DE10005968A1 - Water softener process for pump action movement of fluid in closed circuit used as ion transport medium - Google Patents

Abstract

In a process to operate an electrode de-ionization water softener assembly (1), ions from a permeate are removed from a chamber of dilute fluid and transported by an electric field to a chamber holding concentrated fluid. The ions are then removed by a medium flowing through the concentrate chamber. The concentrate moves especially within an internal closed circuit and following discharge from the concentrate chamber is employed as a transport medium and is returned to the concentrate chamber inlet by pump action. Also claimed is an electrode de-ionization assembly with an internal closed-circuit flow arrangement. The transport medium is especially not fully returned to the overall system. The arrangement has one or more concentrate chambers in which the discharge from the chamber outlet is returned to the chamber inlet. The electro-conductivity of the concentrate is monitored and adjusted to below a pre-determined threshold prior to its return to the concentrate chamber. Adjustment is effected by the admixture of permeate having a lower conductivity. A constant pressure drop is maintained between the dilute and concentrate chambers. The water softener assembly combines reverse osmosis with electrode de-ionization. Permeate from the reverse osmosis is discharged to the electrode de-ionization unit.

Description

The present invention relates to a method for operating an electrodeionization system, where in the case of permeate ions to be processed in an electric field from at least one di luatkammer deposited in at least one concentrate chamber and in the form of a concentrate by means of a transport medium flowing through the at least one concentrate chamber be ported. The present invention further relates to an electrodeionization system with min at least one diluate chamber for a permeate to be processed, which consists of at least one in two ion-selective membranes embedded ion exchange material is formed, at least one concentrate chamber delimited by two ion selective membranes with an inlet opening and an outlet opening for a transport medium for the removal of the separated from the permeate ten ions.

Electrodeionization (EDI) is a combination of one or more ion exchangers, For example, a mixed bed ion exchanger and an electrodialysis. It is used for water treatment tion, for example the production of pure and ultrapure water and is predominant for this purpose downstream of a softening system and a system for reverse osmosis, whereby before the Softening system can also be provided a pre-filtration system. In these plants the water to be treated, which is usually of drinking water quality, calcium and Magnesium salts freed and desalted in a first step. The subsequent electrodeioni station is used for demineralization. The ions are removed from the water to be treated removed and then migrate from the in an electric field water to be treated through ion-selective membranes accumulate on the other Side of the membrane in a concentrate chamber and are removed using a transport medium transported. At the same time, the ion exchanger is regenerated in an electrical field.

The resulting treated water is practically free of ions and therefore has an extremely high ge conductivity.  

However, there are some problems with this method. Due to the electric field precipitates easily occur in the transport medium, which are the ion-selective membranes lay or block. This happens especially when the process from the Reverse osmosis or softened water from the drinking water network, d. H. Soft water used from which protons and hydroxyl ions are withdrawn for regeneration of the ion exchanger become. The precipitation, for example of lime and alkaline earth sulfates, leads to irreparable damage the electrodeionization system, if for example the softening system or the prefiltration system fail. These transport media therefore pose an increased operational risk. You use hinge gene permeate, for example, from the outlet of the reverse osmosis system, which is already a very low one Has ion concentration, a particularly high electrical resistance must be overcome who to generate an electric field with sufficient field strength. A high electrical wi the level means a high energy input, i. H. very high voltages are required be placed, which makes the process very uneconomical.

The transport medium is either disposed of in the sewage network, which leads to uneconomically high levels Water loss of 20% and more leads. Instead, there is also a return before the total plant, d. H. usually before the softening system or pre-filtration. Disadvantageous is that oxidants such as chloride ions, hydrogen peroxide, oxygen and hydrogen with be returned and enriched in the cycle. Since at least 2 liters of gas evolved per hour be enriched, this enrichment leads to the possibility that other parts of the system, such as the reversal osmosis system, can also be irreparably damaged. At the same time, carbon dioxide builds up enriched, which greatly affects the performance of the electrodeionization system. There The returned transport medium must be degassed before it is fed into the overall system the hydrogen, the carbon dioxide and partly the oxygen are removed. The However, chloride ions remain and accumulate.

These problems are particularly important for the production of pure or ultrapure water for the bio technological or pharmaceutical production is important because in this case different An requirements, such as the provisions of the European Pharmacopoeia, USP 23, Appendix 8, Level 1, must be met and the system itself meets the GMP requirements and the requirements of the In Spection Guide of the FDA must suffice. The conductivity of the pure or ultrapure water should be about 1 µS / cm  amount, which can already be prevented by the enrichment of carbonic acid, so that this gas must be bound with sodium hydroxide solution in the form of sodium hydrogen carbonate.

The object of the present invention is therefore a method for operating an electrode ionization onsystem and an electrodeionization system of the above. Provide kind, the removal of the concentrate is carried out in such a way that the disadvantages described above do not occur, in particular the generation of pure or ultrapure water with economical operation of the electrical system deionization system is made possible.

The solution to the procedure is that the concentrate is in an internal circuit run and fed back into the at least one concentrate chamber as a transport medium becomes.

The electrodeionization system according to the invention is characterized in that an internal con Center circuit is provided, which the inlet opening and the outlet opening of the at least connects a concentrate chamber so that the emerging concentrate as a transport medium is returned to the at least one concentrate chamber.

The essence of the present invention is therefore that the transport medium is not in the Entire system is returned. There is no return to the entire system, for example the softening system takes place. Instead, there is a concentrate cycle around the electrode ionization onsanlage provided. The concentrate of the electrodeionization system does not come with that water or the permeate from the reverse osmosis in contact. So that ge does not get any residual hardness, neither from the drinking water nor from the concentrate of the reverse osmosis the electrodeionization system. Precipitation is avoided. There is also no streaking Protection of oxidation substances such as chloride ions, hydrogen, hydrogen peroxide and carbon di oxide, which is the performance of the electrodeionization system or possibly other system parts affect. This also significantly extends the service life. At the same time the concentrate has a sufficiently high conductivity to make the electric field economical, d. H. already when applying low voltages. The transport medium does not have to be discarded be, but is mostly reused, reducing water loss to 2% and below  reduced. The total savings compared to the systems known in the prior art can nen be 40 to 50%.

At the same time, the various requirements placed on pure or ultrapure water are met that, fulfilled. The conductivity of the resulting treated water can be 0.06 µS / cm.

Advantageous further developments result from the subclaims. The conductivity of the con The concentrate should be monitored and regulated before being fed back into the concentrate chamber (s) because with each passage of the concentrate through the cycle, the separated ions be further concentrated. The regulation is therefore advantageously such that a specified upper limit is not exceeded. This is done by feeding water with a lower than the conductivity in the concentrate circuit measured in the concentrate preferably permeate from the cleaning stages upstream of the electrodeionization system.

A particularly preferred development is that a constant pressure drop between Diluate and concentrate chambers is generated. If the concentrate is fed from a Storage tank is done by means of a pump, the pressure drop can be controlled by regulating the pumps power can be set in the storage container. To the electrodeionization system mechanically load as little as possible, it should be operated with a constant, low pressure drop become. With internal leakage, pressure fluctuations within the system or of the overall system for a transfer of the concentrate into the diluate chamber (s). Such a Overflow leads to the depletion of the ion exchange resins and thus to a malfunction the plant. Therefore, a higher pressure is maintained in the diluate chamber or chambers than in the concentrate chamber or chambers. Then, in the event of an internal leakage, con concentrate into the diluate chamber (s).

The subject of the present application is also a water treatment plant, which with the method according to the invention can be operated or at least one electric according to the invention has deionization. A preferred water treatment plant has a softening system plant and a plant for reverse osmosis, which of the at least one electrodeionization are upstream, with the permeate from the reverse osmosis system in the minimum an electrodeionization system is fed.  

The following is an embodiment of the present invention with reference to the accompanying Drawings described in more detail. Show it

Fig. 1 is a schematic representation of the concentrate circuit of an electrical deionization system according to the invention;

Figure 2 is a schematic cross section through an embodiment of an electrodeionization system.

Fig. 3 is a schematic diagram of the electrodeionization process.

The functioning of the electrode ionization can be seen from FIG. 3. The ions are removed by means of the ion exchange resin from an externally supplied permeate (which mostly comes from the outlet of the reverse osmosis system) and transported in the direction of the electrical poles, ie anode and cathode, by an applied voltage. The ion exchange resins are embedded in two ion-selective membranes between the anode and the cathode. The two membranes and the ion exchange resins form a diluate chamber. A concentrate chamber, into which the exchanged ions migrate, is adjacent to two ion-selective membranes. Applying a voltage to the anode and cathode creates an electric field in which the electrons migrate out of the diluate chamber, namely the anions in the direction of the anode and the cations in the direction of the cathode. The ions migrate through the respective ion-selective membrane into the neighboring concentrate chamber and accumulate there, because a return transport to the diluate chamber is not possible due to the membrane properties. The ions are continuously removed from the concentrate chamber. The transport medium usually comes from the concentrate of reverse osmosis or is softened water from the drinking water network.

An embodiment of a system 1 for electrode ionization according to the invention is shown in FIG. 1. In the actual electrodeionization module 2 , permeate, ie pre-cleaned water with an already low ion concentration and thus low electrical conductivity, is supplied from a line 20 via an inlet 21 in a pre-switched softening and reverse osmosis system, not shown here. The water (diluate) cleaned in module 2 passes via an outlet 22 into a line 23 from which it can be removed.

The structure of the module 2 known per se is shown in FIG. 2. The ion exchange resin 200 'or a mixture of ion exchange resins is embedded between two ion-selective membranes 201 and 202 , so that a diluate chamber 200 is formed, which is spirally wound around an ano de 203 , an inner plastic core 204 being provided to increase the stability. The ion-selective membranes 201 and 202 delimit and define a concentrate chamber 205 , the diameter of which is determined by spacers (not shown). The winding is completed with a cathode 206 . An epoxy resin surrounds the winding including the cathode 206 as the outer protective layer 207 .

The inlet 21 for the permeate and a further inlet 28 for a transport medium are embedded in the outer protective layer 207 . The inlet 21 opens into the diluate chamber 200 , while the inlet 28 opens into the concentrate chamber 205 . In the plastic core 204 , the outlet 22 for the diluate exiting from the diluate chamber 200 and an outlet 24 for the concentrate 205 emerging from the concentrate chamber are provided.

The ions remaining in the permeate are exchanged for protons and hydroxyl ions in the ion exchange resin 200 '. The exchanged ions remaining in the ion exchange resin 200 ′ migrate in the electric field from the diluate chamber 200 through the ion-selective membranes 201 , 202 and accumulate in the concentrate chamber 205 . There they are flushed out using the transport medium. The excess energy not used for ion transport splits the water molecules into protons and hydroxyl ions, with which the ion exchange resin or resins are regenerated. In this way, a constant diluate quality is achieved. Module 2 is described, for example, in the magazine Swiss Pharma, issue 7/8 1999, page 25 ff.

How the transport medium is fed in and out is again shown in FIG. 1. The electro-ionization module 2 is preceded by a container 3 which is filled with concentrate. The outlet 24 for the concentrate opens out via a line 25 into an inlet 26 into the return of the container third From there, the concentrate reaches a line 27 which opens into the concentrate chamber 205 of the module 2 via a line 31 and the inlet 28 . In the container 3 there is a frequency-controlled underwater pump 300 which is connected on the pressure side to the inlet 28 .

To ensure that the concentration of the ions in the concentrate does not increase too much, the conductivity value of the concentrate is monitored. For this purpose, a measuring unit 30 is provided which measures the actual value for the conductivity value of the concentrate in line 31 . A line 32 connects the line 20 for the permeate to the line 27 and thus to the line 31 downstream of the measuring point or the measuring unit 30 . The line 32 is closed with a control valve 33 ver. If the actual value rises above a predetermined upper limit, the control valve 33 opens, so that a small amount of permeate (usually a maximum of 5% of the concentrate volume) is metered in from line 20 into line 27 and thus into line 31 until the setpoint for the conductivity value measured by the measuring unit 30 is reached again. In this way, a constant conductivity value is established in the concentrate.

An overflow 302 is provided on the container 3 , in which excess concentrate (for example following an addition of permeate to lower the conductivity value) is discharged into the sewage system. In order to remove the gases produced during the electrodeionization, such as hydrogen and carbon dioxide, the container 3 is degassed and the gases are fed via line 25 into a degassing line 29 , which opens into a degassing nozzle, via which the gases are released into the atmosphere.

In this way, the concentrate circulates in an internal concentrate circuit so that only pure permeate from the upstream cleaning stages can reach the diluate chamber 200 of module 2 via line 20 and inlet 21 . Module 2 is therefore protected against contamination from the drinking water network or residual hardness. By concentrating the concentrate to a predetermined conductivity, the electrical resistance is reduced, so that the electrical field can be maintained economically, ie with low voltages. The transport medium for the separated ions is not returned to the overall system, e.g. upstream of the softening system. No substances harmful to the entire system, such as the oxidation products (including chloride, hydrogen peroxide and hydrogen) that arise during electrodeionization, enter the overall system. There is also no concentration of carbon dioxide in the overall system, which would negatively affect the performance of module 2 .

The exemplary embodiment of a device 1 according to the invention shown in FIG. 1 also has a control which ensures a constant pressure drop between the diluate chamber 200 and the concentrate chamber 205 . The hydraulic pressure in the line 20 and thus the diluate chamber 200 is recorded via a pressure sensor 40 and the actual value is read into a programmable logic controller (PLC). The hydraulic pressure in line 27 or line 31 and thus in concentrate chamber 205 is recorded via a pressure sensor 41 and the actual value is read into the PLC. A differential pressure, ie a pressure drop, is specified via an OP. The predetermined differential pressure is subtracted from the actual value taken up by the pressure sensor 40 . The result serves as a setpoint for frequency control of the pump 300 via the pump motor 301 . The setpoint is compared with the actual value recorded by the pressure transducer 41 . If the actual value recorded by the pressure sensor 41 for the hydraulic pressure in the concentration chamber 205 is too high, the frequency of the pump 300 is reduced. Conversely, if the pressure is too low, the frequency of the pump 300 is increased.

In this way, a constant pressure drop between diluate chamber 200 (higher pressure) and concentrate chamber 205 (lower pressure) is ensured. The module 2 is thus mechanically loaded ge, and there is no leakage of concentrate into the diluate chamber 200 in the event of an internal leak.

The system just described was built according to process diagram CWD23-3379 and one Subject to a 2650 hour test run. The configuration of the plant corresponded to that in the time Swiss Pharma 7 / 8-99, p. 31 and the magazine BioTec 1/99, p. 50 tion, but without a concentrate cycle. The electrodeionization system was a module with the Se serial number SM 1025.017. The following process were carried out over the period of rehearsal operation relevant data recorded and monitored. The results are shown in Table 1.

Since the differential pressure between the diluate chamber and the permeate was controlled, no pressure difference was observed. The deviation in permeate flow PSA 26.1.1 of -1.8% results from temperature fluctuations in the raw water. The deviation of -26% in the circulation quantity in the concentrate circuit resulted from an increase in the pressure losses in the concentration chamber of the EDI module. There was no discrepancy in the conductivity of the diluate. The conductivity of the concentrate when entering the EDI module was kept constant at 145 to 155 µS / cm by means of a motor valve. The current / voltage ratio in the EDI module remained constant. Both the chlorine content (free and bound) and the hydrogen peroxide content in the concentrate circuit remained constant, since the composition of the permeate, the conductivity in the concentrate and the current / voltage ratio in the EDI module were kept constant or remained constant. Since the water softening system worked correctly, the residual hardness in the concentrate cycle remained constant.

Table 1

The system ran smoothly and stably over the entire trial period. All rejections that have occurred Chungen are not critical and not on the systems according to the invention with the concentrate cycle attributed. All discrepancies are more pronounced or in conventional systems equally strong.

Claims (15)

1. A method of operating an electrodeionization system, wherein ions from a permeate to be processed are separated in an electric field from at least one diluate chamber into at least one concentrate chamber and are transported away in the form of a concentrate by means of a transport medium flowing through at least one concentrate chamber, characterized in that the concentrate guided in an internal circuit and fed back into the at least one concentrate chamber as a transport medium. 2. The method according to claim 1, characterized in that the feed from a Storage container by means of a pump. 3. The method according to claim 1 or 2, characterized in that the conductivity of the con the concentrate is monitored and regulated before being fed back into the concentrate chamber. 4. The method according to claim 3, characterized in that the conductivity of the concentrate is adjusted so that a specified upper limit is not exceeded. 5. The method according to claim 4, characterized in that the adjustment by means of feed solution of water with a lower conductivity than that measured in the concentrate worth done. 6. The method according to claim 5, characterized in that the adjustment by means of feed solution of permeate takes place. 7. The method according to any one of the preceding claims, characterized in that a con constant pressure drop between the diluate and concentrate chamber is generated.   8. The method according to claim 7, characterized in that the pressure drop by regulation the pump output takes place in the reservoir. 9. Electrodeionization system ( 1 ), in particular for carrying out the method according to one of claims 1 to 8, with at least one diluate chamber for a permeate to be processed, which is formed from at least one ion exchange exchanger embedded in two ion-selective membranes, limited at least one of two ion-selective membranes Concentrate chamber with an inlet opening and an outlet opening for a transport medium for the removal of the ions separated from the permeate, characterized in that an internal concentrate circuit is provided which connects the inlet opening and the outlet opening from the at least one concentrate chamber so that the emerging concentrate as Means of transport is returned to the at least one concentrate chamber. 10. Electrode ionization system according to claim 9, characterized in that in the concentrate circuit a storage container is provided for the concentrate. 11. Electrode ionization system according to claim 10, characterized in that in the storage container ter a pump is provided to promote the concentrate. 12. Electrode ionization system according to one of claims 9 to 11, characterized in that the concentrate circuit contains an external water supply device. 13. Electrode ionization system according to claim 12, characterized in that the external zu feed device serves the supply of permeate. 14. Water treatment plant, which with a method according to any one of claims 1 to 8 is operable or at least one electrodeionization system according to one of claims 9 to 13. 15. Water treatment plant according to claim 14, in which a softening plant and a System for reverse osmosis upstream of the at least one electrodeionization system  and the permeate from the reverse osmosis system into the at least one electrode nation system is fed.