JP4938299B2 - Operation method of fuel cell power generator - Google Patents

Description

  The present invention provides a fuel cell that supplies a hydrocarbon compound such as city gas, LPG, and methanol as a raw fuel to a reformer and performs steam reforming, and generates electricity using the resulting hydrogen-rich reformed gas as a fuel, A fuel comprising a hydrogen production and supply means that branches the reformed gas from a reformed gas supply pipe to a fuel cell, supplies the hydrogen to a hydrogen purifier, and generates high-purity hydrogen, which can be supplied outside the fuel cell. The present invention relates to a method for operating a battery power generator.

  As described above, the configuration of the fuel cell power generation apparatus including the fuel cell that generates power using the reformed gas as fuel and the hydrogen production and supply means that purifies the reformed gas is partly the same as the inventor of the present application. This is disclosed in the patent document 1 filed. FIG. 5 is a basic system diagram showing the configuration of the reaction gas system of the fuel cell power generator disclosed in Patent Document 1 as FIG.

  To quote the description of Patent Document 1, FIG. 5 shows that “the raw gas is reformed by the reformer 2 and the resulting reformed gas is used as the fuel gas supplied to the fuel electrode 1 b of the fuel cell 1. The fuel cell in which the obtained reformed gas is connected to the fuel electrode 1b of the fuel cell 1 with a branch pipe for branching the reformed gas to the hydrogen purification system including the compressor 4 and the hydrogen purifier 5. Disclosed is “power generation device”. In FIG. 5, 1a is an air electrode, 1c is a cooling plate, 2a is a reformer burner, 2b is a reforming catalyst layer, 3 is a generated water recovery device, and 6 and 7 are valves.

According to the fuel cell power generation apparatus having the configuration of Patent Document 1, “For example, during the daytime, the reformed gas supply destination is selected as the fuel electrode of the fuel cell to perform the power generation operation of the fuel cell, and the power demand amount. At night when the electricity purchase price is low and the electricity purchase price is low, the power generation operation of the fuel cell is stopped and the reform gas supply destination is switched to the hydrogen purification system to produce high-purity hydrogen, which is stored directly or in a tank. Thus, a method of supplying to the user can be adopted, and the reformer is effectively operated regardless of whether or not the fuel cell is in the power generation operation, so that a fuel cell power generator that is operated efficiently can be obtained. "
By the way, in patent document 1, about the concrete method for controlling the temperature of a reformer to the appropriate range which can be operated, and enabling supply of the quantity of high-purity hydrogen according to a demand outside a power generator. There is no description, and there is no particular disclosure in other prior art documents. In order to supply a high-purity hydrogen amount in response to the request, there are the following problems related to the temperature control of the reformer, which will be described in detail below.

  The fuel cell hydrogen utilization (ratio of the amount of hydrogen consumed in the reaction of the fuel cell to the amount of hydrogen supplied to the fuel cell) should be operated as high as possible in order to improve the efficiency of the generator. As an example, the phosphoric acid fuel cell is designed to operate at a hydrogen utilization rate of about 80%. On the other hand, in a PSA (Pressure Swing Adsorption) apparatus generally used as a hydrogen purification apparatus, the hydrogen yield (ratio of the amount of high-purity hydrogen to be separated and purified with respect to the amount of hydrogen supplied to the PSA) is Although there are differences depending on the capacity and operating conditions, it is about 70%.

  By the way, in order to improve the power generation efficiency and hydrogen production efficiency in the entire system, hydrogen is separated and purified by PSA with unreacted hydrogen and fuel off-gas containing flammable components such as methane and carbon monoxide. It is desirable that the residual gas containing hydrogen, methane, carbon monoxide and the like after being supplied is supplied to the reformer burner and used as a heat source for the reforming reaction.

  In general, the reformer has pursued an optimal design for a fuel cell. As a result, the hydrogen utilization rate is about 80%, and the fuel off-gas after consuming hydrogen in the fuel cell is burned by the burner of the reformer. Is designed to balance. If the hydrogen yield of PSA is about 80%, which is the same as the hydrogen utilization rate of the fuel cell, the remaining gas after hydrogen is generated and separated by PSA is burned in the reformer burner together with the fuel off-gas in the fuel cell. Even in such a case, no special control for adjusting the heat balance is required.

  Also, when the hydrogen yield of PSA exceeds 80%, the calorific value of the residual gas in PSA is smaller than that of fuel off-gas in the fuel cell, and is input to the reformer burner. The total calorific value of the generated gas is lower than the calorific value necessary for reforming. Therefore, in this case, since the shortage can be compensated for by reducing the hydrogen utilization rate in the fuel cell and increasing the calorific value of the fuel off gas, the control becomes easy and there is no wasteful consumption of energy.

  However, since the hydrogen yield of currently available PSA is about 70%, the calorific value of the residual gas in PSA is unit compared to the calorific value of the fuel off-gas in a fuel cell with a hydrogen utilization rate of 80%. The value per flow rate is large, and when the entire amount of residual gas in the PSA and fuel off-gas in the fuel cell is burned by the burner of the reformer, it becomes an excessive heat amount state compared to the necessary heat amount. This causes a problem that the temperature of the structural member and the catalyst rises excessively.

  In order to avoid such problems and maintain the reformer temperature at an appropriate temperature without wastefully releasing a part of the residual gas in the PSA, the amount of heat required for the reforming reaction is reduced. On the other hand, it is necessary to appropriately process the surplus heat amount in the apparatus.

In the reformer temperature control of a conventional fuel cell power generator equipped with hydrogen production and supply means, in order to protect the structural members and the filled catalyst, the flow rate of combustion air is increased when the temperature rises excessively. That prevented the temperature from rising. However, in consideration of the pressure loss of the reformer combustion exhaust gas system, the combustion air flow rate cannot be increased without limitation, and an upper limit combustion air flow rate naturally exists.
JP 2000-348750 A

  The present invention has been made in view of the above points, and an object of the present invention is to provide a reformer without wasting a part of the residual gas in the hydrogen purifier (PSA) out of the system. An object of the present invention is to provide a method of operating a fuel cell power generation apparatus having a hydrogen production and supply means that can maintain a temperature at an appropriate temperature and can supply high-purity hydrogen in an amount as required.

In order to solve the above-described problems, the present invention is as follows .

Immediately Chi, a raw fuel gas containing the raw fuel and water vapor comprising a hydrocarbon compound, reformed by a reformer having a burner for the reaction heat supply, the reformed gas rich in hydrogen obtained a fuel cell A fuel cell used as a fuel gas, and a hydrogen production branching the reformed gas from a reformed gas supply pipe to the fuel cell and supplying it to a hydrogen purifier to produce high-purity hydrogen that can be supplied outside the fuel cell A fuel cell power generation apparatus comprising a supply means, wherein a hydrogen yield in the hydrogen purification apparatus is lower than a hydrogen utilization rate in the fuel cell. When the later fuel off-gas and the residual gas after hydrogen purification in the hydrogen purifier are supplied to the burner of the reformer and combusted and the temperature of the reformer rises, it depends on the reformer temperature. System Adjusting the combustion air flow rate to be lowering the temperature of the reformer, when the combustion air flow rate has reached the predetermined upper limit value, S / C (steam to carbon atoms 1 mole of the raw fuel gas The temperature of the reformer is lowered by increasing the molar ratio) (Claim 1 ).

According to the first aspect of the present invention, when the temperature of the reformer rises, the combustion air flow rate is adjusted to lower the reformer temperature, and this combustion air flow rate reaches a predetermined upper limit value. In this case, the S / C is increased. By increasing the S / C, the ratio of converting the raw fuel, which is a hydrocarbon compound, to hydrogen is improved, and the endothermic amount according to, for example, the following formula (Chemical Formula 1) related to the steam reforming reaction of the hydrocarbon compound is reduced. As it increases, the proportion of methane and carbon monoxide decreases with respect to the proportion of hydrogen in the reformed gas.

  As a result, the concentration of methane and carbon monoxide in the fuel off-gas after consuming hydrogen in the fuel cell and the residual gas after separating and purifying high-purity hydrogen in the hydrogen purifier decreases and burns in the reformer burner. Since the calorific value per unit flow rate of gas decreases, it is possible to suppress an excessive increase in the reformer temperature. Further, by increasing the S / C, the amount of water vapor that does not contribute to the reaction increases, but the amount corresponding to the amount of heat required for heating this excess water vapor also contributes to the consumption of the excessive amount of combustion heat.

  In other words, an increase in S / C suppresses excessive temperature rise in the reformer, with the dual effect of increasing the conversion rate of raw fuel to hydrogen, increasing the amount of heat absorbed, and increasing the amount of heat removed from the reformer. can do.

As an embodiment of the invention of claim 1, the inventions of claims 2 to 4 below are preferable. That is, in the operation method of the fuel cell power generator according to claim 1, the hydrogen purifier is a pressure swing adsorption (PSA) device (claim 2 ). Further, in the operation method of the fuel cell power generator according to claim 1, the value of S / C when increasing the S / C is set to 3.25 or more (claim 3 ). Furthermore, in the operation method of the fuel cell power generation device according to claim 1, the reforming steam recovers water generated by a power generation reaction of the fuel cell, and the recovered water is generated by reaction heat of the fuel cell. It is assumed that it has been evaporated (claim 4 ). Details will be described later.

  When the reformed gas is branched from the reformed gas supply pipe of the fuel cell and supplied to the hydrogen purifier, it is necessary to install a compressor between them depending on the operating pressure of the reformer and the hydrogen purifier.

  According to this invention, the reformer temperature is maintained at an appropriate temperature without wastefully releasing a part of the residual gas in the hydrogen purifier (PSA) to the outside of the system, and a high amount according to the request is provided. It is possible to provide a method for operating a fuel cell power generation apparatus including hydrogen production and supply means capable of supplying pure hydrogen.

  An embodiment of the present invention will be described below based on FIGS.

  FIG. 1 is a basic system diagram of a fuel cell power generator according to an embodiment of the present invention. In FIG. 1, members having the same functions as those shown in FIG. In FIG. 1, illustration of the generated water recovery device 3, valves 6, and 7 in FIG. 5 is omitted. On the other hand, in FIG. 1, there are members added to FIG. 5, which will be described in the following description of the configuration and operation of FIG.

  In FIG. 1, reference numeral 1 denotes a fuel cell schematically shown. A plurality of single cells each having an air electrode 1a and a fuel electrode 1b are stacked, and a cooling plate 1c for keeping the fuel cell 1 at a predetermined temperature is provided. The battery cooling water is passed through the cooling plate 1c from the lower side of the water vapor separator 8 through the cooling water circulation pump 9. The fuel gas used for power generation of the fuel cell 1 is mixed with a raw material fuel of a hydrocarbon compound such as city gas, LPG and methanol and water vapor and introduced into the reformer 2 to improve the reforming catalyst layer 2b. A reformed gas rich in hydrogen obtained by a quality reaction is used.

  In FIG. 1, the steam generated by the steam separator 8 by the heat obtained by cooling the fuel cell 1 is used as the reforming steam. In the phosphoric acid fuel cell, the reaction temperature is 180 to 200 ° C., and steam can be directly generated by the heat obtained by cooling. In the polymer electrolyte fuel cell, the reaction temperature is about 80 ° C., so the hot water obtained by cooling is further heated to obtain water vapor. Also, in molten carbonate type (reaction temperature: about 600 ° C) and solid oxide type (reaction temperature: about 1000 ° C) high-temperature fuel cells, use a gas fluid such as air instead of water to cool the cells. Although it is cooled, water vapor is generated by exchanging heat between the gas used for cooling and water, and it is generally used for the reforming reaction, and water vapor is generated by the heat obtained by cooling the battery. Are the same. The steam separator 8 is usually supplied with recovered water from the generated water recovery device 3 shown in FIG. 5, and the recovered water is evaporated to obtain reforming steam.

  Furthermore, the fuel cell power generator in which the operation method of the present invention is implemented has a branch pipe in the pipe for supplying the reformed gas obtained by the reformer 2 to the fuel electrode 1b of the fuel cell 1, and the compressor 4 The reformed gas is introduced into a hydrogen purification system equipped with a hydrogen purifier 5. The hydrogen purifier 5 is a pressure swing adsorption (PSA) device that selectively adsorbs and separates specific gas species by filling a plurality of containers with adsorbents such as activated carbon and zeolite and changing the pressure, and has selective permeability. Use a membrane separator or the like. The high-purity hydrogen gas separated by the hydrogen purifier 5 is used for raw materials, atmospheric gases, etc. in semiconductor manufacturing, metal refining, oil and fat manufacturing, oil refinery / chemical industry, etc., and pressurization to obtain driving power or power for automobiles. It can also be used as a fuel.

  Next, the flow of raw fuel, water vapor and each gas, flow rate control, etc. will be described. In FIG. 1, the raw fuel flow rate measured by the flow meter F1 is controlled by the flow control valve FV-1 according to the load of the fuel cell 1 and the reformed gas flow rate supplied to the hydrogen purification system. The reforming steam measured by the flow meter F2 determines a flow set value by applying a constant to the raw fuel flow measured by F1, and is controlled by the flow control valve FV-2. S / C is the mole ratio of water vapor to 1 mole of carbon atoms in the hydrocarbon-based compound, which is the raw fuel, with respect to the raw fuel and water vapor input to the reforming catalyst layer 2b. The measured value F1 of the raw fuel flow rate is multiplied by the number of carbon atoms determined by the raw fuel composition and the set value of S / C (for example, 3.0) to determine the set value of the water vapor flow rate.

  By the steam reforming reaction in the reforming catalyst layer 2b heated by the reformer burner 2a, the hydrocarbon-based compound is converted into a reformed gas mainly composed of hydrogen, carbon dioxide, and carbon monoxide. Of these, carbon monoxide poisons platinum used as a catalyst for fuel cell electrodes and degrades performance, so the reformed gas is converted from hydrogen monoxide and water vapor from carbon monoxide and water vapor by a carbon monoxide converter (not shown). After conversion to carbon, the fuel cell as a gas with a hydrogen concentration of about 60% (more than 70% excluding water vapor) and carbon dioxide of about 20% (the remainder is water vapor, methane, and some amount of carbon monoxide) 1 to the fuel electrode 1b.

  As described above, when the fuel gas rich in hydrogen is sent to the fuel electrode 1b and allowed to react in the fuel cell 1, hydrogen that is found in a predetermined utilization rate is consumed with the reaction. The fuel off-gas discharged from the fuel electrode 1b still contains a certain amount of hydrogen, which is introduced into the reformer burner 2a of the reformer 2 and mixed and burned with separately supplied combustion air. This is used for heating the reforming catalyst layer 2b. Air is supplied to the air electrode 1a of the fuel cell 1 by a blower or a compressor (not shown) and used for the reaction.

  On the other hand, the residual gas after separating hydrogen from the reformed gas supplied to the hydrogen purifier 5 is a mixture of hydrogen, methane, carbon monoxide flammable components, carbon dioxide, and water vapor. The fuel is introduced into the reformer burner 2a and burned in the same manner as the fuel off-gas of the fuel electrode 1b, and used as a heat source for the reforming reaction.

  The reforming reaction in the reformer 2 is an endothermic reaction, and the amount of heat necessary for the reaction must be continuously and stably supplied. In the reformer 2, the temperature of the reforming catalyst layer 2b is measured with a thermometer T and temperature control is performed. When the temperature is lower than the set temperature of the reforming catalyst layer 2b (for example, 700 to 800 ° C. in the case of city gas), the input amount of raw fuel is increased, and unreacted combustible gas at the fuel electrode 1b. This is provided by increasing the flow rate and heating value of the gas that increases the components and returns to the reformer burner 2a.

  The temperature measurement position is preferably the reforming catalyst layer, particularly the reformed gas outlet of the catalyst layer. However, since the correlation between the temperatures of the respective parts is known in advance by design, for example, the temperature of the container wall filled with the reforming catalyst layer, etc. The position of the reformer can be a representative position.

  On the other hand, when the temperature is higher than the setting, it can be dealt with by increasing the combustion air flow rate. However, from the pressure loss of the reformer burner 2a and piping, the capability of the air blower not shown in FIG. There is an upper limit for the combustion air flow rate. If the catalyst layer temperature of the reformer does not decrease to the set value even when the combustion air flow rate reaches the upper limit, the S / C is increased, the calorific value of the gas returning to the reformer burner 2a is decreased, and the reforming reaction is performed. As a result, the temperature of the catalyst layer of the reformer is reduced and the combustion air flow rate falls within a controllable range. Alternatively, when the temperature of the reformer increases and reaches a predetermined temperature, the temperature of the reformer is decreased by increasing the S / C of the raw fuel gas supplied to the reformer.

  Next, control for increasing S / C will be described in more detail based on an embodiment in the case where the present invention is applied to a phosphoric acid fuel cell.

  Conventionally, the setting value of S / C, which has been generally adopted in fuel cell power generators, is 3.0. Table 1 shows the reformed gas composition (dry%) at the fuel cell inlet (PSA inlet has the same composition) when this is 3.25, 3.5.

The reforming reaction in the reformer 2 is, for example, reforming into hydrogen, carbon dioxide, or carbon monoxide by the reaction of a hydrocarbon compound such as methane with steam, but the amount of steam in the reaction system is increased. As a result, the reaction proceeds further, the methane concentration in the production system decreases, and the hydrogen concentration increases. Accordingly, the fuel off-gas after the reformed gas has consumed hydrogen in the fuel cell 1 and the residual gas after the hydrogen is separated and purified by PSA, the calorific value per unit amount decreases as the S / C increases. . FIG. 2 shows the result. When the S / C is changed, the outlet fuel after being subjected to power generation by the fuel cell (ie, fuel off-gas) and the return gas after purifying and separating hydrogen by PSA (ie, , The amount of heat generated per unit amount of residual gas). In FIG. 2, it is assumed that the fuel cell consumes hydrogen at a hydrogen utilization rate of 80%, and PSA calculates the heating value of each outlet gas with a hydrogen yield of 72%.

  Compared with the change in the composition in Table 1, the change in the calorific value of the gas in FIG. 2 is large, but this is because the hydrogen concentration becomes higher due to the change in S / C, so the amount of reformed gas to be supplied is less than the required amount of hydrogen. As a result, the amount of combustible components other than hydrogen, methane and carbon monoxide, is reduced.

Next, FIG. 3 will be described. FIG. 3 is a diagram showing a combustion air flow rate necessary for combustion of the reformer burner with respect to a change in S / C. The combustion air flow rate shown in FIG. 3 indicates the combustion air flow rate in the following case. Assuming a fuel cell power generation device with a hydrogen production function that combines a fuel cell with a power generation capacity of 100 kW and PSA, the reformed gas to be supplied to the PSA for 75% (= 75 kW) power generation output and hydrogen purification When the flow rate is 30 Nm ³ / h, the fuel off-gas after the consumption of hydrogen by the reaction of the fuel cell and the total amount of residual gas after separation and purification of hydrogen by PSA are returned to the reformer burner for combustion. Considering the case of using as a heat source for the reforming reaction, the combustion air flow rate in this case is shown in FIG. The combustion air flow rate was calculated as an amount capable of maintaining the optimum operation temperature determined by the structural members of the reformer, after the combustion exhaust gas temperature after being used for heating the reformer.

In FIG. 3, a dotted line is attached at a combustion air flow rate of 110 Nm ³ / h. This is the maximum value of the combustion air flow rate when designing a 100 kW fuel cell, for example. If this flow rate is exceeded, excessive increase in pressure loss in combustion system equipment and piping, lack of air blower capacity, etc. will be caused, and the design of the fuel cell needs to be changed. On the other hand, if the S / C is increased from 3.0 to 3.25, 3.5, the amount of heat generated by the gas returning to the burner decreases, so the amount of air required for combustion can be reduced, and as shown in FIG. It is within the scope of the original plan, and no equipment design changes are required.

  According to the present invention, a fuel cell optimized with a high hydrogen utilization rate and a relative hydrogen separation capacity (hydrogen yield) can be obtained by simply changing the set value of S / C, which is one of the operation parameters of the reformer. Even in the case where a fuel cell power generation device having a hydrogen production and supply function is combined by combining a hydrogen purification device with a low rate), it can be operated without changing the constituent devices of the fuel cell.

  The amount of water vapor required for the reforming reaction increases with the increase in S / C, but even if S / C is increased from 3.0 to 3.25 or 3.5, it can be covered by the amount of water vapor generated by the reaction heat of the fuel cell. Yes, it is not necessary to supply a separate heat source for generating steam from outside the apparatus, and it does not affect the power generation efficiency and hydrogen production efficiency of the entire system. That is, by setting the S / C value when increasing the S / C to be 3.5 or more, there is an effect that the design value of the combustion air amount of the fuel cell is below the design value and there is no need to change the device design.

  Next, FIG. 4 will be described. FIG. 4 is a diagram schematically showing the relationship between the load as the power generation device and the flow rate of each part according to the present invention. When a part of the reformed gas is taken out and put into a hydrogen purification system equipped with a reformed gas compressor and a hydrogen purifier in series, the power generation load of the fuel cell is not changed, and the reformed gas that is thrown into the fuel cell The flow rate is also constant. However, when the reformed gas is taken out and charged into the hydrogen purification system, the power generation load of the fuel cell is lower than the rated 100% load. The value varies depending on the reformed gas flow rate to be taken out, but is about 65% to 80% load. This is because if the power generation load is 100% (that is, the reformed gas production amount is also 100% in this case), there is no room for taking out the reformed gas outside the fuel cell.

  Further, as shown in FIG. 4, the raw fuel flow rate is increased in accordance with the reformed gas flow rate input to the hydrogen purifier so that the reformed gas flow rate input to the fuel cell is not changed. Although the reforming steam flow rate is not shown in the figure, the steam flow rate is also increased or decreased in accordance with the raw fuel flow rate. Since the raw fuel flow rate also has a design upper limit value, the total reformed gas flow rate that is input to the fuel cell and the hydrogen purification system does not exceed the total reformed gas flow rate that was found in the upper limit value of the raw fuel. Thus, the flow rate of the reformed gas introduced into the hydrogen purification system is controlled.

1 is a basic system diagram of a fuel cell power generator according to an embodiment of the present invention. The figure which shows the change of the emitted-heat amount of a fuel cell exit fuel and PSA return gas when S / C is changed. The figure which shows the combustion air flow rate required by combustion of a reformer burner with respect to the change of S / C. The figure which shows typically the relationship between the load as an electric power generating apparatus, and the flow volume of each part concerning this invention. 1 is a basic system diagram of a fuel cell power generator disclosed in Patent Document 1. FIG.

Explanation of symbols

  1: fuel cell, 1a: air electrode, 1b: fuel electrode, 1c: cooling plate, 2: reformer, 2a: reformer burner, 2b: reforming catalyst layer, 3: generated water recovery device, 4: compression 5: Hydrogen purifier, 8: Steam separator, 9: Cooling water circulation pump

Claims (4)

A raw fuel gas comprising a hydrocarbon-based raw fuel and steam is reformed by a reformer having a burner for supplying reaction heat, and the resulting hydrogen-rich reformed gas is used as a fuel gas for a fuel cell. A fuel cell to be used; and a hydrogen production and supply means for branching the reformed gas from a reformed gas supply pipe to the fuel cell and supplying the reformed gas to a hydrogen purifier to generate high-purity hydrogen, which can be supplied outside the fuel cell. In the operating method of the fuel cell power generator, the hydrogen yield in the hydrogen purifier is lower than the hydrogen utilization rate in the fuel cell.
When the fuel off gas after the power generation reaction in the fuel cell and the residual gas after the hydrogen purification in the hydrogen purifier are supplied to the burner of the reformer and burned, and the temperature of the reformer rises The combustion air flow rate controlled by the reformer temperature is adjusted to lower the reformer temperature, and when this combustion air flow rate reaches a predetermined upper limit value, S / C (in the raw fuel gas A method of operating a fuel cell power generator, wherein the temperature of the reformer is lowered by increasing the mole ratio of steam to 1 mole of carbon atoms) . 2. The operation method of a fuel cell power generation device according to claim 1 , wherein the hydrogen purification device is a pressure swing adsorption (PSA) device. 2. The method of operating a fuel cell power generator according to claim 1 , wherein the value of S / C when increasing the S / C is 3.25 or more. 2. The operation method of a fuel cell power generation device according to claim 1 , wherein the reforming steam recovers water generated by a power generation reaction of the fuel cell, and evaporates the recovered water by reaction heat of the fuel cell. A method for operating a fuel cell power generation device.

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