JP2004303495A - Fuel cell power generation hot-water supply system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell power generation hot-water supply system composed by stabilizing a hot-water supply temperature by exhaust heat recovery. <P>SOLUTION: This fuel cell power generation hot-water supply system has: a fuel processor 1 for reforming a fuel to generate an anode gas 6 containing hydrogen; and a fuel cell 9 for reacting air 8 with the hydrogen in the anode gas to generate power. The system is equipped with a plurality of heat exchangers 11-1 to 11-4 for exchanging heat with an indirect cooling medium by using, as heat sources, the anode gas 6, a direct cooling medium 12 for cooling the fuel cell, and an anode exhaust gas 14 and a cathode exhaust gas 13 exhausted from the fuel cell; and a plurality of the heat exchangers are arranged in series to the indirect cooling medium flowing through the heat exchangers. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel cell power generation and hot water supply system.
[0002]
[Prior art]
Fuel cells have been developed mainly for electric power. As a result, fuel cells require higher power demands during certain hours like home use, but on average demand is lower. For this reason, it is economical to perform the partial load operation following the power demand. Under such operating conditions, when the flow rate changes, the heat transfer rate changes, so that the inlet and outlet temperatures of the heat exchanger of the exhaust heat recovery system change. Furthermore, if the temperature fluctuates depending on the season and time, there is a problem that the temperature of hot water stored in the hot water tank also fluctuates. However, since the heat exchanger itself is a passive device, there is a problem that it is not possible to cope with these changes. Was.
[0003]
As a prior art, there is a cogeneration system described in JP-A-11-223385. In this prior art, when recovering the heat of the generator, a countermeasure is provided by providing a bypass pipe and a flow path switching valve so as not to put low-temperature water into the hot water storage tank.
[0004]
[Patent Document 1]
JP-A-11-223385
[Problems to be solved by the invention]
In the technology described in Japanese Patent Application Laid-Open No. H11-223385, the flow path switching valve controls the total flow rate to go to either the bypass pipe or the hot water tank, and is one of the applications of this technology. Although it is considered to be optimal for heat sources such as gas engines, in the case of fuel cells that require strict temperature control, consideration is not given to the fact that the inlet and outlet temperatures of the fuel cell fluctuate and it is difficult to obtain stable performance.
[0006]
An object of the present invention is to provide a fuel cell power generation and hot water supply system that stabilizes a hot water supply temperature by exhaust heat recovery.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, in the fuel cell power generation and hot water supply system of the present invention, a fuel processing device that reforms fuel to generate an anode gas containing hydrogen, and reacts oxygen with hydrogen in the anode gas. In a fuel cell power generation hot water supply system having a fuel cell for generating electricity, the anode gas, a direct cooling medium for cooling the fuel cell, and an anode exhaust gas and a cathode exhaust gas discharged from the fuel cell exchange heat with an indirect cooling medium as a heat source. A plurality of heat exchangers are provided, and the plurality of heat exchangers are arranged in series with the indirect cooling medium flowing through the heat exchanger.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Prior to describing the embodiments, the background of the invention will be described. The characteristic of the exhaust heat recovery system of this polymer electrolyte membrane fuel cell power generation system is that the operating temperature of the fuel cell of the main engine is about 70 to 80 ° C., which is lower than the boiling point of water of 100 ° C. It is rich in steam at a temperature lower than the boiling point in terms of a large amount of low-quality thermal energy and protection of the electrolyte of the fuel cell. For this reason, in order to efficiently perform exhaust heat recovery, a method different from a system such as a gas engine is necessary in that steam exhaust heat, that is, latent heat must be efficiently recovered, and There is a background that the fuel cell temperature control requirements must be met, which is stricter than that of a gas engine or the like.
[0009]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a system diagram of a fuel cell power generation and hot water supply system according to one embodiment of the present invention.
[0010]
The fuel cell power generation and hot water supply system shown in FIG. 1 is a fuel processing device 1 for generating an anode gas 6 containing hydrogen and a combustion exhaust gas 7 from a city gas 2, air 3, deionized water 5, and a return anode exhaust gas 4. A fuel cell 9 that generates electricity by reacting the anode gas 6 from 1 with the air 8 flowing from the cathode, and a fuel cell cooling system including a hot water tank 10 and a heat exchanger 11-2 for cooling the fuel cell 9 12, a first heat exchanger 11-1 for bringing the anode gas 6 from the fuel processor 1 to a temperature suitable for entering the anode of the fuel cell 9, and a second heat exchanger 11-1 for recovering heat from the fuel cell cooling system 12. Heat exchanger 11-2, a third heat exchanger 11-3 for heating the cathode air 8 supplied to the fuel cell 9 with the cathode exhaust gas 13 from the fuel cell 9, and a cathode exhaust gas 15 from the heat exchanger 11-3. From A fourth heat exchanger 11-4 for recovering heat from the anode exhaust gas 14 from the fuel cell 9, a flow distribution valve 16 for distributing a flow rate by the temperature measuring unit 18 and the control unit 17, and a flow rate by the temperature measuring unit 19 and the control unit 20. A pump 21 to be controlled, a control unit 25 for controlling the control unit 20 and the control unit 17 in an integrated manner, a hot water tank 22, a bypass line 23 of the hot water tank 22, heat exchangers 11-1, 11-2, 11-. 4, an exhaust heat recovery system 24 including a pump 21.
[0011]
In the fuel cell power generation and hot water supply system configured as described above, first, a specified amount of the hydrogen-rich anode gas 6 and the air 8 whose fuel is reformed by the fuel processor 1 are fed into the fuel cell 9 by an electrochemical reaction. Generates DC power and heat. Part of this heat is removed by the fuel cell cooling system 12, and part of the heat of the remaining cathode exhaust gas 13 is recovered again in the cathode air 8 by the heat exchanger 11-3, and the rest is recovered from the cathode exhaust gas 15. It collects in heat exchanger 11-4. At the same time, the anode exhaust gas 14 from the fuel cell 9 is also recovered by the heat exchanger 11-4. Exhaust heat is recovered by the heat exchanger 11-1 from the generated anode gas 6 of the fuel processor 1, which is another heat source. Incidentally, since the anode gas 6 enters the fuel cell 9 at the outlet of the heat exchanger 11-1, a large deviation from a temperature around 70 ° C. is not allowed. Exhaust heat can be recovered from the combustion exhaust gas 7, but it is excluded from consideration of the amount of heat that can be recovered in view of the cost. Needless to say, if a low-cost heat exchanger that is cost-effective is realized, exhaust heat is recovered.
[0012]
For this reason, among the above, exhaust heat recovery for hot water supply is performed from the heat exchangers 11-1, 11-2, and 11-4. If these three heat exchangers are connected in parallel, control is simple, but hot water supply at a predetermined temperature cannot be obtained. In addition, if these heat exchangers are arranged in series, the temperature relationship may be reversed depending on the temperature and load conditions, resulting in heat transfer instead of heat recovery, which may damage the performance of temperature-sensitive fuel cells. In addition, there is a possibility that the temperature of the anode gas 6 may deviate from a required range of the fuel cell 9 because the heat exchanger may be out of the specification range and the exhaust heat recovery efficiency may be reduced. As it was, monitoring the temperature at the entrance and exit of the heat exchanger, the only way to pass through the heat exchanger was to switch the piping system and obtain the necessary hot water supply, but this method required a complicated piping system. The heat radiation from the pipes increases and the cost also increases, so that it cannot be adopted in a system of about 1 kW such as a home fuel cell power generation and hot water supply system.
[0013]
In order to solve this, in this embodiment, as described above, the heat exchangers 11-1, 11-2, and 11-4 are arranged in series with the indirect cooling medium flowing through these heat exchangers, and The exhaust heat recovery system is formed so that the indirect cooling medium flows in the order from the heat exchangers 11-4, 11-2, and 11-1. Then, the inflow temperature of tap water as the indirect cooling medium in the first-stage heat exchanger 11-4 is set to about 30 ° C., which can be set even in summer, and the outflow temperature of tap water in the last-stage heat exchanger 11-1 is required to be hot water supply. The temperature was set to 60 ° C. or higher. The inflow temperature is controlled by adjusting the flow distribution valve 16 by the control unit 17 by detecting the flow rate passing through the bypass line 23 by the temperature measurement unit 18. At the same time, the outflow temperature is controlled by adjusting the flow rate of the pump 21 by the control unit 20 by detecting the outflow temperature by the temperature measurement unit 19. At the time of this control, both are not controlled at the same time, but are controlled by the control unit 25 in a different time zone by performing time division. The target value is adjusted by time sharing so that the target value does not fall outside the allowable range. Thus, closely related control can be performed stably.
[0014]
The heat exchanger 11-3 exchanges heat between the air 8 entering the cathode and the discharged cathode exhaust gas 13. With this configuration, since heat for condensing the vapor component in the cathode exhaust gas 13 can be used, even if the temperature changes, the condensed water slightly increases or decreases and the temperature due to the generated condensing heat changes only by 2 to 3 ° C. Irrespective of this, there is an effect that the cathode air 8 can maintain a substantially constant temperature. This effect was also confirmed by experiments. Incidentally, the heat exchangers 11-1, 11-2, 11-3, and 11-4 are preferably plate-shaped from the viewpoint of low cost and compactness. Further, since the anode exhaust gas 14 and the cathode exhaust gas 15 have different amounts of heat but have substantially the same temperature conditions for input and output, the heat exchanger 11-4 for recovering heat from the anode exhaust gas 14 and the cathode exhaust gas 15 is more compact. The three-fluid type is desirable because it can be used.
[0015]
With the configuration as described above, the heat exchanger is connected in series in consideration of the temperature order in the exhaust heat recovery system, and a pipeline system and a control system for controlling the input and output temperatures of the heat exchanger group are provided. Fuel cell power generation and hot water supply system that can stably follow partial load operation while maximally recovering waste heat at low cost, and can operate economically without deteriorating fuel cell performance There is an effect that can be provided.
[0016]
Next, another embodiment of the present invention will be described with reference to FIG. This embodiment is different from the embodiment shown in FIG. 1 in that drain drains 26-1 to 26-5 are provided downstream of the heat exchanger or downstream of the anode and cathode exhaust gas outlet gas of the fuel cell 9; This will be described as follows. The drain drain 26-1 drains the drain generated downstream of the anode gas 6 discharged from the fuel processor 1 after passing through the heat exchanger 11-1, and the drain drain 26-2 is discharged from the fuel cell 9. The drain accompanying the anode exhaust gas 14 is drained, and the drain drain 26-3 drains the drain generated in the return anode exhaust gas 4 after the anode exhaust gas 14 has exited the heat exchanger 11-4.
[0017]
Next, a description will be given of the cathode exhaust gas line. The drain drain 26-4 drains the drain in the cathode exhaust gas 13 discharged from the fuel cell 9. The drain drain 26-5 drains a drain generated when the cathode exhaust gas 13 passes through the heat exchanger 11-3. Since both gases are rich in water vapor components, when the temperature decreases, useful heat of condensation is generated in the heat exchanger group 11, but the treatment of condensed water generated at the same time becomes a problem. If not removed, the pressure loss increases, the auxiliary power increases, and the heat exchanger performance decreases. In particular, since the return anode exhaust gas 4 is returned to the fuel processing apparatus 1 and is subjected to combustion, unless the water is removed, misfire, a decrease in combustion performance, and a decrease in combustion temperature are caused. In addition, since these condensed waters have better quality than tap water, they can be reused if collected. Although not shown, the size of the water treatment apparatus can be reduced.
[0018]
The drain drain 26-1 on the downstream side of the heat exchanger 11-1 thought that no drain was generated only from the temperature and moisture conditions. However, the drain drain 26-1 was actually affected by the temperature of tap water to be heat-exchanged. Occurs. The condensed water is generated in the portion after the cathode exhaust gas 14 has passed through the heat exchanger 11-4, but the drain drain is not provided because the cathode exhaust gas outlet is provided and a drain receiving tank (not shown) is provided at the outlet. The reason for this is that condensed water can be recovered simply by providing ()). Although not shown in the drawing of the drain, a drain receiving tank, a solenoid valve provided thereunder and a timer are used to set a time interval for opening and closing the solenoid valve from the accumulated amount and time measured in advance. And remove to the receiving tank by its own weight. However, the solenoid valve is closed so as to leave a certain amount of water so that the gas does not come into contact with the outside air. Desirably, a float type drain drain is used.
[0019]
By doing so, it is possible to stably follow the partial load operation at low cost, and economical operation is possible without deteriorating the performance of the fuel cell. There is an effect that can be provided.
[0020]
FIG. 3 shows a fuel cell power generation system according to another embodiment of the present invention. The difference from the embodiment of FIG. 2 is that the fuel cell cooling system 12 is provided with a bypass line 28, a flow rate distribution valve 27 including a temperature measurement unit 30 and a flow rate control unit 29, whereby the heat exchanger 11 By controlling the inlet temperature of the fuel cell cooling water to 50 ° C. or more by mixing an appropriate amount of water that has not passed through −2 and water that has passed. Desirably, the temperature is maintained at 65 ° C. or higher so that the operating temperature does not lower to cause deterioration of the fuel cell performance. When the partial load operation is performed, at a low partial load, the absolute amount of heat generated from the fuel cell decreases, but the heat radiation loss is substantially constant, so that the temperature of the fuel cell itself decreases. When the fuel cell is cooled by the water passed through the heat exchanger 11-2 as it is, if the fuel cell temporarily enters the deterioration temperature range of the performance of the fuel cell, the operating temperature may further fall into a vicious cycle. It is the configuration of the present embodiment that prevents this.
[0021]
By doing so, it is possible to stably follow the partial load operation at low cost, and economical operation is possible without deteriorating the performance of the fuel cell. There is an effect that can be provided.
[0022]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, it is effective in the ability to provide the fuel-cell power generation hot-water supply system which stabilized the hot-water supply temperature by waste heat recovery.
[Brief description of the drawings]
FIG. 1 is a system diagram of a fuel cell power generation and hot water supply system according to one embodiment of the present invention.
FIG. 2 is a system diagram of a fuel cell power generation / hot water supply system according to another embodiment of the present invention.
FIG. 3 shows a system diagram of a fuel cell power generation / hot water supply system according to another embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Fuel processing apparatus, 2 ... City gas, 3 ... Air, 4 ... Return anode exhaust gas, 5 ... Deionized water, 6 ... Anode gas, 7 ... Combustion exhaust gas, 8 ... Cathode air, 9 ... Fuel cell, 10, 22 ... Hot water storage tank, 11-1 to 11-4 ... Heat exchanger, 12 ... Fuel cell cooling system, 13,15 ... Cathode exhaust gas, 14 ... Anode exhaust gas, 16,27 ... Flow distribution valve, 17,20,25,29 ... Control unit, 18, 19, 30 ... Temperature measurement unit
Reference numeral 21: pump, 23, 28: bypass line, 24: exhaust heat recovery system, 26-1 to 26-5: drain removal.

Claims (11)

In a fuel cell power generation and hot water supply system including a fuel processing device that reforms fuel to generate an anode gas containing hydrogen and a fuel cell that generates power by reacting oxygen and hydrogen in the anode gas,
A plurality of heat exchangers for exchanging heat with the indirect cooling medium using the anode gas, the direct cooling medium for cooling the fuel cell, and the anode exhaust gas and the cathode exhaust gas discharged from the fuel cell as heat sources are provided. A fuel cell power generation and hot water supply system, wherein the heat exchanger is arranged in series with an indirect cooling medium flowing through the heat exchanger. In a fuel cell power generation hot water supply system having a fuel processing device that reforms fuel to generate an anode gas containing hydrogen and a fuel cell that generates power by reacting oxygen in the air and hydrogen in the anode gas,
A first heat exchanger that exchanges heat between the anode gas supplied to the fuel cell and the indirect cooling medium, a second heat exchanger that exchanges heat between the cooling medium that has cooled the fuel cell and the indirect cooling medium, A third heat exchanger for exchanging heat between a cathode exhaust gas discharged from the fuel cell and air supplied to the fuel cell, an anode exhaust gas discharged from the fuel cell and the third heat exchanger. A fourth heat exchanger for exchanging heat between the cathode exhaust gas and the indirect cooling medium is provided, and the first, second, and fourth heat exchangers flow through the first, second, and fourth heat exchangers. A fuel cell power supply system comprising: an exhaust heat recovery system that is arranged in series with an indirect cooling medium so that the indirect cooling medium flows in the order of a fourth, a second, and a first heat exchanger. system. The fuel cell power generation and hot water supply system according to claim 1,
A bypass flow path for bypassing a part of the indirect cooling medium heat-exchanged by the plurality of heat exchangers to a hot water storage tank for the indirect cooling medium, and a bypass for joining the indirect cooling medium supplied to a first stage of the heat exchanger; A fuel cell power generation and hot water supply system comprising: a flow distribution valve for adjusting a bypass flow rate from a flow path; and a pump for supplying an indirect cooling medium passing through the flow distribution valve to the heat exchanger. The fuel cell power generation and hot water supply system according to claim 3,
A control device for controlling a bypass flow rate of the indirect cooling medium to be joined by the flow distribution valve so that a temperature of the indirect cooling medium supplied to the first stage of the heat exchanger is equal to or higher than a predetermined temperature. Fuel cell power generation hot water supply system. The fuel cell power generation and hot water supply system according to claim 3,
A fuel cell, comprising: a controller that controls a flow rate of the indirect cooling medium supplied by the pump so that a temperature of the indirect cooling medium discharged from a final stage of the heat exchanger is equal to or higher than a predetermined temperature. Power generation hot water supply system. The fuel cell power generation and hot water supply system according to claim 1,
A bypass path that bypasses a heat exchanger that exchanges heat with the indirect cooling medium for part of the direct cooling medium supplied to the fuel cell; and a bypass path that joins the direct cooling medium supplied to the fuel cell. A flow distribution valve that adjusts a bypass flow rate from the fuel cell, and a control that controls a bypass flow rate of the direct cooling medium that is joined by the flow distribution valve so that the temperature of the direct cooling medium supplied to the fuel cell is equal to or higher than a predetermined temperature. A fuel cell power generation and hot water supply system comprising the device. The fuel cell power generation and hot water supply system according to claim 1,
The heat exchanger according to claim 1, wherein the heat exchanger is a plate-type heat exchanger. The fuel cell power generation and hot water supply system according to claim 1,
A fuel cell power generation / hot water supply system, comprising: a heat exchanger for heating cathode air of the fuel cell by cathode exhaust gas discharged from the fuel cell. The fuel cell power generation and hot water supply system according to claim 1,
One of the plurality of heat exchangers is a three-fluid heat exchanger for exchanging heat between an anode exhaust gas, a cathode exhaust gas, and an indirect cooling medium. The fuel cell power generation and hot water supply system according to claim 1,
A drain is supplied to at least one of a path for supplying anode gas from the fuel processor to the fuel cell, a path for passing the cathode exhaust gas discharged from the fuel cell, and a path for flowing the anode exhaust gas discharged from the fuel cell. A fuel cell power generation hot water supply system characterized by providing a hole. The fuel cell power generation and hot water supply system according to claim 4 or 5,
A controller is provided for controlling the temperature of the indirect cooling medium supplied to the first stage of the plurality of heat exchangers and the temperature of the indirect cooling medium discharged from the last stage heat exchanger in mutually different time zones. Fuel cell power generation hot water supply system.

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