JP2008198485A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system preventing oxidation deterioration of an anode of a fuel cell stack. <P>SOLUTION: In the fuel cell system 1 having a reformer 2 forming reformed gas by reforming raw gas and an SOFC stack 3 connected to the reformer 2 through a reformed gas supply pipe 9 and generating power with reformed gas obtained with the reformer 2, a raw material supply line 5 for supplying reformed raw material which is a mixture of raw fuel and steam to the reformer 2 is connected to the reformer 2, a heat exchanger 12 for cooling gas (steam and reformed gas) flowing through the reformed gas supply pipe 9 is installed in the reformed gas supply pipe 9, and cooling water or cooling air is supplied to the heat exchanger 12. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell system that generates power by introducing raw fuel and air.

One type of fuel cell system is a solid oxide fuel cell (SOFC) system. In general, a solid oxide fuel cell system is obtained by reforming a hydrocarbon fuel (raw fuel) such as kerosene or city gas to produce a hydrogen-containing gas (reformed gas), and the reformer. A fuel cell stack that electrochemically generates and reacts the reformed gas and air. As such an SOFC system, for example, one described in Patent Document 1 is known.
JP 2005-293951 A

  However, the following problems exist in the prior art. That is, when starting up the fuel cell system, after raising the reformer to a predetermined temperature, steam is required before supplying raw fuel to the reformer so that carbon does not precipitate on the catalyst surface of the reformer. Accordingly, it is necessary to supply air or the like to the reformer. At this time, gas such as water vapor or air heated by the heated reformer is supplied to the fuel cell stack, and the temperature of the fuel cell stack rises due to gas heat transfer at that time. For this reason, when the anode (fuel electrode) of the fuel cell stack is in an oxidizing gas atmosphere such as water vapor or air, the anode is oxidized and deteriorated.

  An object of the present invention is to provide a fuel cell system capable of preventing oxidative deterioration of an anode of a fuel cell stack.

  The fuel cell system of the present invention includes a reformer that reforms a raw fuel to generate a reformed gas, and a reformer that is connected to the reformer via a reformed gas flow path and is generated by the reformer. A fuel cell stack that generates power using gas and a cooling means that cools the gas flowing in the reformed gas flow path are provided.

  When starting up the fuel cell system of the present invention, the temperature of the reformer is raised to a predetermined temperature, and then the raw fuel and steam are supplied to the reformer, for example, so that the raw fuel is supplied by the reformer. A reformed gas is generated by a steam reforming reaction. At this time, it is necessary to supply only steam to the reformer before supplying raw fuel to the reformer so that carbon does not deposit on the catalyst surface of the reformer. The water vapor warmed by the gas flows in the reformed gas flow path toward the fuel cell stack. Therefore, the water vapor flowing in the reformed gas channel is cooled by the cooling means. As a result, the water vapor cooled by the cooling means is supplied to the fuel cell stack. Therefore, until the reformed gas is supplied to the fuel cell stack, the temperature of the fuel cell stack is changed to the oxidation deterioration point of the anode. The following can be maintained. As a result, oxidative deterioration of the anode can be prevented.

  Further, when the fuel cell system of the present invention is stopped, in order to prevent the oxidative deterioration of the anode, the temperature of the fuel cell stack is lowered to a temperature below the oxidative deterioration point of the anode, and then reformed to the fuel cell stack. It is necessary to stop the gas supply. However, since the heat capacity of the fuel cell stack is relatively large, the cooling rate of the fuel cell stack becomes slow. Therefore, a large amount of reformed gas is required until the temperature of the fuel cell stack is lowered to a temperature below the oxidative deterioration point of the anode. Must be supplied to the fuel cell stack. Therefore, the reformed gas flowing in the reformed gas channel is cooled by the cooling means. Thereby, the reformed gas cooled by the cooling means is supplied to the fuel cell stack, so that the cooling rate of the fuel cell stack is increased. Accordingly, since it is not necessary to supply a large amount of reformed gas to the fuel cell stack, it is possible to reduce energy consumption when the temperature of the fuel cell stack is lowered.

  Preferably, the reformer generates reformed gas by adding steam to the raw fuel to cause a reforming reaction of the raw fuel. Examples of such reforming methods include steam reforming (SR) and autothermal reforming (ATR) with high reforming efficiency. In this case, before the reformed gas is supplied to the fuel cell stack, the water vapor flowing in the reformed gas flow path is cooled by the cooling means, so that the anode at the start-up of the fuel cell system as described above. Oxidative degradation can be reliably prevented.

  Preferably, the cooling means includes a heat exchanger provided in the reformed gas flow path, and a fluid supply means for supplying a cooling fluid to the heat exchanger. In this case, by supplying a cooling fluid to the heat exchanger, water vapor, reformed gas, and the like flowing in the reformed gas channel are cooled by heat exchange. From the viewpoint of cost, handling (operation), ease of installation, and the like, it is preferable to use such a heat exchanger as a cooling means. Furthermore, from the viewpoint of promoting heat transfer, it is preferable to fill the reformed gas channel and the cooling fluid channel in the heat exchanger with a filler having high thermal conductivity such as metal particles.

  At this time, the fluid supply means preferably has means for supplying water as a cooling fluid to the heat exchanger and means for supplying air as a cooling fluid to the heat exchanger. When starting the fuel cell system, it is desirable to use water with a large latent heat of vaporization as a cooling fluid. In this case, water vapor or the like flowing in the reformed gas channel can be efficiently cooled. On the other hand, when the fuel cell system is stopped, it is desirable to use air as the cooling fluid in consideration of the influence of evaporative impact of the cooling fluid, for example.

  According to the present invention, oxidative deterioration of the anode of the fuel cell stack can be prevented. Thereby, it becomes possible to improve the durability of the fuel cell stack.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a fuel cell system according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a system configuration diagram showing a first embodiment of a fuel cell system according to the present invention. In the figure, the fuel cell system 1 of the present embodiment includes a reformer 2 that reforms a reforming raw material (raw fuel) to generate a reformed gas, and a reformed gas obtained by the reformer 2. And a solid oxide fuel cell (SOFC) stack 3 that generates electricity using air and air. The reformer 2 and the SOFC stack 3 are accommodated in a module container 4 and modularized.

  The fuel cell system 1 also includes a raw material supply system 5 for supplying a reformed raw material mixed with raw fuel and steam to the reformer 2 from the outside of the module container 4.

  The raw material supply system 5 includes a raw material introduction pipe 6 connected to the reformer 2, an electromagnetic valve 7 that adjusts the supply amount of raw fuel, and an electromagnetic valve 8 that adjusts the supply amount of water vapor. As the raw fuel, for example, a hydrocarbon fuel such as kerosene or city gas is used. The raw material supply system 5 generates reformed raw material gas by, for example, mixing raw fuel gas obtained by a fuel vaporizer (not shown) with water vapor obtained by a water vaporizer (not shown). Then, the reforming raw material gas is introduced into the reformer 2 through the raw material introduction pipe 6.

  The reformer 2 causes a reforming raw material to undergo a steam reforming (SR) reaction with a reforming catalyst to generate a reformed gas containing hydrogen and carbon monoxide. The steam reforming reaction is a very large endothermic reaction, and since the reaction temperature is relatively high at about 550 to 750 ° C., a high-temperature heat source is required. For this reason, the reformer 2 is disposed in the vicinity of the SOFC stack 3 and performs a steam reforming reaction using radiant heat from the SOFC stack 3 and off-gas combustion heat.

  The SOFC stack 3 is connected to the reformer 2 via a reformed gas supply pipe 9 that forms a reformed gas flow path. The SOFC stack 3 is connected to an air introduction pipe 10 for introducing air from the outside of the module container 4. The air introduction pipe 10 is provided with an electromagnetic valve 11 that adjusts the amount of air introduced.

  The SOFC stack 3 is configured by stacking a plurality of battery cells. The battery cell includes an anode (fuel electrode) 3a, a cathode (air electrode) 3b, and an electrolyte 3c disposed between the anode 3a and the cathode 3b. The reformed gas is introduced into the anode 3a, and air is introduced into the cathode 3b. Thereby, an electrochemical power generation reaction is performed in each battery cell. The SOFC stack 3 normally operates at a high temperature of about 550 to 1000 ° C.

  The reformed gas supply pipe 9 is provided with a heat exchanger 12 that cools the gas flowing in the reformed gas supply pipe 9 by exchanging heat with the cooling fluid. The heat exchanger 12 is supplied with water for supplying cooling water (liquid) to the heat exchanger 12 as a cooling fluid, and supplied with air to supply cooling air (gas) to the heat exchanger 12 as a cooling fluid. The tube 14 is connected in parallel. The water supply pipe 13 is provided with an electromagnetic valve 15 for adjusting the supply amount of cooling water, and the air supply pipe 14 is provided with an electromagnetic valve 16 for adjusting the supply amount of cooling air.

  By using the heat exchanger 12 as a cooling means for the gas flowing in the reformed gas supply pipe 9, the structure of the cooling means can be simplified, installation and operation can be performed relatively easily, and the cost can be increased. Is also advantageous.

  The fuel cell system 1 also includes a temperature sensor 17 that detects the temperature in the reformed gas supply pipe 9 and a control device 18 that controls the entire system during operation of the fuel cell system 1. The temperature sensor 17 is, for example, a thermocouple, and an appropriate number of the temperature sensors 17 are arranged at locations where water pools are likely to occur in the reformed gas supply pipe 9.

  The control device 18 controls the electromagnetic valves 7 and 8 to control the introduction amount of raw fuel and water vapor, respectively, controls the electromagnetic valve 11 to control the introduction amount of air, and controls the electromagnetic valves 15 and 16. The supply amounts of cooling water and cooling air are respectively controlled.

  FIG. 2 is a flowchart showing a control processing procedure executed by the control device 18 when the fuel cell system 1 is started. The execution of this control process is started, for example, by operating a start switch (not shown). Hereinafter, the operation method at the start-up of the fuel cell system 1 will be described with reference to the flowchart shown in FIG.

  First, the electromagnetic valve 15 is controlled to supply cooling water to the heat exchanger 12 (procedure 101). Then, the reformer 2 is heated by, for example, a burner or heater (not shown) disposed near the reformer 2 or a heat source such as catalytic combustion heat.

  Thereafter, when the temperature of the reformer 2 is increased to a temperature at which the steam is not condensed, the electromagnetic valve 8 is controlled to supply the reformer 2 with steam (procedure 102). Thus, before supplying the raw fuel to the reformer 2, first, only steam is supplied to the reformer 2, so that carbon is deposited on the reforming catalyst surface of the reformer 2 during the reforming reaction ( Therefore, the reforming catalyst is not clogged or deteriorated and the reforming reaction is not hindered.

  When only the steam is supplied to the reformer 2, the steam flows in the reformed gas supply pipe 9 toward the SOFC stack 3. At this time, since the cooling water flows through the heat exchanger 12, the water vapor in the reformed gas supply pipe 9 is supplied to the anode 3a of the SOFC stack 3 while being cooled by the heat exchanger 12. Become.

  Here, after the supply of water vapor to the reformer 2 is started, the temperature of the water vapor flowing in the reformed gas supply pipe 9 is higher than the boiling point of water (for example, 100 ° C.) based on the detection signal of the temperature sensor 17. In addition, it is desirable to perform PID control, for example, on the electromagnetic valve 15 so that the anode 3a is kept below the oxidation deterioration point (eg, 400 ° C.). As a result, the condensation of water vapor flowing through the reformed gas supply pipe 9 is suppressed, so that a pool of water in the reformed gas supply pipe 9 is prevented.

  Thereafter, when the temperature of the reformer 2 is raised to a temperature at which reforming is possible, the electromagnetic valve 7 is controlled to supply raw fuel to the reformer 2 (procedure 103). Then, reformed gas is generated by the reformer 2, and this reformed gas is supplied to the anode 3 a of the SOFC stack 3 through the reformed gas supply pipe 9.

  Further, the electromagnetic valve 11 is controlled to supply air to the cathode 3b of the SOFC stack 3 (procedure 104). Thereafter, after the temperature of the SOFC stack 3 is raised to a predetermined temperature, electric power is taken out from the SOFC stack 3 to start power generation by the SOFC stack 3. The supply of air to the SOFC stack 3 may be executed before the procedure 103 or simultaneously with the procedure 103.

  Then, after the reformed gas reaches the SOFC stack 3, the electromagnetic valve 15 is controlled to stop the supply of cooling water to the heat exchanger 12 (procedure 105).

  Thereafter, the temperature in the module container 4 is raised by the combustion heat of the anode off gas from the SOFC stack 3 or a heater (not shown). And the heat output from the heat source provided in the reformer 2 or its vicinity is stopped.

  As described above, when the fuel cell system 1 is started, the steam is cooled by the heat exchanger 12 so that the temperature of the steam flowing in the reformed gas supply pipe 9 is kept below the oxidation deterioration point of the anode 3a. Until the reformed gas generated in the reformer 2 starts to be supplied to the SOFC stack 3, the temperature of the SOFC stack 3 is maintained below the oxidation deterioration point of the anode 3a. Therefore, even when the anode 3a is in an oxidizing gas atmosphere such as water vapor or air, the oxidative deterioration of the anode 3a can be prevented. At this time, since the cooling water having a large latent heat of evaporation is supplied to the heat exchanger 12, the water vapor flowing through the reformed gas supply pipe 9 can be efficiently cooled.

  FIG. 3 is a flowchart showing a control processing procedure executed by the control device 18 when the fuel cell system 1 is stopped. The execution of this control process is started, for example, by operating a stop switch (not shown). Hereinafter, the operation method when the fuel cell system 1 is stopped will be described with reference to the flowchart shown in FIG.

  First, the electromagnetic valve 16 is controlled to supply cooling air to the heat exchanger 12 (procedure 111). Subsequently, the supply amount of the reforming raw material to the reformer 2 is reduced by controlling the electromagnetic valves 7 and 8 to reduce the supply amount of raw fuel and steam. Thereby, since the supply amount of the reformed gas generated in the reformer 2 is reduced, the anode off-gas combustion heat from the SOFC stack 3 is reduced. Further, for example, the electromagnetic valve 11 is controlled to increase the amount of air supplied to the cathode 3b of the SOFC stack 3. As a result, the temperature drop in the module container 4 is started (procedure 112).

  At this time, based on the detection signal of the temperature sensor 17, the electromagnetic valve 16 is maintained so that the temperature of the reformed gas flowing in the reformed gas supply pipe 9 is maintained at a temperature not lower than the boiling point of water and not higher than the oxidation deterioration point of the anode 3a. For example, it is desirable to perform PID control. As a result, condensation of moisture contained in the reformed gas flowing in the reformed gas supply pipe 9 is suppressed, so that a water pool is prevented from being generated in the reformed gas supply pipe 9.

  Thereafter, when the temperature of the SOFC stack 3 falls below the oxidation deterioration point of the anode 3a, the electromagnetic valve 7 is controlled to stop the supply of raw fuel to the reformer 2 (procedure 113). Thereby, the supply of the reformed gas from the reformer 2 to the SOFC stack 3 is stopped. Subsequently, the electromagnetic valve 8 is controlled to stop the supply of water vapor to the reformer 2 (procedure 114).

  Here, until the SOFC stack 3 which is difficult to cool compared to the reformed gas in the reformed gas supply pipe 9 is cooled to a temperature lower than the oxidation deterioration point of the anode 3a, the reformed reformed gas is reduced to the SOFC stack. 3 continues to be supplied to the anode 3, so that the oxidative deterioration of the anode 3a is prevented.

  Then, the electromagnetic valve 16 is controlled to stop the supply of cooling air to the heat exchanger 12 (procedure 115).

  Thus, when the fuel cell system 1 is stopped, the reformed gas flowing in the reformed gas supply pipe 9 is cooled by the heat exchanger 12, so that the cooled reformed gas is supplied to the SOFC stack 3. It becomes. This increases the cooling rate of the SOFC stack 3 that has a relatively large heat capacity and is difficult to lower the temperature. Therefore, a large amount of reformed gas and air is supplied to the SOFC stack 3 until the temperature of the SOFC stack 3 is lowered to a temperature lower than the oxidation deterioration point of the anode 3a. 3 need not be supplied.

  Further, immediately after the start of the stop operation, the temperature in the module container 4 is high, and the piping of the heat exchanger 12 is heated to some extent. Therefore, when cooling water is supplied to the heat exchanger 12, the evaporation impact of cooling water The piping of the heat exchanger 12 may be damaged. In the present embodiment, since the cooling air is supplied to the heat exchanger 12 when the system is stopped, the reformed gas flowing in the reformed gas supply pipe 9 can be cooled without causing such an evaporation shock. .

  As described above, according to the present embodiment, it is possible to prevent oxidative deterioration of the anode 3a of the SOFC stack 3 when the fuel cell system 1 is started and stopped. Further, when the fuel cell system 1 is stopped, the amount of reformed gas and air supplied to the SOFC stack 3 can be reduced, so that it is possible to reduce energy consumption.

  FIG. 4 is a system configuration diagram showing a second embodiment of the fuel cell system according to the present invention. In the figure, members and elements that are the same as or equivalent to those in the first embodiment are given the same reference numerals, and descriptions thereof are omitted.

  In the figure, the fuel cell system 20 of the present embodiment is disposed in the module container 4 in addition to the reformer 2 and the SOFC stack 3 and reforms the starting / stopping reforming raw material (raw fuel). Thus, a start / stop reformer 21 for generating reformed gas is provided. In the present embodiment, the reformer 2 described above constitutes a power generation reformer that reforms a power generation reforming raw material to generate a reformed gas.

  The fuel cell system 20 also includes a raw material supply system 22 for supplying the starting / stopping reformed raw material mixed with raw fuel and steam to the starting / stopping reformer 21 from the outside of the module container 4. Yes.

  The raw material supply system 22 includes a raw material introduction pipe 23 connected to the start / stop reformer 21, an electromagnetic valve 24 that adjusts the supply amount of raw fuel, and an electromagnetic valve 25 that adjusts the supply amount of water vapor. is doing. As the raw fuel, a hydrocarbon fuel such as kerosene or city gas is used. As a result, it is possible to share the power source for power generation for making the reforming raw material for power generation and the supply source of the raw fuel for start / stop for making the reforming raw material for start / stop. Similarly to the raw material supply system 6, the raw material supply system 22 is activated by mixing raw fuel gas obtained by a fuel vaporizer (not shown) with, for example, water vapor obtained by a water vaporizer (not shown). A stop reforming source gas is generated. Then, the starting / stopping reforming raw material gas is introduced into the starting / stopping reformer 21 through the raw material introduction pipe 23.

  The start / stop reformer 21 generates a reformed gas having a reducing property by causing the reforming catalyst to undergo a steam reforming reaction with the reforming catalyst when the fuel cell system 20 is started / stopped. It is. Since the start / stop reformer 21 does not particularly contribute to power generation, the capacity may be smaller than that of the power reformer 2.

  The start / stop reformer 21 is branched and connected to the raw material introduction pipe 6 via a reformed gas supply pipe 26 forming a reformed gas flow path. The reformed gas generated by the reformer 21 is supplied to the SOFC stack 3 via the reformed gas supply pipe 26, the raw material introduction pipe 6, the reformer 2, and the reformed gas supply pipe 9. Here, the reformed gas supply pipe 26 is branched and connected to the input side of the reformer 2 in order to reduce the reforming catalyst of the reformer 2 by the reformed gas generated by the reformer 21. The quality gas supply pipe 26 may be connected to the output side (reformed gas supply pipe 9) of the reformer 2. Further, the start / stop reformer 21 may be installed outside the module container 4.

  The reformed gas supply pipe 26 is provided with a heat exchanger 27 that cools the gas flowing through the reformed gas supply pipe 26 by exchanging heat with the cooling fluid. In the heat exchanger 27, a water supply pipe 28 for supplying cooling water as a cooling fluid to the heat exchanger 27 and an air supply pipe 29 for supplying cooling air as a cooling fluid to the heat exchanger 27 are arranged in parallel. It is connected. The water supply pipe 28 is provided with an electromagnetic valve 30 for adjusting the supply amount of cooling water, and the air supply pipe 29 is provided with an electromagnetic valve 31 for adjusting the supply amount of cooling air.

  The fuel cell system 20 includes a control device 32 instead of the control device 18 described above. The control device 32 controls the electromagnetic valves 7 and 8 to control the introduction amounts of raw fuel and water vapor, respectively, controls the electromagnetic valves 24 and 25 to control the introduction amounts of raw fuel and water vapor, respectively, and the electromagnetic valve 11. Is controlled to control the amount of air introduced, and the electromagnetic valves 30 and 31 are controlled to control the supply amount of cooling water and cooling air.

  FIG. 5 is a flowchart showing a control processing procedure executed by the control device 32 when the fuel cell system 20 is started. Hereinafter, the operation method at the time of starting of the fuel cell system 20 will be described using the flowchart shown in FIG.

  First, the electromagnetic valve 30 is controlled to supply cooling water to the heat exchanger 27 (procedure 121). Then, for example, the reformer 21 is heated by a burner or a heater (not shown) disposed in the vicinity of the start / stop reformer 21.

  After that, when the start / stop reformer 21 is heated to a temperature at which the steam is not condensed, the electromagnetic valve 25 is controlled to supply steam to the reformer 21 (procedure 122). Then, the steam flows in the reformed gas supply pipe 26 toward the SOFC stack 3. At this time, since cooling water flows through the heat exchanger 27, the steam in the reformed gas supply pipe 26 is cooled by the heat exchanger 26 and the power reformer 2 and the reformed gas supply pipe. 9 is supplied to the anode 3 a of the SOFC stack 3.

  Here, after the supply of steam to the start / stop reformer 21 is started, the temperature of the steam flowing in the reformed gas supply pipe 26 is equal to or higher than the boiling point of water based on the detection signal of the temperature sensor 17. In addition, it is desirable to perform PID control of the electromagnetic valve 30, for example, so that the anode 3a is maintained below the oxidation deterioration point. As a result, the generation of a water pool due to condensation of water vapor flowing in the reformed gas supply pipe 26 is prevented.

  When the temperature of the start / stop reformer 21 is raised to a temperature at which reforming is possible, the electromagnetic valve 24 is controlled to supply the start / stop raw fuel to the reformer 21 (procedure 123). Then, a reformed gas is generated by the reformer 21, and this reformed gas is supplied to the anode 3 a of the SOFC stack 3 through the reformed gas supply pipe 26, the power generation reformer 2 and the reformed gas supply pipe 9. Is done.

  Further, the electromagnetic valve 11 is controlled to supply air to the cathode 3b of the SOFC stack 3 (procedure 124). The supply of air to the SOFC stack 3 may be performed before the procedure 123 or simultaneously with the procedure 123.

  Then, after the reformed gas reaches the SOFC stack 3, the electromagnetic valve 30 is controlled to stop the supply of cooling water to the heat exchanger 27 (procedure 125).

  Thereafter, the temperature rise in the module container 4 is started by the combustion heat of the anode off gas from the SOFC stack 3 or a heater. When the power reformer 2 is heated to a predetermined temperature, the electromagnetic valve 8 is controlled to supply steam to the reformer 2 (procedure 126). Subsequently, the electromagnetic valve 7 is controlled to supply power generation raw fuel toward the reformer 2 (procedure 127). Then, reformed gas is generated by the reformer 2, and this reformed gas is supplied to the anode 3 a of the SOFC stack 3 through the reformed gas supply pipe 9. Thereafter, after the temperature of the SOFC stack 3 is raised to a predetermined temperature, electric power is taken out from the SOFC stack 3 to start power generation by the SOFC stack 3.

  Subsequently, the electromagnetic valve 24 is controlled to stop the supply of starting / stopping raw fuel toward the starting / stopping reformer 21 (procedure 128). Thereby, supply of the reformed gas generated by the reformer 21 is stopped. Subsequently, the supply of water vapor to the reformer 21 is stopped (procedure 129). Thereafter, the heat output from the start / stop reformer 21 or a heat source provided in the vicinity thereof is stopped.

  As described above, when the fuel cell system 20 is started, the water vapor flowing in the reformed gas supply pipe 26 is cooled by the heat exchanger 27 and the cooled water vapor is supplied to the SOFC stack 3. The temperature of the SOFC stack 3 can be kept below the oxidation deterioration point of the anode 3a until the reformed gas generated in the mass chamber 21 starts to be supplied to the SOFC stack 3. Thereby, the oxidative deterioration of the anode 3a can be prevented.

  FIG. 6 is a flowchart showing a control processing procedure executed by the control device 32 when the fuel cell system 20 is stopped. Hereinafter, the operation method when the fuel cell system 20 is stopped will be described with reference to the flowchart shown in FIG.

  First, the electromagnetic valve 31 is controlled to supply cooling air to the heat exchanger 27 (procedure 131). Subsequently, the reformer 21 is heated by a heater (not shown) or the like disposed in the vicinity of the start / stop reformer 21. Further, the supply amount of the reforming raw material for power generation to the power reformer 2 is reduced by controlling the electromagnetic valves 7 and 8 to reduce the supply amount of raw fuel and steam. Thereby, the supply amount of the reformed gas generated by the power reformer 2 is reduced.

  Then, the electromagnetic valve 25 is controlled to supply a small amount of water vapor to the reformer 21 (procedure 132). Then, the electromagnetic valve 24 is controlled to supply a small amount of starting / stopping raw fuel to the reformer 21 (procedure 133). Then, a small amount of the reformed gas generated by the reformer 21 is supplied to the anode 3a of the SOFC stack 3.

  Subsequently, the electromagnetic valve 7 is controlled to stop the supply of the raw power for power generation to the power reformer 2 (procedure 134). Thereby, supply of the reformed gas generated by the reformer 2 is stopped. Subsequently, the electromagnetic valve 8 is controlled to stop the supply of water vapor to the reformer 2 (procedure 135).

  Subsequently, for example, the electromagnetic valve 11 is controlled to increase the amount of air supplied to the cathode 3 b of the SOFC stack 3. As a result, a decrease in the amount of reformed gas supplied to the SOFC stack 3 and a decrease in the anode off-gas combustion heat from the SOFC stack 3 are reduced. Procedure 136).

  At this time, based on the detection signal of the temperature sensor 17, the electromagnetic valve 31 is maintained so that the temperature of the reformed gas flowing in the reformed gas supply pipe 26 is maintained at a temperature equal to or higher than the boiling point of water and equal to or lower than the oxidation deterioration point of the anode 3a. For example, it is desirable to perform PID control. As a result, the occurrence of a water pool due to condensation of moisture contained in the reformed gas flowing in the reformed gas supply pipe 26 is prevented.

  Thereafter, when the temperature of the SOFC stack 3 becomes equal to or lower than the oxidation deterioration point of the anode 3a, the electromagnetic valve 24 is controlled to stop the supply of starting / stopping raw fuel to the starting / stopping reformer 21 (procedure). 137). As a result, the supply of the starting / stopping reforming raw material to the starting / stopping reformer 21 is stopped, so that the supply of the reformed gas generated by the reformer 21 is stopped. Subsequently, the electromagnetic valve 25 is controlled to stop the supply of water vapor to the reformer 21 (procedure 138).

  Here, while the SOFC stack 3 is lowered to a temperature below the oxidation deterioration point of the anode 3a, the reformed gas generated by the reformer 21 is continuously supplied to the SOFC stack 3, so that the oxidation deterioration of the anode 3a is prevented. The

  Then, the electromagnetic valve 31 is controlled to stop the supply of cooling air to the heat exchanger 27 (procedure 139).

  As described above, when the fuel cell system 20 is stopped, the reformed gas flowing in the reformed gas supply pipe 26 is cooled by the heat exchanger 27, and the cooled reformed gas is supplied to the SOFC stack 3. The cooling rate of the stack 3 is increased. As a result, the amount of reformed gas and air supplied to the SOFC stack 3 before the SOFC stack 3 is cooled to a temperature lower than the oxidation deterioration point of the anode 3a can be reduced, so that energy consumption can be reduced. .

  The present invention is not limited to the above embodiment. For example, in the above-described embodiment, water is supplied as a cooling fluid when the system is started. However, a liquid other than water or a gas such as air may be supplied.

  In the above embodiment, the steam and reformed gas flowing in the reformed gas supply pipe toward the SOFC stack 3 are cooled by the heat exchanger. However, as a means for cooling the steam and reformed gas, The heat exchanger is not limited, and a Peltier heat absorption element or the like may be used.

  Moreover, in the said embodiment, although the reformer which carries out the steam reforming (SR) reaction of the reforming raw material is provided, this invention is provided with the reformer which carries out the autothermal reforming (ATR) reaction of the reforming raw material. It is also applicable to the system. In such autothermal reforming, only the steam is first supplied to the reformer, so that the steam flowing in the reformed gas supply pipe is cooled as in the above embodiment. In addition, when air is supplied to the reformer before the reforming raw material is supplied to the reformer, the steam and air flowing in the reformed gas supply pipe are cooled.

  Furthermore, although the said embodiment is about a solid oxide fuel cell (SOFC), this invention is applicable also to the molten carbonate fuel cell (MCFC) etc. which are the same high temperature type fuel cells as SOFC, for example. is there.

1 is a system configuration diagram showing a first embodiment of a fuel cell system according to the present invention. 2 is a flowchart showing a control processing procedure executed by a control device when the fuel cell system shown in FIG. 1 is started. 2 is a flowchart showing a control processing procedure executed by a control device when the fuel cell system shown in FIG. 1 is stopped. It is a system block diagram which shows 2nd Embodiment of the fuel cell system concerning this invention. 5 is a flowchart showing a control processing procedure executed by the control device when the fuel cell system shown in FIG. 4 is started. 6 is a flowchart showing a control processing procedure executed by the control device when the fuel cell system shown in FIG. 4 is stopped.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 2 ... Reformer, 3 ... Solid oxide fuel cell (SOFC) stack, 3a ... Anode, 9 ... Reformed gas supply pipe (reformed gas flow path), 12 ... Heat exchanger ( Cooling means), 13 ... Water supply pipe (fluid supply means, cooling means), 14 ... Air supply pipe (fluid supply means, cooling means), 20 ... Fuel cell system, 21 ... Reformer, 26 ... Reformed gas supply Pipe (reformed gas flow path), 27 ... heat exchanger (cooling means), 28 ... water supply pipe (fluid supply means, cooling means), 29 ... air supply pipe (fluid supply means, cooling means).

Claims (4)

A reformer for reforming raw fuel to generate reformed gas;
A fuel cell stack connected to the reformer via a reformed gas flow path and generating power using the reformed gas generated by the reformer;
And a cooling means for cooling the gas flowing in the reformed gas flow path.   The fuel cell system according to claim 1, wherein the reformer generates the reformed gas by adding steam to the raw fuel to cause a reforming reaction of the raw fuel.   3. The fuel cell according to claim 1, wherein the cooling means includes a heat exchanger provided in the reformed gas flow path, and a fluid supply means for supplying a cooling fluid to the heat exchanger. system.   4. The fuel according to claim 3, wherein the fluid supply means includes means for supplying water as the cooling fluid to the heat exchanger and means for supplying air as the cooling fluid to the heat exchanger. Battery system.

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