JP2007137719A - Fuel reforming apparatus, and fuel cell power generation apparatus using it and its operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel reforming apparatus capable of continuing or stopping its running by detecting an abnormality of the fuel reforming apparatus without imposing a load on a fuel cell and the fuel reforming apparatus and performing a stable running, and a fuel cell power generation apparatus using the fuel reforming apparatus and its operation method. <P>SOLUTION: In an apparatus for supplying a reformed gas to an apparatus for utilizing hydrogen such as a fuel cell, which is equipped with a reformer for reforming a hydrocarbon fuel and a carbon monoxide transformer and/or a carbon monoxide remover for reducing the carbon monoxide concentration in the reformed gas, a hygrometer to measure the humidity of the reformed gas is installed at a position downstream from the carbon monoxide transformer or the carbon monoxide remover and upstream from the apparatus for utilizing hydrogen. When a dew point indicated on the hygrometer exceeds a threshold value specified in advance, it is judged that an abnormality occurs to the fuel reforming apparatus. When the abnormality occurs to the fuel reforming apparatus, the running of the fuel cell power generation apparatus is stopped or continued by reducing the load or increasing the amount of flowing water for reforming. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel reformer for steam reforming a hydrocarbon gas as a raw fuel or a fuel cell power generator combined with a fuel cell that generates power using reformed hydrogen and a method for operating the same, and more particularly to a fuel reformer. The present invention relates to an abnormality detection method for a quality device and a response method based on the abnormality detection.

  A fuel cell is a device that directly converts chemical energy of fuel into electrical energy without passing through mechanical energy or thermal energy, and can achieve high energy efficiency. As a well-known form of a fuel cell, a pair of electrodes are arranged with an electrolyte layer in between, a fuel gas containing hydrogen is supplied to one electrode (anode side), and oxygen is supplied to the other electrode (cathode side). The electromotive force is obtained by utilizing an electrochemical reaction that occurs between the two electrodes. Below, an equation representing an electrochemical reaction occurring in the fuel cell is shown. (1) represents the reaction on the anode side, (2) represents the reaction on the cathode side, and the reaction represented by the formula (3) proceeds in the entire fuel cell.

H ₂ → 2H ⁺ + 2e ⁻ (1)
1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
H ₂ + 1 / 2O ₂ → H ₂ O (3)
Fuel cell power generators are classified according to the type of electrolyte used. Among these fuel cells, solid polymer fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, etc. Due to the nature, it is possible to use oxidizing gas or carbon dioxide containing carbon dioxide. Therefore, in these fuel cells, normally, air is used as an oxidizing gas, and a gas containing hydrogen generated by steam reforming a hydrocarbon-based raw fuel such as natural gas by a fuel reformer is used as a fuel gas.

  For this reason, a fuel cell system including such a fuel cell is provided with a reformer and a carbon monoxide converter, and the reformer and the carbon monoxide converter reform the raw fuel to supply fuel gas. Is generated.

  Equation (4) shows the reforming reaction of methane in the reformer.

CH ₄ + H ₂ O → CO + 3H ₂ +206.14 KJ / mol ……… （4）
As shown in Formula (4), the reforming reaction of methane is an endothermic reaction, and therefore, after adding water vapor to methane, the granular reforming catalyst is converted to 600 by the combustion exhaust gas obtained by burning the fuel off-gas from the fuel cell. By maintaining at ~ 700 ° C, reformed gas rich in hydrogen is produced.

  This reformed gas leaving the reformer is fed to a carbon monoxide converter to reduce carbon monoxide in the reformed gas, where the carbon monoxide is reduced to less than 1% and phosphoric acid form. In the case of a fuel cell (PAFC), this gas can be introduced into the fuel cell to generate power.

  On the other hand, the polymer electrolyte fuel cell (PEFC) has a low operating temperature of 60 to 80 ° C, so if carbon monoxide is present in the reformed gas, it becomes a catalyst poison that degrades performance. In order to further reduce carbon monoxide, the reformed gas is supplied to a carbon monoxide remover controlled at a predetermined temperature, where the carbon monoxide is reduced to 10 ppm or less.

  By the way, the fuel reforming apparatus is used as a hydrogen production apparatus in various industrial apparatuses using hydrogen in addition to the fuel cell. As an abnormality detection method for this type of fuel reformer, conventionally, as described in Patent Document 1, control for adjusting the flow rate of gas and the amount of reforming water so as to keep the catalyst at a predetermined temperature is performed. Abnormalities are detected by detecting the upper and lower temperature limits. In this case, there were the following problems. This problem will be described with reference to FIG.

  FIG. 4 is a schematic configuration diagram of a conventional fuel cell power generator using a fuel reformer. In FIG. 4, the raw fuel from which the sulfur content has been removed by the desulfurizer 1 is mixed with the steam reforming water supplied by the steam reforming water supply pump 8, and then supplied to the evaporation unit 2, where the steam reforming water is supplied. After being vaporized, it is supplied to the reformer 3 and reformed into a hydrogen-rich reformed gas by the steam reforming reaction shown in the equation (4). Thereafter, the carbon concentration is supplied to the carbon monoxide converter 4 to increase the hydrogen concentration by the carbon monoxide conversion reaction, and is further supplied to the carbon monoxide remover 5 together with a certain amount of air (not shown) to selectively oxidize the carbon monoxide. Thus, after the carbon monoxide is reduced to 10 ppm or less, it is humidified by the fuel gas humidifier 9 and then supplied to the fuel cell 6.

  In addition, the part number 10 is a fuel gas humidification water pump, 11 is an oxidizing gas humidifier, and 12 is an oxidizing gas humidification water pump. A control device 13 inputs necessary information and outputs various commands. In FIG. 4, as an example, a signal line for temperature measurement information from the carbon monoxide transformer temperature measurement point 14a and various control lines are indicated by broken lines. A broken line connecting part numbers 13 and 6 indicates a normal battery control line, for example, a control line for load control including a stop command, abnormality monitoring, temperature control, and the like. Furthermore, a broken line connecting the part numbers 13 and 8 indicates a control line for the supply amount of water for steam reforming.

  By the way, the hydrogen-rich reformed gas generated by the steam reforming reaction shown in the formula (4) is supplied to the carbon monoxide converter 4 and the hydrogen concentration is increased by the carbon monoxide conversion reaction. When carbon monoxide is supplied to the carbon monoxide remover 5 together with a certain amount of air and is reduced to 10 ppm or less by the carbon monoxide selective oxidation reaction, carbon monoxide or carbon dioxide and hydrogen in the reformed gas May react to produce methane gas.

  Expressions (5) and (6) are expressions showing the methanation reaction in the carbon monoxide converter or the carbon monoxide remover.

CO + 3H ₂ → CH ₄ + H ₂ O (5)
CO ₂ + 4H ₂ → CH ₄ + 2H ₂ O (6)
When the methanation reaction of Formulas (5) and (6) occurs, the generated hydrogen is consumed, and the amount of hydrogen supplied to the battery decreases. In addition, water is generated by the reaction, and hydrogen and carbon monoxide or carbon dioxide are consumed to reduce the volume of the gas, so that a gas having a dew point higher than necessary is supplied to the battery, and the inside of the fuel cell and It may become liquid water on the electrode surface and inhibit gas diffusion.

  This reaction is likely to occur when the temperature is around 400 ° C or higher in a carbon monoxide converter, and since the reaction is exothermic, the temperature of the catalyst increases with the reaction, so the temperature further increases. In some cases, the temperature cannot be controlled and the reformer is stopped to lower the temperature.

Conventionally, as disclosed in Patent Document 1, the temperature in the carbon monoxide converter is detected, and the temperature is lowered by increasing the supply amount of the reforming water or the water for conversion. In the case of such anomaly detection by temperature detection, the reaction proceeds to some extent and the reaction proceeds until the temperature of the catalyst rises to a level that can be detected by the sensor. In order to stop the methanation reaction, the temperature cannot be lowered even after the temperature lowering operation because the battery characteristics are deteriorated or the reaction proceeds, and the temperature load is applied to the reformer. It was necessary to stop the reformer urgently.
JP 2003-30726 A

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to detect an abnormality of the fuel reformer without imposing a burden on the fuel cell or the fuel reformer. An object of the present invention is to provide a fuel reforming apparatus that can continue or stop operation and enable stable operation, a fuel cell power generation apparatus that uses the fuel reforming apparatus, and an operation method thereof.

  The above-mentioned subject is achieved by the following. That is, a reformer that reforms a hydrocarbon-based fuel into a reformed gas rich in hydrogen, and a carbon monoxide converter and / or a carbon monoxide remover that reduces the concentration of carbon monoxide in the reformed gas. In the fuel reformer for supplying the obtained reformed gas to the hydrogen utilization facility, reforming is performed downstream of the carbon monoxide converter or carbon monoxide remover and upstream of the hydrogen utilization facility. A hygrometer for measuring the humidity of the gas is provided, and when the dew point indication value of the hygrometer exceeds a predetermined threshold value, it is determined that an abnormality has occurred in the fuel reformer (claim 1). .

  When an abnormality occurs in the fuel reformer, the details will be described later, but the reformed gas humidity rises at an earlier timing than the rise in the catalyst layer temperature. Can be supported.

  2. The fuel reformer according to claim 1, wherein the catalyst used in the carbon monoxide converter and / or the carbon monoxide remover generates methane by reacting carbon monoxide or carbon dioxide with hydrogen. It is characterized by using a catalyst that causes methanation reaction to occur (claim 2). The catalyst that causes the methanation reaction is a noble metal catalyst. For example, there is a Pt catalyst as a carbon monoxide shift catalyst and a Ru catalyst as a carbon monoxide removal catalyst. Cu-Zn catalysts and Fe catalysts are excluded because they do not cause methanation.

  Furthermore, in the fuel cell power generation apparatus that generates power using the reformed gas reformed by the fuel reformer according to claim 1 or 2, the reformed gas is passed from the fuel reformer to the fuel cell power generation apparatus. A hygrometer is provided on the line to be operated, and it is determined that an abnormality has occurred in the fuel reformer when the dew point indication value of the hygrometer exceeds a predetermined threshold (claim 3).

  In addition, as an invention relating to a method of operating a fuel cell power generator when it is determined that an abnormality has occurred in the fuel reformer, any one of the inventions according to claims 4 to 6 is preferable. That is, in the method of operating the fuel cell power generator according to claim 3, the fuel cell power generator is stopped when it is determined that an abnormality has occurred in the fuel reformer (claim 4). ).

  Further, in the method of operating the fuel cell power generator according to claim 3, when it is determined that an abnormality has occurred in the fuel reformer, the operation is continued by reducing the load of the fuel cell power generator. It is characterized (claim 5). By reducing the load, the methanation reaction in the fuel reformer can be reduced, so that the operation can be continued. When the abnormality is recovered, the operation is continued to the stable operation by returning to the rated operation.

  Furthermore, in the method of operating the fuel cell power generator according to claim 3, when it is determined that an abnormality has occurred in the fuel reformer, the flow rate of reforming water to be input to the fuel reformer is increased. The operation is continued by lowering the temperature of the carbon monoxide transformer and / or the carbon monoxide remover (Claim 6). Since the methanation reaction in the fuel reformer can be reduced by lowering the temperature, the operation can be continued.

  According to this invention, the abnormality is detected earlier than the temperature detection by the dew point indication value of the hygrometer, and in the case of the fuel cell power generation device, the flow rate of water for steam reforming is controlled, or the fuel cell is stopped or loaded. By adjusting, it becomes possible to cope with the abnormality before the reaction proceeds, and the operation can be continued or stopped without imposing a burden on the fuel cell or the reformer.

  Next, an embodiment of the present invention will be described based on the examples shown in FIGS. FIG. 1 is a schematic configuration diagram of a fuel reforming apparatus showing an embodiment of the present invention. In FIG. 1, members that are similar or have the same functions as those shown in FIG. The basic difference between FIG. 1 and FIG. 4 is that in FIG. 1, a hygrometer 15 and a control line for connecting the hygrometer and the control device 13 are provided.

  In FIG. 1, the fuel gas humidifier 9 and the fuel gas humidifying water pump 10 shown in FIG. 4 and some control lines shown by broken lines are omitted, but the hygrometer 15 is a fuel gas (not shown). It is provided in front of the humidifier 9.

  In the embodiment shown in FIG. 1, a hygrometer 15 is provided between the fuel reformer and the fuel cell 6, and the dew point of the reformed gas is determined by the control device 13 based on the fuel cell output and the fuel gas flow rate. The dew point is monitored within a certain range, and when the dew point exceeds a predetermined threshold, it is determined that an abnormality has occurred and the operation of the fuel cell 6 and the operation of the fuel reformer including 2, 3, 4, 5 are performed. By stopping, the fuel cell and the reformer can be stopped without imposing a burden.

  The dew point and threshold of the reformed gas will be described in detail later, and FIG. 2 will be described first. FIG. 2 is a schematic configuration diagram showing a different embodiment of the fuel cell power generator of the present invention. The difference between FIG. 1 and FIG. 2 is that, in FIG. 2, a carbon monoxide transformer temperature measurement point 14a and a control line connecting this to the control device 13 are provided.

  In the embodiment shown in FIG. 2, when the controller 13 determines that an abnormality has occurred based on the dew point indication value of the hygrometer 15, the voltage of the steam reforming water supply pump 8 is increased to increase the flow rate of the steam reforming water. Thus, based on the temperature detection at the carbon monoxide transformer temperature measurement point 14a, the temperature of the carbon monoxide transformer 4 is controlled to be kept at an appropriate temperature, without burdening the fuel cell or the fuel reformer. Driving can be continued. Alternatively, by reducing the current value of the fuel cell 6 by the control device 13 and reducing the amount of the reforming raw material gas accordingly, the operation can be continued while reducing the amount of reaction gas and decreasing the methanation reaction. By returning to a predetermined operation output after the indicated value of the hygrometer 15 is stabilized, stable operation can be continued.

  Next, how to determine the dew point of the reformed gas and its threshold value will be described. The theoretical dew point of the reformed gas can be calculated based on the amount of raw material gas, S / C (water amount), reforming rate (reforming temperature), shift temperature, selective oxidized air amount, and the like. The dew point in a certain range determined by the fuel cell output and the fuel gas flow rate mentioned above means the amount of raw material gas corresponding to the required fuel cell output, the basic prescribed amount of S / C, and the actual fuel cell system In this case, the dew point is in a substantially constant range, although there is a slight increase / decrease for controlling the temperature and the like.

  However, in the current fuel cell system, because the hydrogen utilization rate of the fuel cell differs between the rated and low load, the rate of heat burned by the fuel reformer varies, the reforming temperature changes, and the gas amount Due to the difference in reactivity due to the difference in dew point, even with the same S / C due to changes in fuel cell output (gas amount, combustion amount, reforming temperature change), there is a slight difference in dew point.

  On the other hand, however, the humidity change at the time of abnormality of the fuel reformer changes suddenly and greatly as shown in FIG. 3, and thus exceeds the humidity change region associated with the S / C change amount on the system. FIG. 3 is a graph showing changes with time in the catalyst layer temperature and reformed gas humidity when an abnormality occurs in the fuel reformer. According to FIG. 3, the humidity increase S point can be detected about 5 minutes earlier than the temperature increase T point, and in the case of abnormality, the reformed gas humidity increases at an earlier timing than the catalyst layer temperature increase, and the humidity The change in humidity after the rising S point is relatively rapid and large.

  Therefore, the dew point threshold value of the reformed gas can be set by setting a value obtained by slightly adding temperature to the upper limit value of the dew point calculated from the operating conditions in the system. Actually, a threshold value for each load of the fuel cell may be set in advance, and the threshold value may be determined and monitored from “fuel cell output and fuel gas flow rate” during operation.

Next, specific examples of how to determine the threshold value for abnormality determination will be described below for a case of a general hydrogen utilization facility and a case of a fuel cell power generator.
1) In the case of hydrogen-utilizing facilities Use a precious metal system (Pt system or Ru system) as the catalyst, operate at a constant S / C (for example, 3), and the dew point at normal times varies depending on the reforming catalyst layer temperature. Is the humidity of the reformed gas corresponding to a dew point that is 10 ° C. plus the upper limit value of the dew point that is constant in the range of 60 to 65 ° C.
2) In the case of a fuel cell power generator (1) The above-mentioned noble metal system is used as a catalyst, the S / C is operated at a constant (for example, 3), and reforming is performed from the rated operating conditions such as the fuel gas flow rate corresponding to the fuel cell output. The normal dew point of the gas is determined by calculation, and the humidity of the reformed gas corresponding to the dew point plus α (for example, 10 ° C.) is used as the threshold value.
(2) When the fuel cell output and other operating conditions change, prepare a calculation table for the dew point according to the change in the operating conditions, and add the reformed gas corresponding to the dew point plus α to each calculated value. Humidity is a threshold value.
(3) When performing control to temporarily increase the S / C after detecting the abnormality of the fuel reformer, the dew point increases due to the increased steam, so according to the S / C to be temporarily increased To change the threshold setting.

The schematic block diagram which shows the Example of the fuel cell electric power generating apparatus of this invention. The schematic block diagram which shows the Example from which the fuel cell electric power generating apparatus of this invention differs. The figure which shows the time-dependent change of the catalyst layer temperature at the time of abnormality of a fuel reformer, and reformed gas humidity. The schematic block diagram of the conventional fuel cell power generator which uses a fuel reformer.

Explanation of symbols

  1: desulfurizer, 2: steam generator, 3: reformer, 4: carbon monoxide converter, 5: carbon monoxide remover, 6: fuel cell, 8: water supply pump for steam reforming, 11: oxidation Gas humidifier, 12: oxidizing gas humidifying water pump, 13: controller, 14a: carbon monoxide transformer temperature measurement point, 15: hygrometer.

Claims (6)

A reformer that reforms a hydrocarbon-based fuel into a reformed gas rich in hydrogen, and a carbon monoxide converter and / or a carbon monoxide remover that reduces the concentration of carbon monoxide in the reformed gas, In a fuel reformer that supplies the resulting reformed gas to a hydrogen utilization facility,
A hygrometer that measures the humidity of the reformed gas is provided downstream of the carbon monoxide converter or carbon monoxide remover and upstream of the hydrogen utilization facility, and a dew point indication value of the hygrometer is predetermined. A fuel reformer that determines that an abnormality has occurred in the fuel reformer when the threshold value is exceeded.   2. The fuel reformer according to claim 1, wherein the catalyst used in the carbon monoxide converter and / or the carbon monoxide remover is a methanation in which carbon monoxide or carbon dioxide reacts with hydrogen to produce methane. A fuel reformer characterized by being a catalyst that causes a reaction.   3. A fuel cell power generator that generates electric power using the reformed gas reformed by the fuel reformer according to claim 1 or 2 on a line through which the reformed gas flows from the fuel reformer to the fuel cell power generator. A fuel cell power generator comprising: a hygrometer, and determining that an abnormality has occurred in the fuel reformer when a dew point indication value of the hygrometer exceeds a predetermined threshold value.   4. The method of operating a fuel cell power generator according to claim 3, wherein the fuel cell power generator is stopped when it is determined that an abnormality has occurred in the fuel reformer. .   4. The method of operating the fuel cell power generator according to claim 3, wherein when it is determined that an abnormality has occurred in the fuel reformer, the operation is continued by reducing the load of the fuel cell power generator. Operation method of fuel cell power generator.   4. The method of operating a fuel cell power generator according to claim 3, wherein when it is determined that an abnormality has occurred in the fuel reformer, the flow rate of reforming water input to the fuel reformer is increased and carbon monoxide is increased. An operation method for a fuel cell power generator, wherein the operation is continued by lowering the temperature of the transformer and / or the carbon monoxide remover.

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