JP2008097962A - Fuel cell system and its operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent degradation of characteristics of transformation catalyst at start-up after abnormal stoppage of a hydrogen generating device. <P>SOLUTION: The fuel cell system is provided with a hydrogen generating device equipped with a reformer 1 having reforming catalyst generating hydrogen-containing gas from a raw material, a fuel cell generating power with the use of the hydrogen-containing gas supplied from the hydrogen generating device, and a transformer transformation temperature detecting controller 201. The above controller 201 allows starting of supply of the hydrogen-containing gas from the hydrogen generating device to the fuel cell when a temperature of the transformer 6 at least exceeds a first threshold value, and changes the first threshold value to a temperature higher than at normal times, when a temperature of the transformer exceeds a second threshold value in a start-up operation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell system including a hydrogen generator having a transformer that reduces carbon monoxide in a hydrogen-containing gas generated by a reforming reaction by a shift reaction, and an operation method thereof.

  A fuel cell cogeneration system with high power generation efficiency and high overall efficiency has attracted attention as a distributed power generator that effectively uses energy.

  Many fuel cells, for example, phosphoric acid fuel cells that have been put to practical use and solid polymer fuel cells that are currently under development, generate electricity using hydrogen as fuel. However, since hydrogen is not provided as infrastructure, it must be generated at the site where the system is installed.

  One of the hydrogen generation methods is a steam reforming method. Natural gas, LPG, naphtha, gasoline, kerosene and other hydrocarbon-based raw materials or alcohol-based raw materials such as methanol are mixed with steam and subjected to a steam reforming reaction in a reformer provided with a reforming catalyst, and a hydrogen-containing gas There are hydrogen generators that generate

  The conventional hydrogen generator includes a reformer having a reforming catalyst such as Ru for advancing the steam reforming reaction. In the steam reforming reaction that occurs in this reformer, carbon monoxide (CO) is produced as a secondary component, and the hydrogen-containing gas delivered from the reformer contains about 10 to 15% of CO. Since CO contained in the hydrogen-containing gas poisons the electrode catalyst of the polymer electrolyte fuel cell and lowers the power generation capacity, it is necessary to provide means for reducing CO on the downstream side of the reformer. Therefore, a shifter having a shift catalyst that advances a water gas shift reaction in which CO and water vapor react to generate hydrogen and carbon dioxide, and air in the air by supplying air to the hydrogen-containing gas sent from the shifter A CO remover having an oxidation catalyst for oxidizing CO is installed downstream of the reformer, and the hydrogen-containing gas after the reformer is circulated to reduce the CO concentration in the hydrogen-containing gas to 10 ppm or less. Remove.

  The determination as to whether or not the CO concentration in the hydrogen-containing gas can be reduced is often determined by the temperature of the shift catalyst. Although it depends on the amount of catalyst, the amount of feedstock and the amount of water supplied, in general, the shift catalyst has low CO reduction ability at less than about 150 ° C, but CO is reduced to 0.5% or less at about 150 ° C to about 250 ° C be able to. If CO can be reduced to 0.5% or less in the transformer, CO can often be reduced to 10 ppm or less by the CO remover. Therefore, when the temperature of the shift catalyst becomes about 150 ° C. to about 250 ° C., it is determined that the CO concentration in the hydrogen-containing gas at the outlet of the hydrogen generator is 10 ppm or less, and supply to the fuel cell is started.

In addition, a copper-zinc catalyst is widely used as the shift catalyst. In order to exhibit the catalytic properties of the copper-zinc catalyst, it is necessary to keep the copper in a reduced state. During operation, the hydrogen-rich hydrogen-containing gas is supplied, so that the copper is kept in a reduced state. However, during stoppage, air from the outside air may enter the hydrogen generator. Since the copper in the shift catalyst is oxidized when the intrusion reaches the shift converter, it is necessary to perform a stop method that does not allow air to enter. Therefore, as a method for stopping the operation of the hydrogen generator, the hydrogen generator is filled with the raw material gas and sealed, and further, the negative pressure of the reformer caused by the temperature drop in the hydrogen generator after sealing is prevented. Therefore, hydrogen generators have been proposed in which city gas is supplied after a predetermined time, and the interior of the hydrogen generator is again shut off from the outside air and maintained at a positive pressure (see, for example, Patent Document 1 and Patent Document 2).
JP 2003-229156 A JP 2003-288930 A

  However, as described in the above-mentioned patent document, after the temperature is lowered, the raw material gas is supplied, brought to a positive pressure, and after leaving the hydrogen generation device cut off from the outside air in this stopped state for a long period of time, it is started up normally. And after confirming that the temperature of the transformer is equal to or higher than a predetermined temperature at which the CO is expected to be reduced to a level that can be supplied to the fuel cell in the transformer, the hydrogen-containing gas is supplied to the fuel cell. It has been found that the concentration of CO in the hydrogen-containing gas is high, and the anode of the fuel cell is poisoned and the fuel cell may deteriorate significantly.

  The present invention solves the above-described conventional problems, and reliably reduces CO even during startup after being left in a stopped state for a long period of time, and poisons the anode electrode of the fuel cell with CO. It is an object of the present invention to provide a fuel cell system that does not cause problems.

  In order to solve the above-mentioned conventional problems, the present inventor has intensively studied, and as a result, when left standing for a long period of time, air enters the hydrogen generator and thus the transformer due to fluctuations in the outside air temperature or atmospheric pressure. As a result, it has been found that the shift catalyst in the shift converter may be oxidized and deteriorated. Here, when the start-up operation is performed, the shift catalyst that has been oxidized and deteriorated is reduced by the hydrogen-containing gas generated in the reformer, and the shift catalyst may become hotter due to the heat generated by the reduction reaction than during the normal start-up operation. In such a case, it was found that CO in the hydrogen-containing gas can be reduced to a level that can be supplied to the fuel cell by controlling the temperature of the transformer to a temperature higher than that at normal startup.

  A fuel cell system according to a first aspect of the present invention includes a reformer having a reforming catalyst that generates a hydrogen-containing gas from a raw material, a shifter having a shift catalyst that reduces carbon monoxide in the hydrogen-containing gas by a shift reaction, and A hydrogen generator comprising a temperature detector for detecting the temperature of the transformer; a fuel cell for generating electricity using a hydrogen-containing gas supplied from the hydrogen generator; and a controller, wherein at least the temperature detector If the detected temperature is not equal to or higher than the first threshold value, the controller is a fuel cell system that does not allow the supply of hydrogen-containing gas from the hydrogen generator to the fuel cell to start, and the controller performs a startup operation When the temperature detected by the temperature detector is equal to or higher than a second threshold value greater than the first threshold value, the first threshold value is changed to a higher temperature.

  The fuel cell system according to the second aspect of the present invention is characterized in that the shift catalyst contains copper and zinc.

  The fuel cell system operating method of the third aspect of the present invention includes a reformer having a reforming catalyst that generates a hydrogen-containing gas from a raw material, and a shift catalyst that reduces carbon monoxide in the hydrogen-containing gas by a shift reaction. A hydrogen generator comprising a transformer having a temperature detector for detecting the temperature of the transformer, and a fuel cell for generating power using a hydrogen-containing gas supplied from the hydrogen generator, and at least the temperature detector If the detected temperature of the fuel cell system is not equal to or higher than the first threshold value, the operation method of the fuel cell system that does not permit the start of the supply of the hydrogen-containing gas from the hydrogen generator to the fuel cell, When the detected temperature is equal to or higher than a second threshold value that is greater than the first threshold value, the first threshold value is changed to a higher temperature.

  According to the fuel cell system of the present invention, the hydrogen-containing gas is supplied to the fuel cell in a state in which CO is sufficiently reduced even at the start after the air enters the hydrogen generator during the long-term shutdown and the shift catalyst is oxidized and deteriorated. Is supplied and stable power generation operation becomes possible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a configuration diagram of a fuel cell system according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the fuel cell system of Embodiment 1 includes a reformer 1 having a reforming catalyst (not shown) that generates a hydrogen-rich hydrogen-containing gas from a hydrocarbon-based raw material and water. A raw material supplier 2 that controls the amount of raw material supplied to the reformer 1, and a water supplier 3 that controls the amount of water supplied to the reformer 1. Specifically, the raw material supply device 2 is configured with a needle valve, a variable orifice, and the like, and the water supply device 3 is configured with a plunger pump and the like.

  The reformer 1 is provided with a heater 4 for heating the reformer 1 and a reforming temperature detector 5 for detecting the temperature of the reforming catalyst. The supplied raw material and water are heated by the heater 4 in the reformer 1, whereby a hydrogen-containing gas is generated by a steam reforming reaction. Further, the heating amount by the heater 4 is determined by the temperature of the reforming catalyst detected by the reforming temperature detector 5.

  The hydrogen-containing gas generated by the reformer 1 is supplied to the transformer 6. The shifter 6 contains a copper-zinc catalyst (not shown) as a shift catalyst. The transformer 6 is provided with a transformation temperature detector 7 which is a temperature detector of the present invention for detecting the temperature of the transformer 6. The shift temperature detector 7 may be installed at any location as long as the shift temperature detector 7 is disposed at a position where the temperature of the shift catalyst or the temperature of the gas passing through the shift catalyst can be detected. For example, the outer wall of the metamorphic part 6 may be used.

  The hydrogen-containing gas that has passed through the transformer 6 is supplied to the CO remover 8 in order to further reduce CO, and the oxidation reaction proceeds with oxygen in the air supplied by the oxidizing gas supply device 9, and the hydrogen-containing gas. Reduce the concentration of CO to 10 ppm or less.

  Downstream of the CO remover 8, a fuel gas supply path 14 for supplying a hydrogen-containing gas sent from the CO remover 8 as a fuel gas to the fuel cell 11, and an off-fuel gas sent from the fuel cell 11. From an off-gas passage 15 for supplying to the heater 4, a bypass passage 12 that branches off in the middle of the fuel gas supply passage 14, bypasses the fuel cell 11, and is connected to the off-gas passage 15, and a CO remover 8. A switch 10 for switching the flow path of the delivered hydrogen-containing gas to either the fuel cell 11 or the bypass flow path 12, and a valve 16 for shutting off the system from outside air when the fuel cell system is stopped. Prepare. Note that the switch 10 is a three-way valve or the like.

  The controller 13 is a controller that controls the switch 10 based on at least the temperature detected by the transformation temperature detector 7. In the present embodiment, the controller 13 further includes the raw material supplier 2, the water supplier 3, and the heater 4. And the oxidizing gas supply device 9 and the valve 16 are controlled.

  Next, an example of a method for starting the fuel cell system according to the present embodiment will be described.

  As a normal starting method, the controller 13 first switches the raw material supplier 2 while switching the gas sent from the CO remover 8 so as to flow through the bypass flow path 12 and opening the valve 16 by the switch 10. As a raw material, natural gas 2.0 NL / min is supplied to the reformer 1 as well as the number of moles of carbon in the raw material supplied to the reformer 1 and the number of moles of water molecules supplied to the reformer 1. Water is supplied to the reformer 1 by the water supplier 3 so that the steam / carbon ratio (S / C) = 3.0. After passing through the reformer 1, the combustible gas containing the raw material that has passed through the transformer 6 and the CO remover 8 flows through the bypass flow path 12 and the off-gas flow path 15 and is finally supplied to the heater 4 for combustion. Thus, the reformer 1 is heated. The controller 13 further controls the amount of raw material supplied by the raw material supplier 2 and heats the heater 4 so that the temperature detected by the reforming temperature detector 5 becomes 650 ° C. The quality reaction proceeds. The CO concentration in the hydrogen-containing gas delivered from the reformer 1 is about 10 to 15%, and is supplied to the transformer 6 and the CO remover 8 in order to reduce CO.

  In order to generate electricity stably with the fuel cell 11, it is necessary to reduce the CO concentration in the hydrogen-containing gas at the outlet of the hydrogen generator equipped with the reformer 1, the transformer 6 and the CO remover 8 to 10 ppm or less. In the fuel cell system of the present embodiment, the CO concentration in the hydrogen-containing gas delivered from the transformer 6 can be reduced to 0.5% or less, and the CO remover 8 reaches the optimum reaction temperature. The CO concentration in the hydrogen-containing gas delivered from the CO remover 8 can be reduced to 10 ppm or less.

  Whether or not the CO concentration in the hydrogen-containing gas sent from the transformer 6 can be reduced to 0.5% or less can be determined by the temperature detected by the transformation temperature detector 7.

  A curve a obtained by extrapolating the black circle in FIG. 2 shows the relationship between the catalyst temperature detected by the shift temperature detector 7 as a characteristic of the normal shift catalyst and the CO concentration in the hydrogen-containing gas after the shifter 6.

  As shown by the curve a, the CO concentration contained in the hydrogen-containing gas is such that the temperature in the hydrogen-containing gas delivered from the transformer 6 is not increased until the temperature detected by the transformation temperature detector 7 reaches 150 ° C. or higher. The concentration cannot be reduced below 0.5%. Therefore, in a normal start-up operation, the controller 13 detects that the hydrogen-containing gas delivered from the transformer 6 when the temperature detected by the transformation temperature detector 7 exceeds 150 ° C., which is the first threshold value of the present invention. CO removal temperature detector that determines that the CO concentration of the fuel cell is about 0.5% or less, satisfies one condition for permitting the supply of the hydrogen-containing gas to the fuel cell 11, and further detects the temperature of the CO remover 8 When the detected temperature of 17 is equal to or higher than the optimum reaction temperature (for example, 120 ° C.) of the CO remover 8, it is determined that the CO concentration in the hydrogen-containing gas is surely reduced to 10 ppm or less, and the hydrogen is supplied to the fuel cell 11. Another condition for permitting the supply of the contained gas is satisfied, it is determined that the supply of the hydrogen-containing gas to the fuel cell 11 can be permitted, and the supply of the hydrogen-containing gas from the CO remover 8 to the fuel cell 11 is started. To generate electricity. In the above description, whether or not the supply of the hydrogen-containing gas to the fuel cell 11 is determined takes into consideration not only the temperature of the transformer 6 but also the temperature of the CO remover 8, and it is determined whether or not each of them exceeds a predetermined threshold value. If the hydrogen generator is a device configuration in which the temperature of each reactor is highly thermally related, the temperature of the transformer 6 is set as a representative temperature and the temperature of the transformer 6 exceeds a predetermined threshold. Thus, the controller 13 may determine that the hydrogen-containing gas sent from the CO remover 8 can be supplied to the fuel cell 11.

  In any case, in the start-up operation of the fuel cell system of the present invention, the controller 13 does not allow the hydrogen-containing gas to be supplied to the fuel cell 11 unless at least the temperature of the transformer 6 becomes equal to or higher than the first threshold value. .

  Next, an example of a method for stopping the fuel cell system of the present embodiment will be described here. First, when the stop operation is started, the controller 13 stops the supply of the raw material and water from the raw material supply device 2 and the water supply device 3, and also stops the heating by the heater 4. Then, the switcher 10 is switched to the bypass flow path 12 side, and the valve 16 is sealed to prevent air from entering the fuel cell system.

  However, when left standing for a long period of time, the gas flow path in the hydrogen generator becomes below the atmospheric pressure due to the change of the outside air temperature or the fluctuation of the atmospheric pressure as described above, and air enters from the valve 16, As a result, air may penetrate into the transformer 6. In such a case, since the copper of the copper-zinc catalyst used as the shift catalyst in the shift converter 6 is oxidized to copper oxide, it is oxidized by the hydrogen-containing gas generated on the reforming catalyst at the next start-up. The reduced copper may be reduced again, and the shift catalyst may become hotter than during normal startup.

  The curve b obtained by extrapolating the white squares in FIG. 2 indicates the temperature of the shift catalyst after the temperature becomes high as described above and the temperature detected by the shift temperature detector 7 exceeds 350 ° C., which is the second threshold value of the present invention. As a characteristic, the relationship between the catalyst temperature and the CO concentration in the hydrogen-containing gas sent from the transformer 6 is shown.

  As shown by the curve b, after the temperature detected by the shift temperature detector 7 exceeds 350 ° C., the CO in the hydrogen-containing gas delivered from the shift converter 6 even when the temperature of the shift catalyst reaches 150 ° C. It can be seen that the concentration cannot be reduced to 0.5% or less and can be reduced to 0.5% or less at 160 ° C. or higher.

  Therefore, in the fuel cell system of the present embodiment, in the startup operation after the temperature detected by the transformation temperature detector 7 during the startup operation exceeds the second threshold of 350 ° C., the transformer 6 The first threshold for determining that the hydrogen-containing gas sent from the CO remover 8 can be supplied to the fuel cell 11 from 150 ° C. to a higher temperature of 160 ° C. is sufficiently reduced in the hydrogen-containing gas sent out. When the temperature detected by the modification temperature detector 7 reaches 160 ° C., the controller 23 switches the switch 10 to the fuel gas supply path 14 side, and converts the hydrogen-containing gas sent from the CO remover 8 into the fuel cell 11. To supply.

  By the start-up operation of the fuel cell system, air enters the hydrogen generator during a long-term stop, and the hydrogen-containing gas is supplied to the fuel cell 11 in a state in which CO is sufficiently reduced even after start-up after the shift catalyst is oxidized and deteriorated. And stable power generation operation becomes possible.

  Note that when the temperature detected by the shift temperature detector 7 again exceeds 350 ° C. after the start-up when the first threshold is changed to 160 ° C., the CO reduction at a lower temperature of the shift catalyst than the curve b. Since the characteristics may be further deteriorated, it is necessary to reliably reduce CO by further increasing the set temperature of the first threshold value of the present invention such as 160 ° C. to 170 ° C.

  In the above embodiment, the first threshold value is 150 ° C., the second threshold value is 350 ° C., and the threshold value after changing the first threshold value is 160 ° C. What is necessary is just to select an optimal value in a structure etc., and it is not limited to the said value.

  The fuel cell system according to the present invention reliably reduces CO even during start-up after being left in a stopped state for a long period of time, and is stable without poisoning the anode electrode of the fuel cell with CO. Therefore, it is useful as a household fuel cell cogeneration system.

1 is a configuration diagram of a fuel cell system according to Embodiment 1 of the present invention. The figure which shows the relationship between the catalyst temperature detected by the transformation temperature detector of the fuel cell system in Embodiment 1 of this invention, and CO density | concentration in the hydrogen containing gas sent from a transformation device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reformer 2 Raw material supply device 3 Water supply device 4 Heater 5 Reforming temperature detector 6 Transformer 7 Transformation temperature detector 8 CO remover 9 Oxidizing gas supply device 10 Switch 11 Fuel cell 12 Bypass flow path 13 Control 14 Fuel gas supply path 15 Off gas flow path 16 Valve 17 CO removal temperature detector

Claims (3)

A reformer having a reforming catalyst for generating a hydrogen-containing gas from a raw material, a shifter having a shift catalyst for reducing carbon monoxide in the hydrogen-containing gas by a shift reaction, and a temperature detector for detecting the temperature of the shifter A hydrogen generator comprising: a fuel cell that generates electricity using a hydrogen-containing gas supplied from the hydrogen generator; and a controller, wherein at least the temperature detected by the temperature detector is not equal to or higher than a first threshold value The controller does not permit the start of the supply of the hydrogen-containing gas from the hydrogen generator to the fuel cell, and the controller detects the temperature detected by the temperature detector during the start-up operation. The fuel cell system is characterized in that the first threshold value is changed to a higher temperature when the second threshold value is greater than or equal to the second threshold value. The fuel cell system according to claim 1, wherein the shift catalyst contains copper and zinc. A reformer having a reforming catalyst for generating a hydrogen-containing gas from a raw material, a shifter having a shift catalyst for reducing carbon monoxide in the hydrogen-containing gas by a shift reaction, and a temperature detector for detecting the temperature of the shifter And a fuel cell that generates electricity using the hydrogen-containing gas supplied from the hydrogen generator, and at least if the temperature detected by the temperature detector is not equal to or higher than a first threshold value, the hydrogen generator An operation method of a fuel cell system that does not permit the start of supply of a hydrogen-containing gas from an apparatus to the fuel cell, wherein a temperature detected by the temperature detector is greater than or equal to a second threshold value that is greater than the first threshold value in startup operation Then, the operation method of the fuel cell system, wherein the first threshold value is changed to a higher temperature.

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