WO2013036354A1

WO2013036354A1 - Desalination system and method

Info

Publication number: WO2013036354A1
Application number: PCT/US2012/050512
Authority: WO
Inventors: Rihua Xiong; Chengqian Zhang
Original assignee: General Electric Company
Priority date: 2011-09-08
Filing date: 2012-08-13
Publication date: 2013-03-14
Also published as: CN102992521A; TW201315533A

Abstract

A desalination system comprises a silica removal apparatus configured to receive a first feed stream for silica removal. The silica removal apparatus comprises first and second electrodes, and a plurality of paired ion exchange membranes disposed between the first and second electrodes to form a plurality of alternating first and second channels. The silica removal apparatus further comprises a plurality of spacers disposed between each pair of the adjacent ion exchange membranes and between the first and second electrodes and the respective ion exchange membranes. Wherein a first member of each pair of the ion exchange membranes is an anion exchange membrane and a second member of each pair of the ion exchange membranes is an anion exchange membranes, a monovalent cation exchange membrane or a bipolar ion exchange membrane, and wherein the first members and the second members are disposed alternately within the plurality of the paired ion exchange membranes.

Description

DESALINATION SYSTEM AND METHOD

BACKGROUND OF THE DISCLOSURE

[0001] The invention relates generally to desalination systems and methods for water recovery. More particularly, this invention relates to desalination systems and methods using ion exchange membranes for silica removal and water recovery.

[0002] In industrial processes, large amounts of wastewater, such as aqueous saline solutions are produced. Generally, such wastewater is not suitable for direct consumption in domestic or industrial applications. In view of the limited eligible water sources, it is desirable to recover eligible water from the wastewater.

[0003] There have been attempts to remove silica from the wastewater or other water sources containing silica. For example, streams including silica are introduced into desalination apparatuses, such as reverse osmosis apparatuses while pH of such streams is increased for silica removal because higher pH of the streams results in higher ionization of silica. However, in current applications, such processes suffer from complicated and rigorous pretreatment requirements and high cost. Typically, fluctuation and inefficiency of pretreatment may cause scaling or precipitate of sparingly soluble salts, such as calcium sulfate or calcium carbonate sometimes within the silica removal apparatuses, which is disadvantageous for silica removal and the silica removal apparatuses.

[0004] Therefore, there is a need for new and improved desalination apparatus, system and method for silica removal and water recovery.

BRIEF DESCRIPTION OF THE DISCLOSURE

[0005] A desalination system is provided in accordance with one embodiment of the invention. The desalination system comprises a silica removal apparatus configured to receive a first feed stream for silica removal. The silica removal apparatus comprises first and second electrodes, and a plurality of paired ion exchange membranes disposed between the first and second electrodes to form a plurality of alternating first and second channels. The silica removal apparatus further comprises a plurality of spacers disposed between each pair of the adjacent ion exchange membranes and between the first and second electrodes and the respective ion exchange membranes. Wherein a first member of each pair of the ion exchange membranes is an anion exchange membrane and a second member of each pair of the ion exchange membranes is an anion exchange membranes, a monovalent cation exchange membrane or a bipolar ion exchange membrane, and wherein the first members and the second members are disposed alternately within the plurality of the paired ion exchange membranes.

[0006] A desalination system is provided in accordance with another embodiment of the invention. The desalination system comprises a silica removal apparatus. The silica removal apparatus comprises first and second electrodes, and a plurality of paired anion exchange membranes disposed between the first and second electrodes to form a plurality of alternating first and second channels. The silica removal apparatus further comprises a plurality of spacers disposed between each pair of the adjacent anion exchange membranes and between the first and second electrodes and the respective anion exchange membranes.

[0007] Embodiment of the invention further provides a desalination method for removing silica from an aqueous stream. The desalination method comprises passing a first feed stream through first channels defined by paired ion exchange membranes of a silica removal apparatus for silica removal, and passing a second feed stream through second channels defined by the paired ion exchange membranes of the silica removal apparatus to carry away silica removed from the first feed stream. Wherein a first member of each pair of the ion exchange membranes is an anion exchange membrane and a second member of each pair of the ion exchange membrane is an anion exchange membranes, a monovalent cation exchange membrane or a bipolar ion exchange membrane, and wherein the first members and the second members are disposed alternately within the paired ion exchange membranes. [0008] These and other advantages and features will be better understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a schematic diagram of a desalination system in accordance with one embodiment of the invention;

[0010] FIGS. 2-4 are schematic diagram of a silica removal apparatus in accordance with various embodiments of the invention;

[0011] FIG. 5 is a schematic diagram of the desalination system in accordance with another embodiment of the invention; and

[0012] FIG. 6 is an experimental graph illustrating silica removal efficiency of the silica removal apparatus in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0013] Preferred embodiments of the present disclosure will be described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the disclosure in unnecessary detail.

[0014] FIG. 1 is a schematic diagram of a desalination system 10 in accordance with one embodiment of the invention. As illustrated in FIG. 1, the desalination system 10 comprises a desalination apparatus 11 configured to receive a first feed stream 12 having salts or other impurities from a first liquid source (not shown) for desalination and to receive a second feed stream 13 from a second liquid source (not shown) during or after desalination of the first feed stream 12 so as to carry charged species removed from the first feed stream 12 out of the desalination apparatus 1 1. [0015] In non-limiting examples, the salts in the first feed stream 12 may include charged ions, such as magnesium (Mg²⁺), calcium (Ca²⁺), silica, sodium (Na⁺), chlorine (CI ), and/or other ions. In one non-limiting example, the charged ions in the first feed stream 12 at least include a portion of target ions, such as ionized silica so that the desalination apparatus 1 1 may act as a silica removal apparatus. In some applications, the first output stream 14 may be circulated into the desalination apparatus 1 1 or other suitable desalination apparatuses, such as electrodialysis reversal (EDR) apparatuses for further desalination.

[0016] Generally, silica may be sparsely or partially ionized in the first feed stream 12. Increasing pH of the first feed stream 12 causes ionization of silica therein and facilitates removal thereof. Accordingly, as depicted in FIG. 1, the desalination system 10 further comprises a pH adjustment unit 16 in fluid communication with the desalination apparatus 11 and is configured to increase the pH of the first feed stream 12 so as to facilitate ionization of silica in the first feed stream 12.

[0017] In some examples, the pH adjustment unit 16 may adjust the pH of the first feed stream 12 to be greater than about 7, for example, in a range of from about 8 to about 11. In other examples, the pH of the first feed stream 12 may be adjusted to be in a range of from about 9.5 to about 11. After ionization, at least a portion of the silica in the first feed stream 12 may be ionized in a form of HSi0₃ ^" and/or Si0₃ ^2", for example, or other forms of charged species. For easy illustration, the ionized silica is illustrated in the form of HSiCV, for example.

[0018] For some arrangements, the pH adjustment unit 16 may comprise a pH adjustment source (not shown) to introduce additives into the first feed stream 12 to adjust the pH thereof. In non-limiting examples, the pH adjustment unit 16 may introduce basic additives into the first feed stream 12. Non-limiting examples of the basic additives include sodium hydroxide, potassium hydroxide and ammonia hydroxide. The basic additives may be introduced automatically or manually into the first feed stream 12. In certain applications, the pH adjustment unit 16 may not be employed in the desalination system 10 and the pH of the first feed stream 12 may be pre-adjusted. [0019] FIG. 2 illustrates a schematic diagram of the desalination apparatus

11 in accordance with one embodiment of the invention. As illustrated in FIG. 2, the desalination apparatus 1 1 comprises a first electrode 17, a second electrode 18, a plurality of paired ion exchange membranes 19, 20, 21, 22 and a plurality of spacers 23. In the illustrated example, the first and second electrodes 17, 18 are connected to positive and negative terminals of a power source (not shown) so as to act as an anode and a cathode, respectively. Alternatively, the polarity of the first and second electrodes 17, 18 may be reversed.

[0020] In some examples, the first and second electrodes 17, 18 may include metal materials, such as titanium plate or platinum coated titanium plate. In other examples, the first and second electrodes 17, 18 may include electrically conductive materials, which may or may not be thermally conductive, and may have particles with smaller sizes and large surface areas. In some examples, the electrically conductive material may include one or more carbon materials. Non-limiting examples of the carbon materials include activated carbon particles, porous carbon particles, carbon fibers, carbon aerogels, porous mesocarbon microbeads, or combinations thereof. In other examples, the electrically conductive materials may include a conductive composite, such as oxides of manganese, or iron, or both, or carbides of titanium, zirconium, vanadium, tungsten, or combinations thereof.

[0021] In the illustrated example, the first and second electrodes 17, 18 are in the form of plates that are disposed parallel to each other to form a stacked structure. In other examples, the first and second electrodes 17, 18 may have varied shapes, such as a sheet, a block, or a cylinder. In addition, the first and second electrodes 17, 18 may be arranged in varying configurations. For example, the first and second electrodes 17, 18 may be disposed concentrically with a spiraling and continuous space therebetween.

[0022] The paired ion exchange membranes 19-22 are configured to be passable for ions and are disposed between the first and second electrodes 17, 18 so as to form a plurality of alternating first channels 24 and second channels 25 therebetween, respectively. For some arrangements, the first channels 24 may be referred to as dilute channels and the second channels 25 may be referred to as concentrate channels under operating conditions. In the illustrated example, four ion exchange membranes 19-22 are employed to form one first channel 24 and two second channels 25, which are disposed alternatingly. Alternatively, at least three ion exchange membranes may be employed so as to form one or more first channels and one or more second channels between the first and second electrodes 17, 18.

[0023] For the illustrated arrangement in FIG. 2, each of first members 20, 22 and respective second members 19, 21 of each paired of the ion exchange membranes comprises an anion exchange membrane. In some embodiments, each of the anion exchange membrane may comprise one of a monovalent anion exchange membrane and a normal anion exchange membrane. The monovalent anion exchange membrane is configured to be only passable for monovalent anions. The normal anion exchange membrane is configured to be passable for not only the monovalent anions but also polyvalent anions. In non-limiting examples, suitable materials for use in the monovalent anion exchange membrane may include crosslinked copolymers derived from vinylbenzylchloride (VBC), dibutyl amine (DBA), tributyl amine (TBA), and divinylbenzene (DVB).

[0024] The spacers 23 are disposed between each pair of the adjacent ion exchange membranes 19-22, and between the first and second electrodes 17, 18 and the respective adjacent membranes 19, 22. In some embodiments, the spacers 23 may comprise any ion-permeable, electronically nonconductive material, including membranes, and porous and nonporous materials.

[0025] Accordingly, during operation, when the desalination apparatus 1 1 is at a normal polarity state, while an electrical current is applied to the desalination apparatus 1 1, liquids, such as the first and second feed streams 12, 13 are introduced into the first channel 24 and the second channels 25, respectively. In certain applications, the first and second feed stream 12, 13 may or may not be introduced into desalination apparatus 11 simultaneously.

[0026] Due to employment of the anion exchange membranes 19-22, in the dilute channel 24, at least a portion of ionized silica, such as HSiCV and other anions, such as OH^" and CI^" in the first feed stream 12 migrate through the anion exchange membrane 20 towards the anode 17 to enter into the concentrate channels 25. Cations, such as Ca²⁺ and Mg²⁺ in the first feed stream 12 cannot pass through the anion exchange membrane 20 and remain in the dilute channel 24.

[0027] In the concentrate channels 25, cations, such as Na⁺ in the second feed stream 13 may not migrate through the anion exchange membrane 19 and remain in the concentrate channels 25 even though the electrical field exerts a force on the cations toward the respective electrode (e.g. cations are pulled toward the cathode). In the desalination apparatus 1 1, the dilute channels 24 and the concentrate channels 25 are disposed alternatingly, so that anions, such as CI^" and OH^" in the second feed stream 13 in the concentrate channels 25 may migrate through the respective anion exchange membrane 19, 21, for example, to enter into the dilute channel(s) 24 adjacent to the respective concentrate channels 25.

[0028] In non-limiting examples, the second feed stream 13 may comprise soluble salts including active or strongly ionized anions, such as chloride ions (CI^", which is referred to be as Cl^"-rich stream). Accordingly, after the target ions, such as silica are migrated into the concentrate channels 25 from the respective dilute channels 24, in the concentrate channels 25, the active anions in the second feed stream 13 may carry at least a larger portion of the ionic current than the removed target ions in the concentrate channels 25 when the anions continues to migrate from the concentrate channels 25 to the respective dilute channels 24 during operation. In other examples, the active anions include sulfate ions (S0₄ ^2") or hydroxide ions (OH ).

[0029] For example, the soluble salts include sodium chloride (NaCl). At least a larger portion of the ionic current may be carried by CI^" or other active or strongly ionized anions, such as OH^" resulting in that at least a larger portion of the may not carry ionic current. In non-limiting examples, a concentration of the active cations may be greater than a concentration of the removed target ions in the respective concentrate channels 25. In other examples, an ionic mobility of the active ions is greater than the ionic mobility of the removed target ions in the respective concentrate channels 25 when migrated from the concentrate channels 25 to the respective dilute channels 24. In certain applications, during migration, amounts of the active ions in the second feed stream 13 may be greater than amounts of HS1O3^" migrated into the concentrate channels 25 for migration from the concentrate channels 25 to the respective dilute channels 24.

[0030] As a result, a portion of the active cations in the second feed stream 13 in the concentrate channels 25 may migrate through the respective anion exchange membranes to enter into the adjacent dilute channel 24. Since the active anions in the second feed stream 13 may carry a larger portion of the ionic current than the removed target ions in the concentrate channels 25 when continuing to migrate from the concentrate channels 25 to the respective dilute channels 24 during operation, a larger portion of HS1O₃ ^" may not further migrate through the anion exchange membranes 19, 21 to enter into the dilute channels 24 so as to remain in the respective concentrate channels 25 after migrated into the concentrate channels 25 from the respective dilute channels 24.

[0031] For some arrangements, in order to increase the ionic current carried by the active anions in the second feed stream 13 when migrated into the dilute channels 24 from the concentrate channel 25, as illustrated in FIG. l, the desalination system 10 further comprises an ion adjustment unit 26 in fluid communication with the second feed stream 13 so as to facilitate that the active anions in the second feed stream 13 carry at least a larger portion of the ionic current than the removed target ions in the concentrate channels 25 when continuing to migrate from the concentrate channels 25 to the respective dilute channels 24 during operation. In one non-limiting example, the ion adjustment unit 26 introduces sodium chloride solution to increase the concentration of the active ions in the second feed stream 13. In certain applications, the ion adjustment unit 26 may or may not be employed.

[0032] Accordingly, as depicted in FIG. 2, the second feed stream 13 passes through the concentrate channels 25 to carry the target anions, such as HSiCV migrated from the dilute channels 24 out of the desalination apparatus 1 1 so that the dilute stream (a product stream) 14 and the outflow stream 15 may have respective lower and higher concentration of the charged species, such as the target ions including the ionized silica, as compared to the first and second feed streams 12, 13.

[0033] Generally, increasing pH of the first feed stream 12 may cause the scaling or fouling tendency of the cations including, but not limited to Ca²⁺ and Mg²⁺ in the desalination apparatus. For the illustrated arrangement in FIG. 1, due to employment of the desalination apparatus 11, the ionized silica in the first feed stream 12 may be removed while the cations, such as Ca²⁺ and Mg²⁺ in the first feed stream 12 may still remain in the dilute channels 24 and may not concentrate in the concentrate channels, so that the scaling or fouling tendency may be avoided or mitigated in the concentrate channels 25.

[0034] In some examples, the polarity of the first and second electrodes 17, 18 of the desalination apparatus 1 1 may be reversed. In the reversed polarity state, the dilute channels from the normal polarity state may act as the concentrate channels to receive the second feed stream 13, and the concentrate channels from the normal polarity state may function as the dilute channels to receive the first feed stream 12 for desalination of the first feed stream 12, for example, for removal of silica in the first feed stream 12 and alleviation of the fouling tendency of the anions and cations in the desalination apparatus 1 1.

[0035] FIG. 3 illustrates a schematic diagram of a desalination apparatus 30 in accordance with another embodiment of the invention. As illustrated in FIG. 3, the arrangement is similar to the arrangement illustrated in FIG. 2. The two arrangements in FIGS. 2-3 differ in that in FIG. 3, each of second members 31 of the ion exchange membranes 20, 22, 31 of the silica removal apparatus 30 comprises a monovalent cation exchange membranes, so that a plurality of the alternating monovalent cation exchange membranes (the second members) 31 and the anion exchange membranes (first members) 20, 22 form a plurality of alternating first and second channels 24, 25 therebetween respectively, which are also referred to as dilute and concentrate channels 24, 25 under operating conditions.

[0036] The monovalent cation exchange membranes 31 are configured to be passable for monovalent cations. In one non-limiting example, suitable materials for use in the monovalent cation exchange membranes 31 may include crosslinked copolymers derived from acrylamidomethylpropane sulfonic acid (AMPS) and ethylene glycol dimethacrylate (EGDMA).

[0037] Accordingly, similar to the arrangement in FIG. 2, during operation, when the desalination apparatus 30 is at a normal polarity state, while an electrical current is applied to the desalination apparatus 30, first and second feed streams 12, 13 enter into the first channel 24 and the second channels 25, respectively. Due to the removal of the desalination apparatus 30, at least a portion of ionized silica, such as HS1O₃ ^", or other the anions, such as OH^" and CI^" in the first feed stream 12 migrate through the anion exchange membrane 20 towards the anode 17 to enter into the respective second channels 25.

[0038] The polyvalent cations including, but not limited to Ca²⁺ and/or Mg²⁺ in the first feed stream 12 may not migrate through the monovalent cation exchange membrane 31 to move toward to the cathode 18 and thus remain in the dilute channel 24. In some applications, monovalent cations, such as Na⁺ in the first feed stream 12 may migrate through the monovalent cation exchange membrane 31 to move toward to the cathode 18 and enter into the adjacent concentrate channels 25.

[0039] In the concentrate channels 25, due to the presence of the monovalent cation exchange membranes 31, the anions, such as HSiOs^" migrated from the dilute channel 24 may not further migrate through the monovalent cation exchange membrane 31 to move toward to the anode 17 for migration into adjacent dilute channels 24 and thus remain in the respective concentrate channels 25. The cations, such as Na⁺ in the concentrate channels 25 may also remain in the concentrate channels 25 due to the presence of the anion exchange membranes 20, 22.

[0040] As a result, during the second feed stream 13 passes through the concentrate channels 25, the monovalent cations and the anions, such as HS1O₃ ^" and/or S1O3^2" migrated into the concentrate channels 25 from the dilute channels 24 may be carried out of the desalination apparatus 30 so that a dilute stream (a product stream) 14 and an outflow stream 15 may have respective lower and higher concentration of the charged species, such as the ionized silica, as compared to the first and second feed streams 12, 13.

[0041] Accordingly, due to employment of the monovalent cation exchange membranes 31 in the desalination apparatus 30, at least a portion of the ionized silica may be removed from the first feed stream 12. Meanwhile, the cations, such as Ca²⁺ and Mg²⁺ in the first feed stream 12 may still remain in the dilute channels 24 and may not concentrate in the concentrate channels 25 so as to avoid or mitigate scaling or fouling tendency therein.

[0042] FIG. 4 illustrates a schematic diagram of a desalination apparatus 32 in accordance with yet another embodiment of the invention. As illustrated in FIG. 4, the arrangement is similar to the arrangement in FIG. 3. The two arrangements in FIGS. 3-4 differ in that in FIG. 4, each of second members 33 of the ion exchange membranes of the desalination apparatus 32 is a bipolar membrane instead of the monovalent cation exchange membranes 31 in FIG. 3. Thus, a plurality of the alternating bipolar membranes (second members) 33 and anion exchange membranes (first members) 20, 22 are disposed between the first and second electrodes 17, 18 to form a plurality of alternating first and second channels 24, 25.

[0043] In non-limiting examples, the bipolar membrane may generally comprise a cation exchange membrane, an anion exchange membrane and a junction layer disposed between the cation- and anion-exchange membranes. During operation of the bipolar membrane, water diffuses across the cation- and anion-exchange membranes into junction layer so as to be dissociated into H⁺ and OH^" ions. The H⁺ ions migrate through the cation exchange membrane towards the cathode while the OH^" ions migrate through the anion exchange membrane to the anode. Other anions may be excluded from the junction layer by the cation exchange layer and other anions may be excluded from the junction layer by the anion-exchange layer.

[0044] Accordingly, similar to the arrangement in FIG. 3, during operation, in the dilute channels, the anions, such as HS1O₃ ^" in the first feed stream 12 enter into the adjacent concentrate channels 25. The cations, such as such as Ca²⁺ and Mg²⁺ in the first feed stream 12 may not migrate through the bipolar membranes 33 and remain in the respective dilute channels 24. In the concentrate channels 25, due to the exclusion of the bipolar membranes 33, the anions, such as HSi03^~ migrated from the dilute channels remain in the respective concentrate channels 25 and may not enter into the adjacent dilute channels 24.

[0045] Thus, during the second feed stream 13 passes through the concentrate channels 25, the anions, such as HSiCV migrated from the dilute channels 24 may be carried out of the desalination apparatus 32 and separated from the cations, such as Ca²⁺ and Mg²⁺ so as to avoid scaling or fouling in the respective concentrate channels.

[0046] In certain applications, in order to avoid and/or alleviate the scaling tendency of the cations, such as Ca²⁺ and Mg²⁺ in the desalination apparatus 11, 30 or 32, which may be caused by employment of the pH adjustment unit 16, a pretreatment unit may be employed to pretreat a liquid to at least partially remove polyvalent cations in therein so as to produce the first feed stream 12 having a certain total dissolved solids (TDS) level and a certain concentration level of cations, such as Ca²⁺ and Mg²⁺ before the first feed stream 12 is introduced into the silica removal apparatus.

[0047] FIG. 5 illustrates a schematic diagram of the desalination system 10 in accordance with another embodiment of the invention. As illustrated in FIG. 5, the arrangement is similar to the arrangement in FIG. 1. The two arrangements in FIGS. 1 and 5 differ in that in FIG. 5, a pretreatment unit 34 is disposed upstream of and in fluid communication with the desalination apparatus 1 1 to pretreat an input liquid 35 to remove at least a portion of the strongly ionized ions, such as calcium and magnesium ions therein so as to produce a first feed stream 12 with suitable TDS levels and suitable concentration levels of the cations.

[0048] For the illustrated arrangement, the pretreatment unit 34 comprises an electrodialysis reversal (EDR) apparatus. Alternatively, the pretreatment unit 34 may also comprise an electrodialysis (ED) apparatus, a supercapacitor desalination (SCD) apparatus or a softening apparatus to pretreat the input liquid 35. [0049] Accordingly, during operation, the input liquid 35 is introduced into the EDR apparatus 34 for processing so that at least a portion of the anions and/or cations, such as Ca²⁺ and Mg²⁺ may be removed from the input liquid 35 so as to produce the first feed stream 12 having suitable TDS levels and suitable concentration levels of the cations for introduction into the desalination apparatus 1 1. Meanwhile, a second input liquid 36 is also introduced into the EDR apparatus 34 to carry the removed ions from the input liquid 35 out of the EDR apparatus 34 to produce an outflow stream 37, which may have a higher concentration of charged species compared to a second input liquid 36.

[0050] In certain applications, the desalination system 10 may further comprise a precipitation unit 38 in fluid communication with the EDR apparatus 34. The precipitation unit 38 may provide the second input liquid 36 circulated into the EDR apparatus 34. As the circulation of the second input liquid 36 continues, the concentration of the salts or other impurities continually increases, some salts with lower solubility, such as calcium sulphate in the second input liquid 36 is saturated or supersaturated. As a result, the degree of saturation or the supersaturation may reach a point where precipitation begins to take place in the precipitation unit 38. In some examples, at least a portion of the second input liquid 36 may be discharged from the precipitation unit 38 from a passageway 39. A fluid 40 may be introduced to supplement the second input liquid 36. In non-limiting examples, the fluid 40 may has a similar water source to the liquid 35.

[0051] FIG. 6 illustrates an experimental graph illustrating silica removal efficiency of an experimental desalination apparatus 11 in accordance with one embodiment of the invention. For easy illustration, the desalination apparatus 11 in FIG. 2 is taken as an example. In this exemplary experiment, a total dissolved solids (TDS) level of the first feed stream 12 is about 350ppm, which includes 40ppm of silica. The pH of the first feed stream 12 is adjusted to be 11 before being introduced into the desalination apparatus 11. As illustrated in FIG. 6, during continuous processing for about 5 days, the silica removal efficiency of the desalination apparatus 1 1 is about 50% and is relatively stable, which indicates the silica in the first feed stream 12 may be removed efficiently and the scaling in the second feed stream 13 may be mitigated accordingly.

[0052] It should be noted that the arrangements in FIGS. 1-5 are merely illustrative. For some arrangements, the arrangements in FIGS. 1-5 are employed for silica removal from an aqueous stream or a liquid. In other examples, the arrangements in FIGS. 1-5 may be used to remove any other suitable ions, for example divalent anions in a liquid. In embodiments of the invention, in the desalination apparatus 1 1, 30 or 32, a first member of each pair of the ion exchange membranes is an anion exchange membrane and a second member of each pair of the ion exchange membranes is an anion exchange membranes, a monovalent cation exchange membrane or a bipolar ion exchange membrane for silica removal, for example. As a result, the ions, such as silica in the first feed stream 12 may be removed efficiently and stably. In addition, the pretreatment unit may be employed so as to further avoid the scaling or fouling tendency during desalination of the first feed stream 12.

[0053] While the disclosure has been illustrated and described in typical embodiments, it is not intended to be limited to the details shown, since various modifications and substitutions can be made without departing in any way from the spirit of the present disclosure. As such, further modifications and equivalents of the disclosure herein disclosed may occur to persons skilled in the art using no more than routine experimentation, and all such modifications and equivalents are believed to be within the spirit and scope of the disclosure as defined by the following claims.

Claims

WHAT IS CLAIMED IS:

1. A desalination system, comprising:

a silica removal apparatus configured to receive a first feed stream for silica removal and comprising:

first and second electrodes;

a plurality of paired ion exchange membranes disposed between the first and second electrodes to form a plurality of alternating first and second channels;

a plurality of spacers disposed between each pair of the adjacent ion exchange membranes and between the first and second electrodes and the respective ion exchange membranes; and

wherein a first member of each pair of the ion exchange membranes is an anion exchange membrane and a second member of each pair of the ion exchange membranes is an anion exchange membranes, a monovalent cation exchange membrane or a bipolar ion exchange membrane, and wherein the first members and the second members are disposed alternately within the plurality of the paired ion exchange membranes.

2. The desalination system of claim 1, wherein each of the plurality of paired ion exchange membranes of the silica removal apparatus comprises the anion exchange membrane.

3. The desalination system of claim 2, wherein each of the anion exchange membranes comprises a monovalent anion exchange membrane or a normal anion exchange membrane.

4. The desalination system of claim 1, further comprising a pH adjustment unit in fluid communication with the silica removal apparatus and configured to adjust pH of the first feed stream.

5. The desalination system of claim 1, wherein the silica removal apparatus is further configured to receive a second feed stream to carry away the ions removed from the first feed stream.

6. The desalination system of claim 6, further comprising an ion adjustment unit in fluid communication with the silica removal apparatus and configured to adjust concentration of anions in the second feed stream.

7. The desalination system of claim I, further comprising a pretreatment unit in fluid communication with the silica removal apparatus and configured to at least partially remove polyvalent cations in a liquid to produce the first feed stream prior to introduction of the first feed stream into the silica removal apparatus.

8. The desalination system of claim I, wherein the second member of each pair of the ion exchange membranes comprises the bipolar membrane.

9. A desalination system, comprising:

a silica removal apparatus comprising:

first and second electrodes;

a plurality of paired anion exchange membranes disposed between the first and second electrodes to form a plurality of alternating first and second channels; and

a plurality of spacers disposed between each pair of the adjacent anion exchange membranes and between the first and second electrodes and the respective anion exchange membranes.

10. The desalination system of claim 9, wherein the silica removal apparatus is configured to receive a first feed stream for silica removal and a second feed stream to carry way silica removed from the first feed stream through the respective alternating first and second channels.

11. The desalination system of claim 9, further comprising a pH adjustment unit in fluid communication with the silica removal apparatus and configured to adjust pH of the first feed stream.

12. The desalination system of claim 9, further comprising an ion adjustment unit in fluid communication with the silica removal apparatus and configured to increase concentration of anions in the second feed stream.

13. A desalination method for removing silica from an aqueous stream, comprising:

passing a first feed stream through first channels defined by paired ion exchange membranes of a silica removal apparatus for silica removal;

passing a second feed stream through second channels defined by the paired ion exchange membranes of the silica removal apparatus to carry away silica removed from the first feed stream; and

wherein a first member of each pair of the ion exchange membranes is an anion exchange membrane and a second member of each pair of the ion exchange membrane is an anion exchange membranes, a monovalent cation exchange membrane or a bipolar ion exchange membrane, and wherein the first members and the second members are disposed alternately within the paired ion exchange membranes.

14. The desalination method of claim 13, wherein the silica removal apparatus comprises:

first and second electrodes;

a plurality of the paired ion exchange membranes disposed between the first and second electrodes to form the first and second channels disposed alternately; and

a plurality of spacers disposed between each pair of the adjacent ion exchange membranes and between the first and second electrodes and the respective ion exchange membranes.

15. The desalination method of claim 13, wherein each of the paired ion exchange membranes of the silica removal apparatus comprises the anion exchange membrane.

16. The desalination method of claim 13, further comprising adjusting pH of the first feed stream prior to introduction of the first feed stream into the silica removal apparatus.

17. The desalination method of claim 16, wherein the pH of the first feed stream is adjusted to be in a range of from about 9.5 to about 1 1.

18. The desalination method of claim 13, further comprising increasing concentration of anions in the second feed stream prior to introduction of the second feed stream into the silica removal apparatus.

19. The desalination method of claim 18, wherein the anions in the second feed stream comprises active anions, and wherein the active anions comprise one or more of chloride ions, sulfate ions and hydroxide ion.

20. The desalination method of claim 13, further comprising at least partially removing polyvalent cations in a liquid to produce the first feed stream prior to introduction of the first feed stream into the silica removal apparatus.