling agent produced by Shin-Etsu
Silicone Co., Ltd. may be used. The glass coating agent
having a Si-0 structure forms a covalent bond (-0-Si-0-) by
dehydration reaction with an OH group on the surface of the
heat transfer tube 11 which is a base material as
25 illustrated in FIG. 6. Particularly, Crystal coating
(produced by Nikko Co., Ltd.), Crystal X (produced by SMACH
Engineering Corporation), AQUAMICA based on
perhydroxipolysilazane (produced by AZ Electro Materials
Co., Ltd.), and TGA (produced by APOLLORINK Inc.) may be
30 used as the glass coating agent.
[0036] The binder layer 21 having a fine structure and
formed in a film of inorganic material with high reactivity
with the surface layer 12 can suppress the water from
Docket No. PMHA-13017-PCT
making contact with the heat transfer tube 11 thereby
suppressing corrosion.
[0037] The thickness of the binder layer 21 is
preferably in the range from 5 pm to 100 pm, more
5 preferably, from 7 pm to 50 pm, and furthermore preferably,
from 10 pm to 30 pm.
[0038] Similarly to the surface layer 12, the inorganic
material is preferably in a form of liquid which can be
coated by spraying, painting, dipping, or the like. The
10 inorganic material cures by heating, absorbing of moisture,
and effect of catalyst, and thereby the binder layer 21 is
obtained.
[0039] As mentioned above, the organic material
including the inorganic material is used as the raw
15 material of the binder layer 21, so that, similarly to the
surface layer 12, the raw material can easily be applied to
an object such as the heat transfer tube 11 to form a thin
film. Further, by simply applying the organic material
mentioned above, the binder layer 21 can be reformed on the
20 surface of the heat transfer tube 11. So that when the
binder layer 21 has degraded, the binder layer 21 can
easily be reformed by applying the raw material for forming
the binder layer 21 to the heat transfer tube 11.
[0040] The steel covering layer 10B according to the
25 embodiment has a two-layer structure composed of the
surface layer 12 and the binder layer 21. For example, the
combination of the surface layer 12 and the binder layer 21
may preferably be TGA, as the material forming the surface
layer 12, and Fluoro Surf, as the material forming the
30 binder layer 21. Since both TGA used as the material to
form the surface layer 12 and Fluoro Surf used as the
material to form the binder layer 21 can be formed in a
Docket No. PMHA-13017-PCT
12
thin film, each of the surface layer 12 and the binder
layer 21 can be formed to have thicknesses of 10 pm or less.
Exemplary Experiment
[0041] Now the result of evaluating the reducing effect
5 of adhesion of ash, soot, or the like and corrosion
resistance of the steel covering layer 10B according to the
embodiment will be described. A first exemplary experiment
shows the test result of adhesion of ash and soot and
corrosion resistance of the base material for a test piece
10 in which a fluoro resin composition (Fluoro Surf produced
by FluoroTechnology Co., Ltd.) is used as the surface layer
12 and a fluoro resin composition (TGA produced by
APOLLORINK Inc.) is used as the binder layer 21 of the
steel covering layer 10B according to the embodiment for
15 the base material (metal plate). A first comparative
example shows the test result of adhesion of ash, soot, or
the like and corrosion resistance of the base material for
a test piece which is simply a base material.
The adhesion of ash, soot, or the like is evaluated by
20 a releasing force of a piece of fly-ash adhered to the test
piece. The corrosion resistance of the base material is
evaluated by the elapsed time from dipping the test piece
in a sulfuric acid aqueous solution having pH of 2 until
corrosion occurs on the test piece.
25 The test results of the first exemplary experiment and
the first comparative example are shown in Table 1. In the
exemplary experiment, the adhesion of ash and soot is shown
in a value of relative ratio where the amount of ash and
soot adhering to the base material of the first comparative
30 example is 1. The corrosion resistance is shown in a value
of relative ratio where the degree of corrosion of the base
material of the first comparative example is 1.
[0042]
Docket No. PMHA-13017-PCT
13
Table 1
FIRST COMPARATIVE FIRST EXEMPLARY
EXAMPLE I EXPERIMENT 1
or the like adhering to the base material of the first
ADHESION OF
ASH AND SOOT
CORROSION
RESISTANCE
exemplary experiment is about a tenth of that of the first
comparative example, which means, reduction of about 90% is
1 As shown in Table 1, the adhesion of ash, soot,
1
1
5 achieved for the first exemplary experiment compared to the
0.1
6
first comparative example. The corrosion resistance of the
base material of the first exemplary experiment is about a
sixth of the first comparative example.
[0044] Consequently, by providing the steel covering
10 layer 10B according to the embodiment on the base material
as in the first exemplary experiment, the reducing effect
of adhesion of ash, soot, or the like can be improved by
about 10 times compared to the case with solely the base
material, and at the same time, the corrosion resistance
15 can be improved by about six times compared to the case
with solely the base material
[0045] Therefore, since the steel covering layer 10B
according to the embodiment is formed in the two-layer
structure in which the binder layer 21 is formed between
20 the heat transfer tube 11 and the surface layer 12,
adhesion of ash, soot, or the like to the surface of the
steel covering layer 10B according to the embodiment as
well as corrosion of the heat transfer tube 11 can be
suppressed.
25 [0046] As illustrated in FIG. 4, when a great number of
heat transfer tubes provided in a shell of a heat exchanger
are used without any treatment as in the prior art, the
great amount of ash and soot included in the flue gas 15
Docket No. PMHA-13017-PCT
14
adheres to the front surface, opposing the flow direction,
of the heat transfer tube 11 in the forward stage. This
causes adhesion of ash and soot included in the flue gas 15
to the heat transfer tubes 11 provided in the downstream
5 stages, thereby causing deterioration in heat transfer
efficiency of the whole heat transfer tubes 11, which
results in deterioration in the heat exchanging efficiency
of the whole heat exchanger.
[0047] Contrarily, when the steel covering layer 10B
10 according to the embodiment is provided on the surface of
the heat transfer tube 11, the adhesion of ash, soot, or
the like to the surface of the steel covering layer 10B
according to the embodiment as well as corrosion of the
heat transfer tube 11 can be suppressed, thereby
15 suppressing deterioration in heat transfer efficiency of
the heat transfer tube 11 as well as degrading of the heat
transfer tube 11. In this manner, the deterioration in the
heat exchanging efficiency of the whole heat transfer tubes
11 can be suppressed and the heat transfer efficiency can
20 be maintained, allowing stable operation of the heat
exchanger.
[0048] In each of the embodiments described above,
description is made for the case in which the present
invention is applied to the heat transfer tube 11 provided
25 in the fin-tube heat exchanger. However, it is not limited
to the configuration. The present invention may be applied
to a heat exchanger such as an air cooling heat exchanger
and a direct contact heat exchanger using gas-liquid
contact. The steel covering layers 10A and 10B according
30 to the embodiment are not limited to the application to
heat exchangers using gas-liquid contact, and may be
applied to heat exchangers using liquid-liquid contact or
heat exchangers using gas-gas contact. Examples of liquidDocket
No. PMHA-13017-PCT
15
liquid contact heat exchangers include spiral heat
exchangers, plate-type heat exchangers, double-pipe heat
exchangers, shell-and tube-type heat exchangers, spiral
tube heat exchangers, spiral plate heat exchangers, tank
5 with coil heat exchangers, jacketed vessel heat exchangers,
and liquid-liquid direct contact heat exchangers. Examples
of gas-gas contact heat exchangers include static type heat
exchangers, rotary regenerative heat exchangers, periodicflow
regenerative heat exchangers, and vortex-tubes.
10 [0049] In the embodiment, description is made for the
case when the present invention is applied to heat
exchangers. However, the present invention is not limited
to the configuration, and can similarly be applied to
steels and steel structures used under severe environments
15 such as polluted air and corrosive atmosphere.
Reference Signs List
[0050] 10A, 10B STEEL COVERING LAYER
11 HEAT TRANSFER TUBE
12 SURFACE LAYER
13 PRIMER LAYER
15 FLUE GAS
16 DEPOSIT
21 BINDER LAYER
Docket No. PMHA-13017-PCT

CLAIMS
1. A steel covering layer comprising
a surface layer formed of a low surface energy
material and formed on a surface of a heat transfer tube.
5
2. The steel covering layer according to claim 1 further
comprising
a binder layer formed of an inorganic glass-based
material and formed between the heat transfer tube and the
10 surface layer.
3. The steel covering layer according to claim 2, wherein
a thickness of the binder layer is 10 pm or less.
15 4. The steel covering layer according to any one of
claims 1 to 3, wherein the low surface energy material
includes at least one of a (CH4)3-Si structure, a F3C
structure, and a silane coupling reactive group.
20 5. The steel covering layer according to any one of
claims 1 to 4, wherein a thickness of the surface layer is
1 pm or less.
6. A method of surface treatment of a heat transfer tube
25 comprising:
applying a solution including a low surface energy
material to a surface of a heat transfer tube; and
performing heat treatment to cure the solution to form
a surface layer.
7. The method of surface treatment of a heat transfer
tube according to claim 6, wherein a binder layer formed of
an inorganic glass-based material is formed between the
Docket No. PMHA-i301 7-PCT
heat transfer tube and the surface layer.
8. The method of surface treatment of a heat transfer
tube according to claim 7, wherein a thickness of the
5 binder layer is 10 pm or less.
9. The method of surface treatment of a heat transfer
tube according to any one of claims 6 to 8, wherein the low
surface energy material includes at least one of a (CH4)3-
10 Si structure, a F3C structure, and a silane coupling
reactive group.
10. The method of surface treatment of a heat transfer
tube according to any one of claims 6 to 9, wherein a
15 thickness of the surface layer is 1 pm or less.