WO2016160810A1

WO2016160810A1 - Osmotic separation systems and methods

Info

Publication number: WO2016160810A1
Application number: PCT/US2016/024722
Authority: WO
Inventors: Nathan T. HANCOCK; Christopher DROVER; Mary Theresa PENDERGAST
Original assignee: Oasys Water, Inc.
Priority date: 2015-03-30
Filing date: 2016-03-29
Publication date: 2016-10-06

Abstract

The invention generally relates to osmotically driven membrane systems and processes and more particularly to integrating these systems and process with a Solvay process to provide a brine feedstock with an increased concentration and modified composition to improve the soda ash production process.

Description

OSMOTIC SEPARATION SYSTEMS AND METHODS

FIELD OF THE TECHNOLOGY

[0001] One or more aspects relate generally to osmotic separation. More particularly, one or more aspects involve the use of osmotically driven membrane processes, such as forward osmosis, to separate solutes from aqueous solutions and systems and methods for maximizing solvent and/or solute recovery in connection with a soda ash production process.

BACKGROUND

[0002] Forward osmosis has been used for desalination. In general, a forward osmosis desalination process involves a container having two chambers separated by a semi-permeable membrane. One chamber contains seawater. The other chamber contains 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 are then removed from the dilute solution to generate potable water.

[0003] Current soda ash production is typically carried out using Solvay or similar ammonia-soda processes. Generally, these processes are the major industrial processes for the production of sodium carbonate (i.e., soda ash). The ammonia-soda process was developed into its modern form by Ernest Solvay during the 1860s. The ingredients for this process are readily available and inexpensive: salt brine (from inland sources or from the sea) and limestone (from mines). The Solvay process results in soda ash (predominantly sodium carbonate (Na₂C0₃) from brine (as a source of sodium chloride (NaCl)) and from limestone (as a source of calcium carbonate (CaC0₃). The overall process is: 2 NaCl + CaC0₃→ Na₂C0 + CaCl₂. A simplified description can be given using the four different, interacting chemical reactions illustrated below. In one of the first steps in the process, carbon dioxide (C0₂) passes through a concentrated aqueous solution of sodium chloride (table salt, NaCl) and ammonia (NH₃) [NaCl + C0₂ + NH₃ + H₂0→ NaHC0₃ + NH₄C1]. In industrial practice, the reaction is carried out by passing concentrated brine through two towers. In the first, ammonia bubbles up through the brine (salt water) and is absorbed by it. In the second, carbon dioxide bubbles up through the ammoniated brine, and sodium bicarbonate (baking soda) precipitates out of the solution. The ammonia (NH₃) buffers the solution at a basic pH; without the ammonia, a hydrochloric acid byproduct would render the solution acidic, and arrest the precipitation. The necessary ammonia "catalyst" for the first reaction is reclaimed in a later step, and relatively little ammonia is consumed. The carbon dioxide required for the first reaction is produced by heating ("calcination") of the limestone at 950 - 1100 °C. The calcium carbonate (CaC0₃) in the limestone is partially converted to quicklime (calcium oxide (CaO)) and carbon dioxide: [CaC0₃→ C0₂ + CaO]. The sodium bicarbonate (NaHC0₃) that precipitates out in the first reaction is filtered out from the hot ammonium chloride (NH₄C1) solution, and the solution is then reacted with the quicklime (calcium oxide (CaO)) left over from heating the limestone in the second reaction: [2 NH₄C1 + CaO→ 2 NH₃ + CaCl₂ + H₂0]. The calcium oxide makes a strong basic solution. The ammonia from third reaction is recycled back to the initial brine solution of the first reaction. The sodium bicarbonate (NaHC0₃) precipitate from the first reaction is then converted to the final product, sodium carbonate (washing soda: Na₂C0₃), by calcination (160 - 230 °C), producing water and carbon dioxide as byproducts: [2 NaHC0₃→ Na₂C0₃ + H₂0 + C0₂]. The carbon dioxide from the fourth reaction is recovered for re-use in the first reaction. When properly designed and operated, a Solvay plant can reclaim almost all its ammonia, and consumes only small amounts of additional ammonia to make up for losses. The only major inputs to the Solvay process are salt, limestone, and thermal energy, and its only major byproduct is calcium chloride (CaCl₂), which can be sold as road salt. However, the process is energy intensive as the concentrated brine feedstock that is required is typically produced via an energy intensive thermal process, such as the use of a crystallizer. It is, therefore, desirable to use a less energy intensive method of producing the concentrated brine feedstock and further minimizing the various material losses in the process.

SUMMARY

[0004] Aspects of the invention relate generally to osmotically driven membrane systems and methods, including forward osmosis separation (FO), direct osmotic concentration (DOC), or pressure-assisted forward osmosis (PAFO) in combination with a soda ash production process to produce the concentrated brine feedstock for the production of soda ash and recapture various other material streams used throughout the process. For example, in the modified process disclosed herein, portions of the ammonia and carbon dioxide can be rerouted to the FO process for use as draw solutes.

[0005] In one aspect, the invention relates to a system (and its corresponding method steps) for producing a concentrated brine for the production of soda ash. The system includes a forward osmosis module in fluid communication with a concentrated saline stream, where the forward osmosis module includes at least one membrane having a first side and a second side such that the first side of the at least one membrane is configured for receiving the concentrated saline stream and the second side of the at least one membrane is fluidly coupled to a source of a concentrated draw solution, with the at least one membrane osmotically separating a solvent from the saline stream, thereby forming a concentrated brine 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 system further includes a separation system in fluid communication with the forward osmosis module and configured for receiving the dilute draw solution from the forward osmosis module and separating draw solutes from the solvent; and a soda ash production system in fluid communication with the forward osmosis module and the separation system, where the soda ash production system receives the concentrated brine from the forward osmosis module for the production of soda ash, returns a portion of the draw solutes contained within the concentrated brine to the separation system to further recover draw solutes from the dilute draw solution, and outputs Na₂C0₃ (i.e., the soda ash).

[0006] In various embodiments of the foregoing aspect, the system includes a pretreatment system configured for receiving a raw saline feed and outputting the concentrated saline stream. In one embodiment, the pretreatment system further includes a reverse osmosis module in fluid communication with the forward osmosis module and configured for receiving an at least partially concentrated saline stream from the pretreatment system and outputting the concentrated saline stream to the forward osmosis module. The pretreatment system can include at least one of a softening unit, a filtration unit, or an ion exchange unit. In some embodiments, the raw saline feed is seawater. The reverse osmosis module can include a plurality of reverse osmosis membranes disposed in series and/or parallel. In various embodiments, the system includes a reverse osmosis module in fluid communication with the forward osmosis module and configured for receiving a raw saline feed and outputting the concentrated saline stream to the forward osmosis module. In some embodiments, the forward osmosis module includes a plurality of membranes disposed in series and/or parallel. [0007] In further embodiments, the soda ash production system operates as a modified

Solvay system. The concentrated draw solution may include ammonia and carbon dioxide draw solutes in a molar ratio of greater than one to one. In some embodiments, the molar ratio is in the range of about 2.2-3.0. The molarity of the concentrated draw solution can be about 5.0-8.0 mol/L. In various embodiments, the separation system can include a thermal recovery unit for thermally separating the draw solutes from the solvent and/or a filtration device for separating the draw solutes from the solvent. The thermal recovery unit may include a distillation apparatus (e.g., a distillation column or membrane distillation apparatus). In some cases, the soda ash production system provides a source of thermal energy for use in the thermal recovery unit, for example via the lime kiln and/or steam from an ammonia recovery tower. In some

embodiments, the filtration device includes at least one of a nano -filtration membrane or a reverse osmosis membrane. The recovered solvent can be potable water.

[0008] In another aspect, the invention relates to a system (and its corresponding method steps) for the osmotic extraction of a solvent from a first solution. The system includes a plurality of forward osmosis units, each having a first chamber having an inlet fluidly coupled to a source of the first solution, a second chamber having an inlet fluidly coupled to a source of a concentrated draw solution, and a semi-permeable membrane system separating the first chamber from the second chamber and configured for osmotically separating the solvent from the first solution, thereby forming a second solution in the first chamber and a dilute draw solution in the second chamber. The system also includes a separation system in fluid communication with the plurality of forward osmosis units and configured to separate the dilute draw solution into the concentrated draw solution and a solvent stream. [0009] In various embodiments of the foregoing aspects, the concentrated draw solution includes ammonia and carbon dioxide in a desired molar ratio of greater than one to one.

However, other draw solutions are contemplated and considered within the scope of the invention, including, for example, NaCl or any of the various alternative draw solutions disclosed in PCT Patent Publication No. WO2014/078415 (the '415 publication), the disclosure of which is hereby incorporated by reference herein in its entirety. In addition, other systems and methods for separating and recovering draw solutes and the solvent, such as those disclosed in the '415 publication, are contemplated and considered within the scope of the invention.

Furthermore, various pretreatment and post-treatment systems can be incorporated in the forgoing aspects of the invention. The pretreatment systems can include at least one of a heat source for preheating the first solution, means for adjusting the pH of the first solution or the draw solution, means for disinfection (e.g., chemical or UV), separation and clarification, a filter or other means for filtering the first solution (e.g., carbon or sand filtration or reverse osmosis), means for polymer addition, ion exchange, or means for softening (e.g., lime softening) the first solution. The post-treatment systems can include at least one of a reverse osmosis system, an ion exchange system, a second forward osmosis system, a distillation system, a pervaporator, a mechanical vapor recompression system, a heat exchange system, or a filtration system (e.g., nano-, micro-, or ultrafiltration). In additional embodiments, the system can also include a recycling system including an absorber configured to facilitate reintroduction of the draw solutes to the second chamber to maintain the desired molar ratio of the draw solution.

[0010] In yet another aspect, the invention relates to a system that integrates a forward osmosis process (e.g., a membrane brine concentrator) with a Solvay process to produce a brine feedstock for the production of soda ash via the Solvay process. Generally, a traditional Solvay process uses a concentrated brine (>300 g/L) of sodium chloride as feedstock. The use of the FO process provides an economical alternative to the use of a more conventional brine concentrator (e.g., a crystallizer) to produce this brine. For example, by combining certain elements of the FO process with the Solvay process and modifying certain aspects of each process, the overall process can be optimized, producing a synergistic performance that can produce a brine concentration and subsequent soda ash production with dramatically lower operating and capital costs. Accordingly, the invention relates to a system and related process for producing a concentrated brine for the production of soda ash. The system includes a pretreatment unit configured for receiving a raw saline feed and outputting a treated feed for concentration, a reverse osmosis module in fluid communication with the pretreatment unit and configured for receiving the treated feed and outputting a concentrated saline stream, a forward osmosis module in fluid communication with the reverse osmosis module and including at least one membrane having a first side and a second side, the first side of the at least one membrane configured for receiving the concentrated saline stream 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 concentrated saline stream, thereby forming a concentrated brine 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 system further includes a separation system in fluid communication with the forward osmosis module and configured for receiving the dilute draw solution from the forward osmosis module, the separation system configured for separating draw solutes from the solvent, and a soda ash production system in fluid communication with the forward osmosis module and the separation system, the soda ash production system configured for receiving the concentrated brine with a portion of ammonia from the forward osmosis module for the production of soda ash and returning a portion of draw solutes contained within the concentrated brine to the separation system to further recover draw solutes from the dilute draw solution and outputting Na₂C0₃.

[0011] In various embodiments of the foregoing aspect, the pretreatment unit includes at least one of a softening unit, a filtration unit, an ion exchange unit, or combinations thereof. The raw feed can include seawater, although other saline sources are contemplated and considered within the scope of the invention. In some embodiments, the reverse osmosis module may include a plurality of reverse osmosis membranes disposed in series, parallel or combinations thereof. Additionally, the reverse osmosis module can also be in fluid communication with the raw saline feed for introducing at least a portion thereof to the treated feed for concentration within the reverse osmosis module. In various embodiments, the forward osmosis module may include a plurality of membranes disposed in series, parallel or combinations thereof. The soda ash production system can be a modified Solvay system.

[0012] Still other aspects, embodiments, and advantages of these exemplary aspects and embodiments, are discussed in detail below. Moreover, it is to be understood that both the foregoing information and the following detailed description are merely illustrative examples of various aspects and embodiments, and are intended to provide an overview or framework for understanding the nature and character of the claimed aspects and embodiments. Accordingly, 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

[0013] 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:

[0014] FIG. 1 is a schematic representation of a system for osmotic extraction of a solvent in accordance with one or more embodiments of the invention for the production of a brine for use in a soda ash production process; and

[0015] FIG. 1A is a schematic representation of the soda ash production process as incorporated with the system of FIG. 1.

DETAILED DESCRIPTION

[0016] In accordance with one or more embodiments, an osmotic method for extracting water from an aqueous solution may generally involve exposing the aqueous solution to a first surface of a forward osmosis membrane. A second solution, or draw solution, with an increased concentration relative to that of the aqueous solution may be exposed to a second opposed surface of the forward osmosis membrane. Water may then be drawn from the aqueous solution through the forward osmosis membrane and into the second solution generating a water-enriched solution via forward osmosis, which utilizes fluid transfer properties involving movement from a less concentrated solution to a more concentrated solution. The water-enriched solution, also referred to as a dilute draw solution, may be collected at a first outlet and undergo a further separation process to produce purified water. A second product stream, i.e., a depleted or concentrated aqueous process solution, may be collected at a second outlet for discharge or further treatment. Alternatively, the various systems and methods described herein can be carried out with non-aqueous solutions.

[0017] In accordance with one or more embodiments, a forward osmosis membrane module may include one or more forward osmosis membranes. The forward osmosis membranes may generally be semi-permeable, for example, allowing the passage of water, but excluding dissolved solutes therein, such as sodium chloride, ammonium carbonate, ammonium bicarbonate, and ammonium carbamate. Many types of semi-permeable membranes are suitable for this purpose provided that they are capable of allowing the passage of the solvent (e.g., water) while substantially if not completely blocking the passage of the solutes and not reacting with the solutes in the solution. In some embodiments, the membrane(s) may have high selective permeability properties, thereby allowing the aforementioned solutes to pass through the membrane; however alternative types of membranes may be used to maximize performance of the system for a particular application, for example, feed chemistry, draw solution chemistry, ambient conditions, etc. For example, in some cases it may be desirable for the membrane to allow for a certain amount of reverse salt flux of certain draw solutes, such as ammonia salts, that could be beneficial to the soda ash production process when present in the concentrated brine.

[0018] In accordance with one or more embodiments, at least one forward osmosis membrane may be positioned within a housing or casing. The housing may generally be sized and shaped to accommodate the membranes positioned therein. For example, the housing may be substantially cylindrical if housing spirally wound forward osmosis membranes. The housing of the module may contain inlets to provide feed and draw solutions to the module as well as outlets for withdrawal of product streams from the module. In some embodiments, the housing may provide at least one reservoir or chamber for holding or storing a fluid to be introduced to or withdrawn from the module. In at least one embodiment, the housing may be insulated.

[0019] In accordance with one or more embodiments, a forward osmosis membrane module may generally be constructed and arranged so as to bring a first solution and a second solution into contact with first and second sides of a semi-permeable membrane, respectively. Although the first and second solutions can remain stagnant, it is preferred that both the first and second solutions are introduced by cross flow, i.e., flows parallel to the surface of the semipermeable membrane. This may generally increase membrane surface area contact along one or more fluid flow paths, thereby increasing the efficiency of the forward osmosis processes. In some embodiments, the first and second solutions may flow in the same direction. In other embodiments, the first and second solutions may flow in opposite directions. In at least some embodiments, similar fluid dynamics may exist on both sides of a membrane surface. This may be achieved by strategic integration of the one or more forward osmosis membranes in the module or housing.

[0020] In accordance with one or more embodiments, draw solutes may be recovered for reuse. A separation system may strip solutes from the dilute draw solution to produce product water substantially free of the solutes. In some embodiments, the separation system may include a distillation column or other thermal or mechanical recovery mechanism. Draw solutes may then be returned, such as by a recycling system, back to the concentrated draw solution. Gaseous solutes may be condensed or absorbed to form a concentrated draw solution. An absorber may use dilute draw solution as an absorbent. In other embodiments, product water may be used as an absorbent for all or a portion of the absorption of the gas streams from a solute recycling system. Examples of different osmotically driven systems, including separation/recovery systems are described in U.S. Patent Nos. 6,391,205, 8,002,989, 9,039,899, 9,044,711,

9,248,405, and 9,266,065; U.S. Patent Publication Nos. 2011/0203994 and 2014/0224718, and PCT Publication No. WO2015/157031; the disclosures of which are hereby incorporated by reference herein in their entireties.

[0021] FIG. 1 depicts one exemplary embodiment of a system 100 that integrates an FO process/system 120 with a Solvay or Solvay-like process/system 150. As shown in FIG. 1, the system 100 may include a pretreatment process/system 104 for receiving a raw feed. Generally, the raw feed 102 can include any of the feed streams disclosed herein and will typically be seawater or brackish water. The pretreatment system may include at least one of a heat source for preheating the raw feed 102, means for adjusting the pH of the feed, means for disinfection (e.g., chemical or UV), separation and clarification, a filter or other means for filtering the feed (e.g., nano-, micro-, or ultrafiltration, carbon or sand filtration, or reverse osmosis), means for polymer addition, ion exchange, or means for softening (e.g., lime softening). In a particular embodiment, the pretreatment 104 can include softening (e.g., with lime (Ca(OH)₂), a caustic (e.g., NaOH), or soda ash (Na₂C0₃) or combinations thereof) followed by NF/UF filtration (in some embodiments, this order is reversed) and then ion exchange to provide a pretreated feed 106 that can be forwarded to a reverse osmosis (RO) module 110.

[0022] In some embodiments, the NF/UF pretreatment filtration can be a loose NF or tight UF applied to all or only a portion of the raw feed 102 to reduce sulfate concentration with the permeate therefrom (or pretreatment system output generally) being combined with a portion of the raw feed 102 (e.g., seawater) that by-passed the pretreatment system 104 as the feed 108 to the RO module 110. In some cases, the RO feed 108 also includes all or a portion of any product solvent recovered via the FO module, as described in greater detail below. In some embodiments, complete hardness softening follows the RO pre-concentration process prior to being directed to the FO module; however, in other embodiments, it may precede the RO pre- concentration process. In some cases, depending on the feed chemistry, it is desirable to use the softening waste 105 as feedstock to the lime kiln (see FIG. 1A), as the softening sludge is typically mostly CaC0₃, which is chemically equivalent to limestone. In such a scenario, the softening waste (CaC0₃) is calcined into CaO with the rest of the limestone, which results in a net increase in soda ash production and a decrease in waste production. In additional embodiments, also depending on feed chemistry, it is preferable to eliminate the RO module and send the raw or only partially pretreated feed 102' directly to the FO module (for example, if the raw feed was the Red Sea or similar body of water).

[0023] The RO module 110 outputs a permeate stream 118 that can be used as is (e.g., for cooling water), discarded or recycled within the system 100 and a retentate stream 114. The retentate stream (i.e., RO concentrate) is the feed to the FO module 112, examples of which are described in the incorporated references and can include one or more modules arranged in series and/or parallel and incorporate spiral wound, hollow fiber, and/or flat sheet membrane modules. Generally, the membrane array is optimized for maximum brine concentration and maximum flux. The feed stream 114 is introduced on one side of the membrane(s) of the FO system 112, with a concentrated draw solution 116 introduced on the opposite side of the membranes. In a particular embodiment, the draw solution 116 is introduced in a counter flow to the feed 114. Generally, the draw solution comprises draw solutes that are easily removable and provide an osmotic concentration gradient across the membrane(s) such that a solvent and a portion of draw solutes flux across the membranes from the feed 114 to the draw solution 116, thereby creating a further concentrated feed 114' with a portion of draw solutes (e.g., NH₃) and a diluted draw solution 116' exiting the FO module 112.

[0024] The dilute draw solution 116' is directed to a separation system/process 130 for separating the draw solutes from a solvent 148. The separation system 130 can include a thermal (e.g., a distillation apparatus using low grade heat) and/or filtration (e.g., RO) based separation process as described in the incorporated references. In some embodiments, the source of low grade heat is obtained from the Solvay process, for example, waste heat 132a from the lime kiln (C in FIG. 1A) and/or steam 132b used in the ammonia recovery tower (D in FIG. 1A).

[0025] The solvent 148 can be discarded, used as is, or returned and combined with the raw feed 102 or pretreated feed 106. The removed draw solutes can be re-formed into concentrated draw solution 116 and returned to the FO module 112 for use therein. In a particular embodiment, the concentrated draw solution is an ammonia-carbon dioxide based draw solution with an increased N:C molar ratio in the range of about 2.2-3.0, preferably about 2.4-2.8, and more preferably about 2.6-2.7. In addition, the molarity of the concentrated draw solution 116 is increased to about 5.0-8.0 mol/L, preferably about 5.5-7.5 mol/L, and more preferably about 6.0-6.5 mol/L. Typically, the draw to feed volumetric ratio is about 0.2-0.5.

[0026] In some embodiments, for example, where using an NH₃-CO₂ draw solution, certain draw solutes (e.g., NH₃, which forms NH₄C1) will reverse flux through the membrane(s) and enter the feed 114'. The feed 114', including a highly concentrated brine and the ammonia salts, is directed to the Solvay process 150 as the brine feedstock. Certain FO process, such as those described in the references incorporated herein, incorporate a system/process for removing and recovering these draw solutes (e.g., a brine stripping column); however, incorporating the FO module with the Solvay process eliminates the need for the brine stripper, since the Solvay process would otherwise need to add the ammonia to the brine (e.g., via the ammonia absorber A in FIG. 1A). This design reduces the amount of ammonia required to begin the process of producing soda ash. In some embodiments, the feed stream 114' to the Solvay process is treated, for example, to adjust its pH level or regulate the temperature (e.g., to 25-45 °C) of the brine entering the Solvay process 150.

[0027] FIG. 1A generally depicts the modified Solvay system/process 150. Generally, the process includes directing a concentrated brine though an ammonia absorber A, sending the ammoniated brine 114" through a carbonation tower B, where C0₂ is added to the brine 114". Generally, the C0₂ is provided via the lime kiln C, which may incorporate a portion of the pretreatment waste 105 therein and a portion of the waste heat therefrom 132a may be used in the separation system/process 130. The mixture is then sent to a filter where the NaHC0₃ is removed from the mixture and sent to an oven or other heat source E for separating the soda ash 152 therefrom. Within the modified Solvay process, the ammonia absorber A is redesigned (e.g., the tower can be reduced in size or capacity) to accept a brine feedstock (feed 114') containing ammonia in the range of about 1-6 mol/L, preferably about 2-5 mol/L, and more preferably about 3-4 mol/L from the FO module/process 112. As shown in FIGS. 1 and 1A, the Solvay process 150 outputs one or more material/energy streams 140 for use in the FO process 112, such as a return of ammonia and/or carbon dioxide for use as draw solutes or assist in the recovery of draw solutes and/or a source of waste heat that can be used in the separation process 130 (e.g., for a thermal recovery process) to drive the draw solute separation and recovery. In one embodiment, the ammonia gas produced in the ammonia recovery tower D of the Solvay process, is partially rerouted. Instead of all of the ammonia gas being fed back to the ammonia absorber A, a portion of this gas is feed to the separation system 130 of the FO system/process 120. In some embodiments, the separation process/system 130 can be incorporated within the modified Solvay process proximate the sources of the ammonia, carbon dioxide, and waste heat 132a, 132b as needed for regenerating the concentrated draw solution 116.

[0028] The inventive modification and combination of the systems and processes described herein provide for a more efficient and less expensive FO process and Solvay process, as it eliminates the need for stripping draw solutes (e.g., ammonia) from the brine (concentrated feed 114') and reduces the requirements for the first step in the Solvay process (e.g., absorbing ammonia into the brine). The entire system/process 100 remains a theoretical closed cycle for ammonia (real world plants see losses of approximately 0.5%). The elimination of the ammonia stripping from the FO process saves considerable capital and operating expenses, making the FO process the most efficient technology for producing brine feedstock for the Solvay process by a wide margin. In addition, the use of a very highly concentrated draw solution with a high N:C ratio increases the brine concentration of NaCl to a level where the crystallizer typically used can be eliminated, resulting in another massive capital and operational savings. In some

embodiments, the FO process will produce a brine with a ratio of NaCl/water (moles) of at least 0.1, preferably about 0.11, and more preferably about 0.12.

[0029] 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 the 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, 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 pre- and post-treatment 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.

[0030] 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. Membrane leaks may be detected using ion selective probes, pH meters, tank levels, and stream flow rates. Leaks may also be detected by pressurizing a draw solution side of a membrane with gas and using ultrasonic detectors and/or visual observation of leaks at a feedwater side. Other operational parameters and maintenance issues may be monitored. 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.

[0031] 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.

[0032] 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.

Claims

1. A system for producing a concentrated brine for the production of soda ash, the system comprising:

a forward osmosis module in fluid communication with a concentrated saline stream and comprising at least one membrane having a first side and a second side, the first side of the at least one membrane configured for receiving the concentrated saline stream 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 saline stream, thereby forming a concentrated brine 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;

a separation system in fluid communication with the forward osmosis module and configured for receiving the dilute draw solution from the forward osmosis module, the separation system configured for separating draw solutes from the solvent;

a soda ash production system in fluid communication with the forward osmosis module and the separation system, the soda ash production system configured for receiving the concentrated brine from the forward osmosis module for the production of soda ash and returning a portion of draw solutes contained within the concentrated brine to the separation system to further recover draw solutes from the dilute draw solution, and outputting Na₂C0₃.

2. The system of claim 1 further comprising a pretreatment system in fluid communication with the forward osmosis module and configured for receiving a raw saline feed and outputting the concentrated saline stream.

3. The system of claim 2 wherein the pretreatment system further comprises a reverse osmosis module in fluid communication with the forward osmosis module and configured for receiving an at least partially concentrated saline stream and outputting the concentrated saline stream to the forward osmosis module.

4. The system of claim 2, wherein the pretreatment system comprises at least one of a softening unit, a filtration unit, or an ion exchange unit.

5. The system of claim 2, wherein the raw saline feed comprises seawater.

6. The system of claim 3, wherein the reverse osmosis module comprises a plurality of reverse osmosis membranes disposed in series and/or parallel.

7. The system of claim 1 further comprising a reverse osmosis module in fluid

communication with the forward osmosis module and configured for receiving a raw saline feed and outputting the concentrated saline stream to the forward osmosis module.

8. The system of claim 1, wherein the forward osmosis module comprises a plurality of membranes disposed in series and/or parallel.

9. The system of claim 1, wherein the soda ash production system operates as a modified Solvay system.

10. The system of claim 1, wherein the concentrated draw solution comprises ammonia and carbon dioxide draw solutes in a molar ratio of greater than one to one.

11. The system of claim 10, wherein the molar ratio is in the range of about 2.2-3.0.

12. The system of claim 10, wherein a molarity of the concentrated draw solution is about 5.0-8.0 mol/L.

13. The system of claim 1, wherein the separation system comprises a thermal recovery unit for thermally separating the draw solutes from the solvent.

14. The system of claim 13, wherein the thermal recovery unit comprises a distillation apparatus.

15. The system of claim 13, wherein the soda ash production system comprises a source of thermal energy for use in the thermal recovery unit.

16. The system of claim 1, wherein the separation system comprises a filtration device for separating the draw solutes from the solvent.

17. The system of claim 16, wherein the filtration device comprises at least one of a nano- filtration membrane or a reverse osmosis membrane.

18. The system of claim 1, wherein the separation system comprises a thermal recovery unit in fluid communication with a filtration device for separating the draw solutes from the solvent.