System for purifying a liquid

Abstract

A valved raw liquid supply line, which is connected to a filtration unit including a liquid purification unit with an inlet and with outlets for purified liquid and drain liquid, a mixing device, a means for maintaining pressure, a means for maintaining a recirculating flow of liquid, which is located on a line supplying a mixture of raw liquid and concentrate upstream of the liquid purification unit, a recirculating line, a purified liquid line, a drain liquid line, and a control unit, which is connected to the means for maintaining pressure, pressure monitor, the raw liquid supply valve and a drain liquid discharge valve. The means for maintaining pressure is located on a raw liquid supply line upstream of the liquid mixing device. The technical result is a longer system working life, more efficient use of raw liquid, and reduced energy expenditure.

Claims

1. A liquid purification system, comprising: a raw liquid feed valve configured to mount to a raw liquid feed line; a filtration unit comprising: a liquid purification unit with an inlet for raw liquid and an outlet for purified liquid and an outlet for drain liquid, a means for maintaining pressure, a raw liquid/concentrate supply line to supply a mix of raw liquid and concentrate formed in a liquid purification process to the liquid purification unit, a liquid mixing device comprising a pressure tank having a first cavity and a second cavity separated by a flexible partition and connected to the raw liquid/concentrate supply line to supply a mix of the raw liquid and the concentrate to the liquid purification unit from the first cavity, the liquid mixing device connected to receive the concentrate into the first cavity from the liquid purification unit in a way to build pressure within the liquid mixing device by compressing the second cavity during receiving the concentrate during the liquid purification process, a recirculation line, a purified liquid line, a drain liquid line connected to the outlet for drain liquid, a circulating liquid flow maintenance means disposed in the raw liquid/concentrate supply line upstream of the liquid purification unit, and a drain discharge valve disposed in the drain liquid line, wherein in response to opening the drain discharge valve, the drain discharge valve, the liquid mixing device, and the liquid purification device are connected such that drain liquid from the first cavity of the liquid mixing device drains through the liquid purification device using the pressure built in the liquid mixing device with the flexible partition during receiving the concentrate during the liquid purification process and at a drain liquid velocity exceeding a liquid velocity for liquid driven by the means for maintaining pressure, the drain liquid discharging while simultaneously reducing an amount of the concentrate in the liquid mixing device.

2. The liquid purification system according to claim 1, wherein the second cavity is configured to be filled with a compressible medium.

3. The liquid purification system according to claim 1, wherein the recirculation line is connected, via a connection unit, to the raw liquid feed line downstream of the means for maintaining pressure, and to the line to supply the mix of the raw liquid and the concentrate connected to the liquid mixing device.

4. The liquid purification system according to claim 1, further comprising a control unit connected and configured to regulate flushing of the liquid purification unit by periodically deactivating the means for maintaining pressure and opening the drain discharge valve after predetermined time intervals.

5. The liquid purification system according to claim 1, further comprising a purified liquid unit connected to the purified liquid line.

6. The liquid purification system according to claim 5, wherein the purified liquid unit comprises a purified liquid supply means with a liquid disinfection device disposed upstream of the purified liquid supply means.

7. The liquid purification system according to claim 6, wherein the purified liquid unit further comprises a purified liquid circulating flow maintenance means and a purified liquid accumulation device connected to an inlet of the purified liquid feed and to an outlet of the purified liquid circulating flow maintenance means.

8. The liquid purification system according to claim 7, wherein the liquid disinfection device is disposed upstream of the purified liquid accumulation device.

9. A liquid purification method comprising: supplying a mix of raw liquid and concentrate formed in a liquid purification process to a liquid purification unit via a raw liquid/concentrate supply line, receiving concentrate from the liquid purification unit into a liquid mixing device to build pressure within the liquid mixing device, the liquid mixing device comprising a pressure tank connected to the raw liquid/concentrate supply line to supply a mix of the raw liquid and the concentrate to the liquid purification unit, opening a drain discharge valve, in response to opening the drain discharge valve, draining drain liquid from the liquid mixing device through the liquid purification device using the pressure built during the receiving the concentrate, the draining the drain liquid occurring at a drain liquid velocity exceeding a liquid velocity for liquid driven by a means for maintaining pressure during a liquid purification process, the drain liquid discharging while simultaneously reducing an amount of the concentrate in the liquid mixing device.

10. The liquid purification method according to claim 9, further comprising regulating flushing of the liquid purification unit by periodically deactivating the means for maintaining pressure and opening the drain discharge valve after predetermined time intervals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic diagram of a liquid purification system.

DETAILED DESCRIPTION

(2) A liquid purification system (FIG. 1) comprises a raw liquid feed line (1) having a raw liquid feed valve (3) mounted thereon and connected to a filtration unit (2) including a pressure maintenance means (4) mounted on the raw liquid feed line (1), a liquid mixing device (5) connected to a raw liquid/concentrate mixing line (9) and to a raw liquid/concentrate supply line (10) connected to an inlet (12c) of a liquid purification means (12). The raw liquid/concentrate mixing line (9) is connected, via a connection unit (21), downstream of the pressure increasing means (4), to the raw liquid feed line (1) and to a recirculation line (13). Purified liquid outlet (12a) of the liquid purification means (12) is connected through a purified liquid line (17) to a purified liquid unit (18). Drain liquid outlet (12b) of the liquid purification means (12) is connected to the recirculation line (13) connected, via the connection unit (21), to the raw liquid feed line (1) and to the raw liquid/concentrate mixing line (9). A pressure variation monitoring means (22), e.g. a low-pressure switch, is mounted in the raw liquid feed line (1) and coupled to a control unit (not shown in FIG. 1). A prefilter (16) is further provided in the raw liquid feed line (1).

(3) A drain liquid line (14) with a drain discharge valve (15) mounted thereon and coupled to the control unit is connected to the recirculation line (13).

(4) The liquid mixing device (5) is in the form of a pressure tank, whose internal space is separated by a flexible partition (8) into a cavity (6) for mixing raw liquid and the concentrate formed in the liquid purification process, and a cavity (7) filled with a compressible medium e.g. air.

(5) A circulating liquid flow maintenance means (11), e.g. a circulation pump, is mounted in the raw liquid/concentrate supply line (10) upstream of the liquid purification means (12).

(6) The control unit is coupled to the valve (3) mounted in the raw liquid feed line (1), the valve (15) mounted in the drain liquid line (14), the pressure maintenance means (4), the circulating liquid flow maintenance means (11) and the pressure variation monitoring means (22).

(7) The liquid purification means (12) can be in the form of e.g. a reverse osmosis membrane or nano-filtration membrane.

(8) A purified liquid unit (18) connected to a purified liquid line (17) comprises a purified liquid supply means (19) in the form of e.g. a tap. A purified liquid accumulation device (20), e.g. a water-air tank, can be arranged upstream of the purified liquid supply means (19), with a purified liquid circulating flow maintenance means (31), e.g. a circulation pump, mounted upstream of it. A pressure variation monitoring means (23), e.g. a high-pressure switch, is mounted downstream of the purified liquid storage device (20) in the purified liquid line (17), and a liquid disinfection means (30), e.g. a flow-through UV lamp (not shown) can be further provided.

(9) Within the scope of distinctive features, the liquid purification system is intended for implementing the following liquid filtration process.

(10) At startup of the liquid purification system, raw liquid is admitted from a source (not shown in FIG. 1) to the inlet of the raw liquid feed line (1) and through the open valve (3) connected to the control unit enters, via the prefilter (16), a pressure increasing means (4). Then, raw liquid flows through a raw liquid/concentrate mixing line (9) into a liquid mixing device (5). Owing to the fact that the pressure increasing means (4) is disposed upstream of the liquid mixing device (5), raw liquid enters a storage cavity (6) under pressure, which is maintained constant during the liquid filtration cycle and sufficient for passage of liquid through one liquid purification means (12). Further, raw liquid flows through a raw liquid/concentrate supply line (10) via a circulating flow maintenance means (11) into a liquid purification means (12). Purified liquid enters a purified liquid supply line (17). Drain liquid returns through a recirculation line (13) back to the liquid mixing device (5) into a raw liquid/concentrate mixing cavity (6). Furthermore, raw liquid continues flowing through the raw liquid feed line (1) to the raw liquid/concentrate mixing line (9), and further, to the cavity (6) of the raw liquid/concentrate mixing device (5) in the amount equal to that of the produced purified liquid. Uniform mixing of raw liquid with the concentrate takes place in the mixing device (5) in the cavity (6). As mentioned above, the cavity (7) is filled with a compressible medium, e.g. air. When liquid begins filling the cavity (6), pressure in the cavity (7) gradually grows. During the liquid filtration process, at operation of the pressure maintenance means (4), pressure of liquid in the cavity (6) is gradually growing over time.

(11) Like any hydrodynamic process, the liquid adhering to the surface of the membrane moves more slowly than its main stream. While the main stream can be turbulent, the near-surface liquid layer over the membrane remains laminar. This layer is called boundary layer. When raw liquid passes through the membrane (i.e. at the instant when raw liquid is separated into purified and drain), substantially all salt ions remain in the boundary layer near the surface of the membrane. This effect was called “concentration polarization”, at which the concentration of salts on the surface of the liquid purification means increases; it raises the osmotic pressure in it and reduces the specific productivity of the liquid purification means.

(12) During the liquid filtration process, a portion of concentrated liquid is periodically discharged to drain during a short time. At the same time the control unit outputs a signal to open a valve (15). The circulating liquid flow maintenance means (11) can continue to work or be shut down. When the valve (15) opens, pressure in the liquid purification means (12) drastically drops. As the time of opening the valve (15) for draining is very short, and the drop between pressure in the purified liquid line (17) and the liquid purification means (12) is substantial, at closing the drain discharge valve (15) the liquid purification means will experience hydraulic impacts. However, owing to the provision of the liquid mixing device (5) in the system, which accumulates pressure in the liquid filtration process and is mounted downstream of the pressure maintenance means (4), when the drain discharge valve (15) is closed the pressure in the liquid purification means (12) is stabilized. At the instant of opening the drain discharge valve (15) the concentrated liquid under the pressure accumulated in the cavity (7) of the liquid mixing device (5) passes through the raw liquid/concentrate supply line (10) via the circulating liquid flow maintenance means (11) with high velocity into the liquid purification means (12) and is discharged to drain, and at the same time the polarization layer formed at the concentration polarization is removed from the surface of the purification means.

(13) When the purified liquid storage device (20) in the purified liquid unit (18) is fully filled with purified liquid, the liquid mixing device (5) is fully emptied. The control unit receives a signal from a pressure variation monitoring means (23), such as a high-pressure switch, disposed in the purified liquid line (17), and closes the valve (3), deactivates the pressure maintenance means (4), while the circulating liquid flow maintenance means (11) remains activated, and the valve (15) opens. Concentrated liquid flows from the cavity (6) of the mixing device (5) through the raw liquid/concentrate supply line (9) into the circulating liquid flow maintenance means (11), and is discharged to drain via the liquid purification means (12) through the drain discharge line (14) and via the open valve (15). Then, the liquid purification means (12) is flushed with raw liquid. The control unit outputs a signal to open the drain discharge valve (15), while the valve (3) stays open, and the pressure maintenance means (4) stays activated. Raw liquid flows through the raw liquid feed line (1) via the pressure maintenance means (4), into the cavity (6) of the liquid mixing device (5), and further, through the raw liquid/concentrate supply line (10) via the circulating liquid flow maintenance means (11) into the liquid purification means (12), and then, through the drain discharge line (14) via the open drain discharge valve (15) the small amount of raw liquid/drain liquid mix remained in the system is withdrawn from the system. Upon completion of flushing the liquid purification means (12) with raw liquid the system goes to quiescent state until the purified liquid supply means (19) is open and pressure in the purified liquid storage device (20) in the purified liquid unit (18) drops. At this time the control unit receives a signal from the pressure variation monitoring means (22) disposed in the purified liquid line (17), and filtration process is initiated again.

(14) The present description represents a preferred embodiment of the invention. Various modifications can be made in the embodiment without departing from the scope of claims, thereby offering the possibility of its wide application.

(15) Similarly to the liquid purification system taught in the closest prior art and in U.S. Pat. No. 5,503,735, stabilization of pressure at periodic flushing of the liquid purification means with raw liquid is provided owing to the pressure maintenance means impairing high velocity to the liquid flow through the liquid purification means. However, owing to the design features described above, the system according to the present invention provides for stabilization of pressure in the liquid purification means at periodic draining of the liquid flow with a velocity of concentrated liquid exceeding the productivity of the pressure maintenance means, without mixing the concentrated liquid with raw liquid. Owing to the fact that the polarization layer of contaminants, which contributes to salting the liquid purification means, is destroyed at the short-term discharge of drain from the surface of the liquid purification means, the operation stability and the life of the liquid purification means, and hence the entire liquid purification system, increase. The system also provides for recirculation of all concentrated liquid, which results in a more efficient utilization of raw liquid.