Abstract:
A fuel stabilization system includes a first deoxygenator and a second deoxygenator both for removing dissolved oxygen from a hydrocarbon fuel. The first and second deoxygenators are arranged in parallel or series to sequentially remove a portion of dissolved oxygen from the hydrocarbon fuel. The arrangement of several deoxygenators for a single fuel stream improves removal of dissolved oxygen and provides for scalability of the fuel system to meet application specific demands. The arrangement also provides for the preservation of partial system functionality in the event of the failure of one of the deoxygenator modules.

Description:
BACKGROUND OF THE INVENTION 
     This invention generally relates to a fuel stabilization system for an energy conversion device, and more particularly to a fuel stabilization system including several fuel deoxygenators for removing dissolved oxygen from a fuel. 
     Hydrocarbon fuels typically include some amount of dissolved oxygen due to exposure to air during transport or storage. Dissolved oxygen within the fuel limits the temperature to which the fuel may be heated due to 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. Reducing the amount of dissolved oxygen within the fuel decreases the rate of coke deposition and increases the maximum sustainable temperature of the fuel. 
     U.S. Pat. Nos. 6,315,815, and 6,709,432 assigned to Applicant, discloses devices for removing dissolved oxygen using a selective 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. 
     The more dissolved oxygen that can be removed from the fuel, the greater the fuel temperature before coke deposits form, thereby increasing the practical temperatures to which fuel can be heated prior for combustion to improve operating efficiencies. Disadvantageously, the size of a fuel deoxygenator increases proportionably with the requirements for removing oxygen. An increase in oxygen removal from 90% to 99% may require nearly a doubling of deoxygenator size. Further, as operational requirements change, so may the required oxygen removal rate. A single fuel deoxygenator may not adjust readily or be scalable to accommodate variations in oxygen removal requirements. 
     Accordingly, it is desirable to develop a fuel stabilization system that removes dissolved oxygen to allow increased fuel temperatures, and that is scaleable to accommodate changing oxygen removal requirements. 
     SUMMARY OF THE INVENTION 
     An example fuel stabilization system according to this invention includes several fuel deoxygenators operating in concert to remove dissolved oxygen from a hydrocarbon fuel. 
     An example fuel stabilization system according to this invention includes a plurality of fuel deoxygenating devices that are arranged in parallel. Hydrocarbon fuel flows in substantially equal portions through each of the plurality of fuel deoxygenating devices. Each of the fuel deoxygenating devices removes a portion of dissolved oxygen from the hydrocarbon fuel, which then exits the fuel stabilization system with a substantially increased temperature capacity. 
     Another example fuel stabilization system according to this invention includes a plurality of fuel deoxygenators arranged in series. Each of the fuel deoxygenators removes progressively additional amounts of dissolved oxygen. An initial fuel deoxygenator operates at a temperature well below that at which coke and other insoluble byproducts are formed. A second fuel deoxygenator operates at an elevated temperature due to the initial removal of some portion of dissolved oxygen from the fuel. Several fuel deoxygenators in series remove additional amounts of dissolved oxygen and can operate at increasingly elevated temperature that provide increased oxygen removal efficiencies. 
     The modular approach to using a plurality of fuel deoxygenating devices instead of merely using one deoxygenating device provides many advantages. Those advantages include the ability to troubleshoot and replace a specific deoxygenator that may not be operating as desired. Further, the use of fuel deoxygenating devices in series or parallel allows for each device to be operated at different temperatures and thereby provide the hydrocarbon fuel with different usable cooling capacities that can be tailored to specific systems requirements. Finally, spreading the deoxygenation function among several independent fuel stabilization modules may also provide an advantage relative to overall system reliability and functionality, as the failure of one unit would not represent a complete loss of deoxygenation functionality but rather would only impact a portion of the overall system capability. 
     Accordingly, the fuel stabilization system according to this invention increases and optimizes the efficiency of dissolved oxygen removal from a fuel providing significant system benefits. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an example fuel stabilization system according to this invention. 
         FIG. 2  is a schematic illustration of another example fuel stabilization system according to this invention. 
         FIG. 3  is a schematic illustration of yet another example fuel stabilization system according to this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , a fuel stabilization system  10  is schematically illustrated and includes a fuel tank  12  or other fuel source that provides fuel by way of a fuel pump  14  to an engine  15 . A fuel stabilization assembly  16  removes dissolved oxygen from within the fuel. The fuel stabilization assembly  16  includes a plurality of deoxygenators  18 , 20 , 22 , 24 , 26 . The example fuel stabilization assembly  16  includes five deoxygenators  18 ,  20 ,  22 ,  24  and  26 , arranged in a parallel configuration. 
     The parallel configuration provides a substantially uniform pressure drop across the fuel stabilization assembly  16 . Each of the fuel deoxygenators  18 ,  20 ,  22 ,  24  and  26 , provides an identical or very similar drop in fuel pressure. In some instances a single large deoxygenator can cause an undesirable drop in fuel pressure that is compensated for by other system devices such as the pump  14 . However, the use of the plurality of parallel configured deoxygenators  18 ,  20 ,  22 ,  24  and  26  may reduce requirements for adapting to pressure drops as compared to the use of a single larger fuel deoxygenator without sacrificing the amount of dissolved oxygen removes from the fuel. 
     Each of the fuel deoxygenators  18 ,  20 ,  22 ,  24  and  26 , removes a portion of dissolved oxygen from the fuel and exhausts the removed oxygen overboard as is indicated at  30 . The temperature of incoming fuel is within desirable limits that do not encourage the generation of insoluble materials in the presence of dissolved oxygen. Fuel leaving the fuel stabilization assembly  16  includes a reduced amount of dissolved oxygen and therefore can be heated to increased temperatures. A heat transfer device  32  provides for the transfer and heating of the fuel. The heat transfer device  32  may be of any configuration known to a worker skilled in the art. Increased temperature capability of the fuel provides for increased engine efficiencies. The increased temperature capacity of the fuel can thereby be utilized as a heat sink to absorb heat from other systems. Further, increasing the temperature of the fuel can improve combustion by speeding vaporization of the fuel. 
     Referring to  FIG. 2  another example fuel stabilization system according to this invention is generally indicated at  40  and includes a fuel stabilization assembly  45  having a plurality of deoxygenating devices  44 ,  46 ,  48 ,  50 , arranged in series. The series arrangement provides for a sequential and proportional removal of dissolved oxygen from the fuel. A first portion  41  of dissolved oxygen is removed from the hydrocarbon fuel in the first deoxygenator  44 . A second portion  43  is then removed by the second deoxygenator  46 , a third portion  47  removed by the third deoxygenator  48 , and a forth portion  49  is removed by the fourth deoxygenator  50 . The subsequent removal of additional amounts of dissolved oxygen from the hydrocarbon fuel provides for the use of deoxygenators of differing sizes and capacities along with operating each deoxygenator  44 ,  46 ,  48  and  50  at different temperatures to optimize the removal of dissolved oxygen. 
     A hydrocarbon fuel  28  entering the first deoxygenator  44  must be at a temperature below that temperature that may cause an undesirable formation of insoluble materials. However, subsequent deoxygenators such as the second deoxygenator  46  can operate at temperatures above that temperature at which the first deoxygenator  44  must operate due to the removal of the first portion  41  of dissolved oxygen. Accordingly, subsequently aligned fuel deoxygenators can operate at progressively greater and greater temperatures due to the ever decreasing amount of dissolved oxygen contained within the hydrocarbon fuel removed by a previous deoxygenator. 
     Hydrocarbon fuel exiting the fuel stabilization assembly  45  is then introduced into the heat transfer device  32 . As appreciated, the heat transfer device  32  can be of any configuration known to a worker skilled in this art. Further, the heat transfer device  32  may transfer heat from another system requiring cooling to utilize the increased cooling capacity of the hydrocarbon fuel. Additionally, the heat transfer device  32  may heat the fuel to a level to aid vaporization and thereby combustion of the hydrocarbon fuel once it reaches the combustion device disposed within the engine  15 . 
     Referring to  FIG. 3 , another example fuel stabilization system  60  includes a first deoxygenator  64  and a second deoxygenator  68 . The first deoxygenator  64  operates to remove a first portion of dissolved oxygen  65  from the hydrocarbon fuel  28 . The modular approach of configuring the first deoxygenator  64  and the second deoxygenator  68  provides for the utilization of different size deoxygenators. Varying the size and performance of cascaded deoxygenators between a low temperature operational device and a high temperature device provides packaging and operational benefits. Increasing the fuel temperature entering a deoxygenator increases its performance due to enhanced oxygen diffusivity and solubility at higher temperature. 
     The modular approach of this invention can capture the benefit of fuel heating optimally, since for a single deoxygenator the inlet temperature is for example limited to a range of between 250° F. and 325° F. Accordingly, the modular configuration of the fuel stabilization system  60  provides that each successive deoxygenator may have an ever increasing inlet temperature due to the level of deoxygenation that is being accomplished at the previous deoxygenator. 
     In  FIG. 3  the fuel  28  leaves the pump  14  at a first temperature  72 . Once the fuel  28  exits the first heat transfer device  62 , it is at a temperature  74 . The temperature  74  must be within a limited temperature range that does not cause the formation of an unmanageable amount of insoluble materials due to coking. At this point, the temperature  74  must be maintained within a level that accommodates the increased level of oxygen within the hydrocarbon fuel. After the fuel has flowed through the first deoxygenator  64  and the first portion of oxygen  65  has been removed, the temperature can be raised to a temperature indicated at  76  that is higher that the temperature  74 . 
     The hydrocarbon fuel  28  temperature can then further be raised within a second heat transfer device  66  to a fourth temperature  78  that is higher than the fuel temperature of the fuel  28  that first entered the first deoxygenator  64 . The second deoxygenator  68  removes a second portion of oxygen  69  and operates at a higher temperature than the first deoxygenator  64  because of the decreased amount of dissolved oxygen that had been previously removed by the first deoxygenator  64 . The fuel exiting the second deoxygenator  68  is at a temperature  80  that can again be further elevated in temperature to a final temperature  82 . 
     The hydrocarbon fuel temperature is elevated from the temperature  80  to the temperature  82  by a third heat transfer device  70 . Although, two deoxygenators  64 ,  68  are shown in series, additional fuel deoxygenators and heat transfer devices can be arranged to optimally and successively provide for increased fuel temperatures of the hydrocarbon fuel due to the successive decrease in dissolved oxygen within that hydrocarbon fuel. 
     The example fuel stabilization systems of this invention provide deoxygenation of hydrocarbon fuel using a variety of configurations including series and parallel orientations of a plurality of fuel deoxygenators to lower the dissolved oxygen content within a hydrocarbon fuel. The lowering of dissolved oxygen within the hydrocarbon fuel enables fuel temperatures to reach as high as between 800° F. and 900° F. This increases the heat sink capacity of the fuel, which in turn can provide improved system and engine efficiencies. 
     Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.