MEMBRANE SYSTEMS AND PROCESSES

FIELD OF THE TECHNOLOGY

[0001] Generally, the invention relates to osmotically driven membrane systems and processes and more particularly to increased brine concentration for zero liquid discharge (ZLD) using osmotically driven membrane systems and processes. The invention also relates to related draw solute recovery techniques for the osmotically driven membrane systems and processes.

BACKGROUND

[0002] In general, osmotically driven membrane processes involve two solutions separated by a semi-permeable membrane. One solution may be, for example, seawater, while the other solution is a concentrated solution that generates a concentration gradient between the seawater and the concentrated solution. This gradient draws water from the seawater across the membrane, which selectively permits water to pass, but not salts, into the concentrated solution. Gradually, the water entering the concentrated solution dilutes the solution. The solutes then need to be removed from the dilute solution to generate potable water. Traditionally, the potable water was obtained, for example, via distillation; however, the solutes were typically not recovered and recycled.

[0003] In certain prior art systems that use distillation and low grade heat to recover draw solutes, it is necessary to perform condensation and absorption steps under vacuum in an attempt to maximize draw solute recovery. For example, a knock-out pot and an eductor (using air as a driving medium) are disposed downstream of the condensation and/or absorption processes in an attempt to improve draw solute recovery. However, this arrangement requires the venting of the non-condensable gases, which can also result in a loss of draw solutes and possible environmental issues. Additionally, the prior art systems for recovering draw solutes require considerable energy input (e.g., direct steam or electricity) that makes the recovery process inefficient and expensive.

[0004] Furthermore, many existing technologies for concentrating a feed stream are not capable of removing substantially all of the water, or other solvent, (i.e., ZLD) from the stream generally, and in particular without the use of complicated and/or very energy intensive equipment making it expensive and impractical to maximize the concentration of the feed stream to meet ZLD requirements.

SUMMARY

[0005] The invention generally relates to systems and methods for increasing brine concentration to ZLD or near ZLD conditions and for recovering/recycling the draw solutions used in those systems and methods. The draw solutions are used in various osmotically driven membrane systems and methods, for example; forward osmosis (FO), pressure retarded osmosis (PRO), osmotic dilution (OD), direct osmotic concentration (DOC), or other processes that rely on the concentration (or variability thereof) of solutes in a solution. The systems and methods for draw solute recovery may be incorporated in various osmotically driven membrane systems/processes. Examples of osmotically driven membrane systems/processes are disclosed in U.S. Patent Nos. 6,391,205, 7,560,029, and 9,039,899; U.S. Patent Publication Nos.

2011/0203994, 2012/0273417, and 2012/0267306; and PCT Publication No. WO2015/157031; the disclosures of which are hereby incorporated herein by reference in their entireties. In addition, a variety of draw solute recovery systems are disclosed in U.S. Patent Nos. 8,246,791 and 9,044,711; the disclosures of which are also hereby incorporated herein by reference in their entireties. [0006] Generally, the draw solution(s) used are aqueous solutions, i.e., the solvent is water; however, in some embodiments the draw solution is a non-aqueous solution using, for example, an organic solvent. The draw solution is intended to contain a higher concentration of solute relative to a feed or first solution so as to generate an osmotic pressure within the osmotically driven membrane system. The osmotic pressure may be used for a variety of purposes, including desalination, water treatment, solute concentration, power generation, and other applications. In some embodiments, the draw solution may include one or more removable solutes. In at least some embodiments, thermally removable (thermolytic) solutes may be used. For example, the draw solution may comprise a thermolytic salt solution, such as that disclosed in U.S. Patent No. 7,560,029. Other possible thermolytic salts include various ionic species, such as chloride, sulfate, bromide, silicate, iodide, phosphate, sodium, magnesium, calcium, potassium, nitrate, arsenic, lithium, boron, strontium, molybdenum, manganese, aluminum, cadmium, chromium, cobalt, copper, iron, lead, nickel, selenium, silver, and zinc.

[0007] Generally, the feed or first solution may be any solution containing solvent and one or more solutes for which separation, concentration, purification, or other treatment is desired. In some embodiments, the first solution may be non-potable water such as seawater, salt water, brackish water, gray water, and some industrial water. In other embodiments, the first solution may be a process stream containing one or more solutes, such as target species, which it is desirable to concentrate, isolate, or recover. Such streams may be from an industrial process, such as a pharmaceutical or food grade application. Target species may include pharmaceuticals, salts, enzymes, proteins, catalysts, microorganisms, organic compounds, inorganic compounds, chemical precursors, chemical products, colloids, food products, or contaminants. The first solution may be delivered to a forward osmosis membrane treatment system from an upstream unit operation such as an industrial facility, or any other source, such as the ocean.

[0008] In one aspect, the invention relates to an osmotically driven membrane system and related process. Generally, the system includes one or more forward osmosis membrane modules including one or more membranes in each, a source of feed solution in fluid

communication with one side of the one or more membranes, a source of concentrated draw solution in fluid communication with an opposite side of the one or more membranes, and a draw solution recovery system in fluid communication with the forward osmosis membrane module(s).

[0009] In another aspect, the invention relates to a system for concentrating a feed stream and recovering draw solution solutes from an osmotically driven membrane system. The system includes a forward osmosis unit having at least one membrane having a first side and a second side, the first side of the at least one membrane fluidly coupled to a source of a first solution and the second side of the at least one membrane fluidly coupled to a source of a concentrated draw solution, wherein the at least one membrane is configured for osmotically separating a solvent from the first solution, thereby forming a more concentrated first solution on the first side of the at least one membrane and a dilute draw solution on the second side of the at least one membrane and a separation system in fluid communication with the forward osmosis unit and configured for receiving the concentrated first solution and the dilute draw solution from the forward osmosis unit. The separation system includes a first separation apparatus and a second separation apparatus. The first separation apparatus is in fluid communication with the osmotically driven membrane system and includes a first thermal recovery device, a first heat transfer means (e.g., a heat exchanger or other type of condenser) in fluid communication with the forward osmosis unit for receiving the dilute draw solution and coupled to a first inlet of the first thermal recovery device for preheating and introducing the dilute draw solution into the first thermal recovery device, a second heat transfer means coupled to the first thermal recovery device and having an inlet coupled to a first source of thermal energy and an outlet coupled to the first thermal recovery device for directing thermal energy to the first thermal recovery device to cause solutes within the dilute draw solution in the first thermal recovery device to vaporize, a first outlet for removing the vaporized dilute draw solution solutes from the first thermal recovery device, wherein the first outlet is in fluid communication with the first heat transfer means for providing the vaporized draw solution solutes as a source of thermal energy thereto for preheating the dilute draw solution (and partially condensing the vaporized draw solution into at least an intermediary concentrated draw solution), and a second outlet for removing a bottoms product from the first thermal recovery device. The second separation apparatus is in fluid communication with the osmotically driven membrane system and includes a second thermal recovery device, a first heat transfer means in fluid communication with the forward osmosis unit for receiving the concentrated first solution and coupled to a first inlet of the second thermal recovery device for preheating and introducing the concentrated first solution into the second thermal recovery device, a second heat transfer means coupled to the second thermal recovery device and having an inlet coupled to a second source of thermal energy and an outlet coupled to the second thermal recovery device for directing thermal energy to the second thermal recovery device to cause solutes within the concentrated first solution in the second thermal recovery device to vaporize, a first outlet for removing the vaporized solutes from the second thermal recovery device, wherein the first outlet is in fluid communication with the first heat transfer means for providing the vaporized solutes as a source of thermal energy thereto for preheating the concentrated first solution, and a second outlet for removing a bottoms product from the second thermal recovery device.

[0010] In various embodiments of the foregoing aspects, the first and second thermal recovery devices can be distillation apparatus (e.g., column- or membrane-based). In some embodiments, the second thermal recovery device can be a crystallizer. In one or more embodiments, the systems can include one or more compressors in fluid communication with the first outlet of the first thermal recovery device and at least one of the first or second heat transfer means of the first separation apparatus or the second separation apparatus and/or one or more compressors in fluid communication with the first outlet of the second thermal recovery device and the heat transfer means of the first and/or second thermal recovery devices for providing at least a portion of the source of thermal energy to one or both of the thermal recovery devices. Additionally, the systems can include at least one condenser having an inlet in fluid

communication with at least one of the second outlet of the first thermal recovery device and/or the second outlet of the second thermal recovery device for receiving the bottoms product of the first and/or second thermal recovery device and an outlet in fluid communication with the forward osmosis unit for providing the concentrated draw solution thereto. The first and second separation apparatus can be configured for essentially parallel operation and the apparatus can themselves include one or more thermal recovery devices (e.g., distillation apparatus) configured in series, parallel, or combinations thereof.

[0011] In another aspect, the invention relates to a system for concentrating a feed stream and recovering draw solution solutes from an osmotically driven membrane system, where the system includes a forward osmosis unit and a separation system. The forward osmosis unit includes at least one membrane having a first side and a second side, the first side of the at least one membrane fluidly coupled to a source of a first solution and the second side of the at least one membrane fluidly coupled to a source of a concentrated draw solution, wherein the at least one membrane is configured for osmotically separating a solvent from the first solution, thereby forming a more concentrated first solution on the first side of the at least one membrane and a dilute draw solution on the second side of the at least one membrane. The separation system is in fluid communication with the forward osmosis unit and configured for receiving the concentrated first solution and the dilute draw solution from the forward osmosis unit and separating draw solutes therefrom. The separation system includes a first thermal recovery device having first and second heat transfer means, a second thermal recovery device having a third heat transfer means, and a closed-loop heat pump system. The first thermal recovery device is in fluid communication with the osmotically driven membrane system and configured for receiving the dilute draw solution and vaporizing draw solutes out of the dilute draw solution and outputting the vaporized draw solutes and a product solvent. The first heat transfer means (e.g., a heat exchange device such as a condenser) is coupled to the first thermal recovery device and has a first inlet configured for receiving the vaporized draw solutes; a second inlet configured for receiving a source of working fluid for absorbing thermal energy from the vaporized draw solutes; a first outlet configured for outputting condensed draw solutes, which can be returned to the forward osmosis unit, for example directly returned to the second side(s) of the membranes as re-concentrated draw solution, returned via the source of concentrated draw solution (e.g., a draw solution holding tank) or further processed prior to being returned to the forward osmosis unit; and a second outlet configured for outputting the working fluid, which has been heated via the thermal energy from the vaporized draw solutes. The second heat transfer means (e.g., a reboiler or other heat exchange device) is also coupled to the first thermal recovery device and has a first inlet configured for receiving a portion of a bottoms product (typically a portion of the heated dilute draw solution or separated solvent) of the first thermal recovery device, a second inlet configured for receiving the working fluid from the second outlet of the first heat transfer means for providing thermal energy to the bottoms product, a first outlet configured for outputting the (now cooler) working fluid, and a second outlet configured for returning the portion of the bottoms product to the first thermal recovery device for providing the thermal energy thereto to vaporize the draw solutes. The second thermal recovery device is in fluid communication with the osmotically driven membrane system and configured for receiving the more concentrated first solution, vaporizing additional draw solutes out of the more concentrated first solution, and outputting the vaporized draw solutes and a further concentrated first solution. The third heat transfer means (e.g., a reboiler or other heat exchange device) is coupled to the second thermal recovery device and has a first inlet configured for receiving a portion of a bottoms product of the second thermal recovery device (typically a portion of the more concentrated first solution, a portion of the further concentrated first solution, or solvent), a second inlet configured for receiving the working fluid from the first outlet of the second transfer means for providing thermal energy to the bottoms product of the second thermal recovery device, a first outlet configured for returning the bottoms product to the second thermal recovery device for providing thermal energy thereto to vaporize the draw solutes, and a second outlet configured for outputting the (now even cooler) working fluid. The closed-loop heat pump system is in fluid communication with the first, second, and third heat transfer means for providing the working fluid as a source of thermal energy. The heat pump system includes an expansion valve in fluid communication with the second outlet of the third heat transfer means and the second inlet of the first heat transfer means and a compressor in fluid communication with the second outlet of the first heat transfer means and the first inlet of the second heat transfer means.

[0012] In various embodiments of the foregoing aspect, the first thermal recovery device may include an outlet for outputting the product solvent from the first thermal recovery device and may include a second separation apparatus configured for receiving the product solvent from the outlet of the first thermal recovery device. The second separation system may include a filtration unit, such as a reverse osmosis unit or an ultra/nano-filtration unit, that configured for outputting a permeate product (e.g., product water) and a retentate product. In some embodiments, the second separation system can include a thermal recovery device. In various embodiments, a first portion of the retentate product can be directed to the separation system (e.g., combined with the dilute draw solution) and a second portion of the retentate product can be directed to the forward osmosis unit (e.g., it can be added to the source of first solution or introduced directly to the first side(s) of the membranes).

[0013] In still further embodiments, the second thermal recovery device may include an outlet for outputting the vaporized additional draw solutes. In some cases, the first and second thermal recovery devices are in fluid communication and the vaporized additional draw solutes are directed from the second thermal recovery device to the first thermal recovery device, where they can be combined with the vaporized draw solutes within the first thermal recovery device and/or introduce additional thermal energy to the first thermal recovery device. In one or more embodiments, the working fluid is water; however, in some embodiments the working fluid is a refrigerant (e.g., R-22, R-438a, or similar). The working fluid can be selected to suit a particular application, for example, a mixed refrigerant may be used to provide condensation over a wide range of temperatures to allow for different condensation temperatures between the second and third heat transfer means.

[0014] Additionally, the system may include a by-pass circuit (e.g., valves, porting, and plumbing as necessary) for by-passing a portion of the first solution around the forward osmosis unit. For example, the portion of the first solution that is by-passed can be recombined with the concentrated first solution exiting the forward osmosis unit. The system may also include a second by-pass circuit for directing a portion of the concentrated first solution around the separation apparatus. For example, one portion of the concentrated first solution can be directed to the separation apparatus while a second portion can be sent for further processing, e.g., sent to a crystallizer as opposed to the separation apparatus. In various embodiments of the system, the forward osmosis unit may include a plurality of forward osmosis membranes or modules arranged in series and/or parallel. In addition, one or both of the thermal recovery devices may be a distillation apparatus, such as a distillation column or membrane distillation apparatus. In one or more embodiments, the system may include a fourth heat transfer means (e.g., a condenser) in fluid communication with the first heat transfer means and configured for receiving the condensed draw solutes for further cooling/condensing the draw solutes prior to returning the draw solutes to the forward osmosis unit.

[0015] These and other objects, along with advantages and features of the present invention herein disclosed, will become apparent through reference to the following description and the accompanying drawings. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention and are not intended as a definition of the limits of the invention. For purposes of clarity, not every component may be labeled in every drawing. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which:

[0017] FIG. 1 is a schematic representation of an exemplary osmotically driven membrane system/process using a solute recovery system in accordance with one or more embodiments of the invention;

[0018] FIG. 2 is a schematic representation of one embodiment of a draw solution recovery system in accordance with one or more embodiments of the invention;

[0019] FIG. 3 is a schematic representation of an alternative osmotically driven membrane system for enhanced brine concentration and draw solute recovery in accordance with one or more embodiments of the invention;

[0020] FIG. 4 is a schematic representation of another alternative osmotically driven membrane system for enhanced brine concentration and draw solute recovery in accordance with one or more embodiments of the invention;

[0021] FIG. 5 is a schematic representation of an osmotically driven membrane system and another alternative system for enhanced draw solute recovery in accordance with one or more embodiments of the invention; and

[0022] FIG. 6 is a schematic representation of an alternative osmotically driven membrane system for use with hypersaline feed sources in accordance with one or more embodiments of the invention. DETAILED DESCRIPTION

[0023] Various embodiments of the invention may be used in any osmotically driven membrane process, such as FO, PRO, OD, DOC, etc. An osmotically driven membrane process for extracting a solvent from a solution generally involves exposing the solution to a first surface of a forward osmosis membrane. In some embodiments, the first solution (known as a process or feed solution) may be seawater, brackish water, wastewater, contaminated water, a process stream, or other aqueous solution. In at least one embodiment, the solvent is water; however, other embodiments may use non-aqueous solvents. A second solution (known as a draw solution) with an increased concentration of solute(s) relative to that of the first solution is exposed to a second, opposed surface of the forward osmosis membrane. Solvent, for example water, may then be drawn from the first solution through the forward osmosis membrane and into the second solution generating a solvent-enriched solution via forward osmosis. The solvent-enriched solution, also referred to as a dilute draw solution, may be collected at a first outlet and undergo a further separation process. In some embodiments, purified water may be produced as a product from the solvent-enriched solution. A second product stream, i.e., the depleted or concentrated first solution, may be collected at a second outlet for discharge or further treatment. The concentrated first solution may contain one or more target compounds that it may be desirable to concentrate or otherwise isolate for downstream use.

[0024] FIG. 1 depicts one exemplary osmotically driven membrane system/process 10 utilizing a draw solute recovery system 22 in accordance with one or more embodiments of the invention. As shown in FIG. 1, the system/process 10 includes a forward osmosis module 12, such as those incorporated by reference herein, in fluid communication with a feed solution source or stream 14 and a draw solution source or stream 16. The draw solution source 16 can include, for example, a saline stream, such as sea water, or another solution as described herein that can act as an osmotic agent to dewater the feed source 14 by osmosis through a forward osmosis membrane within the module 12. The module 12 outputs a stream of concentrated solution 18 from the feed stream 14 that can be further processed. The module 12 also outputs a dilute draw solution 20 that can be further processed via the recovery system 22, as described herein, where draw solutes and a target solvent can be recovered. In accordance with one or more embodiments of the invention, the draw solutes are recovered for reuse.

[0025] The forward osmosis membranes may generally be semi-permeable, for example, allowing the passage of a solvent such as water, but excluding dissolved solutes therein, such as those disclosed herein. Many types of semi-permeable membranes are suitable for this purpose provided that they are capable of allowing the passage of the solvent, while blocking the passage of the solutes and not reacting with the solutes in the solution. The membrane can have a variety of configurations, including thin films, hollow fiber, spiral wound, monofilaments, and disk tubes. There are numerous well-known, commercially available semi-permeable membranes that are characterized by having pores small enough to allow water to pass while screening out solute molecules, such as, for example, sodium chloride and their ionic molecular species such as chloride. Such semi-permeable membranes can be made of organic or inorganic materials, as long as the material selected is compatible with the particular draw solution used.

[0026] Generally, the material selected for use as the semi-permeable membrane should be able to withstand various process conditions to which the membrane may be subjected. For example, it may be desirable that the membrane be able to withstand elevated temperatures, such as those associated with sterilization or other high temperature processes. In some

embodiments, a forward osmosis membrane module may be operated at a temperature in the range of about 0 degrees Celsius to about 100 degrees Celsius. Likewise, it may be desirable for the membrane to be able to maintain integrity under various pH conditions. For example, one or more solutions in the membrane environment, such as the draw solution, may be more or less acidic or basic. In some embodiments, a forward osmosis membrane module may be operated at a pH level of between about 2 and about 11. In at least one embodiment, the membrane may be an asymmetric membrane, such as with an active layer on a first surface, and a supporting layer on a second surface. One example of a suitable membrane is disclosed in U.S. Patent No. 8,181,794, the disclosure of which is hereby incorporated herein by reference in its entirety.

[0027] Generally, the various draw solutions discussed herein can be regenerated by recovering and recycling the draw solutes using various combinations of distillation apparatus, filters, condensers, crystallizers, compressors, and related components, as shown and described herein. FIG. 2, for example, depicts one embodiment of a draw solute recovery system 122 as can be part of, for example, a membrane brine concentrator. As shown, the system 122 incorporates two separation apparatus; the dilute draw solution (DDS) stripping column 160 and the concentrate stripping column 162. The DDS column feed includes the dilute draw solution 120 and the recovered water from an osmotically driven membrane system. The DDS column 160 eventually outputs the product solvent. The concentrate column feed includes at least the concentrated brine 118 from the membrane system. These columns are in fluid communication with one or more compressors. Mechanical vapor compression (MVC) is incorporated with the distillation columns to recover and re-use heat. Membrane distillation devices are also contemplated and considered within the scope of the invention.

[0028] The vapor 164 exiting the top of the concentrate column is fed to the DDS column in order to reduce the overall energy requirements of the DDS column 160. In some embodiments, the vapor 164 is first compressed (via compressor 175) to the pressure of the DDS column 160 so that the two columns 160, 162 can be operated at different pressures. In some embodiments, this vapor 164 includes additional draw solutes that may have reverse fluxed through the membrane of the osmotically driven membrane system and additional product solvent that did not pass through the membrane. The vapor 166 exiting the top of the DDS column 160 is compressed and exchanged with the DDS column reboiler 168. By compressing the DDS column vapor 166, the vapor condensing temperature is raised to a temperature that is higher than the DDS column reboiler 168 and, therefore, the latent heat of the vapor can be utilized as the supply heat to the column reboiler 168. Typically this vapor 166 will include the draw solutes in gaseous form. The pressure of the DDS column vapor 166 is controlled by a pressure control valve and compressed to the appropriate pressure using a 3 stage rotary lobe blower system or a screw compressor 170. Different compressors/blowers and various numbers of stages may be used to suit a particular application. In one embodiment, with approximately 650 kW of blower input power, the system is able to transfer approximately 6,600 kW of thermal energy. In an alternative embodiment, the heat from each stage is transferred to the column reboiler.

[0029] Leaving the DDS column reboiler heat exchanger 169, the compressed partially condensed DDS column vapor 166' is exchanged with the concentrate column reboiler 172. In this exemplary embodiment, the concentrate column 162 is run under a vacuum (approximately 0.1 - 0.9 atm absolute pressure) in order to reduce the boiling temperature of the reboiler loop water supplying steam to the column in order to exchange the remaining latent heat of the DDS column vapor with the concentrate column reboiler 172. Leaving the concentrate column reboiler heat exchanger 173, the mostly condensed DDS column vapor 166" is fully condensed in a final condenser 174 utilizing cooling water, thereby forming the concentrated draw solution (CDS) 116. Alternatively, the columns 160, 162 can be operated at the same or substantially equivalent pressures and the vapor stream 166 split and sent to each reboiler separately, typically without the use of a compressor. In this embodiment, the partially/mostly condensed DDS columns vapors 166', 166" exiting the reboilers 169, 173 can be combined and sent to the final condenser 174 to form the CDS 116.

[0030] In some embodiments, for example where the vapor exiting the column contains essentially no liquid portion, there is nothing for the draw solutes (e.g., ammonia and carbon dioxide in gaseous form) to be compressed into. The solutes could transition from the gaseous phase directly to the solid phase (e.g., deposition or desublimation), which could potentially render the recovery system 122 inoperable. Where that may be the case, the system 122 can include a by-pass line 161 for directing a portion of the dilute draw solution 120 to the compression operation, thereby providing a liquid for absorbing the gaseous solutes. In some embodiments, the introduction of the dilute draw solution may expedite the absorption of C0 ₂ (e.g., as may be present when using a NH ₃ -C0 ₂ draw solution). As shown, the dilute draw solution can be combined with the vapor 166 before or after any particular compressor to suit a particular application (e.g., a single compressor or series of compressors, the nature of the draw solutes, etc.). Additionally, the dilute draw solution can also be used to provide the liquid injection at the identified points. The by-pass line 161 can include any number and combination of valves and sensors as necessary to suit a particular application.

[0031] FIG. 3 depicts an alternative osmotically driven membrane system 200 configured for enhancing brine concentration in addition to recovering draw solutes. As shown in FIG. 3, the system 200 includes one or more forward osmosis membrane modules 212 (similar to those described above) in fluid communication with a draw solute recovery system 222. In an embodiment with a plurality of forward osmosis membrane modules 212, the modules can be arranged in series, parallel, or a combination of both. The module(s) 212 is also in fluid communication with a feed source or stream 214 and a concentrated draw solution source or stream 216 and outputs a concentrated feed stream 218 (e.g., brine) and a dilute draw solution 220. The draw solute recovery system 222 generally includes one or more separation apparatus in fluid communication with the concentrated feed stream 218 and the dilute draw solution 220 and further includes any necessary valves, heat exchangers, sensors, controls, plumbing, etc.

[0032] Generally, the dilute draw solution 220 is directed to a first separation apparatus

260, such as a thermal recovery device (e.g., one or more distillation columns and/or membrane distillation apparatus). In some embodiments, mechanical separation means (e.g., filtration or chemical manipulation) can be used in place of or in addition to the thermal recovery device. The concentrated feed 218 is directed to a second separation apparatus 262, such as a crystallizer or other thermal separation device for further concentration. In addition, the system 200 can include one or more means 245 for introducing an additive (e.g., anti-scalant, acid, catalyst, seeds, etc.) to one or more streams (e.g., the feed stream 214) and/or system operations. Similar to those described above, the means 245 can include a valve and porting arrangement and any necessary reservoirs, sensors, and/or controls for manual or automatic operation thereof.

[0033] As shown in FIG. 3, the first separation apparatus 260 receives the dilute draw solution 220 and includes a reboiler 268, as commonly known in the art, configured for receiving a source of thermal energy 228a (e.g., steam) and outputting a depleted thermal energy stream 228a' (e.g., condensed steam) that can be discarded or otherwise recycled within the system 200 (e.g., added to the feed stream 214 for purification or used for additional heating). As also shown, the dilute draw solution 220 passes through an optional first preheater 243a before entering the first separation apparatus 260, which outputs a tops product (typically vaporized draw solutes and a portion of solvent) 266 that can be recycled as re-concentrated draw solution 216 (described below) and a bottoms product (typically heated solvent) 252. In some cases, the bottoms product 252 can be recovered as the product solvent or sent for further processing (described below). In one or more embodiments, all or a portion of the product solvent 252 can be used to preheat the incoming dilute draw solution 220 via the preheater 243a. The cooled product solvent 252' can be used as is, discarded, or sent for further processing. For example, all or a portion of the product solvent 252, 252' can be directed to an additional system/process 258, such as filtration (e.g., reverse osmosis or nanofiltration) or additional thermal separation. In one or more embodiments, the additional system 258 is a polishing RO unit that produces a more purified product solvent 254 and a retentate 256 that can be recycled to the feed stream 218 for further processing. In some embodiments, the tops product 266 can be used for preheating the dilute draw solution 220.

[0034] As shown in FIG. 3, all or a portion of the concentrated feed 218 can be directed to the second separation apparatus (e.g., a distillation apparatus or forced circulation crystallizer) 262. Typically, the concentrated feed 218 is going to include a brine having a concentration of about 75,000 to 300,000 total dissolved solids (TDS), preferably about 200,000 TDS or greater. Generally, the greater the concentration, the more efficient the brine concentration process. Typical osmotically driven membrane systems cannot produce a concentrated feed high enough and will require additional thermal separation/concentration process to be performed on the concentrated feed before it can be sent to a crystallizer or other ZLD process. The second separation apparatus operating on a more concentrated brine eliminates the need for additional equipment to bring the concentrated output of the osmotically driven membrane system to saturation, while also recovering additional draw solutes.

[0035] Generally, the concentrated feed 218 passes through an optional second preheater

243b prior to entering the second separation apparatus 263. Similar to that described above, the second preheater 243b receives a source of thermal energy 228b and outputs a depleted thermal energy source 228b' that can be discarded or recycled within the system 200. Typically, certain draw solutes will have reverse fluxed through the membrane module 212 and will be contained within the concentrated feed 218. These draw solutes and additional solvent (collectively product 264) are vaporized within (or otherwise separated from) the second separation apparatus 262 and outputted therefrom, where they can be combined with the product 266 from the first separation apparatus 260 and recovered.

[0036] The combined products 264, 266 are directed to a final condenser 274 to fully absorb the draw solutes into the concentrated draw solution 216 and lower the temperature of the re-concentrated draw solution 216 as necessary for reintroduction into the membrane module(s) 212. Generally, the cooling fluid 276 provided to the final condenser 274 may be an independent source of cooling water or could be another stream within the system 200 that requires heating, such as the feed stream 214. Where the feed stream 214 is preheated via the condenser 274, the exiting cooling fluid (i.e., preheated feed stream) 276' will be directed back to the membrane module(s) 212 for introduction thereto.

[0037] The second separation apparatus 262 also outputs a further concentrated brine 244 that can be discarded or sent for further processing. Typically, the brine 244 is directed to additional dewatering equipment. In one or more embodiments, the brine 244 is sent to a filter press or centrifuge with the resulting mother liquor 244' being directed a crystallizer or back to the second separation apparatus 262 for further processing. In some embodiments, all or a portion of the brine 244 can be recirculated back into the second separation apparatus 262 (e.g., small portion of the brine 244 is recirculated while a larger portion is directed to the filter press or centrifuge). In some embodiments, the system also includes introduction means 245b for introducing seeds or other additives to the concentrated feed 218 and/or brine 244' to, for example, enhance the concentration thereof.

[0038] FIG. 3 depicted a draw solute recovery and brine concentration system/process

222 using direct steam introduction. The system 300 depicted in FIG. 4 is similar to the system 200 of FIG. 3, but incorporates mechanical vapor recompression similar to that described above with respect to FIG. 2, which also includes the use of boiler start-up steam similar to that shown in FIG. 2. As shown in FIG. 4, the system 300 includes one or more forward osmosis membrane modules 312 in fluid communication with a draw solute recovery system 322 that includes first and second separation apparatus 360, 362 similar to those described above. The membrane modules 312 are also in fluid communication with a feed source or stream 314 and a concentrated draw solution source or stream 316 and output a concentrated feed stream 318 and a dilute draw solution 320, where the dilute draw solution 320 and the concentrated feed stream 318 are introduced to the first and second separation apparatus 360, 362 as described above with respect to FIG. 3.

[0039] As shown in FIG. 4, the separation apparatus 360, 362 of the draw solute recovery system 322 each include one or more compressors 370, 375, respectively, for recovering and reusing the heat of the thermal energy introduced to the respective apparatus 360, 362.

However, in some embodiments, the system 300 is a hybrid of the various systems described herein may only include one compressor, which can be used with either separation apparatus 360, 362 with the other apparatus being operated with direct steam. The vapor 366 exiting the first separation apparatus 360 is directed to the compressor(s) 370, with the compressed vapors 366' exiting the compressor 370 and being directed to the reboiler 368 to reduce the overall thermal energy requirement of the first separation apparatus 360. As described with respect to FIG. 2, by compressing the vapor 366, the vapor condensing temperature is raised to a temperature higher than the reboiler 368 such that the latent heat of the compressed vapor 366' can be used as the thermal energy supply to the separation apparatus 360. The number and capacity of the compressor(s) will be selected to suit a particular application (e.g., the required differential temperature at the reboiler, the separation apparatus operating pressure, the compressor's compression ratio, flow rate, and ambient conditions). The partially condensed vapor 366" leaving the reboiler 368 can be directed to a final condenser 374, similar to that described with respect to FIG. 3.

[0040] Further, the vapor 364 exiting the second separation apparatus 362 can also be directed to one or more compressors 375, with the compressed vapors 364' exiting the compressor(s) 375 and being directed to the optional second preheater 343b to reduce the overall thermal energy requirement of the second separation apparatus 362. As described above, the increased vapor condensing temperature allows the latent heat of the compressed vapor 364' to be used as the thermal energy supply to the separation apparatus 362. The number and capacity of the compressor(s) for the second separation apparatus 362 will also be selected to suit a particular application. The partially condensed vapor 364" leaving the preheater 343b can be discarded or combined with vapor 366" and directed to the final condenser 374, similar to that described with respect to FIG. 3. The rest of the system 300 operates similar to that described with respect to FIG. 3. [0041] Generally, in the afore-mentioned embodiments, the draw solute recovery process, and in some cases the additional brine concentration process, is supplied with thermal energy via either direct steam or through the use of MVC. In some cases, the use of MVC has a high capital cost (CapEx) and process complexity associated, at least in part, to the need for large and/or multiple compressors and multiple points of partial condensation in the system.

Additionally, the second separation apparatus (typically the distillation apparatus for further brine concentration) is required to run under vacuum to utilize any partially condensed draw solute vapor stream to power the reboiler. A direct steam system tends to have lower capital cost and be a simpler process; however, direct steam has a high operation cost (OpEx). For example, in some facilities (e.g., the power sector), process steam is nearly twice as expensive as electricity and in those cases the latent heat of the draw solute vapors is not integrated back into the system. Another advantage of steam over MVC is that when concentrating the brine from the osmotically driven membrane system in the brine concentration apparatus (i.e., second separation apparatus), the use of steam eliminates the need to go to the high compression ratios necessary in MVC systems to overcome any boiling point elevation issues in the brine concentration apparatus, which can be more expensive and complex, and in some cases it is just not possible to achieve the necessary boiling points. As such, there is a need for the

afore-mentioned hybrid system that utilizes both direct process steam and electricity/MVC to minimize overall CapEx and OpEx expenses for recovering draw solutes and concentrating the brine output from the osmotically driven membrane system, while providing flexibility in utilizing the best available resources.

[0042] In various hybrid embodiments, the second separation apparatus is operated using direct steam for the thermal energy input, while utilizing MVC and the tops vapors from the second apparatus as the thermal energy for the first separation apparatus. This arrangement of combining process steam and electricity to separate the various streams results in about half of the energy used and a reduction in CapEx where a single compressor can be used. This arrangement also lowers the discharge pressure required on the compressor(s), which gives greater flexibility in the selection of compressors.

[0043] The MVR-based draw solute recovery systems disclosed elsewhere herein (e.g.,

FIG. 2) tend to rely on the direct compression of the vapor stream exiting the distillation apparatus to raise the temperature of the stream and make its enthalpy available to exchange heat with the reboilers located at the bottom of both of the distillation apparatus. The particulars of compressing a three-component vapor phase limits the technology choices for the compressor(s) and may necessitate expensive equipment and, in some cases, the injection of cooling water, all of which can adversely affect the efficiency of the system. Additionally, mitigating the risks of solids formation, which may result depending on the type of draw solutes used (e.g., NH ₃ -CO ₂ chemistry) adds cost and complexity to the system. The system 400 depicted in FIG. 5 allows for the compression of a well-behaved single or mixed-refrigerant stream instead of the vapor stream exiting the distillation apparatus, which allows for less-expensive equipment and eliminates the need for cooling water injection in the compressor. While, there may be some increased costs associated with the additional equipment, any increased equipment costs should be offset by increased system efficiency and simplification.

[0044] As shown in FIG. 5, the osmotically driven membrane system 400 includes one or more FO modules 412 in fluid communication with a draw solute recovery system 422, similar to those described above. As previously described, the FO module(s) 412 are in fluid communication with a source of a feed stream 414 and a concentrated draw solution 416 and output a concentrated feed stream 418 and a dilute draw solution 420, with the concentrated feed 418 and dilute draw solution 420 being directed to the draw solute recovery system 422 to recover the draw solutes from those streams. Generally, the draw solute recovery system 422 includes one or more separation apparatus (e.g., thermal recovery devices, such as a distillation column) for separating the draw solutes from a product solvent (apparatus 460) and recovering draw solutes that reverse fluxed through FO module(s) from the concentrated feed (apparatus 462).

[0045] The draw solute recovery system 422 also includes a heat pump circuit for circulating a separate heat transfer or working fluid 428. Generally, the heat pump circuit includes a compressor 470 to move energy from a low-temperature source, in this case the vapor stream 466 exiting the first thermal recovery device 460, to a higher temperature sink, in this case the reboilers (i.e., second and third heat transfer means) 468, 472 of the thermal recovery device 460, 462. The heat is transferred via the closed loop working fluid 428 (e.g., water, a refrigerant, or a mixture of refrigerants), which undergoes evaporation, compression, condensation, and sub-cooling, with near-isenthalpic expansion through an expansion valve 488 in four separate unit processes. The operating principle is similar to a vapor-compression style heat pump or chiller, with the choice of refrigerant dictated by the condensation and evaporation temperatures required for the application. In the case of a single refrigerant system, both reboilers 468, 472 will have the same condensing temperature of the working fluid 428, but a mixed refrigerant working fluid, allows for condensation over a range of temperatures and, therefore, more distant operating conditions for the two reboilers if required. Generally, a zeotropic mixture of refrigerants, which varies in temperature during a constant pressure phase change process due to the different properties of the materials, allows for the condensation and evaporation over a range of temperatures. This range of temperatures is advantageous in certain applications, for example, where the two or more reboilers (e.g., first and second thermal recovery devices) operate at different temperatures, the heat sources for each could be more closely matched, thereby reducing the work required by the compressor and improving the efficiency of the system.

[0046] Similar to the systems previously described, all or a portion of the dilute draw solution 420 is directed to the first thermal recovery device 460, while all or a portion of the concentrated feed stream 418 is directed to the second thermal recovery device 462. The second thermal recovery device outputs a tops product 464 that includes vaporized draw solutes, which are introduced to the first thermal recovery device 460. The first thermal recovery device 460 outputs a tops product 466 that includes the vaporized draw solutes from the dilute draw solution 420 and the second thermal recovery device 462. The vaporized draw solutes 466 are directed to a heat exchanger/condenser (i.e., first heat transfer means) to provide thermal energy to the separate working fluid 428. The at least partially cooled draw solutes 416' can be sent for further cooling as needed, directed to a concentrated draw solution tank, or recycled directly back to the FO module(s) 412. The separate working fluid 428 is directed to the reboiler heat exchanger 469 of the first thermal recovery device 460 via the heat pump 470, then through the reboiler heat exchanger 473 of the second thermal recovery device 462, and finally through the expansion valve 488.

[0047] FIG. 6 depicts an alternative embodiment of an osmotically driven membrane system 500 similar to those previously described, but configured to treat hypersaline feed streams 514 (typically TDS > 150g/l). Generally, the system 500 includes one or more forward osmosis modules 512 as previously described for receiving the feed stream 514 and a concentrated draw solution 516 and outputting a concentrated feed stream (e.g., brine) 518 and a dilute draw solution 520. The FO module(s) 512 is in fluid communication with a draw solute recovery system 522 that can be configured to suit a particular application and be similar to any of those systems 22, etc., previously described herein. The recovery system 522 receives the dilute draw solution 520, separates draw solutes from a solvent 552, and recycles the draw solutes into the concentrated draw solution 516. The system 500 includes a polishing RO system 558 in fluid communication with the draw solute recovery system 522 for processing the product solvent 552 output by the recovery system 522. In some embodiments, the RO system 558 is part of the draw solute recovery system 522. The polishing RO system 558 includes one or more RO modules arranged in series, parallel or a combination thereof and outputs a final product solvent 554 and a retentate stream 556 that is directed back to the feed stream 514. In some embodiments, all or a portion of the retentate stream 556' can be cycled back through the recovery system 522, for example, to recover additional draw solutes that may have made it through the recovery system 522. Additionally, all or a portion of the concentrated feed stream 518' can be directed to the recovery system to recover any draw solutes that migrated across the FO membrane(s) as previously described. The system 500 can include the necessary valves 577 and associated controls to effectuate these various flow paths.

[0048] Generally, hypersaline feeds result in an increased amount of TDS in the product solvent, which limits the recovery of the RO polishing system, resulting in a large, diluting stream being returned to the feed/input to the FO module(s), which results in increased capital and operating costs for the osmotically driven membrane system. For example, the increased feed volume requires a larger system than would otherwise be required to treat the raw feed without the additional feed volume, and additional energy is required to separate the draw solutes from the increased volume of solvent. The system depicted in FIG. 6, provides an alternative for reducing the increased CapEx and OpEx costs associated with treating a hypersaline feed stream. In some embodiments, this configuration results in about a 20% lower recovery, but with overall 30% lower energy (OpEx) and capital costs (CapEx). In certain applications, use of the system 500 can reduce the size and cost of an evaporator and/or crystallizer system that may be used to provide a full ZLD solution.

[0049] Referring back to FIG. 6, the system 500 also includes a by-pass line 561 for directing a portion (Y) of the hypersaline feed 514 around the FO module(s) 512 and blending the by-pass stream with the concentrated feed output 518. In some embodiments, for example, where multiple FO modules are present, the by-passed feed can be reintroduced elsewhere in the FO module arrangement (e.g., before a final FO module in a series thereof). Typically, the by-pass flow volume will be the same as the volume/portion (X) of the retentate flow 556 being returned to the feed stream 514 prior entering the FO module(s) 512, which results in a fixed feed flow to the FO module(s) 512 that is equal to the raw feed flow. The by-pass flow is directed to the concentrate stream 518 from a point in the feed stream 514 prior to the

introduction of the retentate flow 556. By balancing the flow volumes (i.e., X = Y), the overall size of the system 500 can be reduced (e.g., system sized based on raw feed flow as opposed to larger flow with recycled flow from draw solute recovery system 522. Typically, the volume of streams 556 and 561 is about 10-50% of the original raw feed volume, preferably about 15-25%, and more preferably about 20%. Additionally, the arrangement of the system 500 provides for the introduction of a clean stream 556 from the polishing RO system 558 to the front of the FO module(s) 512, which dilutes the sealants present in the raw feed, thereby reducing the scaling tendency of the system. The flow of the two streams 556, 561 can be controlled via valves 577 and a control system to regulate the flow of the two streams in tandem and maintain the substantially equal flow volumes thereof.

[0050] In accordance with one or more embodiments, the devices, systems and methods described herein may generally include a controller for adjusting or regulating at least one operating parameter of a device or a component of the systems, such as, but not limited to, actuating valves and pumps, as well as adjusting a property or characteristic of one or more fluid flow streams through an osmotically driven membrane module, or other module in a particular system. A controller may be in electronic communication with at least one sensor configured to detect at least one operational parameter of the system, such as a concentration, flow rate, pressure, pH level, or temperature. The controller may be generally configured to generate a control signal to adjust one or more operational parameters in response to a signal generated by a sensor. For example, the controller can be configured to receive a representation of a condition, property, or state of any stream, component, or subsystem of the osmotically driven membrane systems and associated recovery systems. The controller typically includes an algorithm that facilitates generation of at least one output signal that is typically based on one or more of any of the representation and a target or desired value such as a set point. In accordance with one or more particular aspects, the controller can be configured to receive a representation of any measured property of any stream, and generate a control, drive or output signal to any of the system components, to reduce any deviation of the measured property from a target value.

[0051] In accordance with one or more embodiments, process control systems and methods may monitor various concentration levels, such as may be based on detected parameters including pH and conductivity. Process stream flow rates and tank levels may also be controlled. Temperature and pressure may be monitored, along with other operational parameters and maintenance issues. Various process efficiencies may be monitored, such as by measuring product water flow rate and quality, heat flow and electrical energy consumption. Cleaning protocols for biological fouling mitigation may be controlled such as by measuring flux decline as determined by flow rates of feed and draw solutions at specific points in a membrane system. A sensor on a brine stream may indicate when treatment is needed, such as with distillation, ion exchange, breakpoint chlorination or like protocols. This may be done with pH, ion selective probes, Fourier Transform Infrared Spectrometry (FTIR), or other means of sensing draw solute concentrations. A draw solution condition may be monitored and tracked for makeup addition and/or replacement of solutes. Likewise, product water quality may be monitored by conventional means or with a probe such as an ammonium or ammonia probe. FTIR may be implemented to detect species present providing information which may be useful to, for example, ensure proper plant operation, and for identifying behavior such as membrane ion exchange effects.

[0052] Those skilled in the art should appreciate that the parameters and configurations described herein are exemplary and that actual parameters and/or configurations will depend on the specific application in which the systems and techniques of the invention are used. Those skilled in the art should also recognize or be able to ascertain, using no more than routine experimentation, equivalents to the specific embodiments of the invention. It is, therefore, to be understood that the embodiments described herein are presented by way of example only and that, within the scope of the appended claims and equivalents thereto; the invention may be practiced otherwise than as specifically described.

[0053] Moreover, it should also be appreciated that the invention is directed to each feature, system, subsystem, or technique described herein and any combination of two or more features, systems, subsystems, or techniques described herein and any combination of two or more features, systems, subsystems, and/or methods, if such features, systems, subsystems, and techniques are not mutually inconsistent, is considered to be within the scope of the invention as embodied in the claims. Further, acts, elements, and features discussed only in connection with one embodiment are not intended to be excluded from a similar role in other embodiments.