JP2021072256A - Fuel cell device - Google Patents

Abstract

To provide a fuel cell device capable of efficiently recovering water contained in exhaust gas of a fuel cell.SOLUTION: A fuel cell device disclosed herein includes a fuel cell module 1 that generates electricity, a heat exchanger 3 that exchange heat between exhaust gas discharged from the fuel cell and a heat medium to liquefy water in the exhaust gas as condensed water, a first exhaust gas temperature measuring unit that measures the temperature of the exhaust gas discharged from the heat exchanger, a heat medium circulation pump P1 arranged in a circulation flow path Q that circulates the heat medium, and a control device 20. The control device 20 controls the drive of the circulation pump P1 such that first exhaust gas temperature measured by the first exhaust gas temperature measuring unit becomes predetermined target temperature.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a fuel cell device.

The fuel cell uses a hydrogen-containing raw fuel gas and an oxygen-containing gas (air) to generate electricity and supply electricity to the outside. In addition, the fuel cell recovers the heat in the exhaust gas generated by the reforming reaction that reforms the raw fuel gas into a fuel gas containing hydrogen, power generation, combustion of surplus gas, etc., and stores it as hot water. It constitutes a part of a cogeneration system that supplies hot water directly or indirectly to the outside.

By the way, in a fuel cell, water is generated in a reforming reaction. In addition, water is generated in the fuel cell due to the power generation reaction in the cell stack. Therefore, the exhaust gas of the fuel cell contains a large amount of water (water vapor).

Therefore, in the fuel cell device, the exhaust gas discharged from the fuel cell is passed through a heat exchanger or the like to be cooled, and at the time of this heat exchange, the condensed water generated by condensing the water vapor contained in the exhaust gas is recovered. And store it in a water tank, etc. Then, so-called water self-sustaining operation is performed in which the stored water is supplied as reformed water to a reformer that reforms raw fuel such as natural gas by steam reforming.

Regarding the above-mentioned recovery of condensed water, Patent Document 1 discloses a fuel cell system that optimizes heat recovery efficiency even when the sensible heat / latent heat ratio is small. In the control device of this fuel cell system, the target temperature setting unit that sets the target hot water storage water temperature at the heat exchanger outlet and the hot water storage water temperature at the heat exchanger outlet are set according to the hot water storage water temperature at the heat exchanger inlet. It is provided with a delivery amount control unit that controls the delivery amount of the hot water storage water circulation pump so that the target temperature is reached.

Japanese Unexamined Patent Publication No. 2019-21464

An object of the present disclosure is to provide a fuel cell device capable of efficiently recovering water contained in the exhaust gas of a fuel cell.

The fuel cell apparatus of the present disclosure includes a fuel cell that generates power using a fuel gas and an oxygen-containing gas, a heat exchanger that exchanges heat between the exhaust gas discharged from the fuel cell and a heat medium, and the heat exchanger. A first exhaust gas temperature measuring unit for measuring the temperature of the exhaust gas discharged from the gas, a circulation pump arranged in a circulation flow path for circulating a heat medium in the heat exchanger, and a control device are provided.
The control device can execute exhaust gas temperature control that controls the drive of the circulation pump so that the first exhaust gas temperature measured by the first exhaust gas temperature measuring unit becomes a predetermined target temperature.

According to the fuel cell device of the present disclosure, the water contained in the exhaust gas of the fuel cell can be efficiently recovered.

It is a schematic block diagram of the fuel cell apparatus of 1st Embodiment. It is a perspective view which shows the structure of the fuel cell apparatus in an outer case. It is a schematic block diagram of the fuel cell apparatus of 2nd Embodiment.

Hereinafter, embodiments will be described with reference to the drawings. In the following embodiment, the solid oxide fuel cell is exemplified as the fuel cell, but it can also be applied to, for example, a solid polymer fuel cell, and in that case, the configuration may be appropriately changed. ..

FIG. 1 is a block diagram showing an outline of the configuration of the fuel cell device of the first embodiment, and FIG. 2 is a perspective view showing the configuration of the fuel cell device in the outer case. It should be noted that some fuel cell devices, such as general-purpose devices and devices, are not described in detail and are limited to the addition of reference numerals in the drawings.

The fuel cell device 100 shown in FIG. 1 heats the heat and heat energy of the fuel cell module 1, the heat exchanger 3 connected to the fuel cell module 1, and the high temperature exhaust gas discharged from the fuel cell module 1. The heat storage tank 4 which is recovered by heat exchange via the medium circulation flow path Q and stored as hot water, and the condensed water generated by condensing the water contained in the exhaust gas by heat exchange are modified through the condensed water flow path C. A reformed water tank 6 for storing as quality water is provided.

Further, the fuel cell device 100 includes a raw material fuel supply device 13 including a raw material fuel pump, a raw material fuel flow path, and the like, and an oxygen-containing gas supply device 14 including an air blower, an oxygen-containing gas flow path, and the like. Further, the above-mentioned reforming water tank 6 for continuing the water self-sustaining operation, and a reforming water supply device including a reforming water supply pump P2 connected to the reforming water tank 6 and a reforming water flow path R are included.

The fuel cell device 100 is a heat medium circulation system including the heat exchanger 3, the heat storage tank 4, the radiator 5, the heat medium circulation pump P1 described above, and the heat medium circulation flow path Q connecting them in a ring shape. (Heat cycle) is provided. In FIG. 1, the flow path on the upstream side where the relatively low temperature heat medium flows on the inlet side of the heat exchanger 3 is indicated as Q1, and the downstream flow path on the outlet side of the heat exchanger 3 where the relatively high temperature heat medium flows. The flow path on the side is indicated as Q2. The radiator 5 may not be provided.

The fuel cell module 1, which is the heat source of the heat medium circulation system, is housed in the storage container 10. Inside the storage container 10, a cell stack 11 in which a plurality of fuel cell cells are stacked, a reformer 12 that reforms the raw fuel with steam using steam, and ignition for igniting excess fuel gas are ignited. It includes a heater (not shown), an exhaust gas catalyst filled in the catalyst container 2, and the like.

In the fuel cell device 100 having the above-described configuration, the exhaust gas containing water generated in the fuel cell module 1 is led out to the exhaust gas flow path E via the exhaust gas catalyst in the catalyst container 2, and then the fuel cell module. It is introduced into the heat exchanger 3 adjacent to 1.

The heat exchanger 3 is of a countercurrent type in which high-temperature exhaust gas flows downward from the upper side in the drawing and low-temperature heat medium (water) flows upward from the lower side in the drawing. Further, the lowermost portion of the heat exchanger 3 is a brackish water separator that separates water liquefied by heat exchange (condensed water) and exhaust gas from which water has been removed.

The exhaust gas from which water has been removed by the steam separator is discharged to the outside of the machine via the exhaust flow path V. On the other hand, the condensed water separated by the brackish water separator is collected and stored in the reformed water tank 6 via the condensed water flow path C.

The fuel cell device 100 is arranged in a case 30 including each frame 31 and each exterior panel 32 as shown in FIG. In this case 30, around the fuel cell module 1 and each auxiliary machine, in the flow path, piping, etc., the following control means 20, a plurality of measuring devices, sensors, other auxiliary machines, etc. are installed. It is provided.

The fuel cell device 100 assists the power generation operation of the fuel cell in cooperation with a power adjusting device (not shown) and the power adjusting device as a means for controlling the operation of the above-mentioned fuel cell module 1 and each auxiliary machine. It includes a control device 20 that controls the operation of each auxiliary machine, a storage device attached to or built in the control device 20, and the like.

The control device 20 is connected to a storage device and a display device (both not shown), various components and various sensors constituting the fuel cell device 100, and includes each of these functional units and the entire fuel cell device 100. Control and manage. The control device 20 acquires a program stored in a storage device (not shown) attached to the control device 20 and executes this program to realize various functions related to each part of the fuel cell device 100.

Further, the fuel cell device 100 includes a plurality of temperature measuring instruments or thermometers such as a temperature sensor and a thermistor for measuring the temperature of each part inside and outside the housing.

For example, as shown in FIG. 1, as a first exhaust gas temperature measuring unit for measuring the temperature of the exhaust gas discharged from the fuel cell module 1 (combustion unit), the air-water separator portion after passing through the heat exchanger 3 is used. The thermistor TM1 is arranged.

Further, a thermistor TM2 for measuring the temperature of the exhaust gas catalyst in the container is arranged in the catalyst container 2 before being introduced into the heat exchanger 3. The thermistor TM2 may also measure the temperature of the exhaust gas flowing into the heat exchanger 3. Further, the thermistor TM2 may be arranged between the catalyst container 2 and the heat exchanger 3.

Further, in order to measure the temperature of the heat medium flowing through the heat exchanger 3, the thermistor TM3 is connected to the upstream side flow path Q1 of the heat medium circulation flow path Q, which is the heat medium inlet side (low temperature side) of the heat exchanger 3. Are arranged. The thermistor may not be arranged on the downstream side of the heat medium circulation flow path Q, which is the heat medium outlet side (high temperature side) of the heat exchanger 3 conventionally provided.

Further, in the reformed water tank 6, a water detector WL1 for indicating a decrease in the water level of the stored reformed water or a drought is arranged at a predetermined low water level position near the bottom (lower part) of the tank. A water detector WL2 is installed at a high water level position close to a predetermined full water level of the tank to detect that the water level, which is the water level of reformed water, has risen and the amount of stored water has increased. ..

When a control signal or various information is transmitted from the control device 20 to the sensors or other functional units or devices, the control device 20 and the other functional units are connected by wire or wirelessly. Just do it. In each figure, the illustration of the connection line connecting the control device 20, each device constituting the fuel cell, and each sensor may be omitted. Further, the control characteristic of the present embodiment performed by the control device 20 will be described later.

In the embodiment described later, the heat medium circulation pump P1 arranged in the heat medium circulation flow path Q (heat cycle) has a rotary drive motor of a pulse drive type, and the control device 20 is pulse drive. The on / off duty ratio of the pump P1 is increased or decreased to control the rotational driving force of the pump P1 and its discharge amount.

In the fuel cell device 100 having the above configuration, when the fuel cell is operating, the control device 20 is located at the heat exchanger 3 outlet (lower side in the drawing) measured by the thermista TM1 which is the first exhaust gas temperature measuring unit. Exhaust gas temperature control is performed, which controls the drive of the heat medium circulation pump P1 so that the first exhaust gas temperature becomes a predetermined target temperature.

In this way, by driving the heat medium circulation pump P1 based on the exhaust gas temperature on the heat exchanger 3 outlet side, the heat medium circulation is performed so that the heat medium temperature at the heat exchanger outlet becomes the target as before. Compared to controlling the drive of the pump, it is possible to recover the condensed water more efficiently. Hereinafter, the setting of the target temperature will be described with a specific example.

As a first example of control, when the fuel cell device 100 having the above-described configuration is performing power generation operation, the control device 20 uses, for example, reformed water in the reformed water tank 6 in the exhaust gas temperature control as described above. The first target temperature setting control that sets the above-mentioned target temperature based on the water level of the heat exchanger 3 is performed, and the heat medium circulation pump P1 so that the first exhaust gas temperature at the outlet of the heat exchanger 3 becomes the target temperature. A first exhaust gas temperature control that controls the drive can be performed.

That is, during the execution of the exhaust gas temperature control described above, the water level detection or the water level not detected by the low water level water detector WL1 or the high water level water detector WL2, which is the water level detection unit for detecting the water level of the reformed water, is generated. When reported, the control device 20 switches the target temperature with the water level of the reforming water in the reforming water tank 6 as a control priority item, and corrects the drive of the heat medium circulation pump P1 in response to the change in the target temperature. , Perform the first exhaust gas temperature control.

Specifically, for example, when the water detector WL2 that detects the high water level of the reformed water (water surface) in the reformed water tank 6 detects water, the control device 20 is stored in the reformed water tank 6. Judging that the amount of reformed water is close to full water where overflow occurs, the control target temperature is raised to a temperature at which the recovery rate of condensed water decreases. Then, the drive (duty ratio) of the heat medium circulation pump P1 is controlled to be reduced from that before that so as to cope with the increase in the target temperature. As a result, the amount of condensed water recovered can be reduced and the occurrence of overflow can be suppressed.

On the other hand, for example, when the WL2 which detects the high water level of the reformed water (water surface) of the reformed water (water surface) in the reformed water tank 6 does not detect water, or when the water detector WL1 which detects the low water level detects water. If not detected, the control device 20 determines that the amount of reformed water stored in the reforming water tank 6 is insufficient or close to the water level at which drought occurs, and sets the control target temperature to condensed water. Reduce to a temperature at which recovery is improved. Further, the drive (duty ratio) of the heat medium circulation pump P1 is controlled to be increased more than before so as to cope with the decrease in the target temperature. As a result, the amount of coagulated water recovered can be increased, and the risk of insufficient amount of reformed water and the risk of drought can be reduced.

In this way, while efficiently recovering the water contained in the exhaust gas of the fuel cell, the amount of reformed water stored in the reformed water tank 6 is within an appropriate range for continuing independent operation. Can be kept.

When the WL2 that detects the high water level of the reformed water (water surface) detects water during the condensed water recovery control, for example, the drive (duty ratio) of the heat medium circulation pump P1 is set. The drive [minus (-) correction], which is reduced from before, may be executed to reduce the amount of condensed water recovered and suppress the occurrence of overflow.

Next, as a second example of control, when the fuel cell device 100 having the above-described configuration is also performing power generation operation, the control device 20 is based on the exhaust gas fluid value related to the amount of water contained in the exhaust gas. , The second target temperature setting control for setting the target temperature described above can be performed.

Here, the amount of condensed water recovered by driving the heat medium circulation pump P1 will be described in detail. The amount of condensed water can be calculated by subtracting the amount of saturated water vapor that can be contained in the exhaust gas after heat exchange from the amount of water vapor contained in the exhaust gas discharged from the fuel cell module 1. Therefore, by setting the target temperature, the saturated water vapor amount can be calculated and the amount of condensed water that can be recovered can be estimated. In other words, the target temperature can be set according to the amount of condensed water to be collected.

The amount of water vapor contained in the exhaust gas discharged from the fuel cell module 1 is the same as the amount of water derived from the fuel gas input to the fuel cell module 1 when the fuel cell device 100 having the above configuration is performing power generation operation. The amount of water charged into the pawn 12 is the main component. Further, when calculating the amount of water vapor contained in the exhaust gas more accurately, the amount of water contained in the air charged into the fuel cell module 1 may be added.

The amount of water derived from the fuel gas charged into the fuel cell module 1 is converted by calculating the amount of hydrogen contained in the fuel gas flow rate. That is, for example, the ratio of hydrogen is calculated from the ratio of the components containing hydrogen such as methane contained in the fuel gas, and the ratio is converted into the amount of water. The amount of water charged into the reformer 12 may be the amount of reformed water supplied from the reforming water supply pump P2. In other words, it may be a measured value (water amount) measured by the reformed water amount measuring unit. The amount of water contained in the air charged into the fuel cell module 1 can be calculated from the relative humidity, the air temperature, and the amount of air supplied.

Regarding the amount of reformed water measured by the reformed water amount measuring unit, the flow rate of the reformed water may be directly measured by a water flow meter or the like arranged in the reformed water flow path R, and the reformed water supply pump. If P2 can output specifications such as the discharge amount and the number of rotations, the specifications may be used to obtain the specifications by calculation. For example, in the case of a water pump whose discharge amount is represented by the fin rotation speed, by preparing a calibration curve in advance, the product of the rotation speed [rotation / minute] and the rotation drive duration [minute] can be obtained. The amount of water discharged from the pump can be obtained. Further, if the reforming water supply pump P2 is driven by a pulse motor, the amount of discharged water of the pump can be estimated from the duty ratio of the driving.

From the above, the amount of water vapor contained in the amount of exhaust gas discharged from the fuel cell module 1 can be calculated, and in the present specification, the amount of water vapor contained in the amount of exhaust gas is referred to as an exhaust gas fluid value. That is, the exhaust gas fluid value means the amount of water vapor obtained in relation to the amount of exhaust gas discharged from the fuel cell module 1.

Normally, the temperature of the exhaust gas discharged from the fuel cell module 1 is high, and the amount of water contained in the exhaust gas discharged from the fuel cell module 1 is not so large. Therefore, the moisture contained in the high-temperature exhaust gas does not become the saturated water vapor amount of the exhaust gas, and the inlet temperature of the exhaust gas to the heat exchanger 3 is not intentionally considered in the above. However, when considering the saturated water vapor amount of the exhaust gas, in the calculation of the exhaust gas fluid value, the saturated water vapor amount is calculated using the second exhaust gas temperature measured by the thermistor TM2 which is the second exhaust gas temperature measuring unit. The amount of water vapor obtained in relation to the amount of exhaust gas calculated above may be compared with the amount of saturated water vapor. When the amount of water vapor contained in the exhaust gas is large, the value and the exhaust gas fluid value may be used, and when the saturated water vapor amount is large, the value may be used as the exhaust gas fluid value.

Subsequently, the saturated water vapor amount contained in the exhaust gas after heat exchange is calculated by multiplying the exhaust gas flow rate discharged from the heat exchanger 3 (that is, the exhaust gas flow rate discharged from the fuel cell module 1), the exhaust gas temperature, the gas pressure, and the like. To do. The calculation can be performed using the steam state quantity calculation function calculated from the steam table of the Japan Society of Mechanical Engineers published in 1999.

The control device 20 can efficiently recover the condensed water by controlling the drive of the heat medium circulation pump P1 in accordance with the exhaust gas fluid value calculated from the above-mentioned exhaust gas. That is, the control device 20 has a table of the relationship between the temperature and the saturated water vapor amount, and the relationship between the drive of the heat medium circulation pump, the temperature before the heat exchange of the exhaust gas, and the temperature after the heat exchange, which has been investigated in advance. Remember the table.

That is, the control device 20 first calculates the amount of water vapor contained in the exhaust gas, and then determines the amount to be recovered as the amount of condensed water, and as a result, obtains the amount of water vapor contained in the exhaust gas after heat exchange. it can. That is, the temperature corresponding to the saturated water vapor amount of the exhaust gas after heat exchange can be obtained. As a result, the target temperature of the exhaust gas after heat exchange is determined, and from the table of the determined target temperature, the exhaust gas temperature flowing into the heat exchanger 3, and the drive of the heat medium circulation pump P1, the heat medium circulation pump P1 The amount of drive can be controlled.

Further, when the amount of condensed water obtained from the exhaust gas is insufficient, the control device 20 may lower the target temperature. On the other hand, if the amount of condensed water obtained from the exhaust gas is excessive, the target temperature may be raised.

As a result, it is possible to efficiently recover the required amount of condensed water, as compared with controlling the drive of the heat medium circulation pump so that the temperature of the hot water stored at the outlet of the heat exchanger becomes the target as in the past.

In the above example, when the "target temperature" on the outlet side of the heat exchanger 3 is set or switched based on the exhaust gas fluid value, the control device 20 improves the heat exchange efficiency and safety. In consideration of the above, the target temperature is set to a temperature lower than the first temperature, which is a preset upper limit value. The first temperature can be set below 50 ° C.

(Second Embodiment)
Next, a second embodiment having a means for further lowering the exhaust gas temperature (exhaust gas temperature discharged to the outside) on the outlet side of the heat exchanger 3 will be described.

The fuel cell device 101 shown in FIG. 3 has the exhaust gas flow path E and the exhaust flow path V as a configuration for further lowering the exhaust gas temperature on the outlet side of the heat exchanger 3, that is, the exhaust gas temperature discharged to the outside of the device. A bypass flow path 15 that connects the spaces without passing through the heat exchanger 3 and a gas pump P3 arranged in the bypass flow path 15 are provided. A check valve B1 is provided on the bypass flow path 15, and a reverse flow for preventing backflow of exhaust gas is performed on the exhaust gas flow path E between the catalyst container 2 and the heat exchanger 3. A check valve B2 is provided.

Since the configuration of other parts is the same as that of the fuel cell device 100 of the first embodiment, the same reference numerals are given and the description thereof will be omitted.

Then, in the fuel cell device 101 having the above-described configuration, the control device 20 executes a temperature confirmation control for confirming the exhaust gas temperature on the inlet side of the heat exchanger 3, and the exhaust gas temperature is set to a predetermined second temperature. In the above case, the exhaust gas recirculation control is performed by driving the gas pump P3 described above to recirculate the exhaust gas derived from the heat exchanger 3 to the exhaust gas flow path E via the bypass flow path 15. The second temperature can be set to, for example, 70 ° C.

With this configuration, the fuel cell device 101 of the second embodiment can set the temperature of the exhaust gas discharged to the outside of the machine through the exhaust flow path V to a safer low temperature.

1 Fuel cell module 3 Heat exchanger 20 Control device 100,101 Fuel cell device Q Heat medium circulation flow path P1 Heat medium circulation pump TM thermistor

Claims (5)

A fuel cell that generates electricity using fuel gas and oxygen-containing gas,
A heat exchanger that exchanges heat between the exhaust gas discharged from the fuel cell and the heat medium.
A first exhaust gas temperature measuring unit that measures the temperature of the exhaust gas discharged from the heat exchanger,
A circulation pump arranged in a circulation flow path for circulating a heat medium in the heat exchanger,
Equipped with a control device,
The control device is a fuel cell capable of executing exhaust gas temperature control that controls the drive of the circulation pump so that the first exhaust gas temperature measured by the first exhaust gas temperature measuring unit becomes a predetermined target temperature. apparatus. A reformer that steam reforms raw fuel and supplies the fuel gas to the fuel cell,
A reformed water tank that stores the reformed water for steam reforming supplied to the reformer, and
A water level detection unit for detecting the water level of the reformed water stored in the reformed water tank is provided.
The fuel cell device according to claim 1, wherein the control device sets the target temperature based on the water level of the reformed water in the reformed water tank detected by the water level detection unit. A reformer that steam reforms raw fuel and supplies the fuel gas to the fuel cell,
A reformed water amount measuring unit that measures the amount of reformed water supplied to the reformer,
The control device is an exhaust gas fluid value related to the amount of water contained in the exhaust gas, and is an exhaust gas calculated by using the flow rate of the exhaust gas and the flow rate of the reformed water measured by the reformed water amount measuring unit. The fuel cell device according to claim 1, wherein the target temperature is set based on the fluid value. A first temperature, which is an upper limit temperature, is set in advance as the target temperature.
The fuel cell device according to any one of claims 1 to 3, wherein the control device sets the target temperature to a temperature lower than the first temperature. A second exhaust gas temperature measuring unit that measures the temperature of the exhaust gas flowing from the fuel cell into the heat exchanger,
The exhaust gas flow path between the fuel cell and the heat exchanger,
An exhaust flow path that exhausts the exhaust gas discharged from the heat exchanger to the outside of the device,
A bypass flow path that connects the exhaust gas flow path and the exhaust gas flow path without passing through the heat exchanger, and a bypass flow path.
A gas pump arranged in the bypass flow path is provided.
The control device executes temperature confirmation control for confirming the second exhaust gas temperature measured by the second exhaust gas temperature measuring unit, and when the second exhaust gas temperature is equal to or higher than a predetermined second temperature,
The fuel cell according to claim 3 or 4, wherein the gas pump is driven to execute an exhaust gas recirculation control for returning the exhaust gas discharged from the heat exchanger to the exhaust gas flow path via the bypass flow path. apparatus.

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