JP2004164868A - Hot water storage method and device in cogeneration system - Google Patents

Abstract

A hot water storage method and a hot water storage device that have a simple configuration so that the hot water temperature of a hot water storage tank in a cogeneration system can be maintained at a predetermined temperature.
In a cogeneration system in which a hot water storage tank is connected to a fuel cell system, a backup burner is arranged in parallel with a process gas burner of the fuel cell system to constitute a backup water heater. When a large amount of hot water is supplied and the temperature of hot water in the hot water storage tank 5 falls below a predetermined temperature, the backup burner 16 is burned to efficiently heat the hot water. When the temperature of the hot water reaches the predetermined temperature, the combustion of the backup burner 16 is started. Is controlled to be stopped.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hot water storage method and a device thereof in a cogeneration system in which a hot water tank is connected to a fuel cell system.
[0002]
[Prior art]
2. Description of the Related Art A cogeneration system that supplies both electricity and heat is conventionally known. This cogeneration system supplies electric power generated by a fuel cell of a fuel cell system and supplies hot water using exhaust heat generated by the fuel cell system. It was done. As an example of such a cogeneration system, a reformer (consisting of a reformer, a CO converter, and a CO remover) for reforming a raw fuel such as city gas into a reformed gas mainly composed of hydrogen is provided. A fuel cell system or the like is formed by a fuel cell or the like that generates DC power using the reformed gas supplied from the CO remover of this reformer and the air (oxidant gas) supplied from the air fan. A configuration in which a hot water storage tank is connected is disclosed (for example, Patent Document 1).
[0003]
[Patent Document 1]
JP 2001-291525 A
[Problems to be solved by the invention]
According to the above conventional cogeneration system, the composition of the reformed gas is not stable unless the temperature of the catalyst of the reformer rises to the predetermined temperature (about 700 ° C.) at the time of starting the fuel cell system. The quality gas is sent to a process gas burner for combustion without being supplied to the fuel electrode of the fuel cell. The combustion exhaust gas from the process gas burner is used as a heat source for heating by exchanging heat with water in a hot water storage tank. After the operation of the fuel cell is started, a part of the unreacted off gas at the fuel electrode is introduced into the process gas burner and burned, and the combustion exhaust gas is also used as a heat source for heating the water in the hot water storage tank. . Further, the flue gas of the raw fuel burned by the reformer burner to raise the temperature of the catalyst of the reformer is also used as a heat source for heating the water in the hot water storage tank.
[0005]
After the composition of the reformed gas by the reformer is stabilized, the valve is switched so that the reformed gas is supplied to the fuel electrode of the fuel cell, and the introduction to the process gas burner is stopped. Therefore, combustion of the reformed gas in the process gas burner is limited within a relatively short time until the composition of the reformed gas is stabilized. After the operation of the fuel cell is started, most of the unreacted off gas at the fuel electrode is introduced into the reformer burner and burned, so that the amount of off gas supplied to the process gas burner is significantly reduced.
[0006]
City water is supplied to the hot water storage tank, and heat is exchanged between the city water and the combustion exhaust gas from the process gas burner and the combustion exhaust gas from the reformer burner to be heated to about 60 ° C. and stored. However, if the amount of hot water supplied from the hot water storage tank increases, the amount of city water to be supplied increases, and the temperature of the hot water in the hot water storage tank drops to 60 ° C. or lower. In such a case, there is a problem that even if it is desired to quickly raise the temperature of the hot water in the hot water storage tank, the amount of heat exhausted from the process gas burner is limited as described above, and thus the purpose cannot be sufficiently achieved.
[0007]
The present inventors have conducted intensive studies to solve such a conventional problem, and as a result, by adding an additional cooking function to the process gas burner, a drop in the hot water temperature in the hot water storage tank at the time of large-volume hot water supply can be quickly recovered. The inventors have found what can be done, and have completed the present invention. That is, an object of the present invention is to provide a hot water storage method and a device thereof that can maintain the hot water temperature of a hot water storage tank in a cogeneration system at a predetermined temperature with a simple configuration.
[0008]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a cogeneration system in which a hot water storage tank is connected to a fuel cell system, wherein a backup burner is added to a process gas burner of the fuel cell system. A hot water storage method in a cogeneration system, characterized in that the backup burner is burned when the temperature of the hot water in the tank falls below a predetermined temperature, and the combustion of the backup burner is stopped when the temperature of the hot water reaches the predetermined temperature. .
[0009]
Also, the present invention relates to a reformer for reforming a raw fuel into a reformed gas mainly composed of hydrogen, a fuel cell which is supplied with the reformed gas and an oxidizing gas to generate electric power, and In a cogeneration system in which a hot water storage tank is connected to a fuel cell system including a process gas burner that burns the reformed gas until the composition of the reformed gas is stabilized by the reformer, a backup burner is added to the process gas burner A hot water storage device in a cogeneration system, comprising a backup hot water supply.
[0010]
Furthermore, a third aspect of the present invention is characterized in that, in the second aspect, the process gas burner and the backup burner are juxtaposed to integrate a combustion section.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of a hot water storage method and a hot water storage device in a cogeneration system according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic block diagram showing an embodiment of a hot water storage device in a cogeneration system according to the present invention.
[0012]
In FIG. 1, reference numeral 1 denotes a fuel cell system, which includes a reformer 2, a fuel cell 3 (for example, a polymer electrolyte fuel cell), a process gas burner 4, and the like. A hot water storage tank 5 is connected to the fuel cell system 1 to form a cogeneration system 6.
[0013]
The reformer 2 includes a reformer 2a, a CO shift converter 2b, a CO remover 2c, and the like. After the raw fuel such as city gas is adsorbed by a desulfurizer 2d for sulfur content, the reformer 2a Reforming into a gas mainly composed of hydrogen by steam reforming, then converting CO in the reformed gas into CO ₂ in a CO converter 2b, and further performing selective oxidation in a CO remover 2c to form a reformed gas. CO in the water is reduced to a predetermined concentration or less.
[0014]
When the fuel cell system 1 is started, the composition of the reformed gas reformed by the reformer 2 is not stable. Therefore, the switching valve 7 is closed and the switching valve 8 is opened to supply the reformed gas to the process gas burner. 4 and burn. In the reformer 2a, a part of the raw fuel is supplied to the reformer burner 9 and burned in order to raise the temperature of the catalyst.
[0015]
When the composition of the reformed gas becomes stable, the switching valve 8 is closed and the switching valve 7 is opened to supply the reformed gas from the CO remover 2c to the fuel electrode 3a of the fuel cell 3 and to be taken in from outside air by the air fan 10. The air is supplied to the cathode 3b of the fuel cell 3 to start the power generation of the fuel cell 3.
[0016]
In general, the DC power generated by the fuel cell 3 is introduced into the power supply unit 11, converted into AC power through a DC / DC converter, and a DC / AC inverter (not shown), and supplied.
[0017]
During the power generation of the fuel cell 3, off-gas that has not reacted at the fuel electrode 3 a is discharged from the fuel cell 3, and most of the off-gas is introduced into the reformer burner 9 through a pipe 12 and burned. Part of the gas is introduced into the process gas burner 4 through a pipe 13 branched from the pipe 12 and burned. Switching valves 14 and 15 are provided in the middle of the pipes 12 and 13, respectively. The catalyst of the reformer 2a is an exothermic reaction, and it is necessary to introduce an off-gas into the reformer burner 9 and continue burning in order to maintain the reaction temperature of the catalyst. A part of the raw fuel is supplied to the reformer burner 9 and burned only during the temperature rise of the catalyst of the reformer 2a at the time of startup, and is not supplied after the start of operation.
[0018]
In the present embodiment, a backup water heater 17 is configured by adding a backup burner 16 to the process gas burner 4. The configuration example will be described with reference to FIG. 2. The backup water heater 17 includes a combustion section 17a and a heat exchange section 17b, and the process gas burner 4 and the backup burner 16 are arranged in the combustion section 17a in parallel. A plurality of heat recovery water pipes 18 are provided in 17b. The heat recovery water pipe 18 is composed of a plurality of straight pipes, but may be a single bent pipe that is bent a plurality of times in the heat exchange section 17a. Further, a combustion air fan 19 is attached to the combustion section 17a. This backup water heater 17 is connected to the hot water storage tank 5 via a pipe 20 as shown in FIG. 1, and a pump 21 is provided in the pipe 20 in the middle.
[0019]
City water is supplied to the hot water storage tank 5 in a timely manner, and water flows into the pipeline 20 from the bottom of the hot water storage tank 5 by the pump 21 and passes through the heat recovery water pipe 18 connected to the pipeline 20. Then, after being heated in the heat exchange section 17b of the backup water heater 17, the water returns to the upper portion in the hot water storage tank 5. Usually, a fixed amount of hot water is stored in the hot water storage tank 5, and the temperature of the hot water can be gradually raised by repeatedly circulating the water in the manner described above.
[0020]
The hot water storage tank 5 is provided with a temperature sensor 22 so that the temperature sensor 22 can detect the temperature of the hot water in the hot water storage tank 5. When the hot water temperature reaches a predetermined temperature (for example, 60 ° C.), the control device ( (Not shown), the pump 21 is stopped, the circulation of water is cut off, and hot water of 60 ° C. is stored in the hot water storage tank 5.
[0021]
For example, when hot water is used in a kitchen or bathroom in a general household, the hot water is supplied from the hot water storage tank 5. Then, city water is supplied to the bottom of the hot water storage tank 5 in response to the decrease in the amount of hot water in the hot water storage tank 5. When a large amount of hot water is used, a large amount of city water is replenished into the hot water storage tank 5, so that the temperature of the hot water in the hot water storage tank 5 drops to 60 ° C. or less.
[0022]
When the temperature sensor 22 detects the temperature of the hot water of 60 ° C. or less, the pump 21 operates according to a signal from the control device, and the circulation of water with the backup hot water heater 17 starts. The circulating water is heated in the heat exchange section 17b of the backup water heater 17 and returns to the hot water storage tank 5 as described above. At this time, the backup burner 16 is burned to increase the heating speed.
[0023]
As shown in FIG. 2, a backup burner fuel supply pipe 23 is connected to the backup burner 16 to supply city gas, propane gas, or the like as fuel. As described above, the process gas burner 4 is supplied with off-gas (reformed gas at startup) discharged from the fuel cell 3 as fuel. Although it is possible to supply off-gas as fuel for the backup burner 16, most of the off-gas is used as fuel for the reformer burner 9 as described above, and the amount of off-gas supply to the process gas burner 4 is small. The supply of off-gas to the backup burner 16 by branching at a very small amount is extremely small.
[0024]
It is possible to supply the required amount of off-gas to the backup burner 16 by limiting the amount of off-gas supplied to the reformer burner 9. However, the off-gas is a reformed gas mainly composed of hydrogen, and is diffused without mixing with air. The combustion speed is high because it is burned, and backfire tends to occur when a large amount is burned. When the backfire occurs, it is not only dangerous but may even destroy the fuel cell 3. From these facts, it is preferable that the fuel of the backup burner 16 is city gas or propane gas, and the air from the combustion air fan 19 is mixed and burned.
[0025]
In this embodiment, not only off-gas combustion in the process gas burner 4 but also city gas or propane gas combustion in the backup burner 16 is added, so that the backup water heater 17 exhibits a so-called reheating function, and a large amount of hot water is produced. When the temperature of the hot water in the hot water storage tank 5 is reduced to 60 ° C. or less, the circulating water passing through the heat exchange section 17b of the backup hot water supply 17 is efficiently heated to reduce the hot water temperature in the hot water storage tank 5 for a short time. To 60 ° C. When the temperature of the hot water in the hot water storage tank 5 returns to 60 ° C., the supply of fuel to the backup burner 16 is stopped by a command signal of the control device, and only the off-gas combustion in the process gas burner 4 is continued to keep the temperature.
[0026]
In addition, since the backup water heater 17 has a structure in which the process gas burner 4 and the backup burner 16 are arranged side by side and the combustion part 17a is integrated, the total heat quantity of the combustion part 17a is increased and the heat exchange in the heat exchange part 17b is performed. Can be performed efficiently.
[0027]
Further, since the backup water heater 17 is provided not on the hot water storage tank 5 side but on the fuel cell system 1 side, there is no combustion exhaust gas on the hot water storage tank 5 side, and the degree of freedom of the installation location of the hot water storage tank 5 can be increased.
[0028]
When the power generation of the fuel cell 3 is completed and the fuel cell system 1 stops, the supply of the off gas to the process gas burner 4 is cut off. At this time, when the fuel is supplied to the backup burner 16 and burned, the hot water in the hot water storage tank 5 can be kept at a predetermined temperature (60 ° C.). The hot water temperature is detected by the temperature sensor 22, and when the temperature falls below a predetermined temperature, fuel is supplied to the backup burner 16 to burn it. When the temperature reaches the predetermined temperature, the control device stops the fuel supply to the backup burner 16. It is possible to control. Thus, when the fuel cell system 1 is stopped, the temperature of the hot water in the hot water storage tank 5 can be maintained at a predetermined temperature.
[0029]
【The invention's effect】
As described above, according to the first aspect of the present invention, in a cogeneration system in which a hot water storage tank is connected to a fuel cell system, a backup burner is added to a process gas burner of the fuel cell system, and the hot water storage tank is provided. A hot water storage method in which the backup burner is burned when the temperature of the hot water in the inside falls below a predetermined temperature, and the combustion of the backup burner is stopped when the temperature of the hot water reaches the predetermined temperature. When the hot water is supplied to the furnace and the hot water temperature falls below the predetermined temperature, the temperature can be raised to the predetermined temperature in a short time by the combustion of the backup burner, and the temperature can be controlled so as not to exceed the predetermined temperature. Thereby, there is an effect that the hot water temperature of the hot water storage tank can be maintained at the predetermined temperature.
[0030]
Further, according to the invention of claim 2 of the present invention, a reformer for reforming a raw fuel into a reformed gas mainly composed of hydrogen, and a fuel cell for generating electricity by supplying the reformed gas and the oxidizing gas And a cogeneration system in which a hot water storage tank is connected to a fuel cell system including a process gas burner that burns the reformed gas until the composition of the reformed gas is stabilized by the reformer. This hot water storage device features a backup water heater with a backup burner added, and has a simple configuration and does not significantly increase the cost. The backup water heater is not on the hot water storage tank side but on the fuel cell system side. Since there is no combustion exhaust gas on the hot water storage tank side, there is an effect that the degree of freedom of the installation location of the hot water storage tank is improved.
[0031]
Further, according to the third aspect of the present invention, in the second aspect, the process gas burner and the backup burner are juxtaposed and the combustion part is integrated, so that the total heat amount of the combustion part of the backup water heater is reduced. Heat can be efficiently exchanged with the circulating water by increasing the temperature, and the apparatus can be made compact and compact.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram showing an embodiment of a hot water storage device in a cogeneration system according to the present invention according to the present invention.
FIG. 2 is an explanatory diagram showing a configuration example of a backup water heater according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Fuel cell system 2 ... Reformer 3 ... Fuel cell 4 ... Process gas burner 5 ... Hot water storage tank 6 ... Cogeneration system 9 ... Reformer burner 16 ... Backup burner 17 ... Backup water heater 17a ... Combustion part 17b ... Heat exchange Part 18: Heat recovery water pipe 19 ... Combustion air fan 22 ... Temperature sensor 23 ... Backup burner fuel supply pipe

Claims (3)

In a cogeneration system in which a hot water storage tank is connected to a fuel cell system, a backup burner is added to a process gas burner of the fuel cell system, and when the temperature of hot water in the hot water storage tank falls below a predetermined temperature, the backup burner is burned, A method of storing hot water in a cogeneration system, wherein the combustion of the backup burner is stopped when the temperature of the hot water reaches a predetermined temperature. A reformer for reforming raw fuel into a reformed gas mainly composed of hydrogen, a fuel cell for supplying the reformed gas and the oxidizing gas to generate power, and a composition of the reformed gas by the reformer being stabilized In a cogeneration system in which a hot water storage tank is connected to a fuel cell system having a process gas burner that burns the reformed gas up to this point, a backup water heater is configured by adding a backup burner to the process gas burner. Hot water storage device in the cogeneration system. The hot water storage device in a cogeneration system according to claim 2, wherein the process gas burner and the backup burner are arranged side by side to integrate a combustion unit.

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