JP3918537B2 - Fuel cell system and control method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell system, and more particularly to a fuel cell system that improves system efficiency.
[0002]
[Prior art]
A fuel cell system is an energy system that converts chemical energy into electrical energy using a chemical reaction that generates water from hydrogen and oxygen. Although pure hydrogen is ideal as a fuel, from the viewpoint of infrastructure development, a partial oxidation reaction of hydrocarbons, a steam reforming reaction of hydrocarbons and water, or a combination of these two reactions (so-called autothermal reaction) It is realistic to generate hydrogen using this as a fuel.
[0003]
Hydrocarbons can be selected from gaseous states such as methane, ethane, and propane, and liquid states such as gasoline and methanol. However, it has a higher energy density than gaseous ones and assumes a portable fuel cell system. In this case, a liquefied hydrocarbon fuel is suitable.
[0004]
In order to generate a reforming reaction that produces a hydrogen-rich reformed gas using liquefied hydrocarbons as the fuel, it is necessary to vaporize the liquid hydrocarbons once, It is necessary to vaporize water when doing it. However, supply of latent heat of vaporization to a liquid such as liquefied hydrocarbon to form a gas is a factor that reduces the efficiency of the system in terms of energy efficiency. In order to suppress this decrease in efficiency, various techniques for vaporizing a liquid using waste heat and waste energy from a fuel cell system have been studied.
[0005]
In JP-A-8-250142, when water vapor used for reforming is generated, the water is heated in advance by the waste heat of the fuel cell and then heated by the electric heater, thereby reducing the load on the electric heater and improving the efficiency. An improved configuration is disclosed. In this configuration, the electric heater is controlled by the water vapor pressure so that the water vapor amount required by the reformer is obtained.
[0006]
In Japanese Patent Laid-Open No. 7-73893, air is heated using heat discharged from a fuel cell, and water is sprayed into the heated air to obtain the latent heat of vaporization of water. Furthermore, the water is vaporized to expand the volume, and the energy at this time drives the expansion turbine to recover the energy and improve the efficiency.
[0007]
In Japanese Patent Laid-Open No. 5-275101, water is vaporized by exchanging heat with the waste heat of the fuel cell, and the recovery of the waste heat of the fuel cell can be promoted by reducing the vaporization line of the heat exchanger. It is disclosed.
[0008]
[Problems to be solved by the invention]
However, in the technique described in Japanese Patent Laid-Open No. 8-250142, water cannot be vaporized only by the waste heat of the fuel cell, and it is an essential requirement to install an electric heater as a configuration. As a result, the electric heater reduces the efficiency of the fuel cell system.
[0009]
In the technique described in Japanese Patent Application Laid-Open No. 7-73893, the amount of water to be vaporized is very small and cannot provide the amount of water vapor necessary for reforming. This is because the energy of the air heated by the waste heat of the fuel cell is expressed by the specific heat of the air × temperature difference, but the latent heat of vaporization of water is much larger than this energy. In addition, the expansion turbine is driven using volume expansion to recover energy, but if the outlet pressure of the expansion turbine is atmospheric pressure, the inlet pressure needs to be in a pressurized state. If the pressure rises, the water will condense, so (1) heat the air, (2) spray water into the air (water vapor is generated, gas temperature decreases, gas volume increases), (3) A configuration that satisfies the three conditions of driving the expansion turbine is not established.
[0010]
In the technique described in Japanese Patent Application Laid-Open No. 5-275101, the heat supply source of the heat exchanger is fuel cell cooling water, and the temperature of the generated water vapor does not exceed the cooling water temperature. For example, when an ethylene glycol-based refrigerant is used as the cooling water, the upper limit is about 150 ° C. Further, when a compressor is used as the decompression device, water vapor may be condensed at the outlet of the compressor.
[0011]
In view of the above problems, the present invention provides a fuel cell system that stably supplies water vapor without reducing the efficiency of the system.
[0012]
[Means for Solving the Problems]
A first invention includes a reformer that generates hydrogen-rich reformed gas, a fuel cell stack that generates electric power using the reformed gas and an oxidant, and a combustor that burns gas discharged from the fuel cell stack. A vaporizer that vaporizes the reforming fuel and water using the heat of the combustion gas from the combustor, a flow path for supplying the vaporized reforming fuel and water vapor to the reformer, and in the middle of the flow path And a pressure control device that is installed and changes the pressure in the flow path downstream of the carburetor according to the load fluctuation of the fuel cell stack.
[0013]
In a second aspect based on the first aspect, the vaporizer is a heat exchange type evaporator.
[0014]
According to a third invention, in the first or second invention, the pressure control device is a decompression pump or a compressor.
[0015]
According to a fourth invention, in the first or second invention, the pressure control device is a pump that reduces the pressure of the flow path downstream of the carburetor using the energy of the combustion gas.
[0016]
According to a fifth invention, in any one of the first to fourth inventions, a heater is provided that supplies the reformed fuel vaporized by the vaporizer and the steam with a calorific value.
[0017]
According to a sixth invention, in any one of the first to fifth inventions, a drain tank for storing the condensed water generated in the vaporizer is provided.
[0018]
A seventh invention includes a reformer that generates a hydrogen-rich reformed gas, a fuel cell stack that generates electric power using the reformed gas and an oxidant, and a combustor that burns gas discharged from the fuel cell stack. A fuel cell system comprising: a vaporizer that vaporizes the reforming fuel and water using heat of combustion gas from the combustor; and a flow path that supplies the vaporized reforming fuel and water vapor to the reformer. The pressure in the flow path downstream of the carburetor is changed according to the load fluctuation of the fuel cell stack using a pressure control device installed in the middle of the supply flow path.
[0019]
【The invention's effect】
In the first and seventh inventions, a fuel cell is provided with a pressure control device for changing the pressure of the reforming fuel vaporized by the vaporizer using the heat of the combustion gas and the flow path for supplying water vapor to the reformer. Since the pressure in the flow path is changed according to the load fluctuation of the stack, the pressure in the flow path is reduced when the fuel cell stack is heavily loaded, and the vaporization temperature of the reforming fuel and water is reduced. Reduced and efficiently promoted, and obtains heat necessary for vaporization by heat exchange with the heat of combustion gas, thereby suppressing vaporized fuel and water vapor from condensing, and stably vaporizing fuel and water vapor Can be supplied to the reformer, and the response of the fuel cell stack to fluctuations in load can be improved.
[0020]
In the second invention, since the vaporizer is a heat exchange type evaporator, the heat of the combustion gas can be efficiently consumed for vaporization of the reforming fuel and water.
[0021]
In the third invention, since the pressure control device is a decompression pump or a compressor, the pressure in the flow path downstream of the vaporizer can be changed efficiently.
[0022]
In a fourth aspect of the invention, the pressure control device is a pump that uses the energy of the combustion gas to reduce the pressure in the flow path downstream of the carburetor. Since the pressure can be changed, the efficiency of the system can be further improved.
[0023]
The fifth aspect of the present invention includes a heater that supplies the reformed fuel vaporized by the vaporizer and the heat amount of the combustion gas to the steam, so that condensation when the vaporized reformed fuel and the steam are pressurized is suppressed. be able to.
[0024]
In the sixth aspect of the present invention, since the drain tank for storing the condensed water generated in the vaporizer is provided, the water balance of the system is improved by using the condensed water in the drain tank for water replenishment of the polymer electrolyte membrane of the fuel cell. Can be improved.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an example of the configuration of the fuel cell system of the present invention.
[0026]
The reformer 1 is supplied with air supplied from the first air supply line 2, vaporized fuel (for example, hydrocarbon) and steam supplied from the steam supply line 3, and the reformer 1 is modified. A quality gas is generated and supplied to a downstream carbon monoxide remover (hereinafter referred to as a CO remover) 4. The CO remover 4 reduces the concentration of carbon monoxide in the reformed gas to a level at which the fuel cell is not poisoned, and supplies the reformed gas from the reformed gas supply line 5 to the fuel cell stack 7. Further, air is supplied from the second air supply line 6 to the fuel cell stack 7 from the outside, and the fuel cell stack 7 generates power using the reformed gas and air.
[0027]
Exhaust reformed gas and exhaust air discharged from the fuel cell stack 7 are respectively introduced into the combustor 10 through the exhaust air line 8 and the exhaust reformed gas line 9 and combusted. This combustion gas is sent to the vaporizer 12 via the combustion gas line 11, and the vaporizer 12 vaporizes liquefied hydrocarbons and water as reforming fuel supplied from the liquid supply line 13 using the heat of the combustion gas. To do. As the vaporizer 12, for example, a heat exchange type evaporator is suitable. By using such a vaporizer 12, the temperature of the combustion gas is lowered to about the vaporization temperature of vaporized hydrocarbon or water and discharged to the outside. The liquid supply line 13 is provided with a control valve 14 that controls the flow rate of the liquid in the line.
[0028]
The pressure in the decompression vaporization line 16 connecting the vaporizer 12 and the pressure control valve 15 is reduced by a pressure control device 15 such as a decompression pump or a compressor installed downstream of the vaporizer 12. Therefore, as will be described later, the vaporization temperature of fuel and water in the vaporizer 12 is lowered, and vaporization can be promoted efficiently.
[0029]
The vaporized fuel and water vapor are supplied from the pressure control device 15 to the reformer 1 via the steam supply line 3 communicating with the reformer 1 and used to generate reformed gas.
[0030]
In the fuel system of the present invention, the amount of air supplied from the control valve 14 and the pressure control device 15 and the first and second air supply lines 2 and 7 (not shown) is adjusted in accordance with the operating load variation of the fuel cell stack 7. A control device 17 for controlling a control valve for the purpose is installed.
[0031]
By maintaining the reduced pressure vaporization line 16 downstream of the vaporizer 12 in this way, the heat exchange efficiency in the vaporizer 12 is increased, the vaporization of fuel and water is promoted, the energy recovery rate is improved, and the energy of the system is increased. Efficiency can be improved. The case of water will be described in detail by way of example. Water vaporizes at 100 ° C. under atmospheric pressure, but the vaporization temperature becomes lower as the pressure is lower. For example, under 612 Pa, the vaporization temperature becomes 0 ° C. Here, when a heat exchange type vaporizer is used, the temperature of the combustion gas discharged from the vaporizer 12 is substantially equal to the vaporization temperature. Therefore, if the pressure of the reduced pressure vaporization line 16 is 612 Pa, the combustion gas temperature is approximately 0 ° C. Become. Therefore, if the inflow temperature of the combustion gas to the vaporizer 12 is 300 ° C., the difference between the inflow temperature of the combustion gas and the outflow temperature of water vapor from the vaporizer 12 is 300 ° C., and the temperature difference at atmospheric pressure is 200 ° C. ( Combustion gas temperature 300 ° C-vaporization temperature 100 ° C under atmospheric pressure). Therefore, even if the combustion gas temperature is the same, vaporization can be further promoted by setting the reduced pressure vaporization line 16 to a low pressure. In other words, this temperature difference represents the recovery rate of the combustion energy of the combustion gas, meaning that the larger the temperature difference, the better the energy recovery rate, indicating that the thermal efficiency of the fuel cell system can be improved.
[0032]
The control device 17 controls the control valve 14 and the pressure control device 15 according to the operation load of the fuel cell stack 7. Specifically, when the operating load of the fuel cell stack 7 is reduced, it is necessary to control so as to reduce the amount of vaporized fuel and the amount of water vapor supplied to the stack 7. As this method, the pressure control device 15 is controlled so as to temporarily increase the pressure in the vacuum vaporization line 16. By increasing the pressure in the reduced-pressure vaporization line 16, the vaporization temperature is increased as described above, vaporization is suppressed, and the vaporized fuel and the amount of water vapor supplied to the reformer 1 can be reduced. . On the other hand, when the load of the fuel cell stack 7 increases, it goes without saying that the pressure in the decompression vaporization line 16 may be reduced. In addition, the pressure control makes it possible to respond more quickly than the flow rate control, and the operating load response of the fuel cell stack 7 can be improved.
[0033]
As described above, in the present invention, the pressure control device for reducing the pressure in the flow path downstream of the vaporizer for vaporizing the reforming fuel and water is provided, and the gas discharged from the fuel cell stack is burned in the vaporizer. By introducing the combustion gas, it is possible to efficiently vaporize by lowering the vaporization temperature, and it is difficult to condense the vaporized fuel and the like by exchanging heat with the high-temperature combustion gas. There is an effect that can be supplied to the quality device. Furthermore, the pressure control device 15 can improve the responsiveness to fluctuations in the load of the fuel cell stack 7 by changing the pressure in the flow path according to the load of the fuel cell stack 7.
[0034]
The flowchart shown in FIG. 2 is for explaining the control contents executed by the control device 17.
[0035]
First, in step 1, the output of the fuel cell stack 7 is detected, and in the subsequent step 2, fluctuations in the operating load of the fuel cell stack 7 are determined. The output of the fuel cell stack 7 is obtained, for example, by installing a voltmeter that detects the output of the stack 7 and inputting the output of the voltmeter to the control device 17.
[0036]
When there is no change in the operation state of the fuel cell stack 7, the process proceeds to step 3 to maintain the flow rates of the reformed gas and air supplied to the fuel cell stack 7. When the driving load is in a decreasing state, the process proceeds to step 4, and when it is in an increasing state, the process proceeds to step 5.
[0037]
When the operating load of the fuel cell stack 7 decreases, the process proceeds to step 4 where the operation of the pressure control device 15 is in a low load state or stopped. That is, for example, by stopping the pressure control device, the pressure in the decompression vaporization line 16 becomes atmospheric pressure, and the amount of fuel and water to be vaporized is reduced.
[0038]
In subsequent step 6, the opening degree of the fuel control valve 14 is throttled or closed. In step 7, the air flow rate of the first air supply line 2 is decreased according to the flow rate of the steam supply line 4. Further, in step 8, the air flow rate of the second air supply line 6 is decreased according to the flow rate of the reformed gas supply line 5.
[0039]
On the other hand, when the operation load of the fuel cell stack 7 increases, the process proceeds to step 5 where the operation of the pressure control device 15 is set to a high load state and the pressure in the decompression vaporization line 16 is reduced. In subsequent step 9, the opening degree of the fuel control valve 14 is increased. In step 10, the air flow rate of the first air supply line 2 is increased according to the flow rate of the steam supply line 3. Further, in step 11, the air flow rate of the second air supply line 6 is increased according to the flow rate of the reformed gas supply line 5.
[0040]
The second embodiment shown in FIG. 3 has a configuration in which an exhaust operation pump (turbocharger, expansion turbine, etc.) 18 is installed instead of the pressure control device 15 with respect to the first embodiment. In other words, one turbine of the exhaust pump 18 is driven by the combustion gas, so that the other turbine is driven to reduce the pressure in the decompression vaporization line 16. By adopting such a configuration, an external energy source for reducing the pressure and vaporization line 16 to a low pressure is not required, and the efficiency of the system can be improved. Note that the turbine of the exhaust pump 18 is driven by the combustion gas when the exhaust reformed gas and the exhaust oxygen are combusted in the combustor 10 to cause volume expansion due to vaporization of moisture in the gas, and roughening. The increase in the number of moles due to the reaction drives the turbine.
[0041]
The third embodiment shown in FIG. 4 has a configuration in which heating means 19 is installed in the middle of the reduced pressure vaporization line 16 with respect to the first embodiment, and the gas in the reduced pressure vaporization line 16 is heated by the heat of the combustion gas. It is the structure to do. With such a configuration, the temperature of vaporized hydrocarbon or water vapor in the pressure reduction line is increased, so that the vapor does not condense even when pressurized in the steam supply line 3 via the pressure control device 15, and the pressure reduction vaporization is performed. There is an effect that the differential pressure between the line 16 and the steam supply line 3 can be increased.
[0042]
Compared to the first embodiment, the fourth embodiment shown in FIG. 5 has moisture generated by condensation of the combustion gas at a low temperature due to heat exchange in the vaporizer 12 downstream of the vaporizer 12 of the combustion gas line 11. The drain tank 20 for storing the water is installed. The water balance of the system can be improved by using the water generated by the condensation for reforming the fuel cell system or for supplying water to the polymer electrolyte membrane of the fuel cell.
[0043]
The present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea of the present invention.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a configuration of a fuel cell system of the present invention.
FIG. 2 is a flowchart for explaining control contents executed by a control device;
FIG. 3 is a diagram for explaining a configuration of a second exemplary embodiment of the present invention.
FIG. 4 is a diagram for explaining a configuration of a third exemplary embodiment of the present invention.
FIG. 5 is a diagram for explaining a configuration of a fourth embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Reformer 4 Carbon monoxide remover 7 Fuel cell stack 10 Combustor 12 Vaporizer 15 Pressure control device 17 Control device

Claims (7)

A reformer that produces hydrogen-rich reformed gas;
A fuel cell stack for generating electricity using the reformed gas and the oxidant;
A combustor that burns gas discharged from the fuel cell stack;
A vaporizer that vaporizes the reforming fuel and water using the heat of the combustion gas from the combustor;
A flow path for supplying vaporized reforming fuel and water vapor to the reformer;
A fuel cell system comprising: a pressure control device that is installed in the middle of the flow path and changes the pressure in the flow path downstream of the carburetor according to a load variation of the fuel cell stack. The fuel cell system according to claim 1, wherein the vaporizer is a heat exchange type evaporator. The fuel cell system according to claim 1, wherein the pressure control device is a decompression pump or a compressor. 3. The fuel cell system according to claim 1, wherein the pressure control device is a pump that reduces the pressure of the flow path downstream of the carburetor using the energy of the combustion gas. The fuel cell system according to any one of claims 1 to 4, further comprising a heater for supplying heat of combustion gas to the reformed fuel and water vapor vaporized by the vaporizer. The fuel cell system according to any one of claims 1 to 5, further comprising a drain tank that stores condensed water generated in the vaporizer. A reformer that produces hydrogen-rich reformed gas;
A fuel cell stack for generating electricity using the reformed gas and the oxidant;
A combustor that burns gas discharged from the fuel cell stack;
A vaporizer that vaporizes the reforming fuel and water using the heat of the combustion gas from the combustor;
In a fuel cell system comprising a vaporized reforming fuel and a flow path for supplying steam to a reformer,
A control method for a fuel cell system, wherein a pressure in a flow path downstream of a carburetor is changed according to a load fluctuation of the fuel cell stack using a pressure control device installed in the middle of the supply flow path.

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