JP2013243146A - Solid oxide fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid oxide fuel cell system in which a configuration related to condensation recovery means for condensing steam in an exhaust gas and a water recovery tank which stores condensed water has been improved.SOLUTION: The solid oxide fuel cell system comprises condensation recovery means 50 for condensing and recovering steam included in an exhaust gas from a solid oxide fuel cell, a water recovery tank 51 which stores condensed and recovered water, and water supply means 52 for supplying water in the water recovery tank 51 to a reformer 4. The condensation recovery means 50 includes a heat exchanger 54 for condensing steam in the exhaust gas and a recovery channel 58 which connects the heat exchanger 54 and the water recovery tank 51. The recovery channel 58 is provided with first overflow means 82. The water recovery tank 51 is provided with second overflow means 86. The heat exchanger 54, the second overflow means 86, and the first overflow means 82 are arranged in this order from a high position to a low position.

Description

  The present invention relates to a solid oxide fuel cell system that generates power by oxidation and reduction of a reformed fuel gas and an oxidizing material obtained by reforming raw fuel.

  2. Description of the Related Art Conventionally, there has been known a solid oxide fuel cell in which a solid oxide fuel cell using a solid electrolyte as a membrane for conducting oxide ions is accommodated in a storage container. In this solid oxide fuel cell, zirconia doped with yttria is generally used as a solid electrolyte, and a fuel electrode for oxidizing fuel gas is provided on one side of the solid electrolyte. An oxygen electrode for reducing oxygen in the air (oxidant) is provided on the side (see, for example, Patent Document 1). The operating temperature of a solid oxide fuel cell (cell) is relatively high at about 700 to 1000 ° C. Under such a high temperature, hydrogen, carbon monoxide, hydrocarbons in fuel gas and oxygen in the air are electrically connected. Electricity is generated by causing a chemical reaction.

  In recent years, attention has been paid to a solid oxide fuel cell system using such a solid oxide fuel cell. In this solid oxide fuel cell system, a reformer for reforming raw fuel gas is provided. The reformer is supplied with raw fuel gas and steam, and a part of the raw fuel gas and steam are reformed and reformed, and the reformed reformed gas is used in the solid oxide fuel cell. It is fed to the fuel electrode side.

  With regard to such a solid oxide fuel cell system, the present applicant pays attention to the fact that the exhaust gas generated in the solid oxide fuel cell contains water vapor, and condenses the water vapor in the exhaust gas. A system has been proposed in which water is stored in a water recovery tank, and the water stored in the water recovery tank is sent to the reformer and used for the reforming reaction of the raw fuel gas to enable independent operation of water (Japanese Patent Application 2008- 80817). In the proposed solid oxide fuel cell system, a large-scale water supply facility for supplying water from the outside to the reformer is not required, and the entire system can be reduced in size and greatly reduced in cost. You can go down.

JP 2007-273252 A

In the solid oxide fuel cell system proposed by the present applicant, there are the following problems related to water storage. That is, in such a solid oxide fuel cell system, a recovery pump is required to recover the water condensed water vapor in the exhaust gas in the water recovery tank. In particular, in the form of collecting in the water recovery tank through the impurity removing means for removing impurities contained in the condensed water, a recovery pump is required, and in this connection, the configuration of the entire system becomes complicated. At the same time, the manufacturing cost increases.

An object of the present invention is to improve a configuration related to a condensation recovery means for condensing water vapor in exhaust gas and a water recovery tank for storing condensed water, and thereby a solid oxide fuel cell in which a recovery pump can be omitted. Is to provide a system .

Solid oxide fuel cell system according to claim 1 of the present invention, the raw fuel reformer for steam reforming, the reformer at reformed reformed fuel gas and the oxidizing material A solid oxide fuel cell that generates power by oxidation and reduction, a blower for supplying an oxidant to the solid oxide fuel cell, and a supply amount of raw fuel supplied to the reformer A flow rate control valve for controlling, a condensation recovery means for condensing and recovering water vapor contained in the exhaust gas from the solid oxide fuel cell, and for storing water recovered by the condensation recovery means A water recovery tank, and water supply means for supplying water recovered in the water recovery tank to the reformer,
The condensation recovery means includes a heat exchanger for condensing water vapor contained in the exhaust gas by exchanging heat with the exhaust gas from the solid oxide fuel cell , and the heat exchanger and the water recovery A recovery flow path connecting the tank, the recovery flow path is provided with a first overflow means, the water recovery tank is provided with a second overflow means, the heat exchanger, the water recovery tank of the first 2 overflow means and the said 1st overflow means of the said collection | recovery flow path are arrange | positioned in this order from the high position to the low position.

In the solid oxide fuel cell system according to claim 2 of the present invention, the condensation recovery means further removes impurities for removing impurities contained in the water condensed in the heat exchanger. Means, the impurity removing means is disposed in the recovery flow path, and a downstream side portion of the recovery flow path connecting the impurity removing means and the water recovery tank is the first overflow means of the recovery flow path It is characterized by being arranged at a lower position .

According to the solid oxide fuel cell system of the present invention, the condensing and recovering means for condensing the water vapor contained in the exhaust gas from the solid oxide fuel cell comprises heat for condensing the water vapor contained in the exhaust gas. A heat exchanger and a recovery flow path connecting the water recovery tank, wherein the recovery flow path is provided with first overflow means, and the water recovery tank is provided with second overflow means, and the heat exchanger Since the second overflow means of the water recovery tank and the first overflow means of the recovery flow path are arranged in this order from the high position to the low position, a dedicated pump for recovering water is not required, and the height difference The condensed water can be recovered in the water recovery tank as required, and only the necessary water is passed through the impurity removing means, so that the amount of the impurity removing means can be reduced.

1 schematically shows a first embodiment of a solid oxide fuel cell system according to the present invention. FIG. FIG. 2 is a simplified diagram schematically showing a condensing and collecting unit and a configuration related thereto in the solid oxide fuel cell system of FIG. 1. The block diagram which shows the control system of the solid oxide fuel cell system of FIG. The flowchart which shows the flow of control by the control system of FIG. The simplification figure which shows simply the condensation collection | recovery means of the solid oxide fuel cell system of 2nd Embodiment, and the structure relevant to this. FIG. 6 is a block diagram showing a control system of the solid oxide fuel cell system of FIG. 5. 7 is a flowchart showing a flow of control by the control system of FIG.

  Embodiments of a solid oxide fuel cell system according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a simplified diagram showing a first embodiment of a solid oxide fuel cell system of the present invention, and FIG. 2 is a condensing recovery unit of the solid oxide fuel cell system of FIG. FIG. 3 is a block diagram showing a control system of the solid oxide fuel cell system of FIG. 1, and FIG. 4 shows a flow of control by the control system of FIG. It is a flowchart.

  1 to 3, the illustrated solid oxide fuel cell system 2 includes a reformer 4 for reforming a raw fuel gas (for example, natural gas) as a raw fuel, and a reformer 4. A solid oxide fuel cell 6 that generates power by oxidizing and reducing the reformed reformed fuel gas and air as an oxidant; and a blower 8 for supplying air to the solid oxide fuel cell 6. And a control means 100 for controlling the operation of the solid oxide fuel cell 6 and the blower 8.

The solid oxide fuel cell 6 includes a fuel cell main body 12 and a fuel cell stack 14 in which a plurality of solid oxide fuel cells for generating electric power by electrochemical reaction are arranged. The fuel cell main body 12 includes a shielding wall 16, and a high temperature space 18 is defined inside the shielding wall 16. The fuel cell stack 14 is disposed in the high temperature space 18 and the reformer 4 accommodates it. Has been. The solid oxide fuel cell includes a solid electrolyte 20 that conducts oxygen ions, a fuel electrode (not shown) provided on one side of the solid electrolyte 20, and an oxygen electrode provided on the other side of the solid electrolyte 20. (Not shown) and, for example, zirconia doped with yttria is used as the solid electrolyte 20. Further, in relation to the solid oxide fuel cell 6 (cell), an operating temperature detecting means 22 for detecting the operating temperature and an electric power measuring means 24 for measuring the power generation output are provided.

  An introduction side of the fuel electrode side 26 of the fuel cell stack 14 is connected to the reformer 4 via a reformed fuel gas supply channel 28, and the reformer 4 is connected to a raw fuel gas supply channel 30. Are connected to a raw fuel gas supply source 32 (for example, a buried pipe or a storage tank) for supplying the raw fuel gas. The raw fuel gas supply channel 30 is provided with a flow rate control valve 34 for controlling the supply amount of the raw fuel gas. The introduction side of the oxygen electrode side 36 of the fuel cell stack 14 is connected to an air preheater 40 for preheating air via an air supply flow path 38, and the air preheater 40 is connected to the air supply flow path 40. It is connected to the blower 8 through 42.

  A combustion chamber 44 is provided on each discharge side of the fuel electrode stack 26 and the oxygen electrode side 36 of the fuel cell stack 14, and the reaction fuel gas (including residual fuel gas) discharged from the fuel electrode side 26 and the oxygen electrode side 36. The air (including oxygen) discharged from the fuel is supplied to the combustion chamber 44 and burned. The combustion chamber 44 communicates with an air preheater 40 through an exhaust gas supply passage 46, and an exhaust gas discharge passage 48 is connected to the air preheater 40.

  Further, in this solid oxide fuel cell system 2, the condensation recovery means 50 for condensing and recovering water vapor contained in the exhaust gas from the combustion chamber 44, and the water condensed by the condensation recovery means 50 are stored. And a water supply means 52 for supplying water (condensed water) recovered in the water recovery tank 51 to the reformer 4. The condensing and collecting means 50 includes a heat exchanger 54 for condensing water vapor contained in the exhaust gas and an impurity removing means 56 for removing impurities contained in the condensed water. The heat exchanger 54 is disposed in the exhaust gas discharge channel 48, and a water recovery tank 56 is connected to the heat exchanger 54 via a recovery channel 58.

  The impurity removing means 56 includes an ion exchange resin that removes impurities by ion exchange, and the ion exchange resin contains an anion exchange resin. The anion exchange resin takes in the carbon dioxide contained in the exhaust gas from the solid oxide fuel cell 6 and breaks through the carbonic acid, and thus through the carbonic acid breakthrough, the water condensed in the impurity removing means 56 is acidified. In this state, the water downstream from the impurity removing means 56 can be kept in an acidic state. The amount of the anion exchange resin is preferably configured so as to be in a state of carbonic acid breakthrough in, for example, about several hundred hours. Can be kept in an acidic state. By maintaining the acidic state in this way, the bacterial nutrient source can be kept low in the downstream side of the impurity removing means 56, that is, in the water recovery tank 51 and the like, and bacterial growth can be suppressed.

  Further, a hot water storage system 60 for storing the heat of exhaust gas from the solid oxide fuel cell 6 as hot water is provided. The hot water storage system 60 includes a hot water storage tank 64 for storing hot water as hot water. Is connected to the heat exchanger 54. The circulation channel 66 is provided with a circulation pump 68, a circulating water temperature detecting means 70, and a heat radiating means 71. The circulation pump 68 circulates the water stored in the hot water storage tank 64 through the circulation channel 66, the circulating water temperature detecting means 70 detects the temperature of the circulating water circulated through the circulation channel 66, and the heat radiating means 71 is, for example, It is composed of a radiator and radiates the heat of the circulating water circulated through the circulation channel 66.

  The hot water storage tank 64 stores heat generated by the operation of the solid oxide fuel cell 6 as hot water as will be described later. A water supply passage 72 is connected to the hot water storage tank 64, and an open / close valve 74 for controlling the supply of water (tap water) is disposed in the water supply passage 72. Hot water stored in the hot water storage tank 64 is discharged through the hot water supply channel 76. The circulating water temperature detecting means 70 is disposed between the heat exchanger 54 and the hot water storage tank 64 and measures the temperature of the circulating water supplied to the heat exchanger 54, that is, the inlet temperature of the heat exchanger 54, The heat radiating means 71 is disposed between the hot water storage tank 64 and the heat exchanger 54 and radiates the heat of the circulating water supplied to the heat exchanger 54.

  The water supply means 52 includes a water supply passage 78 for supplying the water in the water recovery tank 51 to the reformer 4, and a feed pump 80 is disposed in the water supply passage 78. The feed pump 80 is provided to feed the water in the water recovery tank 51 to the reformer 4 through the water feed channel 78 as reforming water.

  The condensing and collecting means 50 and the water collecting tank 51 are configured as follows. As shown in FIG. 2, a first overflow means 82 is provided on the upstream side portion 58 a of the recovery flow path 58 connecting the heat exchanger 54 and the impurity removing means 5, and the water overflowing from the first overflow means 82 is As shown by the arrows, the water is drained to the outside through the drainage part 84. Further, the water recovery tank 51 is provided with a second overflow means 86, and the water overflowing from the second overflow means 86 is also drained to the outside.

  In this embodiment, the heat exchanger 54, the second overflow means 86, the first overflow means 82, and the downstream side portion 58b of the recovery flow path 58 (the flow path portion connecting the impurity removal means 56 and the water recovery tank 51) are provided. In this order from the high position to the low position, the water condensed in the heat exchanger 54 becomes impurities through the upstream side portion 58a of the recovery flow path 58 using the height difference. It flows to the removal means 56 and flows from the impurity removal means 56 to the water recovery tank 51 through the downstream side portion 58b of the recovery flow path 58. When the water is recovered in the water recovery tank 51 and reaches the level indicated by the broken line 88, the water flowing from the heat exchanger 54 to the impurity removing means 56 overflows from the first overflow means 82 and is drained. The overflow level 82 sets the full water level of the water recovery tank 51. The second overflow means 86 is disposed at a position above the full water level in the water recovery tank 51. When the water in the water recovery tank 51 exceeds the full water level and reaches the second overflow means 82, The water in the recovery tank 51 is drained, and the second overflow means 82 prevents the water level in the water recovery tank 51 from exceeding the abnormal water level.

  In this embodiment, the water recovery tank 51 is provided with a water level detection means 90. The water level detecting means 90 is composed of a low water level sensor 92 and a lower limit water level sensor 94. The low water level sensor 92 arranged on the upper side is for detecting a low water level indicated by a broken line 96, and is arranged on the lower side. The provided lower limit water level sensor 94 is for detecting the lower limit water level indicated by a broken line 98. In this embodiment, it is configured to be able to operate in the water recovery operation mode in addition to the operation operation in the normal operation mode, and the liquid level in the water recovery tank 56 is lowered to the low water level, in other words, the low water level. When the sensor 92 detects the liquid level, the normal operation mode is switched to the water recovery operation mode, as will be described later. Further, when the liquid level in the water recovery tank 56 is lowered to the lower limit water level, in other words, when the lower limit water level sensor 94 detects the liquid level, the operation of the solid oxide fuel cell system 2 is forcibly performed as described later. Is configured to stop.

  The solid oxide fuel cell system 2 described above is controlled by the control means 100 as described later. With reference to FIG. 3, the control means 100 is constituted by, for example, a microprocessor and includes an operation control means 102, a mode switching means 104, an operation determination means 106 and a storage means 108. The operation control means 82 controls operations of the flow control valve 34, the blower 8, the circulation pump 68, the feed pump 80, and the like as will be described later. The mode switching means 104 switches from the normal operation mode to the water recovery operation mode when the water in the water recovery tank 64 is low, and switches from the water recovery operation mode to the normal operation mode when the water in the water recovery tank 64 is recovered. Further, the operation determining means 106 is an operation state in which the hot water storage tank 64 is in a fully stored state (a state in which heat is sufficiently stored) during an operation operation in the water recovery operation mode, or an operation state in which the solid oxide fuel cell 6 is in a deteriorated state. It is determined whether it is. Further, the storage means 108 includes a set operating temperature of the solid oxide fuel cell 6, that is, a set upper limit temperature (for example, about 800 ° C.) that suppresses the progress of deterioration of the solid oxide fuel cell 6, and a solid oxide type. A set rated output (for example, 1 kW) of the fuel cell 6 and a set circulating water temperature (for example, about 30 ° C.) used when determining that the hot water storage tank 64 is fully stored are stored.

  The operation of the solid oxide fuel cell system 2 is performed as follows. The raw fuel gas from the raw fuel gas supply source 32 is supplied to the reformer 4 together with water (water from the water recovery tank 51) described later through the raw fuel gas supply flow path 30. In the reformer 4, a part of the raw fuel gas and water (condensed water) are reformed and reformed, and the reformed fuel gas thus reformed is reformed fuel gas supply passage. 28 to the fuel electrode side 26 of the fuel cell stack 14. In addition, air from the blower 8 is supplied to the air preheater 40 through the air supply passage 42, and heat is exchanged with the exhaust gas in the air preheater 40 and heated, and then the air supply flow The fuel is fed to the oxygen electrode side 36 of the fuel cell stack 14 through the path 38.

  The fuel electrode side 26 of the fuel cell stack 14 oxidizes the reformed reformed fuel gas, and its oxygen electrode side 36 reduces oxygen in the air, oxidation on the fuel electrode side 26 and reduction on the oxygen electrode side 36. Electricity is generated by an electrochemical reaction.

  The power generation output of the solid oxide fuel cell 6 is performed by adjusting the opening degree of the flow rate control valve 34, that is, by adjusting the amount of raw fuel gas fed to the reformer 4. By controlling the valve 34, the power generation output of the solid oxide fuel cell 6 is maintained at the rated power generation output. The electrochemical reaction in the solid oxide fuel cell 6 is performed at a high temperature of about 700 to 1000 ° C. Considering the power generation efficiency and life of the fuel cell stack 14, the solid oxide fuel cell 6 has a set operating temperature. Operation is performed at (for example, about 800 ° C.).

  The reaction fuel gas from the fuel electrode side 26 and the air from the oxygen electrode side 36 are respectively supplied to the combustion chamber 44, and excess fuel gas is combusted using oxygen in the air. Exhaust gas from the combustion chamber 44 is supplied to the air preheater 40 through the exhaust gas supply passage 46, and is used for heat exchange with the air from the blower 8 in the air preheater 40 to be used as an exhaust gas discharge passage. 48 to the heat exchanger 54.

  In the heat exchanger 54, heat exchange is performed between the circulating water circulated from the lower part of the hot water storage tank 64 through the circulation passage 66 and the exhaust gas flowing through the exhaust gas discharge passage 48. Circulating water (warm water) heated by heat exchange is stored in the upper part of the hot water storage tank 64 through the circulation channel 66 by the action of the circulation pump 68. Further, when the temperature of the exhaust gas is lowered to the dew point by heat exchange, the water vapor contained in the exhaust gas is condensed and recovered, and the condensed water (condensed water) passes through the upstream side portion 58a of the recovery flow path 58 to remove impurities. The water from which impurities have been removed by the impurity removing means 56 flows to the water recovery tank 51 through the downstream side portion 58b of the recovery flow path 58 and is stored therein. The exhaust gas after the condensation recovery is discharged to the atmosphere through the exhaust gas discharge channel 48. The water (condensed water) stored in the water recovery tank 51 is fed to the reformer 4 through the water feed channel 78 by the action of the feed pump 80, and the condensed water is used as the reforming water. Independent operation is performed. Further, when the detected temperature of the circulating water temperature detecting means 70 is equal to or higher than a set circulating water temperature (for example, 45 ° C.), the operation determining means 106 sets the hot water in the hot water storage tank 64 based on the detected temperature from the circulating water temperature detecting means 70. Is determined to be fully charged, and the heat dissipating means 71 is activated. When the temperature detected by the circulating water temperature detecting means 70 is lower than the set circulating water temperature by a set temperature (for example, 5 ° C.) (for example, lowered to 40 ° C.), the heat radiating means 71 is deactivated.

  Next, with reference to FIG. 4 together with FIG. 3, the operation control when the water level in the water recovery tank 51 is lowered will be described. In the operation of the above-described normal operation mode of the solid oxide fuel cell system 2, the generation of condensed water is small and the liquid level of the water recovery tank 51 is lowered to the low water level (the low water level sensor 92 detects the liquid level). ), The process proceeds from step S1 through step S2 to step S3, and the operation is switched from the operation in the normal operation mode to the operation in the water recovery operation mode (operation mode in which more water vapor contained in the exhaust gas can be recovered). . When the low water level sensor 92 detects the water surface, a detection signal from the low water level sensor 92 is sent to the control means 100, and on the basis of this detection signal, the mode switching means 104 switches from the normal operation mode to the water recovery operation mode. The oxide fuel cell system 2 is operated in this water recovery operation mode.

When the heat storage as the hot water in the hot water storage tank 64 is full, the temperature of the circulating water circulated through the circulation channel 66 rises (the hot water is stored in layers in the hot water storage tank 64, and hot water is stored in the upper part. When the temperature of the circulating water supplied from the lower part to the circulation channel 66 is high, the temperature of the whole water stored in the hot water storage tank 64 is high, and the heat storage is fully stored. The circulating water having a high temperature is fed to the heat exchanger 54. In addition, when the ambient temperature is high, such as in summer, the temperature of the circulating water is not sufficiently lowered by the heat radiating means 71, and in such a full storage state, the temperature of the exhaust gas flowing out from the heat exchanger 54 is not lowered. Condensation of water vapor contained in the exhaust gas is difficult to be performed, and moisture recovery from the water vapor in the exhaust gas is reduced, which may cause water shortage. In such an operation state, the operation control means 102 operates the heat radiation means 71 (radiator), and the operation in the water recovery operation mode in such a state is performed.

  In the operation of the water recovery operation mode in the fully stored state, it is determined whether or not the solid oxide fuel cell 6 is in a deteriorated state (step S4). When the solid oxide fuel cell 6 is in a deteriorated state, the operating temperature tends to be high if an attempt is made to maintain the set rated output. In such a case, the amount of air blown from the blower 8 is increased to cause solid oxidation. The physical fuel cell 6 is operated to be cooled. If it is in such a deteriorated state, the operation determining means 106 determines that the solid oxide fuel cell 6 is in a deteriorated state based on the air blowing state of the blower 8 and proceeds to step S5 via step S4.

  When the solid oxide fuel cell 6 is in a deteriorated state, the amount of air blown by the blower 8 is increased, whereby a large amount of exhaust gas flows through the exhaust gas discharge passage 48. In such a deteriorated state, the amount of condensed water recovered in the heat exchanger 54 is reduced, the temperature drop of the exhaust gas due to heat exchange in the heat exchanger 54 is small, and the water vapor contained in the exhaust gas is condensed. It becomes difficult and water shortage may occur. In such an operation state, the operation control means 102 returns the air blower 8 to a normal air blow state (that is, control in which the air flow rate of the air blower 8 is increased in order to suppress an increase in operating temperature due to deterioration. The flow rate of the flow control valve 34 so that the operating temperature of the solid oxide fuel cell 6 is maintained at the set operating temperature. Is reduced to reduce the feed amount of the raw fuel gas to reduce the power generation output of the solid oxide fuel cell 6 (step S5), and the operation in the water recovery operation mode in such a state is performed.

  In the operation in the water recovery operation mode in this deteriorated state, the amount of air blown from the blower 8 is reduced, thereby reducing the amount of exhaust gas fed to the heat exchanger 54 through the exhaust gas discharge passage 48. Therefore, at this time, the flow rate of the exhaust gas decreases, the efficiency of heat exchange with the exhaust gas in the heat exchanger 54 increases, the temperature drop of the exhaust gas increases, and the condensation efficiency of water vapor contained in the exhaust gas increases. This increases the amount of water vapor recovered in the exhaust gas. Such operation in the water recovery operation mode is performed until the water level of the water recovery tank 51 rises from the low water level level or falls below the lower limit water level level. In addition, the predetermined setting time of step S6 is set to about 5 to 30 minutes, for example, 10 minutes, for example, and during this time, the operation in the water recovery operation mode is continued.

  If the water level in the water recovery tank 51 rises due to the operation in the water recovery operation mode in step S5 (operation in the reduced power generation output state) and the water level in the water recovery tank 51 exceeds the low water level, the process proceeds to step S9, where solid oxidation is performed. The power generation output of the physical fuel cell 6 is returned to its original state, and then the process returns to step S1, and the solid oxide fuel cell system 2 is operated in the normal operation mode that is the operation state before the water recovery operation mode. When the operation returns to the normal operation mode in this way, the opening degree of the flow rate control valve 34 increases, the feed amount of the raw fuel gas increases, and the output of the solid oxide fuel cell 6 returns to the set rated output. .

  On the other hand, if the water level in the water recovery tank 51 is not recovered by the operation in the water recovery operation mode in step S5 and the water level falls to the lower limit water level, the process proceeds from step S7 to step S8 to step S10, and the operation control means 102 Forcibly stops the operation of the solid oxide fuel cell system 2. That is, when the lower limit water level sensor 94 detects the liquid level, the operation control means 102 stops the operation of the solid oxide fuel cell system 2 based on the detection signal from the lower limit water level sensor 94, and thus stops operating. As a result, abnormal operation due to lack of water for reforming can be avoided. When the water level drops to the lower limit water level as described above, the operation of the solid oxide fuel cell system 2 is resumed after the water recovery tank 51 is replenished with water, for example, to the full water level.

  Next, a second embodiment of the solid oxide fuel cell system will be described with reference to FIGS. FIG. 5 is a simplified diagram showing the condensation recovery means of the solid oxide fuel cell system according to the second embodiment and the configuration related thereto, and FIG. 6 is a diagram of the solid oxide fuel cell of FIG. FIG. 7 is a block diagram showing a control system of the system, and FIG. 7 is a flowchart showing a flow of control by the control system of FIG. In the second embodiment, substantially the same members as those in the first embodiment described above are denoted by the same reference numerals, and the description thereof is omitted.

  With reference to FIGS. 5 and 6, in the second embodiment, when the heat storage as the hot water in the hot water storage tank 64 is fully stored in the operation in the water recovery operation mode, the hot water in the hot water storage tank 64 is stored. The water is discharged into the hot water storage tank 64, and the replenished water is circulated as circulation water through the circulation channel 66. In this case, the heat of the circulation water is increased. A heat dissipating means for dissipating heat can be omitted. More specifically, a drainage flow channel 120 is provided at a predetermined portion (a portion downstream of the heat exchanger 54) of the circulation flow channel 66, and a drainage valve 122 is disposed in the drainage flow channel 120. When the drain valve 122 is in the closed state, the circulating water from the hot water storage tank 64 is returned to the upper part of the hot water storage tank 64 through the circulation channel 66, but when the drain valve 122 is in the open state, the circulating water from the upper part of the hot water storage tank 64 is circulated. Part of the water is drained from the drainage part 84 to the outside through the circulation channel 66 and the drainage channel 120. Note that all the circulating water flowing through the circulation channel 66 may be drained.

  Further, when the water level in the water recovery tank 51A falls below the lower limit water level, the water recovery tank 51A is replenished using part of the water (circulated water) in the hot water storage tank 64. . In the second embodiment, a replenishment flow path 124 is provided in the drainage flow path 120, and the replenishment flow path 124 is a predetermined portion (specifically, first overflow means 82) of the upstream side portion 58 a of the recovery flow path 58. A flow path switching valve 126 is disposed at a connection portion between the drainage flow path 120 and the replenishment flow path 124. The flow path switching valve 126 communicates with the drainage flow path 120 when in the first switching state, enables drainage through the drainage flow path 120, and when in the second switching state, It is possible to supply water to the water recovery tank 51 through the drainage channel 120 and the supply channel 126 by communicating with the supply channel 124.

  Furthermore, in this embodiment, the impurity removal means 56A of the condensation recovery means 50A and the water recovery tank 51A are connected via the connection pipe 130. The connection pipe 130 extends in the vertical direction, and its lower end is connected to the upper end of the impurity removing means 56A, its upper end is connected to the lower end of the connection projection of the water recovery tank 51A, and the connection pipe 130 is connected to the recovery flow path 58A. The downstream side part is comprised.

  Further, in relation to the control means 100A, an input operation means 132 for input operation by an operator is provided, and the input operation means 132 includes a water supply switch 134 for supplying water. Other configurations of the second embodiment are substantially the same as those of the first embodiment described above.

  The control when the water level in the water recovery tank 51A in the solid oxide fuel cell system of the second embodiment is lowered is performed as follows. In the operation of the above-described normal operation mode of the solid oxide fuel cell system, when the amount of condensed water is small and the liquid level of the water recovery tank 51A is lowered to the low water level, the process proceeds from step S21 to step S23 through step S22. The operation is switched from the normal operation mode operation to the water recovery operation mode. That is, as described above, when the low water level sensor 92 detects the water surface, a detection signal from the low water level sensor 92 is sent to the control means 100A, and based on this detection signal, the mode switching means 104 changes from the normal operation mode. Switching to the water recovery operation mode, the solid oxide fuel cell system is operated in this water recovery operation mode.

In the operation in this water recovery operation mode, it is determined whether or not the inlet water temperature of the heat exchanger 54 (the detected temperature of the circulating water temperature detecting means 70) is equal to or higher than a predetermined temperature (step S24). This predetermined temperature is set to an appropriate temperature of about 35 to 45 ° C., for example, 40 ° C. If the detected temperature of the circulating water temperature detecting means 70 is equal to or higher than the set circulating water temperature (for example, 40 ° C.), the operation determining means 106 determines that the heat storage state of the hot water storage tank 64 is full, and the process goes to step S25. move on.

  In step S25, the operation control means 102 holds the flow path switching valve 126 in the first switching state and holds the drain valve 122 in the open state, and the operation of the water recovery operation mode in such a state is performed. Is called. In operation in this water recovery operation mode, part of the circulating water from the upper part of the hot water storage tank 64 flows back through the circulation channel 66 and is drained to the outside through the drain channel 122, and the on-off valve 74 is opened by the drainage. The water is supplied to the hot water storage tank 64 through the water supply passage 72 in a state, and the circulating water whose temperature has decreased is supplied to the heat exchanger 54 through the circulation passage 66. Therefore, at this time, the temperature difference between the exhaust gas from the solid oxide fuel cell in the heat exchanger 54 and the circulating water flowing through the circulation channel 66 becomes large, and the amount of water vapor recovered in the exhaust gas increases.

Next, it is determined whether or not the solid oxide fuel cell is in a deteriorated state (step S26). If it is in such a deteriorated state, the operation determining means 106 determines that the solid oxide fuel cell is in a deteriorated state, and proceeds from step S26 to step S27. In step S27, the operation control means 102 decreases the power generation output of the solid oxide fuel cell by reducing the opening of the flow control valve so that the operating temperature of the solid oxide fuel cell is maintained at the set operating temperature. In such a state, the operation in the water recovery operation mode is performed. In the operation of this water recovery operation mode, the amount of air blown from the blower decreases with a decrease in the power generation output, thereby reducing the flow rate of the exhaust gas and the efficiency of heat exchange with the exhaust gas in the heat exchanger 54. As the temperature increases, the temperature drop of the exhaust gas increases, the condensation efficiency of the water vapor contained in the exhaust gas increases, and the amount of water recovered increases. Such operation in the water recovery operation mode is performed until the water level of the water recovery tank 51A rises from the low water level level or falls below the lower limit water level level.

  When the operation in this water recovery operation mode is performed for a predetermined set time and the water level in the water recovery tank 51A rises and the water level in the water recovery tank 51A exceeds the low water level, the process proceeds from step S28 to step S29 to step S30, where the water is discharged. The valve 122 is closed, and the power generation output of the solid oxide fuel cell returns to the original state (step S31). Thereafter, the flow returns to step S21, and the solid oxide fuel cell system is operated in the original normal operation mode. .

  If the water level in the water recovery tank 51A is not recovered even by this water recovery operation mode operation and the water level falls to the lower limit water level, the process proceeds from step S29 to step S32 to step S33, and the operation control means 102 The operation of the fuel cell system is forcibly stopped. That is, when the lower limit water level sensor 94 detects the liquid level, the operation control means 102 stops the operation of the solid oxide fuel cell system based on the detection signal from the lower limit water level sensor 94.

  When the water recovery tank 51A after the installation of the solid oxide fuel cell system is empty, water supply may be performed by inputting the water supply switch 134. When the water supply switch 134 is pressed, based on the operation signal from the water supply switch 134, the operation control means 102 holds the drain valve 122 in the open state and sets the flow path switching valve 126 in the second switching state. Further, the circulation pump 68 is operated. Thus, the water in the hot water storage tank 64 is fed by the action of the circulation pump 68, and this water is sent to the recovery flow path 58 through the circulation flow path 66, the heat exchanger 54, the drainage flow path 122 and the replenishment flow path 124. Then, the water is supplied to the water recovery tank 51A through the recovery flow path 58A and the impurity removing means 56A, and is replenished to a full water level, for example. This replenishment of water may be replenished for a predetermined time by a timer or the like, or a full water level sensor may be provided at the full water level, and replenishment may be stopped when the full water level sensor detects a water surface, Alternatively, the water supply may be stopped by releasing the water supply switch 134 while visually checking the amount of water in the water recovery tank 51A.

  When the water is replenished to the full water level in this way, the control means 100A holds the drain valve 122 in the closed state, sets the flow path switching valve 126 to the first switching state, and further stops the operation of the circulation pump 68. In this way, the water supply is completed. And after water supply is performed in this way, the operation operation of the solid oxide fuel cell system is started.

  The embodiment of the solid oxide fuel cell system according to the present invention has been described above. However, the present invention is not limited to such an embodiment, and various changes or modifications can be made without departing from the scope of the present invention. It is.

2 Solid Oxide Fuel Cell System 4 Reformer 6 Solid Oxide Fuel Cell 8 Blower 50, 50A Condensation recovery means 51, 51A Water recovery tank 52 Water supply means 54 Heat exchanger 56, 56A Impurity removal means 60 Hot water storage system 64 Hot water storage tanks 82, 84 Overflow means 90 Water level detection means 100, 100A Control means 104 Mode switching means 106 Operation determination means 124 Replenishment flow path

Claims (2)

A reformer for steam reforming raw fuel, a solid oxide fuel cell that generates power by oxidation and reduction of the reformed fuel gas and the oxidant reformed in the reformer, and an oxidant A blower for feeding to the solid oxide fuel cell, a flow rate control valve for controlling the amount of raw fuel fed to the reformer, and from the solid oxide fuel cell Condensation and recovery means for condensing and recovering water vapor contained in the exhaust gas, a water recovery tank for storing the water recovered by the condensation and recovery means, and the reforming of the water recovered in the water recovery tank Water feeding means for feeding to the vessel,
The condensation recovery means includes a heat exchanger for condensing water vapor contained in the exhaust gas by exchanging heat with the exhaust gas from the solid oxide fuel cell , and the heat exchanger and the water recovery A recovery flow path connecting the tank, the recovery flow path is provided with a first overflow means, the water recovery tank is provided with a second overflow means, the heat exchanger, the water recovery tank of the first 2. A solid oxide fuel cell system, wherein the two overflow means and the first overflow means of the recovery flow path are arranged in this order from a high position to a low position. The condensation recovery means further includes an impurity removal means for removing impurities contained in the water condensed in the heat exchanger, the impurity removal means being disposed in the recovery flow path, and the impurities The downstream side portion of the recovery channel connecting the removing unit and the water recovery tank is disposed at a position lower than the first overflow unit of the recovery channel. Solid oxide fuel cell system.

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