JP2021072255A - 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 100 includes a fuel cell module 1 that generates electricity, a reformer 12 that supplies fuel gas, a heat exchanger 3 that exchanges heat between exhaust gas discharged from a fuel cell and a heat medium, 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 heat medium circulation pump P1 according to an exhaust gas fluid value calculated from the exhaust gas.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 reformer that reforms raw fuel with steam and supplies the fuel gas to the fuel cell, and the fuel. It includes a heat exchanger that exchanges heat between the exhaust gas discharged from the battery and the heat medium, a circulation pump arranged in a circulation flow path that circulates the heat medium in the heat exchanger, and a control device.
The control device can execute condensed water recovery control that controls the drive of the circulation pump according to the exhaust gas fluid value calculated from the exhaust gas.

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 embodiment. It is a perspective view which shows the structure of the fuel cell apparatus in an outer case.

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 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, a thermistor TM1 for measuring the temperature of the exhaust gas catalyst in the catalyst container 2 that burns the exhaust gas discharged from the fuel cell module 1 (combustion unit) is arranged. The thermistor TM1 may measure the temperature of the heat medium flowing through the heat exchanger 3. 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, the thermistor may be arranged on the exhaust gas flow path E between the catalyst container 2 and the heat exchanger 3 to measure the exhaust gas temperature.

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 has an "exhaust gas fluid value" calculated by using a predetermined item related to the exhaust gas discharged from the fuel cell module 1. Corresponding to, the drive and discharge of the heat medium circulation pump P1 and the flow rate (circulation amount) of the heat medium circulation flow path Q are controlled.

In this way, by driving the heat medium circulation pump P1 based on the exhaust gas fluid value, it becomes possible to efficiently recover the condensed water. A specific embodiment will be described below.

For example, when the fuel cell device 100 having the above configuration is performing power generation operation, the control device 20 is supplied to the cell stack 11 as a control for efficiently recovering the heat and condensed water discharged from the fuel cell module 1. The heat medium circulation flow path Q is based on the flow rate of the fuel gas, the flow rate of the reforming water supplied to the reformer 12 measured by the reforming water amount measuring unit, and the exhaust gas fluid value calculated in relation to the flow rate. It is possible to control the drive and discharge of the heat medium circulation pump P1.

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.

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 and entering the heat exchanger 3 is high, and the amount of water contained in the exhaust gas discharged from the fuel cell module 1 is not so large. Therefore, at the time of inlet of the heat exchanger 3, the water content in the exhaust gas has not reached the saturated water vapor amount. Therefore, in the above calculation formula, the inlet temperature of the exhaust gas to the heat exchanger 3 is not taken into consideration. However, when considering the saturated water vapor amount of the exhaust gas, the saturated water vapor amount is calculated using the temperature of the exhaust gas measured by the thermistor TM1 in the calculation of the exhaust gas fluid value, and is related to the exhaust gas amount calculated above. The amount of water vapor obtained can 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 efficiently recovers condensed water by controlling the drive and discharge amount (hereinafter collectively referred to as drive) of the circulation pump P1 according to the exhaust gas fluid value calculated from the above-mentioned exhaust gas. It can be carried out. That is, the control device 20 stores a table of 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. Then, the control device 20 derives a predetermined drive of the heat medium circulation pump P1 for obtaining the required condensed water from the amount of water vapor contained in the exhaust gas fluid value calculated from the exhaust gas from the stored table. The heat medium circulation pump P1 is controlled so as to be driven in a predetermined manner.

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 calculating the condensed water required for driving the heat medium circulation pump P1, the drive of the heat medium circulation pump P1 may be controlled based on the water level of the reforming water in the reforming water tank 6. ..

That is, during the execution of the above-mentioned condensed water recovery control, the water level is detected or not detected by the low water level water detector WL1 or the high water level water detector WL2, which is a water level detection unit that detects the water level of the reformed water. When the alarm is issued, the control device 20 executes a control for correcting the drive of the heat medium circulation pump P1 with the water level of the reforming water in the reforming water tank 6 as a priority item.

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 drive (duty ratio) of the heat medium circulation pump P1 during execution of condensed water recovery control is reduced from before [minus (minus (duty)). -) Correction] may be executed. 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 the heat during execution of the condensed water recovery control. The drive (duty ratio) of the medium circulation pump P1 is increased from before, and the drive [plus (+) correction] is executed. 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 kept within an appropriate range for continuing independent operation. be able to.

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.

By the way, in the heat exchanger 3 of the fuel cell device, dirt or the like may adhere to the piping or the like inside the fuel cell device over time, and the heat exchange efficiency may decrease. In the fuel cell device of the present disclosure, the following control is executed in order to cope with this.

That is, the control device 20 of the fuel cell device 100 includes a storage device (not shown) capable of recording the cumulative power generation time of the fuel cell, and the cumulative power generation time counted or counted by this storage device is predetermined. When the first hour or more is reached, the control device 20 executes the discharge amount increase control for correcting and increasing the drive of the circulation pump for a predetermined time during the execution of the condensed water recovery control described above.

It should be noted that increasing the drive of the pump by correcting it for a predetermined time is the same operation as the [plus (+) correction] of the heat medium circulation pump described above. That is, the control device 20 executes [plus (+) correction] of the drive for increasing the drive (duty ratio) of the heat medium circulation pump P1 during the execution of the condensed water recovery control for a predetermined time. ..

As a result, it is possible to suppress a decrease in heat exchange efficiency due to adhesion of dirt over time.

1 Fuel cell module 3 Heat exchanger 12 Reformer 20 Control device 100 Fuel cell device Q Heat medium circulation flow path P1 Heat medium circulation pump

Claims (4)

A fuel cell that generates electricity using fuel gas and oxygen-containing gas,
A reformer that steam reforms raw fuel and supplies the fuel gas to the fuel cell,
A heat exchanger that exchanges heat between the exhaust gas discharged from the fuel cell and the heat medium.
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 device capable of executing condensed water recovery control that controls the drive of the circulation pump according to the exhaust gas fluid value calculated from the exhaust gas. A reformed water amount measuring unit for measuring the amount of reformed water supplied to the reformer is provided.
The control device is
The claim that the exhaust gas fluid value is calculated using the flow rate of the exhaust gas and the flow rate of the reformed water measured by the reformed water amount measuring unit, and the drive of the circulation pump is controlled based on the exhaust gas fluid value. The fuel cell device according to 1. A reformed water tank for storing the reformed water and
A water level detection unit for detecting the water level of the reformed water stored in the reformed water tank is provided.
The control device is
The exhaust gas temperature and
The exhaust gas fluid value and
The water level of the reformed water in the reformed water tank and
The fuel cell device according to claim 1 or 2, wherein the drive of the circulation pump is controlled based on the above. Equipped with a storage device that can record the cumulative power generation time of the fuel cell
When the cumulative power generation time is equal to or longer than a predetermined value, the control device
The fuel cell device according to any one of claims 1 to 3, which executes a discharge amount increase control for increasing the drive of the circulation pump.

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