Electrodialysis Liquid Desiccant Dehumidification System

Abstract

Air flows across the gas-liquid interface, and the liquid desiccant flowing through the interface absorbs water from the air, thereby diluting it and forming an output stream. The output stream circulates through an electrodialysis stack having a central ion exchange membrane and first and second outer ion exchange membranes. A redox shuttle loop circulates around the first and second outer ion exchange membranes. A voltage is applied to the electrodialysis stack, thereby regenerating the liquid desiccant.

Description

[Technical Field]

[0001] The present disclosure relates to an electrodialysis liquid desiccant dehumidification system. Summary of the Invention

[0002] In one embodiment, a liquid desiccant system includes an electrodialysis stack with a liquid desiccant loop having dilute and concentrated streams of liquid desiccant separated by a central heat exchange membrane, and a redox shuttle loop having first and second redox streams separated from the dilute and concentrated streams of the liquid desiccant loop by first and second outer ion exchange membranes, respectively, of a type different from the central ion exchange membrane.

[0003] The liquid desiccant system includes first and second electrodes operable to apply a voltage across an electrodialysis stack. The system has a gas-liquid interface in fluid communication with a concentrated stream of liquid desiccant. The gas-liquid interface exposes the concentrated stream of liquid desiccant to air flowing across the gas-liquid interface, and the concentrated stream is diluted by absorption of water from the air to form an output stream.

[0004] The liquid desiccant system can include a first pump that circulates the liquid desiccant through the electrodialysis stack and the gas-liquid interface. An output stream from the gas-liquid interface can be split into a dilute stream and a concentrate stream upon entering the electrodialysis stack. A second pump can be used to circulate the first and second redox streams across the first and second outer ion exchange membranes.

[0005] In another embodiment, a method includes circulating a liquid desiccant through an air-liquid interface. Air flows across the air-liquid interface, causing the liquid desiccant to absorb water from the air. The liquid desiccant is diluted through water absorption, forming an output stream. The output stream is split into a dilute stream and a concentrate stream at the input to an electrodialysis stack. The electrodialysis stack has a central ion exchange membrane and first and second outer ion exchange membranes of a different type than the central ion exchange membrane. The dilute stream flows between the central ion exchange membrane and the first outer ion exchange membrane, and the concentrate stream flows between the central ion exchange membrane and the second outer ion exchange membrane. A redox shuttle loop circulates around the first and second outer ion exchange membranes. A voltage is applied across the electrodialysis stack, for example, causing ion migration across the central ion exchange membrane and the first outer ion exchange membrane, resulting in the desiccant concentrate moving from the dilute stream to the redox shuttle loop and the concentrate stream. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic diagram of a liquid desiccant system according to an exemplary embodiment. [Figure 1A] FIG. 1 is a schematic diagram of a liquid desiccant system according to an exemplary embodiment. [Figure 2] 1 is a perspective view of an air conditioning system according to an exemplary embodiment; [Figure 3] FIG. 1 is a block diagram of an air conditioning system according to an exemplary embodiment. [Figure 4] FIG. 1 is a schematic diagram of a liquid desiccant system according to an exemplary embodiment. [Figure 5A] FIG. 1 is a schematic diagram of an electrodialysis stack according to an exemplary embodiment. [Figure 5B] FIG. 1 is a schematic diagram of an electrodialysis stack according to an exemplary embodiment. [Figure 6] FIG. 1 is a schematic diagram of a heat exchanger used at a gas-liquid interface according to an exemplary embodiment. [Figure 7] FIG. 1 is a schematic diagram of a multi-stage electrodialysis stack according to an exemplary embodiment. [Figure 8] 1 is a flowchart of a method according to an exemplary embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] This disclosure relates to liquid desiccant systems. Liquid desiccant systems can be used, among other things, in heating, ventilation, and air conditioning (HVAC). Air conditioning accounts for approximately 10% of electricity consumption in the United States, with dehumidification accounting for more than half of the load in humid regions. This disclosure describes an efficient thermodynamic approach to dehumidification for air conditioning. Generally, the system includes a membrane dehumidifier in tandem with a redox-assisted electrodialysis liquid desiccant concentrator.

[0008] The system described herein utilizes a redox-assisted electrodialysis process that enables a membrane-based liquid desiccant air conditioning system. In this redox-assisted electrodialysis (ED) process, an aqueous solution of redox-active species is circulated between the anode and cathode of an electrochemical stack to concentrate the ionic solution, eliminating the heat- or pressure-induced thermodynamic phase changes required for vapor compression (VC) or desiccant-based air conditioning. The liquid desiccant (e.g., an aqueous solution of lithium chloride, LiCl) absorbs water from the air across the membrane interface. The diluted liquid desiccant is efficiently reconcentrated, avoiding the latent heat input required for water evaporation. The increased efficiency of this newly proposed cycle is estimated to lead to annual energy savings of 1.5 quads by 2030.

[0009] The schematic diagram in FIG. 1 illustrates an electrodialysis liquid desiccant air conditioning (ELDAC) system 100 according to an exemplary embodiment. The system 100 includes a desiccant section 102 and a refrigeration section 104. In the desiccant section 102, ambient air 106 (and / or recycled air) is pumped across a liquid-transport membrane dryer 108, also referred to herein as the gas-liquid interface. The air 106 may be ambient air at high temperature and relative humidity (RH). Water 109 from the air 106 is absorbed at the membrane interface 108 into a concentrated liquid desiccant 110, e.g., aqueous LiCl, which then passes through a redox-assisted regenerator 112 to separate a dilute stream 114 (e.g., effluent water) and reconcentrate the desiccant stream 110. Other concentrates, such as NaCl, LiBr, and CaCl, can be used instead of LiCl as the desiccant.

[0010] Humidity is reduced in the air 115 leaving the desiccant section 102, where it is cooled by the cooling section 104. This cooling section 104 may include an evaporator 116 and other components (e.g., condenser, compressor) not shown. Because the air 115 entering the cooling section 104 has a lower relative humidity than the ambient / recirculated air 106, the evaporator 116 is more efficient and can significantly reduce the temperature of the cooled air 120 than if the evaporator 116 were required to condense moisture from the incoming air 115. Experimental results measuring the energy used by redox-assisted electrodialysis to concentrate aqueous ionic solutions indicate that the ELDAC system 100 can have a regeneration specific heat input (RSHI) of less than 0.05 kBTU / lb, which is up to 30 times lower than currently used heat regeneration methods.

[0011] As seen in detail 122 of Figure 1A, the redox-assisted regenerator 112 has two outer ion exchange membranes 124 that separate the outer redox channel 126 from the inner concentrate 110 and diluate 114 streams. In this example, the outer ion exchange membranes 124 are configured as anion exchange membranes (AEMs). The concentrate 110 and diluate 114 streams are separated by a central ion exchange membrane 130, which in this example is a cation exchange membrane (CEM). In other configurations, the central ion exchange membrane 130 can be an AEM and the outer membrane 124 can be a CEM.

[0012] An external voltage 132 induces the oxidation or reduction of redox-active shuttle molecules, driving ion migration across the membranes 124, 130 without splitting water or producing other gaseous by-products (e.g., chlorine) and generating two streams: reconcentrated desiccant 110 and effluent water 114. This goal can be achieved through multiple steps. One proposed redox shuttle is (bis(trimethylammoniopropyl)ferrocene / bis(trimethylammoniopropyl)ferrocenium, [BTMAP-Fc] 2+ / [BTMAP-Fc] 3+ ) 134, which are non-toxic, highly stable, and have extremely fast electrochemical kinetics and negligible membrane permeability. Other redox shuttle solutions include ferrocyanide / ferricyanide ([Fe(CN)6] 4- / [Fe(CN)6] 3- ) or a negatively charged ferrocene derivative. The moving parts of the system can include a low pressure pump for circulating the liquid and a fan for circulating the air.

[0013] In Figure 2, a perspective view shows details of ELDAC system 200 according to an exemplary embodiment. In Figure 3, a block diagram shows the functional relationships between some of the components shown in Figure 2, as well as other components according to additional embodiments. System 200 includes an enclosure 202 that holds various functional components and provides air ducting paths. Humidified air 214 (e.g., outside air and / or return air) is delivered through a first duct 220 via a blower 212. This air 214 is then pumped across a gas-liquid interface dehumidifier 206. In this example, dehumidifier 206 is configured as a rectangular membrane element that fills first duct 220.

[0014] Within the frame 206a of the dehumidifier 206 are one or more planar membranes 206b through which liquid desiccant is circulated. In other embodiments, hollow tubes, liquid surfaces, and liquid sprays can be used in the dehumidifier 206 instead of or in addition to the planar membrane 206b. Movement of the fluid desiccant through the membrane 206b can be achieved using any combination of capillary action, gravity feed, direct pumping of the liquid, etc. A grill 206c can provide mechanical support for the membrane 206b to reduce bending caused by air pressure from the airflow 214. A liquid pump 207 is used to move the liquid desiccant from the optional storage tank 210 to the membrane dehumidifier 206, where it absorbs water from the air 214 and is fed back to the redox-assisted generator 208. The redox-assisted generator 208 separates the water from the liquid desiccant, and the separated water is discharged via a drain 209. It should be noted that although components 207, 208, 210 and associated piping are shown outside of enclosure 202 for ease of illustration, they may be located partially or completely within enclosure 202.

[0015] Air 216 that passes through membrane dehumidifier 206 has a lower RH and can therefore be more efficiently processed by sensible heat rejector 204, such as the evaporator of a refrigerant cycle air conditioner. Cooled air 218 that passes through sensible heat rejector 204 passes through supply duct 220 where it exits enclosure 202 and is used to cool a target space, such as a building, vehicle, etc.

[0016] Note that in FIG. 3, redox storage tank 300 is shown in fluid communication with LD regenerator 208. ELDAC system 200 can include one or both redox and desiccant reservoirs 300, 210. Note that desiccant storage device 210 can store fluids for both the concentrate and dilute streams (e.g., streams 110 and 114 in FIG. 1) by using separate reservoirs or a single reservoir with two or more partitions. Redox reservoir 300 can similarly store concentrated and dilute portions of the redox stream (e.g., the lower and upper portions of stream 126 shown in FIG. 1). These reservoirs 210, 300 can be used as buffers in some embodiments. For example, if the water being discharged from the ELDAC system 200 does not equal the water being absorbed from the air, one of the concentrate or diluted desiccant (or a combination of both) may be drawn from the reservoir 210 to ensure the desiccant loop maintains the desired concentrate level and / or flow rate.

[0017] The reservoirs 210, 300 can be of sufficient capacity to be used for purposes other than dehumidification. For example, as described in U.S. Patent Application Serial No. 16 / 200,289 (Attorney Docket No. 20171214US03 / PARC.225U1), an electrodialysis cell 302 can use the redox solution 300 to generate electricity, thus recovering a portion of the electricity used in dehumidification. Such a process can be performed in conjunction with or separate from dehumidification. For example, power generation can occur overnight when the system is underutilized or shut down.

[0018] 4, a schematic diagram shows additional details of a liquid desiccant system according to an exemplary embodiment. An electrodialysis stack 400 provides an enclosure for a liquid desiccant loop 402 and a redox shuttle loop 404. The loops 402, 404 are separated within the housing 400 by an outer exchange membrane 406, and the diluate / concentrate paths 402a, 402b of the liquid desiccant loop 402 are separated by a central exchange membrane 408. The fluids in the loops 402, 404 are driven by pumps 412, 410, respectively.

[0019] Liquid desiccant loop 402 begins with concentrated liquid desiccant at point 402c. Desiccant loop 402 contains an ionic solution, such as lithium chloride, in water. A typical starting concentration is about 30% desiccant by weight. The concentrated desiccant solution is contacted with an air-membrane interface / exchanger 414, such as membrane dehumidifier 206 shown in FIGS. 2 and 3. At exchanger 414, higher RH air 416 enters and lower RH air 418 exits. Water vapor 420 from the air is drawn across a water-selective membrane 422 (or other liquid-air interface) of exchanger 414 by the desiccant, thereby diluting the desiccant solution, which exits at point 402d at a lower concentration.

[0020] In electrodialysis stack 400, dilute liquid desiccant solution 402d is split at branch point 402e into separate streams 402a, 402b that come into contact with membranes 406, 408 of stack 400. Stream 402b is concentrated as it passes through stack 400 and re-enters pump 412 with the same concentration as at point 402c. The other stream 402a is diluted as it passes through stack 400 and exits as a highly diluted water stream that can be discharged, stored, or used for other purposes.

[0021] Pump 410 circulates the redox shuttle between points 404a and 404b, where it contacts electrode 424. A voltage 426 applied across the electrodialysis stack drives ions from stream 402a to stream 402b, from stream 402a to stream 404b, and from stream 404a to stream 402b. In each case, driving ions through membranes 406, 408 affects concentration. An alternative embodiment of electrodialysis stack 500 uses LiCl as the desiccant concentrate and [BTMAP-Fc] as the redox shuttle. 2+ / [BTMAP-Fc] 3+ 5A using a LiCl desiccant concentrate. The LiCl desiccant concentrate is split into a demineralized water / dilute stream and a concentrate stream 504 by a central ion exchange membrane 506 (in this case a CEM). The redox shuttle loop 508 has first and second redox streams 508a-b separated from the dilute and concentrate streams of the liquid desiccant loop by respective first and second outer ion exchange membranes 507, 590 of a different type (in this case an AEM) than the central ion exchange membrane 506.

[0022] Another alternative embodiment of the electrodialysis stack 510 uses LiCl as the desiccant concentrate and [Fe(CN)6] as the redox shuttle. 4- / [Fe(CN)6] 3- 5A and 5B. The LiCl desiccant concentrate is split into a demineralized water / dilute stream and a concentrate stream 514 by a central ion exchange membrane 516 (in this case, an AEM). A redox shuttle loop 518 has first and second redox streams 518a-b separated from the dilute and concentrate streams of the liquid desiccant loop by respective first and second outer ion exchange membranes 517, 519 of a different type (in this case, a CEM) than the central ion exchange membrane 516. Note that the electrodialysis stacks 500, 510 shown in FIGS. 5A and 5B can be used in any of the dehumidification loops shown herein.

[0023] The dehumidification portion of the system requires only input electricity to drive the pump and electrodialysis stack, as well as the input air stream to be dehumidified. An outlet stream of water and low-RH air will result. While this system is intended for use in dehumidification, it can be adapted for additional applications, such as generating electricity from stored redox solutions. ELDAC is advantageous because it requires significantly less energy than existing dehumidification systems due to the use of electrodialysis concentrations at zero or near-zero overpotential. Because the system does not rely on water separation to drive ionic movement, ELDAC does not produce toxic or flammable gases (e.g., chlorine or hydrogen) when used with concentrated salt solutions, unlike other electrochemical processes such as conventional electrodialysis. In an exemplary application, ELDAC can be used upstream of a conventional air conditioner to eliminate the latent heat load on the air conditioner and reduce air conditioning costs.

[0024] The absorption of moisture in the liquid desiccant is exothermic, resulting in an increase in the temperature of the gas-liquid interface holding the liquid desiccant. This temperature increase can result in an increased load on the sensible cooling section that receives the air passing through the gas-liquid interface. In Figure 6, a schematic diagram shows a system for removing heat from a gas-liquid interface 600, according to an exemplary embodiment. A heat exchanger 602 is thermally coupled to a heat transfer element 604 that distributes heat through a component (e.g., a membrane) at the interface 600.

[0025] Heat transfer element 604 can be a conductive strip (e.g., metal, carbon nanotube, etc.), a gas- or liquid-filled passive heat pipe (e.g., a thermosiphon), a tube through which a gas or liquid is pumped, a radiant heat absorber, or other heat transfer structure known in the art. Heat transferred through element 604 is routed to heat exchanger 602, which is exposed to cooling stream 606. Cooling stream 606 is a gas or liquid flow that can carry heat away from heat exchanger 602 and ultimately release the heat to an ambient heat sink (e.g., air, soil, water). In other embodiments, heat 608 can be transferred (e.g., along heat transfer path 610) to another heat sink, such as electrodialysis stack 612 (which can be the same stack that provides desiccant to interface 600 or a different stack) and / or to exhaust water 614 from the system (e.g., exhaust water 114 in FIG. 1 ).

[0026] In the preceding examples, the electrodialysis stack included a single redox loop. In other embodiments, the stack can include multiple redox loops and associated ionic membranes to further increase the dilution / concentration level and / or increase the amount of desiccant flow that can be processed. In Figure 7, a block diagram shows a two-stage electrodialysis stack 700 according to an exemplary embodiment.

[0027] Electrodialysis stack 700 processes a liquid desiccant loop 702 that is split into a dilute stream 702a and a concentrate stream 702b that passes through a first stage 704. Stream 702a exiting stage 704 is further split into a second dilute stream 702d and a second concentrate stream 702e that passes through a second stage 706. Stream 702e exiting stage 706 is less concentrated than stream 702b exiting stage 704 and can be recombined with output stream 702c and reintroduced into the previous stage 704, rather than recombining with concentrate stream 702b and reintroducing it to the gas-liquid interface 708. To maximize efficiency, the desiccant concentrations in streams 702c and 702e are approximately equivalent (e.g., within 0-20%).

[0028] Each of the stages 704, 706 includes a central ion exchange membrane 704a, 706a separating the dilute streams 702a, 702d and the concentrate streams 702b, 702e. Each of the stages 704, 706 includes a redox shuttle loop 704b, 706b having first and second redox streams 704b, 704bb, 706ba, 706b separated from the dilute streams 702a, 702d and the concentrate streams 702b, 702e of the liquid desiccant loop 702 by respective first and second outer ion exchange membranes 704c, 704d, 706c, 706d. Each of the stages 704, 706 includes first and second electrodes 704e, 704f, 706e, 706f operable to apply a voltage across the stages 704, 706 of the electrodialysis stack 700.

[0029] Gas-liquid interface 708 is in fluid communication with concentrated stream 702b of liquid desiccant exiting first stage 704. Gas-liquid interface 708 exposes concentrated stream 702b of liquid desiccant to air flowing across gas-liquid interface 708, where the concentrated stream is diluted via absorption of water from the air to form output stream 702c. Output stream 702c is combined with output stream 702e exiting second stage 706. First pump 712 circulates the liquid desiccant through electrodialysis stack 700 and gas-liquid interface 708. Output stream 702c from gas-liquid interface 708, after being combined with output stream 702e, enters electrodialysis stack 700 where it is split into diluted stream 702a and concentrated stream 702b.

[0030] The voltage across electrodes 704e, 704f, 706e, 706f causes ion migration across the central ion exchange membranes 704a, 706a and the first outer ion exchange membranes 704c, 706c, resulting in the desiccant concentrate moving from the first diluted stream 702a to the first redox stream 704ba and first concentrated stream 702b of stage 704, and similarly from the second diluted stream 702d to the first redox stream 706ba and second concentrated stream 702e of stage 706. A second pump 714, 716 circulates the redox shuttle loop 704b, 706b, causing the first redox stream 704ba, 706ba and the second redox stream 704bb, 706bb to flow across the respective first outer ion exchange membrane 704c, 706c and second outer ion exchange membrane 704d, 706d. The voltage also induces a second (and similar) ion migration across the second outer membrane 704d, 706d, resulting in the movement of desiccant concentrate from the second redox stream 704bb, 706bb to the concentrate stream 702b, 702e.

[0031] Note that stages 704, 706 can be the same or different. For example, each stage 704 can use a different combination of redox shuttle solutions, central and outer exchange membrane types, voltages, membrane geometries, desiccant flow geometries, redox flow rates, and so forth. In this manner, stages 704, 706 can be optimized for different expected concentrations in portions of dilute streams 702a, 702d and concentrate streams 702b, 702e. Stages 704, 706 can operate simultaneously, and under certain conditions, one or the other may be shut off. For example, if the concentrate level in dilute stream 702a falls below a certain threshold, one of stages 704, 706 can be shut off to save energy and reduce wear. If the concentrate level in dilute stream 702a exceeds this threshold, the inactive stage 704, 706 can be restarted.

[0032] The embodiment shown in FIG. 7 can be expanded to three or more stages 704, 706. Furthermore, while stages 704, 706 are shown as part of a single electrodialysis stack unit 700, they can be implemented as separate enclosures connected by piping, for example, for carrying streams 702a, 702b, 702d, and 702e of desiccant loop 702. In one embodiment, a single redox pump can be used instead of two pumps 714, 716, for example, by running loops 704b, 706b in parallel or series. Note that a multi-stage electrodialysis stack such as that shown in FIG. 7 can be used in any of the embodiments shown above (e.g., FIGS. 1-5) and can incorporate any of the features shown in these and other figures, such as fluid storage reservoirs, heat exchangers, etc.

[0033] In Figure 8, a flowchart illustrates a method according to an exemplary embodiment. The method includes step 800 of circulating liquid desiccant through an air-liquid interface. Air is caused to flow across the air-liquid interface (801) so that the liquid desiccant absorbs water from the air. The liquid desiccant is diluted through water absorption to form an output stream. The output stream is split into a dilute stream and a concentrate stream (802) at the input to an electrodialysis stack. The electrodialysis stack has a central ion exchange membrane and first and second outer ion exchange membranes of a different type (e.g., cation or anion) than the central ion exchange membrane.

[0034] The dilute stream is caused to flow between the central ion exchange membrane and the first outer ion exchange membrane (803). The concentrate stream is caused to flow between the central ion exchange membrane and the second outer ion exchange membrane (804). A redox shuttle loop is circulated around the first and second outer ion exchange membranes (805). A voltage is applied across the electrodialysis stack, causing ion migration across the central ion exchange membrane and the first outer ion exchange membrane. This migration moves the desiccant concentrate from the dilute stream into the redox shuttle loop and the concentrate stream.

[0035] Unless otherwise indicated, all numbers expressing size, quantity, and physical properties of features used in the specification and claims are to be understood as modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the above specification and appended claims are approximations that may vary depending upon the desired properties one of ordinary skill in the art would seek to obtain using the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range. [Explanation of symbols]

[0036] 100 Electrodialysis Liquid Desiccant Air Conditioning (ELDAC) System 102 Desiccant Section 104 Cooling Section 106 Outside Air 108 Liquid transport membrane dryer 109 Water 110 Concentrated Liquid Desiccant 114 Dilute Stream

Claims

1. A liquid desiccant system comprising an electrodialysis stack, the electrodialysis stack comprising: a liquid desiccant loop having a dilute stream and a concentrate stream of a liquid desiccant solution separated by a central ion exchange membrane; a redox shuttle loop having first and second redox streams separated from the dilute and concentrate streams of the liquid desiccant loop by first and second outer ion exchange membranes, respectively, of a type different from the central ion exchange membrane; and first and second electrodes operable to apply a voltage across the electrodialysis stack; the liquid desiccant system further comprising a gas-liquid interface configured to receive the concentrated stream but not the dilute stream of the liquid desiccant solution; the concentrated stream of the liquid desiccant solution is configured to be exposed to air flowing across the gas-liquid interface; the concentrate stream is diluted via absorption of water from the air to form an output stream; 10. A liquid desiccant system configured such that the output stream is split into the dilute stream and the concentrate stream as it is circulated back to the liquid desiccant loop of the electrodialysis stack.

2. a first pump for passing the liquid desiccant solution through the electrodialysis stack and the liquid region of the gas-liquid interface; a second pump for circulating the first and second redox streams across the first and second outer ion exchange membranes; The liquid desiccant system of claim 1 further comprising:

3. the central ion exchange membrane comprises a cation exchange membrane; 10. The liquid desiccant system of claim 1, wherein the first and second outer ion exchange membranes comprise anion exchange membranes.

4. the central ion exchange membrane comprises an anion exchange membrane; 10. The liquid desiccant system of claim 1, wherein the first and second outer ion exchange membranes comprise cation exchange membranes.

5. The liquid desiccant system of claim 1 , further comprising a heat transfer element in thermal communication with the liquid-gas interface.

6. 10. The liquid desiccant system of claim 1, further comprising a reservoir for storing a portion of at least one of the dilute and concentrated streams of the liquid desiccant solution.

7. an electrodialysis cell in fluid communication with a reservoir that stores a portion of the fluid from the redox shuttle loop; 10. The liquid desiccant system of claim 1, wherein the electrodialysis battery utilizes the stored portion to generate electricity.

8. The liquid desiccant system of claim 1 further comprising a reservoir for storing the dilute stream.

9. The first and second electrodes are connected by the voltage. a first ion transfer across the central ion exchange membrane and the first outer ion exchange membrane from the dilute stream to the first redox stream and the concentrate stream; a second ion transfer across the second outer exchange membrane from the second redox stream to the concentrate stream; The liquid desiccant system of claim 1 , configured to cause:

10. 10. The liquid desiccant system of claim 9, wherein the liquid desiccant solution comprises LiCl.

11. The redox shuttle loop is a ferrocyanide / ferricyanide [Fe(CN) 6 10. The liquid desiccant system of claim 9, comprising:

12. 10. The liquid desiccant system of claim 9, wherein the redox shuttle loop comprises a positively charged ferrocene derivative.

13. a second stage electrodialysis stack having a second redox shuttle loop having third and fourth redox streams separated from the second dilute and second concentrate streams of the liquid desiccant loop by third and fourth outer ion exchange membranes, respectively, and a second central ion exchange membrane between the third and fourth outer ion exchange membranes; third and fourth electrodes operable to apply a voltage across the second stage electrodialysis stack; The third and fourth electrodes are connected by the voltage. a first ion transfer across the second central ion exchange membrane and the third outer ion exchange membrane from the second dilute stream to the third redox stream and the second concentrate stream; a second ion transfer across the fourth outer exchange membrane from the fourth redox stream to the second concentrate stream; and configured to cause a first dilute stream of the liquid desiccant loop is split into the second dilute stream and the second concentrate stream upon exiting membrane contact with the first redox shuttle loop, the second dilute stream flowing between the second central ion exchange membrane and the third outer ion exchange membrane, and the second concentrate stream flowing between the second central ion exchange membrane and the fourth outer ion exchange membrane; 10. The liquid desiccant system of claim 1, wherein the second concentrate stream is recombined with the output stream.

14. 14. The liquid desiccant system of claim 13, wherein the second concentrate stream has a concentration level of liquid desiccant solution approximately equal to that of the output stream.

15. circulating the liquid desiccant solution through a liquid region of the gas-liquid interface; flowing air across the gas-liquid interface such that the liquid desiccant solution absorbs water from the air and the liquid desiccant solution is diluted by the water absorption to form an output stream; splitting the output stream into a dilute stream and a concentrate stream at the input to an electrodialysis stack, the electrodialysis stack having a central ion exchange membrane and first and second outer ion exchange membranes of a different type than the central ion exchange membrane; flowing a dilute stream between the central ion exchange membrane and the first outer ion exchange membrane; flowing the concentrate stream between the central ion exchange membrane and the second outer ion exchange membrane; circulating a redox shuttle loop having first and second redox streams around the first and second outer ion exchange membranes; applying a voltage to the electrodialysis stack; the concentrate stream being the only liquid desiccant solution passing through the liquid region of the gas-liquid interface; 1. A method for dehumidifying air with a liquid desiccant solution, comprising:

16. The step of applying a voltage includes: a first ion transfer across the central ion exchange membrane and the first outer ion exchange membrane from the dilute stream to the first redox stream and the concentrate stream; a second ion transfer across the second outer exchange membrane from the second redox stream to the concentrate stream; The method of claim 15, wherein

17. the central ion exchange membrane comprises a cation exchange membrane; 16. The method of claim 15, wherein the first and second outer ion exchange membranes comprise anion exchange membranes.

18. 16. The method of claim 15, further comprising the step of discharging the dilute stream from the electrodialysis stack.

19. storing a portion of the fluid from the redox shuttle loop; using a portion of the fluid to generate electricity via an electrodialysis battery; 16. The method of claim 15, further comprising:

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