JP2021190285A - Solid oxide type fuel cell system - Google Patents

Abstract

To provide a solid oxide type fuel cell system capable of suppressing deterioration on an oxygen electrode side which is easily generated at a time of a shutdown stop.SOLUTION: A solid oxide type fuel cell system 2 comprises: a reformer 4 for performing a moisture vapor reforming of a fuel gas; a cell stack 6 that performs a power generation by oxidation-reduction reaction of a reforming fuel gas in which the moisture vapor reforming has been made and an oxidant gas; a combustor 50 provided in related to the reformer 4; a moisture vapor condensate part 46 condensing a moisture vapor contained in a fuel off-gas; and a recycling passage 56 for returning a part of the fuel off-gas to a fuel gas supply system. A part of the fuel off-gas in which the moisture vapor is removed is returned to a fuel gas supply system via the recycling passage 56, and is combusted after its remaining part is transmitted to the combustor 50. Reductive gas inflow prevention means 92 is provided to prevent a reactive gas in the combustor 50 from entering to an oxygen electrode side 36 of the cell stack 6 at the time of a shut down stop.SELECTED DRAWING: Figure 1

Description

The present invention relates to a solid oxide fuel cell system including a cell stack that generates power by oxidizing and reducing a reformed fuel gas obtained by reforming a fuel gas and an oxidant gas.

Conventionally, a solid oxide fuel cell system including a solid oxide cell stack using a solid electrolyte as a film for conducting oxide ions has been known. In this solid oxide fuel cell system, the cell stack is configured by stacking a plurality of fuel cell cells, and a fuel electrode for oxidizing fuel gas is provided on one side of the solid electrolyte in each fuel cell. An oxygen electrode for reducing oxygen in the air (oxidizing agent gas) is provided on the other surface side. The operating temperature of the fuel cell of this solid oxide fuel cell system is as high as about 700 to 900 ° C, and at such a high temperature, hydrogen, carbon monoxide, and hydrocarbons in the fuel gas (reformed fuel gas) Power is generated by an electrochemical reaction with oxygen in the air.

As such a solid oxide fuel cell system, a reformer for steam reforming fuel gas (raw fuel gas), and oxidation of reformed fuel gas and oxidant gas reformed by the reformer. A cell stack that generates power by reduction and reduction, an air supply means (oxidizer gas supply means) for supplying air as an oxidant gas to the oxygen electrode (air electrode) side of the cell stack, and a fuel gas to the reformer. It has been proposed that a fuel gas supply means for supplying (raw fuel gas) is provided, and a cell stack and a reformer are housed in a high temperature housing kept in a high temperature state (for example, Patent Document 1). reference).

In this solid oxide fuel cell system, a combustion region is provided above the cell stack, and a reformer is disposed above the combustion region. Then, the reformed fuel gas from the reformer is supplied to the fuel electrode side of the cell stack, and the air from the air supply means is supplied to the oxygen electrode side of the cell stack, and the electrochemical reaction (power generation) in this cell stack is performed. Power is generated by the reaction). The fuel off gas from the fuel electrode side of the cell stack (that is, the anode off gas) and the air off gas from the oxygen electrode side (that is, the cathode off gas) are sent to the combustion region and burned, and reformed using this combustion heat. As the vessel and the like are heated, the high temperature space is kept in a high temperature state.

As a solid oxide fuel cell system, a system equipped with a dedicated combustor instead of providing a combustion region on the upper side of the cell stack has also been proposed (see, for example, Patent Document 2). In this solid oxide fuel cell system, fuel off gas (anodic off gas) from the fuel electrode side of the cell stack is supplied to the combustor through the fuel off gas supply flow path, and air off gas from the oxygen electrode side of the cell stack. (Cathonate off gas) is supplied to the combustor through the air off gas supply flow path, and the fuel off gas is burned by the air off gas in this combustor, and the reformer and the like are heated by using this combustion heat, and the temperature is high. The space is kept hot.

In recent years, in such a solid oxide fuel cell system, a system for increasing power generation efficiency has also been proposed (see, for example, Patent Document 3). In this solid oxide fuel cell system, the fuel off gas (anode off gas) from the cell stack is derived from the high temperature space and sent to the steam condensing section, where the steam contained in the fuel off gas is condensed. Will be done. The steam condensing unit includes, for example, an exhaust heat recovery heat exchanger for recovering exhaust heat and a gas-liquid separator for separating condensed water, and the exhaust heat recovery heat exchanger is used, for example, from a hot water storage device. It is cooled by heat exchange with water, and this cooling condenses the water contained in the fuel off gas. Then, a part (about 10 to 40%) of the fuel off gas (anode off gas) from which water has been removed is returned to the decompression region (fuel gas supply system) on the upstream side of the fuel gas supply means (fuel gas supply pump). This returned fuel off gas is mixed with the fuel gas from the fuel gas supply source and supplied to the reformer. On the other hand, the remaining fuel off gas (those that are not returned to the fuel gas supply system) is sent to a combustor in the high temperature space, and is burned by the air off gas (cathode off gas) in this combustor.

By returning a part of the fuel off gas to the fuel gas supply system in this way, the power generation efficiency of the fuel cell system can be improved. Generally, the fuel utilization rate of the cell stack is usually about 82 to 83%, but by returning the fuel off gas to the fuel gas supply system, this fuel utilization rate can be increased to about 87 to 90%. It is possible to improve by about 5 to 7 points, which makes it possible to increase the power generation efficiency.

Japanese Unexamined Patent Publication No. 2005-285340 Japanese Unexamined Patent Publication No. 2008-21596 Japanese Unexamined Patent Publication No. 2018-198116

In this type of solid oxide fuel cell system, the operating temperature of the cell stack is as high as 700 to 900 ° C., and it is necessary to have high power generation performance in such a high temperature state. For example, a mixture of metallic nickel and stabilized zirconia which is an electrolyte material is used, and as the oxygen electrode (air electrode), for example, lanthanum strontium cobalt ferrite (LSCF) or lanthanum manganite is used. Such fuel electrode materials are stable only in a reducing atmosphere, and oxygen electrode materials are stable only in an oxidizing atmosphere, so that reducing gas is always on the fuel electrode side during system start-up, power generation, and shutdown. Flows, and an oxidant gas (air) containing oxygen flows to the oxygen electrode side (air electrode side).

As a general task in this solid oxide fuel cell system, a shutdown operation that shuts down the system, for example, the shutoff valve must be closed immediately during power generation to make an emergency stop (eg, system failure, fuel to the system) When performing an operation that is performed when the gas supply is cut off or an abnormality is detected in various sensors), the cell stack may be adversely affected. Throughout this specification, "shutdown stop" means a stop in which the fuel gas supply flow rate is reduced to zero when the cell stack is in a high temperature state (for example, 500 ° C. or higher).

When shutting down and stopping, the following problems occur on the fuel electrode side of the cell stack. For this fuel electrode, for example, a mixture of metallic nickel and stabilized zirconia, which is an electrolyte material, is used. Therefore, when the shutdown is stopped and the fuel gas supply is stopped, the oxygen electrode side of the cell stack and the exhaust gas are used. Air from the exhaust flow path may reach the fuel electrode side (its outlet side). When air reaches the fuel electrode side when the temperature of the cell stack is high (for example, 400 ° C. or higher), a part of nickel in the fuel electrode (from the particle surface thereof) is oxidized to nickel oxide.

Oxidation on the fuel electrode side returns to metallic nickel, which is in a reduced state, due to the flow of reformed fuel gas (reducing gas) during normal startup after shutdown is stopped. Depending on the number of times, the microstructure and dimensions of the fuel electrode change, which may cause problems such as deterioration of electrode performance and cracking of the solid electrolyte in contact with the fuel electrode.

Further, on the oxygen pole side (air pole side) of the cell stack, the following problems occur. Oxidizing agent gas (air) containing oxygen flows to the oxygen electrode side, but when the shutdown is stopped, the supply of oxidizing agent gas (air) is also stopped at the same time (when the fuel gas supply is stopped). This is because if the air supply to the cell stack is continued, oxygen is eventually supplied from the outlet side to the fuel electrode, and the above-mentioned problems are likely to occur on the fuel electrode side).

When the supply of the fuel gas and the oxidant gas (air) is stopped in a high temperature state (for example, around 700 ° C.) of the cell stack, the following occurs. A vaporizer (steam generator) exists in the fuel gas supply system, and when the system shuts down and stops, reforming water remains in the vaporizer. The combustor for applying heat to the vaporizer stops combustion when the shutdown is stopped, but since the ambient temperature of this combustor is sufficiently high, steam is vaporized in the fuel gas supply system (mainly the vaporizer) in the absence of fuel gas. Occurs. As a result, water vapor containing a small amount of fuel gas flows to the combustor through the fuel electrode side of the stack.

There is no problem if the water vapor mixed with the fuel gas flowing through the combustor is discharged to the outside through the exhaust gas discharge flow path as it is, but in reality, this water vapor is sent to the exhaust gas discharge flow path and the oxide material off gas. It is distributed to the supply flow path (the flow path connecting the oxygen electrode side of the cell stack and the combustor), and a large amount is distributed and flows to these easy-to-flow directions.

When water vapor mixed with fuel gas reaches the oxygen electrode side (air electrode side) of the cell stack at a high temperature (for example, 500 ° C or higher), the LSCF (lanternstrontium cobalt ferrite) electrode (solid oxide fuel cell), which is the material on the oxygen electrode side, is used. When a typical oxygen electrode material of a battery cell, for example, a perovskite-type oxide) undergoes reduction and a part of the oxygen electrode undergoes a reducing action, the LSCF expands, and depending on the degree, the oxygen electrode layer (LSCF layer). ), Or the oxygen electrode layer is partially exfoliated from the solid electrolyte, and once this crack or exfoliation occurs, it leads to irreversible large deterioration.

An object of the present invention is to provide a solid oxide fuel cell system capable of suppressing deterioration on the oxygen electrode side, which tends to occur when shutdown is stopped.

The solid oxide fuel cell system according to claim 1 of the present invention has a vaporizer for vaporizing water for reforming and reforming for steam reforming fuel gas using steam from the vaporizer. The vessel, the cell stack that generates power by oxidizing and reducing the reformed fuel gas and the oxidant gas reformed by the reformer, and the oxidant gas are supplied to the cell stack through the oxidant gas supply flow path. An oxidant gas supply means for supplying the fuel gas, a fuel gas supply means for supplying the fuel gas to the reformer through the fuel gas supply flow path, and a combustor provided in connection with the reformer. The reformer is provided with a steam condensing unit for condensing water vapor contained in the fuel off gas from the cell stack, and a recycling flow path for returning a part of the fuel off gas to the upstream side of the fuel gas supply means. The reformed fuel gas from the cell stack is supplied to the fuel electrode side of the cell stack, the oxidant gas from the oxidant gas supply means is supplied to the oxygen electrode side of the cell stack, and the cell stack is described. The water vapor contained in the fuel off gas from the fuel electrode side is cooled by the water vapor condensing portion and recovered as condensed water, and a part of the fuel off gas from which the water vapor is removed by the steam condensing portion is a part of the recycling flow path. In a solid oxide fuel cell system, which is returned to the upstream side of the fuel gas supply means through the fuel gas supply means, and the balance thereof is fed to the combustor and burned by the oxide off gas from the oxygen electrode side of the cell stack. There,
The vaporizer, the reformer, the cell stack and the combustor are housed in a high temperature housing for defining a high temperature space, and the reducing gas in the combustor is charged in the cell stack when the system shuts down. It is characterized in that a reducing gas inflow preventing means for preventing the inflow to the oxygen electrode side is provided.

Further, in the solid oxide type fuel cell system according to claim 2 of the present invention, the reducing gas inflow prevention means is a backflow prevention provided in the oxidant gas supply means or the oxidant gas supply flow path. The backflow prevention structure is composed of a structure, and the backflow prevention structure prevents the backflow of the oxidant gas in the oxidant gas supply means or the oxidant gas supply flow path when the shutdown of the system is stopped, whereby the combustor. The reducing gas is prevented from flowing into the oxygen electrode side of the cell stack.

Further, in the solid oxide fuel cell system according to claim 3 of the present invention, the reducing gas inflow prevention means is an oxidant gas supply means or an oxidant disposed in the oxidant gas supply flow path. It is composed of a gas flow rate detecting means and a backflow prevention control means for controlling the operation of the oxidant gas supply means to prevent the backflow of the oxidant gas, and the oxidant gas flow rate detecting means when the system is shut down. When the backflow of the oxidant gas is detected, the backflow prevention control means controls the operation of the oxidant gas supply means based on the detection signal from the oxidant gas flow rate detecting means to control the operation of the oxidant gas to the cell. It is characterized in that it is supplied to the oxygen electrode side of the stack, thereby preventing the inflow of the reducing gas from the combustor to the oxygen electrode side of the cell stack.

Further, in the solid oxide fuel cell system according to claim 4 of the present invention, a temperature detecting means for detecting the temperature of the cell stack is further provided, and the oxidant gas flow rate detecting means is the oxidant gas. When the backflow is detected and the temperature detecting means detects the high temperature of the cell stack, the backflow prevention control means controls the operation of the oxidant gas supply means to transfer the oxidant gas to the oxygen electrode of the cell stack. It is characterized by supplying to the side, thereby preventing the inflow of the reducing gas from the combustor to the oxygen electrode side of the cell stack.

Further, in the solid oxide fuel cell system according to claim 5 of the present invention, the reducing gas inflow prevention means supplies the oxide off gas from the oxygen electrode side of the cell stack to the combustor. Oxidizing material The reducing gas adsorbent is composed of a reducing gas adsorbent disposed in the off-gas supply flow path, and the reducing gas adsorbent flows from the combustor to the oxygen electrode side of the cell stack when the system is shut down. It is characterized in that it adsorbs the reducing gas, thereby preventing the inflow of the reducing gas from the combustor to the oxygen electrode side of the cell stack.

According to the solid oxide fuel cell system according to claim 1 of the present invention, the fuel gas (for example, city gas) is steam reformed using steam from the vaporizer in the reformer, and the reforming is performed. The reformed fuel gas from the vessel is supplied to the fuel electrode side of the cell stack, and the oxidizing agent gas (for example, air) from the oxidizing agent gas supply means is supplied to the oxygen electrode side of the cell stack to fuel the cell stack. The steam contained in the fuel off gas from the polar side is cooled by the steam condensing section and recovered as condensed water. In addition, a part of the fuel off gas from which steam has been removed by the steam condensing part is returned to the upstream side of the fuel gas supply means through the recycling flow path, and the rest is sent to the combustor, which is on the oxygen electrode side of the cell stack. Oxidizer off gas from (eg, air off gas) burns.

Since the vaporizer, reformer, cell stack and combustor are housed in the high temperature housing and the reducing gas inflow prevention means is provided to prevent the inflow of reducing gas, the system shuts down at high temperature. Then, steam mixed with reducing gas is generated in the vaporizer, and this reducing gas inflow prevention means prevents the steam from flowing from the combustor to the oxygen electrode side of the cell stack, thereby reducing the reducing property. Deterioration of the oxygen electrode of the cell stack due to gas can be suppressed.

Further, according to the solid oxide fuel cell system according to claim 2 of the present invention, the reducing gas inflow prevention means is a backflow arranged in the oxidant gas supply means (or the oxidant gas supply flow path). Since it is composed of a preventive structure, this backflow preventive structure prevents the backflow of oxidant gas from the oxygen electrode of the cell stack toward the oxidant gas supply means, thereby preventing the oxidant gas from flowing back from the combustor when the shutdown is stopped. It is possible to prevent the inflow of the reducing gas to the oxygen electrode side of the cell stack.

Further, according to the solid oxide fuel cell system according to claim 3 of the present invention, the reducing gas inflow preventing means is an oxidation arranged in the oxidant gas supply means (or the oxidant gas supply flow path). Since it is composed of the agent gas flow rate detecting means and the backflow prevention control means for controlling the operation of the oxidant gas supply means to prevent the backflow of the oxidant gas, the oxidant gas flow rate detecting means is used when the system is shut down. When the backflow of the oxidant gas is detected, the operation of the oxidant gas supply means is controlled so that the backflow of the oxidant gas from the oxygen electrode of the cell stack to the oxidant gas supply means does not occur, thereby stopping the shutdown. Sometimes it is possible to prevent the inflow of reducing gas from the combustor to the oxygen electrode side of the cell stack.

Further, according to the solid oxide fuel cell system according to claim 4 of the present invention, a temperature detecting means for detecting the temperature of the cell stack is further provided, and the oxidant gas flow rate detecting means is the oxidant gas. When the backflow is detected and the temperature detecting means detects the high temperature of the cell stack, the backflow prevention control means controls the operation of the oxidant gas supply means, so that the cell stack can be reduced to the oxygen electrode side in a high temperature state. The inflow of gas can be prevented, thereby preventing the deterioration of the oxygen electrode of the cell stack in a high temperature state.

Further, according to the solid oxide fuel cell system according to claim 5 of the present invention, the reducing gas inflow prevention means is composed of a reducing gas adsorbent disposed in the oxidizing material off-gas supply flow path. Therefore, even if the water vapor mixed with the reducing gas from the combustor flows to the oxygen electrode side of the cell stack when the shutdown is stopped, this reducing gas adsorbent adsorbs the reducing gas, thereby reducing the reducing property. It is possible to prevent the inflow of gas to the oxygen electrode side of the cell stack.

The whole view which shows the 1st Embodiment of the solid oxide fuel cell system according to this invention simply. The whole view which shows the 2nd Embodiment of the solid oxide fuel cell system according to this invention simply. The whole view which shows the 3rd Embodiment of the solid oxide fuel cell system according to this invention simply.

Hereinafter, various embodiments of the solid oxide fuel cell system according to the present invention will be described with reference to the accompanying drawings. First, a first embodiment of the solid oxide fuel cell system according to the present invention will be described with reference to FIG.

In FIG. 1, the illustrated solid oxide fuel cell system 2 uses fuel gas such as city gas and LP gas as raw fuel gas to generate power, and reforms the fuel gas (raw fuel gas). A solid oxide fuel cell that generates power (so-called power generation reaction) by oxidizing and reducing the reformer 4 for the purpose and the reformed fuel gas reformed by the reformer 4 and the air as an oxidizing agent gas. It has a stack 6 and.

The cell stack 6 is configured by stacking a plurality of solid oxide fuel cell cells for generating power by a power generation reaction via a current collecting member, and although not shown, a solid that conducts oxygen ions. A fuel electrode provided on one side of the solid electrolyte, an oxygen electrode (air electrode) provided on the other side of the solid electrolyte, and zirconia doped with itria, for example, are used as the solid electrolyte.

The fuel electrode side 8 of the cell stack 6 is connected to the reformer 4 via the reformed fuel gas supply flow path 10. In this embodiment, the reformer 4 is a vaporizer for vaporizing the reforming water. It is configured as a reforming unit integrally with 12. The vaporizer 12 is configured separately from the reformer 4, and the steam vaporized by the vaporizer 12 is supplied to the reformer 4 via the steam supply flow path (not shown). You may do it.

The vaporizer 12 is connected to a fuel gas supply source (not shown) for supplying fuel gas through the fuel gas supply flow path 14 (for example, composed of a buried pipe, a storage tank, or the like), and is connected to the fuel gas. The fuel gas (raw fuel gas) from the supply source is supplied to the vaporizer 12 through the fuel gas supply flow path 14. The fuel gas supply flow path 14 may be connected to the reformer 4 so that the fuel gas from the fuel gas supply source is directly supplied to the reformer 4.

Further, reforming water is supplied to the vaporizer 12 through the water supply flow path 18. A reforming catalyst is housed in the reformer 4, and for example, an alumina on which ruthenium is supported is used as the reforming catalyst, and the reforming catalyst vaporizes the fuel gas supplied through the fuel gas supply flow path 14. It is steam reformed with the steam vaporized in the vessel 12.

In the fuel gas supply flow path 14, the desulfurizer 20, the first drawing member 22, the fuel gas supply pump 24 (which constitutes the fuel gas supply means), and the second drawing member 26 are in this order from the vaporizer 12 toward the upstream side. , A zero governor 28 as a pressure adjusting member, a fuel flow sensor 30, and a shutoff valve 32 are arranged. The desulfurization device 20 removes the sulfur component (sulfur component in the odorant) contained in the fuel gas, and the fuel gas supply pump 24 pressurizes the fuel gas flowing through the fuel gas supply flow path 14 to the vaporizer 12. By supplying and controlling the rotation speed of the fuel gas supply pump 24, the supply flow rate of the fuel gas is adjusted, and when the rotation speed of the fuel gas supply pump 24 is increased (or decreased), the fuel gas supply flow path 14 is supplied. The supply flow rate of fuel gas supplied through is increased (or decreased).

Further, the zero governor 28 adjusts the fuel gas supplied from the fuel gas supply source (not shown) through the fuel gas supply flow path 14 to a predetermined pressure (that is, atmospheric pressure), and the fuel gas flow rate sensor 30 adjusts the fuel gas. The flow rate of the fuel gas supplied through the supply flow path 14 is measured, and when the shutoff valve 32 is closed, the fuel gas supply flow path 14 is shut off to stop the supply of the fuel gas. Further, the first and second throttle members 22 and 26 located on both sides (that is, the downstream side and the upstream side) of the fuel gas supply pump 24 are used to stabilize the flow rate of the fuel gas flowing through the fuel gas supply flow path 14. Provided, the first throttle member 22 is composed of, for example, a capillary tube, and the second throttle member 26 is composed of, for example, a throttle member having a small orifice. Further, the fuel gas flow rate sensor 30 is composed of, for example, a thermal flow rate sensor. When the fuel gas can be stably supplied, the first drawing member 22 may be omitted, or a buffer tank may be used instead of the second drawing member 26. ..

A water supply pump 34 (which constitutes a water supply means) is arranged in the water supply flow path 18, and the water for reforming is supplied to the vaporizer 12 through the water supply flow path 18 as described later by the water supply pump 34. Will be done. By controlling the rotation speed of the water supply pump 34, the supply flow rate of the reforming water is adjusted, and when the rotation speed of the water supply pump 34 is increased (or decreased), the water is supplied through the water supply flow path 18. The supply flow rate of quality water increases (or decreases).

The oxygen electrode (air electrode) side 36 of the cell stack 6 is connected to an air blower 40 as an oxidant gas supply means via an air supply channel 38 (which constitutes an oxidant gas supply channel). The air blower 40 supplies air (oxidizing agent gas) to the oxygen electrode side 36 (air electrode side) of the cell stack 6 through the air supply flow path 38 (oxidizing agent gas supply flow path). The air supply flow rate is adjusted by controlling the rotation speed of the air blower 40, and when the rotation speed of the air blower 40 is increased (or decreased), the air (oxidizing agent gas) supplied through the air supply flow path 38 is increased. ) Supply flow rate increases (or decreases).

The fuel off gas (that is, the anode off gas) discharged from the fuel electrode side 8 of the cell stack 6 is sent to the steam condensing section 46 through the fuel off gas lead-out flow path 44, and is included in the fuel off gas at the steam condensing section 46. The steam is condensed and removed, and the fuel-off gas from which the steam has been removed is fed to the combustor 50 through the fuel-off gas supply flow path 48. Further, the air off gas (oxidant off gas) (that is, the cathode off gas) discharged from the oxygen electrode side 36 of the cell stack 6 is supplied to the combustor 50 through the air off gas supply flow path 52, and the combustor 50 is used. , The fuel off gas (containing fuel gas) from the fuel electrode side 8 of the cell stack 6 and the air off gas (containing oxygen) from the oxygen electrode side 36 (air electrode side) are burned. The carburetor 12 and the reformer 4 are arranged in contact with or close to the combustor 50, and the carburetor 12 and the reformer 4 are heated by utilizing the combustion heat of the fuel off gas, and the carburetor 12 and the reformer 4 are heated. The high temperature space 64, which will be described later, is kept in a high temperature state. The combustion exhaust gas from the combustor 50 is discharged to the atmosphere through the exhaust gas discharge flow path 54.

Further, a recycling flow path 56 is provided by branching from the fuel off gas supply path 48, and the downstream side of the recycling flow path 56 is a portion where the fuel gas supply flow path 14, specifically, the fuel gas supply pump 24 is arranged. It is connected to a portion between the surface and the arrangement portion of the second drawing member 26. Since the recycling flow path 56 is provided in this way, a part of the fuel off gas (anode off gas) flowing through the fuel off gas supply flow path 48 passes through the recycling flow path 56 and the fuel gas supply pump 24 in the fuel gas supply flow path 14 It is returned to the upstream side of the arrangement portion of the above, and the rest thereof is supplied to the combustor 50 through the fuel off gas supply flow path 48.

In this embodiment, the reformer unit (reformer 4 and vaporizer 12), the cell stack 6 and the combustor 50 are housed in the high temperature housing 62. The high temperature housing 62 is made of metal (for example, made of stainless steel), its inner surface is covered with a heat insulating member (not shown), a high temperature space 64 is defined inside the high temperature housing 62, and a reforming unit (reformer) is defined. 4 and the vaporizer 12), the cell stack 6 and the combustor 50 are kept in a high temperature state in this high temperature space 64.

In the solid oxide fuel cell system 2, a part of the fuel off-gas lead-out flow path 44 is led out to the outside of the high-temperature housing 62 (high-temperature space 64) and connected to the steam condensing section 46, and the fuel from the steam condensing section 46 is connected. A part of the off-gas supply flow path 48 is introduced from the outside of the high temperature housing 62 (high temperature space 64) to the inside thereof and connected to the combustor 50.

In this embodiment, the steam condensing unit 46 removes the first heat exchanger 66 for recovering exhaust heat, the gas-liquid separator 68 for separating the condensed water from the fuel off gas, and impurities contained in the condensed water. The ion exchanger 70 for storing the condensed water and the water recovery container 72 for storing the condensed water are included. The gas-liquid separator 68 is composed of, for example, a drain separator, and the first heat exchanger 66 is used, for example, in combination with a hot water storage device 74 for a cogeneration system for storing the heat of the fuel off gas as hot water. ..

The hot water storage device 74 includes a hot water storage tank 76 for storing hot water, a circulation flow path 78 that circulates through the first heat exchanger 66, and a circulation pump 80 arranged in the circulation flow path 78. When used in combination with the hot water storage device 74, the water in the hot water storage tank 76 is circulated through the circulation flow path 66 by the circulation pump 80, and the water flowing through the circulation flow path 78 and the fuel off-gas lead-out flow in the first heat exchanger 66. Heat exchange is performed with the fuel off gas flowing through the road 44, and hot water heated by the heat exchange is stored in the hot water storage tank 76. Further, the fuel off gas is cooled by this heat exchange, the water vapor contained therein is condensed, and the fuel off gas and the condensed water (condensed water) flow to the gas-liquid separator 68 on the downstream side.

The gas-liquid separator 68 separates the condensed water and the fuel off gas, and the separated condensed water flows to the lower ion exchanger 70, and impurities such as ion components are removed by the built-in ion exchange resin. It is later stored in the water recovery tank 72. The water (condensed water) recovered in the water recovery tank 72 is used as reforming water, and is supplied to the vaporizer 12 through the water supply flow path 18 by the action of the water supply pump 34. In this embodiment, the condensed water condensed by the steam condensing unit 46 is used as the reforming water, but instead of the condensed water, water filled in a water tank or the like may be used. ..

Further, a second heat exchanger 82 for preheating the air is disposed in relation to the air supply flow path 38 (oxidizer gas supply flow path), and the second heat exchanger 82 provides the air supply flow path 38. Heat exchange is performed between the flowing air (oxidizer gas) and the combustion exhaust gas discharged through the exhaust gas discharge flow path 54, and the air heated by this heat exchange is sent to the oxygen electrode side 36 of the cell stack 6. Will be paid.

Further, a third heat exchanger 84 for fuel off-gas residual heat is arranged in connection with the fuel off-gas supply flow path 48, and the third heat exchanger 84 is the fuel-off gas flowing through the fuel-off gas supply flow path 48. Heat is exchanged between the fuel off gas and the fuel off gas flowing through the fuel off gas lead-out flow path 44, and the fuel off gas heated by this heat exchange is sent to the combustor 50. The second and third heat exchangers 82.84 are housed in the high temperature housing 62 (high temperature space 64) and kept in a high temperature state.

The power generation operation of the solid oxide fuel cell system 2 is performed as follows. The fuel gas (raw fuel gas) is supplied to the vaporizer 12 by the action of the fuel gas supply pump 24, and the reforming water (condensed water) is supplied to the vaporizer 12 by the action of the water supply pump 34 to the vaporizer 12. The reforming water is vaporized to become steam, and the generated steam is mixed with fuel gas and sent to the reformer 4. In the reformer 4, the fuel gas reacts with steam to be steam reformed, and the steam reformed reformed fuel gas is supplied to the fuel electrode side 8 of the cell stack 6. Further, air (oxidizing agent gas) is supplied to the oxygen electrode side 8 of the cell stack 6 by the action of the air blower 40.

In the cell stack 6, a power generation reaction is performed by oxidation and reduction of the reformed fuel gas and air (oxidizing agent gas), and the generated power generation is sent to a power load (not shown) and consumed. The fuel off gas (anodide off gas) from the fuel electrode side 8 of the cell stack 6 is sent to the steam condensing unit 46, cooled by heat exchange in the first heat exchanger 66, and the water vapor in the fuel off gas is condensed and condensed. The condensed water is collected in the water recovery container 72. At this time, the hot water heated by the heat exchange in the first heat exchanger 66 is stored in the hot water storage tank 76 of the hot water storage device 74.

The fuel off gas from which the water vapor has been removed is sent to the combustor 50, and the air off gas (cathode off gas) discharged from the oxygen electrode side 36 of the cell stack 6 is also sent to the combustor 50. The fuel off gas from the fuel electrode side 8 of the cell stack 6 and the air off gas from the oxygen electrode side 36 are burned. A part of the fuel off gas flowing through the fuel off gas supply flow path 48 is returned to the fuel gas supply flow path 14 (upstream side of the arrangement portion of the fuel gas supply pump 24) through the recycling flow path 56, and is returned to the fuel gas supply flow path. It is mixed with the fuel gas supplied through 14.

In such a solid oxide fuel cell system 2, the system shuts down and stops due to an abnormal failure of the system or the like. At the time of this shutdown stop, the fuel gas supply pump 24, the water supply pump 34, and the blower blower 40 are stopped. Is stopped, and the supply of fuel gas, reforming water and air is stopped. When the system shuts down when the inside of the high temperature housing 62 is in a high temperature state (for example, in a state of 500 ° C. or higher), the reforming water remains in the vaporizer 12, so that the reforming is performed by the heat around the vaporizer 12. The irrigation water is vaporized to become steam, and steam mixed with fuel gas (reformed fuel gas) (that is, reducing gas) flows to the combustor 50 through the fuel electrode side 8 of the cell stack 6. The water vapor (reducing gas) mixed with the fuel gas that has flowed to the combustor 50 is distributed and flows to the exhaust gas discharge flow path 54 and the air off gas supply flow path 52 (oxidant off gas supply flow path), and a part thereof. Is discharged to the outside through the exhaust gas discharge flow path 54, but the rest thereof flows back to the oxygen electrode side 36 of the cell stack 6 through the air off gas supply flow path 52. When the water vapor mixed with the regurgitated fuel gas reaches the oxygen electrode side 36, the oxygen electrode side 36 is reduced, and the oxygen electrode layer (air electrode layer) is partially exfoliated or partially cracked. There is a risk.

The solid oxide fuel cell system 2 is further configured as follows in order to prevent the water vapor mixed with the fuel gas from flowing back from the combustor 50 to the oxygen electrode side 36 of the cell stack 6. More specifically, in the first embodiment, the reducing gas inflow preventing means 92 for preventing the water vapor mixed with the fuel gas from flowing into the oxygen electrode side 36 of the cell stack 6 is related to the air supply flow path 38. The reducing gas inflow prevention means 92 is composed of a backflow prevention structure 94. The backflow prevention structure 94 allows the flow of air from the blower blower 40 to the oxygen pole side 36 of the cell stack 6, but blocks the flow of air from the oxygen pole side 36 to the blower blower 40 side. Yes, for example, it is composed of a commercially available backflow prevention damper.

As shown in FIG. 1, the backflow prevention structure 94 is preferably disposed at a portion located outside the high temperature housing 62 in the air supply flow path 38, and by providing the backflow prevention structure 94 at such a portion, the backflow prevention structure is formed. The 94 is not exposed to high temperatures and its life can be maintained for a long time.

When the backflow prevention structure 94 is provided in this way, the system shuts down and stops in a high temperature state, the reforming water in the vaporizer 12 is vaporized to become steam, and the steam mixed with the fuel gas is the fuel electrode side 8 of the stack 6. When it flows to the combustor 50 through the fuel gas, the water vapor mixed with the fuel gas is distributed to the exhaust gas discharge flow path 54 and the air off gas supply flow path 52 (oxidant off gas supply flow path) and tries to flow. , The backflow prevention structure 94 distributes the water vapor from the combustor 50 to the cell stack 6 (oxygen electrode side 36) in order to block the flow of air from the cell stack 6 (oxygen electrode side 36) to the blower blower 40. The flow is blocked, whereby all of the water vapor mixed with the fuel gas that has flowed into the combustor 50 is discharged to the outside through the exhaust gas discharge flow path 54 without flowing back to the oxygen electrode side 36 of the cell stack 6. As a result, deterioration of the oxygen electrode of the cell stack 6 due to the reducing gas when the shutdown is stopped can be suppressed.

In this first embodiment, the backflow prevention structure 94 is composed of a backflow prevention damper, but instead of the backflow prevention damper, it may be composed of a backflow prevention valve, or it may be composed of an electromagnetic on-off valve. When the shutdown is stopped, the electromagnetic on-off valve may be operated to block the air supply flow path 38.

Further, in the first embodiment, the reducing gas inflow preventing means 92 is arranged in the air supply flow path 38 (oxidizing agent gas supply flow path), but instead of such a configuration, the blower blower 40 ( It may be built in the oxidant gas supply means).

Next, a second embodiment of the solid oxide fuel cell system according to the present invention will be described with reference to FIG. In this second embodiment, the configuration of the reducing gas inflow prevention means is different from that of the first embodiment. In the following embodiments, the same reference numbers are assigned to those substantially the same as those of the first embodiment, and the description thereof will be omitted.

In FIG. 2, in the solid oxide fuel cell system 2A of the second embodiment, the gas adsorber 102 is provided in the air off gas supply flow path 52 (oxidant off gas supply flow path), and the gas adsorber 102 is provided. The reducing gas adsorbent is filled in 102, and the gas adsorber 102 containing the reducing gas adsorbent functions as the reducing gas inflow prevention means 92A. As the reducing gas adsorbent, for example, a material containing cobalt oxide, nickel oxide, lanthanum strontium cobalt ferrite (LSCF) used as an oxygen electrode (air electrode), lanthanum manganite, or the like can be used. The other configurations of this second embodiment are substantially the same as the first embodiment described above.

In the solid oxide fuel cell system 2A of the second embodiment, the system shuts down and stops in a high temperature state, the reforming water in the vaporizer 12 is vaporized, and the water vapor mixed with the fuel gas is the fuel electrode of the stack 6. When flowing to the combustor 50 through the side 8, the water vapor mixed with the fuel gas is distributed to the exhaust gas discharge flow path 54 and the air off gas supply flow path 52 (oxidant off gas supply flow path), and the water vapor is distributed. A part of the exhaust gas is discharged to the outside through the exhaust gas discharge flow path 54, and the rest thereof flows to the oxygen electrode side 36 of the cell stack 6 through the air off gas supply flow path 52 and the gas adsorber 102. At this time, the fuel gas (reducing gas) mixed with the water vapor is adsorbed by the reducing gas adsorbent and removed, and the water vapor from which the fuel gas has been removed flows to the oxygen electrode side 36 of the cell stack 6.

Therefore, the water vapor flowing back to the oxygen electrode side 36 of the cell stack 6 does not contain the fuel gas (reducing gas), and the oxygen electrode of the cell stack 6 is not subjected to the reducing action by the fuel gas. It is also possible to suppress the deterioration of the oxygen electrode of the cell stack 6 due to the reducing gas when the shutdown is stopped.

In the second embodiment, the gas adsorber 102 is arranged in the air off gas supply flow path 52 (oxidant off gas supply flow path), but the present invention is not limited to such a configuration, and the air off gas supply is not limited to this. A reducing gas adsorbent as a means for preventing the inflow of reducing gas may be provided on the inner peripheral surface of the piping member defining the supply flow path 52 to adsorb the fuel gas mixed with the water vapor.

Next, a third embodiment of the solid oxide fuel cell system according to the present invention will be described with reference to FIG. In this third embodiment, the configuration of the reducing gas inflow prevention means is different from that of the first and second embodiments.

In FIG. 3, in the solid oxide fuel cell system 2B of the third embodiment, a temperature sensor 112 (which constitutes a temperature detecting means) is arranged in contact with or close to the cell stack 6 in the high temperature housing 62. , The temperature sensor 112 detects the temperature of the cell stack 6. Further, an air flow rate sensor 114 (which constitutes an oxidant gas flow rate detecting means) is provided in the air supply flow path 38 (oxidizer gas supply flow path), and the air flow rate sensor 114 is used for air flowing through the air supply flow path 38. Detect the flow rate. Further, a controller 116 for operating and controlling the fuel gas supply pump 24 (fuel gas supply means), the blower fan 40 (oxidizer gas supply means), and the water supply pump 34 (water supply means) is provided, and the controller 116 is provided. , Includes a backflow prevention control means 118 for controlling the operation of the blower fan 40 to prevent backflow of air (oxidizing agent gas).

In this solid oxide fuel cell system 2B, the detection signals of the temperature sensor 112, the fuel gas flow rate sensor 30, and the air flow rate sensor 114 are sent to the controller 116, and the controller 116 detects the detection signals from these sensors 112, 30, 114. The fuel gas supply pump 24, the blower blower 40, and the water supply pump 34 are operated and controlled based on the above, and as will be understood from the following description, the temperature sensor 112, the air flow sensor 114, and the backflow prevention control means 118 of the controller 116 are reduced. The sex gas inflow prevention means 92B is configured, and the blower blower 40 (oxidizer gas supply means) also functions as a part of the reducing gas inflow prevention means 92B. The other configurations of this third embodiment are substantially the same as those of the first embodiment described above.

In the solid oxide fuel cell system 2B of the third embodiment, when the system shuts down and stops, the detection signals from the temperature sensor 112 (temperature detecting means) and the air flow sensor 114 (oxidizing agent gas flow rate detecting means) become the controller. It will be sent to 116. At this time, if the inside of the high temperature housing 62 is in a high temperature state, the reforming water in the vaporizer 12 is vaporized, and steam mixed with fuel gas flows to the combustor 50 through the fuel electrode side 8 of the stack 6 and the steam. A part of the air flows to the oxygen electrode side 36 side of the cell stack 6 through the air off gas supply flow path 52 (oxidant off gas supply flow path). Then, when a part of this water vapor flows to the oxygen electrode side 36 of the cell stack 6, it is pushed by the flow of this water vapor, and the air (oxidizing agent gas) in the air supply flow path 38 (oxidizing agent gas supply flow path) is pushed. Will flow back toward the blower blower 40.

In this way, the air in the air supply flow path 38 flows backward in a high temperature state, in other words, the temperature sensor 112 (temperature detecting means) detects a high temperature (for example, 500 ° C. or higher), and the air flow sensor 114 (oxidizing agent). When the gas flow rate detecting means) detects the backflow of air (that is, the flow from the oxygen electrode side 36 of the cell stack 6 toward the blower blower 40), the backflow prevention control means 118 of the controller 116 generates a backflow prevention signal. The blower blower 40 is operated in the feeding direction based on this backflow prevention signal.

Thus, the air (oxidizing agent gas) from the blower blower 40 flows to the combustor 50 through the air supply flow path 36 and the oxygen electrode side 36 of the cell stack 6, and the air off gas supply flow path 52 (oxidation) from the combustor 50. The water vapor distributed to the material off-gas supply channel) is returned to the combustor 50 by this air flow, whereby the water vapor mixed with the fuel gas does not flow back to the oxygen electrode side 36 of the cell stack 6 without flowing back. All of them are discharged to the outside through the exhaust gas discharge flow path 54, and even with such a configuration, deterioration of the oxygen electrode of the cell stack 6 due to the reducing gas at the time of shutdown can be suppressed.

At this time, when the supply flow rate of the air sent to the oxygen electrode side 36 of the cell stack 6 increases, the supplied air flows from the combustor 50 through the fuel off gas supply flow path 48 and the fuel off gas lead out flow path 44 of the cell stack 6. There is a possibility that the fuel electrode will flow to the fuel electrode side 8 and the fuel electrode will be oxidized and deteriorated. Therefore, in the feed flow rate of air (oxidizer gas) at this time, the water vapor in the combustor 50 is the air off gas feed flow. It is desirable that the flow does not flow back to the road 52.

In the third embodiment, the backflow of air is detected by the air flow rate sensor 114 (oxidizing agent gas flow rate detecting means) arranged in the air supply flow path 38 (oxidizing agent gas supply flow path). Instead of such a configuration, a rotation speed detection sensor may be provided in the blower blower 40 to detect the air flow rate (including the backflow of air) based on the detection rotation speed of the rotation speed detection sensor. In this case, , This rotation speed detection sensor functions as an oxidant gas flow rate detecting means.

Further, in the third embodiment, the temperature sensor 112 is provided, and the blower blower 40 is operated when the temperature sensor 112 detects a high temperature (for example, 500 ° C. or higher). Omitted, a timer means that operates when the shutdown is stopped is provided, and the backflow of air is monitored by the air flow rate sensor 114 (oxidant gas flow rate detecting means) until the timer means measures a predetermined time (for example, about 10 to 20 minutes). You may try to do it.

Although the embodiment of the solid oxide fuel cell system according to the present invention has been described above, the present invention is not limited to these embodiments, and various changes or modifications can be made without departing from the scope of the present invention. Is.

2,2A, 2B Solid oxide fuel cell system 4 Reformer 6 Cell stack 12 Vaporizer 46 Steam condensing unit 62 High temperature housing 92, 92A, 92B Reducing gas inflow prevention means
94 Backflow prevention structure 102 Gas adsorber 112 Temperature sensor (Temperature detection means)
114 Air flow rate sensor (oxidizing agent gas flow rate detecting means)
118 Backflow prevention control means

Claims (5)

A vaporizer for vaporizing the reforming water, a reformer for steam reforming the fuel gas using the steam from the vaporizer, a reformed fuel gas reformed by the reformer, and the reformer. A cell stack that generates power by oxidizing and reducing the oxidant gas, an oxidant gas supply means for supplying the oxidant gas to the cell stack through the oxidant gas supply flow path, and a fuel gas supply flow for supplying the fuel gas. A fuel gas supply means for supplying the reformer through the path, a combustor provided in connection with the reformer, and a steam condensing unit for condensing the steam contained in the fuel off gas from the cell stack. A recycling flow path for returning a part of the fuel off gas to the upstream side of the fuel gas supply means is provided, and the reformed fuel gas from the reformer is supplied to the fuel electrode side of the cell stack. Then, the oxidant gas from the oxidant gas supply means is supplied to the oxygen electrode side of the cell stack, and steam contained in the fuel off gas from the fuel electrode side of the cell stack is sent to the steam condensing portion. A part of the fuel off gas, which has been cooled and recovered as condensed water and whose steam has been removed by the steam condensing portion, is returned to the upstream side of the fuel gas supply means through the recycling flow path, and the rest thereof is described as described above. A solid oxide fuel cell system that is fed to a combustor and burned by an oxide off gas from the oxygen electrode side of the cell stack.
The vaporizer, the reformer, the cell stack and the combustor are housed in a high temperature housing for defining a high temperature space, and the reducing gas in the combustor is charged in the cell stack when the system shuts down. A solid oxide fuel cell system, characterized in that a reducing gas inflow preventing means for preventing the inflow to the oxygen electrode side is provided. The reducing gas inflow prevention means is composed of the oxidant gas supply means or a backflow prevention structure disposed in the oxidant gas supply flow path, and the backflow prevention structure is said when the system is shut down. The backflow of the oxidant gas in the oxidant gas supply means or the oxidant gas supply flow path is prevented, whereby the inflow of the reducing gas from the combustor to the oxygen electrode side of the cell stack is prevented. The solid oxide fuel cell system according to claim 1, wherein the solid oxide type fuel cell system is characterized. The reducing gas inflow preventing means controls the operation of the oxidant gas supply means or the oxidant gas flow rate detecting means arranged in the oxidant gas supply flow path and the oxidant gas supply means to control the operation of the oxidant. It is composed of a backflow prevention control means for preventing backflow of gas, and when the oxidant gas flow rate detecting means detects the backflow of the oxidant gas when the system is shut down, the backflow prevention control means is said to oxidize. The operation of the oxidant gas supply means is controlled based on the detection signal from the agent gas flow rate detecting means to supply the oxidant gas to the oxygen electrode side of the cell stack, whereby the oxidizer gas is supplied from the combustor to the cell stack. The solid oxide fuel cell system according to claim 1, wherein the inflow of the reducing gas to the oxygen electrode side is prevented. When the temperature detecting means for detecting the temperature of the cell stack is further provided, the oxidant gas flow rate detecting means detects the backflow of the oxidant gas, and the temperature detecting means detects the high temperature of the cell stack. The backflow prevention control means controls the operation of the oxidant gas supply means to supply the oxidant gas to the oxygen electrode side of the cell stack, whereby the oxygen electrode side of the cell stack is supplied from the combustor. The solid oxide fuel cell system according to claim 3, wherein the inflow of the reducing gas into the reducting gas is prevented. The reducing gas inflow preventing means is composed of a reducing gas adsorbent arranged in an oxidizing material off gas supply flow path for supplying the oxidizing material off gas from the oxygen electrode side of the cell stack to the combustor. The reducing gas adsorbent adsorbs the reducing gas flowing from the combustor to the oxygen electrode side of the cell stack when the system is shut down, whereby the combustor to the cell stack said. The solid oxide type fuel cell system according to claim 1, wherein the inflow of the reducing gas to the oxygen electrode side is prevented.

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