Patent Publication Number: US-11658320-B2

Title: Fuel cell system containing water injector and method of operating the same

Description:
FIELD 
     Aspects of the present invention relate to fuel cell systems and methods, and more particularly, to fuel cell systems including a water injector configured to inject water into an anode exhaust recycle stream. 
     BACKGROUND 
     Fuel cells, such as solid oxide fuel cells, are electrochemical devices which can convert energy stored in fuels to electrical energy with high efficiencies. High temperature fuel cells include solid oxide and molten carbonate fuel cells. These fuel cells may operate using hydrogen and/or hydrocarbon fuels. There are classes of fuel cells, such as the solid oxide regenerative fuel cells, that also allow reversed operation, such that oxidized fuel can be reduced back to unoxidized fuel using electrical energy as an input. 
     SUMMARY 
     According to various embodiments, a fuel cell system comprises a fuel cell stack, an anode exhaust conduit configured to receive an anode exhaust from the stack, and a water injector configured to inject water into the anode exhaust in the anode exhaust conduit. 
     According to various embodiments, a method of operating a fuel cell system comprises providing at least a portion of an anode exhaust from a fuel cell stack to a water injector, supplying water to the water injector, and injecting the water from the water injector into the at least the portion of the anode exhaust to vaporize the water and generate a humidified anode exhaust. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate example embodiments of the invention, and together with the general description given above and the detailed description given below, serve to explain the features of the invention. 
         FIG.  1    is a schematic of a fuel cell system, according to various embodiments of the present disclosure. 
         FIG.  2 A  is a sectional view showing components of the hot box of the system of  FIG.  1   ,  FIG.  2 B  shows an enlarged portion of the system of  FIG.  2 A ,  FIG.  2 C  is a three dimensional cut-away view of a central column of the system of  FIG.  2 A , and  FIG.  2 D  is a perspective view of an anode hub structure disposed below the central column of the system of  FIG.  2 A , according to various embodiments of the present disclosure. 
         FIGS.  3 A- 3 C  are sectional views showing fuel and air flow through the central column of the system of  FIG.  2 A , according to various embodiments of the present disclosure. 
         FIG.  4 A  is a partial perspective view of a water injector disposed in the central column of the system of  FIG.  2 A ,  FIG.  4 B  is a top view of components of the water injector of  FIG.  4 A , and  FIG.  4 C  is a perspective view of the water injector, according to various embodiments of the present disclosure. 
         FIG.  5    is a side cross-sectional view showing an alternative embodiment of the components of the hot box of the system of  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION 
     The various embodiments will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. References made to particular examples and implementations are for illustrative purposes, and are not intended to limit the scope of the invention or the claims. 
     In a solid oxide fuel cell (SOFC) system, a fuel inlet stream may be humidified in order to facilitate fuel reformation reactions such as steam reformation and water-gas shift reactions. In addition, during system startup, shutdown, and power grid interruption events, water may be added to a fuel inlet stream in order to prevent coking of system components such as catalysts. Conventionally, such humidification is performed by vaporizing water in a steam generator containing corrugated tubing. Water flows through the corrugated tubing and is heated by the cathode recuperator heat exchanger exhaust stream which flows around the outside of the tubing. However, utilizing relatively low-temperature cathode recuperator exhaust stream generally requires substantial lengths of corrugated tubing, in order to absorb enough heat to vaporize the water. Further, the steam generator is relative large and bulky, which also adds to the system size, complexity and manufacturing costs. 
     In contrast, embodiments of the present disclosure provide a water injector configured to inject water directly into the anode exhaust recycle stream which provides heat to vaporize the water into steam and/or aerosolize the water into droplets small enough to be entrained in the anode exhaust stream. The anode exhaust recycle stream is recycled into the fuel inlet stream provided into the fuel cell stack, such that humidified fuel is provided to the fuel cells of the fuel cell stack. Thus, the prior art steam generator may be omitted to reduce system size, complexity and cost. In addition, the embodiment system may operate using relatively short, non-corrugated water conduit, which may improve system response times and reduce system size and cost. 
       FIG.  1    is a schematic representation of a SOFC system  10 , according to various embodiments of the present disclosure. Referring to  FIG.  1   , the system  10  includes a hotbox  100  and various components disposed therein or adjacent thereto. The hot box  100  may contain fuel cell stacks  102 , such as a solid oxide fuel cell stacks containing alternating fuel cells and interconnects. One solid oxide fuel cell of the stack contains a ceramic electrolyte, such as yttria stabilized zirconia (YSZ), scandia stabilized zirconia (SSZ), scandia and ceria stabilized zirconia or scandia, yttria and ceria stabilized zirconia, an anode electrode, such as a nickel-YSZ, a nickel-SSZ or nickel-doped ceria cermet, and a cathode electrode, such as lanthanum strontium manganite (LSM). The interconnects may be metal alloy interconnects, such as chromium-iron alloy interconnects. The stacks  102  may be arranged over each other in a plurality of columns. 
     The hot box  100  may also contain an anode recuperator heat exchanger  110 , a cathode recuperator heat exchanger  120 , an anode tail gas oxidizer (ATO)  130 , an anode exhaust cooler heat exchanger  140 , a splitter  510 , a vortex generator  550 , and a water injector  160 . The system  10  may also include a catalytic partial oxidation (CPOx) reactor  200 , a mixer  210 , a CPOx blower  204  (e.g., air blower), a system blower  208  (e.g., air blower), and an anode recycle blower  212 , which may be disposed outside of the hotbox  100 . However, the present disclosure is not limited to any particular location for each of the components with respect to the hotbox  100 . 
     The CPOx reactor  200  receives a fuel inlet stream from a fuel inlet  300 , through fuel conduit  300 A. The fuel inlet  300  may be a fuel tank or a utility natural gas line including a valve to control an amount of fuel provided to the CPOx reactor  200 . The CPOx blower  204  may provide air to the CPOx reactor  202  during system start-up. The fuel and/or air may be provided to the mixer  210  by fuel conduit  300 B. Fuel (e.g., the fuel inlet stream  1721  described below with respect to  FIGS.  4 A- 4 C ) flows from the mixer  210  to the anode recuperator  110  through fuel conduit  300 C. The fuel is heated in the anode recuperator  110  by a portion of the fuel exhaust and the fuel then flows from the anode recuperator  110  to the stack  102  through fuel conduit  300 D. 
     The main air blower  208  may be configured to provide an air stream (e.g., air inlet stream) to the anode exhaust cooler  140  through air conduit  302 A. Air flows from the anode exhaust cooler  140  to the cathode recuperator  120  through air conduit  302 B. The air is heated by the ATO exhaust in the cathode recuperator  120 . The air flows from the cathode recuperator  120  to the stack  102  through air conduit  302 C. 
     An anode exhaust stream (e.g., the fuel exhaust stream described below with respect to  FIGS.  3 A- 3 C ) generated in the stack  102  is provided to the anode recuperator  110  through anode exhaust conduit  308 A. The anode exhaust may contain unreacted fuel and may also be referred to herein as fuel exhaust. The anode exhaust may be provided from the anode recuperator  110  to the splitter  510  by anode exhaust conduit  308 B. A first portion of the anode exhaust may be provided from the splitter  510  to the anode exhaust cooler  140  through the water injector  160  and the anode exhaust conduit  308 C. A second portion of the anode exhaust is provided from the splitter  510  to the ATO  130  through the anode exhaust conduit  308 D. The first portion of the anode exhaust heats the air inlet stream in the anode exhaust cooler  140  and may then be provided from the anode exhaust cooler  140  to the mixer  210  through the anode exhaust conduit  308 E. The anode recycle blower  212  may be configured to move anode exhaust though anode exhaust conduit  308 E, as discussed below. 
     Cathode exhaust generated in the stack  102  flows to the ATO  130  through exhaust conduit  304 A. The vortex generator  550  may be disposed in exhaust conduit  304 A and may be configured to swirl the cathode exhaust. The anode exhaust conduit  308 D may be fluidly connected to the vortex generator  550  or to the cathode exhaust conduit  304 A or the ATO  130  downstream of the vortex generator  550 . The swirled cathode exhaust may mix with the second portion of the anode exhaust provided by the splitter  510  before being provided to the ATO  130 . The mixture may be oxidized in the ATO  130  to generate an ATO exhaust. The ATO exhaust flows from the ATO  130  to the cathode recuperator  120  through exhaust conduit  304 B. Exhaust flows from the cathode recuperator and out of the hotbox  100  through exhaust conduit  304 C. 
     Water flows from a water source  206 , such as a water tank or a water pipe, to the water injector  160  through water conduit  306 . The water injector  160  injects water directly into first portion of the anode exhaust provided in conduit  308 C. Heat from the first portion of the anode exhaust (also referred to as a recycled anode exhaust stream) provided in exhaust conduit  308 C vaporizes the water to generate steam. The steam mixes with the anode exhaust, and the resultant mixture is provided to the anode exhaust cooler  140 . The mixture is then provided from the anode exhaust cooler  140  to the mixer  210  through the anode exhaust conduit  308 E. The mixer  210  is configured to mix the steam and first portion of the anode exhaust with fresh fuel (i.e., fuel inlet stream). This humidified fuel mixture may then be heated in the anode recuperator  110  by the anode exhaust, before being provided to the stack  102 . The system  10  may also include one or more fuel reforming catalysts  112 ,  114 , and  116  located inside and/or downstream of the anode recuperator  100 . The reforming catalyst(s) reform the humidified fuel mixture before it is provided to the stack  102 . 
     The system  10  may further a system controller  225  configured to control various elements of the system  10 . The controller  225  may include a central processing unit configured to execute stored instructions. For example, the controller  225  may be configured to control fuel and/or air flow through the system  10 , according to fuel composition data. 
       FIG.  2 A  is a sectional view showing components of the hot box  100  of the system  10  of  FIG.  1   , and  FIG.  2 B  shows an enlarged portion of  FIG.  2 A .  FIG.  2 C  is a three dimensional cut-away view of a central column  400  of the system  10 , according to various embodiments of the present disclosure, and  FIG.  2 D  is a perspective view of an anode hub structure  600  disposed in a hot box base  101  on which the column  400  may be disposed. 
     Referring to  FIGS.  2 A- 2 D , the fuel cell stacks  102  may be disposed around the central column  400  in the hot box  100 . For example, the stacks  102  may be disposed in a ring configuration around the central column  400  and may be positioned on the hot box base  101 . The column  400  may include the anode recuperator  110 , the ATO  130 , and the anode exhaust cooler  140 . In particular, the anode recuperator  110  is disposed radially inward of the ATO  130 , and the anode exhaust cooler  140  is mounted over the anode recuperator  110  and the ATO  130 . In one embodiment, an oxidation catalyst  112  and/or the hydrogenation catalyst  114  may be located in the anode recuperator  110 . A reforming catalyst  116  may also be located at the bottom of the anode recuperator  110  as a steam methane reformation (SMR) insert. 
     The ATO  130  comprises an outer cylinder  130 A that is positioned around inner ATO insulation  130 B/outer wall of the anode recuperator  110 . Optionally, the insulation  130 B may be enclosed by an inner ATO cylinder  130 C. Thus, the insulation  130 B may be located between the anode recuperator  110  and the ATO  130 . An ATO oxidation catalyst may be located in the space between the outer cylinder  130 A and the ATO insulation  130 B. A fuel inlet path bellows  854  may be located between the anode exhaust cooler  140  and the inner ATO cylinder  130 C. An ATO thermocouple feed through  1601  extends through the anode exhaust cooler  140 , to the top of the ATO  130 . The temperature of the ATO  130  may thereby be monitored by inserting one or more thermocouples (not shown) through this feed through  1601 . 
     The anode hub structure  600  may be positioned under the anode recuperator  110  and ATO  130  and over the hot box base  101 . The anode hub structure  600  is covered by an ATO skirt  1603 . The vortex generator  550  and fuel exhaust splitter  510  are located over the anode recuperator  110  and ATO  130  and below the anode exhaust cooler  140 . An ATO glow plug  1602 , which initiates the oxidation of the stack fuel exhaust in the ATO during startup, may be located near the bottom of the ATO  130 . 
     The anode hub structure  600  is used to distribute fuel evenly from the central column to fuel cell stacks  102  disposed around the central column  400 . The anode flow hub structure  600  includes a grooved cast base  602  and a “spider” hub of fuel inlet conduits  300 D and outlet conduits  308 A. Each pair of conduits  300 D,  308 A connects to a fuel cell stack  102 . Anode side cylinders (e.g., anode recuperator  110  inner and outer cylinders and ATO outer cylinder  130 A) are then welded or brazed into the grooves in the base  602 , creating a uniform volume cross section for flow distribution as discussed below. 
     A lift base  1604  is located under the hot box base  101 , as illustrated in  FIG.  2 C . In an embodiment, the lift base  1604  includes two hollow arms with which the forks of a fork lift can be inserted to lift and move the system, such as to remove the system from a cabinet (not shown) for repair or servicing. 
     As shown by the arrows in  FIGS.  2 A and  2 B , air enters the top of the hot box  100  and then flows into the cathode recuperator  120  where it is heated by ATO exhaust (not shown) from the ATO  130 . The heated air then flows inside the cathode recuperator  120  through a first vent or opening  121 . The air then flows through the stacks  102  and reacts with fuel (i.e., fuel inlet stream) provided from the anode hub structure  600 . Air exhaust flows from the stacks  102 , through a second vent or opening  123 . The air exhaust then passes through vanes of the vortex generator  550  and is swirled before entering the ATO  130 . 
     The splitter  510  may direct the second portion of the fuel exhaust exiting the top of the anode recuperator  100  through openings (e.g., slits) in the splitter into the swirled air exhaust (e.g., in the vortex generator  550  or downstream of the vortex generator in conduit  304 A or in the ATO  130 ). At such the fuel and air exhaust may be mixed before entering the ATO  130 . 
       FIGS.  3 A and  3 B  are side cross-sectional views showing flow distribution through the central column  400 , and  3 C is top cross-sectional view taken through the anode recuperator  110 . Referring to  FIGS.  2 A,  2 B,  3 A, and  3 C , the anode recuperator  110  includes an inner cylinder  110 A, a corrugated plate  110 B, and an outer cylinder  110 C that may be coated with the ATO insulation  130 B. Fuel from fuel conduit  300 C enters the top of the central column  400 . The fuel then bypasses the anode exhaust cooler  140  by flowing through its hollow core and then flows through the anode recuperator  110 , between the outer cylinder  110 C and the and the corrugated plate  110 B. The fuel then flows through the hub base  602  and conduits  300 D of the anode hub structure  600  shown in  FIG.  3 B , to the stacks  102 . 
     Referring to  FIGS.  2 A,  2 B,  2 C,  3 A, and  3 B , the fuel exhaust flows from the stacks  102  through conduits  308 A into the hub base  602 , and from the hub base  602  through the anode recuperator  110 , between in inner cylinder  110 A and the corrugated plate  110 B, and through conduit  308 B into the splitter  510 . The first portion of the fuel exhaust flows from the splitter  510  to the anode exhaust cooler  140  through conduit  308 C, while the second portion flows from the splitter  510  to the ATO  130  through conduit  308 D, as shown in FIG.  1 . Anode exhaust cooler inner core insulation  140 A may be located between the fuel conduit  300 C and bellows  852 /supporting cylinder  852 A located between the anode exhaust cooler  140  and the vortex generator  550 , as shown in  FIG.  3 A . This insulation minimizes heat transfer and loss from the first portion of the anode exhaust stream in conduit  308 C on the way to the anode exhaust cooler  140 . Insulation  140 A may also be located between conduit  300 C and the anode exhaust cooler  140  to avoid heat transfer between the fuel inlet stream in conduit  300 C and the streams in the anode exhaust cooler  140 . In other embodiments, insulation  140 A may be omitted from inside the cylindrical anode exhaust cooler  140 . 
       FIG.  3 B  also shows air flowing from the air conduit  302 A to the anode exhaust cooler  140  (where it is heated by the first portion of the anode exhaust) and then from the anode exhaust cooler  140  through conduit  302 B to the cathode recuperator  120 . The first portion of the anode exhaust is cooled in the anode exhaust cooler  140  by the air flowing through the anode exhaust cooler  140 . The cooled first portion of the anode exhaust is then provided from the anode exhaust cooler  140  to the anode recycle blower  212  shown in  FIG.  1   . 
     As will be described in more detail below and as shown in  FIGS.  2 A and  3 B , the anode exhaust exits the anode recuperator  110  and is provided into splitter  510  through conduit  308 B. The splitter  510  splits the anode exhaust into first and second anode exhaust portions (i.e., streams). The first stream is provided into the anode exhaust cooler  140  through conduit  308 C. The second stream is provided to the ATO  130  through conduit  308 D. 
     The relative amounts of anode exhaust provided to the ATO  130  and the anode exhaust cooler  140  is controlled by the anode recycle blower  212 . The higher the blower  212  speed, the larger portion of the anode exhaust is provided into conduit  308 C and a smaller portion of the anode exhaust is provided to the ATO  130  via conduit  308 D, and vice-versa. 
     The anode exhaust provided to the ATO  130  is not cooled in the anode exhaust cooler  140 . This allows higher temperature anode exhaust to be provided into the ATO  130  than if the anode exhaust were provided after flowing through the anode exhaust cooler  140 . For example, the anode exhaust provided into the ATO  130  from the splitter  510  may have a temperature of above 350° C., such as from about 350 to about 500° C., for example, from about 375 to about 425° C., or from about 390 to about 410° C. Furthermore, since a smaller amount of anode exhaust is provided into the anode exhaust cooler  140  (e.g., not 100% of the anode exhaust is provided into the anode exhaust cooler due to the splitting of the anode exhaust in splitter  510 ), the heat exchange area of the anode exhaust cooler  140  may be reduced. The anode exhaust provided to the ATO  130  may be oxidized by the stack cathode (i.e., air) exhaust and provided to the cathode recuperator  120  through conduit  304 B. 
       FIG.  4 A  is a sectional perspective view showing the water injector  160  in the central column of  FIG.  2 A ,  FIG.  4 B  is a top view showing an injector ring  162  and a baffle  168  of  FIG.  4 A , and  FIG.  4 C  is a perspective view of the water injector  160 , according to various embodiments of the present disclosure according to various embodiments of the present disclosure. In the embodiment of  FIG.  4 A , the splitter  510  may comprise tubes that extend through the outer wall of the anode exhaust conduit  308 B rather than horizontal slits shown in  FIG.  3 A . It should be understood that either the tube or slit type of splitter  510  may be used with the water injector  160  of the present embodiment. Referring to  FIGS.  1 ,  4 A,  4 B and  4 C , the water injector  160  may include the injector ring  162 , restraint tabs  164 , a shroud  166 , and the baffle  168 . 
     The injector ring  162  may be disposed inside the anode exhaust conduit  308 C between the anode exhaust cooler  140  and the anode recuperator  110  and may be fluidly connected to the water conduit  306 . The injector ring  162  is a tube that extends around the fuel conduit  300 C. The injector ring  162  may include injection apertures (i.e., openings)  162 A configured to inject water directly into the first portion of the anode exhaust flowing in the conduit  308 C from the splitter  510  and anode recuperator  110 . The water may be vaporized by the hot first portion of the anode exhaust. The injection apertures  162 A may be configured to generate streams or droplets of water, which may be vaporized instantaneously or within seconds of emerging from the injector ring  162 . The injection apertures  162 A may be located on any one or more surfaces of the injector ring  162 , such as the upper surface of the injector ring  162  (as shown in  FIG.  4 A ), the inner surface of the injector ring  162  (as shown in  FIG.  4 C ), the lower surface of the injector ring  162  and/or the outer surface of the injector ring  162 . For example, as shown in the embodiment of  FIG.  4 A , the injection apertures  162 A may be evenly distributed on an upper surface of the injector ring  162  to provide uniform water upward into the anode exhaust to decrease the amount of water dripping down toward the splitter  510 . The injector ring  162  may also be sized to provide substantially uniform circumferential flow of water therein and to minimize a pressure drop in the anode exhaust flowing thereby. 
     The restraint tabs  164  may be attached to the fuel conduit  300 C and/or the shroud  166  and may be configured to support the injector ring  162 . In particular, the restraint tabs  164  may be configured to align and control the orientation of the injector ring  162  and prevent uneven water distribution or buildup thereon. For example, the restraint tabs  164  may be configured to horizontally align the injector ring  162 . The restraint tabs  164  may also prevent water from accumulating on the injector ring  162  in any particular location. As such, the restraint tabs  164  may be configured to prevent water from accumulating on the outer surface of the injector ring  162  and dripping in only one location, which may be especially important if the injector ring  162  is not perfectly level. 
     The shroud  166  may be a cylinder which surrounds the injector ring  162 . The shroud  166  may be configured to segregate the water from the second portion of the anode exhaust flowing into the ATO  130  through the splitter  510 . In particular, the second portion of the anode exhaust flowing outside of the shroud  166  may be directed by the splitter  510  radially outward toward the anode exhaust conduit  308 D and the ATO  130 , while the first portion of the anode exhaust flowing inside of the shroud  166  is directed upward by the splitter  510  toward the injector ring  162  in the anode exhaust conduit  308 C. Accordingly, the shroud  166  may be configured to prevent or reduce the amount of water and/or the first portion of the anode exhaust that has been humidified by the injected water from being injected into the ATO  130  by the splitter  510 . In other words, the shroud  166  is configured such that substantially all of the water and the humidified first portion of the anode exhaust are directed towards the anode exhaust cooler  140 . 
     The baffle  168  may be disposed inside the anode exhaust conduit  308 C below the injector ring  162  and around the fuel conduit  300 C. The baffle  168  may include a baffle ring  168 A and baffle tabs  168 B that extend therefrom. The baffle tabs  168 B may contact the fuel conduit  300 C and the shroud  166  and may operate to keep both the shroud  166  and the baffle ring  168 A aligned around the fuel conduit  300 C within the central column  400 . In particular, the baffle ring  168 A may be aligned to vertically overlap with (e.g., be concentric with) the injector ring  162 , as shown in  FIG.  4 B . 
     Therefore, the baffle  168  may operate as a surface to catch and vaporize water droplets that do not instantaneously transform into steam and drip from the injector ring  162 . Accordingly, the baffle  168  also protects brazed joints of the anode recuperator  110  that located below the injector ring  162  from contact with water droplets and the corresponding thermal shock. 
     In various embodiments, the water injector  160  may optionally include a mesh  169  or porous material disposed below the baffle  168 . The mesh  169  may be configured to capture any droplets that drip from the injector ring  162  and bypass the baffle  168 , such that the captured droplets are vaporized before reaching the anode recuperator  110  and/or the splitter  510 . 
       FIG.  5    illustrates an alternative configuration of hot box  100  components of the fuel cell system  10 . As illustrated in  FIG.  5   , the central column  400  includes the slit type splitter  510  described above with respect to  FIG.  3 A  instead of the tube type splitter  510  described above with respect to  FIG.  4 A . Furthermore, the water injector  160  of  FIG.  5 A  includes injection apertures  162 A on the inner surface of the injector ring  162 . Finally, the catalysts  112 ,  114  and  116  of  FIG.  5    are located inside the inner plenum which is surrounded by the anode recuperator  110 , similar to the configuration described in U.S. Pat. No. 9,287,572 B2, issued Mar. 15, 2016 and incorporated herein by reference in its entirety. Other components shown in  FIG.  5    are the same as or similar to those shown in  FIG.  4 A  and will not be described further to avoid redundancy. Any one or more components from the central column shown in  FIG.  5    may be used in the central column shown in  FIG.  4 A . 
     Furthermore, while the water injectors  160  shown in  FIGS.  4 A to  4 C and  5    include an injector ring  162  with injection apertures  162 A, other water injector configurations may be used instead. For example, the water may be injected into the first portion of the anode exhaust directly from the water conduit  306  without using the injector ring  162 . Alternatively, water may be injected from plural tubes arranged in any suitable configuration in the exhaust conduit  308 C. The tubes may be fluidly connected to the water conduit  306 . Furthermore, one or more of the shroud  166 , the baffle  168  and/or mesh  169  may be omitted. 
     During operation of the fuel cell system  10 , such as during system startup, water is generally not required until the stack  102  reaches a temperature of about 300° C. or more, such as a temperature ranging from about 300° C. to about 325° C. Once the stack  102  approaches about 300° C., water is provided from the water source  206  to water conduit  306  at the top of the central column  400 . The water conduit  306  passes through the insulation  140 A that that is located between and separates the fuel conduit  300 C from the anode exhaust cooler  140 . The insulation reduces the amount of heat exchange between the water in the water conduit  306  and the anode exhaust cooler  140 . Accordingly, while passing through water conduit  306 , the water may be slightly heated above ambient temperature by anode exhaust in the surrounding toroidal anode cooler  140 . However, while not wishing to be bound by a particular theory, it is believed that at least the majority of the water remains in a liquid state while in the water conduit  306 . 
     The water is then provided by the water conduit  306  to the water injector  160 . For example, the water is provided by the water conduit into the injector ring  162 . The water flows circumferentially in the injector ring  162  and is circumferentially dispersed before being ejected into the first portion of the anode exhaust through the injection apertures  162 A. In one embodiment, at least a portion of the water is injected in the liquid state into the first portion of the anode exhaust stream. The water is then vaporized in the first portion of the anode exhaust to form a humidified anode exhaust. The humidified anode exhaust is then provided through conduit  308 E to the mixer  210  for mixing with fresh fuel (i.e., fuel inlet stream) before being provided to the anode recuperator  110  and the stack  102  as discussed above. 
     Referring to all drawings described above, the fuel cell system  10  includes the fuel cell stack  102 , the anode exhaust conduit  308 C configured to receive an anode exhaust from the stack  102 , and the water injector  160  configured to inject water into the anode exhaust in the anode exhaust conduit  308 C. 
     In one embodiment, the system  10  also includes the anode recuperator  110  located below the water injector  160  and configured to receive the anode exhaust from the stack  102 , to heat fuel provided to the stack  102  using heat from the anode exhaust and to provide the anode exhaust to the anode exhaust conduit  308 C and the water injector  160 . The system  10  also includes the anode exhaust cooler  140  disposed above the water injector  160  and the anode recuperator  110  and configured to heat air provided to the stack  102  using the anode exhaust provided from the water injector and the anode recuperator. 
     In one embodiment, the system  10  also includes a water conduit  306  extending through the anode cooler insulation  140 A surrounded by the anode exhaust cooler  140  and configured to provide the water to the water injector  160 . In one embodiment, the system  10  does not include a steam generator, and the water injector  160  includes the injector ring  162  disposed between the anode exhaust cooler  140  and the anode recuperator  110 . The injector ring  162  is fluidly connected to the water conduit  306 , and the injector ring  162  is configured to inject the water into the anode exhaust which flows in the anode exhaust conduit  308 C from the anode recuperator  110  to the anode exhaust cooler  140 . The injector ring  162  comprises injection apertures  162 A in a surface thereof and configured to inject the water into the anode exhaust. 
     In one embodiment, the system  10  also includes a fuel conduit  300 C surrounded by the anode cooler insulation  140 A and the anode exhaust conduit  308 C. The fuel conduit extends  300 C through the middle of the injector ring  162  and is configured to provide the fuel to the stack  102  through the anode recuperator  110 . 
     In one embodiment, the water injector  160  further comprises a shroud  166  surrounding the injector ring  162 . In one embodiment, the water injector  160  further comprises restraint tabs  164  connected to the fuel conduit  300 C and to the shroud  166 . The restraint tabs  164  are configured to support the injector ring  162  such that the injector ring is disposed in a substantially horizontal plane. In one embodiment, water injector  160  further comprises a mesh or a porous material  169  disposed below the injector ring  162  and configured to reduce or prevent water from dripping onto the anode recuperator  110 . 
     In one embodiment, the water injector  160  further comprises a baffle  168  disposed below the injector ring  162 . The baffle  168  comprises a baffle ring  168 A disposed around the fuel conduit  300 C and vertically overlapped with the injector ring  162 , and baffle tabs  168 B extending from the baffle ring  168 A and configured to align the baffle ring  168 A such that the baffle ring is vertically overlapped with injector ring  162 . 
     In one embodiment, the system  10  also includes an anode tail gas oxidizer  130 , and a splitter  510  configured to direct a first portion of the anode exhaust provided from the anode recuperator  110  into the anode exhaust conduit  308 C and the water injector  160 , and to direct a second portion of the anode exhaust provided from the anode recuperator  110  into the anode tail gas oxidizer  130 . An anode recycle blower is configured to recycle the first portion of the anode exhaust into the fuel conduit  300 C. The shroud  166  is configured to direct the water away from the splitter  510 . 
     A method of operating a fuel cell system comprises providing at least a portion of an anode exhaust from the fuel cell stack  102  to the water injector  160 , supplying water to the water injector  160 , and injecting the water from the water injector  160  into the at least the portion of the anode exhaust to vaporize the water and generate a humidified anode exhaust. 
     In one embodiment, supplying water to the water injector comprises supplying the water in a liquid state to the water injector  160  after the stack  102  reaches a temperature of about 300° C. or more. In one embodiment, the method also includes providing the anode exhaust from the stack  102  to an anode recuperator  110  to heat a fuel inlet stream flowing to the stack  102 , splitting the anode exhaust provided from the anode recuperator into a first portion of the anode exhaust and a second portion of the anode exhaust and providing the first portion of the anode exhaust into the water injector  160 . The water is vaporized completely or vaporized partially and entrained in the first portion of the anode exhaust stream to form the humidified anode exhaust, while the second portion of the anode exhaust is provided into an anode tail gas oxidizer  130 . The method further includes providing the humidified anode exhaust into an anode cooler  140  to heat air flowing to the stack  102 , and providing the humidified anode exhaust from the anode cooler  140  into the fuel inlet stream flowing to the stack  102  through the fuel conduit  300 C. 
     As described above, in one embodiment the water injector  160  comprises an injector ring  162  disposed between the anode exhaust cooler  140  and the anode recuperator  110 . The water flows through water conduit  306  into the injector ring  162 , and the water is injected from the injector ring  162  through apertures  162 A in the injector ring into the first portion of the anode exhaust stream. The fuel inlet stream flows to the stack  102  through the fuel conduit  300 C surrounded by anode cooler insulation  140 A and by the injector ring  162 . The anode cooler  140  surrounds the anode cooler insulation  140 A and the water conduit extends  306  through the anode cooler insulation  140 A. 
     In one embodiment, the water injector  160  further comprises a shroud  166  surrounding the injector ring  162 . The shroud prevents or reduces water flow into the anode tail gas oxidizer  130 . Restraint tabs  164  are connected to the fuel conduit  300 C and to the shroud  166 , and configured to support the injector ring  162  in a substantially horizontal plane. 
     In one embodiment, the water injector further comprises a mesh or a porous material  169  disposed below the injector ring  162 . The mesh or porous material reduces or prevents water from dripping onto the anode recuperator  110 . In one embodiment, the water does not pass through a steam generator between being provided into the system  10  from the water source  206  until it is injected into anode exhaust in the conduit  308 C. 
     Accordingly, various embodiments provide a water injector that is more economical than previous designs that relied upon a steam generator containing water coils in which the water is vaporized. As such, the embodiment water injector also provides a more compact design than previous systems, allowing for improved space efficiency within a system hot box. Further, the embodiment water injector also provides for faster response times, due to having shorter conduit lengths than previous systems. Faster response times may be especially beneficial when responding to power grid interruptions and/or sudden changes to balance of plant loads. 
     The preceding description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.