Combined heat and power system

Abstract

According to the present invention, a cogeneration system has a fuel cell, a fuel cell system, and an indirect supply line. The fuel cell system is positioned inside the fuel cell or near the fuel cell outside the fuel cell and has a first heat exchange unit that makes a heat medium recover heat generated by the fuel cell, a heat storage tank, and a waste heat recovery line. The heat storage tank stores the heat medium and provides heat in accordance with demand for hot water supply. The waste heat recovery line makes the heat medium circulate between the fuel cell and the heat storage tank. The indirect supply line includes a second heat exchange unit that performs a heat exchange between a medium and the heat medium stored at the heat storage tank and thereby supplies heat.

Description

[Technical Field]

[0001] The present disclosure relates to combined heat and power systems. [Background technology]

[0002] BACKGROUND ART A domestic cogeneration system is known that generates electricity using a fuel cell, recovers heat emitted from the fuel cell, and uses the recovered heat to heat and supply city water (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-298863 Summary of the Invention [Problem to be solved by the invention]

[0004] In cogeneration systems using fuel cells, it has been difficult to provide the required amount of heat to the hot water supplied using only the recovered heat.

[0005] Therefore, an object of the present disclosure, which has been made in consideration of the above-mentioned problems of the conventional technology, is to provide a cogeneration system capable of providing required heat to a large amount of medium. [Means for solving the problem]

[0006] In one embodiment, (1) a combined heat and power system includes a fuel cell system having a fuel cell, a first heat exchange unit located adjacent to the outside of or inside the fuel cell and using a heat transfer medium to recover heat generated by the fuel cell, a heat storage tank that stores the heat transfer medium and provides heat in response to hot water supply demands, and a waste heat recovery line that circulates the heat transfer medium between the fuel cell and the heat storage tank, and an indirect supply line including a second heat exchange unit that supplies heat by heat exchanging the heat transfer medium stored in the heat storage tank with a medium.

[0007] (2) In the cogeneration system described in (1) above, the fuel cell system has a third heat exchange section that exchanges heat between the exhaust gas of the fuel cell and the heat medium circulating through the waste heat recovery line.

[0008] (3) In the cogeneration system described in (2) above, the third heat exchange unit is located upstream of the first heat exchange unit in the waste heat recovery line.

[0009] (4) In the cogeneration system according to (2) or (3) above, the fuel cell system has a heat dissipation section in the waste heat recovery line between the heat storage tank and the third heat exchange section.

[0010] (5) In the combined heat and power supply system described in any one of (2) to (4) above, the fuel cell system has a temperature control unit located in the waste heat recovery line between the first heat exchange unit and the third heat exchange unit and capable of heating or cooling the heat medium circulating in the waste heat recovery line.

[0011] (6) In the cogeneration system described in (5) above, the temperature adjustment unit includes a burner.

[0012] (7) In the combined heat and power supply system described in (5) or (6) above, the waste heat recovery line includes a first flow path downstream of the third heat exchange unit that bypasses the temperature adjustment unit and connects to the first heat exchange unit.

[0013] (8) In the combined heat and power supply system described in any one of (2) to (7) above, the waste heat recovery line includes, downstream of the heat storage tank, a second flow path that bypasses the third heat exchange unit and connects to the first heat exchange unit, and a third flow path that branches off from the second flow path and connects to the third heat exchange unit.

[0014] (9) The cogeneration system according to any one of (1) to (8) above includes a direct supply line that supplies heat by flowing a heat medium stored in the heat storage tank.

[0015] (10) The heat and power cogeneration system described in any one of (2) to (9) above includes a control device, wherein the waste heat recovery line includes a heat medium outlet line for discharging the heat medium from the heat storage tank, an exhaust gas heat exchange line having the third heat exchange section, a heat medium cooling line for cooling the heat medium, a heat medium heating line for heating the heat medium, and a heat medium inlet line capable of recovering heat generated in the fuel cell to the heat medium and for causing the heat medium to flow into the heat storage tank, wherein the heat medium outlet line and the heat medium inlet line are capable of switching the passage of the heat medium to any one of the exhaust gas heat exchange line, the heat medium cooling line, and the heat medium heating line, or are capable of switching the order of passage of the heat medium to at least two or more of the exhaust gas heat exchange line, the heat medium cooling line, and the heat medium heating line, and the control device switches the passage path of the heat medium in the waste heat recovery line depending on the operating state of the fuel cell and whether or not there is a request for hot water supply.

[0016] (11) In the combined heat and power supply system described in (10) above, the exhaust gas heat exchange line includes a third heat exchange section that exchanges heat between the exhaust gas of the fuel cell and the heat medium, and the combined heat and power supply system further includes a condensed water tank that stores condensed water generated in the third heat exchange section.

[0017] (12) In the combined heat and power supply system described in (10) or (11) above, when the fuel cell is in operation, the control device switches the path through which the heat medium passes in the waste heat recovery line depending on the relationship between the temperature of the lower part of the heat storage tank and a temperature threshold, and the first temperature threshold, which is the temperature threshold when there is no hot water supply request, is lower than the second temperature threshold, which is the temperature threshold when there is a hot water supply request.

[0018] (13) In the cogeneration system described in (12) above, when there is no hot water supply request and the temperature of the lower part of the heat storage tank is equal to or lower than the first temperature threshold, the control device switches the waste heat recovery line so that the heat medium passes only through the exhaust gas heat exchange line.

[0019] (14) In the combined heat and power supply system described in (12) above, when there is no request for hot water supply and the temperature at the bottom of the heat storage tank is higher than the first temperature threshold, the control device switches the waste heat recovery line so that the heat medium passes through the heat medium cooling line and the exhaust gas heat exchange line in that order.

[0020] (15) In the combined heat and power supply system described in any one of (10) to (14) above, when the fuel cell is in operation and there is a request for hot water supply, the control device switches the path through which the heat medium passes in the waste heat recovery line based on the inflow heat quantity, which is the heat quantity of the heat medium flowing into the heat storage tank, and the provided heat quantity, which is the heat quantity provided by the heat storage tank in response to the hot water supply request.

[0021] (16) In the combined heat and power supply system described in (15) above, when the temperature of the lower part of the heat storage tank is equal to or lower than a third temperature threshold and the amount of incoming heat is smaller than the amount of provided heat, the control device switches the waste heat recovery line so that the heat medium passes through the heat medium heating line.

[0022] (17) In the combined heat and power supply system described in (15) above, the control device switches the waste heat recovery line so that the heat medium passes only through the exhaust gas heat exchange line when the temperature of the lower part of the heat storage tank is below a fourth temperature threshold and the amount of inflow heat is greater than the amount of provided heat, or when the temperature of the lower part of the heat storage tank is higher than the fourth temperature threshold and the amount of inflow heat is less than the amount of provided heat.

[0023] (18) The combined heat and power supply system described in (17) above further includes a condensed water tank for storing condensed water generated in the third heat exchange section, and when the temperature of the lower part of the heat storage tank is higher than a fifth temperature threshold and the amount of incoming heat is greater than the amount of provided heat, the control device changes the order in which the heat medium passes through the exhaust gas heat exchange line and the heat medium cooling line in the waste heat recovery line depending on the amount of water in the condensed water tank.

[0024] (19) In the combined heat and power supply system described in (18) above, when the amount of water in the condensate tank is greater than a first water amount threshold, the control device switches the circulation line so that the heat transfer medium passes through the exhaust gas heat exchange line and then the heat transfer medium cooling line.

[0025] (20) In the combined heat and power supply system described in (18) above, when the water volume in the condensate tank is equal to or less than a second water volume threshold, the control device switches the circulation line so that the heat transfer medium passes through the heat transfer medium cooling line and then the exhaust gas heat exchange line.

[0026] (21) In the combined heat and power supply system described in any one of (18) to (20) above, the control device reduces the power generation amount of the fuel cell when the temperature of the heat medium inlet in the third heat exchanger is equal to or higher than a sixth temperature threshold and the amount of water in the condensed water tank is equal to or lower than a third water amount threshold.

[0027] (22) In the combined heat and power supply system described in any one of (10) to (21) above, when the fuel cell is stopped and there is no request for hot water supply, the control device switches the waste heat recovery line so that the heat medium passes through the exhaust gas heat exchange line and the heat medium heating line in that order when the temperature at the bottom of the heat storage tank is below a seventh temperature threshold.

[0028] (23) In the combined heat and power supply system described in any one of (10) to (22) above, when the fuel cell is stopped and there is a request for hot water supply, the control device switches the waste heat recovery line so that the heat medium passes only through the heat medium heating line when the temperature at the bottom of the heat storage tank is below an eighth temperature threshold.

[0029] (24) The cogeneration system described in (23) above limits the ability of the heat storage tank to provide heat when the temperature at the bottom of the heat storage tank is equal to or lower than a ninth temperature threshold. [Effects of the Invention]

[0030] According to the cogeneration system of the present disclosure configured as described above, the required heat can be efficiently imparted to the medium. [Brief explanation of the drawings]

[0031] [Figure 1] 3 is a schematic diagram showing the flow state of the heat medium in the cogeneration system according to the first embodiment when the heat medium is heated by a temperature adjustment unit. FIG. [Figure 2] FIG. 2 is a structural diagram schematically showing the internal configuration of the fuel cell of FIG. [Figure 3] 3 is a schematic diagram showing the flow state of the heat medium in the cogeneration system according to the first embodiment when the heat medium is cooled by a temperature adjustment unit. FIG. [Figure 4] FIG. 10 is a schematic configuration diagram of a fuel supply system according to a second embodiment. [Figure 5] FIG. 10 is a schematic configuration diagram of a cogeneration system according to a third embodiment. [Figure 6] FIG. 10 is a schematic configuration diagram of a cogeneration system according to a fourth embodiment. [Figure 7] 7 is a flowchart for explaining the control executed by the control device of FIG. 6. [Figure 8] 7 is a flowchart for explaining the control executed by the control device of FIG. 6. [Figure 9]7 is a flowchart for explaining the control executed by the control device of FIG. 6. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, an embodiment of a cogeneration system to which the present disclosure is applied will be described with reference to the drawings.

[0033] 1 , a combined heat and power system 100 according to an embodiment of the present disclosure includes a fuel cell system 11 and an indirect supply line 12. The combined heat and power system 100 is installed in, for example, a home. The combined heat and power system 100 may include a control device 35.

[0034] The fuel cell system 11 generates power using raw fuel gas, air, and water. The fuel cell system 11 generates heat during operation to generate power. The heat generated by the fuel cell system 11 is recovered using a heat transfer medium. The indirect supply line 12 exchanges heat between the heat transfer medium and a medium supplied from, for example, a water supply, to supply hot water to, for example, a customer facility.

[0035] The fuel cell system 11 includes a fuel cell 16, a heat storage tank 17, and a waste heat recovery line 18. The fuel cell system 11 may include a third heat exchange unit 20 and a temperature adjustment unit 21a.

[0036] The fuel cell 16 may include at least one of a reformer and a cell stack. The fuel cell 16 may be a fuel cell module containing the reformer and the cell stack within a housing. The reformer generates fuel such as hydrogen by causing a steam reforming reaction between gas supplied as raw fuel and water. The cell stack is, for example, a solid oxide fuel cell (SOFC), and generates electricity through an electrochemical reaction using an oxidizer such as oxygen contained in the air and fuel generated by the reformer. The cell stack also generates water through an electrochemical reaction. Unreacted fuel and unreacted oxidizer discharged from the cell stack are combusted to provide energy for the steam reforming reaction in the reformer. The water discharged from the cell stack is discharged from the fuel cell 16 in the form of a high-temperature gas along with combustion gases resulting from the combustion of the unreacted fuel and unreacted oxidizer. The cell stack may be a polymer electrolyte fuel cell (PEFC). In this case, any other appropriate configuration may be used.

[0037] The exhaust gas discharged from the fuel cell 16 may contain combustion gas and gaseous water. The exhaust gas discharged from the fuel cell 16 may be heat exchanged with a heat medium using a third heat exchange unit 20 described below. The exhaust gas cooled by heat exchange may be separated into gaseous exhaust gas and condensed liquid water by a gas-liquid separator 23. The condensed liquid water may be stored in a condensed water tank of the fuel cell system 11. A water volume sensor may be provided to measure the water volume W of the condensed water tank. The separated exhaust gas may be discharged outside the fuel cell system 11. The separated water may be sent to the fuel cell 16 as water to be used in the steam reforming reaction.

[0038] The heat storage tank 17 stores a heat medium and supplies heat in response to a hot water supply request. The heat medium recovers heat generated from the fuel cell 16. The heat medium is a fluid with a large specific heat, such as water or antifreeze.

[0039] The waste heat recovery line 18 circulates the heat medium stored in the heat storage tank 17 between the fuel cell 16 and the heat storage tank 17. A normal path of the waste heat recovery line 18 may be a circulation path that starts at the heat storage tank 17, passes through the third heat exchange unit 20 and the first heat exchange unit 19 in this order, and returns to the heat storage tank 17. A first pump 40 may be provided in the waste heat recovery line 18. The first pump 40 may increase the pressure of the heat medium stored in the heat storage tank 17 so as to circulate it.

[0040] A first three-way valve 31 may be provided in the waste heat recovery line 18 downstream of the third heat exchange unit 20. A first flow path 18g may be connected to the first three-way valve 31. The first flow path 18g may be connected to the waste heat recovery line 18 upstream of the first heat exchange unit 19, bypassing the temperature adjustment unit 21a.

[0041] A fourth flow path 19a may be connected to the first three-way valve 31. In the waste heat recovery line 18, the fourth flow path 19a may be connected upstream of the temperature adjustment unit 21a. That is, the fourth flow path 19a may be connected upstream of the temperature adjustment unit 21a of a second flow path (temperature adjustment line) 18e, which will be described later.

[0042] A second three-way valve 32 may be provided in the waste heat recovery line 18 downstream of the heat storage tank 17. A second flow path 18e may be connected to the second three-way valve 32. The second flow path 18e is a bypass path different from the above-mentioned normal path. The second flow path 18e may bypass the third heat exchange unit 20 and be connected to the waste heat recovery line 18 upstream of the first heat exchange unit 19.

[0043] A third three-way valve 33 may be provided in the second flow path 18e downstream of the temperature adjustment unit 21a. A third flow path (second bypass flow path) 19b may be connected to the third three-way valve 33. The third flow path 19b may be connected to the waste heat recovery line 18 upstream of the third heat exchange unit 20.

[0044] The first heat exchange unit 19 may be located close to the outside of the fuel cell 16 (outside the housing 29) or inside the fuel cell 16 (inside the housing 29). When the first heat exchange unit 19 is located close to the outside of the fuel cell 16, it may be located so as to be in contact with the outside of the fuel cell 16. When the first heat exchange unit 19 is located inside the fuel cell 16, it may be located around at least one of the reformer 26 and the cell stack 27. In this case, the first heat exchange unit 19 may be located around at least one of the reformer 26 and the cell stack 27 without any thermal insulation. For example, as shown in FIG. 2, the first heat exchange unit 19 may be formed by providing a pipe 25, through which the medium flowing in the waste heat recovery line 18 passes, around at least one of the reformer 26 and the cell stack 27 without any thermal insulation. In this disclosure, a thermal insulator is a material that prevents heat transfer, and may be, for example, a fiber-based thermal insulator such as glass wool or a foam-based thermal insulator such as resin foam. Therefore, in this disclosure, the housing 29 described below is not included in the thermal insulator. "Without an insulating material" means that no insulating material is located on the shortest line connecting at least a portion of the surface of the duct 25 with at least one surface of the reformer 26 and the cell stack 27. Therefore, even if the packing 28 made of an insulating material is located closer to the reformer 26 or the cell stack 27 than the duct 25, it can still function as the first heat exchanger 19.

[0045] The pipe 25 for the heat medium in the first heat exchange section 19 may be provided inside a housing 29 that surrounds at least one of the reformer 26 and the cell stack 27. In a configuration in which the pipe 25 is provided inside the housing 29, a heat insulating material 30 may be located between the pipe 25 and the housing 29. Alternatively, the pipe 25 may be located close to the outside of the housing 29 within a range that allows heat transfer from at least one of the reformer 26 and the cell stack 27.

[0046] The first heat exchange unit 19 recovers heat generated in the fuel cell 16 using the heat medium circulating through the waste heat recovery line 18. More specifically, the heat is recovered as follows: The outer surface of the pipe 25 is heated by radiation from the reformer 26 or the cell stack 27 or by convection of the surrounding gas. The first heat exchange unit 19 recovers heat by transferring heat from the outer surface to the heat medium circulating through the waste heat recovery line 18 as it flows through the pipe 25.

[0047] 1, the third heat exchange unit 20 is, for example, a heat exchanger. The third heat exchange unit 20 exchanges heat between the exhaust gas discharged from the fuel cell 16 and a heat medium circulating through the waste heat recovery line 18. The third heat exchange unit 20 may be located upstream of the first heat exchange unit 19 in the waste heat recovery line 18. The exhaust gas discharged from the fuel cell 16 is generally at a lower temperature (for example, about 200 to 300°C) than the ambient temperature of the reformer 26 and the cell stack 27. Therefore, the third heat exchange unit 20 functions as a heat medium preheater for the first heat exchange unit 19.

[0048] The temperature adjustment unit 21a may heat or cool the heat medium circulating through the waste heat recovery line 18. The temperature adjustment unit 21a is, for example, a fin pipe. The temperature adjustment unit 21a may include a burner 22. The burner 22 has a fuel injection line for supplying gas fuel and an air supply line for forcibly drawing in outside air using a blower and supplying it. The burner 22 mixes the gas fuel and outside air at an ignition port and burns the mixture. The heat medium may be heated via the temperature adjustment unit 21a by combustion in the burner 22. As shown in FIG. 3, the burner 22 may forcibly draw in outside air using a blower and send it to the temperature adjustment unit 21a while not burning. The heat medium is cooled via the temperature adjustment unit 21a by the air sent.

[0049] A medium may be supplied from, for example, tap water to the indirect supply line 12. A first flow control valve 43 that adjusts the amount of medium supplied may be provided to the indirect supply line 12. The medium is, for example, water.

[0050] The indirect supply line 12 includes a second heat exchange unit 14. The second heat exchange unit 14 may exchange heat between the medium and a heat medium stored in a heat storage tank 17. The indirect supply line 12 supplies hot water to, for example, a consumer facility. In other words, the indirect supply line 12 may be a hot water supply path. The indirect supply line 12 may be provided with a bypass path 44 that bypasses the second heat exchange unit 14. The bypass path 44 may be provided with a second flow rate control valve 45. The temperature of the medium delivered from the indirect supply line 12 can be adjusted by adjusting the flow rate of the medium bypassing the bypass path 44 with the second flow rate control valve 45.

[0051] The control device 35 includes one or more processors and memories. The processor may be a general-purpose processor that loads a specific program to execute a specific function, or a dedicated processor specialized for a specific process. The dedicated processor may include an application-specific integrated circuit (ASIC). The processor may include a programmable logic device (PLD). The PLD may include a field-programmable gate array (FPGA). The control device 35 may be either a system-on-a-chip (SoC) or a system-in-a-package (SiP) in which one or more processors work together. The control device 35 may control components of the cogeneration system 100, such as the burner 22, the first three-way valve 31, the second three-way valve 32, and the third three-way valve 33. An example of control by the control device 35 is described below.

[0052] When the indirect supply line 12 is supplying the medium, the medium is heated by heat exchange with the heat medium in the heat storage tank 17 in the second heat exchange section 14. Therefore, the temperature of the heat medium stored in the heat storage tank 17 decreases. The control device 35 may control the operations of the first three-way valve 31, the second three-way valve 32, the third three-way valve 33, and the burner 22, for example, based on the temperature of the heat medium stored in the heat storage tank 17.

[0053] The heat transfer medium in the heat storage tank 17 flows downstream via a first pump 40 arranged in the waste heat recovery line 18 .

[0054] As a normal path of the waste heat recovery line 18 , the control device 35 may control the second three-way valve 32 to cause the heat medium in the heat storage tank 17 to flow through the third heat exchange unit 20 .

[0055] In the third heat exchange unit 20, the heat medium is heated by heat exchange with the exhaust gas discharged from the fuel cell 16. The control device 35 controls the first three-way valve 31 to cause the heat medium flowing out of the third heat exchange unit 20 to flow into the first heat exchange unit 19 through the first flow path 18g.

[0056] In the first heat exchange section 19, the heat medium is heated by the heat generated by the fuel cell 16. The heat medium then flows into the heat storage tank 17.

[0057] On the other hand, when the heat medium needs to be further heated or cooled, the control device 35 controls the first three-way valve 31 and the second three-way valve 32 to cause the heat medium flowing out of the third heat exchanger 20 to flow through the second flow path 18e and the fourth flow path 19a to the temperature adjustment device 21a. Here, the control device 35 controls the burner 22 of the temperature adjustment device 21a. That is, when heat is required for the heat medium, referring to FIG. 1, the control device 35 causes the burner 22 to combust and provide heat to the heat medium. On the other hand, when the heat medium needs to be cooled, referring to FIG. 3, the control device 35 stops the combustion of the burner 22 of the temperature adjustment device 21a. At the same time, the control device 35 causes the blower of the burner 22 to forcibly draw in outside air and send it to the temperature adjustment device 21a to cool the heat medium. The control device 35 may control the third three-way valve 33 in accordance with the heat of the heat medium to cause the heat medium that has flowed through the temperature adjustment unit 21a to flow through the third flow path 19b to the upstream side of the third heat exchange unit 20. The control device 35 may control the third three-way valve 33 in accordance with the heat of the heat medium to cause the heat medium that has flowed through the temperature adjustment unit 21a to flow to the upstream side of the first heat exchange unit 19.

[0058] In the first heat exchange section 19, the heat transfer medium exchanges heat with the fuel cell 16. Therefore, the heat transfer medium is heated. Then, the heat transfer medium flows into the heat storage tank 17.

[0059] 4, a combined heat and power system 200 according to the second embodiment of the present disclosure has a configuration similar to that of the combined heat and power system 100. Hereinafter, the same configuration as that of the combined heat and power system 100 will not be described again, and only the configuration different from that of the combined heat and power system 100 will be described.

[0060] The fuel cell system 11 may have a heat dissipation unit 49 in the waste heat recovery line 18 downstream of the heat storage tank 17. The heat dissipation unit 49 is, for example, a radiator, and dissipates heat from the heat medium by exchanging heat between the heat medium and outside air supplied by a blower. A third heat exchange unit 20 may be provided downstream of the heat dissipation unit 49.

[0061] A temperature adjustment unit 21b may be provided in the waste heat recovery line 18 between the first heat exchange unit 19 and the third heat exchange unit 20. The temperature adjustment unit 21b may heat or cool the heat medium circulating through the waste heat recovery line 18. The temperature adjustment unit 21b may include a heater and may heat the heat medium using heat generated by the heater. The heater may be an electric heater. Electric power may be supplied to the electric heater from at least one of a commercial grid and the fuel cell 16. The first heat exchange unit 19 may be located downstream of the temperature adjustment unit 21b.

[0062] The combined heat and power supply systems 100 and 200 of this embodiment configured as described above comprise a fuel cell system 11 having a first heat exchange unit 19 located either inside or close to the outside of the fuel cell 16 and causing a heat medium to recover heat generated from the fuel cell 16, a heat storage tank 17 for storing the heat medium, and a waste heat recovery line 18 for circulating the heat medium between the fuel cell 16 and the heat storage tank 17, and an indirect supply line 12 including a second heat exchange unit 14 for exchanging heat between the heat medium stored in the heat storage tank 17 and a medium.

[0063] In a typical cogeneration system using a fuel cell, waste heat is recovered by heat exchange between the fuel cell's exhaust gas and a medium. However, it is difficult to sufficiently heat the medium and temporarily supply a large amount of hot water. A cogeneration system that recovers waste heat from exhaust gas and therefore has difficulty temporarily supplying a large amount of heat requires a water heater to meet the demand for a large amount of heat. In contrast, the cogeneration systems 100 and 200 of the present embodiment, having the above-described configuration, can recover a larger amount of heat than a system that recovers waste heat from exhaust gas because both the reformer 26 and the cell stack 27 generally operate at a higher temperature than the exhaust gas. Furthermore, the cogeneration systems 100 and 200 include a heat storage tank 17 that stores a heat transfer medium. The heat transfer medium can store a large amount of heat. Therefore, the cogeneration systems 100 and 200 can temporarily supply a large amount of medium. Therefore, a water heater is not required in the cogeneration systems 100 and 200. Therefore, the combined heat and power systems 100 and 200 can be miniaturized.

[0064] Furthermore, in the combined heat and power systems 100 and 200 of the present embodiment, the fuel cell system 11 has a third heat exchange unit 20 that exchanges heat between the exhaust gas from the fuel cell 16 and a heat medium circulating through the waste heat recovery line 18. With this configuration, the combined heat and power systems 100 and 200 can lower the temperature of the exhaust gas from the fuel cell 16.

[0065] Furthermore, the third heat exchange unit 20 of the combined heat and power generation systems 100 and 200 of this embodiment is located upstream of the first heat exchange unit 19 in the waste heat recovery line 18. With this configuration, the heat transfer medium is heated in the third heat exchange unit 20 and then flows upstream of the first heat exchange unit 19, which recovers heat generated by the fuel cell 16. This prevents the low-temperature heat transfer medium from removing a large amount of heat from the fuel cell 16. This allows the power generation efficiency of the fuel cell 16 to be maintained.

[0066] Furthermore, the third heat exchange unit 20 of the combined heat and power supply system 200 of this embodiment has a heat radiating unit 49 between the heat storage tank 17 and the third heat exchange unit 20 in the waste heat recovery line 18. With this configuration, the heat medium in the heat storage tank 17 is cooled by the heat radiating unit 49 before flowing upstream of the third heat exchange unit 20. Therefore, the third heat exchange unit 20 can sufficiently cool the exhaust gas of the fuel cell 16 and recover the reforming water to be supplied to the fuel cell 16.

[0067] The cogeneration system 100 of this embodiment also includes a temperature adjustment unit 21a that is located in the waste heat recovery line 18 between the first heat exchange unit 19 and the third heat exchange unit 20 and that is capable of heating or cooling the heat medium circulating through the waste heat recovery line 18. With this configuration, the cogeneration system 100 can further heat the heat medium, for example, when the heat supplied to the heat medium is insufficient.

[0068] Furthermore, the waste heat recovery line 18 of the fuel cell system 11 of the combined heat and power supply system 100 of this embodiment includes a first flow path 18g downstream of the third heat exchanger 20, bypassing the temperature control unit 21a and connecting to the first heat exchanger 19. With this configuration, when the temperature control unit 21a neither heats nor cools the heat medium, the temperature control unit 21a is bypassed, thereby reducing pressure loss. Therefore, the load on the first pump 40 can be reduced.

[0069] Furthermore, the waste heat recovery line 18 of the fuel cell system 11 of the combined heat and power supply system 100 of this embodiment includes, downstream of the heat storage tank 17, a second flow path 18e that bypasses the third heat exchanger 20 and connects to the first heat exchanger 19, and a third flow path 19b that branches off from the second flow path 18e and connects to the third heat exchanger 20. With this configuration, when cooling a heat medium as shown in Fig. 3, the heat medium can be cooled in the temperature adjustment unit 21a via the second flow path 18e and the third flow path 19b, and then the cooled heat medium can flow into the third heat exchanger 20.

[0070] 5, a cogeneration system 10 according to a third embodiment of the present disclosure includes a fuel cell system 11, a direct supply line 50, and an indirect supply line 13. The cogeneration system 10 is installed in, for example, a home.

[0071] The fuel cell system 11 generates power using raw fuel gas, air, and water. The fuel cell system 11 generates heat during operation to generate power. The heat generated by the fuel cell system 11 is recovered using a heat transfer medium. The direct supply line 50 supplies heat to an area where the direct supply line 50 is located by flowing a heat transfer medium. As described below, the indirect supply line 13 may have at least one of a second heat exchange unit 14 and a fourth heat exchange unit 15, and supplies heat as a heated medium by heat-exchanging the heat transfer medium with the medium through at least one of the second heat exchange unit 14 and a fourth heat exchange unit 15.

[0072] The fuel cell system 11 includes a fuel cell 16 and a heat storage tank 17. The fuel cell system 11 may include a waste heat recovery line 18, a first heat exchange unit 19, a third heat exchange unit 20, a heating unit 21, and a heat dissipation unit 64.

[0073] The waste heat recovery line 18 circulates the heat medium between the fuel cell 16 and the heat storage tank 17. A first pump 24 may be provided in the waste heat recovery line 18. The first pump 24 may increase the pressure of the heat medium so that it flows from the heat storage tank 17 toward the fuel cell 16.

[0074] The first heat exchange section 19 may be located around at least one of the reformer and the cell stack.

[0075] The pipe 25 for the heat medium in the first heat exchange section 19 may be provided inside a housing 29 that surrounds at least one of the reformer 26 and the cell stack 27. In a configuration in which the pipe 25 is provided inside the housing 29, a heat insulating material 30 may be located between the pipe 25 and the housing 29. Alternatively, the pipe 25 may be located outside the housing 29 to the extent that heat from at least one of the reformer 26 and the cell stack 27 can be transferred.

[0076] The heating unit 21 is, for example, a heater. The heating unit 21 may be located in the waste heat recovery line 18 between the first heat exchange unit 19 and the third heat exchange unit 20. The heating unit 21 may heat the heat medium circulating through the waste heat recovery line 18. The heating unit 21 may be an electric heater. Electric power may be supplied to the electric heater from at least one of a commercial grid and the fuel cell 16.

[0077] The heat radiating unit 64 may be located downstream of the heat storage tank 17 and upstream of the third heat exchange unit 20 in the waste heat recovery line 18. Furthermore, the heat radiating unit 64 may be provided downstream of a connection portion of the waste heat recovery line 18 with a first indirect supply line 37, which will be described later. The heat radiating unit 64 is, for example, a radiator, and radiates heat from the heat medium by exchanging heat between the heat medium and outside air supplied by a fan.

[0078] As described above, the direct supply line 50 supplies heat by flowing the heat medium stored in the heat storage tank 17. The direct supply line 50 may be connected to a pipe buried inside the floor or wall of a home, for example. The direct supply line 50 can supply the heat medium to the pipe.

[0079] The direct supply line 50 may include a delivery path 66 and a return path 67. In the direct supply line 50, the heat medium at a relatively high temperature in the heat storage tank 17 is delivered via the delivery path 66. In the direct supply line 50, the heat medium at a relatively low temperature due to the supply of heat flows into the heat storage tank 17 via the return path 67. A pump 36 for delivering the heat medium to the direct supply line 50 may be provided in the return path 67.

[0080] The delivery path 66 may branch into a high-temperature delivery path 68 and a low-temperature delivery path 69. The low-temperature delivery path 69 may be connected to the return path 67. The low-temperature delivery path 69 may be connected to the return path 67 via a three-way valve 70. The low-temperature delivery path 69 may deliver a heat medium at a lower temperature than that of the high-temperature delivery path 68 by mixing the low-temperature heat medium flowing through the return path 67 with the high-temperature heat medium delivered from the heat storage tank 17. The delivery path 66 and the return path 67 may be connected via piping buried inside the floor or wall of the home. The heat medium delivered from the delivery path 66 may flow into the return path 67 via this piping. In the high-temperature delivery path 68, the high-temperature heat stored in the heat medium can be used as is, thereby reducing temperature loss. Supplying heat using the high-temperature delivery path 68 is suitable for appliances requiring a delivery temperature of approximately 80°C, such as a high-temperature heater (bathroom dryer).

[0081] As described above, the indirect supply line 13 supplies heat by exchanging heat with the heat medium stored in the heat storage tank 17. The medium is, for example, water. Part of the medium may be supplied from outside the facility in which the cogeneration system 10 is installed. Furthermore, part of the medium may be supplied by circulating part of the medium sent out from the cogeneration system 10 back.

[0082] The indirect supply line 13 may include a first indirect supply line 37 and a second indirect supply line 38. The first indirect supply line 37 may include a second heat exchanger 14. The second heat exchanger 14 may perform heat exchange between the medium flowing through the first medium supply path 39, which is the first indirect supply line 37, and the heat medium stored in the heat storage tank 17. The second indirect supply line 38 may include a fourth heat exchanger 15. The fourth heat exchanger 15 may perform heat exchange between the medium flowing through the second medium supply path 65, which is the second indirect supply line 38, and the heat medium stored in the heat storage tank 17.

[0083] One end of the first heat medium line 71 flowing from the heat storage tank 17 to the second heat exchange unit 14 and one end of the second heat medium line 72 flowing from the heat storage tank 17 to the fourth heat exchange unit 15 may be connected to the waste heat recovery line 18. For example, one downstream end of the first heat medium line 71 and one downstream end of the second heat medium line 72 are connected to the waste heat recovery line 18 downstream of the heat storage tank 17. Furthermore, one downstream end of the first heat medium line 71 may be provided in the waste heat recovery line 18 between the heat storage tank 17 and the heat radiator 64. In other words, the heat radiator 64 may be provided downstream of the connection between the first heat medium line 71 and the waste heat recovery line 18. One downstream end of the second heat medium line 72 may be provided in the waste heat recovery line 18 between the heat storage tank 17 and the heat radiator 64. The first heat medium line 71 may be provided with a pump 41 for delivering the heat medium to the first heat medium line 71. The second heat medium line 72 may be provided with a pump 42 for delivering the heat medium to the second heat medium line 72.

[0084] The first medium supply path 39 is, for example, a hot water supply path. More specifically, the first medium supply path 39 heats clean water supplied from outside the facility where the cogeneration system 10 is installed using the first heat exchanger 19, and supplies hot water to, for example, a customer facility. The first medium supply path 39 may be provided with a first flow rate adjustment valve 43 that adjusts the amount of medium supplied.

[0085] The first medium supply path 39 may be provided with a bypass path 44 that bypasses the second heat exchanger 14. The bypass path 44 may be provided with a second flow rate adjustment valve 45. By adjusting the flow rate of the heat medium bypassing the bypass path 44 with the second flow rate adjustment valve 45, the temperature of the medium delivered from the first medium supply path 39 can be adjusted.

[0086] The second medium supply path 65 is, for example, a bathtub hot water supply path. In a more detailed example, the second medium supply path 65 heats water collected from the bathtub using the fourth heat exchanger 15 and supplies hot water to the bathtub. The second medium supply path 65 may be provided with a pump 46 for sending the medium to the second medium supply path 65.

[0087] The first medium supply path 39 may branch downstream of the first heat exchanger 19. One of the branch paths may be connected to the second medium supply path 65 downstream of the fourth heat exchanger 15. In other words, the delivery path of the first medium supply path 39 and the delivery path of the second medium supply path 65 may be connected.

[0088] One of the branch paths may be provided with a check valve 47. The check valve 47 prevents backflow of the medium from the second medium supply path 65 to the first medium supply path 39. One of the branch paths may be provided with a bathtub water inlet valve 48. When opened, the bathtub water inlet valve 48 increases the amount of hot water in the bathtub.

[0089] In the indirect supply line 13 configured as described above, the clean water is indirectly heated, making it easy to control the hot water temperature on the user side due to indirect heating, and there are no hygiene issues. Therefore, the indirect supply line 13 improves safety and convenience for applications that come into contact with the human body, such as hot water supply and bathroom use.

[0090] The combined heat and power system 10 of this embodiment configured as described above has the direct supply line 50 that supplies heat by flowing the heat medium stored in the heat storage tank 17, and the indirect supply line 13 that supplies heat by heat exchange between the heat medium stored in the heat storage tank 17 and a medium. With this configuration, the combined heat and power system 10 can utilize the waste heat of the fuel cell system 11 in a variety of ways.

[0091] Furthermore, in the cogeneration system 10 of this embodiment, the indirect supply line 13 includes a first indirect supply line 37 and a second indirect supply line 38. The first indirect supply line 37 includes a second heat exchanger 14 that exchanges heat between the medium flowing through the first medium supply path 39 and the heat medium. The second indirect supply line 38 includes a fourth heat exchanger 15 that exchanges heat between the medium flowing through the second medium supply path 65 and the heat medium. The outlet path of the first medium supply path 39 is connected to the outlet path of the second medium supply path 65. With this configuration, the cogeneration system 10 can, for example, reheat hot water stored in a bathtub by circulating the second medium supply path 65, and can increase the amount of hot water in the bathtub by supplying hot water heated in the first medium supply path 39 to the second medium supply path 65. In this way, the cogeneration system 10 can utilize the waste heat of the fuel cell system 11 in a variety of ways.

[0092] In the combined heat and power system 10 of this embodiment, the fuel cell system 11 includes a waste heat recovery line 18 that circulates a heat transfer medium between the fuel cell 16 and the heat storage tank 17, and a first heat exchanger 19 that is located around at least one of the reformer 26 and the cell stack 27 included in the fuel cell 16 without any intervening insulation and that allows the heat transfer medium circulating through the waste heat recovery line 18 to recover heat generated by the fuel cell 16. Conventional combined heat and power systems using fuel cells recover waste heat by exchanging heat between the exhaust gas from the fuel cell 16 and the heat transfer medium. However, it is difficult to sufficiently heat the heat transfer medium and therefore difficult to temporarily supply a large amount of heat. In contrast, the combined heat and power system 10 of this embodiment, configured as described above, can recover a large amount of heat compared to systems that recover waste heat from exhaust gas because both the reformer 26 and the cell stack 27 generally operate at a higher temperature than the exhaust gas. Therefore, the combined heat and power system 10 can temporarily supply a large amount of heat. In a combined heat and power system that recovers waste heat from exhaust gas and has difficulty in temporarily supplying a large amount of heat, a water heater is required to meet the demand for a temporary large amount of heat.On the other hand, combined heat and power system 10 can temporarily supply a large amount of heat, so a water heater is not required.

[0093] Furthermore, in the combined heat and power supply system 10 of this embodiment, the fuel cell system 11 has a third heat exchange unit 20 that exchanges heat between the exhaust gas of the fuel cell 16 and a heat medium circulating through the waste heat recovery line 18. With this configuration, the combined heat and power supply system 10 can cool the exhaust gas in the third heat exchange unit 20 and recover reformed water to be supplied to the fuel cell 16.

[0094] Furthermore, in the cogeneration system 10 of this embodiment, the third heat exchange unit 20 is located upstream of the first heat exchange unit 19 in the waste heat recovery line 18. With this configuration, the cogeneration system 10 can preheat the heat medium before heating in the first heat exchange unit 19, thereby preventing an extreme drop in the temperature of the fuel cell 16 due to heat exchange with the heat medium in the first heat exchange unit 19. Therefore, even though the cogeneration system 10 is provided with the first heat exchange unit 19, it can prevent the operation of the fuel cell 16 from becoming unstable due to a drop in temperature.

[0095] Furthermore, in the cogeneration system 10 of this embodiment, the fuel cell system 11 has a heating unit 21 located between the first heat exchange unit 19 and the third heat exchange unit 20 in the waste heat recovery line 18, which heats the heat medium circulating through the waste heat recovery line 18. With this configuration, the cogeneration system 10 can supply heat to meet demand even when the heat supply from the fuel cell 16 is insufficient to meet the heat demand. Note that an insufficient heat supply from the fuel cell 16 to meet the heat demand may occur, for example, when the amount of heat required via the direct supply line 50 or the indirect supply line 13 increases, or when the fuel cell 16 stops.

[0096] Furthermore, in the combined heat and power system 10 of this embodiment, the fuel cell system 11 has a heat dissipation unit 64 provided downstream of the connection portion of the waste heat recovery line 18 with the first heat medium line 71. While heat is supplied to the outside of the combined heat and power system 10 via the direct supply line 50 or the indirect supply line 13, the cooled heat medium returns to the waste heat recovery line 18, and the heat medium is cooled upstream of the third heat exchange unit 20 in the waste heat recovery line 18. In the third heat exchange unit 20, the cooled heat medium can recover water contained in the exhaust gas. On the other hand, if the heat medium is not sufficiently cooled upstream of the third heat exchange unit 20, the amount of water recovered decreases. On the other hand, the fuel cell system 11 having the above-described configuration can cool the heat accumulated in the heat medium even if the heat medium is not sufficiently cooled upstream of the third heat exchange unit 20, such as when the amount of heat supplied to the outside of the combined heat and power system 10 via the direct supply line 50 or the indirect supply line 13 is low. Therefore, the fuel cell system 11 can prevent a drastic decrease in the amount of water recovered from the exhaust gas.

[0097] 6, a fuel cell system 11 according to a fourth embodiment of the present disclosure includes a fuel cell 16, a heat storage tank 17, a waste heat recovery line 18, and a control device 35. The fuel cell system 11 is installed in, for example, a home.

[0098] The heat storage tank 17 stores a heat medium. The heat medium is, for example, a fluid with a large specific heat capacity, such as water or antifreeze. The heat storage tank 17 provides heat in response to a hot water supply request. Temperature sensors 51 and 52 may be provided at the inlet and outlet of the heat storage tank 17, respectively, to measure the temperatures T1 and T2 of the heat medium. In addition to the temperature sensor 52 at the outlet of the heat storage tank 17, a temperature sensor 53 may be provided at the bottom of the heat storage tank 17 to measure the temperature T3 of the heat medium. A single sensor may serve as both the temperature sensor 52 and the temperature sensor 53. A flow rate sensor 61 may be provided at the outlet of the heat storage tank 17 to measure the flow rate of the heat medium. Instead of the flow rate sensor 61, a flow rate sensor that measures the flow rate F1 of the heat medium may be provided at the inlet of the heat storage tank 17.

[0099] The waste heat recovery line 18 circulates the heat medium stored in the heat storage tank 17 between the fuel cell 16 and the heat storage tank 17. The waste heat recovery line 18 includes a heat medium outflow line 18a, an exhaust gas heat exchange line 18b, a heat medium cooling line 18c, a heat medium heating line 18d, and a heat medium inflow line 18f.

[0100] The waste heat recovery line 18 is capable of switching between the heat medium outlet line 18a and the heat medium inlet line 18f between switching the passage of the heat medium through one of the exhaust gas heat exchange line 18b, the heat medium cooling line 18c, and the heat medium heating line 18d, and switching the passage order through multiple lines among the exhaust gas heat exchange line 18b, the heat medium cooling line 18c, and the heat medium heating line 18d. Specific examples of the connection configuration of the exhaust gas heat exchange line 18b, the heat medium cooling line 18c, and the heat medium heating line 18d in the waste heat recovery line 18 are described below.

[0101] As an example of a configuration that enables switching of the passage of the heat transfer medium as described above, the waste heat recovery line 18 may further include a first three-way valve 31, a second three-way valve 32, a third three-way valve 33, a first bypass flow path 19a, a second bypass flow path 19b, and a third bypass flow path 19c.

[0102] The heat medium outlet line 18a allows the heat medium to flow out from the heat storage tank 17. The heat medium outlet line 18a may include a first end connected to the heat storage tank 17 and a second end connected to the first three-way valve 31.

[0103] The exhaust gas heat exchange line 18b exchanges heat between the exhaust gas of the fuel cell 16 and the heat medium through the third heat exchange unit 20. The exhaust gas heat exchange line 18b may include a first end connected to the first three-way valve 31 and a second end connected to the second three-way valve 32.

[0104] The heat medium cooling line 18c cools the heat medium. The heat medium heating line 18d heats the heat medium. As described below, the heat medium cooling line 18c and the heat medium heating line 18d may be the same line or separate lines. In the following description, the heat medium cooling line 18c and the heat medium heating line 18d are described as the same line. In the description common to the heat medium cooling line 18c and the heat medium heating line 18d, the heat medium cooling line 18c and the heat medium heating line 18d are referred to as the temperature adjustment line 18e. The temperature adjustment line 18e may include a first end connected to the first three-way valve 31 and a second end connected to the third three-way valve 33.

[0105] The heat medium inlet line 18f can recover heat generated in the fuel cell 16 from the heat medium by the first heat exchange unit 19. The heat medium inlet line 18f causes the heat medium to flow into the heat storage tank 17. The heat medium inlet line 18f may include a first end connected to the heat storage tank 17 and a second end connected to the second three-way valve 32.

[0106] The waste heat recovery line 18 may be provided with a first pump 40. The first pump 40 may increase the pressure of the heat medium stored in the heat storage tank 17 so as to circulate it.

[0107] As described above, the first three-way valve 31 may be connected to the second end of the heat medium outlet line 18a, the first end of the exhaust gas heat exchange line 18b, and the first end of the temperature adjustment line 18e. As described above, the second three-way valve 32 may be connected to the second end of the exhaust gas heat exchange line 18b and the second end of the heat medium inlet line 18f. Furthermore, the second three-way valve 32 may be connected to the first end of the first bypass flow path 19a. As described above, the third three-way valve 33 may be connected to the second end of the temperature adjustment line 18e. Furthermore, the third three-way valve 33 may be connected to the first end of the second bypass flow path 19b and the first end of the third bypass flow path 19c.

[0108] A first end of the first bypass flow passage 19a may be connected to the second three-way valve 32 as described above. A second end of the first bypass flow passage 19a, which is opposite to the first end, may be connected to the temperature adjustment line 18e between the first three-way valve 31 and a burner 22 described below. A first end of the second bypass flow passage 19b may be connected to the third three-way valve 33 as described above. A second end of the second bypass flow passage 19b, which is opposite to the first end, may be connected to the exhaust gas heat exchange line 18b between the first three-way valve 31 and the third heat exchange section 20. A first end of the third bypass flow passage 19c may be connected to the third three-way valve 33 as described above. A second end of the third bypass flow passage 19c, which is opposite to the first end, may be connected to the heat medium inlet line 18f between the second three-way valve 32 and the first heat exchange section 19.

[0109] By switching the first to third three-way valves 31 to 33 and operating the burner 22, the waste heat recovery line 18 can switch the passage of the heat medium between the heat medium outlet line 18a and the heat medium inlet line 18f to any one of the exhaust gas heat exchange line 18b, the heat medium cooling line 18c, and the heat medium heating line 18d, or can switch the order in which the heat medium passes through at least two or more of the exhaust gas heat exchange line 18b, the heat medium cooling line 18c, and the heat medium heating line 18d.

[0110] As shown in Fig. 6, the third heat exchange unit 20 exchanges heat between the exhaust gas discharged from the fuel cell 16 and the heat medium circulating through the waste heat recovery line 18. The exhaust gas discharged from the fuel cell 16 is generally at a lower temperature (for example, about 200 to 300°C) than the ambient temperature of the reformer 26 and the cell stack 27. Therefore, the third heat exchange unit 20 functions as a heat medium preheater for the first heat exchange unit 19. A temperature sensor 54 for measuring the temperature T4 of the heat medium may be provided at the heat medium inlet of the third heat exchange unit 20.

[0111] The heat transfer medium cooling line 18c may be cooled by a cooler provided nearby, such as a radiator.

[0112] The heat medium heating line 18d may be heated by a heater provided nearby. The heater is, for example, a burner 22 located near the heat medium heating line 18d so as to be able to heat the heat medium heating line. Alternatively, the heater may be an electric heater or the like. The burner 22 has a fuel injection line for supplying gas fuel and an air supply line for forcibly drawing in outside air using a blower. The burner 22 mixes the gas fuel and outside air at an ignition port and burns the mixture. The heat medium may be heated by combustion by the burner 22.

[0113] The heat transfer medium cooling line 18c and the heat transfer medium heating line 18d may be the same line, the temperature adjustment line 18e, as described above. In such a configuration, the cooler and the heater may be provided separately or integrated. As an example of a configuration in which the cooler and the heater are integrated, the burner 22 may be equipped with a blower. The temperature adjustment line 18e may include a finned pipe. The finned pipe may be heated by the burner 22 provided nearby. The burner 22 burns and heats the finned pipe, thereby heating the heat transfer medium in the temperature adjustment line 18e. When the supply of raw fuel gas to the burner 22 is stopped, the blower blows air onto the finned pipe, thereby cooling the heat transfer medium in the temperature adjustment line 18e. A temperature sensor 57 may be provided near the point where the burner 22 heats or cools the finned pipe, for example, toward the second end of the temperature adjustment line 18e.

[0114] In response to a hot water supply request, the indirect supply line 12 exchanges heat between the heat medium and a medium supplied from, for example, a water supply, and supplies hot water to, for example, a customer facility. A medium may be supplied to the indirect supply line 12 from, for example, a water supply. The medium is, for example, water. A first flow control valve 43 that adjusts the amount of medium supplied may be provided in the indirect supply line 12. A flow sensor 62 that measures the flow rate of the medium may be provided upstream of the first flow control valve 43 in the indirect supply line 12. A temperature sensor 55 that measures a temperature T5 of the heat medium may be provided upstream of the first flow control valve 43 in the indirect supply line 12.

[0115] The indirect supply line 12 includes a second heat exchanger 14. The second heat exchanger 14 may exchange heat between the medium and a heat medium stored in a heat storage tank 17 in response to a hot water supply request. The indirect supply line 12 supplies hot water to, for example, a customer facility. In other words, the indirect supply line 12 may be a hot water supply path. The indirect supply line 12 may be provided with a bypass path 44 that bypasses the second heat exchanger 14. The bypass path 44 may be provided with a second flow control valve 45. The temperature of the medium delivered from the indirect supply line 12 can be adjusted by adjusting the flow rate of the medium bypassing the bypass path 44 with the second flow control valve 45. A temperature sensor 56 that measures a temperature T6 of the heat medium may be provided in the indirect supply line 12, downstream of the second heat exchanger 14, at the point where the bypass path 44 and the indirect supply line 12 join.

[0116] The control device 35 switches the path through which the heat medium passes in the waste heat recovery line 18 depending on the operating state of the fuel cell 16 and whether or not there is a request to supply hot water to the heat storage tank 17. An example of switching will be described below. The control device 35 may further switch the path through which the heat medium passes based on the temperature of the lower part of the heat storage tank 17 measured by the temperature sensor 53.

[0117] When the fuel cell 16 is in operation, the control device 35 may switch the passageway of the heat medium in the waste heat recovery line 18 depending on the relationship between the temperature T3 of the lower part of the heat storage tank 17 and the temperature threshold. The first temperature threshold Th1, which is the temperature threshold when there is no hot water supply request, may be lower than the second temperature threshold Th2, which is the temperature threshold when there is a hot water supply request. The first temperature threshold Th1 is, for example, 30°C. The second temperature threshold Th2 is, for example, 40°C. Switching of the passageway while the fuel cell 16 is in operation will be described below.

[0118] The control device 35 may perform the first control when there is no request for hot water supply and the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the first temperature threshold Th1. In the first control, the waste heat recovery line 18 is switched so that the heat medium passes only through the exhaust gas heat exchange line 18b.

[0119] Specific behaviors in the first control will be described below with reference to FIG. 6. The control device 35 controls the first three-way valve 31 to connect the second end of the heat medium outlet line 18a to the first end of the exhaust gas heat exchange line 18b. Furthermore, the control device 35 controls the second three-way valve 32 to connect the second end of the exhaust gas heat exchange line 18b to the second end of the heat medium inlet line 18f. The control device 35 controls the third three-way valve 33 to disconnect the first end of the third bypass flow path 19c from the first end of the second bypass flow path 19b. The control device 35 may also control the third three-way valve 33 to connect the second end of the temperature adjustment line 18e to the first end of the second bypass flow path 19b or the first end of the third bypass flow path 19c. The control device 35 stops combustion in the burner 22 and stops the blower of the burner 22. The control device 35 stops the second pump 41.

[0120] When the first control is performed, the heat medium from the heat storage tank 17 flows through the heat medium outlet line 18a, the exhaust gas heat exchange line 18b, and the heat medium inlet line 18f in this order. In the third heat exchange section 20 of the exhaust gas heat exchange line 18b, the heat medium exchanges heat with the exhaust gas discharged from the fuel cell 16 and is heated. In the first heat exchange section 19 of the heat medium inlet line 18f, the heat medium exchanges heat with the fuel cell 16. Therefore, the heat medium is further heated. The heat medium then flows into the heat storage tank 17.

[0121] The control device 35 may perform the second control when there is no request for hot water supply and the temperature T3 of the lower part of the heat storage tank 17 is higher than the first temperature threshold value Th1. In the second control, the waste heat recovery line 18 is switched so that the heat medium passes through the heat medium outflow line 18a, the heat medium cooling line 18c, and the exhaust gas heat exchange line 18b in this order.

[0122] Specific behavior in the second control will be described below. The control device 35 controls the first three-way valve 31 to communicate the second end of the heat medium outlet line 18a with the first end of the heat medium cooling line 18c (temperature adjustment line 18e). The control device 35 controls the second three-way valve 32 to communicate the second end of the exhaust gas heat exchange line 18b with the second end of the heat medium inlet line 18f. The control device 35 controls the third three-way valve 33 to communicate the second end of the heat medium cooling line 18c with the first end of the second bypass flow path 19b. The control device 35 stops combustion in the burner 22 and operates the blower of the burner 22, causing the temperature adjustment line 18e to function as the heat medium cooling line 18c. The control device 35 may adjust the amount of air flowing to the burner 22 so that the temperature T7 measured by the temperature sensor 57 becomes equal to a predetermined first temperature target value Tt1, taking into account the amount of heat that the heat medium can acquire through heat exchange with the fuel cell 16. After flowing through the heat medium cooling line 18c, the heat medium flows through the exhaust gas heat exchange line 18b and then through the heat medium inlet line 18f. Taking into account the amount of heat that the heat medium can acquire through heat exchange in the exhaust gas heat exchange line 18b after flowing through the heat medium cooling line 18c, the first temperature target value Tt1 may be set lower than the second temperature target value Tt2 or the third temperature target value Tt3 in the third or fifth control. Note that in the third or fifth control, the heat medium flowing through the temperature adjustment line 18e has already passed through the exhaust gas heat exchange line 18b.

[0123] When the second control is performed, the heat medium from the heat storage tank 17 flows through the heat medium outflow line 18a to the heat medium cooling line 18c. The blower of the burner 22 draws in outside air and sends it to the heat medium cooling line 18c, cooling the heat medium flowing through the heat medium cooling line 18c. The heat medium then flows through the exhaust gas heat exchange line 18b and the heat medium inflow line 18f in that order.

[0124] When the fuel cell 16 is in operation and there is a request for hot water supply, the control device 35 may switch the passageway of the heat medium in the waste heat recovery line 18 based on the inflow heat quantity, which is the heat quantity of the heat medium flowing into the heat storage tank 17, and the provided heat quantity, which is the heat quantity provided by the heat storage tank 17 in response to the hot water supply request. Switching of the passageway when the fuel cell 16 is in operation and there is a request for hot water supply will be described below. Furthermore, the control device 35 may also base the switching of the passageway based on the inflow heat quantity and the provided heat quantity on the temperature T3 at the bottom of the heat storage tank 17.

[0125] The amount of inflowing heat may be calculated based on the temperatures T1, T2 of the heat medium and the flow rate F1 of the heat medium at the inlet and outlet of the heat storage tank 17. Temperature sensors 51, 52 may be provided to measure the temperatures T1, T2 of the heat medium at the inlet and outlet of the heat storage tank 17. A flow rate sensor 61 may be provided to measure the flow rate F1 of the heat medium at the outlet of the heat storage tank 17. Instead of the flow rate sensor 61, a flow rate sensor may be provided at the inlet of the heat storage tank 17 to measure the flow rate F1 of the heat medium.

[0126] The heat output may be calculated based on the amount of water entering the indirect supply line 12 and the temperature of the medium at the inlet and outlet of the indirect supply line 12. A flow sensor 62 may be provided to measure the amount of water entering the indirect supply line 12. Temperature sensors 55, 56 may be provided to measure the temperature of the medium at the inlet and outlet of the indirect supply line 12.

[0127] The control device 35 may perform the third control when the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the third temperature threshold and the amount of inflowing heat is smaller than the amount of provided heat. In the above-described configuration in which the temperature threshold is switched depending on whether or not there is a hot water supply request, the third temperature threshold Th3 may be the same as the second temperature threshold Th2. In the third control, the waste heat recovery line 18 is switched so that the heat medium passes through at least the heat medium heating line 18d (temperature adjustment line 18e). In the third control, as described below, the heat medium may pass through the exhaust gas heat exchange line 18b before the heat medium heating line 18d.

[0128] The behavior during the third control will be described below. The control device 35 controls the first three-way valve 31 to connect the second end of the heat medium outflow line 18a to the first end of the exhaust gas heat exchange line 18b. The control device 35 controls the second three-way valve 32 to connect the second end of the exhaust gas heat exchange line 18b to the first end of the first bypass flow path 19a. The control device 35 controls the third three-way valve 33 to connect the second end of the heat medium heating line 18d to the first end of the third bypass flow path 19c. The control device 35 activates the burner 22 to cause the temperature adjustment line 18e to function as the heat medium heating line 18d. The control device 35 activates the second pump 41 to flow the heat medium into the second heat exchange unit 14. The control device 35 may adjust the amount of raw fuel gas flowing to the burner 22 so that the temperature T7 measured by the temperature sensor 57 becomes equal to a predetermined second temperature target value Tt2, taking into account the amount of heat that can be obtained by the heat medium through heat exchange with the fuel cell 16. The heat medium flows through the heat medium heating line 18d and then through the heat medium inlet line 18f. Taking into account the amount of heat that can be obtained by the heat medium through heat exchange in the heat medium inlet line 18f, the second temperature target value Tt2 may be set lower than the fifth temperature target value Tt5 or the sixth temperature target value Tt6 in the seventh or eighth control described below. The second temperature target value Tt2 may be set so that the temperature of the heat medium after heat exchange with the fuel cell 16 in the heat medium inlet line 18f becomes equal to the fifth temperature target value Tt5 or the sixth temperature target value Tt6. Note that in the seventh or eighth control, the fuel cell 16 is stopped, so the temperature of the heat medium in the heat medium inlet line 18f changes little.

[0129] When the third control is performed, the heat medium from the heat storage tank 17 flows through the heat medium outlet line 18a, the exhaust gas heat exchange line 18b, the heat medium heating line 18d, and the heat medium inlet line 18f in this order. The burner 22 burns and heats the heat medium flowing through the heat medium heating line 18d. The medium flowing through the indirect supply line 12 exchanges heat with the heat medium in the second heat exchange section 14 and is heated.

[0130] The control device 35 may perform the fourth control when the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the fourth temperature threshold Th4 and the inflow heat amount is greater than the provided heat amount, or when the temperature T3 of the lower part of the heat storage tank 17 is higher than the fourth temperature threshold Th4 and the inflow heat amount is less than the provided heat amount. The fourth temperature threshold Th4 may be the same as the second temperature threshold Th2 in the configuration in which the temperature threshold is switched depending on whether or not there is a hot water supply request as described above. Alternatively, the fourth temperature threshold Th4 may be the same as the third temperature threshold Th3 in the configuration in which the third control is performed based on a comparison with the temperature T3 of the lower part of the heat storage tank 17 as described above. In the fourth control, the waste heat recovery line 18 is switched so that the heat medium passes through the heat medium outflow line 18a and the exhaust gas heat exchange line 18b in that order. In the fourth control, the waste heat recovery line 18 may be switched so that the heat medium passes only through the exhaust gas heat exchange line 18b between the heat medium outflow line 18a and the heat medium inflow line 18f.

[0131] The behavior in the fourth control will be described below. The control device 35 controls the first three-way valve 31 to connect the second end of the heat medium outlet line 18a to the first end of the exhaust gas heat exchange line 18b. The control device 35 controls the second three-way valve 32 to connect the second end of the exhaust gas heat exchange line 18b to the second end of the heat medium inlet line 18f. The control device 35 controls the third three-way valve 33 to disconnect the first end of the third bypass flow path 19c from the first end of the second bypass flow path 19b. The control device 35 may control the third three-way valve 33 to connect the second end of the temperature adjustment line 18e to the first end of the second bypass flow path 19b or the first end of the third bypass flow path 19c. The control device 35 stops combustion in the burner 22 and stops the blower of the burner 22. The control device 35 operates the second pump 41 to cause the heat medium to flow through the second heat exchange section 14.

[0132] When the fourth control is performed, the heat medium from the heat storage tank 17 flows in the order of the heat medium outflow line 18a, the exhaust gas heat exchange line 18b, and the heat medium inflow line 18f. In the third heat exchange section 20 of the exhaust gas heat exchange line 18b, the heat medium is heated by heat exchange with the exhaust gas discharged from the fuel cell 16. In the first heat exchange section 19 of the heat medium inflow line 18f, the heat medium exchanges heat with the fuel cell 16. Therefore, the heat medium is further heated. The heat medium then flows to the heat storage tank 17. The medium flowing through the indirect supply line 12 is heated by heat exchange with the heat medium in the second heat exchange section 14.

[0133] When the temperature T3 of the lower part of the heat storage tank 17 is higher than the fifth temperature threshold Th5 and the amount of inflow heat is greater than the amount of provided heat, the control device 35 may switch the path based on the amount of inflow heat and the amount of provided heat based on the water volume W of the condensed water tank of the fuel cell system 11. Specifically, the control device 35 may change the order in which the heat medium in the waste heat recovery line 18 passes through the exhaust gas heat exchange line 18b and the heat medium cooling line 18c, depending on the water volume W of the condensed water tank of the fuel cell system 11. The fifth temperature threshold Th5 may be the same as the second temperature threshold Th2 in the above-described configuration in which the temperature threshold is switched depending on whether or not there is a hot water supply request. Alternatively, the fifth temperature threshold Th5 may be the same as the third temperature threshold Th3 or the fourth temperature threshold Th4 in the above-described configuration in which the third control or the fourth control is performed based on a comparison with the temperature T3 of the lower part of the heat storage tank 17. Hereinafter, switching of the passage path when the temperature T3 of the lower part of the heat storage tank 17 is higher than the fifth temperature threshold value Th5 and the amount of incoming heat is greater than the amount of provided heat will be described.

[0134] The control device 35 may perform a fifth control when the water volume W in the condensed water tank of the fuel cell system 11 is greater than a first water volume threshold W1. In the fifth control, the waste heat recovery line 18 is switched so that the heat medium passes through the heat medium cooling line 18c (temperature adjustment line 18e) after passing through the exhaust gas heat exchange line 18b. The first water volume threshold W1 may be determined, for example, by providing a water level sensor in the condensed water tank, and the control device 35 may determine the water volume W in the condensed water tank based on the detection of this water level sensor. The first water volume threshold may be set appropriately to, for example, 50 to 80% of the capacity of the condensed water tank.

[0135] The behavior in the fifth control will be described below. The control device 35 controls the first three-way valve 31 to connect the second end of the heat medium outflow line 18a to the first end of the exhaust gas heat exchange line 18b. The control device 35 controls the second three-way valve 32 to connect the second end of the exhaust gas heat exchange line 18b to the first end of the first bypass flow path 19a. The control device 35 controls the third three-way valve 33 to connect the second end of the heat medium cooling line 18c to the first end of the third bypass flow path 19c. The control device 35 stops combustion in the burner 22 and operates the blower of the burner 22. The control device 35 operates the second pump 41 to flow the heat medium into the second heat exchange unit 14. The control device 35 may adjust the amount of air supplied to the burner 22 so that the temperature T7 measured by the temperature sensor 57 becomes equal to a predetermined third temperature target value Tt3, taking into consideration the amount of heat that can be obtained by heat exchange between the heat medium and the fuel cell 16. The third temperature target value Tt3 may be equal to the second temperature threshold value Th2. The third temperature target value Tt3 may be less than the second temperature threshold value Th2.

[0136] When the fifth control is performed, the heat medium from the heat storage tank 17 flows in the order of the heat medium outflow line 18a, the exhaust gas heat exchange line 18b, the heat medium cooling line 18c, and the heat medium inflow line 18f. The blower of the burner 22 draws in outside air and sends it to the heat medium cooling line 18c, cooling the heat medium flowing through the heat medium cooling line 18c, causing the temperature adjustment line 18e to function as the heat medium cooling line 18c. The medium flowing through the indirect supply line 12 is heated by heat exchange with the heat medium in the second heat exchange section 14.

[0137] The control device 35 may perform the sixth control when the water volume W in the condensed water tank of the fuel cell system 11 is equal to or less than the second water volume threshold W2. In the configuration in which the fifth control is performed by comparing the water volume W in the condensed water tank as described above, the second water volume threshold W2 may be the same as the first water volume threshold W1. In the sixth control, the waste heat recovery line 18 is switched so that the heat medium passes through the heat medium cooling line 18c (temperature adjustment line 18e) and then through the exhaust gas heat exchange line 18b.

[0138] The behavior during the sixth control will be described below. The control device 35 controls the first three-way valve 31 to connect the second end of the heat medium outlet line 18a to the first end of the heat medium cooling line 18c. The control device 35 controls the second three-way valve 32 to connect the second end of the exhaust gas heat exchange line 18b to the second end of the heat medium inlet line 18f. The control device 35 controls the third three-way valve 33 to connect the second end of the heat medium cooling line 18c to the first end of the second bypass flow path 19b. The control device 35 stops the combustion of the burner 22 and operates the blower of the burner 22, causing the temperature adjustment line 18e to function as the heat medium cooling line 18c. The control device 35 operates the second pump 41 to flow the heat medium into the second heat exchange unit 14. The control device 35 may adjust the amount of air to the burner 22 so that the temperature T7 measured by the temperature sensor 57 becomes a predetermined fourth temperature target value Tt4, taking into account the amount of heat that the heat medium can acquire through heat exchange with the fuel cell 16. After flowing through the heat medium cooling line 18c, the heat medium flows through the exhaust gas heat exchange line 18b and the heat medium inlet line 18f, in that order. Taking into account the amount of heat that the heat medium can acquire through heat exchange in the exhaust gas heat exchange line 18b and the heat medium inlet line 18f, the fourth temperature target value Tt4 may be set lower than the second temperature target value Tt2 or the third temperature target value Tt3.

[0139] When the sixth control is performed, the heat medium from the heat storage tank 17 flows through the heat medium outflow line 18a to the heat medium cooling line 18c. The blower of the burner 22 draws in outside air and sends it to the heat medium cooling line 18c, cooling the heat medium flowing through the heat medium cooling line 18c. The heat medium then flows through the exhaust gas heat exchange line 18b and the heat medium inflow line 18f in that order. The medium flowing through the indirect supply line 12 exchanges heat with the heat medium in the second heat exchange section 14 and is heated.

[0140] The control device 35 may perform the seventh control when the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the seventh temperature threshold Th7 while the fuel cell 16 is stopped and there is no hot water supply request. The seventh temperature threshold Th7 may be the same as the first temperature threshold Th1 in the above-described configuration in which the temperature threshold is switched depending on whether or not there is a hot water supply request. In the seventh control, the waste heat recovery line is switched so that the heat medium passes through the exhaust gas heat exchange line 18b and then the heat medium heating line 18d.

[0141] The behavior during the seventh control will be described below. The control device 35 controls the first three-way valve 31 to connect the second end of the heat transfer medium outlet line 18a to the first end of the exhaust gas heat exchange line 18b. The control device 35 controls the second three-way valve 32 to connect the second end of the exhaust gas heat exchange line 18b to the first end of the first bypass flow path 19a. The control device 35 controls the third three-way valve 33 to connect the second end of the heat transfer medium heating line 18d to the first end of the third bypass flow path 19c. The control device 35 activates the burner 22 to cause the temperature adjustment line 18e to function as the heat transfer medium heating line 18d. The control device 35 stops the second pump 41. The control device 35 may adjust the amount of raw fuel gas to the burner 22 and the speed of the pump 40 so that the temperature T7 measured by the temperature sensor 57 becomes equal to a predetermined fifth temperature target value Tt5. The fifth temperature target value Tt5 is, for example, 75°C.

[0142] When the seventh control is performed, the heat medium from the heat storage tank 17 flows in the order of the heat medium outflow line 18a, the exhaust gas heat exchange line 18b, the heat medium heating line 18d, and the heat medium inflow line 18f. The burner 22 burns and heats the heat medium flowing in the heat medium heating line 18d.

[0143] Furthermore, when the temperature of the fuel cell 16 is greater than the seventh temperature threshold Th7 and less than the tenth temperature threshold Th10, the control device 35 may switch the waste heat recovery line 18 so that the heat medium passes through the heat medium outflow line 18a and then the heat medium heating line 18d (temperature adjustment line 18e) instead of performing the seventh control described above. This switching allows the heat medium to circulate more quickly in the waste heat recovery line 18. Therefore, the heat medium can be heated more quickly.

[0144] When the fuel cell 16 is stopped and there is a request for hot water supply, and the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than an eighth temperature threshold Th8, the control device 35 may switch the waste heat recovery line 18 so that the heat medium passes only through the heat medium heating line 18d (temperature adjustment line 18e). The eighth temperature threshold Th8 may be higher than the second temperature threshold Th2. The eighth temperature threshold Th8 is, for example, 50°C.

[0145] The behavior during the eighth control will be described below. The control device 35 controls the first three-way valve 31 to connect the second end of the heat medium outlet line 18a to the first end of the heat medium heating line 18d. The control device 35 controls the second three-way valve 32 to disconnect the second end of the heat medium inlet line 18f from the first end of the first bypass flow path 19a. The control device 35 may control the second three-way valve 32 to connect the second end of the exhaust gas heat exchange line 18b to the second end of the heat medium inlet line 18f. The control device 35 controls the third three-way valve 33 to connect the second end of the heat medium heating line 18d to the first end of the third bypass flow path 19c. The control device 35 activates the burner 22 to cause the temperature adjustment line 18e to function as the heat medium heating line 18d. The control device 35 may adjust the amount of raw fuel gas to the burner 22 so that the temperature T7 measured by the temperature sensor 57 becomes a predetermined sixth target temperature value Tt6. In the configuration in which the seventh control is performed as described above, the sixth target temperature value Tt6 may be the same as the fifth target temperature value Tt5. The control device 35 operates the second pump 41 to flow the heat medium through the second heat exchange unit 14.

[0146] When the eighth control is performed, the heat medium from the heat storage tank 17 flows through the heat medium outlet line 18a, the heat medium heating line 18d, and the heat medium inlet line 18f in this order. The burner 22 is activated and heats the heat medium flowing through the heat medium heating line 18d. The medium flowing through the indirect supply line 12 is heated by heat exchange with the heat medium in the second heat exchange section 14.

[0147] The control device 35 may perform the following control, for example, periodically, in addition to switching the waste heat recovery line. This control may be performed at any time, but may also be performed in conjunction with the second and sixth controls. The control device 35 may reduce the amount of power generated by the fuel cell 16 when the temperature T4 of the heat medium inlet of the third heat exchanger 20 is equal to or higher than the sixth temperature threshold Th6 and the water volume W of the condensed water tank of the fuel cell system 11 is equal to or lower than the third water volume threshold W3. The sixth temperature threshold Th6 is, for example, 50°C. In a configuration in which the fifth control or the sixth control is performed based on a comparison with the water volume W of the condensed water tank as described above, the third water volume threshold W3 may be the same as the first water volume threshold W1 or the second water volume threshold W2. Specifically, the control device 35 may reduce the amount of raw fuel gas or air supplied to the fuel cell 16 to reduce the amount of power generated by the fuel cell 16.

[0148] Furthermore, the control device 35 may limit the heat-providing ability of the heat storage tank 17 when the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the ninth temperature threshold Th9. In the above-described configuration in which the temperature threshold is switched depending on whether or not there is a hot water supply request, the ninth temperature threshold Th9 may be the same as the second temperature threshold Th2. In the above-described configuration in which the third control, the fourth control, the fifth control, or the sixth control is performed based on a comparison with the temperature T3 of the lower part of the heat storage tank 17, the ninth temperature threshold Th9 may be the same as the third temperature threshold Th3, the fourth temperature threshold Th4, or the fifth temperature threshold Th5. Specifically, the control device 35 may control the first flow control valve 43 in the indirect supply line 12 to adjust the amount of medium supplied.

[0149] Next, the processing executed by the control device 35 in this embodiment will be described with reference to the flowcharts of Figures 7 to 9. The control device 35 may execute this processing at regular intervals.

[0150] 7, when the fuel cell is operating (step S101) and there is no hot water supply request (step S102), the control device 35 determines whether the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the first temperature threshold Th1 (step S103). When the control device 35 determines that the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the first temperature threshold Th1, the control device 35 performs the first control (step S104). When the control device 35 determines that the temperature T3 of the lower part of the heat storage tank 17 is not equal to or lower than the first temperature threshold Th1, the control device 35 performs the second control (step S105).

[0151] When the fuel cell is in operation (step S101) and there is a hot water supply request (step S102), the control device 35 starts supplying hot water (step S106). Specifically, the control device 35 activates the second pump 41 to cause the heat medium to flow through the second heat exchanger 14. The control device 35 determines whether the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the third temperature threshold Th3 (the second temperature threshold Th2 or the fourth temperature threshold Th4) (step S107). When the control device 35 determines that the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the third temperature threshold Th3, the control device 35 determines whether the inflow heat amount is higher than the provided heat amount (step S108). When the control device 35 determines that the inflow heat amount is higher than the provided heat amount, the control device 35 performs the fourth control (step S109). When the control device 35 determines that the inflow heat amount is not higher than the provided heat amount, the control device 35 performs the third control (step S110).

[0152] If the control device 35 determines in step S107 that the temperature T3 of the lower part of the heat storage tank 17 is higher than the third temperature threshold Th3 (fifth temperature threshold Th5), it determines whether the inflow heat amount is less than the provided heat amount (step S111). If the control device 35 determines that the inflow heat amount is less than the provided heat amount, it performs the fourth control described above (step S109). If the control device 35 determines that the inflow heat amount is not less than the provided heat amount, it determines whether the desired condensed water recovery is possible (step S112).

[0153] In one example of the determination made in step S112, the temperature sensor 54 measures the heat medium inlet temperature T4 of the third heat exchange unit 20. If the temperature T4 is lower than the sixth temperature threshold Th6, the control device 35 determines that the desired condensed water recovery is possible. In another example, the control device 35 may determine whether the water volume W of a condensed water tank that stores condensed water generated in the third heat exchange unit 20 is equal to or greater than the first water volume threshold W1 (the second water volume threshold W2 or the third water volume threshold W3). The water volume W of the condensed water tank may be measured by a water level sensor. The water volume W of the condensed water tank may be calculated based on measurements of the amount of heat medium flowing into and out of the condensed water tank. The water volume W of the condensed water tank may be calculated based on the temperature of the exhaust gas from the fuel cell 16.

[0154] If the control device 35 determines that the desired condensed water recovery is possible, the control device 35 performs the fifth control (step S113). If the control device 35 determines that the desired condensed water recovery is not possible, the control device 35 performs the sixth control (step S114).

[0155] 8, when the fuel cell is stopped (step S101) and there is no hot water supply request (step S102), the control device 35 determines whether the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the seventh temperature threshold Th7 (step S115). When the control device 35 determines that the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the seventh temperature threshold Th7, the control device 35 performs a seventh control (step S116). When the control device 35 determines that the temperature T3 of the lower part of the heat storage tank 17 is not equal to or lower than the seventh temperature threshold Th7, the control device 35 transitions the fuel cell system 11 to a standby state (step S117). The standby state refers to a state in which the fuel cell 16 is not operating, the heat storage tank 17 is not providing heat, no fuel gas is being provided to the burner 22, the blower of the burner 22 is not blowing air, and the first pump 40 is stopped.

[0156] When the fuel cell is stopped (step S101) and there is a hot water supply request (step S102), the control device 35 starts supplying hot water (step S118). Specifically, the control device 35 operates the second pump 41 to cause the heat medium to flow through the second heat exchanger 14. The control device 35 determines whether the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the eighth temperature threshold Th8 (step S119). When the control device 35 determines that the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the eighth temperature threshold Th8, the control device 35 performs the eighth control (step S120). When the control device 35 determines that the temperature T3 of the lower part of the heat storage tank 17 is not equal to or lower than the eighth temperature threshold Th8, the process ends.

[0157] In the eighth control, the control device 35 may perform additional control, which will be described below, for example, periodically. The control device 35 determines whether the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the eighth temperature threshold Th8 (step S121). If the control device 35 determines in step S110 that the temperature T3 of the lower part of the heat storage tank 17 is higher than the eighth temperature threshold Th8, the control device 35 stops the supply of gas fuel to the burner 22 (step S122). As a result, the amount of heat supplied to the heat medium in the waste heat recovery line 18 decreases. The control device 35 may stop the first pump 40. The control device 35 ends the process.

[0158] If the control device 35 determines in step S121 that the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the eighth temperature threshold Th8, the control device 35 further determines whether the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the ninth temperature threshold Th9 (step S123). When the control device 35 determines that the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the ninth temperature threshold Th9, the control device 35 limits the heat-providing capacity of the heat storage tank 17 (step S124). As described above, the control device 35 may control the first flow control valve 43 in the indirect supply line 12 to adjust the amount of medium supplied. When the control device 35 determines that the temperature T3 of the lower part of the heat storage tank 17 is higher than the ninth temperature threshold Th9, the control device 35 terminates the additional control.

[0159] Furthermore, the control device 35 may periodically perform the control described below with reference to FIG. 9. This control may be performed at any time, but may also be performed in conjunction with the second and sixth controls. The control device 35 determines whether the temperature T4 of the heat medium inlet of the third heat exchanger 20 is equal to or lower than the sixth temperature threshold Th6 (step S125). If the control device 35 determines in step S125 that the temperature T4 of the lower part of the heat storage tank 17 is equal to or lower than the sixth temperature threshold Th6, it maintains the airflow rate of the blower of the burner 22 (step S126). If the control device 35 determines that the temperature T4 of the lower part of the heat storage tank 17 is not equal to or lower than the sixth temperature threshold Th6, it increases the airflow rate of the blower of the burner 22 (step S127). The airflow rate of the blower of the burner 22 may be increased by increasing the rotation speed of the blower.

[0160] After a predetermined time has elapsed since step S127, the control device 35 determines whether the temperature T4 of the heat medium inlet of the third heat exchange unit 20 is equal to or lower than the sixth temperature threshold Th6 (step S128). If the control device 35 determines that the temperature T4 of the heat medium inlet of the third heat exchange unit 20 is equal to or lower than the sixth temperature threshold Th6, the control device 35 maintains the airflow rate of the blower of the burner 22 (step S126). If the control device 35 determines that the temperature T4 of the heat medium inlet of the third heat exchange unit 20 is not equal to or lower than the sixth temperature threshold Th6, the control device 35 determines whether the desired condensed water recovery is possible, as described above (step S129).

[0161] If the control device 35 determines in step S129 that the desired condensed water recovery is possible, the control device 35 maintains the air flow rate of the blower of the burner 22 (step S126). If the control device 35 determines that the desired condensed water recovery is not possible, the control device 35 reduces the amount of power generated by the fuel cell 16 (step S130). Specifically, the control device 35 reduces the amount of power generated by the fuel cell 16 by reducing the amount of raw fuel gas or air supplied to the fuel cell 16.

[0162] The fuel cell system of this embodiment configured as described above includes a waste heat recovery line 18 that circulates the heat medium between the fuel cell 16 and the heat storage tank 17, and the waste heat recovery line 18 is capable of switching the passage of the heat medium to any one of the exhaust gas heat exchange line 18b, the heat medium cooling line 18c, and the heat medium heating line 18d between the heat medium outflow line 18a and the heat medium inflow line 18f, or is capable of switching the order in which the heat medium passes through at least two or more of the exhaust gas heat exchange line 18b, the heat medium cooling line 18c, and the heat medium heating line 18d, and the control device 35 switches the passage path of the heat medium in the waste heat recovery line 18 depending on the operating state of the fuel cell 16 and whether or not there is a request for hot water supply.

[0163] In a typical fuel cell system using a fuel cell, exhaust heat is recovered by heat exchange between the fuel cell's exhaust gas and a medium. However, it is difficult to sufficiently heat the medium and temporarily supply a large amount of hot water. In a fuel cell system that recovers exhaust heat from exhaust gas and therefore has difficulty temporarily supplying a large amount of heat, a water heater is required to meet the demand for a large amount of heat. In contrast, the fuel cell system 11 of this embodiment, which has the above-described configuration, can recover a larger amount of heat than a configuration that recovers exhaust heat from exhaust gas because both the reformer 26 and the cell stack 27 generally operate at a higher temperature than the exhaust gas. The fuel cell system 11 also includes a heat storage tank 17 that stores a heat medium. The heat medium can store a large amount of heat. Therefore, the fuel cell 16 can temporarily supply a large amount of medium. Therefore, a water heater is not required in the fuel cell system 11. Therefore, the fuel cell system 11 can be made smaller.

[0164] Furthermore, by having the above-described configuration, the fuel cell system 11 of this embodiment can increase the temperature of the heat medium stored in the heat storage tank 17 while appropriately operating the fuel cell 16 according to the operating state of the fuel cell 16 and the hot water supply demand.

[0165] In the fuel cell system 11 of this embodiment, when the fuel cell 16 is operating, the control device 35 switches the heat transfer medium path in the waste heat recovery line 18 according to the relationship between the temperature T3 at the bottom of the heat storage tank 17 and the temperature threshold. The first temperature threshold Th1, which is the temperature threshold when no hot water supply request is made, is lower than the second temperature threshold Th2, which is the temperature threshold when hot water supply request is made. When hot water supply request is made, the heat storage tank 17 supplies heat to the medium flowing through, for example, the indirect supply line 12. Therefore, when hot water supply request is made, the rate at which heat is removed from the heat transfer medium stored in the heat storage tank 17 is increased. In this configuration, by setting the temperature threshold when hot water supply request is made higher than when hot water supply request is not made, the switching of the heat transfer medium path in the waste heat recovery line 18 can be accelerated when hot water supply request is made. Therefore, the fuel cell system 11 can maintain the heat transfer medium stored in the heat storage tank 17 at a high temperature regardless of whether hot water supply request is made or not.

[0166] In the fuel cell system 11 of this embodiment, when there is no request for hot water supply and the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the first temperature threshold Th1, the control device 35 switches the waste heat recovery line 18 so that the heat medium passes only through the exhaust gas heat exchange line 18b. With this configuration, the fuel cell system 11 can heat the heat medium in the exhaust gas heat exchange line 18b with the exhaust gas from the fuel cell 16, while cooling the exhaust gas from the fuel cell 16 and recovering condensed water to be supplied to the fuel cell 16. The fuel cell system 11 can reduce energy consumption by stopping heating the heat medium in the heat medium heating line 18d and cooling the heat medium in the heat medium cooling line 18c.

[0167] In the fuel cell system 11 of this embodiment, when there is no request for hot water supply and the temperature T3 of the lower part of the heat storage tank 17 is higher than the first temperature threshold Th1, the control device 35 switches the waste heat recovery line so that the heat medium passes through the heat medium outflow line 18a, the heat medium cooling line 18c, and the exhaust gas heat exchange line 18b in this order. When the fuel cell 16 is in operation, the exhaust gas of the fuel cell needs to be cooled by the heat medium so that condensed water to be supplied to the fuel cell 16 can be sufficiently recovered. When there is no request for hot water supply and the heat medium stored in the heat storage tank 17 is at a high temperature, the exhaust gas may not be sufficiently cooled by the heat medium. Therefore, the fuel cell system 11 needs to actively cool the heat medium. In this configuration, the fuel cell system 11 cools the high-temperature heat medium flowing out of the heat storage tank 17 in the heat medium cooling line 18c before passing it through the exhaust gas heat exchange line 18b. Therefore, in the fuel cell system 11, the low-temperature heat medium cools the exhaust gas of the fuel cell in the exhaust gas heat exchange line 18b, and the condensed water to be supplied to the fuel cell 16 can be sufficiently recovered.

[0168] In the fuel cell system 11 of this embodiment, when the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the third temperature threshold Th3 and the amount of inflowing heat is smaller than the amount of provided heat, the control device 35 switches the waste heat recovery line 18 so that the heat medium passes through the heat medium heating line 18d. With this configuration, the fuel cell system 11 can further heat the heat medium in the heat medium heating line 18d when the heat medium stored in the heat storage tank 17 is at a low temperature and the amount of heat supplied to the heat medium is insufficient from the amount of heat obtained from the fuel cell 16 alone. Therefore, the heat medium is sufficiently heated, and the amount of heat provided by the heat storage tank 17 can be ensured.

[0169] In the fuel cell system 11 of this embodiment, the control device 35 switches the waste heat recovery line 18 so that the heat medium passes through the heat medium outflow line 18a and the exhaust gas heat exchange line 18b in this order when the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the fourth temperature threshold Th4 and the inflow heat amount is greater than the provided heat amount, or when the temperature T3 of the lower part of the heat storage tank 17 is higher than the fourth temperature threshold Th4 and the inflow heat amount is less than the provided heat amount. With this configuration, the fuel cell system 11 can reduce energy consumption by not heating the heat medium in the heat medium heating line 18d when the amount of heat supplied to the heat medium can be sufficiently recovered from the amount of heat obtained from the fuel cell 16.

[0170] In the fuel cell system 11 of this embodiment, when the water volume W in the condensed water tank is greater than the first water volume threshold W1, the control device 35 switches the waste heat recovery line 18 so that the heat medium passes through the heat medium cooling line 18c after passing through the exhaust gas heat exchange line 18b. With this configuration, the fuel cell system 11 can cool the heat medium stored in the heat storage tank 17 so that the temperature of the heat medium does not become too high. Furthermore, the fuel cell system 11 can stop cooling the heat medium in the heat medium cooling line 18c, thereby reducing energy consumption.

[0171] In the fuel cell system 11 of this embodiment, when the water volume W in the condensed water tank is equal to or less than the second water volume threshold W2, the control device 35 switches the waste heat recovery line 18 so that the heat medium passes through the heat medium cooling line 18c and then through the exhaust gas heat exchange line 18b. The condensed water is supplied to the fuel cell 16 and used for the steam reforming reaction. When the water volume W in the condensed water tank is equal to or less than the second water volume threshold W2, there is a risk of a shortage of condensed water, which may adversely affect the fuel cell 16. Therefore, the fuel cell system 11 needs to recover the condensed water by cooling the exhaust gas of the fuel cell 16 with the heat medium. If the heat medium is at a high temperature, the fuel cell system 11 needs to cool the heat medium before cooling the exhaust gas. In this configuration, the fuel cell system 11 cools the high-temperature heat medium flowing out of the heat storage tank 17 in the heat medium cooling line 18c before flowing it through the exhaust gas heat exchange line 18b. Therefore, the fuel cell system 11 can cool the exhaust gas from the fuel cell 16 with a low-temperature heat medium in the exhaust gas heat exchange line 18b, and can sufficiently recover the condensed water to be supplied to the fuel cell 16.

[0172] In the fuel cell system 11 of this embodiment, the control device 35 reduces the amount of power generated by the fuel cell 16 when the temperature T4 of the heat medium inlet of the third heat exchanger 20 is equal to or higher than the sixth temperature threshold Th6 and the amount of water in the condensed water tank is equal to or lower than the third water volume threshold. When the amount of water W in the condensed water tank is equal to or lower than the third water volume threshold W3, there is a risk of a shortage of condensed water being supplied to the fuel cell 16 and used in the steam reforming reaction. In this case, there is a risk of adverse effects on the fuel cell 16 when the amount of power generated by the fuel cell 16 is high. In this configuration, the fuel cell system 11 can reduce adverse effects on the fuel cell 16 by reducing the amount of power generated by the fuel cell 16 when the amount of water W in the condensed water tank is equal to or lower than the third water volume threshold W3.

[0173] In the fuel cell system 11 of this embodiment, when the fuel cell 16 is stopped and there is no hot water supply request, and the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the seventh temperature threshold Th7, the control device 35 switches the waste heat recovery line 18 so that the heat medium passes through the exhaust gas heat exchange line 18b and the heat medium heating line 18d in that order. With this configuration, the fuel cell system 11 can heat the heat medium with the exhaust gas from the fuel cell when still warm exhaust gas is discharged from the fuel cell even when the fuel cell 16 is stopped. The fuel cell system 11 can further heat the heat medium in the heat medium heating line 18d. Therefore, the fuel cell system 11 can efficiently heat the heat medium. The heated heat medium can be used when hot water supply is requested in the future.

[0174] In the fuel cell system 11 of this embodiment, when the fuel cell 16 is stopped and there is a request for hot water supply, the control device 35 switches the waste heat recovery line 18 so that the heat medium passes only through the heat medium heating line 18d when the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than the eighth temperature threshold Th8. When the heat medium stored in the heat storage tank 17 is low temperature and there is a request for hot water supply, the heat medium needs to be heated quickly to meet the request. In this configuration, when the fuel cell 16 is stopped and the heat medium cannot be heated by the fuel cell exhaust gas, the fuel cell system 11 can circulate the heat medium through the waste heat recovery line 18 without passing it through the exhaust gas heat exchange line 18b. This shortens the time the heat medium circulates through the waste heat recovery line 18, and the fuel cell system 11 can quickly return the heated heat medium to the heat storage tank 17.

[0175] In the fuel cell system 11 of this embodiment, when the temperature T3 of the lower part of the heat storage tank 17 is equal to or lower than a ninth temperature threshold Th9, the control device 35 limits the ability of the heat storage tank 17 to provide heat. For example, when the amount of heat of the heat medium stored in the heat storage tank 17 is small, the fuel cell system 11 can maintain the temperature of the medium (hot water supply temperature) at the outlet of the indirect supply line 12 by controlling the first flow rate adjustment valve 43 in the indirect supply line 12 to adjust the amount of medium supplied.

[0176] The drawings illustrating the embodiments of the present disclosure are schematic, and the dimensional ratios and the like in the drawings do not necessarily correspond to the actual ones.

[0177] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art could make various modifications or alterations based on the present disclosure. Therefore, it should be noted that these modifications or alterations are included in the scope of the present disclosure. For example, the functions included in each component can be rearranged so as not to cause logical inconsistencies, and multiple components can be combined or divided into one.

[0178] All of the features described in this disclosure and / or all steps of all of the disclosed methods or processes may be combined in any combination except combinations in which these features are mutually exclusive. Furthermore, each feature described in this disclosure may be replaced by an alternative feature serving the same, equivalent, or similar purpose, unless expressly denied. Thus, unless expressly denied, each disclosed feature is only one example of a generic series of identical or equivalent features.

[0179] Furthermore, embodiments of the present disclosure are not limited to the specific configurations of any of the above-described embodiments, but rather extend to any novel feature or combination thereof described herein, or any novel method or process step or combination thereof described herein.

[0180] In this disclosure, descriptions such as "first" and "second" are identifiers for distinguishing the configuration. In this disclosure, the configurations distinguished by descriptions such as "first" and "second" can have their numbers interchanged. For example, the first heat exchange unit can have its identifiers "first" and "second" interchanged with the second heat exchange unit. The identifiers are interchanged simultaneously. The configurations remain distinguished even after the identifiers are interchanged. The identifiers may be deleted. A configuration from which an identifier has been deleted is distinguished by a symbol. The identifiers "first" and "second" in this disclosure should not be used solely to interpret the order of the configurations or to justify the existence of an identifier with a smaller number. [Explanation of symbols]

[0181] 10,100,200 Combined Heat and Power System 11 Fuel Cell System 12 Indirect supply lines 13 Indirect supply lines 14 Second heat exchange section 15 Fourth heat exchange section 16 Fuel Cell 17 Heat storage tank 18 Waste heat recovery line 18a Heat transfer medium outflow line 18b Exhaust gas heat exchange line 18c Heat transfer medium cooling line 18d Heat medium heating line 18e Second flow path (temperature control line) 18f Heat medium inlet line 18g First flow path 19 First heat exchange section 19a Fourth flow path (first bypass flow path) 19b Third flow path (second bypass flow path) 19c Third bypass flow path 20 Third heat exchange section 21 Heating section 21a,21b Temperature control section 22 Burner 23 Gas-liquid separator 24 First Pump 25 Conduit 26 Reformer 27 Cell Stack 28 Gasket 29 Case 30 Insulation 31 First three-way valve 32 Second three-way valve 33 Third three-way valve 35 Control device 36 Pump 37 First Indirect Supply Line 38 Second Indirect Supply Line 39 First medium supply path 40 First Pump 41 Second Pump 42 Pump 43 First flow control valve 44 Bypass Road 45 Second flow control valve 46 Pump 47 Check valve 48 Bathtub water inlet valve 49 Heat radiation part 50 Direct Supply Line 51, 52, 53, 54, 55, 56, 57 Temperature sensors 61,62 Flow sensor 64 Heat radiation part 65 Second medium supply path 66 Sending route 67 Return Route 68 High temperature delivery path 69 Low temperature delivery path 70 Three-way valve 71 First heat transfer line 72 Second heat transfer line

Claims

1. a fuel cell system having a fuel cell, a first heat exchange unit located close to the outside of the fuel cell or located inside the fuel cell and recovering heat generated by the fuel cell using a heat medium, a heat storage tank that stores the heat medium and provides heat in response to a hot water supply request, and a waste heat recovery line that circulates the heat medium between the fuel cell and the heat storage tank; an indirect supply line including a second heat exchange unit that supplies heat by exchanging heat between the heat medium stored in the heat storage tank and a medium, the fuel cell system has a third heat exchange unit that exchanges heat between the exhaust gas of the fuel cell and the heat medium circulating through the waste heat recovery line, The fuel cell system has a temperature adjusting unit that is located in the waste heat recovery line between the first heat exchange unit and the third heat exchange unit and that is capable of heating or cooling the heat medium circulating in the waste heat recovery line. Combined heat and power system.

2. 2. The combined heat and power system of claim 1, In the waste heat recovery line, the third heat exchange unit is located upstream of the first heat exchange unit. Combined heat and power system.

3. 3. The combined heat and power system according to claim 1 or 2, In the waste heat recovery line, the fuel cell system has a heat radiating section between the heat storage tank and the third heat exchange section. Combined heat and power system.

4. 3. The combined heat and power system according to claim 1 or 2, the waste heat recovery line includes a first flow path downstream of the third heat exchange unit that bypasses the temperature adjustment unit and is connected to the first heat exchange unit. Combined heat and power system.

5. 3. The combined heat and power system according to claim 1 or 2, The waste heat recovery line is provided downstream of the heat storage tank. a second flow path that bypasses the third heat exchange unit and connects to the first heat exchange unit; a third flow path branching from the second flow path and connecting to the third heat exchange section, Combined heat and power system.

6. 3. The combined heat and power system according to claim 1 or 2, A direct supply line for supplying heat by flowing the heat medium stored in the heat storage tank, Combined heat and power system.

7. 3. The combined heat and power system according to claim 1 or 2, a control device; The waste heat recovery line a heat medium outlet line for causing the heat medium to flow out from the heat storage tank, an exhaust gas heat exchange line having the third heat exchange unit, a heat medium cooling line for cooling the heat medium, a heat medium heating line for heating the heat medium, and a heat medium inlet line for causing the heat medium to flow into the heat storage tank, the heat medium being capable of recovering heat generated by the fuel cell into the heat medium; The passage of the heat medium to any one of the exhaust gas heat exchange line, the heat medium cooling line, and the heat medium heating line can be switched between the heat medium outflow line and the heat medium inflow line, or the order of passage of the heat medium to at least two or more of the exhaust gas heat exchange line, the heat medium cooling line, and the heat medium heating line can be switched, The control device switches the passage of the heat medium in the waste heat recovery line depending on the operating state of the fuel cell and whether or not there is a request for hot water supply. Combined heat and power system.

8. 8. The combined heat and power system according to claim 7, When the fuel cell is operating, the control device switches the path through which the heat transfer medium passes in the waste heat recovery line depending on the relationship between the temperature of the lower part of the heat storage tank and a temperature threshold, and the first temperature threshold, which is the temperature threshold when there is no hot water supply request, is lower than the second temperature threshold, which is the temperature threshold when there is a hot water supply request.

9. 9. The combined heat and power system according to claim 8, The control device is a combined heat and power supply system that switches the waste heat recovery line so that the heat transfer medium passes only through the exhaust gas heat exchange line when there is no request for hot water supply and the temperature at the bottom of the heat storage tank is below the first temperature threshold.

10. 9. The combined heat and power system according to claim 8, The control device is a combined heat and power supply system that switches the waste heat recovery line so that the heat transfer medium passes through the heat transfer medium cooling line and the exhaust gas heat exchange line in that order when there is no request for hot water supply and the temperature at the bottom of the heat storage tank is higher than the first temperature threshold.

11. 8. The combined heat and power system according to claim 7, The control device is a combined heat and power supply system that, when the fuel cell is in operation and there is a request for hot water supply, switches the path through which the heat medium passes in the waste heat recovery line based on the inflow heat quantity, which is the heat quantity of the heat medium flowing into the heat storage tank, and the provided heat quantity, which is the heat quantity provided by the heat storage tank in response to the hot water supply request.

12. 12. The combined heat and power system of claim 11, The control device switches the waste heat recovery line so that the heat medium passes through the heat medium heating line when the temperature of the lower part of the heat storage tank is below a third temperature threshold and the amount of heat flowing in is smaller than the amount of heat provided.

13. 12. The combined heat and power system of claim 11, The control device is a combined heat and power supply system that switches the waste heat recovery line so that the heat medium passes only through the exhaust gas heat exchange line when the temperature of the lower part of the heat storage tank is below a fourth temperature threshold and the inflow heat amount is greater than the provided heat amount, or when the temperature of the lower part of the heat storage tank is higher than the fourth temperature threshold and the inflow heat amount is less than the provided heat amount.

14. 14. The combined heat and power system of claim 13, further comprising a condensed water tank that stores condensed water generated in the third heat exchange unit; The control device is a combined heat and power supply system that, when the temperature of the lower part of the heat storage tank is higher than a fifth temperature threshold and the amount of incoming heat is greater than the amount of provided heat, changes the order in which the heat medium passes through the exhaust gas heat exchange line and the heat medium cooling line in the waste heat recovery line depending on the amount of water in the condensate water tank.

15. 15. The combined heat and power system of claim 14, The control device is a combined heat and power supply system that reduces the power generation amount of the fuel cell when the temperature of the heat medium inlet in the third heat exchange unit is higher than a sixth temperature threshold and the water volume in the condensate tank is lower than a third water volume threshold.

16. 8. The combined heat and power system according to claim 7, The control device is a combined heat and power supply system that, when the fuel cell is stopped and there is no request for hot water supply, switches the waste heat recovery line so that the heat medium passes through the exhaust gas heat exchange line and the heat medium heating line in that order when the temperature at the bottom of the heat storage tank is below a seventh temperature threshold.

17. 8. The combined heat and power system according to claim 7, The control device is a combined heat and power supply system that, when the fuel cell is stopped and there is a request for hot water supply, switches the waste heat recovery line so that the heat medium passes only through the heat medium heating line when the temperature at the bottom of the heat storage tank is below an eighth temperature threshold.

18. 18. The combined heat and power system of claim 17, A combined heat and power system that limits the ability of the thermal storage tank to provide heat when the temperature of a lower portion of the thermal storage tank is below a ninth temperature threshold.

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