Patent Publication Number: US-2022216487-A1

Title: Solid oxide fuel cell power generation system

Description:
CROSS REFERENCE TO PRIOR APPLICATION 
     This application claims priority to Korean Patent Application No. 10-2021-0001858 (filed on Jan. 7, 2021), which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     The present invention relates to a solid oxide fuel cell (SOFC) power generation system using a chemical reaction, and more particularly, to a high-temperature solid oxide fuel cell power generation system that is capable of being installed on a place such as a desert where it is not easy to supply water to improve a power generation efficiency by means of air bearing supports and air cooling and capable of controlling a recycling flow rate in real time by means of an ambient temperature performance map and measured data for a temperature and pressure at a high-temperature operating point to thus enhance high power generation efficiency thereof. 
     Generally, a solid oxide fuel cell (SOFC) is a device which produces water and electricity through an electrochemical reaction occurring between hydrogen and oxygen. In specific, the supplied hydrogen is separated into hydrogen ions and electrons at a catalyst of a negative electrode, and the separated hydrogen ions migrate to positive electrodes through an electrolyte membrane. 
     To obtain a required potential in a real use, a fuel cell stack is constructed by stacking a number of unit cells, and under a configuration of the fuel cell stack, hydrogen flows into a negative electrode (anode), while air or oxygen is flowing into a positive electrode (cathode), so that an electrochemical reaction occurs in the fuel cell stack to generate electrical energy at high efficiencies and water. 
     For example, a cylindrical solid oxide fuel cell is disclosed in Korean Patent No. 10-1364131 (issued on Feb. 20, 2014). 
     According to the conventional solid oxide fuel cell, however, a power generation system of the solid oxide fuel cell has an average power generation efficiency of 45 to 50%, which is relatively low, and besides, the conventional solid oxide fuel cell does not satisfy operating conditions at a high temperature greater than or equal to 700° C. as an operating temperature of the solid oxide fuel cell power generation system, so that the power generation system of the conventional solid oxide fuel cell does not ensure high reliability and durability, thereby undesirably providing low marketability. 
     SUMMARY 
     Accordingly, the present invention has been made in view of the above-mentioned problems occurring in the related art, and it is an object of the present invention to provide a solid oxide fuel cell power generation system that is configured to allow an unreacted fuel after the reaction of a fuel cell module to be recycled through a blower and then supplied to an anode of the fuel cell module to improve a power generation efficiency thereof, configured to allow a motor used to operate the blower to be cooled by means of air cooling, and configured to allow air used for cooling the blower to be recycled to a cathode of the fuel cell module, thereby improving the overall efficiency thereof. 
     To accomplish the above-mentioned object, according to the present invention, there is provided a solid oxide fuel cell power generation system including: a fuel cell module; a blower for supplying a gaseous fuel to the fuel cell module; an air supplier for supplying air to the fuel cell module; and a fuel supplier for supplying the gaseous fuel to the blower, wherein the blower recycles at least a portion of an unreacted gaseous fuel to the fuel cell module. 
     According to the present invention, desirably, the fuel cell module may include a stack having an anode and a cathode and generating electricity, and the gaseous fuel supplied to the blower from the fuel supplier is mixed with the unreacted gaseous fuel transferred to the blower and then transferred to the stack. 
     According to the present invention, desirably, the air supplier transfers the air to the blower to allow the blower to be cooled by the air and thus supplies the air whose temperature is raised after cooling the blower to the fuel cell module. 
     According to the present invention, desirably, the solid oxide fuel cell power generation system may further include an air-blowing heat exchanger for heating the air, the air supplier supplying the air whose temperature is raised after cooling the blower to the fuel cell module through the air-blowing heat exchanger. 
     According to the present invention, desirably, the fuel cell module may include a reformer adapted to perform a reforming reaction for the gaseous fuel supplied from the blower. 
     According to the present invention, desirably, the blower may include: a motor disposed therein; a motor stator for supporting the motor; a shaft rotating with the power supplied from the motor; an impeller rotatably coupled to one end portion of the shaft to generate the flow of a fluid; a heat shield for blocking the heat generated by the rotation of the shaft; a volute for inducing the flow of the gaseous fuel supplied to the interior thereof from a linear direction to a centrifugal direction with respect to the rotary axis of the shaft; and a diffuser extended from the volute to restore the pressure of gaseous fuel reduced by the volute. 
     According to the present invention, desirably, the shaft may include a disc disposed on one side thereof to surround the outer peripheral surface thereof, and the blower may include journal foil bearings for surrounding at least a portion of the outer peripheral surface of the shaft and thrust foil bearings for surrounding at least a portion of the outer peripheral surface of the disc. 
     According to the present invention, desirably, the blower may further include a sealing member disposed between the shaft and the impeller. 
     According to the present invention, desirably, the air supplier may include: a filter for filtering the air; an air blower for transferring the filtered air; and an air flow meter for measuring the flow rate of air transferred to the blower from the air blower. 
     According to the present invention, desirably, the blower may include: an air inlet allowing the air transferred by the air blower to be introduced thereinto; and an air outlet allowing the air introduced through the air inlet to be exhausted to the outside thereof, and the air transferred to the interior of the blower from the air inlet through the air blower cools the blower so that the air whose temperature is raised after cooling the blower is transferred to the fuel cell module. 
     According to the present invention, desirably, the fuel supplier may include: a fuel pump for transferring the gaseous fuel; a fuel flow meter for measuring the flow rate of the gaseous fuel transferred to the blower through the fuel pump; and a desulfurizer for removing sulfur from the gaseous fuel transferred to the blower through the fuel pump. 
     According to the present invention, desirably, the fuel supplier may include: a first valve for controlling the flow rate of the gaseous fuel supplied to the blower through the fuel pump; and a second valve for controlling the flow of the unreacted gaseous fuel. 
     According to the present invention, desirably, the solid oxide fuel cell power generation system may further include a catalyst for removing harmful components existing in the air in a process where after the air and the gaseous fuel that are supplied to the fuel cell module have been reacted with each other in the fuel cell module, the air and the gaseous fuel are exhausted. 
     According to the present invention, desirably, the solid oxide fuel cell power generation system may further include a heat collector for collecting waste heat in the air and the gaseous fuel in a process where after the air and the gaseous fuel that are supplied to the fuel cell module have been reacted with each other in the fuel cell module, the air and the gaseous fuel are exhausted. 
     According to the present invention, desirably, the heat collector may include: a heat-collecting heat exchanger for performing heat exchange between the air and the gaseous fuel when the air and the gaseous fuel are exhausted after reacted with each other in the fuel cell module; and a vent for exhausting the air and gaseous fuel whose heat exchange is completed in the heat-collecting heat exchanger. 
     According to the present invention, desirably, the heat collector may include: a low temperature fluid supplier for supplying a low temperature fluid to the heat-collecting heat exchanger and a high temperature fluid supplier for supplying a high temperature fluid produced after the fluid supplied from the low temperature fluid supplier has been heated by the heat-collecting heat exchanger to the outside thereof. 
     According to the present invention, desirably, the solid oxide fuel cell power generation system may further include a controller for controlling the blower and the fuel supplier, the fuel supplier having a fuel pump adapted to supply the gaseous fuel to the blower, and the controller controlling the blower and the fuel pump to control the ratio of the gaseous fuel to the unreacted gaseous fuel supplied to the fuel cell module from the blower. 
     According to the present invention, desirably, the controller may include an input device for inputting the ratio of the gaseous fuel to the unreacted gaseous fuel supplied to the fuel cell module from the blower. 
     According to the present invention, desirably, the controller may control the fuel pump according to a recycle ratio received through the input device to allow the quantity of gaseous fuel supplied to the blower to be controlled. 
     According to the present invention, desirably, the recycle ratio is set to 50 to 70%. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the embodiments of the invention in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagram showing a solid oxide fuel cell power generation system according to the present invention; 
         FIG. 2  is a sectional view showing a blower of the solid oxide fuel cell power generation system according to the present invention; 
         FIG. 3  is a diagram showing the flow of air in the solid oxide fuel cell power generation system according to the present invention; 
         FIG. 4  is a sectional view showing the flows of air and gaseous fuel inside the blower of the solid oxide fuel cell power generation system according to the present invention; 
         FIGS. 5 and 6  are diagrams showing the circulation of gaseous fuel through valves in the solid oxide fuel cell power generation system according to the present invention; 
         FIG. 7  is a diagram showing a control configuration of the solid oxide fuel cell power generation system according to the present invention; 
         FIGS. 8 to 11  are diagrams showing simulation modeling for performance analysis of the solid oxide fuel cell power generation system according to the present invention; 
         FIGS. 12 to 19  are diagrams showing the processes of setting a rotating speed of a motor according to a target mass flow rate in the solid oxide fuel cell power generation system according to the present invention; 
         FIG. 20  is a diagram showing a method for predicting the flow rate in the solid oxide fuel cell power generation system according to the present invention; and 
         FIG. 21  is a graph showing changes in steam-to-carbon ratios and fuel quantities according to a recycle ratio in the solid oxide fuel cell power generation system according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Before the present invention is disclosed and described, the terminology used herein will be explained briefly. 
     All terms used herein, including technical or scientific terms, unless otherwise defined, have the same meanings which are typically understood by those having ordinary skill in the art. The terms, such as ones defined in common dictionaries, should be interpreted as having the same meanings as terms in the context of pertinent technology, and should not be interpreted as having ideal or excessively formal meanings unless clearly defined in the specification. 
     In the description, when it is said that one portion is described as “includes” any component, one element further may include other components unless no specific description is suggested. 
     The present invention may be modified in various ways and may have several exemplary embodiments. Specific exemplary embodiments of the present invention are illustrated in the drawings and described in detail in the detailed description. However, this does not limit the invention within specific embodiments and it should be understood that the invention covers all the modifications, equivalents, and replacements within the idea and technical scope of the invention. 
     Objects, characteristics and advantages of the present invention will be more clearly understood from the detailed description as will be described below and the attached drawings. 
     Hereinafter, the present invention will be explained in detail with reference to the attached drawings. 
     Referring to  FIGS. 1 and 2 , a solid oxide fuel cell power generation system  1000  according to the present invention largely includes a fuel cell module  100 , a blower  200  for supplying a gaseous fuel to the fuel cell module  100 , an air supplier  300  for supplying external air to the fuel cell module  100 , and a fuel supplier  400  for supplying the gaseous fuel to the blower  200 , wherein the blower  200  recycles at least a portion of an unreacted gaseous fuel to the fuel cell module  100 . 
     First, the fuel cell module  100  is provided. The fuel cell module  100  includes a stack  110  having an anode  111  and a cathode  112  and generating electricity through an electrochemical reaction, a gaseous fuel supply line adapted to allow the fuel supplier  400  to communicate with the stack  110  so as to supply the gaseous fuel to the stack  110 , and an air supply line adapted to allow the air supplier  300  to communicate with the stack  110  so as to supply the air to the stack  110 . 
     Further, the fuel cell module  100  includes a reformer  120  adapted to perform a reforming reaction for the gaseous fuel supplied from the blower  200 , and the reformer  120  communicates with the gaseous fuel supply line. In this case, a water supply line may be connected to the reformer  120  so as to supply water used in the reformer  120 . 
     Next, the blower  200  is provided. The blower  200  is controlled by a controller  800  as will be discussed later and serves to transfer the gaseous fuel supplied from the fuel supplier  400  to the stack  110 . 
     In this case, the gaseous fuel supplied to the blower  200  from the fuel supplier  400  is mixed with the unreacted gaseous fuel transferred to the blower  200 , and accordingly, a mixture is transferred to the stack  110  through the reformer  120 . In specific, the gaseous fuel transferred to the fuel cell module  100  is electrochemically reacted with an oxidant to generate electrical energy. In this case, the unreacted gaseous fuel, which has not been reacted with the oxidant and thus has remained, is transferred again to the blower  200 . That is, the blower  200  serves to transfer the gaseous fuel supplied from the fuel supplier  400  and the unreacted gaseous fuel remaining in the interior of the fuel cell module  100  to the fuel supplier  400 . In specific, the blower  200  serves to mix the unreacted gaseous fuel remaining in the fuel cell module  100  and the gaseous fuel supplied from the fuel supplier  400  with each other and thus to recycle the mixture between the unreacted gas and the gaseous fuel to the fuel cell module  100 . 
     In this case, the blower  200  includes a motor  201  disposed inside a casing constituting an outer shape thereof, a motor stator  202  for supporting the motor  201 , a shaft  203  rotating with the power supplied from the motor  201 , an impeller  204  rotatably coupled to one end portion of the shaft  203  to generate the flow of a fluid, a heat shield  205  for blocking the heat generated by the rotation of the shaft  203 , a volute  206  for inducing the flow of the gaseous fuel supplied to the interior thereof from a linear direction to a centrifugal direction with respect to the rotary axis of the shaft  204 , a diffuser  207  extended from the volute  206  to restore the pressure of the gaseous fuel reduced by the volute  206 , and journal foil bearings  208  and thrust foil bearings  209  for supporting the shaft  203 . In this case, the journal foil bearings  208  and the thrust foil bearings  209  are foil-air bearings. 
     In more specific, the shaft  203  is provided inside the casing in a longitudinal direction of the casing. One end portion of the shaft  203  is coupled to the motor  201  so that the shaft  203  rotates by the rotation of the motor  201 , and the other end portion thereof is coupled to the impeller  204  to transfer the rotary force of the motor  201  to the impeller  204 . Further, the shaft  203  includes a disc  203 - 1  disposed on one side thereof. The disc  203 - 1  surroundingly extends radially from the outer peripheral surface of the shaft  203 . In this case, the disc  203 - 1  serves to prevent the shaft  203  from being transferred axially or generating vibrations. As the impeller  204  rotates, in specific, an axial force may be generated due to a pressure difference between the front side and the rear side of the impeller  204 , and accordingly, the disc  203 - 1  supports the axial force. In this case, the disc  203 - 1  has a hole axially passing therethrough, and the disc  203 - 1  and the shaft  203  may be cooled by means of the air introduced through an air inlet  230  as will be discussed later. 
     Further, the impeller  204  is coupled to the other end portion of the shaft  203 . In this case, the impeller  204  rotates together with the rotation of the shaft  203 , and so as to generate the flow of fluid through the rotation of the impeller  204 , blades are disposed radially from the center of the impeller  204 . In specific, the impeller  204  has a hollow portion formed at the inside thereof so that it can fit to the other end portion of the shaft  203 , and the blades are located around the outer peripheral surface of the impeller  204  so that they rotate by the rotation of the shaft  203  to generate the flow of fluid. 
     Further, the heat shield  205  is fitted to the other end portion of the shaft  203  to surround the outer peripheral surface of the shaft  203 . In specific, the heat shield  205  is coupled to the shaft  203 , while being adjacent to the rear end of the impeller  204 , to thus prevent the heat generated by the rotation of the shaft  203  from being emitted. 
     Further, the volute  206  is coupled to the front side of the casing to seal the interior of the casing. Further, the volute  206  has a pathway formed therein to the shape of tornado around the rotary center axis of the shaft  203  so as to induce the flow of the gaseous fuel supplied to the interior of the blower  200  from the linear direction to the centrifugal direction with respect to the rotary axis of the shaft  203 . 
     Further, the diffuser  207  is coupled to the tornado-shaped pathway of the volute  206  and has a sectional area gradually increasing toward the end portion thereof from the volute  206 , so that the diffuser  207  reduces the flow rate of the gaseous fuel, which is reduced by the volute  206 , to thus increase a static pressure. That is, the diffuser  207  restores the pressure of gaseous fuel reduced by the volute  206 . 
     Further, the journal foil bearings  208  are provided to surround at least a portion of the outer peripheral surface of the shaft  203  at a point where the outer peripheral surface of the shaft  203  and the inner peripheral surface of the casing interfere with each other, and thus, the journal foil bearings  208  serve to support the shaft  203 . Further, the thrust foil bearings  209  are provided to surround at least a portion of the outer peripheral surface of the disc  203 - 1  at a point where the outer peripheral surface of the disc  203 - 1  and the inner peripheral surface of the casing interfere with each other, and thus, the thrust foil bearings  209  serve to support the axial force generated from the shaft  203 . In this case, one or more journal foil bearings  208  and one or more thrust foil bearings  209  may be provided, and the journal foil bearings  208  and the thrust foil bearings  209  are made of a heat-resistant material so that even in the case where heat is generated by the operation of the motor  201 , they can support the shaft  203 . Further, coated layers may be formed on the outer peripheral surfaces of the journal foil bearings  208  and the thrust foil bearings  209 , and the coated layers may include Teflon. Accordingly, the heat-resisting properties of the bearings are more improved, and in this case, the durability of the blower  200  in a high temperature environment can be improved. 
     Also, the blower  200  includes a fuel inlet  210  located in front of the volute  206  to communicate with the volute  206  and adapted to introduce the gaseous fuel transferred from the fuel supplier  400  and the unreacted gaseous fuel thereinto, and a fuel outlet  220  located on the end portion of the diffuser  207  to transfer the gaseous fuel transferred from the fuel supplier  400  and the unreacted gaseous fuel to the fuel cell module  100 . In this case, the fuel inlet  210  and the fuel outlet  220  communicate with the gaseous fuel supply line. That is, the gaseous fuel transferred from the fuel supplier  400  and the unreacted gaseous fuel are transferred to the blower  200 , mixed with each other in the blower  200 , and supplied again to the fuel cell module  100 , so that the efficiency of the fuel cell module  100  can be more improved. 
     Next, the air supplier  300  is provided. The air supplier  300  serves to supply external air to the fuel cell module  100 . In specific, the air supplier  300  includes a filter  310  for filtering the external air, an air blower  320  for transferring the filtered air, and an air flow meter  330  for measuring the flow rate of air transferred to the blower  200  from the air blower  320 . 
     In this case, the air supplier  300  transfers the external air to the blower  200  to allow the blower  200  to be cooled by the external air and supplies the external air whose temperature is raised after cooling the blower  200  to the fuel cell module  400 . That is, if the external air is supplied to the blower  200  through the air blower  320 , the blower  200 , which is heated by means of the high-temperature unreacted gaseous fuel, becomes cooled by the external air. After that, the external air heated after cooling the blower  200  is transferred to the cathode  112  by means of the air blower  320 . As the temperature of the air supplied to the fuel cell module  100  is raised, that is, the reaction efficiency of the fuel cell module  100  at a high temperature becomes more improved. 
     In this case, the solid oxide fuel cell power generation system  1000  according to the present invention further includes an air-blowing heat exchanger  500  for heating the external air. That is, the air-blowing heat exchanger  500  serves to raise the temperature of the air supplied to the fuel cell module  100 . 
     Referring to  FIG. 3 , the air supplier  300  supplies the external air whose temperature is raised after cooling the blower  200  to the fuel cell module  400  via the air-blowing heat exchanger  500 . In specific, the external air transferred to the blower  200  through the air blower  320  cools the blower  200 , so that it is primarily heated, and next, the external air is transferred to the air-blowing heat exchanger  500  through the air blower  320 , so that it is secondarily heated. Next, the external air is transferred to the cathode  112 , thereby advantageously more improving the efficiency of the fuel cell module  100 . 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Without 
                 With 
               
               
                   
                 Division 
                 blower 
                 blower 
               
               
                   
                   
               
             
            
               
                   
                 Recycle ratio 
                 — 
                   68% 
               
               
                   
                 S/C ratio 
                 3.0 
                 3.0 
               
               
                   
                 Water supply quantity 
                 0.175 kmol/hr 
                 — 
               
               
                   
                 Power generation efficiency 
                  41.3% 
                 57.13% 
               
               
                   
                   
               
            
           
         
       
     
     For example, Table 1 shows the results obtained by making process flows of the temperatures and operating points of the power generation system acquired by the test estimation and operating optimization of the stack  110  using data and a piping and instrumentation diagram (P&amp;ID) and performing computer simulation analysis for the process flows. As the temperature of air supplied to the fuel cell module  100  is increased by means of the blower  200 , that is, the power generation efficiency of the solid oxide fuel cell power generation system  1000  according to the present invention is more raised by 15 to 17% than that of the conventional solid oxide fuel cell power generation system. 
     Now, an explanation of the computer simulation analysis will be given in detail. A user-defined function (UDF) program available to ASPEN software for system analysis is used, and simulation modeling as shown in  FIGS. 8 to 11  is suggested. First, VN is an open circuit voltage (OCV) or a reversible voltage of a solid oxide fuel cell, and Gibbs free energy is changed according to a reactant and a temperature, pressure and concentration of a product, which are provided as shown in  FIG. 8 . A first order term of the expression is ideal potential E 0 , and a second order term indicates the temperature, pressure, and temperature of the reactant applied to fuel cells and an influence of the product applied to the cell voltage. In this case, T avg  is a temperature of an inlet and outlet stream (K) of the solid oxide fuel cell, R g  is a gas constant of 8.314 J/mol-K, and P i  is an average partial pressure of gas (atm). Further,  FIG. 9  shows all electrochemical equations for calculating activated polarization of the solid oxide fuel cell. Referring further to  FIG. 10 , ohmic losses are generated from the resistances caused by the flows of electrons through ion flows of electrolyte and electrodes, and polarization of ohm according to Ohm&#39;s law is represented. Also, a concentration higher than the potential is generated by the concentration-gradient (concentration reduction of material) in electrode-electrolyte interface due to the resistance to transportation, and if it is desired to calculate a concentration for a potential difference, the concentrations of gas species on triple phase boundary (TPB) have to be analyzed, which expressions are shown in  FIG. 11 . 
     Next, the analysis results of the conventional solid oxide fuel cell power generation system are suggested in Table 2 wherein the power generation efficiency is 41.3%, and the specific analysis results of the solid oxide fuel cell power generation system  1000  according to the present invention are suggested in Table 3 wherein the power generation efficiency is 57.13%. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Parameters 
                 Symbol 
                 Unit 
                 Value 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Fuel utilization of stack 
                 Fusofc 
                 % 
                 58.5 
               
               
                 Air utilization 
                 Uair 
                 % 
                 45.0 
               
               
                 Recycle ratio 
                 RR 
                 % 
                 0.0 
               
               
                 Flow rate of water in 
                 WATER-IN 
                 Kmole/Hr 
                 0.175 
               
               
                 Flow rate of air in 
                 AIR-IN 
                 Kmole/Hr 
                 0.697 
               
            
           
           
               
               
               
               
               
            
               
                 Flow rate 
                 in Reformer 
                 FUEL-IN 
                 Kmole/Hr 
                 0.0533 
               
               
                 of Fuel supply 
                 in Burner 
                 Fuel-in-Bur 
                 Kmole/Hr 
                 0.0 
               
            
           
           
               
               
               
               
            
               
                 LHV of fuel 
                 LHV_F 
                 J/mole 
                 816588 
               
               
                 V_Cell 
                 V 
                 V 
                 0.7 
               
               
                 I_Current 
                 I 
                 A 
                 71.4 
               
               
                 Number of Cells 
                 Num_Cell 
                 — 
                 100 
               
               
                 Efficiency 
                 Eff. 
                 % 
                 41.3 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Parameters 
                 Symbol 
                 Unit 
                 Value 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Fuel utilization of stack 
                 Fusofc 
                 % 
                 58.5 
               
               
                 Air utilization 
                 Uair 
                 % 
                 45.0 
               
               
                 Recycle ratio 
                 RR 
                 % 
                 68.0 
               
               
                 Flow rate of water in 
                 WATER-IN 
                 Kmole/Hr 
                 0.0 
               
               
                 Flow rate of air in 
                 AIR-IN 
                 Kmole/Hr 
                 0.697 
               
            
           
           
               
               
               
               
               
            
               
                 Flow rate 
                 in Reformer 
                 FUEL-IN 
                 Kmole/Hr 
                 0.383 
               
               
                 of Fuel supply 
                 in Burner 
                 Fuel-in-Bur 
                 Kmole/Hr 
                 0.0 
               
            
           
           
               
               
               
               
            
               
                 LHV of fuel 
                 LHV_F 
                 J/mole 
                 816588 
               
               
                 V_Cell 
                 V 
                 V 
                 0.69 
               
               
                 I_Current 
                 I 
                 A 
                 71.4 
               
               
                 Number of Cells 
                 Num_Cell 
                 — 
                 100 
               
               
                 Efficiency 
                 Eff. 
                 % 
                 57.13 
               
               
                   
               
            
           
         
       
     
     Referring next to  FIG. 4 , the blower  200  includes the air inlet  230  communicating with one side of the casing to allow the external air transferred by the air blower  320  to be introduced thereinto and an air outlet  240  communicating with the other side of the casing to allow the external air introduced thereinto through the air inlet  230  to flow to the interior thereof in the longitudinal direction thereof, to perform cooling therefor, and to be then transferred to the air-blowing heat exchanger  500 . In this case, the air inlet  230  and the air outlet  240  communicate with the air supply line. Accordingly, the external air introduced into the blower  200  through the air inlet  230  flows to the entire interior of the blower  200 , cools the interior of the blower  200 , and is then transferred to the fuel cell module  100 . In this case, the shaft  203  is a hollow shaft whose one end is open and has a plurality of holes formed radially on the other end thereof, through which the external air flows to the interior of the shaft  203  to make the shaft  203  cooled. 
     Further, the blower  200  includes a sealing member  250  for preventing the external air introduced thereinto through the air inlet  230  from leaking to a gap between the shaft  203  and the impeller  204 . That is, the sealing member  250  serves to prevent the external air transferred to the interior of the blower  200  from leaking to the volute  206  and being thus mixed with the gaseous fuel. 
     Next, the fuel supplier  400  is provided. The fuel supplier  400  serves to supply the gaseous fuel to the fuel cell module  100 . In specific, the fuel supplier  400  includes a fuel pump  410  for transferring the gaseous fuel, a fuel flow meter  420  for measuring the flow rate of gaseous fuel transferred to the blower  200  through the fuel pump  410 , and a desulfurizer  430  for removing sulfur from the gaseous fuel. That is, the fuel pump  410  provides a driving force so that the gaseous fuel can be supplied to the blower  200 . As the output of the fuel pump  410  is controlled, accordingly, the quantity of gaseous fuel supplied to the fuel cell module  100  can be controlled. 
     Referring to  FIGS. 5 and 6 , the fuel supplier  400  includes a first valve  441  for controlling the flow of gaseous fuel supplied to the blower  200  through the fuel pump  410  and a second valve  442  for controlling the flow of unreacted gaseous fuel. In this case, the first valve  441  and the second valve  442  are solenoid valves whose opening and closing are controlled by the controller  800  as will be discussed later, and the second valve  442  may be a three way valve. If the first valve  441  is open, that is, the gaseous fuel transferred through the fuel pump  410  is supplied to the blower  200 , and if the first valve  441  is closed, the gaseous fuel transferred through the fuel pump  410  is not supplied to the blower  200 . As the second valve  442  is controlled, further, the unreacted gaseous fuel may be transferred to the blower  200  or a heat collector  700  as will be discussed later. 
     Next, the solid oxide fuel cell power generation system  1000  according to the present invention further includes a catalyst  600  for removing harmful components existing in the external air in a process where the external air supplied to the fuel cell module  100  through the air supplier  300  is transferred to the heat collector  700 . That is, the catalyst  600  serves to remove the harmful components existing in the air in a process where in a process where after the air and the gaseous fuel that are supplied to the fuel cell module  100  have been reacted with each other in the fuel cell module  100 , the air and the gaseous fuel are exhausted. Further, the catalyst  600  serves to remove the harmful components existing in the gaseous fuel in a process where the gaseous fuel supplied to the fuel cell module  100  through the blower  200  is transferred to the heat collector  700 . 
     Next, the solid oxide fuel cell power generation system  1000  according to the present invention further includes the heat collector  700  for collecting waste heat in the air and the gaseous fuel when the air and the gaseous fuel are exhausted after the air and the gaseous fuel that are supplied to the fuel cell module  100  have been reacted with each other in the fuel cell module  100 . In specific, the heat collector  700  includes a heat-collecting heat exchanger  710  for performing heat exchange between the air and the gaseous fuel when the air and the gaseous fuel are exhausted after they have been supplied to the fuel cell module  100  and reacted with each other in the fuel cell module  100  and a vent  720  for exhausting the air and gaseous fuel whose heat exchange is completed. Further, the heat collector  700  includes a low temperature fluid supplier  730  for supplying a low temperature fluid to the heat-collecting heat exchanger  710  and a high temperature fluid supplier  740  for supplying a high temperature fluid produced after the fluid supplied from the low temperature fluid supplier  730  has been heated by the heat-collecting heat exchanger  710  to the outside thereof. 
     Referring next to  FIG. 7 , the solid oxide fuel cell power generation system  1000  according to the present invention further includes the controller  800  for controlling the blower  200  and the fuel supplier  400 . In addition to the blower  200  and the fuel supplier  400 , in this case, the controller  800  controls the fuel cell module  100 , the air supplier  300 , the air-blowing heat exchanger  500 , the catalyst  600 , and the heat collector  700 . 
     In this case, the controller  800  controls the blower  200  and the fuel pump  410  to control the ratio of the gaseous fuel to the unreacted gaseous fuel supplied to the fuel cell module  100  from the blower  200 . If the operation of the fuel pump  410  is stopped, that is, 100% of the gaseous fuel supplied to the blower  200  is recycled, and as the quantity of the gaseous fuel supplied to the blower  200  through the fuel pump  410  is increased, the recycle ratio of the gaseous fuel is decreased. 
     In more specific, the controller  800  includes an input device  810  for receiving the ratio of the gaseous fuel to the unreacted gaseous fuel supplied to the fuel cell module  100  from the blower  200 . In this case, the input device  810  may be a computer or smartphone, or any one which transmits information to the controller  800  through wired or wireless communication. That is, if the recycle ratio is transmitted to the controller  800  through the input device  810  by a user, the controller  800  controls the fuel pump  410  to adjust the quantity of gaseous fuel supplied to the blower  200 , so that the recycle ratio of the gaseous fuel can be controlled. 
     If the fuel pump  410  does not operate, for example, the flow rate of gaseous fuel supplied from the fuel supplier  400  to the anode  111  is zero, so that the recycle ratio of the gaseous fuel through the blower  200  is 100%. If the fuel pump  410  operates to allow the gaseous fuel supplied to the blower  200  to correspond to 10% of the flow rate of the gaseous fuel supplied from the blower  200  to the anode  111 , 10% of the flow rate of the gaseous fuel supplied to the anode  110  is exhausted to the outside through the vent  720  under the control of the second valve  442 , so that the recycle ratio of the gaseous fuel through the blower  200  is 90%. 
     Referring to  FIG. 21 , in this case, the recycle ratio of the gaseous fuel can be set to 50 to 70%. If the recycle ratio is less than 50%, the efficiency of the power generation system may become drastically low. If the recycle ratio is greater than 70%, the consumption power of the blower  200  for the recycling may be increased and the flow rate of air needed to keep the stack  110  to an appropriate temperature may be increased, so that the consumption power of the air blower  320  may be suddenly increased to thus decrease the output of the power generation system. As the recycle ratio becomes increased, further, the ratio of the fuel used again becomes raised, so that the proportion of the fuel may be decreased to undesirably cause the output reduction. So as to enhance the efficiency of the power generation system, that is, the flow rate of fuel has to be minimized to increase the utilization of the fuel and the recycle ratio of the fuel. If the flow rate of fuel is reduced and the recycle ratio thereof is increased, however, the temperature of the stack  110  is raised to increase a temperature difference between the anode  111  and the cathode  112 , so that the stack  110  may be cracked due to the temperature unbalance. As a result, the recycle ratio of the gaseous fuel may be set to 50 to 70% in consideration of the power generation efficiency and output of the power generation system and the operating stability of the stack  110 . That is, the fuel supplier  400  is controlled to supply the gaseous fuel of 30 to 50% of a target mass flow rate as will be discussed later to the blower  200 . 
     Next, the controller  800  receives the target mass flow rate from the input device  810  and controls the rotating speed of the motor  201  according to the received target mass flow rate. In this case, the controller  800  converts ambient temperature test data into high temperature test data using an ambient temperature performance map based on the inlet temperature, inlet pressure, and rotating speed of the blower  200  and the physical properties of the fluid component flowing to the blower  200  and thus controls the rotating speed of the motor  201 , so that the recycle flow rate of the blower  200  is controlled. In this case, the blower  200  is at a high temperature, and accordingly, a flow meter cannot be installed around the blower  200 . Therefore, the controller  800  controls the rotating speed of the motor  201  according to the received target mass flow rate and thus regulates the flow rate of mass supplied to the stack  110 . 
     Referring in specific to  FIG. 12 , first, the controller  800  receives the target mass flow rate from the input device  810  and stores the received target mass flow rate. In this case, the ambient temperature performance map has been transmitted to the controller  800  and stored therein. 
     After that, the controller  800  receives measured values from a plurality of sensors  820  and stores the measured values. In this case, the sensors  820  measure a temperature and pressure around the blower  200 , a temperature and pressure of the inlet of the blower  200 , into which the fluid flows, a temperature and pressure of the outlet of the blower  200 , from which the fluid is exhausted, the rotating speed and temperature of the motor  201 , and the power consumption of the motor and then transmits the measured values to the controller  800 . 
     After that, the controller  800  receives constants from the input device  810  and stores the received constants. In this case, as shown in  FIG. 13 , constant values may include a gas constant, a heat capacity ratio, an inner diameter of the inlet, an inner diameter of the outlet, a reference mass flow rate, a minimum rotating speed, a maximum rotating speed, and a control gain. In this case, the sizes of pipes are determined according to the inner diameters of the pipes, and the control gain is suggested with respect to an initial value, which may be controlled according to control response speeds upon a test. 
     After that, the controller  800  converts the ambient temperature test data into the high temperature test data, based on the ambient temperature performance map. Referring to  FIG. 14 , for example, the right values of the Table show the converted values in the case where the inlet temperature T 1  is 550° C. and the inlet pressure P 1  is 101.325 kPa. If two variables are given, that is, the controller  800  calculates the rest of variables based on the ambient temperature performance map, and intermediate values can be obtained through linear interpolation. In this case, an expression for the conversion is suggested with the following mathematical expression 1. 
     
       
         
           
             
               
                 
                   
                     
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     where N represents the rotating speed of the motor  201 , X 1i  corrected rotating speed, γ heat capacity ratio, R a value obtained by dividing a gas constant into the molar mass of gas, T i  the inlet temperature of the blower  200 , Q m, i  mass flow rate, x 2i  corrected mass flow rate, P ri  the predicted value of a compression ratio on control conditions converted into similarity conditions, and x 3i  a pressure ratio (outlet pressure/inlet pressure). 
     Accordingly, if x 1  (corrected rotating speed on reference conditions) is multiplied by conversion constant sqrt(γRT), N i  (converted rotating speed) can be obtained. Further, if x 2  (corrected mass flow rate) is multiplied by conversion constant sqrt(γRT), Q m  (mass flow rate) can be obtained. Moreover, x3 (pressure ratio) has similar values because a difference value before and after correction is small, and accordingly, it is indicated with an equal sign. Further, γ as the heat capacity ratio and R as the gas constant are the physical properties of a thermodynamic fluid. In this case, γ (specific heat ratio)=C p  (the specific heat at constant pressure)/C v  (the specific heat at constant volume), and generally, air has the specific heat ratio of about 1.4[−]. Further, R represents the value obtained by dividing a gas constant into the molar mass of gas. For example, air has the gas constant of about 287 [J/kg/K]. In addition, T[K] represents a fluid temperature on inlet. 
     After that, the controller  800  compares limitation conditions with the received and calculated values and thus determines as to whether the power generation system can operate. For example, as shown in  FIG. 15 , the limitation conditions may include maximum winding temperature, maximum motor power, corrected mass flow rate, maximum and minimum mass flow rates, maximum and minimum rotating speeds, and maximum inlet temperature. Referring to  FIG. 16 , that is, the controller  800  determines that the power generation system can operate if the received and calculated values are within the operating range of the blower  200  (ARB). That is, the operating range of the blower  200  (ARB) is between the minimum rotating speed N min  and the maximum rotating speed N max  and between the minimum mass flow rate Q m, min  and the maximum mass flow rate Q m, max . 
     In the case where it is determined that the power generation system can operate, next, the controller  800  performs repeated calculation until the operating range reaches a mass error range. For example, as shown in  FIG. 17 , the controller  800  calculates a required total pressure ratio, a mass flow rate assumption value, density and velocity of inlet and outlet, total pressure and pressure ratio of inlet and outlet, and a current mass flow rate and thus derives the current mass flow rate. Next, the controller  800  compares the current mass flow rate with the target mass flow rate and performs repeated calculation until the difference value between the current mass flow rate and the target mass flow rate is within the error range. In this case, the output value is suggested as the following mathematical expression 2, and a required flow rate error range is determined according to the following mathematical expression 3. 
     
       
         
           
             
               
                 
                   
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     where ΔN represents speed difference value, Q m, r  required flow rate, Q m, cur  current flow rate, and Q N  control gain. 
     Referring to  FIG. 13 , for example, the control gain Q N  has an initial value of 0.0005, and if a response speed in control upon test is slow, the control gain value is reduced, whereas if a response speed in control is fast, the control gain value is increased. In this case, ΔN represents a speed difference value as control input. For example, if it is assumed that the required flow rate Q m, r  is 1 and the current flow rate Q m, cur  at the current rotating speed of the motor  201  is 0.9, Q m, r −Q m, cur =0.1. Like this, if there is a lack of flow rate, the rotating speed of the motor  201  has to be increased, and in this case, the increasing value in the rotating speed is determined by the control gain. For example, if the control gain value is 0.001, the speed difference value ΔN is 0.1/0.001=100 rpm. That is, the rotating speed of the motor  201  has to be increased by 100 rpm. Contrarily, if the current flow rate is faster than the required flow rate, that is, if Q m, r −Q m, cur =−0.1, the speed difference value ΔN is −0.1/0.001=−100 rpm. That is, the rotating speed of the motor  201  has to be reduced by 100 rpm. Further, if there is a difference between the current flow rate and the required flow rate, the motor  201  rotates at the same speed as before. 
     
       
         
           
             
               
                 
                   
                     
                       
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     where Q m, r  represents required flow rate, Q m, cur  current flow rate, and err REQ  set error inputted. That is, the speed difference value ΔN is changed until the error value (%) of the required flow rate Q m, r  to the current flow rate Q m, cur  is less than or equal to the set error. For example, if the required flow rate Q m, r  is 1 in a state where the err REQ  is set to 1%, the speed difference value ΔN is changed until the current flow rate Q m, cur  is within the range of 0.99 to 1.01. 
     Referring to  FIGS. 18A to 19 , that is, the controller  800  receives the inputted value from the input device  810  and the measured values from the sensors  820 , calculates the values in the manner mentioned above, controls the rotating speed of the motor  201  with the calculated values, and thus controls the flow rate of the mass supplied to the stack  110 . In more specific, referring to  FIG. 18A , if the required flow rate Q m, r  is inputted by the worker, the controller  800  calculates the speed difference value ΔN based on the inlet and outlet pressures of the blower  200 , the inlet temperature of the blower  200 , and the rotating speed of the motor  201 . After that, the controller  800  controls the rotating speed of the motor  201  by the speed difference value ΔN and thus controls the rotating speed of the blower  200 . In this case, the controller  800  performs repeated calculation until the speed difference value ΔN is within the error range. 
     In the state where the pressure P 1 , temperature T 1 , and rotating speed N are sensed by the sensors  820  and the measured values are transmitted to the controller  800 ,  FIG. 18B  shows that the measured values of the sensors  820  are converted into current signals. If a signal Δm REQ_dot  is transmitted to the controller  800 , the controller  800  calculates the speed difference value ΔN and generates a given signal, and the given signal is converted into ΔI[mA] and transmitted to the motor  201 . Next, the motor  201  transfers a torque of Δτ[Nm]. Referring to  FIG. 19 , that is, if flow rate control is performed by the controller  800  at step S 10 , the controller  800  receives the measured values from the sensors  820  and stores the received values at step S 20 . Next, the controller  800  receives the inputted value, that is, required flow rate Q m, r  from the input device  810  and stores the received value at step S 30 . After that, the controller  800  calculates the speed difference value ΔN based on the measured values and the input value at step S 40 . Next, the controller  800  changes the rotating speed of the motor  201  according to the speed difference value ΔN calculated at step S 50 , and then, the controller  800  calculates the current flow rate Q m, cur  at step S 60 . After that, the controller  800  determines whether the error value % between the required flow rate Q m, r  and the current flow rate Q m, cur  is less than or equal to the set error value at step S 70 . In this case, if it is determined that the error value % between the required flow rate Q m, r  and the current flow rate Q m, cur  is not within the set error value, the controller  800  re-calculates the speed difference value ΔN at step S 40 . Contrarily, if it is determined that the error value % between the required flow rate Q m, r  and the current flow rate Q m, cur  is within the set error value, the controller  800  stops speed changing for the motor  201 . After a given period of time has passed, next, the controller  800  re-starts the flow rate control and consistently controls the blower  200 . In  FIGS. 18A to 19 , a main system represents the power generation system, and a signal m_dot represents mass flow rate Q m . 
     Referring to  FIG. 20 , accordingly, if a performance map measured at 200° C. and 101.325 kPa is stored, for example, it is converted into a performance map on a condition of 500° C. through a conversion expression suggested therein. If the inlet and output pressure ratio of 1.1 and the rotating speed of 100% (139678 rpm) are obtained on the performance map on the condition of 500° C., the flow rate of about 500 lpm can be predicted. 
     That is, the required flow rate of the solid oxide fuel cell power generation system according to the present invention is controlled through the blower  200 , and the recycle flow rate of the required flow rate is controlled through the fuel pump  410 . 
     In conclusion, the unreacted fuel after the reaction of the fuel cell module  100  is recycled through the blower  200  and supplied to the anode, and the motor  201  used to operate the blower  200  is cooled by means of air cooling. The air used for cooling the blower  200  is recycled to the cathode of the fuel cell module  100 , and the fuel pump  410  is controlled to set the recycle ratio. As a result, advantageously, the efficiency of the fuel cell module  100  can be improved. 
     As set forth in the foregoing, the solid oxide fuel cell power generation system according to the present invention is configured to allow the unreacted fuel after the reaction of the fuel cell module to be recycled through the blower and then supplied to the anode, configured to allow the motor used to operate the blower to be cooled by means of air cooling, configured to allow the air used for cooling the blower to be recycled to the cathode of the fuel cell module, and configured to control the fuel pump so as to set the recycle ratio, thereby improving the efficiency of the fuel cell module. 
     That is, the solid oxide fuel cell power generation system according to the present invention is provided with the air cooled high temperature blower having the foil-air bearings to thus allow the air heated after cooling the high temperature blower to be recycled to the cathode, thereby improving the power generation efficiency thereof. 
     Further, the solid oxide fuel cell power generation system according to the present invention converts the performance map in real time using the ambient temperature performance map and the measured data for the temperature and pressure at the high temperature operating point for the control of the high temperature blower, controls the rotating speed of the motor, and controls the recycle flow rate, so that as an orifice flow meter available at a high temperature is not used, a differential pressure loss can be reduced. 
     If the orifice flow meter is used, that is, a differential pressure is generated to cause the power for the high temperature blower to be additionally consumed, but the solid oxide fuel cell power generation system according to the present invention does not use the orifice flow meter, thereby improving the power generation efficiency thereof. 
     The technical configurations disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one of ordinary skill in the art to variously employ the present invention in virtually any appropriately detailed structure. 
     The present invention may be modified in various ways and may have several exemplary embodiments. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto, and it should be understood that the invention covers all the modifications, equivalents, and replacements within the idea and technical scope of the invention.