Patent Application
20200197835
The invention pertains to methods and apparatuses for jet fuel deoxygenation using composite hollow fiber membrane comprised of an amorphous fluoropolymer layer superimposed on a porous poly(aryl ether ketone), i.e., PAEK, polymer substrate.
The jet fuel on board aircraft is frequently used as a heat transfer fluid in heat exchangers for cooling purposes as a replacement to ram air. As flight speeds for advanced aircraft, rocket, and missiles increase to the high supersonic and hypersonic regime, the temperature of the ram air taken on board the vehicle becomes too high to cool aircraft systems. Therefore, it is increasingly necessary to utilize the fuel as the primary coolant.
One of the consequences of using jet fuel as a coolant in high performance aircraft is the production of carbonaceous deposits that result from the autoxidation of the fuel by oxygen that is dissolved in the fuel. These deposits cause fouling of critical aircraft components and can lead to catastrophic failure of the engine system. When air-saturated fuel is heated to temperatures above about 120° C. (250° F.) or above about 150° C. (300° F.), the dissolved oxygen forms free radical species (coke precursors) which initiate and propagate other autoxidation reactions that in turn lead to the formation of objectionable deposits, called “coke” or “coking”. As fuel temperature increases beyond the autoxidation temperature (typically about 150° C. (300° F.)), the process of autoxidation consumes oxygen and forms carbonaceous deposits. The temperature at which autoxidation begins depends upon which fuel is being heated. It should be noted that 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 carbonaceous deposits impairs the normal function of the fuel delivery system, either with respect to an intended heat exchange function or the efficient injection of the fuel.
Many attempts have been made to solve the problem of oxidation of liquid hydrocarbons. U.S. Pat. No. 8,388,740 discloses the application of oxygen-free gas for removal of the oxygen from the hydrocarbon fuel mixture. The introduction of additives into liquid hydrocarbons has been used successfully for many years. For example, U.S. Pat. No. 5,382,266 discloses the application of phosphine and phosphates to distillate fuels to prevent fuel degradation (such as color degradation, particulate formation, and/or gum formation). U.S. Pat. No. 5,509,944 discloses the stabilization of gasoline through addition of an effective amount of a primary antioxidant, such as phenylene diamine, a hindered monophenol, or mixtures of these, and also a secondary antioxidant, such as dimethyl sulfoxide. U.S. Pat. No. 5,362,783 discloses the combination of phosphine and hindered phenols as a stabilizer in thermoplastic polymers to prevent discoloration. U.S. Pat. No. 6,475,252 discloses an additive composition comprising a hindered phenol, a peroxide decomposer, and a phosphine compound for prevention of oxidation and peroxide formation.
The U.S. Air Force JP-8+100 program developed an additive package for jet fuel that significantly increases the thermal stability of the fuel by preventing the formation of deposits resulting from fuel oxidation within aircraft fuel systems. See Heneghan, S. P., Zabarnick, S., Ballal, D. R., Harrison, W. E., J. Energy Res. Tech. 1996, 118, 170-179; and Zabarnick, S., and Grinstead, R. R., Ind. Eng. Chem. Res. 1994, 33, 2771-2777. The JP-8+100 jet fuel incorporates additives for providing thermal stability to 425° F. At high temperatures)(>425°, however, the JP-8+100 additive package loses effectiveness either due to temperature induced failure of the active mechanisms or due to the thermal degradation of the additive compounds themselves.
Thus, while laboratory testing and field implementation of JP-8+100 have been very successful at temperatures up to 425° F., application of similar additive technologies to achieve thermal stabilities on the order of 900° F. is considered unlikely. The difficulty does not lie in the approach, because modifying a fuel through the addition of additives remains a cost-effective and efficient method for tailoring a fuel to specific temperature requirements. Rather, the difficulty lies in the fundamental limits imposed by high-temperature chemistry since fuel molecules decompose at high temperatures. It remains to be seen whether an improved jet fuel additive will be developed that will inhibit the oxidation of the fuel at high temperatures (>425° F.).
A fuel stabilization unit that reduces the amount of oxygen dissolved within the fuel is needed. Reducing the amount of oxygen in the fuel increases the maximum allowable exposure temperature of the fuel, thereby increasing its heat sink capacity when used for cooling components onboard the aircraft.
One method of removing dissolved oxygen from fuels is by using a semi-permeable membrane deoxygenator. In a membrane deoxygenator, fuel is pumped over an oxygen permeable membrane. As the fuel passes over the membrane, a partial oxygen pressure differential across the membrane is generated that promotes the transport of oxygen out of the fuel through the membrane. Exemplary deoxygenators remove 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 portions of the fuel system having high temperatures and/or constricted flow paths.
U.S. Pat. No. 6,315,815 discloses the use of a membrane filter for removal fo oxygen from the liquid fuel. The membrane is formed from PTFE polymer. However, the disclosed membrane filter exhibits an extremely low oxygen removal rate and thus is inefficient for oxygen removal. Furthermore, a high rate of fuel loss through evaporation occurs during the deoxygenation process due to the porous nature of the membrane. U.S. Pat. No. 7,175,693 discloses a method for removal of oxygen from the liquid fuel by using a composite membrane from PVDF substrate superimposed with an amorphous Teflon layer, such as AF2400. However, the PVDF substrate is formed by the phase inversion method from a solution which makes the composite membrane unstable once in contact with liquid fuels that contain significant amount of aromatic hydrocarbons.
U.S. Pat. Nos. 7,393,388, 7,465,335, 7,465,336, 7,615,104, 7,824,470 and 8,177,814 disclose methods of oxygen removal from liquid hydrocarbon fuel using flat sheet or textured plate membranes. However, these methods suffer from an inefficient mass transfer of oxygen. The excessive size and weight of the device needed to overcome this inefficiency limits its use on board aircraft where every bit of mass and volume counts.
U.S. Pat. No. 5,876,604 discloses the use of amorphous Teflon formed from an amorphous copolymer of perfluoro-2,2-dimethyl-1,3-dioxole for gasifying or degassing a liquid. However, the disclosed membrane configurations and substrates are compatible with only a limited number of liquids such as water and blood. Thus, they are not suitable for the removal of oxygen from jet fuel since jet fuel contains liquid hydrocarbons.
In view of the foregoing discussion, there is a need for an improved solution for inhibiting or preventing thermal degradation of jet fuel that is not limited to temperatures less than 425° F. There is also a need for an improved solution for inhibiting or preventing thermal degradation of jet fuel whose components in contact with jet fuel don't exhibit failure upon such contact. There is also a need for an improved solution for inhibiting or preventing thermal degradation of jet fuel whose size and weight do not limit their use aboard aircraft.
There is disclosed a method for producing oxygen-depleted liquid hydrocarbon fuel for combustion in an energy conversion device in which the oxygen-depleted liquid hydrocarbon fuel is used as a cooling medium that includes the following steps. A flow of liquid hydrocarbon fuel containing dissolved oxygen is fed into a membrane device comprising a composite hollow fiber membrane that is comprised of a porous PAEK substrate with a thin layer of an amorphous perfluoro polymer superimposed thereon. The fed flow of dissolved oxygen-containing liquid hydrocarbon fuel is allowed to come into contact with a first side of the membrane, thereby permeating at least some of the dissolved oxygen across the membrane from the first side to a second side of the membrane. A flow of at least partially deoxygenated liquid hydrocarbon fuel is withdrawn from the membrane device that is depleted of dissolved oxygen in comparison to the flow of the dissolved oxygen-containing liquid hydrocarbon fuel that is fed to the membrane device. A gas stream is withdrawn from the membrane device containing the permeated oxygen that is removed from the fed flow of the dissolved oxygen-containing liquid hydrocarbon fuel.
There is disclosed an apparatus for removing amounts of dissolved oxygen from a flow of dissolved oxygen-containing liquid hydrocarbon fuel for an energy conversion device, comprising: a tank containing dissolved oxygen-containing liquid hydrocarbon fuel, said tank being adapted and configured to contain an amount of the dissolved oxygen-containing liquid hydrocarbon fuel; a first liquid pump in upstream flow communication with said tank; a membrane device in upstream flow communication with said first liquid pump and comprising a pressure vessel having a feed inlet, a permeate gas outlet, and a deoxygenated liquid hydrocarbon fuel outlet, contained within the pressure vessel is a composite hollow fiber membrane that is comprised of a porous PAEK substrate with a thin layer of an amorphous perfluoro polymer superimposed thereon, wherein: said first pump is adapted and configured to pump a flow of dissolved oxygen-containing liquid hydrocarbon fuel from said tank, said membrane device is adapted and configured to place the flow of dissolved oxygen-containing liquid hydrocarbon fuel in contact with a first side of said composite hollow fiber membrane, and said membrane device being adapted and configured to selectively permeate amounts of oxygen from the dissolved oxygen-containing liquid hydrocarbon from the first side of the composite hollow fiber membrane to a second side of the composite hollow fiber membrane to yield a flow of permeate gas containing the permeated oxygen from said permeate gas outlet and a flow of deoxygenated liquid hydrocarbon fuel from said deoxygenated liquid hydrocarbon fuel outlet.
An aircraft fueled by at least partially deoxygenated liquid jet fuel, comprising an apparatus for removing amounts of dissolved oxygen from a flow of dissolved oxygen-containing liquid hydrocarbon fuel for an energy conversion device, comprising: a tank containing dissolved oxygen-containing liquid hydrocarbon fuel, said tank being adapted and configured to contain an amount of the dissolved oxygen-containing liquid hydrocarbon fuel; a first liquid pump in upstream flow communication with said tank; a membrane device in upstream flow communication with said first liquid pump and comprising a pressure vessel having a feed inlet, a permeate gas outlet, and a deoxygenated liquid hydrocarbon fuel outlet, contained within the pressure vessel is a composite hollow fiber membrane that is comprised of a porous PAEK substrate with a thin layer of an amorphous perfluoro polymer superimposed thereon, wherein: said first pump is adapted and configured to pump a flow of dissolved oxygen-containing liquid hydrocarbon fuel from said tank, said membrane device is adapted and configured to place the flow of dissolved oxygen-containing liquid hydrocarbon fuel in contact with a first side of said composite hollow fiber membrane, and said membrane device being adapted and configured to selectively permeate amounts of oxygen from the dissolved oxygen-containing liquid hydrocarbon from the first side of the composite hollow fiber membrane to a second side of the composite hollow fiber membrane to yield a flow of permeate gas containing the permeated oxygen from said permeate gas outlet and a flow of deoxygenated liquid hydrocarbon fuel from said deoxygenated liquid hydrocarbon fuel outlet, wherein said tank is a jet fuel tank, the dissolved oxygen-containing liquid hydrocarbon fuel is jet fuel, the energy conversion device is an aircraft engine, and a flow of at least partially deoxygenated jet fuel is received by the aircraft engine from the membrane device.
The method, apparatus, or aircraft may include one or more of the following aspects:
heat is transferred from the energy conversion device, a heat sink, or a fluid to the withdrawn flow of the at least partially deoxygenated liquid hydrocarbon fuel so as to cool the energy conversion device and heat the at least partially deoxygenated liquid hydrocarbon fuel.
the deoxygenated liquid hydrocarbon fuel is heated to a temperature of at least 250° F.
the deoxygenated liquid hydrocarbon fuel is heated to a temperature of at least 300° F.
the deoxygenated liquid hydrocarbon fuel is heated to a temperature of at least 425° F.
the deoxygenated liquid hydrocarbon fuel is heated to a temperature of at least 900° F.
heat is transferred from the energy conversion device to the deoxygenated liquid hydrocarbon fuel.
a positive partial pressure differential for oxygen across the membrane from the first side to the second side is increased by applying a vacuum is applied to the second side of the membrane device.
the positive partial pressure differential for oxygen across the membrane from the first side to the second side is increased by feeding a sweep gas is fed to the second side of the membrane device.
a positive partial pressure differential for oxygen across the membrane from the first side to the second side is increased by feeding a sweep gas to the second side of the membrane device.
the sweep gas is an amount of liquid hydrocarbon fuel, before or after deoxygenation at the membrane device, that has been allowed to vaporize.
the sweep gas is: nitrogen generated by an on board air separation system; or
nitrogen or argon from an inert gas generator.
the withdrawn gas stream is directed into a head space of a fuel tank from which the flow of dissolved oxygen-containing liquid hydrocarbon fuel was obtained.
at least some of the oxygen-containing liquid hydrocarbon fuel fed to the membrane device also permeates, in the form of vapor, across the membrane from the first side to the second side along with the permeating oxygen.
the membrane is characterized by a room temperature permeance of propane of lower than 15 GPU.
the membrane is characterized by a room temperature permeance of propane of lower than 10 GPU.
the membrane is characterized by a room temperature permeance of propane of lower than 8 GPU.
the membrane is characterized by a room temperature permeance of oxygen of at least 70 GPU.
the thin layer of amorphous perfluoro polymer is superimposed upon an outer surface of the PAEK substrate.
the thin layer of amorphous perfluoro polymer is superimposed on an inner surface of the hollow fiber that forms the first side of the membrane.
the fed flow of dissolved oxygen-containing liquid hydrocarbon fuel is pumped by a pump to the membrane device at a pressure between 100 and 400 psig.
the energy conversion device is an aircraft engine;
the dissolved oxygen-containing liquid hydrocarbon fuel is jet fuel;
the fed flow of dissolved oxygen-containing liquid hydrocarbon fuel is obtained from an aircraft jet fuel tank;
the withdrawn flow of at least partially deoxygenated liquid hydrocarbon fuel is returned to the aircraft jet fuel tank.
the dissolved oxygen-containing liquid hydrocarbon fuel is jet fuel;
the withdrawn flow of at least partially deoxygenated liquid hydrocarbon fuel is fed to the aircraft engine.
the dissolved oxygen-containing liquid hydrocarbon fuel is selected from the group consisting of kerosenes, gasolines, biofuels, ethanol, and mixtures of a gasoline and ethanol.
a conduit is adapted and configured to receive heat from an energy conversion device and has first and second ends, said conduit first end being in upstream flow communication with said deoxygenated liquid hydrocarbon fuel outlet, thereby cooling the energy conversion device and heating the flow of deoxygenated liquid hydrocarbon fuel yielded by said membrane device.
a first end of a conduit also having a second end is in upstream flow communication with said deoxygenated liquid hydrocarbon fuel outlet, wherein said conduit second end is in upstream flow communication with said tank so as to direct the flow of deoxygenated liquid hydrocarbon fuel, that is yielded by said membrane device, to said tank, and said apparatus further comprises a fuel feed line having first and second ends, said fuel feed line first end being in upstream flow communication with said tank and said fuel feed line second end being adapted and configured to feed a flow of at least partially deoxygenated liquid hydrocarbon fuel from said tank to an energy conversion device.
a vacuum pump or ejector is in vacuum communication with the second side of the composite hollow fiber membrane so as to increase an oxygen partial pressure difference across the composite hollow fiber membrane from said first side to said second side.
a source of a sweep gas is in upstream flow communication with the second side of the composite hollow fiber membrane so as to increase an oxygen partial pressure difference across the composite hollow fiber membrane from said first side to said second side.
a source of a sweep gas is in upstream flow communication with the second side of the composite hollow fiber membrane so as to increase an oxygen partial pressure difference across the composite hollow fiber membrane from said first side to said second side.
said source of a sweep gas is a headspace of said tank and said sweep gas is an amount of liquid hydrocarbon fuel, before or after deoxygenation at the membrane device.
said source of a sweep gas is an air separation system adapted and configured to separate air into oxygen-enriched air and nitrogen-enriched air and said sweep gas is nitrogen-enriched air produced by said air separation system.
a conduit has first and second ends, said conduit first end being in upstream flow communication with said deoxygenated liquid hydrocarbon fuel outlet, wherein said conduit second end is adapted and configured to be placed in upstream flow communication with the energy conversion device so as to direct the flow of deoxygenated liquid hydrocarbon fuel, that is yielded by said membrane device, to the energy conversion device for combustion thereat.
the permeate gas outlet is in upstream flow communication with a head space of said tank so as to receive the flow of permeate gas, containing the permeated oxygen, from said permeate gas outlet.
a room temperature oxygen permeance of the composite hollow fiber membrane is higher than a room temperature propane permeance of the composite hollow fiber membrane.
the room temperature oxygen permeance is at least 30 GPU and no more than 5000 GPU and the room temperature propane permeance is lower than 15 GPU.
the room temperature oxygen permeance is at least 30 GPU and no more than 5000 GPU and the room temperature propane permeance is lower than 10 GPU the room temperature oxygen permeance is at least 30 GPU and no more than 5000 GPU and the room temperature propane permeance is lower than 8 GPU.
the thin layer of amorphous perfluoro polymer is superimposed upon an outer surface of the PAEK substrate.
the thin layer of amorphous perfluoro polymer is superimposed on an interior surface of the PAEK substrate.
the fed flow of dissolved oxygen-containing liquid hydrocarbon fuel is pumped by a pump to the membrane device at a pressure between 100 and 400 psig.
a filter is disposed in fluid communication between said pump and said membrane device and is adapted and configured to remove particulates from the flow of deoxygenated liquid hydrocarbon fuel to said membrane device.
the energy conversion device is an aircraft engine, said tank is a jet fuel tank, and the dissolved oxygen-containing liquid hydrocarbon fuel is jet fuel.
the feed inlet is disposed on an outer circumferential surface of the membrane device adjacent an upstream end of the membrane device; disposed concentrically within the pressure vessel is a hollow center tube having apertures formed therein at an upstream end of the membrane device; the deoxygenated liquid hydrocarbon fuel outlet is disposed at a downstream, axial end in downstream flow communication with an interior of the hollow center tube; the gaseous permeate outlet is disposed at a upstream, axial end of the membrane device; and the membrane device is adapted and configured to produce a flow of dissolved oxygen-containing liquid hydrocarbon fuel radially toward the composite hollow fiber membrane and axially along the composite hollow fiber membrane in an upstream to downstream direction and to produce a flow of permeate gas constituting dissolved oxygen that permeates across the composite hollow fiber membrane from the dissolved oxygen-containing liquid hydrocarbon fuel in counter-flow fashion with respect to the upstream to downstream axial flow of dissolved oxygen-containing liquid hydrocarbon fuel.
the feed inlet is disposed at an upstream, axial end of the membrane device; the deoxygenated liquid hydrocarbon fuel outlet is disposed on an outer circumferential surface of the membrane device adjacent a downstream end of the membrane device; disposed concentrically within the pressure vessel is a hollow center tube having apertures formed therein at an upstream end of the membrane device; the gaseous permeate outlet is disposed at the upstream, axial end of the membrane device; and the membrane device is adapted and configured to produce a flow of dissolved oxygen-containing liquid hydrocarbon fuel axially along the composite hollow fiber membrane in an upstream to downstream direction and to produce a flow of permeate gas constituting dissolved oxygen that permeates across the composite hollow fiber membrane from the dissolved oxygen-containing liquid hydrocarbon fuel in counter-flow fashion with respect to the upstream to downstream axial flow of dissolved oxygen-containing liquid hydrocarbon fuel.
the feed inlet of the membrane device is disposed at an upstream end of the membrane device; disposed concentrically within the pressure vessel is a hollow center tube having apertures formed therein at an upstream end of the membrane device; the gaseous permeate outlet is disposed at an axial, upstream end of the membrane device; the deoxygenated fuel outlet is disposed on an outer circumferential surface of the membrane device adjacent a downstream end of the membrane device; and the membrane device is adapted and configured to produce a flow of dissolved oxygen-containing liquid hydrocarbon fuel axially along the composite hollow fiber membrane in an upstream to downstream direction and to produce a flow of permeate gas constituting dissolved oxygen that permeates across the composite hollow fiber membrane from the dissolved oxygen-containing liquid hydrocarbon fuel in counter-flow fashion with respect to the upstream to downstream axial flow of dissolved oxygen-containing liquid hydrocarbon fuel.
A liquid hydrocarbon fuel containing dissolved oxygen may be at least partially deoxygenated by a membrane device that includes a composite hollow fiber membrane which includes a thin layer of amorphous perfluoro polymer superimposed upon an outer surface of a porous PAEK substrate. The superior oxygen/hydrocarbon selectivity of the amorphous perfluoro polymer allows separation of the dissolved oxygen from the liquid hydrocarbon fuel. The superior flux of oxygen through the porous PAEK substrate allows for relatively high productivity of dissolved oxygen removal. After at least partial deoxygenation by the membrane device, the liquid hydrocarbon fuel may be combusted in an energy conversion device. Prior to, or concurrent with, combustion of the liquid hydrocarbon fuel by the energy conversion device, the fuel may be used to cool a heat sink, the energy conversion device itself, or a fluid in a heat exchanger.
As shown in
As illustrated in
Two streams are withdrawn from the membrane device 19. The permeated oxygen is withdrawn as a flow of gaseous permeate 27 via the gaseous permeate outlet 55. Optionally and as illustrated in
While each of the membrane devices 19 of
In the membrane device 19 of
In contrast to the membrane device 19 of
While the membrane device 19 of
The directions of the flow of dissolved oxygen-containing liquid hydrocarbon fuel, the flow of permeate gas, and the flow of deoxygenated liquid hydrocarbon fuel, within the membrane device 19, are not limited to the embodiments of
Before it is combusted in the energy conversion device 21, the deoxygenated liquid hydrocarbon fuel in the conduit leading away from the deoxygenated fuel outlet 57 may be used to cool an apparatus or fluid.
For example, the at least partially deoxygenated liquid hydrocarbon fuel from the membrane device 19 may exchange heat with a heat sink prior to being fed to the energy conversion device 21. In this manner, the heat sink is cooled and the at least partially deoxygenated liquid hydrocarbon fuel is heated. As shown in
In a second example, and as illustrated in
As shown in
Alternatively and as illustrated in
The oxygen partial pressure differential across the membrane from the first side to the second side may be increased in any of three different ways.
In a first embodiment and as shown in
In a second embodiment and as illustrated in
In a third embodiment and as shown in
Whether or not the aforementioned embodiments for increasing the oxygen partial pressure differential across the membrane are used, typically at least 30% of the dissolved oxygen is removed from the dissolved oxygen-containing liquid hydrocarbon fuel through permeation across the membrane. More typically 50% of the dissolved oxygen is removed, and even more typically, 90% of the dissolved oxygen is removed.
The energy conversion device includes any apparatus, system, or installation in which a liquid hydrocarbon fuel, at some point prior to eventual combustion in the energy conversion device, acquires sufficient heat to support autoxidation reactions and coking if no attempts are made to at least partially remove the dissolved oxygen. Such energy conversion devices include but are not limited to power generation facilities (such as those utilizing a boiler, steam turbine, or gas turbine), engines, and furnaces. Typically, the energy conversion device is an engine, including but not limited to those used for ground transportation (such as for cars, trucks, busses, or other motorized heavy equipment), those used for non-transportation machinery (such as generators, boilers, or mills), and those used for aircraft. Specific types of aircraft engines include reciprocating (piston) engines as well as turbine engines such as turbojet, turboprop, turbofan and turboshaft engines.
The specific type of liquid hydrocarbon fuel that may be at least partially deoxygenated by the membrane device is driven by the type of energy conversion device. Specific types of liquid hydrocarbon fuels includes but is not limited to: kerosene, gasoline, gasoline/ethanol mixtures, and ethanol. In the case of an energy conversion device that is an aircraft engine, specific types of hydrocarbon fuels include jet fuel (such as Jet-A type kerosene-based jet fuel) and aviation gasoline (also called avgas). Aviation gasoline, for example, has a higher octane rating than automotive gasoline to allow higher compression ratios, power output, and efficiency at higher altitudes.
A particular type of liquid hydrocarbon fuel is jet fuel. Jet fuels are chemically complex mixtures having a wide variety of molecules with different number of carbons and may have more than thousands of species. The major categories of jet fuel components include alkanes, cycloalkanes (naphthenes), aromatics, and alkenes. Alkanes (such as dodecane, tetradecane, and isooctane) are the most abundant components and account for 50-60% by volume of the jet fuel. Cycloalkanes (such as methylcyclohexane, tetralin, and decalin) and aromatics (such as toluene, xylene, and naphthalene) represent 20-30% by volume, and alkenes account for less than 5%.
When the invention is implemented in association with a power generation facility or furnace, the liquid hydrocarbon fuel may be preheated through heat exchange with a hot fluid, such as steam or flue gas, prior to being combusted. By preheating the fuel prior to combustion, more energy or power can be produced by the power generation facility or furnace for a given amount of fuel in comparison to a power generation facility or furnace not utilizing fuel preheating. Looked at another way, preheating the fuel prior to combustion allows less fuel to be combusted for producing a given amount of energy power by the energy conversion device. Any technique known in the field of power generation or furnaces utilizing preheated fuel may be used for achieving the fuel preheating in the invention. For example, the fuel may be preheated in a shell and tube heat exchanger. Regardless of the specific mode of fuel preheating, because the fuel has been at least partially deoxygenated, buildup of coking deposits occurs less rapidly at the outlet of the fuel injector of the burner or at portions of a burner in close proximity to fuel-rich regions of the flame from the burner. This is because the relative lack of oxygen decreases the potential for or degree of coking of the liquid hydrocarbon fuel after heating the at least partially deoxygenated fuel to temperatures supporting autoxidation reactions. This allows the fuel to be preheated to temperatures exceeding 250° F., 300° F., 425° F., or even temperatures reaching as high as 900° F. By reducing the rate at which coking deposits forms, maintenance for removal of such deposits may be performed less frequently. As a result, there is less down-time for the burner or for the power generation facility or furnace because they will be taken out of service less frequently or for shorter periods of time.
When the invention is implemented in association with an aircraft engine, the fuel deoxygenated by the membrane device may first be used as a cooling medium for receiving heat form a heat exchanger or heat sink associated with the aircraft, such as electronic control systems of the aircraft. Alternatively, it may be used as a cooling medium for cooling air used in a system for cooling electronic control systems of the aircraft.
When the invention is implemented in association with engine used either for aircraft or other purpose, the fuel deoxygenated by the membrane device may be used as a cooling medium for the engine itself. As discussed above with respect to power generation facilities and furnaces, preheating fuel prior to combustion in the engine allows more energy or power to be produced by the engine for a given amount of fuel or allows less fuel to be consumed for a given amount of energy or power produced by the engine. Again as discussed above, because the fuel has been at least partially deoxygenated, buildup of coking deposits occurs less rapidly at or adjacent to the fuel injectors of the engine. This allows the fuel to be preheated to temperatures exceeding 250° F., 300° F., 425° F., or even temperatures reaching as high as 900° F. By reducing the rate at which coking deposits forms, maintenance for removal of such deposits may be performed less frequently. As a result, there is less down-time for the engine because they will be taken out of service less frequently or for shorter periods of time.
The composite hollow fiber membrane of the membrane device includes a porous hollow fiber substrate made of one or more PAEKs and an ultra-thin layer of an amorphous perfluoro polymer that is superimposed on the porous hollow fiber substrate. PAEK represent a class of semi-crystalline engineering thermoplastics with outstanding thermal properties and chemical resistance. One of the representative polymers in this class is poly(ether ether ketone), sometimes referred to as PEEK, which has a reported continuous service temperature of approximately 250° C. PAEK polymers are virtually insoluble in all common solvents at room temperature. These properties make PAEK ideal material for contact with liquid fuels.
The preferred porous PAEK substrates are semi-crystalline. Namely, a fraction of the poly(aryl ether ketone) polymer phase is crystalline and is thus not subject to a chemical modification. A high degree of crystallinity is preferred since it imparts solvent resistance and improves thermo-mechanical characteristics to the article. In some embodiments of this invention the degree of crystallinity is at least 15%, preferably at least 25%, most preferably at least 36%. When pre-formed, shaped porous substrates are utilized to form the composite membranes of this invention, the porous substrate may be formed by any method known in the art.
Each of the PAEKs is independently selected from the formula:
[—Ar′—CO—Ar″]n,
wherein Ar′ ad Ar″ are aromatic moieties and n is an integer from 20 to 500. At least one of the aromatic moieties contains a diarylether or diarylthioether functional group which is a part of the polymer backbone.
Typically, each PAEK is selected from the homopolymers of the following repeating units:
wherein x is an ether unit.
The PAEK(s) can have a weight average molecular weight in the range of 20,000 to 1,000,000 Daltons, preferably between 30,000 to 500,000 Daltons. The preferred PAEKs are semi-crystalline polymers that are not soluble in organic solvents at conventional temperatures. Two typical such PAEKs include poly(ether ether ketone) (i.e., PEEK) and poly(ether ketone) (i.e., PEK), each available from Victrex Corporation under the trade name of Victrex. Another typical such PAEK is poly(ether ketone ketone) (i.e., PEKK) available from Oxford Performance Materials under the trade name OXPEKK.
Typically, the porous PAEK substrate is formed by melt processing, for example, by the methods disclosed in U.S. Pat. Nos. 6,887,408, 7,176,273, 7,229,580, 7,368,526, and 9,610,547. Certain version of porous PAEK hollow fibers are available commercially from Air Liquide Advanced Technologies US.
The composite membranes are prepared by forming a perfluoro hydrocarbon layer on top of a porous PAEK substrate. Optionally, the perfluoro hydrocarbon is chemically attached to the PAEK polymer of the substrate. While this may be achieved by any way known in the field of polymer grafting, perfluoro polymers with functional amino groups can be chemically attached to the PAEK substrate through reaction with ketone groups in the backbone of poly(aryl ether ketone) polymer.
Particular examples of suitable perfluoro polymers include Teflon AF amorphous polymers, such as AF1600 or AF 2400 (originally manufactured by DuPont), Hyflon polymers, such AD60 and AD80 (manufactured by Solvay), and Cytop perfluorobutenyl vinyl ether (manufactured by Asahi Glass). Other perfluoro polymers include amorphous polymers, such as copolymers of perfluoro (2-methlene-4,5-dimethyl-1,3-dioxolane) and perfluoro (2-methylene-1,3-dioxolane) as described in Y. Okamoto et al., Journal of Membrane Science, Volume 471, page 412-419, 2014.
The perfuoro polymer layer can be formed from a single amorphous perfluoro polymer, or from a blend of two or more different amorphous perfluoro polymers. In one example, the blend is comprised of Teflon AF1600 and Hyflon AD 60, as described in U.S. Pat. No. 6,723,152, incorporated herein by reference in its entirety.
The composite hollow fibers used to form membranes of this invention preferably have an outside diameter from about 50 to about 5,000 micrometers, more preferably from about 80 to about 1,000 micrometers, with a wall thickness from about 10 to about 1,000 micrometers, preferably from 20 to 500 micrometers. While the term “composite hollow fiber membrane” is a singular tense noun, those of ordinary skill in the art will readily recognize that such a term as used in the art encompasses a plurality of composite hollow fibers assembled into a single mass. Such artisans will further readily recognize that, for bore-fed membranes, the totality of each of the bores of the hollow composite fibers constitutes the first side of the membrane (in the case of bore-fed membranes) and the totality of each of the outer surfaces of the hollow composite fibers constitutes the second side of the membrane. Such artisans will readily recognize that the opposite is equally true for shell-fed membranes. In the membrane of the invention, the membrane typically includes from 100 to 1,000,000 hollow fibers, more typically from 100 to 500,000 hollow fibers constructed into module. Also, the dissolved oxygen-containing liquid hydrocarbon fuel may be at least partially deoxygenated by more than one membrane. For that matter, it may be at least partially deoxygenated by two or more membranes arranged in parallel or in series.
The composite hollow fiber membrane preferably exhibits an oxygen permeance between 30 GPU and 5000 GPU, more preferably between 100 GPU and 2000 GPU. The permeance or the flow flux of the gas component through the membrane is expressed as 1 gas permeation unit (GPU)=10−6 cm3(S.T.P)/(s·cm2·cm Hg), and it is derived by the following equation:
J=the volume flux of a component (cm3(S.T.P)/cm2·s);
P*=membrane permeability that measures the ability of the membrane to permeate gas (cm3(S.T.P)·cm/(s·cm2·cm Hg));=membrane permeance (cm3(S.T.P.)/(s·cm2·cm Hg))*;
δ=the membrane thickness (cm);
x=the mole fraction of the gas in the feed stream;
y=the mole fraction of the gas in the permeate stream;
Pf=the feed-side pressure (cm Hg);
Pρ=the permeate-side pressure (cm Hg).
Additional details regarding methods of calculating the permeance can be found in “Technical and Economic Assessment of Membrane-based Systems for Capturing CO2 from Coal-fired Power Plants” by Zhai, et al. in Presentation to the 2011 AIChE Spring Meeting, Chicago, Ill.
The hydrocarbons in the liquid hydrocarbon have a greater than zero permeance across the membrane. In order to limit the loss of these hydrocarbons due to permeation across the membrane along with the dissolved oxygen, the amorphous perflouro polymer or blend of such polymers is utilized because permeation of the hydrocarbons is greatly inhibited. The liquid hydrocarbon fuel often contains a blend of many hydrocarbons of different chain lengths, especially as seen in the description of jet fuel above. Because of this, it is impractical to characterize the permeation of each of these separate molecules across the membrane. Propane is a heavy hydrocarbon with a relatively high vapor pressure in comparison to the hydrocarbon components in the liquid hydrocarbon fuel. Those of ordinary skill in the art will recognize that the permeance of propane can be conveniently measured in the lab with much high accuracy. Therefore, propane is a good surrogate for assessing the degree to which the hydrocarbons permeate across the membrane and whether the membrane exhibits a satisfactorily low permeance of such hydrocarbons. While the membrane typically has a room temperature oxygen permeance of 30-5000 GPU (and a minimum permeance of at least 70 GPU, typically at least 100 GPU, and more typically at least 130 GPU), in order to limit the hydrocarbon loss through simultaneous permeation, the membrane should have a room temperature propane permeance lower than 15 GPU, and more typically lower than 10 GPU, or even lower than 8 GPU. A desired propane permeance may be achieved by varying the thickness of the thin layer of amorphous perfluoro polymer.
The perfluoro polymer layer can be applied to PAEK porous substrate by methods known in the art such as solution based coating, such as that disclosed in U.S. Pat. No. 6,540,813. As shown in
While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.
The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.
“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of “comprising.” “Comprising” is defined herein as necessarily encompassing the more limited transitional terms “consisting essentially of” and “consisting of”; “comprising” may therefore be replaced by “consisting essentially of” or “consisting of” and remain within the expressly defined scope of “comprising”.
“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.
Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.
Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.
This application claims the benefit of U.S. Provisional Application No. 62/784,410, filed Dec. 22, 2018.
| Number | Date | Country | |
|---|---|---|---|
| 62784410 | Dec 2018 | US |
