Patent Application
20050214607
1. Field of the Invention
The present invention is related to a polymer electrolyte membrane fuel cell power generation system, and also, to a home-use stationary distributed power supply system with employment of the polymer electrolyte membrane fuel cell power generation system.
2. Description of the Related Art
Fuel cells correspond to such power generation systems that chemical energy owned by both fuel gas and oxidant gas is directly generated as electric energy by way of an electrochemical reaction occurred between the fuel gas such as hydrogen, and the oxidant gas such as air, or oxygen. Fuel cells are mainly constituted by anodes which are reacted to hydrogen and cathodes which are reacted to air, while both the anodes and the cathodes sandwich therebetween electrolyte. Various sorts of fuel cells are available, depending upon utilizations and characteristics, for instance, a phosphoric acid type fuel cell, a molten carbonate type fuel cell, a solid-state oxide type fuel cell, a polymer electrolyte membrane fuel cell, and the like. Among these fuel cells, in particular, a polymer electrolyte membrane fuel cell featured by employing a polymer film as electrolyte owns the following merits. That is, since output power density of the polymer electrolyte membrane fuel cell is large, this fuel cell can be easily made compact, and furthermore, since the polymer electrolyte membrane fuel cell can be operated under low temperature (approximately 70 to 80 degrees) condition, deteriorations as to performance and characteristics thereof which are caused by initiating/stopping this fuel cell are low, so that long lifetime of this polymer electrolyte membrane fuel cell can be realized. As a consequence, very wide applications can be expected for such polymer electrolyte membrane fuel cells as mobile-purpose power supplies such as automobiles, and stationary distributed power supplies, or home-use distributed power supplies. Among these various utilization fields, distributed power supply systems (for instance, co-generation power generation systems) with employment of such polymer electrolyte membrane fuel cells correspond to such power supply systems that both electric energy generated by the polymer electrolyte membrane fuel cells and heat which is produced by way of electrochemical reactions during power generations are collected at the same time so as to effectively utilize energy.
In a distributed power supply system using the above-described polymer electrolyte membrane fuel cell, since 50,000 hours, or more hours have been requested as a lifetime of this distributed power supply system, the following items are desirable. That is, lowering of output voltages and lowering of power generation efficiencies should be reduced as low as possible, which may give an adverse influence to durability of the distributed power supply system. In an actual case, there are many possibilities that in this distributed power supply system, the polymer electrolyte membrane fuel cell is operated under a load (will be referred to as “low load” hereinafter) of ranges from 80% to 30% with respect to the rated load. When this polymer electrolyte membrane fuel cell is operated under low load condition for a long time period, since the fuel cell performs power generations in correspondence with loads, liquid water tends to be gradually stored inside a separator which is provided between anode and cathode which is located adjacent to anode. The storage of the water inside the separator is caused by the following reason. That is, since an amount of supplied gas is decreased in correspondence with the loads, liquid water in a channel of a gas channel which is provided within the separator cannot be sufficiently exhausted by the supplied gas. Then, when the water components are stored in the channel for the gas channel, flows of the gas become unequal to each other. As a result, a distribution of the gas supplied to the electrodes becomes unequal, which may conduct that the output voltage is varied in an irregular manner and the output voltage is lowered. Accordingly, there is such a problem that the power generations cannot be performed under stable condition with respect to the distributed power supply system which continuously generates the electric power for the long time period.
Further, when this polymer electrolyte membrane fuel cell is operated under the low load condition for a long time period, since the hydrogen supply amount of the fuel gas is decreased in correspondence with the low load, a very small amount of either air or oxygen is penetrated (gas cross) from the cathode through the polymer electrolyte film, and then, is mixed into the anode. The very small amount of this mixed air, or mixed oxygen may oxidize the electrode catalyst of the anode to form a localized cell on the surface of the electrode catalyst, which may cause both a formation of an oxidation film and cohesion of the electrode catalyst. More specifically, since reactions becomes inactive on the surface covered by this oxidation film, the performance of the electrode catalyst is lowered, so that the cell performance is deteriorated, for example, the output voltage of the fuel cell is lowered. This phenomenon may cause such a problem that the stable power generations cannot be carried out as to such a distributed power supply system which originally generates electric power under stable condition for a long time period. As a result, various recovering methods capable of recovering cell performance have been requested in such a case that electrode performance is deteriorated and an output voltage of a distributed power supply system is lowered.
Under such a circumstance, very recently, several recovering methods have been proposed (for instance, JP-A-2003-123812, pages 2 to 3) in such a case that in a long-term continuous operation of a polymer electrolyte membrane fuel cell, metal ions and contaminative substances which are melted from a structural member such as a separator are stored within the polymer electrolyte membrane fuel cell, which may deteriorate the performance of this polymer electrolyte membrane fuel cell and durability thereof. The recovering method disclosed in JP-A-2003-123812 corresponds to such a recovering method that as to the polymer electrolyte membrane fuel cell whose performance has been lowered, the characteristics of this polymer electrolyte membrane fuel cell may be recovered by loading this fuel cell in high current density, or by reversing the energizing direction, or by supplying acid water whose “pH” is lower than, or equal to 7 to the gas path so as to clean this gas path.
However, in accordance with the conventional method for recovering the characteristic of the polymer electrolyte membrane fuel cell disclosed in JP-A-2003-123812, while the polymer electrolyte membrane fuel cell is operated in the continuous mode, in such a case that the performance of this fuel cell is deteriorated, any one of the below-mentioned three solving means is carried out:
As a consequence, in order to recover the cell performance in accordance with this conventional recovering method, the large current must flow through the fuel cell for a time being, or the operation of this fuel cell must be temporarily stopped. This conventional recovering method owns the following problem. That is, the operability as to such a distributed power supply system which is originally driven under stable condition and in a continuous manner for a long time period would be deteriorated.
Also, in the above-described conventional method for recovering the characteristic of the polymer electrolyte membrane fuel cell disclosed in JP-A-2003-123812, the above-described problems cannot be still solved. That is, since the water is stored inside the separator due to the low load operation for the long time period, or the performance of the electrode is deteriorated due to the oxidation of the electrode catalyst of the anode, the performance of the fuel cell is deteriorated, for example, the output voltage is lowered.
An object of the present invention is to provide a polymer electrolyte membrane fuel cell power generation system capable of maintaining performance of the fuel cell under stable condition for a long time period is provided, while a fuel cell is refreshed without interrupting a power generation by the fuel cell. Also, an object of the present invention is to provide a home-use stationary distributed power supply system with employment of the above-described polymer electrolyte membrane fuel cell power generation system.
A polymer electrolyte membrane fuel cell power generation system, recited in claim 1 of the present invention, is featured by such a polymer electrolyte membrane fuel cell power generation system comprising: a fuel cell unit equipped with a fuel cell stack for stacking a unit cell which is arranged by a polymer electrolyte membrane, both anode and cathode which are provided by sandwiching therebetween the polymer electrolyte membrane, a first separator having a channel for supplying/exhausting fuel gas, which is provided outside the anode, and also, a second separator having a channel for supplying/exhausting air, which is provided outside the cathode; a hydrogen generating apparatus unit for supplying the fuel gas to the fuel cell unit; an oxidant gas supplying unit for supplying oxidant gas to the fuel cell unit; a power converting unit for converting DC power generated from the fuel cell unit into AC power so as to supply the AC power to a load; a heat collecting unit for collecting heat which is produced from the fuel cell unit; a load detecting unit for detecting a load supplied by the power converting unit; and a control unit for controlling the fuel cell unit, the hydrogen generating apparatus unit (reformer), the oxidant gas supplying unit, the power converting unit, and the heat collecting unit; wherein: the control unit owns a function capable of controlling that when a load detected by the load detecting unit is not equal to a predetermined time rated load, the fuel cell unit is operated in a power generation mode corresponding to the predetermined time rated load.
A polymer electrolyte membrane fuel cell power generation system, recited in claim 2 of the present invention, is featured by that the control unit owns a function capable of controlling that when the fuel cell unit is operated in the power generation mode corresponding to the predetermined time rated load, both an amount of the fuel gas and an amount of the oxidant gas which are supplied to the fuel cell unit are supplied at a rate of 100 to 200% of gas supply amounts which correspond to a power generation mode of a rated load.
A polymer electrolyte membrane fuel cell power generation system, recited in claim 3 of the present invention, is featured by such a polymer electrolyte membrane fuel cell power generation system comprising: a fuel cell unit equipped with a fuel cell stack for stacking a unit cell which is arranged by a polymer electrolyte membrane, both anode and cathode which are provided by sandwiching therebetween the polymer electrolyte membrane, a first separator having a channel for supplying/exhausting fuel gas, which is provided outside the anode, and also, a second separator having a channel for supplying/exhausting air, which is provided outside the cathode; a hydrogen generating apparatus unit for supplying the fuel gas to the fuel cell unit; an oxidant gas supplying unit for supplying oxidant gas to the fuel cell unit; a power converting unit for converting DC power generated from the fuel cell unit into AC power so as to supply the AC power to a load; a heat collecting unit for collecting heat which is produced from the fuel cell unit; a voltage detecting unit for detecting a cell voltage of the fuel cell unit; and a control unit for controlling the fuel cell unit, the hydrogen generating apparatus unit, the oxidant gas supplying unit, the power converting unit, and the heat collecting unit; wherein: the control unit owns a function capable of controlling that when a variation of the cell voltage detected by the voltage detecting unit is higher than, or equal to a predetermined voltage, both an amount of the fuel gas and an amount of the oxidant gas which are supplied to the fuel cell unit are supplied at a rate of 100 to 200% of gas supply amounts which correspond to a power generation mode of a rated load.
A polymer electrolyte membrane fuel cell power generation system, recited in claim 4 of the present invention, is featured by such a polymer electrolyte membrane fuel cell power generation system comprising: a fuel cell unit equipped with a fuel cell stack for stacking a unit cell which is arranged by a polymer electrolyte membrane, both anode and cathode which are provided by sandwiching therebetween the polymer electrolyte membrane, a first separator having a channel for supplying/exhausting fuel gas, which is provided outside the anode, and also, a second separator having a channel for supplying/exhausting air, which is provided outside the cathode; a hydrogen generating apparatus unit for supplying the fuel gas to the fuel cell unit; an oxidant gas supplying unit for supplying oxidant gas to the fuel cell unit; a power converting unit for converting DC power generated from the fuel cell unit into AC power so as to supply the AC power to a load; a heat collecting unit for collecting heat which is produced from the fuel cell unit; a voltage detecting unit for detecting a cell voltage of the fuel cell unit; and a control unit for controlling the fuel cell unit, the hydrogen generating apparatus unit, the oxidant gas supplying unit, the power converting unit, and the heat collecting unit; wherein: the control unit owns a function capable of controlling that when a cell voltage detected by the voltage detecting unit is lower than, or equal to a predetermined voltage, both an amount of the fuel gas and an amount of the oxidant gas which are supplied to the fuel cell unit are supplied at a rate of 100 to 200% of gas supply amounts which correspond to a power generation mode of a rated load.
A polymer electrolyte membrane fuel cell power generation system, recited in claim 5 of the present invention, is featured by that in the polymer electrolyte membrane fuel cell power generation system recited in claim 4, the control unit owns a function capable of controlling that when the cell voltage detected by the voltage detecting unit is lower than, or equal to the predetermined voltage, fuel gas is supplied from the hydrogen generating apparatus unit to the fuel cell unit, the concentration of which is set to a rate of 100 to 200% of such fuel gas concentration corresponding to the power generation mode of the rated load.
A polymer electrolyte membrane fuel cell power generation system, recited in claim 6 of the present invention, is featured by that in the polymer electrolyte membrane fuel cell power generation system recited in any one of claim 1 to claim 5, the power converting unit is comprised of a rechargeable secondary battery; and the control unit owns a function capable of controlling that when electric power generated by the fuel cell unit becomes excessive with respect to the load power detected by the load detecting unit, the excessive power is charged into the secondary battery, whereas when electric power generated by the fuel cell unit becomes short with respect to the load power detected by the load detecting unit, the shortage power is discharged from the secondary battery.
A polymer electrolyte membrane fuel cell power generation system, recited in claim 7 of the present invention, is featured by that in the polymer electrolyte membrane fuel cell power generation system recited in any one of claim 1 to claim 5, the power converting unit is comprised of a rechargeable capacitor; and the control unit owns a function capable of controlling that when electric power generated by the fuel cell unit becomes excessive with respect to the load power detected by the load detecting unit, the excessive power is charged into the rechargeable capacitor, whereas when electric power generated by the fuel cell unit becomes short with respect to the load power detected by the load detecting unit, the shortage power is discharged from the rechargeable capacitor.
A polymer electrolyte membrane fuel cell power generation system, recited in claim 8 of the present invention, is featured by that in the polymer electrolyte membrane fuel cell power generation system recited in any one of claim 1 to claim 7, the heat collecting unit is comprised of a heating means; and the control unit owns a function capable of controlling that when electric power generated by the fuel cell unit becomes excessive with respect to the load power detected by the load detecting unit, the excessive power is converted into heat by the heating means so as to collect the heat.
A home-use stationary distributed power supply system, recited in claim 9 of the present invention, is featured by such a home-use stationary distributed power supply system comprising: the polymer electrolyte membrane fuel cell power generation system recited in any one of claim 1 to claim 8.
In accordance with the invention recited in claim 1, while the fuel cell is refreshed without interrupting the power generation of the fuel cell, the stable cell performance can be maintained for a long time period.
In accordance with the invention recited in claim 2, while the fuel cell is refreshed without interrupting the power generation of the fuel cell, the stable cell performance can be maintained for a long time period.
In accordance with the invention recited in claim 3, while the fuel cell is refreshed without interrupting the power generation of the fuel cell, the stable cell performance can be maintained for a long time period.
In accordance with the invention recited in claim 4, while the fuel cell is refreshed without interrupting the power generation of the fuel cell, the stable cell performance can be maintained for a long time period.
In accordance with the invention recited in claim 5, while the fuel cell is refreshed without interrupting the power generation of the fuel cell, the stable cell performance can be maintained for a long time period.
In accordance with the invention recited in claim 6, while the fuel cell is refreshed without interrupting the power generation of the fuel cell, the stable cell performance can be maintained for a long time period.
In accordance with the invention recited in claim 7, while the fuel cell is refreshed without interrupting the power generation of the fuel cell, the stable cell performance can be maintained for a long time period.
In accordance with the invention recited in claim 8, while the fuel cell is refreshed without interrupting the power generation of the fuel cell, the stable cell performance can be maintained for a long time period.
In accordance with the invention recited in claim 9, while the fuel cell is refreshed without interrupting the power generation of the fuel cell as the home-use stationary distributed power supply system, the stable cell performance can be maintained for a long time period.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.
Next, a detailed explanation is made of an embodiment mode of a polymer electrolyte membrane fuel cell power generation system according to the present invention.
In
The hydrogen generating apparatus ex. (reformer) unit 10 produces hydrogen by a reforming device 13, and supplies this produced hydrogen to the fuel cell unit 20 as a fuel, while the reforming device 13 reforms either town gas, LPG, and natural gas of an original gas, or various sorts of hydrocarbon-series fuels such as lamp oil, gasoline, and methanol so as to produce hydrogen. In the fuel cell unit 20, electric power is generated by a fuel cell stack 200 of this fuel cell unit 20 based upon an electrochemical reaction between air and hydrogen of the fuel supplied from the hydrogen generating apparatus unit 10. The power converting unit 30 is arranged by a power conditioner 31, and a power storage means 32. In the power conditioner 31, DC power which has been obtained by the generation of the fuel cell unit 20 is boosted by a chopper, and then, this boosted DC power is converted into AC power by an inverter. The power storage means 32 is realized by a rechargeable secondary battery, or a capacitor. In the hot-water storing/hot-water supplying unit 40, exhaust heat of either the hydrogen generating apparatus unit 10 or the fuel cell unit 20 is stored as hot water in a hot water bath 41, and the stored hot water is supplied to a user within a home, or the like. It should be noted that a heater capable of collecting excessively generated power as thermal energy may be alternatively provided within the hot water bath 41. The control unit 50 is arranged by logic circuits mainly containing a microcomputer. The control unit 50 contains a signal processing means 51 for performing a signal process operation by a CPU, a storage means 52 constructed of a memory such as a ROM and a RAM, and also, input/output ports (not shown) for inputting/outputting various sorts of signals. The control unit 50 controls an entire system of the polymer electrolyte membrane fuel cell power generation system 1. While the microcomputer and the like are utilized, this control unit 50 executes a control operation of the power converting unit 30; control operations as to operations of the hydrogen generating apparatus unit 10, of the fuel cell unit 20, and of the oxidant gas supplying unit 60, which are operated so as to generate electric power in correspondence with a load which is required for this polymer electrolyte membrane fuel cell power generation system 1; a control operation of the hot-water storing/hot-water supplying unit 40; and a control operation as to an auxiliary appliance (not shown) such as an air blower and a water pump. The oxidant gas supplying unit 60 supplies oxidant gas such as air to the fuel cell unit 20 by operating the air blower.
Next, an embodiment mode of the polymer electrolyte membrane fuel cell power generation system 1 according to the present invention will now be described more in detail based upon a flow of gas shown in
As to an original fuel corresponding to various sorts of hydrocarbon fuels such as city gas, LPG, natural gas, or lamp oil, gasoline, methanol, which are supplied to the hydrogen generating apparatus unit 10, a sulfur component is eliminated by a desulfurizing device 11 by way of a catalyst. The sulfur component has been contained in the original fuel as a small adding material, and may lower catalyst performance of the reforming device 13, so that this sulfur component is harmful. Next, the original fuel from which this sulfur component has been eliminated is vaporized and temperature-increased in combination with water added in the vaporizer 12, and then, the resulting original gas is fed to the reforming device 13.
Gas mixed with the original fuel and the water vapor, which has been fed to the reforming device 13, is reformed/reacted in the reforming device 13, so that hydrogen rich gas (may also be called as “reformed gas”, but will be referred to as “fuel gas” hereinafter) is produced. In this case, a reforming reaction catalyst which is adapted to a sort of reforming reactant (fuel) is provided in the reforming device 13. An internal temperature of the reforming device 13 is maintained at such a temperature which is suitable for a reforming reaction by controlling a heat value supplied from a burner unit 16. While a heating source of the reforming device 13 is realized by heat supplied by the burner unit 16, as fuel which is supplied to the burner unit 16, the original fuel which will be supplied to the hydrogen generating apparatus unit 10, or off gas (will be referred to as “remaining fuel gas” hereinafter) of such fuel gas which has been supplied to the fuel cell unit 20 so as to be used in the reaction.
As to a reforming reaction which is progressed in the reforming device 13, various sorts of mode systems such as a water vapor reforming system, a partially oxidizing system, and an auto-thermal system made by combining both the above-described systems may be selected. As to the catalyst equipped in the reforming device 13, such a catalyst may be selected to be employed in response to a reforming reaction selected from the above-described mode system.
As to the fuel gas produced in the reforming device 13, a carbon monoxide (CO) which diminishes a voltage of the fuel cell is removed by way of a shift reaction and by using a catalyst mounted on a CO transforming device 14 (will also be referred to as “CO shift reactor”). A shift reaction corresponds to such a reaction that both a carbon dioxide (CO2) and hydrogen gas are produced from a carbon monoxide and water vapor, which are contained in a fuel gas. Concentration of the carbon monoxide contained in the fuel gas can be reduced to approximately 1% by this shift reaction.
As to the fuel gas derived from the CO transforming device 14, a carbon monoxide is further removed by catalyst provided in a CO removing device 15 by way of a selective oxidation reaction. The selective oxidation reaction corresponds to such a reaction that a carbon monoxide is selectively oxidized prior to hydrogen gas contained in fuel gas. By this selective oxidation reaction, concentration of the carbon monoxide can be reduced lower than, or equal to 10 ppm, and thus, lowering of the catalyst performance of the fuel cell can be prevented.
The amount of the fuel gas derived from the CO removing device 15 is controlled to such a gas amount which has been set in correspondence with a load by the control unit 50, and then, the controlled amount of the fuel gas is supplied to an anode 203-a of the fuel cell unit 20. Similarly, an amount of compressed air which is supplied from a blower (not shown) of the oxidant gas supplying unit 60 is controlled to such an air amount which has been set in correspondence with the load by the control unit 50, and then, the controlled amount of the air is supplied to a cathode 200-b of the fuel cell 20. Since the fuel cell unit 20 continuously uses both the fuel gas and the air which are supplied, this fuel cell unit 20 can continuously generate electric power based upon electromotive force which is produced by an electrochemical reaction.
The remaining fuel gas of the fuel gas which has been supplied and reacted to the anode 203-a of the fuel cell unit 20 is supplied as off gas to the burner unit 16 of the hydrogen generating apparatus unit 10, and is burned in the burner unit 16. The exhaust gas after combustion is supplied to an exhaust heat collecting apparatus (not shown), and after the heat has been collected therefrom, and the resulting exhaust gas is exhausted in the atmosphere. The remaining air of the air which has been supplied to the cathode 203-b of the fuel cell unit 20 is directly exhausted as off gas to the atmosphere, or is supplied to the exhaust heat collecting apparatus in a similar manner to that of the remaining fuel gas. After the heat is collected from this remaining air, the resultant air is exhausted in the atmosphere.
This polymer electrolyte membrane 202 corresponds to such a very thin film having a thickness of several tens μm, in which an ion exchange film made of a fluoride resin series called as “NAFION® (manufactured by Dupon) is mainly employed. This very thin film has a proton (hydrogen ion) conductivity (conductivity is obtained by movement of proton), and a gas separation function (this gas separation function is capable of avoid that fuel gas and oxidant gas (air) are mutually moved via electrolyte to opposite poles). As a result, the thickness of the unit cell 201 using MEA can be made thin, and the size of the fuel cell stack 200 can be made compact. It should be understood that since proton is moved within the polymer electrolyte membrane 202 in combination with water, if a sufficiently large amount of water is not present, then movement of proton is disturbed, so that the conductivity is lowered (namely, internal resistance of fuel cell become large). As a consequence, a water management is very important by which a large amount of water is secured within the polymer electrolyte membrane 202, and thus, both the fuel gas and the oxidant gas (air) must be humidified by water components at a proper temperature so as to supply the humidified fuel gas and oxidant gas to the fuel cell stack 200.
The anode 203-a is constituted by an electrode catalyst-layer 205-a and a gas diffusion layer 206-a. The cathode 203-b is constituted by an electrode catalyst layer 205-b and a gas diffusion layer 206-b. It should also be noted that both the anode 203-a and the cathode 203-b which have been constructed in the above-described manner are also called as a gas diffusion electrode. Since the operating temperature of this unit cell 201 is low, for example, approximately 70 to 80° C., both the catalyst layers 205-a and 205-b are employed so as to urge the electrochemical reaction (power generation). These catalyst layers 205-a and 205-b are manufactured in such a manner that while rare metals such as Pt, palladium, iridium, ruthenium, rhodium, gold, silver, and alloys thereof are employed as catalyst, which have been manufactured in very fine particles, these rare metal particles and alloy particles are distributed/carried on an electroconductive carbon material as a base material such as a carbon cloth, a carbon felt, and carbon paper. The gas diffusion layer 206-a has a sheet-shaped structure having a porous member in order to conduct the fuel gas supplied via the first separator 204-a to the catalyst layer 205-a, and employs such an electric conductive carbon material as a carbon cloth, a carbon felt, and carbon paper as a base. Similarly, the gas diffusion layer 206-b has a sheet-shaped structure having a porous member in order to conduct the air supplied via the second separator 204-b to the catalyst layer 205-b, and employs such an electric conductive carbon material as a carbon cloth, a carbon felt, and carbon paper as a base.
The separator 204 comprises a channel in order to supply both fuel gas and air which are required to generate power in the fuel cell stack 200. In the first separator 204-a, a channel has been formed in one surface side located opposite to the anode, by which fuel gas can be supplied and exhausted. In the separator 204-b, a channel has been formed in the other surface side located opposite to the cathode, by which air can be supplied and exhausted. Both the first separator 204-a and the second separator 204-b employ a highly electric conductive material in which carbon has been compressed as an electric conductive material having a gas non-transmitting characteristic. It should also be noted that such surfaces of the first separator 204-a and the second separator 204-b, where the channels capable of supplying/exhausting the gas have not been formed, are joined to each other so as to form an integral type separator, and this integral form separator may be alternatively employed.
A cooling water-purpose separator 207 is employed as a channel by which necessary cooling water is supplied in order to cool the fuel cell stack 200. An object to cool the fuel cell stack 200 is given as follows. That is, since the electrochemical reaction of this fuel cell generates electric power and also produces heat, the temperature within the fuel cell stack 200 must be kept at a proper temperature (approximately 70 to 80 degrees) in order to avoid that the polymer electrolyte membrane 202 is deteriorated by heat, and also to emphasize the electrochemical reaction.
The fuel cell stack 200 shown in
Next, a description is made of a method for controlling the polymer electrolyte membrane fuel cell power generation system 1 according to the present invention.
Generally speaking, in lower power fuel cell power generation systems, a parallel operation with mains (without reverse tidal current) is carried out. Although there is such an operation method for operating a low power fuel cell power generation system under continuously constant power irrespective of increase/decrease of a load, a load following operation method is mainly employed which automatically follows increase/decrease of a load in a gradual manner. The power generation system 1 of the present invention also employs the load following operation method. A magnitude of a load is measured by an AC ammeter (not shown) which is provided in the power converting unit 30, and then, this measured signal is entered to the control unit 50. In the case that the load is varied, the control unit 50 recognizes the measured load signal, and causes the signal processing means 51 to process such a set changing signal. This set changing signal changes/sets an original fuel accepting amount, a reforming-purpose water vapor mount, a combustion-purpose air amount, a CO eliminator supplying air amount, a fuel cell stack reaction air amount, and the like into such amounts which are fitted to the load a previously-set load changing speed which has been stored in the storage means 52. The control unit 50 calculates an output value of the inverter adaptable with respect to the load based upon actually measured values as to the original fuel accepting amount, the reforming-purpose water vapor mount, the combustion-purpose air amount, the CO eliminator supplying air amount, and the fuel cell stack reaction air amount, and then, an output instruction is applied to the inverter of the power conditioner 31 by the signal processing means 51.
As a consequence, reaction gas amounts (fuel gas amount and air amount) which are sufficiently fitted to the power outputted from the inverter may be continuously supplied to the fuel cell stack 200, and thus, such a protection is performed. That is, in the case that a sufficiently large amount of the original fuel is not supplied to the fuel cell stack 200, this fuel cell stack 200 is not largely damaged based upon excessive heavy loads caused by a shortage of fuel gas and a shortage of air (oxygen). At this time, the temperature of the fuel cell stack 200 is managed within a preset temperature range which has been previously set by controlling a temperature of cooling water and an amount of the cooling water by the control unit 50 based upon a temperature which has been measured by a temperature sensor provided in the fuel cell stack 200.
Next, it should be noted that although features of the present invention will be exemplified by considering embodiments, the present invention is not limited thereto.
That is to say, the control unit 50 reads a load of this system 1, which is detected by the AC ammeter provided in the power converting unit 30 (step S11). Next, the control unit 50 judges as to whether or not the load read in this step S11 amounts to 80% to 30% load (will be referred to as “low load” hereinafter) of the rated load (step S12). In this case that the control unit 50 judges that the load of this system 1 corresponds to the low load in the step S12, the control unit 50 counts time in synchronism with a clock at the same time when this judgement is made (step S13). The control unit 50 judges as to whether or not the time counted in the step S13 is reached to 1 hour (step S14). In such a case that the control unit 50 judges that the time counted in the step S14 is equal to 1 hour, a rated load mode signal is simultaneously outputted to both the hydrogen generating apparatus unit 10 and the oxidant gas supplying unit 60 by the signal processing means (step S15). This rated load mode signal forcibly causes the load of this system 1 to become the rated load. The control unit 50 counts time in synchronism with the clock at the same time when the rated load mode signal is outputted in the step S15 (step S16). The control unit 50 judges as to whether or not the time counted in the step S15 is reached to 10 minutes (step S17). When the control unit 50 judges that the time counted in the step S17 is reached to 10 minutes, the control unit 50 accomplishes this routine 1. In the case that the control unit 50 judges that the load of this system 1 is not brought into the low load in the step S12, the process operation is returned to the previous step S11 in which the control unit 50 again reads the load of the system 1. Also, in such a case that the control unit 50 judges that the time counted in the step S14 is not reached to 1 hour, the process operation is returned to the step S11, the control unit 50 again reads this count time. In such a case that the control unit 50 judges that the time counted in the step S17 is not reached to 10 minutes, the process operation is returned to the step S16, the control unit 50 again reads time until the counted time is reached to 10 minutes.
Next, both a comparison example and an embodiment of the above-described refresh processing routine 1 are shown.
As previously explained, the polymer electrolyte membrane fuel cell power operation system 1 according to the present invention can avoid that the water is stored inside the separator even when the operation of this power generation system 1 is carried out for the long time period under low load, since the refresh processing operation is forcibly carried out after this power generation system 1 has been commenced. As a consequence, since the flows of the fuel gas in the anode and the flows of the air in the cathode do not become unequal to each other, the polymer electrolyte membrane fuel cell power generation system 1 according to the present invention can perform the power generation operation under stable condition for the long time period while the output voltage is not substantially lowered.
That is to say, in this step S26, after the load mode has been set to the rated load mode in the step S25, such a setting signal is outputted to both the hydrogen generating apparatus unit 10 and the oxidant gas supplying unit 60. This setting signal is used to forcibly set both a fuel gas amount and an air amount which are supplied to the fuel cell unit 20 to a range of 100 to 200% of the rated load, preferably, a range of 130 to 170% thereof. In this case, if both a fuel gas amount and an air amount which are supplied are smaller than 100% of the rated load, then water contained in the separator cannot be effectively removed. On the other hand, if both a fuel gas amount and an air amount which are supplied are larger than 200% of the rated load, then the gas and the air are excessively supplied with respect to the water removing effect within the separator. As a result, a utilization efficiency of the fuel gas is especially deteriorated. In a step S27, the control unit 50 outputs the setting signal of this gas amount, and at the same time, counts time in synchronism with the clock. The control unit 50 judges as to whether or not the time counted in the step S27 is reached to 10 minutes in the next step S28. When the control unit 50 judges that the time counted in the step S27 is reached to 10 minutes, the control unit 50 accomplishes this routine 2 in this step S28.
Next, both an embodiment of the above-described refresh processing routine 2 and a comparison example are indicated. A solid line portion (namely, line indicated by 8-a) of
When the result shown in this solid line portion of
As previously explained, the polymer electrolyte membrane fuel cell power generation system 1 according to the present invention can more firmly avoid that the water is stored inside the separator even when the operation of this power generation system 1 is carried out for the long time period under low load, since the refresh processing operation 2 is forcibly carried out after this power generation system 1 has been commenced. As a consequence, since the flows of the fuel gas in the anode and the flows of the air in the cathode do not become unequal to each other, the polymer electrolyte membrane fuel cell power generation system 1 according to the present invention can perform the power generating operation under stable condition for the long time period while the output voltage is not substantially lowered.
In the case that the control unit 55 does judge in the step S32 that this variation of the output voltage of the fuel cell stack 200 is higher than, or equal to 5 V, the control unit 50 again reads the output voltage of the fuel cell stack 200 in a step S31. When the control unit 50 judges in the step S35 that the counted time is not reached to 10 minutes, the process operation is returned to the step S34 in which the control unit 50 again reads the output voltage until the counted time is reached to 10 minutes.
Next, both an embodiment of the above-described refresh processing routine 3 and a comparison example are indicated. A solid line portion (namely, line indicated by 10-a) of
As previously explained, the polymer electrolyte membrane fuel cell power generation system 1 according to the present invention can avoid that the water is stored inside the separator even when the operation of this power generation system 1 is carried out for the long time period under low load, since the refresh processing operation 3 is forcibly carried out after this power generation system 1 has been commenced. As a consequence, since the flows of the fuel gas in the anode and the flows of the air in the cathode do not become unequal to each other, the polymer electrolyte membrane fuel cell power generation system 1 according to the present invention can perform the power generating operation under stable condition for the long time period while the output voltage is not substantially lowered.
Next, both an embodiment of the above-described refresh processing routine 4 and a comparison example are indicated. A solid line portion (namely, line indicated by 12-a) of
As previously explained, the polymer electrolyte membrane fuel cell power generation system 1 according to the present invention can avoid that the catalyst performance of the anode is deteriorated even when the operation of this power generation system 1 is carried out for the long time period under low load, since the refresh processing operation 4 is forcibly carried out after this power generation system 1 has been commenced. As a consequence, since the catalyst performance of the anode is maintained, the polymer electrolyte membrane fuel cell power generation system 1 according to the present invention can perform the power generating operation under stable condition for the long time period while the output voltage is not substantially lowered.
Next, both an embodiment of the above-described refresh processing routine 5 and a comparison example are indicated. A solid line portion (namely, line indicated by 14-a) of
On the other hand, if the hydrogen concentration of the fuel gas to be supplied is larger than that of 200% of the rated load, then the fuel gas is excessively supplied with respect to the effect of removing the oxidation film of the electrode catalyst surface, so that the utilization efficiency of the fuel gas is deteriorated. When the result shown in this solid line portion of
As previously explained, the polymer electrolyte membrane fuel cell power generation system 1 according to the present invention can avoid that the catalyst performance of the anode is deteriorated even when the operation of this power generation system 1 is carried out for the long time period under low load, since the refresh processing operation 5 is forcibly carried out after this power generation system 1 has been commenced. As a consequence, since the catalyst performance of the anode is maintained, the polymer electrolyte membrane fuel cell power generation system 1 according to the present invention can perform the power generating operation under stable condition for the long time period while the output voltage is not substantially lowered.
The control unit 50 compares a signal of a load which is detected by the AC ammeter employed in the power converting unit 30 with a signal of generated electric power which is detected by the voltmeter provided in the fuel cell unit 20, and when the generated electric power is larger than the load, the control unit 50 outputs such a signal by which generated dump electric power is charged into the power storage means 32 provided in the power converting unit 30. Also, when a load is larger than the generated electric power, the control unit 50 outputs such a signal for discharging electric power to the power storage unit 32 in order to back up a shortage component of the generated power. This back-up purpose power storage means 32 may be realized by any means such as a secondary battery and a capacitor, which is capable of charging/discharging electric power. As this secondary battery, any secondary batteries known in this field may be employed, for instance, a lead battery, a nickel-hydrogen secondary battery, a nickel-cadmium secondary battery, and a lithium secondary battery may be employed. As the capacitor, any capacitors known in the field may be employed, for instance, a large capacitance electrolyte capacitor may be employed which will also be referred to as a “ultra capacitor (otherwise, super capacitor).” It should also be noted that this back-up purpose power storage means 32 may also constitute an initiation-purpose power supply.
The control unit 50 also compares a signal of a load which is detected by the AC ammeter employed in the power converting unit 30 with a signal of generated electric power which is detected by the voltmeter provided in the fuel cell unit 20, and when the generated electric power is larger than the load, the control unit 50 outputs such a signal to a heater 42 which is provided within a hot-water storage tank 41. This signal causes this generated dump electric power to heat hot water. As the heater 42, any heaters known in the field may be employed, for instance, a resistance heating heater for converting electric energy into heat may be employed.
There are some possibilities that if externally supplied water is directly used so as to cool a fuel cell, then the fuel cell may be adversely influenced such as corrosion by an impurity, for example, chloride ions and metal ions such as iron and copper which are contained in this water. In such a case, the temperature of the externally supplied water may be indirectly increased by a means having a heat exchanging function such as a heat exchanger so as to produce hot water. Since the hot water which has been produced by utilizing this heat collection may become hot water having a temperature of, for example, 50 to 60 degrees, if this hot water is stored in a hot-water tank and is used, then hot water which is used in a home equipment such as a kitchen and a bath may be provided instead of a hot-water supplying device. In addition, since the electric power which has been obtained by the power generation is utilized as power supplies for various sorts of electric appliances within the home in combination with externally supplied electric power, the amount of the externally supplied electric power may be reduced. Apparently, if the power generation amount of the fuel cell becomes larger than the electric power used in the home, then no electric power is supplied outside the home. Also, in such a case that either the power generation amount of the fuel cell or the electric power used in the home is varied and thus a power balance becomes unbalanced, an adverse influence given to this home-use stationary type distributed power supply 300 may be reduced by employing the secondary battery, or the like, which has been provided as the power storage means.
As previously explained, although the home-use stationary type distributed power supply which has employed the polymer electrolyte membrane fuel cell power generation system is such a home-use distributed power supply whose load variation is large, since the refresh processing operation of the fuel cell can be carried out in a proper manner, the home-use stationary type distribution power supply can be operated under stable condition for a long time period as a co-generation system having a high energy efficiency.
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-088461 | Mar 2004 | JP | national |
