DE7432299U - DEVICE FOR CORROSION PROTECTION OF HOT WATER RESERVOIRS, AS WELL AS THESE RESERVOIR PIPELINES AND FITTINGS - Google Patents

Description

G 3/74 K / Kn.

Guldager Electrolyse GmbH & Co. KG, 4660 Gelsenkirchen-Buer

Device for the corrosion protection of those exposed to hot water Containers and pipes and fittings downstream of these containers.

The invention relates to a device for the corrosion protection of warm water-driven containers as well as pipes and fittings downstream of these containers by means of sacrificial anodes made of pure aluminum which are built into the containers and are supplied with external current and which are fed by at least one direct current source. - ^:

Devices of this type are known from DT-PS 2,144,514. There, electrically insulated pure aluminum anodes are installed in the container with the plus pole connected to a DC power source. The container

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with its usually made of unalloyed, black or unalloyed, hot-dip galvanized steel, walls and walls to be protected against corrosion are at the minus pole connected to the DC power source. The tubes are preferably made made of unalloyed, hot-dip galvanized steel. The externally charged Pure aluminum anodes serve two purposes:

a) The cathodic corrosion protection of the tank including its internals,

b) electrolytic water treatment to protect the pipelines downstream of the tank from corrosion and fittings.

ι The terms "cathodic corrosion protection" and "electrolytic j

see water treatment "are explained below.

Cathodic corrosion protection

The corrosion of metals in an electrolyte is an electrochemical process in which it occurs on the metal surface with the formation of potential differences, a current flows from the anodic to the cathodic areas. After Publication by J. Lepper in "Industrie-Anzeiger" No. 23, from March 20, 1962, p.11 ff., Run according to the thermo-

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dynamic representation of anodic and cathodic partial reactions, a typical anodic partial reaction is the Metal dissolution:

Important cathodic partial reactions are the reduction of oxygen and protons:

+ H ₂ O + 2e ~ ► 2 (OH) "(II)

H ⁺ + e ~ ► H (III)

Through the external supply of electrons, the cathodic Partial reactions added electrons and thus the anodic partial reactions, i.e. the metal dissolution the container walls and fittings are reduced. The corrosion is then completely suppressed if that of the external current source flows through an auxiliary anode built into the container on the container walls Great after is at least equal to the cathodic partial current strength. This amperage is therefore used as the minimum operating amperage of the cathodic corrosion protection I.

In the electrodynamic representation, it is assumed that

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that on the metallic container surface geometrically separated - in a rough approximation arranged like a chessboard - anodic and cathodic regions with potentials U. and Uj. are distributed. The suppression of by the driving tension

U = ^u a ~ ^U K

Corrosion current caused between the local anodic and cathodic areas by the application of an external current means that the cathode potential U _{v is} reduced to at least the rest potential U. of the anode. This is the case when the container wall is protected by means of external current when the sum of the resting potential of the cathode and the voltage drop across the cathode resistance is equal to the resting potential of the anode. With R _v as the resistance in the cathodic zone, there is therefore the minimum current strength of the cathodic corrosion protection

¹ K ■ ^(U AV ^{/ R} K ■■. ·: ' ^(V)

In the practice of corrosion protection, it is less the absolute value of the minimum current I _K than the so-called minimum operating current density of the cathodization i. as the operating variable used, which is the quotient of Ι _χ , measured in mA and

represents the container surface F, measured in m.

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The quantity i "depends on a whole series of variables, for example on the electrolytic conductivity, the temperature, the p" value, the flow rate, etc. It accordingly has a considerable spectrum, but it also has a whole spectrum for a very specific case certain value. This can be approximately determined in the laboratory and in practice can be determined with any precision by examining the open container at certain time intervals.
For water of medium hardness, the i _v values are between

100 mA / m ² and 250 mA / m ² .

Electrolytic water treatment

The electrolytic water treatment is the subject of DT-PS 1 771 805. While the effects of the cathodic corrosion protection are limited to the immediate current range of the anodes within the container and are thus connected Electrolytic water treatment enables the pipelines and fittings cannot be protected Build-up of anti-corrosion layers in the pipes and fittings. This procedure - in the literature also with "Guldager Electrolysis process "called - is based on the following principle:

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Pure aluminum anodes built into the container are generated as a result of the current flowing through them into the electrolyte
electrolytically dissolved. The reaction products of the deposited aluminum with the electrolyte are partly ir.
the pipelines downstream of the container
and through colloidal chemical secondary reactions with ■ the pipeline material cause the formation of cover layers,

which, with a suitable external current density, each additional Kcrro-:;

Prevent Ii sion attack. That in the dissolution of the aluminum jj

'i high-volume, strong || formed on the pure aluminum anode Hydrous aluminum hydroxide hydrate goes into colloidal

Form in solution. When passing the pipelines form

then, depending on the pipe material, cover layers consisting of mixed crystals of aluminum, iron or zinc hydroxides ^! stand and, depending on the water composition, i

j have silicon dioxide and lime deposits. |

The current densities required for the formation of pore-free and dense protective layers j exceed the minimum operating current density of cathodic corrosion protection i ,, considerable.

A functional connection between Kir.destbetriebsstromensity of the cathodic corrosion protection i '^ and the current density of the electrolytic water treatment i., Is in the
DT-PS 1 771 505 mentioned above. According to this, i ^ must be reduced by 50 %

*) / O C \ r \ ^ γλ

'H · ^ι ί''.' I- y < Π P Π1 7R

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• ·

up to 300 % _{t are} preferably increased by 100 % to 2GO % _t , ie

i = 1 ς i Ii i '(VI)

¹ W ¹ ^ ¹ K ** ^ ¹ K

preferably

i - 2 i ^ i ( ^VI1 )

W ^ ¹ K ^ K »

where the preferred range is generally for hot water systems is applicable.

It is the object of the invention, the known devices for electrolytic V / as Ser treatment in economic and tech nical aspects to be optimized.

This object is achieved in a device for corrosion protection of the type mentioned in that fiction according to the anode material is distributed so that apart from the predominantly arranged in a first part of the container Sacrificial anodes made of pure aluminum are predominantly provided in a second part of the container arranged inert anodes.

Corrosion protection devices designed in this way have a number of technical and economic factors Benefits on. This can be seen from the following:

The inventive use of inert anodes that practically do not dissolve under the influence of the current, it is possible to keep sludge generation in the lower part of the container to a minimum to lower.

In-depth experimental and theoretical investigations led to the surprising finding that the pure aluminum anodes arranged in the lower part of the container only make a negligible contribution to the production of aluminum compounds that are active on the outer layer, and that the aluminum hydroxide hydrate produced there for the most part, namely about 90 % _t as a top layer inactive anode sludge settles on the bottom of the tank. This eliminates the invention.

Another advantage is that built-in components, e.g. heating devices, Temperature measuring devices and the like, are less exposed to sludge deposits. So it could be under Particularly unfavorable circumstances happen that the efficiency of built-in heating devices is reduced quite significantly has been.

A considerable part of the tank for electrolytic Electrical energy added to water treatment, which used to produce nearly useless aluminum hydroxide sludge can now be saved.

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With this saving of electrical energy, there is a reduction the costly sacrificial anode material, which has to be renewed every several years.

Inert anodes alone are problematic with regard to the formation of oxyhydrogen, especially in hot water systems. The oxyhydrogen gas mixture that is always formed there and that collects in the upper bowl of the container must be in be made harmless at regular intervals while observing the strictest security measures. In addition, get inevitably also parts of the oxyhydrogen gas mixture in the downstream pipelines, thus providing for the building in those who have such systems installed represent an operating risk. These facts made experts reluctant to use inert anodes or not to be used at all with regard to the existing safety regulations.

The situation is completely different with a corrosion protection device according to the invention: the oxygen which is also formed here as a result of the inert anodes does not even get into the upper bowl of the container, where it could form the dangerous oxyhydrogen gas mixture with the hydrogen produced. The anodically dissolving aluminum of the sacrificial anodes binds the oxygen; In addition, the oxygen even supports the formation of aluminum compounds that are active on the surface.

Another surprising effect of the invention is made clearly follows: Scientific investigations of the Sludge have shown that in special cases, in particular, if this sludge is not drained regularly, due to the oxygen depletion of the water conditions created for anaerobic bacterial growth, which can lead to malodorous: water. The one under the influence The oxygen that forms in the inert anode prevents this entirely without counteracting the corrosion protection.

The advantages of the invention therefore exist in particular in economic terms in that

a) aluminum anode material is saved,

b) the consumption of electrical energy falls,

and in technical terms in that

c) the sludge production drops to a minimum,

d) the period between desludging is no longer critical,

e) the efficiency of heating and measuring devices is not impaired,

f) oxyhydrogen formation can be prevented and

g) anaerobic bacterial growth, which leads to a reduction the water quality leads, can be switched off.

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With conventional water heaters or boilers, the hot water outlet is close to the upper cooling of the tank, the cold water inlet near the lower curving. According to the invention, the inert anodes are therefore in the one adjacent to the cold water inlet point, the pure aluminum anodes in the middle and that of the hot water outlet point adjacent upper container part, each container part corresponding to one third of the container volume, which is present between the cold water inlet point and the hot water outlet point.

If heating devices or other built-in components are provided in the container, they are also assigned inert anodes, since such internals are predominantly in the lower part of the container are located.

In order to achieve an optimal protective effect, it is advisable to distribute the entire amount of anode material so that at least 33 1/3 %, preferably 33 1/3 to 50 % of the amount of anode material consists of pure aluminum, whereby the anode material used to protect the internals is not is included.

The im

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Dimensioning regulations given under German patent 2 1 ^ 4 514, It should be noted that the anode systems, which are made up of sacrificial and inert anodes are to be put in relation to the corresponding quantities.

To achieve an optimal protective effect and to avoid side effects, both the inert anode system and the sacrificial anode system are fed from separate protective circuits, the effective current density of the inert anodes being approximately the minimum operating current density of the cathodic corrosion protection i. is equivalent to. The pure aluminum anodes are i according to "the teaching of German Patent · 1,771,805 with the optimum for the particular application operating current density of the electrolytic water treatment. _R fed.

While an adjustable power source, e.g. a variable transformer, is sufficient for the power supply of the inert anodes downstream rectifier, the power source for the sacrificial anodes should be designed such that it automatically adapts to different operating conditions. This can be implemented, for example, in that i ^ varies in particular as a function of the flow rate will.

The anode material for the sacrificial anodes is - according to the

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DT-PS 1 771 805 or DT-PS 2 144 514 pure aluminum intended, i.e. aluminum with the least possible contamination by other metals or metal compounds, since those are the Significantly accelerate self-corrosion of the anodes, so that their operating time is greatly reduced and thus the profitability is questioned. A noble metal or one with a is recommended as the anode material for the inert anodes Metal core coated with inert material. The metal core can be made from one or more of the metals titanium, tantalum, Zirconium or niobium, or be composed of an alloy which mainly consists of at least one of these metals. as Inert material is a 2.5 to 10 µm thick coating Platinum, iridium, rhodium, palladium, ruthenium or osmium or from their alloys or from any of the aforementioned oxides Platinum metals and platinum metal alloys, preferably with a base metal oxide addition of up to 50 percent by weight, to recommend.

Further details of the invention, in particular advantageous electrode configurations and details of the protective circuits are explained in more detail below with reference to the exemplary embodiments shown in the drawings.

Here shows:

Fig.l is a longitudinal section through a hot water tank with built-in inert and pure aluminum anodes,

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2 shows a cross section in the direction Ä through the upper ^! Container part of the hot water tank shown in Fig.l,

3 shows a cross section in direction B through the lower Container part of the hot water tank shown in Fig.l and

4 shows an embodiment of a circuit arrangement for Feeding of the inert and pure aluminum anodes built into the hot water tank according to FIGS. 1-3.

The embodiment shown in Figures 1-3 represents a hot water tank in which all for the immediate Understanding of the invention, essential details have not been omitted. This container can be used as a hot water tank serve, but is also used when starting up the built-in heating devices, not shown in the figures To use water heater. The construction of the heating devices of Warir.water heaters with pure aluminum anodes is For example, Figures 4, 5, 9, 10 and 14 of DT-PS 2 144 refer to.

The container consists of a substantially cylindrical Middle part 1, to which a lower curling 2 and a

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Connect the upper dome 3. The container is provided with a neck piece ¹ I, which is closed by a manhole cover 5 and with a serving as the cold water entry point "6 nozzles. Are located in the upper dishing a hot water outlet 7 and an air vent valve 8. At the bottom of the container is in the lower dishing a desludging nozzle 9 is attached.

On four bushings 10, 11, 12 and 13 (the bushings 11 and 13 cannot be seen from the figures; their location will only indicated by the reference numbers) is an anode cage made of pure aluminum with electrodes A, B and C. arranged. The ends of the anodes A facing the upper dome are connected to one another by anode pieces B. It it is advisable to at least partially pass the anode cage in the area of the fastening point on the bushings 10-13 Additionally angled anode reinforcement pieces C made of pure aluminum to solidify. A further stiffening of the pure aluminum cage cannot be done by a "in .'den" figures shown, C-shaped pure aluminum ring are effected, which the lower dome facing ends of the anodes A connects with each other. On the other four bushings IA, 15, 16 and 17 is a cylindrical inert anode arrangement, which includes the anodes D, E, F attached. G is another inert anode. Which is parallel to the longitudinal axis of the Container extending anodes D are

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here by the ring-shaped anodes E and F firmly connected to each other, so that a rigid and torsion-free Construction results.

As a material for both pure aluminum and inert anodes

flat bars with a cross section of 20xoO mm are used. However, it is also conceivable to use wire with a diameter of preferably 0.5 to 1.5 mm, round rods up to a maximum of 50 mm diameter and flat bars up to 90 mm edge length to be used as inert anode material.

In the case of the container of the exemplary embodiment that holds approx. 2 no water, approx. 25 g of pure aluminum are per liter of container volume built-in. In the case of containers with a larger 3 πι content, less Material required per unit of volume. Most of the time, a few g of pure aluminum per liter of container volume are sufficient. That However, anode material is always distributed in all containers in such a way that that the inert anodes D, E and F in the lower one adjacent to the cold water inlet point 6, the pure aluminum anodes A, B and C are arranged in the middle and the upper container part adjacent to the hot water outlet point 7.

The circuit arrangement according to Figure 4 essentially has two separate circuits on:

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The first circuit - fed by the secondary winding I of the transformer 101 - supplies the inert anodes D, E, F via the rectifier and a fuse 103, the second circuit - fed by the secondary winding II - supplies a current controller S ₁ , a rectifier 104 and a fuse 105 the pure aluminum anodes A, B, C. A third secondary winding III is used to supply power to a control device S to be explained in more detail. The secondary winding I has various taps I ,, Ip, ♦ ··> I _n , for varying the protective current density i, of the inert anode system. An adjustable resistor 106 enables fine adjustment of the protective current density i. . The total flowing protective current of the inert anode system can be read on an ammeter 107, that for the sacrificial anodes on an ammeter 107 '.

The circuit for the pure aluminum anodes A, B, C is somewhat more extensive. In order to adapt the current density of the electrolytic water treatment i _ir to the respective operating conditions, this circuit is provided with a current regulator S ₁ , which in turn is connected to the control device S. The current regulator and control device are designed so that the intermittent water consumption or the required current density i of the electrolytic water treatment can be taken into account. To example-

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way to take into account the relatively low water withdrawal during the night, the control unit S has a Timer Z au: ", cie acts in such a way that the current density i is reduced in certain, adjustable times.

Another way of influencing the protective current density i. consists in controlling the electricity feeding the pure aluminum anodes A, 3, C directly depending on the water consumption. For this purpose, a flow monitor SW is provided in the pipeline 108 (indicated schematically). If water is withdrawn at one point in the pipeline network, the flow monitor responds and causes the control unit S to increase the current density i. In order to take into account brief water withdrawals which do not in themselves require an increase in current density of i _t , a delay circuit VZ known per se can be arranged between the flow monitor SW and the control unit. On the other hand, it has proven to be advantageous, whenever water has been withdrawn, not to lower the current density of the electrolytic water treatment i again immediately, but to maintain it for a certain adjustable time at the previous level corresponding to the increased consumption . For this purpose, the control device has a switch-off delay for the current controller S ^, which can be combined with the aforementioned switch-on delay circuit in one structural unit.

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The physical and chemical properties of the feed water are usually the same for certain systems. However, changes in the water supply can result in non-negligible changes in the protective current density of the cathodization i. and thus the protective current density of the electrolytic water treatment i _w . In order to take these changes into account, the invention provides for suitable detectors D-, Dp,. These detectors in turn act together with the control device S on the current controller S_ and thus enable "a
Control of the current strength or the protective current density as a function of these quantities.

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Claims (1)

α 3/74 Protection claims 1. Equipment for the corrosion protection of hot water vehicles nen containers as well as pipes and fittings connected downstream of these containers by means of sacrificial anodes made of pure aluminum built into the containers, which are exposed to foreign current and which are fed by at least one direct current source, characterized in that the anode material is distributed in such a way that, in addition to the predominantly in A first part of the container arranged sacrificial anodes (A, B, C) made of pure aluminum predominantly in a second Part of the container arranged inert anodes (D, E, P, G) are provided. Device according to claim 1, characterized in that the inert anodes (D, E, P, G) i ⁿ th ^e bottom of the cold water inlet point (6) adjacent, and the center, the pure aluminum anodes (A, B, C) in the central and the hot water outlet (7) adjacent upper container part are arranged, each of said container parts corresponds to a third of the container volume that is present between the cold water inlet point (6) and hot water outlet point (7). 743229S 08.0176 "" - 21 - O 3/74 3. Device according to claim 1 or 2, characterized in that inert anodes are arranged in the vicinity of internals are. 4. Device according to claim 1, 2 or 3, characterized in that at least 33 1/3 % _t, preferably 33 1/3 to 50 % of the total amount of anode material consists of pure aluminum, not including the anode material used to protect the internals. 5. Device according to one or more of claims 1 to 4, characterized in that for containers up to approx. 3 m content, a maximum of 25 g of pure aluminum per liter of container volume are intended as sacrificial anode material. 6. Device according to one or more of claims 1 to 4, characterized in that for containers with a Contents greater than 3 m, a maximum of 18 g of pure aluminum per liter of container volume al3 sacrificial anode material provided are. 7. Device according to one or more of claims 1 to 6, characterized in that the sacrificial anodes (A, B, C) in Are arranged in the form of a cage whose diameter belonging to the head side is equal to or greater than that (t * t t * - 22 "- G 3/74 the diameter belonging to the long side and whose longitudinal axis coincides with the longitudinal axis of the container, and that the inert anodes (D, E, F), provided they are not used for Serve cathodic protection of any internals, arranged symmetrically with respect to the longitudinal axis of the container are. 8. Device according to one or more of claims 1 to 6, characterized in that the sacrificial anodes (A, B, C) arranged in the form of a wheel rim lying symmetrically to the longitudinal axis of the container with at least one spoke are. 9. Device according to one or more of claims 1 to 8, characterized in that the anode material consists of wire with a diameter of preferably 0.5 to 1.5 mm, consists of round bars with a maximum diameter of 50 mm or flat bars with a maximum edge length of 90 mm. 10. Device according to one or more of claims 1 to 9, characterized in that the surface of the inert anodes (D, E, F, G) made of a noble metal, preferably a Platinum group precious metal. 11. Device according to one or more of claims 1 to it I I * 1 ι a · · f • it ifi I | l r ItII · ■ It - 23 - G 3/74 9, characterized in that the inert anodes consist of metal cores which are coated with preferably 2.5 to 10 μ thick inert materials. 12. Device according to claims 10 and 11, characterized in that that the inert material consists of platinum, iridium, rhodium, palladium, ruthenium or osmium or from their Alloys or an oxide of these platinum metals and platinum metal alloys, preferably with a base metal oxide addition of at most 50 percent by weight. 13 · Device according to claim 11, characterized in that that the core of the inert anode is made up of one of the metals titanium, tantalum, zirconium, niobium or an alloy which consists mainly of at least one of these metals. 7432299 01/08/76