CA2837210A1

CA2837210A1 - Membrane desalination system and method

Info

Publication number: CA2837210A1
Application number: CA2837210A
Authority: CA
Inventors: Chengqian Zhang; Rihua Xiong; Zijun Xia; Wei Cai
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2011-06-10
Filing date: 2012-06-05
Publication date: 2012-12-13
Also published as: WO2012170406A1; CN102815810A; AU2012268364A1; CN102815810B; RU2013153467A

Abstract

[0042] A desalination system comprises a membrane separation device (12) and an adjustment unit (14). The membrane separation device (12) is configured to receive a feed stream (11) including one or more antiscalants and produce a permeate stream (15) and a concentrated stream (16). The adjustment unit (14) is configured to adjust at least a portion of the one or more antiscalants in the concentrated stream (16) from the membrane separation device (12)by decreasing pH of the concentrated stream or by increasing the temperature of the concentrated stream, thereby releasing ions of sparsely soluble salts from their complexes with the antiscalants. The precipitated is separated in a concentration device (13). The concentrated stream is returned to the feed side of the membrane separation device (12), the pH being increased in stream (17) by means of an activation device (18). A desalination method is also presented.

Description

MEMBRANE 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 employing membrane separation devices for 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 liquid streams, such as wastewater, seawater or brackish water.

[0003] Typically, membrane separation devices, such as reverse osmosis (RO) devices are employed for processing such liquid steams, for example for water purification. Generally, such liquid streams may include sparsely soluble salts, such as calcium sulfates. Due to solubility limits of such sparsely soluble salts in the liquid streams, during processing, the sparsely soluble salts may scale or precipitate on membranes of the membrane separation devices, which results in loss of permeate flux through the membranes and damage to the membrane separation devices.

[0004] There have been attempts to inhibit scale formation of the sparsely soluble salts within the membrane separation devices during processing of the liquid streams. For example, antiscalants have been widely used to inhibit the scale formation of the sparsely soluble salts so as to increase efficiency of water recovery.
However, due to limits of concentration tolerance of the sparsely soluble salts in the liquid streams, although the antiscalants are used, in current applications, the sparsely soluble salts may still scale or precipitate to damage the membranes, which is disadvantageous for the membrane separation devices for water recovery.

[0005] Therefore, there is a need for new and improved desalination systems and methods employing membrane separation devices to avoid the scale formation of the sparsely soluble salts and increase the water recovery during processing of liquid streams.
BRIEF DESCRIPTION OF THE DISCLOSURE
[0006] A desalination system is provided in accordance with one embodiment of the invention. The desalination system comprises a membrane separation device and an adjustment unit. The membrane separation device is configured to receive a feed stream including one or more antiscalants and produce a permeate stream and a concentrated stream. The adjustment unit is configured to adjust at least a portion of the one or more antiscalants in the concentrated stream from the membrane separation device.

[0007] A desalination method is provided in accordance with another embodiment of the invention. The desalination method comprises passing a first stream including one or more antiscalants through a membrane separation device to produce a permeate stream and a concentrated stream, and adjusting at least a portion of the one or more antiscalants in the concentrated stream from the membrane separation device.

[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.
DETAILED DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] FIG. 1 illustrates a schematic diagram of a desalination system 10 in accordance with on embodiment of the invention for processing, for example, for purification of a feed stream 11, such as wastewater, seawater or brackish water. In some examples, various salts may exist in the feed stream 11. In some examples, the salts may include soluble salts and sparsely or partially soluble salts. Non-limiting examples of the soluble salts include sodium chloride and magnesium chloride.
Non-limiting examples of the sparsely or partially soluble salts include calcium sulfate and barium sulfate. In one example, the sparsely or partially soluble salts include calcium sulfate.

[0012] As illustrated in FIG. 1, the desalination system 10 comprises a membrane separation device 12, a concentration device 13, and an adjustment unit 14.
For some arrangements, the term "membrane separation device" may generally indicate a device that is employed for desalination of a liquid stream via membrane separation. During the membrane separation, with introduction of a liquid stream into the membrane separation device, at least a portion of the liquid stream may permeate or pass through a membrane (not shown) of the membrane separation device as a result of a driving force(s) to produce a permeate stream. Meanwhile, another portion of the liquid stream may not permeate or pass through the membrane and may be retained by the membrane to produce a concentrated stream. In some applications, the permeate stream may be a dilute stream having a lower concentration of the salts than the liquid stream. The concentrated stream may have a higher concentration of the salts than the liquid stream.

[0013] In embodiments of the invention, the membrane separation device 12 may not comprise any specific membrane separation devices. Non-limiting examples of the membrane separation device 12 may comprise a reverse osmosis device, a nanofiltration device, an electrodialysis device, an electrodialysis reversal device, a membrane distillation device, or combinations thereof In one example, the membrane separation device 12 comprises the reverse osmosis device.

[0014] In the illustrated example in FIG. 1, the membrane separation device 12 is configured to process, for example, for purification of the feed stream 11. With the introduction of the feed stream 11 into the membrane separation device 12, a permeate stream 15 and a concentrated stream 16 are produced.

[0015] In some applications, the feed stream 11 includes sparsely or partially soluble salts, such as calcium sulfate. During desalination of the feed stream 11, with the increase of the concentration of the partially soluble salts, the partially soluble salts may scale or precipitate within the membrane separation device 12.

[0016] For some arrangements, in order to avoid or inhibit the scale formation, one or more antiscalants may be added into the feed stream 11 before the feed stream 11 is introduced into the membrane separation device 12, so that the one or more antiscalants may chelate with ions of the sparsely soluble salts to inhibit the scale formation within the membrane separation device 12. For example, the one or more antiscalants chelate with calcium ions of the calcium sulfate, and thus the sulfate ions may not combined with calcium ions so as to inhibit the scale formation of the calcium sulfate.

[0017] Accordingly, during the desalination, the concentrated stream 16 is produced and at least includes a portion of the components in the feed stream 11, such as the one or more antiscalants, the sparsely soluble salts, and other salts including, but not limited to the soluble salts, which are separated by the membrane of the membrane separation device 12.

[0018] In some examples, the one or more antiscalants may not comprise any specific antiscalants and may be selected based on different applications, for example base on species of the sparsely or partially soluble salts. In non-limiting examples, the one or more antiscalants may comprise one or more of polyacrylates, organo-phosphonates, and acrylamide copolymers.

[0019] For the illustrated arrangement, the concentration device 13 is in fluid communication with the membrane separation device 12 and configured to receive the concentrated stream 16 from the membrane separation device 12 so as to facilitate precipitation of at least a portion of the sparsely soluble salts therein and produce a precipitated stream 17 after precipitation. In certain applications, in order to improve water recovery of the feed stream 11, the precipitated stream 17 may be reintroduced into the feed steam 11 for further processing in the membrane separation device 12.
In non-limiting examples, the concentration device 13 may comprise a container for accommodation of the concentrated stream 16. The precipitate and a portion of a stream may be discharged from a bottom portion (not labeled) of the concentration device 13 through a pipeline 19.

[0020] For some arrangements, the one or more antiscalants chelate with the sparsely soluble salts in the concentrated stream 16. For facilitating the precipitation of the sparsely soluble slats in the concentration device 13, as depicted in FIG. 1, the adjustment unit 14 is employed to be in fluid communication with the concentration device 13 for adjustment, for example, for deactivation of at least a portion of the one or more antiscalants so that the chelate between the one or more antiscalants and the sparsely soluble salts is changed, for example, deactivated accordingly.

[0021] In some applications, the term "adjustment of at least a portion of the one or more antiscalants" means the chelate between the at least a portion of the one or more antiscalants and respective ions of the sparsely or partially soluble salts is adjusted, for example, deactivated or disconnected so that the chelated ions of the sparsely soluble salts are released for formation of the precipitation.

[0022] Thus, the chelated ions of the sparsely soluble salts may be released for facilitation of production of the precipitation. For example, the calcium ions are released and combined with sulfate ions accordingly after deactivation of the one or more antiscalants. When the concentration of the sparsely or partially soluble salts in the concentrated stream 16 is in a relative higher level, such as in a saturation level or a supersaturation level, the precipitation of the sparsely soluble salts may occur.

[0023] In some applications, the precipitation of the sparsely or partially soluble salts may not occur until the degree of the saturation or supersaturation thereof is very high. Accordingly, in certain examples, seed particles (not shown) may be added into the concentration device 13 to induce the precipitation at a relative lower concentration of the sparsely soluble salts. In certain applications, the seed particles may comprise solid particles including, but not limited to calcium sulfate particles and their hydrates to induce the precipitation.

[0024] In some embodiments, the adjustment unit 14 may comprise a first pH
adjustment unit configured to decrease pH of the concentrated stream 16 for adjustment of at least a portion of the one or more antiscalants. In non-limiting examples, the first pH adjustment unit may be configured to provide one or more acidic additives. Non-limiting examples of the one or more acid additives include one or more of hydrochloric acid and sulfuric acid. In certain examples, the pH of the concentrated stream 16 may be adjusted to be less than about 5.

[0025] For the illustrated arrangement, the adjustment unit 14 adjusts at least a portion of the one or more antiscalants in the concentrated stream 16 after the concentrated stream 16 is introduced into the concentration device 13.
Alternatively, the adjustment unit 14 may adjust at least a portion of the one or more antiscalants prior to the introduction of the concentrated stream 16 into the concentration device 13.

[0026] In some examples, the precipitated stream 17 may include at least a portion of one or more adjusted antiscalants. Before the precipitated stream 17 is mixed into the feed stream 11, the desalination system 10 may further comprise an activation unit 18 in fluid communication with the concentration device 13 and configured to activate at least a portion of the one or more adjusted antiscalants therein, so that at least a portion of the one or more antiscalants in the precipitated stream 17 may be reused after introduction of the precipitated stream 17 into the feed stream 11 for chelate with respective ions of the sparsely or partially soluble salts. In other examples, the activation unit 18 may not be employed. As used herein, the term "activation" means the chelate between the one or more antiscalants and respective ions of the sparsely or partially soluble salts are recovered or connected.

[0027] For some arrangements, the activation unit 18 may comprise a second pH adjustment unit configured to increase the pH of the precipitated stream 17 from the concentration device 13. In non-limiting examples, the second pH
adjustment unit may be configured to provide one or more basic additives. Non-limiting examples of the one or more basic additives include one or more of sodium hydroxide, potassium hydroxide, and ammonia hydroxide. In certain examples, the pH of the precipitated stream 17 may be adjusted to be greater than the pH of the concentrated stream 16.
The pH of the activation unit 18 may be greater than the pH of the adjustment unit 14.
Based on different species of the one or more antiscalants, the pH of the concentrated and precipitated streams 16, 17 may vary after adjustment.

[0028] It should be noted that the arrangement in FIG. 1 is merely illustrative.
In the illustrated example, one membrane separation device 12 is illustrated and the activation unit 18 is configured to activate the antiscalants before the precipitated stream 17 is mixed into the feed stream 11. In other applications, more than one membrane separation device may be employed. The activation unit 18 may activate at least a portion of the one or more antiscalants in the precipitate stream 17 after the precipitate stream 17 is mixed into the feed stream 11.

[0029] Accordingly, during operation, the feed stream 11 including the one or more antiscalants is introduced into the membrane separation device 12 for desalination. With the introduction of the feed stream 11, the permeate stream 15 and the concentrated stream 16 are produced. Due to the chelate between the one or more antiscalants and at least a portion of the sparsely soluble salts, the scale formation may be avoid or inhibited so as to ensure operation of the membrane separation device 12.

[0030] Subsequently, the concentrated stream 16 at least including a portion of the one or more antiscalants and a portion of the sparsely soluble salts are introduced into the concentration device 13. Meanwhile, the adjustment unit 14 provides the one or more acid additives to adjust at least a portion of the one or more antiscalants so as to release the ions chelated with the one or more antiscalants. With the increase of the concentration of the sparsely soluble salts in the concentrated stream 16, the precipitate may occur in the concentration device 13.

[0031] Finally, the precipitated stream 17 from the concentration device 13 is reintroduced into the membrane separation device 12 for further processing so as to improve water recovery. In some examples, prior to introduction of the precipitated stream 17 into the membrane separation device 12, the activation unit 18 may be provided to activate at least a portion of the one or more antiscalants in the precipitated stream 17. Alternatively, the step for activation of at least a portion of the one or more antiscalants in the precipitated stream 17 may not employed.

[0032] Thus, for some arrangements, due to existence of the one or more antiscalants in the feed stream 11, during operation, the scale formation may be inhibited. In addition, the adjustment unit 14 may be employed to adjust at least a portion of the one or more antiscalants in the concentrated stream 16 so as to facilitate the precipitation in the concentration device 13 and reduce the concentration of the sparsely or partially soluble salts in the precipitated stream 17. After the precipitated stream 17 is reintroduced into the membrane separation device 12, the water recovery may be improved and the possibility for the scale formation within the membrane separation device 12 may also be reduced.

[0033] As illustrated in FIG. 1, in certain applications, the adjustment unit 14 may comprise a temperature adjustment unit for adjustment of at least a portion of the one or more antiscalants in the concentrated stream 16. In some examples, the temperature adjustment unit may be configured to increase the temperature of the concentrated stream 16. Non-limiting examples of the temperature adjustment unit include a heater.

[0034] Similarly, during operation, prior to or after the concentrated stream 16 from the membrane separation device 12 is introduced into the concentration device 13, the temperature adjustment unit heats the concentrated stream 16 to adjust at least a portion of the one or more antiscalants for facilitation of the precipitate.
In other applications, the seed particles may also be employed in the concentration device 13.
The activation unit 18 may or may not be employed when the temperature adjustment unit 14 is employed.

[0035] Two non-limiting examples are now described to illustrate the operations of the adjustment unit 14 comprising the first pH adjustment unit and the temperature adjustment unit of the desalination system 10. For easy illustration, the sparsely soluble salts of the calcium sulfate (CaSO4) in the concentrated stream 16 are taken as an example.

[0036] In this exemplary experiment, the concentrated stream 16 comprises an about 200m1 CaSat solution with 600% supersaturation level. An antiscalant (MDC
151 from GE Water & Process Technologies) of about 3ppm exist in the solution to inhibit the CaSat to precipitate out at the supersaturated level. Under this condition, the conductivity of the solution is about 19.23 mS/cm, the pH is about 6.5 and turbidity is about 0.113 NTU.

[0037] Subsequently, a Imola hydrochloric acid (HC1) solution is added into the CaSat solution to adjust the pH of the CaSat solution to be about 1.3 so as to adjust the antiscalant. Under such a condition, the Ca504 solution become turbid after the pH adjustment and Ca504 particles are observed in the solution. After the pH
adjustment, the conductivity of the CaSat solution after adjustment is about 15.37 mS/cm, the pH is about 1.3 and the turbidity is about 4226 NTU, which indicates the C aS 04 precipitate are produced.

[0038] In this exemplary experiment, the concentrated stream 16 comprises an about 200m1 Ca504 solution with 600% supersaturation level. An antiscalant (MDC
151 from GE Water & Process Technologies) of about 3ppm exist in the solution to inhibit the CaSat to precipitate out at the supersaturated level. Under this condition, the conductivity of the solution is about 19.23 mS/cm, the pH is about 6.5 and turbidity is about 0.113 NTU.

[0039] Subsequently, the solution is heated to about 100 C so as to adjust the antiscalant, and then cooled down to a room temperature. The CaSat solution become turbid during the heating process, and the CaSat particles are observed in the solution. After being cooled down to the room temperature, under such a condition, the conductivity of the CaSat solution after adjustment is about 15.61 mS/cm, the pH

was 1.7 and the turbidity is about 3175 NTU, which also indicates the CaSat precipitate are produced.

[0040] From the above two exemplary experiments, due to the employment of the adjustment unit 14, at least a portion of the one or more antiscalants in the concentrated stream 16 may be adjusted to facilitate the precipitate of the sparsely soluble salts. Thus, the concentration of the sparsely soluble salts in the precipitated stream 17 may be reduced. As a result, when the precipitated stream 17 is reintroduced into the membrane separation device 12, the water recovery may be improved and the possibility for the scale formation within the membrane separation device 12 may also be alleviated. For some arrangements, the activation unit 18 may also be employed to activate at least a portion of the one or more antiscalants in the precipitated stream 17 for recycle of at least a portion of the one or more antiscalants.

[0041] 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

1. A desalination system, comprising:
a membrane separation device configured to receive a feed stream including one or more antiscalants and produce a permeate stream and a concentrated stream; and an adjustment unit configured to adjust at least a portion of the one or more antiscalants in the concentrated stream from the membrane separation device.

2. The desalination system of claim 1, wherein the feed stream comprises sparsely soluble salts, and wherein the adjustment unit is configured to disconnect chelate between the one or more antiscalants and ions of the sparsely soluble salts.

3. The desalination system of claim 1, wherein the adjustment unit comprises one or more of a first pH adjustment unit and a temperature adjustment unit.

4. The desalination system of claim 3, wherein the first pH adjustment unit is in fluid communication with the membrane separation device and configured to decrease pH of the concentrated stream from the membrane separation device.

5. The desalination system of claim 4, further comprising a concentration device in fluid communication with the membrane separation device and configured to receive the concentrated stream from the membrane separation device.

6. The desalination system of claim 5, further comprising an activation unit in fluid communication with the concentration device and configured to activate at least a portion of the one or more antiscalants in a precipitated stream from the concentration device.

7. The desalination system of claim 6, wherein the activation unit comprises a second pH adjustment unit configured to increase pH of the precipitated stream.

8. The desalination system of claim 7, wherein the pH of the activation unit is higher than the pH of the adjustment unit.

9. The desalination system of claim 1, further comprising seed particles disposed in the concentration device for facilitation precipitation.

10. The desalination system of claim 1, wherein the membrane device comprises one or more of a reverse osmosis device, a nanofiltration device, a microfiltration device, an ultrafiltration device, and a membrane distillation device.

11. A desalination method, comprising:
passing a first stream including one or more antiscalants through a membrane separation device to produce a permeate stream and a concentrated stream;
and adjusting at least a portion of the one or more antiscalants in the concentrated stream from the membrane separation device.

12. The desalination method of claim 11, wherein the adjusting step is performed via an adjustment unit, and wherein the adjustment unit comprises one or more of a first pH adjustment unit and a temperature adjustment unit.

13. The desalination method of claim 12, wherein the adjusting step comprising heating the concentrated stream through the temperature adjustment unit.

14. The desalination method of claim 12, wherein the first pH adjustment unit is in fluid communication with the membrane separation device and configured to decrease pH of the concentrated stream from the membrane separation device.

15 The desalination method of claim 14, further comprising introducing the concentrated stream from the membrane separation device into a concentration device and produce a precipitated stream.

16 The desalination method of claim 15, further comprising introducing seed particles into the concentration device to facilitate precipitation.

17. The desalination method of claim 15, further comprising activating at least a portion of the one or more antiscalants in the precipitated stream via an activation unit.

18. The desalination method of claim 17, wherein the activation unit comprises a second pH adjustment unit configured to increase pH of the precipitated stream.

19. The desalination method of claim 18, wherein the pH of the precipitated stream is higher than the pH of the concentrated stream after pH
adjustment.

20. The desalination method of claim 11, wherein the feed stream comprises partially soluble salts, and wherein chelate between the one or more antiscalants and ions of the partially soluble salts is disconnected in the adjusting step.