Patent Publication Number: US-7900453-B1

Title: Metal fuel combustion and energy conversion system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is continuation in part to related to U.S. nonprovisional patent application Ser. No. 11/272,424 filing date Nov. 8, 2005, now U.S. Pat. No. 7,430,866 hereby incorporated herein by reference, entitled “Air-Independent Fuel Combustion Energy Conversion,” joint inventors William A. Lynch and Neal A. Sondergaard. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     The following description was made in the performance of official duties by employees of the Department of the Navy, and, thus the claimed invention may be manufactured, used, licensed by or for the United States Government for governmental purposes without the payment of any royalties thereon. 
    
    
     TECHNICAL FIELD 
     The following description relates generally to a method and apparatus for providing energy conversion, more particularly, to a combustion system that utilizes the burning of a solid metal fuel to produce energy, such as electrical or mechanical energy, which may be used to drive a water vessel such as a submarine. 
     BACKGROUND 
     Combustion systems may be used to generate energy to propel commercial and military sea vessels. In combustion systems, fuels typically react with oxidants, such as oxygen or fluorine. When oxygen is utilized as the oxidant, the oxygen is typically obtained from atmospheric air. In combustion systems for subsurface vehicles such as submarines, it would be advantageous to utilize air-independent oxidation sources. 
     Combustion byproducts discharged from the combustion systems typically include carbon dioxide (CO 2 ) and other chemicals. These common combustion byproducts are readily detectable thereby making vehicles utilizing these combustion systems detectable as well. This is particularly undesired in military vehicles, such as submarines wherein the detection of the vessel may compromise the health and safety of its occupants. 
     Solid light-weight fuels such as aluminum and magnesium powder mixtures may be employed in combustion systems. The aluminum type fuel mixture advantageously provides an excellent energy density as a result of the combustion. However, its associated combustion discharge byproduct forms a slag responsible for agglomerating and clogging problems with respect to the exhaust port of the combustor. The magnesium type of fuel mixture is advantageously more readily combustible under a lower boiling point than the aluminum type, but provides for a significantly lower energy density. It is desired to have a combustion system that is designed to utilize a combination of aluminum and magnesium that provides the advantages associated with aluminum and magnesium fuel mixtures while avoiding the latter referred to problems associated therewith. Also, it is desired that the combustion system has the ability to be air-independent. Additionally, it is desired to have a combustion system that produces a byproduct having a non-detectable signature. 
     SUMMARY 
     In one aspect, the invention is a metal fuel combustion system having a metal fuel mixture, an oxidant, and a water source. The system further includes a combustion device for combusting the metal fuel mixture, the combustion device having an inner chamber and an outer chamber. In this aspect, the invention also has at least one fluid inlet attached to the outer chamber for directing water from the water source into the outer chamber, and at least one oxidant inlet attached to the inner chamber for directing the oxidant into the inner chamber. In this aspect, the system further includes at least one fuel feeder having the metal fuel mixture, the fuel feeder feeding the metal fuel mixture into the inner chamber of the combustion device. Additionally, the system includes at least one first outlet attached to the outer chamber for discharging steam, and at least one second outlet attached to the inner chamber for discharging hydrogen and steam. A byproduct collector is also included, the byproduct collector having a processing device for processing the byproduct. 
     In another aspect, the invention is a combustion arrangement for processing a metal fuel mixture. The combustion arrangement includes a combustor having an inner chamber and an outer chamber, the inner chamber inside the outer chamber. In this aspect, the arrangement also has a fluid inlet attached to the outer chamber for directing water from the water source into the outer chamber, and an oxidant inlet attached to the inner chamber for directing one or more oxidants into the inner chamber. The combustion arrangement also has a fuel feeder for feeding the metal fuel mixture, the fuel feeder feeding the metal fuel mixture into the inner chamber of the combustion device. A first outlet attached to the outer chamber for discharging steam is also included, and a second outlet attached to the inner chamber for discharging hydrogen and steam. In this aspect, the invention further includes a byproduct collector, the byproduct collector having a processing device for processing the byproduct. 
     In yet another aspect, the invention is an energy conversion and storage method. The method is directed towards a combustion arrangement comprising a combustor having an inner chamber and an outer chamber, the inner chamber inside the outer chamber, a turbine communicating with the outer chamber, and a byproduct collector attached to the inner chamber. In this aspect, the energy conversion and storage method includes the feeding of liquid water into the outer chamber of the combustor and the feeding of a metal fuel into the inner chamber of the combustor, the metal fuel comprising silicon, magnesium, and aluminum. The method further includes the feeding of an oxidant into the inner chamber of the combustor, the burning of the metal fuel creating steam in the outer chamber and creating hydrogen, steam, and metal oxide byproducts in the inner chamber, and the directing of the steam from the outer chamber into the turbine. Additionally, the method includes the expelling of the hydrogen byproduct from the inner chamber, and the depositing of the metal oxide byproduct from the inner chamber into the byproduct collector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features will be apparent from the description, the drawings, and the claims. 
         FIG. 1  is a perspective view of a combustion system according to an embodiment of the invention; 
         FIG. 2  is a perspective view taken substantially through a plane indicated by section line  2 - 2  in  FIG. 1 , illustrating an exemplary arrangement for a combustion device; 
         FIG. 3  is a perspective view of a combustion system according to an embodiment of the invention; and 
         FIG. 4  is a flow chart of an energy conversion and storage method according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of a combustion system  100  according to an embodiment of the invention. The combustion system  100  may be employed in water vessels, such as ships or submarines.  FIG. 1  shows a combustion device  101  for burning a lightweight metal fuel mixture. The combustion device  101  includes an outer chamber  105  surrounding an inner chamber  110 . The outer chamber having an outer shell wall  106  and the inner chamber having an inner shell wall  111 . The combustion system  100  includes a first inlet  115  that is connected to the outer chamber  105  for directing liquid water into the outer chamber. The water may be obtained from a water source  107 . The water source may contain purified and de-ionized sea-water. The combustion system  100  also includes second and third inlets  118  and  120 . 
     As shown in  FIG. 1 , inlet  118  extends through the outer chamber  105  and extends into the inner chamber  110 . Inlet  118  is used to direct an oxidant into the inner chamber. The oxidant used is preferably water, but may also be other known oxidants such as liquid oxygen, chlorine or other halides. When water is used as the oxidant, the water may be fed from the water source  107  to the inlet  118 . The water source  107  may have different connectors for feeding water to the inlets  105  and  118 . These connectors may also include pumps and valves for varying the pressure of the water fed to the inlets  105  and  118 . 
       FIG. 1  also shows the inlet  120  extending through the outer chamber  105  and into the inner chamber  110 . The inlet  120  is used to feed the lightweight metal fuel mixture  122  into the inner chamber  110 . The fuel mixture  122  comprises magnesium, aluminum, and silicon. The fuel  122  is preferably a pre cordierite alloy with a net composition such as Mg 2 Al 4 Si 5 . This metal fuel mixture  122  has a significantly lower melting point than any of the pure oxides. The metal fuel mixture  122  may comprise for example, a wire made up of a thin walled aluminum tube containing a mixture of silicon, magnesium and possibly aluminum in its core. A sample may be made by drawing molten magnalium under inert atmospheric conditions into an aluminum tube containing silicon powder under a vacuum. In production, the metal fuel mixture  122  may be made by drawing through dies and winding on a large take up spool.  FIG. 1  illustrates a fuel feeding device  125 , which may be a servo driven feeding spool from which the fuel may be fed into the inlet  120  and subsequently into the combustor device  101 . Alternatively, the metal fuel mixture  122  may be prepared as pellets, powder, or as a liquid. The pellets could be similar to the fuel wire in composition and structure. Depending on the type of fuel mixture, i.e., pellets, powder, or liquid, other fuel feeding devices may be employed. 
     The combustion system  100  further includes a first outlet, an exhaust steam line  130 , extending from the outer chamber  105 . The exhaust steam line  130  is connected to a turbine  135 , the steam line  130  directing steam from the outer chamber  105  to the turbine  135 . The turbine  135  includes a turbine exhaust  143  that extends to a condenser  145 , the condenser for converting the steam into liquid water, which may be redirected to the water source  107 . The turbine  135  may be used to convert the energy produced by the combustion device  101  into mechanical and electrical energy or a combination thereof. 
     The combustion system  100  further includes a byproduct exhaust funnel  150  for channeling the combustion byproduct into a byproduct collector  155 . Combustion temperatures may be manipulated to produce a solid or a liquid byproduct. A byproduct processor  160  may be attached to the byproduct collector  155 , the processor for processing the byproduct. As shown in  FIG. 1 , the system  100  also includes a second outlet  170  for discharging hydrogen and steam from the inner chamber  110 . 
     In operation, the combustion system  100  may be used to provide energy to water vessels, including submarines and the like. The system may operate as follows. Liquid water is fed into the outer chamber  101  of the combustion device via inlet  105 . The water may be supplied by the water source  107 . Liquid water is fed into the inner combustion chamber  110  via the inlet  118 . This water may also be supplied by the water source  107 . Metal fuel mixture  122 , is fed into the inner combustion chamber by feeder  125 . In one embodiment, the metal fuel mixture may be wrapped around the reel of a servo driven spool, which feeds the fuel into the inner combustion chamber  110 , via inlet  120 . The fuel is burnt in the water. As outlined above, the metal fuel mixture is preferably Mg 2 Al 4 Si 5 . When Mg 2 Al 4 Si 5  is used as the fuel, the combustion byproduct is the eutectic cordierite oxide, Mg 2 Al 4 Si 5 O 18 , which passes through funnel  150 , into the byproduct collector  155 . The inner chamber may be coated with an inner lining material such as rhenium, to prevent damage from the high temperatures associated with combustion. 
     According to an embodiment, the Mg 2 Al 4 Si 5  burns at a lower temperature than individual components magnesium aluminum, and silicon, and the byproduct is more readily gathered in the collector  155 . The combustion byproduct, mineral cordierite, has a lower melting point of 1467° C. compared with 1713° C., 2054° C., and 2826° C. for silicon, aluminum, and magnesium respectively. The combustion temperature may be manipulated to enable the collecting of the byproduct as a liquid rather than a solid, thereby avoiding the undesired slag agglomeration that occurs at higher melting points. The liquid byproduct is processed in the processor  160 , which may include a spray nozzle, to solidify the Mg 2 Al 4 Si 5 O 18  byproduct. The byproduct could be solidified as droplets or pellets. These could be crushed into a sand-like substance, which is similar in composition to basalt oceanic crust. The composition and appearance of the byproduct is advantageous because its emission should not produce a detectable signature or have an adverse environmental impact. 
     The burning of the metal fuel mixture also produces gaseous hydrogen and steam, which is directed out of the inner chamber  110  via exhaust  170 . A separating device such as a steam trap may be used to separate the water vapor from the hydrogen. The hydrogen may be stored for subsequent use, and the water may be recycled to the water source  107  for repeated use in the system  100 . 
     The heat created by the reaction in the inner chamber  110  turns the liquid water in the outer chamber  105  into steam. This steam exits the out chamber  110  via the first outlet, exhaust steam line  130 . The steam is fed to the turbine  140 , which converts the thermal energy from the steam into mechanical energy. The mechanical energy may drive one or more propellers of the water vessel. Alternatively, a generator may be used to convert the mechanical energy from the turbine, into electrical energy. This electrical energy may be used to drive the water vessel, or may be stored in a storage device. 
     It should be noted that although  FIG. 1  illustrates only three inlets and two outlets, the combustion system  100  may include as many inlets and outlets as desired. For example, the system  100  may include multiple inlets for feeding fuels, multiple inlets for feeding oxidant, and multiple inlets for feeding steam. Similarly, the system may have a plurality of outlets for disbursing the hydrogen and steam from the inner chamber, and/or multiple outlets for discharging the steam from the outer chamber. 
       FIG. 2  is a perspective view taken substantially through a plane indicated by section line  2 - 2  in  FIG. 1 , showing an arrangement  200  for the combustion device  101 , according to an embodiment of the invention. The arrangement  200  provides additional means for producing energy in a combustion system. In operation, the arrangement  200  may be used to provide energy to water vessels, including submarines and the like, by utilizing the heat and luminous/radiant energy produced in the combustion chamber. 
       FIG. 2  shows the combustion device  101  having the outer shell wall  106  and the inner shell wall  111 . As shown in  FIG. 2 , the outer shell wall  106  is internally coated with an electrically insulating protective lining  205 , such as silicon rubber. A protective lining such as silicon rubber prevents corrosion caused by the high pressure hot temperature steam conditions within the outer chamber. A plurality of photovoltaic materials  210  having photovoltaic cells are internally mounted on the protective lining  205 . The arrangement  200  may include one or more layers of photovoltaic materials on the lining  205 . The lining  205  may also serve as an adhesive for attachment of the photovoltaic materials  210 . The photovoltaic cells convert radiant energy produced by the combustion chamber, directly into electrical energy, which may be delivered for use outside of the arrangement  200 . 
     As shown in  FIG. 2 , the inner shell wall  111  comprises a double wall structure comprising single walls  212  and  215 , with the wall  212  defining the outer boundary of the inner chamber.  FIG. 2  further shows a plurality of thermoelectric materials  220  having thermoelectric cells sandwiched between the combustor shell  212  and  215 . The arrangement  200  may include one or more layers of thermoelectric materials between the walls  212  and  215 . The thermoelectric cells are provided to convert some of the combustion heat directly into electrical energy. The electrical energy may be delivered for use outside of the arrangement  200 . The wall  212  may be composed of a refractory material such as rhenium which has the ability to act as shield, which protects the cells and wall  215  from excessive heat imposed by direct contact with the flame or from abrasive damage associated with the combustion products. 
       FIG. 3  is a perspective view of a combustion system  300  according to an embodiment of the invention. As shown,  FIG. 3  includes the general system of  FIG. 1 , i.e., a combustion system having a combustion device  101  with outer and inner chambers,  105  and  110  respectively. The combustion system  300  of  FIG. 3  also includes the outlet  170  for expelling hydrogen and steam, two of the byproducts of the combustion of Mg 2 Al 4 Si 5  in water. As illustrated, the outlet leads to a separation device  310 , such as a steam trap, which separates the steam from the hydrogen. The steam is preferably separated as liquid water, which may be fed back to the water source  107  for reuse. The separated hydrogen may be fed into a fuel cell  330 . Prior to being fed into the fuel cell, the hydrogen may be temporarily stored in a hydrogen storage device  320 . 
     The fuel cell  330  may be a hydrogen-oxygen fuel cell, which requires a liquid oxygen source  335 . The source  335  may also be compressed oxygen gas. Perchlorates such as lithium perchlorate may be utilized to provide oxygen. The fuel cell  330  produces electric energy with water as a byproduct, via an electrochemical energy conversion process. As shown in  FIG. 3 , the water byproduct from the fuel cell may be directed to the water source  107 . Because the hydrogen fuel for the fuel cell may be stored in a storage device  320 , the fuel cell  330  may be operated independent of the combustion device  101 , and may be used according to energy demands. 
     The arrangement  300  may also include an energy storage device  340  for storing energy produced from combustion. The energy storage device  340  may store electrical energy produced by the fuel cell  330  and/or the turbine  135 . In situations where the combustion arrangement  200  is utilized, the storage device  340  may also store electrical energy produced by the photovoltaic and the thermoelectric cells. The energy storage device may comprise lithium ion cells, or the like, and may be a single device, or it may comprise a plurality of different electrical energy storage devices. The arrangement  300  may also include one or more pumps  350 , for regulating the flow of water from elements  145 ,  310 , and  330 , back to the water source  107 . 
       FIG. 4  is a flow chart of an energy conversion and storage method  400  according to an embodiment of the invention. The method  400  is directed towards combustion systems and arrangements similar to those illustrated in  FIGS. 1-3 . For example, the method may be directed to a combustion system having a combustion device  101  with an inner chamber  110  and an outer chamber  105  as shown in  FIG. 1 . Additionally, the system may include a turbine  135  communicating with the outer chamber  105 , and a byproduct collector  155  attached to the inner chamber. The method  400  comprises step  410 , the feeding of liquid water into the outer chamber of the combustor. This process has been outlined in the description of the embodiments of  FIGS. 1 and 3 , wherein liquid water is fed into the outer chamber via an inlet. 
     Step  420  is the feeding of a metal fuel into the inner chamber of the combustor, the metal fuel comprising magnesium, aluminum, and silicon. Again, this process has been outlined in the description of the embodiments of  FIGS. 1 and 3 . As outlined above, the metal fuel may be fed into the inner chamber via a servo drive spool. Step  430  is the feeding of an oxidant into the inner chamber of the combustor. The oxidant is preferably water fed via an inlet, as illustrated in  FIGS. 1-3 . It should be noted that steps  410 ,  420 , and  430  may be performed in any preferred order, and may not be performed in the order illustrated in  FIG. 4 . 
     Step  440  is the burning of the metal fuel in the inner chamber of the combustor. The burning produces heat which energizes the transformation of liquid water into steam in the outer chamber. Additionally, the reaction in the inner chamber creates hydrogen, steam, and metal oxide as byproducts in the inner chamber. At step  450 , the steam from the outer chamber is directed into the turbine, as shown in  FIGS. 1 and 2 . At step  460 , the hydrogen byproduct is expelled from the inner chamber via an outlet. As shown in  FIG. 3 , the hydrogen may be stored and/or directed into a fuel cell for producing more energy. Step  470  is the depositing of the metal oxide byproduct from the inner chamber into the byproduct collector. 
     A number of exemplary implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example, suitable results may be achieved if the steps of described techniques are performed in a different order and/or if components in a described component, system, architecture, or devices are combined in a different manner and/or replaced or supplemented by other components. Accordingly, other implementations are within the scope of the following claims.