Hollow fiber membrane modules for use in distillation systems

A membrane module comprising an outer casing having an interior region, a seal disposed within the outer case, thereby dividing the interior region into a first chamber and a second chamber, and a plurality of hollow fiber membranes extending through the first chamber and the second chamber, where at least a portion of the plurality of hollow fiber membranes have first segments located within the first chamber and second segments located within the second chamber, the first segments being configured to allow vapor transmission therethrough, and the second segments being configured to substantially prevent vapor transmission therethrough, and further configured to allow transmission of thermal energy therethrough.

BACKGROUND

The present invention relates to distillation systems for liquid treatment processes. In particular, the present invention relates to distillation systems containing hollow fiber membrane modules for separating distillate fluids from feed solutions in liquid treatment processes.

In recent years, membrane distillation has become increasingly popular in a variety of fluid-treatment applications. The membranes are typically hydrophobic and microporous to keep the feed solution separated from that of the distillate during operation. Hollow fiber membranes are typically employed in tube/shell configurations, where bundles of hollow fiber membranes are arranged along the longitudinal axes of the modules. For membrane distillation, each hollow fiber membrane in the bundle is typically a hydrophobic, microporous membrane having an exterior surface and an inner hollow tubular region. The exterior surfaces of the hollow fiber membranes face a shell side of the module, which is the portion of the module containing the feed solution. The inner hollow tubular regions define a tube side of the module, which provides a conduit for collecting the distillate fluids separated from the feed solution.

During operation, the feed solution is typically heated to form a temperature differential across the wall of the hollow fiber membranes. This temperature differential creates a vapor pressure differential between the tube side and the shell side of the module, which causes vapor transport through the hollow fiber membranes. The transmitted vapor then condenses within the hollow fiber membranes, thereby providing the desired distillate fluid.

During steady state operations, the mass transfer across the hollow fiber membranes can provide good product rates of distillate fluids for a variety of distillation systems. However, a common issue with hollow fiber membrane modules involves the thermal efficiencies of the modules. As the distillate fluid evaporates and transmits through the hollow fiber membranes, latent heat accompanies the transmitted vapor, passing from the shell side to the tube side of the module. Furthermore, the temperature differential between the shell side and the tube side of the module can result in conductive heat transfers across the wall of the hollow fiber membranes. Overall, a large amount of heat is transported through the membrane. If the heat is not recuperated, a high operating cost in terms of thermal energy would result. Thus there is an ongoing need for increased thermal efficiencies in distillation systems containing hollow fiber membrane modules.

SUMMARY

The present invention relates to a hollow fiber membrane module and a distillation system incorporating the hollow fiber membrane module. The hollow fiber membrane module includes an outer casing having an interior region divided into a first chamber and a second chamber, and a plurality of hollow fiber membranes extending through the first and second chambers. At least a portion of the hollow fiber membranes have first segments located within the first chamber and second segments located within the second chamber, where the first segments allow vapor transmission therethrough, and the second segments allow transmission of thermal energy therethrough, but substantially prevent vapor transmission therethrough.

DETAILED DESCRIPTION

FIG. 1is a schematic illustration of distillation system10, which includes membrane modules12, feed loop14, and distillate loop16, and is a suitable system for separating a desired distillate fluid from a feed solution. Examples of suitable feed solutions for use with distillation system10include solutions containing compounds that are separable by vapor pressure differentials across hydrophobic, microporous membranes, such as seawater, brackish water, and other aqueous brine solutions for water and wastewater treatment processes. As used herein, the term “solution” refers to a carrier liquid that contains one or more solids that are fully dissolved, partially dissolved, dispersed, emulsified, or otherwise suspended in the carrier liquid(s). For example, the feed solution may be an aqueous brine solution containing salt that is at least partially dissolved in a water carrier. In this example, distillation system10may be used to separate at least a portion of the water from the aqueous brine solution to provide the clean water as the distillate fluid. Distillation system10also desirably includes standard fluid processing equipment (not shown), such as process control units, fluid pumps, and filters.

Membrane modules12are hollow fiber membrane modules that separate the distillate fluid from the feed solution (e.g., water from an aqueous brine solution). Examples of particularly suitable modules for membrane modules12include direct contact membrane distillation (DCMD) modules. As discussed below, membrane modules12are each divided into a shell side (not shown inFIG. 1) and a tube side (not shown inFIG. 1), where the shell side is in fluid communication with feed loop14, and the tube side is in fluid communication with distillate loop16. During operation, the feed solution travels from feed loop14to the shell sides of membrane modules12. While the feed solution flows through the shell sides of membrane modules12, the feed solution is separated into the desired distillate fluid and a residual feed solution. The desired distillate fluid transfers to the tube sides of membrane modules12, and enters distillate loop16. The residual feed solution remains on the shell sides of membrane modules12and reenters feed loop14.

While distillation system10is shown with three membrane modules12operating in a parallel arrangement, distillation system10may alternatively include additional or fewer numbers of membrane modules12. Examples of suitable numbers of membrane modules12for use in distillation system10range from one to one hundred; particularly suitable numbers of membrane modules12for use in distillation system10range from one to twenty five; and even more particularly suitable numbers of membrane modules12for use in distillation system10range from one to ten.

Feed loop14is a fluid pathway for the feed solution, and includes feed source line18, feed conveyance lines20a-20d, feed inlet lines22, feed outline lines24, discharge line28, feed reservoir tank30, and heat exchanger26. Feed source line18is a valve-controlled fluid conduit for transferring the feed solution from a feed solution source (not shown) to feed loop14. When distillation system10reaches a steady state operation, portions of the feed solution are separated within membrane modules12to provide the desired distillate fluid in distillate loop16. As such, feed line18desirably provides the feed solution to balance the steady state flow in feed loop14.

Feed conveyance lines20a-20dare fluid conduits for feed loop14, and provide a counter-clockwise flow path in the embodiment shown inFIG. 1. Feed inlet lines22are fluid conduits that interconnect feed conveyance line20dand membrane modules12, thereby allowing the feed solution to flow into the shell sides of membrane modules12. Feed outlet lines24are fluid conduits that interconnect feed loop line20ato membrane modules12. This allows the distilled feed solution to exit the shell sides of membrane modules12, and reenter feed loop14.

Discharge line28is a valve-controlled fluid conduit interconnecting feed conveyance lines20aand20b, which allows a portion of the feed solution to bleed out of feed loop14. This is beneficial to control the concentration of the residual feed solution during a steady state operation. Feed reservoir tank30is a container fed by feed conveyance line20b, which provides a reservoir of the feed solution during operation. Feed reservoir tank30is also connected to feed conveyance line20cfor supplying the feed solution to heat exchanger26. Heat exchanger26is a heat-providing heat exchanger that interconnects feed conveyance lines20cand20d. Accordingly, heat exchanger26increases the temperature of the feed solution passing from feed conveyance line20cto feed conveyance line20d. As discussed below, the increased temperature of the feed solution assists in creating vapor pressure differentials within membrane modules12, thereby allowing membrane modules12to transport the vapor from the feed solution side to the distillate side.

Distillate loop16is a fluid pathway for the distillate fluid, and includes heat exchanger32, distillate conveyance lines34a-34d, distillate reservoir tank36, distillate inlet lines38, distillate outlet lines40, recovery line42, and storage tank44. In addition to the distillate fluid obtained from the separation processes within membrane modules12, distillate loop16also desirably contains a flow of cool distillate fluid to further assist the separation processes. Heat exchanger32is a cooling heat exchanger that interconnects distillate conveyance lines34aand34b, thereby lowering the temperature of the distillate fluid flowing through distillate conveyance line34ato distillate conveyance line34b.

Distillate conveyance lines34a-34dare fluid conduits for distillate loop16, and provide a clockwise flow path for the distillate fluid in the embodiment shown inFIG. 1. Distillate reservoir tank36is a container fed by distillate conveyance line34b, which provides a reservoir of the cool distillate solution during operation. Distillate reservoir tank36is also connected to distillate conveyance line34cfor supplying the distillate fluid to distillate inlet lines38, thereby allowing the distillate fluid to flow into membrane modules12. Distillate outlet lines40are fluid conduits that interconnect membrane modules12and distillate conveyance line34d. This allows the distillate fluid to exit membrane modules12, and reenter distillate loop16.

Recovery line42is a valve-controlled fluid conduit connected to distillate conveyance line34dfor transferring a portion of the distillate fluid from distillate loop16to storage tank44. Storage tank44is a container for receiving the distillate fluid obtained from membrane modules12. As discussed above, when distillation system10reaches a steady state operation, a portion of the feed solution is separated at membrane modules12to provide the distillate fluid in distillate loop16. As such, recovery line42and storage tank44allow the obtained amounts of distillate fluid to be removed from distillate loop16and stored as a recovered product (e.g., clean water from a brine solution). This allows distillate loop16to substantially maintain a steady state flow.

During a steady state operation, the feed solution flows in a counter-clockwise direction around feed loop14, and is heated in part by heat exchanger26to an elevated temperature. Suitable elevated temperatures may vary depending on the composition of the feed solution. For aqueous feed solutions, examples of suitable elevated temperatures range from about 50° C. to less than 100° C., with particularly suitable elevated temperatures ranging from about 70° C. to about 90° C. While flowing through feed loop14, a portion of the heated feed solution flows into the shell sides of membrane modules12via feed inlet lines22, and the remaining portion of the heated feed solution continues to flow through feed conveyance line20d. In an alternative embodiment, feed loop14may require all of the heated feed solution to flow into the shell sides of membrane modules12via feed inlet lines22. In this embodiment, heat exchanger26only interconnects feed conveyance line20cand feed inlet lines22.

Also during the steady state operation, a supply of the distillate fluid flows in a clockwise direction around distillate loop16, and is cooled in part by heat exchanger32to a lowered temperature. Suitable lowered temperatures for the distillate fluid may vary depending on the composition of the distillate fluid. For aqueous distillate fluids, examples of suitable lowered temperatures range from about 5° C. to less than 50° C., with particularly suitable lowered temperatures ranging from about 20° C. to less than 40° C. While flowing through distillate loop16, the cooled distillate fluid flows into the tube sides of membrane modules12via distillate inlet lines38.

The cool distillate fluid and the heated feed solution flowing into membrane modules12create temperature differentials between the shell and tube sides of membrane modules12. The temperature differentials correspondingly create vapor pressure differentials, higher vapor pressure on the shell side versus lower vapor pressure on the tube side. The membranes inside the modules12allow only vapor to be transported across the membrane wall into the bore side of the tube. The distillate fluid may then be collected in recovery tank44as the desired distillate product (e.g., clean water in a water treatment process).

While flowing through the shell sides of membrane modules12, the feed solution also loses thermal energy due to latent and conductive heat transfers. In a standard membrane module, the transferred heat will be carried away from the modules. However, as discussed below, membrane modules12also function as heat exchangers to recoup at least a portion of the thermal energy inside the modules. This increases the thermal efficiency of distillation system10, thereby reducing the amount of energy required and the size of heat exchangers26and32. As a result, distillation system10may operate with lower operation costs. Additionally, while membrane modules12are shown inFIG. 1in use with distillation system10, membrane modules12may alternatively be used with a variety of systems for separating a distillate fluid from a feed solution, and for reducing thermal energy requirements in the given systems.

FIG. 2is a schematic illustration of an interior of membrane module12, which corresponds to one of the membrane modules12shown inFIG. 1. As shown inFIG. 2, membrane module12includes outer casing46, potting resin walls48,50, and52, connection conduit54, hollow fiber membranes56, and baffles58and60. Outer casing46is a rigid structure extending along a longitudinal axis (referred to as longitudinal axis62), and defines interior region64of membrane module12. Outer casing46also desirably includes couplings (not shown) for connecting membrane module12to feed inlet line22, feed outlet line24, distillate inlet line38, and distillate outlet line40.

Potting resin walls48,50, and52are seals extending perpendicular to longitudinal axis62, and are formed from one or more sealant materials, such as acrylate and epoxy-based materials. Accordingly, potting resin walls48,50, and52divide interior region64into distillate inlet chamber66, contactor chamber68, recuperator chamber70, and distillate outlet chamber72. Distillate inlet chamber66is the chamber disposed between outer casing46and potting resin wall52, and is open to distillate inlet line38. Contactor chamber68is the chamber disposed between potting resin walls50and52, within outer casing46, and is open to feed inlet line22and connection conduit54. Recuperator chamber70is the chamber disposed between potting resin walls48and50, within outer casing46, and is open to feed outlet line24and connection conduit54. Distillate outlet chamber72is the chamber disposed between outer casing46and potting resin wall48, and is open to distillate outlet line40.

As discussed below, contactor chamber68is the section of membrane module12where separation through distillation occurs, and recuperator chamber70is the section of membrane module12where a portion of the heat from the hot distillate flowing on one side of hollow fiber membranes56is transferred to the cooler feed residual feed solution on the other side of hollow fiber membranes56. Suitable dimensions for contactor chamber68and recuperator chamber70may vary depending on the desired heat and mass transfer properties. Examples of suitable lengths along longitudinal axis62for each of contactor chamber68and recuperator chamber70range from about 13 centimeters (about 5 inches) to about 76 centimeters (about 30 inches), with particularly suitable lengths ranging from about 25 centimeters (about 10 inches) to about 51 centimeters (about 20 inches), and with even more particularly suitable lengths ranging from about 30 centimeters (about 12 inches) to about 41 centimeters (about 16 inches). Examples of suitable diameters orthogonal to longitudinal axis62for each of contactor chamber68and recuperator chamber70range from about 3 centimeters (about 1 inch) to about 41 centimeters (about 16 inches), with particularly suitable diameters ranging from about 5 centimeters (about 2 inches) to about 30 centimeters (about 12 inches), and with even more particularly suitable diameters ranging from about 8 centimeters (about 3 inches) to about 13 centimeters (about 5 inches).

Connection conduit54is a shell-side conduit that allows the feed solution to travel from contactor chamber68to recuperator chamber70during operation. Hollow fiber membranes56are a plurality of tubular membranes that extend along longitudinal axis62between distillate inlet chamber66and distillate outlet chamber72. Hollow fiber membranes56are desirably bundled together within the volume of interior region64to increase the total membrane surface area. In one embodiment, hollow fiber membranes56substantially fill the open volumes of contactor chamber68and recuperator chamber70. This allows the feed solution to travel through contactor chamber68and recuperator chamber70in the interstitial voids between the membranes. Alternatively, one or more portions of contactor chamber68and recuperator chamber70may be unoccupied by hollow fiber membranes56, thereby providing larger flow paths for the feed solution.

Hollow fiber membranes56each include an inner hollow region (not shown inFIG. 2) that extends through potting resin walls48,50, and52and baffles58and60along longitudinal axis62. This provides a tube-side flow path for the distillate fluid between distillate inlet chamber66and distillate outlet chamber72(i.e., the distillate fluid may flow through the inner hollow regions of hollow fiber membranes56). Conversely, the shell-side flow path of the feed solution extends between the exterior surfaces of hollow fiber membranes56, within contactor chamber68and recuperator chamber70, and through connection conduit54.

The segments of hollow fiber membranes56at contactor chamber68are formed from one or more hydrophobic, microporous materials that are capable of separating the distillate fluid from the feed solution via vapor pressure differentials. In contrast, the segments of hollow fiber membranes56at recuperator chamber70are non-porous, thereby preventing mass transfer across the membranes, but allow conductive heat transfer to occur. As such, recuperator chamber70functions as a heat exchanger for increasing the thermal efficiency of membrane module12and distillation system10(shown inFIG. 1).

Baffles58and60are shell-side flow barriers (e.g., acrylate and epoxy-based barriers) within contactor chamber68and recuperator chamber70that direct the flow of the feed solution in cross patterns relative to hollow fiber membranes56. As shown, baffles58have axially-centric openings, thereby directing the flow paths of the feed solution toward the axial centers of contactor chamber68and recuperator chamber70. Baffles60, however, have openings that are non-axially centric (e.g., adjacent outer casing46), which directs the flow paths of the feed solution away from the axial centers of contactor chamber68and recuperator chamber70. Accordingly, the alternating arrangement of baffles58and60force the feed solution to flow across hollow fiber membranes56in a quasi-cross flow geometry and the feed solution passes axially down chamber68, thereby increasing the mass and heat transfers across hollow fiber membranes56. Suitable numbers of baffles58and60may vary depending on the dimensions of contactor chamber68and recuperator chamber70, and on the desired flow paths of the feed solution. Examples of suitable numbers of baffles (e.g., baffles58and60) for each of contactor chamber68and recuperator chamber70range from one baffle to ten baffles, with particularly suitable numbers of baffles ranging from one baffle to five baffles.

During operation, the heated feed solution enters contactor chamber68via feed inlet line22. The feed solution is then directed around the openings of baffles58and60toward potting resin wall52, where baffles58and60cause the feed solution to move in a cross flow pattern relative to hollow fiber membranes56. While the feed solution flows through contactor chamber68, the cool distillate fluid enters distillate inlet chamber66via distillate inlet line38, and flows through the inner hollow regions of hollow fiber membranes56toward distillate outlet chamber72. As the heated feed solution flows around the exterior surfaces of hollow fiber membranes56, the temperature differentials between the exterior surfaces and the inner hollow regions of hollow fiber membranes56create vapor pressure differentials across hollow fiber membranes56within contactor chamber68. This causes a portion of the distillate fluid in the feed solution to evaporate and transmit through the micropores of hollow fiber membranes56. When the vapor passes into the inner hollow regions of hollow fiber membranes56, the cool supply of distillate fluid causes the vapor to condense within the inner hollow regions and mix with the supply of distillate fluid. The distillate fluid then flows toward distillate outlet chamber72, and into distillate outlet line40.

As discussed above, while the distillate fluid separates from the feed solution, latent and conductive heat also transfers from the feed solution to the distillate fluid flowing through the inner hollow regions of hollow fiber membranes56. While flowing through contactor chamber68, the feed solution gradually cools down due to the heat transfer across hollow fiber membranes56. Thus, within contactor chamber68, the feed solution bulk temperature drops to the lowest value just before entering connection conduit54and recuperator chamber70. In contrast, while flowing through the inner hollow regions of hollow fiber membranes56within contactor chamber68, the distillate fluid gradually heats up due the heat transfer across hollow fiber membranes56. This heat transfer within contactor chamber68increases the temperature of the distillate fluid and decreases the temperature of the feed solution such that the bulk temperature of the distillate fluid entering recuperator chamber70on the tube side of membrane module12is greater than the bulk temperature of the residual feed solution entering recuperator chamber70on the shell side of membrane module12.

Upon entering recuperator chamber70from connection conduit54, the residual feed solution flows through recuperator chamber70toward feed outlet line24. Baffles58and60accordingly cause the distilled feed solution to flow in a quasi-cross flow path relative to hollow fiber membranes56. As discussed above, however, the segments of hollow fiber membranes56within recuperator chamber70are non-porous. Thus, distillate fluid vapor does not penetrate across hollow fiber membranes56within recuperator chamber70. Nonetheless, conductive heat is capable of traveling across the segments of hollow fiber membranes56within recuperator chamber70. As a result, at least a portion the thermal energy acquired during the separation process within contactor chamber68is transferred from the distillate fluid (i.e., from the tube side of membrane module12) back to the feed solution (i.e., to the shell side of membrane module12).

During the steady state operation, heat exchanger26(shown inFIG. 1) desirably maintains the feed solution within feed loop14(shown inFIG. 1) at the elevated temperature despite heat losses within membrane module12. Similarly, heat exchanger32(shown inFIG. 1) desirably maintains the distillate fluid within distillate loop16(shown inFIG. 1) at the lowered temperature despite heat acquired within membrane module12. Thus, the heat recovery within recuperator chamber70reduces the amount of energy required by heat exchanger26to heat the feed solution flowing through feed loop14, and by heat exchanger32to cool the distillate fluid flowing through distillate loop16. This increases the thermal efficiency of distillation system10(shown inFIG. 1), thereby reducing operation costs required to produce the distillate fluid.

FIG. 3is an expanded sectional view of membrane74, which is an example of a single membrane of hollow fiber membranes56(shown inFIG. 2). As shown inFIG. 3, membrane74includes segments76and78, and inner hollow region80, where segment76is the portion of membrane74within contactor chamber68(shown inFIG. 2), and segment78is the portion of membrane74within recuperator chamber70(shown inFIG. 2). Segments76and78each include membrane wall82, which is formed from one or more hydrophobic materials and includes a plurality of micropores (not shown) that allow the transmission of gases and vapors, but restricts the flow of liquids and solids. This allows the distillate fluid to separate from the feed solution via vapor pressure differentials.

Examples of suitable wall thicknesses for membrane wall82range from about 50 micrometers to about 200 micrometers, with particularly suitable wall thicknesses ranging from about 100 micrometers to about 150 micrometers. Examples of suitable average micropore sizes for membrane wall82range from about 0.1 micrometers to about 1.0 micrometers, with particularly average suitable micropore sizes ranging from about 0.3 micrometers to about 0.7 micrometers. Examples of suitable materials for membrane wall82include polymeric materials, such as polypropylenes, polyethylenes, polysulfones, polyethersulfones, polyetheretherketones, polyimides, polyphenylene sulfides, polytetrafluoroethylenes, polyvinylidene difluorides, and combinations thereof.

As further shown, segment78also includes coating84, which desirably covers the entire exterior surface of membrane wall82at segment78. Coating84is a non-porous coating that blocks the transmission of gases and vapors, thereby preventing mass transfer across membrane74within recuperator chamber70. Suitable materials for coating84include any hydrophobic polymeric material that are stable to the heat and aqueous solutions. Examples of suitable materials for coating84include the suitable polymeric materials discussed above for membrane wall82, except that coating84does not include micropores. Coating84may be formed on membrane wall82with a variety of coating techniques, such as dip coating, wash coating, and spray coating. In alternative embodiments, the micropores of membrane wall82at segment78may be filled to block the transmission of gases and vapors, or membrane wall82at segment78may be formed without micropores. In these embodiments, membrane wall82is capable of blocking the transmission of gases and vapors, and coating84may be omitted.

As discussed above, while within contactor chamber68, the cool distillate fluid flows through inner hollow region80of membrane74and the heated feed solution flows adjacent to the exterior surface of membrane wall82. This creates a vapor pressure differential across membrane wall82, allowing distillate fluid vapor to penetrate through the micropores of membrane wall82into inner hollow region80. Correspondingly, the distillate fluid vapor carries latent heat from the feed solution to the distillate fluid within inner hollow region80. Additionally, thermal energy also conductively transfers across membrane wall82from the feed solution to the distillate fluid within inner hollow region80.

Within recuperator chamber70, coating84substantially prevents mass transfer across segment78of membrane74. Thus, distillate fluid vapor does not penetrate across segment78. However, segment78allows thermal energy to conductively transfer across membrane wall82and coating84, thereby recovering heat from the distillate fluid flowing through inner hollow region76to the feed solution flowing adjacent coating84. This increases the thermal efficiency of membrane module12(shown inFIG. 2).

FIG. 4is a schematic illustration of an interior of membrane module112, which is an alternative to membrane module12(shown inFIG. 2), where the reference numerals of the corresponding components are increased by 100. As shown inFIG. 4, membrane module112includes outer casing146, potting resin walls148,150, and152, connection conduit154, and hollow fiber membranes156, which function in the same manner as the corresponding components of membrane module12. Accordingly, outer casing146is a rigid structure extending along longitudinal axis162, and defines interior region164of membrane module112. Outer casing146also desirably includes couplings (not shown) for connecting membrane module112to feed inlet line22, feed outlet line24, distillate inlet line38, and distillate outlet line40of distillation system10(shown inFIG. 1). While shown with a tubular geometry, outer casing146may exhibit alternative geometries, such as rectangular geometries.

Potting resin walls148,150, and152are seals that divide interior region164into distillate inlet chamber166, contactor chamber168, recuperator chamber170, and distillate outlet chamber172, where the length-to-width ratio of interior region164differs from that of interior region64(shown inFIG. 2). Accordingly, in the embodiment shown inFIG. 4, the flow paths of the feed solution through contactor chamber168and recuperator chamber170are perpendicular to lengths of hollow fiber membranes156. This creates a cross flow relative to hollow fiber membranes156to increase the mass and heat transfers across hollow fiber membranes156. Thus, in this embodiment, baffles corresponding to baffles58and60(shown inFIG. 2) are omitted.

Connection conduit154is a shell-side conduit that allows the feed solution to travel from contactor chamber168to recuperator chamber170during operation. Hollow fiber membranes156are a plurality of tubular membranes that extend along longitudinal axis162between distillate inlet chamber166and distillate outlet chamber172, and function in the same manner as hollow fiber membranes56(shown inFIG. 2). Accordingly, the segments of hollow fiber membranes156at contactor chamber168are formed from one or more hydrophobic, microporous materials that are capable of separating the distillate fluid from the feed solution. In contrast, the segments of hollow fiber membranes156at recuperator chamber170are non-porous, thereby preventing mass transfer across the membranes, but allow conductive heat transfer to occur. As such, recuperator chamber170functions as a heat exchanger in the same manner as recuperator chamber70(shown inFIG. 2) for increasing the thermal efficiency of membrane module112and distillation system10.

During operation, the heated feed solution enters contactor chamber168via feed inlet line22. While the feed solution flows through contactor chamber168toward connection conduit154, the cool distillate fluid enters distillate inlet chamber166via distillate inlet line38, and flows through the inner hollow regions of hollow fiber membranes156toward distillate outlet chamber172. The vapor pressure differentials that are created across hollow fiber membranes156within contactor chamber168cause a portion of the distillate fluid in the feed solution to evaporate and transmit through the micropores of hollow fiber membranes156. As discussed above, latent and conductive heat also transfers from the feed solution to the distillate fluid flowing through the inner hollow regions of hollow fiber membranes156.

Upon entering recuperator chamber170from connection conduit154, the distilled feed solution flows through recuperator chamber170toward feed outlet line24. As discussed above, the segments of hollow fiber membranes56within recuperator chamber170are non-porous. Thus, distillate fluid vapor does not penetrate across hollow fiber membranes156within recuperator chamber170. Nonetheless, conductive heat is capable of traveling across the segments of hollow fiber membranes156within recuperator chamber170. As a result, at least a portion the thermal energy acquired during the separation process within contactor chamber168is transferred from the distillate fluid back to the distilled feed solution. This heat recovery within recuperator chamber170reduces the amount of energy required by heat exchangers26and32(shown inFIG. 1), thereby increasing the thermal efficiency of distillation system10.