WO2017072177A1 - Protection cathodique d'un échangeur de chaleur - Google Patents

Protection cathodique d'un échangeur de chaleur Download PDF

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Publication number
WO2017072177A1
WO2017072177A1 PCT/EP2016/075806 EP2016075806W WO2017072177A1 WO 2017072177 A1 WO2017072177 A1 WO 2017072177A1 EP 2016075806 W EP2016075806 W EP 2016075806W WO 2017072177 A1 WO2017072177 A1 WO 2017072177A1
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WO
WIPO (PCT)
Prior art keywords
anode
heat exchanger
space
plate
anodes
Prior art date
Application number
PCT/EP2016/075806
Other languages
English (en)
Inventor
Matthias Graff
Mitja MAZEJ
Tine Ogorevc
Original Assignee
Danfoss A/S
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Danfoss A/S filed Critical Danfoss A/S
Publication of WO2017072177A1 publication Critical patent/WO2017072177A1/fr

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F19/00—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers
    • F28F19/004—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers by using protective electric currents, voltages, cathodes, anodes, electric short-circuits

Definitions

  • the present invention relate to forming a protection of the plates in order to reduce the observed corrosion problems.
  • Cathodic protection is a general used technique applied to structures to control the corrosion of a metal surface by making it into the cathode of an electrochemical cell.
  • the simple idea of the protection is to connect the metal to be protected to a more easily corroded "sacrificial metal" to act as the anode.
  • the sacrificial metal then corrodes instead of the protected metal.
  • CP can also be used in order to protect installations like water heating and storage tanks; these might be technical water systems, but also installations for drinking water in household applications. In the latter case, adverse effects of the CP system on the water quality must effectively be avoided.
  • the present system relate to a heat exchanger such as a plate type having an opening forming communication from fluid distributions to flow paths within the heat exchanger where an anode is inserted into said opening to provide galvanic protection to said heat exchanger.
  • the heat exchanger is connected to a power supply making the galvanic protection a impressed current cathodic protection having the advantage the material of the anode are not removed thus prolonging the life time before having to be exchanged.
  • the anode may be fixed to a back plate opposite to the opening in a manner where it does not interfere with the fluid connection. It optionally may be equipped with windings such that it may be fixed to the back plate by screwing, the back plate thus being equipped with the respective means to match the windings of the anode.
  • the protection operate by a Galvanic ("sacrificial") anode this having the advantage no power supply is needed.
  • the anode is positioned in the area below and opening but is formed as a wire anode being spirally wound ensuring free flow of the fluids entering from the opening to the area where it is distributed to connected flow paths formed between the individual neighbouring heat exchanger plates.
  • FIG. 7 Illustration of a plate type heat exchanger where an anode is fixed in a branch of a tap connected to the connection opening.
  • Fig. 1 illustrate one kind of heat exchanger where to the present invention with advantage could be applied, the figure showing a plate kind heat exchanger (1 ) (PHEX) formed of a plural of structured plates (2) (formed with corrugations, dimples etc. as it is well known) arranged in a stack and brazed together in their contact areas, such as but not limited to Cu brazing.
  • a top-plate (6) that often is unstructured and significantly thicker and more rigid than the structured heat exchanger plates (2), is positioned on top of the stack and comprise connection openings (3) forming inlets (T1 1 , T21 ) and outlets (T12, T22) communicating with a heating fluid circuit.
  • Each heat exchanger plate (2) comprises openings (4) such that when stacked they form distribution spaces (5) (see e.g. Fig. 3) below the connection openings (3) for fluid communication to and from the flow paths formed by the plate structures between two neighbouring plates.
  • the openings (4) are combined in pairs such that one pair form inlets and outlets for every second of the formed flow paths corresponding to the primary side with inlet T1 1 and outlet T12 to be connected e.g. to the heating fluid supply.
  • the second pair then are connected to the other every second formed of the flow paths being at the opposing sides of the plates to the first pair of flow paths correspond to the secondary side with inlet T21 and outlet T22 to be connected e.g. to the cold fluid supply to be heated, e.g. domestic water.
  • the heat exchanger (1 ) and the rear side relative to the side of the top-plate (6) is equipped with a back- plate (12) often thicker and more rigid than the heat exchanger plates (2), like the top-plate (6).
  • Some of the connection openings (3) and inlet/outlets (T1 1 , T12, T21 , T22) may be formed in the back-plate (12) rather than the top-plate (6),
  • Fig. 2 illustrate the basic principles of galvanic corrosion, that occurs if metals with different potentials are connected in an electrical leading way, e. g. by direct contact, while an electrolyte covering both metallic partners is closing the circuit.
  • the less noble (7) metal delivers electrons to the more noble (8) metal and thus, goes into solution in form of metals ions.
  • the "nobility" of a metal or an alloy depends on its potential in the electrochemical series.
  • galvanic corrosion means that the less noble material sacrifices itself for the more noble material. This is accurately the same in the application of cathodic protection, where willingly a less noble material is brought into contact with another (more noble) material in order to protect this.
  • cathodic Protection For the different metals or alloys, specific protection potentials are known which have to be reached in connection with the sacrificial material.
  • Cathodic Protection CP requires some basic facts being present in order to result in a proper corrosion protection of the parts to be protected. These technical preconditions are described in the following.
  • the protected part must provide continuous metallic conductivity of all surfaces to be protected; this is e.g. the case for copper brazed heat exchangers as illustrated in Fig. 1 .
  • the electrolyte being in contact with the metallic surfaces to be protected must provide continuous electrolytic connection; in most of the domestic water throughout this is not a problem as the electrical conductivity usually is sufficiently high.
  • the dispersion of current like the dispersion of light; in this example, the anode delivering the current would be the bulb "shining" with the electrons on the surface. As with light, there will also be “shaded” areas in the dispersion of the current; however, these shaded areas are not protected as good as areas in the "light”.
  • the current density is known from published tables and e.g. for copper the protective potential is -0.20 mV; stainless steel requires a protective potential between 0 and -0.10 mV.
  • Cathodic Protection is often accompanied by chemical changes of the media where it is installed. In the case of drinking water, no negative influences are accepted; this applies mainly for ions being transferred into the water by dissolving anodes, but also for the formation of gases, e. g. chlorine in water with high chloride content (chlorination).
  • gases e. g. chlorine in water with high chloride content (chlorination).
  • Cathodic Protection is to use galvanic ("sacrificial") anodes.
  • the protective current provided by a galvanic anode is produced by the chemical reaction of the anode with the protected cathode, leading to dissolution of the anode.
  • the dissolved material will occur in the form of sludge.
  • the speed of dissolution depends of the surface ratio between anode and cathode. A small anode area compared to the cathode surface will lead to fast dissolution of the anode; a big anode area compared to the cathodic area will increase the lift time of the anode.
  • the driving force for the chemical reaction between anode and cathode is the difference in potential as mentioned above.
  • protection potentials are formulated in standards.
  • every metal can act as an anode for a more noble metal; in practice, however, some un-noble materials are widely used for production of anodes.
  • the anode materials being widely used are aluminium, zinc and magnesium. Looking at Table 1 it is easily to see that these metals are the least noble metals available. There is also beryllium, but this is a quite seldom metal being far too expensive for being used as anode material.
  • magnesium anodes are to be used in drinking water installations, but magnesium is also favourable from an electrochemical point of view.
  • the values for the theoretical "current content” of magnesium is around 2185 Ah/kg, while the practical “current content” is around 1 100 Ah/kg which fits well the 1230 Ah/kg (originally "Amp-hrs per kg") for Mg mentioned in table 1 below showing properties of some materials for sacrificial anodes.
  • Anodes are available in different forms, as rods, bullets, plates, wires and wire mesh.
  • the form is not crucial and can be adjusted to the design requirements of the part to be protected.
  • the anodes are installed by an electrical leading mounting, e. g. a metal thread, or in an electrically isolated mode. In the latter case, the anode must be connected by a wire with the part to be protected.
  • ICCP active cathodic protection
  • Inert anodes being used for impressed current CP (ICCP) do not "sacrifice" themselves but last virtually untouched for a long time. They must be installed being electrically isolated from the metallic part to be protected. The protective current is delivered by a power supply and not by chemical reaction of an anode.
  • Inert anodes for ICCP have to be installed electrically isolated from the part to be protected.
  • the protective current is going through the medium between anode and metal surface of the part. Therefore, the medium must have some electrical conductivity as already mentioned above.
  • Inert anodes for ICCP consist of noble metals, e. g. titanium; some of them are equipped with coatings of noble metals, some have mixed metal oxide (MMO) coatings. They are available in different shapes like sacrificial anodes; often relatively thin wires are used. This is possible as the anode geometry (volume) will not be changed under service.
  • CMOS complementary metal-oxide-semiconductor
  • CMOS complementary metal-oxide-semiconductor
  • CP cathodic protection
  • the anodes (9) can be placed in the space (5) below the connection openings (3)of the plate type heat exchanger formed by openings (4), where Fig 3 illustrate an anode (9) being inserted into the space (5) having means for connecting it to the heat exchanger (1 ), where these means in the illustrated embodiment is formed as a fastener (10) adapted to be fixed to the opening (3) area, e.g. to a tap reaching out from the top-plate (6) or to the top-plate (6) itself.
  • the parts being connected may optionally be winded to secure a fixed connection.
  • the fastener (10) may form a conductive connection of the anode (9) and / or heat exchanger (1 ) to a power grid.
  • the fastener (10) comprises a path forming fluid communication between the space (5) and the heating circuit connected to the connection openings (3) where the path may distribute the fluid to the external side of the anode (9) or communicate with a flow communication path of the anode (9).
  • the anode (9) has a width smaller than that of the openings (4) of the space (5) such that fluid may be communicated along its external surface to and from the flow paths formed between the neighbouring heat exchanger plates (2), all of this formed in such a way still allowing water flow through the connection openings (3).
  • a piece (1 1 ) is formed or fixed on the inner side of the back endplate (12) of the plate type heat exchanger reaching into a space (5) and the anode then may be fixed to this piece (1 ) such as by forming an internal winded hole in the bottom of the anode (9) adapted to match similar windings of the piece (1 1 ) such that the two parts are fixed together by screwing.
  • the anode (9) formed such that is shorter than the height of the space (5) and thus does not interfere with the fluid communication through connection openings (3), just as it has a smaller width than the space (5).
  • a further problem might be the turbulent flow in the intake area. This will most likely remove corrosion products on the anodes quite fast; this makes the anode working, but on the other hand, anodes will not be protected in any kind and "corrosion", i.e. dissolution of the anode, will happen with maximum speed. It is for the time being not possible to give any figures or calculations as there is no experience in this regard.
  • the requirements for placing an inert anode for an ICCP system are the same as for a galvanic anode. However, inert anodes can be a bit smaller than galvanic anodes as their power is not depending of the volume. Thus, places providing space for installation of galvanic anodes are suitable for inert anodes too.
  • auxiliary opening (14) in connection to the space (5) and formed in the top- (6) or back- (12) plate not having the connection opening (3) forming fluid connection to the space (5).
  • the auxiliary opening (14) is formed in the back-plate (12).
  • the anode (9) then could comprise a connector (13) as seen in Fig. 5 with on the rear side being fixed in or to the auxiliary opening (14) sealing it.
  • the fixation in the usual manner may be by winding.
  • the inert anode wouldn't interfere with the water connection and it would be easy to connect the anode electrically through the connector (13) that could form part of the electrical connection from the power grid to the anode (9) and/or heat exchanger (1 ).
  • the auxiliary opening (14) may be formed such that the anode (9) may be positioned into the space (5) through it, this also making it easy to access the anode (9) e.g. when to be replaced.
  • Fig. 5 further illustrates an embodiment where the anode (9) is formed as a spiral leaving free space for the fluids to flow within the space (5).
  • This shape could also apply to any other embodiment of fixing the anode (9) in the space (5), either as illustrated or not illustrated in the present document.
  • Fig. 6 illustrate an embodiment where an electric wire (15) is inserted through the connection opening (3) to contact an anode (9) within the space (5) (the anode not seen in the figure) to the power grid.
  • the electric wire (15) may be spirally formed as in the illustration.
  • connection opening (3) comprises a tap with a branch (16) where the anode (9) may be attached by fixing means (17) e.g. similar connection (13) means as that of a previous embodiment and / or where the fixing means (17) itself form part of the anode (9).
  • the anode (9) then further may comprise the L-piece reaching through the connection opening (3) into the opening (5), where it may be fixed at the bottom.
  • This L-piece may be formed as a thin wire.
  • Titanium anodes or MMO/Mixed Metal Oxide anodes will last for decades. There might again be some influence of the turbulent water current in this area.
  • the electrical power could be of any kind of imaginable source like the public electricity network, a solar cell, a battery, a fuel cell etc.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Prevention Of Electric Corrosion (AREA)

Abstract

Des échangeurs de chaleur de manière générale et, plus particulièrement, des échangeurs de chaleur du type à plaque de cuivre (Cu) brasée, formés d'une pluralité de plaques empilées à surface structurée, brasées ensemble par du cuivre, présentent de sérieux problèmes de corrosion dans certaines parties du monde. La présente invention concerne la formation d'une protection des plaques afin de réduire les problèmes de corrosion observés.
PCT/EP2016/075806 2015-10-29 2016-10-26 Protection cathodique d'un échangeur de chaleur WO2017072177A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DKPA201500667 2015-10-29
DKPA201500667 2015-10-29

Publications (1)

Publication Number Publication Date
WO2017072177A1 true WO2017072177A1 (fr) 2017-05-04

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2751676C1 (ru) * 2019-10-24 2021-07-15 Данфосс А/С Пластинчатый теплообменник с торцевыми пластинами
CN113430525A (zh) * 2021-07-09 2021-09-24 潍柴巴拉德氢能科技有限公司 一种燃料电池发动机及其热交换器防腐蚀系统

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1379832A (en) * 1971-08-13 1975-01-08 Preformed Line Products Co Cathodic protection apparatus
GB1591123A (en) * 1977-09-26 1981-06-17 Apv Co Ltd Plate heat exchangers
WO1986001837A1 (fr) * 1984-09-19 1986-03-27 Alfa-Laval Thermal Ab Protection contre la corrosion pour echangeurs de chaleur
JPH0382783A (ja) * 1989-08-28 1991-04-08 Sumitomo Metal Ind Ltd ステンレス鋼管内面の防食方法
US20110081134A1 (en) * 2010-12-15 2011-04-07 Salyer Ival O Water heating unit with integral thermal energy storage
WO2014096105A1 (fr) * 2012-12-18 2014-06-26 Valeo Systemes Thermiques Tube plat pour échangeur de chaleur d'air de suralimentation et échangeur de chaleur d'air de suralimentation correspondant

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1379832A (en) * 1971-08-13 1975-01-08 Preformed Line Products Co Cathodic protection apparatus
GB1591123A (en) * 1977-09-26 1981-06-17 Apv Co Ltd Plate heat exchangers
WO1986001837A1 (fr) * 1984-09-19 1986-03-27 Alfa-Laval Thermal Ab Protection contre la corrosion pour echangeurs de chaleur
JPH0382783A (ja) * 1989-08-28 1991-04-08 Sumitomo Metal Ind Ltd ステンレス鋼管内面の防食方法
US20110081134A1 (en) * 2010-12-15 2011-04-07 Salyer Ival O Water heating unit with integral thermal energy storage
WO2014096105A1 (fr) * 2012-12-18 2014-06-26 Valeo Systemes Thermiques Tube plat pour échangeur de chaleur d'air de suralimentation et échangeur de chaleur d'air de suralimentation correspondant

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2751676C1 (ru) * 2019-10-24 2021-07-15 Данфосс А/С Пластинчатый теплообменник с торцевыми пластинами
CN113430525A (zh) * 2021-07-09 2021-09-24 潍柴巴拉德氢能科技有限公司 一种燃料电池发动机及其热交换器防腐蚀系统

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