Patent Publication Number: US-2005137441-A1

Title: Multi-stage fuel deoxygenator

Description:
BACKGROUND OF THE INVENTION  
      This invention generally relates to a fuel delivery system for an energy conversion device, and specifically to a fuel delivery system including a fuel deoxygenator and an oxygen scavenger module for removing dissolved oxygen to increase the usable cooling capability of a fuel.  
      A gas turbine engine is an energy conversion device typically used in aircraft and in power generation applications. A gas turbine engine typically includes a compressor, a combustor and a turbine. Air entering the compressor is compressed and directed toward a combustor. Fuel is combined with the high-pressure air and ignited. Combustion gases produced in the combustor drive the turbine.  
      It is common practice to use fuel as a cooling medium for various systems onboard an aircraft. The usable cooling capacity of a particular fuel is limited by the formation of insoluble products referred to as “coke”. The formation of coke deposits is dependent on the amount of dissolved oxygen present within the fuel due to prior exposure to air. Reducing the amount of oxygen dissolved within the fuel decreases the rate of coke deposition and increases the maximum allowable temperature.  
      U.S. Pat. Nos. 6,315,815, and ______ assigned to Applicant, disclose devices for removing dissolved oxygen using a gas-permeable membrane disposed within the fuel system. As fuel passes along the permeable membrane, oxygen molecules in the fuel diffuse out of the fuel across the gas-permeable membrane. An oxygen partial pressure differential across the permeable membrane drives oxygen from the fuel, which is unaffected and passes over the membrane.  
      Another fuel deoxygenating device utilizes a catalytic material exposed to fuel flow. The catalytic material initiates reactions with components of the fuel to prevent dissolved oxygen from combining with other elements within the fuel and form coke-producing products. The catalytic material causes formation of components less likely to form coke-precursors within the fuel delivery system.  
      It is also known to remove dissolved oxygen from fuels with the use of oxygen scavengers. Oxygen scavengers are inorganic materials for removing dissolved oxygen. Oxygen scavengers are mostly inert materials that are non-toxic, non-flammable and easily regenerated. However, the quantity of oxygen scavenging material required for fuel de-oxygenation aboard an aircraft is impractical.  
      The more dissolved air that can be removed from the fuel the greater the fuel temperature before coke deposits form, and the greater usable cooling capacity available. Disadvantageously, the size of a fuel deoxygenator increases disproportionably with the requirements for removing oxygen. An increase in oxygen removal from 90% to 99% requires nearly a doubling of deoxygenator size. As appreciated, space aboard an aircraft is limited and any increase in device size affects overall configuration and operation.  
      Accordingly, it is desirable to develop a fuel delivery system for a gas turbine engine that removes dissolved oxygen for increasing the usable cooling capability of a fuel without requiring substantial amounts of additional space.  
     SUMMARY OF INVENTION  
      This invention is a fuel delivery system for an energy conversion device including a fuel deoxygenator and an oxygen scavenger module for removing dissolved oxygen and increasing the usable cooling capability of a fuel.  
      The fuel delivery system of this invention includes a fuel deoxygenator and an oxygen scavenger module. Fuel flowing though the fuel delivery system flows through the fuel-deoxygenating device. The fuel-deoxygenating device removes a first portion of oxygen from the fuel. Fuel emerging from the fuel-deoxygenating device flows into the oxygen-scavenging module where a second portion, smaller than the first portion of oxygen is removed from the fuel.  
      Fuel emerging from the oxygen scavenger is substantially free of any dissolved oxygen. The substantially oxygen free fuel is flowed through a heat exchanger for absorbing heat from another system. The removal of dissolved oxygen increases the exploitable cooling capacity of the fuel. This provides for increased engine temperature that in turn increases overall engine efficiency.  
      The combination of the oxygen scavenger and the fuel deoxygenator provides for an increase in removal of dissolved oxygen relative to the use of either device alone. The size of a fuel deoxygenator or oxygen scavenger module capable of removing the proportion of dissolved air removed by the combination is not optimal. The combination provides the desired increase in deoxygenation of fuel without the corresponding increase in device size.  
      Accordingly, the fuel delivery system of this invention provides for the removal of increased amounts of dissolved oxygen, resulting in increased usable cooling capability of fuel without requiring substantial amounts of additional space. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:  
       FIG. 1  is a schematic view of an energy conversion assembly and fuel delivery system according to this invention;  
       FIG. 2  is a schematic view of a fuel deoxygenator according to this invention;  
       FIG. 3  is a schematic view of another fuel deoxygenator according to this invention;  
       FIG. 4  is a cross-sectional view of a permeable membrane according to this invention;  
       FIG. 5  is a schematic view of another fuel deoxygenator according to this invention including catalytic material; and  
       FIG. 6 , is a schematic view of an oxygen-scavenging module according to this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Referring to  FIG. 1 , a gas turbine engine assembly  10  includes a compressor  12 , a combustor  14  and a turbine  16 . Airflow  18  entering the compressor  12  is compressed to a high pressure and directed towards the combustor  14 . In the combustor  14 , fuel is mixed with the high-pressure air and ignited. Resulting hot combustion gases  15  exhausted from the engine  10  drive the turbine  16 . Fuel is delivered to the combustor  14  through a fuel delivery system  20 . Although a gas turbine engine  10  is shown, other energy conversion assemblies known to a worker skilled in the art would benefit from application of this invention. The fuel delivery system  20  of this invention includes a fuel deoxygenator  22  and an oxygen scavenger module  24 .  
      The fuel system  20  also includes a heat exchanger  26  for rejecting heat from other systems, schematically shown at  32  to fuel  28 . The other system can include cooling of cooling air or other fluids circulated through the engine  10 . The specific cooling requirement dictates the configuration of the heat exchanger  26 . A worker skilled in the art with the benefit of this disclosure would understand how to configure the heat exchanger  26  and fuel system  20  to utilize the increased cooling capacity of fuel provided by this invention.  
      Referring to  FIG. 2 , a fuel deoxygenating device  22 ′ according to this invention includes a housing  40  defining a fuel inlet  46  and outlet  48 . A plurality of fuel plates  42  are stacked within the housing  40  to define fuel passages  44 . The fuel plates  42  include a composite permeable membrane  73 . A vacuum outlet  50  is in communication with the fuel plates  42  and a vacuum source  82 . Fuel containing dissolved oxygen enters the inlet  46  and flows through the fuel passages  44 . Oxygen within the fuel diffuses through the composite permeable membrane  73  under the driving force of an oxygen partial pressure differential created by the vacuum  82 . Oxygen  52  removed from the fuel flow is exhausted and flows out the vacuum outlet  50 .  
      Referring to  FIG. 3 , another fuel deoxygenating device  22 ″ according to this invention includes a housing  60  defining a fuel inlet  68  and a fuel outlet  70 . A plurality of tubular members  62  are arranged within the housing  60  and provide passages  64  for a strip gas  80 . Fuel entering the housing  60  flows over and around the tubular members  62 . Each tubular member  62  includes the composite permeable membrane  73  that draws oxygen from the fuel and into the passages  64 . The strip gas  80  flows through the passages  64  to create an oxygen partial pressure differential across the permeable membrane  73 . The partial pressure differential drives the oxygen from the fuel and through the permeable membrane  73 . The removed oxygen is then exhausted from the device  22 ″ and removed from the strip gas.  
      Referring to  FIG. 4 , the composite permeable membrane  73  is shown in cross-section and preferably includes a permeable layer  74  disposed over a porous backing  72 . The porous backing  72  supplies the required support structure for the permeable layer  74  while still allowing maximum oxygen diffusion from fuel. The permeable layer  74  is coated on to the porous backing  72  and a mechanical bond between the two is formed. The permeable layer  74  is preferably a 0.5-20 μm thick coating of Teflon AF  2400  over a 0.005-in thick porous backing  72  of polyvinylidene fluoride (PVDF) with a 0.25 μm pores size. Other supports of different material, thickness and pore size can be used that provide the requisite strength and openness. Preferably the permeable layer  74  is Dupont Telfon AF Amorphous Fluoropolymer, however other materials known to workers skilled in the art are within the contemplation of this invention, such as Solvay Hyflon AD perfluorinated glassy polymer and Asahi Glass CYTOP polyperfluorobutenyl vinyl ether. Each composite permeable membrane  73  is supported on a porous substrate  76 . The porous substrate  76  is in communication with the vacuum source  82  to create an oxygen partial pressure differential across the composite permeable membrane  73 .  
      In operation a partial pressure differential is created by the vacuum source  82  between a non-fuel side  75  of the permeable membrane  73  and a fuel side  77 . Oxygen indicated at arrows  80  diffuses from fuel  28  across the composite permeable membrane  73  and into the porous substrate  76 . From the porous substrate  76  the oxygen  80  is pulled and vented out of the fuel system.  
      Referring to  FIG. 5 , another fuel deoxygenator  22 ′″ according to this invention is schematically shown and includes a catalytic material  84  supported on a support structure  86  within the flow of fuel  28 . The catalytic material  84  promotes reactions with components within the fuel that are less likely to form coke-producing products. The catalytic material  84  can be a metal such as copper, nickel, chromium, platinum, molybdenum, rhodium, iridium, ruthenium, palladium, and any combination of these materials. Further, the catalytic material  36  may also be a zeolite. A worker having the benefit of this disclosure would understand the specific composition of catalyst required to consume dissolved oxygen without forming coke precursors.  
      Preferably, the catalytic material  84  is supported on a honeycomb structure  86  disposed within the fuel deoxygenator  22 ′″. However, the catalytic material may be supported on granules, extrudates, monoliths, or other known catalyst support structures.  
      Although embodiments of fuel deoxygenators  22  are shown and described, a worker skilled in the art with the benefit of this application would understand that other configurations of fuel deoxygenators are within the contemplation of this invention.  
      The size of the fuel-deoxygenating device  22  is dependent on the amount of oxygen removal required. The size of the fuel-deoxygenating device  22  increases disproportionately with increases in oxygen removal demands. For example, increasing the percent removal of oxygen from 90% to 99% would require substantially a doubling in size of the fuel-deoxygenating device  22 . This is so because as oxygen is removed from the fuel, the oxygen pressure differential decreases exponentially. This decrease in available oxygen pressure differential reduces the amount of oxygen that can be removed with the fuel deoxygenator  22 .  
      The fuel delivery system of this invention combines the fuel deoxygenator  22  with the oxygen scavenger module  24 . The oxygen scavenger module  24  is disposed within the fuel flow  28  after the fuel deoxygenator  22  to remove remaining oxygen within the fuel.  
      Referring to  FIG. 6 , the oxygen scavenger module  24  includes a housing  23  that receives a module  27  containing an oxygen absorbent material  25 . Oxygen absorbent materials are known for use in removing oxygen from solutions and containers. Oxygen absorbent material removes oxygen by initiating reactions with oxygen present to form inert products. The oxygen absorbent material  25  may be of any type known to a worker skilled in the art. For example, oxygen-scavenging polymers in the form of bead material, or salts bonded to a support structure disposed within the fuel stream. A worker with the benefit of this disclosure would understand that the selection of oxygen scavenging material is application dependent and the use of any known oxygen scavenging materials are within the contemplation of this invention.  
      Oxygen absorbent materials are typically inert, non-toxic, non-flammable and regenerable. The disadvantage being that large quantities are required for the removing oxygen in sufficient quantities from fuel to prevent undesirable coking. The oxygen-scavenging module  24  is therefore placed after the fuel-deoxygenating device  22  to remove only a portion of oxygen from the fuel.  
      Preferably, the oxygen-scavenging module  24  includes a sufficient amount of oxygen absorbent material to remove approximately 10% of oxygen contained with fuel. The fuel-deoxygenating device  22  is configured to remove approximately 90% of the dissolved oxygen. Accordingly, the amount of oxygen absorbent material  25  required is small enough to be practically installed within the module  27  that can be replaced after a desired duration of operation. For example, removing 10% of the dissolved oxygen from a fuel system flowing 1000 gallons/hour must absorb approximately 425 grams of oxygen every 20 hours. 10 kilograms of oxygen absorbent material would be required to remove the desired amount of oxygen. As appreciated, this is an example and a worker with the benefit of this disclosure would understand how to determine the amount of sorbent material required for a specific application.  
      Referring to  FIG. 1 , in operation, fuel flowing though the fuel delivery system  20  flows through the fuel-deoxygenating device  22 . The fuel-deoxygenating device  22  includes a partial oxygen pressure differential across the permeable membrane  73  ( FIG. 4 ) that draws out a first portion of oxygen  80  from the fuel  28 . Fuel emerging from the fuel-oxygenating device  22  flows into the oxygen-scavenging module  24  where a second portion, smaller than the first portion of oxygen is removed from the fuel  28 . Fuel emerging from the oxygen scavenger  24  can then be routed through a heat exchanger  26  or other heat transfer device to absorb heat. The removal of dissolved oxygen from the fuel increases the exploitable cooling capacity of the fuel. This provides for increased engine temperatures that in turn increase overall efficiency of operating the engine.  
      The foregoing description is exemplary and not just a material specification. The invention has been described in an illustrative manner, and should be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications are within the scope of this invention. It is understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.