Liquid purification system

Abstract

The invention relates to a system for purifying and / or desalinating a liquid. The system comprises a raw liquid supply line with a valve connected to a filtration unit, which comprises a liquid purification device with an inlet and an outlet for purified liquid and discharge liquid, a mixing device, a device for maintaining pressure, a device for maintaining liquid recirculation flow on the line supplying a mixture of raw liquid and concentrate upstream of the liquid purification device, a recirculation line, a purified liquid line, a discharge liquid line, and a control unit connected to all of the following devices: the device for maintaining pressure, the device for monitoring pressure variations, the raw liquid supply valve and the discharge liquid discharge valve. The device for maintaining pressure is located on the raw liquid supply line upstream of the liquid mixing device in the form of a pressure tank connected to the raw liquid and concentrate mixing line. The technical effect is: extended service life of the system, more efficient use of raw liquid, and reduced energy consumption.

Description

Technical Field

[0001] This invention relates to a system for the purification and / or desalination of liquids (primarily water) for use in residential and / or industrial environments, and for the supply of domestic and / or drinking water in summer villas and garden communities. Background Technology

[0002] Various liquid purification systems are known and quite widely used.

[0003] US Patent 6290856 (C02F 1 / 50, Publication Date 18.09.2001, Applicant: Worldwide Water Inc., US) discloses a reverse osmosis liquid treatment system. The liquid purification system includes: a feedstock supply line with a feedstock supply valve mounted thereon; a filter unit including a liquid purification device with a feedstock inlet and purified liquid and discharge outlets; a purified liquid line; and a discharge line. The filter unit further includes a liquid storage device, which in one embodiment includes a water-water tank having a purified liquid storage chamber and a discharge chamber, wherein the storage chamber is connected to the purified liquid line, and the discharge chamber is connected to a line for supplying discharge liquid into the discharge chamber. In a second embodiment, the liquid storage device includes a water-air tank having a purified liquid storage chamber and a discharge chamber filled with compressed gas (e.g., air). A line for supplying discharge liquid into the discharge chamber and having a discharge supply valve mounted thereon is connected to the discharge line. Valves installed on the raw liquid supply line and the line supplying the effluent to the discharge chamber respond to pressure changes in the purified liquid line. A pressure controller is installed in the discharge line to maintain the pressure in the liquid purification unit at a predetermined level, thereby preventing contaminant buildup on the surface of the liquid purification unit. The system also includes an antimicrobial agent dispenser connected upstream of the liquid purification unit to the purified liquid supply line.

[0004] The liquid purification system operates as follows: The raw liquid enters the liquid purification device of the filtration unit via the raw liquid supply line and the open raw liquid supply valve. After the liquid purification device, the purified liquid reaches the storage chamber of the liquid storage device via the purified liquid line. As the storage chamber fills, the pressure therein and in the purified liquid line gradually increases. Once a predetermined pressure is reached, the valve in the raw liquid supply line closes the flow of raw liquid into the system. The liquid purification process is interrupted. The pressure in the purified liquid line decreases as purified liquid is drawn from the storage chamber of the liquid storage device. Once the pressure in the purified liquid line reaches a predetermined level, the valves in the raw liquid supply line and the drain supply line in the discharge chamber of the liquid storage device open. The raw liquid flows into the liquid purification device via the raw liquid supply line used for purification. The drained liquid enters the discharge chamber via the drain supply line. Once the pressure of the drained liquid entering the discharge chamber exceeds the pressure of the purified liquid in the storage chamber, the purified liquid is discharged into the purified liquid line. When the intake of the purified liquid stops, the pressure in the purified liquid pipeline and the purified liquid storage chamber of the liquid storage device gradually increases, and the drained liquid is discharged from the discharge chamber of the liquid storage device to the drain port. When the pressure in the purified liquid pipeline and the purified liquid storage chamber of the liquid storage device rises to a predetermined level, the valves in the original liquid supply pipeline and the discharge supply pipeline in the discharge chamber of the liquid storage device close. The system enters a static state, and a predetermined amount of liquid containing antimicrobial agent is supplied from the antimicrobial agent supply unit to the liquid purification device; this liquid remains in the membrane until the system switches to the original liquid purification mode.

[0005] According to the system described in US 6290856, during liquid purification, the amount of effluent produced far exceeds the amount of purified liquid produced, and the liquid purification system does not provide recirculation of the effluent. The effluent is discharged from the system throughout the filtration process, which reduces the utilization efficiency of the original liquid. Although a controller installed in the effluent line maintains the pressure in the liquid purification unit at a level necessary to prevent contaminant buildup, over time, a polarized thin layer forms on the surface of the liquid purifier, which eventually solidifies and impairs the efficiency of membrane operation. The liquid purification system according to patent US 6290856 does not provide flushing of the liquid purification unit. Flushing of the liquid purification unit to prevent contaminant deposition is replaced by supplying a portion of liquid containing an antimicrobial agent to the liquid purification unit. As described in the specification of US 6290856, the liquid purification unit is additionally flushed to completely remove the antimicrobial agent from the system. The present invention overcomes these disadvantages, particularly by providing liquid recirculation and removing contaminants from the liquid purification unit without replenishment.

[0006] Another liquid purification system is disclosed in US 5503735 (B01D 61 / 12, Water Factory Systems, US). This system includes: a raw liquid supply line with a raw liquid supply valve mounted thereon; a filtration unit including a pressure maintaining device, a liquid purification device having a raw liquid inlet and purified liquid and effluent outlets, a purified liquid line, a effluent line with a effluent discharge valve, and a recirculation line; and a control unit connected to the pressure maintaining device, a pressure monitoring device, and a valve installed in the raw liquid supply line. The effluent discharge line includes a pressure reducing valve and a flow restrictor. A flushing line is connected upstream of the pressure reducing valve to the effluent discharge line, and a recirculation line is connected downstream of the pressure reducing valve to the effluent discharge line and upstream of the pressure maintaining device to the raw liquid supply line. The flushing valve is installed in the flushing line. The control unit of the liquid purification system is further connected to the flushing valve in the flushing line.

[0007] The liquid purification system operates as follows: The raw liquid enters the liquid purification unit via the raw liquid supply line and a pressure maintaining device. After the liquid purification unit, the purified liquid flows to the purified liquid line. After the liquid purification unit, the system discharges the waste liquid via the drain line, pressure relief valve, and flow restrictor. However, a small amount of liquid flows into the recirculation line and mixes with the raw liquid before entering the pressure maintaining device. When the system switches to flushing mode, the flushing valve opens in the flushing line, and the raw liquid reaches the liquid purification unit via the raw liquid supply line and the pressure maintaining device. It is then discharged at high speed through the flushing line via the open flushing valve to the drain port, carrying away contaminants from the liquid purification unit in a turbulent manner.

[0008] The periodic flushing of the liquid purification device with the undiluted solution is achieved through a pressurization device, which is activated to ensure rapid turbulent flow of the liquid through the device. However, similar to previous technologies, despite flushing, a polarized thin layer of contaminants accumulates on the membrane surface, attracting larger particles and causing blockage, thus shortening the lifespan of the liquid purification device and therefore the entire system. The pressure maintaining device also functions as a circulating liquid flow maintaining device, for example, in the form of a high-load pump. The pump's performance must exceed the discharge rate to provide the necessary high liquid velocity and stabilize the pressure within the liquid purification device. Furthermore, this system only recovers a portion of the discharged liquid, whereas the liquid purification system according to the invention provides the recovery of all discharged liquid.

[0009] The liquid purification system most closely related to this invention is disclosed in patent US 6190558 (B01D 61 / 00, NimbusWater Systems, Inc., US).

[0010] The system according to US 6190558 includes: a raw liquid supply line having a raw liquid supply valve mounted thereon; a filtration unit, the filtration unit including: a liquid purification device having a raw liquid inlet and a purified liquid and a drain outlet, a mixing device, a pressure maintaining device, lines for supplying raw liquid and concentrate formed in the liquid purification process in the liquid purification device, a recirculation line, a purified liquid line, and a drain line; and a control unit connected to the pressure maintaining device and a pressure change monitoring device. In the filtration unit, a mixing device, such as a mixer unit, is simultaneously connected to the raw liquid supply line, the recirculation line, and the raw liquid / concentrate supply line upstream of the pressure maintaining device and upstream of the liquid purification device. Additionally, the liquid purification system includes a purified liquid circulation line with a solenoid valve and a pressure sensor mounted thereon, the purified liquid circulation line being connected to the purified liquid line and the mixing device. A conductivity sensor is provided in the recirculation line. In addition to the pressure maintaining device and the pressure maintaining monitoring device, the conductivity sensor, the raw liquid supply valve, and a valve in the line for recirculating the purified liquid back to the mixing device are connected to the control unit. A flow restrictor is installed in the drain line connected to the liquid purification device.

[0011] The liquid purification system operates as follows: Once the valve in the purified liquid line opens, the pressure in the purified liquid line drops. Simultaneously, the pressure sensor in the purified liquid recirculation line sends a signal to the control unit to activate the pressure maintaining device and open the valve in the raw liquid supply line. The raw liquid flows through the raw liquid supply line via the opened raw liquid supply valve into the mixing unit, and further through the pressure maintaining device into the liquid purification unit. After the liquid purification unit, the purified liquid enters the purified liquid line. The discharged liquid flows through the recirculation line into the liquid mixing unit, where it mixes with the raw liquid and flows into the purification unit. Once the valve in the purified liquid line closes, the pressure in the purified liquid line increases. The control unit receives a signal from the pressure sensor in the purified liquid recirculation line and opens the valve in the purified liquid recirculation line. The purified liquid enters the liquid mixing unit, mixes with the raw liquid, and then flows into the liquid purification unit through the pressure maintaining device. Thus, liquid with a reduced contaminant level passes through the system, and a portion of this mixture is continuously discharged into the drain port. As previously mentioned, the recirculation line includes a conductivity sensor connected to the control unit. As the raw / purified solution mixture passes through the system, the conductivity sensor sends a signal to the control unit. When a predetermined low impurity concentration is reached in the mixture, the control unit deactivates the pressure maintaining device and closes the valves in the purified solution recirculation line and the liquid supply line. The system then enters a static state until the valve in the purified solution line is reopened.

[0012] Similar to prior art methods (US 5503735), in order to provide rinsing for the liquid purification device and discharge of the liquid flow, it is necessary to provide an increased velocity and pressure for the liquid flow, which is imparted by a pressure maintaining device. Therefore, as in the prior art, the pressure maintaining device also functions as a circulating liquid flow maintaining device and includes a high-load pump. The pump's performance must exceed the discharge rate of the liquid flow to provide the required high liquid velocity and stabilize the pressure in the liquid purification device. According to patent US 6190558, during rinsing in the liquid purification system, a purifying liquid is added to the original liquid, which reduces the amount of contaminants in the liquid entering the membrane during the rinsing process. Liquid purification is completed during the supply of the original liquid / purifying liquid mixture to the liquid purification device; the resulting purifying liquid is immediately supplied to the liquid mixing device for a new cycle. Multiple cycles in this manner are sufficient to achieve a predetermined low impurity concentration in the mixture. This operating mode of the system results in uneconomical use of the purifying liquid and the electricity consumed in operating the pressure maintaining device. Summary of the Invention

[0013] The purpose and technical effect of this invention is to provide a new liquid purification system, thereby extending the life of the liquid purification system, improving the utilization efficiency of the raw liquid, and reducing energy consumption.

[0014] The objective and technical effect of this invention are achieved in a liquid purification system comprising: a raw liquid supply line having a raw liquid supply valve mounted thereon and connected to a filtration unit, the filtration unit comprising: a liquid purification device having an inlet for the raw liquid and an outlet for purified liquid and a drain; a liquid mixing device; a pressure maintaining device; a line for supplying a mixture of the raw liquid and a concentrate formed during the liquid purification process in the liquid purification device; a recirculation line; a purified liquid line; a drain line; and a control unit connected to the pressure maintaining device, a pressure change monitoring device, and the raw liquid supply valve, wherein, according to the invention, the filtration unit is adapted to stabilize the pressure in the liquid purification device while periodically discharging a liquid flow at a discharge rate exceeding the performance of the pressure maintaining device arranged upstream of the liquid mixing device in the raw liquid supply line, the liquid mixing device being in the form of a pressure tank and connected to the line for mixing the raw liquid and the concentrate formed during the filtration process, while the amount of concentrate in the liquid mixing device is regulated by connection of the control unit to: a device for maintaining the pressure in the pressure tank-type liquid mixing device and a circulating liquid flow device arranged upstream of the liquid purification device in the raw liquid / concentrate supply line. The liquid mixing device includes a holding device and a drain valve arranged in the drain line; wherein the internal space of the liquid mixing device in the form of a pressure tank is divided by a flexible partition into a chamber for mixing the stock solution and the concentrate formed during the liquid purification process and a chamber filled with a compressible medium; wherein the recirculation line is connected via a connecting unit to a stock solution supply line downstream of the pressure maintaining device and a line for mixing the stock solution and the concentrate formed during the liquid filtration process, and the line for mixing the stock solution and the concentrate formed during the liquid filtration process is connected to the stock solution / concentrate mixing device; wherein the control unit is configured to regulate the flushing of the liquid purification device by periodically deactivating the pressure maintaining device and opening the drain valve after a predetermined time interval; wherein the liquid purification system further includes a purification liquid unit connected to the purification liquid line; wherein the purification liquid unit includes a purification liquid supply device having a liquid disinfection device arranged upstream of the purification liquid supply device; wherein the purification liquid unit further includes a purification liquid circulation flow maintaining device and a purification liquid accumulation device, the purification liquid accumulation device being connected to the inlet of the purification liquid supply device and the outlet of the purification liquid circulation flow maintaining device. Attached Figure Description

[0015] Figure 1 A schematic diagram of a liquid purification system is shown. Detailed Implementation

[0016] Liquid purification system ( Figure 1The system includes a raw liquid supply line (1) having a raw liquid supply valve (3) mounted thereon and connected to a filter unit (2). The filter unit (2) includes a pressure maintaining device (4) installed in the raw liquid supply line (1) and a liquid mixing device (5) connected to a raw liquid / concentrate mixing line (9) and a raw liquid / concentrate supply line (10), the raw liquid / concentrate supply line (10) being connected to the inlet of a liquid purification device (12). The raw liquid / concentrate mixing line (9) is connected downstream of the pressure maintaining device (4) (pressurization device) to the raw liquid supply line (1) and the recirculation line (13) via a connecting unit (21). The purified liquid outlet of the liquid purification device is connected to a purified liquid unit (18) via a purified liquid line (17). The drain outlet of the liquid purification device is connected to a recirculation line (13), which is connected via a connection unit (21) to the raw liquid supply line (1) and to the raw liquid / concentrate mixing line (9). For example, a pressure change monitoring device (22) of a low-pressure switch is installed in the raw liquid supply line (1) and connected to a control unit ( Figure 1 (Not shown in the image) Connection. A pre-filter (16) is also provided in the raw liquid supply line (1).

[0017] The drain line (14) is connected to the recirculation line (13), and the drain valve (15) is installed on the drain line and connected to the control unit.

[0018] The liquid mixing device (5) is in the form of a pressure vessel, the internal space of which is divided by a flexible partition (8) into a liquid / concentrate mixing chamber (6) for mixing the raw liquid and the concentrate formed during the liquid purification process, and a chamber (7) filled with a compressible medium such as air.

[0019] For example, the liquid circulation maintenance device (11) of the circulating pump is installed in the raw liquid / concentrate supply line (10) upstream of the liquid purification device (12).

[0020] The control unit is connected to the raw liquid supply valve (3) installed in the raw liquid supply line (1), the drain valve (15) installed in the drain line (14), the pressure maintaining device (4), the liquid circulation maintaining device (11), and the pressure change monitoring device (22).

[0021] The liquid purification device (12) can be, for example, in the form of a reverse osmosis membrane or a nanofiltration membrane.

[0022] The purification liquid unit (18) connected to the purification liquid line (17) includes, for example, a purification liquid supply device (19) in the form of a faucet. A purification liquid storage device (20), for example, a water-gas tank, may be arranged upstream of the purification liquid supply device (19), and a purification liquid circulation flow maintenance device (not shown), for example, a circulation pump, may be installed upstream of the purification liquid collection device. A pressure change monitoring device (23), for example, a high-pressure switch, may be installed in the purification liquid line (17) downstream of the purification liquid storage device (20), and a liquid disinfection device, for example, a flow-through UV lamp (not shown), may also be provided.

[0023] Within a range of different characteristics, liquid purification systems are used to implement the following liquid filtration processes.

[0024] When the liquid purification system is started, the raw liquid is drawn from the source ( Figure 1 The liquid (not shown) enters the inlet of the raw liquid supply line (1) and, via the pre-filter (16), enters the pressurization unit (4) through the open valve (3) connected to the control unit. Then, the raw liquid flows into the liquid mixing unit (5) through the raw liquid / concentrate mixing line (9). Since the pressurization unit (4) is located upstream of the liquid mixing unit (5), the raw liquid enters the raw liquid / concentrate mixing chamber (6) under pressure, which remains constant during the liquid filtration cycle and is sufficient for the liquid to pass through a liquid purification unit (12). Furthermore, the raw liquid enters the liquid purification unit (12) through the raw liquid / concentrate supply line (10) via the liquid circulation flow maintenance device (11). The purified liquid enters the purified liquid line (17). The drained liquid returns to the liquid mixing unit (5) through the recirculation line (13) and enters the raw liquid / concentrate mixing chamber (6). Furthermore, the raw liquid continues to flow into the raw liquid / concentrate mixing line (9) through the raw liquid supply line (1), and further into the raw liquid / concentrate mixing chamber (6) of the (raw liquid / concentrate) liquid mixing device (5) in an amount equal to the amount of purified liquid produced. Uniform mixing of the raw liquid and concentrate occurs in the raw liquid / concentrate mixing chamber (6) within the liquid mixing device (5). As described above, the chamber (7) is filled with a compressible medium, such as air. The pressure in the chamber (7) gradually increases as liquid begins to fill the raw liquid / concentrate mixing chamber (6). During liquid filtration, the liquid pressure in the raw liquid / concentrate mixing chamber (6) gradually increases over time under the operation of the pressure maintaining device (4).

[0025] As with any fluid dynamics process, the liquid adhering to the membrane surface moves more slowly than its mainstream. Although the mainstream may be turbulent, the liquid layer near the membrane surface remains laminar. This liquid layer is called the boundary layer. When the feed solution passes through the membrane (i.e., at the moment the feed solution is separated into the purified solution and the discharge solution), essentially all the salt ions are retained in the boundary layer near the membrane surface. This effect is called "concentration polarization," during which the salt concentration on the surface of the liquid purification device increases; it increases the osmotic pressure therein and reduces the specific productivity of the liquid purification device.

[0026] During the liquid filtration process, a portion of the concentrate is periodically discharged to the drain port within a short period of time. Simultaneously, the control unit outputs a signal to open the drain valve (15). The liquid circulation maintenance device (11) can continue operating or be closed. When the drain valve (15) is opened, the pressure in the liquid purification device (12) drops sharply. Because the time for opening the drain valve (15) for drainage is very short, and the pressure drop between the purified liquid line (17) and the liquid purification device (12) is large, the liquid purification device will experience hydraulic shock when the drain valve (15) is closed. However, due to the liquid mixing device (5) installed in the system, which accumulates pressure during the liquid filtration process and is installed downstream of the pressure maintenance device (4), the pressure in the liquid purification device (12) stabilizes when the drain valve (15) is closed. At the moment the drain valve (15) is opened, the concentrated liquid under pressure accumulated in the chamber (7) of the liquid mixing device (5) enters the liquid purification device (12) at high speed through the original liquid / concentrated liquid supply line (10) via the liquid circulation flow maintenance device (11) and is discharged to the drain port. At the same time, the polarization layer formed in the concentration polarization is removed from the surface of the purification device.

[0027] When the purification liquid storage device (20) in the purification liquid unit (18) is full of purification liquid, the liquid mixing device (5) is completely emptied. The control unit receives a signal from a pressure change monitoring device (23) such as a high-pressure switch located in the purification liquid line (17), and closes the raw liquid supply valve (3), disables the pressure maintaining device (4), while the circulating liquid flow maintaining device (11) remains active, and the drain valve (15) is opened. The concentrate flows from the chamber (6) of the liquid mixing device (5) into the circulating liquid flow maintaining device (11) through the raw liquid / concentrate supply line (9), through the liquid purification device (12), through the drain line (14), and through the open drain valve (15) to the drain port. Then, the liquid purification device (12) is flushed with raw liquid. While the raw liquid supply valve (3) remains open, the control unit outputs a signal to open the drain valve (15), and the pressure maintaining device (4) remains active. The raw liquid flows through the raw liquid supply line (1) via the pressure maintaining device (4), into the chamber (6) of the liquid mixing device (5), and further into the liquid purification device (12) via the raw liquid / concentrate supply line (10) and the circulating liquid flow maintaining device (11). Then, a small amount of raw liquid / discharge mixture remaining in the system is extracted from the system via the drain line (14) and the open drain valve (15). When the flushing of the liquid purification device (12) with raw liquid is completed, the system enters a static state until the purification liquid supply device (19) is opened and the pressure in the purification liquid storage device (20) in the purification liquid unit (18) drops. At this time, the control unit receives a signal from the pressure change monitoring device (22) installed in the purification liquid line (17) and restarts the filtration process.

[0028] This specification illustrates preferred embodiments of the invention. Various modifications may be made to the embodiments without departing from the scope of the claims, thereby providing the possibility of its wide application.

[0029] Similar to the liquid purification system taught in the closest prior art and US 5503735, the pressure stabilization means of periodically flushing the liquid purification device with the concentrate is provided because the pressure maintaining device reduces the high velocity of the liquid flow through the liquid purification device. However, due to the above-described design features, the system according to the invention provides pressure stabilization in the liquid purification device when the liquid flow is periodically discharged (the rate of the concentrate exceeds the productivity of the pressure maintaining device, without mixing the concentrate with the concentrate). Since the polarization layer of contaminants causing salinization in the liquid purification device is destroyed when the drain is briefly discharged from the surface of the liquid purification device, the operational stability and lifespan of the liquid purification device, and therefore the entire liquid purification system, are increased. The system also provides for the recirculation of all concentrate, thereby utilizing the concentrate more efficiently.

Claims

1. A liquid purification system, comprising: A raw liquid supply line, having a raw liquid supply valve mounted thereon and connected to a filtration unit, the filtration unit comprising: a liquid purification device having an inlet for the raw liquid and an outlet for purified liquid and drained liquid; a liquid mixing device; a pressure maintaining device; a line for supplying a mixture of the raw liquid and a concentrate formed during the liquid purification process in the liquid purification device; a recirculation line; a purified liquid line; a drained liquid line; and a control unit connected to the pressure maintaining device, a pressure change monitoring device, and the raw liquid supply valve, characterized in that the filtration unit is adapted to enable the liquid purification device to... Pressure stabilization: The liquid flow is periodically discharged at a discharge rate exceeding the performance of a pressure maintaining device, which is located in the raw liquid supply line upstream of a liquid mixing device in the form of a pressure tank. This liquid mixing device is connected to a line for mixing the raw liquid and the concentrate formed during filtration. Simultaneously, the amount of concentrate in the liquid mixing device is regulated by a control unit connected to a device for maintaining pressure in the pressure tank-type liquid mixing device, a circulating liquid flow maintaining device located upstream of the liquid purification device in the raw liquid / concentrate supply line, and a discharge valve located in the discharge line. The internal space of the pressure tank-type liquid mixing device is divided by a flexible partition into a chamber for mixing the raw liquid and the concentrate formed during the liquid purification process, and a chamber filled with a compressible medium.

2. The liquid purification system according to claim 1, characterized in that, The recirculation line is connected downstream of the pressure maintaining device to the crude liquid supply line and the crude liquid / concentrate mixing line via a connecting unit, and the crude liquid / concentrate mixing line is connected to the crude liquid / concentrate mixing device.

3. The liquid purification system according to claim 1, characterized in that, The control unit is configured to regulate the flushing of the liquid purification device by periodically deactivating the pressure maintaining device and opening the drain valve after a predetermined time interval.

4. The liquid purification system according to claim 1, characterized in that, The liquid purification system also includes a purification liquid unit connected to the purification liquid pipeline.

5. The liquid purification system according to claim 4, characterized in that, The purification liquid unit includes a purification liquid supply device, and a liquid disinfection device is provided upstream of the purification liquid supply device.

6. The liquid purification system according to claim 5, characterized in that, The purification liquid unit also includes a purification liquid circulation maintenance device and a purification liquid accumulation device, wherein the purification liquid accumulation device is connected to the inlet of the purification liquid supply device and the outlet of the purification liquid circulation maintenance device.

7. The liquid purification system according to claim 6, characterized in that, The purification liquid unit includes a disinfection device located upstream of the purification liquid accumulation device.

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