阅读说明：本技术 脱盐系统和方法 (Desalination system and method ) 是由 菲利普·安德鲁·戴维斯 于 2019-05-01 设计创作，主要内容包括：本发明涉及一种脱盐系统和操作脱盐系统的方法。实例实施方式包括脱盐系统(100),该脱盐系统包括：分隔容器(101),容纳将容器(101)分隔成各自具有可变体积的上游隔室(114)和下游隔室(115)的可移动分隔件(102),分隔容器(101)具有在容器(101)的上游端处的第一入口端口(121)、在容器(101)的下游端处的第二入口端口(122)、和在容器(101)的下游端处的出口端口(124)；膜容器(104),容纳将膜容器(104)分成盐水隔室(131)和脱盐隔室(132)的错流半透膜(105),盐水隔室(131)包括第一错流端口和第二错流端口(106、107),脱盐隔室(132)包括脱盐水出口端口(113)；进给泵(108),被连接以将盐水供应供给到第一入口端口(121)；补给泵(109),具有连接到第二错流端口(107)的入口和连接到第二入口端口(122)的出口,以将盐水供给到下游隔室(115)中；主阀(110),连接在出口端口(124)和第一错流端口(106)之间；旁通阀(111),在一侧上连接到入口端口(121),并且在另一侧上连接到第二错流端口(107)和补给泵(109)的入口；以及清洗阀(112),在一侧上连接到第一错流端口(106)和主阀(110),并且在另一侧上连接到清洗端口(123)。(The present invention relates to a desalination system and a method of operating a desalination system. An example embodiment includes a desalination system (100) comprising: a separation vessel (101) housing a moveable partition (102) separating the vessel (101) into an upstream compartment (114) and a downstream compartment (115) each having a variable volume, the separation vessel (101) having a first inlet port (121) at an upstream end of the vessel (101), a second inlet port (122) at a downstream end of the vessel (101), and an outlet port (124) at the downstream end of the vessel (101); a membrane container (104) containing a cross-flow semi-permeable membrane (105) dividing the membrane container (104) into a saltwater compartment (131) and a desalination compartment (132), the saltwater compartment (131) comprising a first and a second cross-flow port (106, 107), the desalination compartment (132) comprising a desalinated water outlet port (113); a feed pump (108) connected to supply a supply of brine to the first inlet port (121); a make-up pump (109) having an inlet connected to the second cross-flow port (107) and an outlet connected to the second inlet port (122) to supply brine into the downstream compartment (115); a main valve (110) connected between the outlet port (124) and the first cross-flow port (106); a bypass valve (111) connected on one side to the inlet port (121) and on the other side to the second cross-flow port (107) and to an inlet of the make-up pump (109); and a purge valve (112) connected on one side to the first cross-flow port (106) and the main valve (110) and on the other side to the purge port (123).)

1. A desalination system (100), comprising:

a partitioned container (101) housing a moveable partition (102) that partitions the container (101) into an upstream compartment (114) and a downstream compartment (115) each having a variable volume, the partitioned container (101) having a first inlet port (121) at an upstream end of the container (101), a second inlet port (122) at a downstream end of the container (101), and an outlet port (124) at the downstream end of the container (101);

a membrane container (104) containing a cross-flow semi-permeable membrane (105) dividing the membrane container (104) into a saltwater compartment (131) and a desalination compartment (132), the saltwater compartment (131) comprising a first and a second cross-flow port (106, 107), the desalination compartment (132) comprising a desalinated water outlet port (113);

a feed pump (108) connected to supply a supply of saline to the first inlet port (121);

a make-up pump (109) having an inlet connected to the second cross-flow port (107) and an outlet connected to the second inlet port (122) to supply saline into the downstream compartment (115);

a main valve (110) connected between the outlet port (124) and the first cross-flow port (106);

a bypass valve (111) connected on one side to the inlet port (121) and on the other side to the second cross-flow port (107) and an inlet of the make-up pump (109); and

a purge valve (112) connected on one side to the first cross-flow port (106) and the main valve (110) and on the other side to a purge port (123).

2. The desalination system (100) of claim 1, comprising a controller (125) connected to the desalination system and configured to operate the desalination system (100), the controller (125) configured to:

in a first pressurization phase, closing the bypass valve (111) and the purge valve (112), opening the main valve (110) and operating the feed pump (108) to provide a supply of brine to the upstream compartment (114) of the partitioned vessel (101), causing the moveable partition (102) to move and thereby flow brine from the downstream compartment (115) into the brine compartment (131) of the membrane vessel (104), causing desalinated water to exit from the desalination compartment (132) of the membrane vessel via the desalinated water outlet port (113); and

in a second replenishment phase, the bypass valve (111) and the purge valve (112) are opened, the main valve (110) is closed and the replenishment pump (109) and the feed pump (108) are operated to supply brine to the second inlet port (122) of the partitioned vessel (101) and into the brine compartment (131) of the membrane vessel (104) via the second cross-flow port (107) to cause brine to flow out through the purge port (123) via the first cross-flow port (106).

3. The desalination system (100) of claim 2, wherein, in the first pressurization phase, the controller is configured to operate the make-up pump (109) to supply saltwater from the saltwater compartment (131) to the second inlet port (122) of the partitioned container (101).

4. The desalination system (100) of claim 2 or 3, wherein the controller (125) is configured to repeat the pressurization phase and the replenishment phase.

5. The desalination system (100) of any one of claims 2-4, comprising a first sensor (126) arranged to provide a signal to detect when the moveable partition (102) has reached an upstream end of the partitioned container (101) in the replenishment phase, the controller being configured to end the replenishment phase upon detecting the signal from the first sensor (126).

6. The desalination system (100) of any one of claims 2-5, comprising a second sensor (127) arranged to provide a signal to detect when the moveable partition (102) has reached the downstream end of the partitioned container (101) in the pressurization phase, the controller being configured to end the pressurization phase upon detection of the signal from the second sensor (127).

7. The desalination system (100) of any preceding claim, wherein the partitioned container is a cylindrical container (101) and the moveable partition is a piston (102) slidably mounted within the cylindrical container (101).

8. The desalination system (100) of any preceding claim, wherein the membrane vessel is a cylindrical vessel (104).

9. The desalination system (400) of any of the preceding claims, comprising:

one or more further partitioned containers (401b-c), each partitioned container housing a moveable partition (402b-c) that partitions the container into an upstream compartment (114) and a downstream compartment (115) each having a variable volume, each further partitioned container (401b-c) having a first inlet port (121) at an upstream end of the container, a second inlet port (122) at a downstream end of the container, and an outlet port (124) at the downstream end of the container;

one or more further membrane containers (404b-c), each membrane container housing a cross-flow semi-permeable membrane (105) dividing the membrane container into a saline compartment (131) and a desalinated compartment (132), the saline compartment (131) comprising a first cross-flow port (106) and a second cross-flow port (107), the desalinated compartment (132) comprising a desalinated water outlet port (113),

wherein the feed pump (108) is connected to supply a supply of brine to the first inlet port (121) of each divided vessel, the make-up pump (109) is connected between the second cross-flow port (107) of each membrane vessel and the second inlet port (122) of each divided vessel to supply brine into the downstream compartment (115) of each vessel, the main valve (110) is connected between the outlet port (124) of each divided vessel and the first cross-flow port (106) of each membrane vessel, the bypass valve (111) is connected on one side to the inlet port (121) of each divided vessel and on the other side to the second cross-flow port (107) of each membrane vessel, and the purge valve (111) is connected on one side to the first cross-flow port (106) of each membrane vessel.

10. The desalination system (100, 400) according to any of the preceding claims, wherein the semi-permeable membrane is of a reverse osmosis type.

11. The desalination system (100, 400) according to any of the preceding claims, wherein the controller (125) is configured to electrically control the operation of the main valve (110), the bypass valve (111) and the purge valve (112).

12. The desalination system (100, 400) of any of claims 1-10, wherein the controller (125) is configured to electrically control operation of the purge valve (112), and wherein the main valve (110) and the bypass valve (111) are actuated between an open position and a closed position by a water pressure level within the desalination system (100, 400).

13. The desalination system (100, 400) of claim 12, wherein the main valve (110) is configured to open when a water pressure level within the desalination system (100, 400) is above a threshold pressure level, and the bypass valve (111) is configured to open when the water pressure level is below the threshold pressure level.

14. The desalination system (100, 400) of claim 13, wherein the main valve (600) comprises:

a housing (611) having an inlet (608) and an outlet (609);

a plunger (603) slidably mounted to the housing (611) and having a sealing surface (605) arranged to seal against an inner surface (606) of the housing (611) to prevent flow between the inlet (608) and the outlet (609); and

a biasing element (607) arranged to bias the sealing surface (605) away from the inner surface (606) of the housing (611) to maintain a flow path between the inlet (608) and the outlet (609) when the water pressure level within the main valve (600) is less than the threshold pressure level, and to close the flow path when the water pressure level within the main valve (600) is greater than the threshold pressure level.

15. The desalination system (100, 400) of claim 13 or 14, wherein the bypass valve (800) comprises:

a housing (811) having an inlet (808) and an outlet (809);

a plunger (803) slidably mounted to the housing (811) and having a sealing surface (805) arranged to seal against an inner surface (806) of the housing (811) to prevent flow between the inlet (808) and the outlet (809); and

a biasing element (807) arranged to bias the sealing surface (805) against the inner surface (806) of the housing (811) to close the flow path between the inlet (808) and the outlet (809) when the water pressure level within the bypass valve (800) is less than the threshold pressure level, and to open the flow path when the water pressure level within the bypass valve (800) is greater than the threshold pressure level.

16. The desalination system (100, 400) of any of claims 13-15, wherein the threshold pressure level is about 1 bar gauge.

17. A method of operating a desalination system (100), the desalination system (100) comprising:

a partitioned container (101) housing a moveable partition (102) that partitions the container (101) into an upstream compartment (114) and a downstream compartment (115) each having a variable volume, the partitioned container (101) having a first inlet port (121) at an upstream end of the container (101), a second inlet port (122) at a downstream end of the container (101), and an outlet port (124) at the downstream end of the container (101);

a membrane container (104) containing a cross-flow semi-permeable membrane (105) dividing the membrane container (104) into a saline compartment (131) and a desalinated compartment (132), the saline compartment (131) comprising a first and a second cross-flow port (106, 107), the desalinated compartment (132) comprising a desalinated water outlet port (113);

a feed pump (108) connected to supply a supply of saline to the first inlet port (121);

a make-up pump (109) connected between the second cross-flow port (107) and the second inlet port (122) to supply saline into the downstream compartment (115);

a main valve (110) connected between the outlet port (124) and the first cross-flow port (106);

a bypass valve (111) connected on one side to the inlet port (121) and on the other side to the second cross-flow port (107) and the make-up pump (109); and

a purge valve (111) connected on one side to the first cross-flow port (106) and the main valve (110) and on the other side to a purge port (123),

the method comprises the following steps:

in a first pressurization phase, closing the bypass valve (111) and the purge valve (112), opening the main valve (110) and operating the feed pump (108) to provide a supply of brine to the upstream compartment (114) of the partitioned container (101), causing the moveable partition (102) to move and thereby cause brine to flow from the downstream compartment (115) into the brine compartment (131) of the membrane container (104), causing desalinated water to exit from the desalinated water compartment (132) of the membrane container via the desalinated water outlet port (113); and

in a second replenishment phase, the bypass valve (111) and the purge valve (112) are opened, the main valve (110) is closed and the replenishment pump (108) and the feed pump (108) are operated to supply brine to the second inlet port (122) of the partitioned vessel (101), into the brine compartment (131) of the membrane vessel (104) via the second cross-flow port (107) and out through the purge port (123) via the first cross-flow port (106).

18. The method of claim 17, wherein the first pressurization stage comprises operating the make-up pump (109) to supply saline from the saline compartment (131) to the second inlet port (122) of the partitioned container (101).

19. The method of claim 17 or claim 18, comprising repeating the pressurization phase and the replenishment phase.

20. The method of any one of claims 17 to 19, comprising detecting a signal from a first sensor (126) when the moveable separation member (102) has reached the upstream end of the divided container (101) in the replenishment phase, and ending the replenishment phase when the signal from the first sensor (126) is detected.

21. The method according to any one of claims 17 to 20, comprising detecting a signal from a second sensor (127) when the moveable separation member (102) has reached the downstream end of the divided container (101) in the pressurisation phase, and ending the pressurisation phase when a signal from the second sensor (127) is detected.

Technical Field

The present invention relates to a desalination system and a method of operating a desalination system.

Background

Desalination systems have many industrial applications. For example, one application is the separation of drinking water from groundwater which is saline and therefore unsuitable for drinking. Other applications include the treatment of seawater and the treatment of salt waste water produced by textile mills.

In desalination applications, it is often desirable to maximize recovery. The term recovery is the volume of fresh water produced at the output of the system as a fraction of the volume of saltwater supplied at the input. High recovery rates are often required to maximize the useful output of the system and minimize the required input.

Disclosure of Invention

According to a first aspect of the present invention, there is provided a desalination system comprising:

a separation vessel containing a moveable partition separating the vessel into an upstream compartment and a downstream compartment each having a variable volume, the separation vessel having a first inlet port at an upstream end of the vessel, a second inlet port at a downstream end of the vessel, and an outlet port at the downstream end of the vessel;

a membrane container containing a cross-flow semi-permeable membrane that divides the membrane container into a saltwater compartment and a desalination compartment, the saltwater compartment comprising a first cross-flow port and a second cross-flow port, the desalination compartment comprising a desalinated water outlet port;

a feed pump connected to supply a supply of brine to the first inlet port;

a make-up pump having an inlet connected to the second cross-flow port and an outlet connected to the second inlet port to supply saline into the downstream compartment;

a main valve connected between the outlet port and the first cross-flow port;

a bypass valve connected on one side to the inlet port and on another side to the second cross-flow port and an inlet of the make-up pump; and

a purge valve connected on one side to the first cross-flow port and the main valve and on the other side to the purge port.

The invention described herein is particularly useful for achieving high recovery and high output of fresh/desalinated water without incurring excessive energy losses.

The desalination system can further include a controller coupled to and configured to operate the desalination system, the controller configured to:

in a first pressurisation stage, closing the bypass valve and the purge valve, opening the main valve and operating the feed pump to provide a supply of brine to the upstream compartment of the partition vessel, causing the partition to move and thereby cause brine to flow from the downstream compartment into the brine compartment of the membrane vessel, causing desalinated water to exit from the desalination compartment of the membrane vessel via the desalinated water outlet port; and

in a second makeup stage, the bypass valve and the purge valve are opened, the main valve is closed and the makeup pump and the feed pump are operated to supply brine to the second inlet of the separation vessel and into the brine compartment of the membrane vessel via the second cross-flow port to cause brine to flow out through the purge port via the first cross-flow port.

In the first pressurization phase, the controller may be configured to operate the make-up pump to supply the brine from the brine compartment to the second inlet of the partitioned container.

The controller may be configured to repeat the pressurization phase and the replenishment phase.

The desalination system can further include a first sensor arranged to provide a signal to detect when the moveable separation member has reached the upstream end of the separation vessel during a replenishment stage, the controller being configured to end the replenishment stage upon detecting the signal from the first sensor.

The desalination system can further include a second sensor arranged to provide a signal to detect when the moveable separation member has reached the downstream end of the separation vessel in a pressurization phase, the controller configured to end the pressurization phase upon detecting the signal from the second sensor.

The separation vessel may be a cylindrical vessel and the moveable separation member may be a piston slidably mounted within the cylindrical vessel.

The membrane container may be a cylindrical container.

In the case where the separation vessel is a first separation vessel and the membrane vessel is a first membrane vessel, the desalination system may further comprise:

one or more additional separation vessels, each separation vessel housing a moveable partition separating the vessel into an upstream compartment and a downstream compartment each having a variable volume, each additional separation vessel having a first inlet port at an upstream end of the vessel, a second inlet port at a downstream end of the vessel, and an outlet port at a downstream end of the vessel;

one or more additional membrane containers, each membrane container housing a cross-flow semi-permeable membrane dividing the membrane container into a saline compartment and a desalinated compartment, the saline compartment comprising a first cross-flow port and a second cross-flow port, the desalinated compartment comprising a desalinated water outlet port,

wherein a feed pump is connected to supply a brine supply to the first inlet port of each partitioned vessel, a make-up pump is connected between the second cross-flow port of each membrane vessel and the second inlet port of each partitioned vessel to supply brine into the downstream compartment of each vessel, a main valve is connected between the outlet port of each partitioned vessel and the first cross-flow port of each membrane vessel, a bypass valve is connected on one side to the inlet port of each partitioned vessel and on the other side to the second cross-flow port of each membrane vessel, and a purge valve is connected on one side to the first cross-flow port of each membrane vessel.

The semi-permeable membrane may be of the reverse osmosis type.

The controller may be configured to electrically control operation of the main valve, the bypass valve, and the purge valve. In other arrangements, the controller may be configured to electrically control operation of the purge valve, and wherein the main valve and the bypass valve are actuated between the open position and the closed position by a water pressure level within the system.

The main valve may be configured to open when a water pressure level within the system is above a threshold pressure level, and the bypass valve may be configured to open when the water pressure level is below the threshold pressure level.

In some embodiments, the main valve may comprise:

a housing having an inlet and an outlet;

a plunger slidably mounted to the housing and having a sealing surface arranged to seal against an inner surface of the housing to prevent flow between the inlet and the outlet; and

a biasing element arranged to bias the sealing surface away from the inner surface of the housing to maintain a flow path between the inlet and the outlet when the water pressure level within the main valve is less than a threshold pressure level, and to close the flow path when the water pressure level within the main valve is greater than the threshold pressure level.

In some embodiments, the bypass valve may comprise:

a housing having an inlet and an outlet;

a plunger slidably mounted to the housing and having a sealing surface arranged to seal against an inner surface of the housing to prevent flow between the inlet and the outlet; and

a biasing element arranged to bias the sealing surface against an inner surface of the housing to close the flow path between the inlet and the outlet when a water pressure level within the bypass valve is less than a threshold pressure level, and to open the flow path when the water pressure level within the bypass valve is greater than the threshold pressure level.

The threshold pressure level may be about 1 bar gauge, i.e. a 1 bar difference between the water pressure level in the system and the external atmospheric pressure.

According to a second aspect, there is provided a method of operating a desalination system, the desalination system comprising:

a separation vessel containing a moveable partition separating the vessel into an upstream compartment and a downstream compartment each having a variable volume, the separation vessel having a first inlet port at an upstream end of the vessel, a second inlet port at a downstream end of the vessel, and an outlet port at the downstream end of the vessel;

a membrane container containing a cross-flow semi-permeable membrane dividing the membrane container into a saline compartment and a desalinated water compartment, the saline compartment comprising a first cross-flow port and a second cross-flow port, the desalinated water compartment comprising a desalinated water outlet port;

a feed pump connected to supply a supply of brine to the first inlet port;

a make-up pump connected between the second cross-flow port and the second inlet port to supply brine into the downstream compartment;

a main valve connected between the outlet port and the first cross-flow port;

a bypass valve connected on one side to the inlet port and on another side to the second cross-flow port and the make-up pump; and

a purge valve connected on one side to the first cross-flow port and the main valve and on the other side to the purge port,

the method comprises the following steps:

in a first pressurisation stage, closing the bypass valve and the purge valve, opening the main valve and operating the feed pump to provide a supply of brine to the upstream compartment of the partition vessel, causing the partition to move and thereby cause brine to flow from the downstream compartment into the brine compartment of the membrane vessel, thereby causing desalinated water to exit from the desalinated water compartment of the membrane vessel via the desalinated water outlet port; and

in a second makeup stage, the bypass valve and the purge valve are opened, the main valve is closed and the makeup pump and the feed pump are operated to supply brine to the second inlet of the separation vessel, into the brine compartment of the membrane vessel via the second cross-flow port and out through the purge port via the first cross-flow port.

The first pressurization stage may include operating a make-up pump to supply saline from the saline compartment to the second inlet of the partitioned container.

The method may include repeating the pressurization phase and the replenishment phase.

The method may include detecting a signal from the first sensor when the moveable separation member has reached the upstream end of the separation vessel during the replenishment phase, and ending the replenishment phase when the signal from the first sensor is detected.

The method may include detecting a signal from the second sensor when the moveable separation member has reached the downstream end of the separation vessel during the pressurization phase, and ending the pressurization phase when the signal from the second sensor is detected.

Other features of the first aspect may also be applied to the method according to the second aspect.

Drawings

The invention is described in more detail below by way of example and with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an example desalination system;

FIG. 2 is a schematic diagram of an example desalination system in a first stage of operation;

FIG. 3 is a schematic diagram of an example desalination system in a second stage of operation;

FIG. 4 is a schematic diagram of an alternative example desalination system in which multiple vessels are used for increased desalinated water output;

FIG. 5 is a schematic flow diagram illustrating an example method of operating a desalination system;

FIG. 6 is a schematic cross-sectional view of an example pressure actuated valve in a closed position;

FIG. 7 is a schematic cross-sectional view of the valve of FIG. 6 in an open position;

FIG. 8 is a schematic cross-sectional view of an alternative example pressure actuated valve in a closed position;

FIG. 9 is a schematic cross-sectional view of the valve of FIG. 8 in an open position;

FIG. 10 is a schematic cross-sectional view of an alternate example of the valve of FIG. 6 in a closed position;

FIG. 11 is a schematic cross-sectional view of the valve of FIG. 10 in an open position;

FIG. 12 is a schematic cross-sectional view of an alternate example of the valve of FIG. 8 in a closed position; and

FIG. 13 is a schematic cross-sectional view of the valve of FIG. 12 in an open position.

Detailed Description

One example type of common desalination system is known as a continuous flow system, in which brine is pumped under pressure so that it flows tangentially to the surface of a semi-permeable membrane. As the brine is collected and transferred from the membrane, its concentration increases greatly. Corresponding to this high concentration, a high osmotic pressure is generated and a high operating pressure is required. This pressure determines the power consumption of the feed pump according to the well-known relationship:

power-volumetric flow rate of supplied water/operating pressure

Thus, a high operating pressure leads to increased power and thus to a high electrical energy consumption of the feed pump. Such high electrical energy consumption is undesirable because it is expensive for the operation of the desalination system and may be harmful to the environment.

A second example is known as a semi-batch desalination system, for example as described in US 4,983,301. In this system, the pressure is carefully changed in time so that only the pressure required to drive the water through the membrane is provided at each moment. However, a disadvantage of semi-batch systems is the mixing of the incoming brine with the more concentrated brine already contained in the system, which results in inefficient and unnecessary use of energy.

A third example is an intermittent desalination system such as described in Davies et al, "A desalination system with efficiency improving the organic limits" (desalination and water treatment, 57(2016)23206- "23216). This system is designed to avoid the mixing problem described above. However, existing batch desalination systems have limited daily output associated with their mode of operation. Its operation requires three phases: (i) a pressurizing stage; (ii) a cleaning stage; and (iii) a refill phase. However, useful output occurs only during the first of these phases. Output pauses throughout the second and third phases reduce the daily output of the system.

According to the invention described herein, there is provided a desalination system that allows for an intermittent desalination process that is cyclic and requires only two operational stages, namely: (i) a pressurization phase and (ii) a purge-refill phase. As shown in fig. 1, the system includes a first compartmentalized container 101 and a second membrane container 104, whereby the compartmentalized container 101 is divided into an upstream compartment 114 and a downstream compartment 115 by a movable partition or piston 102. A supply of pressurized saline is provided to the upstream compartment 114 by the first feed pump 108, which causes a gradual increase in the volume of the upstream compartment 114 (which may initially be zero) causing the partition 102 to move, moving saline from the downstream compartment 115 and into the membrane container 104, thereby causing the desalinated water to permeate through the semi-permeable membrane 105 extending across the membrane container 104. The membrane 105 is shown schematically in fig. 1 as extending diagonally across the membrane vessel 104, but in practice the membrane geometry may take various forms, such as a spiral wound or hollow fiber geometry, to increase the available surface area of the membrane 105. When the partition 102 reaches the end of its stroke, it is returned to its original position by a second low pressure make-up pump 109 which refills the downstream compartment 115, while the bypass valve 111 allows the feed water provided by the first pump 108 to purge the membrane vessel 104. Thus, the present invention allows the non-productive period of cleaning and refilling to be minimized by performing cleaning and refilling simultaneously. These two operating phases can be repeated continuously and indefinitely in a cyclic manner.

In some examples, the first vessel 101 and/or the second vessel 104 may be split into multiple vessels connected in parallel to allow the desalination system 100 to provide greater throughput through the parallel operation of easily configured smaller vessels.

Advantages associated with the present invention include:

1. minimum energy consumption during operation

2. High recovery of fresh water from brine

3. High daily output of desalted water

4. The design is simplified by minimizing the number of valves required.

Fig. 1 shows an example desalination system 100 in which a partitioned vessel 101 provides a saltwater supply to a membrane vessel or vessel 104 containing a semi-permeable membrane 105 to provide a desalinated water supply via an outlet port 113. The semi-permeable membrane 105 divides the membrane vessel 104 into a brine compartment 131 and a desalination compartment 132. In this example, the separate container is a cylindrical container 101 that houses a piston 102, the piston 102 being slidably mounted within the cylindrical container 101. The vessel 101 may be made of glass reinforced plastic, stainless steel, or some other material that is pressure resistant and resistant to salt water corrosion. The inner diameter of the vessel 101 may typically be four inches (about 10.2 cm). The piston 102 is machined to a diameter of just less than four inches so that it can slide freely within the cylindrical container 101. To prevent water from leaking between the compartments on either side of the piston, the piston may be fitted with an O-ring seal 103. Alternatively, the piston 102 may be machined with sufficiently tight tolerances to prevent significant leakage, and therefore does not require any seals.

The container 104 containing the membrane 105 may be in the form of a second cylindrical container containing a semi-permeable membrane element 105 of the type that allows cross-flow to occur, since it is important to remove the concentrated salt solution from the surface of the membrane 105. The first and second cross-flow ports 106, 107 allow cross-flow to enter and exit the vessel 104 in two directions, respectively, i.e. into and out through the second cross-flow port 107 and through the first cross-flow port 106, and vice versa. The membrane element 105 used may be of the spiral wound reverse osmosis type, such as commonly used in the desalination industry. Hollow fiber or flat sheet reverse osmosis membranes may also be used.

Fig. 1 also shows a first high-pressure feed pump 108 and a second low-pressure make-up pump 109. The first pump 108 provides a supply of brine to a first inlet 121 of the cylindrical vessel 101. A bypass valve 111 connected between the first pump 108 and the second cross-flow port 107, when open, allows brine to bypass the cylindrical vessel 101 from the feed pump 108 and flow into the brine compartment 131 of the membrane vessel 104 via the second cross-flow port 107 and to the make-up pump 109 to a second inlet 122 located at a downstream end of the cylindrical vessel 101 opposite the first inlet 121. A purge valve 112 connected between the first cross-flow port 106 and the purge outlet 123, when open, allows concentrated brine from the brine compartment 131 of the membrane vessel 104 to flow from the first cross-flow port 106 to the purge outlet 123. A main valve 110 connected between the first cross-flow port 106 and the outlet 124 of the separation vessel 101 allows, when open, brine to flow from the outlet 124 to the first cross-flow port 106 of the membrane vessel 104. The valves 110, 111, 112 may be solenoid valves. To minimize power consumption when actuating the valve, the main valve 110 may be normally open, while the bypass valve 111 and the purge valve 112 may be normally closed. The valves 110, 111, 112 may be motorized or pneumatically actuated, or in some cases, particularly for the bypass valve 111 and the main valve 110, may be pressure actuated, as described in more detail below.

An electrical control unit or controller 125 is connected and configured to operate the valves 110, 111, 112 in response to sensors 126, 127 arranged to detect the position of the piston 102. A first sensor 126 may be provided at the second inlet 122 to detect when the piston 102 moves back to the starting position, i.e. towards the upstream end of the first inlet 121 end of the container 101. A second sensor 127 may be provided at the inlet 121 to detect when the piston 102 has moved to the downstream end of the container 101. The sensors 126, 127 may be pressure or flow sensors. For a pressure sensor, when the piston 102 reaches either end of the container 101, it will cause the pressure in the upstream compartment 114 or downstream compartment 115 to rise, which can be detected by the associated sensors 126, 127. The pressure difference between the sensors 126, 127 located at or near the outlet 124 and inlet 127, respectively, can be used to detect when the piston 102 has reached either end of the container 101. For a flow sensor, when the piston 102 reaches either end of the container 101, a reduction in flow rate will result. First sensor 126 may be, for example, a pressure sensor because the pressure available from first pump 108 is relatively large. The second sensor 127 may be a flow sensor because the pressure change will be smaller when the piston 102 returns to the upstream end of the reservoir 101. In an alternative arrangement, the sensors 126, 127 may be proximity sensors configured to provide a signal when the piston 102 is in proximity to the sensors, thereby detecting when the piston 102 is at the upstream or downstream end of the partitioned container 101.

The various components of the desalination system 100 can be connected by pressure and corrosion resistant piping, as shown in solid lines in fig. 1. These pipes are typically constructed of polyvinyl chloride or stainless steel and are connected by threads or flanges using techniques well known to those skilled in the art of designing and constructing desalination systems.

The brine feed water enters the system at inlet 128 of feed pump 108 and is separated into desalinated water that exits via permeate port 113, while concentrated brine exits via purge valve 112 and purge port 123. As mentioned above, the operating method to achieve this separation comprises only two phases: pressurization and purge-refill, as explained below with reference to fig. 2 and 3, respectively. In both figures, the pipes carrying the water flow are indicated by solid lines, while the pipes not carrying the water flow are indicated by dashed lines. The flow is opened and closed by the respective solenoid valves 110, 111, 112. The closed position of the valves 110, 111, 112 is indicated by solid line shading, while the open position is indicated by valves drawn with unshaded contour lines.

Fig. 2 specifically shows the arrangement of the system 100 in a pressurization phase, during which the feed pump 108 supplies saline to the upstream compartment 114 on the left side of the piston 102. In this stage, the purge valve 112 and the bypass valve 111 are closed, while the main valve 110 is open. The feed pump 108 causes the water in the upstream compartment 114 to become pressurized such that the action of the pressurized water on the piston 102 causes it to slide to the right, thereby displacing the brine held in the downstream compartment 115 and causing the water to flow under pressure into the brine compartment 131 of the membrane vessel 104 via the first cross-flow port 106. To induce cross-flow in the brine compartment 131, the low pressure pump 109 draws brine from the brine compartment 131 via the second cross-flow port 107 and returns it to the downstream compartment 115 in a recirculation loop that is switched on by opening the main valve 110. The recirculation of water at a higher flow rate (e.g., a flow rate several times the flow rate of the feed pump 108) has the advantage of maintaining a well-mixed and uniformly concentrated flow throughout the circuit. This feature of rapid recirculation is important to mitigate high local concentrations of salts (known as concentration polarization). The rapid recirculation also mitigates concentration gradients along the membrane 105 of the membrane vessel 104 that would otherwise result in high osmotic pressure at the outlet port 113, resulting in higher required pumping power. Thus, in a general aspect, the make-up pump 109 is configured to pump at a flow rate that is two or more times the flow rate of the feed pump 108, such as between two and ten times the flow rate of the feed pump 108. The rightward movement of the piston 102 causes a gradual reduction in volume within this circuit, as fresh water permeates the membrane 105 to collect via the permeate outlet port 113, while the concentration of brine in the circuit gradually increases.

Once the piston 102 is fully moved to the right, the saline reaches a maximum concentration and needs to be purged from the system. Thus, the purge-refill or replenishment phase shown in FIG. 3 now begins. Purging is achieved by opening the bypass valve 111 and the purge valve 112, allowing a volume of water to be supplied by the feed pump 108 to the brine compartment 131 of the partitioned vessel 104 via the second cross-flow port 107, and concentrated brine to exit the system 100 through the purge valve 112 and the purge port 123. At the same time, the main valve 110 is closed so that the low pressure makeup pump 109 no longer causes recirculation through the brine compartment 131 of the membrane vessel 104. Conversely, the flow of saline from the make-up pump 109 into the downstream compartment 115 causes the piston 102 to move rearwardly, i.e., fully to the left of the reservoir 101 with reference to fig. 3, toward its initial position at the upstream end of the partitioned reservoir 101. Thus, water discharged from the upstream compartment 114 flows to the inlet of the low pressure pump 109 via the bypass valve 111.

Figure 4 shows an alternative example comprising a plurality of separate containers 401a-c and a plurality of membrane containers 404a-c for increasing the output of desalinated water. In this example, three identical cylindrical containers 401a-c house respective pistons 402 a-c. The piping manifold 441 connects the three partitioned vessels 401a-c at the left-hand upstream end, thereby providing one interconnected upstream compartment. Similarly, the piping manifolds 442 and 443 connect the partitioned containers 401a-c at the right-hand downstream end to provide one interconnected downstream compartment. The manifolds 441, 442, 443 can be of uniform size such that water flows evenly between the reservoirs 401a-c and the pistons 402a-c move at the same speed, thus reaching the end of each stroke at about the same time. The film containers 404a-c are similarly connected by manifolds 444, 445, 446. Other features of the desalination system 400 are similar to those of the desalination system 100 described above, except that a plurality of vessels operating in parallel are used. The method of operation of the desalination system 400 may also be similar to that described above.

It will be appreciated that the number of separation vessels 401a-c and membrane vessels 404a-c may be greater than that shown, and that the number of each may be the same or different. In fact, a substantially greater number may be arranged to provide an output of desalinated water that increases substantially in proportion to the number of containers used.

In an example method of operation, the duration of the pressurization phase may typically be about 2 minutes or 2.5 minutes, while the duration of the purge-refill or replenishment phase is typically about 20 or 30 seconds. In general terms, the duration of the pressurization phase may typically be between about 1 and 5 minutes, while the duration of the replenishment phase may be between about 15 and 60 seconds. In other words, the pressurization stage may be 1 to 20 times as long as the replenishment stage. These durations will vary depending on the selected use conditions, but typically the pressurisation phase will last several times, for example more than twice, longer than the wash-and-refill phase, and accordingly the pause in water output during the latter phase is relatively short. As a result, the use of a normally open valve for the main valve 110 and a normally closed valve for the purge valve 112 and the bypass valve 111 will result in a saving of power when operating the desalination system.

FIG. 5 illustrates in schematic form an example method of operation of a desalination system of the type described above. In a first step 501, the bypass valve 111 and the purge valve 112 are closed, and the main valve 110 is opened. In a second step 502, feed pump 108 and make-up pump 109 are operated to supply brine to upstream compartment 114 of partitioned vessel 101 and to recirculate the brine through brine compartment 131 of membrane vessel 104, respectively. In a third step 503 it is checked whether the piston 102 has reached the downstream end of the separate container 101. If not, the process continues at step 502. Once the piston 102 has reached the downstream end of the separation vessel 101, the process moves to step 504, where the bypass valve 111 and the purge valve 112 are opened, and the main valve 110 is closed. At step 505, the feed pump 108 and the make-up pump 109 are operated, and at step 506, it is checked whether the piston 102 has returned to the upstream end of the separate container 101. If not, the process continues at step 505. Once the piston reaches the downstream end of the separation vessel 101, the process returns to step 501 and the process begins again.

Steps 503, 506 may enable detection of when the piston 102 reaches the downstream end and the upstream end of the separation vessel 101 by using sensors, such as the sensors 126, 127 described above.

The desalination system 100, 400 as described above comprises three valves: a bypass valve 111, a main valve 110 and a purge valve 112. Each of these valves may be controlled by a controller 125 (fig. 1) that provides electrical signals to actuate each valve at the appropriate time during the pressurization and replenishment phases. The valve may be, for example, a solenoid valve to allow such electrical operation. However, solenoid valves and other electrically operated valves have certain disadvantages, such as continuous power consumption upon actuation. Even if the valve can only be actuated for a relatively short period of time during the replenishment phase, the power consumption at this time may be higher, thus increasing the capacity of the required power source. Solenoid valves are also rather expensive and not always reliable, and they may significantly restrict flow, although the advantage is that they are standard components and therefore readily available.

An alternative to using solenoid valves or other electrically operated valves for the bypass and main valves is to use pressure actuated valves. Thus, such a valve can be actuated solely by the water pressure within the system, and does not require electrical power to actuate it. Only the purge valve 112 needs to be electrically actuated. The use of pressure actuated valves has the advantage of reducing the power consumption of the system and simplifying the control circuitry.

As detailed above, the system operates cyclically, alternating between production pressurization phases and non-production makeup (i.e., purge-refill) phases. At the beginning of the pressurization phase, the pressure inside the system rises rapidly (typically over a period of several seconds) to initially reach a pressure of, for example, about 5 bar gauge, and then gradually increases further to reach a higher pressure of typically about 15 bar gauge. The exact value of the pressure will depend on the salinity level and flow rate, but the pressure during the pressurization phase is relatively high and in the range of about 5-15 bar. At the beginning of the make-up phase, when the purge valve 112 is opened, the pressure in the system will therefore suddenly drop to a value less than 1 bar gauge, being kept at low pressure throughout the remainder of the phase. This large swing in pressure means that it is possible to use a spring-loaded pressure-actuated valve that responds to the difference between the internal pressure and the external atmospheric pressure (i.e., gauge pressure). Gauge pressure may be used to move a plunger that is spring loaded and has a sealing surface that may block or allow flow through the valve depending on the position of the plunger. Such pressure actuated valves are not conventional spring loaded valves that respond to a pressure differential between their inlet and outlet ports. In contrast, there is a large pressure difference between the interior of the valve and the outside atmosphere, which reaches a considerable level. The pressure difference between the inlet and outlet ports will tend to remain small, typically less than 0.5 bar.

In the case of the bypass valve 111, this valve needs to be closed when the pressure inside the system is high, i.e. during the pressurization phase. An example design of a valve to achieve this is shown in fig. 6 and 7. The valve 600 comprises a housing 611 having a main body 601 and a flange 602 which together house a slidably mounted plunger 603. The shaft of the plunger 603 extends outwardly from the body 601 and a sliding seal 604 is provided between the plunger 603 and the body 601 to prevent water leakage. The inner end of the plunger 603 comprises a sealing surface 605 which can seal against a corresponding inner surface 606 of the body 601. A sealing O-ring may be provided on the sealing surface 605 to provide a water-tight seal against the inner surface 606. A biasing element, such as a spring 607 biases the sealing surface 605 away from the inner surface 606 so that when the pressure inside the valve is low, the valve opens to allow fluid to flow between the inlet 608 and the outlet 609 of the valve 600. This open position is shown in fig. 7. An increase in pressure inside the valve 600 causes the plunger 603 to slide such that the sealing surface 605 is forced against the inner surface 606, causing flow between the inlet 608 and the outlet 609 to stop, as shown in fig. 6. Once the internal pressure is sufficiently reduced, the biasing element 607 causes the plunger 603 to slide back and open flow between the inlet 608 and the outlet 609. A circlip 610 may be provided on the plunger 603 to limit the travel of the plunger 603. The range of travel of the plunger may alternatively or additionally be limited by an end stop within the housing of the valve 600.

Thus, in a general aspect, the valve 600 includes:

a housing 611 having an inlet 608 and an outlet 609;

a plunger 603 slidably mounted to the housing 611 and having a sealing surface 605 arranged to seal against an inner surface 606 of the housing 611 to prevent flow between the inlet 608 and the outlet 609; and

a biasing element 607 arranged to bias the sealing surface 605 away from the inner surface 606 of the housing 611 when the pressure within the valve 600 is less than the threshold pressure level to maintain a flow path between the inlet 608 and the outlet 609, and to close the flow path when the pressure within the valve 600 is greater than the threshold pressure level.

The threshold pressure level may be set to be greater than the external pressure (i.e., atmospheric pressure) by a preset amount, such as 1 bar. Thus, the valve may remain open as long as the pressure within the valve is less than 1 bar gauge, i.e. nominally 2 bar absolute, and close when the pressure is above this level.

In the case of the main valve 110, an example pressure actuated valve 800 is shown in FIGS. 8 and 9. The structure of the valve 800 is substantially similar to that of the valve 600 of fig. 6 and 7, in that the valve 800 includes a housing 811 having a body 801 and a flange 802, a plunger 803 slidably mounted with a sliding seal 804 within the body 801 and having a sealing surface 805 that seals against an inner surface 806 of the housing. However, in this example, the plunger is held normally closed by the biasing element 807 in an unpressurized condition, preventing flow between the inlet 808 and the outlet 809. When the gauge pressure rises, the plunger 803 is pushed to the right and the valve 800 opens, allowing flow between the inlet 808 and the outlet 809. This open position is shown in fig. 9. A circlip 810 or other type of end stop limits the travel of the plunger to hold the valve 800 in its open position under pressure.

Thus, in a general aspect, the valve 800 includes:

a housing 811 having an inlet 808 and an outlet 809;

a plunger 803 slidably mounted to housing 811 and having a sealing surface 805 arranged to seal against an inner surface 806 of housing 811 to prevent flow between inlet 808 and outlet 809; and

a biasing element 807 arranged to bias the sealing surface 605 against an inner surface 806 of the housing 811 to close the flow path between the inlet 808 and the outlet 809 when the pressure within the valve 800 is less than a threshold pressure level, and to open the flow path when the pressure within the valve 800 is greater than the threshold pressure level.

The threshold pressure level may be set to be greater than the external pressure (i.e., atmospheric pressure) by a preset amount, such as 1 bar. Thus, the main valve may remain closed as long as the pressure within the valve is less than 1 bar gauge, i.e. nominally 2 bar absolute, and open when the pressure is above this level.

Valves 600, 800 of the type described above may be incorporated into the systems 100, 400 as bypass valves and main valves, with the normally open valve 600 acting at the bypass valve 111, i.e. closed during the pressurization phase and open during the replenishment phase, and the normally closed valve 800 acting as the main valve 110, i.e. open during the pressurization phase and closed during the replenishment phase. Thus, the pressurization of the system 100, 400 is controlled by the operation of the purge valve 112 and the operation of the feed pump 108.

Fig. 10 and 11 show an alternative example of a valve used as a bypass valve, the operation of which is similar to that shown in fig. 6 and 7. The valve 1000 includes a housing 1011 which houses a slidably mounted plunger 1003. The shaft of the plunger 1003 extends outwardly from the housing 1011 providing a sliding seal 1004 between the plunger 603 and the body 601 to prevent water leakage. The interior portion of the plunger 1003 includes a sealing surface 1005 that may seal against a corresponding interior surface 1006 of the housing 1011. A sealing O-ring (not shown) may be disposed on the sealing surface 1005 to provide a water-tight seal against the inner surface 1006. A biasing element, such as a spring 1007, biases the sealing surface 1005 away from the inner surface 1006 such that when the pressure inside the valve 1000 is low, the valve opens to allow fluid to flow between the inlet 1008 and the outlet 1009 of the valve 1000. This open position is shown in fig. 11. An increase in pressure inside the valve 1000 causes the plunger 1003 to slide, pressing the sealing surface 1005 against the inner surface 1006, causing flow between the inlet 1008 and the outlet 1009 to stop. Once the internal pressure is sufficiently reduced, the biasing element 1007 causes the plunger 1003 to slide back and open flow between the inlet 1008 and the outlet 1009. An end stop 1010 may be provided to limit the travel of the plunger 1003.

Fig. 12 and 13 show an alternative example of a valve used as a main valve, the operation of which is similar to that shown in fig. 8 and 9. The structure of the valve 1200 is substantially similar to that of the valve 1000 of fig. 10 and 11, in that the valve 1200 includes a housing 1211 within which a plunger 1203 is slidably mounted by a sliding seal 1204 and has a sealing surface 1205 that seals against an inner surface 1206 of the housing 1211. However, in this example, the plunger 1203 is held normally closed by the biasing element 1207 in an unpressurized condition, thereby preventing flow between the inlet 1208 and the outlet 1209. When the gauge pressure rises, the plunger 1203 is pushed up and the valve 1200 opens, allowing flow between the inlet 1208 and the outlet 1209. This open position is shown in fig. 13. An end stop may be provided to limit the travel of the plunger 1203 in order to hold the valve 1200 in its open position under pressure.

Other embodiments are intended to be within the scope of the invention, which is defined by the following claims.