DE4329595C2 - Method and device for recycling rinsing or treatment liquids - Google Patents

Description

The invention relates to a method for recycling rinsing or treatment liquids, especially from chromating baths, where the liquid from a rinsing or treatment bath evaporated and then condensed again.

The invention further relates to a device for performing of such a procedure.

DE 42 03 767 A1 describes a method and a device known according to the above type.

The wastewater or rinse water from pre-treatment plants evaporated and then condensed again, the Condensate is reused for rinsing purposes and in Evaporator concentrated rinse water in the treatment basin is returned.

Metallic parts, especially aluminum parts, are common subjected to surface treatment by chromating, wherein the surfaces of these parts to create protective layers in acidic solutions, the chromic acid or chromate as well as others  Contain components to be treated. Chromating improves the corrosion resistance, especially of aluminum and gives a good primer for paint coatings, so that a Chromating often also as a pre-treatment for one after the following paint or powder coating is carried out. The Chromating can be done in immersion baths or by spraying treatment carried out, for example, in a spray tunnel be, the chromating liquid in a collecting container is collected. There are usually several chromating baths Rinsing baths downstream, which mostly in cascade are interconnected. That is, the fluid level the rinse bath from which the treated parts pass last be kept constant while the liquid levels of the remaining rinsing baths due to overflows from the previous ones outgoing rinsing baths are kept at a constant level will. Thus, the liquid of the chromating bath from the first rinse bath added.

To maintain optimal washing results, the Cascade flushing technology requires flushing water. The amount of rinse water depends on the desired or specified conductivity of the water dripping from the workpiece after the final rinse and the number of rinses or rinsing baths.

But since mostly more liquid is required for the flushing technology is evaporated on the surface in the chromating bath Liquid removed from the chromating bath.

The liquid removed from the chromating bath can now be Evaporators are supplied and then condensed again be so that the condensate is then used as a rinsing liquid can be reused. This way the wastewater the overall system is reduced.  

Such a conventional system is shown schematically in FIG. 1 and is designated overall by the number 10 . The chromating bath 12 and the subsequent rinsing baths 14 , 16 , 18 are connected by a cascade connection in the manner already mentioned. Liquid can be removed from the chromating bath 12 and fed to an evaporator 24 for evaporation via a valve. The evaporated liquid is then condensed by means of a condenser 26 and collected in a container 22 . The condensed liquid can then be returned to the first rinsing bath 18 from the container 22 via a valve and a pump.

The residue in the evaporator is from time to time removed and disposed of.

The high restion content of the condensate obtained has proven to be problematic in such a system. In order to achieve sufficiently good washing results, a full demineralization device 20 must therefore be provided when the condensate is reused as the rinsing liquid in order to ensure the necessary purity of the last rinsing bath 18 . The use of such a demineralization plant is relatively expensive and complex. In addition, the system's ion exchangers must be regenerated from time to time as soon as they are exhausted. Hydrochloric acid and lye must be used for the regeneration. At the same time, a lot of wastewater is produced, which has to be disposed of or detoxified.

Another treatment process for those at treatment pro rinsing wastewater occurring is from DE 16 21 648 A1 known.

Here, the rinse water is added during the rinsing process dragged components separated by evaporation of water and concentrated, the vapor generated in the evaporator is fed to a heat exchanger, in which the vapor vapor below Heat emission to a liquid flowing through the heat exchanger condensed and the condensed vapor vapor to the rinse water is added again in a rinsing device.

An ion exchange system ensures that the rinsing water has the necessary purity.

The previously known system is therefore with the previously described Disadvantages of an ion exchange system.

A similar system, which also uses an ion exchanger is used is from "INDUSTRIAL AND ENGINEERING CHEMISTRY", 47 (1955), pages 85/86.

In addition, DE 15 21 858 A1 describes a method for Known to apply chromate coatings on metal surfaces, in which the workpieces with an acidic, aqueous, at least a compound of hexavalent chromium and activator ions containing solution are brought into contact, from to Removal of the metal surface or by reduction of the hexavalent chromium came into the solution a part separated and passed over a cation exchange resin and after returning to the treatment solution is passed, the concentrations of effective Be components constant within certain limits by adding being held. For this purpose the conductivity of the  Treatment solution returned solution at any interval measured and when a specified deviation is exceeded from the setpoint the proportion of the cation exchange resin flowing solution changed so that the set point again is achieved.

However, this procedure only concerns the monitoring of Ion concentration in a treatment liquid to this to act within a desired setpoint range. Evaporation and subsequent condensation occurs here not done.

The invention is therefore based on the object of a method for recycling rinsing or treatment liquids, in particular that of chromate baths, in which the liquid from a Rinsing or treatment bath evaporates and then again is condensed to improve such that a possible simple and inexpensive process management guaranteed and the environmental impact is kept as low as possible. An application is also intended in particular for chromating driving advantageously be possible.

Furthermore, a device is to be specified which is to be implemented tion of such a method is suitable.

With regard to the method, this object is achieved according to the invention solved in that in a method of the aforementioned The type of residue content of the condensate is monitored, and that the condensate when a specified limit is undershot the residual content of the rest of the condensate, the rest ion content exceeds the limit is separated.  

According to the invention, the fact is exploited that at one Evaporation process the resulting condensate first has relatively high restion content, since in the first phase the evaporation relatively many foreign components in the condensate be kidnapped. As evaporation continues the residual content of the condensate decreases over time, so after a period of time in a batch evaporation process the condensate is very pure, so that this immediately can be used for rinsing purposes without additional Actions are required.

According to the invention, the restion content of the resulting Condensate is monitored and then if this a predetermined Below the limit, the condensate from the rest of the condensate sat, which has a higher restion content, separated.

Thus the condensate, which has a sufficiently high purity has easily be used for flushing purposes, so that also the high demands on the washing quality high-quality parts can be achieved,  without the use of a demineralization facility is. This also allows guidelines, such as the so-called comply with the "GSB guideline" regarding the flushing technology, after which the dripping water in high-quality parts Conductance of maximum 30 µS / cm. According to the invention the condensate is only used for rinsing purposes, if its residue content has a predetermined limit falls below, so that the rinsing bath only condensate with a sufficiently high purity is supplied.

In an advantageous development of the invention, an im Evaporator residue usually completely with the condensate, the restion content of which Limit exceeded, mixed and the treatment bath again fed.

This measure has the advantage that the evaporation residue, which for the most part still contains valuable substances that are can be reused almost completely Treatment bath is fed again instead of being disposed of. According to the invention the fact is further exploited that in the condensate, which has a high restion content, likewise also valuable substances are contained in the treatment treatment bath, in particular reused in the chromating bath can be. Thus, the treatment solution, esp in particular the chromating solution again essentially Mixing the evaporation residue with the condensate, which has a high restion content, in a corresponding ver reattachment and at least partly to replace the Use chromate bath.

With the method according to the invention the total amount of wastewater is reduced without this Use of a demineralization plant is absolutely necessary.  

Although the restion content in a particularly simple Execution of the method also, for example, with the help of Handheld meters could be monitored, then a manual one Redirection of the condensate when a predetermined one is reached Restion content is preferably carried out at one automated process of the residual content of the condensate monitored by monitoring electrical conductivity.

In an advantageous development of the method, the Ver vaporization temperature reduced by negative pressure.

This on the one hand increases the risk of incrustation and The build-up of residues in the evaporator is reduced. On the other hand is the result of the reduced evaporation temperature Evaporation carried out in a particularly gentle manner, so that in particular a thermal decomposition of components of the Treatment bath is avoided. For example, if Chromating solution prepared, it is only through the lowered Evaporation temperature decomposes the components of the Chromating solution largely avoided during evaporation. Consequently both the evaporation that occurs during evaporation residues as well as the condensate to recycle the chroma use animal solution.

It is understood that only one Treatment bath again setting the treatment bath to the required target concentration can be achieved. Without further additions, a suitable one will be used despite re-introduction Mixture of the evaporation residue and the condensate from From time to time the treatment bath may be chemically exhausted that then a complete or at least partial exchange is required. However, can be by the inventive  Process achieve multiple use of the rinse water, thereby on the one hand there is a cost reduction and on the other hand the accumulation of waste water and waste to be disposed of considerably is reduced.

A device for performing the invention The method comprises at least one rinsing or treatment bath, whose liquid can be fed to an evaporator, and a condensation downstream of the evaporator device for condensing the steam, and further comprises a device for monitoring the restion content of Condensate on, which with a switching device for diversion of the condensate when falling below a predetermined limit of the restion content is coupled.

It is understood that the application of the invention is not limited to Rinsing or treatment baths is limited, but that the Invention equally advantageous for recycling dishwashing or treatment liquids can be used in spray systems, in which the liquids are supplied to spray registers. Since only one switching device is required to Redirect condensate if a corresponding change in the Restion salary is registered is a quick response the device according to the invention for sudden changes ensures the restion content of the condensate, so that a good separation is ensured.

In an advantageous development of the invention is for monitoring the restion content a device for monitoring the electrical conductivity of the condensate is provided.  

In this way, the restion content can be particularly simple Way are monitored, and the switching device for redirection the condensate can be monitored with the device electrical conductivity are automatically coupled.

At least two containers for the condensate are expedient provided which with the switching device for separate Introduction of the condensate into the tank depending on the Restion content are coupled.

Falls below the restion content or the electrical conductivity the specified limit value, the condensate introduced into a separate container, while at over If this limit value is exceeded, the condensate in another Container is collected. The liquid from the container with a low restion content can then be fed to a rinsing bath be while the liquid from the container with high Restion content in the manner already mentioned for re-preparation of treatment liquid, for example for the re-use of chromate solution can be mixed with residues from the evaporator.

In a further advantageous embodiment of the invention Treatment bath with one or more rinsing baths in cascades circuit coupled, and the treatment bath is connected to the Ver The steamer can be coupled to process the liquid.

As mentioned earlier, the condensate has low resections content preferably fed to one of the rinsing baths for rinsing purposes, while the condensate with high restion content at least partially mixed with the residue in the evaporator is to at least partially replace the treatment bath of treatment liquid to be supplied again. In which Evaporator, preferably at a reduced temperature  a vacuum source is operated as a vacuum source in advantageous development of the invention a water jet pump be provided.

Depending on the measured electrical conductivity the condensate can then either with a correspondingly high conductivity ability to open an upstream valve via a first water jet pump is introduced into the container, in which the condensate with a high residue content is collected, while falling below the specified limit first valve is closed and the condensate when opened a second valve of a second water jet pump which opens into the second container, which is used for storage the liquid with a low restion content is provided.

Instead of having a water jet pump for each container, can also in an advantageous development of the invention common water jet pump can be provided, which with the Condensate is fed and their output depending on the measured conductivity of the condensate either in the Containers with condensation or low content other container is fed.

In this way there is only a single water jet pump required, so that there is a cheaper structure.

Further features and advantages of the invention result from the following description of preferred exemplary embodiments with reference to the drawing. Show it:

Figure 1 shows a conventional device in which a treatment bath with three rinsing baths is connected in cascade and liquid from the treatment bath an evaporator for evaporation and subsequent condensation can be supplied.

Figure 2 shows an inventive device for recycling rinsing or treatment liquids in a chroma animal process.

Fig. 3 shows the profile of the electrical conductivity of the condensate as a function of evaporation time in a schematic representation;

FIG. 4 shows a detail of a device slightly modified compared to FIG. 2, in which only the part relating to the container and the water jet pump is shown;

Fig. 5 shows a further modification of the apparatus shown in FIG. 2, and

Fig. 6 shows a further modification of the device according to. 2. A first embodiment of a device according to the invention is shown in Fig. 2 and indicated generally by the numeral 30. Fig.

A treatment bath 32 for chromating is connected to subsequent rinsing baths 34 , 36 , 38 in a cascade connection, as indicated by arrow 46 . In addition, a further rinsing bath 40 is provided, which is arranged independently of the other rinsing baths 34 , 36 , 38 and, in order to maintain a particularly high purity of the rinsing liquid, is cleaned in a circuit by a pump 44 with a demineralization system 42 .

The treatment bath 32 is connected via a line 54 and a valve 56 to an evaporator 50 , which is heated via a heating coil 52 . Vapor generated in the evaporator 50 is fed via a line 64 to a condensation device 66 , which can be a cooler cooled by a fan. At the output of the condensation device 66 , a conductivity meter 68 is provided, by means of which the electrical conductivity of the condensate can be monitored. The condensate is then fed via a line 70 either to a first valve 72 and a downstream water jet pump 76 which opens into a first container 88 , or via a second valve 74 to a downstream second water jet pump 78 which opens into a second container 90 . Both water jet pumps 76 , 78 are each fed from the tank 88 , 90 in the circuit via a pump 80 , 82 and a line 84 , 86 . Liquid can be removed from the first container 88 via a valve 94 and fed via a line 96 to a pump 62 which is connected to the treatment bath 32 via a line 48 .

An evaporation residue can also be removed from the condenser 50 via a valve 58 and likewise fed to the pump 62 via a line 60 , which is connected to the line 48 which opens into the treatment bath 32 .

Liquid can be withdrawn from the second container 90 via a valve 98 and can be introduced via a pump 100 and a line 92 into the last 38 of the rinsing baths 34 , 36 , 38 which are connected to one another via a cascade connection.

The conductivity meter 68 is connected via a control line 67 to control electronics 69 , by means of which control lines 71 , 73 control the opening and closing of the valves 72 and 74, respectively.

To explain the process sequence of the flow of the electrical conductivity of the condensate after evaporation and subsequent condensation is in Fig. 3 schematically shown over the time.

As curve A shows for a batch evaporator, this is electrical conductivity at the beginning of the evaporation process relatively high, which shows that the condensate is still with many Is contaminated with foreign ions. After a few hours, the elec tric conductivity, however, so that the now obtained Condensate a significantly lower conductivity and thus a has very low restion content.

The dashed line C represents one here arbitrarily given setpoint for the electrical conductivity. Im Example shown is the setpoint after about two and a half Hours of evaporation is reached and then continues Course essentially adhered to, with periodic fluctuation gene can occur. Curve B shows the course of the elec conductivity with a continuously operated Vaporizers that take a considerable amount of time has a higher value.

According to the invention, a batch evaporator is now used, whereby with the help of a device for monitoring the resection volume stop, preferably with the help of a conductivity meter, it is determined when the restion content the specified Falls below the limit. If the limit is undershot  the condensate is collected separately from the rest of the condensate The condensate obtained in this way with a low restion content can be used advantageously for rinsing while the Condensate with a high content of residues together with the treatment bath with residues from the evaporator in a suitable mixing ratio ratio can be fed again.

The system shown in Fig. 2 is therefore operated as follows:

At the beginning of an evaporation process, the first valve 72 is normally open, while the second valve 74 is closed. At the start of an evaporation process after the evaporator 50 has been filled, the condensate is thus passed through the first valve 72 into the first water jet pump 76 and thus into the first container 88 .

As soon as the conductivity meter 68 registers a drop in the electrical conductivity below the predetermined target value, the first valve 72 is closed and the second valve 74 is opened via the control electronics 69 , so that the condensate now obtained, the electrical conductivity of which is below the predetermined limit value , in the second water jet pump 78 and thus in the second container 90 .

Should the conductivity rise again in the course of the evaporation process in such a way that the target value is exceeded, this is registered via the conductivity meter 68 , and the condensate is redirected into the first container 88 by opening the first valve 72 and closing the second valve 74 becomes.

The result of this is that, in the course of the evaporation process, only condensate with a high conductivity and thus a high content of residues is collected in the first container 88 , while only condensate with a low electrical conductivity, that is to say with a low content of residues, is collected in the second tank 90 becomes.

The condensate from the second container 90 is removed via a valve 98 and used via the pump 100 and the line 92 to supplement the rinsing liquid of the rinsing bath 38 . On the other hand, the condensate in the first container 88 has a significantly too high restion content to be used for rinsing purposes.

The condensate from the first container 88 is therefore removed via the valve 94 and via the line 96 together with evaporation residues, which are removed from the evaporator 50 via the valve 58 , fed to the pump 62 in a suitable mixing ratio and via the line 48 in the treatment bath 32 initiated in order to supplement or refresh the treatment bath.

According to the invention, the fact that the condensate with a high content of residues still contains a large number of valuable substances which can be fed back into the chromating bath as active components is advantageously used to supplement the chroma bath. In order to avoid decomposition of the chromating solution during evaporation, the evaporation is carried out under reduced pressure, which is why the water jet pumps 76 and 78 are provided.

According to the invention, the treatment bath 32 , the target concentration of which constantly decreases as a result of the rinsing liquid that regularly runs in from the first rinsing bath 34 , can be returned to the target value without the need to use fresh chromating solution. Resection portions still initially contained in the condensate are advantageously returned to the treatment bath.

Overall, this is done without the additional use of flushing solutions and without additional desalination plant the quality of the rinsing significantly improved and at the same time a recovery of the Ingredients of the treatment bath enables.

From time to time stands despite repatriation of evaporation back and despite returning condensate content with high residual ions yet exhausted the treatment bath 32 when it is chemically consumed.

The treatment bath 32 must therefore be replaced completely or at least partially from time to time.

However, during continuous operation, the chemical consumption of the treatment bath 32 is considerably reduced by the partial recycling of the evaporation residues and the condensate with a high content of residues, which leads to considerable cost savings and to waste reduction.

It goes without saying that the additional rinsing bath 40 is only optionally provided and that, depending on the desired rinsing quality, this additional bath can be completely dispensed with or that the number of cascade-like coupled rinsing baths 34 , 36 , 38 can be increased or decreased.

A modification of the device according to FIG. 2 is shown in FIG. 4. The same parts are identified with the same reference numbers. Since FIG. 4 only shows a section of the overall device, namely the area of the two containers 88 , 90 and the water jet pump, the illustration is somewhat enlarged compared to FIG. 2.

The condensate is fed via line 70 to a common water jet pump 128 , which is fed either via a valve 122 from the first container 88 or via a valve 124 from the second container 90 by means of a pump 126 via the line 130 . The liquid emerging from the water jet pump 128 is directed via a line 132 either via a valve 134 into the first container 88 or via a valve 136 into the second container 90 . The switching of the valves 122 , 134 and 124 or 136 takes place via the control lines 71 or 138 and 73 or 140 depending on the measured conductivity by the control device 69 . If the electrical conductivity of the condensate exceeds the predetermined limit value, the valves 122 and 134 are open, while the valves 124 and 136 are closed. Thus, high-conductivity condensate gets into the first tank 88 .

If the electrical conductivity of the condensate falls below the predetermined limit, which the control device 69 registers via the control line 67 , the valves 122 and 134 are closed by the control device 69 and the valves 124 and 136 are opened, so that the condensate is now in via the valve 136 arrives at the second container 90 , from which the water jet pump 128 is fed in a circuit via the valve 124 and the pump 126 . Thus, in the second container 90, condensate with a low residue content is again obtained, while in the first container 88, condensate with a high residue content is collected. The condensate from the second container 90 can thus again be removed via the valve 98 and used in a known manner, for flushing purposes, while the condensate from the first container 88, as already mentioned previously removed via the valve 94 and may be used to supplement the treatment bath 32 .

A device that is simplified compared to FIG. 2 is designated overall by the number 110 in FIG. 5. The same reference numbers have been used for corresponding plant parts. The device 110 differs from the device 30 according to FIG. 2 in that no device for lowering the evaporation temperature is provided, so that no water jet pumps are provided.

Although such a device for reprocessing Chromating liquid is not suitable, as this can result would thermally decompose the higher evaporation temperature, is such a simplified device for regeneration other treatment baths suitable, which have a higher thermal Have durability.

A further modification of the system according to the invention compared to the embodiment according to FIG. 5 is shown in FIG. 6 and is designated overall by the number 150 .

The same reference numbers have been used for corresponding system parts. The device 150 differs from the device 110 according to FIG. 5 essentially in that the collecting container for collecting the condensate has been completely dispensed with and that the evaporator can be supplied not only with liquid from the chromating bath 32 but also optionally from the first rinsing bath 34 .

Liquid can thus optionally be supplied to the evaporator 50 via the line 54 and the valve 56 from the chromating bath 32 or via a valve 152 and the line 154 from the first rinsing bath 34 . It goes without saying that liquid could of course also be fed to the evaporator from other rinsing baths and that a simultaneous supply of liquid from the chromating bath 32 and one of the rinsing baths may also be possible.

If the condensate is measured by the conductivity meter 68 to exceed the predetermined limit value, the valve 74 is closed via the control device 69 and the valve 72 is opened, so that the condensate is fed directly via a line 158 to the pump 62 , so that it is passed through the line 48 gets back into the chromating bath 32 .

If, on the other hand, the conductivity falls below the limit in the condensate, the valve 72 is closed and the valve 74 is opened, so that the now very pure condensate is fed directly into the last rinsing bath 38 via the pump 100 and a line 156 .

Claims (15)

1. Process for recycling rinsing and treatment liquid, in particular from chromating baths, in which the liquid is evaporated from a rinsing or treatment bath ( 32 ) and then condensed again, characterized in that the evaporation process is carried out as a batch process in that the residue content of the condensate is monitored, and that the condensate is separated from the rest of the condensate, the residue content of which exceeds the limit value, when a predetermined limit value of the residue content is undershot. 2. The method according to claim 1, characterized in that the condensate separated off when the predetermined limit of the restion content is undershot is fed to a rinsing bath ( 38 ) for rinsing purposes. 3. The method according to claim 1 or 2, characterized in that an evaporation residue obtained in the evaporator ( 50 ) is at least partially fed back to the treatment bath ( 32 ). 4. The method according to one or more of the preceding claims, characterized in that the condensate, the Restionengehalt exceeds the predetermined limit, the treatment bath ( 32 ) is at least partially fed back. 5. Method according to one or more of the preceding Claims, characterized in that the restion content by monitoring electrical conductivity is monitored.   6. Method according to one or more of the preceding Claims, characterized in that the evaporation temperature is reduced by negative pressure. 7. Apparatus for recycling rinsing or treatment liquid by a method according to one of claims 1 to 6, characterized in that at least one rinsing or treatment bath ( 32 ) is provided, the liquid of which can be fed to an evaporator ( 50 ) that a the evaporator ( 50 ) downstream condensation device ( 66 ) is provided for the condensation of the steam, and that a device for monitoring the restion content of the condensate is provided, which with a switching device ( 72 , 74 ; 134 , 136 , 138 , 140 ) for diverting the Condensate is coupled below a predetermined limit of the restion content. 8. The device according to claim 7, characterized in that the device for monitoring the restion content is a device ( 68 ) for monitoring the electrical conductivity speed. 9. Apparatus according to claim 7 or 8, characterized in that at least two containers ( 88 , 90 ) are provided for the condensate, which with the switching device ( 72 , 74 ) for separate introduction of the condensate into the container ( 88 , 90 ) in Dependence on the restion content are coupled. 10. The device according to one or more of claims 7 to 9, characterized in that a treatment bath ( 32 ) is coupled with one or more rinsing baths in cascade connection, and that the treatment bath ( 32 ) with the evaporator ( 50 ) for returning evaporator residues in the treatment bath ( 32 ) can be coupled. 11. The device according to one or more of claims 7 to 10, characterized in that the condensate with a low restion content one of the rinsing baths ( 38 ) can be supplied for rinsing purposes. 12. The device according to one or more of claims 7 to 11, characterized in that the container with the condensate with a high restion content ( 88 ) can be coupled to the treatment bath ( 32 ) for at least partial recycling of the condensate with a high restion content. 13. The device according to one or more of claims 7 to 12, characterized in that the evaporator ( 50 ) with at least one vacuum source ( 76 , 78 ; 128 ) can be coupled. 14. The apparatus according to claim 13, characterized in that the vacuum source ( 76 , 78 ; 128 ) is a water jet pump. 15. The apparatus according to claim 14, characterized in that a common water jet pump ( 128 ) is provided which is fed with the condensate and the output depending on the measured conductivity of the condensate either in the container with condensate low resions content ( 90 ) or is fed into another container ( 88 ).