JP2013157134A - Solid oxide fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid oxide fuel cell system capable of securing steam from startup to start of power generation without enlarging the scale of a device.SOLUTION: Fuel reformed by a reformer 4 is supplied to the anode 2 of a stack 1, a part of anode off-gas discharged from the anode 2 is circulated to the reformation passage of the reformer 4, and the remaining anode off-gas is mixed with cathode off-gas discharged from the cathode 3 of the stack 1 and used for heating of the reformer 4. In such a solid oxide fuel cell system, the cathode 3 and the reformer 4 are heated upon startup, a gas containing steam is circulated to the anode 2, and a combustor 11 for startup that supplies steam to an anode circulation route for startup is provided in an anode circulation route during startup operation.

Description

  The present invention relates to a fuel cell system using a solid oxide fuel cell, and more particularly to a technique for securing water vapor in an anode circulation path from startup to power generation.

  As a conventional solid oxide fuel cell, one described in Non-Patent Document 1 is known. This non-patent document 1 adopts a system in which anode exhaust gas is recirculated to the reformer at a high temperature, and all the possibilities of the heat balance of the entire system, such as the reformer and the solid oxide fuel cell stack, are adopted. In pursuit of this, the heat of anode exhaust gas is used for reformer or cathode gas heating, and the exhaust gas of cathode gas is used for evaporator so that heat recovery can be performed as much as possible.

  During power generation, the anode exhaust gas is recirculated to the reformer, so that water produced by electrochemical reaction is used for reforming. This eliminates the need for an evaporator.

Hiromichi Miwa and 1 other, "Determining the specifications and performance evaluation for in-vehicle systems", results report, Fukuoka Industrial and Science and Technology Foundation, March 2008, p28-37

  However, in the conventional example disclosed in Non-Patent Document 1 described above, there may be a shortage of water vapor from the start of the fuel cell to power generation. Problems such as deterioration of the catalyst may occur. In order to solve this problem, if an activation water tank and an evaporator for generating water vapor are provided, the entire apparatus becomes large-scale.

  The present invention has been made to solve such a conventional problem, and the object of the present invention is to secure water vapor from start-up to the start of power generation without increasing the scale of the apparatus. The object is to provide a solid oxide fuel cell system.

  The solid oxide fuel cell system according to the present invention heats the cathode and the reformer during startup, circulates a steam-containing gas to the anode, and varies the amount of water vapor in the anode circulation path during startup operation. It has a mechanism to do.

  According to the present invention, since the steam-containing gas is supplied into the anode circulation flow path when the stack is started, an arbitrary amount of steam is supplied before fuel reforming by the reformer is started before power generation by the stack is started. Can be circulated and stored in the anode circulation channel. Accordingly, it is possible to prevent carbon deposition from occurring when the reforming fuel and the reforming air are supplied to the reformer. As a result, power generation by the fuel cell system can be started without supplying water from the outside from the start to power generation.

1 is a block diagram showing a configuration of a solid oxide fuel cell system according to a first embodiment of the present invention. It is explanatory drawing which shows the structure of the starting combustor used for the solid oxide fuel cell system which concerns on 1st Embodiment of this invention. It is a block diagram which shows the structure of the solid oxide fuel cell system which concerns on 2nd Embodiment of this invention. It is explanatory drawing which shows the structure of the gas generator for anode circulation used for the solid oxide fuel cell system which concerns on 2nd Embodiment of this invention. FIG. 10 is a characteristic diagram illustrating changes in the supply amount of anode circulation gas and the supply amount of reformed gas according to the second embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a solid oxide 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 stack 1 having an anode 2 and a cathode 3, a reformer 4 that reforms the fuel and supplies the reformed fuel to the anode 2 of the stack 1, And a start-up combustor 11 that supplies combustion gas to the cathode of the stack 1 at the time of start-up.

  The reformer 4 has a heating passage 6 and a reforming passage 5. The reforming passage 5 has a reforming fuel output from a fuel pump (not shown) and a compressor (not shown). (Omitted) is supplied with reforming air. Then, the reformed fuel is sent to the anode of the stack 1 through the flow path 18. The heating passage 6 is connected to the outlet of the cathode 3 of the stack 1 via a flow path 14, and heats the reforming fuel supplied to the reforming passage 5 by the heat of the cathode offgas output from the cathode 3. To do.

  In addition, the anode 2 outlet of the stack 1 is connected to the circulation device 7 via the flow path 19, and the output side of the circulation device 7 is connected to the branch device 8. The branching device 8 branches the anode off-gas supplied from the circulation device 7 into two systems, and the heating gas passage 16 as the first branching path is connected to the cathode 3 outlet of the stack 1, A circulation gas passage 17, which is an eye branch, is connected to the reforming passage 5 inlet of the reformer 4.

  The start-up combustor 11 is supplied with fuel and air and combusts, supplies the generated combustion gas to the cathode 3 of the stack 1, and partially converts the combustion gas via the combustion gas passage 20 to the reformer 4. To the reforming passage 5. Details of the start-up combustor 11 will be described later.

  The outlet of the heating passage 6 of the reformer 4 is connected to the high temperature side of the air preheater 12 via the flow path 15 to heat the air introduced to the low temperature side of the air preheater 12, and then Exhausted. On the other hand, the low temperature side of the air preheater 12 is connected to the cathode 3 inlet. Therefore, the air introduced into the air preheater 12 is heated by the gas discharged from the heating passage 6 of the reformer 4 and then supplied to the cathode 3 of the stack 1.

  In the present embodiment, a part of the combustion gas generated by the start-up combustor 11 between the start of the stack 1 and the start of power generation is transferred to the reforming passage via the combustion gas passage 20. 5, water vapor is supplied to the anode circulation path (path that circulates the reforming passage 5, the anode 2, the flow path 19, and the circulation gas passage 17). Further, the circulation device 7 and the branch device 8 are adjusted so that the circulation amount of the anode off gas becomes a desired flow rate. That is, the start-up combustor 11, the circulation device 7, and the branch device 8 function as a mechanism that varies the amount of water vapor in the anode circulation path during the start-up operation.

  Next, the detailed configuration of the start-up combustor 11 will be described with reference to FIG. The start-up combustor 11 generates a combustion gas when the stack 1 is started, supplies the combustion gas to the cathode 3 and the heating passage 6 and raises the temperature. Further, a part of the combustion gas is burned into the combustion gas passage. It is circulated through the reforming passage 5 of the reformer 4 via 20. That is, the steam-containing gas is supplied to the anode circulation path.

  As shown in FIG. 2, the start-up combustor 11 has a two-stage (multi-stage) configuration in which a small diffusion combustor 21 that functions as a precombustor and a catalytic combustor 22 that functions as a main combustor are connected. have.

  The small diffusion combustor 21 includes an air introduction path 24 into which combustion air is introduced, a fuel injection valve 23 that injects fuel, and an ignition device 25, and burns a gas that is a mixture of fuel and air. Pre-combustion gas is generated, and this pre-combustion gas is introduced into the air inlet of the catalytic combustor 22. A part of the precombustion gas is taken out from the combustion gas outlet 26 and supplied to the reformer 4 through the combustion gas passage 20 shown in FIG.

  At this time, if the pre-combustion gas generated in the small diffusion combustor 21 is stoichiometric combustion gas, it can be introduced into the reformer 4 as it is, and even if it is not stoichiometric combustion gas, By additionally supplying the reforming fuel to be supplied or the reforming air, it can be introduced into the reformer 4 as a stoichiometric combustion gas.

  The catalytic combustor 22 includes a secondary air supply port 28 and a fuel supply port 27, fuel supplied from the fuel supply port 27, air supplied from the secondary air supply port, and small diffusion combustion. The pre-combustion gas delivered from the vessel 21 is mixed, and this mixed gas is combusted in the combustion section 29 to generate a large amount of main combustion gas, which is supplied to the cathode 3 of the stack 1 as a cathode heating gas. . Thereby, the temperature of the cathode 3 and the reformer 4 can be raised when the stack 1 is started.

  As the fuel supply device provided in the catalyst combustor 22, there are options such as sprayed fuel by a fuel injection valve and fuel gas supply by a fuel evaporator. Further, the combustion section 29 of the catalytic combustor 22 can be selected according to the composition of fuel used in the system by the catalytic combustor, the pre-evaporation premixed lean combustor, the exhaust requirement, and the like.

  In the present embodiment, an example in which the small diffusion combustor 21 is used as the precombustor has been shown. However, in addition to this, an electric heating catalyst or a low-temperature active catalyst is used depending on the temperature state of the fuel and air, and a catalyst is used. It is also possible to cause combustion.

  Next, the operation of the fuel cell system 100 according to the present embodiment configured as described above will be described. First, the operation during normal power generation will be described.

  During normal power generation, air heated by the air preheater 12 is supplied to the cathode of the stack 1. Further, a part of the reforming fuel, reforming air, and anode off gas are mixed and supplied to the reforming passage 5 of the reformer 4, and reformed in the reforming passage 5. The reformed gas is supplied to the anode 2 of the stack 1 via the flow path 18, and power generation is performed in the stack 1. That is, the stack 1 is supplied with a gas containing hydrogen to the anode 2 and a gas containing oxygen to the cathode 3 to generate power.

  The anode off-gas generated in the stack 1 is supplied to the circulation device 7 via the flow path 19 and is pumped to the branch device 8 by the circulation device 7, and part of the anode off-gas is improved via the circulation gas passage 17. Reintroduced into the reforming passage 5 of the mass device 4. That is, the anode off gas is circulated. At this time, since the anode off gas contains a large amount of water vapor, it is possible to prevent the occurrence of carbon deposition by circulating the anode off gas through the anode circulation path. Further, the anode off-gas that is not circulated through the anode circulation path is supplied to the heating passage 6 of the reformer 4 via the heating gas passage 16 and becomes a heat source for reforming.

  During power generation by the stack 1, the anode off gas is recirculated to the reformer 4 so that water generated by the electrochemical reaction can be used for reforming. Supply is unnecessary.

  Next, the operation at the time of starting the stack 1 will be described. When the stack 1 is activated, the activation combustor 11 is operated, and the combustion gas generated by the activation combustor 11 is supplied to the cathode 3 to raise the temperature of the stack 1. Further, the gas discharged from the cathode 3 is introduced into the heating passage 6 of the reformer 4 as a cathode off gas, and the reformer 4 is heated.

  On the other hand, in the anode circulation path connected to the anode 2, a part of the combustion gas of the start-up combustor 11 is taken out through the combustion gas passage 20, and this combustion gas (steam-containing gas) is discharged from the reformer 4. It is introduced into the reforming passage 5. Further, the anode off-gas is supplied to the anode 2 via the flow path 18, and thereafter, the anode off-gas passes through the circulation device 7 via the flow path 19, and enters the reforming passage 5 via the branch device 8 and the circulation gas passage 17. Returned. That is, a circulation path for the combustion gas for the anode is formed. A part of the combustion gas in the anode circulation path flows out to the cathode system flow path via the heating gas path 16. The outflow amount is an amount corresponding to the supply amount of the combustion gas supplied through the combustion gas passage 20 when the circulation device 7 is operating under a constant condition.

  At this time, the circulation device 7 is provided on the upstream side of the branch device 8, and by controlling the circulation device 7, the ratio of the amount of gas branched into the heating gas passage 16 and the circulation gas passage 17 can be adjusted. it can. For example, when the amount of combustion gas supplied from the combustion gas passage 20 is constant, increasing the discharge amount of the circulation device 7 increases the ratio of the amount of gas circulated to the circulation gas passage 17 rather than the heating gas passage 16. Become. Accordingly, the amount of combustion gas flowing in the anode circulation path formed by the reforming passage 5, the flow path 18, the anode 2, the flow path 19, the circulation device 7, and the circulation gas path 17 of the reformer 4 can be increased. it can. For this reason, the water vapor contained in the combustion gas can be increased, and the amount of water vapor contained in the anode circulation path can be adjusted by adjusting the circulation device 7.

  Alternatively, the amount of combustion gas supplied from the combustion gas passage 20 can be increased in a state where the ratio of the amount of gas branched into the heating gas passage 16 and the circulation gas passage 17 in the branch device 8 is kept constant. The amount of combustion gas flowing in the anode circulation path can be increased.

  Further, the amount of combustion gas flowing in the anode circulation path can also be increased by reducing the amount of gas branched into the circulation gas passage 17 by the branch device 8.

  That is, by increasing the amount of combustion gas flowing in the anode circulation path by these means, the steam along with nitrogen and carbon dioxide is fed into the anode circulation path from the start of the stack 1 until power generation. Can be created. From this state, carbon deposition can be prevented by water vapor in the anode system even when the reforming fuel and reforming air are supplied to the reformer.

  In this way, in the solid oxide fuel cell system 100 according to the first embodiment, during the start-up operation of the stack 1, a mechanism that circulates the steam-containing gas in the anode circulation path and further varies the amount of steam is provided. Since it is provided, it is possible to prevent the occurrence of carbon deposition when the stack 1 is activated.

  In addition, since a part of the combustion gas (steam-containing gas) generated by the start-up combustor 11 is introduced into the anode circulation path through the combustion gas passage 20, from the start of the stack 1 until power generation is performed. It is possible to ensure the amount of water vapor in the anode circulation path between the two.

  Furthermore, by supplying the combustion gas obtained by stoichiometric combustion by the start-up combustor 11 as a steam-containing gas to the anode circulation path, it is possible to supply a steam-containing gas with less impurities.

  Further, since the circulation device 7 is installed in the flow path 19 at the outlet of the anode 2 and the branch device 8 is further installed on the outlet side to branch the anode off gas, the amount of water vapor circulated in the circulation gas passage 17 can be adjusted. And the occurrence of carbon deposition can be prevented.

  Furthermore, by controlling the amount of water vapor-containing gas introduced into the anode circulation path to gradually increase from the start of the stack 1, the amount of water vapor introduced into the anode circulation path can be prevented from changing suddenly, and carbon The occurrence of precipitation can be prevented.

  Further, the start-up combustor 11 is a two-stage type (multiple-stage type) of a small diffusion combustor (pre-combustor) 21 and a catalytic combustor (main combustor) 22 to efficiently generate combustion gas. In addition, a part of the precombustion gas sent from the small diffusion combustor 21 can be used as a water vapor-containing gas introduced into the anode circulation path.

[Description of Second Embodiment]
Next, a second embodiment of the present invention will be described. FIG. 3 is a block diagram showing the configuration of the solid oxide fuel cell system 101 according to the second embodiment of the present invention. The fuel cell system 101 according to the second embodiment has no combustion gas path from the start-up combustor 11 via the combustion gas passage 20 as compared with the fuel cell system 100 shown in the first embodiment. This is different from the above point in that an anode circulation gas generator 30 is provided. Since the other configuration is the same as that of FIG. 1, the same reference numerals are given and the description of the configuration is omitted.

  In the fuel cell system 101 according to the second embodiment, the anode circulation gas generator 30 (in parallel with the flow path for supplying the reformed fuel and the reformed air to the reforming passage 5 is provided. Hereinafter, a “circulation gas generator 30” is provided.

  Combustion air is introduced into the circulation gas generator 30 from a reforming air passage supplied from a compressor (not shown), combustion gas is generated together with the gas generating fuel 31, and anode circulation passage as stoichiometric combustion gas. To be supplied.

  FIG. 4 is an explanatory diagram showing a configuration of the circulating gas generator 30 shown in FIG. As shown in FIG. 4, the circulating gas generator 30 is supplied with fuel from a fuel supply device (not shown), and is supplied with air from a combustion air supply port 34. Combustion gas is generated by combustion in the section 36. Then, this combustion gas is heat-exchanged with the air supplied to the combustion air supply port 34 in the heat exchanging portion 37, and thereafter, as the anode circulation gas, the reforming passage shown in FIG. 5 is supplied. Use of a catalyst as the main combustion section 36 is advantageous in terms of the capacity of the apparatus. The fuel supply device and the combustion air supply port 34 are provided with heaters 38 and 39 for heating.

  In the solid oxide fuel cell system according to the second embodiment, the amount of water vapor stored in the anode circulation path is more precisely controlled by providing the anode circulation gas generator 30 separately from the start-up combustor 11. It becomes possible.

  Next, the operation at the time of stack activation of the solid oxide fuel cell system 101 according to the second embodiment will be described.

  At the time of starting the stack 1, the heating gas generated by the starting combustor 11 is supplied to the cathode 3 to raise the temperature of the stack 1, and the cathode off gas is introduced into the heating passage 6 of the reformer 4. The reformer 4 is heated.

  On the other hand, when the temperature of the stack 1 and the reformer 4 starts to rise due to the start of the start-up combustor 11 and reaches a temperature at which steam condensation does not occur, the circulating gas generator 30 is operated. Then, by gradually increasing the amount of combustion gas generated in the circulating gas generator 30, the generated combustion gas is introduced into the reforming passage 5 of the reformer 4 via the flow path 32. That is, the combustion gas is introduced into the reforming passage 5 while gradually increasing. Further, the combustion gas is introduced into the anode 2 through the flow path 18, further passes through the flow path 19 and the circulation device 7, is branched by the branch device 8, and passes through the circulation gas passage 17 to the reforming passage 5. Returned. That is, the combustion gas delivered from the circulation gas generator 30 is supplied into the circulation path of the anode combustion gas, and the water vapor is accumulated in the anode circulation path before the power generation during the activation of the stack 1 is reached. Will be created.

  Even when the warm-up is completed and the reformer 4 starts to supply the reforming fuel and the reforming air, carbon deposition due to the reforming fuel is not caused by the water vapor in the anode circulation path. That is, since the combustion gas (steam-containing gas) by the circulating gas generator 30 is introduced into the anode circulation path from when the stack 1 is started to when power generation is started, water vapor is supplied into the anode circulation path. And the occurrence of carbon deposition can be prevented.

  FIG. 5 is a characteristic diagram showing a change in the amount of circulating gas in the anode circulation path during the time elapsed from the start of the start-up combustor 11 to the completion of warm-up until the stack 1 is started.

  When the start-up combustor 11 is started at time t0 shown in FIG. 5, the temperature of the stack 1 and the reformer 4 starts to rise. At time t1, when the stack 1 and the reformer 4 reach a temperature at which steam condensation does not occur, the operation of the circulating gas generator 30 is started.

  In the circulating gas generator 30, the amount of combustion gas to be sent out gradually increases with time. When the warm-up is completed at time t2, at this time, the amount of water vapor that does not cause carbon deposition when the reforming fuel and reforming air are supplied to the reformer 4 is stored in the anode circulation path. Will be.

  The amount of water vapor that does not cause carbon deposition is determined by the amount of fuel supplied from the outside necessary for generating hydrogen and carbon monoxide as reformed gas components required for power generation by the fuel cell, and the anode system filled with combustion gas. Depending on the amount and distribution of the reformed fuel and air from when the fuel cell is generated until the fuel cell generates power, the stack is further increased depending on the amount of gas used for raising the temperature of the cathode system and the amount of circulating anode gas. It depends on the tolerance of the pressure difference between the cathode and the anode generated in the inside, and is finely controlled by the operating state.

  When the warm air is completed, the gas from the circulating gas generator 30 is supplied, while the reforming fuel and the reforming air are supplied to the reforming passage 5 of the reformer 4, and the reformed gas is supplied. Start mixing in the anode circulation path. In accordance with this, the gas supply from the circulating gas generator 30 is reduced, and finally the gas supply from the circulating gas generator 30 is stopped at time t3. Thereby, all the gas circulating in the anode circulation path is replaced with the reformed gas.

  Thus, by finely controlling the amount of combustion gas delivered from the circulating gas generator 30, the supply amount of the combustion gas is gradually increased, and after the warm air is completed, the supply amount of the combustion gas is gradually decreased, Eventually, the entire circulating gas can be replaced with the reformed gas.

  Thus, in the solid oxide fuel cell system 101 according to the second embodiment, the circulating gas generator 30 is installed on the inlet side of the reforming passage 5 and the circulating gas generator 30 is activated when the stack 1 is started. Is operated to supply combustion gas (steam-containing gas) into the anode circulation channel, so that steam can be supplied into the anode circulation channel after the stack 1 is activated until power generation is started. And the occurrence of carbon deposition can be prevented.

  Further, by adjusting the amount of combustion gas output from the circulating gas generator 30, the amount of water vapor circulating can be adjusted, and the supply amount of combustion gas can be gradually increased. Therefore, the amount of water vapor supplied into the anode circulation channel can be gradually increased, and a rapid change in the amount of water vapor can be prevented, so that the occurrence of carbon deposition can be prevented.

  Further, after the stack warming is finished, the reformed fuel and the air are circulated in the anode circulation flow path, and then the output of the combustion gas by the circulation gas generator 30 is stopped. Therefore, the circulation in the anode circulation flow path is stopped. The gas can be smoothly replaced with the reformed gas, and the occurrence of carbon deposition can be prevented.

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

  INDUSTRIAL APPLICABILITY The present invention can be used to perform power generation by a stack without supplying water from the outside during startup to power generation.

DESCRIPTION OF SYMBOLS 1 Stack 2 Anode 3 Cathode 4 Reformer 5 Reforming passage 6 Heating passage 7 Circulating device 8 Branching device 11 Start-up combustor 12 Air preheater 14, 15, 18, 19, 32 Flow path 16 Heating gas passage DESCRIPTION OF SYMBOLS 17 Circulation gas path 20 Combustion gas path 21 Small diffusion combustor 22 Catalytic combustor 23 Fuel injection valve 24 Air introduction path 25 Ignition device 26 Combustion gas extraction port 27 Fuel supply port 28 Secondary air supply port 29 Combustion part 30 Circulation gas generation (Anode circulation gas generator)
Reference Signs List 31 Gas generating fuel 34 Combustion air supply port 35 Precombustion section 36 Main combustion section 37 Heat exchange section 38, 39 Heater 100, 101 Solid oxide fuel cell system

Claims (8)

A new fuel is introduced into the reformer, the reformed fuel is supplied to the anode of the fuel cell stack, and a part of the anode off-gas discharged from the anode is circulated through the reforming passage of the reformer. In the solid oxide fuel cell system, the remaining anode off gas is mixed with the cathode off gas discharged from the cathode of the fuel cell stack and used for heating the reformer.
A solid oxide comprising a mechanism that heats the cathode and the reformer at the time of start-up, circulates water vapor-containing gas to the anode, and makes the amount of water vapor in the anode circulation path during start-up operation variable. Type fuel cell system.   A startup combustor that raises the temperature of the cathode at the time of startup of the fuel cell stack is provided, and a part of the combustion gas generated in the startup combustor is a steam-containing gas that is circulated to the anode. The solid oxide fuel cell system according to claim 1.   The solid oxide fuel cell system according to claim 2, wherein the start-up combustor generates the water vapor-containing gas by stoichiometric combustion.   The start-up combustor is a multi-stage combustor, and the combustion gas delivered from the most upstream first-stage combustor is introduced into the anode as the steam-containing gas. The solid oxide fuel cell system according to any one of claims 2 and 3.   2. The solid according to claim 1, further comprising an anode circulation gas generator for supplying combustion gas to the anode circulation path, and introducing the steam-containing gas into the anode circulation path by the anode circulation gas generator. Oxide fuel cell system.   A circulation device and a branching device for branching the anode off-gas circulated by the circulation device and circulating a part thereof to the anode system in the flow path on the outlet side of the anode, and adjusting the circulation device and combustion gas The solid oxide fuel cell system according to any one of claims 1 to 5, wherein the amount of water vapor-containing gas circulating to the anode is adjusted by at least one of the increase and decrease of the amount.   7. The solid oxide fuel cell system according to claim 6, wherein the amount of water vapor-containing gas circulated to the anode is gradually increased from the start of startup of the stack.   2. After the end of warming of the fuel cell stack, the reformed fuel and reformed air are added to the steam-containing gas and circulated through the anode circulation path, and then the introduction of the steam-containing gas is stopped. The solid oxide fuel cell system according to any one of 1 to 7.

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