Fuel cell system and control method thereof

Abstract

To provide a fuel cell system that eliminates the need for supply means for reforming water from outside and waste water treatment on drain as well as water self-sustained operation.SOLUTION: A fuel cell system comprises: a hot module (4) which comprises a reforming part for generating reforming gas, a fuel cell using the reforming gas and air to generate electricity, and a combustion part, and discharges exhaust gas generated through the electricity generation and combustion; a heat exchange part (14) which is installed in an exhaust passage (12), and exchanges heat with the exhaust gas; an exhaust temperature sensor (20) which detects the temperature of the exhaust gas; a tank (reforming water tank 6) which collects and reserves condensed water from the exhaust gas through the heat exchange by the heat exchange part, and supplies it as reforming water to the hot module; a water level sensor (level sensor 24) which detects a predetermined water level in the tank; and a control part (22) which controls heat exchanging capability of the heat exchange part according to detection information from the water level sensor and exhaust temperature sensor so that the exhaust gas reaches a temperature equal to or higher than a dew-point temperature, or lower than the dew-point temperature depending upon the water level in the tank.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed herein relates to a control technology for a fuel cell system that performs so-called water-sustained operation, in which moisture contained in exhaust gases from power generation and combustion is recovered and used for power generation. [Background technology]

[0002] In recent years, fuel cell systems have been developed as a highly efficient means of generating electricity with a low environmental impact. These fuel cell systems supply a hydrogen-rich reformed gas, which is produced by reacting fuel gas with reforming water, to the fuel cell itself. In the fuel cell system, hydrogen and oxygen in the reformed gas undergo an electrochemical reaction to generate electricity, producing reaction product water. Furthermore, fuel cell systems utilize the heat of combustion of air and the remaining hydrogen in the exhaust gas that has passed through the fuel cell to generate reformed gas, which produces combustion product water. Furthermore, fuel cell systems perform so-called water self-sustaining control, in which the exhaust gas after combustion is condensed to recover the reaction product water and combustion product water contained in the water vapor state and use it as reforming water for the fuel gas.

[0003] In a fuel cell power generation system, cathode exhaust and burner exhaust are circulated and heat exchanged with a refrigerant flowing through an internal refrigerant flow path for exhaust heat recovery, thereby condensing the exhaust, and the condensed water is stored in a storage tank, or this condensed water is used as reforming water (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-218353 Summary of the Invention [Problem to be solved by the invention]

[0005] Fuel cell systems are used, for example, to generate part or all of the electricity used by individuals, apartment complexes, and other facilities, such as plants and facilities, or to connect to a commercial power grid as a backup power source in the event of a power outage. Installing a fuel cell system requires, for example, wiring to supply the generated power to power loads, as well as construction to connect the system to gas piping for fuel gas such as city gas or propane gas. Furthermore, if the condensed water generated by a fuel cell system is discharged without being used as reforming water, the system requires drainage equipment, including neutralization treatment, because the condensed water contains components of the fuel gas. This creates significant construction work when installed in existing buildings, and depending on the equipment, may be difficult to install. In particular, when using a cogeneration system that stores heat by exchanging heat with a heat transfer medium or water in the exhaust flow path of the fuel cell system and uses the stored heat to provide hot water, extensive construction is required. Furthermore, although a large amount of condensed water is constantly generated due to the high heat recovery efficiency, it is not possible to utilize all of the condensed water, so drainage equipment is required.

[0006] With regard to such a problem, the configuration disclosed in Patent Document 1 cannot solve the problem presented by the present disclosure.

[0007] The inventors of the present disclosure have discovered that by operating the heat exchange unit according to the water storage state in the tank and controlling the temperature of the exhaust gas, it is possible to condense and recover only the amount of water generated by power generation and combustion that is necessary for water self-sustaining.

[0008] Therefore, the technology disclosed herein aims to provide a fuel cell system that achieves water-independent operation by recovering condensed water from exhaust gas, and that controls the condensation process of exhaust gas based on the detected water level in the tank, thereby eliminating the need for an external reforming water supply means or wastewater treatment equipment such as a drain. [Means for solving the problem]

[0009] In order to achieve the above object, one aspect of a fuel cell system of the present disclosure includes a reforming unit that generates reformed gas from reforming water and fuel gas, a fuel cell that generates electricity using the reformed gas and air, and a combustion unit, and includes a hot module that discharges exhaust gas generated by power generation and combustion, a heat exchange unit that is installed in an exhaust flow path through which the exhaust gas flows and exchanges heat with the exhaust gas, an exhaust temperature sensor that detects the temperature of the exhaust gas, a tank that collects and stores water condensed from the exhaust gas by heat exchange in the heat exchange unit and supplies it to the hot module as reforming water, and a storage tank in the tank. The water level in the tank reaches the preset low and high reference values. a water level sensor for detecting the water level; When it is detected that the water level in the tank has fallen below the low reference value, the exhaust gas temperature sensor By The exhaust gas is at or above the dew point temperature When the water level sensor detects that the water level in the tank has reached the high reference value, the exhaust gas temperature sensor detects that the exhaust gas temperature has reached the high reference value. Below dew point temperature or stopping the heat exchange unit when and a control unit for controlling the heat exchange capacity of the heat exchange unit.

[0010] In the fuel cell system, the control unit but When the low reference value is reached, heat exchange is performed so that the temperature of the exhaust gas becomes less than the dew point temperature, and when the high reference value is reached, the heat exchange unit is controlled so that the temperature of the exhaust gas becomes equal to or higher than the dew point temperature. In the above fuel cell system, the heat exchange unit is equipped with a cooling fan that dissipates heat from the exhaust gas by blowing air into the exhaust flow path, and the control unit controls the rotation speed of the cooling fan based on at least the detected temperature of the exhaust gas after heat exchange. The fuel cell system further comprises a storage unit that stores at least the detection information of the water level sensor, the detection information of the exhaust gas temperature sensor, and control information for the heat exchange unit.

[0011] The above fuel cell system further includes an air volume sensor that measures the amount of air supplied to the hot module, a gas volume sensor that measures the amount of fuel gas supplied, and a pump that pressurizes water in the tank to the hot module, and the control unit sets the pumping capacity of the pump based on detection information from the air volume sensor and the gas volume sensor, and sets the dew point temperature of the exhaust gas to control the heat exchange capacity of the heat exchange unit. In the fuel cell system, the control unit sets a reference temperature that is higher than the dew point temperature of the exhaust gas by a predetermined temperature, and High standard value After this, the heat exchange unit is controlled so that the temperature of the exhaust gas becomes the reference temperature or a temperature close to this reference temperature.

[0012] In order to achieve the above object, one aspect of a control method for a fuel cell system of the present disclosure is a control method for a fuel cell system including a reforming unit that generates reformed gas from reforming water and fuel gas, a fuel cell that generates electricity using the reformed gas and air, and a hot module that includes a combustion unit and discharges exhaust gas generated by power generation and combustion, wherein the method detects the temperature of the exhaust gas with an exhaust temperature sensor, recovers condensed water from the exhaust gas through heat exchange in a heat exchange unit installed in an exhaust flow path through which the exhaust gas flows, stores the recovered water in a tank, and supplies it to the hot module as reforming water, The water level in the tank reaches the preset low and high reference values. is detected by a water level sensor, and the water level sensor When it is detected that the water level in the tank has fallen below the low reference value, the exhaust gas temperature sensor By The exhaust gas is at or above the dew point temperature When the water level sensor detects that the water level in the tank has reached the high reference value, the exhaust gas temperature sensor detects that the exhaust gas temperature has reached the high reference value. Below dew point temperature If detected, The control unit shutting down the heat exchange section, or The method includes controlling the heat exchange capacity of the heat exchange section.

[0013] In the control method for the fuel cell system ,before This includes processing to perform heat exchange so that the temperature of the exhaust gas is below the dew point temperature when the detection information of the water level sensor is the low reference value, and to control the heat exchange unit so that the temperature of the exhaust gas is above the dew point temperature when the detection information of the water level sensor reaches the high reference value. [Effects of the Invention]

[0014] According to the configuration of the present disclosure, the following effects can be obtained.

[0015] (1) The generated moisture can be released in gaseous form together with the exhaust gas, eliminating the need to install drainage equipment, thereby reducing the installation work load.

[0016] (2) Since drainage equipment is no longer required, the degree of freedom in the location of the fuel cell system relative to the facility is increased.

[0017] (3) Energy savings can be achieved by controlling the heat exchange capacity of the heat exchange unit to increase when it is necessary to replenish reforming water based on the water level in the tank.

[0018] (4) A stable power supply is possible by preventing fluctuations in the power generation capacity of the fuel cell due to the storage state of the reforming water in the tank. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a diagram showing an example of the configuration of a fuel cell system according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating a configuration example of a function of recovering condensed water and supplying reforming water. [Figure 3] FIG. 10 is a diagram showing a control process for a heat exchange function based on the water level in a reforming water tank and the exhaust temperature. [Figure 4] 4 is a flowchart showing a control process of the fuel cell system. [Figure 5] FIG. 10 is a diagram showing an example of the configuration of a fuel cell system according to a second embodiment. [Figure 6] FIG. 2 is a diagram illustrating an example of the configuration of a control unit. [Figure 7] 4 is a flowchart showing a control process of the fuel cell system. [Figure 8] FIG. 10 is a diagram showing a control process for a heat exchange function in a fuel cell system according to a third embodiment. [Figure 9] 4 is a flowchart showing a control process of the fuel cell system. DETAILED DESCRIPTION OF THE INVENTION

[0020] [First embodiment] Fig. 1 shows an example of the configuration of a fuel cell system according to Embodiment 1. The configuration shown in Fig. 1 is just an example, and the technology of the present disclosure is not limited to such a configuration. 1, this fuel cell system 2A includes a hot module 4, which is a unit that reforms fuel gas and performs power generation processing, a reforming water tank 6, a reforming water passage 8, a reforming water supply unit 10, an exhaust passage 12, a heat exchange unit 14, an exhaust unit 16, a condensed water recovery passage 18, an exhaust temperature sensor 20, a control unit 22, and a level sensor 24. In the fuel cell system 2A, water W is supplied from the reforming water tank 6 to the hot module 4 as reforming water for producing reformed gas from fuel gas FG, and exhaust gas EG containing water vapor generated by the power generation processing and residual gas combustion processing is discharged from the hot module 4, and water is recovered from the exhaust gas EG and stored in the reforming water tank 6, thereby performing a so-called water-independent power generation processing.

[0021] The hot module 4 is an example of a functional unit that has functions for reforming fuel gas FG and power generation, and includes, for example, a fuel cell stack 26, a fuel processing unit 28, and a combustion unit 30. The hot module 4 is connected to a gas supply unit and an air supply unit (not shown), and is supplied with fuel gas FG and air Air used for power generation. A reforming water flow path 8 is also connected to the hot module 4, and water W used for reforming is supplied from a reforming water tank 6.

[0022] The fuel cell stack 26 includes, for example, a solid oxide fuel cell (SOFC). A hydrogen-rich reformed gas is supplied to the fuel cell stack 26 from the fuel processing unit 28, and the hydrogen in the reformed gas is introduced into the anode side to convert hydrogen ions H + and electron e - In addition, heated air is introduced into the cathode side of the fuel cell stack 26, and hydrogen ions H + This combines with oxygen in the air to produce water H2O, and electrons e -The generated energy is transferred to the cathode side and extracted as generated energy. This generated energy is sent to a power conditioner 34, which is a type of inverter, via a power supply line 32 and is supplied to the power load side.

[0023] The fuel processing unit 28 is an example of a fuel reforming unit, and receives fuel gas FG and reforming water W, which are passed through a catalyst or the like at high temperature to generate a hydrogen (H2)-rich reformed gas. In generating the reformed gas, for example, by-products other than hydrogen (H2), such as carbon dioxide (CO2) and a small amount of carbon monoxide (CO), are separated from the fuel gas FG. The combustion unit 30 is an example of a fuel reforming means, and burns the post-power generation off-gas that flows in from the fuel cell stack 26 to supply heat to the fuel processing unit 28. The post-power generation off-gas contains unreacted hydrogen and oxygen, and by burning these, the heat required for reforming is obtained. In the combustion process, for example, HO produced by a chemical reaction in the power generation process, unreacted reforming water W in the reforming process, and water produced by combustion in the reaction of oxygen and hydrogen in the combustion process are discharged in a water vapor state into the exhaust flow path 12 together with the exhaust gas produced by combustion.

[0024] The reforming water tank 6 is an example of a means for recovering and storing water condensed from the exhaust gas EG in the heat exchanger 14 and supplying the stored water W to the hot module 4 as reforming water to be used for fuel reforming. A reforming water passage 8 is installed between the reforming water tank 6 and the hot module 4, for example, and a condensed water recovery passage 18 is connected to the heat exchanger 14. The reforming water passage 8 is provided with a reforming water supply unit 10 including, for example, a pump for pressure-feeding the water W to the hot module 4, making it possible to control the flow rate adjustment and supply timing of the water W required for the reforming process. The condensed water recovery passage 18 may also be provided with a water purifier 54 (FIG. 5) for removing impurities contained in the condensed water or neutralizing specific components. Furthermore, the reforming water tank 6 is provided with a level sensor 24 for detecting the water level of the stored water W. Water level information detected by this level sensor 24 is an example of control information used for the condensed water recovery process of the fuel cell system 2A.

[0025] The heat exchanger 14 is an example of a means for cooling the high-temperature exhaust gas EG flowing through the exhaust flow path 12 by heat exchange, and may be, for example, a means for dissipating heat by blowing cooling air generated by a cooling fan against a pipe line, or a means for absorbing heat from the exhaust gas EG by contacting the exhaust gas with a pipe line through which a refrigerant (not shown) flows. The heat exchanger 14 turns the cooling process on and off in response to instructions from the control unit 22, and is also capable of adjusting the cooling capacity. The exhaust gas EG that has passed through the heat exchange unit 14 is adjusted to a set temperature and released into the outside air through the exhaust unit 16. Furthermore, water W condensed from the exhaust gas EG flows into the reforming water tank 6 through a condensed water recovery passage 18. The exhaust unit 16 and the condensed water recovery passage 18 are formed by branching off from a pipe connected to the outlet side of the heat exchange unit 14. This branching portion is an example of a gas-liquid separation means, and for example, the condensed water recovery passage 18, through which the water W that has turned into a liquid state and is heavier than water vapor flows, may be arranged in the direction of gravity to fall downward, and warm, light exhaust gas EG may be flowed into the exhaust unit 16 that branches off horizontally or upward from the upper side of the condensed water recovery passage 18 at a position close to the branching portion.

[0026] The exhaust temperature sensor 20 is an example of a means for detecting the temperature of the exhaust gas EG after heat exchange in the heat exchanger 14, and is installed, for example, on the exhaust section 16. The exhaust temperature sensor 20 notifies the control section 22 of the detected temperature of the exhaust gas EG constantly or at predetermined intervals.

[0027] The control unit 22 is an example of a control means of the fuel cell system 2A. The control unit 22 is configured as a computer, and receives temperature information detected by the exhaust temperature sensor 20 and water level information in the reforming water tank 6 from the level sensor 24, and outputs instructions to control the heat exchange capacity of the heat exchange unit 14 based on this information. In addition, the control unit 22 controls the supply amounts of fuel gas FG, air Air, and water W from the reforming water tank 6, thereby performing a power generation function including a fuel gas reforming process.

[0028] <Condensed water recovery function> Fig. 2 is a diagram showing an example of the configuration of the condensed water recovery and reforming water supply functions. The configuration shown in Fig. 2 is one example. In Fig. 2, the same parts as in Fig. 1 are given the same reference numerals.

[0029] 2, water W condensed from exhaust gas in the heat exchanger 14 is supplied to the reforming water tank 6, and water W is consumed from the reforming water tank 6 by the hot module 4 as reforming water to be used in the power generation process. Therefore, the amount of water W stored in the reforming water tank 6 increases or decreases according to control instructions from the controller 22. More specifically, in the fuel cell system 2A, a power generation state is basically maintained except for processes such as monitoring for equipment abnormalities, and an amount of water W determined in accordance with power generation control in the fuel cell stack 26 is consumed from the reforming water tank 6. Therefore, in this fuel cell system 2A, if the heat exchange capacity of the heat exchanger 14 is increased so that the amount of condensation from exhaust gas exceeds the amount of water W required for power generation, the water level in the reforming water tank 6 can be raised, and if heat exchange in the heat exchanger 14 is stopped or reduced to a level where condensed water is not generated, the water level will be lowered.

[0030] The water level in the reforming water tank 6 is monitored by a level sensor 24. This level sensor 24 includes, for example, at least two different height sensor units 40-1, 40-2 installed in the reforming water tank 6. The sensor unit 40-1 is, for example, an example of a first reference water level and detects when the water level of the water W reaches a high position H. The sensor unit 40-2 is, for example, an example of a second reference water level and detects when the water level of the water W reaches a low position L. The water level at this low position L may be set to a water level that can store the minimum amount of water necessary to supply the reforming water required by the hot module 4, for example, at normal power generation output. Furthermore, the level sensor 24 is electrically connected to each of the sensor units 40-1, 40-2 and includes a detection circuit 42 that supplies power, detects resistance values, and monitors the water level. This level sensor 24 may be, for example, a sensor that uses each sensor unit 40-1, 40-2 as an electrode and monitors whether or not electricity is flowing due to contact with water W, or a PTC (Positive Temperature Coefficient) thermistor that generates Joule heat due to electrical resistance when electricity is passed through sensor units 40-1, 40-2 and determines whether or not the sensor is underwater from the difference in detected voltage values ​​based on the change in resistance value at that time, or a float-type sensor in which sensor units 40-1, 40-2 are formed as floats that float on the surface of water W and detect the water level by capturing vertical displacement.

[0031] <Regarding the timing of control over the heat exchange unit 14> Fig. 3 shows an example of control processing of the heat exchange function based on the water level and exhaust gas temperature in the reforming water tank 6. The processing contents shown in Fig. 3, as well as the timing of outputting instructions and the timing of indicating state changes, are examples.

[0032] When the control unit 22 acquires water level information in the reforming water tank 6 and detected temperature information from the exhaust temperature sensor 20 as part of the control processing of the fuel cell system 2A, it outputs instruction information to the heat exchange unit 14 based on this information, condensing moisture from the exhaust gas EG and increasing the water level in the reforming water tank 6. The control unit 22 operates the heat exchange unit 14, for example, at timing t1 when it determines that the water level has reached the low position L, which is the second reference water level, or has fallen below the second reference water level. As a result, the exhaust temperature Te of the exhaust gas EG begins to decrease. At timing t2 when the exhaust temperature Te of the exhaust gas EG drops to the dew point temperature X, the moisture in the exhaust gas EG condenses and water W begins to separate out, and flows into the reforming water tank 6. The control unit 22 controls the heat exchange unit 14 so that the exhaust temperature Te becomes the set temperature Y1. Then, for example, between timing t2 and timing t3 when the exhaust temperature Te becomes the set temperature Y1, the amount of condensed water deposited in the reforming water tank 6, i.e., the amount of water W flowing in as reforming water, becomes greater than the flow rate of the water W flowing out as reforming water. At this time, the heat exchange capacity of the heat exchange unit 14 is controlled so that the exhaust temperature Te becomes constant at the set temperature Y1, for example. Therefore, if the discharge amount of exhaust gas EG is constant, the flow rate of the water W flowing into the reforming water tank 6 can be stable or close to that.

[0033] At time t4, when the control unit 22 determines from the detection result of the level sensor 24 that the water level in the reforming water tank 6 has reached the high position H, which is the first reference water level, the control unit 22 outputs a control instruction to the heat exchange unit 14 to turn off heat exchange or to set the heat exchange capacity so that the exhaust temperature Te becomes greater than the dew-point temperature X. Then, in the heat exchange unit 14, condensation from the exhaust gas EG ceases at time t5, when the exhaust temperature Te exceeds the dew-point temperature X. As a result, almost all of the moisture generated by power generation, combustion processes, etc. is discharged in a gaseous state from the exhaust unit 16 together with the exhaust gas EG. Due to this control process, in this fuel cell system 2A, the period up to time t5 is the water recovery process period for water self-sustaining.

[0034] <Control process of fuel cell system 2A> Fig. 4 shows a control process of a fuel cell system. The control process shown in Fig. 4 is an example of a control method of the present disclosure. The process contents and process procedures shown here are an example, and the technology of the present disclosure is not limited to such contents.

[0035] This control process is realized by a control program executed by the control unit 22, for example. The control unit 22 performs initialization, for example, when the fuel cell system 2A starts operating or when the system is restarted after being stopped due to an abnormality determination or the like (S11). This initialization process includes preparation processes such as setting the power generation capacity of the fuel cell stack 26, checking the connection state with the power load side, checking the set supply amounts of fuel gas FG and air Air, and starting the operation of the reforming water supply unit 10. After the fuel cell system 2A starts operating, the control unit 22 determines whether power is being generated (S12), and if power is being generated (YES in S12), it moves on to monitoring the water level in the reforming water tank 6, and if power is not being generated (NO in S12), it goes into standby mode. When the control unit 22 determines, based on the monitoring result of the level sensor 24 of the reforming water tank 6, that the water level of the stored water W has reached the second reference value of the low reference L (YES in S13), the reforming water has been consumed and the process shifts to water supply processing, so it outputs a control instruction to the heat exchange unit 14 to precipitate water W by condensing the exhaust gas EG. This control instruction includes, for example, content to set the heat exchange capacity so that the exhaust temperature Te becomes a set temperature Y1 that is equal to or lower than the dew-point temperature X. Furthermore, if the water level in the reforming water tank 6 does not detect the second reference value (NO in S13), the control unit 22 returns to S12 and continues the monitoring process.

[0036] In this water supply process, the control unit 22 monitors the temperature detected by the exhaust gas temperature sensor 20 and determines whether the exhaust gas temperature Te is equal to or higher than the dew-point temperature X (S14). If the exhaust gas temperature Te is equal to or higher than the dew-point temperature X (YES in S14), the control unit 22 outputs an operation instruction to the heat exchange unit 14 (S15). This operation instruction includes instructions to start the heat exchange unit 14 or to increase the heat exchange capacity. If the exhaust gas temperature Te is lower than the dew-point temperature X (NO in S14) or if the control unit 22 has output an operation instruction to the heat exchange unit 14, the control unit 22 monitors whether the water level in the reforming water tank 6 has reached a high position H, which is a first reference value (S16). When the control unit 22 determines that the water level has reached the high position H based on the detection result of the level sensor 24 (YES in S16), it proceeds to a process of stopping the water supply process. On the other hand, when the water level in the reforming water tank 6 has not reached the high position H (NO in S16), the control unit 22 continues to instruct the heat exchange unit 14 to operate. The control unit 22 may monitor the detected temperature of the exhaust temperature sensor 20 until the detected water level reaches the high position H, and output an operation instruction to the heat exchange unit 14 so that the exhaust temperature Te becomes the set temperature Y1.

[0037] If the exhaust temperature Te is lower than the dew-point temperature X (YES in S17), the control unit 22 instructs the heat exchange unit 14 to stop heat exchange or to limit its operation (S18) as a process to stop the water supply process. If the control unit 22 has output a stop instruction to the heat exchange unit 14 or if the exhaust temperature Te is already equal to or higher than the dew-point temperature X (NO in S17), the control unit 22 returns to S12 as a process to monitor the power generation process again.

[0038] <Effects of the first embodiment> According to this configuration, one of the following effects can be obtained.

[0039] (1) By adjusting the heat exchange capacity of the heat exchange unit 14, only the amount of moisture generated by the power generation process and combustion process necessary for water self-sustaining is condensed and recovered, and the rest is discharged in a gaseous state, eliminating the need for wastewater treatment equipment and reducing the installation load of the fuel cell system 2A.

[0040] (2) Since no wastewater treatment equipment is required, the degree of freedom in selecting the installation location of the fuel cell system 2A is improved.

[0041] (3) By releasing the water, which is the drainage generated by chemical reactions and combustion reactions, into the atmosphere in a gaseous state rather than discharging it in a liquid state, the environmental impact on the walls of the facility where the fuel cell system 2A is installed and the surrounding soil can be reduced.

[0042] (4) By condensing the water contained in the exhaust gas EG and making it self-sustaining, there is no need to install a water supply means for reforming water.

[0043] (5) By not varying the power generation capacity of the fuel cell stack 26 or the supply amounts of fuel gas FG and air Air depending on the storage state of the water W in the reforming water tank 6, it is possible to supply power through a stable power generation reaction.

[0044] Second Embodiment Fig. 5 shows an example of the configuration of a fuel cell system according to the second embodiment. The configuration shown in Fig. 5 is an example, and the technology of the present disclosure is not limited to such a configuration. In Fig. 5, the same parts as those in Fig. 1 are denoted by the same reference numerals.

[0045] In this fuel cell system 2B, the configuration for achieving water self-sustaining, including heat exchange control of exhaust gas EG, the configuration of the fuel gas FG and air Air supply means, and the process for setting the dew point temperature X and set temperature Y1 in the heat exchange process are specified. As shown in Fig. 5, for example, the fuel cell system 2B is provided with a gas cooler 50 and a cooling fan 52 on the exhaust flow path 12 as the heat exchange unit 14, and a water purifier 54 on the condensed water recovery flow path 18. Furthermore, a reforming water pump 56 is provided on the reforming water flow path 8 as the reforming water supply unit 10.

[0046] The gas cooler 50 is an example of a device that exchanges heat between the high-temperature exhaust gas EG flowing through the exhaust flow path 12 and cold air or a refrigerant, and may be provided with heat dissipation fins or the like, for example, to increase the heat exchange efficiency by bending the exhaust flow path 12 internally. The cooling fan 52 is a blower that blows cooling air to the gas cooler 50, and may send cooling air directly to the exhaust flow path 12, or may supply cooling air to dissipate heat from the refrigerant that has exchanged heat with the exhaust gas EG. The cooling fan 52 is a means for increasing or decreasing the heat exchange capacity of the heat exchanger 14, and turns its rotation on or off or increases or decreases its rotation speed based on a control command from the control unit 22. The cooling fan 52 may be driven, for example, by using DC power generated in the hot module 4.

[0047] The reforming water pump 56 is an example of a means for pumping the water W in the reforming water tank 6 as reforming water to the hot module 4. The reforming water pump 56 controls the driving force based on an operation instruction from the control unit 22 based on, for example, set value information on the amount of power generation and information on the supply amount of fuel gas FG, and adjusts the supply amount of water W.

[0048] Additionally, the fuel cell system 2B is provided with, for example, a gas flow meter 60 and a gas supply unit 62 on the fuel gas FG supply pipe side, and an air flow meter 64 and an air supply unit 66 on the air Air supply pipe side. The gas flow meter 60 is a means for measuring the flow rate of gas flowing in from an external gas supply source, and notifies the control unit 22 of the measured value. The gas supply unit 62 is an example of a functional unit that adjusts the inflow of fuel gas FG flowing from the gas supply source into the fuel cell system 2B and removes impurities, and includes, for example, a gas solenoid valve, a source pressure sensor, a zero governor that adjusts the gas pressure, a desulfurizer that separates sulfur components in the fuel gas FG, and a gas pump. The air flow meter 64 is a means for measuring the flow rate of air taken in from outside and notifies the control unit 22 of the measured value. The air supply source may be, for example, atmospheric air, or air purified for industrial use or air containing many components necessary for power generation. The air supply unit 66 is an example of a means for taking in air from the outside and a functional unit for removing impurities, and includes, for example, an air filter and an air blower that allow air to pass through. The gas pump of the gas supply unit 62 and the air blower of the air supply unit 66 have their operating capabilities, such as rotation speed, set based on an operation instruction from the control unit 22, for example.

[0049] <Regarding the control unit 22> FIG. 6 shows an example of the configuration of the control unit. 6A, for example, the control unit 22 acquires detected temperature information from the exhaust temperature sensor 20 and water level information in the reforming water tank 6 from the level sensor 24, as well as information on the supply amount of fuel gas FG from the gas flow meter 60 and information on the supply amount of air Air from the air flow meter 64, in order to achieve water self-sufficiency and exhaust water through heat exchange processing of the exhaust gas EG. Based on this acquired measurement information, the control unit 22 then generates instruction information for the heat exchange capacity and outputs the instruction information to the cooling fan 52, and also generates flow rate information for the water W required for the reforming processing and outputs the instruction information to the reforming water pump 56.

[0050] When generating the instruction information for the heat exchange capacity, the dew-point temperature X of the exhaust gas EG may be calculated using information such as the component information of the supplied fuel gas FG, the air component information and its flow rate information, the components and amount of the reformed gas generated by reforming, the theoretical air ratio in power generation, and temperature information in the hot module 4 measured by a temperature sensor (not shown). Alternatively, the dew-point temperature X of the exhaust gas EG may be calculated by referring to a database stored in the memory unit 72 based on acquired measurement information or preset information. The control unit 22 then sets a set temperature Y1 as instruction information for the cooling fan 52 at the calculated or calculated dew-point temperature X so that the water W condenses at a flow rate greater than the flow rate of the reforming water supplied. In this heat exchange process, the flow rate of the condensed water W can be set, for example, depending on the temperature difference from the dew-point temperature X. In addition, the control unit 22 performs control processes such as setting information for the amount of power generation in the fuel cell system 2B (not shown) and controlling the supply of fuel gas FG and air Air.

[0051] 6B, the control unit 22 is configured by a computer, and is composed of a processor 70, a storage unit 72, and a display unit 74. The storage unit 72 also includes a memory 76 and a RAM (Random-Access Memory) 78. The processor 70 executes and processes various programs, such as an OS (Operating System) (not shown) and a fuel cell control program, stored in the memory 76 in the storage unit 72, and performs power generation control of the fuel cell system 2B, supply control of fuel required for power generation, and heat exchange process control required for water self-sustaining and exhaust treatment. The storage unit 72 is an example of a storage area that stores programs and operation information for operating the fuel cell system 2B. A memory 76 that constitutes the storage unit 72 stores various programs, as well as measurement information acquired from the exhaust gas temperature sensor 20, the level sensor 24, the gas flow meter 60, and the air flow meter 64, instruction information output from the control unit 22 to the components of the cooling fan 52, the reforming water pump 56, the gas supply unit 62, and the air supply unit 66, and a control log including the date and time when the measurement information was acquired and the date and time when the instruction information was output. The RAM 78 that constitutes the storage unit 72 functions as a calculation processing area for the OS and the fuel cell control program. The display unit 74 may display, for example, the power generation status, information on the water level in the reforming water tank 6, control instruction information for the cooling fan 52, etc., according to control instructions from the processor 70.

[0052] <Control process of fuel cell system 2B> Fig. 7 shows a control process for a fuel cell system. The control process shown in Fig. 7 is an example of a control method according to the present disclosure. The process contents and procedures shown here are merely examples, and the technology of the present disclosure is not limited to such contents.

[0053] This control process is realized by a control program executed by the control unit 22, for example. For example, after initializing the fuel cell system 2B (S21), the control unit 22 proceeds to a monitoring process (S22) to determine whether power generation is in progress, and if power generation is in progress (YES in S22), the control unit 22 detects the supply amounts of fuel gas FG and air Air used in the power generation process of the fuel cell (S23).Then, the control unit 22 checks the supply amount of water W required for the reforming process based on, for example, the supply amounts of fuel gas FG and air Air and other information (S24). Then, the control unit 22 sets the dew-point temperature X of the exhaust gas EG from the power generation setting information including the detected supply amounts of fuel gas FG and air Air, and information on the supply amount of reforming water (S25). Furthermore, if power generation is not in progress (NO in S21), the control unit 22 goes into a standby state.

[0054] The control unit 22 monitors the level in the reforming water tank 6 to achieve water self-sufficiency through the heat exchange process of the exhaust gas EG and to discharge water generated by power generation and combustion (S26). In this level monitoring, based on the monitoring results of the level sensor 24 in the reforming water tank 6, it determines whether the water level of the stored water W has reached a second reference value of the low position L. The control unit 22 determines whether water needs to be supplied to the reforming water tank 6 based on this water level determination (S27). Then, when the control unit 22 determines that water needs to be supplied to the reforming water tank 6 because the water level has reached the second reference value of the low position L (YES in S27), it controls the rotation speed of the cooling fan 52 (S28) to cool the exhaust gas EG in the gas cooler 50 and condense the water W, which is then collected in the reforming water tank 6. This rotation speed control includes, for example, setting the rotation speed of the cooling fan 52 so that the exhaust temperature Te becomes a set temperature Y1 that is equal to or lower than the dew-point temperature X. When the control unit 22 determines that it is not necessary to supply water to the reforming water tank 6 because the water level has not reached the second reference value of the low position L (NO in S27), it continues to monitor the level in the reforming water tank 6 (S26).

[0055] The control unit 22 monitors the detected temperature of the exhaust temperature sensor 20, and if the exhaust temperature Te is the set temperature Y1 (YES in S29), determines whether the water level in the reforming water tank 6 has reached the high position H, which is the first reference value (S30). If the exhaust temperature Te is not the set temperature Y1 (NO in S29), the control unit 22 returns to S28 and increases or decreases the rotation speed of the cooling fan 52.

[0056] When the water level in the reforming water tank 6 reaches a first reference value (YES in S30), the control unit 22 controls the rotation speed of the cooling fan 52 so as to stop the cooling fan 52 or reduce its cooling capacity (S31). The control unit 22 continues to monitor the water level in the reforming water tank 6 and control the rotation speed of the cooling fan 52 until the water level in the reforming water tank 6 reaches the first reference value (NO in S30). Then, the control unit 22 records the detection information acquired from the various sensors and the control information output to each functional unit in the storage unit 72 (S32).

[0057] <Effects of the second embodiment> According to this configuration, the following effects can be obtained.

[0058] (1) The same effects as those of the first embodiment can be obtained. (2) The dew point temperature X of the exhaust gas EG is calculated based on the amount of fuel gas FG and air supplied, power generation control information, etc., and is used in the heat exchange process. This enables condensation processing to be performed according to the amount of reforming water consumed, and prevents shortages of reforming water, etc. (3) Based on the power generation information and supply information such as fuel gas FG, the water supply flow rate of the water W according to the consumption status of the required reforming water can be determined. Therefore, by precisely controlling the rotation speed of the cooling fan 52 and the like and not increasing or decreasing it excessively, deterioration of the equipment and unnecessary energy consumption can be avoided.

[0059] Third Embodiment Fig. 8 shows the control processing state of the heat exchange function according to the third embodiment. The processing contents, timing, temperature and water level states shown in Fig. 8 are examples.

[0060] In this fuel cell system 2, as shown in FIG. 8, a set temperature Y2 that is a predetermined temperature higher than the dew-point temperature X is set as control information for the exhaust gas temperature Te. This set temperature Y2 is a threshold value for adjusting the temperature of the exhaust gas EG at times other than the timing of water recovery for water self-sustaining. For example, the control unit 22 outputs control instructions to the cooling fan 52 of the heat exchanger 14 and the like to control the exhaust gas temperature Te to the set temperature Y2, for example, during the period from the start of power generation processing by the fuel cell or an arbitrarily set time t0 to the time t1 when the water level in the reforming water tank 6 detects a second reference value. The control unit 22 may also perform exhaust gas temperature control after time t5 when the water recovery processing is completed.

[0061] <Control process of fuel cell system 2> Fig. 9 shows a control process for a fuel cell system. The control process shown in Fig. 9 is an example of a control method according to the present disclosure. The process contents and procedures shown here are merely examples, and the technology of the present disclosure is not limited to such contents.

[0062] After the fuel cell system 2 starts operating, the control unit 22 determines whether power is being generated (S41), and if power is being generated (YES in S41), it moves on to monitoring the water level in the reforming water tank 6, and if power is not being generated (NO in S41), it goes into standby mode. When the control unit 22 determines, based on the monitoring results of the level sensor 24 of the reforming water tank 6, that the water level of the stored water W has reached the second reference value of the low position L (YES in S42), it proceeds to a water recovery process (S46 to S50) in which water is condensed through heat exchange with the exhaust gas EG by the heat exchange unit 14. This water recovery process (S46 to S50) may, for example, be similar to S14 to S18 (FIG. 4) shown in the first embodiment, or, as shown in the second embodiment, may be performed to calculate the dew-point temperature X of the exhaust gas EG based on the supply amounts of fuel gas FG and air Air, power generation control information, and the like, and control the heat exchange capacity of the heat exchange unit 14 (S26 to S32), and the description thereof will be omitted.

[0063] When the control unit 22 determines that the water level in the reforming water tank 6 has not reached the second reference value (NO in S42), that is, when a sufficient amount of water W is stored in the reforming water tank 6, the control unit 22 proceeds to exhaust temperature control of the exhaust gas EG. In this exhaust temperature control, the control unit 22 acquires the exhaust temperature Te detected by the exhaust temperature sensor 20 (S43) and determines whether this exhaust temperature Te is at a set temperature Y2 (S44). This set temperature Y2 may be set as a predetermined temperature, for example, +10°C, relative to a dew-point temperature X that is set in advance or calculated or determined from power generation setting information, etc. Note that this set temperature Y2 may be changed, for example, depending on the outside air temperature at the installation location of the fuel cell system 2. In other words, this set temperature Y2 is preferably a temperature that is close to the dew-point temperature X and that does not easily condense the exhaust gas EG when it is released to the outside.

[0064] If the exhaust temperature Te is equal to the set temperature Y2 (YES in S44), the control unit 22 returns to the power generation state monitoring process, and if the exhaust temperature Te is not equal to the set temperature Y2 (NO in S44), it outputs a control instruction to the heat exchange unit 14 (S45).

[0065] In this exhaust temperature control, the control unit 22 may, for example, increase the timing for monitoring the temperature detected by the exhaust temperature sensor 20, i.e., set the monitoring frequency to be lower. This reduces the number of times the heat exchange unit 14 is controlled, thereby preventing the exhaust temperature Te of the exhaust gas EG from repeatedly increasing and decreasing around the set temperature Y2, a so-called chattering state. In addition, the control unit 22 may provide hysteresis in the temperature control of the exhaust temperature Te by changing the output conditions and timing of control instructions to the heat exchange unit 14 depending on whether the exhaust temperature Te is increasing or decreasing relative to the set temperature Y2 due to the heat exchange capacity of the heat exchange unit 14.

[0066] <Advantages of the third embodiment> According to this configuration, the following effects can be obtained. (1) The same effects as those of the first and second embodiments can be obtained. (2) When water recovery processing for water independence is not being performed, the heat exchange section 14 is operated and the temperature of the exhaust gas EG is controlled to the set temperature Y2, so that the exhaust gas EG at a lower temperature can be discharged from the exhaust section 16, thereby improving safety. (3) Since the exhaust gas EG can be discharged at a low temperature, the degree of freedom in the installation position of the fuel cell system 2 and the position of the exhaust unit 16 relative to the building, etc., is increased. (4) By controlling the exhaust gas temperature Te to a temperature that is lower than the temperature immediately after the exhaust gas is discharged from the hot module 4 and close to the dew point temperature X, the temperature change when the process shifts to water recovery is reduced, and the responsiveness to condensing water from the exhaust gas EG is improved. This improved responsiveness can also contribute to, for example, downsizing the reforming water tank 6.

[0067] Other Embodiments Modifications of the above-described embodiment are listed below.

[0068] (1) In the above embodiment, the exhaust temperature sensor 20 installed in the exhaust section 16 detects only the temperature of the exhaust gas EG, which has been cooled after heat exchange. However, this is not limited to this. The high-temperature exhaust gas temperature Te immediately after being discharged from the hot module 4 and immediately before flowing into the heat exchange section 14 may also be measured, and the heat exchange capacity of the heat exchange section 14 may be controlled based on the exhaust gas temperature Te. Furthermore, the heat exchange section 14 may be controlled using information on the difference between the exhaust gas temperature Te before and after the heat exchange.

[0069] (2) In the above embodiment, the level sensor 24 that monitors whether the water surface has reached a set height is used as the means for monitoring the water level of the water W stored in the reforming water tank 6, but this is not limited to this. The means for detecting the water level may be, for example, a sensor that measures the amount of water stored in the reforming water tank 6 or a water level sensor that can constantly measure the water surface position. Such water level detection is not limited to, for example, a level sensor that performs measurement and analysis processing for the purpose of measuring the water level itself, but may also be a weight sensor that measures the weight of the reforming water tank 6, calculates the amount of stored water W from the measured weight, and determines the water level.

[0070] Furthermore, in this fuel cell system 2, by constantly monitoring the water level in the reforming water tank 6 using a weight sensor or the like, it is possible to monitor changes in the amount of water, such as the tendency of the stored water W to be consumed and the tendency of the water W to increase during the water recovery process. By monitoring such changes in the amount of water, the control unit 22 may determine that the heat exchange capacity is insufficient when the amount of water in the reforming water tank 6 is decreasing during the water recovery process, for example, and output a control instruction to the heat exchange unit 14. The control unit 22 may also perform processing to predict the timing to transition to the water recovery process based on the tendency of the water in the reforming water tank 6 to decrease.

[0071] (3) In the above embodiment, the set temperature Y1 of the exhaust temperature Te for performing the water recovery process is set in advance, but this is not limited to this. For example, the control unit 22 may set the set temperature Y1 by comparing the flow rate of the water W required for the reforming process with the amount of water W that precipitates by condensation based on the dew-point temperature X. More specifically, the control unit 22 may control the heat exchange unit 14 so that the flow rate of water flowing through the condensed water recovery passage 18 is greater than the flow rate supplied to the hot module 4 side. The flow rate of water W compared here may be, for example, the instantaneous flow rate, or the power generation process may be divided into predetermined periods and the flow rate of water W supplied to the hot module 4 during those periods may be compared with the flow rate of water W recovered in the heat exchange section 14.

[0072] (4) The fuel cell systems 2, 2A, and 2B shown in the above embodiments may be provided with a water replenishment means for replenishing the water W from the outside to the reforming water tank 6. This water replenishment means is configured to be able to supply tap water or water W purified by equipment (not shown), for example, and may supply the necessary reforming water to the fuel cell systems 2, 2A, and 2B in cases where sufficient water W cannot be condensed from the exhaust gas EG in the heat exchanger 14.

[0073] As explained above, the most preferred embodiment of the technology of the present disclosure has been described. The technology of the present disclosure is not limited to the above description. Various modifications and changes are possible for those skilled in the art based on the gist of the claims or disclosed in the description for carrying out the invention. It goes without saying that such modifications and changes are included in the scope of the technology of the present disclosure. [Industrial Applicability]

[0074] According to the configuration of the present disclosure, the heat exchange unit is controlled so that the amount of water required for water self-sustaining is condensed and recovered from the exhaust gas depending on the water level in the reforming water tank, and at other times the water is discharged to the outside in a water vapor state. This makes it possible to introduce a fuel cell system into an existing building, etc., without using a water supply means or wastewater treatment means, and is useful because low-temperature exhaust increases safety. [Explanation of symbols]

[0075] 2, 2A, 2B fuel cell systems 4 Hot Module 6. Reformed water tank 8. Reformed water flow path 10. Reformed Water Supply Section 12 Exhaust flow path 14 Heat exchange section 16 Exhaust section 18 Condensate recovery channel 20 Exhaust gas temperature sensor 22 Control Unit 24 Level Sensor 26 Fuel Cell Stack 28 Fuel Processing Section 30 Combustion section 40-1, 40-2 Sensor section 42 Detection circuit 50 Gas Cooler 52 Cooling fan 54 Water Purifier 56 Reformed water pump 60 Gas flow meter 62 Gas supply section 64 Air flow meter 66 Air supply section 70 processors 72 Memory section 74 Display section 76 memory 78 RAM

Claims

1. a hot module including a reforming unit that generates reformed gas from reforming water and fuel gas, a fuel cell that generates electricity using the reformed gas and air, and a combustion unit that discharges exhaust gas generated by power generation and combustion; a heat exchanger that is installed in an exhaust flow path through which the exhaust gas flows and that exchanges heat with the exhaust gas; an exhaust gas temperature sensor that detects the temperature of the exhaust gas; a tank that collects and stores water condensed from the exhaust gas by heat exchange in the heat exchange unit and supplies the water as reforming water to the hot module; a water level sensor that detects when the water level in the tank reaches a low reference value and a high reference value that are preset in the tank; a control unit that operates the heat exchange unit when the water level sensor detects that the water level in the tank has fallen below the low reference value and when the exhaust gas temperature sensor detects that the exhaust gas is at or above a dew point temperature, and that stops the heat exchange unit or controls the heat exchange capacity of the heat exchange unit when the water level sensor detects that the water level in the tank has reached the high reference value and the exhaust gas temperature sensor detects that the exhaust gas is below the dew point temperature; A fuel cell system comprising:

2. The fuel cell system of claim 1, characterized in that the control unit controls the heat exchange unit so that the temperature of the exhaust gas is below the dew point temperature when the water level sensor indicates the low reference value, and controls the heat exchange unit so that the temperature of the exhaust gas is above the dew point temperature when the water level sensor indicates the high reference value.

3. the heat exchanger includes a cooling fan that sends air to the exhaust flow path to dissipate heat from the exhaust gas, 3. The fuel cell system according to claim 1, wherein the control unit controls the rotation speed of the cooling fan based on at least the detected temperature of the exhaust gas after heat exchange.

4. 4. The fuel cell system according to claim 1, further comprising a storage unit for storing at least the detection information of the water level sensor, the detection information of the exhaust gas temperature sensor, and control information for the heat exchanger.

5. an air flow sensor that measures the amount of air supplied to the hot module; a gas amount sensor that measures the amount of fuel gas supplied; a pump that pumps the water in the tank to the hot module; Equipped with 5. The fuel cell system according to claim 1, wherein the control unit sets the pumping capacity of the pump based on detection information from the air amount sensor and the gas amount sensor, and sets a dew point temperature of the exhaust gas to control the heat exchange capacity of the heat exchange unit.

6. 6. A fuel cell system as described in any one of claims 1 to 5, characterized in that the control unit sets a reference temperature that is a predetermined temperature higher than the dew point temperature of the exhaust gas, and controls the heat exchange unit so that the temperature of the exhaust gas becomes the reference temperature or a temperature close to it after the water level in the tank reaches the high reference value.

7. A control method for a fuel cell system including a hot module that includes a reforming unit that generates reformed gas from reforming water and fuel gas, a fuel cell that generates electricity using the reformed gas and air, and a combustion unit that discharges exhaust gas generated by power generation and combustion, the method comprising: The temperature of the exhaust gas is detected by an exhaust gas temperature sensor; water condensed from the exhaust gas by heat exchange in a heat exchange unit installed in an exhaust flow path through which the exhaust gas flows is collected and stored in a tank, and the collected water is supplied to the hot module as reforming water; A water level sensor detects that the water level in the tank has reached a low reference value and a high reference value preset in the tank; When the water level sensor detects that the water level in the tank has fallen below the low reference value, and when the exhaust gas temperature sensor detects that the exhaust gas is at or above the dew point temperature, the heat exchange unit is operated, and when the water level sensor detects that the water level in the tank has reached the high reference value and the exhaust gas temperature sensor detects that the exhaust gas is below the dew point temperature, the control unit stops the heat exchange unit or controls the heat exchange capacity of the heat exchange unit.

2. A method for controlling a fuel cell system, comprising:

8. When the detection information of the water level sensor is the low reference value, heat exchange is performed so that the temperature of the exhaust gas is below the dew point temperature, When the detection information of the water level sensor reaches the high reference value, the heat exchanger is controlled so that the temperature of the exhaust gas becomes equal to or higher than a dew point temperature.

8. The method for controlling a fuel cell system according to claim 7, further comprising the steps of:

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