U.S. patent application number 14/357114 was filed with the patent office on 2014-10-23 for block-type plate heat exchanger with anti-fouling properties.
The applicant listed for this patent is ALFA LAVAL CORPORATE AB. Invention is credited to Jonas Anehamre, Mats Nilsson.
Application Number | 20140311718 14/357114 |
Document ID | / |
Family ID | 47172654 |
Filed Date | 2014-10-23 |
United States Patent
Application |
20140311718 |
Kind Code |
A1 |
Nilsson; Mats ; et
al. |
October 23, 2014 |
BLOCK-TYPE PLATE HEAT EXCHANGER WITH ANTI-FOULING PROPERTIES
Abstract
An block-type plate that has a stack of heat transfer plates
which includes a first heat transfer plate and a second heat
transfer plate. At least a part of each of the first heat transfer
plate and the second heat transfer plate comprises a coating that
i) has a layer thickness of 1-30 .mu.m, ii) is prepared by sol-gel
processing, iii) comprises silicon oxide (SiOx) having an atomic
ratio of O/Si>1, and iv) comprises .gtoreq.10 atomic percent
carbon (C).
Inventors: |
Nilsson; Mats; (Lund,
SE) ; Anehamre; Jonas; (Lund, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALFA LAVAL CORPORATE AB |
Lund |
|
SE |
|
|
Family ID: |
47172654 |
Appl. No.: |
14/357114 |
Filed: |
November 15, 2012 |
PCT Filed: |
November 15, 2012 |
PCT NO: |
PCT/EP2012/072722 |
371 Date: |
May 8, 2014 |
Current U.S.
Class: |
165/133 |
Current CPC
Class: |
F28F 2245/00 20130101;
F28F 3/08 20130101; F28F 19/02 20130101; F28D 9/0037 20130101; F28F
9/001 20130101 |
Class at
Publication: |
165/133 |
International
Class: |
F28F 3/08 20060101
F28F003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2011 |
EP |
11190887.7 |
Claims
1. A plate heat exchanger comprising: a top head, a bottom head and
four side panels that are bolted together with a set of corner
girders to form a sealed enclosure, and a stack of heat transfer
plates that is arranged in the sealed enclosure, the stack of heat
transfer plates comprising: pairs of heat transfer plates that are
stacked such that a flow path for a first fluid is formed between
the stacked pairs of heat transfer plates, wherein a pair of the
stacked pairs of heat transfer plates comprises a first heat
transfer plate and a second heat transfer plate that are joined
such that a flow path for a second fluid is formed between the
first and second heat transfer plates, the first heat transfer
plate and the second heat transfer plate comprising a coating that
has a layer thickness of 1-30 .mu.m; is prepared by sol-gel
processing; comprises silicon oxide (SiOx) having an atomic ratio
of O/Si>1; and comprises .gtoreq.5 atomic percent carbon
(C).
2. A heat exchanger according to claim 1, wherein the first heat
transfer plate and the second heat transfer plate has a thickness
(m1) of 0.6-1.4 mm.
3. A heat exchanger according to claim 1, wherein each of the first
heat transfer plate and the second heat transfer plate has a heat
transfer area (m2) of 0.05-0.30 m.sup.2.
4. A heat exchanger according to claim 1, wherein any of the top
head and the bottom head has a thickness (m3) of 45-145 mm.
5. A heat exchanger according to claim 1, wherein each of the four
side panels has a thickness (m4) of 35-85 mm.
6. A heat exchanger according to claim 1, wherein each of the
corner girders comprises a cross-sectional side (m5) that measures
35-85 mm.
7. A heat exchanger according to claim 1, wherein the sealed
enclosure has a volume of 0.02-0.40 m.sup.3.
8. A heat exchanger according to claim 1, wherein the layer
thickness of the coating is 1.5-25 .mu.m.
9. A heat exchanger according to claim 1, wherein the silicon
oxide, SiOx, has an atomic ratio of O/Si=1.5-3.
10. A heat exchanger according to claim 1, wherein the coating has
a content of carbon of 20-60 atomic %.
11. A heat exchanger according to claim 1, comprising a gasket that
is at least partially coated with the coating.
12. A heat exchanger according to claim 1, wherein the first heat
transfer plate and the second heat transfer plate are made of
stainless steel.
13. A heat exchanger according to claim 1, wherein the layer
thickness of the coating is 2-20 .mu.m.
14. A heat exchanger according to claim 1, wherein each of the
first heat transfer plate and the second heat transfer plate has a
heat transfer area (m2) of 0.6-1.8 m.sup.2.
15. A heat exchanger according to claim 1, wherein any of the top
head and the bottom head has a thickness (m3) of 190-250 mm.
16. A heat exchanger according to claim 1, wherein the layer
thickness of the coating is 3-10 .mu.m.
17. A heat exchanger according to claim 1, wherein the silicon
oxide, SiOx, has an atomic ratio of O/Si=2-2.5.
18. A heat exchanger according to claim 1, wherein the coating has
a content of carbon of 30-40 atomic %.
19. A heat exchanger according to claim 1, wherein the first heat
transfer plate and the second heat transfer plate has a thickness
(m1) of 0.8-1.2 mm.
20. A heat exchanger according to claim 1, wherein each of the four
side panels has a thickness (m4) of 65-175 mm.
Description
TECHNICAL FIELD
[0001] The invention relates to a block-type plate heat exchanger
that comprises a top head, a bottom head and four side panels that
are bolted together with a set of corner girders to form a sealed
enclosure. A stack of heat transfer plates is arranged in the
sealed enclosure. The block-type plate heat exchanger has
properties that reduce fouling and facilitate cleaning the heat
exchanger.
BACKGROUND ART
[0002] Today several different types of plate heat exchangers exist
and are employed in various applications depending on their type.
One certain type of plate heat exchanger is assembled by bolting a
top head, a bottom head and four side panels to a set of corner
girders to form a box-like enclosure around a stack of heat
transfer plates. This certain type of plate heat exchanger is
referred to as a block-type heat exchanger. One example of a
commercially available block-type heat exchanger is the heat
exchanger offered by Alfa Laval AB under the product name
Compabloc. Other block-type plate heat exchangers are disclosed in
patent documents EP165179 and EP639258.
[0003] In the block-type plate heat exchanger fluid paths for two
heat exchange fluids are formed between the heat transfer plates in
the stack of heat transfer plates. During operation fouling of the
heat transfer plates is of concern, for example due to deposits,
microbial growth, dirt etc. that arise from the fluids that pass
between the heat transfer plates. Fouling typically reduces a heat
transfer capability and increases a pressure drop of the heat
exchanger, which lead to an overall reduced performance. The
problem of fouling is typically solved by removing one or more of
the side panels such that the stack of heat transfer plates may be
accessed and the plates may be cleaned.
[0004] For other types of heat exchangers it is known to coat areas
of the heat exchanger that are susceptible to fouling. Examples of
coating techniques may be found in a number of patent documents,
such as in US20090123730, US20060196644, WO2008119751 and
WO2009034359.
[0005] Even though the these coating techniques may reduce fouling,
it appears that they are not optimal for a block-type plate heat
exchanger that typically is used in aggressive, high pressure
applications where safety demands are high. For example, the
coating would typically after some time be worn of its coating
surface. Moreover, the unique design and structure of the
block-type plate heat exchanger calls for a different coating that
has been optimized in respect of the inherent design structure of
the block-type plate heat exchanger.
SUMMARY
[0006] It is an object of the invention to find a coating that
reduces fouling of a block-type plate heat exchanger. Another
object is to find embodiments of a block-type plate heat exchanger
that ensure that the coating stays on the coated areas for a long
operational time of the heat exchanger.
[0007] To fulfill these objects a block-type plate heat exchanger
is provided. The block-type heat exchanger comprises a top head, a
bottom head and four side panels that are bolted together with a
set of corner girders to form a sealed enclosure, and a stack of
heat transfer plates that is arranged in the sealed enclosure. The
stack of heat transfer plates comprises pairs of heat transfer
plates that are stacked such that a flow path for a first fluid is
formed between the stacked pairs of heat transfer plates, wherein a
pair of the stacked pairs of heat transfer plates comprises a first
heat transfer plate and a second heat transfer plate that are
joined such that a flow path for a second fluid is formed between
the first and second heat transfer plates. At least a part of each
of the first heat transfer plate and the second heat transfer plate
comprises a coating that i) has a layer thickness of 1-30 .mu.m,
ii) is prepared by sol-gel processing, iii) comprises silicon oxide
(SiOx) having an atomic ratio of O/Si>1, and iv) comprises
.gtoreq.5 or .gtoreq.10 atomic percent carbon (C).
[0008] The block-type plate heat exchanger is advantageous in that
fouling of the heat transfer plates is significantly reduced. As a
consequence no or less cleaning is required. This reduces use of
strong detergents and/or potentially abrasive, mechanical cleaning
as well as reduces an operational downtime of the plate heat
exchanger. Moreover, the coating is, comparison with prior art
coatings, quite wear resistant and has a relatively resistance
against formation of cracks in the coating which otherwise might
from due to torque and tension forces that act on the heat transfer
plates. Generally, each side or each both sides of the respective
heat transfer plate may comprise the coating.
[0009] The plate heat exchanger may have predetermined measurements
for a number of the components it comprises. For example, the first
heat transfer plate and the second heat transfer plate may have a
thickness of 0.6-1.4 mm or 0.8-1.2 mm. Each of the first heat
transfer plate and the second heat transfer plate may have a heat
transfer area of 0.05-0.30 m.sup.2 or 0.6-1.8 m.sup.2. Any of the
top head and the bottom head may have a thickness of 45-145 mm or
190-250 mm. Each of the four side panels may have a thickness of
35-85 mm or 65-175 mm. Each of the corner girders may comprise a
cross-sectional side that measures 35-85 mm or 110-190 mm. Finally,
the sealed enclosure may have a volume of 0.02-0.40 m.sup.3 or
0.7-5.0 m.sup.3.
[0010] Empirical tests as well as finite element-based analysis
have shown that each of these measurements, either alone or one or
more in combination, provide a structure of the heat exchanger that
is particularly suitable for the coating. The underlying reasons
for this is that the measurements provide a structure for the heat
transfer plates that prevents extensive flexing of the heat
transfer plates when the heat exchanger is operated. This is of
great advantage since the coating then remains on the plates for a
long period of time (flexing cause the coating to fall off or wear
out faster). Thus, the coating together with one or more of the
predetermined measurements provide a block-type heat exchanger that
has been optimized in respect of resisting fouling for a longer
period of time.
[0011] The layer thickness of the coating may be 1.5-25 .mu.m, or
2-20 .mu.m, or 2-15 .mu.m, or 2-10 .mu.m, or 3-10 .mu.m. The
silicon oxide, SiOx, may have an atomic ratio of O/Si=1.5-3, or may
have an atomic ratio of O/Si=2-2.5. The coating may have a content
of carbon of 20-60 atomic % or 30-40 atomic %. The heat exchanger
may comprise a gasket that is at least partially coated with the
coating. The first heat transfer plate and the second heat transfer
plate may be made of stainless steel.
[0012] Further features, objectives, aspects and advantages of the
invention will appear from the following detailed description as
well as from the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Embodiments of the invention will now be described, by way
of example, with reference to the accompanying schematic drawings,
in which
[0014] FIG. 1 is an exploded view of a block-type heat exchanger
with a stack of heat transfer plates,
[0015] FIG. 2 is a top view of pairs of heat transfer plates that
are used for the stack of heat transfer plates of FIG. 1.
[0016] FIG. 3 is a cross-sectional view along section A-A of FIG.
2.
[0017] FIG. 4 is a cross-sectional view along section B-B of FIG.
2.
[0018] FIG. 5 is an enlarged view of section C of FIG. 3, and
[0019] FIG. 6 is a schematic, cross-sectional view of a coated heat
transfer plate that is part of the stack of heat transfer plates of
FIG. 1.
DETAILED DESCRIPTION
[0020] With reference to FIG. 1 a plate heat exchanger 2 of a
block-type is shown. The plate heat exchanger 2 comprises a top
head 15, a bottom head 16 and four side panels 11, 12, 13, 14 that
are bolted together with a set of (typically four) corner girders
21-24 for assembling the plate heat exchanger 2. When assembled,
the plate heat exchanger 2 has a box-like or block-like shape and
an enclosure is formed by the top head 15, the bottom head 16 and
the side panels 11-14. A stack of heat transfer plates 30 is
arranged within the enclosure and comprises, as will be described
in further detail, a number of pairs of heat transfer plates. The
stack of heat transfer plates 30 also has a box-like or block-like
shape, which shape corresponds to the shape of the enclosure formed
by the heads 15, 16 and the side panels 1114. The stack of heat
transfer plates 30 has at its corners four linings 31-34 that are
arranged to face the corner girders 21-24.
[0021] The assembly of the plate heat exchanger 2 is typically
performed by using conventional methods and bolts (not shown) that
attach the mentioned components to each other via bolt holes like
holes 35 and 36. In brief, assembling the plate heat exchanger 2
includes arranging the stack of heat transfer plates 30 on the
bottom head 16, sliding the corner girders 21-24 into the linings
31-34 and bolting them to the bottom head 16. A channel end plate
38 is arranged on top of the stack of heat transfer plates 30 and
the top head 15 is bolted to the corner girders 21-24. Thereafter
the side panels 11-14 are bolted to the corner girders 21-24 and to
the heads 15, 16. Generally, the plate heat exchanger 2 also has a
base 17 that facilitates attachment of the plate heat exchanger 2
to the ground.
[0022] Gaskets, such e.g. gasket 131, are arranged on the side
panels 11-14 at sections that face the corner girders 21-24 and the
heads 15, 16, such that the enclosure formed by the heads 15, 16
and side panels 11-14 is properly sealed for preventing leakage
from the plate heat exchanger 2.
[0023] A first side panel 11 and a second side panel 12 of the side
panels 11-14 comprise inlets and outlets for two fluids. In detail,
the first side panel 11 has an inlet 41 and an outlet 42 for a
first fluid. The inlet 41 and outlet 42 of the first panel 11 form
a flow path for the first fluid in combination with the stack of
heat transfer plates 30, where the flow path extends from the inlet
41, within the stack of heat transfer plates 30 and to the outlet
42. This flow path is illustrated by the broken arrows that extend
in directions parallel to the direction D1. Conventional baffles,
such as baffle 39, are connected to sides of the stack of heat
transfer plates 30 for directing the flow of the first fluid in a
number of passes within the stack 30 (four passes in the
illustrated figure).
[0024] The second side panel 12 has an inlet 43 and an outlet 44
for a second fluid. The inlet 43 and outlet 44 of the second side
panel 12 form a flow path for the second fluid in combination with
the stack of heat transfer plates 30, where the flow path extends
from the inlet 43, within the stack of heat transfer plates 30 and
to the outlet 44. This flow path is illustrated by the broken
arrows that extend in directions parallel to the direction D2.
Conventional baffles connected to sides of the stack of heat
transfer plates 30 direct the flow of the second fluid in a number
of passes within the stack 30 (here the same number of passes as
for the first fluid).
[0025] The arrangement of baffles is per se accomplished by
employing conventional techniques. However, the first flow path for
the first fluid is between the pairs of heat transfer plates in the
stack 30, while the second flow path for the second fluid is within
the pairs of heat transfer plates in the stack 30. A pair of heat
transfer plates comprises a first heat transfer plate and a second
heat transfer plate, as will be described further on. This means
that the flow of the first fluid is between heat transfer plates of
different pairs of heat transfer plates, while the flow of the
second fluid is between a first and a second heat transfer plate of
the same pair, i.e. within a pair. The linings 31-34 seal the
corners of the stack of heat transfer plates 30, which ensures that
the two different fluids paths are separated.
[0026] With reference to FIGS. 2, 3 and 4 a first and a second pair
50, 60 of heat transfer plates are exemplified, where FIG. 3 is a
cross-sectional view along section A-A of FIG. 2 and FIG. 4 is a
cross-sectional view along section B-B of FIG. 2. The pairs 50, 60
of heat transfer plates are part of the stack of heat transfer
plates 30 illustrated in FIG. 1. The stack 30 comprises a number of
pairs of heat transfer plates that are similar to the pairs 50, 60,
such, as 4-200 pairs or even more.
[0027] For the pairs 50, 60 of heat transfer plates exemplified by
FIGS. 2, 3 and 4, the first pair 50 of heat transfer plates
comprises a first heat transfer plate 51 and a second heat transfer
plate 52. The second pair 60 of heat transfer plates is typically
similar to the first pair 50 of heat transfer plates, which means
that it also comprises a first heat transfer plate 61 and a second
heat transfer plate 62. Thus, the first heat transfer plate 61 of
the second pair 60 of heat transfer plates is typically similar to
the first heat transfer plate 51 of the first pair 50 of heat
transfer plates, while the second heat transfer plate 62 of the
second pair 60 of heat transfer plates may be similar to the second
heat transfer plate 52 of the first pair 50 of heat transfer
plates.
[0028] Also, the first heat transfer plate 51 and the second heat
transfer plate 52 of the first pair 50 of heat transfer plates have
similar shapes.
[0029] Each heat transfer plate has, as exemplified by the first
heat transfer plate 51 of the first pair 50 of heat transfer
plates, a rectangular shape with a first 511, a second 512, a third
513 and a fourth elongated side 514. When the stack of heat
transfer plates 30 is arranged within the enclosure of the plate
heat exchanger 2, the first elongated side 511 is facing the first
side panel 11 while the third side 513 is facing the third side
panel 13. The first heat transfer plate 51 is joined with the
second heat transfer plate 52 via a joint 78 at the first elongated
side 511 and via a joint 79 at the third elongated side 513, as may
be seen in FIG. 3.
[0030] The first heat transfer plate 51 comprises sets of
corrugations 101-106 that are arranged on respective sides of
elongated joints 72-76 that join the first and second heat transfer
plates 51, 52. It may also be said that the corrugations 101-106
are separated by the elongated joints 72-76. The sets of
corrugations 101-106 extend a direction that is parallel to the
joints 72-76, which direction in the exemplified embodiment is
parallel to the direction D2. The sets of corrugations 101-106 have
two outermost sets of corrugations 101, 106, and further joints 71,
77 may be arranged intermediate the outer sets of corrugations 101,
106 and the corresponding, closest elongated side 513, 511. As
previously indicated, since all heat transfer plates may be
similar, all or some of the heat transfer plates of the stack of
heat transfer plates 30, such as plates 52, 61 and 62, may have the
same properties and structural shape as plate 51.
[0031] The corrugations 101-106 comprise ridges and grooves that
extend in a direction D1 that is 45.degree.-90.degree. transverse a
direction D2 along which the elongated joints 71-77 extend. The
directions D1. D2 are here the same directions as previously
discussed in respect of the flow of the first and second fluid.
Corrugations 101, 102 on the first heat transfer plate 51 and
corresponding corrugations 201, 202 on the second heat transfer
plate 52 each comprise ridges and grooves, such as ridge 92 and
groove 93 of the first heat transfer plate 51 and ridge 192 and
groove 193 of the second heat transfer plate 52.
[0032] The first pair 50 of heat transfer plates comprises
elongated joint grooves, as exemplified by joint grooves 81-87 of
the first heat transfer plate 51, along which the elongated joints
71-77 are arranged. Each corrugation of the set of corrugations
101-106 comprising ridges and grooves that extend in a direction D1
that is transverse a direction D2 along which the elongated joint
grooves 81-87 extend.
[0033] The ridges of the first heat transfer plate 51 may be
aligned with the ridges of the second heat transfer plate 52, as
seen in a direction parallel to a normal direction N of the first
pair 50 of heat transfer plates. This is advantageous in that
efficient heat transfer and flow of fluid may be accomplished.
[0034] As shown, the joints 71-77 are arranged in a respective
joint groove 81-87. Since the second heat transfer plate 52 is
similar to the first heat transfer plate 51 it also comprises
elongated joint grooves along which the elongated joints 71-77 are
arranged.
[0035] With reference to FIG. 3 and to FIG. 5 illustrating the
enlarged section C of FIG. 3, it is shown that e.g. joint groove 82
of the first heat transfer plate 51 abut a corresponding joint
groove 182 of the second heat transfer plate 52. The heat transfer
plates 51, 52 are then joined at the joint grooves 82, 182 by
virtue of the joint 72. In this context, a backside surface 515 of
the joint groove 82 of the first heat transfer plate 51 is in
contact with a backside surface 525 of the joint groove 182 of the
second heat transfer plate 52.
[0036] The joints are typically formed by welding but may also be
formed by brazing or by some other, suitable means of joining. The
heat transfer plates 51, 52, 61, 62 are typically made of metal,
such as stainless steel. When welding is used for forming the
joints, i.e. when the joint are welds, laser welding may be used as
well as other welding techniques, such as resistance welding.
[0037] Each of the joints 71-77 may comprise two at least partially
overlapping joint sections, as exemplified by a first section 721
and a second section 722 of the joint 72. The joint sections 721,
722 may be overlapping by a predetermined distance, such as 5-30
mm. The two joint sections 721, 722, or welding sections when the
joints are formed by welding, may begin at a respective end section
of the joint groove, as illustrated by the two end sections 821,
822 of joint groove 82.
[0038] As indicated, the joining of the first heat transfer plate
51 with the second heat transfer plate 52 at the first and third
elongated sides 511, 513 may be accomplished by a first set of
opposite, elongated side joints 78, 79, such that a flow path 57
for the second fluid is formed between the first set of opposite,
elongated side joints 78, 79, i.e. within the first pair 50 of heat
transfer plates. The flow path 57 is then parallel to the direction
D2 discussed in connection with FIG. 1.
[0039] For facilitating joining of the plates in a pair 50, the
first and second heat transfer plates 51, 52 have peripheral
sections like sections 53, 54 that are folded towards each other.
The peripheral sections 53, 54 are folded towards each other since
the second heat transfer plate 52 is arranged as an inverted
mirror-image of the first heat transfer plate 51, having in mind
that the plates 51, 52 are similar. The related weld 79 is applied
at a contact surface formed between the folded sections 53, 54.
[0040] The joint grooves 81-87 may extend unbroken along the flow
path 57 that is formed between the first and second heat transfer
plates 51, 52. Also since the first heat transfer plate 51 and the
second heat transfer plate 52 are typically joined by multiple
elongated joints 71-77, the flow path 57 for the second fluid
formed between the first and second heat transfer plates 51, 52
comprises multiple parallel flow channels 571-576.
[0041] To form the stack of heat transfer plates 30, pairs of heat
transfer plates like the first pair 50 of heat transfer plates and
the second pair 60 of heat transfer plates are joined via opposite,
elongated side joints. Such joints are exemplified by a set of
opposite, elongated side joints 781, 782 arranged between the first
pair 50 of heat transfer plates and the second pair 60 of heat
transfer plates. Such elongated side joints 781, 782 are transverse
the first set of elongated side joints 78, 79 and joins a pair of
heat transfer plates (exemplified by pair 50) with an adjacent pair
of heat transfer plates (exemplified by pair 60). For facilitating
joining, the plates 51, 52, 61, 62 have respective peripheral
sections that are folded towards a heat transfer plate that belongs
to another pair of heat transfer plates, such as folded sections 56
and 65. The related weld 781 is applied at a contact surface formed
between the folded sections 56, 65.
[0042] When the pairs 50, 60 of heat transfer plates are joined, a
flow path 67 for the first fluid is formed between the pairs 50, 60
of heat transfer plates. Since the pairs 50, 60 are joined only at
the second set of side joints 781, 782 a so called free-flow path
is formed between the joints 781, 782, i.e. a free-flow path is
formed between the pairs 50, 60 of heat transfer plates. A
free-flow path may in this context be defined as a flow path
without any contact points intermediate the side joints 781, 782.
Generally, free-flow has been observed to be advantageous since
occurrence of e.g. deposits from the fluid or the presence of
bacteria may be reduced or, in practice, even eliminated.
[0043] To form the complete stack of heat transfer plates 30, a
number of pairs of heat transfer plates are stacked adjacent each
other and joined to each other in a manner like the joining of the
first and the second pairs 50, 60 of heat transfer plates. The
joining of the pairs may be accomplished by using the same methods
(welding, brazing etc.) as when joining the plates of one pair.
[0044] For efficiently joining the heat transfer plates to the
linings 31-34 each heat transfer plate has four protrusions at its
corners, such as protrusions 515-518 of the first heat transfer
plate 51. The protrusions are then joined to the linings 31-34 by
e.g. welding, brazing or by some other suitable means of joining.
The linings 31-34 partially surround the set of corner girders
21-24 when the plate heat exchanger 2 is assembled, such that the
stack of heat transfer plates 30 is firmly fixed within the
enclosure that is formed by the heads 15, 16 and the side panels
11-14.
[0045] The heat transfer plates 51, 52, 61, 62 may per se be
manufactured from steel sheets that are pressed with a press tool
that forms the corrugations and the weld grooves. A cutting machine
thereafter cuts the pressed plates along their periphery and the
edges of the cut plates are folded in a machine that forms the
folded, peripheral sections.
[0046] The heat transfer plates in the stack of heat transfer
plates 30 comprises a coating. The coating may be referred to as a
non-stick coating and makes it easy to clean the plates. The coated
plates provide improved heat transfer over time compared to
conventional heat transfer plates since the latter gets fouled much
quicker, which decreases the heat transfer performance to a larger
extent. The coating also results in a much more even surface on the
plates, which gives better flow characteristics. Also, a pressure
drop over the plates is reduced over time for the plate heat
exchanger 2 in comparison with conventional block-type plate heat
exchangers, since the buildup of impurities, microorganisms and
other substances is reduced.
[0047] The coated plates may easily be cleaned by using high
pressure washing with water. Moreover, there is no need for
extensive, time consuming mechanical cleaning or cleaning using
strong acids, bases or detergents, such as e.g. NaOH and
HNO.sub.3.
[0048] The heat transfer plates in the stack 30 are in a sol-gel
process coated with a coating that comprises organosilicon
compounds. The organosilicon compounds are starting materials that
are used in the sol-gel process and are preferably silicon alkoxy
compounds. In the sol-gel process a sol is converted into a gel to
produce nano-materials. Through hydrolysis and condensation
reactions a three-dimensional network of interlayered molecules is
produced in a liquid. Thermal processing stages are then used to
process the gel further into nano-materials or nanostructures,
which results in a final coating. The coating comprising said
nano-materials or nanostructures mainly comprise silicon oxide,
SiO.sub.x, having an atomic ratio of O/Si>1, alternatively an
atomic ratio within the range of O/Si=1.5-3, or alternatively
within the range of O/Si=2-2.5. By an "atomic ratio of O/Si>1"
is meant that the number of Oxygen atoms (O) of the silicon oxide
(SiO.sub.x) divided by the number of Silicon atoms (Si) of the
silicon oxide (SiO.sub.x) is larger than one. Correspondingly, for
the alternatives the number of Oxygen atoms (O) divided by the
number of Silicon atoms is within the range of 1.5-3, or within the
range of 2-2.5.
[0049] A preferred silicon oxide is silica, SiO.sub.2. The
siliconoxide forms a three dimensional network having excellent
adhesion to the plates. All heat transfer plates of the stack 30,
such as the first heat transfer plate 51 and the second heat
transfer plate 52, may be coated. Typically the plates are coated
on the sides that face either one or both of the flow path for the
first fluid and the flow path for the second fluid.
[0050] The coating has a content of carbon originating from
hydrocarbon chains. The hydrocarbons chains may have functional
groups such as those found in hydrocarbon chains or aromatic
groups, e g C.dbd.O, C--O, C--O--C, C--N, N-C-O, N-C.dbd.O, etc.
Preferably the content of the carbon is .gtoreq.10 atomic %, or in
the range of 20-60 atomic %, or in the range of 30-40 atomic %. The
carbon impart flexibility and resilience to the coating which is
important if the plates during operation flex due to high pressures
exerted on the plates in the stack 30. The hydrocarbon chains are
hydrophobic and oleophobic, which results in the non-stick
properties of the coating.
[0051] With reference to FIG. 6 a schematic view is shown where the
first heat transfer plate 51 is provided with a siliconoxide sol
gel coating 701 as described above. The coating is also referred to
as siliconoxide layer 701. Closest to the plate 51 the siliconoxide
layer 701 forms an interface 702 between the coating siloxane and a
metal oxide film of the plate 51. A bulk of the coating 701 is the
siloxane network 703 that has organic linker chains and voids that
impart flexibility to the coating 701. The siloxane network 703 is
"on top" of the interface 702. The siliconoxide layer 701 forms an
outermost layer in from of a functional surface 704 that has
hydrophobic and oleophobic properties that reduce fouling. There
are no sharp boundaries between the interface 702 and the siloxane
network 703 respectively the siloxane network 703 and the
functional surface 704, but rather gradual transitions
[0052] All plates in the stack 30 that are coated may have the
coating described in connection with FIG. 6. The coating is both
durable and flexible and provides a plate for a block-type plate
heat exchanger that has excellent non-stick properties and wear-
and crack-resistance.
[0053] In one embodiment at least one sol comprising organosilicon
compounds is applied to the surface of the heat transfer plates
that are coated. The surface may be wetted/coated with the sol in
any suitable way. The surface coating may e.g. be applied by
spraying, dipping or flooding. Typically, all surfaces of a heat
transfer plate that is in contact with a fluid that may cause
fouling are coated. Also, the gaskets like gasket 131 arranged on
the side panels 11-14 may be coated, typically with the same type
of coating that is used for the heat transfer plates. The coating
is then typically applied at least on the surfaces of the gaskets
that are in contact with the fluid that may cause fouling.
[0054] A method of coating the heat transfer plates of the stack 30
comprises pretreatment of at least the surfaces on the heat
transfer plates to be coated. This pretreatment may be carried out
by means of dipping, flooding or spraying. The pretreatment is used
to clean the surfaces to be coated in order to obtain increased
adhesion of the coating. Examples of pretreatments are treatment
with acetone and/or alkaline solutions, e.g. caustic solution.
[0055] The method of coating the heat transfer plates may comprise
thermal processing stages, e.g. a drying operation may be carried
out after a pretreatment and a drying and/or curing operation may
be used after the coating of the plate has taken place. The coating
may be subjected to heat by using conventional heating apparatuses,
such as ovens.
[0056] The coating, which as indicated comprises SiOx, is applied
to the plates of the stack 30. The application of the coating is
done by means of sol-gel processing. The coating is preferably
between 1 and 30 .mu.m thick. A coating thickness below 1 .mu.m is
considered being not enough wear resistant since the plates in the
plate heat exchanger 2 are able to flex slightly during operation.
Flexing of the plates causes wear on the coating and with time the
coating wear down. Still, the thickness of the coating has an upper
limit since the application of substances on the heat transfer
plates influences the their heat transfer capability and thus the
overall performance of the plate heat exchanger. The upper limit
for the thickness of the coating is preferably 30 .mu.m. Thus, the
coating thickness of the silicon oxide sol containing coating is
1-30 .mu.m, and in alternatives preferably 1.5-25 .mu.m, preferably
2-20 .mu.m, preferably 2-15 .mu.m, preferably 2-10 .mu.m or
preferably 3-10 .mu.m.
[0057] The material of which the heat transfer plates in the stack
30 are made of may be chosen from several metals and metal alloys.
Preferably, the material is stainless steel or titanium. The
material may also be chosen from nickel, copper, any alloys of the
mentioned metals and/or carbon steel.
[0058] In an attempt to find more a foul resistant block-type plate
heat exchanger, tests were conducted on two low surface energy
glass ceramic coatings of which both are of the type of coating
described above. The tested coatings are referred to as Coat 1 and
Coat 2. The tests, the analysis and the results are presented
below. Coat 1 is a silan terminated polymer in butyl acetate and
Coat 2 is a polysiloxan-urethan resin in solvent
naphtha/butylacetate. The test were performed on coated heat
transfer plates in the stack 30. In the following a plate for which
tests is performed is also referred to as "substrate".
[0059] The tests shows properties of the coatings in respect of
substrate wetting, substrate adhesion, contact angle, coating
thickness and stability against 1.2% HNO.sub.3 in H.sub.2O, 1% NaOH
in H.sub.2O and crude oil. The results are summarized below in
Table 1.
TABLE-US-00001 TABLE 1 Coat 1 Coat 2 Substrate Excellent Excellent
wetting Substrate Al: 0/0 Al: 0/0 adhesion Stainless steel: 0/0
Stainless steel: 0/0 Ti: 0/0 (see below) Ti: 0/0 (see below)
Contact angle H2O: 102-103.degree. H2O: 102-103.degree.
measurements Coating 4-10 .mu.m 2-4 .mu.m thickness Stability 1.2%
HNO3 in H2O: 1.2% HNO3 in H2O: 11/2 h at 75.degree. C. 11/2 h at
75.degree. C. 1% NaOH in H2O: 3 h at 1% NaOH in H2O: 2 h at
85.degree. C. 85.degree. C. Crude oil: 6 months Crude oil: 6 months
at 20.degree. C. at 20.degree. C.
[0060] Both coatings showed excellent wetting when spray coated
onto either stainless steel or titanium substrates.
[0061] Adhesion was determined by cross-cut/tape test according to
the standard DIN EN ISO 2409. Rating is from 0 (excellent) to 5
(terrible). 0 or 1 is acceptable while 2 to 5 is not. First digit
indicates rating after cross cut (1 mm grid) and the second digit
gives rating after tape has been applied and taken off again.
[0062] To obtain proper adhesion for Coat 1 and Coat 2 the
substrates were subjected to pre-treatment. To obtain a proper
adhesion of Coat 1 on stainless steel the substrate was pre-treated
by submerging it in an alkaline cleaning detergent for 30 minutes.
Next the substrate was washed with water and demineralized water
and dried before Coat 1 was applied (applied within half an hour to
achieve optimal adhesion). Tests have shown that the adhesion is
reduced if cleaning of the substrate is only carried out with
acetone. Pre-treatment was also used for stainless steel substrates
that are coated with Coat 2. This coating displayed unaffected
adhesion whether an alkaline detergent or acetone was used as
pre-treatment or not. If the pre-treatment step is neglected or not
properly made the coating adhesion will be effected.
[0063] Both coatings showed good stability under acidic condition.
The coatings were stable for 11/2% hours at 75.degree. C. and more
than 24 hours at room temperature.
[0064] Under alkaline conditions Coat 1 showed a better result than
Coat 2. Coat 1 could withstand the alkaline conditions for 3 hours
at 85.degree. C. and Coat 2 for 2 hours at 85.degree. C. Both
coatings showed no decomposition or reduction in oleophobic
properties after being subjected to crude oil for 6 months at a
temperature of 20.degree. C.
[0065] Heat transfer plates in the stack 30 were then coated with
Coat 1 and Coat 2. The heat exchanger plates were in this test made
of titanium and the heat exchanger 2 was used in a crude oil
application. All coated heat transfer plates underwent
pre-treatment, which comprised treatment with acidic and alkaline
solutions to remove fouling and high pressure washing of the plates
with water. The plates were left to dry before application of
coating.
[0066] The pre-treatment was completed a day before Coat 1 and Coat
2 were applied to the plates. As the plates have been left to dry
at ambient temperature (approximately cover 20.degree. C.), some
plates were still wet. More precisely, a third of the plates were
coated with Coat 1 and a third of the plates were coated with Coat
2, while a remaining third of the plates were kept uncoated. The
coating is accomplished by spraying the respective coat into the
flow paths 57, 67 that are formed by the plats in the stack 30,
such that the sides of the that faces the flow paths are coated.
The thickness of the coating was measured to be 2-4 .mu.m.
Curing/drying for the two coatings was performed for 11/2 hours in
an oven at elevated temperatures of 200.degree. C. respectively
160.degree. C.
[0067] The stack 30 with the coated heat transfer plates were then
arranged in the heat exchanger of FIG. 1 and an evaluation of the
coated plates was performed after about seven months of operation
of the plate heat exchanger 2.
[0068] The plates were analyzed after the seven months. In detail,
three different silicon oxide-coated heat transfer plates were
analyzed by means of XPS (X-ray Photoelectron Spectroscopy), also
known as ESCA (Electron Spectroscopy for Chemical Analysis). The
XPS method provides quantitative chemical information, including a
chemical composition expressed in atomic % for the outermost 2-10
nm of a surface.
[0069] A measuring principle of the XPS method comprises that a
sample (i.e. a heat transfer plate coated with Coat 1, a heat
transfer plate coated with Coat 2 and an uncoated plate) is placed
in high vacuum and is irradiated with well defined x-ray energy,
which results in an emission of photoelectrons from the sample.
Only photoelectrons from the outermost surface of the sample reach
the detector. By analyzing the kinetic energy of the
photoelectrons, their binding energy can be calculated, thus giving
their origin in relation to a chemical element (including the
electron shell) of the sample.
[0070] XPS provided quantitative data on both the elemental
composition and different chemical states of a chemical element of
the sample (such as different functional groups, chemical bonding,
oxidation state, etc). All chemical elements except hydrogen and
helium are detected and the obtained chemical composition of the
sample is expressed in atomic %.
[0071] XPS spectra were recorded using a Kratos AXIS Ultra.sup.DLD
x-ray photoelectron spectrometer. The samples were analyzed using a
monochromatic Al x-ray source. The analysis area was below 1
mm.sup.2. In the analysis so a called wide spectra run was
performed to detect chemical elements present in the surface of the
sample. The relative surface compositions were obtained from
quantification of each chemical element.
[0072] When heat transfer plates with different types (in respect
of a content of C, O and Si) of the silicon oxide coating described
herein are analyzed, or more precisely when the chemical elements
of the coating is analyzed, a relative surface composition in
atomic % and an atomic ratio O/Si may be found. It has then been
observed that mainly C, O and Si may be detected on the outermost
surfaces of the coating. A content of C is typically 41.9-68.0
atomic %, a content of O is 19.5-34.3 atomic % while a content of
Si is 8.6-23.4 atomic %. The atomic ratio O/Si is 1.46-2.30. Note
that for the atomic ratio O/Si, the total amount of oxygen is used.
This means that also oxygen in functional groups with carbon is
included. Otherwise, for silica a theoretical ratio O/Si of 2.0 is
expected (i.e. SiOx in form of SiO.sub.2).
[0073] After four months of operation a pre-inspection by
thermo-imaging was performed. A thermo-image was taken of a mid
region of the heat exchanger 2 when the heat exchanger was
operated. From the image it was obvious that some heat transfer
plates show increased heat transfer compared to other heat transfer
plates in the heat exchanger.
[0074] The inspection showed an elevated temperature at the coated
plates. The non-coated plates showed a lower operating temperature.
The difference in temperature is an effect of different fouling,
where coated plats has elevated temperatures.
[0075] A visual inspection revealed that the plates with the
coating designated Coat 1 was covered with the least amount of
fouling on the crude oil facing plate side. Also, Coat 2 had a
reduced amount of fouling on the crude oil facing plate side
compared to the bare titanium surface, but to a lesser extent then
Coat 1. The bare titanium plates were completely covered in a thick
layer of crude oil that "fouled" the plates. The term "fouling" is
here used to describe deposits formed on the heat transfer plates
during operation. The fouling is residues and deposits formed by
the crude oil and consists of a waxy, organic part and a
mineral/inorganic part.
[0076] By subtracting the average weight of a clean plate from the
weight recorded for the individual fouled plates the average amount
of fouling per surface type was calculated (table 2). The weight of
the coating was not compensated for and so the real fouling
reduction is slightly higher. For the heat transfer plates used in
the test the heat transfer surface is 0.85 m.sup.2, so for a plate
with a 4 .mu.m thick coating on both sides the total volume of
coating material is around 6.8 cm.sup.3. If the coating is
estimated to be pure SiO.sub.2 (density 2.6 g/cm.sup.3) then the
amount of coating per plate is about 20 g.
TABLE-US-00002 TABLE 2 Average Fouling Surface fouling (g)
reduction (%) Titanium 585 -- Coat 1 203 65 Coat 2 427 27
[0077] For both Coat 1 and Coat 2 the fouling of the plates were
more easily removed compared to the fouling on bare titanium
plates, see Table 3. The difference in cleaning requirements was
tested by manually wiping of the plates with a tissue and by high
pressure water cleaning. Just wiping the plates with a tissue
showed that the fouling was very easily removed from the coated
plates, contrary to the uncoated plates. By using high pressure
water cleaning all fouling except for one or two small patches
could be removed from the Coat 1 coated surface. On the Coat 2
coated surface somewhat more fouling was present after water jet
cleaning. This fouling had the form of slightly burnt oil. The
coating was in a good condition. The crude oil has passed through
the first flow path of the heat exchanger 2, while sea water has
passed through the second flow path. On plate surfaces that face
the seawater both coatings had deteriorated.
TABLE-US-00003 TABLE 3 Coat 1 Coat 2 Uncoated View very little
fouling reduced fouling fouling significant and widespread Wipe
very easy to very easy to fouling was not with remove fouling
remove fouling removed tissue High the plates most of the fouling
even after attempts pressure appeared as new was removed of manual
removal water of fouling, still a washing considerable layer
remains
[0078] The coatings resistance to cold conditions was tested
submerging the plates in liquid nitrogen having a temperature of
-196.degree. C. Next the plates were washed by high pressure water,
which removed almost all fouling. No coating failure was observed
for either Coat 1 or Coat 2.
[0079] Turning back to FIGS. 1, 2 and 4, the plate heat exchanger 2
has predetermined measurements for a number of the components it
comprises. For example, the first heat transfer plate and the
second heat transfer plate may have a thickness m1 of 0.6-1.4 mm or
0.8-1.2. Each of the first heat transfer plate and the second heat
transfer plate may have a heat transfer area m2 of 0.05-0.30
m.sup.2 or 0.6-1.8 m.sup.2. Any of the top head and the bottom head
may have a thickness m3 of 45-145 mm or 190-250 mm. Each of the
four side panels may have a thickness m4 of 35-85 mm or 65-175 mm.
Each of the corner girders may comprise a cross-sectional side m5
that measures 35-85 mm or 110-190 mm. Finally, the sealed enclosure
may have a volume of maximum 0.02-0.40 m.sup.3 or 0.7-5.0 m.sup.3.
As explained, these measurements provides, each alone or in
combination, conditions where the heat transfer plates in the stack
30 flex less which allows the coating to remain on the heat
transfer plates for a longer period of time. Still, the components
are not unnecessarily over-dimensioned but the measurements has
been optimized in respect of allowing the coating to remain for a
longer period of time while still assuring that reasonable amounts
of materials are used for the heat exchanger 2.
[0080] In detail, the measurements m1-m5 may be optimized in
respect of each other. For example, in one embodiment the first
heat transfer plate and the second heat transfer plate have a
thickness of 0.7-0.9 mm and a heat transfer area of 0.02-0.035
m.sup.2, while any of the top head and the bottom head has a
thickness of 35-45 mm, each of the four side panels may has a
thickness of 35-45 mm, each of the corner girders comprises a
cross-sectional side that measures 35-45 mm, and the sealed
enclosure has a volume of 0.005-0.020 m.sup.3.
[0081] In another embodiment the first heat transfer plate and the
second heat transfer plate have a thickness of 0.7-0.9 mm and a
heat transfer area of 0.05-0.07 m.sup.2, while any of the top head
and the bottom head has a thickness of 45-55 mm, each of the four
side panels may has a thickness of 35-65 mm, each of the corner
girders comprises a cross-sectional side that measures 45-55 mm,
and the sealed enclosure has a volume of 0.02-0.06 m.sup.3.
[0082] In another embodiment the first heat transfer plate and the
second heat transfer plate have a thickness of 0.7-0.9 mm and a
heat transfer area of 0.09-0.11 m.sup.2, while any of the top head
and the bottom head has a thickness of 45-55 mm, each of the four
side panels may has a thickness of 35-65 mm, each of the corner
girders comprises a cross-sectional side that measures 45-55 mm,
and the sealed enclosure has a volume of 0.04-0.22 m.sup.3.
[0083] In another embodiment the first heat transfer plate and the
second heat transfer plate have a thickness of 0.9-1.1 mm and a
heat transfer area of 0.13-0.19 m.sup.2, while any of the top head
and the bottom head has a thickness of 60-80 mm, each of the four
side panels may has a thickness of 45-85 mm, each of the corner
girders comprises a cross-sectional side that measures 55-65 mm,
and the sealed enclosure has a volume of 0.12-0.26 m.sup.3.
[0084] In another embodiment the first heat transfer plate and the
second heat transfer plate have a thickness of 0.9-1.1 mm and a
heat transfer area of 0.24-0.30 m.sup.2, while any of the top head
and the bottom head has a thickness of 120-160 mm, each of the four
side panels may has a thickness of 45-85 mm, each of the corner
girders comprises a cross-sectional side that measures 65-105 mm,
and the sealed enclosure has a volume of 0.2-0.6 m.sup.3.
[0085] In another embodiment the first heat transfer plate and the
second heat transfer plate have a thickness of 0.9-1.1 mm and a
heat transfer area of 0.50-0.80 m.sup.2, while any of the top head
and the bottom head has a thickness of 170-230 mm, each of the four
side panels may has a thickness of 90-160 mm, each of the corner
girders comprises a cross-sectional side that measures 100-140 mm,
and the sealed enclosure has a volume of 1.0-2.4 m.sup.3.
[0086] In another embodiment the first heat transfer plate and the
second heat transfer plate have a thickness of 1.1-1.3 mm and a
heat transfer area of 1.4-2.0 m.sup.2, while any of the top head
and the bottom head has a thickness of 120-400 mm, each of the four
side panels may has a thickness of 110-250 mm, each of the corner
girders comprises a cross-sectional side that measures 120-240 mm,
and the sealed enclosure has a volume of 2.4-5.9 m.sup.3.
[0087] From the description above follows that, although various
embodiments of the invention have been described and shown, the
invention is not restricted thereto, but may also be embodied in
other ways within the scope of the subject-matter defined in the
following claims. For example, optimization calculations may show
that other measurements for components of the heat exchanger may
provide a structure that allows the coating to remain on the coated
surface for long period of time. Also, the heat transfer plates may
have another pattern of corrugation than the shown one. In other
embodiments the elongated joints and their associated joint grooves
on the heat transfer plates may be omitted such that e.g.
corrugations cover the heat transfer areas of the plates.
* * * * *