Patent Publication Number: US-2004043265-A1

Title: Staged fuel cell with intercooling

Description:
BACKGROUND OF TIE INVENTION  
       [0001] The present invention relates generally to a field of fuel cells and more particularly to the field of thermal management of a fuel cell stack or assembly.  
       [0002] In a wide variety of applications, a staged fuel cell stack such as a staged solid oxide fuel cell stack, have demonstrated a potential for high efficiency and low pollution in power generation. However, problems associated with thermal management of the staged fuel cell stacks persist, particularly pertaining to intercooling and preheating of the fluid between a fuel cell stack and an adjacent fuel cell stack. It is desirable that a fluid from an exit of the fuel cell stack of the staged fuel cell assembly undergoes intercooling before entering in the adjacent fuel cell stack of the staged fuel cell assembly. Additionally, the fluid entering the fuel cell stack of the staged fuel cell assembly needs to undergo preheating. Intercooling as well as preheating of the fluid is desirable to ensure uniform thermal potential of the staged fuel cell assembly architecture and provide internal fuel reforming. Accordingly, there is a need in the art to develop an improved thermal management system, which addresses issues pertaining to intercooling and preheating of the fluid handled by the staged fuel cell assembly.  
       SUMMARY  
       [0003] The present invention provides a staged fuel cell assembly comprising a plurality of fuel cells, each fuel cell being in fluid communication with at least one primary fluid delivery system; at least one heat exchanger, each heat exchanger being in fluid communication with the primary fluid delivery system disposed between adjacent fuel cells. The primary fluid delivery system, being in thermal communication with the at least one heat exchanger, delivers a primary fluid to the fuel cells. The present invention provides a method for thermal management of a staged fuel cell assembly. The method comprises delivering the primary fluid to the plurality of fuel cells where each fuel cell is in fluid communication with the at least one primary fluid delivery system.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0004] These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings;  
     [0005]FIG. 1 is an exemplary cross sectional view of a staged fuel cell assembly according to one embodiment of the invention;  
     [0006]FIG. 2 is an exemplary cross sectional view of the staged fuel cell assembly with a secondary fluid delivery system according to another embodiment of the invention;  
     [0007]FIG. 3 is an exemplary cross sectional view of the staged fuel cell assembly with the secondary fluid delivery system and a supplemental fluid delivery system according to another embodiment of the invention;  
     [0008]FIG. 4 is an exemplary cross sectional view of the staged fuel cell assembly with another supplemental fluid delivery system according to another embodiment of the invention;  
     [0009]FIG. 5 is an exemplary cross sectional view of a staged fuel cell assembly with the secondary fluid delivery system and the supplemental fluid delivery system according to another embodiment of the invention;  
     [0010]FIG. 6 is an exemplary cross sectional view of a staged fuel cell assembly with a heat exchanger and the supplemental fluid delivery system according to another embodiment of the invention;  
     [0011]FIG. 7 is an exemplary cross sectional view of a staged fuel cell assembly with the secondary fluid delivery system, the heat exchangers and the supplemental fluid delivery system according to another embodiment of the invention; and  
     [0012]FIG. 8 is an exemplary cross sectional view of a staged fuel cell assembly with a pressure vessel according to another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0013] Referring to FIG. 1, one embodiment of the present invention illustrates a staged fuel cell assembly  1000 , such as a solid oxide fuel cell assembly. The staged fuel cell assembly  1000  comprises a plurality of fuel cells  10  being stacked together either in series or in parallel to construct a fuel cell stack architecture. The plurality of fuel cells  10  is an energy conversion device, which produces electricity, by electrochemically combining a fuel and an oxidant across an ionic conducting layer.  
     [0014] Referring to FIG. 1 and FIG. 2, the fuel cell stack architecture comprises exemplary modular fuel cell stacks  200 ,  210 ,  220 . The staged fuel cell assembly  1000  in FIG. 1 comprises a plurality of fuel cells  10 , each fuel cell  10  being in fluid communication with an at least one primary fluid delivery system  20 ); at least one heat exchanger  30 , each heat exchanger  30  being in fluid communication with the primary fluid delivery system  20  between adjacent fuel cells  10 . The primary fluid delivery system  20  is in thermal communication with the heat exchanger  30  to deliver a primary fluid  50  to the fuel cells  10 .  
     [0015] In one embodiment of the present invention, a secondary fluid delivery system  55  of FIG. 2 delivers a secondary fluid  70  to the heat exchanger  30 . The secondary fluid  70  undergoes thermal exchange with the primary fluid  50 . Referring to embodiments illustrated in FIGS.  3 , and  5   7 , each heat exchanger  30  further comprises a secondary fluid delivery system  55  to deliver a secondary fluid  70  for thermal exchange with the primary fluid  50 . The secondary fluid  70  is selected from the group including, but not limited to fuel, oxidant, steam, and a fuel and steam mixture.  
     [0016] In the present invention, the term temperature conditioning is defined to include intercooling of the primary fluid  50  of FIG. 2 as well preheating of the primary fluid  50 .  
     [0017] Heat transfer between the secondary fluid  70  of FIG. 2 and the primary fluid  50  intercools the primary fluid  50  when the primary fluid  50  enters into an exemplary fuel cell stack  210  from an adjacent fuel cell stack  200 . In addition, thermal exchange of the secondary fluid  70  for example air, with a primary fluid  50  temperature conditions the primary fluid  50  before entering the staged fuel cell assembly  1000  when the primary fluid  50  and the secondary fluid  70  are same. Temperature conditioning the primary fluid  50  facilitates maintaining a desired temperature level of the primary fluid  50  before entering the staged fuel cell assembly  1000 . Intercooling the primary fluid  50  between the adjacent fuel cell stacks, for example between the fuel cell stack  210  and an preceding fuel cell stack  200 , beneficially provides maintaining uniform thermal potential across the staged fuel cell assembly  1000 . Maintaining uniform thermal potential across the staged fuel cell assembly  1000  results in avoiding thermal hot spots at localized regions of the exemplary staged fuel cell assembly  1000 . Additionally, appropriate temperature conditioning of the primary fluid  50  helps maintaining a desired uniform electrochemical reaction rate between the fuel and the oxidant across the exemplary fuel cell sub stacks  200 ,  210 ,  220  of the staged fuel cell assembly  1000 . Uniform electrochemical reaction rate across the exemplary fuel cell sub stacks  200 ,  210 ,  220  beneficially provides steady, time independent, output power characteristics from the staged fuel cell assembly  1000 .  
     [0018] In one embodiment of the present invention, when the primary fluid  50  and the secondary fluid  70  are independent, the degree of temperature conditioning of the primary fluid  50  is controlled by regulating the flow of the secondary fluid  70  to control the thermal exchange between the primary fluid  50  and the secondary fluid  70  in the heat exchanger  30 . In another particular embodiment of the present invention, when the primary fluid  50  and the secondary fluid  70  are independent and the flow rate of the primary fluid  50  is restricted to that required for the staged fuel cell assembly  1000 , the secondary flow  70  is controlled by a variable bypass flow control system (not shown in FIG. 2) to determine the temperature conditioning that occurs in the heat exchanger  30 . In another specific embodiment of the present invention, when the primary fluid  50  and the secondary fluid  70  are the same fluid, then the primary fluid  50  and the secondary fluid  70  are both restricted in series unless there is some type of a bypass means provided to change the mass flow rate in the primary fluid  50  going through the heat exchanger  30 .  
     [0019] Bypass means configurations are well known in the art and hence are not described in detail here. An artisan skilled in the art is left to determine the bypass means necessary to control both the temperature conditioning of the primary fluid  50  and the thermal exchange between the primary fluid  50  and the secondary fluid  70  in the heat exchanger  30 .  
     [0020] Heat exchangers  30  are known and hence are not described in detail herein. According to one exemplary embodiment of the present invention, the heat exchanger  30  comprises at least one heat exchanger  30  of shell and tube configuration. In other embodiment of the present invention, the heat exchanger  30  comprises at least one heat exchanger  30  of plate and fin configuration.  
     [0021] In one exemplary embodiment of the present invention, a secondary fluid flow direction  60  in the secondary fluid delivery system  55  is antiparallel to a primary fluid flow direction  40  in the primary fluid delivery system  20 . In other embodiment of the present invention, the secondary fluid flow direction  60  in the secondary fluid delivery system  55  is parallel to the primary fluid flow direction  40  in the primary fluid delivery system  20  (not shown in FIG. 2). In other embodiment of the present invention, the secondary fluid flow direction  60  in the secondary fluid delivery system  55  is orthogonal to the primary fluid flow direction  40  in the primary fluid delivery system  20  (not shown in FIG. 2). However, an artisan skilled in the art can select an appropriate heat exchanger  30  in accordance with appropriate heat exchangers design options as known in the art. Such appropriate heat exchanger design options pertain to factors such as, geometry of the heat exchanger  30  and fluid flow direction, for example, secondary fluid flow direction  60  relative to the primary fluid flow direction  40  in the heat exchanger  30 . Choosing the appropriate heat exchanger design options for the appropriate heat exchanger  30  depends on optimization of limiting parameters of the heat exchanger  30  such as, thermal efficiency, and overall size.  
     [0022] The fuel cell  10  can be any type of fuel cell, including, but not limited to, a solid oxide fuel cell, a proton exchange membrane fuel cell, a molten carbonate fuel cell, a phosphoric acid fuel cell, an alkaline fuel cell, a direct methanol fuel cell, a regenerative fuel cell, a zinc air fuel cell, and a protonic ceramic fuel cell.  
     [0023] According to one embodiment of the present invention, the plurality of fuel cells  10 , such as solid oxide fuel cells comprises at least one fuel cell  10  having a planar configuration. In other embodiment of the present invention, the plurality of fuel cells  10  comprises at least one fuel cell  10  having a tubular configuration.  
     [0024] According to one exemplary embodiment illustrated in FIG. 3, the primary fluid delivery system  20  is coupled to an at least one supplemental fluid source  110  by an at least one supplemental fluid delivery system  90 . The supplemental fluid source  110  and the supplemental fluid delivery system  90  are configured to deliver a supplemental fluid  100  to the primary fluid delivery system  20 . The supplemental fluid  100  supplied from the supplemental fluid source  110  ensures uninterrupted availability of the staged fuel cell assembly  1000 . Ensuring uninterrupted availability of the staged fuel cell assembly  1000  is critical for uniform output power generation of the staged fuel cell assembly  1000  in response to factors such as fluctuating power demand, and failure of primary fluid delivery system  20 . The supplemental fluid  100  is selected from the group including, but not limited to a fuel, an oxidant, a steam, and a fuel and steam mixture.  
     [0025] In one embodiment, the primary fluid delivery system  20 , the supplemental fluid source  110 , and the supplemental fluid delivery system  90  are configured to deliver the fuel to the fuel cell  10 . In other embodiment, the primary fluid delivery system  20 , the supplemental fluid source  110 , and the supplemental fluid delivery system  90  are configured to deliver the steam to the fuel cell  10 . In another embodiment, the primary fluid delivery system  20 , the supplemental fluid source  110 , and the supplemental fluid delivery system  90  are configured to deliver the oxidant to the fuel cell  10 . Still in another embodiment, the primary fluid delivery system  20 , the supplemental fluid source  110 , and the supplemental fluid delivery system  90  are configured to deliver the fuel and steam mixture to the fuel cell  10 ).  
     [0026]FIGS. 4 through 7 depict exemplary cross sectional views of the staged fuel cell assembly with another primary fluid delivery system  25  configured to deliver another primary fluid to the at least one fuel cell  10 . FIGS. 4 through 7 also depict another supplemental fluid source  115 , and another supplemental fluid delivery system  92  configured to deliver another supplemental fluid to the at least one fuel cell  10 .  
     [0027] According to one exemplary embodiment of the present invention, one primary fluid delivery system  20 , one supplemental fluid source  110 , and one supplemental fluid delivery system  90  are configured to deliver the fuel to the at least one fuel cell  10 , while another primary fluid delivery system  25 , another supplemental fluid source  115 , and another supplemental fluid delivery system  92  are configured to deliver the oxidant to the at least one fuel cell  10 .  
     [0028] FIGS.  4 - 7  depict other embodiment of the present invention, where one primary fluid delivery system  20 , one supplemental fluid source  110 , and one supplemental fluid delivery system  90  are configured to deliver the fuel and steam mixture to the at least one fuel cell  10  while another primary fluid delivery system  25 , another supplemental fluid source  115 , and another supplemental fluid delivery system  92  are configured to deliver the oxidant to the at least one fuel cell  10 .  
     [0029]FIGS. 5 through 7 represents an exemplary embodiment illustrating the secondary fluid  70  exit from the heat exchanger  30  while entering into primary fluid delivery system  20  forming a closed loop heat transfer system. Such closed loop heat transfer system substantially enhances thermodynamic effectiveness of the heat exchanger  30 .  
     [0030] According to one embodiment of the present invention, the secondary fluid delivery system  55  of FIGS.  5 - 7  is configured to deliver the fuel to the heat exchanger  30 , and the fuel exits from the heat exchanger  30  and enters the primary fluid delivery system  20 . In another embodiment of the present invention, the secondary fluid delivery system  55  is configured to deliver the oxidant to the heat exchanger  30 , and the oxidant exits from the heat exchanger  30  and enters the primary fluid delivery system  20 . Yet, in another embodiment of the present invention, the secondary fluid delivery system  55  is configured to deliver the steam to the heat exchanger  30 , and the steam exits from the heat exchanger  30  and enters the primary fluid delivery system  20 . Still in another embodiment of the present invention, the secondary fluid delivery system  55  is configured to deliver the fuel and steam mixture to the heat exchanger  30 , and the fuel and steam mixture exits from the heat exchanger  30  and enters the primary fluid delivery system  20 . The artisan who is skilled in the art is left to select the desired combination of fuel, steam, fuel and steam mixture, and oxidant supplied to the fuel cells based on a specific operational characteristics desired and other design constraints such as space limitations. Likewise, the artisan who is skilled in the art is left to determine the final number and arrangement of the heat exchangers based on the specific application design requirements.  
     [0031] According to one embodiment of the present invention, illustrated in FIG. 8, the plurality of fuel cells  10  further comprises a pressure vessel  80  enclosing the fuel cells  10 . In another embodiment of the present invention, the heat exchanger  30  is enclosed within the pressure vessel  80  not shown in FIG. 8.  
     [0032] A method embodiment of the present invention is provided for the thermal management of the staged fuel cell assembly  1000  of FIG. 1. The method comprises flowing at least one primary fluid  50  through a primary fluid delivery system  20  between a plurality of fuel cells  10 , where the primary fluid delivery system  20  is in thermal communication with at least one heat exchanger.  
     [0033] Another method embodiment of the present invention is provided for the thermal management of the staged fuel cell assembly  1000  of FIG. 1. The method comprises flowing at least one primary fluid  50  through the primary fluid delivery system  20  between the plurality of fuel cells  10 , where the primary fluid delivery system  20  is in thermal communication with the at least one heat exchanger. Additionally, the primary fluid delivery system  20  is coupled to the at least one supplementary fluid source  110  by the at least one supplemental fluid delivery system  90 , to afford adding the at least one supplemental fluid  100  to the primary fluid  50 .  
     [0034] A specific method embodiment of the present invention is provided for the thermal management of the staged fuel cell assembly  1000  of FIG. 1. The method comprises flowing the at least one primary fluid  50  through the primary fluid delivery system  20  between the plurality of fuel cells  10 , where the primary fluid delivery system  20  is in thermal communication with the at least one heat exchanger  30 . Additionally, the at least one heat exchanger  30  further comprises the secondary fluid delivery system  55 , wherein the secondary fluid  70  is flowed through the secondary fluid delivery system  55  such that the secondary fluid  70  is in thermal exchange with the primary fluid  50 .  
     [0035] Transferring heat between the primary fluid  50  of FIG. 2 and the secondary fluid  70  intercools the primary fluid  50  when the primary fluid  50  enters into an exemplary fuel cell stack  210  from a preceding fuel cell stack  200 . Additionally, transferring heat between the primary fluid  50  and the secondary fluid  70  ensures temperature conditioning the primary fluid  50  before entering the staged fuel cell assembly  1000 . Temperature conditioning the primary fluid  50  facilitates maintaining a desired temperature level of the primary fluid  50  before entering the staged fuel cell assembly  1000 . Intercooling the primary fluid  50  between the adjacent fuel cell stacks, for example between the fuel cell stack  210  and the preceding fuel cell stack  200 , beneficially maintains a uniform thermal potential of the staged fuel cell assembly  1000 . Maintaining the uniform thermal potential of the staged fuel cell assembly  1000  results in avoiding thermal hot spots at localized regions of the exemplary staged fuel cell assembly  1000 . Additionally, temperature conditioning of the primary fluid  50  helps maintain a desired uniform electrochemical reaction rate between the fuel and the oxidant across the exemplary fuel cell sub stacks  200 ,  210 ,  220  of the staged fuel cell assembly  1000 . Uniform electrochemical reaction rate across the exemplary fuel cell sub stacks  200 ,  210 ,  220  beneficially results in steady time independent output power characteristics from the staged fuel cell assembly  1000 . In one embodiment of the present invention, the degree of temperature conditioning of the primary fluid  50  is controlled by adjusting a thermal exchange rate between the primary fluid  50  and the secondary fluid  70  in the heat exchanger  30 , when the secondary fluid  70  for example air is different from the primary fluid  50 . In one specific embodiment of the present invention, adjusting the heat transfer rate between the primary fluid  50  and secondary fluid  70  is achieved by controlling the flow rate of the primary fluid  50  and the secondary fluid  70  across the heat exchanger  30 .  
     [0036] Although only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.