(12) United States Patent
`Spadaccini et al.
`
`(10) Patent N0.:
`
`(45) Date of Patent:
`
`US 6,315,815 B1
`Nov. 13, 2001
`
`US006315815B1
`
`FOREIGN PATENT DOCUMENTS
`
`9/1991 (DE) ......................................... .. 96/6
`4006465A *
`9/1990
`0385947A *
`9/1991 (JP) ........................................ .. 95/46
`03—213103A *
`04—290502A * 10/1992 (JP) ........................................ .. 95/46
`04—349902A * 12/1992
`0668875A *
`6/1979
`........................................ .. 96/6
`1646572A *
`5/1991 (RU)
`OTHER PUBLICATIONS
`
`
`
`S. Darah, “Jet Fuel Deoxigenation”, Geo Centers, Inc., (Oct.
`1988),
`Interim
`Report
`under
`Contract
`AFWAL—TR—88—2081, 28 pages.
`J.D. Seader et al., “Separation Process Principles”, John
`Wiley & Sons, Inc., (Dec. 1997), pp. 720-726.
`
`* cited by examiner
`
`Primary Exami/1er—Robert H. Spitzer
`
`(57)
`
`ABSTRACT
`
`Apparatus and method for the deoxygenation of liquid fuel
`in the fuel system of an energy conversion device, such as
`an aircraft gas turbine engine. A membrane filter is disposed
`in the fuel system and is selected to remove oxygen from the
`fuel, typically a hydrocarbon, While excluding the fuel. The
`membrane filter may be permeable or porous to the oxygen
`and, in a preferred embodiment, is of polytetraflouroethyl-
`ene. Fuel with dissolved oxygen (typically from air) is
`flowed in contact with one surface of the membrane filter,
`and removed oxygen is collected from the opposite surface
`of the filter. The difference in the partial pressure of oxygen
`across the membrane filter may be controlled to regulate the
`driving force for moving oxygen through the membrane.
`Reduction of the oxygen concentration in jet fuel to less than
`10 ppm at liquid space velocities of 100/hr and greater are
`attained.
`
`22 Claims, 8 Drawing Sheets
`
`(54)
`
`(75)
`
`MEMBRANE BASED FUEL
`DEOXYGENATOR
`
`Inventors: Louis J. Spadaccini, Manchester;
`Richard A. Meinzer; He Huang, both
`of Glastonbury, all of CT (US)
`
`(73)
`
`Assignee: United Technologies Corporation,
`Hartford, CT (US)
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`Appl. No.: 09/464,112
`
`Filed:
`
`Dec. 16, 1999
`
`Int. Cl.7 .......................... .. B01D 19/00; B01D 53/22
`U.S. Cl.
`............................. .. 95/46; 95/54; 96/6; 96/8;
`96/11
`Field of Search .................................. .. 95/45, 46, 54;
`96/4, 6-8, 10, 12, 13
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`......................... .. 95/46
`5/1981 Shindo et al.
`4,268,279 *
`..
`96/6X
`9/1985 Tomita et al.
`4,539,113 *
`. . . . . . . . . .
`. . . . . . .. 96/6
`3/1988 Shirato et al.
`4,729,773 *
`4/1988 Kulprathipanja et al.
`.. 95/54 X
`4,740,219 *
`9/1989 Kalfoglou . . . . . . . . . . . . . .
`. . . . .. 95/46
`4,869,732 *
`1/1992 Tozawa et al.
`.
`.... .. 95/46
`5,078,755 *
`5,695,545 * 12/1997 Cho etal.
`. . . . . . .
`. . . . .. 95/46
`5,723,035 *
`3/1998 Mazanec et al.
`96/6 X
`5,762,684 *
`6/1998 Hayashi et al.
`.... .. 95/46 X
`..
`5,830,261 * 11/1998 Hamasaki et al.
`.... .. 95/46 X
`..
`5,888,275 *
`3/1999 Hamasaki et al.
`.... .. 95/46 X
`..
`5,968,366 * 10/1999 Deckman et al.
`.... .. 95/45 X
`6,168,648 *
`1/2001 Ootani et al.
`.......................... .. 95/46
`
`
`
`(21)
`
`(22)
`
`(51)
`(52)
`
`(58)
`
`(56)
`
`
`
`GE-1005.001
`
`GE-1005.001
`
`

`
`U.S. Patent
`
`Nov. 13, 2001
`
`Sheet 1 of 8
`
`US 6,315,815 B1
`
`OXYGEN, ppm
`
`50
`
`CARBON,
`
`,u,g/cm2
`25
`
`-0- 02 ppm
`
`40 + DEPOSIT RACE
`
`10
`
`20
`
`15
`
`10
`
`5
`
`0
`
`
`
`0
`0
`
`50
`
`100
`
`150
`
`200
`
`250
`
`300
`
`BULK FUEL TEMPERATURE, C
`
`FlG.]
`Prior Art
`
`GE-1005.002
`
`GE-1005.002
`
`

`
`U.S. Patent
`
`Nov. 13, 2001
`
`Sheet 2 of 8
`
`US 6,315,815 B1
`
`TEMPERATURE,F
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`GE-1005.003
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`PYROLYSIS
`
`AUTOXIDATION
`
`I-|.LVé;l NO|l|SOdE|0 :|O 001
`
`GE-1005.003
`
`

`
`
`
`U.S.Patent
`
`Nov. 13, 2001
`
`Sheet 3 of 8
`
`US 6,315,815 B1
`
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`GE-1005.004
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`Nov. 13, 2001
`
`Sheet 4 of 8
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`US 6,315,815 B1
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`GE-1005.005
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`Nov. 13, 2001
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`
`GE-1005.007
`
`
`

`
`U.S. Patent
`
`Nov. 13, 2001
`
`Sheet 7 of 8
`
`US 6,315,815 B1
`
`
`
`
`
`MEMBRANE:1—mi|—thickPTFE
`
`FILTER3,T=308F
`
`
`
`FUEL:JP—8
`
`
`
`RESIDENCETIME,3
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`GE-1005.008
`
`GE-1005.008
`
`

`
`U.S. Patent
`
`Nov. 13, 2001
`
`Sheet 8 of 8
`
`US 6,315,815 B1
`
`GE-1005.009
`
`GE-1005.009
`
`

`
`US 6,315,815 B1
`
`1
`MEMBRANE BASED FUEL
`DEOXYGENATOR
`
`TECHNICAL FIELD
`
`This invention relates to the removal of oxygen from fuels
`and more particularly, to the removal of dissolved oxygen
`from liquid hydrocarbon fuels.
`BACKGROUND ART
`Because of its relative abundance in the air of the
`
`atmosphere, relatively large quantities of oxygen, as well as
`nitrogen and other gases, readily dissolve into various liquid
`media. The presence of dissolved oxygen, in particular, in
`some liquids, such as hydrocarbon fuels, may be objection-
`able because it supports oxidation reactions that yield unde-
`sirable by-products.
`For instance, jet fuel in aircraft may be used as a coolant
`for various systems in the aircraft. When air-saturated fuel is
`heated to temperatures above about 250° F. —300° F., the
`dissolved oxygen reacts to form free radical species (coke
`precursors) which initiate and propagate other autoxidation
`reactions leading to the formation of objectionable deposits,
`called “coke” or “coking”. This relationship is illustrated in
`FIG. 1 for jet fuel, where it is seen that as temperature
`increases beyond about 150° C. (300° F.), the process of
`autoxidation consumes oxygen and forms carbonaceous
`deposits. The temperature at which autoxidation begins
`differs for different fuels. These autoxidation reactions may
`also occur in jet fuel as it is heated immediately prior to
`injection for combustion, such that deposits may occur in the
`injectors.
`In any event,
`the formation of such deposits
`impairs the normal functioning of a fuel delivery system,
`either with respect to an intended heat exchange function or
`the efficient injection of fuel.
`Still further, such autoxidation reactions may create
`objectionable deposits by oxygen-laden hydrocarbon fuels
`when used in other energy conversion devices and systems,
`as for instance fuel cells.
`
`Referring to FIG. 2, the above mentioned reaction path is
`dominant at temperatures up to about 700° F., but becomes
`unimportant when the concentration of dissolved oxygen is
`reduced from its saturated value (about 70 ppm) to very low
`levels (5 ppm or less). Indeed, reduction of the dissolved
`oxygen to levels less than 20 ppm and particularly less than
`10 ppm, yield dramatic reductions in the formation of
`deposits by autoxidation reactions. Since pyrolysis occurs at
`higher temperatures than autoxidation, reducing the oxygen
`concentration allows the fuel
`to be heated to a higher
`temperature before thermal decomposition occurs.
`Previous methods of reducing the oxygen content of fuels
`are discussed in a report, dated Oct. 1988, by S. Darrah
`entitled “Jet Fuel Deoxygenation” under Air Force Contract
`F33615-84-C-2412. These methods included the use of
`
`chemical getters (reducing agents), molecular sieve
`adsorbents, and nitrogen sparging. The report discussed each
`in some detail, and expressed a preference for nitrogen
`sparging for large quantities of fuel. However, each of these
`methods has proven impractical at least for aircraft appli-
`cations because they are costly, heavy and bulky, and/or may
`even be dangerous. Chemical getters involve the use of
`active metals, which pose containment and disposal issues.
`Molecular sieves do not pose reactivity limitations, but
`present issues of volume and weight, particularly in aircraft.
`Nitrogen sparging may be unfeasible because of the volume
`of nitrogen required during a mission.
`What is needed is a method and/or means for deoxygen-
`ating hydrocarbon fuel in a cost effective, size efficient,
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`weight efficient, and/or safe manner. The fuel deoxygenation
`technique should be capable of on-line operation, i.e., con-
`tinuous use at flow rates which are consistent with the rate
`
`of fuel use in the intended energy conversion device, such as
`an aircraft jet engine or the like. Moreover, the deoxygen-
`ation technique should be capable of removing oxygen to a
`level at least below that at which significant coking would
`otherwise occur. As used herein, “significant coking” is the
`minimum amount of coking which, if it occurred in the
`interval between normal intended maintenance events for
`
`such portions of the fuel system, would be viewed as
`objectionable. Such coking occurs most readily in the por-
`tions of the fuel system having high temperatures and/or
`constricted flow paths.
`DISCLOSURE OF INVENTION
`
`The present invention relates to the deoxygenation of
`liquid fuel in the fuel system of an energy conversion device.
`More particularly, the present invention relates to a method
`and to a deoxygenator apparatus for removing dissolved
`oxygen from the liquid fuel
`in a cost effective, weight
`efficient and/or safe manner.
`According to the present invention, there is provided a
`fuel deoxygenator having a membrane filter disposed in a
`liquid fuel system. The membrane filter is of such material,
`and is positioned, structured, and operated for liquid fuel to
`flow into contact with a fuel-side surface of the filter such
`
`that oxygen is removed from the fuel to a level at least below
`that at which significant coking occurs. The membrane filter
`passes oxygen molecules and excludes the liquid fuel suf-
`ficiently to remove oxygen from the fuel to a level at least
`below 20 ppm, preferably below about 10 ppm at a liquid
`space velocity
`
`volume flowrate
`S V =A =
`reactor volume
`
`1
`residence time
`
`of at least 100/hr., and more preferably, to a level of about
`5 ppm.
`The membrane filter may be a permeable membrane
`which operates by a solution-diffusion mechanism, such as
`silicone-rubber; a porous membrane that operates by allow-
`ing dissolved oxygen to diffuse through angstrom sized
`pores, such as a layer of zeolite particles; or, preferably, is
`from the family of polytetrafiouroethylene type compounds.
`The membrane filter may be disposed on the surface of a
`porous substrate for support.
`The fuel system includes a deoxygenation chamber, with
`the membrane filter so structured and positioned therein as
`to provide a fuel region and a removed oxygen region on
`opposite sides of the filter. Means may be provided for
`regulating the partial pressures of oxygen across the mem-
`brane to regulate the driving force for moving oxygen
`through the membrane. In the interest of safety, any possible
`fuel leaks through the membrane filter are isolated from the
`environment by returning fuel and/or gases in the removed
`oxygen region to a fuel tank.
`The foregoing features and advantages of the present
`invention will become more apparent in light of the follow-
`ing detailed description of exemplary embodiments thereof
`as illustrated in the accompanying drawings.
`BRIEF DESCRIPTION OF DRAWINGS
`
`FIG. 1 graphically depicts the corresponding consumption
`of oxygen and formation of deposits as fuel temperature
`increases;
`
`GE-1005.010
`
`GE-1005.010
`
`

`
`US 6,315,815 B1
`
`3
`FIG. 2 graphically depicts the rate at which deposits occur
`as a function of temperature, both for fuel containing oxygen
`and for deoxygenated fuel;
`FIG. 3 is a simplified schematic of a test system for
`measuring the oxygen removal rate from jet fuel using a
`membrane filter deoxygenator in accordance with the inven-
`tion;
`FIG. 4 is a simplified depiction of a membrane filter for
`a fuel deoxygenator in accordance with the invention;
`FIG. 5 graphically depicts the influence of temperature on
`the rate of fuel deoxygenation for a particular membrane
`filter material in accordance with the invention;
`FIG. 6 graphically depicts the effect of membrane thick-
`ness on the rate of fuel deoxygenation for the membrane
`material of FIG. 5;
`FIG. 7 graphically depicts a mass transfer enhancement
`effect, resulting from increased fuel turbulence, on the rate
`of fuel deoxygenation for the membrane material of FIG. 5;
`FIG. 8 graphically depicts the relative effects of a vacuum
`and a nitrogen purge on the rate of fuel deoxygenation when
`applied to the side of the membrane filter opposite the side
`receiving the fuel; and
`FIG. 9 is a simplified schematic block diagram of an
`energy conversion device (ECD) and an associated fuel
`system employing a fuel deoxygenator in accordance with
`the invention.
`
`BEST MODE FOR CARRYING OUT THE
`INVENTION
`
`As described above with reference to FIGS. 1 and 2, the
`effects of the autoxidation reaction on fuel containing a
`substantial amount of dissolved oxygen, as the fuel tem-
`perature increases between 300° and 700° F., is to produce
`quantities of objectionable carbonaceous deposits, or cok-
`ing. Moreover, FIG. 2 reveals generally the extent to which
`the problem can be ameliorated by deoxygenating the fuel
`before subjecting it to operation in that temperature range.
`The inventors herein were aware of the limitations to the
`
`above mentioned techniques for deoxygenating hydrocarbon
`fuels, particularly for use in aircraft. They have discovered
`that membrane filters of certain materials overcome some of
`
`the prior limitations, particularly when structured and oper-
`ated in preferred manners. There have been recent uses of
`similar membrane filter materials to remove oxygen from
`water where pure supply water is required, as in the manu-
`facture of semiconductors, but the inventors are not aware of
`any suggestion that such membranes may be used for
`deoxygenating hydrocarbon fuels to reduce coking in energy
`conversion devices, and particularly for aircraft.
`Generally speaking, the inventors have found materials in
`two broad classes of membrane filters to provide improved
`results. Those classes include porous membranes, which
`allow dissolved oxygen (and other gases) to diffuse through
`angstrom-size holes but exclude the larger fuel molecules,
`and permeable membranes which use a solution-diffusion
`mechanism to dissolve the oxygen (and the other gases) and
`allow it (or them) to diffuse through the membrane, while
`excluding the fuel. The family of polytetraflouroethylene
`type compounds (PTFE), often identified under the trade-
`mark “Teflon” registered to E. I. DuPont de Nemours of
`Wilmington, Del., have proven to provide the best results for
`fuel deoxygenation. The PTFE material is believed to use a
`solution-diffusion mechanism, but may also operate via its
`porosity, depending on formulation and structure. A further
`example of a porous membrane material is a thin layer of 50
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`Angstrom porous alumina ceramic, or zeolite. A further
`example of a permeable membrane is a thin layer of silicone
`rubber.
`
`Referring to FIG. 3, there is illustrated a schematic of the
`test system used to measure the oxygen removal rate from jet
`fuel, shown using a membrane filter deoxygenator 10 of the
`invention. As depicted functionally in greater detail in FIG.
`4,
`the deoxygenator 10 includes a membrane filter 12
`supported within a housing or deoxygenation chamber 14.
`The membrane filter 12 is typically so structured and posi-
`tioned within the chamber 14 as to divide the chamber into
`a fuel region 16 and a removed oxygen region 18. The
`chamber 14 includes a fuel inlet 20 for admitting fuel which
`may contain dissolved oxygen to the fuel region 16, a fuel
`outlet 22 for discharging fuel from the fuel region 16 which
`normally has been deoxygenated by flowing over the fuel-
`contacting surface of the membrane filter 12, and an oxygen
`outlet 24 for discharging at least oxygen from the removed
`oxygen region 18. The membrane filter 12 is typically,
`though not necessarily, supported on and by a substrate 26
`of suitably porous material, as for example, sintered steel. As
`will be described below, control of the fuel temperature or
`of the difference in partial pressures of oxygen on opposite
`sides of the membrane filter 12 serves to regulate the rate at
`which oxygen moves through the membrane. At or near the
`fuel inlet 20 there may optionally be included structure (not
`shown) for inducing/increasing turbulence in the fuel flow to
`enhance mass transfer, as will be described.
`Returning to a brief description and discussion of the
`salient features of the test system of FIG. 3, JP-8 jet fuel 30
`is stored in a tank or reservoir 32. The fuel 30, for reference
`purposes, typically is saturated with dissolved air to estab-
`lish an oxygen maximum and, oppositely,
`is purged by
`nitrogen to displace oxygen and establish an oxygen mini-
`mum. The air and/or nitrogen are introduced by a sparging
`system 34. The dissolved oxygen is representative of normal
`operation in which the amount of such oxygen may be near
`a saturation level of 70 ppm. Alternatively, nitrogen may be
`introduced to displace the oxygen to obtain reference data
`for calibration.
`Fuel 30 is delivered from reservoir 32 to the fuel inlet 20
`
`of membrane filter deoxygenator 10 via a valve 36, filter 38,
`pump 40, pressure regulator 42, and heater 44. The pump 40
`supplies the requisite driving force/pressure to move the
`fuel. The pressure regulator 42 allows adjustment of pres-
`sure for test purposes. Pressure sensors P sense and monitor
`the pressure. An accumulator 46 accommodates surges. The
`filter assures a particle-free fuel flow into the membrane
`filter deoxygenator 10. The heater 44 simulates the heat
`input the fuel 30 could receive in the course of its use, often
`as a coolant, in a conventional operating system. Atempera-
`ture sensor T senses and monitors the temperature of the fuel
`just prior to its admission to the deoxygenator 10.
`Deoxygenated fuel 30 exits the deoxygenator 10 at fuel
`outlet 22 and, in the test apparatus, is recirculated, either
`directly via valve 36 or more usually through return to the
`reservoir 32. In either event,
`that return path from the
`deoxygenator to the valve 36 includes a cooler 50 and a
`pressure regulator 52. The cooler 50 returns the fuel 30 to a
`predetermined reference temperature, e.g., ambient. The
`pressure regulator 52 regulates fuel pressure in the return
`path to a reference pressure, e.g., ambient. An accumulator
`54 accommodates pressure surges, and the temperature and
`pressure of the deoxygenated and possibly cooled fuel 30 is
`monitored by pressure and temperature sensors P and T,
`respectively. Importantly, the oxygen level in the deoxygen-
`ated fuel 30 at the reference condition is monitored by an
`oxygen sensor 56.
`
`GE-1005.011
`
`GE-1005.011
`
`

`
`US 6,315,815 B1
`
`5
`Avacuum pump 58 aids in regulating the partial pressure
`of oxygen in the removed oxygen region 18, thus regulating
`the difference in partial pressures of oxygen across mem-
`brane filter 12. Additionally, the vacuum pump 58 assists
`oxygen removed from the fuel 30 in the deoxygenator 10 to
`exit the deoxygenator via outlet 24. A vacuum gauge 60
`monitors the level of pressure/vacuum existing in the
`removed oxygen region 18 of the deoxygenator. In the test
`system,
`the surplus oxygen may be vented to the atmo-
`sphere; however, it may be preferable to return the oxygen
`to fuel reservoir 32, as would be done for reasons of safety
`in an actual system and is shown in broken line in FIG. 3.
`The concern for safety arises from the possible occurrence
`of any liquid/vapor fuel that may leak past the membrane
`filter 12.
`
`Using the test system of FIG. 3, various parameters
`associated with the design and operation of deoxygenator 10
`were varied, and the results measured. The significant results
`are displayed in FIGS. 5-8, and a discussion of their
`significance follows. In each instance, the graphs plot dis-
`solved oxygen concentration versus the residence time of the
`fuel 30 in contact with the surface of membrane filter 12.
`
`The several constants throughout the tests viewed in FIGS.
`5-8 are the use of JP-8 jet fuel as the liquid hydrocarbon fuel
`under consideration, the use of PTFE as the material of the
`membrane filter 12, and a constant surface area to volume
`ratio (S/V: 55 cm‘1). The S/V ratio is the surface area (S) of
`membrane 12 relative to the volume (V) of the fuel region
`16, and favors an arrangement having only a thin layer of
`fuel passing over a relatively large membrane area. Unless
`stated otherwise, the thickness of the PTFE membrane was
`1 mil. Although the other classes of materials described
`earlier as providing the advantages of the invention were
`also evaluated in similar ways and yielded similar results,
`those results were collectively of lesser positive significance
`than for the use of PTFE.
`
`The influence of temperature is depicted in FIG. 5 for a
`1-mil-thick membrane 12. In the instance of oxygenated fuel
`30 entering the deoxygenator 10 at a first temperature,T1, of
`234° F.,
`the initial dissolved oxygen of 70 ppm(100%
`saturation) was reduced to and below a target level of 10
`ppm (about 14% saturation)in about 100 seconds. Fuel at a
`second temperature, T2, of 276° F., was deoxygenated to the
`loppm level in about 50 seconds. Fuel at a third temperature,
`T3, of 308° F., was deoxygenated to the 10 ppm level in less
`than 40 seconds. These rates of deoxygenation correspond to
`space velocities
`
`volume flowrate
`SV =T =
`reactor volume
`
`l
`residence time
`
`of approximately 36 h‘1’ 7° h‘1, and 100 h‘1, respectively.
`Thus, greater space velocities (shorter residence times) can
`be obtained when the fuel temperature is increased, thereby
`increasing the partial pressure of oxygen in the fuel and the
`permeability of the membrane.
`The influence of membrane thickness is depicted in FIG.
`6, where the fuel temperature is maintained at 308° F. A first
`PTFE membrane 12 is 1-mil thick, and results in trace Thl,
`which indicates deoxygenation to the 10 ppm level in less
`than 9 seconds. Asecond PTFE membrane 12 is 2-mil-thick,
`and results in trace Th2, which indicates deoxygenation to
`the 10 ppm level
`in about 14 seconds. A third PTFE
`membrane 12 is also 2-mil-thick, but is made by a different
`manufacturer than made the second membrane. That third
`
`membrane results in trace Th3, which indicates that deoxy-
`
`6
`genation to the 10 ppm level requires approximately 17
`seconds. This test emphasizes the desirability of the PTFE
`membrane filter being relatively thin, i.e., less than about
`2-mils and preferably, 1-mil.
`The benefits of mass transfer enhancement are depicted in
`FIG. 7, in which the tests were conducted at a fuel tempera-
`ture of 308° F., using a PTFE membrane of 1-mil-thickness.
`Afirst membrane filter 12 is symbolically depicted as having
`a few large openings as defining the fuel inlet 20, and
`similarly the fuel outlet 22. This results in a somewhat
`laminar flow of fuel 30 over the membrane 12, thereby
`limiting mass transfer. The result is depicted in trace MT1,
`which requires about 33 seconds to deoxygenate to the 10
`ppm level, and in turn corresponds to a space velocity of
`approximately 100 h‘1. A second membrane filter 12‘ is
`depicted as having a fuel inlet 20‘ which is modified to
`increase the turbulence of the fuel passing over the mem-
`brane. The inlet 20‘ may include a porous sintered metal
`member through which the fuel passes and is agitated or
`mixed to increase turbulence and mass transfer. The result is
`
`depicted in trace MT2, which deoxygenates to the 10 ppm
`level in about 9 seconds, which corresponds to a space
`velocity of 380 h‘1. A third trace MT3represents use of the
`membrane filter 12‘ with modified fuel inlet 20‘, but in which
`that membrane has been made even thinner than 1-mil by
`heating and stretching it. In that instance, trace MT3 indi-
`cates a rapid deoxygenation to 10 ppm in about 4 seconds,
`which corresponds with a space velocity of 820 h‘1.
`FIG. 8 illustrates the relative effects of using a nitrogen
`purge, represented by trace N, vs. a vacuum (0.08 psia),
`represented by trace V, applied to the removed oxygen
`region 18 to reduce the partial pressure of oxygen on that
`side of the membrane 12 relative to its partial pressure on the
`opposite side. This has the effect of increasing the difference
`in oxygen partial pressures across the membrane 12, which
`enhances the rate of transfer of oxygen from the fuel to, and
`through, the membrane 12. Trace V shows deoxygenation to
`the 10 ppm (14%) level
`in about 13 seconds, with the
`nitrogen purge trace N revealing a similar performance of
`about 10 seconds.
`
`Although the actual embodiments of the deoxygenator of
`the invention may vary depending upon a number of factors
`including intended use and economics, a representative
`embodiment is illustrated in FIG. 9. A fuel supply system
`100 for an energy conversion device (ECD) 104 includes a
`deoxygenator 110 that receives liquid fuel 130 from a
`reservoir 132. The fuel 130 is typically a hydrocarbon. The
`ECD 104 may exist in a variety of forms in which the fuel,
`at some point prior to eventual use for processing, for
`combustion or for some form of energy release, acquires
`sufficient heat to support autoxidation reactions and coking
`if dissolved oxygen is present to any significant extent in the
`fuel.
`
`A likely form of ECD 104 is the gas turbine engine, and
`particularly such engines in high performance aircraft.
`Typically,
`the fuel serves as a coolant for one or more
`sub-systems in the aircraft, and in any event becomes heated
`as it
`is delivered to fuel
`injectors immediately prior to
`combustion.
`
`In FIG. 9 there is illustrated a heat exchange section 106,
`to represent the one or several regions of operation through
`which the fuel passes in a heat exchange relationship. The
`heat exchange section(s) may be directly associated with the
`ECD 104 (as shown), and/or distributed elsewhere in the
`larger system.
`The illustrated deoxygenator 110 is of the tube and shell
`type, with the shell being designated 111 and the tubes being
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`GE-1005.012
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`US 6,315,815 B1
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`7
`designated 113. Generally speaking, the fuel 130 may pass
`either inside or outside the tubes 113, with the removed
`oxygen occurring in the other of the two. This requires the
`membrane filter 112 to at least be in direct contact with the
`fuel 130. In the illustrated embodiment, the fuel 130 flows
`into the shell region via fuel inlet 120 and over the mem-
`brane filter 112 on the exterior surface of the tubes 113.
`
`Correspondingly, the oxygen removed from the fuel occurs
`and collects within the tubes 113, which in turn connect to
`a manifold 117 containing the removed oxygen outlet 124.
`This construction maximizes the area of membrane filter 112
`
`contacted by fuel 130 and minimizes the volume of shell
`111, particularly with the inclusion of flow baffles 119 in the
`shell 111 to cause the fuel to follow a lengthy, tortuous path
`over the membrane filter 112 to the fuel outlet 122.
`
`Depending upon the requirements of the deoxygenator
`110, the tubes 113 may be constructed either entirely of the
`material forming the membrane filter 112 or they may
`comprise a micro-porous structural substrate having a thin
`exterior layer or coating of the membrane filter material as
`shown in FIG. 4. If the tubes 113 include a structural
`
`substrate, they may conveniently be porous sintered steel or
`other similar suitable material.
`
`The membrane filter material is preferably PTFE having
`a thickness of 2 mils or less, and preferably 1 mil or less. The
`PTFE is available from various sources,
`including E.
`I.
`DuPont de Nemours of Delaware under the registered trade-
`mark “Teflon”. The PTFE may be overlaid on the substrate
`of tubes 113 by one of several known techniques.
`As generally understood from the discussion of the test
`system of FIG. 3, fuel 130 stored in reservoir 132 normally
`contains dissolved oxygen, possibly at a saturation level of
`70 ppm. The fuel 130 is drawn from reservoir 132, typically
`by a pump 140, and is connected via conduit 175 and valve
`136 to the fuel inlet 120 of deoxygenator 110. The pressure
`applied by pump 140 aids in circulating the fuel 130 through
`the deoxygenator 110 and other portions of the system. As
`the fuel 130 passes over the surface of membrane filter(s)
`112, the oxygen is selectively removed into and through the
`membrane 112 and into the interior of tubes 113. The
`
`flows from the fuel outlet 122, via
`deoxygenated fuel
`conduit 177, to heat exchange sub-systems 106, and to the
`ECD 104, such as the injectors of a gas turbine engine. A
`portion of the deoxygenated fuel may be recirculated, as
`represented in broken line, by conduit 179 to either the
`deoxygenator or, more likely, the reservoir 132. Any fuel
`leakage through the membrane filter 112 and the removed
`oxygen within the tubes 113 are evacuated from the deoxy-
`genator 110, by means such as a vacuum or aspirating pump
`158, via oxygen outlet 124 and conduit 181 connected to the
`reservoir 132. This controlled removal of any fuel leakage
`prevents it from entering the environment and possibly
`posing a safety risk.
`As discussed with respect to FIG. 8, control of the oxygen
`partial pressures on opposite sides of the membrane filter
`112 can beneficially affect the rates of deoxygenation and
`thus, space velocities, SV. The use of a relatively reduced
`pressure (partial vacuum) on the removed oxygen side aids
`this parameter, as does an elevation of fuel temperature to
`about 200—250° F. on the fuel side. The latter serves to
`relatively increase the oxygen partial pressure by thermally
`liberating oxygen. An increase in the pressure of the oxy-
`genated fuel will not have a significant benefit because it
`won’t significantly change the oxygen partial pressure dif-
`ference across the membrane or increase the membrane’s
`
`permeability. Importantly, care must be taken to not increase
`the pressure to a level that either damages the membrane
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`filter 112 and/or tubes 113 or forces the fuel through the
`membrane. In lieu of reducing the oxygen partial pressure by
`removing oxygen with a vacuum pump, it is also possible to
`displace and remove oxygen using a nitrogen purge and
`accomplish the same result.
`Although the invention has been described and illustrated
`with respect
`to the exemplary embodiments thereof,
`it
`should be understood by those skilled in the art that the
`foregoing and various other changes, omissions and addi-
`tions may be made without departing from the spirit and
`scope of the invention.
`What is claimed is:
`1. Amethod for removing dissolved oxygen from a liquid
`fuel in the fuel system of an energy conversion device,
`comprising the steps of:
`(a) disposing a selected filter membrane in a deoxygen-
`ation chamber in the fuel system to divide the chamber
`into a fuel region and a removed oxygen region on
`opposite sides of the membrane filter;
`(b) flowing fuel into the fuel region of the deoxygenation
`chamber and into contact with a fuel-side surface of the
`filter; and
`(c) controlling the difference of partial pressures of oxy-
`gen across the membrane,
`thereby to regulate the
`driving force for moving oxygen through the mem-
`brane exclusive of the fuel to deoxygenate the fuel.
`2. The method of claim 1 comprising the steps of:
`(a) substantially continuously flowing fuel into contact
`with the filter membrane to substantially continuously
`deoxygenate the fuel;
`(b) substantially continuously removing deoxygenated
`fuel from the fuel region of the deoxygenation cham-
`ber; and
`(c) substantially continuously removing oxygen from the
`removed oxygen region of the deoxygenation chamber.
`3. A fuel deoxygenator for removing dissolved oxygen
`from a liquid fuel in the fuel system of an energy conversion
`device, comprising a membrane filter disposed in the fuel
`system and positioned for liquid fuel to flow into contact
`with a fuel-side surface of the filter, the membrane filter
`being capable of removing oxygen from the fuel to a level
`at least below that at which significant coking occurs.
`4. The deoxygenator of claim 3 wherein the membrane
`filter passes oxygen molecules and excludes the liquid fuel
`sufficiently to remove oxygen from the fuel to a level at least
`below about 20 ppm.
`5. The deoxygenator of claim 4 wherein the