JP2006156015A - Fuel cell system and fuel gas supply method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of obtaining a total amount of water necessary for fuel reforming from fuel exhaust gas. <P>SOLUTION: In a solid oxide type fuel cell 1 having a fuel reformer 11, a desired amount of fuel exhaust gas from a fuel electrode 2 side is divided into division passages 6, and distributed fuel exhaust gas is sent to a condenser 12 for generating condensed water. The condensed water is mixed with raw fuel G without using other service water and sent to the fuel reformer 11, and then, the reformed fuel gas is sent to the fuel electrode 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system using a solid oxide fuel cell and a method for supplying fuel gas to a fuel electrode thereof.

As described in Patent Document 1, Patent Document 2, and the like, a solid oxide fuel cell (SOFC) is known as one of fuel cells. SOFC has a high operating temperature of 800 ° C. to 1000 ° C., and not only pure hydrogen but also methane, carbon monoxide and the like can be directly used for power generation as fuel. For this purpose, city gas and LP gas are used as SOFC fuel, and city gas contains ethane, propane, butane, etc. having C _{2 to} C ₄ in addition to methane as a main component. Therefore, a reforming process for reforming methane and C ₂ or more hydrocarbons to hydrogen and carbon monoxide is finally performed, and the reformed fuel gas is sent as fuel to the fuel electrode of the SOFC.

  The above-described reforming treatment is generally performed by mixing city gas as raw fuel and heated steam and bringing them into contact with a reforming catalyst. In Patent Documents 1 and 2, mixing of raw fuel (city gas) and heated steam is mixed with city gas by steaming city water, or the fuel exhaust gas on the fuel electrode side of SOFC is hot and generates power. Since it contains water (steam) as a product, it is described that exhaust gas containing steam is mixed with raw fuel (city gas) or both.

Japanese Patent Laid-Open No. 7-230816 JP 2003-229164 A

  When city water is used for supplying steam accompanying fuel reforming, it is necessary to separately provide a water treatment device for removing impurities contained in city water. The water (steam) contained in the fuel exhaust gas has a higher purity than that of city water. If pure water required for reforming can be obtained from the fuel exhaust gas containing water vapor, the water supply in the power generation system is substantially reduced. The water supply facility and water treatment facility provided outside the system can be omitted or greatly simplified, and the fuel cell system can be simplified.

  In the case of a fuel cell system equipped with SOFC, the fuel exhaust gas contains a sufficient amount of water and a sufficient amount of heat required for fuel reforming, and theoretically without introducing city water from the outside. The required fuel reforming can be performed. However, the operating temperature of SOFC is as high as 800 ° C to 1000 ° C, and the temperature of the fuel exhaust gas is so high, and there is no fan that can withstand that temperature as a general-purpose product. Therefore, it is extremely difficult to mix with city gas as raw fuel, and it is practically impossible. Although it is possible to reduce the temperature of the fuel exhaust gas to some extent by passing it through an appropriate heat exchanger, it is not easy to recover from the magnitude of the heat to the latent heat if the fuel exhaust gas is completely heat exchanged. Condensed water cannot be obtained unless a large external condenser is separately provided as in the case of.

  For this reason, in a fuel cell system equipped with SOFC as a power generation device, the procurement of the entire amount of pure water necessary for reforming raw fuel from fuel exhaust gas has not yet been put into practical use at the actual equipment level. It is. The present invention has been made in view of the above circumstances, and in a fuel cell system including a solid oxide fuel cell (SOFC) including a fuel reformer, pure water required for fuel reforming is provided. It is an object of the present invention to provide a fuel cell system and a method for supplying fuel gas to a battery fuel electrode, which make it possible to procure the entire amount from fuel exhaust gas at the actual machine level as a power generator.

  The fuel cell system according to the present invention basically includes a fuel exhaust gas distribution path in a fuel exhaust gas flow path from the fuel electrode side of a solid oxide fuel cell equipped with a fuel reformer, and water vapor distributed to the distribution path. It is characterized by the fact that a condenser capable of recovering latent heat from fuel exhaust gas containing water to obtain condensed water is arranged, and the generated condensed water is mixed with raw fuel and sent to the fuel reformer. To do.

  The fuel gas supply method according to the present invention is basically a fuel gas supply method to a fuel electrode of a solid oxide fuel cell equipped with a fuel reformer, and includes a fuel containing water vapor from the fuel electrode side. The desired amount of exhaust gas is distributed to the distribution passage, the fuel exhaust gas distributed to the desired amount is sent to the condenser to generate condensed water, and only the condensed water generated without using other city water is mixed with the raw fuel. Thereafter, the fuel gas is fed into a fuel reformer, and the reformed fuel gas is fed into the fuel electrode.

  In the present invention, during operation of a solid oxide fuel cell (SOFC), pure water is produced in an amount (or slightly larger amount) necessary for reforming the supplied raw fuel (for example, city gas). An amount of fuel exhaust gas containing as much water vapor as possible is distributed from the total amount of fuel exhaust gas. And it collect | recovers from fuel exhaust gas distributed with the condenser to latent heat, produces | generates condensed water, mixes it with raw fuel, without using other city water etc., and performs the required modification | reformation. This is a heat recovery process for the distributed amount, not the total amount of the high-temperature fuel exhaust gas, and it can be sufficiently handled by a normally available condenser. Moreover, since city water is not used, it is not necessary to install a water purification device or the like outside, or the water purification device can be simplified and water supply to the system can be completed within the system. Therefore, the system can be simplified. The fuel exhaust gas that has not contributed to the generation of condensed water can be sent to another exhaust heat utilization section while retaining high thermal energy, and the overall thermal efficiency is also improved.

  The amount of distribution varies depending on the power generation capacity of the solid oxide fuel cell used in the fuel cell system or the capacity load ratio during operation. An optimum amount may be selected while actually measuring. Therefore, it is preferable to provide a flow rate adjusting means capable of adjusting the distribution amount of the fuel exhaust gas to the distribution path continuously or stepwise. The maximum amount of fuel exhaust gas required for fuel reforming in actual operation may be predicted in advance, and a fixed bypass path that distributes that amount of fuel exhaust gas may be provided as a distribution path. In this case, some energy loss occurs during low-load operation, but the system is further simplified.

  It is desirable that the condensed water is heated or steamed and mixed with the raw fuel. For this purpose, the condenser is provided with a heat exchanging means between the generated condensed water and the flowing fuel exhaust gas, and the generated condensed water is heated by exchanging heat with the heat of the fuel exhaust gas with the condenser, It is more preferable and realistic to configure the mixing. Also, even if the distributed fuel exhaust gas is small in quantity, it still has a large amount of heat, so that the distributed fuel exhaust gas reaches the condenser in order to reduce the heat recovery burden on the condenser. Therefore, it is desirable to construct a system so that the desired heat exchange can be performed between the fuel exhaust gas and other materials. Examples of other materials for performing heat exchange include air (oxidant) sent to the air electrode, raw fuel such as city gas, and reformed fuel gas.

  In the present invention, conventionally known solid oxide fuel cells and fuel reformers as described in Patent Documents 1 and 2 described above can be used as they are. The same applies to the condenser, and the existing condenser can be used as it is. Further, in the present invention, when it is predicted that it may be impossible to procure fuel exhaust gas containing the amount of steam necessary for reforming, such as at the time of start-up or sudden load fluctuations, Can also be supplied in an auxiliary manner.

  According to the present invention, in a fuel cell system as a power generator equipped with a solid oxide fuel cell (SOFC) equipped with a fuel reformer, the entire amount of pure water required for fuel reforming is procured from the fuel exhaust gas. This is possible at the actual machine level.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram showing a fuel cell system according to the present invention.

  In FIG. 1, reference numeral 1 denotes a power generation unit of a solid oxide fuel cell (SOFC), which has a fuel electrode 2 and an air electrode 3. Along with power generation, exhaust gas at about 1000 ° C. is discharged from the fuel electrode 2 and the air electrode 3. The fuel exhaust gas from the fuel electrode 2 contains water (steam) as a power generation product. A distribution valve 5 having a flow rate adjusting function is provided in the exhaust gas flow path 4 of the fuel exhaust gas, and a distribution pipe 6 is distributed from there.

  A fuel gas obtained by reforming city gas, which is a raw fuel, is supplied to the fuel electrode 2 side of the SOFC, and air (oxidant) is supplied to the air electrode 3. In this example, an air heat exchanger 8 is arranged in the air supply path 7, and a fuel heat exchanger 10 and a reformer 11 are arranged in the fuel supply path 9. Although not limited to the fuel supply path 9, the city gas G is supplied as raw fuel in this example.

  The amount of fuel exhaust gas distributed by the distribution valve 5 passes through the distribution pipe 6, and is discharged to the condenser 12 while releasing heat from the reformer 11, the heat exchanger 8 for air, and the heat exchanger 10 for fuel. Inflow. The condenser 12 recovers from the fuel exhaust gas that has flowed in to the sensible heat of water vapor, thereby generating condensed water. Components other than water are discharged as exhaust gas. The produced condensed water is collected in the cistern 13, passes through the water conduit 14 from there, and is heated by exchanging heat with the fuel exhaust gas flowing in the condenser 12.

The heated condensed water flows into the heat exchanger 10 for fuel together with the raw fuel (city gas G) flowing in the fuel supply path 9 and further heated, and then flows into the reformer 11. A conventionally known reaction such as CH ₄ + H ₂ O → CO + 3H ₂ proceeds, and the raw fuel is reformed into a fuel gas for SOFC. Then, the reformed fuel gas is supplied to the fuel electrode 2 of the SOFC 1, and in the SOFC 1, H ₂ + 1 / 2O ₂ → H ₂ O + electricity with the air (oxygen) supplied to the air electrode 3. As the reaction proceeds, electricity is obtained, and the generated water (H ₂ O) is discharged together with the fuel exhaust gas.

  As described above, the fuel exhaust gas in SOFC has a high temperature of about 1000 ° C., a large amount of heat, and contains a large amount of moisture. Even if the entire amount is heat-exchanged by a normal heat exchanging means (condenser), it is not easy to recover condensed water from the magnitude of the heat amount to sensible heat. In the system of the present invention, only a necessary amount of fuel exhaust gas is branched by, for example, the distribution valve 5 and then distributed to a normal condenser 12 where heat is recovered and condensed water is generated. Therefore, it is possible to supply water necessary for reforming at the actual machine level.

  FIG. 2 is a graph showing an example of the relationship between the fuel exhaust gas distribution ratio and the SOFC capacity load. In this example, about 70% fuel exhaust gas distribution is required at a load of 100%, and about 85% fuel exhaust gas distribution is required at a load of 50%. And it turns out that both have the relation which changes substantially linearly. From this, it can be seen that the operation can be performed with high thermal efficiency by controlling the distribution valve 5 provided with the flow rate adjusting function arranged in the exhaust gas flow path 4 according to the capacity load of the SOFC. On the other hand, since the maximum distribution rate is about 85%, the operation of the SOFC can be continued without any trouble even if a distribution valve with a fixed distribution amount is provided without using the distribution valve 5 having a flow rate adjustment function. You can see what you can do.

  Although not particularly illustrated, it is also possible to further incorporate a system that can supply city water for fuel reforming when necessary (for example, at the time of start-up or sudden load fluctuation).

1 is a system diagram showing a fuel cell system according to the present invention. The graph which shows the relationship between a fuel exhaust gas distribution rate and the capacity load of SOFC.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Solid oxide fuel cell (SOFC), 2 ... Fuel electrode, 3 ... Air electrode, 4 ... Fuel exhaust gas flow path, 5 ... Distribution valve, 6 ... Distribution pipe line, 7 ... Air supply path, 8 ... For air 9 ... Fuel supply path, 10 ... Fuel heat exchanger, 11 ... Fuel reformer, 12 ... Condenser, 13 ... Sistern, 14 ... Water pipeline, G ... City gas (raw fuel)

Claims (5)

  A fuel exhaust gas flow path is provided in the fuel exhaust gas flow path from the fuel electrode side of a solid oxide fuel cell equipped with a fuel reformer, and latent heat is recovered from the fuel exhaust gas containing water vapor distributed to the distribution path and condensed. A fuel cell system characterized in that a condenser capable of obtaining water is arranged, and the produced condensed water is mixed with raw fuel and sent to a fuel reformer.   The fuel cell system according to claim 1, further comprising a flow rate adjusting means capable of adjusting a distribution amount of the fuel exhaust gas to the distribution path.   The condenser is provided with a heat exchange means between the generated condensed water and the flowing fuel exhaust gas, and the generated condensed water is heated by heat exchange in the condenser and then mixed with the raw fuel. The fuel cell system according to claim 1 or 2, wherein   A fuel gas supply method to a fuel electrode of a solid oxide fuel cell including a fuel reformer, wherein a desired amount of fuel exhaust gas including water vapor from the fuel electrode side is distributed to a distribution path, and the desired amount is obtained. The distributed fuel exhaust gas is sent to the condenser to generate condensed water, and only the condensed water generated without using other city water is mixed with the raw fuel, then sent to the fuel reformer, and the reformed fuel gas Is supplied to the fuel electrode.   5. The fuel gas supply method according to claim 4, wherein the generated condensed water is heated by exchanging heat with a heat exchanger, and the heated condensed water is mixed with raw fuel.

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