JP5813469B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  In recent years, fuel cells that have high energy conversion efficiency and do not generate harmful substances due to power generation reactions have attracted attention. An example of such a fuel cell is a solid oxide fuel cell. A fuel cell has a basic structure in which an electrolyte body is disposed between a fuel electrode and an air electrode. An electrochemical reaction is performed by supplying a fuel gas containing hydrogen to the fuel electrode and an oxidant gas containing oxygen to the air electrode. To generate electricity.

  The fuel gas used in the fuel cell is, for example, a mixture of a hydrocarbon-based raw fuel such as kerosene, natural gas, LPG, or naphtha or an alcohol-based raw fuel such as methanol and steam, and steam reforming with a reformer. It is obtained with. Fuel gas (reformed gas) obtained by reforming is supplied to the fuel electrode of the fuel cell and used for power generation. Steam used for steam reforming of the raw fuel is generated by heating the reforming water.

  Further, a fuel cell system has been developed that generates power by a fuel cell, heats water using heat generated by power generation, and stores the heated water in a hot water tank (for example, Patent Documents 1 to 4). reference). In this fuel cell system, heat recovery water stored in a hot water tank is heated by exchanging heat with high-temperature exhaust gas discharged from the fuel cell, or heat recovery water heat-exchanged with the exhaust gas.

Japanese Patent Laid-Open No. 2004-199920 JP 2006-24430 A JP 2008-135356 A JP 2010-33880 A

  In the above situation, the present inventor has come to recognize the following problems. That is, in the fuel cell system described above, condensed water recovered by cooling the exhaust gas by heat exchange with the heat recovery water can be used as the reforming water used for steam reforming of the raw fuel. If all the reforming water can be supplemented with condensed water, it is not necessary to take in city water from the outside, so that precipitation of calcium and silica contained in the city water can be avoided. Moreover, since the water used as the reforming water is used through the ion exchange resin, the load on the ion exchange resin can be reduced by not taking in city water. As a result, the life of the fuel cell system can be extended. Therefore, in the fuel cell system having a solid oxide fuel cell, water independence is strongly desired.

  When it is desired to increase the amount of condensed water recovered in order to maintain water independence, as one method, the temperature at the heat exchanger inlet of the heat recovery water passing through the heat exchanger (hereinafter, this temperature is appropriately referred to as “heat recovery water inlet (Referred to as “temperature”). Thereby, since exhaust gas can be lowered | hung to lower temperature, the production amount of condensed water can be increased. In particular, since solid oxide fuel cells have a higher operating temperature than solid polymer fuel cells and the like, exhaust gas is also hot. Therefore, the amount of reduction in exhaust gas temperature necessary for the generation of condensed water is large. Therefore, in a fuel cell system having a solid oxide fuel cell, it is effective to lower the heat recovery water inlet temperature of the heat recovery water in order to recover the amount of condensed water necessary for maintaining water self-sustainability.

  On the other hand, when the fuel cell system has a configuration in which the heat recovery water is stored in the hot water storage tank, the heat recovery water is desirably recovered at a constant temperature in order to maintain temperature stratification in the hot water storage layer. Therefore, when the exhaust gas is cooled by lowering the heat recovery water inlet temperature as described above, the temperature at the heat exchanger outlet of the heat recovery water (hereinafter, this temperature is appropriately referred to as “heat recovery water outlet temperature”) is kept constant. In order to maintain, it is necessary to reduce the flow rate of the heat recovery water passing through the heat exchanger. However, when the flow rate of the heat recovery water is reduced, scale that is a deposit such as calcium is likely to be generated on the inner wall of the heat recovery water flow path of the heat exchanger. Further, downsizing of hot water storage tanks is naturally required due to the demand for downsizing of the entire fuel cell system, and when the hot water storage tank is downsized, it is necessary to increase the temperature of the heat recovery water stored in the hot water storage layer. Therefore, it is required to reduce the amount of heat recovery water used for heat exchange with exhaust gas. Therefore, the scale is more likely to occur.

  When a scale occurs, the effective heat exchange area in the heat exchanger decreases due to the scale, and the function of the heat exchanger decreases. For this reason, the exhaust gas temperature remains high, the amount of condensed water generated decreases, and the heat recovery efficiency also decreases. In order to suppress the generation of scale, it is conceivable to increase the flow rate of the heat recovery water passing through the heat exchanger. In that case, the temperature of the heat recovery water outlet decreases and the storage temperature of the hot water storage tank decreases. This hinders the miniaturization of the hot water tank.

  This invention is made | formed in view of such a condition, The objective is to provide the fuel cell system which can suppress generation | occurrence | production of a scale, aiming at maintenance of water independence.

  One embodiment of the present invention is a fuel cell system. The fuel cell system includes a power generation unit having a fuel cell including an anode and a cathode, an exhaust gas passage through which exhaust gas discharged from the power generation unit flows, a storage tank that stores a heat medium for recovering heat of the exhaust gas, Stores the heat exchange part that exchanges heat between the exhaust gas flowing through the exhaust gas flow path and the heat medium, the circulation path for supplying the heat medium in the storage tank to the heat exchange part, and the heat medium that has passed through the heat exchange part A circulation return path to be sent to the tank, a heat medium circulation flow path having a bypass flow path for joining the heat medium that has passed through the heat exchange section to the circulation forward path without passing through the storage tank, and a heat medium in the heat medium circulation flow path. It is recovered from the exhaust gas that has passed through the heat exchange unit, the circulation device that circulates and adjusts the flow rate of the heat medium, the distribution rate adjustment unit for adjusting the distribution rate of the flow rate of the heat medium to the circulation return path and the bypass flow path, and To store the condensed water And a detection unit for detecting a state relating to the amount of water in the tank and transmitting a state signal, and based on the state signal, adjusting the distribution ratio so as to maintain the amount of condensed water recovered from the exhaust gas within a predetermined range And a control unit for controlling the circulation device so that the temperature of the heat medium subjected to heat exchange in the heat exchange unit falls within a predetermined range.

  According to this aspect, generation of scale can be suppressed while maintaining water independence.

  In the above aspect, the power generation unit further includes a reforming unit and a combustion unit, the reforming unit generates reformed gas to reform the raw fuel and supply the fuel cell, and the combustion unit includes the fuel and the anode. At least one of the off-gas may be mixed with at least one of the combustion oxygen-containing gas and the cathode off-gas and burned to heat the reforming unit.

  In the above aspect, when the state of the fuel cell system is a state in which the amount of water in the tank is to be increased, the control unit increases the distribution ratio to the circulation return path to lower the heat exchange unit inlet temperature of the heat medium and heat. The flow rate of the heat medium passing through the exchange unit may be reduced.

  In the above aspect, the control unit may reduce the power generation output of the fuel cell when the distribution ratio to the circulation return path is the maximum.

  In any one of the above aspects, when the state of the fuel cell system is a state in which the amount of water in the tank is to be decreased, the control unit may increase the power generation output of the fuel cell.

  In the above aspect, when the power generation output of the fuel cell is the maximum, the control unit increases the distribution ratio to the bypass flow path to increase the heat exchange unit inlet temperature of the heat medium and heat passing through the heat exchange unit. The flow rate of the medium may be increased.

  In any one of the above aspects, the detection unit detects the water level in the tank, and when the water level falls below a predetermined lower limit, the control unit increases the distribution ratio to the circulation return path to perform heat exchange of the heat medium. The flow rate of the heat medium passing through the heat exchange part may be reduced while lowering the part inlet temperature.

  In any one of the above aspects, the detection unit detects the water level in the tank, and when the water level exceeds a predetermined upper limit, the control unit increases the distribution ratio to the bypass flow path to increase the heat medium heat. The flow rate of the heat medium passing through the heat exchange unit may be increased while raising the temperature at the exchange unit inlet.

  In any one of the above aspects, the detection unit detects the temperature of the exhaust gas, and the difference between the collected amount of condensed water and the amount of water used in the tank is determined according to the temperature of the exhaust gas, and the temperature of the exhaust gas is When the difference is a temperature lower than a predetermined lower limit value, the control unit increases the distribution ratio to the circulation return path to lower the heat exchange unit inlet temperature of the heat medium and the flow rate of the heat medium passing through the heat exchange unit. May be reduced.

  In any one of the above aspects, the detection unit detects the temperature of the exhaust gas, and the difference between the collected amount of condensed water and the amount of water used in the tank is determined according to the temperature of the exhaust gas, and the temperature of the exhaust gas is When the difference is a temperature exceeding a predetermined upper limit value, the control unit increases the distribution ratio to the bypass flow path to increase the heat exchange unit inlet temperature of the heat medium and the heat medium passing through the heat exchange unit. The flow rate may be increased.

  In any of the above aspects, the detection unit detects the water pressure in the tank, and when the water pressure falls below a predetermined lower limit value, the control unit increases the distribution ratio to the circulation return path to exchange heat of the heat medium. The flow rate of the heat medium passing through the heat exchange part may be reduced while lowering the part inlet temperature.

  In any one of the above aspects, the detection unit detects the water pressure in the tank, and when the water pressure exceeds a predetermined upper limit value, the control unit increases the distribution ratio to the bypass flow path to increase the heat medium heat. The flow rate of the heat medium passing through the heat exchange unit may be increased while raising the temperature at the exchange unit inlet.

  In any one of the above aspects, the fuel cell system may include a reforming unit that is disposed upstream of the fuel cell and reforms the raw fuel.

  A combination of the above-described elements as appropriate can also be included in the scope of the invention for which patent protection is sought by this patent application.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel cell system which can suppress generation | occurrence | production of a scale can be provided, aiming at the maintenance of water independence.

1 is a flow diagram illustrating a schematic configuration of a fuel cell system according to Embodiment 1. FIG. 3 is a flowchart of operation control of the fuel cell system according to Embodiment 1. 5 is a flowchart of another operation control of the fuel cell system according to Embodiment 1. FIG. 5 is a flow diagram illustrating a schematic configuration of a fuel cell system according to Embodiment 2. It is a figure which shows the relationship between the temperature of waste gas, and a water balance. 5 is a flowchart of operation control of the fuel cell system according to Embodiment 2. FIG. 5 is a flow diagram illustrating a schematic configuration of a fuel cell system according to Embodiment 3. 10 is a flowchart of operation control of the fuel cell system according to Embodiment 3.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

(Embodiment 1)
FIG. 1 is a flow chart showing a schematic configuration of the fuel cell system according to Embodiment 1. In addition, the flow path diagram of FIG. 1 is a diagram schematically showing mainly the functions and connections of each component, and does not limit the positional relationship or arrangement of each component.

  The fuel cell system 1 according to the present embodiment includes a fuel cell 100, a power generation unit 2 having a reforming unit 110 and an off-gas combustion unit 112 (combustion unit), an exhaust gas flow channel 120, a hot water storage tank 130 (storage tank), Heat exchanger 140 (heat exchange unit), heat recovery water circulation channel 150 (heat medium circulation channel), distribution ratio adjustment valve 160 (distribution ratio adjustment unit), tank 170, and water level sensor 180 (detection unit) And a control unit 190. The fuel cell system 1 also includes a reformed gas channel 200, a condensate separator 210, a reforming water channel 220, a circulation pump 230 (circulation device), and a temperature sensor 240. In addition, each structure mentioned above may be accommodated in one housing | casing, for example, accommodating a power generation system and a thermal storage system in a separate housing | casing, and is accommodated in several housing | casing according to a function. Also good. As for the power generation unit 2, the fuel cell 100, the reforming unit 110, and the off-gas combustion unit 112 may be housed in the same housing, or may be housed in a plurality of housings. Each configuration will be described below.

  The fuel cell 100 is, for example, a solid oxide fuel cell. The fuel cell 100 includes a fuel cell stack (not shown) in which a plurality of cells each provided with an electrolyte body 106 containing a solid oxide are connected in series between an anode 102 (fuel electrode) and a cathode 104 (air electrode). ). The fuel cell 100 generates power using a hydrogen-containing gas as a fuel and an oxygen-containing gas as an oxidant. For example, as a fuel, a hydrogen-enriched gas obtained by reforming a raw fuel containing hydrogen atoms such as city gas, LPG, kerosene, and alcohol (hereinafter, this hydrogen-enriched gas is referred to as “reformed gas” as appropriate). ), Pure hydrogen, or the like can be used. As the oxidant, oxygen-enriched air, pure oxygen, or the like can be used in addition to air that is easy to handle.

  In this embodiment, reformed gas is used as fuel. This reformed gas is supplied to the anode 102 from a reforming unit 110 described later. That is, the reformed gas generated in the reforming unit 110 is supplied to the anode 102 through the reformed gas channel 200, and hydrogen contained in the reformed gas is used as fuel. The reformed gas may contain a small amount of carbon monoxide, and this carbon monoxide can also be used as a fuel.

  In the present embodiment, air is used as the oxidizing agent. This air is taken into the fuel cell system 1 from the outside of the fuel cell system 1. The air taken into the fuel cell system 1 is filtered to remove dust and suspended matters, heated, and supplied to the cathode 104.

When the reformed gas and air are supplied, electrode reactions represented by the following formulas (1), (2), and (3) occur at the anode 102 of each cell of the fuel cell 100. On the other hand, an electrode reaction represented by the following formula (4) occurs at the cathode 104. The electrode reaction in each cell is performed in a temperature range of about 600 ° C to about 1000 ° C.
Anode: H ₂ + O ²⁻ → H ₂ O + 2e ⁻ (1)
CO + O ²⁻ → CO ₂ + 2e ⁻ (2)
CH ₄ + 3O ²⁻ → CO ₂ + 2H ₂ O + 6e ⁻ (3)
Cathode: 1 / 2O ₂ + 2e ⁻ → O ²⁻ (4)

  In the anode 102, as shown in the above formula (1), hydrogen contained in the supplied reformed gas releases electrons and reacts with oxygen ions that have moved from the cathode 104 through the electrolyte body 106 to form water. Is generated. Alternatively, as shown in the above formula (2), carbon monoxide contained in the supplied reformed gas emits electrons and reacts with oxygen ions that have moved from the cathode 104 through the electrolyte body 106 to form carbon dioxide. Carbon is produced. Alternatively, as shown in the above formula (3), methane, which is a hydrocarbon contained in the supplied reformed gas, emits electrons and reacts with oxygen ions that have moved through the electrolyte body 106 from the cathode 104. Water and carbon dioxide are produced. The electrons travel to the cathode 104 through an external circuit. On the other hand, at the cathode 104, as shown in the above formula (4), oxygen contained in the supplied air reacts with electrons that have moved from the anode 102 side to become oxygen ions. Oxygen ions move inside the electrolyte body 106 toward the anode 102. In this manner, in the external circuit, electrons move from the anode 102 toward the cathode 104, so that electric power is taken out.

  The DC power generated in the fuel cell 100 is converted into DC power having a predetermined voltage (eg, 350V) by a converter (not shown), and then converted to AC power (eg, 100V) by an inverter (not shown). The AC power converted by the inverter is output to a system (not shown). The DC power of a predetermined voltage converted by the converter is used as a power source for the control unit 190 and the like. In the present embodiment, the fuel cell system 1 performs load following operation. That is, the fuel cell system 1 performs an operation of changing the power generation amount of the fuel cell 100 in accordance with fluctuations in power demand.

  The reforming unit 110 is a device that generates reformed gas mainly containing hydrogen gas by steam reforming the raw fuel. The reforming unit 110 is supplied with raw fuel such as kerosene, natural gas, and LPG. The reforming unit 110 includes, for example, a reforming catalyst layer (not shown) having a Ru-based reforming catalyst in which ruthenium (Ru) is supported as metal particles on a support such as alumina.

The raw fuel and steam are supplied to the reforming unit 110, and steam reforming of the raw fuel is performed in the presence of the reforming catalyst. In this steam reforming, as shown by the following formula (5), for example, a reforming reaction occurs in which methane and steam in the raw fuel react to generate hydrogen and carbon monoxide. The reforming reaction is performed, for example, in the range of about 600 ° C to about 700 ° C.
CH ₄ + H ₂ O → 3H ₂ + CO (5)

  Steam necessary for the reforming reaction is generated by vaporizing the reforming water. For example, in the fuel cell system 1, a vaporization unit (not shown) that vaporizes the reforming water is disposed on the upstream side of the reforming unit 110 in the power generation unit 2, and the vaporization unit uses an off-gas combustion unit 112 described later. The water for reforming is vaporized by heating and supplied to the reforming unit 110. The reforming water is supplied from a tank 170 described later by a reforming water pump (not shown). The supply amount of the reforming water can be adjusted by controlling the discharge amount of the reforming water pump.

  An off-gas combustion unit 112 is provided in the power generation unit 2. The off-gas combustion unit 112 is located on the downstream side of the anode 102 and the cathode 102 of the fuel cell 100, and at least one of the anode off-gas discharged from the anode outlet and the raw fuel taken from the outside of the fuel cell system 1, and the cathode outlet The cathode off-gas discharged from the gas and at least one of combustion oxygen-containing gas (for example, air taken in from the outside of the fuel cell system 1) are mixed and burned. The entire power generation unit 2 is heated by the combustion of the mixed gas by the off-gas combustion unit 112. By this heating, the fuel cell 100 and the reforming unit 110 are adjusted to temperatures suitable for the respective reactions. The reformed gas generated by the reforming reaction in the reforming unit 110 is supplied to the anode 102 of the fuel cell 100 through the reformed gas channel 200.

  High-temperature exhaust gas generated in the off-gas combustion unit 112 is discharged from the off-gas combustion unit 112 to the exhaust gas flow channel 120. The exhaust gas channel 120 includes an exhaust gas channel 122 before heat exchange and an exhaust gas channel 123 after heat exchange. One end of the pre-heat exchange exhaust gas flow path 122 is connected to the exhaust gas outlet of the off-gas combustion unit 112, and the other end is connected to the exhaust gas inlet 141 of the heat exchanger 140. One end of the heat exchange exhaust gas passage 123 is connected to the exhaust gas outlet 142 of the heat exchanger 140, and the other end is connected to the exhaust gas inlet of the condensed water separator 210. The exhaust gas discharged from the off-gas combustion unit 112 is supplied to the heat exchanger 140 through the exhaust gas passage 122 before heat exchange. The exhaust gas that has passed through the heat exchanger 140 is supplied to the condensed water separator 210 through the exhaust gas passage 123 after heat exchange.

  The condensed water separator 210 separates condensed water from the exhaust gas. The exhaust gas from which the condensed water has been separated is released to the outside air through the exhaust pipe 124. The condensed water recovered from the exhaust gas passes through the condensed water channel 125 and is stored in the tank 170. A reforming water channel 220 is connected between the tank 170 and the reforming unit 110, and the condensed water accommodated in the tank 170 is supplied to the reforming unit 110 through the reforming water channel 220. Used as reforming water. The reforming water is subjected to water treatment in a water treatment device (not shown) such as an ion exchange resin. When an ion exchange resin is used as the water treatment apparatus, the ion exchange resin may be integrated with the condensed water separator 210 or the tank 170, or within the flow path system of the condensed water flow path 125 or the reforming water flow path 220. May be arranged.

  A water level sensor 180 is provided in the tank 170. The water level sensor 180 is connected to the control unit 190 through a signal cable, detects the water level in the tank 170 as a state relating to the amount of water in the tank 170, and transmits a state signal to the control unit 190. Specifically, the water level sensor 180 is a two-point water level detection type sensor that detects a predetermined lower limit water level and a predetermined upper limit water level of the condensed water stored in the tank 170, and the water level in the tank 170 is a predetermined level. A state signal indicating that the water level has fallen below the lower limit value when it falls below the lower limit value is transmitted to the control unit 190, and a state signal indicating that the water level has exceeded the upper limit value when the water level has exceeded the predetermined upper limit value Is transmitted to the control unit 190. From the viewpoint of cost reduction, the water level sensor 180 may be a one-point water level detection type sensor that detects only one water level.

  The hot water tank 130 stores heat recovery water (heat medium) for recovering the heat of the exhaust gas. City water is supplied to the hot water tank 130 as heat recovery water through, for example, a water pipe. The hot water storage tank 130 and the heat exchanger 140 are connected by a heat recovery water circulation channel 150, and the heat recovery water stored in the hot water storage tank 130 is supplied to the heat exchanger 140 by the circulation pump 230.

  The heat exchanger 140 performs heat exchange between the exhaust gas flowing through the exhaust gas passage 120 and the heat recovery water flowing through the heat recovery water circulation passage 150. Specifically, the exhaust gas that has passed through the pre-heat exchange exhaust gas flow path 122 and supplied to the heat exchanger 140 and the second flow path 152 of the heat recovery water circulation flow path 150 are supplied to the heat exchanger 140. Heat exchange with the recovered heat water. Thus, the heat recovery water is heated by the heat energy generated in the power generation unit 2, and hot water is stored in the hot water storage tank 130. Thus, since the heat energy generated in the power generation unit 2 can be stored as hot water in the hot water storage tank 130, the exhaust heat of the power generation unit 2 can be recovered without waste.

  The heat recovery water circulation channel 150 includes a first channel 151 to a fifth channel 155. One end of the first channel 151 is connected to the outlet of the hot water tank 130, and the other end is connected to the water inlet of the circulation pump 230. One end of the second flow path 152 is connected to the water supply port of the circulation pump 230, and the other end is connected to the heat recovery water inlet 143 of the heat exchanger 140. The third flow path 153 has one end connected to the heat recovery water outlet 144 of the heat exchanger 140 and the other end connected to the inlet 161 of the distribution ratio adjustment valve 160. The fourth channel 154 has one end connected to the first outlet 162 of the distribution ratio adjusting valve 160 and the other end connected to the inlet of the hot water storage tank 130. One end of the fifth flow path 155 is connected to the second outlet 163 of the distribution ratio adjusting valve 160, and the other end is connected to an intermediate portion of the first flow path 151.

  The first flow path 151 and the second flow path 152 form a circulation path for supplying the heat recovery water in the hot water storage tank 130 to the heat exchanger 140. Further, the third flow path 153 and the fourth flow path 154 form a circulation return path for sending the heat recovery water that has passed through the heat exchanger 140 to the hot water storage tank 130. Further, the third flow path 153 and the fifth flow path 155 form a bypass flow path that joins the heat recovery water that has passed through the heat exchanger 140 to the circulation forward path without passing through the hot water storage tank 130.

  The distribution ratio adjusting valve 160 can adjust the opening degree of the first outlet 162 and the opening degree of the second outlet 163 continuously or stepwise. The distribution ratio adjusting valve 160 is connected to the control unit 190 via a signal cable, receives a control signal from the control unit 190, and changes the opening degrees of the first outlet 162 and the second outlet 163. Thereby, the distribution ratio adjustment valve 160 can adjust the distribution ratio of the flow rate of the heat recovery water discharged from the heat exchanger 140 to the circulation return path and the bypass flow path. In addition, the distribution ratio adjustment valve 160 transmits the opening degrees of the first outlet 162 and the second outlet 163 to the control unit 190 as signals. Thereby, the control part 190 can grasp | ascertain the distribution ratio of heat recovery water.

  In the present embodiment, the distribution ratio adjustment valve 160 is arranged at the junction of the third flow path 153, the fourth flow path 154, and the fifth flow path 155, but the arrangement of the distribution ratio adjustment valve 160 is not limited to this. . For example, the distribution ratio adjustment valve 160 may be installed at the junction of the first flow path 151, the second flow path 152, and the fifth flow path 155. In the case where the flow rate of the heat recovery water is larger in the fifth flow path 155 (bypass flow path) than in the fourth flow path 154 (circulation return path) without adjusting the distribution ratio of the heat recovery water. The distribution ratio adjusting valve 160 composed of a two-way valve is installed in the middle of the fifth flow path 155, and the opening degree of the distribution ratio adjusting valve 160 is adjusted to return the heat recovery water flow circulation return path and bypass flow path. You may adjust the distribution ratio to. In the case where the flow rate of the heat recovery water is larger in the fourth flow path 154 (circulation return path) than in the fifth flow path 155 (bypass flow path) without adjusting the distribution ratio of the heat recovery water. May adjust the distribution ratio of the heat recovery water by installing a distribution ratio adjusting valve 160 comprising a two-way valve in the middle of the fourth flow path 154 and adjusting the opening of the distribution ratio adjusting valve 160. .

  In the distribution ratio adjusting valve 160 of the present embodiment, when the opening degree of the first outlet 162 is increased, the opening degree of the second outlet 163 is reduced, and when the opening degree of the first outlet 162 is reduced, the second outlet 163 is opened. It is a valve that increases in degree. When the opening degree of the first outlet 162 is increased, the amount of heat recovery water that is heated by the heat exchanger 140 and then sent to the hot water tank 130 increases. On the other hand, when the opening degree of the second outlet 163 is increased, the amount of heat recovery water that is heated by the heat exchanger 140 and then supplied to the heat exchanger 140 without being returned to the hot water tank 130 increases. .

  The circulation pump 230 is a pump that circulates the heat recovery water in the heat recovery water circulation flow path 150, and can adjust the amount of heat recovery water delivered continuously or stepwise. The flow rate of the heat recovery water passing through the heat exchanger 140 can be changed by adjusting the amount of heat recovery water delivered by the circulation pump 230. The circulation pump 230 is connected to the control unit 190 through a signal cable, receives the control signal from the control unit 190, and changes the flow rate of the heat recovery water circulating in the heat recovery water circulation channel 150.

  A temperature sensor 240 for detecting the temperature of the heat recovery water that has passed through the heat exchanger 140 is provided in the vicinity of the heat recovery water outlet 144 of the heat exchanger 140. The temperature sensor 240 is connected to the control unit 190 through a signal cable, and transmits the detected temperature of the heat recovery water to the control unit 190 as a signal.

  The control unit 190 is realized by a CPU that executes various arithmetic processes as a hardware configuration, a ROM that stores various control programs, a RAM that is used as a work area for data storage and program execution, and the software configuration is It is realized by a computer program or the like. The control unit 190 receives the state signal from the water level sensor 180 and controls the distribution ratio adjusting valve 160 based on the received state signal. The control unit 190 receives the temperature signal from the temperature sensor 240 and controls the circulation pump 230 so that the temperature of the heat recovery water at the heat recovery water outlet 144 of the heat exchanger 140 falls within a predetermined range. Adjust the water flow rate. Furthermore, the control unit 190 adjusts the power generation output of the fuel cell 100 as necessary.

  Next, the operation of the fuel cell system 1 having the above-described configuration will be described.

  Based on the state signal received from the water level sensor 180, the control unit 190 controls the distribution ratio adjustment valve 160 so as to maintain the amount of condensed water recovered from the exhaust gas within a predetermined range. Specifically, the control unit 190 increases the distribution ratio to the circulation return path, that is, the fourth flow path 154 when the state relating to the water amount in the tank 170 is a state in which the water amount should be increased. Further, when the state relating to the amount of water in the tank 170 is a state where the amount of water should be reduced, the control unit 190 increases the distribution ratio to the bypass flow path, that is, the fifth flow path 155. In the present embodiment, when the water level in the tank 170 falls below a predetermined lower limit value, the water amount should be increased, and when the water level in the tank 170 exceeds a predetermined upper limit value, the water amount should be reduced. Yes.

  If the water level in the tank 170 continues to drop, the reforming water supplied to the reforming unit 110 will eventually become insufficient, so the amount of condensed water recovered from the exhaust gas by the condensed water separator 210 is increased. It is hoped that Therefore, when the water level in the tank 170 falls below a predetermined lower limit value, the control unit 190 increases the distribution ratio of the flow rate of the heat recovery water to the fourth flow path 154 as described above. Thereby, since the amount of heat recovery water returned to the hot water tank 130 increases, the amount of heat recovery water supplied from the hot water tank 130 to the heat exchanger 140 increases. As a result, the heat recovery water inlet 143 of the heat exchanger 140 is supplied with lower temperature heat recovery water than before increasing the distribution ratio to the circulation flow path. As the temperature of the heat recovery water supplied to the heat exchanger 140 is lower, the amount of heat recovered from the exhaust gas by the heat recovery water increases, so that the exhaust gas that passes through the heat exchanger 140 can be made lower in temperature. Thereby, a larger amount of condensed water can be produced | generated and the collection amount of condensed water can be increased.

  Further, the control unit 190 controls the circulation pump 230 based on the temperature signal from the temperature sensor 240 so as to keep the temperature of the heat recovery water near the heat recovery water outlet 144 constant. As described above, when the temperature of the heat recovery water at the heat recovery water inlet 143 is lowered, the temperature rise width of the heat recovery water from the heat recovery water inlet 143 to the heat recovery water outlet 144 increases, so that the control is performed. The unit 190 controls the circulation pump 230 to reduce the flow rate of the heat recovery water.

  As described above, when the water level in the tank 170 falls below a predetermined lower limit, the amount of heat recovery water flow is increased by increasing the distribution ratio to the circulation flow path to increase the amount of condensed water generated, thereby improving the reforming unit. Reforming water necessary for the reforming reaction at 110 can be secured.

  On the other hand, if the water level in the tank 170 continues to rise, any excess condensed water will be discharged from the tank 170, so the amount of condensed water recovered from the exhaust gas by the condensed water separator 210 is reduced. It is hoped that. Therefore, when the water level in the tank 170 exceeds a predetermined upper limit value, the control unit 190 increases the distribution ratio of the flow rate of the heat recovery water to the fifth flow path 155 as described above. As a result, the amount of heat recovery water re-supplied to the heat exchanger 140 without being returned to the hot water storage tank 130 increases, so that the heat recovery water inlet 143 of the heat exchanger 140 has a distribution ratio to the bypass channel. Heat recovery water having a higher temperature than that before the increase is supplied. The higher the temperature of the heat recovery water supplied to the heat exchanger 140, the smaller the amount of heat recovered from the exhaust gas by the heat recovery water, so the temperature decrease of the exhaust gas becomes smaller. Thereby, the production amount of condensed water can be reduced and the collection amount of condensed water can be reduced.

  Further, when the temperature of the heat recovery water at the heat recovery water inlet 143 is increased as described above, the temperature rise width of the heat recovery water from the heat recovery water inlet 143 to the heat recovery water outlet 144 is reduced. The control unit 190 controls the circulation pump 230 to increase the flow rate of the heat recovery water.

  As described above, when the water level in the tank 170 exceeds the predetermined upper limit value, the distribution ratio of the flow rate of the heat recovery water to the bypass channel is increased to reduce the generation amount of the condensed water, thereby reducing the excess condensed water. Therefore, it is possible to reduce the load on the water treatment apparatus such as an ion exchange resin. As a result, the life of the water treatment apparatus can be extended, and as a result, the life of the fuel cell system 1 can be extended. Moreover, since the discharge of excess condensed water can be avoided, the structure for discharging condensed water from the tank 170 can be omitted. Thereby, size reduction of the fuel cell system 1 can be achieved. In addition, since the flow rate of heat recovery water is increased while reducing the amount of condensed water generated, it is possible to suppress the generation of scales such as calcium deposits on the inner wall of the heat recovery water flow path of the heat exchanger. can do.

  The “predetermined lower limit value” is set higher than the minimum amount by adding a margin to the minimum amount of condensed water that can maintain the supply of reformed gas to the anode 102 of the fuel cell 100, for example. It is the value. The “predetermined upper limit value” is a value set lower than the accommodation limit amount by subtracting a margin from the accommodation limit amount of the tank 170, for example. The “predetermined lower limit value” and the “predetermined upper limit value” can be appropriately set based on experiments and simulations by the designer. When the water level sensor 180 is a one-point water level detection type sensor, the “predetermined lower limit value” is below the detected water level of the water level sensor 180, and the “predetermined upper limit value” is the water level sensor 180. It is in a state of exceeding the detected water level.

  Hereinafter, the flow of operation control of the fuel cell system 1 will be described in detail. FIG. 2 is a flowchart of operation control of the fuel cell system according to the first embodiment. This flowchart is an example when the water level sensor 180 is a two-point water level detection type. This flow is executed by the control unit 190, and is started when the fuel cell system 1 is started, and is ended when the fuel cell system 1 is stopped, for example.

  When the control flow starts, the control unit 190 determines whether or not the water level in the tank 170 is within a predetermined range (step 101: hereinafter abbreviated as S101. The same applies to other steps). The control unit 190 determines that the water level is within the predetermined range when the water level is equal to or lower than the predetermined upper limit value and equal to or higher than the predetermined lower limit value. When the water level is within the predetermined range (Y in S101), the control unit 190 determines whether the power generation output of the fuel cell 100 is maximum (S102). When the power generation output of the fuel cell 100 is not the maximum (N in S102), the control unit 190 increases the power generation output of the fuel cell 100 (S103) and returns to Step 101. When the power generation output of the fuel cell 100 is the maximum (Y in S102), the control unit 190 returns to Step 101 without increasing the power generation output of the fuel cell 100.

  As described above, when the water level in the tank 170 is within the predetermined range, the power generation output of the fuel cell 100 is increased so that the amount of power supplied by the fuel cell system 1 is increased. When the fuel cell system 1 performs a load following operation that increases or decreases the power generation output according to the power demand, the control unit 190 determines whether the power generation output of the fuel cell 100 is within a predetermined preferable range with respect to the power demand. However, when the power generation output is out of this preferable range, the power generation output of the fuel cell 100 may be controlled to be adjusted. The “preferable range” refers to a value that is lower by a certain value than the power load that is the load in the load following operation. It may be the same value as the load. In this case, while the power generation output is controlled within the preferred range by the control unit 190, if it is determined in step 101 that the water level is within the predetermined range, the power generation maximum output (maximum allowable power generation output) is increased. By increasing the allowable maximum power generation output, the water level becomes less than the lower limit value, and the power generation output reduction flag is set to ON (details will be described later), thereby increasing the allowable maximum power generation output that has been suppressed.

  When the water level is not within the predetermined range (N in S101), the control unit 190 determines whether the water level in the tank 170 is less than the predetermined lower limit (S104). When the water level is less than the predetermined lower limit (Y in S104), the control unit 190 determines whether the distribution ratio of the heat recovery water to the circulation channel is the maximum (S105). When the distribution ratio to the circulation channel is not the maximum (N in S105), the control unit 190 increases the distribution ratio to the circulation return path by increasing the opening degree of the first outlet 162 by a predetermined amount, and the heat recovery water outlet The flow rate of the heat recovery water is reduced so that the temperature of the heat recovery water at 144 falls within a predetermined range (S106).

  Comparison of the amount of condensed water per unit volume of exhaust gas and water in the fuel cell system 1 when the power generation output of the fuel cell 100 is the same, the distribution ratio of the heat recovery water is varied by controlling the distribution ratio of the heat recovery water, and the water in the fuel cell system 1 The balance (g / min) is shown in Tables 1 and 2.

  As shown in Tables 1 and 2, the exhaust gas temperature (exhaust gas outlet temperature) at the exhaust gas outlet 142 decreases as the heat recovery water inlet temperature is decreased by increasing the distribution ratio to the circulation flow path, and the exhaust gas per unit volume of exhaust gas. Both the amount of condensed water and the water balance increase. Therefore, the water level in the tank 170 can be raised by increasing the distribution ratio to the circulation channel and lowering the temperature of the heat recovery water at the heat recovery water inlet 143. In other words, the water level in the tank 170 can be lowered by increasing the temperature of the heat recovery water at the heat recovery water inlet 143.

  The amount of increase in the opening degree of the first outlet 162 can be set as appropriate. Also, from the viewpoint of suppressing the generation of scale on the inner wall of the heat recovery water flow path of the heat exchanger, a minimum flow rate of heat recovery water is arbitrarily determined in advance, and the heat recovery water heat exchanger outlet temperature is kept within a predetermined range. The distribution ratio to the circulation return path may be increased so that the flow rate reduced as much as possible does not fall below this minimum flow rate. For example, in this embodiment, the heat recovery water temperature of the first flow path 151 is 10 ° C., and the distribution ratio of the heat recovery water can be changed in the range of bypass flow path: circulation flow path = 0: 100 to 61:39. Is set. Moreover, the heat recovery water inlet temperature which can be taken in the range of this distribution ratio is 10 to 50 degreeC. Of course, the distribution ratio of the heat recovery water and the temperature of the heat recovery water inlet are not limited to this range.

  When the distribution ratio of the heat recovery water to the circulation channel is the maximum (Y in S105), the control unit 190 determines whether the power generation output of the fuel cell 100 is the minimum (S107). When the power generation output of the fuel cell 100 is not minimum (N in S107), the control unit 190 reduces the power generation output of the fuel cell 100 (S108). For example, the control unit 190 reduces the power generation output of the fuel cell 100 by lowering the set value (power generation output upper limit value) of the maximum power generation output of the fuel cell 100. When the fuel cell system 1 is performing the load following operation, the control unit 190 can reduce the power generation output of the fuel cell 100 by reducing the set value of the maximum power generation output of the fuel cell 100. Note that the power generation output can be reduced to a predetermined value or by a predetermined amount. The control unit 190 reduces the power generation output of the fuel cell 100 and sets the power generation output reduction flag to ON.

  Table 3 shows the comparison of the amount of condensed water per unit volume of exhaust gas and the water balance (g / min) in the fuel cell system 1 when the heat recovery water inlet temperature is the same and the power generation output of the fuel cell 100 is varied. Show.

  As shown in Table 3, when the power generation output of the fuel cell 100 is reduced, the exhaust gas outlet temperature decreases, and both the amount of condensed water per unit volume of the exhaust gas and the water balance increase. That is, when the power generation output of the fuel cell 100 is reduced, the flow rate of reforming water and the flow rates of raw fuel and air to be input are reduced, so that the exhaust gas flow rate discharged from the fuel cell 100 is reduced. Thereby, since the flow rate of the exhaust gas passing through the heat exchanger 140 is reduced, the heat exchange between the exhaust gas and the heat recovery water proceeds further, and the exhaust gas temperature after the heat exchange gradually approaches the heat recovery water inlet temperature. As a result, the amount of condensed water per unit volume of exhaust gas increases. Further, since the amount of reformed gas supplied to the fuel cell 100 is reduced, the amount of condensed water in the tank 170 is reduced. Therefore, the water balance in the fuel cell system 1 increases. Therefore, the water level in the tank 170 can be raised by reducing the power generation output of the fuel cell 100.

  Note that it is determined in step 104 that the water level is less than the lower limit (Y in S104) as a result of the fuel cell 100 being operated at a high output by repeating steps 101 to 103. Therefore, in a situation where the water level is determined to be less than the lower limit value, the hot water in the hot water storage tank 130 is considered even if relatively low temperature city water is supplied by normal use of the hot water in the hot water storage tank 130. It is relatively hot. Therefore, even when Steps 105 and 106 are repeated and the distribution ratio to the circulation channel is maximized, the amount of decrease in the heat recovery water inlet temperature is relatively small. Therefore, in Table 3, both the heat recovery water temperature and the heat recovery water inlet temperature of the first flow path 151 are set to 40 ° C. as an example.

  When the power generation output of the fuel cell 100 is minimum (Y in S107), the control unit 190 maintains the opening degree of the first outlet 162 and the power generation output of the fuel cell 100 as they are. When the opening degree of the first outlet 162 and the power generation output of the fuel cell 100 are maintained, the temperature of the heat recovery water in the first flow path 151 decreases with the passage of time due to the use of hot water in the hot water storage tank 130 and the like. The recovered water inlet temperature decreases and the amount of condensed water recovered increases, and as a result, the water level in the tank 170 is expected to gradually increase. Note that the control unit 190 stops the fuel cell system 1 when the water level in the tank 170 does not exceed the lower limit value even after a predetermined time has elapsed, or the administrator or the like via an operation panel (not shown). Control such as notifying the user of the lack of reforming water may be performed.

  When the water level is not less than the predetermined lower limit (N in S104), in this case, the water level is higher than the predetermined upper limit, and the control unit 190 determines whether the power generation output of the fuel cell 100 is maximum. (S109). The control unit 190 can determine whether the power generation output of the fuel cell 100 is maximum, for example, by determining whether or not the power generation output reduction flag is set to ON. When the power generation output of the fuel cell 100 is not the maximum (N in S109), the control unit 190 increases the power generation output of the fuel cell 100 (S110). For example, the power generation output of the fuel cell 100 is increased by increasing the set value of the maximum power generation output of the fuel cell 100. Note that the increase in the power generation output may be increased to a predetermined value, or may be increased by a predetermined amount. When the fuel cell system 1 is performing the load following operation, the control unit 190 determines in step 109 whether the power generation output of the fuel cell 100 is less than the power demand, and when the power generation output is less than the power demand. In step 110, control may be performed so as to adjust the power generation output of the fuel cell 100 in accordance with the power demand.

  Table 4 shows the comparison of the amount of condensed water per unit volume of exhaust gas and the water balance (g / min) in the fuel cell system 1 when the heat recovery water inlet temperature is the same and the power generation output of the fuel cell 100 is varied. Table 5 shows.

  As shown in Tables 4 and 5, when the power generation output of the fuel cell 100 is increased, the exhaust gas outlet temperature increases, and both the amount of condensed water per unit volume of the exhaust gas and the water balance decrease. The same can be said from Table 3. That is, when the power generation output of the fuel cell 100 is increased, the flow rate of the exhaust gas discharged from the fuel cell 100 increases, so that the flow rate of the exhaust gas passing through the heat exchanger 140 increases. Therefore, the amount of heat exchange between the exhaust gas and the heat recovery water is reduced. As a result, the amount of condensed water per unit volume of exhaust gas decreases. Further, since the amount of the reformed gas supplied to the fuel cell 100 increases, the amount of condensed water in the tank 170 increases. Therefore, the water balance in the fuel cell system 1 is reduced. Therefore, the water level in the tank 170 can be reduced by increasing the power generation output of the fuel cell 100.

  For example, comparing the cases where the heat recovery water inlet temperature in each of Table 1 and Table 2 is 10 ° C., increasing the power generation output of the fuel cell 100 increases the water balance. However, in step 110 for increasing the power generation output of the fuel cell 100, when it is determined that the water level in the tank 170 has exceeded the upper limit of the predetermined range (N in S104), that is, the fuel cell 100 has already been operated for a certain period of time. Will be executed after. Therefore, the hot water in the hot water storage tank 130 is almost always relatively high, and the heat recovery water inlet temperature is rarely 10 ° C. That is, there are few situations where the water balance increases due to an increase in the power generation output of the fuel cell 100. Even if the heat recovery water inlet temperature is 10 ° C., in other words, even if the increase in the power generation output of the fuel cell 100 increases the water balance, the subsequent distribution ratio increase control to the bypass channel Water balance will decline. Therefore, the situation where the water balance increases due to an increase in the power generation output of the fuel cell 100 is temporary. Therefore, in consideration of the merit that the power supply amount by the fuel cell system 1 can be increased, the power generation output of the fuel cell 100 is preferentially increased.

  When the power generation output of the fuel cell 100 is the maximum (Y in S109), the control unit 190 determines whether the distribution ratio of the heat recovery water to the bypass flow path is the maximum (S111). When the distribution ratio to the bypass flow path is not the maximum (N of S111), the control unit 190 increases the distribution ratio to the bypass flow path by increasing the opening degree of the second outlet 163 by a predetermined amount, and heat recovery water The flow rate of the heat recovery water is increased so that the temperature of the heat recovery water at the outlet 144 falls within a predetermined range (S112).

  As shown in Tables 1 and 2, the amount of condensed water per unit volume of exhaust gas and the water balance both decrease as the heat recovery water inlet temperature is increased by increasing the distribution ratio to the bypass channel. Therefore, the water level in the tank 170 can be lowered by increasing the distribution ratio to the bypass flow path and increasing the temperature of the heat recovery water at the heat recovery water inlet 143. In addition, the increase amount of the opening degree of the 2nd exit 163 can be set suitably.

  When the distribution ratio to the bypass channel is the maximum (Y in S111), the control unit 190 maintains the opening degree of the second outlet 163 and the power generation output of the fuel cell 100 as they are. As shown in Table 1, when the power generation output of the fuel cell 100 is increased (700 W state) and the distribution ratio to the bypass channel is maximum, the water balance in the fuel cell system 1 (g / min) ) Is negative. Therefore, it is expected that the water level in the tank 170 gradually decreases by maintaining the distribution ratio to the bypass channel and the power generation output of the fuel cell 100 as they are.

  Next, another operation control flow of the fuel cell system 1 will be described. FIG. 3 is a flowchart of another operation control of the fuel cell system according to the first embodiment. This flowchart is an example when the water level sensor 180 is a one-point water level detection type. This flow is executed by the control unit 190, and is started when the fuel cell system 1 is started, and is ended when the fuel cell system 1 is stopped, for example. In the following description, the same points as the operation control when the above-described water level sensor 180 is a two-point water level detection type will be omitted as appropriate.

  When the control flow starts, the control unit 190 determines whether the water level in the tank 170 is less than a predetermined lower limit value (S201). When the water level is less than the predetermined lower limit (Y in S201), the control unit 190 determines whether the distribution ratio of the heat recovery water to the circulation channel is the maximum (S202). When the distribution ratio to the circulation channel is not the maximum (N in S202), the control unit 190 increases the distribution ratio to the circulation return path by increasing the opening degree of the first outlet 162 by a predetermined amount, and the heat recovery water outlet The flow rate of the heat recovery water is reduced so that the temperature of the heat recovery water at 144 falls within a predetermined range (S203).

  When the distribution ratio of the heat recovery water to the circulation channel is the maximum (Y in S202), the control unit 190 determines whether the power generation output of the fuel cell 100 is the minimum (S204). When the power generation output of the fuel cell 100 is not minimum (N in S204), the control unit 190 reduces the power generation output of the fuel cell 100 (S205). When the power generation output of the fuel cell 100 is minimum (Y in S204), the control unit 190 maintains the opening degree of the first outlet 162 and the power generation output of the fuel cell 100 as they are.

  When the water level is not less than the predetermined lower limit (N in S201), in this case, the water level is higher than the predetermined upper limit, and the control unit 190 determines whether the power generation output of the fuel cell 100 is maximum. (S206). When the power generation output of the fuel cell 100 is not maximum (N in S206), the control unit 190 increases the power generation output of the fuel cell 100 and returns to Step 201 (S207). When the power generation output of the fuel cell 100 is the maximum (Y in S206), the control unit 190 determines whether the distribution ratio of the heat recovery water to the bypass flow path is the maximum (S208).

  As described above, when the water level in the tank 170 exceeds the upper limit value, that is, when the reforming water is not insufficient, the power generation output of the fuel cell 100 is increased to satisfy the user's power demand. To control. In addition, when the fuel cell system 1 performs the load following operation, the control unit 190 determines whether the power generation output of the fuel cell 100 satisfies the power demand, and when the power generation output does not satisfy the power demand, You may control so that the electric power generation output of the battery 100 may be adjusted.

  When the distribution ratio to the bypass flow path is not the maximum (N in S208), the control unit 190 increases the distribution ratio to the bypass flow path by increasing the opening degree of the second outlet 163 by a predetermined amount, and the heat recovery water The flow rate of the heat recovery water is increased so that the temperature of the heat recovery water at the outlet 144 falls within a predetermined range (S209). When the distribution ratio to the bypass channel is maximum (Y in S208), the control unit 190 maintains the opening degree of the second outlet 163 and the power generation output of the fuel cell 100 as they are.

  As described above, in the fuel cell system 1 according to this embodiment, the heat recovery water circulation channel 150 includes the circulation return path for returning the heat recovery water that has passed through the heat exchanger 140 to the hot water storage tank 130, and the heat exchanger 140. The heat recovery water that has passed through is supplied to the heat exchanger 140 without passing through the hot water storage tank 130. Further, the control unit 190 controls the distribution ratio adjustment valve 160 so as to maintain the amount of condensed water recovered from the exhaust gas within a predetermined range based on the information regarding the amount of water in the tank 170 received from the water level sensor 180. ing. In addition, the control unit 190 controls the circulation pump 230 together with the control of the distribution ratio adjustment valve 160 to adjust the flow rate of the heat recovery water.

  Thus, the fuel cell system 1 raises the temperature of the heat recovery water supplied to the heat exchanger 140 when the remaining amount of condensed water in the tank 170 exceeds a predetermined upper limit value, thereby The amount of production is reduced. Further, when the remaining amount of condensed water in the tank 170 falls below a predetermined lower limit value, the fuel cell system 1 decreases the temperature of the heat recovery water supplied to the heat exchanger 140 and increases the amount of condensed water recovered. ing.

  Therefore, the fuel cell system 1 according to the present embodiment can maintain water independence. This eliminates the need to take in city water from the outside as reforming water, so that precipitation of calcium and silica contained in the city water can be avoided, and the load on the water treatment device such as ion exchange resin can be reduced. Can do. Moreover, since the excessive production | generation of condensed water can be avoided, the load concerning a water treatment apparatus can be reduced. As a result, the life of the fuel cell system 1 can be extended. In addition, since a structure necessary for discharging excessive condensed water can be omitted, the fuel cell system 1 can be downsized.

  Moreover, since the flow rate of the heat recovery water is increased in a state where there is a surplus in the remaining amount of condensed water, the generation of scale can be suppressed. Thereby, the lifetime of the fuel cell system 1 can be extended. In the fuel cell system 1 according to this embodiment, a bypass flow path is provided in the heat recovery water circulation path 150 to adjust the temperature of the heat recovery water supplied to the heat exchanger 140. Therefore, for example, when the operating environment temperature of the fuel cell system 1 is lowered, not by reducing the flow rate of the heat exchange water but by increasing the temperature of the heat recovery water supplied to the heat exchanger 140, The temperature of the heat recovery water at the outlet 144 can be raised to the target temperature. That is, even when the use environment temperature of the fuel cell system 1 changes, the flow rate of the heat exchange water flowing through the heat exchanger 140 can be ensured, so that the generation of scale can be suppressed.

(Embodiment 2)
The fuel cell system 1 according to Embodiment 2 detects the temperature of the exhaust gas as a state relating to the amount of water in the tank 170. Hereinafter, this embodiment will be described. The main configuration of the fuel cell system 1 according to the present embodiment is the same as that of the first embodiment. The same components as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted as appropriate.

  FIG. 4 is a flow diagram illustrating a schematic configuration of the fuel cell system according to the second embodiment. As shown in FIG. 4, the fuel cell system 1 according to the present embodiment has passed through the heat exchanger 140 instead of the water level sensor 180 of the first embodiment as a detection unit that detects a state relating to the amount of water in the tank 170. An exhaust gas temperature sensor 250 (detection unit) for detecting the temperature of the exhaust gas is provided. The exhaust gas temperature sensor 250 is provided, for example, in the exhaust gas passage 123 after heat exchange, and detects the temperature of the exhaust gas after heat exchange is performed by the heat exchanger 140. The exhaust gas temperature sensor 250 is connected to the control unit 190 via a signal cable, and transmits the detected exhaust gas temperature to the control unit 190 as a state signal.

  FIG. 5 is a diagram showing the relationship between the temperature of exhaust gas and the water balance. In FIG. 5, the vertical axis is the water balance (g), and the horizontal axis is the exhaust gas temperature (° C.). As shown in FIG. 5, the temperature of the exhaust gas detected by the exhaust gas temperature sensor 250 and the water balance, which is the difference between the amount of condensed water recovered and the amount of water used in the tank 170, have an inversely proportional relationship. That is, the water balance is determined according to the temperature of the exhaust gas. Specifically, for example, when the temperature of the exhaust gas is about 37 ° C., the water balance is 1.5 g / min, and when the temperature of the exhaust gas rises to about 45 ° C., the water balance becomes 0 g / min. When the temperature of the exhaust gas exceeds about 45 ° C., the water balance becomes a negative value, and the water level in the tank 170 decreases with time. The relationship between the exhaust gas temperature and the water balance is obtained by calculation based on the supply amount of raw fuel and reforming water to the reforming unit 110, the supply amount of oxidant air to the fuel cell 100, and the dew point thereof. Can do.

  The control unit 190 stores in advance a plurality of conversion tables in which the exhaust gas temperature detected by the exhaust gas temperature sensor 250 is associated with the water balance. The plurality of conversion tables are created by changing the supply amounts of raw fuel, reforming water, and air within a possible range based on experiments and simulations by the designer. As for the air dew point, a device for measuring the air dew point may be attached, and data based on the signal may be used, or a conversion table having a margin for the dew point may be created. The control unit 190 receives a temperature signal from the exhaust gas temperature sensor 250, and acquires a water balance from the temperature signal using a conversion table.

  Based on the state signal received from the exhaust gas temperature sensor 250, the control unit 190 controls the distribution ratio adjustment valve 160 so as to maintain the amount of condensed water recovered from the exhaust gas within a predetermined range. When the temperature of the exhaust gas is a temperature at which the water balance falls below a predetermined lower limit value, the control unit 190 assumes that the state relating to the amount of water in the tank 170 is to increase the amount of water, and determines the distribution ratio to the circulation return path. Increase and reduce the flow rate of heat recovery water. In addition, the control unit 190 determines that the state relating to the amount of water in the tank 170 is to reduce the amount of water when the temperature of the exhaust gas is a temperature at which the water balance exceeds a predetermined upper limit value. Increase distribution rate and increase heat recovery water flow rate.

  For example, the “predetermined lower limit value” is set to 0 g per minute, and the control unit 190 causes the circulation return path when the temperature of the exhaust gas exceeds 45 ° C., which is the temperature at which the water balance becomes 0 g per minute. Increase the distribution ratio to. When the temperature of the exhaust gas exceeds 45 ° C., that is, when the water balance falls below 0 g per minute, the amount of water in the tank 170 decreases, so the distribution ratio to the circulation return path is increased and the amount of condensed water recovered is increased. .

  Further, the “predetermined upper limit value” is set to, for example, 1.5 g / min, and the control unit 190 has the temperature of the exhaust gas lower than 37 ° C., which is the temperature when the water balance is 1.5 g / min. Sometimes the distribution rate to the bypass channel is increased. If the temperature of the exhaust gas is less than 37 ° C., that is, if the water balance exceeds 1.5 g per minute, the amount of condensed water recovered becomes excessive, so the distribution ratio to the bypass channel is increased to reduce the amount of condensed water recovered. Reduce. Note that the “predetermined lower limit value” and the “predetermined upper limit value” can be set as appropriate based on experiments and simulations by the designer.

  Hereinafter, the flow of operation control of the fuel cell system 1 will be described in detail. FIG. 6 is a flowchart of operation control of the fuel cell system according to the second embodiment. In the following description, the same points as in the first embodiment are omitted as appropriate.

  When the control flow starts, the control unit 190 determines whether the temperature of the exhaust gas is within a predetermined range (S301). The control unit 190 determines that the temperature of the exhaust gas is within the predetermined range when the temperature of the exhaust gas is equal to or lower than the predetermined upper limit value and equal to or higher than the predetermined lower limit value (when the exhaust gas temperature is within the range indicated by the oblique lines in FIG. 5). Here, the predetermined upper limit value of the exhaust gas temperature is a temperature (45 ° C. in FIG. 5) at which the water balance becomes a predetermined lower limit value (0 g per minute in FIG. 5), and when the exhaust gas temperature exceeds this upper limit value, The water balance is below the specified lower limit. Further, the predetermined lower limit value of the exhaust gas temperature is a temperature (37 ° C. in FIG. 5) at which the water balance becomes a predetermined upper limit value (1.5 g / min in FIG. 5), and the exhaust gas temperature falls below this lower limit value. The water balance exceeds the specified upper limit.

  When the temperature of the exhaust gas is within the predetermined range (Y in S301), the control unit 190 determines whether the power generation output of the fuel cell 100 is the maximum (S302). When the power generation output of the fuel cell 100 is not the maximum (N in S302), the control unit 190 increases the power generation output of the fuel cell 100 (S303) and returns to Step 301. When the power generation output of the fuel cell 100 is the maximum (Y in S302), the control unit 190 returns to step 301 without increasing the power generation output of the fuel cell 100.

  When the temperature of the exhaust gas is not within the predetermined range (N in S301), the control unit 190 determines whether the temperature of the exhaust gas exceeds a predetermined upper limit value (S304). When the temperature of the exhaust gas exceeds the predetermined upper limit value (Y in S304), the control unit 190 determines whether the distribution ratio of the heat recovery water to the circulation channel is the maximum (S305). When the distribution ratio to the circulation channel is not the maximum (N in S305), the control unit 190 increases the distribution ratio to the circulation return path by increasing the opening degree of the first outlet 162 by a predetermined amount, and the heat recovery water outlet The flow rate of the heat recovery water is reduced so that the temperature of the heat recovery water in 144 falls within a predetermined range (S306).

  When the distribution ratio to the circulation channel is the maximum (Y in S305), the control unit 190 determines whether the power generation output of the fuel cell 100 is the minimum (S307). When the power generation output of the fuel cell 100 is not minimum (N in S307), the control unit 190 reduces the power generation output of the fuel cell 100 (S308). When the power generation output of the fuel cell 100 is minimum (Y in S307), the control unit 190 maintains the opening degree of the first outlet 162 and the power generation output of the fuel cell 100 as they are.

  When the temperature of the exhaust gas does not exceed the predetermined upper limit (N in S304), the control unit 190 determines whether the power generation output of the fuel cell 100 is the maximum (S309). When the power generation output of the fuel cell 100 is not the maximum (N in S309), the control unit 190 increases the power generation output of the fuel cell 100 (S310). When the power generation output of the fuel cell 100 is maximum (Y in S309), the control unit 190 determines whether the distribution ratio of the heat recovery water to the bypass channel is maximum (S311).

  When the distribution ratio to the bypass flow path is not the maximum (N in S311), the control unit 190 increases the opening ratio of the second outlet 163 by a predetermined amount to increase the distribution ratio to the bypass flow path, and heat recovery water The flow rate of the heat recovery water is increased so that the temperature of the heat recovery water at the outlet 144 falls within a predetermined range (S312). When the distribution ratio to the bypass channel is the maximum (Y in S311), the control unit 190 maintains the opening degree of the second outlet 163 and the power generation output of the fuel cell 100 as they are.

  As described above, the fuel cell system 1 according to the present embodiment controls the distribution ratio adjusting valve 160 so as to maintain the recovered amount of condensed water within a predetermined range based on the temperature of the exhaust gas that is an indicator of the water balance. doing. Even by such control, the same effects as the fuel cell system 1 according to Embodiment 1 can be obtained.

(Embodiment 3)
The fuel cell system 1 according to Embodiment 3 detects the water pressure in the tank 170 as a state relating to the amount of water in the tank 170. Hereinafter, this embodiment will be described. The main configuration of the fuel cell system 1 according to the present embodiment is the same as that of the first embodiment. The same components as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted as appropriate.

  FIG. 7 is a flow chart showing a schematic configuration of the fuel cell system according to Embodiment 3. As shown in FIG. 7, the fuel cell system 1 according to the present embodiment detects the water pressure in the tank 170 instead of the water level sensor 180 of the first embodiment as a detection unit that detects a state relating to the amount of water in the tank 170. A water pressure sensor 260 (detection unit) is provided. The water pressure sensor 260 is connected to the control unit 190 via a signal cable, and transmits the detected water pressure to the control unit 190 as a state signal.

  Based on the state signal received from the water pressure sensor 260, the control unit 190 controls the distribution ratio adjustment valve 160 so as to maintain the amount of condensed water recovered from the exhaust gas within a predetermined range. When the water pressure falls below a predetermined lower limit, the control unit 190 assumes that the state relating to the amount of water in the tank 170 is to increase the amount of water and increases the distribution ratio to the circulation return path and the flow rate of the heat recovery water. Decrease. In addition, when the water pressure exceeds a predetermined upper limit value, the control unit 190 assumes that the state relating to the water amount in the tank 170 is a state in which the water amount should be reduced, and increases the distribution ratio to the bypass channel and heat recovery. Increase water flow rate.

  The “predetermined lower limit value” is detected, for example, by adding a margin to the minimum amount of condensed water that can maintain the supply of reformed gas to the reforming unit 110 and setting the amount of water higher than the minimum amount. Is the water pressure value to be applied. The “predetermined upper limit value” is, for example, a water pressure value detected by a water amount set lower than the accommodation limit amount by adding a margin to the accommodation limit amount of the tank 170. The “predetermined lower limit value” and the “predetermined upper limit value” can be appropriately set based on experiments and simulations by the designer.

  Hereinafter, the flow of operation control of the fuel cell system 1 will be described in detail. FIG. 8 is a flowchart of operation control of the fuel cell system according to Embodiment 3. In the following description, the same points as in the first embodiment are omitted as appropriate.

  When the control flow starts, the control unit 190 determines whether the water pressure is within a predetermined range (S401). The control unit 190 determines that the water pressure is within a predetermined range when the water pressure is equal to or lower than a predetermined upper limit value and equal to or higher than a predetermined lower limit value. When the water pressure is within the predetermined range (Y in S401), the control unit 190 determines whether the power generation output of the fuel cell 100 is maximum (S402). When the power generation output of the fuel cell 100 is not the maximum (N in S402), the control unit 190 increases the power generation output of the fuel cell 100 (S403) and returns to Step 301. When the power generation output of the fuel cell 100 is the maximum (Y in S402), the control unit 190 returns to step 301 without increasing the power generation output of the fuel cell 100.

  When the water pressure is not within the predetermined range (N in S401), the control unit 190 determines whether the water pressure is less than a predetermined lower limit (S404). When the water pressure is less than the predetermined lower limit (Y in S404), the control unit 190 determines whether the distribution ratio of the heat recovery water to the circulation flow path is the maximum (S405). When the distribution ratio to the circulation flow path is not the maximum (N in S405), the control unit 190 increases the distribution ratio to the circulation return path by increasing the opening degree of the first outlet 162 by a predetermined amount, and the heat recovery water outlet The flow rate of the heat recovery water is reduced so that the temperature of the heat recovery water at 144 falls within a predetermined range (S406).

  When the distribution ratio to the circulation channel is the maximum (Y in S405), the control unit 190 determines whether the power generation output of the fuel cell 100 is the minimum (S407). When the power generation output of the fuel cell 100 is not minimum (N in S407), the control unit 190 reduces the power generation output of the fuel cell 100 (S408). When the power generation output of the fuel cell 100 is minimum (Y in S407), the control unit 190 maintains the opening degree of the first outlet 162 and the power generation output of the fuel cell 100 as they are.

  When the water pressure is not less than the predetermined lower limit (N in S404), the control unit 190 determines whether the power generation output of the fuel cell 100 is maximum (S409). When the power generation output of the fuel cell 100 is not the maximum (N in S409), the control unit 190 increases the power generation output of the fuel cell 100 (S410). When the power generation output of the fuel cell 100 is the maximum (Y in S409), the control unit 190 determines whether the distribution ratio of the heat recovery water to the bypass flow path is the maximum (S411).

  When the distribution ratio to the bypass flow path is not the maximum (N in S411), the control unit 190 increases the distribution ratio to the bypass flow path by increasing the opening degree of the second outlet 163 by a predetermined amount, and the heat recovery water The flow rate of the heat recovery water is increased so that the temperature of the heat recovery water at the outlet 144 falls within a predetermined range (S412). When the distribution ratio to the bypass channel is the maximum (Y in S411), the control unit 190 maintains the opening degree of the second outlet 163 and the power generation output of the fuel cell 100 as they are.

  As described above, the fuel cell system 1 according to the present embodiment controls the distribution ratio adjusting valve 160 so as to maintain the recovered amount of condensed water within a predetermined range based on the water pressure in the tank 170. Even by such control, the same effects as the fuel cell system 1 according to Embodiment 1 can be obtained.

  The present invention is not limited to the above-described embodiments, and various modifications such as design changes can be added based on the knowledge of those skilled in the art, and the embodiments to which such modifications are added are also possible. It is included in the scope of the present invention. As modifications of each embodiment mentioned above, the following can be mentioned, for example.

  In each of the embodiments described above, an example has been described in which water self-sustainment and scale generation are suppressed by heat exchange between exhaust gas and heat recovery water in the power generation process of the fuel cell system. However, the fuel cell system is stopped. Also in the process, it is possible to maintain water independence and suppress scale generation by the same control. For example, in the stop process of the fuel cell system, combustion in the off-gas combustion unit and power generation of the fuel cell are stopped, and air is supplied to the power generation unit to cool the inside of the power generation unit. The air used for cooling in the power generation unit is sent from the power generation unit to the heat exchanger as high-temperature exhaust gas. And the control mentioned above is implemented with respect to this waste gas. In this case, since both the demand power and the generated power are 0 W, Y is always selected in the step of determining whether the generated power is maximum or minimum (for example, S102, S107, S111 in the flow shown in FIG. 2). Is done.

  DESCRIPTION OF SYMBOLS 1 Fuel cell system, 2 Power generation part, 100 Fuel cell, 110 Reforming part, 112 Off-gas combustion part, 120 Exhaust gas flow path, 130 Hot water storage tank, 140 Heat exchanger, 150 Heat recovery water circulation flow path, 160 Distribution ratio adjustment valve, 170 tank, 180 water level sensor, 190 control unit, 230 circulation pump, 240 temperature sensor, 250 exhaust gas temperature sensor, 260 water pressure sensor.

Claims (11)

A power generation unit having a fuel cell including an anode and a cathode;
An exhaust gas flow path through which exhaust gas discharged from the power generation unit flows;
A storage tank for storing a heat medium for recovering heat of the exhaust gas;
A heat exchanging section for exchanging heat between the exhaust gas flowing through the exhaust gas passage and the heat medium;
A circulation forward path for supplying the heat medium in the storage tank to the heat exchange section, a circulation return path for sending the heat medium that has passed through the heat exchange section to the storage tank, and a heat medium that has passed through the heat exchange section A heat medium circulation flow path having a bypass flow path that merges with the circulation forward path without passing through the storage tank;
A circulation device that circulates the heat medium in the heat medium circulation flow path and adjusts the flow rate of the heat medium;
A distribution ratio adjusting unit for adjusting a distribution ratio of the flow rate of the heat medium to the circulation return path and the bypass flow path;
A tank for storing condensed water recovered from the exhaust gas that has passed through the heat exchange section;
A detection unit for detecting a state relating to the amount of water in the tank and transmitting a state signal;
Based on the state signal, the distribution ratio adjusting unit is controlled to maintain the amount of condensed water recovered from the exhaust gas within a predetermined range, and the temperature of the heat medium subjected to heat exchange in the heat exchanging unit is determined. A control unit for controlling the circulation device to be within a predetermined range;
Equipped with a,
When the state is a state where the amount of water should be increased, the control unit increases a distribution ratio to the circulation return path and reduces a flow rate of the heat medium passing through the heat exchange unit. Fuel cell system. The power generation unit further includes a reforming unit and a combustion unit,
The reforming unit reforms raw fuel to generate reformed gas to be supplied to the fuel cell,
2. The fuel cell system according to claim 1, wherein the combustion unit mixes and combusts at least one of a fuel and an anode off gas with at least one of a combustion oxygen-containing gas and a cathode off gas, and heats the reforming unit. 2. The fuel cell system according to claim 1 , wherein the control unit reduces the power generation output of the fuel cell when a distribution ratio to the circulation return path is maximum. 3. If the state is a condition to reduce the water volume, the control unit, the fuel cell system according to any one of claims 1 to 3 increase the power output of the fuel cell. Wherein, when the power generation output of the fuel cell is at a maximum, according to claim 4 to increase the flow rate of the heat medium passing through the heat exchanging portion with increasing the distribution ratio to the bypass channel Fuel cell system. The detection unit detects a water level in the tank,
6. The control unit according to any one of claims 1 to 5 , wherein when the water level falls below a predetermined lower limit value, the control unit increases a distribution ratio to the circulation return path and reduces a flow rate of the heat medium passing through the heat exchange unit. The fuel cell system according to claim 1. The detection unit detects a water level in the tank,
When the water level exceeds a predetermined upper limit value, the control unit, of claims 1 to 6 to increase the flow rate of the heat medium passing through the heat exchanging portion with increasing the distribution ratio to the bypass channel The fuel cell system according to any one of claims. The detection unit detects the temperature of the exhaust gas,
The difference between the amount of condensed water recovered and the amount of water used in the tank is determined according to the temperature of the exhaust gas,
When the temperature of the exhaust gas is a temperature at which the difference is less than a predetermined lower limit value, the control unit increases the distribution ratio to the circulation return path and reduces the flow rate of the heat medium passing through the heat exchange unit. The fuel cell system according to any one of claims 1 to 7 . The detection unit detects the temperature of the exhaust gas,
The difference between the amount of condensed water recovered and the amount of water used in the tank is determined according to the temperature of the exhaust gas,
When the temperature of the exhaust gas is a temperature at which the difference exceeds a predetermined upper limit value, the control unit increases the distribution ratio to the bypass flow path and sets the flow rate of the heat medium passing through the heat exchange unit. the fuel cell system according to any one of claims 1 to 8 to increase. The detection unit detects water pressure in the tank,
10. The control unit according to any one of claims 1 to 9 , wherein when the water pressure falls below a predetermined lower limit, the control unit increases a distribution ratio to the circulation return path and reduces a flow rate of the heat medium passing through the heat exchange unit. The fuel cell system according to claim 1. The detection unit detects water pressure in the tank,
If the water pressure exceeds a predetermined upper limit value, the control unit, of claims 1 to 10 to increase the flow rate of the heat medium passing through the heat exchanging portion with increasing the distribution ratio to the bypass channel The fuel cell system according to any one of claims.

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