Method of operating a reverse osmosis water treatment plant

Abstract

The invention relates to a method of operating a reverse osmosis water treatment plant (1). The water treatment plant (1) used comprises a reverse osmosis membrane (3) having a retentate side (RS) and a permeate side (PS). It is designed such that, when untreated water (RW) is fed under pressure to the retentate side (RS), permeate (P) exits on the permeate side (PS), while the untreated water (RW) is concentrated on the retentate side (RS) with respect to its mineral content to form retentate (R). The plant (1) comprises devices (4, 5, 6, 7) for adjusting a retentate outflow (AR) from the retentate side (RS) of the membrane (3). In the method of the invention, a target service life (tz) of the membrane (3) and a target progression (VPz) of the permeate output of the membrane (3) over said target service life (tz) at a particular untreated water pressure are defined. The water treatment plant (1) is then operated at the particular untreated water pressure and at a particular retentate outflow (AR). During operation, the permeate output (VPr) of the membrane (3) is ascertained and compared to the target permeate output (VPz). If the comparison shows that the permeate output (VPr) ascertained varies from the target permeate output (VPz) by a particular magnitude, the retentate outflow (AR) is altered depending on the variance ascertained.

Description

[0001] P191886PC00

[0002] 1

[0003] Method for operating a reverse osmosis water treatment plant

[0004] TECHNICAL AREA

[0005] The invention relates to a method for operating a reverse osmosis water treatment plant, a plant for carrying out the method, and a use of the plant for supplying a humidifier with permeate according to the preambles of the independent claims.

[0006] STATE OF THE ART

[0007] Water treatment plants that use reverse osmosis membranes require membrane replacement after a shorter or longer period of operation, depending on operating conditions and raw water quality, to ensure the desired permeate quality and throughput. Since the membranes are expensive and used membranes generate waste, it is desirable to use them for as long as possible. The retentate discharge rate can be adjusted during operation to influence membrane lifespan; however, if a higher retentate discharge is set to extend membrane life, this leads to higher water and energy costs.

[0008] If these water treatment plants are part of a larger system with permeate consumers, which are also subject to specific maintenance intervals, efficient system maintenance becomes difficult because the membrane replacement intervals of the water treatment plants usually do not coincide with the maintenance intervals of the permeate consumers. Furthermore, the raw water quality is often variable, making a reliable estimate of the membrane lifespan difficult. Accordingly, either the membrane P191886PC00

[0009] Either the membranes are replaced before reaching their service life to avoid an additional maintenance intervention, or an additional maintenance intervention is required to utilize the membrane's full service life. Both scenarios are unsatisfactory.

[0010] PRESENTATION OF THE INVENTION

[0011] The task therefore arises to provide technical solutions that do not exhibit the aforementioned disadvantages of the state of the art, or at least partially avoid them.

[0012] This problem is solved by the subject matter of the independent patent claims.

[0013] According to this, a first aspect of the invention relates to a method for operating a reverse osmosis water treatment plant, which preferably provides demineralized water (permeate) for a humidifier.

[0014] The water treatment plant used to carry out the process comprises a reverse osmosis membrane, which has a retentate side and a permeate side. It is designed such that when raw water is supplied under pressure to the retentate side of the membrane, permeate exits on the permeate side of the membrane, while on the retentate side of the membrane, the raw water concentrates as retentate with respect to its mineral content.

[0015] The system includes facilities for supplying raw water to the retentate side of the membrane, for removing retentate from the retentate side of the membrane, and for removing permeate from the permeate side of the membrane.

[0016] Furthermore, the system includes facilities for adjusting the retentate outflow (mass or volume flow) from the retentate side of the membrane, while simultaneously allowing raw water to flow to the retentate side.

[0017] According to the inventive method, a target lifetime of the membrane and a target progression P191886PC00 are determined.

[0018] 3. The permeate performance of the membrane over the target lifetime at a specific raw water pressure is determined.

[0019] The water treatment plant is then operated with the specified raw water pressure and a specific retentate flow rate.

[0020] During operation, the permeate performance of the membrane is determined at at least one time point within the target lifetime of the membrane and compared with the target permeate performance according to the target permeate performance curve at that at least one time point.

[0021] If the comparison shows that the determined permeate throughput of the membrane deviates from the target permeate throughput by a certain amount, which is in particular greater than a previously defined permissible deviation, the retentate outflow is changed depending on the determined deviation, preferably in such a way that the deviation from the target permeate throughput decreases during further operation.

[0022] For this purpose, it is preferred that the retentate outflow is increased if the determined permeate flow rate falls short of the target permeate flow rate by a certain amount, and that it is decreased if the determined permeate flow rate exceeds the target permeate flow rate by a certain amount.

[0023] If the water treatment plant is operated continuously, it is preferable that the aforementioned steps be carried out repeatedly during operation, advantageously at regular intervals. This allows the membrane's service life to be perfectly aligned with the service interval of a permeate consumer supplied by the plant (target service life), while simultaneously minimizing the water and energy costs caused by retentate discharge.

[0024] If the water treatment plant is operated intermittently, it is preferred that the aforementioned steps be carried out for each interval. P191886PC00

[0025] 4

[0026] This is particularly useful when the water treatment plant supplies a permeate consumer that receives a specific amount of permeate at intervals. In such applications, the permeate output of the membrane can be easily determined by measuring the time it takes for the water treatment plant to deliver the specified amount of permeate.

[0027] The retentate flow can be adjusted continuously or in stages, the latter variant offering the advantage, when the process is carried out with an automated water treatment plant, that the system can be designed relatively simply and cost-effectively by switching back and forth between different restrictors with each fixed flow cross-section, without the need for complex control loops and control valves.

[0028] In a preferred embodiment of the process, the raw water is supplied to the retentate side under pressure by means of a raw water pump belonging to the system. This is particularly advantageous if the system pressure of the supplying water system is too low or fluctuates significantly. If the system pressure of the supplying water system is sufficient and stable, it is preferable to dispense with a raw water pump.

[0029] A second aspect of the invention relates to a plant for carrying out the method according to the first aspect of the invention.

[0030] The system comprises a reverse osmosis membrane, which has a retentate side and a permeate side. It is designed such that when raw water is supplied under pressure to the retentate side of the membrane, permeate exits on the permeate side of the membrane, while on the retentate side the raw water concentrates as retentate with respect to its mineral content.

[0031] The system also includes facilities for supplying raw water to the retentate side of the membrane, to P191886PC00

[0032] 5

[0033] Removal of retentate from the retentate side of the membrane and removal of permeate from the permeate side of the membrane. Devices are also provided for adjusting the retentate outflow (mass or volume flow) from the retentate side of the membrane.

[0034] According to the invention, the system comprises a system control for the automated operation of the system according to the method according to the first aspect of the invention, in particular for the automated execution of the claimed steps d) e) and f) of the inventive method during the operation of the system at a predetermined target lifetime of the membrane and a predetermined target profile of the permeate output of the membrane over the target lifetime of the membrane at a specific raw water pressure.

[0035] Advantageously, the devices for controlling the retentate outflow comprise several, in particular different, restrictors, each with a fixed flow cross-section, and are designed such that the retentate outflow can selectively occur via individual restrictors, specific groups of restrictors, or all restrictors. Such systems can be provided relatively easily and inexpensively.

[0036] A third and final aspect of the invention relates to the use of the system according to the second aspect of the invention for supplying a humidifier with permeate. The advantages of the invention become particularly evident in such uses.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Further embodiments, advantages, and applications of the invention will become apparent from the dependent claims and from the following description with reference to the figures. These figures show:

[0039] Fig. 1 shows a schematic diagram of a reverse osmosis water treatment plant according to the invention; P191886PC00

[0040] 6

[0041] Fig. 2 shows a diagram illustrating the target curve of the permeate output of the membrane of the system over its target lifetime;

[0042] Fig. 3 shows a diagram like Fig. 2, in which an exemplary course of the actual permeate performance of the membrane of the system and the retentate discharge volume over the target lifetime is shown.

[0043] WAYS TO IMPLEMENT THE INVENTION

[0044] Fig. 1 shows a simplified system diagram of a reverse osmosis water treatment system 1 according to the invention, which supplies an evaporative humidifier 2 with permeate P (demineralized water).

[0045] As can be seen, the core component of system 1 is a reverse osmosis membrane 3, which has a retentate side RS and a permeate side PS. The membrane 3 is designed such that when raw water RW is supplied under pressure to its retentate side RS, permeate P exits from its permeate side PS, while on the retentate side RS, the raw water RW concentrates as retentate R with respect to its mineral content.

[0046] The system has a raw water supply line 10, through which, during normal operation of the system 1, raw water RW is pumped by a raw water pump 8 at a specific supply pressure of 4 bar to the retentate side RS of the membrane 3. If the supplying raw water system has a corresponding and stable supply pressure, a simple switching valve (not shown) can be used instead of the raw water pump 8.

[0047] Furthermore, the system has a permeate discharge line 12 with a check valve 13, through which, during normal operation of the system 1, permeate P is discharged from the permeate side PS of the membrane 3 and fed to the evaporative humidifier 2, which is supplied with permeate P by the system. P191886PC00

[0048] 7

[0049] The system also includes a retentate discharge line 11 with a check valve 13, through which, during normal operation of the system 1, retentate R is discharged from the retentate side RS of the membrane 3 and supplied to the required devices 4, 5, 6, 7 for adjusting the retentate discharge AR from the retentate side RS. These devices consist of a triple solenoid valve 4 and three restrictors 5, 6, 7. The three restrictors 5, 6, 7 are designed such that different volume flows of retentate R can flow through them at the specified raw water supply pressure, namely 800 ml / min through the first restrictor 5, 200 ml / min through the second restrictor 6, and 450 ml / min through the third restrictor 7.

[0050] The system 1 has a system control unit 9, with which the solenoid valve 4 can be controlled and thereby brought into different switching states, so that a retentate discharge AR is optionally possible only via the first restrictor 5 (800 ml / min), via the first restrictor 5 and the second restrictor 6 (1000 ml / min), via the first restrictor 5 and the third restrictor 7 (1250 ml / min) or via all three restrictors 5, 6, 7 (1450 ml / min).

[0051] How this is done according to the inventive method is explained below with reference to Figures 2 and 3.

[0052] The system control unit 9 stores a target profile VPz for the permeate output (permeate volume flow rate) of membrane 3 at a specific raw water pressure over the target service life tz of membrane 3, which was selected according to the service interval of the humidifier 2. This target profile VPz is shown in the diagram according to Fig. 2. As can be seen, it is initially set to 0.8 l / min and at the end of the target service life to 0.5 l / min. P191886PC00

[0053] The assumed raw water pressure of 4 bar is ensured via the raw water pump 8.

[0054] A tolerance range is defined around the target curve VPz of the permeate power (shown in bold), which is limited downwards by the curve of a tolerable maximum undershoot AVPtol- of the target curve VPz and upwards by the curve of a tolerable maximum exceedance AVPtol+ of the target curve VPz.

[0055] The evaporative humidifier 2, supplied with permeate P from the water treatment system, has a permeate tank 14 with a level sensor 15, which sends a corresponding start signal to the system controller 9 when a certain minimum level is reached, and a corresponding stop signal to the system controller 9 when a certain maximum level is reached. There is a specific permeate quantity MP of 0.9 liters between the minimum and maximum levels.

[0056] When the plant control system receives a start signal, it activates the raw water pump 8 and plant 1 produces permeate P and retentate R. When it receives a stop signal, it stops the raw water pump 8 and plant 1 enters standby mode. Accordingly, the water treatment plant 1 is operated intermittently.

[0057] Fig. 3 shows a diagram like Fig. 2, in which, by way of example, the course of the actual permeate power VPr of the membrane 3 (shown as dotted lines) and the course of the retentate discharge AR set by the plant control 9 as a function of the actual permeate power VPr over the target lifetime tz of the membrane 3 are shown.

[0058] At start time tO with new membrane 3, the retentate outflow AR is set to a mean as a start condition - P191886PC00

[0059] 9. The flow rate is set to 1000 ml / min, for which the system control 9 releases the second restrictor 6 in addition to the first restrictor 5 via the valve 4.

[0060] In each operating interval of the water treatment plant 1, i.e., each time the permeate container 14 of the humidifier 2 is filled, the current permeate output VPr of the membrane 3 is determined and compared with the respective target permeate output VPz according to the target profile at this time t.

[0061] In this case, each point on the curve of the actual permeate output VPr represents an operating interval. The actual permeate output VPr for each interval is determined by calculating the time it takes for the water treatment plant 1 to provide the specified permeate quantity MP of 0.9 liters.

[0062] In the event that the determined permeate output VPr deviates from the target permeate output VPz by a certain amount, which is greater than the positive and negative deviations AVPtol+ and AVPtol- respectively allowed by the tolerance range, the plant control 9 changes the setting of the retentate discharge AR for the next operating interval in such a way that this deviation decreases in the following operation.

[0063] As can be seen, the actual permeate flow rate VPr of membrane 3 falls below the target permeate flow rate VPz increasingly with the ongoing operating time of system 1 at the set retentate outflow AR of 1000 ml / min, until at time tl the actual permeate flow rate VPrl reaches the lower limit of the tolerance range, which is given by the maximum tolerable underrun AVPtol of the target permeate flow rate VPz l.

[0064] As can be seen from the course of the retentate flow AR, the system control 9 now sets an increased flow rate of 1250 ml / min by adding the P191886PC00 via valve 4 in addition to the first restrictor 5.

[0065] 10. Third restrictor 7 is released and second restrictor 6 is deactivated.

[0066] As a result of the increased retentate outflow AR, the actual permeate flow rate VRr of membrane 3 now increases with the ongoing operating time of the system 1 at the set retentate outflow AR of 1250 ml / min, until it reaches the upper limit of the tolerance range at time t2, which is given by the maximum tolerable exceedance AVPtol+ of the target permeate flow rate VPz l .

[0067] As can be seen from the course of the retentate flow AR, the retentate flow is now reduced to 1000 ml / min by the plant control 9, by releasing the second restrictor 6 and deactivating the third restrictor 7 via the valve 4 in addition to the first restrictor 5.

[0068] As a result of the reduced retentate outflow AR, the real permeate power VRr decreases very rapidly again until it reaches the real permeate power VPr3 at time t3, which corresponds to the lower limit AVPtol- of the tolerance range.

[0069] Due to the rapid deterioration of the actual permeate performance VRr between time t2 and time t3, the system controller 9 detects that the membrane 3 is already partially clogged and that a significantly increased retentate outflow AR is required for the membrane to continue operating within the tolerance range. Accordingly, the system controller 9 now sets a significantly increased retentate outflow rate of 1450 ml / min by opening the third restrictor 7 via valve 4, in addition to the first restrictor 5 and the second restrictor 6.

[0070] As can be seen, the actual permeate flow rate VPr of membrane 3 now increases again with the ongoing operating time of system 1 at the set retentate outflow AR of 1450 ml / min and thereby exceeds the target permeate flow rate VPz within the tolerance range. P191886PC00

[0071] 11

[0072] 5 Reichs, until they essentially correspond to the target permeate power VPz upon reaching the target lifetime tz.

[0073] Membrane 3 is now consumed at time tz, and only as much retentate R was removed over its lifetime as was necessary to keep the permeate performance VPr within the tolerance range.

[0074] While preferred embodiments of the invention are described in the present application, it should be clearly pointed out that the invention is not limited to these and can also be carried out in other ways within the scope of the following claims.

Claims

P191886PC00 12 PATENT CLAIMS 1. Method for operating a reverse osmosis water treatment plant (1), in particular for a humidifier (2), with a reverse osmosis membrane (3) having a retentate side (RS) and a permeate side (PS) and designed such that when raw water (RW) is supplied under pressure to the retentate side (RS) of the membrane (3), permeate (P) exits on the permeate side (PS) of the membrane (3), while on the retentate side (RS) of the membrane (3) the raw water (RW) concentrates as retentate (R) with respect to its mineral content, and with devices (4, 5, 6, 7) for controlling a retentate outflow (AR) from the retentate side (RS) of the membrane (3), comprising the steps: a) determining a target lifetime (tz) of the membrane (3); b) Determining a target profile (VPz) of the permeate output of the membrane (3) over the target lifetime (tz) of the membrane (3) at a specific raw water pressure;c) Operating the water treatment plant (1) with the specified raw water pressure and a specified retentate discharge (AR); d) Determining the permeate output (VPrl, VPr2, VPr3) of the membrane (3) at at least one time point; (tl, t2, t3) within the target lifetime (tz) of the membrane; e) comparing the determined permeate power (VPrl, VPr2, VPr3) with the respective target permeate power (VPzl, VPz2, VPz3) according to the target profile (VPz) of the permeate power at at least one time point (tl, t2, t3) within the target lifetime (tz); and, in the event that the determined permeate power (VPrl, VPr2, VPr3) of the membrane (3) is P191886PC00 13. The target permeate output (VPzl, VPz2, VPz3) deviates according to the target curve (VPz); f) Changing the retentate outflow (AR) depending on the determined deviation.

2. Method according to claim 1, wherein, in the event that the determined permeate output (VPrl, VPr2, VPr3) falls short of the target permeate output (VPzl, VPz2, VPz3) by a certain amount, the retentate outflow (AR) is increased, and in the event that the determined permeate output (VPrl, VPr2, VPr3) exceeds the target permeate output (VPzl, VPz2, VPz3) by a certain amount, the retentate outflow (AR) is decreased.

3. Method according to any of the preceding claims, wherein the retentate outflow (AR) is stopped continuously or in stages.

4. Method according to any of the preceding claims, wherein a target lifetime (tz) of the membrane (3) is determined which corresponds to a maintenance interval of an associated permeate consumer (2), in particular a humidifier supplied with permeate (P) by the water treatment plant (1).

5. Method according to any of the preceding claims, wherein the water treatment plant is operated continuously and steps d) , e) and f) are carried out repeatedly, in particular at regular intervals.

6. Method according to any one of claims 1 to 4, wherein the water treatment plant (1) is operated intermittently and steps d) , e) and f) are carried out for each interval. P191886PC00 14 7. Method according to claim 6, wherein the water treatment plant (1) supplies a permeate consumer (2) which receives a specific amount of permeate (MP) at intervals, and wherein the permeate output (VPr) of the membrane (3) is determined by determining the time (t) that elapses until the water treatment plant (1) has provided the specific amount of permeate (MP) for the permeate consumer.

8. Method according to one of the preceding claims, wherein the raw water (RW) is supplied under pressure to the retentate side (RS) of the membrane (3) by means of a raw water pump (8).

9. Plant (1) for carrying out the method according to one of the preceding claims, comprising a reverse osmosis membrane (3) which has a retentate side (RS) and a permeate side (PS) and is configured such that when raw water (RW) is supplied under pressure to the retentate side (RS) of the membrane (3), permeate (P) exits on the permeate side (PS) of the membrane (3), while on the retentate side (RS) the raw water (RW) concentrates with respect to its mineral content to retentate (R), comprising devices (10, 11, 12) for supplying raw water (RW) to the retentate side (RS) of the membrane (3), for removing retentate (R) from the retentate side (RS) of the membrane (3) and for removing permeate (P) from the permeate side (PS) of the membrane (3), comprising devices (4, 5, 6, 7) for Setting the retentate outflow (AR) from the retentate side (RS) of the membrane ( 3 ) , and with a plant control (9) for automated operation of the plant (1) according to the procedure.

10. System according to claim 9, wherein the devices (4, 5, 6, 7) for adjusting the retentate outflow (AR) comprise several, in particular different, restrictors P191886PC00 15 5 (5, 6, 7) each with a fixed flow cross-section and are designed in such a way that the retentate outflow (AR) can optionally occur via individual restrictors (5; 6; 7), certain groups of restrictors (5, 6; 5, 7) or all restrictors (5, 6, 7). 10 11. Use of the system (1) according to one of claims 9 to 10 for supplying a humidifier (2) with permeate (P) . 15

Images