WO2004050952A1

WO2004050952A1 - Method and device for preventing corrosion in an installation

Info

Publication number: WO2004050952A1
Application number: PCT/DE2002/004445
Authority: WO
Inventors: Werner Seita
Original assignee: Werner Seita
Priority date: 2002-12-04
Filing date: 2002-12-04
Publication date: 2004-06-17
Also published as: DE10297847D2; AU2002360889A1

Abstract

The invention relates to a method and a device for preventing corrosion in an installation using a liquid. Said method comprises the following steps: introduction of the liquid (1) into an internal chamber (11) of a container (4), in which an anode (10) consisting of magnesium and a cathode (16) are arranged, in such a way that a respective contact is formed between the liquid (1) and the anode (10) and between the liquid (1) and the cathode (16); generation of a periodic current using a current source (21); application of the periodic current to the anode (10) and the cathode (16); formation of sacrificial micro-anodes by means of the fractal decomposition of the anode (10); diffusion of at least part of the sacrificial micro-anodes into the liquid (1); and flushing of the liquid (1) containing said sacrificial micro-anodes out of the container (4).

Description

Method and device for avoiding corrosion in a plant

The invention relates to a method and a device for avoiding corrosion in a plant, in which a liquid is enriched with micro sacrificial anodes made of magnesium by means of a reaction process in a reactor which is supported electrolytically.

Corrosion damage to water supply systems is a major economic problem. According to a report by the Association of German Property Insurers, more than half of all reported water damage in the building services sector is due to corrosion. There are estimates that approximately 5-8% of an industrialized nation's national income is destroyed annually by corrosion. This estimate does not take into account the secondary energy losses to be set as much higher. B. caused by cross-sectional constricting rust bulbs in pipes or rust deposits on heating surfaces.

In a few areas of technology, corrosion protection is neglected as in house technology, which however transports the most important food, "water". This neglect causes very high additional costs for the renovation, since the installation is almost always installed in the masonry and the renovation can only be achieved by replacing the pipes.

The use of magnesium for corrosion protection in both galvanic and classic cathodic corrosion protection (KKS) has been state of the art for decades. Known corrosion protection processes use sacrificial magnesium anodes. Here, a liquid is enriched with magnesium ions. The term liquid in the meaning used here includes liquids with a water content, in particular drinking water and process water. To achieve an enrichment of the liquid with magnesium ions with a method according to the prior art, the liquid must remain in a special anode chamber for a longer time, as a rule more than 30 minutes, or through several chambers or connected to one another in a row Container flow. Storage tanks with volume are used to process even smaller volume flows (> 2m ³ / h) of several hundred liters necessary. In order to ensure sufficient enrichment, very large cathode areas, asymmetrically installed anode towers with considerable amounts of pure magnesium and the use of potentiostats are required. An inner wall of the anode chamber or of the container, which is generally made of steel, usually serves as the cathode surface. A method of this kind is described in Austrian patent specification 280728.

With the help of this established process, corrosion protection can be guaranteed for containers if properly designed. However, a corrosion protection effect in a downstream installation or even a renovation of an already partially corroded piping system is not possible because the magnesium ion is reactive, reacts quickly and is therefore ineffective in terms of corrosion. Furthermore, the methods described above can often not be implemented because of the space requirement and the high costs associated with the creation of the corrosion protection system.

In contrast to the classic processes mentioned above, which follow the laws of homogeneous, aqueous chemistry, newer processes are based on heterogeneous and catalyzed processes. Already at the beginning of the 1920s and 1930s it was observed that the classical use of magnesium sacrificial anodes showed an electrical energy balance that deviated significantly from the classic stoichiometry. It has been known since the mid-1950s that magnesium dissolves under the influence of galvanic-chemical factors rather than under the typical electrochemical conditions according to other laws. In 1954, Petty et al. (Petty R .; Davidson A .; Kleinberg A., J. Am. Chem. Soc. 76, 366 (1954)) states that the formation of local elements in the magnesium anode surface is particularly violent and whole metal particles break out or possibly to a colloid-like aggregate formation of an (unstable) monovalent, hydra-

9-1- tied magnesium species could lead, which reacts to Mg.

It was shown that under certain conditions, for example with systematic adaptation of the electrode polarization of anodically switched metal, magnesium disintegrates according to fractal laws, colloids containing clusters being formed in layers. The resulting reactive particles contain a variable proportion of undamaged, ie metallic Magnesium in the cluster center, unused magnesium in the intermediate layer as a solid compound of the sum formula Mg ₂ O, which is embedded in a root structure, together with oxide hydroxide of magnesium, and a relatively good (meta) stability in water, especially with low conductivity having. The outermost colloid layer is linked with magnesium hydroxide and possibly magnesium carbonate with the former, formed and, with small colloids and from conductivities above approx. 200 μS / cm, results in a very good corrosion protection effect, so that even in drinking water these colloids can be used effectively. The estimated diameter for these aggregated colloids is approximately 250-600 µm, the primary particles probably alone containing approximately 2,000 univalent and probably also metallic, ie intact but redox-active particles.

It has been found that the integration into an electrolytic process is necessary in order to provide and form a sufficient number of mobile micro sacrificial anodes by means of such an electrolysis-induced method. Such processes take place in a container. In an interior of the container, a liquid flows around a magnesium anode and a cathode. An inner wall of the interior of the container, which is generally made of stainless steel, generally serves as the cathode. A constant direct current from a current source is applied to the anode. This promotes the fractal decay of the magnesium anode into magnesium micro sacrificial anodes and the diffusion of these magnesium micro sacrificial anodes into the liquid. With the liquid, the magnesium micro sacrificial anodes flow into a pipeline system arranged downstream of the container and can prevent corrosion in this, just as effectively as in the container, so that corrosion protection for systems with a container and pipeline system is formed.

The object of the invention is to provide an improved method for preventing corrosion with the aid of micro sacrificial anodes made of magnesium and a device for carrying out the method in which an intended decomposition reaction of a magnesium anode is promoted and an enrichment of a liquid with the Micro sacrificial anodes is increased. The object is achieved by a method according to claim 1 and an apparatus according to claim 8.

The invention comprises the idea of applying a periodic current to the anode and cathode. This supports the formation of micro sacrificial anodes that are both mobile and redox-active and effectively prevent corrosion in a system. By using the periodic current, both the anode reactions and the corresponding associated cathode reactions are promoted.

An advantage of the invention is that due to the use of the periodic current, both a pulse current density, a pulse time and a time between two pulses can be selected independently of one another. With a method according to the state of the art, which uses a constant direct current, however, only an average current density can be selected. This has proven to be non-functional. Because the parameters pulse current density, pulse time and time between the two pulses can be freely selected, it is possible to easily adapt to inexactly predictable variables such as flow velocity, hydrodynamic conditions, liquid analysis, etc. by changing these electrical parameters.

Furthermore, the use of a time-periodic current means that, in comparison to the use of a direct current, as is provided in the prior art, a transpassive metal resolution is already possible at a lower average current density, which is necessary for the formation of the desired redox-active particles, namely the mobile ones Micro sacrificial anodes made of magnesium, is required. The number of mobile micro sacrificial anodes formed can be selected to be so high that a corroded downstream pipe system can be remediated. Furthermore, when the periodic current is used, the heavy metal contamination of the liquid associated with any corrosion, in particular in lead or copper pipes, is also avoided.

A further development of the method provides that the time-periodic current is formed as a sequence of rectangular pulses. An advantage of this development is that a rectangular pulse current can be generated electronically with simple means. Another embodiment provides that the liquid is introduced tangentially to a side inner wall of the interior of the container in the interior of the container in order to generate a cyclonic movement of the liquid in the interior of the container. This has the advantage that the liquid travels a longer way in the interior and is thus in contact with a cathode surface for longer, which promotes electrolytic cathode reactions and thus an intended decomposition of the anode.

An advantageous further development of the method for avoiding corrosion consists in that the liquid is introduced by tapering a cross section in an inlet of the container in the interior of the container, so that a turbulent flow is generated in the interior of the container. A turbulent flow promotes the rapid removal and delivery of particles contained in the liquid in a diffusion layer on the cathode, which leads to an improvement in the reaction kinetics of the cathode reactions.

An expedient development of the invention provides that a flow signal is generated by means of a flow detector as a function of a throughput of the liquid through the container, and the application of the periodic current to the anode and the cathode is controlled by a control device as a function of the flow signal. This ensures that decomposition of the anode in micro sacrificial anodes is only supported when liquid is removed by means of the periodic current. In this way, optimal utilization of an anode material is achieved.

Another embodiment of the method provides that ions dissolved in the liquid are removed in a cation exchanger before the liquid is introduced into the interior of the container. In this way, use of the method with so-called hard liquids, i.e. H. Liquids with an alkaline earth metal content of more than 2 mmol / 1 are possible, which would otherwise fail due to secondary reactions of the liquid.

Another expedient development consists in dividing the liquid into a partial flow and a further partial flow by means of a separating device, the partial flow flowing through the cation exchanger and the container and the partial flow with the micro- Sacrificial anodes are enriched and combined with the further partial flow, which is bypassed the cation exchanger and the container in a bypass tube. It is advantageous that the container for the enrichment of the liquid with micro sacrificial anodes only has to be designed for a subset of the total amount of liquid that flows through the entire system. The container can thus be smaller than in a method which does not use a diversion of the further partial flow past the cation exchanger and the container.

An advantageous further development of the device for avoiding corrosion is that an elongated outlet pipe is arranged in a longitudinal direction of the container in the interior of the container, one end of the outlet pipe being fixedly connected to the outlet and another end of the outlet pipe being a small distance away has a bobbin bottom of the container and the inlet is arranged on a bobbin bottom opposite end of the container. This enables the liquid to be guided in a so-called outflow-upflow process, ie. H. good liquid guidance along the anode and cathode is achieved.

A further development of the device provides that the cathode comprises a side inner wall of the interior of the container and an outer wall of the outlet tube. This can save a separate cathode. A compact construction of the container becomes possible.

A further development of the invention is that a minimum distance of the anode from the outer wall of the outlet tube is equal to a minimum distance of the anode from the inner side wall of the interior of the container. In this way, an optimal current density field is formed in the liquid in the interior of the container during the application of the periodic current to the anode and the cathode to promote the formation of micro sacrificial anodes and an enrichment of the liquid therewith. Another development provides that the anode comprises several rods. In this way, a surface of the anode can be enlarged compared to a cylindrical anode. Furthermore, rods can be manufactured inexpensively and are easy to handle during maintenance.

Another embodiment of the device for preventing corrosion provides that the several rods of the anode are arranged distributed on a circle which is concentric with the inner side wall of the interior of the container, the inner side wall of the interior being cylindrical. This is a simple arrangement that ensures that all rods are equidistant from the surfaces of the cathode.

It is advantageous that an area ratio of a surface of the anode to a surface of the cathode is at most 1 to 4 and ideally 1 to I. This ensures that an optimal amount of magnesium is present in the device and that there is no excessive or weak decomposition of the anode, which would result in unnecessary anode wear or an inadequate corrosion protection effect.

Another embodiment provides that the inlet is arranged tangentially to the inner side wall of the interior of the container. This causes a cyclonic flow in the container, which leads to a longer residence time of the liquid in the interior of the container and requires an enrichment of the liquid with micro sacrificial anodes.

An advantageous embodiment provides that a cross section of the inlet has a taper. This can be used to generate a turbulent flow, in particular at the cathode. The resultant rapid mass transfer and mass removal requires the cathode reactions and thus also a decomposition reaction of the anode in micro sacrificial anodes.

Another embodiment can provide that a flow detector for generating a flow signal is arranged on the container. This enables the removal of the liquid to be monitored over time. Another expedient development comprises a control device coupled to the flow detector for controlling the application of the periodic current to the anode and the cathode as a function of a flow signal generated by the flow detector. This enables optimal control of the device, which leads to optimal utilization of the anode material used.

An advantageous embodiment provides that a cation exchanger is arranged at the inlet. The cation exchanger prevents a liquid with a high proportion of dissolved ions from entering the interior of the container. A liquid with a high ion content in the interior of the container could lead to undesirable secondary reactions or changes in the chamber resistance.

A further development of the invention comprises a separation device with an inlet, an outlet and a further outlet for dividing a liquid flow, the one outlet being in fluid communication with the outlet via the cation exchanger and the container and the further outlet with the outlet via a bypass pipe the container is in flow connection. This device enables only a portion of the liquid to be softened and enriched with micro sacrificial anodes. As a result, a container volume of the container can be designed to be smaller at a fixed daily throughput than in the case of a device which has no bypass pipe.

Another development of the invention is that the control means for periodically varying the current can generate a rectangular pulse current. Such a control means is particularly easy to manufacture from electronic components and is therefore particularly inexpensive.

The invention is explained in more detail below using exemplary embodiments with reference to a drawing. Here show:

Figure 1 is a schematic sectional drawing of a device for corrosion prevention;

FIG. 2 shows a current-time graph of a time-periodic current; FIG. 3 shows a further schematic illustration of a device for preventing corrosion;

FIG. 4 shows a photographic illustration of another embodiment of a device for preventing corrosion; and

Figure 5 is a schematic strand diagram of an embodiment of a device for reducing corrosion.

Figure 1 shows a schematic sectional view of a device for corrosion prevention. A liquid 1 flows through a flow detector 2 and an inlet 3 into an interior 11 of a container 4, which is a reactor container. The container 4 comprises a side wall 5, a clapper base 6, legs 7 and a blind flange 8. Instead of the legs 7, a wall mounting rail can be provided. As an alternative to the embodiment shown in FIG. 1, the flow detector 2 can also be arranged at an outlet 19 of the container 4. The flow detector 2 can comprise paddle or piston switch systems for a smaller container volume. For containers 4 with a nominal diameter of DN 150 or more, only calorimetric flow detectors are preferred.

The blind flange 8 is arranged on an end 9 of the container 4 opposite the clapper base 6 and is releasably connected in a fluid-tight manner to the closure of the container 4 with the side wall 5 of the container 4. At a lower end of the bobbin case 6, an outlet tap 28 is arranged, which can be used for pressure relief in the interior 11 during maintenance operations and for flushing out larger flushed-in particles.

In the interior 11 of the container 4, an anode 10 made of magnesium is arranged, which comprises rods 12. The bars 12 are round. The anode 10 is electrically insulated from the blind flange and is arranged on the blind flange 8. The bushings 12 are connected in an electrically conductive manner to terminals 14 via bushings 13. A side inner wall 15 of the interior 11 of the container 4, which is conductive, forms part of a cathode 16.

An outlet pipe 17 extends from the blind flange 8 into the interior 11 of the container 4th into it. One end 18 of the outlet pipe 17 is connected to an outlet 19. Another end 20 of the outlet tube 17 ends near the clapper bottom 6. An outer wall 27 of the outlet tube 17 serves as a further part of the cathode 16.

Due to the arrangement of the inlet 3, the outlet pipe 17 and the outlet 19, a flow direction through the interior 11 of the container 4 is predetermined for the liquid 1. The incoming liquid 1 initially flows downward in the interior 11, is then deflected by the clapper base 6, in order to then flow upwards through the outlet pipe 17 to the outlet 19 and to leave the container 4 through the outlet 19. The outlet pipe 17 is also referred to as a deflection pipe. Because of the flow behavior, the method for avoiding corrosion, which uses the container 4 shown in FIG. 1, is referred to as the outflow-upflow method.

A current source 21 is electrically connected to the connection contacts 14 of the anode 10 and the cathode 16 by means of electrical lines 22, 23. A signal line 24 connects the flow detector 2 to a control device 30, which is included in the embodiment according to FIG. 1 by the current source 21. The current source 21 further comprises a control means 31 for generating a time-periodic current.

A periodic current is understood to mean any current with an amplitude that fluctuates in time around a predetermined amplitude value. In this sense, a time-periodic current is not only a current that has the same amplitude value in each case after a fixed time interval, but rather any current in which the predetermined amplitude value occurs after each of a plurality of possibly differently long time intervals, the amplitude possibly during the plurality time intervals of different lengths are different from the predetermined amplitude value.

A method for avoiding corrosion using the device according to FIG. 1 is described below. The liquid 1 flows through the flow detector 2. A flow signal is generated here. The liquid 1 is then introduced through the inlet 3 in the interior 11 of the container 4. The inlet 3 is arranged on the container 4 so that the liquid 1 enters the interior 11 tangentially to the side inner wall 15. As a result, a cyclonic flow of the liquid 1 becomes in the interior 11 causes. A distance covered in the interior 11 of the container 4 is lengthened by a factor of 2.8 due to the cyclonic flow. A residence time of the liquid 1 in the interior 11 of the container 4 is thus extended due to the cyclonal flow. This means that the time period available for enriching the liquid 1 with micro sacrificial anodes is longer.

The inlet 3 has a taper 29 of its inner cross section. The flow through the taper 29 creates a turbulent flow of the liquid 1 in the interior 11 of the container 4. This results in a cyclonic, turbulent flow of the liquid 1 in the interior 11, which flows around the cathode 16 and the anode 10. The turbulent flow, particularly on the cathode surface, is deliberate and decisive. For an effective process sequence, not only a metal dissolution of the magnesium of the anode 10 is required, but also a rapid sequence of associated cathode reactions. The cathode reactions which inevitably always take place at the cathode 16 with constituents of the liquid 1 are accelerated into a diffusion layer on the cathode 16 by rapid mass transfer and mass transfer, which is promoted by the turbulent flow.

Since self-corrosion and the resulting jamming of an anode surface play an important role in the decomposition of the anode 10 in micro sacrificial anodes, an external current supply of the anode 10 made of magnesium is important. When a periodically current is used, stationary diffusion layers on the anode 10 and cathode 16, which are determined by hydrodynamics, overlap periodically periodically pulsating diffusion layers.

In order to obtain a particularly favorable design of the diffusion layer on the cathode 10 and the diffusion layer on the anode 10, the outlet pipe 19 is arranged centrally in the interior 11, which is cylindrical. The rods 12 of the anode 10 are arranged on a circle, the center of which is concentric with the cylindrical inner side wall 15 of the interior of the container 4. A radius of the circle is chosen so that a minimum distance of the rods 12 to the side inner wall 15 of the interior 11 of the container 4 is equal to a minimum distance of the rods 12 to the outer wall 27 of the outlet pipe 17.

The current source 21 generates in cooperation with that encompassed by the current source 21 Control means 31 the periodic current with which the anode 10 and the cathode 16 are applied.

FIG. 2 shows an example of a current-time graph of a time-periodic current to act on the anode 10 and the cathode 16. A current density i is plotted against a time t. In direct current electrolysis according to the prior art, only an average current density can be freely selected. This has proven to be non-functional. When using direct current, the size of an anodic current depends on hydrodynamic conditions. Due to a low chamber resistance, which is determined by a surface 25 of the anode 10 and a surface 26 of the cathode 16 and distances between the surfaces 25, 26, the anode 10 can already with a current of 25 at voltages below 0.5 to 24V up to 1500 mA per m surface 26 of the cathode 16 in a turbulent liquid flow. When using the time-periodic current in the form of a pulse current, the average current density is determined by three independently selectable parameters, a pulse current density i _p , a pulse time t _p and a time between two pulses t ' _p . In Figure 2, these individual parameters are exemplified for a rectangular pulse current.

In addition, the duration t _{pp of} the application of the anode and the cathode can be selected. Since the micro sacrificial anodes diffusing into the liquid 1 have to be carried away from the container 4 with a sufficiently large amount of liquid, it is advantageous to control the periodic current by means of the control device 30 (cf. FIG. 1). The control device 30 causes the anode 10 and the cathode 16 to be supplied with the periodic current as a function of the flow signal of the flow detector 2. It is advantageous to provide that the periodic current is only applied when the flow detector generates a flow signal, ie, a flow of the liquid 1 into or out of the container 4 is detected. The flow signal is transmitted to the control device 30 via the signal line 24.

The decomposition reaction of the anode 10 strongly depends on an area ratio of the surface 25 of the anode 10 and the surface 26 of the cathode 16. The area ratio should be a maximum of 1: 3 to 1: 4 and ideally 1: 1. The area ratio of anode 10 to cathode 16 must, however, be related to a container volume of the container 4, as will be explained in more detail below, since otherwise only an insufficient number of redox-active, mobile micro sacrificial anodes will be formed or the anode will be drained too much. which necessitates frequent maintenance or frequent changing of the anode 10.

The area ratio can be optimized by varying a nominal width of the container 4, which can be in particular between DN 80 to DN 800, and changing the length of the container.

When dimensioning the container 4, it should be noted that, due to the diffusion-controlled processes described, the container volume specifies a maximum amount that can be enriched per unit of time with a sufficient number of micro sacrificial anodes for corrosion protection. A day is usually chosen as the reference variable for the time unit, so that a maximum daily volume and a maximum daily throughput correspond to a container volume. Based on a volume calculation, the daily throughput for tank 4 with a nominal diameter up to DN 150 can be quantified with a factor of 280 to 400 times the tank volume. For tank 4 with a nominal diameter above DN 150 to DN 800, the daily throughput rates have to be stated with an 80 to 150 times the factor of the tank volume. The specified ranges are due to different operating modes, which result from simultaneity calculations for a dispensing behavior of the liquid 1 (the more consumers, i.e. the more daily throughput is generated, the fewer simultaneity factors are given).

FIG. 3 shows an illustration of an embodiment of a device for preventing corrosion. Identical features in FIGS. 1 and 3 are designated with the same reference symbols. In this embodiment, the container 4 comprises a tubular frame 32, the bobbin case 6 welded to it with the outlet tap 28 and the blind flange 8. The blind flange 8 is detachably and fluid-tightly connected to the tubular frame 32 by means of a seal 33 and screws 34.

On the blind flange 8, the inlet 3 with the flow detector 2, the outlet 19 and a concealed anode system arranged in the interior of the container 4 are arranged. The individual components consist of commercially available materials. The pipe frame 32 is made from a material with a number 1.4301, the flange 8 from a material with a number 1.4541 and the fittings from a material with a number 1.4571.

A turbulent flow in the interior of the container 4 is achieved by tapering a cross section of the inlet 3 and by introducing the liquid 1 tangentially to the side inner wall 15 in the interior 11 of the container 4. In the embodiment according to FIG. 1, the tangential introduction of the liquid is made possible by the inlet 3 welded tangentially into the side wall 5. The embodiment according to FIG. 1 is advantageous for the container 4 with a nominal diameter of more than DN 150. If the nominal width of the container 4 is less than or equal to DN 150, as in the embodiment according to FIG. 3, it is advantageous if the inlet comprises a 90 ° pipe piece fastened to the flange 8, which is located in the interior 11 of the container 4 and whose mouth is arranged tangentially to the inner side wall 15 of the container 4.

Up to a hardness range of approximately 2.0 mmol / 1 alkaline earth metals, a device for preventing corrosion can be operated without a liquid treatment system. A liquid that contains more than about 2.0 mmol / 1 alkaline earth metals is referred to here as a hard liquid. In the case of a hard liquid or a liquid with a high lime precipitation potential, at least part of the liquid 1 is softened by means of a commercially available cation exchanger before it is passed through the container 4. Usually it is only necessary to soften a partial flow of liquid 1 and to enrich it with micro sacrificial anodes. Depending on the daily throughput, about 50% of the liquid has to be passed through the cation exchanger and the container 4.

FIG. 4 shows a section of a plant in which the invention is carried out. This system is intended for use with a hard liquid 1. The same reference numerals are used for the same features in FIGS. 1, 3 and 4. The liquid 1 passes through an inlet 60 into a separating device 51. In the separating device 51, the liquid 1 is separated into a partial flow 52 and a further partial flow 53. The partial stream 52 passes through an outlet 64 into a cation exchanger 54 for softening the partial stream 52. Subsequently, the partial stream 52 flows through the flow detector 2 and enters the interior 11 of the container 4. The cathode 16 comprises the inner side wall 15 of the inner space 11 and the outer wall 27 of the outlet tube 17. The rods 12 arranged in the inner space 11 of the container 4 form the anode 10. When flowing through the flow detector 2, the control device 30 is caused via the signal line 24, one To generate electricity by means of the current source 21, which is converted into a periodically periodic current by means of the control means 31. As long as the flow detector detects a flow of the liquid, the periodic current is applied to the anode 10 and the cathode 16. The control means 31 is electrically conductively connected to the current source 21 and the anode 10 via supply lines 61 and 63.

Due to the tangential feed and the tapering 29 of the cross section in the inlet 3, the liquid 1 flows around the cathode 16 and the anode 10 with a cyclonic, turbulent flow. Here, the anode 10 decomposes by means of electrolytically induced fractal decay into micro sacrificial anodes which diffuse into the liquid 1 of the partial flow 52. The partial stream 52 enriched with micro sacrificial anodes flows through the outlet tube 17 to an outlet 19. The outlet 19 is connected via a diversion tube 67 to a further outlet 68 of the separating device 51, so that the further partial stream 53 is in contact with the softened, micro- Partial stream 52 enriched with sacrificial anodes combined and can enter a downstream line system.

FIG. 5 shows a schematic strand diagram of an embodiment of the device for preventing corrosion. Identical features in FIGS. 1 to 5 are provided with identical reference symbols. The liquid 1 flows through a main shut-off valve 70. After flowing through a water meter 71 and a further valve 72, the liquid 1 is filtered in a filter 73. Liquid 1 is assumed to be a hard liquid. At a T-piece 79, the liquid 1 is divided into the partial flow 52 and the further partial flow 53. The partial flow 52 flows through the shut-off valve 74 into the cation exchanger 54. The partial flow 52 is softened in the cation exchanger 54. Any softening device can be used instead of a cation exchanger. The partial flow 52 flows via a connecting line 75 into the container 4, in which the partial flow 52 is enriched with micro sacrificial anodes. The partial flow 52 enriched with micro sacrificial anodes flows through a further shut-off valve 76 to a blending valve 77. stream 53, which reaches the blending valve 77 via the diversion pipe 67, is combined with the partial stream 52 enriched with micro sacrificial anodes and flows into house distribution lines 78.

The features disclosed in the above description, the drawing and the claims can be of importance both individually and in any combination for realizing the invention in its various embodiments.

Claims

Expectations

1. A method for avoiding corrosion in a system with a liquid (1), the method comprising the following steps:

- Introducing the liquid (1) into an interior (11) of a container (4) in which an anode (10) made of magnesium and a cathode (16) are arranged, so that between the liquid (1) and the anode (10 ) and a contact is formed between the liquid (1) and the cathode (16);

- Generating a time-periodic current by means of a current source (21);

- Applying the periodic current to the anode (10) and the cathode (16);

- Formation of micro sacrificial anodes by fractal decomposition of the anode (10);

- diffusing at least part of the micro sacrificial anodes into the liquid (1); and outflow of the liquid (1) from the container (4).

2. The method according to claim 1, characterized in that the time-periodic current is formed as a sequence of rectangular pulses.

3. The method according to claim 1 or 2, characterized in that the liquid is introduced tangentially to a side inner wall (15) of the interior (11) of the container (4) in the interior (11) of the container (4) to a cyclonic To generate movement of the liquid (1) in the interior (11) of the container (4).

4. The method according to any one of the preceding claims, characterized in that the liquid (1) through a taper (29) of a cross section in an inlet (3) of the container (4) in the interior (11) of the container (4) introduced is so that a turbulent flow is generated in the interior (11) of the container (4).

5. Verfaliren according to any one of the preceding claims, characterized in that by means of a flow detector (2) in dependence on a throughput of the liquid speed (1) through the container (4) a flow signal is generated and the application of anode (10) and the cathode (16) with the periodic current is controlled by a control device (30) as a function of the flow signal.

6. The method according to any one of the preceding claims, characterized g ekennz ei chnet that in the liquid (1) dissolved ions removed before introducing the liquid (1) in the interior (11) of the container (4) in a cation exchanger (54) become.

7. The method according to claim 6, characterized in that the liquid (1) is divided into a partial flow (52) and a further partial flow (53) by means of a separating device (51), the partial flow (52) through the cation exchanger ( 54) and the container (4) flows and the partial flow (52) is enriched with the micro sacrificial anodes and combines with the further partial flow (53) which is connected to the cation exchanger (54) and the container (4) in a bypass pipe ( 67) is passed by.

8. Device for avoiding corrosion in a liquid (1) carrying system with a container (4) having an inlet (3) for introducing the liquid (1) into an interior (11) of the container (4) and an outlet (19) for the outflow of the liquid (1) from the interior (11) of the container (4), a cathode (16) arranged in the interior (11) of the container (4), one in the interior (11) of the container (4) arranged anode (10) made of magnesium, which is in liquid contact with the cathode (16), and a current source (21) for generating a current which is electrically conductive with the anode (10) and the Cathode (16) is connected, marked by a control means (31) for automatic time-periodic variation of the current.

9. The device according to claim 8, characterized in that an elongated outlet pipe (17) is arranged in a longitudinal direction of the container (4) in the interior (11) of the container (4), one end of the outlet pipe (17) being fixed the outlet (19) is connected and another end of the outlet pipe (17) a small distance from one Has bobbin bottom (6) of the container (4) and the inlet (3) is arranged at an end of the container (4) opposite the bobbin bottom (6).

10. The device according to claim 9, characterized g ekennzei chnet that the cathode (16) comprises a side inner wall (15) of the interior (11) of the container (4) and an outer wall (27) of the outlet tube (17).

11. The device according to one of claims 8 to 10, characterized in that a minimum distance of the anode (10) from the outer wall (27) of the outlet tube (17) is equal to a minimum distance of the anode (10) from the side inner wall (15th ) of the interior

(11) of the container (4).

12. The device according to one of claims 8 to 11, characterized in that the anode (10) comprises a plurality of rods (12).

13. The apparatus according to claim 12, characterized in that the plurality of rods

(12) the anode (10) are arranged distributed on a circle which is concentric with the side inner wall (15) of the interior (11) of the container (4), the side inner wall (15) of the interior (11) being cylindrical.

14. Device according to one of claims 8 to 13, characterized in that an area ratio of a surface of the anode (10) to a surface of the cathode (16) is at most 1 to 4, preferably 1 to 1.

15. The device according to one of claims 10 to 14, characterized g ekennzei chnet that the inlet (3) is arranged tangentially to the side inner wall (15) of the interior (11) of the container (4).

16. The device according to one of claims 8 to 15, characterized g ekennze i chnet that a cross section of the inlet (3) has a taper (29).

17. Device according to one of claims 8 to 16, characterized in that a flow detector (2) for generating a flow signal is arranged on the container (4).

18. The apparatus of claim 17, g ekennze i chnet by a with the flow detector (2) coupled control device (30) for controlling the application of the anode (10) and the cathode (16) with the periodic current depending on one of the Flow detector (2) generated flow signal.

19. Device according to one of claims 8 to 18, characterized in that a cation exchanger (54) is arranged at the inlet (2).

20. The device according to claim 19, characterized by a separating device (51) having an inlet (60), an outlet (64) and a further outlet (68) for dividing a liquid flow, the outlet (64) via the cation exchanger ( 54) and the container (4) with the outlet (19) in a flow connection and the further outlet (68) via a diversion pipe (67) with the outlet (19) of the container (4) is in a flow connection.

21. Device according to one of claims 8 to 20, characterized in that the control means (31) for periodically varying the current can generate a rectangular pulse current.