JP2005071949A - Fuel battery electric power generator and its operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel battery electric power generator and its operation method, in which degradation due to the oxidation of an anode and a cathode during the stop of actuation is suppressed so as to improve durability. <P>SOLUTION: A fuel battery electric power generator includes an electrolyte 1, a pair of electrodes 21 and 22, a fuel battery 5 composed of a pair of separator plates 41 and 42 and gas replacing section for replacing all or a part of oxidant gas remaining in the fuel battery 5 with inert gas and then further replacing all or a part of inert gas with fuel gas. The anode 21 and the cathode 22 enclose the fuel gas by replacing the gas in the cathode 22 with the fuel gas during the stop of the operation of the fuel battery 5 so that degradation due to the oxidation of the anode 21 and the cathode 22 is suppressed so as to improve the durability of the fuel battery generator. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a fuel cell power generation apparatus and a method for operating the fuel cell power generation apparatus that suppress deterioration due to start / stop or improve durability.

  The configuration and operation of a conventional general solid polymer electrolyte fuel cell will be described with reference to FIG. In FIG. 8, 1 is a solid polymer electrolyte made of perfluorocarbon sulfonic acid having hydrogen ion conductivity, and a pair of electrodes 21 and 22 are formed on both surfaces of the electrolyte 1. The electrodes 21 and 22 include a catalyst layer made of a mixture of a catalyst in which a noble metal such as platinum is supported on porous carbon and a polymer electrolyte having hydrogen ion conductivity, and air permeability and electronic conductivity laminated on the catalyst layer. A gas diffusion layer having Gaskets 31 and 32 for preventing gas mixing and leakage are disposed around the electrodes 21 and 22, respectively, and conductive materials having gas flow paths for supplying and discharging fuel gas and oxidant gas to the electrodes 21 and 22, respectively. Is sandwiched between separator plates 41 and 42.

  A stack obtained by stacking a plurality of single cells having the above configuration is referred to as a stack, and the single cell or stack is collectively referred to as a fuel cell 5. The electrode 21 on the fuel gas supply side is the anode, and the electrode 22 on the oxidant gas supply side is the cathode.

When the fuel gas and the oxidant gas are supplied to the anode 21 and the cathode 22, respectively, and an electronic load is connected, the hydrogen contained in the fuel gas supplied to the anode 21 releases electrons at the interface between the anode 21 and the electrolyte 1 to generate hydrogen. It becomes an ion (Chemical formula 1).
(Chemical formula 1)
H ₂ → 2H ⁺ + 2e ⁻
The hydrogen ions move to the cathode 22 through the electrolyte 1, receive electrons at the interface between the cathode 22 and the electrolyte 1, react with oxygen contained in the oxidant gas supplied to the cathode 22, and generate water ( 2).
(Chemical formula 2)
1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O
The total reaction is shown in (Chemical Formula 3).
(Chemical formula 3)
H ₂ + 1 / 2O ₂ → H ₂ O
At this time, the flow of electrons flowing through the electronic load can be used as DC electrical energy. Moreover, since a series of reactions are exothermic reactions, the reaction heat can be used as thermal energy.

  Next, the configuration and operation of a general fuel cell power generator including the fuel processing unit 7 will be described with reference to FIG. In FIG. 8, the raw material gas containing hydrocarbons, such as methane, is supplied to the desulfurization part 6, and the sulfur compound contained in an odorant etc. is adsorbed and removed. Then, it is reformed by the fuel processing unit 7 to become a fuel gas containing hydrogen, and is supplied to the anode 21 of the fuel cell 5. The fuel processing unit 7 includes a reforming unit 71 that reforms methane and the like, a CO conversion unit 72 that converts generated carbon monoxide (CO), and a CO removal unit 73 that further removes CO.

When methane is used as the source gas, in the reforming unit 71, the reaction shown in (Chemical Formula 4) occurs with water vapor, and about 10% of CO is generated together with hydrogen.
(Chemical formula 4)
_{CH 4 + H 2 O → CO} + 3H 2
Thereafter, the generated CO is oxidized to carbon dioxide at the CO conversion section 72 as shown in (Chemical Formula 5), and is reduced to about 5000 ppm. Since the downstream CO remover 73 oxidizes not only CO but also hydrogen of the fuel gas, the CO concentration needs to be reduced as much as possible in the CO shift section 72.
(Chemical formula 5)
CO + H ₂ O → CO ₂ + H ₂
Further, the remaining CO is oxidized by the CO remover 73 as shown in (Chemical Formula 6), and its concentration is reduced to about 10 ppm or less.
(Chemical formula 6)
CO + 1 / 2O ₂ → CO ₂
The overall reaction formula is shown in (Chemical Formula 7).
(Chemical formula 7)
_{CH 4 + 2H 2 O → CO} 2 + 4H 2
Since platinum contained in the anode 21 is poisoned by CO in the operating temperature range of the fuel cell 5 and its catalytic activity deteriorates, a catalyst having CO resistance such as platinum-ruthenium is usually used for the anode 21. However, even in a CO-resistant catalyst, the CO concentration contained in the fuel gas must be suppressed to at least 10 ppm or less.

  The fuel cell power generation device is mainly composed of the fuel cell 5 and the fuel processing unit 7 described above. However, when a raw material gas such as city gas mainly composed of methane is used for home use, the merit of utility cost is increased. For this reason, an operation method is effective in which the vehicle is stopped during a time period with a small amount of electricity consumption and is operated during a time period with a large amount of electricity consumption. In general, DSS (Daily Start-up & Shut-down) operation, which operates in the daytime and stops operation in the middle of the night, can increase the utility cost, and the fuel cell power generator has an operation pattern including start and stop. It is desirable to be able to respond flexibly.

  Further, in the conventional phosphoric acid type fuel cell power generator, from the viewpoint of safety, it is necessary to replace the fuel gas remaining inside the apparatus with an inert gas such as nitrogen when stopped. Several stopping methods using an inert gas purge have been reported for solid polymer electrolyte fuel cell power generators.

  For example, the fuel gas and the oxidant gas remaining in the fuel cell are replaced with water or a humidified inert gas and stopped in a sealed state (see Patent Document 1). Thereby, the water retention state of the electrolyte 1 is maintained, and power generation can be started quickly upon restart.

Alternatively, the fuel cell 5 is stopped by generating power in the state where the supply of the oxidant gas is stopped, consuming oxygen from the cathode 22, and then replacing the anode 21 with an inert gas such as nitrogen (Patent Document). 2). Thereby, not only the oxidation of the cathode 22 can be suppressed, but also hydrogen diffused from the anode 21 through the electrolyte 1 can reduce and remove impurities adhering to the cathode 22.
JP-A-6-251788 JP 2002-93448 A

  However, in the conventional method of purging water or humidified inert gas, the temperature of the fuel cell 5 decreases when the fuel cell is stopped, condensation occurs inside the fuel cell 5, a decrease in volume occurs, and a negative pressure is generated. For this reason, there have been problems such as the inflow of external oxygen, the electrolyte 1 being damaged, and the electrodes 21 and 22 being short-circuited.

  Further, in the conventional method in which the cell is generated in a state where the supply of the oxidant gas is stopped and oxygen in the cathode 22 is consumed, and then the inert gas is purged in the anode 21, the remaining oxygen that cannot be consumed in the cathode 22 remains. In addition, there is a problem that the cathode 22 is oxidized and deteriorated due to the influence of air mixed in due to diffusion or leakage. In addition, since oxygen is forcibly consumed by power generation, the potential of the cathode 22 is not uniform, and the activation state of the cathode is different every time it is stopped, and the battery voltage at startup varies.

  The present invention solves the above-described conventional problems. When the fuel cell is stopped, the oxidant gas remaining in the fuel cell 5 is replaced with an inert gas, and further replaced with the fuel gas. Another object of the present invention is to provide a fuel cell generator operating method that suppresses deterioration due to oxidation of the cathode 22 during start-up and stops and improves durability.

  In order to solve the above-described conventional problems, a fuel cell power generation device and an operation method thereof according to the present invention include a fuel cell including an electrolyte, a pair of electrodes, and a pair of separator plates, and a fuel cell interior when the fuel cell is stopped. And a gas replacement part for replacing all or part of the inert gas with fuel gas after replacing all or part of the remaining oxidant gas with inert gas. All or part of the gas is replaced with fuel gas through an inert gas.

  As a result, the anode and the cathode are sealed with the fuel gas containing hydrogen, deterioration due to oxidation of the anode and the cathode is suppressed, and the durability of the fuel cell power generator can be improved.

  Further, since the oxidant gas is replaced with the fuel gas via the inert gas, the oxygen contained in the oxidant gas and the hydrogen contained in the fuel gas are not in direct contact, and the replacement can be performed safely.

  As described above, according to the fuel cell power generator of the present invention and the operation method thereof, the cathode is replaced with the fuel gas, so that deterioration due to oxidation of the cathode is suppressed and the durability of the fuel cell power generator is improved. Can do.

  The invention according to claim 1 supplies and discharges an electrolyte, a pair of electrodes sandwiching the electrolyte, and a fuel gas containing at least hydrogen on one of the electrodes, and supplies and discharges an oxidizing gas containing at least oxygen on the other. After substituting all or part of the oxidant gas remaining in the fuel cell with at least one cell comprising a pair of separator plates having gas flow paths and the fuel cell when the fuel cell is stopped with an inert gas And a gas replacement unit that replaces all or part of the inert gas with the fuel gas, and the cathode is replaced with the fuel gas via the inert gas, thereby suppressing deterioration due to oxidation of the cathode, and the fuel cell. The durability of the power generation device can be improved.

  The invention described in claim 2 is provided with a shut-off valve in the fuel gas and oxidant gas supply unit and the discharge unit according to claim 1 in particular, and all or part of the oxidant gas is replaced with an inert gas. After that, all or part of the inert gas is replaced with fuel gas, the shutoff valve is closed, and the fuel gas is sealed in the fuel cell, so that the anode and cathode are diffused from the outside (oxygen). Oxidation of the electrolyte and drying of the electrolyte can be suppressed, mixing of impurities and the like can be prevented, and the durability of the apparatus can be improved.

  The invention according to claim 3 supplies and discharges an electrolyte, a pair of electrodes sandwiching the electrolyte, and a fuel gas containing at least hydrogen on one of the electrodes, and supplies and discharges an oxidant gas containing at least oxygen on the other. After substituting all or part of the oxidant gas remaining in the fuel cell with at least one cell comprising a pair of separator plates having gas flow paths and the fuel cell when the fuel cell is stopped with an inert gas And a gas replacement unit that replaces the inert gas with the fuel gas, and a voltage detection unit that detects the voltage of the fuel cell. When the fuel cell is stopped, the supply of the fuel gas and the oxidant gas is stopped at the same time. After the detection unit detects that the fuel cell voltage is equal to or lower than a predetermined voltage, all or part of the oxidant gas remaining in the fuel cell is replaced with inert gas, and all or part of the inert gas is further replaced. When the supply of fuel gas and oxidant gas was stopped at the same time by replacing with gas, hydrogen diffused from the anode through the electrolyte adhered to the oxide film formed on the cathode platinum surface or the cathode. Since impurities are reduced and removed, the cathode is activated, and the battery voltage, which has been reduced due to these factors, can be recovered at the time of startup.

  In addition, when the anode in which hydrogen remains is used as a reference, the cathode potential can be estimated from the voltage detected by the voltage detector. When the cathode is activated by the hydrogen diffused from the anode, the cathode potential decreases, so the activation status of the cathode can be known from the voltage detected by the voltage detector, and the cathode is always activated at a constant voltage. If it does, the battery voltage at the time of starting can be stabilized.

  In addition, since all or part of the oxidant gas remaining in the fuel cell is replaced with inert gas after the voltage of the fuel cell is lowered to a predetermined voltage, deterioration due to oxidation of the cathode is suppressed, and fuel cell power generation The durability of the apparatus can be improved.

  The invention according to claim 4 supplies and discharges an electrolyte, a pair of electrodes sandwiching the electrolyte, and a fuel gas containing at least hydrogen on one of the electrodes, and supplies and discharges an oxidizing gas containing at least oxygen on the other. After substituting all or part of the oxidant gas remaining in the fuel cell with at least one cell comprising a pair of separator plates having gas flow paths and the fuel cell when the fuel cell is stopped with an inert gas In addition, a gas replacement unit that replaces the inert gas with the fuel gas and a voltage detection unit that detects the voltage of the fuel cell are provided. When the fuel cell is stopped, the supply of the oxidant gas is stopped while the fuel gas is supplied. After the voltage detector detects that the fuel cell voltage is equal to or lower than the predetermined voltage, all or part of the oxidant gas remaining in the fuel cell is replaced with inert gas, and all of the inert gas or By replacing the parts with the fuel gas, when stopping the feed of still oxidant gas was supplied to the fuel gas, can be the anode of the reference potential is more stable, cathode activation situation be further stabilized.

  The invention according to claim 5 supplies and discharges an electrolyte, a pair of electrodes sandwiching the electrolyte, a fuel gas containing at least hydrogen on one of the electrodes, and an oxidant gas containing at least oxygen on the other. After substituting all or part of the oxidant gas remaining in the fuel cell with at least one cell comprising a pair of separator plates having gas flow paths and the fuel cell when the fuel cell is stopped with an inert gas In addition, a gas replacement unit that replaces the inert gas with the fuel gas and a voltage detection unit that detects the voltage of the fuel cell are provided. When the fuel cell is stopped, the supply of the oxidant gas is stopped while the fuel gas is supplied. After replacing all or part of the oxidant gas remaining in the fuel cell with an inert gas, and the voltage detection unit detects the voltage of the fuel cell below a predetermined voltage, all or part of the inert gas The Charge by replacing the gas, when the left oxidant gas was supplied to the fuel gas was replaced with an inert gas, since the forcibly discharged cathodes oxygen can be activated earlier. Moreover, since oxygen remaining in the gas diffusion layer or the like that cannot be replaced only by stopping the gas is also replaced, deterioration can be further suppressed.

  The invention described in claim 6 is provided with a shutoff valve in the oxidant gas supply section and discharge section according to claims 3 to 5 in particular, and the oxidant gas remaining in the fuel cell when the fuel cell is stopped. After all or part of the gas is replaced with inert gas, and all or part of the inert gas is replaced with fuel gas, the shut-off valve is closed, and the shut-off valve is opened immediately before starting, so that all or part of the fuel gas is replaced. By replacing the part with an inert gas, the oxygen contained in the oxidant gas introduced at the time of start-up and the hydrogen contained in the enclosed fuel gas are not in direct contact with each other. can do.

  The invention described in claim 7 is provided with a shutoff valve in the fuel gas and oxidant gas supply section and discharge section according to claims 3 to 5, and the oxidation remaining in the fuel cell when the fuel cell is stopped. After replacing the agent gas with an inert gas 2 to 5 times the volume of the gas flow path, the inert gas is further replaced with a fuel gas 2 to 5 times the volume of the gas flow path, and the shut-off valve is closed and started. By enclosing the fuel gas in the fuel cell, the active state of the cathode can be maintained with the minimum necessary replacement amount.

  According to an eighth aspect of the present invention, in particular, the fuel gas and oxidant gas supply section and the discharge section according to any one of the fourth to fifth aspects are provided with shutoff valves, and the fuel gas is supplied to the gas flow path when the fuel cell is stopped. After the supply of the oxidant gas is stopped while being supplied at a flow rate 2 to 5 times the volume, the oxidant gas remaining in the fuel cell is replaced with an inert gas 2 to 5 times the volume of the gas flow path, Furthermore, after replacing the inert gas with fuel gas 2 to 5 times the volume of the gas flow path, the shut-off valve is closed, and the fuel gas is sealed in the fuel cell until it starts, so that the minimum amount of combustion gas is required. Can activate the cathode.

  The invention according to claim 9 includes a desulfurization section for desulfurizing the raw material gas and a fuel processing section for generating fuel gas from the desulfurized raw material gas, and in particular, desulfurized as the inert gas according to claims 1 to 8 By using the raw material gas, a gas cylinder such as nitrogen becomes unnecessary, and not only the apparatus can be miniaturized, but also maintenance and cost required for replacing the cylinder can be greatly reduced.

(Embodiment 1)
FIG. 1 shows a configuration diagram of a fuel cell power generator according to a first embodiment of the present invention.

  In FIG. 1, reference numeral 1 denotes a membrane-shaped solid polymer electrolyte made of a perfluorocarbon sulfonic acid polymer having hydrogen ion conductivity, and a pair of electrodes, an anode 21 and a cathode 22 are formed on both surfaces of the electrolyte 1. When the electrolyte 1 takes in moisture, the hydrogen ions of the sulfonic acid groups in the electrolyte 1 are dissociated to become charge carriers, and the electrolyte 1 passes through a reverse micelle structure formed by aggregation of several sulfonic acid groups. Shows hydrogen ion conductivity. When the water content decreases, the conductivity of the electrolyte 1 decreases. Therefore, a method was adopted in which the gas was humidified and supplied to prevent the membrane from drying.

  In addition, during power generation, when hydrogen ions move to the cathode 22, they move with water on the anode 21 side, so that the water content of the electrolyte 1 is high on the cathode 22 side and low on the anode 21 side. In order to correct this, the thickness of the electrolyte 1 was reduced so that water was back-diffused. As a result, the conductivity is increased, but the permeation of hydrogen, which is a fuel gas, and oxygen, which is an oxidant gas, is also increased, and the gas reacts directly through the electrolyte 1 to reduce current efficiency. .

  In the present invention, the property which can be said to be the conventional defect is used in reverse, and oxygen which oxidizes and deteriorates the cathode 22 at the time of starting and stopping is directly reacted with hydrogen leaking through the electrolyte 1 to efficiently remove and activate. Thus, the durability of the fuel cell power generator is improved. Further, the cathode 22 largely dominates the battery performance. In particular, the battery performance can be improved by activating the cathode 22.

  The anode 21 and the cathode 22 have a catalyst layer made of a mixture of a catalyst in which a noble metal such as platinum is supported on porous carbon and a polymer electrolyte having hydrogen ion conductivity, and air permeability and electronic conductivity laminated on the catalyst layer. It consists of a gas diffusion layer having properties. For the anode 21, an alloy catalyst such as platinum-ruthenium having CO resistance was used. Moreover, carbon paper or carbon cloth subjected to water repellent treatment was used for the gas diffusion layer.

  Gaskets 31 and 32 for preventing gas mixing and leakage are disposed around the anode 21 and the cathode 22, respectively, and further, a gas flow path for supplying and discharging fuel gas and oxidant gas to the anode 21 and cathode 22, respectively. The conductive separator plates 41 and 42 having n The voltage generated by the single cell configured as described above is about 0.75 V, and a plurality of single cells corresponding to the required voltage can be stacked in series to form a stack.

  In addition, current collector plates, insulating plates, and end plates were disposed at both ends of the separator plates 41 and 42, and fixed with fastening rods. And the electronic load 8 and the voltage detection part 9 were connected to the current collection board, and the voltage of the fuel cell 5 when a fixed electric current was sent was detected.

  In FIG. 1, 6 is a desulfurization part and can adsorb and remove (desulfurize) a sulfur compound contained as a odorant in the raw material gas. In this example, city gas 13A mainly composed of methane, ethane, propane and butane was used as a raw material gas. The desulfurized raw material gas is supplied to the fuel processing unit 7 together with water, and a fuel gas containing hydrogen is generated by a reforming reaction. The fuel processing unit 7 includes a reforming unit 71 that reforms methane and the like, a CO conversion unit 72 that converts generated CO, and a CO removal unit 73 that removes CO.

  The generated fuel gas is supplied to the anode 21 of the fuel cell 5 at a predetermined flow rate by the flow rate control unit 101. The oxidant gas is taken in from the atmosphere by a fan or the like, and is supplied to the cathode 22 of the fuel cell 5 by the flow rate control unit 102 at a predetermined flow rate. Further, fuel gas and oxidant gas were supplied after being humidified so as not to dry the membrane.

  Reference numeral 11 denotes a switching valve, which can switch the flow path so that the desulfurized source gas is supplied to the fuel processing unit 7 during power generation of the fuel cell 5 and is supplied to the cathode 22 of the fuel cell 5 when stopped. When the fuel cell 5 is stopped, the desulfurized source gas is supplied to the cathode 22 by the flow rate control unit 102 at a predetermined flow rate.

  Reference numerals 121a, 121b, 122a and 122b are shut-off valves for sealing fuel gas into the anode 21 and the cathode 22 respectively when the fuel cell 5 is stopped. 122a was also used as a switching valve capable of switching the flow path so that the fuel gas generated in the fuel processing unit 7 was also supplied to the cathode 22 of the fuel cell 5 when stopped.

  As described above, the desulfurization unit 6 for desulfurizing the raw material gas, the fuel processing unit 7 for generating the fuel gas, the flow rate control unit 102, the switching valve 11, the shutoff valves 121a, 121b, 122a and 122b, and the piping connecting them. The gas flow path is integrated into a gas replacement part that replaces and fills the cathode 22 with an inert gas (desulfurized source gas) when the fuel cell 5 is stopped.

  Using the fuel cell power generator configured as described above, after purging the raw material gas desulfurized to the cathode 22 at the time of stopping and starting, an operation method for purging the fuel gas and replacing the remaining oxidant gas was studied.

First, a predetermined amount of fuel gas is supplied to the anode 21 and oxidant gas is supplied to the cathode 22 so that the cell temperature is about 70 ° C., the fuel gas utilization rate is about 75%, and the oxidant gas utilization rate is about 40%. A constant current of about 0.2 A / cm ² was applied to the substrate. At this time, the battery voltage detected by the voltage detector 9 connected to the fuel cell 5 was about 0.75V. The fuel gas and the oxidant gas were supplied after being humidified so that the dew points were 65 ° C. and 70 ° C., respectively.

  FIG. 2 is a flowchart of the operation method in the first embodiment. When the fuel cell 5 was stopped, the electronic load 8 was first stopped (STEP 1), and the supply of fuel gas and oxidant gas was stopped simultaneously (STEP 2). Subsequently, the oxidant gas remaining on the cathode 22 is replaced with an inert gas (desulfurized raw material gas) (STEP 3), and the inert gas is further replaced with the fuel gas generated in the combustion processing section 7 (STEP 4). 121a, 121b, 122a and 122b were closed, and fuel gas was sealed in the anode 21 and the cathode 22 (STEP 5).

  In this example, a raw material gas desulfurized to an inert gas was used. By using desulfurized source gas, it is possible to use infrastructure such as city gas, eliminating the need for gas cylinders such as nitrogen, not only miniaturizing equipment, but also greatly reducing maintenance and costs required for cylinder replacement, etc. Can do.

  Further, by replacing the oxidant gas with the fuel gas through the desulfurized raw material gas, oxygen and oxidative species that cause oxidative degradation by adsorbing to noble metals such as platinum contained in the cathode 22 are reduced or removed. And the durability of the fuel cell power generator can be improved.

  Further, after replacing the oxidant gas, the shutoff valves 121a, 121b, 122a and 122b are closed, and the fuel gas is sealed in the fuel cell 5, whereby the anode 21 and oxygen 21 diffused from outside (oxygen) and Oxidation of the cathode 22 and drying of the electrolyte 1 can be suppressed, contamination of impurities and the like can be prevented, and durability of the fuel cell power generator can be improved.

In addition, since the inert gas (raw material gas) that replaces the oxidant gas remaining in the fuel cell is supplied without being humidified, its volume is set to the minimum necessary so that the electrolyte 1 membrane is not dried. Assuming that the concentration of the oxidant gas existing in the gas flow path before replacement is C ₀ and the volume of the gas flow path is V, when the inert gas is allowed to flow by ΔV during the time Δt, the concentration C _t1 after Δt Is represented by (Equation 1).
(Equation 1)
C _t1 = C ₀ (V / V + ΔV) = C ₀ (1 / (1+ (ΔV / V)))
Further, the density C _t2 after Δt is expressed by (Equation 2).
(Equation 2)
C _t2 = C _t1 (1 / (1+ (ΔV / V))) = C ₀ (1 / (1+ (ΔV / V))) ²
Therefore, the concentration C _tn after nΔt is expressed by (Equation 3).
(Equation 3)
C _tn = C ₀ (1 / (1+ (ΔV / V))) ⁿ
At this time, if the inert gas flows k times the volume V of the gas flow path, (Equation 4) holds.
(Equation 4)
kV = nΔV
Therefore, (Equation 3) is expressed by (Equation 5).
(Equation 5)
C _tn = C ₀ (1 / (1+ (k / n))) ⁿ
Using the binomial theorem and Taylor expansion, (Equation 6) can be derived from (Equation 5).
(Equation 6)
lim (C _tn ) = lim (C ₀ (1 / (1+ (k / n)) ⁿ ) = C ₀ e ^{−k
n → ∞ n → ∞}
According to (Expression 6), when the inert gas is flowed 2 to 5 times the volume of the gas flow path, the concentration of the oxidant gas to be replaced is replaced to about 14 to 0.7% of the initial concentration. Can do.

  In this example, the oxidant gas remaining in the gas channel was replaced with an inert gas having a volume three times that of the gas channel. Since air was used as the oxidant gas, it was found that the oxygen concentration in the gas flow path of the cathode 22 was reduced to only about 1%. In this state, the inert gas is further replaced with the fuel gas, and the fuel gas is sealed in the anode 21 and the cathode 22, so that deterioration due to oxidation of the anode 21 and the cathode 22 can be suppressed.

  Further, since the gas is replaced with the minimum necessary volume, the influence on the moisture retention state of the electrolyte 1 can be reduced.

(Embodiment 2)
FIG. 3 is a flowchart of the operation method according to the second embodiment. When the fuel cell 5 was stopped, the electronic load 8 was first stopped (STEP 11), and the supply of fuel gas and oxidant gas was stopped simultaneously (STEP 12). As a result, hydrogen in the anode 21 diffuses to the cathode 22 through the electrolyte 1, reacts with oxygen to generate water, and consumes oxygen in the cathode 22, so that the voltage of the fuel cell 5 gradually decreases. When the voltage detection unit 9 detects that the voltage of the fuel cell 5 is equal to or lower than a predetermined voltage (STEP 13), the oxidant gas remaining in the fuel cell 5 is replaced with an inert gas (STEP 14), and the inert gas is fueled. The fuel gas generated in the processing unit 7 was replaced (STEP 15), the shut-off valves 121a, 121b, 122a and 122b were closed, and the fuel gas was sealed in the fuel cell 5 (STEP 16).

  The difference from the operation method of the first embodiment is that the voltage of the fuel cell 5 is detected and lowered to a predetermined voltage, and then the cathode 22 is replaced with the fuel gas via an inert gas.

  By simultaneously stopping the supply of the fuel gas and the oxidant gas, the hydrogen diffused from the anode 21 through the electrolyte 1 reduces the oxide film formed on the platinum surface of the cathode 22 and the impurities attached to the cathode 22. Therefore, the cathode 22 is activated, and the battery voltage that has been lowered due to these factors can be recovered at the time of startup.

  At this time, the voltage of the fuel cell 5 finally decreases to 0 to 0.2 V, but in this embodiment, when the voltage drops to 0.2 V or less, it is replaced with an inert gas. By lowering the voltage to 0.2 V or less, the potential of the cathode 22 is lowered, and the platinum surface of the cathode 22 is sufficiently activated. Activation occurs even at a voltage higher than 0.2 V, but the higher the voltage, the weaker the activation effect and the smaller the voltage recovered at startup.

  Further, when the anode 21 in which hydrogen remains is used as a reference, the potential of the cathode 22 can be estimated from the voltage detected by the voltage detector 9. When the cathode 22 is activated by the hydrogen diffused from the anode 21, the potential of the cathode 22 is lowered. Therefore, the activation state of the cathode 22 can be known from the voltage detected by the voltage detection unit 9 and detected. By activating with voltage, the battery voltage at the time of start-up can be stabilized.

  Further, since the oxidant gas is replaced with the fuel gas through the inert gas remaining in the fuel cell 5 after the voltage of the fuel cell 5 is lowered to a predetermined voltage, the anode 21 and the cathode 22 are deteriorated due to oxidation. It is suppressed and the durability of the fuel cell power generator can be improved.

  The battery voltage is an open circuit voltage from when the electronic load 8 is stopped until the gas supplied to the anode 21 and the cathode 22 is stopped. At this time, the open circuit voltage is 0.9 V or more, and the potential of the cathode 22 is exposed to a high potential. When the potential of the cathode 22 exceeds 0.9V, the catalytic reaction area decreases due to elution and sintering of platinum, and the reaction area decreases due to platinum oxidation and adsorption of oxidizing species. Until the gas supplied to the anode 21 and the cathode 22 is stopped as much as possible to shorten the time for maintaining the open circuit voltage, or when the electronic load 8 is stopped, so that the open circuit voltage is not generated. It is preferable to reduce the voltage by passing a current through a resistor or the like.

  When the gas supplied to the anode 21 is stopped earlier than the cathode 22, the potential of the anode 21 rises due to oxygen diffused and transmitted from the cathode 22. When the potential of the anode is exposed to a high potential, ruthenium contained in the catalyst is eluted, and CO poisoning performance is lowered. Therefore, the cathode 22 is connected simultaneously with the cathode 22 or the cathode 22 so that the potential of the anode 21 does not increase. It is preferable to stop the anode after stopping.

(Embodiment 3)
FIG. 4 is a flowchart of the operation method according to the third embodiment. When the fuel cell 5 was stopped, the electronic load 8 was first stopped (STEP 21), and the supply of the oxidant gas was stopped while the fuel gas was being supplied (STEP 22). As a result, hydrogen in the anode 21 diffuses to the cathode 22 through the electrolyte 1, reacts with oxygen to generate water, and consumes oxygen in the cathode 22, so that the voltage of the fuel cell 5 gradually decreases. When the voltage detector 9 detects that the voltage of the fuel cell 5 is equal to or lower than a predetermined voltage (STEP 23), the oxidant gas remaining in the fuel cell 5 is replaced with an inert gas (STEP 24), and the inert gas is further fueled. The fuel gas generated by the processing unit 7 is replaced (STEP 25), the supply of the fuel gas to the anode 21 and the cathode 22 is stopped (STEP 26), the shutoff valves 121a, 121b, 122a and 122b are closed, and the fuel gas is supplied to the fuel cell 5 It was enclosed in (STEP27).

  The difference from the operation method of the second embodiment is that the oxidant gas is first stopped, the voltage of the fuel cell 5 is lowered to a predetermined voltage, and then the cathode 22 is replaced with the fuel gas via an inert gas. The point is that the supply of fuel gas to the anode 21 and the cathode 22 is stopped.

  By stopping the supply of the oxidant gas while supplying the fuel gas, even if hydrogen permeates to the cathode 21 due to diffusion, hydrogen continues to be supplied to the anode 21, so that the reference potential of the anode 21 is stabilized and the cathode The electric potential of 22 falls earlier than the operation method 2, and the cathode 22 can be activated more.

  In addition, since the potential of the cathode 22 quickly decreases, the time for which the cathode 22 is held at a high potential such as an open circuit voltage can be shortened, and deterioration of the cathode 22 can be further suppressed.

(Embodiment 4)
FIG. 5 is a flowchart of the operation method according to the fourth embodiment. When the fuel cell 5 was stopped, first, the electronic load 8 was stopped (STEP 31), and the supply of the oxidant gas was stopped while supplying the fuel gas (STEP 32). Next, the supply of the oxidant gas was stopped, and at the same time, an inert gas was supplied to the cathode 22 side, and the oxidant gas remaining on the cathode 22 was replaced with the inert gas (STEP 33).

  As a result, hydrogen in the anode 21 diffuses to the cathode 22 through the electrolyte 1, reacts with oxygen to generate water, and consumes oxygen in the cathode 22, so that the voltage of the fuel cell 5 decreases instantaneously. When the voltage detector 9 detects that the voltage of the fuel cell 5 is equal to or lower than the predetermined voltage (STEP 34), the inert gas at the cathode 21 is replaced with fuel gas (STEP 35), and finally the fuel gas at the anode 21 and the cathode 22 is changed. Supply was stopped (STEP 36), shut-off valves 121a, 121b, 122a and 122b were closed, and fuel gas was sealed in the fuel cell 5 (STEP 37).

  The difference from the operation method of the third embodiment is that the oxidant gas is stopped and at the same time an inert gas is supplied to the cathode 22, the voltage of the fuel cell 5 is lowered to a predetermined voltage, and the inert gas is further converted into a fuel gas. It is a point to replace with.

  By replacing the oxidant gas with an inert gas while supplying the fuel gas, the oxygen of the cathode 22 can be forcibly discharged, and the potential of the cathode 22 is lowered more quickly than the operation method of the third embodiment. And more activated. Moreover, since oxygen remaining in the gas diffusion layer or the like that cannot be replaced only by stopping the gas can be replaced, deterioration can be further suppressed.

(Embodiment 5)
FIG. 6 is a flowchart of the operation method according to the fifth embodiment. When the fuel cell 5 was stopped, the electronic load 8 was first stopped (STEP 41), and the supply of the oxidant gas was stopped while the fuel gas was being supplied (STEP 42). Next, the supply of the oxidant gas was stopped, and at the same time, an inert gas was supplied to the cathode 22 side, and the oxidant gas remaining on the cathode 22 was replaced with the inert gas (STEP 43).

  As a result, hydrogen in the anode 21 diffuses to the cathode 22 through the electrolyte 1, reacts with oxygen to generate water, and consumes oxygen in the cathode 22, so that the voltage of the fuel cell 5 decreases instantaneously. When the voltage detector 9 detects that the voltage of the fuel cell 5 is equal to or lower than a predetermined voltage (STEP 44), the inert gas of the cathode 22 is further replaced with the fuel gas (STEP 45), and the supply of the fuel gas of the anode 21 and the cathode 22 is performed. (STEP 46), the shut-off valves 121a, 121b, 122a and 122b were closed, and fuel gas was sealed in the fuel cell 5 (STEP 47).

  Then, immediately before the start of the fuel cell 5 (STEP 48), the shut-off valves 121a, 121b, 122a and 122b are opened (STEP 49), the fuel gas in the cathode 22 is replaced with an inert gas (STEP 50), and then the anode 21 Fuel gas and oxidant gas were supplied to the cathode 22 and the cathode 22, respectively (STEP 51), and the load was started (STEP 52).

  The difference from the operation method of the fourth embodiment is that the inert gas is again supplied to the cathode 22 immediately before the start of the fuel cell 5.

  By supplying an inert gas for a certain period of time immediately before starting, hydrogen contained in the fuel gas sealed in the cathode 22 during stoppage and direct contact between oxygen contained in the oxidant gas introduced for power generation The fuel cell 5 can be safely started without causing combustion or the like.

(Embodiment 6)
FIG. 7 is a flowchart of the operation method according to the sixth embodiment. When the fuel cell 5 was stopped, first, the electronic load 8 was stopped (STEP 61), and the supply of the oxidant gas was stopped while the fuel gas of the anode 21 was being supplied (STEP 62). Next, the flow rate of the fuel gas is reduced to 2 to 5 times the volume of the gas flow path of the anode 21, and the supply of the oxidant gas is stopped. At the same time, an inert gas is supplied to the cathode 22, and the oxidant gas remaining on the cathode 22 Was replaced with an inert gas (STEP 63).

  As a result, hydrogen in the anode 21 diffuses to the cathode 22 through the electrolyte 1, reacts with oxygen to generate water, and consumes oxygen in the cathode 22, so that the voltage of the fuel cell 5 decreases instantaneously. When the voltage detector 9 detects that the voltage of the fuel cell 5 is equal to or lower than the predetermined voltage (STEP 64), the inert gas of the cathode 22 is further replaced with fuel gas (STEP 65), and the fuel gas of the anode 21 and cathode 22 is supplied. (STEP 66), the shut-off valves 121a, 121b, 122a and 122b were closed, and fuel gas was sealed in the fuel cell 5 (STEP 67).

  Then, immediately before the start of the fuel cell 5 (STEP 68), the shut-off valves 121a, 121b, 122a and 122b are opened (STEP 69), the fuel gas in the cathode 22 is replaced with an inert gas (STEP 70), and then the anode 21 Fuel gas and oxidant gas were supplied to the cathode 22 and the cathode 22, respectively (STEP 71), and the load was started (STEP 72).

  The difference from the operation method of the fifth embodiment is that the supply of the oxidant gas at the cathode 22 is stopped while the fuel gas flow rate at the anode 21 is reduced, and the oxidant gas is replaced with an inert gas.

  When the fuel cell is stopped, the supply of the oxidant gas is stopped while the fuel gas is supplied at a flow rate 2 to 5 times the volume of the gas flow path, and the oxidant gas remaining in the fuel cell is reduced to the volume of the gas flow path. After substituting with 2 to 5 times the inert gas, and further substituting the inert gas with the fuel gas 2 to 5 times the volume of the gas flow path, the shutoff valve is closed, and the fuel gas is put into the fuel cell until starting. By encapsulating the cathode, the cathode can be activated with a minimum amount of combustion gas.

  INDUSTRIAL APPLICABILITY The fuel cell power generation device and the operation method thereof according to the present invention have an effect of suppressing deterioration due to start and stop or improving durability, and are useful for power generation devices and devices using a polymer solid electrolyte membrane.

  Further, since a source gas such as city gas is used as the inert gas, it is useful for a stationary fuel cell cogeneration system.

Configuration diagram of fuel cell power generator in Embodiments 1 to 6 of the present invention The flowchart which shows the driving | running method in Embodiment 1 of this invention. The flowchart which shows the driving | running method in Embodiment 2 of this invention. The flowchart which shows the driving | running method in Embodiment 3 of this invention. The flowchart which shows the driving | running method in Embodiment 4 of this invention. The flowchart which shows the driving | running method in Embodiment 5 of this invention. The flowchart which shows the driving | running method in Embodiment 6 of this invention. Configuration diagram of conventional fuel cell power generator

Explanation of symbols

1 Electrolyte 21 Electrode (Anode)
22 electrode (cathode)
41, 42 Separator plate 5 Fuel cell 6 Desulfurization unit 7 Fuel processing unit 9 Voltage detection unit 121a, 121b, 122a, 122b Shut-off valve

Claims (9)

A pair of electrodes having an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas flow path for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes and supplying and discharging an oxidizing gas containing at least oxygen to the other of the electrodes A fuel cell comprising at least one cell comprising a separator plate, and after replacing all or part of the oxidant gas remaining in the fuel cell when the fuel cell is stopped with an inert gas, A fuel cell power generator comprising a gas replacement unit that replaces all or part of the active gas with the fuel gas. The fuel gas and oxidant gas supply unit and discharge unit are provided with shut-off valves, and when the fuel cell is stopped, all or part of the oxidant gas is replaced with inert gas, and then all or all of the inert gas or The fuel cell power generator according to claim 1, wherein a part of the fuel gas is replaced with the fuel gas, the shutoff valve is closed, and the fuel gas is sealed in the fuel cell. A pair of electrodes having an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas flow path for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes and supplying and discharging an oxidizing gas containing at least oxygen to the other of the electrodes A fuel cell comprising at least one cell comprising a separator plate, and after replacing all or part of the oxidant gas remaining in the fuel cell when the fuel cell is stopped with an inert gas, A gas replacement unit that replaces all or part of the active gas with the fuel gas; and a voltage detection unit that detects a voltage of the fuel cell, and when the fuel cell is stopped, the fuel gas and the oxidant gas The supply is stopped at the same time, and after the voltage detection unit detects the voltage of the fuel cell as a predetermined voltage or less, all or part of the oxidant gas remaining in the fuel cell is Replaced with inert gas, further operating method of the fuel cell power plant to replace all or part of the inert gas in the fuel gas. A pair of electrodes having an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas flow path for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes and supplying and discharging an oxidizing gas containing at least oxygen to the other of the electrodes A fuel cell comprising at least one cell comprising a separator plate, and after replacing all or part of the oxidant gas remaining in the fuel cell when the fuel cell is stopped with an inert gas, A gas replacement unit that replaces all or part of the active gas with the fuel gas; and a voltage detection unit that detects a voltage of the fuel cell, and the oxidation is performed while the fuel gas is supplied when the fuel cell is stopped. All or part of the oxidant gas remaining in the fuel cell after the supply of the oxidant gas is stopped and the voltage detection unit detects the voltage of the fuel cell to be equal to or lower than a predetermined voltage Said replaced with an inert gas, further operating method of the fuel cell power plant to replace all or part of the inert gas in the fuel gas. A pair of electrodes having an electrolyte, a pair of electrodes sandwiching the electrolyte, and a gas flow path for supplying and discharging a fuel gas containing at least hydrogen to one of the electrodes and supplying and discharging an oxidizing gas containing at least oxygen to the other of the electrodes A fuel cell comprising at least one cell comprising a separator plate, and after replacing all or part of the oxidant gas remaining in the fuel cell when the fuel cell is stopped with an inert gas, A gas replacement unit that replaces all or part of the active gas with the fuel gas; and a voltage detection unit that detects a voltage of the fuel cell, and the oxidation is performed while the fuel gas is supplied when the fuel cell is stopped. The supply of the agent gas is stopped, all or part of the oxidant gas remaining in the fuel cell is replaced with the inert gas, and the voltage detection unit determines the voltage of the fuel cell. After detecting the following constant voltage, operating method of the fuel cell power plant to replace all or part of the inert gas in the fuel gas. Provided with shutoff valves in the oxidant gas supply section and discharge section, when the fuel cell is stopped, all or part of the oxidant gas remaining in the fuel cell is replaced with an inert gas, and further the inert gas 4. After replacing all or part of the gas with fuel gas, close the shutoff valve, open the shutoff valve immediately before starting, and replace all or part of the fuel gas with the inert gas. 6. A method for operating the fuel cell power generator according to any one of claims 5 to 6. Provided with a shutoff valve in the fuel gas and oxidant gas supply section and discharge section, and when the fuel cell is stopped, the oxidant gas remaining in the fuel cell is 2 to 5 times the volume of the gas flow path. And replacing the inert gas with the fuel gas of 2 to 5 times the volume of the gas flow path, closing the shutoff valve, and sealing the fuel gas in the fuel cell until startup. Item 6. A method for operating a fuel cell power generator according to any one of Items 3 to 5. A supply valve and a discharge portion for the fuel gas and the oxidant gas are provided with a shut-off valve, and when the fuel cell is stopped, the fuel gas is supplied in a volume 2 to 5 times the volume of the gas flow path. And the oxidant gas remaining in the fuel cell is replaced with an inert gas 2 to 5 times the volume of the gas flow path, and the inert gas is further replaced with 2 to 5 times the volume of the gas flow path. 6. The method of operating a fuel cell power generator according to claim 4, wherein the fuel gas is sealed in the fuel cell until the shut-off valve is closed and started after the fuel gas is replaced with twice the fuel gas. The desulfurization part which desulfurizes raw material gas and the fuel processing part which produces | generates fuel gas from the said desulfurized said raw material gas are used, The said desulfurized raw material gas is used as inert gas of any one of Claims 1-8. Operation method of fuel cell power generator.

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