JP2012063044A - Exhaust heat recovery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust heat recovery system with excellent energy efficiency, capable of storing a heating medium at high temperature.SOLUTION: The exhaust heat recovery system includes a first heat storage tank TNK1 and a second heat storage tank TNK2, as heat storage tanks TNK1 and TNK2, as well as a control means C for controlling the communication mode of a heating medium. The control means C causes the heating medium taken out of the first heat storage tank TNK1 to flow into a heat exchange part 1, and is configured to be able to switch between a first heat storage state in which the heating medium that flows out of the heat exchange part 1 is made to flow into the first heat storage tank TNK1 and a second heat storage state in which the heating medium that flows out of the heat exchange part 1 is caused to flow into the second heat storage tank TNK2, according to at least one temperature selected from among the temperature of the heating medium stored in the first heat storage tank TNK1, the temperature of the heating medium stored in the second heat storage tank TNK2, and the temperature of the heating medium that flows out of the heat exchange part 1.

Description

  The present invention includes a heat storage tank capable of storing heat by storing a heat medium, and the heat medium is circulated between a heat exchange tank to which exhaust heat from the fuel cell is supplied and the heat storage tank. The present invention relates to an exhaust heat recovery system that recovers exhaust heat.

  Many exhaust heat recovery systems for recovering exhaust heat from a fuel cell as a heat source have been proposed. However, when an internal combustion engine is used as a heat source, the heat medium after exhaust heat recovery becomes high temperature, but the temperature of the heat medium after exhaust heat recovery from the fuel cell is relatively low. If the capacity of the heat storage tank that stores the heat medium is the same, the temperature of the heat medium that collects the exhaust heat is low (that is, the temperature of the heat medium stored in the heat storage tank is low). This means that the total amount of heat that can be stored is reduced. If the capacity of the heat storage tank is increased (that is, if a large amount of low-temperature heat medium is stored), the total amount of heat can be increased, but the tank becomes large.

  In general, the higher the temperature of the heat medium, the better in terms of widening the use of the heat medium. For example, a heat medium having a relatively low heat medium temperature of 60 ° C. can be used for hot water supply applications, but may not be used for heating applications such as floor heaters or desiccant dehumidifiers. Therefore, even if the temperature of the heat medium is low, if the large-capacity heat storage tank is used as described above, the total amount of heat that can be stored in the heat storage tank can be increased, but the use of the heat medium is limited. This problem cannot be solved.

  Patent Document 1 describes an exhaust heat recovery system that recovers exhaust heat of a fuel cell. This exhaust heat recovery system includes two hot water storage tanks, a hot water storage tank for storing hot water (60 ° C. to 80 ° C.) and a hot water storage tank for storing low temperature (40 ° C. to 60 ° C.) hot water. Tap water as cooling water is allowed to flow into the heat exchange part of the fuel cell, and when the temperature of hot water flowing out from the heat exchange part of the fuel cell is high, it is transferred to a hot water storage tank, or the fuel cell When the temperature of hot water flowing out from the heat exchanger is low, it is transferred to a low temperature hot water storage tank. The hot water storage tank is provided with heat retaining means (such as a heat retaining heater) for keeping the temperature of the hot water at 60 ° C. or higher.

Japanese Patent Laid-Open No. 2002-75390 (FIG. 1, paragraphs 0019 to 0020)

  Since the exhaust heat recovery system described in Patent Document 1 has relatively low-temperature tap water flowing into the heat exchange part of the fuel cell, the temperature of hot water flowing out from the heat exchange part of the fuel cell is set to a desired high temperature. There is a high possibility that it will not be improved. In particular, since the temperature of tap water becomes very low in winter, it is difficult to change the low-temperature tap water to, for example, 80 ° C. hot water with a fuel cell with a small amount of exhaust heat.

  In addition, the exhaust heat recovery system described in Patent Document 1 keeps the temperature of hot water in a high-temperature hot water storage tank in a high temperature region by using a heat retaining heater or the like. That is, it can be said that this exhaust heat recovery system consumes energy and obtains hot water separately from the exhaust heat of the fuel cell. Therefore, there is a problem that the energy efficiency of the exhaust heat recovery system is lowered.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an exhaust heat recovery system capable of storing a high-temperature heat medium and having good energy efficiency.

In order to achieve the above object, a feature configuration of an exhaust heat recovery system according to the present invention includes a heat storage tank capable of storing heat by storing a heat medium, and the heat exchange unit to which exhaust heat from a fuel cell is supplied, An exhaust heat recovery system for recovering exhaust heat of the fuel cell by circulating the heat medium with a heat storage tank,
A first heat storage tank and a second heat storage tank as the heat storage tank, and a control means for controlling the flow mode of the heat medium;
The control means causes the heat medium taken out from the first heat storage tank to flow into the heat exchanging unit, the temperature of the heat medium stored in the first heat storage tank, and the second heat storage. The heat medium flowing out from the heat exchange unit according to at least one of the temperature of the heat medium stored in the tank for use and the temperature of the heat medium flowing out from the heat exchange unit Is configured to be switchable between a first heat storage state in which the refrigerant flows into the first heat storage tank and a second heat storage state in which the heat medium flowing out from the heat exchange section flows into the second heat storage tank. It is in.

According to the above characteristic configuration, in the first heat storage state, the heat medium taken out from the first heat storage tank is caused to flow into the heat exchange part of the fuel cell, and the heat medium flowing out from the heat exchange part of the fuel cell is allowed to flow into the first heat storage part. Re-enter the tank. That is, the first heat storage state can be regarded as a state in which the temperature of the heat medium in the first heat storage tank that will flow into the heat exchange section of the fuel cell is repeated.
In the second heat storage state, the heat medium taken out from the first heat storage tank is caused to flow into the heat exchange part of the fuel cell, and the heat medium flowing out from the heat exchange part of the fuel cell is caused to flow into the second heat storage tank. . That is, the second heat storage state is a state in which the heat medium in the first heat storage tank that has been heated to some extent in the first heat storage state is further heated in the heat exchange section of the fuel cell and stored in the second heat storage tank. Can be considered.
As described above, if necessary, the temperature of the heat medium stored in the first heat storage tank is raised in the first heat storage state using the exhaust heat of the fuel cell, and then stored in the first heat storage tank. The heated heat medium can be further heated using the exhaust heat of the fuel cell and stored in the second heat storage tank. Therefore, even in a situation where the temperature of clean water is low, such as in winter, a high-temperature heating medium can be obtained using exhaust heat of the fuel cell without consuming energy separately.
Therefore, it is possible to provide a waste heat recovery system that can store a high-temperature heat medium and has good energy efficiency.

  Another feature of the exhaust heat recovery system according to the present invention is that the control means is a heat medium that is taken out of the heat medium stored in the first heat storage tank and flows into the heat exchange unit. When the temperature is higher than the first target temperature, which is the target temperature of the heat medium stored in the first heat storage tank, heat is stored in the second heat storage state, and when the temperature is equal to or lower than the first target temperature, The point is that heat is stored in one heat storage state.

According to the above characteristic configuration, the temperature of the heat medium that is taken out of the heat medium stored in the first heat storage tank and flows into the heat exchange section is higher than the first target temperature or lower than the first target temperature. Depending on whether or not, the first heat storage state and the second heat storage state are switched.
That is, the heat medium flowing into the second heat storage tank becomes a heat medium obtained by further raising the temperature of the heat medium higher than the first target temperature taken out from the first heat storage tank in the heat exchange part of the fuel cell. As a result, a heat medium having a temperature higher than the first target temperature can be selectively stored in the second heat storage tank.

  Another characteristic configuration of the exhaust heat recovery system according to the present invention is that the control means convects the heat medium inside the first heat storage tank when storing heat in the first heat storage state.

When the heat medium is stored in the first heat storage tank while forming a temperature stratification, the heat medium heated in the heat exchange part of the fuel cell is stored in the first heat storage tank while maintaining its temperature substantially. . That is, since the heat medium having a high temperature and the heat medium having a low temperature coexist in the first heat storage tank, the temperature of all the heat mediums in the first heat storage tank is close to the first target temperature. You must wait until the entire heat storage tank is replaced with a hot medium.
However, according to this characteristic configuration, the temperature of the heat medium inside the first heat storage tank is made uniform overall by convection of the heat medium inside the first heat storage tank. That is, in the first heat storage state, when the heat medium heated in the heat exchange part of the fuel cell flows into the first heat storage tank, it is mixed with the low-temperature heat medium and the heat inside the first heat storage tank. The temperature of the medium increases as a whole. As a result, the temperature of all the heat media inside the first heat storage tank can be raised relatively quickly to the first target temperature.

  Another characteristic configuration of the exhaust heat recovery system according to the present invention is that, when the control means performs heat storage in the second heat storage state, the heat medium on the low temperature side stored in the second heat storage tank is taken out. The point is to flow into the first heat storage tank.

  According to the above characteristic configuration, in the second heat storage state, the high temperature heat medium is stored in the second heat storage tank, and the low temperature side heat medium stored in the second heat storage tank is transferred to the first heat storage tank. By doing so, the low-temperature-side heat medium inside the second heat storage tank can be replaced with a high-temperature heat medium. Further, the low-temperature side heat medium stored in the second heat storage tank can be continuously stored using the first heat storage tank. Thus, even if it is necessary to expel a part of the heat medium from the second heat storage tank, the heat amount of the expelled heat medium is continuously stored in the first heat storage tank without being discarded. As a result, a decrease in energy efficiency is suppressed.

  According to another characteristic configuration of the exhaust heat recovery system according to the present invention, the control means is configured such that the temperature of the heat medium on the low temperature side stored in the second heat storage tank is higher than the first target temperature. When the temperature is equal to or higher than two target temperatures, the heat medium on the low temperature side is allowed to flow into the first heat storage tank while forming a temperature stratification inside the first heat storage tank.

  According to the above characteristic configuration, when the low temperature side heat medium stored in the second heat storage tank is continuously stored using the first heat storage tank, the low temperature side heat medium stored in the second heat storage tank is stored. When the temperature is equal to or higher than the second target temperature higher than the first target temperature, the low-temperature heat medium is caused to flow into the first heat storage tank while forming a temperature stratification inside the first heat storage tank. . That is, a high-temperature heat medium that is equal to or higher than the second target temperature can be stored in the first heat storage tank in addition to the second heat storage tank.

It is a figure which shows the distribution | circulation form of the heat carrier in a 1st heat storage state. It is a figure which shows the distribution | circulation form of the heat medium in a 2nd heat storage state when the heat storage amount is not full in the 2nd heat storage tank. It is a figure which shows the distribution | circulation form of the heat medium in a 2nd heat storage state when the heat storage amount is full in the 2nd heat storage tank. It is a figure which shows the distribution | circulation state of the heat medium in a heat use state. It is a flowchart of a waste heat recovery driving | operation.

<First Embodiment>
The exhaust heat recovery system according to the first embodiment will be described below with reference to the drawings.
FIG. 1 is a diagram illustrating the configuration of an exhaust heat recovery system. As shown in the figure, the exhaust heat recovery system includes heat storage tanks TNK1 and TNK2 that can store heat by storing a heat medium, the heat exchange unit 1 to which exhaust heat from the fuel cell FC is supplied, and the heat storage tank TNK1, Exhaust heat of the fuel cell FC is recovered by circulating a heat medium with the TNK 2. In the present embodiment, the exhaust heat recovery system includes a first heat storage tank TNK1 and a second heat storage tank TNK2 as heat storage tanks, and a control unit C as control means for controlling the flow mode of the heat medium. The heat medium is, for example, water. In the present invention, the type of the fuel cell is not limited. For example, various types of fuel cells such as a polymer electrolyte fuel cell and a solid oxide fuel cell can be used.

  A heat medium stored in the first heat storage tank TNK1 is directly supplied to the heat exchange unit 1 of the fuel cell FC. That is, the heat medium stored in the second heat storage tank TNK2 is not directly supplied to the heat exchange unit 1 of the fuel cell FC. Comparing the roles of the first heat storage tank TNK1 and the second heat storage tank TNK2, the first heat storage tank TNK1 is for storing a relatively low-temperature heat medium, and the second heat storage tank TNK2 is relatively It is for storing high-temperature heat medium.

  Between the heat exchanging part 1, the first heat storage tank TNK1, and the second heat storage tank TNK2 of the fuel cell FC, flow paths L1 to L7 through which water as a heat medium can flow are installed. The flow path L1 connects the lower part of the first heat storage tank TNK1 and the inlet 1a of the heat exchange part 1 of the fuel cell FC. A control valve CV5 is provided in the middle of the flow path L1. The flow path L2 connects the outlet 1b of the heat exchange unit 1 of the fuel cell FC and the upper part of the second heat storage tank TNK2. A control valve CV1 is provided in the middle of the flow path L2. The flow path L3 connects the middle of the flow path L2 and the lower part of the first heat storage tank TNK1. Specifically, the flow path L3 branches from the flow path L2 in the control valve CV1, and is connected to the connection portion 5 below the first heat storage tank TNK1. In the middle of the flow path L3, a control valve CV2 and a control valve CV3 are sequentially provided from the control valve CV1 toward the first heat storage tank TNK1. The flow path L4 connects the middle of the flow path L3 and the upper part of the first heat storage tank TNK1. Specifically, the flow path L4 branches from the flow path L3 in the control valve CV3 and reaches the upper part of the first heat storage tank TNK1. The flow path L5 connects the middle of the flow path L3 and the lower part of the second heat storage tank TNK2. Specifically, the flow path L5 branches from the flow path L3 in the control valve CV2 and reaches the lower part of the second heat storage tank TNK2. The flow path L6 connects the upper part of the first heat storage tank TNK1 and the lower part of the second heat storage tank TNK2. The flow path L7 connects the upper part of the first heat storage tank TNK1 and the middle of the flow path L1. Specifically, the flow path L7 reaches from the upper part of the first heat storage tank TNK1 to the control valve CV5.

  In the exhaust heat recovery system, flow paths L8 to L10 are also installed. The flow path L8 connects the supply source of clean water and the lower part of the first heat storage tank TNK1. The flow path L9 connects the second heat storage tank TNK2, the hot water supply destination of water (heat medium), and the heat use destination. The flow path L10 connects the middle of the flow path L8 and the middle of the flow path L9. A control valve CV4 is provided in the middle of the flow path L10. Specifically, the flow path L10 is branched by the branch part 3 in the middle of the flow path L8 and reaches the junction part 4 in the middle of the flow path L9.

  In FIG. 1, the symbols corresponding to the three flow paths of the control valves CV1, CV2, CV3, and CV5 are indicated by “a”, “b”, and “c”. The control unit C switches the heat medium distribution state in the control valves CV1, CV2, CV3, and CV5 to any one of “ab distribution state”, “ac distribution state”, “bc distribution state”, and “abc distribution state”. Can do. Moreover, the control part C can adjust the opening degree of the control valve CV4. Although illustration is omitted, the flow of the heat medium in the flow path is adjusted by the control unit C.

  A backup boiler B is provided in the middle of the flow path L9. Specifically, the backup boiler B is provided on the downstream side of the junction 4 in the flow path L9. The operation of the backup boiler B is controlled by the control unit C.

  In each part through which the heat medium flows, temperature sensors T1 to T7 for measuring the temperature of the heat medium are provided. The temperature measurement result is sent to the control unit C. The temperature sensor T1 is provided in the middle of the flow path L1. Specifically, it is provided in the flow path L1 in the vicinity of the inlet 1a of the heat exchange part 1 of the fuel cell FC. That is, the temperature sensor T1 can measure the temperature of the heat medium immediately before flowing into the heat exchange unit 1 of the fuel cell FC. The temperature sensor T2 is provided in the middle of the flow path L2. Specifically, it is provided in the flow path L2 in the vicinity of the outlet 1b of the heat exchange unit 1 of the fuel cell FC. That is, the temperature sensor T2 can measure the temperature of the heat medium immediately after flowing out of the heat exchange unit 1 of the fuel cell FC. The temperature sensor T3 is provided in the lower part (bottom part) of the first heat storage tank TNK1. That is, the temperature sensor T3 can measure the temperature of the heat medium stored around the bottom of the first heat storage tank TNK1. The temperature sensor T4 is provided at the center of the first heat storage tank TNK1. That is, the temperature sensor T4 can measure the temperature of the heat medium stored around the center of the first heat storage tank TNK1. The temperature sensor T5 is provided on the top (top) of the first heat storage tank TNK1. That is, the temperature sensor T5 can measure the temperature of the heat medium stored around the top of the first heat storage tank TNK1. The temperature sensor T6 is provided in the lower part (bottom part) of the second heat storage tank TNK2. That is, the temperature sensor T6 can measure the temperature of the heat medium stored around the bottom of the second heat storage tank TNK2. The temperature sensor T7 is provided in the upper part (top part) of the second heat storage tank TNK2. That is, the temperature sensor T7 can measure the temperature of the heat medium stored around the top of the second heat storage tank TNK2.

Next, heat storage in the first heat storage tank TNK1 and the second heat storage tank TNK2 will be described.
In the present embodiment, the control unit C causes the heat medium taken out from the first heat storage tank TNK1 to flow into the heat exchange unit 1 of the fuel cell FC, and the temperature of the heat medium stored in the first heat storage tank TNK1. And the first heat storage state in which the heat medium flowing out from the heat exchange unit flows into the first heat storage tank TNK1 according to the temperature of the heat medium stored in the second heat storage tank, and from the heat exchange unit 1 The second heat storage state in which the flowing heat medium flows into the second heat storage tank TNK is switchable. That is, the control unit C performs the first heat storage state when the temperature of the heat medium can be raised in the heat exchange unit 1 of the fuel cell FC but cannot be sufficiently raised, and the heat medium in the heat exchange unit 1 of the fuel cell FC. When the temperature can be sufficiently raised, the second heat storage state is performed. Here, the fact that the temperature of the heat medium cannot be sufficiently increased means that the temperature cannot be increased because the heat exchange unit 1 of the fuel cell FC does not have enough heat to recover the heat medium. In other words, the control unit C stores the heat medium that has not been sufficiently heated in the first heat storage tank TNK1, and stores the heat medium that has been sufficiently heated in the second heat storage tank TNK2. For example, when the temperature of the heat medium flowing into the heat exchange unit 1 of the fuel cell FC is about 37 ° C., the control unit C has a temperature of the heat medium flowing out of the heat exchange unit 1 of about 85 ° C. to 90 ° C. It is controlled to become.

[First heat storage state]
FIG. 1 is a diagram showing a flow mode of the heat medium in the first heat storage state. In the figure, the flow of the heat medium is indicated by a bold line.
The control unit C causes the heat medium taken out from the first heat storage tank TNK1 to flow into the heat exchange unit 1 of the fuel cell FC, and causes the heat medium flowing out from the heat exchange unit 1 to flow into the first heat storage tank TNK1. The exhaust heat recovery of the fuel cell FC can be performed in the first heat storage state. Specifically, in the first heat storage state, the control unit C causes the heat medium taken out from the upper portion of the first heat storage tank TNK1 to flow into the heat exchange unit 1 of the fuel cell FC, and also the heat exchange unit of the fuel cell FC. 1 is caused to flow into the lower part of the first heat storage tank TNK1. In order to distribute the heat medium in such a form, the control unit C switches the control valve CV1 to the ac distribution state, switches the control valve CV2 to the ab distribution state, switches the control valve CV3 to the ab distribution state, and controls the control valve CV5. To ac distribution state.

  The controller C performs heat storage in the first heat storage state among the heat medium stored in the first heat storage tank TNK1 and the temperature of the heat medium that is taken out and flows into the heat exchange unit 1 (see FIG. 1 when the temperature measured by the temperature sensor T5 is equal to or lower than the first target temperature. The first target temperature is the target temperature of the heat medium stored in the first heat storage tank. Since the heat medium flowing into the heat exchange unit 1 also plays a role of cooling the fuel cell FC, it is required that the temperature of the heat medium flowing into the heat exchange unit 1 is not too low and not too high. Accordingly, the first target temperature is, for example, a temperature of 40 ° C. or lower (37 ° C., for example) that can cool the fuel cell FC. That is, in the first heat storage state, the heat medium flowing into the heat exchange unit 1 of the fuel cell FC has a relatively low temperature. Therefore, the temperature of the heat medium flowing out from the heat exchange unit 1 does not increase. This state means a state where the room temperature heating medium is heated to near the first target temperature when the clean water is supplied to the first heat storage tank TNK1 as it is.

  In the first heat storage state, after the temperature of the low-temperature heat medium stored in the upper part of the first heat storage tank TNK1 is raised in the heat exchange unit 1 of the fuel cell FC, the first heat storage tank TNK1 is used as the high-temperature heat medium. Return to the bottom of the. As shown in FIG. 1, a rectifying plate 2 is provided in the vicinity of the connection portion 5 into which the heat medium below the first heat storage tank TNK1 flows. Therefore, the heat medium flowing in from the lower connection portion 5 of the first heat storage tank TNK1 flows upward, causing convection inside the first heat storage tank TNK1. Further, since the rectifying plate 2 is provided between the connection portion 5 and the temperature sensor T3, the temperature of the heat medium flowing into the connection portion 5 directly affects the detection result of the temperature sensor T3. There is no. As described above, when heat storage is performed in the first heat storage state, the temperature of the heat medium is made uniform throughout the first heat storage tank TNK1 by convection of the heat medium inside the first heat storage tank TNK1. In this state, the temperature rises as a whole, and only a part of the heat medium does not reach a high temperature.

[Second heat storage state]
(1) State in which heat storage amount is not full in second heat storage tank TNK2 FIG. 2 is a diagram showing a flow form of the heat medium in the second heat storage state before the second heat storage tank TNK2 becomes full. is there.
The control unit C causes the heat medium taken out from the first heat storage tank TNK1 to flow into the heat exchange unit 1 of the fuel cell FC, and causes the heat medium flowing out from the heat exchange unit 1 to flow into the second heat storage tank TNK2. The exhaust heat recovery of the fuel cell FC can be performed in the second heat storage state. Specifically, in the second heat storage state, the control unit C causes the heat medium taken out from the upper part of the first heat storage tank TNK1 to flow into the heat exchange unit 1 of the fuel cell FC, and also the heat exchange unit of the fuel cell FC. The heat medium flowing out from 1 flows into the upper part of the second heat storage tank TNK2. In addition, the control unit C has a temperature of the low temperature side heat medium stored in the second heat storage tank TNK2 (temperature measured by the temperature sensor T6 in FIG. 1) higher than the first target temperature. 2 When the temperature is lower than the target temperature (for example, 80 ° C.), it is determined that the heat storage amount is not full in the second heat storage tank TNK2, and the low temperature stored in the second heat storage tank TNK2 The side heat medium (in this embodiment, the heat medium stored in the lower part of the second heat storage tank TNK2) is taken out and flows into the lower part of the first heat storage tank TNK1. That is, the second target temperature is the target temperature of the heat medium stored in the second heat storage tank TNK2. In order to distribute the heat medium in such a form, the control unit C switches the control valve CV1 to the ab distribution state, switches the control valve CV2 to the ac distribution state, switches the control valve CV3 to the ab distribution state, and controls the control valve CV5. To ac distribution state.

  The control unit C performs heat storage in the second heat storage state because the temperature of the heat medium that is taken out and flows into the heat exchange unit 1 out of the heat medium stored in the first heat storage tank TNK1 (FIG. 1). , When the temperature measured by the temperature sensor T5 is higher than the first target temperature. For example, when the temperature of the heat medium flowing into the heat exchange unit 1 of the fuel cell FC is about 37 ° C. as the first target temperature, the temperature of the heat medium flowing out from the heat exchange unit 1 is, for example, about 85 ° C. to 90 ° C. Then, the heat medium flows into the upper part of the second heat storage tank TNK2.

  In the second heat storage state, a somewhat high temperature heat medium stored in the upper part of the first heat storage tank TNK1 is heated in the heat exchange unit 1 of the fuel cell FC, and then used as a higher temperature heat medium for the second heat storage. It flows into the upper part of the tank TNK2. Inside the second heat storage tank TNK2, the heat medium is stored so that temperature stratification is formed. Thus, in the second heat storage state, the low-temperature heat medium flows out from the lower part of the second heat storage tank TNK2, and the high-temperature heat medium flows into the upper part of the second heat storage tank TNK2. As a result, the high-temperature heat medium continues to accumulate while forming a temperature stratification in order from the top of the second heat storage tank TNK2, and eventually the entire second heat storage tank TNK2 is replaced with the high-temperature heat medium. .

(2) State in which heat storage amount is full in second heat storage tank TNK2 FIG. 3 is a diagram for explaining the configuration of the exhaust heat recovery system, in particular after the second heat storage tank TNK2 is full. It is a figure which shows the distribution | circulation form of the heat carrier in a 2nd heat storage state. In the present embodiment, the control unit C determines that the temperature of the low-temperature side heat medium stored in the second heat storage tank TNK2 (the temperature measured by the temperature sensor T6 in FIG. 1) is higher than the first target temperature. When the temperature is equal to or higher than the high second target temperature (for example, 80 ° C.), it is determined that the heat storage amount of the second heat storage tank TNK2 is full.

As in the case described above with reference to FIG. 2, the control unit C causes the heat medium taken out from the first heat storage tank TNK1 to flow into the heat exchange unit 1 of the fuel cell FC and outflow from the heat exchange unit 1. The exhaust heat recovery of the fuel cell FC can be performed in the second heat storage state in which the heat medium to be introduced flows into the second heat storage tank TNK2.
Further, as shown in FIG. 3, when the control unit C determines that the second heat storage tank TNK2 is full in the second heat storage state, the control unit C uses the heat medium taken out from the lower portion of the first heat storage tank TNK1 as a fuel. While flowing into the heat exchange part 1 of the battery FC, the heat medium flowing out from the heat exchange part 1 of the fuel cell FC is caused to flow into the upper part of the second heat storage tank TNK2. In addition, the control unit C takes out the low-temperature heat medium stored in the second heat storage tank TNK2 (in this embodiment, the heat medium stored in the lower part of the second heat storage tank TNK2), It flows into the upper part of the first heat storage tank TNK1. Thereby, temperature stratification is formed inside the first heat storage tank TNK1. In order to distribute the heat medium in such a form, the control unit C switches the control valve CV1 to the ab distribution state, switches the control valve CV2 to the ac distribution state, switches the control valve CV3 to the bc distribution state, and controls the control valve CV5. To the ab distribution state.

  That is, after the second heat storage tank TNK2 becomes full, the high-temperature heat medium stored in the second heat storage tank TNK2 starts to be transferred and stored also on the first heat storage tank TNK1. At this time, the heat medium stored in the lower part of the first heat storage tank TNK1 is supplied to the heat exchange unit 1 of the fuel cell FC.

[Heat use condition]
While performing the first heat storage state and the second heat storage state described above, the heat medium is a heat utilization destination including a hot water supply destination such as a bath or shower, a high-temperature water utilization facility such as a desiccant dehumidifier or a floor heating device. There may be a situation where the heat supplied to the is used. FIG. 4 is a diagram showing a circulation state of the heat medium in the heat use state. In the present embodiment, the heat medium stored in the upper part of the second heat storage tank TNK2 is supplied to the hot water supply destination and the heat utilization destination. Then, at the same time as the heat medium is supplied from the upper part of the second heat storage tank TNK2 to the hot water supply destination and the heat utilization destination through the flow path L9, the first heat storage tank TNK1 is supplied from the upper part through the flow path L6. The heat medium is replenished to the lower part of the second heat storage tank TNK2, and further the clean water is replenished to the lower part of the first heat storage tank TNK1 through the flow path L8. That is, the amount of the heat medium reduced from the second heat storage tank TNK2 is replenished by the high-temperature side heat medium stored in the first heat storage tank TNK1. Further, when the temperature of the heat medium supplied from the second heat storage tank TNK2 to the hot water supply destination and the heat utilization destination from the second heat storage tank TNK2 is higher than a desired temperature, the control unit C sets the opening degree of the control valve CV4. The temperature of the heat medium is adjusted by mixing low temperature clean water from the flow path L9 to the flow path L10 and supplied from the second heat storage tank TNK2 to the hot water supply destination and the heat utilization destination via the flow path L9. When the temperature of the heating medium is lower than the desired temperature, the temperature of the heating medium is adjusted by operating the backup boiler B to raise the temperature.

[Operation stop condition]
As described above, when the heat storage is performed in the first heat storage state or the second heat storage state and the heat is used, the control unit C, when the operation stop condition is satisfied, the fuel cell FC and the exhaust heat recovery Stop system operation.
In the present embodiment, the controller C has a temperature of the low-temperature side heat medium stored in the second heat storage tank TNK2 equal to or higher than a third target temperature (for example, 70 ° C.) lower than the second target temperature. In the state, when the temperature of the low-temperature side heat medium stored in the first heat storage tank TNK1 reaches the first target temperature, it is determined that the operation stop condition is satisfied.

  In the above-mentioned operation stop condition, the former condition that “the temperature of the low-temperature side heat medium stored in the second heat storage tank TNK2 is equal to or higher than the third target temperature (for example, 70 ° C.)” This means that the amount of heat stored in the tank TNK2 is substantially full. In addition, the condition that “the temperature of the low-temperature side heat medium stored in the second heat storage tank TNK2 is equal to or higher than the third target temperature (for example, 70 ° C.)” is the condition from the second heat storage tank TNK2. It means that the temperature of the heat medium flowing into the first heat storage tank TNK1 is very high as viewed from the first target temperature of the first heat storage tank TNK1, that is, the third target temperature or higher.

  In the above operation stop condition, the latter condition that “the temperature of the low-temperature side heat medium stored in the first heat storage tank TNK1 becomes the first target temperature” flows into the heat exchange unit 1 of the fuel cell FC. It means that the temperature of the heat medium becomes the first target temperature. In addition, since the temperature of the heat medium flowing from the second heat storage tank TNK2 to the first heat storage tank TNK1 is a high temperature equal to or higher than the third target temperature, the temperature of the heat medium flowing into the heat exchange unit 1 of the fuel cell FC Is in a state where the temperature is raised to a temperature higher than the first target temperature (that is, the fuel cell FC may not be effectively cooled).

  As described above, if the operation of the fuel cell FC and the exhaust heat recovery system is continued in the state where the operation stop condition is satisfied, the heat exchange unit 1 of the fuel cell FC is inappropriate for cooling the fuel cell FC. A temperature heating medium is supplied. Accordingly, when the control unit C determines that the operation stop condition is satisfied, the control unit C stops the operation of the fuel cell FC and the exhaust heat recovery system.

[Exhaust heat recovery operation in the exhaust heat recovery system]
Next, the exhaust heat recovery operation in which the first heat storage state and the second heat storage state are combined will be described with reference to FIG. FIG. 5 is a flowchart of the exhaust heat recovery operation.
In step # 10, the control unit C determines that the temperature detected by the temperature sensor T5 (the temperature of the heat medium that is taken out and flows into the heat exchange unit 1 out of the heat medium stored in the first heat storage tank TNK1). It is determined whether the temperature is higher than one target temperature. That is, the control unit C determines whether or not the heat medium having the first target temperature can be supplied from the first heat storage tank TNK1 to the heat exchange unit 1 of the fuel cell FC. When the heat medium having the first target temperature is supplied to the heat exchange unit 1 of the fuel cell FC, the temperature of the heat medium flowing out from the heat exchange unit 1 of the fuel cell FC is suitable for heat storage in the second heat storage tank TNK2. It becomes hot. That is, in step # 10, the control unit C determines whether or not the high-temperature heat medium can be supplied to the second heat storage tank TNK2.

  When it is determined in step # 10 that the temperature detected by the temperature sensor T5 is equal to or lower than the first target temperature (in the case of “No” in step # 10), the control unit C proceeds to step # 20 and enters the first heat storage state. To store heat. As a result, the heat medium flowing out from the heat exchange unit 1 of the fuel cell FC is supplied to the first heat storage tank TNK1, and the temperature of the heat medium in the first heat storage tank TNK1 is increased. At this time, the heat medium is transferred from the upper part of the first heat storage tank TNK1 to the heat exchange unit 1. Thereafter, the control unit C returns to the beginning of this flowchart.

When determining that the detected temperature of the temperature sensor T5 is higher than the first target temperature in the process # 10 (in the case of “Yes” in the process # 10), the control unit C proceeds to the process # 30 and detects the temperature sensor T6. It is determined whether or not the temperature (the temperature of the low-temperature heat medium stored in the second heat storage tank TNK2) is equal to or higher than the second target temperature. That is, the control unit C determines whether or not the heat storage amount of the second heat storage tank TNK2 is full.
When determining that the detected temperature of the temperature sensor T6 is lower than the second target temperature in Step # 30 (when not full), the control unit C proceeds to Step # 40 and stores heat in the second heat storage state. Since the second heat storage state here is the second heat storage state when the heat storage amount is not full in the second heat storage tank TNK2, the lower part of the second heat storage tank TNK2 is shown in FIG. The heat medium is transferred from the upper part of the first heat storage tank TNK1 to the lower part of the first heat storage tank TNK1, and the heat medium is transferred from the upper part of the first heat storage tank TNK1 to the heat exchange unit 1 of the fuel cell FC.

Thereafter, in step # 50, the control unit C determines whether or not all detected temperatures of the temperature sensors T3, T4, and T5 of the first heat storage tank TNK1 are equal to or lower than the first target temperature. Even if the heat is being stored in the second heat storage state, when the above heat use state occurs, clean water flows into the first heat storage tank TNK1, and the temperature of the heat medium in the first heat storage tank TNK1 decreases. Because there is a possibility of doing. In particular, if all the detected temperatures of the temperature sensors T3, T4, and T5 of the first heat storage tank TNK1 are equal to or lower than the first target temperature, the temperature of the heat medium flowing into the heat exchanging unit 1 of the fuel cell FC is also changed. It becomes 1 target temperature or less, and it is necessary to switch to the heat storage in the first heat storage state again.
Therefore, when all the detected temperatures of the temperature sensors T3, T4, and T5 are equal to or lower than the first target temperature (that is, when heat storage in the first heat storage state is necessary), the control unit C starts the flowchart. The process returns to step # 30 if all the detected temperatures of the temperature sensors T3, T4, and T5 are not equal to or lower than the first target temperature (when heat storage in the first heat storage state is not necessary yet).

When the controller C determines in step # 30 that the temperature detected by the temperature sensor T6 is equal to or higher than the second target temperature (that is, when the heat storage amount of the second heat storage tank TNK2 is full), the control unit C proceeds to step # 60. Then, it is determined whether or not the operation stop condition described above is satisfied.
When it is determined that the operation stop condition is satisfied, the control unit C proceeds to step # 70 and stops the operation of the fuel cell FC and the exhaust heat recovery system.

After stopping the operation of the fuel cell FC and the exhaust heat recovery system in Step # 70, the controller C starts the fuel cell start condition in which the temperature detected by the temperature sensor T6 is set to be equal to or lower than the second target temperature in Step # 100. It is determined whether or not the temperature is lower. As described above, when the heat use state occurs, the first heat storage tank is simultaneously supplied from the upper part of the second heat storage tank TNK2 to the hot water supply destination and the heat utilization destination through the flow path L9. Since the relatively low-temperature heat medium is replenished from the upper part of TNK1 to the lower part of the second heat storage tank TNK2 via the flow path L6, the temperature of the heat medium stored in the lower part of the second heat storage tank TNK2 is Lower. That is, even if the operation stop condition is satisfied once in step # 70, the heat storage amount of the second heat storage tank TNK2 is not full with the occurrence of the subsequent heat use state, that is, the fuel cell FC and the exhaust heat It may be necessary to resume operation of the recovery system.
Therefore, when the temperature detected by the temperature sensor T6 is lower than the fuel cell activation condition temperature, the control unit C proceeds to step 110, activates the fuel cell FC, and resumes exhaust heat recovery of the fuel cell FC. The fuel cell starting condition temperature is 40 ° C., for example.

When determining that the operation stop condition is not satisfied in Step # 60, the control unit C proceeds to Step # 80 and performs heat storage in the second heat storage state. Since the second heat storage state here is the second heat storage state when the heat storage amount is substantially full in the second heat storage tank TNK2, as shown in FIG. 3, the second heat storage tank The heat medium is transferred from the lower part of TNK2 to the lower part of the first heat storage tank TNK1, and the heat medium is transferred from the upper part of the first heat storage tank TNK1 to the heat exchange unit 1 of the fuel cell FC.
Thereafter, in step # 90, the controller C detects all of the temperature sensors T3, T4, and T5 of the first heat storage tank TNK1 in consideration of the occurrence of the heat use state as in the case of step # 50 described above. It is determined whether the temperature is equal to or lower than the first target temperature. When all the detected temperatures of the temperature sensors T3, T4, and T5 are equal to or lower than the first target temperature, the control unit C returns to the beginning of the flowchart, and all the detected temperatures of the temperature sensors T3, T4, and T5 are the first. If not below the target temperature, the process returns to step # 60.

  As described above, in the exhaust heat recovery system of the present embodiment, if necessary, the temperature of the heat medium stored in the first heat storage tank TNK1 is increased using the exhaust heat of the fuel cell FC in the first heat storage state. Above, the heating medium stored in the first heat storage tank TNK1 can be further heated using the exhaust heat of the fuel cell FC and stored in the second heat storage tank TNK2. Therefore, even in a situation where the temperature of clean water is low, such as in winter, a high-temperature heating medium can be obtained by using the exhaust heat of the fuel cell FC without consuming energy separately. Therefore, it is possible to provide a waste heat recovery system that can store a high-temperature heat medium and has good energy efficiency.

Second Embodiment
In 1st Embodiment, the control part C is 1st according to the temperature of the heat medium stored in the 1st heat storage tank TNK1, and the temperature of the heat medium stored in the 2nd heat storage tank TNK2. Although the example comprised so that switching between a thermal storage state and a 2nd thermal storage state was demonstrated, you may switch a 1st thermal storage state and a 2nd thermal storage state according to another parameter | index. For example, the control unit C may switch between the first heat storage state and the second heat storage state according to the temperature of the heat medium flowing out from the heat exchange unit 1 of the fuel cell FC.

  Specifically, in the present embodiment, in step # 10 of FIG. 5, the control unit C determines whether or not the temperature measured by the temperature sensor T5 of the first heat storage tank TNK1 is higher than the first target temperature. Instead, it is determined whether or not the temperature of the heat medium flowing out from the heat exchange unit 1 of the fuel cell FC is higher than the fifth target temperature (for example, 80 ° C.). That is, the control unit C performs the first heat storage state when the temperature of the heat medium is not sufficiently raised in the heat exchange unit 1 of the fuel cell FC, and the heat medium is sufficiently increased in the heat exchange unit 1 of the fuel cell FC. When it is warm, the second heat storage state is performed. By performing such control, a high-temperature heat medium can be selectively stored in the second heat storage tank TNK2.

<Another embodiment>
<1>
In the above embodiment, the operation stop condition can be changed as appropriate.
For example, the temperature detected by the temperature sensor T2 of the flow path L2 from which the heat medium flows out from the heat exchange unit 1 of the fuel cell FC in the process # 60 of FIG. 5 is less than the fourth target temperature (for example, 80 ° C.). May be changed so as to determine that the operation stop condition is satisfied. That is, in the step # 60, after it is determined that the temperature detected by the temperature sensor T6 of the second heat storage tank TNK2 is equal to or higher than the second target temperature (that is, the heat storage amount of the second heat storage tank TNK2 is full). It is a state in which heat storage is continued in the second heat storage state. Thus, for example, when a heat medium of less than 80 ° C. newly flows into the second heat storage tank TNK2 filled with the heat medium of 80 ° C. or higher, the temperature of the heat medium of the second heat storage tank TNK2 Will fall. Therefore, when the control unit C determines that the operation stop condition is satisfied, the control unit C stops the operation of the fuel cell FC and the exhaust heat recovery system, and prevents the temperature of the heat medium in the second heat storage tank TNK2 from decreasing.

<2>
In the embodiment described above, the configuration of the flow path of the heat medium that connects the heat exchange unit 1 of the fuel cell FC, the first heat storage tank TNK1, and the second heat storage tank TNK2 can be changed as appropriate.

<3>
Although a plurality of target temperature values are exemplified in the above embodiment, the present invention is not limited to these numerical values. The value of each target temperature can be set as appropriate.

  The present invention can be used in an exhaust heat recovery system that recovers exhaust heat of a fuel cell.

DESCRIPTION OF SYMBOLS 1 Heat exchange part 1a Inlet 1b Outlet FC Fuel cell TNK1 1st heat storage tank TNK2 2nd heat storage tank C Control part (control means)

Claims (5)

A heat storage tank that can store heat by storing the heat medium is provided, and the heat medium is circulated between the heat storage tank to which the exhaust heat from the fuel cell is supplied and the heat storage tank, thereby discharging the fuel cell. An exhaust heat recovery system for recovering heat,
A first heat storage tank and a second heat storage tank as the heat storage tank, and a control means for controlling the flow mode of the heat medium;
The control means causes the heat medium taken out from the first heat storage tank to flow into the heat exchanging unit, the temperature of the heat medium stored in the first heat storage tank, and the second heat storage. The heat medium flowing out from the heat exchange unit according to at least one of the temperature of the heat medium stored in the tank for use and the temperature of the heat medium flowing out from the heat exchange unit The exhaust is configured to be switchable between a first heat storage state in which the refrigerant flows into the first heat storage tank and a second heat storage state in which the heat medium flowing out from the heat exchange section flows into the second heat storage tank. Heat recovery system.   The control means is a heating medium in which the temperature of the heating medium taken out of the heating medium stored in the first heat storage tank and flowing into the heat exchange section is stored in the first heat storage tank. 2. The exhaust heat according to claim 1, wherein heat storage is performed in the second heat storage state when the temperature is higher than the first target temperature, and heat storage is performed in the first heat storage state when the temperature is equal to or lower than the first target temperature. Collection system.   3. The exhaust heat recovery system according to claim 2, wherein the control unit convects the heat medium inside the first heat storage tank when performing heat storage in the first heat storage state.   The said control means takes out the said low-temperature-side heat medium stored in the said 2nd heat storage tank, and makes it flow into the said 1st heat storage tank, when storing heat | fever in the said 2nd heat storage state. The exhaust heat recovery system according to any one of the above.   When the temperature of the heat medium on the low temperature side stored in the second heat storage tank is equal to or higher than a second target temperature higher than the first target temperature, the control means is configured to perform the heat on the low temperature side. The exhaust heat recovery system according to claim 4, wherein the medium is allowed to flow into the first heat storage tank while forming a temperature stratification inside the first heat storage tank.

Images