JPH0529012A - Fuel cell and heat recovery method in exhaust gas system - Google Patents

Abstract

PURPOSE:To heighten partial pressure of steam in gas so as to increase the recovery of exhaust heat in exhaust gas heat exchangers by mixing blowdown water from a fuel cell cooling water circuit with fuel exhaust gas from a reformer. CONSTITUTION:Exhaust gas generated in a fuel cell body 1 is sent to an exhaust gas heat exchanger 10 so that heat is recovered, and the heat of exhaust gas generated in a reformer 2 is recovered by means of an exhaust gas heat exchanger 11. Exchangers 10 and 11 are connected to a condenser 6, and the gas from which heat is recovered is condensed further by means of the condenser 6, and is released into the air, and water generated at this time is sent to a water treatment device 7, and is used as a part of cooling water. The first blowdown circuit 8 is connected upstream of the heat exchanger 11 through a three way directional control valve 12 from a steam separator 5, and on the other hand, the three way directional control valve 12 is connected to the second blowdown circuit 13, and this second blowdown circuit is connected downstream of the heat exchangers 10 and 11 as well as upstream of the condenser 6, and the directional control valve 12 is controlled by means of a controller 15 according to operation of a sensor 14 so as to switch the circuits 8 and 13.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a fuel cell and an exhaust heat recovery method capable of recovering exhaust heat more efficiently from exhaust gas of the fuel cell.

[0002]

PRIOR ART AND PROBLEMS Generally, two fuel cells are used.
Two exhaust gases are emitted. For example, in FIG. 3, one is a gas discharged from the air electrode of the fuel cell main body 1 and contains unreacted components of the air supplied to the air electrode and water vapor generated at the air electrode. The other is gas discharged from the reformer 2, and fuel such as city gas supplied through the ejector 9 is reformed into hydrogen-rich gas by the reformer 2 and supplied to the fuel cell body 1. The unreacted hydrogen after being burned in the fuel electrode of the fuel cell body 1 is the exhaust gas burned in the reformer 2.

In FIG. 3, an exhaust heat recovery heat exchanger 3, a temperature control heat exchanger 4, a steam separator 5, a water treatment device 7 are shown.
Form a cooling water circuit C of the fuel cell body 1.

When recovering exhaust heat from these exhaust gases,
Conventionally, as shown in FIG. 3, both exhaust gases are mixed and heat is recovered by the exhaust heat recovery heat exchanger 10. In addition, Japanese Patent Application No. 2-
As shown in No. 280810 (FIG. 4), both are separated, and heat is recovered separately by the exhaust heat recovery heat exchangers 10 and 11, so that the exhaust gas outlet temperature is mixed within the range of 60 to 75 ° C. The amount of heat recovered can be increased as compared with the case of recovering.

FIG. 4 shows the separation / recovery system diagram, FIG. 5 shows the relationship between the exhaust gas outlet temperature and the recovered heat amount when mixed and recovered, and FIG. 6 shows the relationship between the exhaust gas outlet temperature and the recovered heat amount when separated and recovered. Show.

On the other hand, in the past, when the blowdown water from the battery cooling water system C is heat-recovered by the exhaust gas system, the blowdown circuit 8 has a confluence of both exhaust gases and an exhaust heat recovery heat exchanger as shown in FIG. The blowdown water was connected to an exhaust gas pipe in the middle of 6 and condensed in the exhaust heat recovery heat exchanger 6 and then led to the water treatment device 7. Further, in the separation / recovery system as shown in FIG. 4, the treatment method of the blowdown water has not been studied, and the heat recovery utilizing the heat quantity of the blowdown water sufficiently has not been performed.

[0007]

It is an object of the present invention to solve the above problems by mixing blowdown water from a battery cooling water circuit with combustion exhaust gas from a reformer to reduce the partial pressure of water vapor in the gas. It is an object of the present invention to provide a fuel cell and an exhaust gas system heat recovery method that are controlled so as to increase the exhaust heat recovery amount in an exhaust heat recovery exchanger.

[0008]

In order to solve the above problems, a fuel cell according to the present invention is a fuel cell main body which inputs hydrogen and oxygen to generate power and, at the same time, generates heat.
A reformer for reforming city gas or the like to supply hydrogen to the fuel cell body, and a first exhaust gas provided to recover exhaust heat from exhaust gas exhausted from an air electrode of the fuel cell body. A second exhaust heat recovery heat exchanger provided to recover exhaust heat from the exhaust gas discharged from the heat recovery heat exchanger and the reformer, the first exhaust heat recovery heat exchanger, and the second exhaust heat recovery heat exchanger. 2. A cooling water circuit for cooling a fuel cell main body in a fuel cell including a condenser provided for mixing exhaust gases discharged from the exhaust heat recovery heat exchanger and condensing water in the exhaust gas. And a flow of blowdown water from the cooling water circuit to an exhaust gas pipe between the reformer and the second exhaust heat recovery heat exchanger in order to suppress concentration of impurities in the cooling water of the cooling water circuit. BLOW DOWN CIRCUIT AND THE FIRST BRODER A second blowdown circuit for flowing blowdown water between the middle of the condenser circuit and the two heat recovery heat exchangers from the condenser to the condenser; and the first blowdown circuit to the second blowdown circuit. A three-way switching valve installed at a branch point at which the blowdown circuit of
Of the exhaust heat recovery heat exchanger, and a controller that sends a control signal to the three-way switching valve based on the measurement value measured by the temperature sensor.

In the fuel cell exhaust gas heat recovery method according to the present invention, hydrogen and oxygen are input to generate electric power, and at the same time, the fuel cell main body generates heat and hydrogen is supplied to the fuel cell main body. From a reformer for reforming city gas and the like, a first exhaust heat recovery heat exchanger provided for recovering exhaust heat from exhaust gas discharged from the air electrode of the fuel cell main body, and the reformer A second exhaust heat recovery heat exchanger provided for recovering exhaust heat from the exhaust gas discharged, and exhausted from the first exhaust heat recovery heat exchanger and the second exhaust heat recovery heat exchanger. A condenser provided to mix the respective exhaust gases to condense the water in the exhaust gas, a cooling water circuit for cooling the fuel cell main body, and to suppress the concentration of impurities in the cooling water of the cooling water circuit. From the cooling water circuit to the reformer and before A first blowdown circuit for flowing blowdown water to an exhaust gas pipe in the middle of a second exhaust heat recovery heat exchanger, and two exhausts from the middle of the first blowdown circuit to the condenser and the condenser. A second blowdown circuit for flowing blowdown water in the middle of the heat recovery heat exchanger;
A three-way switching valve installed at a branch point where the second blowdown circuit branches from the first blowdown circuit, a sensor that detects an exhaust gas temperature at the outlet of the second exhaust heat recovery heat exchanger, and When the exhaust gas outlet temperature measured by the temperature sensor of the fuel cell including a controller that sends a control signal to the three-way switching valve based on the measurement value measured by the temperature sensor is equal to or lower than a predetermined temperature level. Switches the three-way switching valve so that blowdown water flows through the first blowdown circuit, and conversely, when the exhaust gas temperature is equal to or higher than a predetermined temperature level, the second
By switching the three-way switching valve so as to flow through the blow-down circuit, the control is performed so that the exhaust heat recovery amount in the second exhaust heat recovery heat exchanger is maximized.

[0010]

The features of the present invention and the difference from the prior art The present invention is an exhaust heat recovery heat exchanger in which the partial pressure of water vapor in the combustion exhaust gas is increased by mixing the combustion exhaust gas from the reformer with blowdown water. It is characterized in that it is controlled so as to increase the amount of exhaust heat recovery.

So far, no method has been disclosed which can efficiently recover the thermal energy of blowdown water when the exhaust gas from the fuel cell air electrode and the combustion gas from the reformer are separated and heat is recovered.

[0012]

EXAMPLE FIG. 1 shows an example of the present invention.

In the figure, 1 is a fuel cell main body, 2 is a reformer, 3 is a cooling water system waste heat recovery heat exchanger, 4 is a temperature control heat exchanger, 5 is a steam separator, 6 is a condenser, 7 is a water treatment device, 8 is a first blowdown circuit, 9 is an ejector, 1
Reference numeral 0 is a first exhaust heat recovery heat exchanger, 11 is a second exhaust heat recovery heat exchanger, 12 is a three-way switching valve, 13 is a second blowdown circuit, 14 is a temperature sensor, and 15 is a controller.

As is clear from this figure, in the fuel cell according to the present invention, fuel such as city gas is conveyed to the reformer 2 through the injector 9, and the hydrogen-rich gas reformed by the reformer 2 is used as fuel. It is configured to be transported to the fuel electrode of the cell body 1, and unreacted hydrogen in this fuel electrode can be transported to the burner system of the reformer 2. On the other hand, air is configured to be conveyed to the burner system and the air electrode of the fuel cell.

The fuel cell body 1 is connected to an exhaust heat recovery heat exchanger 10, and the exhaust gas generated in the fuel cell body 1 is sent to the exhaust heat recovery exchanger 10 to recover heat. There is.

On the other hand, the reformer 2 comprises an exhaust heat recovery exchanger 11
The exhaust gas generated in the reformer 2 is recovered by the exhaust heat recovery heat exchanger 11.

The exhaust heat recovery heat exchangers 10 and 11 are connected to the condenser 6, and the heat recovered exhaust gas is further condensed in the condenser 6 and released into the atmosphere. At this time, the generated water is sent to the water treatment device 7 and forms a part of the cooling water.

The fuel cell main body 1 is cooled by a cooling water circuit C, and the cooling water circuit includes an exhaust heat recovery unit 3, a temperature control exchanger 4, a steam separator 5 and a water treatment unit 7. Consists of. The cooling water that has cooled the fuel cell body 1 enters the steam water separator 7 through the exhaust heat recovery device 32 and the temperature control exchanger 4, separates the gas and water, and then guides the water to the fuel cell body 1 again. The fuel cell body 1 is cooled. On the other hand, new water is supplied to the steam / water separator 5 through the water treatment device 7, and the steam / water separator 5 is supplied.
A part of the cooling water therein is blown down to suppress the concentration of impurities in the cooling water.

The blowdown circuit (first blowdown circuit) 8 is a three-way switching valve 12 from the steam separator 5.
Is connected upstream of the exhaust heat recovery heat exchanger 11. On the other hand, the three-way switching valve 12 is connected to a second blowdown circuit 13, which is connected downstream of the exhaust heat recovery heat exchangers 10 and 11 and upstream of the condenser 6. Has been done.

The three-way switching valve 12 is controlled by the controller 15 by the action of the sensor 14, and switches between the first blowdown circuit 8 and the second blowdown circuit. .

In the fuel cell as described above, the exhaust gas from the air electrode of the fuel cell body 1 and the combustion gas from the reformer 2 are the first exhaust heat recovery heat exchanger 10 and the second exhaust heat recovery heat. It is discharged to the atmosphere through the exchanger 11. On the other hand, the heat recovered by the first and second exhaust heat recovery heat exchangers 10 and 11 is transported to the outside of the device and used.

Exhaust gas discharged from the air electrode of the fuel cell main body 1 mainly contains nitrogen, oxygen, water vapor, etc., and their contents are 5.25, 0.
It is about 7, 1.40 Kmol / h. In addition, the reformer 2
The combustion exhaust gas discharged from the
Carbon dioxide and water vapor are contained, and their contents are 1.32, 0.17, 0.44, 1.
It will be about 23 Kmol / h.

As described above, both exhaust gases contain water vapor, and the combustion exhaust gas discharged from the reformer 2 is higher when the partial pressures of water vapor in the two exhaust gases are compared. Therefore, as shown in FIG. 6, when the two exhaust gases are separated and recovered, the steam in the combustion exhaust gas discharged from the reformer 2 starts to condense at about 75 ° C., and both exhaust gases are mixed as shown in FIG. The exhaust heat recovery amount can be increased in the range of 60 to 75 ° C. as compared with the case of recovering the exhaust heat.

Further, by mixing the blowdown water (first blowdown circuit 8) with the combustion exhaust gas from the reformer 2 before the second exhaust heat recovery heat exchanger 11, the partial pressure of water vapor in the exhaust gas is mixed. Can be increased and the amount of heat recovery can be increased. Fig. 2 shows the relationship between the exhaust gas outlet temperature and the heat recovery amount at this time.
Shown in. By comparing FIG. 2 and FIG. 6, the exhaust heat recovery amount is larger in the exhaust gas outlet when the exhaust gas outlet is 75 ° C. or higher (FIG. 6), but the blow down water is supplied when the exhaust gas outlet is 75 ° C. or lower. It can be seen that the one (Fig. 2) has a large amount of exhaust heat recovery.

Therefore, in the case of the present embodiment, when the exhaust gas outlet temperature detected by the temperature sensor 14 is 75 ° C. or higher, the blowdown water is made to flow through the second blowdown circuit 13 by a command from the controller 15. When the exhaust gas temperature detected by the temperature sensor 14 is 75 ° C. or lower by switching the three-way switching valve 12 so as to flow, the controller 15 issues a command to blow down water to the first blow down circuit 8
The three-way switching valve 12 is switched so as to flow through.

In this way, by controlling the three-way switching valve 12 in accordance with the exhaust gas outlet temperature, the position where the blowdown water is poured is changed, and in this embodiment, the exhaust gas is discharged within the range of 75 ° C. or lower in comparison with the conventional one. It was possible to increase the amount of heat recovery. In addition, the blowdown water is supplied to the first blowdown circuit 8
The exhaust gas outlet temperature for determining whether to flow through the second blowdown circuit 13 is determined by the amount of blowdown water.

[0027]

According to the present invention, even when the exhaust gas from the fuel cell air electrode and the combustion exhaust gas from the reformer are separated and heat is recovered, the thermal energy of the blowdown water can be effectively utilized. As shown in the examples, the exhaust gas outlet temperature is 7
When the temperature is 5 ° C. or less, more heat can be recovered than before.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the exhaust gas outlet temperature and the amount of recovered heat in an example of the present invention.

FIG. 3 is a system diagram when two exhaust gases are mixed to recover heat.

FIG. 4 is a diagram showing the relationship between the exhaust gas outlet temperature and the amount of recovered heat when two exhaust gases are mixed and heat is recovered.

FIG. 5 is a system diagram when two exhaust gases are separated and heat is recovered.

FIG. 6 is a diagram showing the relationship between the exhaust gas outlet temperature and the amount of recovered heat when two exhaust gases are separated and heat is recovered.

FIG. 7 is a diagram showing a conventional blowdown method.

[Explanation of symbols]

1 Fuel cell body 2 reformer 3 Cooling water system waste heat recovery heat exchanger 4 Temperature control heat exchanger 5 steam separator 6 condenser 7 Water treatment equipment 8 First blowdown circuit 9 ejector 10 First waste heat recovery heat exchanger 11 Second exhaust heat recovery heat exchanger 12 three-way switching valve 13 Second blowdown circuit 14 Temperature sensor 15 Controller

Claims (2)

[Claims] 1. A fuel cell main body for inputting hydrogen and oxygen to generate power and generating heat at the same time, and a reformer for reforming city gas or the like to supply hydrogen to the fuel cell main body. A first exhaust heat recovery heat exchanger provided for recovering exhaust heat from exhaust gas discharged from the air electrode of the fuel cell body, and for recovering exhaust heat from exhaust gas discharged from the reformer. Moisture in the exhaust gas by mixing the second exhaust heat recovery heat exchanger provided with each exhaust gas discharged from the first exhaust heat recovery heat exchanger and the second exhaust heat recovery heat exchanger In a fuel cell provided with a condenser provided to condense the cooling water circuit for cooling the fuel cell main body, and to suppress the concentration of impurities in the cooling water of the cooling water circuit, The reformer and the second exhaust heat recovery heat exchanger A first blowdown circuit for flowing blowdown water to an intermediate exhaust gas pipe and a blowdown circuit between the first blowdown circuit and the two exhaust heat recovery heat exchangers from the condenser to the condenser. A second blowdown circuit for flowing down water, a three-way switching valve installed at a branch point where the second blowdown circuit branches from the first blowdown circuit, and the second exhaust heat recovery heat exchange A fuel cell comprising: a sensor for detecting the exhaust gas temperature at the outlet of the reactor; and a controller for sending a control signal to the three-way switching valve based on the measurement value measured by the temperature sensor. 2. A fuel cell main body which inputs hydrogen and oxygen to generate electric power and generate heat at the same time, and a reformer for reforming city gas or the like to supply hydrogen to the fuel cell main body. A first exhaust heat recovery heat exchanger provided for recovering exhaust heat from exhaust gas discharged from the air electrode of the fuel cell body, and for recovering exhaust heat from exhaust gas discharged from the reformer. Moisture in the exhaust gas by mixing the second exhaust heat recovery heat exchanger provided with each exhaust gas discharged from the first exhaust heat recovery heat exchanger and the second exhaust heat recovery heat exchanger A condenser provided for condensing the fuel cell, a cooling water circuit for cooling the fuel cell body, and a reformer from the cooling water circuit for suppressing the concentration of impurities in the cooling water of the cooling water circuit. The exhaust gas pipe in the middle of the second exhaust heat recovery heat exchanger is blown up. A second blowdown circuit for flowing downwater, and a second blowdown water for flowing between the first blowdown circuit and the two exhaust heat recovery heat exchangers from the middle of the first blowdown circuit to the condenser and the second condenser. Blowdown circuit of
A three-way switching valve installed at a branch point where the second blowdown circuit branches from the first blowdown circuit, a sensor that detects an exhaust gas temperature at the outlet of the second exhaust heat recovery heat exchanger, and When the exhaust gas outlet temperature measured by the temperature sensor of the fuel cell including a controller that sends a control signal to the three-way switching valve based on the measurement value measured by the temperature sensor is equal to or lower than a predetermined temperature level. Switches the three-way switching valve so that blowdown water flows through the first blowdown circuit, and conversely, when the exhaust gas temperature is equal to or higher than a predetermined temperature level, the second
The exhaust gas recovery system for fuel cells, characterized in that the three-way switching valve is switched so as to flow through the blow-down circuit of 1. Heat recovery method.