JP2013004467A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system which can improve the efficiency of power generation without causing carbon deposition.SOLUTION: A new fuel flow rate introduced into a fuel reformer 15a is determined according to a request for fuel cell output, and further a discharged fuel circulation rate Ry or a ratio of branching by a first branch valve 25, a discharged fuel circulation rate Rd or a ratio of branching by a second branch valve 26, and O2/C are set on the basis of the determined fuel flow rate so as to heighten the operating efficiency of a fuel cell 11. Meanwhile, control means controls the first branch valve 25 and the second branch valve 26 so that each of the branching ratios will be achieved. Furthermore, the amount of air supplied to the fuel reformer 15a is controlled so that the O2/C will be achieved. As a result, it is possible to run a fuel cell system with high efficiency without causing carbon deposition and without causing insufficiency of the amount of heat required for reforming.

Description

  The present invention relates to a fuel cell system that generates electricity by reacting a reformed gas obtained by reforming a hydrocarbon fuel and an oxidizing gas such as air, and more particularly to a technique for improving energy efficiency.

  In a fuel cell system, in order to reform the hydrocarbon fuel introduced into the fuel electrode without carbon deposition, it is necessary to reform at a high temperature of, for example, 700 ° C. or higher depending on the type of hydrocarbon fuel. For this reason, it is necessary to increase the flow rate of oxygen introduced into the reformer, or to increase the fuel for the burner for heating the reformer, resulting in a problem that the power generation efficiency of the entire fuel cell system is reduced. appear.

  Further, as a conventional fuel cell system, for example, as disclosed in Patent Document 1, energy efficiency is improved by circulating water vapor and unused fuel contained in the anode exhaust gas of the fuel cell to the reformer. What is to be known is known.

JP-A-9-115541

  As described above, the conventional fuel cell system has a problem that energy efficiency is lowered because it is necessary to reform the hydrocarbon fuel at a high temperature depending on the type of the hydrocarbon fuel.

  The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide a fuel cell capable of reforming a hydrocarbon fuel at a high temperature without reducing energy efficiency. To provide a system.

  In order to achieve the above object, the present invention provides a fuel cell having a cathode and an anode, reforming means for reforming fuel and supplying reformed gas to the anode, and fuel discharged from the anode. A branching unit that circulates at least a part of the exhausted fuel as the first circulating exhausted fuel to the reforming unit and supplies the other exhausted fuel as the second circulating exhausted fuel to the outlet passage of the reforming unit, And the second circulating exhaust fuel and the reformed gas sent from the reforming means are mixed and supplied to the anode.

  In the fuel cell system according to the present invention, a branching means is provided in the flow path on the anode outlet side of the fuel cell, and a part of the discharged fuel discharged from the anode by the branching means is circulated to the reforming means as the first circulating exhaust fuel. The other is supplied to the outlet side flow path of the reforming means as the second circulating exhaust fuel. That is, the flow rate of the discharged fuel that circulates to the reforming means is reduced by the amount of the second circulating discharged fuel. Therefore, the amount of heat required for reforming can be reduced, and efficient operation is possible.

1 is a block diagram showing a configuration of a fuel cell system according to an embodiment of the present invention. It is a flowchart which shows the processing operation of the fuel cell system which concerns on 1st Embodiment of this invention. It is a map figure which shows the relationship between the request | requirement output and the supply amount of a new fuel referred with the fuel cell system which concerns on 1st Embodiment of this invention. It is a map figure which shows the relationship between S / C, O2 / C, and power generation efficiency referred with the fuel cell system which concerns on 1st Embodiment of this invention. It is a map figure which shows the relationship between "1-Ry" and Tab which are referred with the fuel cell system which concerns on 1st Embodiment of this invention. It is a map figure which shows the relationship between Rd, O2 / C, and electric power generation efficiency referred with the fuel cell system which concerns on 1st Embodiment of this invention. It is a flowchart which shows the processing operation of the fuel cell system which concerns on 2nd Embodiment of this invention. It is a flowchart which shows the processing operation of the fuel cell system which concerns on 2nd Embodiment of this invention. It is a block diagram which shows the 2nd structural example of the fuel cell system which concerns on embodiment of this invention. It is a block diagram which shows the 3rd structural example of the fuel cell system which concerns on embodiment of this invention. It is a block diagram which shows the 4th structural example of the fuel cell system which concerns on embodiment of this invention. It is a flowchart which shows the processing operation of the fuel cell system which concerns on the modification of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Description of First Embodiment]
FIG. 1 is a block diagram showing a configuration of a fuel cell system 100 according to the first embodiment of the present invention. As shown in FIG. 1, the fuel cell system 100 includes a fuel cell 11 including a cathode 11a and an anode 11b, a fuel reformer 15a, a combustion burner 15b for heating the fuel reformer 15a, and a heat exchanger. And a reformer 15 provided with 15c. The reformed gas sent from the fuel reformer 15 a is supplied to the anode 11 b of the fuel cell 11. Further, the exhaust gas from the cathode 11a is supplied to the combustion burner 15b.

  Furthermore, the 1st air blower 12 which supplies air to the cathode 11a of the fuel cell 11, the air heating heat exchanger 13 which heats the air sent out from this 1st air blower 12, and the 1st air blower 12 and air heating An air branch valve 23 provided between the heat exchanger 13 and a circulation blower 16 installed on the outlet side of the anode 11b for circulating the anode exhaust gas to the fuel reformer 15a, and on the outlet side of the circulation blower 16 A first branch valve 25 and a second branch valve 26 are provided.

  The first branch valve 25 operates under the control of the control unit 31 to be described later, supplies a part of the anode exhaust gas sent from the circulation blower 16 to the combustion burner 15b, and supplies the remaining anode exhaust gas to the second. It is sent to the branch valve 26 side. At this time, the ratio sent to the second branch valve 26 side is defined as the exhaust fuel circulation rate Ry. Therefore, out of the total anode exhaust gas flow rate, the exhaust fuel circulation rate Ry is sent to the second branch valve 26 side, and (1-Ry) is sent to the combustion burner 15b side.

  The second branch valve 26 is also operated by the control of the control unit 31, and a part of the anode exhaust gas sent from the first branch valve 25 (this is referred to as “second circulation exhaust fuel [m 3 / sec]”. Is supplied to the anode 11b of the fuel cell 11 (the outlet of the fuel reformer 15a), and the remaining anode exhaust gas (referred to as “first circulating exhaust fuel [m 3 / sec]”) is fuel-modified. It is made to circulate to the quality device 15a. At this time, the ratio of the first circulating exhaust fuel is defined as an exhaust fuel circulation fraction Rd. That is, Rd is expressed by the following equation (1).

Rd = (first circulating exhaust fuel)
/ {(First circulating exhaust fuel) + (second circulating exhaust fuel)} (1)
Further, the fuel cell system 100 includes a second air blower 17 that supplies air to the fuel reformer 15a of the reformer 15, a first fuel pump 18 that supplies fuel to the fuel reformer 15a, and the first A fuel evaporator 14 that evaporates liquid fuel delivered from one fuel pump 18, a third air blower 20 that supplies air to the combustion burner 15b, a second fuel pump 27 that supplies fuel to the combustion burner 15b, It has. Therefore, the air sent from the second air blower 17, the fuel gas vaporized by the fuel evaporator 14, and the anode exhaust gas (first circulating exhaust fuel) sent through the second branch valve 26 are mixed gas. To the fuel reformer 15a.

  Further, the anode exhaust gas branched from the first branch valve 25, the fuel supplied from the second fuel pump 27, and the air sent out from the third air blower 20 are mixed and supplied to the combustion burner 15b. Further, the exhaust gas discharged from the combustion burner 15b is heat-exchanged by the air heating heat exchanger 13, and then supplied to the fuel evaporator 14 to be used as a heat source for fuel evaporation.

  Further, on the inlet side of the cathode 11a, a start combustion burner 24 is provided for raising the fuel cell 11 to a predetermined temperature when starting the fuel cell 11. A third fuel pump 21 and a fuel evaporator 22 are provided on the inlet side of the starting combustion burner 24 and are connected to the outlet of the air branch valve 23. The startup combustion burner 24 mixes the fuel supplied from the third fuel pump 21 and vaporized by the fuel evaporator 22 with the air supplied from the air branch valve 23 and burns it. 11a. Thereby, the cathode 11a can be heated.

  The fuel cell 11 is, for example, a solid oxide fuel cell (SOFC), which generates electric power by reacting a reformed gas supplied to the anode 11b and air supplied to the cathode 11a. Supplied to power demand facilities such as motors. Further, the reformed gas sent from the fuel reformer 15a and the second circulation exhaust fuel (circulation exhaust fuel branched from the second branch valve 26) are supplied to the anode 11b.

  The reformer 15 is a heat exchanger type reformer, for example, and is heated by the heat supplied from the combustion burner 15b. That is, since the reforming reaction in the fuel reformer 15a is basically operated so as to be an endothermic reaction, the anode exhaust gas is combusted and the heat generated by this combustion is transferred to the fuel reformer 15a. It has a mechanism. And it operates so that the gas temperature produced | generated in the combustion burner 15b may become high with respect to the operating temperature of the fuel reformer 15a. Further, the fuel supplied from the first fuel pump 18, the mixed gas of the air sent from the second air blower 17 and the anode exhaust gas is reformed using a catalytic reaction, and the reformed fuel (hydrogen) A reformed gas containing gas) is supplied to the anode 11 b of the fuel cell 11.

  Further, the fuel cell system 100 is provided with a control unit (control means) 31, a storage unit 32 for storing various data, and an anode exhaust gas flow path to detect the amount of water vapor contained in the anode exhaust gas. A steam flow rate sensor N1 for performing combustion, a combustion burner temperature sensor T1 for detecting the combustion temperature of the combustion burner 15b, a reforming temperature sensor T2 for detecting the reforming temperature Trf of the fuel reformer 15a, and a second fuel pump 27. A fuel temperature sensor T3 for detecting the temperature of the fuel to be discharged, and an air temperature sensor T4 for detecting the temperature of the air sent from the second air blower 17. The detection signals of the sensors N1, T1, T2, T3, and T4 are output to the control unit 31.

  The control unit 31 can be configured by, for example, a microcomputer including a CPU, a RAM, a ROM, various operators, and the like. The first air blower 12, the second air blower 17, the third air blower 20, the first 1 is connected to each device of the fuel pump 18 and the third fuel pump 21 (connection wiring is not shown), and a control signal is output to each of these devices, so that the fuel cell system 100 is generally Control. In particular, in the present embodiment, the control unit 31 performs the first branch valve 25 according to the processing procedure described later based on the detection signals detected by the steam flow rate sensor N1, the combustion burner temperature sensor T1, and the reforming temperature sensor T2. And the opening degree of the 2nd branch valve 26 is adjusted, and also the air quantity sent out from the 2nd air blower 17 is controlled.

  The storage unit 32 stores each map used for the arithmetic processing of the control unit 31. For example, the maps shown in FIGS. 3 to 6 are stored. FIG. 3 is a map (first map) showing the relationship between the required output of the fuel cell 11 and the flow rate of the new fuel. FIG. 4 shows the relationship between the S / C and O 2 / C and the efficiency of the fuel cell 11. It is a map (2nd map) shown. Here, “S / C” is a ratio of steam (steam) and carbon (carbon). Specifically, (Steam flow rate in the first circulation exhaust fuel [mol / sec]) / (fuel reforming) The flow rate of carbon introduced into the vessel [mol / sec]). "O2 / C" is the ratio of oxygen to carbon, (oxygen flow rate introduced into the fuel reformer [mol / sec]) / (carbon flow rate introduced into the fuel reformer [mol / sec]) Indicated by

  FIG. 5 is a map (third map) showing the relationship between “1-Ry” and the combustion burner gas temperature Tab, which is supplied from the fuel newly introduced into the combustion burner 15 b, that is, from the second fuel pump 27. When the fuel Bf increases, the combustion burner gas temperature Tab increases, and when the newly introduced air, that is, the air Ba supplied from the third air blower 20, increases, the combustion burner gas temperature Tab changes.

  FIG. 6 is a map (fourth map) showing the relationship between the exhaust fuel circulation fraction Rd and O 2 / C and the efficiency of the fuel cell 11. Rd is expressed by the above-described equation (1).

  Next, the operation of the fuel cell system 100 according to the present embodiment configured as described above will be described. In this embodiment, by setting S / C, O 2 / C, and Rd by a method described later, the reformer 15 does not deposit carbon, the reforming required heat flow does not run short, and the fuel cell 11 is operated with high efficiency. The procedure for setting S / C, O 2 / C, and Rd will be described below with reference to the flowchart shown in FIG.

  When the required output is given in step S11, in step S12, the control unit 31 determines the flow rate of new fuel corresponding to the required output based on the first map shown in FIG. That is, the flow rate of fuel supplied from the first fuel pump 18 to the fuel reformer 15a is determined.

  In step S13, the control unit 31 detects the water vapor flow rate during the exhaust fuel circulation by the water vapor flow rate sensor N1.

  In step S14, the control unit 31 acquires the combustion burner gas temperature Tab detected by the combustion burner temperature sensor T1 and the reforming temperature Trf detected by the reforming temperature sensor T2, and further detected by the fuel temperature sensor T3. The temperature of the new fuel (the temperature of the fuel output from the second fuel pump 27) and the air temperature detected by the air temperature sensor T4 (the temperature of the air output from the second air blower 17) are acquired.

  In step S15, the control unit 31 determines Ry, O 2 / C, and Rd according to the following procedure. First, combustion is performed by adjusting the new fuel supplied to the combustion burner 15b, that is, the fuel flow rate Bf supplied from the second fuel pump 27, or the new air, that is, the air flow rate Ba supplied from the third air blower 20. The burner gas temperature Tab is controlled to be a desired temperature. This control can be controlled with reference to the third map shown in FIG.

  Next, a map showing the relationship between S / C and O 2 / C when the combustion burner gas temperature Tab determined in the above process and the reforming temperature Trf detected in the process of step S14 are constant, ie, FIG. Referring to the second map shown in FIG. 4, the S / C is set so that the carbon does not precipitate, the reforming required heat flow is not insufficient, and the efficiency becomes high. A plurality of second maps shown in FIG. 4 are set in advance for combinations of the combustion burner gas temperature Tab and the reforming temperature Trf, and are stored in the storage unit 32 shown in FIG. 1 as described above. And when the combination of Tab and Trf is determined, the control part 31 reads the 2nd map corresponding to this from the memory | storage part 32, and performs the process which sets said S / C.

  Thereafter, with reference to the map showing the relationship between the exhaust fuel circulation ratio Rd and O2 / C when S / C is constant, that is, the fourth map shown in FIG. Rd and O 2 / C are set so that the required heat flow does not become insufficient and the efficiency becomes high. A plurality of maps shown in FIG. 6 are set in advance for the combination of the combustion burner gas temperature Tab and the reforming temperature Trf and the numerical value of S / C, and are stored in the storage unit 32 described above. When the S / C is determined in addition to the combination of the combustion burner gas temperature Tab and the reforming temperature Trf, the control unit 31 reads the fourth map corresponding to this from the storage unit 32, and the above Rd and A process of setting O 2 / C is executed.

  In step S <b> 16, the control unit 31 executes the operation of the fuel cell 11.

  In this way, it is possible to set the O2 / C, S / C, and the exhaust fuel circulation fraction Rd that do not cause carbon deposition, do not have the required reforming heat flow, and increase the efficiency. Further, since the amount of water vapor in the exhaust fuel circulation (the amount of water vapor contained in the anode exhaust gas) has been acquired in the process of step S12, the exhaust fuel circulation is based on the fuel flow rate supplied to the fuel reformer 15a. By adjusting the rate Ry, a desired S / C can be obtained. That is, the exhaust fuel circulation rate Ry is determined.

  Then, the control unit 31 adjusts the opening degree of the first branch valve 25 so as to achieve this exhaust fuel circulation rate Ry, and opens the second branch valve 26 so as to achieve the above-described exhaust fuel circulation fraction Rd. The fuel cell 11 can be operated with high efficiency by adjusting the degree and further setting the air supply amount by the second air blower 17 so as to be the above-mentioned O2 / C. Specifically, the fuel cell 11 can be operated at an efficiency of 55%, which is the highest efficiency shown in the fourth map shown in FIG.

  Thus, in the fuel cell system 100 according to the present embodiment, by providing the second branch valve 26, a part of the circulated anode exhaust gas (second circulated exhaust fuel) is discharged from the fuel reformer 15a. To supply. When the required output of the fuel cell 11 is determined, a new fuel flow rate (the fuel flow rate sent from the first fuel pump 18) is determined according to the required output, and the maps shown in FIGS. Based on this, it is possible to set an operating condition in which carbon is not deposited, the required heat quantity for reforming is not short, and the efficiency is highest. Specifically, the numerical values of S / C, Rd, and O2 / C can be determined. Therefore, the entire system can be operated with high efficiency, and more power generation output can be obtained with less fuel.

  Further, by providing the second branch valve 26, the diversion ratio between the first circulating exhaust fuel and the second circulating exhaust fuel can be changed, so that the required output changes as in a fuel cell mounted on a vehicle. In this case, it is possible to set the optimum efficiency corresponding to this change.

  Each of the maps shown in FIGS. 3 to 6 shows an example, and the present embodiment is not limited to these maps.

[Description of Second Embodiment]
Next, a second embodiment of the present invention will be described. The fuel cell system according to the second embodiment has the same apparatus configuration as that of the first embodiment described above, but differs in the method for calculating the operating conditions. That is, in the first embodiment, the operating conditions are set with reference to the maps shown in FIGS. 3 to 6, but in the second embodiment, the operating conditions are set by an arithmetic expression as shown below. Hereinafter, the operation of the fuel cell system according to the second embodiment will be described in detail with reference to the flowcharts shown in FIGS.

  FIG. 7 is a flowchart showing a schematic operation of the fuel cell system according to the second embodiment, and FIG. 8 is a flowchart showing a detailed operation of step S35 shown in FIG.

  First, when the required output is given in step S31 of FIG. 7, in step S32, the control unit 31 determines the flow rate of the new fuel corresponding to the required output based on the first map shown in FIG. That is, the flow rate of fuel supplied from the first fuel pump 18 to the fuel reformer 15a is determined.

  In step S33, the control unit 31 detects the water vapor flow rate during fuel circulation by the water vapor flow rate sensor N1.

  In step S34, the control unit 31 acquires the combustion burner gas temperature Tab detected by the combustion burner temperature sensor T1 and the reforming temperature Trf detected by the reforming temperature sensor T2, and further detected by the fuel temperature sensor T3. The temperature of the new fuel (the temperature of the fuel output from the second fuel pump 27) and the air temperature detected by the air temperature sensor T4 (the temperature of the air output from the second air blower 17) are acquired.

  In step S35, the control unit 31 performs the processing shown in FIG. 8 so that the exhaust fuel circulation flow rate, the first circulation exhaust fuel, the new air amount supplied to the fuel reformer 15a, the exhaust air amount from the cathode of the combustion burner 15b, A new fuel amount and an air amount to be supplied to the combustion burner 15b are determined. Thereafter, in step S36, the control unit 31 executes the operation of the fuel cell 11.

  Next, the procedure for determining each operating condition will be described with reference to the flowchart shown in FIG.

  First, in step S51, the reforming temperature Trf = x is set. Next, in step S52, the exhaust fuel circulation rate Ry = y is set. In step S53, the exhaust fuel circulation fraction Rd = z is set. In step S54, the ratio of oxygen flow rate to carbon flow rate is set to O2 / C = f.

  Thereafter, in step S55, it is determined whether or not the heat flow from the combustion burner 15b can be supplied with respect to the required heat amount necessary for fuel reforming. In this process, the exhaust fuel circulation rate Ry, the exhaust fuel circulation fraction Rd, and O2 / C are provisionally determined to predetermined values under the condition of the detected reforming temperature Trf, and with respect to the required heat flow required for reforming, It is determined whether or not a heat flow can be supplied from the combustion burner.

  If the supply of heat flow is not possible (NO in step S55), it is determined in step S65 whether the combustion heat from the fuel introduced into the combustion burner 15b is a sufficient amount of heat. That is, it is determined whether or not the combustion heat from the fuel supplied from the second fuel pump 27 and the exhaust fuel branched from the first branch valve 25 and supplied to the combustion burner 15b has a sufficient amount of heat.

  As a result, when it is determined that it is sufficient (YES in step S65), in step S66, the new air flow rate Ba supplied to the combustion burner 15b and the air flow rate Ea introduced from the cathode 11a to the combustion burner 15b are set. Decreasing the temperature of the combustion burner 15b to increase the temperature of the combustion burner 15b makes it possible to determine whether or not the required reforming heat flow can be satisfied.

  If it can be satisfied (YES in step S65), Ba and Ea are determined in step S68 so that the reforming required heat flow can be satisfied.

  On the other hand, if the combustion heat is not sufficient (NO in step S65), and if the reforming required heat flow cannot be satisfied by reducing Ea and Ba (NO in step S66), in step S67, the reforming request is made. Bf, Ba, and Ea that satisfy the heat quantity are determined. In other words, when the required reforming heat quantity cannot be satisfied, a new fuel is supplied from the second fuel pump 27 to the combustion burner 15b to increase the heat generation amount so as to satisfy the required reforming heat quantity.

  If the processes in steps S67 and S68 are completed, and if YES is determined in the process in step S55, the process proceeds to step S56.

  In step S56, it is determined whether or not there is a possibility of carbon deposition when the fuel is reformed by the fuel reformer 15a. In this process, based on the reforming temperature, the exhaust fuel circulation rate, the exhaust fuel circulation fraction, and O 2 / C, it is determined whether or not carbon is deposited in the fuel reformer 15 a using a well-known arithmetic expression. If it is determined that there is no possibility of carbon deposition (YES in step S56), the power generation efficiency of the entire fuel cell system is calculated in step S57. The power generation efficiency can be calculated using a known arithmetic expression.

  In step S58, it is determined whether or not the calculated power generation efficiency is a maximum value. If it is the maximum value (YES in step S58), each data is stored in a memory (not shown) in step S59. Specifically, the reforming temperature Trf is stored as MTrf, the exhaust fuel circulation rate Ry is stored as MRy, the exhaust fuel circulation rate Rd is stored as MRd, and O2 / C is stored as MO2 / C. The fuel flow rate Bf is stored as MBf, the new air flow rate Ba is stored as MBa, and the air flow rate Ea is stored as MEa. The above “M” indicates a stored numerical value.

  In step S60, it is determined whether O2 / C is 1 or less. If it is 1 or less (YES in step S60), f = f + Δf is set in step S69, and the process returns to step S54. That is, the O2 / C numerical value f is increased by a minute numerical value Δf, and the processing from step S54 is repeated.

  In step S61, it is determined whether or not the exhaust fuel circulation ratio Rd is 1 or less. If it is 1 or less (YES in step S61), z is set to z + Δz in step S70, and the process is performed in step S53. return. That is, the numerical value z of Rd is increased by a minute numerical value Δz, and the processing from step S53 is repeated.

  In step S62, it is determined whether or not the exhaust fuel circulation rate Ry is 1 or less. If it is 1 or less (YES in step S62), y is set to y + Δy in step S71, and the process returns to step S52. . That is, the numerical value y of Ry is increased by a minute numerical value Δy, and the processing from step S52 is repeated.

  In step S63, it is determined whether or not the reforming temperature Trf is equal to or lower than the maximum value Trfmax. If the reforming temperature Trf is equal to or lower than the maximum value Trfmax (YES in step S63), x = x + Δx is set in step S72, and the process proceeds to step S51. Return processing. That is, the numerical value x of Trf is increased by a minute numerical value Δx, and the processing from step S51 is repeated.

  If NO is determined in steps S60 to S63, the operating conditions are determined to be MTrf, MRy, MRd, MO2 / C, MBf, MBa, and MEa in step S64. That is, the data stored in the memory will eventually store the numerical values that are the conditions for the highest power generation efficiency. By setting these conditions as operating conditions, the power generation efficiency is the highest. The fuel cell system 100 can be operated under conditions.

  In addition, in the case where the efficiency is higher when reforming the fuel at a temperature higher than the immediately preceding reforming temperature due to a change in the required load from a low load to a high load, in addition to the heat necessary for reforming, Since it is necessary to raise the temperature of the reformer itself, this temperature rise is also taken into account as the heat flow required for reforming.

  Specifically, when the reforming temperature is changed to a higher temperature, the required heat flow required for reforming is equal to the heat capacity of the reformer and the immediately preceding reforming temperature, compared to reforming at a constant temperature. The product of the target reforming temperature differences is added to the required heat flow. As a result, the load followability of the in-vehicle fuel cell system can be improved.

  Thus, in the fuel cell system 100 according to the second embodiment, as in the first embodiment described above, by providing the second branch valve 26, a part of the circulated anode exhaust gas (second circulation exhaust) The fuel is supplied to the outlet side of the fuel reformer 15a. Then, when the required output of the fuel cell 11 is determined, a new fuel flow rate (the fuel flow rate sent from the first fuel pump 18) is determined according to this required output, and further, the carbon is not precipitated by the calculation and reforming is performed. It is possible to set an operating condition in which the required heat quantity is not insufficient and the efficiency is highest.

  That is, while appropriately changing the reforming temperature Trf, the exhausted fuel circulation rate Ry, the exhausted fuel circulation rate Rd, and O 2 / C, a condition for obtaining the highest power generation efficiency is obtained by calculation. Since the battery system 100 is operated, the fuel cell system 100 can be operated with high efficiency without carbon deposition.

  Further, by providing the second branch valve 26, the diversion ratio between the first circulating exhaust fuel and the second circulating exhaust fuel can be changed, so that the required output changes as in a fuel cell mounted on a vehicle. In this case, it is possible to set the optimum efficiency corresponding to this change.

  Even if the fuel to be introduced is a high-grade carbon-containing fuel (a fuel having a large C ratio), if it can be reformed without carbon deposition at a temperature of about 700 ° C., the first circulating exhaust fuel flow rate is set to By appropriately controlling, high efficiency operation can be performed without introducing additional fuel into the combustion burner 15b. However, if carbon deposition is suppressed and the required heat flow necessary for reforming is satisfied, The control range is narrow and difficult to control. Furthermore, in the case of a higher-grade carbon-containing fuel, it is necessary to reform at a higher temperature in order to suppress carbon deposition.

  For this reason, in the present embodiment, the flow rate of the air flow rate Ba discharged from the fuel cell 11 or the new airflow flow rate Bf introduced into the combustion burner 15b is reduced, and the fuel discharged without circulation (the first branch) Combustion gas at a higher temperature is generated in the combustion burner 15b together with the exhaust fuel branched off by the valve 25). Therefore, when the heat flow necessary for reforming is sufficiently satisfied, the amount of exhaust fuel circulated (that is, the exhaust fuel circulation rate Ry) is increased, and the exhaust fuel discharged from the anode 11a is supplied to the fuel reformer. By circulating to 15a, it becomes possible to widen the controllable range without depositing carbon in the fuel reformer 15a, and control becomes easy.

  In addition, if the heat flow necessary for reforming cannot be obtained by controlling the flow rate of air discharged from the cathode 11a and the flow rate of new air introduced into the combustion burner 15b, new fuel is supplied from the second fuel pump 27. By supplying, a larger amount of combustion gas higher than the reforming temperature is generated in the combustion burner 15b, and a heat flow necessary for reforming is ensured.

  As a result, even if the fuel to be introduced is a high-grade carbon-containing fuel, it becomes possible to operate with high efficiency without causing carbon deposition.

[Description of modification]
Next, modified examples of the first and second embodiments described above will be described. FIG. 9 is a block diagram showing the configuration of the fuel cell system 101 according to the first modification, which is different from the fuel cell system 100 shown in FIG. 1 in that the second branch valve 26 is not provided. In this modification, by setting the length and diameter of the pipe on the outlet side of the first branch valve 25 to a desired size, the anode exhaust gas sent from the first branch valve 25 is supplied to the desired exhaust fuel circulation. Set to fraction Rd. That is, when there is no need to change the exhaust fuel circulation fraction Rd, the flow rate of the first circulation exhaust fuel and the flow rate of the second circulation exhaust fuel are set by initially setting the length and diameter of the pipe. Since it can be determined, the second branch valve 26 can be omitted.

  That is, the piping provided on the downstream side of the first branch valve 25 can have a function as the second branch means, and the anode exhaust gas can be diverted at a desired ratio.

  FIG. 10 is a block diagram showing the configuration of the fuel cell system 102 according to the second modification. In the fuel cell system 100 shown in FIG. 1, a discharge valve (discharge means) is provided in the outlet piping path of the cathode 11a. The difference is that 41 is provided, and the difference is that the exhaust gas discharged from the discharge valve 41 is supplied to the fuel evaporator 14 as a heat source. In the fuel cell system 102, a part of the air discharged from the cathode 11a is discharged and supplied to the combustion burner 15b. Therefore, the temperature of the combustion gas generated by the combustion burner 15b can be easily adjusted. It becomes possible.

  FIG. 11 is a block diagram showing the configuration of the fuel cell system 103 according to the third modification. A mixer 42 is provided on the inlet side of the anode 11b with respect to the fuel cell system 100 shown in FIG. It is different in point. That is, a mixer 42 having a function of mixing the reformed gas reformed by the fuel reformer 15a and the second circulating exhaust fuel branched by the second branch valve 26 is provided. By using the mixer 42, the reformed gas and the second circulating exhaust fuel can be uniformly mixed and supplied to the anode 11b, and stable power generation can be achieved in a short time.

  As the mixer 42, a gas diffusion plate or a porous body for inducing mixing may be packed in the container, and as an ejector, a new fuel and a reformed gas pressurized by pressurizing air are used. The pressure for introducing the fuel to the anode 11b may be generated by mixing while drawing the second circulating exhaust fuel.

  A reformer can be used as the mixer 42. When a reformer is used, the reformed gas (sending gas from the fuel reformer 15a) having a high temperature and the second circulating gas containing steam are mixed and subjected to adiabatic reforming, and steam and fuel reforming are performed. By endothermic reaction with hydrocarbons that have not been reformed in the vessel 15a, hydrogen and carbon monoxide can be decomposed, and carbon deposition in the fuel cell 11 can be made difficult.

  Further, by causing the mixer 42 to exchange heat with another cooling medium, the sensible heat of the fuel introduced into the fuel cell 11 can be reduced, and the fuel reformer 15a and the fuel cell 11 can be reduced. It is also possible to adjust the temperature of the fuel cell 11 that generates heat during power generation by separating the thermal linkage between them.

  Next, a fourth modification will be described. The fourth modification has the same device configuration as that of FIG. 1 described above, and further includes fuel composition detection means (not shown) for detecting the composition of the fuel supplied from the first fuel pump 18. FIG. 12 is a flowchart showing the processing operation of the fuel cell system according to the fourth modification. Hereinafter, the processing operation of the fuel cell system according to the fourth modification will be described.

  First, when a required output is given in step S90 of FIG. 12, in step S91, the control unit 31 acquires the composition (CH ratio) in the fuel detected by the fuel composition detecting means, and further, this composition. To determine the combustion heat. Specifically, in step S911, the timing of refueling is detected from the outside, the CH ratio in the fuel is detected in step S912, and the combustion heat (enthalpy) is predicted in step S913.

  In step S92, the control unit 31 determines the flow rate of the new fuel based on the combustion heat of the fuel. That is, the process similar to the process of step S12 of FIG. 2 described in the first embodiment is executed in consideration of the combustion heat of the fuel.

  In step S93, the control unit 31 detects the water vapor flow rate in the circulating gas (anode exhaust gas) based on the CH ratio in the fuel and the power generation status of the fuel cell 11. That is, the same process as the process of step S13 in FIG. 2 is executed in consideration of the CH ratio of the fuel and the power generation state of the fuel cell 11.

  In step S94, the control unit 31 performs the same process as in step S14 of FIG. 2, and calculates the combustion burner gas temperature Tab, the reforming temperature Trf, the temperature of the new fuel, and the air temperature detected by the combustion burner temperature sensor T1. get.

  In step S95, the control unit 31 searches for the most efficient operation condition in which the fuel reformer 15a does not deposit carbon from the CH ratio in the fuel, and the exhaust fuel circulation flow rate, the first exhaust fuel circulation flow rate, the fuel A new air amount to be supplied to the reformer 15a and a new fuel amount to be supplied to the combustion burner 15b are determined. In step S <b> 96, the control unit 31 executes the operation of the fuel cell 11.

  Thus, in the fuel cell system according to the fourth modification, the composition of new fuel is sequentially detected and set to highly efficient operating conditions, so even if the fuel composition changes (for example, gasoline The composition may vary from region to region), allowing for highly efficient operation.

  The fuel composition detection means detects the timing of refueling from the outside, and detects the CH ratio of the introduced fuel by fuel composition analysis. As a method of fuel composition analysis, a gas temperature before and after combustion when fuel and air are burned, a method of measuring based on oxygen concentration detection, and the like can be used.

  Although the fuel cell system of the present invention has been described based on the illustrated embodiment, the present invention is not limited to this, and the configuration of each part is replaced with an arbitrary configuration having the same function. Can do.

  The present invention can be used to operate a fuel cell system with high efficiency.

DESCRIPTION OF SYMBOLS 11 Fuel cell 11a Cathode 11b Anode 12 1st air blower 13 Air heating heat exchanger 14 Fuel evaporator 15 Reformer 15a Fuel reformer 15b Combustion burner 15c Heat exchanger 16 Circulation blower 17 2nd air blower 18 1st fuel Pump 20 Third air blower 21 Third fuel pump 22 Fuel evaporator 23 Air branch valve 24 Start combustion burner 25 First branch valve (first branch means)
26 Second branch valve (second branch means)
27 Second fuel pump 31 Control unit 32 Storage unit 41 Drain valve (discharge unit)
42 Mixer 100, 101, 102, 103 Fuel cell system N1 Water vapor flow rate sensor T1 Combustion burner temperature sensor T2 Reforming temperature sensor T2
T3 Fuel temperature sensor T4 Air temperature sensor Rd Exhaust fuel circulation fraction Ry Exhaust fuel circulation rate Tab Combustion burner gas temperature Trf Reforming temperature

Claims (8)

A fuel cell having a cathode and an anode;
Reforming means for reforming fuel and supplying reformed gas to the anode;
Of the exhaust fuel discharged from the anode, at least a part of the exhaust fuel is circulated to the reforming means as a first circulation exhaust fuel, and the other exhaust fuel is circulated as a second circulation exhaust fuel to the outlet flow of the reforming means. Branching means for supplying to the road,
The fuel cell system, wherein the second circulating exhaust fuel and the reformed gas delivered from the reforming means are mixed and supplied to the anode. A first branching means for supplying at least a part of the discharged fuel discharged from the anode to the outlet side of the cathode and supplying other discharged fuel to the downstream side;
A part of the exhaust fuel provided downstream of the first branching unit and sent downstream from the first branching unit is circulated to the reforming unit as a first circulation exhausted fuel, and the like. Second branching means for supplying the exhausted fuel as a second circulating exhausted fuel to the outlet passage of the reforming means,
Combustion means for supplying the gas discharged from the cathode and the exhaust fuel branched by the first branching means to burn and transmitting heat generated by the combustion to the reforming means;
The fuel cell system according to claim 1, comprising:   3. The fuel cell system according to claim 1, further comprising a mixing unit configured to mix the second circulating exhaust fuel and the reformed gas sent from the reforming unit. 4. A control means for controlling the opening degree of the first branching means, the opening degree of the second branching means, and the amount of air supplied to the reforming means;
The control means determines a fuel flow rate to be introduced into the reforming means in response to an output request of the fuel cell, and further, based on the fuel flow rate, the operation efficiency of the fuel cell is increased. The branch ratio by the first branch means and the branch ratio by the second branch means are set, the first branch means and the second branch means are controlled so that these branch ratios are obtained, and the revision 4. The fuel cell system according to claim 2, wherein the amount of air supplied to the quality means is controlled.   5. The branching ratio by the first branching unit, the branching ratio by the second branching unit, and the amount of air introduced into the reforming unit are determined with reference to a preset map. The fuel cell system described.   The fuel cell system according to claim 4, wherein the branching ratio by the first branching unit, the branching ratio by the second branching unit, and the amount of air introduced into the reforming unit are determined by calculation.   The apparatus further comprises discharge means for discharging a part of the gas supplied from the cathode to the combustion means to the outside, and the control means adjusts the gas flow rate discharged by the discharge means, thereby adjusting the temperature of the combustion means. It controls, The fuel cell system of any one of Claims 2-6 characterized by the above-mentioned. Further comprising a composition detecting means for detecting the composition of the fuel introduced into the reforming means,
The control means controls the air flow rate introduced into the reforming means, the first circulation exhaust fuel flow rate, and the fuel flow rate newly introduced into the combustion means based on the composition detected by the composition detection means. The fuel cell system according to any one of claims 1 to 7, wherein

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