Abstract:
The invention discloses an apparatus for filtration of water from hydrocarbons comprised of a fresh-feed inlet, a first dead end filter, having a filter medium that is hydrophobic, a second cross-flow filter, having a membrane that is hydrophobic, a common housing to contain both the first and second filters, a system for the recirculation of the retentate, a chamber for water settling, and an outlet for clean fuel permeate. This invention takes advantage of the properties of the functional groups of a surfactant, by using the surfactant to allow a hydrophobic medium to attract water, attach the water molecules to the hydrophobic medium, and then allow for agglomeration of the water molecules, which finally become large enough to detach and be swept away by the cross-flow. The hydrocarbon may then pass through the second membrane filter uncontaminated by water and be used as clean fuel. This invention can thus be used to remove high concentrations of water, up to 5%, in hydrocarbons, while allowing a high flow rate by preventing blockage of the final filter by water.

Description:
FEDERALLY SPONSORED RESEARCH 
     This application arose out of work under Contract #DAAE07-010-C-L023, Jan. 31, 2001, entitled “A Compact Self-cleaning Surfactant Resistant Fuel Filter”, DoD SBIR A99-089, Sponsored by U.S. Army TACOM 
    
    
     CROSS-REFERENCES TO RELATED APPLICATIONS 
     Not Applicable 
     SEQUENCE LISTING, TABLE OR COMPUTER PROGRAM 
     Not Applicable 
     FIELD OF THE INVENTION 
     This invention relates to filtration to remove emulsified water from various types of liquid hydrocarbons, such as fuels and other solvents, where the emulsification is accomplished through the use of surfactants. 
     BACKGROUND OF THE INVENTION 
     When water is present in a fuel or other solvent, the preferred method of removal is through the use of a hydrophobic filter screen that prevents the passage of water. Such a screen can become covered with water, and the covering prevents the passage of fuel through the filter. Water may then be removed by backflushing or sweeping the surface with a flow to carry away the trapped water. However, the need for backflushing imparts an additional function that suspends the action of the filter for a period of time. 
     Other methods have used hydrophobic prefilters, but these suffer from the same need to backflush or sweep with a flow to remove the water on the filter surface. 
     In order to obviate the need to backflush, hydrophilic filters are often chosen for the first filter in a system. The hydrophilic filter will allow the passage of water into its interior, where the particles are absorbed onto the filter medium surface and there they coalesce into larger globules of water. These then eventually break free and pass into the gap separating the first filter from the second filter. There a stream of fuel carries away the water that has passed the first filter. However, when the fuel being filtered contains an emulsifying agent, the particles of water will remain suspended and pass through the first filter without coalescing, and continue on to the second filter. The emulsified water will then pass through this last filter under pressure, and continue to contaminate the fuel. 
     In this typical construction of the prior art used to remove water from jet fuel, a conventional fuel-water separator is usually comprised of two different filter cartridges. The two cartridges are arranged in series. The first is a water-coalescing cartridge, and the second is a water-separating cartridge. This latter cartridge is hydrophobic and operates to exclude water as described. Fuel contaminated with water passes through the coalescing filter cartridge first, which has a pore size range of 1 μm to 100 μm, preferably in the range of 1 μm to 20 μm. The coalescing cartridge usually has a pleated design or a string wound design utilizing hydrophilic material, such as cotton. Fine water droplets are absorbed by the filter fibers due to their hydrophilic surface property. As more and more water is absorbed in the filter cartridge, agglomeration occurs and larger water globules (greater than 100×100 mesh typically used) are formed. The jet fuel flowing through this first cartridge then carries these away. Then the jet fuel containing water globules flows into the separation cartridge, which is made from 100×100 mesh PTFE screen. In the prior art, the mesh size must be this large to prevent the buildup of water on the surface, which will occur with smaller mesh sizes. The jet fuel freely passes through the screen, but, due to its hydrophobic surface property, the PTFE screen retains the water globules and prevents their passage. The retained water globules then settle down to the bottom of the water collection chamber. 
     Surfactant fuel additives are often added to jet fuel for the purpose of cleaning the aircraft fuel system and allowing the engine components to operate more effectively and efficiently at higher temperatures. One particularly useful additive is SPEC-AID 8Q462, as sold by BetzDearborn In., Trevose, Pa., which is known as a +100 additive because it allows engine operation temperature to be increased by up to 100 degrees Fahrenheit. However, the side effect of surfactant fuel additives is that they break down the water droplets to much smaller sizes (1 μm to 10 μm), forming a stable water emulsion in the jet fuel. Each water droplet is surrounded by surfactant, the molecules of which consist of a hydrophilic head functional group (hydrophilic head) and a hydrophobic tail functional group (hydrophobic tail). The hydrophilic heads of the surfactant molecules attach to the water droplet and the hydrophobic tails face outward, where they are solvated by the jet fuel and form a stable emulsion. Very small droplets of water bound by surfactant thus characterize this emulsion. Since the surfactant-coated water droplets are thus hydrophobic at their surface, they will not be absorbed in the hydrophilic coalescing filter cartridge of the prior art. Therefore, there will be no water coalescing effect in the coalescing filters. Consequently, the jet fuel and the fine surfactant-bound water droplets freely pass through the first filter without coagulation, remain dispersed in the flow stream and reach the PTFE screen filter cartridge, where, due to the much larger pore size of the screen, they pass through and continue to contaminate the fuel. 
     In the instant invention, the filter medium is chosen to be hydrophobic in contrast to the accepted prior art. However, since the water molecules are bound with surfactant, and are now functionally hydrophobic, the water is not repelled by the hydrophobic filter medium, and passes into the filter. Because the tail of the surfactant molecule is hydrophobic, it is attracted to the surface of the hydrophobic filter medium. At the surface of the hydrophobic filter, the surfactant-bound water attaches and waits until a larger build-up occurs. As the surfactant-bound water molecules pass into and build up on the surface of the hydrophobic filter, the water agglomerates, breaking the boundary of the surfactant. The coagulated water then passes out of the filter into the stream between the first and second filter. 
     Similar to the conventional fuel-water separator, the instant invention is also comprised of two filter cartridges: A water coagulation cartridge and a hydrophobic water separation cartridge. But here the similarity ends. The water coagulation cartridge of the instant invention is a hydrophobic depth filter cartridge. The filter medium can be nylon, polyester, polyvinylidene difluoride or polypropylene. As discussed above, the surfactant-coated water droplets have a hydrophobic surface when surfactant fuel additives are present in the jet fuel. As the jet fuel and the now “hydrophobic water droplets” flow through the hydrophobic filter cartridge, the “hydrophobic water droplets” attempt to be absorbed by the hydrophobic filter fibers and become contained within the filter. As more water droplets are absorbed in the cartridge, multi-layer water/additive globules are formed and, when they become large enough, are carried away by the jet fuel flow. A globule of water/additive is comprised of multiple water droplets. Its size is usually 5 to 10 times larger than that of a single emulsified water droplet, which would typically be in the range of 1 μm to 10 μm. This action within the filter greatly reduces the degree of water emulsification in the jet fuel. However, the globules are still in the range of micron sizes and don&#39;t settle down easily. The second function of the water coagulation filter is to separate dirt, bacteria, and other suspended solids from the jet fuel. 
     Next the jet fuel and water/additive globules flow to the water separation filter cartridge, which is formed with a hydrophobic membrane (e.g., PTFE) of 0.1 μm pore size, which is approximately three orders of magnitude smaller than used in prior art technology. Use of a filter with such a small pore size with the technology taught in the prior art will result in rapid blocking of the filter surface by water and shut down of the fuel flow. A bypass-flow or cross-flow is maintained on the membrane surface at the feed side. The cross-flow is used to sweep the membrane surface with high shear motion and to carry the suspension away from the filter surface, while the fuel component of the liquid (e.g., jet fuel) penetrates into the membrane pores under pressure. Examples of cross-flow designs include spiral wound module cartridges, tubular cartridges, and hollow fiber cartridges. The desirable flow ratio of cross-flow rate to the fresh-feed rate is 1:1 to 1:30 by volume. 
     When jet fuel has surfactant added to it, three things are needed to successfully separate water from jet fuel with surfactants, particularly when used with surfactants known as “+100 additive”. These are 
     1) hydrophobic membrane 
     2) sub micron pore size (e.g., 0.1 μm), and 
     3) cross-flow. 
     Theoretically, hydrophilic membranes can be used for the separation filter in this type of application. However, water droplets are not always completely coated with the hydrophobic substance (additive). Therefore, uncoated water droplets can freely pass through the pores of a hydrophilic membrane. Using a hydrophobic membrane ensures that the uncoated water droplets cannot go through its pores. Since the surface energy of the coated water droplets is similar to jet fuel, the coated water droplet and jet fuel should have similar wettability on the hydrophobic membrane surface. In this case, separation is only controlled by the given pore size of the hydrophobic membrane. The membrane rejects any suspended particle with greater size than the membrane pores. Studies by the inventor have shown that a 0.1 μm PTFE membrane gives desirable water rejection rate and permeate flow rate. Due to the hydrophobic property of the coated water droplets, they favor remaining on the hydrophobic membrane surface. If a water boundary layer is formed on the membrane surface, a certain amount of water will bleed through the membrane under pressure. To solve this problem, a cross-flow of fuel is formed on the membrane surface to sweep away the water droplets. With a 0.1 μn PTFE membrane, it is important to maintain a differential pressure that does not exceed 50 psi between the feed solution and the permeate, in order to prevent bleed through of water at the membrane filter. The inventor has also found that the temperature should not exceed 130 degrees Fahrenheit in order to prevent water from vaporizing, passing through both filters and then condensing in the clean fuel. 
     After exiting the water separation cartridge, the cross-flow stream (or concentrate) carries the concentrated emulsified water droplets and then enters a water-settling chamber. In this chamber, a relatively quiet environment is maintained. Fine water droplets agglomerate and form a heavier phase within the chamber. As more water droplets agglomerate in the heavier phase, water emulsion breakdown occurs, and free water is formed at the bottom of the water-settling chamber. 
     The water separation filter cartridge (PTFE membrane cartridge) works well by itself without the coagulation filter cartridge, if the water concentration is below 0.5% in the feed. However, the permeate flow rate can significantly drop if the water concentration is higher than 1% because the water forms a layer that blocks the surface of the filter. To make a fuel filter commercially practical, it must pass a test with a 3% water concentration in jet fuel and a permeate flow flux of at least 0.5 gallon/min./sq.-ft. of membrane area. The hydrophobic coagulation filter cartridge is a critical component to ensure adequate permeate flow rate with 3% water concentration in the feed. If no prefilter is present, there is a buildup of water that blocks further fuel from passing through the filter. When there is a hydrophilic pre-filter, filtration is excellent, so long as there is no surfactant present to emulsify the water. However, when surfactant is present, the hydrophilic filter allows passage of the water that is emulsified, which then goes through the second filter, since there has been no coalescence. 
     DESCRIPTION OF RELATED ART 
     U.S. Pat. No. 6,042,722 to Lenz teaches a single separator for removal of water by specific gravity from various fuels, including diesel and jet fuel. 
     U.S. Pat. No. 6,203,698 and U.S. Pat. No. 5,916,442 both to Goodrich teach the use of hydrophobic filter media to reject water from passage through the filter. 
     U.S. Pat. No. 5,993,675 to Hagerthy teaches the use of microfibers, which are impervious to the passage of water, but which allow the fuel to flow through. 
     U.S. Pat. No. RE37,165, U.S. Pat. No. 5,766,449 and U.S. Pat. No. 5,507,942 all to Davis all teach a single filter, which is hydrophobic so that it rejects water penetration. 
     Although some of these methods rely on a hydrophobic material to reject water, all of these methods utilize a single filter and none of them utilizes the hydrophobic filter to capture and coalesce surfactant-bound water. They function merely by rejection of normal size water droplets, and would be inadequate for rejection of emulsified water. 
     U.S. Pat. No. 4,988,445 to Fulk teaches the use of multiple spirally wound filters used in two stages. Fulk teaches a “means for enabling concentrate from said first stage module to pass directly to said second stage modules without passing through a pump; [a] means for forcing said feed stream through said first and second stages; and [a] means for recycling a portion of the concentrate from said second stage to said first stage.” 
     U.S. Pat. No. 6,146,535 to Sutherland teaches the use of hollow microfibers for phase separation, by exclusion of the aqueous phase through pore size hydrophobicity. 
     Neither of these patents teaches the use of a hydrophobic first filter for the removal of surfactant-bound water through the use of the functional group properties of the surfactant, as is the case with the present invention. 
     Among other patents, several are of particular interest in evaluating the present invention: 
     There are “a number of devices that are able to remove suspended water from fuels. Among these are coalescing devices and electrostatic precipitators.” “These coalescing devices become filled with water during operation and must be maintained carefully to prevent water from being pumped with the fuel to the point of use.” (U.S. Pat. No. 4,814,087 to Taylor) 
     U.S. Pat. No. 4,372,847 to Lewis teaches the use of a cartridge for filtration that comprises a coalescing stage and a separating stage. This invention is specifically geared to separation of emulsified liquids. It functions through the formation of coalesced droplets that form due to a different specific gravity at the coalescing stage and remain free for removal at the second hydrophobic separating stage. 
     U.S. Pat. No. 4,814,087 to Taylor teaches a single stage cross-flow hydrophobic separator comprised of a microporous material. Cross-flow is used to clear the water from the separator. 
     U.S. Pat. No. 5,149,433 to Lien teaches the use of two spirally wound filters in series, whereby the second filter only functions for the removal of water from fuel if the first one fails. Cross-flow is used for the first filter to sweep away water as it accumulates. 
     U.S. Pat. No. 4,846,976 to Ford teaches a filtration system for a water-containing emulsion that is comprised of two stages, both comprised of hydrophobic microfilters. A backwash accomplishes cleaning of the first microfilter. While this uses hydrophobic material, this invention serves to remove small quantities of emulsified oil and fat from the water, thus providing clean water for disposal, rather than removal of water from the hydrocarbons. 
     U.S. Pat. No. 5,443,724 to Williamson et al., teaches the use of two filters, the first being a coalescing unit and the second being a separating unit. Coalescence is accomplished by a choice of physical shape of packing material for a critical wetting surface energy “intermediate the critical wetting surface tension of the discontinuous and continuous phases”. 
     The present invention differs from these examples of prior art in the following distinct ways: 
     The principal function of the present invention is the removal of emulsified water from fuel. The present invention utilizes two stages of filtration to accomplish the goal of removal of water from fuel. Much of the prior art utilizes single stages that are less effective at removal and cannot remove emulsified water, as it would pass through their filters. Other two stage filtration systems also suffer from the inability to separate emulsified water from the fuel. 
     The present invention functions by providing a coalescing surface which is near the surface energy of the hydrophobic tail end of the surfactant molecule, whose head end is attached to a water molecule. Due to the attraction of the matching coalescing surface and the tail end of the surfactant, there is a build-up of bound water molecules to form and agglomerate, which agglomerate is then swept through by the jet fuel. Once in the flow between the first and second stages, the agglomerated water is swept away by the cross-flow. 
     The present invention differs from U.S. Pat. No. 4,846,976 to Ford, in that Ford essentially teaches the opposite. I.e., removal of small quantities of dispersed, surfactant-bound, fats and oils from water by hydrophobic filters. This would imply that to do the opposite, that is, to remove dispersed, surfactant-coated water, one would require hydrophilic filters (as is the case for conventional two-stage filters). 
     The present invention differs from U.S. Pat. No. 4,372,847 to Lewis, since Lewis utilizes specific gravity for the coalescing function. 
     The present invention differs from U.S. Pat. No. 4,814,087 to Taylor, in that Taylor uses a single stage hydrophobic filter and removes only dissolved water. Taylor does mention that coalescers may be used for removal of suspended water, but does not describe a method or apparatus for so doing. 
     The present invention differs from U.S. Pat. No. 5,443,724 to Williamson et al., in that Williamson et al. utilizes physical shape of the packing material for coalescence in the fashion of a baffle, and further that Williamson et al. specifies that the coalescer must allow wetting by the fuel, but not by the suspended water (discontinuous liquid phase). In the present invention, the coalescer is specifically hydrophobic to match the hydrophobic tail of the wetting agent, and its surface tension is thus near to or lower than that of the surfactant-bound water. Thus, the surface energy of the coalescing cartridge of the instant invention has no relationship to the surface tension of unbound water, but is specifically wet by the suspended water (discontinuous phase). 
     According to Williamson et al., the coalescing element must have a surface energy (or critical wetting surface tension) which is greater than the surface tension of the continuous liquid phase. In fact, Williamson et al. specifically requires that the surface energy be intermediate the continuous phase (fuel) and the discontinuous phase (water). Since jet fuel is approximately 23 mN/m and water is 72.5 mN/m, this would lead to practice of the art in Williamson et al. with a coalescer of approximately 48 mN/m, which is clearly much greater than for the hydrophobic materials of the present invention, which are typically around 30 mN/m or less. 
     In the instant invention, the coalescing element may have a surface energy lower than the surface tension of the continuous phase, and is preferably as close as possible to the surface tension of the continuous phase. The surface tension of the discontinuous phase is wholly irrelevant, since it is bound with surfactant molecules, whose very function is to transform the discontinuous phase into a material having a surface tension that is very close to the continuous phase. 
     OBJECTS AND ADVANTAGES 
     The present invention offers significant objects and advantages over the above prior art devices and methods. 
     1. This invention provides a method and a device to remove water (up to 5%) in fuel and to obtain a clean output fuel with less than 5 ppm of water, while maintain a high flow rate not possible with the prior art. 
     2. Instead of coalescing water from fuel in between the first stage and the second stage as in a conventional fuel filter design, this invention uses a hydrophobic depth filter and a PTFE cross-flow membrane filter to separate and concentrate contaminated fuel. The concentrate goes to a settling chamber after the two filtration stages. Free water settles down in the chamber. 
     3. The coagulation filter cartridges and water separation filter cartridges may be installed in one filter housing with multiple chamber design. 
     4. The internal circulating pump design eliminates the need for a working tank, which is necessary for common cross-flow filter systems. 
     5. This invention solves the problem of inefficiently and ineffectively removing emulsified water from fuel with surfactant additives when using a conventional fuel-water separator. 
     6. This invention overcomes the common problem of the filter becoming dry and requiring change-out, when it is idle after use. This will occur where hydrophilic materials are used for the filter, as they will crack when they dry out. Synthetic fibers do not suffer this problem and are typically hydrophobic. 
     By reviewing and considering the drawings and descriptions further objects and advantages of the instant invention will be apparent. 
     BRIEF SUMMARY OF THE INVENTION 
     The instant invention is a self-contained, multi-chambered two-stage filtration system, wherein there is both a water coagulation stage and a water separation stage. The first stage comprises a dead-end filter with hydrophobic media having a pore size range of 0.5 μm to 100 μm. The second stage comprises a cross-flow filter with a membrane that is hydrophobic, and which is typically made of polytetrafluoroethylene (PTFE), with a pore size of approximately 0.1 μm. 
     Water coalescing takes place in the first stage and thus no coalescing needs to take place between the first and second stages, nor in the second stage. 
     An internal circulating pump is used to create cross-flow. The ratio of cross-flow to permeate flow is in the range of 1:1 to 1:30. 
     No working tank is required for the concentrate. 
     Flow takes place from the outside to the inside of the coagulation cartridge. The flow is parallel to the membrane surface of the separation cartridge. 
     There is a chamber for settling of water in retentate, and this has baffles to restrict and direct flow, and also to quiet the chamber to facilitate the settling of the water. 
     The system is capable of treating fuel with additives up to 5% water concentration. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     In the drawings which illustrate the embodiments presently contemplated for carrying out the present invention: 
     FIG. 1 depicts the spiral-wound enhanced filtration system in top sectional view and in cross sectional view. 
     FIG. 2A shows a cross sectional view of the membrane filter and its assembly into its non-perforated tube sleeve. 
     FIG. 2B shows a cross sectional view of the coagulation filter and its assembly into its perforated tube sleeve. 
     FIG. 3 illustrates the operation of the surfactant-bound water being attracted to the hydrophobic filter surface, forming globules and flowing out into the space between the first and second filters. 
     FIG. 4 is a cross sectional view of an alternative embodiment of the invention, in which the perforated tube is no longer required for the coagulation filter. 
     FIG. 5 shows by diagram another embodiment of the invention, in which the two filters are no longer in a common housing, but are now connected in series in individual housings. 
    
    
     REFERENCE NUMERALS IN DRAWINGS 
       2 . Coagulation hydrophobic filter cartridge 
       4 . Water separation hydrophobic membrane cartridge 
       5 . Water separation cartridge housing 
       6 . Filter housing 
       7 . Coagulation cartridge housing 
       8 . Top chamber 
       10 . Feed chamber 
       12 . Retentate chamber for water settling 
       14 . Permeate chamber 
       16 . Feed separation plate 
       18 . Retentate plate 
       20 . Permeate separation plate 
       22 . Tube 
       24 . Fresh feed inlet 
       26 . Sight glass tube 
       28 . Drain valve 
       30 . Concentrate outlet 
       32 . Circulation pump 
       34 . Recirculation feed inlet 
       36 . Outer baffle plate 
       38 . Inner baffle plate 
       40 . Horizontal plate 
       42 . Clean fuel outlet 
       46 . Cartridge exit 
       48 . Ribs or tabs 
       50 . Perforated tube sleeve 
       52 . Non-perforated tube sleeve 
       54 . O-rings or C-rings 
       55 . Gasket 
       56 . Removable cap 
       57 . V shape seal ring 
       58 . Feed 
       60 . Center permeate tube 
       62 . Concentrate flow 
       64 . Small opening 
       65 . Retentate bushing 
       70 . Emulsified water molecule 
       72 . Water molecule 
       74 . Hydrophilic functional group (head) 
       76 . Hydrophobic functional group (tail) 
       78 . Filter surface 
       80 . Water bound to filter surface 
       82 . Coalescing water 
       84 . Water agglomerate breaching surfactant coating 
       86 . Large water globule 
       90 . Retentate downspout 
       92 . Ring support 
       94 . Drain 
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred Embodiment 
     The coagulation filter cartridges  2  and water separation filter cartridges  4  are installed in a filter housing  6 , in which four chambers (top  8 , feed  10 , retentate  12 , and permeate  14 ) are formed using isolation plates, as shown in FIG.  1 . Two groups of inner tube sleeves  50 , 52  (for the coagulation filters and water separation filters) are fixed between the feed separation plate  16  and the retentate plate  18  in the feed chamber  10 , as shown in FIGS. 2A and 2B. The number of tube sleeves  50 , 52  in both of these groups can vary depending on the process rate. The feed separation plate  16  has openings corresponding to the tube sleeves  50 , 52 . The coagulation cartridges  2  and membrane cartridges  4  are installed in their respective tube sleeves  50 , 52 . The function of the tube sleeves  50 , 52  is to guide filter cartridge  2 , 4  installation and to direct flow in the housing  6 . The tube sleeves of the coagulation cartridges  2  are perforated tubes  50 , and the sleeves of membrane cartridges  4  are non-perforated tubes  52 . 
     As seen in FIG. 2B, the coagulation cartridges  2 , are attached with o-rings  54  and gaskets  55  at their ends, are inserted into the perforated tube sleeves  50 , and sit on the retentate bushing  65 . A removable cap  56 , attached with an o-ring  54 , is placed on the top of each cartridge. A compression force (e.g., using clamps or bolt) is applied on each cap  56  to compress the gaskets  55  at each end of the cartridge. The o-ring  54  on the cap  56  touches the inside wall of the opening on the feed separation plate  16 . No fluid bypass is allowed due to the o-ring seals. 
     The water separation cartridge  4  (or membrane cartridge) shown in FIG. 2A is a spiral-wound design. Feed  58  enters the cartridge at one end. The permeate flow comes out from the center tube  60 . The concentrate flow  62  (cross-flow, or bypass-flow) comes out at the other end of the cartridge. A V shape seal ring  57  sits in the seal groove of the end cap  56  located at the flow exit end of the cartridge. The V seal ring  57  is used to prevent flow bypass between the inner wall of the tube sleeve and the outer wall of the cartridge. Two o-rings  54  are attached to the outer wall of the permeate center tube  60  at the flow exit end  46  of the cartridge, preventing the bypass of unfiltered fluid to the permeate stream. The membrane cartridge  4  is inserted into the membrane tube sleeve  52  and sits on several ribs or tabs  48 , which are welded onto the retentate bushing  65 . The purpose of the tabs is to create flow passages for the concentrate flow. Several small openings  64  are placed near the tabs  48  to drain the concentrate to the settling chamber  12  through the retentate bushing  65 . The permeate center tube  60  is inserted into an opening on the retentate bushing  65 . The two o-rings  54  on the center tube touch the inner wall of the opening. A tube  22  is attached to the opening at the other side of the retentate bushing  65  to direct the permeate flow to the permeate chamber  14 . 
     In FIG. 1, the fresh feed inlet  24  is located at the middle of the feed chamber  10 . Jet fuel with water is fed into the feed chamber  10 . The feed passes through the perforated tube sleeves  50  and the coagulation cartridges  2 , and flows out from the top of each coagulation cartridge  2 . The filtrate from the coagulation cartridges  2  turns 180 degrees in the top chamber  8  and flows downward into the membrane cartridges  4  inside the non-perforated tube sleeves  52 . The permeate from each membrane cartridge  4  is guided to the permeate chamber  14 , and the concentrate drains into the settling chamber  12 , in which a relatively quiet environment is maintained so that water droplets can settle down on the permeate separation plate  20 . A sight glass tube  26  is mounted on the outside wall of the chamber to monitor the water level. Free water is drained through the drain valve  28 . 
     The outlet for the concentrate  30  (located at the upper portion of the settling chamber) is attached to the suction port of the internal circulation pump  32 . The discharge of the pump is connected to the recirculation feed inlet  34  through an appropriate one-way check valve (not shown). This pump  32  is used to generate extra flow as cross-flow or bypass-flow inside the membrane cartridges  4 . The suction and discharge of the pump are attached to the filter housing  6  using quick disconnects so that the filter housing  6  and the pump  32  can be easily assembled and disassembled. In order to enhance the water settling efficiency, two parallel angled baffle plates  36 , 38  are vertically placed near the concentrate outlet  30  inside the settling chamber  12 . The left and right sides of each baffle plate are welded on the inner wall of the filter housing. The upper end of the inner baffle plate  36  is attached to the retentate plate  18 , and the lower end of the outer baffle plate  38  is welded on a horizontal plate  40 , which is also welded to the inner wall of the filter housing  6 . Concentrate from the membrane cartridges first flows downward into the settling chamber  12 . Heavier water droplets stay at the lower portion of the settling chamber  12 . The light liquid phase at the middle of the chamber turns 180 degrees and enters into the passage created by the two parallel angled baffle plates  36 , 38 . At the end of the passage, the flow turns at least 90 degrees and exits from the concentrate outlet  30 . The fluid from the concentrate outlet  30  is sent back to the feed chamber  10  using the internal circulation pump  32 . Fresh feed is constantly fed into the feed chamber through the fresh feed port  24 . The feed rate of the fresh feed is the same as the production rate (permeate rate). 
     Operation of the Preferred Embodiment 
     The fuel filter of the instant invention has one fresh feed inlet  24 , located at the middle of the filter housing  6 , and one clean fuel outlet  42 , located at the bottom of the housing  6 . The fresh feed inlet  24  is connected to a fuel storage tank (not shown), and the clean fuel outlet  42  is connected to the fuel supply tank of a fuel filling station (not shown) or to an engine. The internal circulating pump  32  continuously runs during the filtration operation. This pump can be a centrifugal pump, or a gear pump, driven by an electric motor. Free water is drained through the drain valve  28 . A sight glass tube  26  is mounted on the outside wall of the chamber to monitor the free water level. A pressure differential gauge (not shown) is used to monitor the pressure between the feed and the clean fuel. 
     In a hydrocarbon, such as jet fuel, which contains a surfactant, there will be present an emulsion of water in the fuel. This emulsified water is small enough to pass through both filters and will continue to contaminate the fuel unless it is removed. FIG. 3 depicts emulsified water molecules  70  dispersed throughout the fuel. In order to form the emulsion, each water molecule  72  has attached to it several molecules of surfactant. Each surfactant molecule has a hydrophilic functional group (head)  74  that attaches to the water molecule  72  and a hydrophobic functional group (tail)  76  that extends away from the water molecule  72  and which is solvated by the hydrocarbon jet fuel. As these emulsified water molecules  70  pass into the filter, they are attracted to the filter surface  78 , binding to it as shown at  80 . The hydrophobic tail  76  attaches to the filter surface and holds the water molecule  72  in place. As more emulsified water molecules gather, they group together and coalesce as shown at  82 . Eventually, the surfactant coating is breached and the water molecules join together still attached to the surface of the filter as shown at  84 . In time, the water globule becomes too large for the forces holding the hydrophobic tail to the surface of the filter, and they break away as shown at  86 . As it passes out of the filter, the water is caught by the cross-flow of the jet fuel in the region between the first and second filter. Many of these agglomerations are carried away by the cross-flow of the fuel. Some however, are carried to the second filter, where because of their large size, they are unable to pass. The cross-flow then carries them away to the retentate settling chamber. 
     Because of the operation of the instant invention, it is possible to provide cleaned hydrocarbon fuel containing less than 5 ppm of water, even in the presence of surfactants. The initial water concentration can be as high as 5%. 
     In the case where there is no surfactant present in the jet fuel, the water will pass through the first filter and be rejected by the second filter in the normal fashion for a single stage filter. 
     Description—Additional Embodiment 
     FIG. 4 illustrates an alternative embodiment of the invention, in which the perforated tube sleeve  50  shown in FIG. 2B is no longer required for the coagulation filter  2  (filter shown in FIG. 1 only; removed from FIG. 4 for clarity). In the embodiment shown in FIG. 4, the coagulation filter  2  (filter shown in FIG. 1 only; removed from FIG. 4 for clarity) is seated inside a ring support  92 , which serves as a guide. In order to allow drainage of fluid when the coagulation filter  2  (filter shown in FIG. 1 only; removed from FIG. 4 for clarity) is removed, a drain  94  is provided. An additional change has been added to this embodiment, wherein the inner baffle plate  36  from FIG. 1, has been replaced by a downspout  90 . Other than the addition of a downspout  90 , the second non-perforated tube sleeve  52  of the water separation hydrophobic membrane cartridge  4  (filter shown in FIG. 1 only; removed from FIG. 4 for clarity) remains unchanged. 
     Operation—Additional Embodiment 
     This alternative embodiment functions similarly to the preferred embodiment of FIG. 1, wherein feed solution flows into the first filter, which is the coagulation cartridge  2  (filter shown in FIG. 1 only; removed from FIG. 4 for clarity) and then passes to the second filter, which is the water separation hydrophobic membrane cartridge  4  (filter shown in FIG. 1 only; removed from FIG. 4 for clarity). However, instead of flowing into the coagulation filter  2  (filter shown in FIG. 1 only; removed from FIG. 4 for clarity) through a perforated tube sleeve  50 , both as shown in FIG. 1, the feed fluid surrounds the coagulation cartridge  2  (filter shown in FIG. 1 only; removed from FIG. 4 for clarity) directly, and passes into it. Flow out of this first filter is the same as in the preferred embodiment of FIG.  1 . Additionally in this alternative embodiment, shown in FIG. 4, fluid departing the second filter now passes out through a downspout  90 , which functions in the same fashion as the inner baffle plate  36  depicted in FIG. 1, aiding in the settling down of water. 
     Description—Additional Embodiment 
     An additional embodiment is shown in FIG.  5 . In this embodiment, the filter cartridges have been arranged in series in separate housings  5 , 7 . Coagulation filter  2  is enclosed in housing  7 , with a fresh feed inlet  24  attached thereto. The water separation hydrophobic membrane cartridge is in housing  5 . Connected thereto are the inlet from the first filter, a concentrate outlet  30 , a circulation pump  32  and a recirculation feed inlet  34 , with an appropriate one-way check valve (not shown). Prior to passing into the circulation pump  32 , the concentrate passes into a retentate chamber for water settling  12 , to which is attached a sight glass  26  and a drain valve  28 . Additionally, there is a center permeate tube  60  followed by a clean fuel outlet  42  within this cartridge. 
     Operation—Additional Embodiment 
     In FIG. 5, coagulation cartridge  2  is enclosed in housing  7  and accepts the feed solution through the fresh feed inlet  24 . Solution passes into the cartridge and flows out to the water separation hydrophobic membrane cartridge  4 . Cross-flow is maintained within the housing  5 , which contains the water separation hydrophobic membrane cartridge, and concentrate passes out through the concentrate outlet  30 , to a retentate chamber for water settling  12 , then through the circulation pump  32  where it returns to the coagulation cartridge  2  through the recirculation feed inlet  34 . The permeate passes into the center permeate tube  60 , where it departs the filtration system through the clean fuel outlet  42 , which connects to an engine (not shown) or external fuel storage tank (not shown). Settled water level can be seen in the sight glass  26  and removed from the retentate chamber for water settling  12  by opening the drain valve  28 . 
     Conclusions, Ramifications, and Scope 
     The present invention utilizes a novel concept of employing a hydrophobic first filter to capture and agglomerate water molecules that are bound into an emulsion through the action of the functional group properties of a surfactant. Prior art has used hydrophilic first filters to capture free water, but these will not function to agglomerate water when the water is emulsified into very small particles that are coated with surfactant. 
     While the invention has been described with reference to specific details and examples of the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof, without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of this invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims below and their legal equivalents.